Lightweight expanded clay aggregate as a building material – An overview

Construction and Building Materials 170 (2018) 757–775

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Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat

Review

Lightweight expanded clay aggregate as a building material – An overview Alaa M. Rashad Building Materials Research and Quality Control Institute, Housing & Building National Research Center, HBRC, Cairo, Egypt

h i g h l i g h t s  LECA decreased density, shrinkage and mechanical strength, but increased workability.  LECA decreased chloride penetration, but increased thermal and sound insulation.  LECA increased fire resistance, but decreased freeze/thaw resistance.  LECA could be employed into geopolymers.  Various materials could be added to improve special properties of LECA media.

a r t i c l e

i n f o

Article history: Received 22 January 2018 Received in revised form 23 February 2018 Accepted 1 March 2018

Keywords: LECA Lightweight Insulation Fresh and hardened properties

a b s t r a c t LECA is the abbreviation of lightweight expanded clay aggregate. LECA is produced from special plastic clay with no or very little content of lime. The clay is dried, heated and burned in rotary kilns at 110 0–1300 °C. LECA is porous ceramic product with a uniform pore structure with almost potato shape or round shape due to the kiln circular movement. The abundant numbers of small, air-filled cavities in LECA give its lightweight, thermal as well as sound isolation characterizes. In this article, the earlier studies which focused on using LECA as a part of building materials in traditional cementitious materials, as well as inorganic polymers (geopolymers), have been briefed. Furthermore, various materials which added to modify some properties of LECA concrete and mortar have been briefed and reported. The main findings of this review are the incorporation of LECA in the matrix increased its workability, decreased density, decreased mechanical strength, decreased freeze/thaw resistance, increased water absorption, decreased chloride penetration resistance, but increased thermal insulation and fire resistance. Ó 2018 Elsevier Ltd. All rights reserved.

Contents 1. 2.

3. 4.

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Conventional cementitious materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.1. Workability and segregation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2. Density . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3 Creep . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.4. Mechanical strength . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.5. Porosity, water absorption and chloride penetration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.6. Shrinkage and cracking tendency. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.7. Fire, freeze/thaw and chemical resistance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.8. Sound isolation and thermal conductivity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Geopolymers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Adding materials to improve some properties of LECA matrices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.1. Supplementary cementing materials – SCMs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2. Fibers/cementitious materials reinforced with fibers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.3. Other materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

E-mail addresses: [email protected], [email protected] https://doi.org/10.1016/j.conbuildmat.2018.03.009 0950-0618/Ó 2018 Elsevier Ltd. All rights reserved.

758 759 759 760 763 763 765 766 767 767 768 769 769 770 771

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Benefits, shortages and applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 771 Remarks and future work scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 772 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 773

1. Introduction LECA is an acronym term of lightweight expanded clay aggregate. It is also known as LIAPOR (porous lias clay), grow rocks or hydrocorns [1]. LECA is produced in many countries (more than twenty countries) with various products name. Particular countries produce LECA with approximately similar method such as UK, Iran, Portugal, Finland, Germany, Italy, Denmark and Switzerland branded it as ‘‘leca”, whilst Sweden, China, Poland and Russia branded it as ‘‘Keramzite”. Spain branded it as ‘‘liapour”, whilst South Africa branded it as ‘‘Argex”. Whatever, LECA is produced from special plastic clay with no or very little content of lime. The clay is dried, heated and burned in rotary kilns at very high temperatures of approximately 1100–1300 °C [2]. During heating, gas is released inside the pellets and entrapped in it during cooling, whilst the organic compounds burnt off forcing the pellets to expand (or bloated) producing ceramic pellets with porous, lightweight and high crushing resistance material (Fig. 1). LECA pellet may expand up to 5–6-fold, by volume [3]. LECA has almost potato shape or round shape due to the kiln circular movement. Inside LECA particles, there are holes of different sizes which are mostly interconnected (Fig. 2). Other types have different structures and geometries. This depends on the manufacturer process, of which increasing temperature during sintering led to an increase in the total porosity and producing continuous pores. Further increase temperature above the pyro-plasticity range let to a reduction in the pore size and porosity [4]. LECA consists of rounded pellets which when broken open shows a vesicular texture [5]. In most cases, LECA is a dark brown or reddish or brown-red or gray colours. Yellow or black colours are also available. These differences in colours could be associated

to the varieties in LECA chemical composition and its manufacture method. It is an inert lightness substance and does not contain harmful materials with natural pH value (nearly 7), it does not damage in water, moisture impermeable, non-combustible, nonbiodegradable, non-decomposition against severe conditions, excellent thermal insulation, fire resistance, soundproofing by its high acoustic resistance. LECA may have different sizes (from 0.1 to 25 mm) which suitable for fine aggregate, coarse aggregate and both of them (Fig. 3). The lightness of LECA could be associated to the multi-separated air spaces which exist inside and among the aggregates. LECA has many loose bulk densities fluctuated from 250 to 710 kg/m3 [1] which mainly depends on its size. The chemical composition of LECA consists mainly of SiO2, Al2O3, Fe2O3, CaO and some alkalis such as Na2O and K2O [2]. Table 1 presents the chemical composition of LECA for various studies. It can be noted that the content of SiO2 in the total composition fluctuated from 53.3% to 70%, Al2O3 fluctuated from 15.05% to 27%, Fe2O3 fluctuated from 1% to 14.3% and CaO fluctuated from 0.2% to 3.92%. LECA has many interesting physical properties. Its thermal conductivity in the range of 0.097 to 0.123 W/m K [6]. Ardakani and Yazdani [7] found a wide range of the crushing resistance, dry density, 24 h water absorption, loose bulk density of LECA. Table 2 briefs some of the physical properties of LECA of different studies. The numerous densities of LECA can be considered as one advantage of using this type of aggregate, of which these make it suitable for both structural and nun-structural lightweight concretes. LECA is an impressive versatile material which is used in a various number of applications. For example, in the construction field, it can be used widely in the production of lightweight blocks, concrete, precast as well as in structural backfill against foundations. In

Fig. 1. The flowchart of LECA production (http://www.ftmmachinery.com).

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A.M. Rashad / Construction and Building Materials 170 (2018) 757–775

water treatment field, LECA can be used as an imbibing for removal of fluoranthene, phenanthrene as well as pyrene from water [8]. In horticulture or agriculture field, LECA can be used for agricultural wastewater treatment, of which LECA has displayed a comprehensive high capability to remove numerous pollutants presented in wastewater of agricultural such as chemical oxygen demand and total suspended solids, polyphenols, nitrogen, pesticide and pharmaceutical [9]. In addition, LECA can drainage the groundwater and surface water to regulate the pressure of groundwater. Currently, there are many publications related to using LECA as a construction material. These publications focused on using LECA as a partial or complete substitution of normal weight aggregates. Unfortunately, there is no review article which accumulates and briefs these widely spread publications. Consequently, the intention of this review is to cumulate and brief the earlier publications related to conducting LECA as a partial or full replacement of normal weight aggregates in concretes and mortars manufactured from traditional Portland cement (PC) as well as geopolymers. Hardened properties, fresh properties, and durability of various matrices containing LECA have been briefed. Different strategies that are conducted to improve the mechanical strength of LECA matrices have been summarized. This review can be used to know what was already published and what should be published in the incoming investigations.

2. Conventional cementitious materials 2.1. Workability and segregation Jόz´wiak-Niedz´wiedzka [32] found more workable concrete mixtures by partially replacing normal weight sand with various percentages of prewetted LECA (size 0–2 mm), by volume. The

Fig. 2. Interconnected holes and air-filled cavities of different sizes.

Fig. 3. Different grain sizes of LECA.

Table 1 Chemical composition of LECA. Composition

[10]

[11]

[12]

[13]

[8]

[14]

[15]

[16]

[17]

[18]

[19]

[20]

[21]

SiO2 Al2O3 Fe2O3 K2O MgO CaO Na2O P2O5 SO3 SrO TiO2 MnO Extra oxides LOI

70 20 8.7 – 1.3

66.05 16.57 7.1 2.69 1.99 2.46 0.69 0.21 0.03 – – – – 0.84

58 27 1 2.3 0.4 0.2 0.3 – – – 1.3 – – –

53.3 16.6 6.2 – 2.8 2 – – – – – – – –

62 18 7 4 3 3 2 – – – – – – 1.36

61.67 18.51 6.14 3.18 3.97 3.5 1.54 0.19 0.23 0.13 0.65 – – –

61.85 19.78 9.52 4.1 0.78 1.05 0.17 – – – 0.92 – – 15.11

61.05 15.74 6.1 2.67 2.52 3.92 5.62 0.21 0.03 – – – 0.84 0.75

66.05 16.57 7.1 2.69 1.99 2.46 0.69 – – – – – – –

66.2 16 6.4 4 – 1.8 1.8 – 0.1 – – 2.7 – 0.1

59.5 – 14.3 – 1.5 2

60.1 17.7 7.85 4 2.95 2.1 1.75 0.2 0.55 – 0.9 0.1 – 1.8

64.83 15.05 7.45 2.55 3.67 2.98 1.1 0.13 – – 0.63 0.13 – 1.37

– – – – – – – –

– 1 – – 0.2 – 0.18

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A.M. Rashad / Construction and Building Materials 170 (2018) 757–775

Table 2 Physical properties of LECA. Property

[22]

[23]

[24]

[25]

[8]

[26]

[27]

[28]

[29]

[30]

[31]

[7]

Specific gravity Moisture content Water absorption Bulk density (kg/m3) Dry density (kg/m3) Fineness modulus Porosity

1 0.257% 24.03% 306

1.23 – 40 at 4 h 650

– – 15.8 at 24 h 624

– – 12.3 at 24 h 613

– – – 750

– – 12.3 at 24 h 613

1.78 – 40 111

– – 26.2 358

– – 23.2 at 24 h 681

– – 12.6 at 24 h 681

– – – 562

– – 24.1 at 24 h 279

– 1.735 –

600 – –

1076 – 40.7 open at 24 h

1068 – 60 total

1600 – –

1068 – 60 total

– 2.7 –

– 5.77 –

1092 – –

1092 – –

1060 – 59 total

503 – –

slump was increased by 128.57% and 100% with the incorporation of 33.33% and 50% prewetted LECA, respectively. Basalt (size 2–4 and 8–16 mm) which was used as coarse aggregate was replaced with various percentages of prewetted LECA (size 2–4 mm). The results illustrated more workable mixtures with the incorporation of prewetted LECA. The slump was increased by 14.3% and 71.43% with the incorporation of 50% and 100% prewetted LECA, respectively. Gopi et al. [33] found more workable SCC mixtures by partially replacing normal weight sand with prewetted LECA coupled with fly ash (FA) as fine aggregate, by volume. The slump flow was increased by 3.64%, 10%, 25.27% and 30.36% with the incorporation of 5%, 10%, 15% and 20% prewetted LECA coupled with 5% FA, respectively. Shankar [27] found more workable SCC mixtures by partially replacing normal weight sand with 10%, 15% and 20% LECA, by volume. Shebannavar et al. [22] found more workable concrete mixtures by replacing normal weight coarse aggregate with LECA (size 4.75– 20 mm). Youm et al. [34] prepared normal weight concrete mixture and concrete mixture containing LECA (maximum size 8 mm) as coarse aggregate with water to binder (w/b) ratio of 0.28 and 0.242, respectively. The results illustrated more workable LECA concrete mixture in spite of it containing lower w/b ratio, at which slump was increased by 4.5%. Bogas and Nogueira [35] found higher workability of concrete mixtures with introducing LECA (size 4–12 mm) as coarse aggregate in comparison with the normal weight concrete mixture. The average slump of LECA mixtures was 174.4 mm, whilst it was 166.5 mm for the normal weight one. Bogas and Gomes [25] manufactured lightweight concrete mixtures from LECA (maximum size 12.5 mm). The total porosity of the LECA was 60%. Different w/b ratios of 0.3, 0.35, 0.4 and 0.45 were used. The results displayed an increase in the workability with the incorporation of LECA, of which the slump was increased by an average of 27.55%. Kumar and Prakash [36] replaced cinder coarse aggregate in concretes with LECA at percentages fluctuated from 10% to 100%, by volume. The results displayed more workable LECA mixtures. The slump was increased by 18.52%, 25.9%, 81.48%, 107.4%, 100%, 88.9%, 77.8%, 51.85%, 40.74% and 33.3% with the incorporation of 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% and 100% LECA, respectively. Moravia et al. [37] manufactured concrete mixtures containing LECA (maximum size 19 mm) as coarse aggregate with different estimated compressive strength values of 20, 25, 30 and 40 MPa coupled with w/b ratios of 0.63, 0.55, 0.48 and 0.41, respectively. Their results illustrated more workable LECA concrete mixtures in comparison with the normal weight ones at w/b ratios of 0.55, 0.48 and 0.41. The slump was increased by 17.86%, 3% and 3.45% at w/b ratios of 0.55, 0.48 and 0.41, respectively. Wegian [38] found more workability of concrete mixtures containing LECA (size 2–4, 4–8, 8–20 mm) as both fine and coarse aggregates in comparison with that containing normal weight sand as fine aggregate coupled with gravel or dolomite as coarse aggregate at various contents of cement (250, 300 and 350 kg/m3). Concrete mixtures containing LECA exhibited slump values fluctuated from 112 to

114 mm, whilst that containing normal weight aggregates exhibited slump values fluctuated from 58 to 78 mm. Dilli et al. [39] manufactured lightweight concrete mixtures from two different types of LECA (size 4–10 mm). A portion of coarse aggregate was replaced with LECA1 (water absorption 26%) or LECA2 (water absorption 23.2%). The results illustrated lesser workability with the incorporation of LECA1, whilst the incorporating of LECA2 increased it. Bocca and Rossetti [40] found lesser workability of concrete mixture by replacing normal weight coarse aggregate with LECA (size 8–15 mm). The slump was reduced by 58.33% with the incorporation of LECA. Abdeen and Hodhod [41] found lesser workability of concrete mixture by replacing normal weight fine aggregate and coarse aggregate with LECA (size  25 mm with 40%-50% size of 2.4–4.76 mm). The slump was reduced by 85% with the incorporation of LECA. Bogas et al. [42] mentioned that SCC mixtures containing LECA (maximum size 12.5 mm) as coarse aggregate exhibited adequate segregation resistance when the volume of fine materials related to those of fine aggregate was in the range of 0.55–0.75. Table 3 briefs the influence of LECA on concrete workability. It is completely known that the workability of any mixture depends on the type of mixture composition and lightweight aggregate type. The prior studies in this section extrapolated that the incorporation of LECA in the mixture instead of normal weight aggregates increased workability as illustrated by a lot of investigations (78.3%). In spite of LECA has a high water absorption in comparison with the normal weight aggregates, which has a negative effect on the workability, LECA has rounded surface, which has a positive effect on the workability. Thus, in most cases, the workability of a mixture containing LECA is greater than that containing normal weight one. The influence of LECA on segregation still lackey and needs to be studied further, but according to the available quoted study, the incorporation of LECA in the mixture can resist segregation. It is noteworthy mentioning that the mix design must take into account the greater difference of density between the LECA and the surrounding matrix. 2.2. Density Madadi et al. [43] found a declination in the density of ferrocement specimens with introducing 55, 135 and 199 kg/m3 LECA (size 23 mm). This declination increased with the increase the amount of LECA. Maghsoudi et al. [44] mentioned that SCCs containing 175 kg/m3 LECA (size 4.75–9.5 mm) as coarse aggregate accounted 28 days density fluctuated from 1890 to 1870 kg/m3. Sharigh et al. [45] found that concrete containing 180 kg/m3 LECA (maximum nominal size 8 mm) as a part of coarse aggregate accounted 1809 and 1801 kg/m3 dry density and oven density, respectively, at age of 28 days. Bogas et al. [30] mentioned that fresh density of concrete mixtures of 1897 and 1719 kg/m3 can be obtained by using two different types of LECA (size 4–11..2 mm). Bogas and Cunha [46] mentioned that concrete specimens containing LECA (diameter 4–8 mm) as coarse aggregate, 130 kg.

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A.M. Rashad / Construction and Building Materials 170 (2018) 757–775 Table 3 Influence of LECA on the workability of concrete. Reference

Replaced aggregate type

Type

LECA content (%)

LECA size (mm)

Effect

Jόz´wiak-Niedz´wiedzka [32] Jόz´wiak-Niedz´wiedzka [32] Gopi et al. [33] Shankar [27] Shebannavar et al. [22] Youm et al. [34] Bogas and Nogueira [35] Bogas and Gomes [25] Kumar and Prakash [36] Moravia et al. [37] Wegian [38] Dilli et al. [39] Bocca and Rossetti [40] Abdeen and Hodhod [41]

Fine Coarse Fine Fine Coarse Coarse Coarse Coarse Coarse Coarse Fine + coarse Coarse Coarse Fine + coarse

Concrete Concrete Concrete Concrete Concrete Concrete Concrete Concrete Concrete Concrete Concrete Concrete Concrete Concrete

33.33–50 50–100 5–20 10–20 100 100 100 100 10–100 100 100 NA 100 100

0–2 2–4, 8–16 NA NA 4.75–20 8 4–12 12.5 NA 19 2–4, 4–8, 8–20 4–10 8–15 25 with 40–50% 2.4–4.75

Positive Positive Positive Positive Positive Positive Positive Positive Positive Positive Positive Negative Negative Negative

m3 cement and 280 kg/3 lime filler showed 1000 and 865 kg/m3 fresh and dry density at age of 28 days, respectively. Bastons et al. [47] mentioned that dry bulk density of concrete blocks in the range of 1458 to 836 kg/m3 can be obtained with introducing LECA as coarse aggregate in the range of 50% to 90% when cement amount was 155 kg/m3. When cement amount was 214 kg.m3, the dry bulk density ranging from1487 to 871 kg.m3 can be obtained with introducing LECA as coarse aggregate in the range of 50% to 90%. Corinaldesi and Moriconi [48] mentioned that SCCs containing 226 kg/m3 LECA as fine aggregate (size 0–4 mm) and 367 kg/m3 LECA as coarse aggregate (size 0–15 mm) exhibited 17.4% lesser oven dry density than that containing 100 kg/m3 LECA (size 0–4 mm) coupled with 345 kg/m3 normal weight sand (size 0–6 mm) as fine aggregates. Ali and Lazim [49] mentioned that concrete containing LECA (size 4–10 mm) as coarse aggregate exhibited density of 1435 kg/m3 at age of 28 days. This density was increased by 11.5%, 18.95% and 26.13% when LECA was partially replaced with normal weight coarse aggregate at levels of 15%, 20% and 25%, by volume, respectively. Dilli et al. [39] manufactured lightweight concretes from two different types of LECA (size 4–10 mm). A portion of coarse aggregate was replaced with LECA1 (26% water absorption) or LECA2 (23.2% water absorption). The results illustrated 26.36% and 12.53% lesser density in the fresh state of concrete mixtures with the incorporation of LECA1 and LECA2, respectively, at w/b ratio of 0.42, whilst 28.1% and 16% lesser dry weight density was obtained at age of 28 days, respectively. Real et al. [24] found lesser density, in the dry state, of mortars with introducing LECA. The density decreased by increasing LECA volume in the mixtures. The reduction in the density was 12.7%, 16.58% and 19.72% with the incorporation of 250, 300 and 400 L/ m3 LECA, respectively. Macˇiulaitis et al. [50] mentioned that 1526 kg/m3 density of concrete can be obtained by replacing normal weight sand and gravel with LECA (size 0–4 mm and 4–10 mm). Kumar and Prakash [51] mentioned that concrete containing LECA as aggregates showed the density of 1454.81 kg/m3 at age of 28 days. Pinto et al. [52] stated that the 28 days density of concrete specimens containing LECA: cement: water with the ratio of 6: 1: 1 fluctuated from 551.1 to 604.4 kg/m3. Sivakumar and Kameshwari [53] found 2.86%, 5.9%, 9.63%, 11%, 12.17%, 12.8% and 13.97% lesser dry density of concretes by partially replacing cement, normal weight fine and coarse aggregates with FA, bottom ash and LECA (size 10 mm), respectively, at percentages of 5%, 10%, 15%, 20%, 25%, 30% and 35%, respectively. Lakshmi et al. [54] found 9.71%, 10.38%, 15.13% and 19% declination in the 28 days density of concretes by partially substituting normal weight coarse aggregate with 45%, 50%, 60% and 70% LECA, respectively. Salem et al. [55] found 16.36% lesser 90 days oven dry density of concrete by substituting normal weight coarse aggregate by LECA (size 4–16 mm). Youm et al. [34] found 16.14% and 21.4%

lesser 28 days wet density and oven dry density of concretes with the incorporation of LECA (maximum size 8 mm) as coarse aggregate respectively, in comparison with the reference. Yoon et al. [56] found 18.2% lesser 28 days density of concrete by substituting normal weight coarse aggregate by LECA (size  10 mm). Fenyvesi [57] found 18.7% and 19.36% lesser fresh density and 28 days saturated density of concretes by substituting normal weight coarse aggregate by LECA (size 4–8 mm), respectively. Malešev et al. [58] found 21% lesser 28 days density of concrete by substituting normal weight coarse aggregate by LECA (size 4–15 mm). Moravia et al. [37] manufactured concrete mixtures containing LECA (maximum size 19 mm) as coarse aggregate with different estimated compressive strength values of 20, 25, 30 and 40 MPa coupled with w/b ratios of 0.63, 0.55, 0.48 and 0.41, respectively. Their results illustrated lesser fresh density and dry density with the incorporation of LECA. For the estimated compressive strength of 20, 25, 30 and 40 MPa, the reduction in the fresh density was 29.68%, 30.61%, 31.52% and 32%, respectively. The declination in the 3 days density was 30.1%, 30.38%, 31% and 31.2% for concretes with estimated compressive strength of 20, 25, 30 and 40 MPa, respectively, while the declination in the density at age of 28 days was 31.48%, 31%, 31.15% and 31.74%, respectively. Campione et al. [59] found 34.92% lesser 28 days density of concretes with the incorporation of LECA (size 3–17 mm) as coarse aggregate in comparison with the reference. Shebannavar et al. [23] found 36.51%, 35.15% and 34.22% lesser 3, 7 and 28 days density of concretes with the incorporation of LECA (size 4.75–20 mm) as coarse aggregate in comparison with the reference, respectively. Bocca and Rossetti [40] found 42% lesser fresh density of concrete by substituting normal weight coarse aggregate by LECA (size 8–15 mm). Bogas et al. [42] found 21.1% lesser 28 days density of SCCs by replacing normal weight coarse aggregate with LECA (maximum size 12.5 mm). Bogas and Nogueira [35] found about 21.73% and 25.18% lesser fresh density and 28 days dry density of concretes with the incorporation of LECA (size 4–12 mm) as coarse aggregate in comparison with the normal weight concrete, respectively. Bogas and Gomes [31] found 21.2% and 24.38% lesser fresh and hardened density of concretes with the incorporation of LECA (maximum size 12.5 mm) as coarse aggregate when cement amount was 350 kg/m3. When cement amount was 450 kg/m3, the fresh density was reduced by 21.32%, while dry density was reduced by 24.31%. The fresh density and dry density were reduced by 32.81% and 37.58% with the incorporation of LECA as fine and coarse aggregates. Bogas et al. [60] found 24.38% and 24.3% lesser oven dry density of concretes by replacing normal weight coarse aggregate with LECA (size 4–12 mm), when cement amount was 350 and 450 kg/m3, respectively. When cement amount was 450 kg/m3, the oven dry density was reduced by 37.58% with the incorporation of LECA as both fine aggregate (size 0–3 mm) and

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coarse aggregate (size 4–12 mm). Cavaleri et al. [61] found 27.74% declination in the 28 days unit weight of concrete specimens by replacing normal weight aggregates with LECA (size 3–7, 7–15 mm). Wegian [38] found lesser 28 days density of concrete containing LECA (size 2–4, 4–8, 8–20 mm) as both fine and coarse aggregates in comparison with that containing normal weight sand as fine aggregate coupled with gravel or dolomite as coarse aggregate at various contents of cement (250, 300 and 350 kg/m3). Concrete mixtures containing LECA exhibited 28 days density values fluctuated from 1360 to 1760 kg/m3, whilst that containing normal weight aggregates exhibited density values fluctuated from 1900 to 2390 kg/m3. Abdeen and Hodhod [41] found 44.4% lesser 28 days bulk density of concrete containing LECA (size  25 mm with 40%–50% size of 2.4–4.76 mm) as both fine aggregate and coarse aggregate in comparison with the reference. Shankar [27] found 0.8%, 2%, 3.17% and 3.97% lesser density, in fresh state, of SCC mixtures by partially substituting normal weight sand with 5%, 10%, 15% and 20% LECA, by volume, respectively, whilst the 7 days hardened density was reduced by 2%, 3.2%, 3.6% and 4.8%, respectively. Jόz´wiak-Niedz´wiedzka [32] found 3.4% and 4.2% lesser density, in the fresh state, of concrete mixtures by partially substituting normal weight sand by prewetted LECA (size 0–2 mm) at levels of 33.33% and 50%, by volume, respectively. Basalt (size 2–4 and 8–16 mm) which was used as coarse aggregate was replaced with various percentages of prewetted LECA (size 2–4 mm). The results illustrated 0.9% and 3.9% lesser fresh density with the incorporation of 50% and 100% prewetted LECA, respectively. Muñoz-Ruiperez et al. [28] partially replaced normal weight sand in mortar specimens by a combination of 18.75% LECA (size 2–4 mm) and 56.25% LECA (size 3–8 mm), by volume. The results illustrated 32.63% and 36.37% lesser fresh and hardened bulk density of the mortars with the incorporation of LECA, respectively. Shendy [23] mentioned that concrete containing LECA (maximum size 4 mm) as fine aggregate exhibited density of 1610 kg/m3, which accounted 35.6% lesser a density than that of the reference. Koñáková et al. [62] found 46.75% declination in the lime-burnt clay shale plaster bulk density by replacing normal weight silica sand with LECA (size 0–4 mm). Rashad [6] mentioned that cement mortar manufactured

from LECA as a fine aggregate (size  4.75 mm) exhibited 48.61% lesser 28 days density in comparison with the reference. Table 4 briefs the influence of LECA on concrete and mortar density. From the prior studies in this section, it could be clearly extrapolated that the incorporation of LECA in the matrix declined its density. The density declined as the LECA amount increased. The introduction of LECA as coarse aggregate can reduce the density at levels fluctuated from 16.36% [55] to 36.51% [22] and the declination can be reached as high as 42% [40]. This depends on many factors such as original density of the normal weight aggregate, chemical and physical properties of the employed LECA in addition of its size. The incorporation of LECA as a fine aggregate can reduce the density by approximately 35% [23], whilst the levels of reduction fluctuated from 37.58% [60] to 44.4% [41] can be obtained when LECA was incorporated as both fine and coarse aggregates. The reduction in the density with the incorporation of LECA could be associated to its low specific gravity in comparison with that of normal weight aggregate. Furthermore, the incorporation of LECA in the matrix can produce a porous structure which can contribute this reduction. It worth mentioning that the elastic modulus of LECA is affected by its particle dry density. LECA with particle dry densities in the range of 480–1100 kg/m3 exhibited elastic moduli in the range of 0.6–6.3 GPa [7]. It was reported that there is a linear relationship between particle density of LECA and elastic modulus [7]. According to the density of LECA as well as the mix design, the concrete production could be classified as nonstructural or structural lightweight concrete, of which LECA density has a major effect on the concrete density. The concrete density increased with increasing LECA density. It was reported that as the concrete density increased as the compressive strength increased [39]. In spite of there are a lot of publications associated to the influence of LECA on the density of concrete, most of them (about 60.5% of total publications) focused on comprising LECA as coarse aggregate, whilst comprising LECA as fine aggregate came in the second place (about 21% of total publications). Replacing both normal weight fine aggregate and coarse aggregate with LECA came in the last place (about 18.42% of total publications). In such a way,

Table 4 Influence of LECA on the density of concrete and mortar. Reference

Replaced aggregate type

Type

LECA content (%)

LECA size (mm)

LECADensity (480 kg/m3)

Reduction (%)

Sivakumar and Kameshwari [53] Lakshmi et al. [54] Salem et al. [55] Youm et al. [34] Yoon et al. [56] Fenyvesi [57] Malešev et al. [58] Moravia et al. [37] Campione et al. [59] Shebannavar et al. [22] Bocca and Rossetti [40] Bogas et al. [42] Bogas and Nogueira [35] Bogas and Gomes [31]

Coarse Coarse Coarse Coarse Coarse Coarse Coarse Coarse Coarse Coarse Coarse Coarse Coarse Coarse Fine + Coarse Coarse Fine + Coarse Fine + Coarse Fine + Coarse Fine + Coarse Fine Fine Coarse Fine Fine Fine Fine

Concrete Concrete Concrete Concrete Concrete Concrete Concrete Concrete Concrete Concrete Concrete Concrete Concrete Concrete Concrete Concrete Concrete Concrete Concrete Concrete Mortar Concrete Concrete Mortar Concrete Mortar Mortar

5–35 45–70 100 100 100 100 100 100 100 100 100 100 100 100 100 + 100 100 100 + 100 100 + 100 100 + 100 100 + 100 5–20 33.33–50 50–100 75 100 100 100

10 NA 4–16 8 10 4–8 4–15 19 3–17 4.75–20 8–16 12.5 4–12 4–12 0–3 + 4–12 4–12 0–3, 4–12 3–7, 7–15 2–4, 4–8, 8–20 2.4–4.76, 25 NA 0–2 2–4 2–4, 3–8 4 4 4.75

480 NA 518 (bulk) 1130 (particle) 1178 (specific), 692 (bulk) 1907 113 (dry), 637 (bulk) NA 650 (apparent) 306 (bulk) 360 1068 (dry), 613 (bulk) 1068 (dry), 613 (bulk) 1068 (dry), 613 (bulk) 1060 (dry), 562 (bulk) fine + coarse 1068 (dry), 613 (bulk) 1060 (dry), 562 (bulk) fine + coarse NA 510 580 (bulk) 1112 (bulk) NA NA 358 and 300 (bulk) 650 (bulk), 600 (dry) 575 (bulk), 1025 (particle) 627 (bulk)

2.86–13.97 9.71–19 16.36 16.14–21.4 18.2 18.7–19.36 21 29.68–32 34.92 34.22–36.51 42 21.1 21.73–25.18 21.2–24.38 32.81–37.58 24.3–24.38 37.58 27.74 28.4–26.36 44.4 2–4.8 3.4–4.2 0.9–3.9 32–36.37 35.6 46.75 48.6

Bogas et al. [60] Cavaleri et al. [61] Wegian [38] Abdeen and Hodhod [41] Shankar [27] Jόz´wiak-Niedz´wiedzka [32] Muñoz-Ruiperez et al. [28] Shendy [23] Koñáková et al. [62] Rashad [6]

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the density of LECA concrete has more attention (about 85.7% of total publications) than that of LECA mortar (about 14.3%). 2.3 Creep Shen et al. [63] partially replaced coarse aggregate in concretes with prewetted LECA (size 4.7–9.5 mm) at percentages of 10%, 30% and 50%, by volume. Their results illustrated lower specific tensile creep with the incorporation of LECA. The specific tensile creep at cracking time was 71 me/MPa, 44 me/MPa, 33 me/MPa, and 50 me/MPa, with the incorporation of 0%, 10%, 30% and 50% LECA, respectively, which presented an apparent declination in the specific tensile creep with introducing LECA. The maximum compressive creep for concretes containing 0%, 10%, 30% and 50% LECA was 192, 215, 238 and 251 me, respectively, which offered 83%, 105%, 106% and 117% of the maximum free expansive strain. They also found that the supreme compressive creep increased by increasing prewetted LECA content. During the restrained expansion mode, all creep strains were negative increments for mixtures containing 10%, 30% and 50% LECA, whilst during the restrained shrinkage mode, all creep strains were positive increments (Fig. 4). From the prior study in the current section, it could be extrapolated that the effect of LECA on the creep of concrete and mortar still lackey and requires to be studied further. According to the available quoted study, the incorporation of prewetted LECA in concrete decreased the specific tensile creep. The reduction in the creep allowed by prewetted LECA could have withheld the lower restraining action on creep and shrinkage caused by lightweight aggregate with a lower stiffness than the normal weight aggregate. The same tendency of the results was observed in concrete containing expanded slate as a lightweight coarse aggregate [64]. 2.4. Mechanical strength Nepomuceno et al. [65] found compressive strength values between 35 and 57 MPa for SCCs containing LECA as coarse aggregate when w/c ratios between 0.29 and 0.61, respectively, whilst the SCCs containing normal weight coarse aggregate exhibited compressive strength values between 53 and 87 MPa, respectively. Ardakani and Yazdani [7] used volume ratios of LECA/total volume of a composite of 0.1, 0.2, 0.3 and 0.4 in mortars. The results illustrated lesser elastic modulus with the incorporation of LECA. The elastic modulus fluctuated from 0.6 to 6.3 GPa when the dry density of the LECA fluctuated from 480 to 1100 kg/m3. The elastic

Fig. 4. Influence of LECA coarse aggregate on creep strain of concrete [63].

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modulus decreased as LECA particle size increased from 4 mm to 14 mm. Real et al. [24] found lesser mortars compressive strength with introducing LECA. The compressive strength decreased as the amount of LECA increased. The compressive strength was decreased by 19.81%, 20.19% and 26.73% with the incorporation of 250, 300 and 400 L/m3 LECA, respectively. Madadi et al. [43] found a declination in the modulus of elasticity and compressive strength of ferrocement specimens with including 55, 135 and 199 kg/m3 LECA (size 23 mm). This declination increased as the amount of LECA increased. Maghsoudi et al. [44] mentioned that SCCs containing 175 kg/m3 LECA (size 4.75–9.5 mm) exhibited 28 days modulus of elasticity and compressive strength in the range of 22.6–30.2 GPa, and 20.8–28.5 MPa, respectively. Sharigh et al. [45] mentioned that concrete containing 180 kg/m3 LECA (maximum nominal size 8 mm) as a part of coarse aggregate accounted 30.8 and 26.6 MPa 28 days compressive strength when the specimens were cured in moist and dry curing, respectively. Bastons et al. [47] mentioned that the concrete blocks compressive strength at age of 28 days in the variety of 8.95 to 5.63 MPa can be obtained with introducing LECA as coarse aggregate in the range of 50% to 90% when cement amount was 155 kg/m3. When cement amount was 214 kg/m3, the 28 days compressive strength in the variety of 11.7 to 5.39 MPa can be obtained Corinaldesi and Moriconi [48] mentioned that SCCs containing 226 kg/m3 LECA as fine aggregate (size 0–4 mm) and 367 kg/m3 LECA as coarse aggregate (size 0–15 mm) exhibited 21.26%, 27.54% and 17.98% lesser 1, 7 and 28 days compressive strength than that containing 100 kg/m3 LECA (size 0–4 mm) coupled with 345 kg/m3 normal weight sand (size 0–6 mm) as fine aggregates. In such a way, the 28 days static elastic modulus and splitting tensile strength were decreased by 29.76% and 12.63%, respectively. Bogas and Nogueira [35] mentioned that the 28 days tensile strength of concretes containing LECA (size 4–12 mm) as coarse aggregate was about 80–85% from the normal weight one, of identical strength. This can be decreased to 70% by incorporating lightweight fine aggregate. The 28 days modulus of rupture of LECA concretes cured in the air was about 50–80% of the normal weight one, of identical strength. Bogas et al. [28] obtained the compressive strength of 37.2 and 19.2 MPa by incorporating two different types of LECA (size 4–12 mm) as coarse aggregate. Macˇiulaitis et al. [50] mentioned that 28 days compressive strength of 16.69 MPa can be obtained by replacing normal weight sand and gravel in concrete with LECA (size 0–4 mm and 4–10 mm). Ali and Lazim [49] mentioned that concrete containing LECA (size 4–10 mm) as coarse aggregate showed 17.9 MPa compressive strength at age of 28 days. This strength was increased by 19%, 29.1% and 36.9% when LECA was partially replaced with normal weight coarse aggregate at levels of 15%, 20 and 25%, by volume, respectively. Pinto et al. [52] stated that the 28 days compressive strength of concretes containing LECA: cement: water with the ratio of 6: 1: 1 fluctuated from 10.66 to 17.2 kg/m3. Sivakumar and Kameshwari [53] found lesser 7, 28 and 56 days flexural strength, compressive strength and splitting tensile strength of concretes by partially replacing cement, normal weight coarse aggregate, normal weight fine aggregate with FA, LECA (size 10 mm) and bottom ash, respectively, at levels fluctuated from 5 to 35%. As the replacement level increased as the reduction in the mechanical strength increased. At replacement levels of 5%, 15%, 20%, 25%, 30% and 35%, the declination in the compressive strength at age of 28 days was 0.15%, 4.45%, 10.54%, 25.36%, 39%, 43.33% and 45.9%, respectively, whilst it was 0.8%, 8.66%, 14.57%, 16.93%, 19.29%, 22.83% and 25.2% for the 28 days splitting tensile strength, respectively. Priyanga et al. [66] found 8.67%, 17.92%, 22.83% and 28% declination in the compressive strength of concrete at age of 28 days by partially replacing normal weight coarse aggregate with 45%, 50%, 60% and 70% LECA, respectively. Lakshmi et al. [54] found

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8%, 10.38%, 15.13% and 19% declination in the flexural strength of concretes at age of 28 days by partially replacing normal weight coarse aggregate with 45%, 50%, 60% and 70% LECA, respectively. Scotta and Giorgi [67] found comparable 28 days compressive strength between normal weight concrete and concrete containing LECA (size 0–15 mm) as coarse aggregate admixed with 0.4% hooked steel fibers. They found 47.9% and 24.86% lesser 28 days flexural strength and static modulus of elasticity with the incorporation of LECA, respectively. Kumar and Prakash [36] replaced cinder, which was incorporated as coarse aggregate in the mixtures of concrete, with LECA at percentages fluctuated from 10% to 100%, by volume. Their results displayed lesser 7 and 28 days tensile strength as well as compressive strength with introducing LECA. As the LECA content increased as the reduction in strength increased. The incorporation of 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% and 100% LECA caused 0.44%, 1.44%, 5%, 7.33%, 21.23%, 29.47%, 37.51%, 45.44%, 54.67% and 56% declination in the tensile strength at age of 28 days, respectively. Campione et al. [59] found 0.8% declination in the compressive strength of concretes at age of 28 days with the incorporation of LECA (size 3–7, 7–17 mm) as coarse aggregate in comparison with the reference. Salem et al. [55] found 7.25%, 38.71% and 37% lesser 3, 28 and 90 days compressive strength of concrete by replacing normal weight coarse aggregate with LECA (size 4–16 mm), respectively. Dilli et al. [39] manufactured lightweight concretes from two different types of LECA (size 4–10 mm) at w/b ratios of 0.34, 0.42 and 0.5. A portion of coarse aggregate was replaced with LECA1 (26% water absorption) or LECA2 (23.2% water absorption). Depending on w/b ratio, the average 120 days compressive strength of normal weight concrete varied between 61 MPa and 75 MPa, whilst it varied between 24 MPa and 31 MPa for concrete containing LECA1 (with an average reduction of 59.56%). The average compressive strength of concrete containing LECA2 varied between 52 MPa and 68 MPa (with an average reduction of 11.76%). The same trend of the results was observed for modulus of elasticity. Bocca and Rossetti [40] found 39.82% lesser 28 days compressive strength of concretes by substituting normal weight coarse aggregate with LECA (size 8–15 mm). Nemes [68] found 13%, 20% and 20% lesser 3, 7 and 28 days compressive strength of concretes by replacing gravel with LECA (size > 4 mm), respectively. Malešev et al. [58] found 21.2% lesser 28 days compressive strength of concrete by substituting normal weight coarse aggregate by LECA (size 4–15 mm). Substituting normal weight coarse aggregate by LECA caused 35.1% and 36.51% reduction in the dynamic and static modulus of elasticity. Yoon et al. [56] found 30.1% lesser 28 days compressive strength of concrete by substituting normal weight coarse aggregate by LECA (size 10 mm). Bogas and Gomes [31] found 34.5% and 15.22% lesser concretes compressive strength at age of 28 days with the incorporation of LECA (maximum size 12.5 mm) as a coarse aggregate when cement amount was 350 and 450 kg/m3, respectively. When cement amount was 450 kg/m3, 50.79% declination in the compressive strength at age of 28 days was obtained with the incorporation of LECA as both fine aggregate and coarse aggregate. Moravia et al. [37] manufactured concrete mixtures containing LECA (maximum size 19 mm) as coarse aggregate with different estimated compressive strength values of 20, 25, 30 and 40 MPa coupled with w/b ratios of 0.63, 0.55, 0.48 and 0.41, respectively. Their results displayed a declination in the 3, 7, 28 days compressive strength with the incorporation of LECA. For estimated compressive strength of 20, 25, 30 and 40 MPa, 27.42%, 27.75%, 35.83% and 17.23% declination in the 3 days compressive strength was achieved, respectively, whilst 22.47%, 27.31%, 22.42% and 26.1% declination in the 28 days compressive strength was obtained, respectively. Youm et al. [69] found 19.1%, 17.76% and 20.65% lesser 28, 91 and 365 days compressive strength of concretes with introducing LECA (maximum

size 8 mm) as coarse aggregate, respectively, in comparison with the reference, whilst the declination in the modulus of elasticity was 33.1%, 32.36% and 32.85%, respectively. Fenyvesi [57] found 20% lesser 28 days compressive strength of concrete by substituting normal weight coarse aggregate by LECA (size 4–8 mm). Shebannavar et al. [22] found 45.32%, 28.66% and 25.45% lesser 3, 7 and 28 days compressive strength of concretes containing LECA (size 4.75–20 mm) as coarse aggregate in comparison with the reference, respectively, while the declination in the splitting tensile strength was 19.23%, 26.95%, 16.43%, respectively. The flexural strength was reduced by 23.36% and 25.2% at ages of 7 and 28 days, respectively. Youm et al. [34] found 29.67%, 32.8% and 47.53% lesser 28 days splitting tensile strength, compressive strength and modulus of elasticity of concretes with introducing LECA (maximum size 8 mm) as coarse aggregate, respectively in comparison with the reference. At age of 91 days the reduction in the splitting tensile strength, compressive strength and modulus of elasticity was 26.74%, 35.75% and 42.6%, respectively. Bogas and Gomes [25] manufactured lightweight concretes from LECA (maximum size 12.5 mm). The total porosity of the LECA was 60%. .Various w/b ratios of 0.3, 0.35, 0.4 and 0.45 were used. The results illustrated 38.8%, 36.2%, 37.4% and 34.4% reduction in the 28 days compressive strength with including LECA at w/b ratios of 0.3, 0.35, 0.4 and 0.45, respectively. Bogas et al. [42] found 36.31% lesser 28 days compressive strength of SCCs by replacing normal weight coarse aggregate with LECA (maximum size 12.5 mm). Bogas et al. [60] found 34.5% and 36.22% lesser 28 days compressive strength of concretes by substituting normal weight coarse aggregate with LECA (size 4–12 mm), when cement amount was 350 and 450 kg/m3, respectively. When cement amount was 450 kg/m3, the declination in the compressive strength at age of 28 days was 50.8% with the incorporation of LECA as both fine (size 0–3 mm) and coarse (size 4–12 mm) aggregates. Khafaga [70] found 22.5%, 3.4% and 22.25% lesser 28 days modulus of elasticity, compressive strength and splitting tensile strength of concretes by partially substituting normal weight aggregates with 50% LECA, by volume. Cavaleri et al. [61] found 43.26%, 8.3% and 15.38% declination in the 28 days elastic modulus, compressive strength and splitting tensile strength of concretes by substituting normal weight aggregates with LECA (size 3–7, 7–15 mm), respectively. Wegian [38] found 60.42% and 61.79% lesser 14 and 28 days compressive strength of concretes, respectively, by replacing normal weight sand and gravel with LECA (size 2–4, 4–8, 8–20 mm) when cement amount was 250 kg/m3. This reduction was 69.45% and 68.1% when normal weight sand and dolomite were replaced with LECA, respectively. When cement amount was 300 kgm 3, the compressive strength was reduced by 45.36% and 61.31% at ages of 14 and 28 days by substituting normal weight sand and gravel with LECA, respectively, whilst replacing normal weight sand and dolomite with LECA exhibited a reduction of 65.11% and 67.2%, respectively. When cement amount was 350 kg/m3, replacing normal weight sand and gravel with LECA caused 37.59% and 52.55% reduction in the 14 and 28 days compressive strength, respectively, whilst replacing normal weight sand and dolomite with LECA caused a reduction of 59.8% and 61.5%, respectively. The similar trend was observed in the splitting tensile strength results. Nováková et al. [71] found 48.73% lesser 28 days compressive strength of concretes by partially replacing normal weight aggregates (basalt size 0–4, 4–8 and 8–16 mm) with LECA (size 0–4 and 4–8 mm). Abdeen and Hodhod [41] found 49% and 55.97% lesser 7 and 28 days compressive strength of concretes containing LECA (size  25 mm with 40%-50% size of 2.4–4.76 mm) as aggregates, respectively. The reduction in the modulus of elasticity, tensile strength and impact resistance at age of 28 days was 71.5%, 41.57% and 196.3% with the incorporation of LECA, respectively. Kumar and Prakash [51] found

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47.33% and 50.41% lesser 7 and 28 days compressive strength of concretes by including of LECA as aggregates. Jόz´wiak-Niedz´wiedzka [32] found 12.4% and 6.26% lesser 28 days compressive strength of concretes by partially substituting normal weight sand with prewetted LECA (size 0–2 mm) at percentages of 33.33% and 50%, by volume, respectively, while the declination in the 28 days dynamic modulus was 12.12% and 14.37%, respectively. Shankar [27] found 1.42%, 25.45%, 23.26% and 31.24% lesser 7 days compressive strength of SCCs by partially substituting normal weight sand with 5%, 10%, 15% and 20% LECA, by volume, respectively, while the reduction in the tensile strength was 8.47%, 22%, 25.42% and 42.37%, respectively. Rajamanickam and Vaiyapuri [72] partially replaced normal weight sand in SCCs by LECA at levels fluctuated from 5% to 25%, by volume. The results illustrated lesser 7 and 28 days compressive strength, flexural strength, modulus of elasticity and splitting tensile strength for all replacement levels except the level of 15% at age of 28 days. Muñoz-Ruiperez et al. [28] partially replaced normal weight sand in mortar specimens with a combination of 18.75% LECA (size 2–4 mm) and 56.25% LECA (size 3–8 mm), by volume. The results illustrated that the 28, 90 and 365 days compressive strength was decreased by 44.51%, 54% and 41.25%, respectively, while the flexural strength was decreased by 37.6%, 49.55% and 42.1%, respectively, with the incorporating of LECA. Rashad [6] found 15% lesser 28 days compressive strength of mortar by substituting normal weight sand with LECA (size  4.75 mm). Table 5 briefs the influence of LECA on the compressive strength of mortar and concrete. From the prior investigations in this segment, it could be clearly extrapolated that the incorporation of LECA in the matrix declined the mechanical strength. The mechanical strength declined as the content of the LECA increased. The introduction of LECA as coarse aggregate can reduce the compressive strength at levels fluctuated from 34.4% to 38.8% as reported in [25], whilst other studies reported that this reduction could be fluctuated from 34.5% to 36.22% [60] or fluctuated from 7.15% to 38.71% [55] or etc. The introduction of LECA as both fine and coarse aggregates directed

to extra declination in the compressive strength. The declination in the compressive strength might fluctuate from 47.33% [51] to 55.97% [41]. This depends mostly on many reasons such as concrete age, cement amount, properties of normal weight aggregates, w/b ratio, crushing resistance of LECA, properties of LECA, LECA size etc. More than one factor are responsible for the lower mechanical strength of LECA concrete. As mentioned before that the incorporation of LECA decreased the density of concrete. Respectively the mechanical strength declined, at which it was reported that as the concrete density increased as the compressive strength increased [39]. LECA has lower crushing strength, particle strength and open voids compared to normal weight aggregate. The shape of LECA, in most cases, is spherical. This shape showed lesser bond strength with the surrounding paste than the angular one. As LECA is a porous material, the fracture usually caused in aggregate [25]. In spite of there are a lot of publications associated to the influence of LECA on the mechanical strength of concrete, most of these publications (about 72.5% of total publications) focused on including LECA as coarse aggregate (Fig. 5), whilst the incorporation of LECA as both fine and coarse aggregates came in the second place (about 20% of total publications). Replacing fine aggregate with LECA came in the last place. In such a way, the mechanical strength of LECA concrete has more attention (about 91.67% of total publications) than that of LECA mortar (about 8.3% of total publication). This means further studies are still needed for LECA mortar. 2.5. Porosity, water absorption and chloride penetration Bogas et al. [73] mentioned that partially replacing normal weight fine aggregate or coarse aggregate with LECA in concretes exhibited higher initial and long-term capillary absorption than the reference. Real et al. [24] found an increment in the capillary absorption coefficient of mortars by including LECA. The coefficient of capillary absorption increased as the LECA volume in the mixture increased. The capillary absorption coefficient was increased by 27.9%, 28.85% and 34.62% with the incorporation of LECA when

Table 5 Influence of LECA on the compressive strength of concrete and mortar. Author(s)

Replaced aggregate type

Type

LECA content (%)

LECA size (mm)

Reduction (%)

Sivakumar and Kameshwari [53] Priyanga et al. [66] Scotta and Giorgi [67] Kumar and Prakash [36] Campione et al. [59] Salem et al. [55] Nemes [68] Malešev et al. [58] Yoon et al. [56] Bocca and Rossetti [40] Bogas and Gomes [31] Moravia et al. [37] Youm et al. [69] Fenyvesi [57] Shebannavar et al. [22] Youm et al. [34] Bogas and Gomes [25] Bogas et al. [42] Bogas et al. [60]

Coarse Coarse Coarse Coarse Coarse Coarse Coarse Coarse Coarse Coarse Coarse Coarse Coarse Coarse Coarse Coarse Coarse Coarse Coarse Fine + Coarse Fine + Coarse Fine + Coarse Fine + Coarse Fine + Coarse Fine + Coarse Fine + Coarse Fine Fine Fine Fine

Concrete Concrete Concrete Concrete Concrete Concrete Concrete Concrete Concrete Concrete Concrete Concrete Concrete Concrete Concrete Concrete Concrete Concrete Concrete Concrete Concrete Concrete Concrete Concrete Concrete Concrete Concrete Concrete Mortar Mortar

5–35 45–70 100 10–100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 + 100 50 + 50 100 + 100 100 + 100 100 + 100 100 + 100 100 + 100 5–20 33.33–50 75 100

10 NA 0–15 NA 3–7, 7–17 4–16 >4 4–15 10 9–15 12.5 19 8 4–8 4.75–20 8 12.5 12.5 4–12 0–3, 4–12 NA 3–7, 7–15 2–4, 4–8, 8–20 0–4, 4–8 2.4–4.76, 25 NA NA 0–2 2–4, 3–8 4.75

0.15–45.9 8.67–28 0 0.44–56 0.8 7.25–38.71 13–20 21.2 30.1 39.82 15.22–50.79 17.23–35.83 19.1–20.65 20 25.45–45.32 32.8–35.75 12.5–38.8 36.31 34.5–36.22 50.8 3.4 8.3 37.59–69.45 48.73 49–55.97 47.33–50.41 1.4–31.24 6.26–12.4 41.25–54 15

Khafaga [70] Cavaleri et al. [61] Wegian [38] Nováková et al. [71] Abdeen and Hodhod [41] Kumar and Prakash [51] Shankar [27] Jόz´wiak-Niedz´wiedzka [32] Muñoz-Ruiperez et al. [28] Rashad [6]

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Fig. 5. Relative research number of mechanical strength for the incorporation of LECA in the matrix as coarse aggregate, fine aggregate and both of them.

its volume was 250, 300 and 400 L/m3, respectively. Salem et al. [55] found 55.5% increment in the 90 days water porosity of concrete by substituting normal weight coarse aggregate with LECA (size 4–16 mm). Youm et al. [34] found lesser resistance of chloride penetration in concrete specimens with the incorporation of LECA (maximum size 8 mm) as a coarse aggregate at age of 28 days in comparison with the reference. The 28 days total charge passed (Coulombs) was increased by 111.43% with the incorporation of LECA, whilst the chloride diffusion coefficient was increased by 41.67%. The charge passed amount of LECA concrete specimens converged with that of the reference at age of 91 days. Bogas and Gomes [31] found 28.1% lesser concrete chloride penetration resistance by including LECA (maximum size 12,5 mm) as coarse aggregate when cement amount was 450 kg/m3. Bastons et al. [47] found higher percentage of water absorption of concrete blocks with increasing LECA content from 55% to 90% as coarse aggregate. Jόz´wiak-Niedz´wiedzka [32] found 4.34% higher fresh porosity of concrete mixture by partially replacing normal weight sand with 33.33% prewetted LECA (size 0–2 mm), by volume; whilst partially replacing normal weight sand with 50% prewetted LECA led to 8.69% lesser fresh porosity. Basalt (size 2–4 and 8–16 mm) which was used as coarse aggregate was replaced with various percentages of prewetted LECA (size 2–4 mm). The results illustrated 8.69% lesser fresh porosity with the incorporation of 50% prewetted LECA, whilst the incorporation of 100% LECA caused an increment of 4.45%. Koñáková et al. [62] found 47% reduction in the open porosity of lime-burnt clay shale plaster by replacing normal weight silica sand with LECA (size 0–4 mm). Nováková et al. [71] replaced basalt (size 2–4, 4–8 and 8–16 mm) which was used as normal weight aggregates in concrete specimens by LECA (size 2–4 and 4–8 mm). After curing for 28 days, the permeability of the surface layer of concrete specimens was measured. The results illustrated 12.46% higher surface permeability of the specimens containing LECA after 10 min from starting the test, whilst 41.48% reduction was observed after 60 min from starting the test. Muñoz-Ruiperez et al. [28] partially replaced normal weight sand in mortar specimens by a combination of 18.75% LECA (size 2–4 mm) and 56.25% LECA (size 3–8 mm). Their results displayed 0.11% and 0.08% water absorption for the reference and LECA mortars, respectively. As noted from the prior investigations, it could be extrapolated that most of these investigations (about 62% of the total) believed that the incorporation of LECA in the matrix increased the percentage of water absorption and decreased its resistance to chloride penetration. Variously, few studies (about 38% of the total) believed that the incorporation of LECA in the matrix declined the percentage of water absorption. This depends mainly on the degree of porosity and the density of the outer shell of LECA. In

general, LECA is more porous material in comparison with the normal weight aggregate. This led to an increase in the speed of chloride diffusion and capillary absorption. Zhang and Gjorv [74] and Hobbs [75] found higher chloride diffusion in more porous aggregate. The interconnected pores in LECA can contribute the absorption, increase the aggregate accessibility and increase chloride permeability. Bogas et al. [26] mentioned that the absorption of mortars containing different types of LECA was higher for more porous aggregate and higher percentage of broken particles. Similar higher water permeability was observed in lightweight concrete containing Lytag aggregate [76]. However, for LECA has lower porosity but with denser outer shell, this resulted in a good quality of the interfacial transition zone (ITZ) and paste as well as restriction water access to the interior matrix. Because the LECA porous structure is more roughness than the paste, there is a significant reduction in the degree of absorption close LECA particles [73]. In all cases, this item still lacking and needs to be studied further. This topic can be used for incoming studies. 2.6. Shrinkage and cracking tendency Muñoz-Ruiperez et al. [28] found lesser shrinkage of mortars, up to 224 days, by partially replacing normal weight sand with a combination of 18.75% LECA (size 2–4 mm) and 56.25% LECA (size 3–8 mm), by volume. The rate of shrinkage of LECA mortar and the reference tended to converge over time. Shen et al. [63] partially replaced coarse aggregate in concretes with prewetted LECA (size 4.7–9.5 mm) at percentages of 10%, 30% and 50%. Their results illustrated lesser autogenous shrinkage up to 60 h with the incorporation of LECA. As the prewetted LECA content increased as the reduction in the autogenous shrinkage increased. This could be associated to the capability of prewetted lightweight aggregate to resource water to the paste, which maintained higher relative humidity due to the effect of self-desiccation [77]. Schwesinger and Sickert [78] incorporated LECA with spherical shape and pore volume of approximately 55% for HPC production. The results illustrated lesser autogenous shrinkage with the incorporation of LECA. They related this reduction in the shrinkage to the internal moisture conditions that LECA caused in HPC. Bogas et al. [60] found lesser total shrinkage of concretes containing LECA (size 4–12 mm) as coarse aggregate up to 3 months, whilst at latter ages concrete containing LECA exhibited higher total shrinkage. The total shrinkage of concretes containing LECA at age of 30 days was 0.56 of the reference. Variously, after 365 days the concretes containing LECA as coarse aggregate exhibited 1.54 times total shrinkage of that obtained for the reference. Additional replacement of normal weight fine aggregate with LECA (size 0–3 mm) resulted in an increase in the total shrinkage at all ages. This increment can reach as high as twice that of the reference at age of 365 days. Corinaldesi and Moriconi [48] mentioned that SCCs containing 226 kg/m3 LECA as fine aggregate (size 0–4 mm) and 367 kg/m3 LECA as coarse aggregate (size 0–15 mm) exhibited higher drying shrinkage up to 90 days than that containing 100 kg/m3 LECA (size 0–4 mm) coupled with 345 kg/m3 normal weight sand (size 0–6 mm) as fine aggregates. Fenyvesi [57] mentioned that concrete containing LECA (size 4–8 mm) as coarse aggregate showed lower crack tendency in comparison with the reference. From the prior studies herein, it may be extrapolated that the influence of LECA on the shrinkage of concrete and mortar still lacking and requires to be studied further. However, related to the presented investigations, the incorporation of LECA in the matrix decreased shrinkage in spite of LECA is a porous material and its modulus is small, which could lead to less restriction on the probable shrinkage of cement paste. LECA, similar to the other types of lightweight aggregate, has a greater number of pores with

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large size than that of normal weight one, whilst it has fewer small size pores in comparison with that of normal weight one. In addition, LECA was exposed to high temperature during its manufacturing process, which led to formation large size of pores. The micropores were loosed as a result of recrystallization, resulting in a limited micropores numbers. The internal surface area is almost governed by the content of small size pores [79]. As LECA has a limited size pores, this can lead to a limited internal surface area. Consequently, the alteration of its length is mitigated. When LECA soaked in water, water moves into micropores and resulting in rapid swelling due to the higher absorbed surface area. By further soaking, water penetrates into large pores resulted in an increase in the content of water and a reduction in the swelling [79]. During drying, the content of water decreases and shrinkage occurs slowly, of which water still remains into micropores. Further progressing of drying until evaporating water from micropores, shrinkage increases significantly. In the event of prewetted LECA, the declination in the shrinkage resulting in internal curing of concrete [80]. The internal curing leads water to transport from the prewetted LECA to cement pores resulting in a reduction in their desiccation. Thus, the shrinkage decreases [80]. The similar trend was observed in concrete containing expanded shale as a lightweight fine aggregate [81] and concrete containing expanded slate as a lightweight coarse aggregate [64]. As LECA matrix has lower shrinkage, the tendency of cracks is low in comparison with the normal weight one. In addition, LECA concrete or mortar has lower E-modulus which leads to lower crack tendency due to the lower tensile stress induced by the same strain [79]. 2.7. Fire, freeze/thaw and chemical resistance Bodnárová et al. [82] mentioned that there were no significant damages were observed on the concretes containing LECA aggregates (size 1–4 and 4–8 mm) after being exposed to elevated temperature according to standard temperature–time curve ISO 834. Bogas and Cunha [46] exposed concrete specimens containing LECA (diameter 4–8 mm) as coarse aggregate, 130 kg.m3 cement and 280 kg/3 lime filler to elevated temperatures for 1 h. The results illustrated 8.62%, 22.4%, 34.48% and 51.7% reduction in the compressive strength after subjecting to 200 °C, 400 °C, 600 °C and 800 °C, respectively, compared to their original before heating. Rashad [82] and Hodhod et al. [83] found higher remaining capacity of reinforced concrete column samples coated with LECA (size  4.75 mm) coupled with 500 kg/m3 cement than those coated with normal weight sand coupled with 300 kg/m3 cement after subjecting to 650 °C for thirty minutes. In the event of using 15 mm of plaster thickness, the column samples plastered with LECA-cement showed 63.1% remaining capacity, while those plastered with normal weight sand-cement showed 50.46%. Abdeen and Hodhod [41] subjected concretes comprising LECA (size  25 mm with 40%–50% size of 2.4–4.76 mm) aggregates to 400 °C for one hour. Their results illustrated that concretes comprising LECA can retain residual compressive strength of 85%, whilst those containing normal weight aggregates can keep only 46% of its original strength. Nováková et al. [71] replaced basalt (size 2–4, 4–8 and 8– 16) which was used as normal weight aggregates in concrete specimens with LECA (size 2–4 and 4–8 mm). The specimens were exposed to normative heat curve ISO 834. The results illustrated that concrete specimens containing LECA exhibited less damage after being exposed to elevated temperature. Netinger et al. [84] mentioned that concrete containing LECA as an aggregate can be categorized as fire resistance concrete. Lublόy and Balázs [85] mentioned that concrete comprising LECA as coarse aggregate showed 10% to 20% lesser remaining compressive strength afterward being

767

exposed to high temperatures up to 800 °C for 2 h compared to that containing gravel coarse aggregate. Youm et al. [34] mentioned that concrete specimens containing LECA (maximum size 8 mm) as coarse aggregate exhibited lesser freeze/thaw resistance than the reference. Jόz´wiak-Niedz´wiedzka [32] found lesser freeze/thaw resistance of concretes by partially replacing normal weight sand with prewetted LECA (size 0–2 mm) at percentages of 33.33 and 50%, by volume. Basalt (size 2–4 and 8–16 mm) which was used as coarse aggregate was replaced with prewetted LECA (size 2–4 mm) at percentages of 50% and 100%. The results illustrated lesser freeze/thaw resistance with the incorporation of prewetted LECA. The reduction in the freeze/thaw resistance increased as LECA content increased. Motamednia et al. [86] exposed normal weight concrete and those containing LECA (size 2–4 mm and 4–12 mm) to 15% hydrochloric acid (HCl) for 3 months, 5% sulfuric acid (H2SO2) for 6 weeks and 5% lactic acid (CH3CHOHCOOH) for 3 months. The results illustrated that specimens containing LECA exhibited higher resistance against HCl and CH3CHOHCOOH than that of the normal weight one. Variously, concrete containing LECA exhibited less resistance against H2SO2 in comparison with the normal weight one. From the prior studies in this section, it could be extrapolated that the influence of LECA on chemical resistance and fire resistance, freeze/thaw resistance of concrete and mortar still lacking and needs to be studied further. However, related to the presented quoted investigations, the incorporation of LECA in the matrix enhanced the resistance of fire. This positive effect could be associated to the high temperature (1200 °C) which LECA exposed during its manufacturing process. Another possible reason might be associated to the lesser thermal expansion of LECA in comparison with that of the normal weight aggregate. Thus, the number and size of cracks, which can facilitate the diffusion of flame and heat into the matrix during heating, will be reduced. It is noteworthy mentioning that the coefficient of thermal expansion of LECA is between 50 and 70% which still lesser than that of gravel [87]. In addition, the interconnected voids, as well as air pockets within the pellet can produce excellent insulation barrier for heat transfer, which led to a reduction in the harmful causing by elevated temperature. It is noteworthy mentioning that during firing, LECA has no reaction with fire, does not emit smoke or gases. According to the available quoted studies regarding to the influence of LECA on the resistance of freeze/thaw, it could be extrapolated that introducing LECA in the matrix reduced the resistance of freeze/thaw. This might be associated to the higher percentage of water absorption of LECA compared to the normal weight aggregate. Whatever, the resistance of freeze/thaw of LECA concrete depends on the percentage of water absorption of LECA, as the percentage of water absorption of LECA increased as the degradation by freeze/thaw increased. 2.8. Sound isolation and thermal conductivity Sousa et al. [88] mentioned that masonry units containing LECA as part of aggregates (0.53 m3 normal weight sand coupled with 0.14 m3 LECA with the size of 2–4 mm and 0.73 m3 LECA with size of 3–8 mm) exhibited high sound insulation as well as thermal insulation. The thermal conductivity reached 0.5 W/m K with the incorporation of LECA. Bastons et al. [47] mentioned that thermal conductivity of 0.51, 0.44 and 0.33 W/m K of concrete blocks can be obtained with the incorporation of 65%, 70% and 80% LECA as coarse aggregate, respectively, when cement amount was 214 kg/m3. Hubertova and Hela [89] mentioned that thermal conductivity of 0.2429 W/m K of SCC can be obtained by replacing normal weight aggregates with LECA (size 1–4 mm, 4–8 mm). Zach et al. [90]

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mentioned that different types of LECA concretes showed thermal conductivity of 0.1376, 0.1521 and 0.1649 W/m.K when measured by hot-wire method. Bogas and Cunha [46] mentioned that concrete specimens containing LECA (diameter 4–8 mm) as coarse aggregate, 130 kg.m3 cement and 280 kg/m3 lime filler exhibited thermal conductivity of 0.23 W/m.K. Grabois et al. [91] mentioned that the incorporation of LECA (size 0.4–20 mm) as coarse aggregate instead of normal weight one and 30% LECA (size 0.06– 10 mm) instead of normal weight sand can reduce the thermal conductivity by 60%, whilst specific heat was increased by 3.62%. Rashad [6] and Hodhod et al. [83] mentioned that incorporating LECA (size  4.75 mm) coupled with 500 kg/m3 cement as plaster exhibited 71.75% declination in the thermal conductivity compared to that containing normal weight sand coupled with 300 kg/m3 cement. From the prior studies herein, it could be extrapolated that the influence of LECA on the resistance of noise still lacking and needs to be studied further. Whatever, related to the quoted study, introducing LECA in the matrix improved its sound isolation. The cellular and porous structure of LECA contribute to assure good noise absorption. The incorporation of LECA in the matrix not only improved its sound isolation, but also increased its thermal insulation. As the content of LECA in the mixture increased as the thermal insulation increased, of which the thermal conductivity of the LECA is low in comparison with that of normal weight aggregate. It is expected result, because LECA has lesser density as well as higher porosity than the normal weight aggregate, which led to lesser thermal conductivity or higher thermal isolation. In addition, the interconnected pores in the LECA pellets help to reduce thermal conductivity, at which air into pores is a good insulation material. The higher thermal insulation properties of LECA which used in a construction can improve buildings energy performance and contribute energy reduction.

3. Geopolymers Paul and Babu [19] activated slag/FA by a solution of sodium silicate and NaOH to prepare geopolymer concretes. The normal weight coarse aggregate was replaced with LECA (size 4–10 mm) at percentages of 40%, 60%, 80% and 100%. Their results illustrated lesser mechanical strength with the incorporation of LECA. The mechanical strength decreased as LECA content increased. The 28 days compressive strength decreased from 44 MPa for concrete containing 40% LECA coarse aggregate to 8 MPa for concrete containing 100% LECA coarse aggregate. The 28 days splitting tensile strength, flexural strength and density decreased from 2.4 MPa, 5.6 MPa and 2350 kg/m3 for concretes containing 40% LECA coarse aggregate to 0.54 MPa, 0.72 MPa and 1450 kg/m3 for concretes containing 100% LECA coarse aggregate, respectively. Abdulkareem et al. [92,93] activated FA with a solution of NaOH and sodium silicate to prepare geopolymer concretes. Normal weight sand was used as fine aggregate, whilst LECA was used as coarse aggregate. The specimens were subjected to high temperatures at levels fluctuated from 100 °C to 800 °C with a step of 100 °C for 1 h. Their results illustrated an enhancement in the residual compressive strength of specimens after being subjected to 100 °C, 200 °C and 300 °C. Next, the residual strength began to decline after being subjected to temperatures of 400 °C up to 800 °C. This reduction could be associated to the variance in the thermal expansion amongst aggregate and paste. Rickard et al. [94] activated FA by a solution of sodium silicate and NaOH to prepare geopolymer concretes. Normal weight aggregates were replaced with LECA (sizes 0–2, 4–8 and 8–16 mm). The results illustrated more workability and more air content with the

incorporation of LECA aggregates, of which the flow diameter and air content were increased by 11.63% and 160.87%, respectively. The fresh bulk density, 56 days density and 56 days compressive strength was decreased by 38.1%, 40.87% and 74.19%, respectively, with the incorporation of LECA. Variously, the air permeability at age of 200 days was increased by 491.77% with the incorporation of LECA. The specimens were subjected to 100, 300, 500 and 750 °C for 60 min. The relative remaining compressive strength of concretes comprising LECA was higher than those of the normal weight one (Fig. 6). The higher thermal-expansion of the normal weight aggregates led to larger losses of strength in comparison with LECA one. At temperature  300 °C, the damage in the LECA concretes was less than those of the normal weight concretes as a result of the lower permeability of the normal weight aggregates. Gluth et al. [95] activated FA by a solution of sodium silicate and NaOH to prepare geopolymer concretes. Normal weight aggregates (sand and gravel) were replaced with LECA (sizes 0–2, 4–8 and 8–16 mm). The specimens were subjected to standard fire curve of ISO 834-1. The results illustrated that specimens containing normal weight aggregates exhibited significant formation of cracks during heating nearby the temperature of the ɑ-b transition of quartz (573 °C) and during cooling, whilst the specimens containing LECA exhibited formation of cracks during cooling only. The better compatibility between LECA aggregates and geopolymer paste can inhibit the significant damage during heating. Although there are cracks in specimens containing LECA during cooling, this deterioration still less than that containing normal weight aggregates. Table 6 briefs the influence of LECA on geopolymer matrix. As of the prior investigations herein, it could be extrapolated that the incorporation of LECA in geopolymer matrix still lacking and needs to be studied further. However, according to the available quoted studies, it could be observed that it is promising to incorporate LECA as aggregate in geopolymer system. The incorporation of LECA in this system has positive effects regarding to increasing workability, increasing air content, decreasing density, increasing relative residual strength after firing and decreasing number of cracks during firing. Variously, the incorporation of LECA in this system has a negative effect regarding to mechanical strength, of which mechanical strength decreases as LECA content increases.

Fig. 6. Influence of LECA on the relative compressive strength of geopolymer concrete after exposure to elevated temperatures [94].

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Table 6 Influence of LECA on geopolymer matrix. Author(s)

LECA (%)

Replaced aggregate type

Size (mm)

Type

Paul and Babu [19]

40–100

Coarse

4–10

Concrete

Abdulkareem et al. [93]

100

Coarse

NA

Concrete

Rickard et al. [94]

100 + 100

Fine + Coarse

0–2, 4–8, 8–16

Concrete

Gluth et al. [95]

100 + 100

Fine + Coarse

0–2, 4–8, 8–16

Concrete

4. Adding materials to improve some properties of LECA matrices 4.1. Supplementary cementing materials – SCMs Youm et al. [34] mentioned that partially replacing cement with 3.5% and 7% silica fume (SF) in concrete specimens containing LECA (maximum size 8 mm) as coarse aggregate enhanced the mechanical strength and resisted chloride penetration, but decreased workability and density. The slump was decreased by 4.35% and 30.43% with the incorporation of 3.5% and 7% SF, respectively. The 28 days wet density was decreased by 0.73% and 2.29% with the incorporation of 3.5% and 7% SF, respectively. The compressive strength at age of 28 days was enhanced by 1.95% and 3.9% with the incorporation of 3.5% and 7% SF, respectively, while the 28 days splitting tensile strength was enhanced by 0.6% and 2.23%, respectively. The 28 days modulus of elasticity was increased by 4.76% and 3.5%, respectively. The 28 days total charge passed was decreased by 57.48% and 78.72% with the incorporation of 3.5% and 7% SF, whilst the 90 days total charge passed was decreased by 69.74% and 87.63%, respectively. Sarkar [18] mentioned that adding 4.7% SF to concrete containing LECA (size 2–6 and 4–10 mm) as coarse aggregate enhanced the compressive strength at ages of 1, 7 and 28 days by 1.7%, 6.8% and 10.64%, respectively. Mohammadi et al. [96] found 3.8%, 6.63% and 12.97% improvement in the 90 days compressive strength of SCCs containing LECA (maximum size 5 mm) as a fine aggregate by partially substituting cement by SF at percentages of 5%, 10% and 15%, respectively. Mahdy [97] found 30.16%, 37.4% and 32.55% improvement in the compressive strength, at age of 3 days, of concretes comprising LECA (size 2.36–10 mm) as coarse aggregate (0.65 of total aggregate) by adding 5%, 10% and 15% SF, respectively, while the compressive strength at age of 7 days was enhanced by 32.41%,

Effect - Decreased mechanical strength - Decreased density - Residual strength increased at 100–300 °C, but decreased at 400–800 °C - Increased workability, air content and air permeability - Decreased density and compressive strength - Increased relative residual strength after firing - Less cracks during firing

34.62% and 29.9%, respectively. The 28 days compressive strength increased by 30.32%, 37.17% and 32.39%, respectively. The compressive strength of concretes containing LECA coarse aggregate can be modified by including 10% and 20% solution of SF, by mixing water weight. The 3, 7 and 28 days compressive strength was enhanced by 8.75%, 15.9% and 15.39% by including 10% SF solution, respectively. The incorporation of 20% SF solution enhanced the compressive strength at ages of 7 and 28 days by 6.64% and 11.29%, respectively. Hosseinpoor [98] reported an improvement in the tensile strength and compressive strength, at ages of 7, 14 and 28 days, of concrete specimens comprising LECA (size 0.075– 0.15 mm) as a part of fine aggregate by partially substituting cement by 10% and 15% SF. The compressive strength at age of 28 days was enhanced by 65.32% and 76.81% with introducing of 10% and 15% SF, respectively, while the tensile strength was enhanced by 26.2% and 34.28%, respectively. The incorporation of 10% SF in the mixture decreased the percentage of water absorption, whilst the incorporation of 15% SF increased it. Sajedi and Shafigh [17] mentioned that it is conceivable to increase mechanical strength and obtain high strength lightweight concrete containing LECA as coarse aggregate by incorporation of 55 kg/m3 SF (8% of total powders) coupled with 165 kg/m3 limestone (LS) powder (24% of the total powders). Real et al. [24] found 16.94% and 1.86% declination in the capillary absorption coefficient of LECA mortar by partially substituting cement with 6% and 9% SF, respectively. Subasßi [99] mentioned that partially substituting cement by 10% FA, by weight, can decline the porosity and increase the compressive strength of concretes comprising LECA (size 4–8 mm) as coarse aggregate coupled with LECA (sizes 0–2 mm and 2–4 mm) as a part of fine aggregate (70% of total fine aggregate). The incorporation of 10% FA reduced the 28 days porosity by 46.15% and enhanced the 28 days compressive strength by 7.51% when total binder was 450 kg/m3. Kumar and

Table 7 Influence of different types of cementitious materials on some properties of LECA matrices. Author(s)

Additive(%)

Type

Youm et al. [34]

3.5 and 7 SF

Concrete

Sarkar [18] Mohammadi et al. [96] Mahdy [97] Hosseinpoor [98]

4.7 SF 5–15 SF 5–15 SF 10, 20 SF solution 10, 15 SF

Concrete Concrete Concrete Concrete Concrete

Sajedi and Shafigh [17] Real et al. [24] Subasßi [99]

8 SF + 24 LS 6, 9 SF 10 FA

Concrete Mortar Concrete

Kumar and Prakash [36] Bogas and Gomes [31]

20 slag 22 and 40 FA

Concrete Concrete

Bogas et al. [60]

22 and 40 FA 1.8 nano-SiO2

Concrete Concrete

Effect -

Decreased workability, density, total charge passed Increased mechanical strength Increased compressive strength Increased compressive strength Increased compressive strength Increased compressive strength Increased compressive and tensile strength 10% SF decreased water absorption, but 15% increased it Increased mechanical strength Decreased capillary absorption Decreased porosity Increased compressive strength Increased compressive strength Decreased fresh dry density Increased chloride penetration Decreased density Decreased long-term total shrinkage

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and coarse aggregate by adding 1% steel fibers, respectively, while the flexural strength was increased by 10.53%. Bagherzadeh et al. [102] mentioned that the addition of 0.15% polypropylene fibers (length of 12 mm) enhanced the 7, 14 and 28 days compressive strength of concretes containing LECA (maximum size 10 mm) as coarse aggregate by 6.67%, 3.3% and 11.72%, respectively, whilst the addition of 0.35% polypropylene fibers enhanced it by 14.28%, 4.94% and 18.47%, respectively. The incorporation of 0.35% polypropylene fibers increased the 28 days flexural strength by 30.1%, while the splitting tensile strength was increased by approximately 31%. The addition of polypropylene fibers can reduce the drying shrinkage. As the polypropylene fibers content increased as the drying shrinkage decreased. Variously, the addition of polypropylene fibers increased the water absorption percentage. As the polypropylene fibers content increased as the percentage of water absorption increased. Bodnárová et al. [82] found 2.32% and 28.57% enhancement in the 28 days compressive strength of concretes comprising LECA (size 1–4 and 4–8 mm) as aggregates by adding 0.8% polypropylene fibers. Variously, the flexural strength was decreased by 37.33%. Zohrabi et al. [101] found 2.3% and 7.48% enhancement in the 7 and 28 days compressive strength of concretes containing LECA aggregates with introducing 1% polypropylene fibers, respectively. Abdeen and Hodhod [41] attempted to improve some properties of concretes comprising LECA (size  25 mm with 40%-50% size of 2.4–4.76 mm) as fine and coarse aggregates by incorporating 0.4% linen fibers. Their results illustrated 296.76%, 131.5% and 49.66% improvement in the 28 days impact resistance, modulus of elasticity and splitting tensile strength by introducing linen fibers, respectively. Variously, the incorporation of linen fibers slightly increased the bulk density and declined the compressive strength. Momtazi et al. [103] mentioned that compressive strength at age of 28 days of concretes comprising LECA as a fine aggregate can be enhanced by partially replacing cement with 10% SF coupled with 0.1% polypropylene fibers. Zohrabi et al. [101] found 36.36% and 35.37% enhancement in the 28 days compressive strength of concretes containing LECA (size 0–4 mm and 4–10 mm) as fine aggregate and coarse aggregate by adding 1% polypropylene fibers coupled with 10% metakaolin (MK), as cement replacement. Adding 1% steel fibers coupled with 10% MK, as cement substitution, increased the 7 and 28 days compressive strength by 51.14% and 48.13%, respectively, whilst the 28 days flexural strength was enhanced by 68.42%. Table 8 briefs the influence of fibers coupled with cementitious materials on some characteristic of LECA matrices

Prakash [36] mentioned that partially replacing cement with 20% slag can enhance the compressive strength of concretes comprising 40% LECA and 60% cinder coarse aggregates by 7.34%, at age of 28 days. Bogas and Gomes [31] found 2.1% and 4.1% lesser density, in fresh state, of concrete mixtures comprising LECA (maximum size 12.5 mm) as coarse aggregate by partially replacing cement with 22% and 40% FA, respectively, whilst the dry density was reduced by 2.13% and 4.14%, respectively. Partially replacement cement with 22% and 40% FA increased the 360 days chloride penetration by 4.9% and 73.17%, respectively. Bogas et al. [60] found 2.13% and 23.66% lesser oven dry density of concrete containing LECA (size 4–12 mm) as coarse aggregate by partially replacing cement with 22% and 40% FA, by weight, respectively. They also mentioned that partially replacing cement with 1.8% nano-SiO2 in concretes containing LECA as coarse aggregate decreased the long-term total shrinkage. The incorporation of nano-SiO2 led to 5% reduction in the total shrinkage at age of 350 days. Table 7 briefs the influence of various types of cementitious materials on some properties of LECA matrices 4.2. Fibers/cementitious materials reinforced with fibers Grabois et al. [91] mentioned that the incorporation of 0.5% steel fibers, by volume, in SCCs containing LECA (size 0.4–20 mm) as a coarse aggregate can increase the flow of slump from 670 to 675 mm. The incorporation of steel fibers improved the tensile Young’s modulus and strain at tensile peak stress as well as tensile strength. Variously, at age of 28 days, the water absorption and density were increased by 25.64% and 6.29%, respectively, and the compressive strength was declined by 4.4%. The incorporation of steel fibers increased the drying shrinkage. Hassanpour et al. [100] stated that the mechanical strength of concretes comprising LECA (size 4.75–12.5 mm) as coarse aggregate could be enhanced by including steel fibers. The 28 days flexural strength, splitting tensile strength and compressive strength can be enhanced by 6–69%, 21–77% and 14–32% by adding 0.25%-1% steel fibers, by volume. Campione et al. [59] mentioned that flexural strength, tensile strength and fracture toughness of lightweight concretes containing LECA (size 3–17 mm) as coarse aggregate can be enhanced by incorporating 0.5%, 1% and 2% steel fibers. By incorporating 2% steel fibers, the 28 days flexural strength, splitting tensile strength and compressive strength was enhanced by 93.39%, 117.9% and 30%, respectively. Zohrabi et al. [101] found 14.2% and 13.55% enhancement in the compressive strength, at age of 28 days, of concretes containing LECA (size 0–4 mm and 4–10 mm) as fine aggregate

Table 8 Influence of fibers/fibers coupled with other material on some properties of LECA matrices. Author(s)

Additive (%)

Type

Grabois et al. [91]

0.5 Steel fibers

Concrete

Hassanpour et al. [100] Campione et al. [59]

0.25–1 Steel fibers 0.5–2 Steel fibers

Concrete Concrete

Zohrabi et al. [101] Bagherzadeh et al. [102]

1 Steel fibers 0.15 and 0.35 Polypropylene fibers

Concrete Concrete

Bodnárová et al. [82]

0.8 Polypropylene fibers

Concrete

Zohrabi et al. [101] Abdeen and Hodhod [41]

1 Polypropylene fibers 0.4 Linen fibers

Concrete Concrete

Momtazi et al. [102] Zohrabi et al. [101]

10 SF + 1 Polypropylene fibers 1 Polypropylene fibers + 10 MK 1 Steel fibers + 10 MK

Concrete Concrete Concrete

Effect -

-Increased workability -Increased Young’s modulus and tensile strength -Increased water absorption and density -Decreased compressive strength Increased mechanical strength Increased mechanical strength Increased fracture toughness Increased flexural strength and compressive strength Increased mechanical strength Decreased drying shrinkage Increased water absorption Increased compressive strength Decreased flexural strength Increased flexural strength and compressive strength Increased splitting tensile strength, modulus of elasticity and impact resistance Decreased compressive strength Increased compressive strength Increased flexural strength and compressive strength Increased flexural strength and compressive strength

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4.3. Other materials Bernhardt et al. [104] applied different additives aiming to improve the production process and properties of LECA. The addition of 5% Na2CO3 decreased the viscosity of glass phase at pellets surfaces, but brought less expansion, pellets lingering together with an irregular shape. The addition of 10% SiO2 amorphous or 5% SiO2 crystalline did not show an obvious change in the LECA properties. The incorporation of 5% Fe2O3 produced greater pores in the pellet center, but has no effect on total porosity, density and strength. The incorporation of 5% metallic iron powder (Fe) caused an expansion increase, a reduction in the mechanical strength and particle density. Thus, Fe can be used as an improver for density reduction of LECA in the applications which required low density. Macˇiulaitis et al. [50] mentioned 24.3% improvement in the compressive strength, at age of 28 days, of concretes comprising LECA aggregates can be obtained by partially replacing cement with 15% catalyst, by weight. Macˇiulaitis et al. [105] mentioned that the incorporation of 30% waste catalyst (size 0.04–400 mm) as filler, by cement weight, enhanced the compressive strength, at ages of 2, 14 and 28 days, of concretes containing 396.5 kg/m3 LECA (size 0–4 mm) as a part of fine aggregate. The incorporation of the waste catalyst can reduce the total open porosity by 8.52%. Islam et al. [16] tried to improve some properties of LECA by partially replacing clay with 20%, 35% and 50% soda lime silica glass. The sintering temperatures were 850, 950 and 1050 °C. Their results illustrated that the crushing resistance of LECA increased with the increase of soda lime silica glass from 20% to 50% and sintering temperature from 850 °C to 1050 °C, whilst the bulk density and water absorption of the LECA decreased. Deveciog˘lu and Biçer [106] prepared mixtures containing LECA (size 4–8 mm) coupled with cement. The amounts of LECA in the mixtures were 5%, 10% and 20%, by cement weight. These mixtures were modified by adding 1% tragacanth (natural resin). The addition of 1% tragacanth can reduce the density by 19.63%, 13.23% and 23.9% for mixtures containing 5%, 10% and 20% LECA, respectively. The thermal conductivity was decreased by 27.75%, 28.53% and 35.24%, respectively. Variously, the addition of 1% tragacanth increased the percentage of water absorption and decreased the compressive strength by 44.74%, 48.75% and 75.97%, respectively. Korjakins et al. [107] found a slight improvement in the mechanical strength with comprising LECA (size 4–10, 10–20 mm) as coarse aggregate by replacing natural sand with waste dolomite (size 0–4 mm). The enhancement in the 7 and 28 days compressive strength was 2.94% and 1.55% with the incorporation of waste dolomite, respectively, while the improvement in the tensile strength at age of 28 days was 8.13% and the reduction in the water penetration was 17.14%. Variously, the frost resistance was decreased with the incorporation of waste dolomite. Form the above-quoted references about using different additives to improve some properties of LECA, it could be extrapolated that most of these studies preferred to use cementitious materials (40.74% of the total) for this purpose. Using fibers came in the second place (37% of the total), whilst using other materials such as Na2CO3, catalyst etc came in the last place. 5. Benefits, shortages and applications The incorporation of LECA as fine aggregate, coarse aggregate or both of them in the matrix illustrated particular benefits, at which some properties are improved, and particular shortages, at which some properties are dropped down. The profits of applying LECA in the mixture are modifying workability, adequate segregation resistance, decreasing density, decreasing creep, decreasing thermal conductivity which led to good thermal insulation, absorbing noise which led to good sound insulation, increasing fire resis-

tance, increasing resistance against hydrochloric acid and lactic acid, decreasing crack tendency and decreasing shrinkage. In addition, by using LECA, the quarrying of normal weight virgin aggregates can be reduced. On the contrary, the deficiencies of applying LECA in the mixture are reducing mechanical strength, reducing freeze/thaw resistance, reducing resistance against sulfuric acid and increasing chloride penetration and water absorption (Table 9). These shortages can be alleviated by incorporation of various additives illustrated in the prior section. LECA is a multipurpose material, is employed in many uses. In the construction field, it can be applied widely in the production of lightweight blocks, concrete and precast or in-cast structural aspects such as panels and partitions (Fig. 7). It could be utilized in a lightweight and heat insulation tiles, thermal proofing plaster, plaster against noise and in flooring and roofing with good sound and thermal insulation. As a result of its good shear strength and low weight, LECA is used for lightweight fill in structures to decrease pressure on structures and decrease settlement [1]. It is possible to use LECA (size 1–25 mm) with a density of 330–430 kg/m3, porosity volume fraction of 73–88 vol% and thermal conductivity of 0.09–0.1 W/m K to produce metal composite foam. This composite exhibited energy absorption capacity, yield strength and relative density of 18 MJ/m3, 35.9 MPa and 0.44, respectively [108]. Recently, LECA can be incorporated in geopolymers to produce lightweight and good fire resistance geopolymers. LECA cannot be used only in the construction field, but it also could be used in other fields such as agriculture and water treatment. It could be utilized with soil and peat and a growing medium in hydroponics systems to retain water during periods of drought and improve drainage. as a growing intermediate in hydroponics systems, and mixed with other growing mediums like peat and soil to modify retain water during drought periods, drainage, provide roots with increased levels of oxygen promoting very vigorous growth and isolate roots throughout frost. LECA can be blended by heavy soil to decrease the landscapes soils and weight of plants. LECA can be utilized in water treatment facilities for the purification and filtration drinking water and wastewater. It is noteworthy mentioning that the temperature required to manufacture LECA (1100–1300 °C) is higher than that required for the manufacture other similar lightweight materials such as expanded perlite (900–1200 °C) [109] and expanded vermiculite (650–950 °C) [110]. This means that LECA manufacture is higher cost than manufacture of expanded perlite or expanded vermiculite. Comparing thermal conductivity of LECA with that of expanded perlite and expanded vermiculite, it could be noted that expanded perlite exhibited the lowest thermal conductivity (0.04–0.06 W/m K) [109], expanded vermiculite came in the second place (0.04–0.12 W/m K) [110], whilst LECA came in the last

Table 9 Benefits and shortages of using LECA. Property

Effect

Workability Density Creep Sound isolation Thermal isolation Fire resistance Shrinkage Crack tendency Hydrochloric acid resistance Lactic acid resistance Sulfuric acid resistance Mechanical strength Freeze/thaw resistance Chloride penetration Water absorption

Positive Positive Positive Positive Positive Positive Positive Positive Positive Positive Negative Negative Negative Negative Negative

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Fig. 8. Thermal conductivity of LECA plaster versus other plaster types [83].

protection followed by expanded vermiculite followed by LECA, whilst normal weight sand came in the last place. 6. Remarks and future work scope The current review purposes to brief the prior studies conducted on the properties of conventional cementitious materials and geopolymers comprising LECA. The main annotations of the present review can be briefed as follows:

Fig. 7. LECA concrete/block in the hardened state.

place (0.097–0.123 W/m K). In such a way, expanded perlite exhibited the lowest bulk density in comparison with those of expanded vermiculite and LECA, whilst the bulk density of expanded vermiculite came in the second place and those of LECA came in the last place. This means that expanded perlite can produce concrete/ mortar lighter than those produced by expanded vermiculite or LECA, whilst expanded vermiculite can produce concrete/mortar lighter than those of produced by LECA. This means that expanded perlite exhibited the highest thermal insulation followed by expanded vermiculite then LECA. This order in thermal insulation was confirmed by Hodhod et al. [83]. They obtained thermal conductivity of 0.045, 0.085 and 0.123 W/m K for expanded perlite sample, expanded vermiculite sample and LECA sample, respectively. They employed these materials as well as normal weight sand with cement to produce coating materials and the results are presented in Fig. 8. They used these materials as coating layers aiming to protect RC column samples against fire. The coated RC column samples were exposed to 650 °C for 30 min. When 15 mm of plastering was employed, the RC samples coated by expanded perlite-cement, expanded vermiculite-cement and LECA-cement showed 81.67%, 64.29% and 63.1% remaining capacity, respectively, while that plastered with normal weight sand-cement showed 50.46% residual capacity. This means that expanded perlite is more effective in thermal insulation and fire

1. The incorporation of LECA in the mixture produced more workable mixture (as reported by several studies) and higher segregation resistance. 2. The density of the matrix decreased as LECA content increased. The incorporation of LECA as a coarse aggregate can cause 16.36% to 36.51% lesser density. The incorporation of LECA as a fine aggregate can reduce the density by 35%, whilst reduction levels fluctuated from 37.58% to 44.4% can be obtained when LECA was used as both fine and coarse aggregates. 3. In spite of the mechanical behavior of lightweight concrete/ mortar strongly depends on the type of lightweight aggregate and mixture composition, the incorporation of LECA in the matrix decreased mechanical strength. The mechanical strength decreased as LECA content increased. The reduction in the compressive strength could be in the range of 12.5% to 38.8% when LECA was used as coarse aggregate, whilst the reduction could be in the range of 47.33% to 55.97% when LECA was used as both fine aggregate and coarse aggregate. 4. The incorporation of LECA in the mixture increased water absorption, decreased its resistance to chloride penetration, decreased its shrinkage and decreased its freeze/thaw resistance. 5. The introduction of LECA in the mixture increased thermal insulation, sound insulation and fire resistance. 6. Recently LECA was used in geopolymer to increase workability, increase air content, decrease density, increase relative residual strength after firing and decrease the number of cracks during firing. Variously, the mechanical strength was decreased. 7. A suitable content of SF, FA, slag, steel fibers and polypropylene fibers can be used to modify some properties of concrete containing LECA aggregates like increasing mechanical strength and decreasing capillary absorption Depending on this review, it is useful to used LECA in both conventional cementitious materials and geopolymers to produce lightweight matrices. Already the prior literature containing many studies concerning to applying LECA into conventional cementitious materials, but abundant of them are addressed on mechanical strength (33.33% of the total), density (27.41% of the total) and workability (11.11% of the total), whilst less attention was

A.M. Rashad / Construction and Building Materials 170 (2018) 757–775

Fig. 9. Relative research number versus the influence of LECA on each property of conventional cementitious materials.

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