Influence of content and maximum size of light expanded clay aggregate on the fresh, strength, and durability properties of self-compacting lightweight concrete reinforced with micro steel fibers

Construction and Building Materials 233 (2020) 117922

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Influence of content and maximum size of light expanded clay aggregate on the fresh, strength, and durability properties of self-compacting lightweight concrete reinforced with micro steel fibers Ali H. Nahhab ⇑, Ali K. Ketab Department of Civil Engineering, Babylon University, Babylon, Iraq

h i g h l i g h t s  Self-compacting lightweight concrete with 21.3–46 MPa was produced.  Three different maximum sizes of LECA, 10, 14, and 20 mm were investigated.  Three different levels of micro steel fibers, 0.25, 0.5, and 0.75% were investigated.  The size of 10 mm gave the best compressive and flexural strengths.  Increasing fiber content improved sorptivity and diminished drying shrinkage.

a r t i c l e

i n f o

Article history: Received 22 August 2019 Received in revised form 14 December 2019 Accepted 19 December 2019

Keywords: Self compacting lightweight concrete Light expanded clay Steel fibers Fresh properties Sorptivity Drying shrinkage

a b s t r a c t The effects of maximum size of aggregate (dmax), light expanded clay coarse aggregate (LECA) content, and volume fraction of micro steel fibers (Vf) on the properties of self-compacting lightweight concrete (SCLWC) were investigated. A total of 18 mixes with dmax of 10, 14, and 20 mm, LECA contents of 50% and 100%, and Vf of 0.25, 0.5, and 0.75% were prepared. The investigated fresh properties were fresh density, slump flow, T50 cm, V-funnel flow time, and L-box height ratio, while the investigated hardened properties were compressive strength, flexural strength, oven dry density, water sorptivity, drying shrinkage and weight loss. The results revealed that increasing dmax led to decrease the superplasticizer dosage required to keep the slump flow at 700–750 mm. The dmax of 10 mm gave the best compressive and flexural strengths. The water sorptivity was generally higher as the dmax, LECA content, and Vf increased. The drying shrinkage, on the other hand, was generally diminished with increasing dmax and Vf. Ó 2019 Elsevier Ltd. All rights reserved.

1. Introduction Self-compacting concrete (SCC) has been utilized in many civil engineering applications owing to its excellent flowability, stability, mechanical, and durability features. However, this promising concrete has higher density than conventional concrete because of the present of higher powder content. A possible solution for such problem is the partial or total substitution of natural aggregate by lightweight aggregate such as light expanded clay aggregate (LECA) to produce self-compacting lightweight concrete (SCLWC). This new concrete, therefore, has the features of both SCC and lightweight concrete (LWC) like reducing the mass of concrete members which allows to use longer spans and reduce the dimensions of members. In addition, the construction becomes safer, more

⇑ Corresponding author. E-mail address: [email protected] (A.H. Nahhab). https://doi.org/10.1016/j.conbuildmat.2019.117922 0950-0618/Ó 2019 Elsevier Ltd. All rights reserved.

economic, higher environmental friendliness because of the reduction of labors, limiting the construction period, and using the ultrafines materials like limestone powder in SCC [1]. LECA has been used successfully in the production of LWC. The source of LECA is clay which is subjected to desiccation, heating, and firing at elevated temperatures in the order of 1100–1300 °C [2]. This leads to produce expanded clay with a tough ceramic shell in which holes of various sizes are present which are typically interrelated [3]. The behavior of SCC and SCLWC is reliant on many factors like the water-powder ratio, superplasticizer (SP) content, powder type, powder content, fibers, as well as aggregate size and content [4,5]. Abdelazim [6] reported that there was an optimum dosage of SP of 0.8% beyond which the fresh properties of SCLWC with LECA went down. In another study on SCLWC with expanded shale, the V-funnel flow time were found to be decreased while L-box height ratio and slump flow increased due to the increase of waterpowder ratio and SP dosage which meant that the filling ability and passing ability improved [7]. The passing ability was found

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to be adversely affected by increasing the powder content though the stability (segregation resistance) improved [7]. Cui et al. [8] found that the river sand gave better flowability for SCLWC than the crushed stone when they were used as fine aggregates. They also found an optimum powder content of 550 kg/m3 beyond which the flowability started to drop. Nepomuceno et al. [9] studied the mix design of structural SCLWC incorporating LECA as a coarse aggregate and limestone powder as a filler. The values of slump flow spread, V-funnel flow time, and L-box height ratio were 64.8–70.5 cm, 14.3–26.28 s, and 0.72–0.84, respectively. When the w/c ratio was varied from 0.29 to 0.61 by mass, the compressive strengths of SCLWC was 35–57 MPa, while this range became 53–87 MPa for normal weight SCC. Mineral admixtures were also found to have a certain effect on SCLWC. The outcomes of Mohammadi et al. [10] suggested that increasing the replacement level of cement by silica fume up to the investigated content of 15% improved the stability, filling ability, and compressive strength of SCLWC irrespective of whether the lightweight aggregates were LECA or perlite though the former performed better. Iqbal et al. [11] proved the effectiveness of fly ash at 15–25% by weight of binder as the only filler to produce SCLWC such that the compressive strength of 50 MPa was achieved with low fresh density of 1709–1744 kg/m3. Steel fibers have been used recently in the SCLWC mixtures. Iqbal et al. [12] observed a reduction in the slump flow of SCLWC due to increasing micro steel fiber content. They also found that the incorporation of steel fibers led to a slight decrease in compressive strength and an increase in tensile strength. On the other hand, Grabois et al. [13] found that the slump flow diameter of SCLWC increased slightly whereas the V-funnel flow time diminished due to the macro steel fiber inclusion. Their results also revealed that the effect of fibers on the drying shrinkage was variable depending on the class of concrete such that the steel fibers restricted the drying shrinkage for 100% sanded LWC while they increased it for the partially sanded LWC. In the literature, the effect of maximum aggregate size on the fracture parameters for SCC and recently for SCLWC has been considered. However, the size effect on strength or durability properties like sorptivity and drying shrinkage has not been investigated so far. Beygi et al. [14] found that the increase in aggregate size resulted in an increase in fracture energy and characteristic length of normal weight SCC. In the same way, the results of Karamloo et al. [1] revealed an improvement in fracture energy, toughness, as well as the ductility of SCLWC with increasing the maximum size of LECA. 2. Research significance As mentioned earlier, SCLWC combines the benefits of two special concretes, namely SCC and LWC, so this new generation of building materials has become of interest recently. Though, many experimental investigations are available in the literature regarding fresh, mechanical, and durability properties of SCC and LWC, the available studies on SCLWC are insufficient particularly in some areas which are considered in the present work. Accordingly, the effects of LECA maximum size, LECA content, and micro steel fiber volume fractions were studied herein with respect to fresh, strength, drying shrinkage and sorptivity properties of SCLWC. 3. Experimental plan 3.1. Raw materials 3.1.1. Binder and filler The cement categorized as an ordinary Portland cement according to IQS 5 [15] was used as a binder while limestone powder was

used as a filler. The properties of the cement and limestone powder are listed in Table 1. 3.1.2. Aggregates The Karbala sand complying with IQS 45 [16] was used as only fine aggregate. Two types of coarse aggregate were used, namely natural coarse aggregate (NCA) and light expanded clay aggregate (LECA). The LECA was utilized at three different maximum sizes, namely 10, 14, and 20 mm as illustrated in Fig. 1. The mixes consisted of 100% LECA or 50% LECA + 50% NCA. Typical gradation curves for coarse aggregate and fine aggregate are shown in Fig. 2. The water absorption was 1.2 and 0.4% for sand and gravel, respectively while it was 8.2, 6.7, and 5.8% for 10, 14, and 20 mm LECA, respectively. The bulk density of sand and gravel was 1650 and 1610 kg/m3, respectively whereas it was 320, 290, and 250 kg/m3 for 10, 14, and 20 mm LECA, respectively. The specific gravity of sand, NCA and LECA was 2.65, 2.60 and 0.6, respectively. 3.1.3. Superplasticizer The superplasticizer (SP) commercially called (sika viscocrete 5930L), was used in this study which complied the requirements of ASTM-C494/ C494M type F [17]. 3.1.4. Micro steel fibers The copper coated micro-steel fibers shown in Fig. 3 were used. Table 2 illustrates their properties as given by the manufacturer. 3.2. Mix proportions of self-compacting lightweight concrete Achieving the fresh and hardened properties of self-compacting lightweight concrete (SCLWC) requires many trial mixes with different proportion of materials because the absent of a standard method that deals with the design of such new generation of concrete. Therefore, many trails were done in the laboratory to reach

Table 1 Properties of Portland cement and limestone powder. Item

Portland cement (PC)

Limit of IQS 5 [15]

Limestone powder (LP)

CaO (%) SiO2 (%) Al2O3 (%) Fe2O3 (%) MgO (%) SO3 (%)

62.79 20.58 5.60 3.28 2.79 2.35

54.6 3.20 0.03 0.16 0.56 0.64

Free CaO (%) Loss on ignition (%) Insoluble residue (%) Lime saturation factor (%)

1.32 1.94 1.00 0.90

– – – – 5 2.5 if C3A  5 2.8 if C3A > 5 – 4 1.5 – –

–

Compounds C3S C2S C3A (%) C4AF (%) Physical properties Specific surface, Blaine (m2/kg) Specific gravity Initial setting time (min) Final setting time (min) Compressive strength (MPa) 2 days 28 days

50.12 21.26 9.29 9.98 314

230

3.15 122

– 45

193

600

21.0 45.8

– –

– 43.6 – –

3

A.H. Nahhab, A.K. Ketab / Construction and Building Materials 233 (2020) 117922

Fig. 1. Lightweight expanded clay coarse aggregate used.

120

% Passing

100 80 60 20 mm

40

14 mm

20

10 mm Sand

0 0.1

1

10

100

Sieve size (mm)

the acceptable mix proportions with respect to fresh and strength properties. As seen in Table 3, a total of 18 mixes were prepared in the current study. The mixes can be divided into three groups according to the maximum aggregate size (dmax) which was 10, 14, and 20 mm. In other words, each group consisted of 6 mixes; three of them were prepared with 50% LECA and incorporated with micro steel fibers at three different percentages by volume, namely 0.25, 0.5, and 0.75%, while the others were made with 100% LECA and micro steel fibers with the same volume fractions mentioned above. As seen in Table 3 a code has been given for each mix depending on its composition and proportions. For example, the mix 50L14M0.25VF was made with 50% LECA, 14 mm-maximum aggregate size, and 0.25% volume fraction of micro steel fibers.

Fig. 2. Grading of sand and coarse aggregates.

3.3. Concrete mixing, placing and curing procedures The high water absorption capacity of LECA leads to the slump loss of fresh mixes. So, LECA was immersed in water for about one day to ensure the condition of saturated surface dry (SSD). Then, the LECA was spread and left to dry until the free water from the surface of particles was removed. The mixing process was then initiated in a drum mixer. First, the dry materials including cement, limestone powder, sand, coarse aggregate were mixed until the homogeneity of the dry mixture was achieved. Thereafter, 1/3 of mixing water was poured into the mixing machine and mixed for about one min. The rest of water was then poured along with all quantity of superplasticizer. Finally, micro steel fibers were gradually added during mixing and the procedure lasted for about 3 min more. The mixture was kept for 2 min at rest before pouring. The concrete in fresh state was thereafter poured into molds without any compaction and left in the molds for 24 h. After demolding, the samples of drying shrinkage were air cured in the laboratory at about 23 ± 2 °C and 50 ± 5% relative humidity while all other samples were put in water tank until the testing age.

Fig. 3. Micro steel fibers used.

Table 2 Properties of micro steel fibers. Density (kg/m3)

Length (mm)

Diameter (mm)

Aspect ratio

Tensile strength (MPa)

7800

13

0.2

65

2600

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Table 3 Mix proportions of SCLWC. Mixtures

Maximum size of aggregate (mm)

LECA content (%)

50L10M0.25VF 50L10M0.50VF 50L10M0.75VF 100L10M0.25VF 100L10M0.50VF 100L10M0.75VF 50L14M0.25VF 50L14M0.50VF 50L14M0.75VF 100L14M0.25VF 100L14M0.50VF 100L14M0.75VF 50L20M0.25VF 50L20M0.50VF 50L20M0.75VF 100L20M0.25VF 100L20M0.50VF 100L20M0.75VF

10 10 10 10 10 10 14 14 14 14 14 14 20 20 20 20 20 20

50 50 50 100 100 100 50 50 50 100 100 100 50 50 50 100 100 100

Material (kg/m3) PC

LP

Sand

LECA

NCA

Water

SP (% by wt. of cement)

Micro steel fibers

455 455 455 455 455 455 455 455 455 455 455 455 455 455 455 455 455 455

150 150 150 150 150 150 150 150 150 150 150 150 150 150 150 150 150 150

820 820 820 820 820 820 820 820 820 820 820 820 820 820 820 820 820 820

93 93 93 186 186 186 93 93 93 186 186 186 93 93 93 186 186 186

420 420 420 0 0 0 420 420 420 0 0 0 420 420 420 0 0 0

150 150 150 150 150 150 150 150 150 150 150 150 150 150 150 150 150 150

2.5 3.1 3.5 1.5 2.5 2.5 1.6 1.9 2.6 1.5 1.8 2.5 1.3 1.7 2.9 1.3 1.7 2.7

19.5 (0.25%) 39 (0.5%) 58.5 (0.75%) 19.5 (0.25%) 39 (0.5%) 58.5 (0.75%) 19.5 (0.25%) 39 (0.5%) 58.5 (0.75%) 19.5 (0.25%) 39 (0.5%) 58.5 (0.75%) 19.5 (0.25%) 39 (0.5%) 58.5 (0.75%) 19.5 (0.25%) 39 (0.5%) 58.5 (0.75%)

PC: Portland cement. LP: Limestone powder. NCA: Natural coarse aggregate. SP: Superplasticizer.

3.4. Testing methods 3.4.1. Fresh properties tests The fresh density of SCLWC mixes was measured in accordance with ASTM C138/ C138 M [18]. The workability features of SCLWC were evaluated by means of four tests following the guidelines of EFNARC [19], namely slump flow, T50 cm, L-box, and V-funnel. The apparatus used for slump flow was Abram’s cone with 30 cm height, 10 cm diameter at top, and 20 cm diameter at bottom rested on the smooth wooden base. First, the cone was moistened and put on the wooden base. Then, the cone was filled with fresh mixture without compaction. The cone was thereafter lifted to let the concrete flowed freely creating a circle. The slump flow value was the average of maximum diameter of the circle and the perpendicular diameter on it. The T50 cm, on the other hand was a period between the instant that cone leaved the base to the moment at which the concrete firstly touched the circle of 50 cm diameter. The box of L shape was used to assess the filling ability of SCLWC. The box was provided by a slide gate and 2ɸ12 smooth bars. First, the plastic concrete was poured into the vertical part of the apparatus. Thereafter, the slide gate was lifted thus leaving concrete to flow out through the horizontal portion of the box. The L-box height ratio was therefore the ratio of concrete height at the end of the horizontal part to the concrete height at the beginning of the same part. The funnel of V shape was used to evaluate filling ability of SCLWC. The funnel was provided by a slide gate at the bottom to allow concrete to discharge after filling. The V-funnel time was the time period required for discharging all fresh mixture. It is worth noting that the T50 cm and V-funnel flow time also give an indication about the viscosity of plastic concrete.

3.4.2. Strength tests The compressive strength and flexural strength of all mixes were determined at the age of 28 days. The guidelines of B.S. 1881: Part 116 [20] was used to measure the compressive strength of 150 by 150 by 150 mm cubes, while the ASTM C78/ C78M [21] was followed to evaluate the flexural strength of 100 by 100 by 400 mm simple beams loaded at two points spaced at one-third of the span (third-point loading).

3.4.3. Oven dry density test The 28-day oven dry density was evaluated following the ASTM C642/C642M [22] after drying the cubical specimen of 150 by 150 by 150 mm at 100 ± 2 °C in the oven for 24 h. 3.4.4. Sorptivity test The sorptivity was measured using ASTM C 1585 [23] at the age of 28 days. The cubical samples of 150 by 150 by 150 mm were used. They were first oven dried at 100 ± 2° C for one day and then their sides were sealed by silicone sealing. The samples were put on the glass balls located in a pan. The level of water in the pan exceeded the bottom level of the samples by about 3 mm (see Fig. 4). The gain in mass which was due to the sorption of capillary water was measured at various time intervals up to 2 h. The mass gain was divided by the area of the contact face with water and by the water density so that the results were the volumes of the absorbed water. Thereafter, the values of these volumes were plotted against square root of time and the water sorptivity was the slope of the line that best fitted the data. 3.4.5. Drying shrinkage and weight loss tests The standards adopted for conducting drying shrinkage test was the ASTM C157/C157M [24] and ASTM C490/C490M [25]. Prior to length measuring, the samples were weighed in order to determine the weight loss caused by drying. The measurements of length change was performed on 50 by 50 by 200 mm prisms by means of a digital comparator length device as shown in Fig. 5. The first reading was taken directly after removing the samples from the molds while additional readings were taken at different ages up to the end of air curing period which was 90 days. The drying shrinkage strain was the change in length at any age divided by the gauge length of the sample which was 180 mm. 4. Results and discussion 4.1. Fresh properties Fig. 6 shows the fresh density as affected by LECA content, maximum aggregate size and volume fraction of micro steel fibers. The fresh density was ranged from 1913–2104 kg/m3, 1854–1938 kg/m3, and 1705–1877 kg/m3, for mixtures with dmax of 10, 14,

A.H. Nahhab, A.K. Ketab / Construction and Building Materials 233 (2020) 117922

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Fig. 4. Sorptivity test set up.

Fig. 5. Drying shrinkage test set up.

and 20 mm, respectively. In other words, the fresh density diminished as the aggregate size increased. This could be related to the lower density of larger particles and the present of larger voids between these particles as compared to the smaller ones which in turn lowered the packing density. The fully LECA mixtures showed lower fresh density than the 50% LECA mixtures by up to about 10%. On the other hand, increasing the percentage of micro steel fibers generally led to enhance the fresh density slightly. Similarly, other researchers [12,13] reported that the fresh density remained almost constant though the steel fiber content was increased from 0.5% to 1.25%. Fig. 7 illustrates the results of slump flow test for all mixtures while Fig. 8 shows the SP dosage required to maintain the slump flow at 700–750 mm. According to EFNARC [19], SCC is classified into three classes depending on the slump flow value. These are SF1, SF2, and SF3 when the slump flow ranges from 550 to 650 mm, 660–750 mm, and 760–850 mm, respectively. So, all mixes of the present study can be classified as SF2. As seen in Fig. 8, the dosage of SP needed to achieve the desired slump decreased with increasing maximum size of coarse aggregate. For the same LECA content and the volume fraction of micro steel fibers, the dosage of SP generally decreased by increasing dmax. This might be related to that, the specific surface area of aggregate declined with enhancing the aggregate size, thus less cement paste

was needed for covering these particles. This meant that there was an excess paste in the composite which reduced the internal friction between particles thus enhancing flowability. As seen in Fig. 8, the mixes with higher micro steel fibers required more dosage of SP to keep the slump flow at 700–750 mm. In addition, the dosage of SP decreased with increasing the amount of LECA. This finding agreed the literature that the spherical shape and relatively smooth surface of LECA facilitated the flow of aggregate particles and paste, thus reducing the internal friction [26]. T50 cm slump flow is another important parameter that evaluates the flow rate. Fig. 9 shows the T50 cm values for different mixtures which were between 2 and 3.5 s. The T50 cm values declined with an increase in the volumetric LECA replacement level because of the spherical shape of this type of lightweight aggregate which enabled the particles to flow more easily. Increasing dmax also diminished the T50 cm values which were 2.44–3.5 s, 2.11–3.30 s, and 2–3.15 s for mixes with 10, 14, and 20 mm, respectively. This trend was also previously observed by other authors [1]. The explanation of such behavior could be related to the reduction in the specific surface area of the larger aggregate which led to less water requirement and less cement paste required to coat the particle surfaces. On the other hand, the T50 cm values improved and hence the viscosity of mixes increased with increasing the percentage of micro steel fibers because more interlocking and friction occurred. For example, the mix 100L14M0.25VF (with 0.25% fibers) had a T50 cm value of 2.11 s, while the mix 100L14M0.75VF (with 0.75% fibers) had a 3.25 s. Fig. 10 gives the V-funnel time as affected by different investigated parameters. This test measures filling ability of SCC and gives an indication about the viscosity though it does not measure viscosity directly. The flow time was found to be increased when the maximum size of aggregate increased though the increment in the V-funnel time was more pronounced in mixes with 100% LECA. The V-funnel flow time of concrete was in the range of 19–25 s, 22–30 s, and 20–35 s for the mixtures with dmax of 10, 14 and 20 mm, respectively. The reason of such trend was perhaps due to the lower unit weight of larger LECA particles which supplied less weight to concrete to flow under gravity. Similar conclusion was drawn by [27]. When the quantity of LECA increased, greater values were reported for the V-funnel flow time because of the decreased fresh density of concrete. In addition, increasing fiber content prolonged the V-funnel flow time because of the blockage of steel fibers within the restricted area of the V-funnel. Fig. 11 shows the relationship between V-funnel flow time and T50 cm for all mixes. According to EFNARC [19], SCC is classified as VS1/VF1 when T50 cm and V-funnel flow time is less than or equal 2 and 8 s, respectively, while SCC is categorized as VS2/VF2 when T50 cm exceeds 2 s and V-funnel flow time ranges from 9 to 25 s. Obviously, two-third of mixes were in the category of VS2/VF2. Indeed,

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Fig. 6. Fresh density for all SCLWC mixes.

Fig. 7. Slump flow for all SCLWC mixes.

out of the 18 mixes, only 6 mixes were out of VS2/VF2 class. These mixes were 100L14M0.5VF, 100L14M0.75VF, 50L20M0.75VF, 100L20M0.25VF, 100L20M0.5VF, and 100L20M0.75VF which showed a delay in V-funnel flow time of 1, 5, 9, 1, 6, and 10 s, respectively. This rising was clarified previously by influences of steel fibers and aggregate size. It is worth noting that the SCC which is classified as VS2/ VF2 viscosity class with SF2 slump flow diameter can be applicable for constructing ramps and walls/columns [17]. Fig. 12 shows the L-box results obtained from the experimental work done in this study. The results showed that the highest L-Box height ratio values were generally reported for mixes with 100% LECA followed by mixes with 50% LECA such that these values were 0.88–0.98% and 0.86–0.95%, respectively. This trend was also established in the study of [28], which publicized that the lightweight particles enhanced the flow characteristics of self-compacting concrete such that the blocking ratio

(L-Box height ratio) increased from 0.9 to 1. Fig. 12 also showed that the L-box height ratio increased with increasing the maximum size of LECA regardless of its content. This behavior was perhaps due to the lower internal friction between larger particles as compared to the smaller ones. The results also demonstrated that enhancing micro steel fiber percentage diminished the value of L-box height ratio. ASTM C1611/C1611M [29] uses the visual stability index (VSI) to describe the stability (segregation resistance) of SCC. According to the value of VSI, SCC is highly stable, stable, unstable, or highly unstable. SCC is highly stable (VSI = 0) when there is no indication of segregation or bleeding while it is stable (VSI = 1) when there is no sign of segregation but a slight bleeding is observed as sheen on the concrete mass. SCC is unstable (VSI = 2) when a slight mortar halo (10 mm) and/or aggregate pile is present in the center of the concrete mass while it is highly unstable (VSI = 3) when there is a large mortar halo (>10 mm) and/or a large aggregate pile in the

A.H. Nahhab, A.K. Ketab / Construction and Building Materials 233 (2020) 117922

7

Fig. 8. Superplasticizer dosage required to maintain slump flow at 700–750 mm.

Fig. 9. T50

cm

results for all SCLWC mixes.

center of the concrete mass. The typical photographs for fresh SCC after the flow tests are shown in Fig. 13. Obviously, all SCLWC mixes made with different maximum aggregate sizes, LECA contents, and micro steel fiber levels were highly stable because the visual examination showed no evidence of bleeding or segregation. This meant that the SCLWC remained homogenous even with the presence of micro steel fibers because of the uniform distribution of these short fibers in the matrix and relatively their low contents. 4.2. Strength properties 4.2.1. Compressive strength The results shown in Fig. 14 reflect the effect of different parameters namely, dmax, Vf, and LECA content on the 28-day compressive strength of SCLWC. The compressive strength ranged from

37.5 to 46 MPa and 21.3–28.4 MPa for mixes incorporated with 50% and 100% LECA, respectively. It is worth noting that the weakest phase in lightweight concrete system is aggregate and not the interfacial transition zone as in the case of normal weight concrete. In other words, the characteristics of aggregate play an important role in determining the strength of lightweight concrete. So, the compressive strength reduction due to the replacement of NCA with LECA was related to the low strength and density of LECA. Indeed, the bulk density of LECA did not exceed 320 kg/m3 while the bulk density of NCA was about 1610 kg/m3. As seen in Fig. 14, the compressive strength decreased with increasing dmax regardless of LECA content and micro steel fiber percentage. The mixes with 14 mm and 20 mm exhibited a reduction in compressive strength ranging from 2 to 10% and 12–20%, respectively in comparison with those made with 10 mm. Simi-

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Fig. 10. V-funnel flow time for all SCLWC mixes.

Fig. 11. Variation of V-funnel flow time with T50

larly, Rathish Kumar and Krishna Rao [30] found that the 10 mm maximum size was better than the 12.5 mm with respect to the compressive strength of lightweight concrete containing fly ash. Indeed, the consequence of lowering the maximum aggregate size of most of lightweight aggregate is the enhancement in what is called as strength ceiling, which is the maximum compressive strength achievable in concrete produced with a certain type of aggregate using an equitable amount of cement. Moreover, the compressive strength of smaller aggregate particles is higher than that of larger ones [3]. The results also showed that the compressive strengths of mixes with 0.25% and 0.5% fibers were somewhat comparable while those with the highest fiber inclusion, 0.75% showed generally better strength particularly at maximum size of 10 mm. The enhanced compressive strength caused by increasing the volume fractions of micro steel fibers was also reported by other authors but for vibrated lightweight concrete [31]. This increase was probably due to (1) the uniform distribution of steel fiber within the

cm.

highly workable concrete which guaranteed the strongest consistent, and (2) the control of cracking and failure mode through post cracking ductility. On the other hand, the less pronounced effect of micro steel fibers at the largest maximum size of 20 mm was probably because the non- uniform distribution of steel fibers within the matrix. 4.2.2. Flexural strength The 28-day flexural strength for all SCLWC mixes is plotted in Fig. 15. Owing to the low strength and density of LECA, the flexural strength for fully LECA mixtures was lower than that for 50% LECA mixtures by about 2–15%. When the SCLWC was loaded in flexure, cracks passed through the weakest phase in the system (lightweight aggregate) thus leading to failure. In other words, the tensile strength of SCLWC was controlled by the tensile strength of LECA particles. As seen in Fig. 15, the flexural strength was directly proportional to the micro steel fiber content for both 50% and 100% LECA

A.H. Nahhab, A.K. Ketab / Construction and Building Materials 233 (2020) 117922

9

Fig. 12. L-box height ratio for SCLWC mixes.

mixes though the effect of fibers was more pronounced for 100% LECA mixtures particularly for the lowest aggregate size of 10 mm. With increasing steel fibers contents the concrete became more able to carry the flexural load and more resistant to crack propagation. The more marked influence of micro steel fiber at 100% LECA mixtures compared to 50% LECA mixtures, was probably because the following reason. Unlike the 50% LECA mixtures, all aggregate particles of 100% LECA mixes were brittle and had weak strengths thus resulting in low flexural strengths, and when increasing the steel fiber level the mixtures became more ductile and more resistant to first crack propagation. Likewise, Ali et al. [32] showed that the efficacy of fibers to improve lightweight aggregate concrete’s toughness was much higher than normal weight aggregate concrete due to the higher brittleness of the former. Other investigators observed an 18% improvement in the indirect tensile strength of high strength steel fiber reinforced self-compacting concrete due to the increase of micro steel fiber volume fraction from 0.5 to 1.25% [12]. Among the three maximum sizes investigated, the best one was 10 mm at which the flexural strength was generally maximum as seen in Fig. 15. This might be attributed to the increased packing density and reduced voids between particle as well as the increased strength of the smallest particles. The positive effect of decreasing maximum aggregate size on the tensile strength of the cement-based materials has also been proved previously for other types of special concretes such as high-strength concrete and ultra-high performance concrete which was attributed to the enhanced homogeneity of the system [33,34]. Observing the results of both types of strengths indicated that the ratio of flexural strength to compressive strength was varied from 0.10 to 0.18.

LECA, respectively. The reduction in oven dry density was attributed mainly to the increased proportion of LECA. However, a small part of the reduction might have occurred due to the higher water absorption capacity of LECA which led to further moisture loss during oven drying. The results also showed that the SCLWC with higher maximum aggregate size showed lower oven dry density. This finding agreed well with that of Rathish Kumar and Krishna Rao [30]. When the results of fresh density and oven dry density were compared, it was observed that the differences between them were higher at dmax of 10 mm compared with other larger sizes. The differences were up to 90, 65, and 50 kg/m3 at 10, 14, and 20 mm, respectively. This was perhaps related to the higher water absorption capacity of smaller particles which led to higher moisture loss caused by drying. As with the fresh density, the oven dry density generally improved as the volume content of micro steel fibers increased though the increase was not significant. ACI committee 213R-03 [35] defines the structural lightweight aggregate concrete as a concrete that has a compressive strength of higher than 17 MPa at 28 days, an equilibrium density of order of 1120 and 1920 kg/m3, and contains 100% lightweight aggregate or a blend of normal weight aggregate and lightweight aggregate. However, the ACI committee states that these limits are not specifications and dependent on the conditions of a project. It is agreed that it is difficult to determine the equilibrium density in the laboratory. Instead, oven dry density is measured easily noting that the oven dry density exceeds the equilibrium density by 50 kg/m3 [36]. Accordingly, the equilibrium density of the SCLWC became 1707–1893 kg/m3 at 100% LECA and 1871–2094 kg/m3 at 50% LECA. In other words, all of the fully LECA mixes and some of 50% LECA mixes were within the above limits.

4.3. Oven dry density 4.4. Water sorptivity The test results of 28-day oven dry density for all SCLWC mixes are shown in Fig. 16. The oven dry density was varied from 1657–2044 kg/m3. The relatively high variation of this property among mixes was due to the variation in LECA content, maximum aggregate size, and micro steel fiber content though the most significant parameter was LECA content followed by maximum aggregate size. As can be seen in Fig. 16, the oven dry density was in the order of 1821–2044 kg/m3 and 1657–1843 kg/m3 at 50% and 100%

The effects of different investigated factors on the 28-day water sorptivity are graphically represented in Fig. 17. It can be seen that the water sorptivity was in the order of 0.012 to 0.114 mm/min0.5 depending on LECA content, maximum aggregate size and micro steel fiber content. The minimum value of sorptivity was recorded for mix 50L10M0.25VF, while the largest one was recorded for mix 100L20M0.75VF. The sorptivity increased as the dmax increased for

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Fig. 13. SCLWCs show no sign of bleeding or segregation.

Fig. 14. Compressive strength for SCLWC as affected by different parameters.

the two levels of LECA substitution, 50% and 100%. Indeed, water sorptivity of concrete is influenced by many factors such as aggregate type, matrix type, w/c ratio, and ITZ between the aggregate particles and paste. In the present study, the properties of ITZ seemed to exercise a vital importance on the permeation properties of concrete. The ITZ for the mixtures with the lowest maximum aggregate size of 10 mm appeared to be less porous than that of other sizes thus leading to minimize water sorptivity. This was probably related to that the smaller aggregates absorbed more water in pre-soaking process before mixing stages than the larger particles due to the increased specific surface area. So, the water inside the smaller LECA particles contributed to the internal curing of concrete more efficiently, thus leading to denser ITZ and hence less water sorptivity. Liu et al. [37] also reported that the dense ITZ between the lightweight aggregate and the cement paste might have reduced concrete sorptivity despite using aggregate of higher porosity. As seen in Fig. 17, there was an increase in the sorptivity with increasing micro steel fiber percentage particularly at 20 mm maximum aggregate size. A possible explanation of this behavior is that the inclusion of micro steel fibers at the relatively high percentages

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Fig. 15. Flexural strength for SCLWC as affected by different factors.

of fibers along with the use of the largest maximum aggregate size, 20 mm might have increased the porosity of ITZ thus increasing the water sorptivity. The adverse effect of fibers on the ITZ was also previously reported for other concrete, fiber reinforced concrete [38]. The results also indicated that the fully LECA mixtures showed higher sorptivity than 50% LECA mixes. This can be explained by the more amount of the porous aggregate, which thereby increased the porosity of concrete. This finding agreed with other authors that the sorptivity increased as the lightweight aggregate content increased [39–41]. 4.5. Drying shrinkage and weight loss

Fig. 16. Oven dry density for SCLWC mixes as affected by different factors.

Fig. 17. Sorptivity for SCLWC mixes as affected by different parameters.

It is generally agreed that, the important factors that affects the drying shrinkage of concrete is the aggregate content, aggregate type (normal weight versus lightweight), and water content in the mix. The growth of drying shrinkage strains with age for SCLWC mixes up to 90 days is shown in Fig. 18a and b while the final strains are summarized in Fig. 19. The drying shrinkage developed quickly through the early period of drying such as almost 40% of ultimate strains occurred at 7–28 days beyond which the rate began to decrease and thereafter stabilized beyond the age of 60 days. The results of weight loss shown in Fig. 20a and b clearly confirmed this outcome. Also, the drying shrinkage strains and weight loss were positively influenced by increasing the dmax such that the minimum values were recorded for mixtures with 20 mm dmax, which recorded up to 27% strain reduction and up to 24% weight loss reduction compared to those with 10 mm. This possible explanation of such behavior is that the larger aggregate size needed lower dosage of superplasticizer as shown in Table 3. It is known that the inclusion of high level of superplasticizer affects the pore structure of hardened cement paste which alters the condition of evaporable water and thus the trend of shrinkage [42]. So, in SCLWCs with higher contents of such chemical admixtures, the evaporation was higher and thus the drying shrinkage and weight loss were lower. On the other hand, enhancing the LECA content from 50% to 100% generally increased the drying shrinkage particularly at dmax of 14, and 20 mm as seen in Fig. 19. The reason behind this behav-

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Fig. 18. Development of drying shrinkage with age for (a) 50% LECA mixtures and (b) 100% LECA mixtures.

Fig. 20. Weight loss versus age for (a) 50% LECA mixtures and (b) 100% LECA mixtures.

Fig. 19. Drying shrinkage at 90 days as affected by different parameters.

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ior could be attributed to the lower modulus of elasticity and stiffness of LECA with respect to natural aggregate which meant less restriction to the cementitious paste and hence higher shrinkage. This finding was also confirmed by the relatively higher weight losses of 100% LECA mixtures. Though the micro steel fiber content had no effect on the drying shrinkage at early ages, its effect became more obvious beyond the ages of 14 days as shown in Fig. 18. The inefficiency of fibers at early age of curing may be due to the weak bond between fibers and matrix at these ages. Beyond 14 days, the bond was stronger and thus the composite became more resistant to length changes. Overall, the negative effect of lightweight aggregate on the drying shrinkage can be reduced by using fibers especially at relatively higher percentages of 0.5% and 0.75%. Similarly, Domagala [43] proved the efficiency of steel fibers on reducing drying shrinkage of vibrated lightweight concrete. Though the well distributed steel fibers in the matrix generally revealed some restriction to the length change, the role of fibers in restraining deformation is not fully understood owing to their random spreading inside the matrix as well as nonuniform desiccating of the cementitious paste [44] In short, the ultimate drying shrinkage of the investigated concretes was in the range of between 399 and 610 microstrain which could be considered acceptable. 5. Conclusions The outcomes of the present work might be used to draw the following conclusions: 1. The fresh density and oven dry density of SCLWC was lower as the maximum aggregate size increased whereas they increased slightly as the volume fractions of micro steel fibers increased. 2. The SP dosage required to obtain the target slump flow dropped with increasing the LECA content or maximum aggregate size while it increased with increasing the fiber content. 3. The increase of maximum aggregate size led to enhance V-funnel flow time and L-box height ratio. 4. The T50 cm and V-funnel flow time prolonged as the volume fraction of micro steel fibers increased. 5. The best compressive and flexural strengths were observed for mixes with the smallest maximum aggregate size of 10 mm followed by the next size of 14 mm. 6. The positive influence of enhancing fiber content was more pronounced on the flexural strength than compressive strength. 7. The measured oven dry densities of between 1657 and 2044 kg/m3 suggested that most of mixes particularly those with 100% LECA could be classified as structural lightweight aggregate concrete in accordance with ACI committee 213R03 definition. 8. The water sorptivity was generally adversely affected by increasing the maximum size of aggregate, fiber content, and LECA content. 9. The SCLWC mixes with maximum aggregate size of 20 mm showed minimum drying shrinkage strains. 10. It was found that the drying shrinkage beyond the age of 14 days was lower as the fiber content increased. Author Contributions Ali H. Nahhab planned the experiments, analysed the data, supervised on the experimental work and wrote the manuscript. Ali K. Ketab carried out the experiments.

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Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. References [1] M. Karamloo, M. Mazloom, G. Payganeh, Effects of maximum aggregate size on fracture behaviors of self-compacting lightweight concrete, Constr. Build. Mater. 123 (2016) 508–515. [2] A.M. Rashad, Lightweight expanded clay as a building material-an overview, Constr. Build. Mater. 170 (2018) 757–775. [3] S. Chandra, L. Berntsson, Lightweight Aggregate Concrete Science, Technology, and Applications, Noyes Publications, William Andrew Publishing, Norwich, New York, U.S.A, 2002. [4] T.Z.H. Ting, M.E. Rahman, H.H. Lau, M.Z.Y. Timg, Recent development and perspective of lightweight aggregates based self-compacting concrete, Constr. Build. Mater. 201 (2019) 763–777. [5] K. Heiza, F. Eidand, T. Masoud, Lightweight self-compacting concrete with light expanded clay aggregate (LECA), MATEC Web of Conf. 162 (2018) 02031. [6] G.E.A. Abdelaziz, Study on the performance of lightweight self-consolidated concrete, Mag. Concr. Res. 61 (2009) 1–11. [7] A. Lotfy, K.M. Hossain, M. Lachemi, Mix design and properties of lightweight self-consolidating concretes developed with furnace slag, expanded clay and expanded shale aggregates, J. Sust. Cement-Based Mater. (2015) 1–27. [8] H.Z. Cui, T.Y. Lo, F. Xing, Properties of self-compacting lightweight concrete, Mater. Res. Innovations 14 (2010) 392–396. [9] M.C.S. Nepomuceno, L.A. Pereira-de-Oliveira, S.F. Pereira, Mix design of structural lightweight self-compacting concrete incorporating coarse lightweight expanded clay aggregates, Constr. Build. Mater. 166 (2018) 373– 385. [10] Y. Mohammadi, S. Mousavi, F. Rostami, A. Danesh, The effect of silica fume on the properties of self-compacted lightweight concrete, Curr. World Environ. 10 (Special-Issue 1) (2015) 381–388. [11] S. Iqbal, A. Ali, K. Holschemacher, Y. Ribakov, T.A. Bier, Effect of fly ash on properties of self-compacting high strength lightweight concrete, Periodica Polytechnica Civil Eng. 6 (2017) 81–87. [12] S. Iqbal, A. Ali, K. Holschemacher, T.A. Bier, Effect of change in micro steel fiber content on properties of high strength steel fiber reinforced lightweight selfcompacting concrete (HSLSCC), Procedia Eng. 122 (2015) 88–94. [13] T.M. Grabois, G.C. Cordeiro, R.D. Toledo Filho, Fresh and hardened-state properties of self-compacting lightweight concrete reinforced with steel fibers, Constr. Build. Mater. 104 (2016) 284–292. [14] M.H.A. Beygi, M.T. Kezemi, J.V. Amiri, I.M. Nikbin, S. Rabbanifar, E. Rahmani, Evaluation of the effect of maximum aggregate size on fracture behavior of self-compacting concrete, Constr. Build. Mater. 55 (2014) 202–211. [15] Iraqi Organization of Standards, IQS 5/1984, for Portland cement, 1984. [16] Iraqi Organization of Standards, IQS 45/1984; for aggregate, 1984. [17] ASTM C494/C494M, Standard Specification for Chemical Admixtures Concrete, American Society for Testing and Materials, West Conshohocken, PA, 2017. [18] ASTM C138/C138M, Standard Test Method for Density (Unit weight), Yield, and Air Content (Gravimetric) of Concrete, American Society for Testing and Materials, West Conshohocken, PA, 2017. [19] EFNARC, Specifications and Guidelines for Self-Compacting Concrete, English, European Federation for Specialist Construction Chemicals & Concrete Systems, 2005. [20] British Standard B.S:(1881:part 116), Testing Concrete -Part 116: Method for Determination of Compressive Strength of Concrete Cubes, 1989. [21] ASTM C78/C78M, Standard Test Method for Flexural Strength of Concrete (Using Simple Beam with Third Point Loading). American Society for Testing and Materials, West Conshohocken, PA, 2016. [22] ASTM C642, Standard Test Method for Density, Absorption, and Voids in Hardened Concrete, American Society for Testing and Material, West Conshohocken, PA, 2013. [23] ASTM C 1585, Standard Test Method for Measurement of Rate of Absorption of Water by Hydraulic- Cement Concretes, American Society for Testing and Materials, West Conshohocken, PA, 2013. [24] ASTM C 157/C157M, Standard Specification for Length Change of Hardened Hydraulic-Cement Mortar and Concrete, American Society for Testing and Materials, West Conshohocken, PA, 2017. [25] ASTM C 490/C490M, Standard Practice for Use of Apparatus for the Determination of Length Change of Hardened Cement Paste, Mortar, and Concrete, American Society for Testing and Materials, West Conshohocken, PA, 2017. [26] Z. Wu, Y. Zhang, J. Zheng, Y. Ding, An experimental study on the workability of self-compacting lightweight concrete, Constr. Build. Mater. 23 (5) (2009) 2087–2092. [27] S. Revathy, J. Thomas, Light weight characteristics of self compacting concrete using aluminum powder and fine pumice powder, Int. Res. J. Eng. Technol. (IRJET) 3 (2016) 960–965. [28] B. Basa, J. Sethi, Fresh and hardened properties of self compacting concrete using fly ash light weight aggregate as partial replacement of natural coarse aggregate, Int. J. Civil Eng. Technol. (IJCIET) 7 (2016) 498–505.

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A.H. Nahhab, A.K. Ketab / Construction and Building Materials 233 (2020) 117922

[29] ASTM C1611/C1611M, Standard Test Method of Slump Flow of Selfconsolidating Concrete, American Society for Testing and Materials, West Conshohocken, PA, 2005. [30] Kumar P. Rathish, M.V.A. Krishna Rao, Study on the effect of size of aggregate on the strength and sorptivity characteristics of cinder based light weight concrete, Res. J. Eng. Sci. 1 (6) (2012) 27–35. [31] M. Hassanpour, P. Shafigh, H.B. Mahmud, Lightweight aggregate concrete fiber reinforcement - a review, Constr. Build. Mater. 37 (2012) 452–461. [32] N. Ali, M. Shekarchi, M. Mahoutian, P. Soroushian, Mechanical properties of hybrid fiber reinforced lightweight aggregate concrete made with natural pumice, Constr. Build. Mater. 25 (5) (2011) 2458–2464. [33] ACI 211.4R-08, Guide for Selecting Proportions for High-strength Concrete Using Portland Cement and Other Cementitious Materials: Report of ACI Committee 211, 2008. [34] P. Richard, M. Cheyrezy, Composition of reactive powder concretes, Cem. Concr. Res. 25 (7) (1995) 1501–1511. [35] ACI.213R03, Guide for Structural Lightweight Aggregate Concrete: Report of ACI Committee 213, 2003. [36] A.M. Neville, Properties of Concrete, Longman, New York, 1995. [37] X. Liu, K.S. Chia, M. Zhang, Water absorption, permeability, and resistance to chloride-ion penetration of lightweight aggregate concrete, Constr. Build. Mater. 25 (1) (2011) 335–343.

[38] Z. Li, C. Li, Y. Shi, X. Zhou, Experimental investigation on mechanical properties of hybrid fibre reinforced concrete, Constr. Build. Mater. 157 (2017) 930–942. [39] E. Güneyisi, M. Gesog˘lu, O. Pursunlu, K. Mermerdasß, Durability aspect of concretes composed of cold bonded and sintered fly ash lightweight aggregates, Compos. B 53 (2013) 258–266. [40] M. Gesog˘lu, E. Güneyisi, B. Ali, K. Mermerdasß, Strength and transport properties of steam cured and water cured lightweight aggregate concretes, Constr. Build. Mater. 49 (2013) 417–424. [41] G. Dhinakaran, S. Madhumitha, Durability characteristics of ceramic waste based light weight concrete, Int. J. Eng. Technol. 7 (2018) 369–373. [42] C.M. Tam, V.W.Y. Tam, K.M. Ng, Assessing drying shrinkage and water permeability of reactive powder concrete produced in Hong Kong, Constr. Build. Mater. 26 (2012) 79–89. [43] L. Domagała, Modification of properties of structural lightweight concrete with steel fibers, J. Civil Eng. Manag. 17 (1) (2011) 36–44. [44] Z. Li, M.A.P. Lara, J.E. Bolander, Restraining effects of fibers during nonuniform drying of cement composites, Cem. Concr. Res. 36 (9) (2006) 1643– 1652.