Recycled aggregates

Recycled aggregates Said Kenai University of Saad-Dahleb-Blida, Blida, Algeria

3.1

3

Introduction

Recycling of materials is a very old concept as Romans used to reuse the demolished statues materials to build new ones. After the Second World War, recycling of materials from demolished buildings became an alternative economical solution. For more sustainable world, construction industry companies are now putting sustainability into their business strategies, and recycling is one of their environmental management tools for achieving a sustainable construction industry. Construction industry generates huge amounts of debris that needs to be recycled and reused. Recycling reduces waste and reduces energy consumption. Recycled concrete aggregates have been used extensively in road construction. However, their use in reinforced concrete is limited because of several barriers (economic, environmental, legal, and social) and also to technical difficulties. In this chapter, recycled aggregates’ (RAs) concrete production and performance at the fresh and hardened state are summarized.

3.2

Why recycling?

Construction industry produces about 31% of the total waste materials in Europe (Eurostat, 2017). These waste materials are generated in construction materials factories, construction sites, and demolition sites. Other sources of construction waste are road construction (asphalt and concrete) and embankment earth work. These materials are generally dumped if not used. Around big cities, land space is scarce for dumping and reuse and recycling becomes a necessity to reduce transport cost and for the reduction of the consumption of existing nonrenewable natural resources such as natural aggregates (NAs). In recent years, because of the need for rapid development of infrastructures, the demand of quality NA has increased rapidly especially in developing countries such as India and China. The global aggregates market is estimated at 48 billion tons in 2015 and expected to expand to 66.3 billion tons by 2022 (Freedonia, 2012). Efforts are also undertaken toward a more sustainable construction in developing countries by using low carbon concrete through the use of RA and supplementary cementitious materials (SCMs). Kenai et al. (2014a) have reviewed the Algerian case where construction and demolition waste (CDW) from old structures and after natural disasters are reused. Waste and Supplementary Cementitious Materials in Concrete. DOI: https://doi.org/10.1016/B978-0-08-102156-9.00003-1 Copyright © 2018 Elsevier Ltd. All rights reserved.

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In 2014, 534 million tons of CDW debris were generated in the United States according to the Environmental Protection Agency (EPA, 2016). In 2014 the total waste generated in the EU-28 by all economic activities and households amounted to 2503 million tons; of which 34.7% comes from construction and demolition activities (Eurostat, 2017). The total CDW for England was estimated at 77.4 million tons in 2010 (Defra, 2010). In China, in 2011, the CDW is estimated at more than 2185 million tons of which 62.3% from demolition, 19.6% from construction, and 18.1% from renovation. About five million tons of recycled concrete and masonry are available in Australia (CCA Australia, 2008). The natural resources are limited, and recycling is a necessity to reduce natural materials consumption, energy consumption, and pollution. Also, due to environmental pressures, local legislation is implementing landfill taxes. In addition, recycling is becoming mandatory in most countries. Most developed countries have set up laws that made it mandatory to reuse and recycle construction materials wastes for economic and environmental reasons. Waste materials are mandatorily sent to fixed and mobile crushing facilities that are installed all over Europe to crush waste concrete into aggregates. The European Union parliament has set a target of 70% of recycling CDW by 2020 (EC, 2008).

3.3

Sources of recycled aggregate

The average annual production of CDW is about 500 kg/habitant (Hansen, 1992). Most countries have set up a target of recycling of 50% 90% of CDW. The main sources of RA are construction sites, ready mixed concrete plants, and demolition sites of old buildings or after natural disaster (earthquakes, hurricanes, etc.). The main materials origins are concrete and masonry mainly fired bricks. Concrete has the largest portion (70%), followed by asphalt concrete (14%). Wood products made up 7% and the other products accounted for 9% combined. The demolition represented over 90% of total CDW debris generation as opposed to construction which represented less than 10%. The composition of CDW in different countries is given in Table 3.1. The amount of recycled demolition wastes vary from country to country and are about 20% 80%.

Table 3.1

Composition of CDW in different countries (Lauritzen, 2004)

Material

Belgium

Denmark

Spain

France

United Kingdom

Ireland

Holland

Concrete Masonry Asphalt Others

40 41 12 7

83

20 60 20

30 50 5 15

42 28 24 6

30 60 2 8

43 29 20 8

10 7

Recycled aggregates

3.4

81

Production and manufacturing

The main sources of RA are either from construction and ready mixed concrete sites, demolition sites or from roads. The demolition sites produce a heterogeneous material, whereas ready mixed concrete or prefabricated concrete plants produce a more homogeneous material. RAs are mainly produced in fixed crushing plant around big cities where CDWs are available. However, for roads and to reduce transportation cost, mobile crushing installations are used. The materiel for RA manufacturing does not differ from that of producing NA in quarries. However, it should be more robust to resist wear, and it handles large blocks of up to 1 m. The main difference is that RAs need the elimination of contaminants such as wood, joint sealants, plastics, and steel which should be removed with blast of air for light materials and electro-magnets for steel. The materials are first separated from other undesired materials then treated by washing and air to take out contamination. The quality and grading of aggregates depend on the choice of the crusher type. The main crushers’ types are: G

G

G

G

G

G

Jaw crusher: The material is crushed between a fixed jaw and a mobile jaw. The feed is subjected to repeated pressure as it passes downwards and is progressively reduced in size until it is small enough to pass out of the crushing chamber. This crusher produces less fines but the aggregates have a more elongated form. Percussion crusher: The aggregates are produced by impact and hence higher fines content. Hammer (impact) crusher: The feed is fragmented by kinetic energy introduced by a rotating mass (the rotor) which projects the material against a fixed surface causing it to shatter causing further particle size reduction. This crusher produces more rounded shape. Gyrating or cone crusher: It uses a repeated compression action with fixed and moving crushing members. This kind of crusher produces less than 20% fines, and the aggregates are rather of cubic form. Roller crusher: This crusher is composed of two cylinders rotating in opposite directions around two parallel axes. Rotary bottom crusher.

The main manufacturing steps are as follows: G

G

G

G

G

G

G

G

Site selection and separation Weighting and control Fragmentation Primary crushing Steel separation by magnetic means Manual separation of plastic, wood, and paper Secondary crushing Sieving

82

3.5

Waste and Supplementary Cementitious Materials in Concrete

Obstacles for the use of recycled aggregate

The use of RA has been limited mainly to nonstructural applications such as sidewalks and road base (McGinnis et al., 2017a). The main obstacles hindering their use include the variability in their properties and hence lack of confidence, the lack of experience, the lack of case studies on the service, ultimate load performance of concrete structures, and the few engineering guidelines and standards for the design and construction of reinforced concrete utilizing RA (McGinnis et al., 2017a). Raoa et al. (2007) stated other barriers such as the lack of awareness, lack of government support, and lack of appropriately located recycling facilities. Silva et al. (2017) mentioned some other obstacles for using RA such as long distances between recycling plants and demolition sites, availability of raw materials, availability of demand, absence of environmental taxation on NA, and taxation on landfill to prevent depletion of natural resources and lack of deconstruction approach during demolition.

3.6

Physical properties of recycled aggregate

3.6.1 Grading It is possible to achieve almost any gradation with recycled materials. However, the type of crusher could affect the shape and the amount of fines. The crushing operation may also leave some residual dust on the aggregate surfaces, and hence it is sometimes necessary to wash the aggregate before use.

3.6.2 Density RAs have a relative density lower than that of virgin materials by about 5% 10%. Usually, recycled coarse aggregate (RCA) has a specific gravity of 2.2 2.5 in the saturated surface dry (SSD) condition whereas recycled sand has a relative density of approximately 1.8 2.3 SSD (ACI E1-16, 2016; Kasai, 1994; Tavakoli and Soroushian, 1996). This is due to the low density of the adhered cement mortar on the surface of the aggregates. Table 3.2 summarizes some of the properties of RA (fine and coarse)

Table 3.2

Properties of the recycled aggregates (Kenai et al., 2014b)

Fine aggregates CA 3/8 CA 8/15 CA: coarse aggregate.

Bulk density (kg/m3)

Specific density (kg/m3)

Water absorption coefficient (Ab) (%)

Humidity (%)

1390 1241 1278

2290 2310 2330

7.03 6.50 4.67

4.70 3.84 2.29

Recycled aggregates

83

obtained by crushing of 1 m 3 1 m concrete slabs with a thickness of 10 cm. Slabs were manufactured in the laboratory and stored for 28 days in water. They were initially subjected to a preliminary manual crushing before a final processing using a mechanical crusher. The crushed material is passed through a sieve to obtain different fractions of RA.

3.6.3 Water absorption Water absorption of RA is much higher than that of NA. It is typically 2% 7% for coarse aggregates and 4% 13% for fine aggregates. The higher water absorption is due to the old cement mortar attached to the particles. Table 3.3 summarizes the water absorption coefficients of many investigations. The higher water absorption could negatively affect the freeze thaw resistance of concrete. Water absorption also affects the workability of the concrete mixture. Hence, it is recommended to sprinkle them with water to a moisture content that is greater than SSD prior to mixing in concrete. Otherwise, extra water should be added to the mixture to offset the water absorbed by the aggregate. Because fine aggregates made by crushing concrete are very angular and have a high absorption, it is generally necessary to limit their use to approximately 10% 20% of the fine aggregates content in a mixture.

Table 3.3

Water absorption of recycled aggregates

Authors

Water absorption of natural aggregates Coarse

Hansen (1992) Tavakoli and Soroushian (1996) Kasai (1994) Quebaud (1996) Hadjieva-Zaharieva (1998) Debieb (1999) Gomez-Sobreon (2002) Sani et al. (2005) Sagoe-Crentsil et al. (2001) Tu et al. (2006) Rahal (2007) Kumar (2017) Ghorbel and Wardeh (2017) McGinnis et al. (2017a) Pedro et al. (2017) Sadati et al. (2017)

Fine

0.8 3.7

0.4 1.5 0.8 1.1

1.8 1 1.49

1 1 0.68 0.48 0.74 1.6 1.8 0.26 1.3 0.2 4.56 6.3

1.7 1.3

Water absorption of recycled aggregates

Coarse

Fine

4 8.7 4.48 1.7 10 5.8 5.8 3.5 5.8 6.8 7.4 5.6 5 3.47 4.23 6.8 6.5 8.2 5.01 9.68 6.1 0.4

9.8 8.1 4.7 13.2 12.2 12.5 11.5 8.16 15.8 10

3.6 3.9 2.63

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Waste and Supplementary Cementitious Materials in Concrete

Figure 3.1 Visual appearances of recycled concrete aggregates and natural coarse aggregates (Omrane et al., 2017).

As the mortar that adheres to the surface of RA is the main reason for the loss of performance of concrete with RA, attempts have been made to enhance the performance by the removal of adhered mortar by either acetic acid or microwave treatment or treating with polymer emulsions (Shi et al., 2016).

3.6.4 Hardness (Los Angeles) The abrasion resistance as measured by Los Angles coefficient or Micro-Deval is reduced. The reduction depends on the grade of the original concrete and its aggregates size. It should be noted that abrasion loss is not a concern for RA as it is in the range of 22% 40% which is acceptable and conform to ASTM C-33 and BS 882, 1201 Part 2 limits of 30% 50%. Kenai et al. (2002) reported a Los Angeles coefficient of 50.4% for RA as compared with 36.4% for the NA used.

3.6.5 Flakiness index and angularity number Flakiness and angularity numbers are most affected by the crusher type used. The visual inspection of aggregates revealed their greater angularity, roughness, and porosity of crushed concrete aggregates as compared with NA (Fig. 3.1).

3.6.6 Contamination Contaminations of aggregates could come from plaster in demolition sites but also from residual chlorides in a mixture, as from application of deicing salts to a pavement, from chloride corroded structures near marine environments, or from sulfate contaminated sewage plants. Usually the level of contamination is below the threshold values for both fine and coarse aggregates and is not a concern. If the level of contamination is high, the leaching into water could eliminate the chloride and sulfates as these ions are not linked to the cementitious microstructure.

Recycled aggregates

85

Chlorides content (%)

RA-Cl (4/14)

RA-Cl (14/20)

5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0.0

0.12 0

10

20

30

Time (days)

Figure 3.2 Chlorides content in coarse RA soaked in water for 2 weeks (Debieb et al., 2010).

Debieb et al. (2010) contaminated concrete specimens for 1 year in the laboratory with either chloride (Cl) or sulfate (Su) or sea water (SW) and then crushed them to obtain contaminated aggregates. After 15 days of total immersion into water the coarse RA resulting from the contamination of concrete by chlorides, lost up to 96% of their chlorides showing that these chlorides are unbound chlorides (Fig. 3.2). Although leaching into water could eliminate completely the risk of expansion, precautions are needed to be taken, with aggregates from hazardous or critical origin such as sewage water plants (Debieb et al., 2010). The type of contamination of RA does not affect porosity and permeability of the concrete with RA but increases the initial absorption and porosity, whatever the type of contamination. Although porosity is higher, the resistance to freeze thaw cycles is good. However, contamination with chlorides has a significant impact on concrete durability and, specifically, on reinforcement corrosion (Debieb et al., 2010). ACI E1-16 (2016) specifies that RA from concretes that contain known D-cracking aggregates should be tested and its alkali silica reaction (ASR) potential should be determined prior to its use. The determination of its ASR potential is similar to that used for virgin aggregates.

3.7

State of codes and standards

New standards and guidelines are now issued and applied in most developed countries to conform environmental regulations. These international standards specify the use and characteristics of RA. Most of these standards specify the nature and the physical and mechanical characterization of the RA such as density, water absorption, flakiness index, grading, aggregate impact value, micro-Deval and Los Angeles coefficients, sand equivalent, fines content, and sulfate and chloride contents. Most standards limit the level of substitution of recycled fine to 0% 20% and coarse aggregates to 20% 100% depending on the quality of the RA, and the strength class of the concrete and the environmental exposure conditions. de Brito and Saikia (2013) dedicated a full chapter on concrete with RA in international codes.

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Waste and Supplementary Cementitious Materials in Concrete

The main standards include the following: G

G

G

G

G

G

G

G

G

G

G

G

G

RILEM TC 121-DRG (1994) specifications classify the RA into three categories mainly according to their density at SSD condition and water absorption. These types are type I: aggregates from masonry; type II: aggregates from demolition waste; type III: a mix of NA (a minimum of 80%) and demolition aggregates. In Japan, the BCSJ (1977) and JIS A 5021 (2011), RAs are classified into three categories and are recommended for concrete design strength of 12 18 MPa intended mainly for foundations. In Brazil, NBR 15.116 (2005) allows the use of both fine and coarse RA for nonstructural applications. In Germany, DIN 4226-100 (2002), RAs are classified into four categories according to the bulk density and maximum water absorption, and limits are set up on fine and coarse RA according to exposure condition and type of RA. In Hong Kong the WBTC No. 12/2002 (2002) limits the use of coarse RA to 20% for concrete C35 and 100% for C20. The specifications give limits on some of the properties of RA such as dry density, water absorption, and grading. In Denmark, DS/EN 1992-1-1 (2008) allows 10% of fine RA and 20% of coarse RA issued from structural concrete to be used for structural concrete up to class C30 in X0 and XC1 exposure environment. In Great Britain, the British standard for concrete, BS 8500 (2015) specifies that RA from concrete can be used in concrete C25 up to C50 with a maximum of 20% of coarse RA in most exposure classes except exposure to salt (XS, XD), severe freeze thaw (XF2 XF4) or aggressive ground more severe than DC-1. In Germany, DIN 1045-2 (2008) allows 25% 45% of RA above 2 mm size. In Holland, CUR (1983) accepts up to 50% of RA issued from concrete for concrete C15 to C50 exposed to all environments and from 50% to 100% for concrete up to C25 exposed to all environments except XD and XS. In Norway, NB 26 (2003) allows 10% and 30% fine and coarse RA, respectively for use in concrete C20/25 and only coarse RA up to 20% for concrete C45/55. In Italy, NTC: DM (2008) allows the use of up to 30% of RA issued from demolished concrete in concrete C30/37 and up to 60% of RA in concrete C20/25. In United States, ACI E1-16 (2016) states that while up to 100% of the coarse aggregates can be a recycled material, the percentage of fine aggregate is usually limited to 10% 20%, with the remainder being virgin material. In Qatar the Qatari national construction standards (QCS, 2014) in Section 5: part 2.9 limits the mass fraction of RCAs to 20% for structural concrete of up to C30, 50% for nonstructural concrete, and 100% for blocks.

3.8

Effect of recycled aggregates on the fresh concrete properties

The external aspects of the fresh concrete made of RA compared with that made of NA are similar. The fresh density is slightly reduced and entrained air increased by about 0.6% (Kenai et al., 2002). Kumar (2017) reported reduction of the fresh density of the concrete mixes by 6% 8%. The reduction is mainly due to a lower-specific

Recycled aggregates

87

GBC

SBC

GBrC

SBrC

1 0.95 0.9 0.85 Weff /C

0.8 0.75 0.7 0.65 0.6 0.55 0.5 0

25

50 75 Recycled aggregates (%)

100

Figure 3.3 Variation of Weff/C ratio with the level of substitution of NA by RA (Kenai and Debieb, 2010).

gravity of RA and to the comparatively higher content of entrapped air due to more angular particle shape and surface texture. The angularity of coarse RA and the mortar adhered on their surface reduce the workability of coarse RA concrete mixes to maintain the same slump without the use of admixtures. Concrete mixes with RA needs more water compared with NA concrete. Fig. 3.3 shows the effect of level of substitution of NA by either coarse or fine aggregates from crushed brick (GBrC and SBrC) or from crushed concrete (GBC and SBC). However, the effect on workability is more important for fine RA than for coarse RA. It has been reported that up to 5% and 15% of additional water is needed for concrete with only coarse RA and both fine and coarse RA, respectively (Hansen, 1992; Tori et al., 1984). The reduction in the slump is mainly due to the change in the nature of particle shape and surface texture of RA compared with NA.

3.9

Effect of recycled aggregates on the hardened concrete properties

3.9.1 Compressive strength Most researchers have reported a decrease in the strength of concrete with RA compared with NA concrete. Compression strength of mixes made with coarse RA decreased as compared with NA mixes by an average of 16.6% and 26.4% for 50% and 100% replacement, respectively when testing RA from 13 different sources around the United States (McGinnis et al., 2017a). Khatib (2005) reported a decrease of compressive strength at 7 days and comparable compressive strength at

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Waste and Supplementary Cementitious Materials in Concrete

60 1 day 7 days 28 days 90 days

S (N/mm2)

50 40 30 20 10 0

0

25

50

75

100

% CC

Figure 3.4 Effect of RA substitution on compressive strength (Khatib, 2005).

28 days for 25% 75% substitution level and a decrease of strength for 100% substitution (Fig. 3.4). Pedro et al. (2017) investigated concrete mixes with replacement percentages for fine- and coarse-recycled concrete aggregates: 25/25, 50/50, 100/0, 0/100, and 100/100%. The results show that it is possible to achieve similar concrete compressive strengths using RA from two different sources of concrete having similar compressive strengths. Because of the good quality of the RA the decreases reported are slightly lower. They were of 3% 10%, 7% 17%, and 13% 19% for the replacements of 25%, 50%, and 100%, respectively. The decrease in compressive strength for concrete with RA is mainly due to the high water absorption of fine and coarse RA, the lower strength of RA, and the lower quantity of interfacial transition zones (ITZs) and their higher size (Ravindraradjah and Tam, 1985). Kumar (2017) attributed the reduction in compressive strength to the presence of many micropores and cracks in the mortar attached with aggregates from RA and also due to the presence of soft aggregates such as pieces of bricks as he used field demolition concrete. The gradation of coarse aggregates impacted concrete with RA in a similar way to concrete with NA. The compressive strength and stiffness are lower by 10% 15% for ASTM #57 (25 mm) aggregates compared with ASTM #8 aggregates (10 mm) (McGinnis et al., 2017a). The reduction in compressive strength is about 10% 25% and 35% for coarse RA alone and fine RA alone, respectively (Etxeberria et al., 2007a; Hansen, 1992; Ravindraradjah and Tam, 1985; Ravindraradjah et al., 1987; Tori et al., 1984). When both fine RA and coarse RA are substituted, the decrease in compressive strength is between 24% and 35% (Hansen, 1992; Katz, 2003; Zaharieva et al., 2003). When only 30% of fine RA is substituted, the decrease in compressive strength is negligible (Evangelista and de Brito, 2007). Pedro et al. (2017) also concluded that the decrease in compressive strength is more important for fine RA than coarse RA. For 100% replacement level the reduction in the compressive strength was 5.4% 7.9% and 9.9% 15.3%, for coarse RA and fine RA, respectively. Hence, it is recommended to limit the substitution level of fine RA. The loss in compressive strength depends also on the compressive strength of the original concrete as the decrease is more pronounced for lower grade concretes

Compressive strength (MPa)

Recycled aggregates

89

40 35 30 25 20 15 10 5 0

3 days 7 days 28 days 90 days

0%

25% 50% 75% Coarse crushed brick aggregates

100%

Figure 3.5 Compressive strength of concrete with coarse-crushed brick aggregates (Debieb and Kenai, 2008).

and for higher substitution levels as the use of high-performance coarse RA tends to create a stronger bond between the matrix and the aggregate and hence higher strength (Poon et al., 2004; Tabsh and Abdelfatah, 2009). Similar behavior has been found for coarse- and fine-crushed bricks aggregates but with a higher reduction in compressive strength (Debieb and Kenai, 2008). In this study, NAs (coarse, fine, or both) were substituted (by weight) with crushed bricks at rates varying from 0% to 100% (in steps of 25). The results of this investigation indicate that it is possible to manufacture concrete containing crushed bricks with adequate performance (Fig. 3.5). The effect of contamination of aggregates on the mechanical properties seems to be negligible. Debieb et al. (2010) investigated the mechanical properties using contaminated RA and reported lower mechanical properties for concrete mixes with RA (40% for compressive strength (Rc), 19% for flexural strength (Rt), and 38% for modulus of elasticity (E)) compared to concrete mixes with NA but the contamination of the RA with sulfate (Su), chloride (Cl), or SW does not seem to have a significant effect on these properties up to 28 days of age (Fig. 3.6). Many methods have been used to improve the performance of RA such as the carbon conditioning, the combination with crumb rubber, and the coating with Polycarboxylate (PC) dispersant. RAs have been combined with an optimal crumb rubber content and found to display a good compressive behavior compared to NA concrete (Xie et al., 2015). Recent work showed that the performance of concrete with RA could be enhanced with carbon conditioning of RA as this reduces porosity and water absorbency of RA (Tam et al., 2016). The coating of coarse RA with water soluble PC dispersant was also found to improve the compressive and tensile strength (Ryou and Lee, 2014).

3.9.2 Tensile strength The tensile strength of concrete with RA as measured by indirect tensile strength methods such as four points or three points flexural strength or splitting tensile

Waste and Supplementary Cementitious Materials in Concrete

Properties

90

45 40 35 30 25 20 15 10 5 0

39.8

Rc (MPa)

Rt (MPa)

E (GPa)

30.8 24.2 19.6

3.1

2.6

NC

RC-VRA

22.3

25.2

23.6 19.7

18.4

19.2

2.4

2.5

2.6

RC-Cl

RC-Su

RC-Sw

Type of concrete

Figure 3.6 Compressive strength, tensile strength, and elasticity modulus of concrete of contaminated aggregates (Debieb et al., 2010).

strength seems to be less affected than compressive strength (Kou et al., 2011). The rougher surface of the RA and their angularity seems to affect positively the bond between aggregates and mortar and hence positively affect the tensile strength. The effect of the substitution with the smaller size of natural coarse aggregate, i.e., 4.75 10 mm, is more pronounced on the development of the flexural strength (a reduction up to 20%) than the larger size of the aggregate (10 20 mm) probably because the finer size aggregates require more paste compared to larger size aggregates (Kumar, 2017). Pedro et al. (2017) observed decreases of 13% 17% and 28% 36% when 100% replacement is used for coarse NA or fine NA, respectively. Evangelista and de Brito (2007) found 30% decrease in splitting strength for 100% of both coarse RA and fine RA, whereas Yang et al. (2011) reported around 14% decrease when only coarse NA are substituted. Khoshkenari et al. (2014) obtained a decrease of 26% 32%, when both fine NA and coarse NA were replaced with RA. Kenai et al. (2002) found a decrease in flexural strength of about 20% at 28 days and up to 70% at 90 days of age. The loss in tensile strength depends also as with the compressive strength of the original concrete grade as the decrease is more pronounced for weak concrete than for stronger concrete (Fig. 3.7) and also more pronounced for higher substitution levels (Ravindraradjah and Tam, 1985; Tabsh and Abdelfatah, 2009).

3.9.3 Modulus of elasticity The modulus of elasticity depends on the compressive strength and hence is also negatively affected by the level of substitution of RA and by the original concrete grade. The modulus of elasticity decreases almost linearly with the increase of the replacement (Kenai et al., 2002). Reductions of 15% up to 45% are reported (Kheder and Al-Windawi, 2005; Ravindraradjah and Tam, 1985; Tabsh and Abdelfatah, 2009). Pedro et al. (2017) reported reductions of about 5% 14%, 14% 20%, and 21% 28%, respectively for concrete with 25%, 50%, and 100% replacement. Again the fine fraction of RA has the larger decrease in the modulus of elasticity as the use

Recycled aggregates

91

Figure 3.7 Effect of original concrete grade on tensile strength (Tabsh and Abdelfatah, 2009).

of fine RA leads to a more porous paste. The reductions were 8.5% 9.2% and 13.9% 25.8% for concrete with 100% coarse RA and 100% fine RA, respectively. The decrease could be related to the incorporation of fine RA that leads to a more porous paste and higher water/cement (w/c) ratios. The greater irregularity of the fine RA and the poor adhesion with cement paste may also be detrimental factors. The decrease in the modulus of elasticity is also due to the lower elastic modulus of the RA and to the microcracks of the RA. McGinnis et al. (2017a) reported that stiffness of mixes made with RA decreased as compared with NA mixes by an average of 26.4% and 34.4% at 50% and 100% replacement, respectively for the 13 various RA tested. Evangelista and de Brito (2007) also reported decreases in compressive, tensile strength, and modulus of elasticity.

3.9.4 Flexural and shear strength Full-scale tests on reinforced concrete beams under flexure have shown that the mid-span deflection is greater for beams with RA (Fathifazl et al., 2009; Maruyama et al., 2004; Sato et al., 2007; Sogo et al., 2004). The increase in deflection is about 10% for 100% replacement ratio. This is mainly attributed to the low elastic modulus of concrete with RA. However, the standard predicted mid-span deflections by ACI Committee 318 (2011) and Euro code 2 (2004) are more important than deflections produced by the use of RA. The use of RA increases slightly crack width and reduces slightly crack spacing due to the additional ITZ region in concrete with RA which is a weak point for cracking to occur (Batayneh et al., 2007). The reduction is small and does not hinder beams made of RA to be used as structural members. It should be noted that the ultimate moment is not affected by the use of RA provided that steel yielding occurs prior to concrete crushing but the cracking moment is slightly lower for concrete with RA (Fathifazl et al., 2009). Ignjatovi´c et al. (2017) tested beams with 0%, 50%, and 100% of coarse RA with and without shear reinforcement under four-point loading until failure. They concluded that the shear behavior and shear strength are very similar for NA and

92

Waste and Supplementary Cementitious Materials in Concrete

RA beams. Similar results were observed by other researchers where the shear strength was hardly affected when 25% of RA was used (Choi and Kang, 2008; Etxeberria et al., 2007b). However, up to 30% reduction in shear strength is reported by other researchers (Wentao and Ingham, 2010). Zaki et al. (2017) tested 8 two-way simply slab specimens supported on four edges under a central patch load using concrete with NA or RA at substitution level of 0%, 30%, 60%, and 100% and concluded that the first punch crack load, the ultimate punch load, the stiffness, and the energy absorption decrease as the level of substitution of NA by RA increases.

3.9.5 Fracture Few studies are available in the literature on the fracture properties of concrete with RA. Ghorbel and Wardeh (2017) investigated the fracture properties of 10 3 10 3 40 cm prenotched concrete specimens under three points bending tests prepared with different recycled gravel content (0%, 30%, 65%, and 100%) by volume of the total coarse gravel. The force-crack mouth opening displacement curves (Fig. 3.8) show that concrete mixes with RA presents a lower fracture energy. The postpeak curve is steeper the higher the substitution level and hence RA mixes are more brittle. The decrease in fracture energy was explained by the increase in porosity of concrete and to the cracks network which is denser for RA concrete than for NA concrete beams. It was observed that the cracks pass through the RA while they remain localized in the paste around NA. This study also concluded that the critical crack width decreases with the RA content.

8 7 NAC RAC30 RAC65 RAC150

Force (kN)

6 5 4 3 2 1 0

0

0.5

1 Displacement (mm)

1.5

2

Figure 3.8 Force-crack mouth opening displacement curves as a function of repalcement ratio (Ghorbel and Wardeh, 2017).

Recycled aggregates

93

3.9.6 Bond strength Bond strength between the concrete and reinforcing steel is an important property that depends mainly on chemical adhesion and the friction between the reinforcing bar surface and the surrounding concrete. It is affected by the depth of cover, the bar diameter, and concrete properties. The bond strength influences the performance of concrete namely the transverse crack development, the tension stiffening, and flexural curvature. Few studies are available in the literature on concrete with RA and contradicting results are reported. Xiao and Falkner (2007) used pull-out samples to investigate bond strength of concrete made with 0%, 50%, and 100% RCA replacement from three different sources. They reported for samples with plain bars a decrease in the normalized bond strength of 7% for 50% RA concrete mixes and an increase of 5% for 100% RA concrete mixes. For the case of samples cast with deformed bars the normalized bond strength increased for both mixes by 4% and 12% for 50% and 100% RA replacement, respectively. However, Breccolotti and Materazzi (2013) reported no significant difference between the normalized bond strength of the reference concrete and the mixtures proportioned with 50% and 100% RA produced from crushing the test residuals of a concrete laboratory. Butler et al. (2011) reported that bond strength of concrete mixes with 100% RA was between 9% and 19% lower than concrete mixes with 100% NA when investigating two types of commercial RA. Sadati et al. (2017) studied the bond strength between concrete and reinforcing steel in 11 full-scale beams constructed with concrete with 50% of coarse RA replacement as well as with 50% class C Pulverised Fly Ash (PFA) and 50% RA. Both mixes with RA with and without fly ash exhibited about 15% higher normalized bond strength compared with beams with NA concrete mixes. They found that the ACI Committee 408 (2003) analytical model provides a conservative prediction of the ultimate bond strength of the investigated concrete made with high contents of RA and fly ash and recommends it for estimating bond strength of reinforced concrete cast with up to 50% RA and 50% fly ash replacements. Prince et al. (2017) investigated bond behavior of concrete with RA of 24 beams. They concluded that the bond behavior and failure mode were similar for both concretes with NA and RA and that the effect of RA replacement levels on bond strength was marginal. Kou and Poon (2013) showed that the use of three types of fine RA in rendering mortar increased the bond strength at the interface between mortar and masonry bricks as determined by the triplet test. The increase in bond strength was attributed mainly to the better permeation of mortar prepared with RA into the brick surface and hence a better physical interlock.

3.9.7 Abrasion resistance Abrasion resistance is an important property for concrete uses in pavements as it is subjected to dynamic loading from traffic. It is affected by concrete strength, surface finishing, and mainly the aggregates properties. The abrasion resistance seems

94

Waste and Supplementary Cementitious Materials in Concrete

not to be affected by the use of RA in concrete mixes. Pedro et al. (2017) tested concrete specimens with and without RA at 91 days using the Bo¨hme disk and reported that the abrasion resistance was not affected by the use of RA, with thickness losses of approximately 3.5 and 4.5 mm for coarse RA and both coarse and fine RA mixes, respectively. However, mixes where only fine RAs were used gave the worst performance compared to total or partial substitution of both fine and coarse NA with decreases in abrasion resistance of 40% 47%. Decreases of about 50% are reported by Pereira et al. (2012). However, for mixes with 100% coarse RA, the resistance to abrasion even increases between 5% and 14% as coarse RAs have greater roughness allowing better bond with the cement matrix. Similar results are also reported by Fonseca et al. (2011) where 100% coarse RA mixes showed a decrease in abrasion wear depth between 4.1% and 15.5%. Mixes with 100% fine RA and with similar compressive strengths also reached identical losses (of about 50%). Kumar (2017) investigated the effect of incorporating recycled concrete aggregates of two concrete mixes with two different w/c ratios at the age of 28 days by subjecting the specimens to the impingement of air driven silica sand and measuring the mass loss. He concluded that RA reduces the abrasion resistance by 18% 22%. The reduction is higher for mixes with fine RA. However, the abrasion resistance was acceptable for the RA to be used for concrete pavement construction.

3.9.8 Shrinkage As for concrete with NA, drying shrinkage of concrete with RA is higher the higher w/c ratio. Concrete with RA presents a higher drying shrinkage of 25% 60% compared to that of concrete with NA whereas for total substitution with both fine RA and coarse RA, the increase in shrinkage is about 70% (Hansen, 1992; Ravindraradjah et al., 1987; Sagoe-Crentsil et al., 2001). This increase occurs mainly at later age than at early age. Kenai et al. (2002) and Kenai and Debieb (2010) concluded that the shrinkage of RA concrete was comparable at early age but increases of up to 40%, 70%, and 85% were observed at later ages for coarse, fine and both coarse and fine RA, respectively (Fig. 3.9). Similar results are reported by Coquillat (1984) with an increase of shrinkage compared to NA concrete of about 80%. Pedro et al. (2017) reported increases of 4% 42% at 7 days and between 15% and 106% at 91 days (Fig. 3.10). The RAs work as internal water reservoir controlling the autogenous shrinkage at early age by the internal curing phenomenon allowing the compensation of the evaporated water present in the RA (Maruyama and Sato, 2005). The maximum shrinkage registered around 106% is in agreement with the findings of other researchers (70% 100%) (Hasaba et al., 1981; Ravindraradjah et al., 1987). Sadati (2017) established strong correlations between water absorption, ovendry-specific gravity and Los Angeles abrasion of RA with drying shrinkage of concrete. His experimental work showed that up to 17% and 55% increase in 90-day shrinkage were observed for mixes with 30% RA and 100% RA, respectively.

Recycled aggregates

95 BT

B 75/25

B 100/50

B 25/75

B 50/100

50/50

100/100

100/100 +

1000

Shrinkage (µm/m)

800

600

400

200

0 2

7

28 Age (days)

60

90

Figure 3.9 Variation of shrinkage for concrete mixes with concrete RA (coarse/fine) (Kenai and Debieb, 2010).

0

Shrinkage deformation (µm/m)

C 25F 25C-LC C 100F-LC

RC C 100F 100C-LC

C 50F 50C-LC C 100C-LC

–100 –200 –300 –400 –500 –600

0

7

14

21

28

35

42 49 Time (days)

56

63

70

77

84

91

Figure 3.10 Shrinkage deformation over time (Pedro et al., 2017).

The increase in shrinkage may be attributed to the adhered mortar on the RA surface, the increase in water demand, and to the lower modulus of elasticity of concrete with RA (Tori et al., 1984). It should be noted that although shrinkage increases significantly with the incorporation of RA, for mixes with the same

96

Waste and Supplementary Cementitious Materials in Concrete

Figure 3.11 Evolution of the autogenous strain according to the equivalent age (Delsaute and Staquet, 2017).

mechanical performance, it is possible to get the same shrinkage performance at 365 days according to the Euro code (EC2) (Pedro et al., 2017). Some researchers have reported expansion of concrete with RA due to the presence of sulfates in contaminated concrete used to produce RA. An increase of expansion of 20% 60% compared to concrete with NA is reported (Hansen, 1992; Quebaud, 1996). The early age shrinkage was little investigated. Delsaute and Staquet (2017) studied the early age shrinkage of concrete with RA. The substitution of NA by RA was studied on three concretes for which NA was substituted by RA at 0%, 30%, and 100% of the aggregate volume fraction. It was observed that the high porosity and the subsequent internal curing effect of RA decrease the autogenous shrinkage (Fig. 3.11) and increase thermal expansion coefficient of up to 50%. This was explained by the decrease of relative humidity inside the cement paste that is compensated by the RA acting as a water storage agent refilling the capillary pores during the hardening process and reducing the self-desiccation mechanism comparable to what is observed with light weight concrete.

3.9.9 Creep Creep of concrete with RA is reported up to 50% higher mainly because of its low elastic modulus and hence its lower capacity to oppose the creep deformation as well as the adhered old mortar to aggregates which could have creep deformation (Hansen, 1992; Ravindraradjah et al., 1987). In addition, the increase of the w/c ratio for concrete mixes with RA to maintain the same workability increases the creep deformation. The creep coefficient at 91 days was of 0.9, whereas the RA mixes have values between 1.2 and 1.8 (Pedro et al., 2017). Silva et al. (2015b) proposed a conservative correction factor for the creep coefficient of 1.80. Geng et al. (2016) tested 40 specimens of concrete with coarse RA with w/c ratios varying between 0.3 and 0.6 subjected to sustained loading for up to 8 months

Recycled aggregates

97

and measured the creep deformation. They reported an increase in creep of concrete with RA of 50% 120%. The increase in creep deformation was more pronounced for concrete with lower w/c ratio and for aggregates from original concrete with higher w/c ratio. In addition to the effect of residual mortar content, they introduce a water-to-cement ratio factor to the available creep prediction EC2 model for a more accurate prediction. Domingo-Cabo et al. (2010) tested specimens at 180 days and also observed higher total creep deformation and higher-specific creep deformation of concrete with coarse RA as compared with concrete with NA. They observed 35%, 42%, and 51% increase in total creep deformation and 25%, 29%, and 32% increase in higherspecific creep deformation when NAs were substituted by 20%, 50%, and 100% of RA. Limbachiya (2010) reported comparable creep strain when only 30% of coarse NA was substituted by coarse RA whereas the increase in creep strain was 13% and 54% when the substitution level was increase to 50% and 100%, respectively.

3.10

Effect of recycled aggregates on the durability of concrete

3.10.1 Porosity and water absorption Porosity of concrete with RA is reported to be up to double that of concrete with NA and up to 50% higher if only coarse RAs are substituted (Gomez-Sobreon, 2002; Katz, 2003; Ravindraradjah et al., 1987). Porosity of concrete mixes with RA increases with the level of substitution of NA by RA. This is related to the increase in the volume of paste and the porosity of the RA (Gomes and de Brito, 2009; GomezSobreon, 2002). The paste volume was 29.6%, 30.6%, 36%, and 37.8% for NA, 30% RA, 65% RA, and 100% RA mixes, respectively (Ghorbel and Wardeh, 2017).

3.10.2 Water absorption by immersion RAs are more porous than NA and hence concrete made with RA presents a higher water absorption. The water absorption by immersion is higher for mixes with RA. The water absorption by immersion is about 10% for NA mixes and 20% for RA mixes. Due to the higher absorption of fine RA, the incorporation of 100% fine RA has a more adverse effect with increases of 33.2% 43.1%. This is in agreement with the 46% increase reported by Evangelista and de Brito (2010). The increases for 100% coarse RA are between 22% and 37% and are comparable to the increases of 25% 32% reports by other researchers (Amorim et al., 2012; Matias et al., 2014; Rao et al., 2011; Soares et al., 2014). Kenai and Debieb (2010) reported higher increases of water absorption of 1.5 times to 3.5 times according to the level of substitution of NA with RA from crushed brick or concrete (Fig. 3.12). Katz (2003) also reported about two times increase in water absorption.

98

Waste and Supplementary Cementitious Materials in Concrete

Beton

Brique

Water absorption (%)

22 20 18 16 14 12 10 8 6 4 0

0

/5

50

0

10

0/

10

0+

10

/ 00

5

/2

75

50

0/

10

1 Coarse/fine recycled aggregates (%)

0

/5

25

00

/1

50

Figure 3.12 Effect of recycled aggregates (coarse/fine) on water absorption (Kenai and Debieb, 2010).

3.10.3 Capillary absorption Water absorption by capillary is also higher for mixes incorporating fine RA than mixes incorporating only coarse RA and mixes with NA. Increases of 70% to more than 100% are reported when 100% fine RA is used. When both fine RA and coarse RA were used, the increases were 40.6% 46.9%, 59.4% 71.9%, and 134.4% 153.1% for replacements of 25%, 50%, and 100%, respectively (Evangelista and de Brito, 2010; Pedro et al., 2017). Olorunsogo and Padayachee (2002) reported comparable increases of the sorptivity of up to 29% when 100% of the aggregates are RA.

3.10.4 Water permeability The high water absorption of RA gives a higher water permeability of concrete with RA. The increase is up to two to three times for concrete with 100% RA (Hansen, 1992; Quebaud, 1996; Wainwright et al., 1994; Zaharieva et al., 2003). Fig. 3.13 shows the water penetration depth as measured according to RILEM CPC 13.1 (1979) for different concrete mixes with either concrete (B) or crushed brick (C) or a mixture (D) where either coarse or fine RAs were used. Water permeability was up to double with RA concrete compared with NA concrete. Hence, it is necessary to take precautions when designing mixes using RA to avoid cracking and to reduce durability problems for structural applications. Olorunsogo and Padayachee (2002) also found that durability as measured by chloride conductivity, water sorptivity, and oxygen permeability was reduced with increase of the level of substitution of NA by RA, and they explain this by the cracks which were formed in RA during processing and hence rendering the aggregate more susceptible to diffusion and absorption of fluids.

Recycled aggregates

99

160 140 120 100 80 60 40

D3

D1

C 100/100 +

C 50/50

C 100/0

B 100/100 +

B 50/50

0

B 100/0

20 BT

Water penetration depth (mm)

180

Types of concrete mix

Figure 3.13 Water penetration depth variation of RA concrete mixes (Kenai and Debieb, 2010).

3.10.5 Carbonation Carbonation is an important aspect of concrete durability as it could lead to corrosion of reinforced concrete. The carbonation depth is reported to increase with the increase of the level of substitution of NA with RA. The effect is more pronounced with fine RA. The increase could be as high as 100% when total substitution of NA is used and this increase is attributed to the high porosity of RA (Levy and Helene, 2004; Silva et al., 2015b; Xiao et al., 2012). The carbonation depth increases with the decrease of water binder ratio, the decrease of binder content, and the increase of fine RA content (Bravo et al., 2015; Xiao et al., 2012). The use of mineral admixtures such as PFA also increases the depth of carbonation (Kou and Poon, 2012). However, it should be noted that the differences in carbonation depths between concrete mixes with NA and concrete mixes with 100% RA is not important. Evangelista and de Brito (2010) and Pedro et al. (2017) reported differences in carbonation depth of less than 6 mm at 91 days, whereas Soares et al. (2014) found an increase less than 1.2 mm when using high-grade concrete for the RA. For 25%, 50%, and 100% replacement ratios the carbonation coefficient depends on the nature and source of RA and increases by about 37% 52%, 45% 63%, and 67% 127%, respectively (Pedro et al., 2017).

3.10.6 Frost resistance The resistance to frost attack of concrete with RA is generally lower than that of concrete with NA (Hansen, 1992; Zaharieva et al., 2004). However, there are contradictory findings from different researchers probably because of the

100

Waste and Supplementary Cementitious Materials in Concrete

concrete grade of the original concrete. Some researchers found comparable performance of concrete with RA when the quality of the concrete rubble is good (Gokce et al., 2004). However, most researchers reported low freeze thaw resistance unless the RAs are originated from air entrained concretes (Salem and Burdette, 1998; Zaharieva et al., 2004). The lack of performance under freeze thaw is mainly attributed to the porous structure of the old adhering mortar to the surface of RA which absorbs mixing water and hence increases the w/c ratio of the paste. Total substitution of fine NA by fine RA led to about 37.9% mass loss as compared with 12.6% mass loss in concrete with NA after 300 freeze thaw cycles (Bogas et al., 2015). The presoaking of RA seems to enhance the performance and gives comparable results to concrete with NA (Yildirim et al., 2015) and the reduction of adhered mortar content also increases the freeze thaw resistance (Gokce et al., 2004). The use of mineral admixtures such as metakaolin and the use of crumb rubber also improve the resistance to freeze thaw (Gokce et al., 2004; Richardson et al., 2016).

3.10.7 Resistance to aggressive environment Sulfate resistance is believed to be lower for concrete with RA. Hansen (1986) reported a decrease of strength after sulfate attack of 18% 60% when testing RA issued from 25 different original concrete. Other researchers reported a lower decrease of 1% 9% (Gallia, 1999). Bulatovi´c et al. (2017) tested eight mixes with coarse NA and RA using two types of cement and two different w/c ratios by immersion in 5% Na2SO4 or 5% MgSO4 solutions for 90, 180, and 365 days. They concluded that concrete with RA was more sensitive to sulfate aggression than concrete with NA but the effects of w/c ratio and cement type on sulfate resistance are higher than the effect of the type of aggregates (natural or recycled). The chloride-ion diffusion increased with the replacement ratio as RAs are more permeable, and the concrete mixes with RA have higher w/c ratios but the increase was not significant. At 91 days the chloride-ion diffusion was 8 and 11 3 10212 m2/s for NA and RA mixes, respectively (Pedro et al., 2017). However, if the aggregates are contaminated with chlorides (RC-Cl), sulfates (RC-Su), or Sea Water (RC-SW), the risk of corrosion is important. Fig. 3.14 shows measurements of half-cell potential on recycled reinforced concrete beams with 100% of coarse and fine RAs that were contaminated. The values of potential of 0.57, 0.35, and 0.44 V were measured for RC-Cl, RC-Su, and RC-SW, respectively. It is generally admitted that chloride content, reported to the cement weight, between 0.3% and 0.5% and even below these values, can generate a risk of corrosion (ASTM C 876-09, 2009). With regard to the limits imposed by ASTM C 876 80 standards the probability of corrosion of steel rebars in reinforced concrete with 100% of RA by chlorides and/or sulfates is more than 90%.

Recycled aggregates

101

Half-cell potential (V)

0.6 0.5 0.4

Allowable limit in concrete (ASTM C876-09)

0.3 0.2 0.1 0 NC

RC-VRA

RC-Cl

RC-Su

RC-Sw

Type of concrete

Figure 3.14 Half-cell potential of recycled reinforced concrete beams (Debieb et al., 2010).

3.10.8 Use of supplementary cementitious materials to mitigate durability problems The use of SCM such as granulated glass blast furnace slag (GGBFS), Metakaolin (MK) and PFA could mitigate the adverse effects of RA on the durability performance of concrete. Dodds et al. (2017) studied the durability performance of concrete with three different coarse RAs, and they concluded that the incorporation of GGBFS can overcome the detrimental effect on the microstructure and water ingress. Mirza and Saif (2013) found that concrete with RA, and 30% PFA and 60% GGBS enhanced the performance of concrete with RA as compared to concrete with RA but without PFA or GGBFS. Compressive strength was comparable; the rate of chloride transportation was lowered and the resistance to sulfate attack was higher. The resistance to frost was either increased for 30% PFA or at the same level for 60% GGBFS. Kapoor et al. (2017) observed that when 10% MK was added to concrete mixes with fine and coarse RAs, the chloride-ion penetration was significantly lower than that of concrete with NA. The addition of MK was also effective in reducing the initial rate of water absorption.

3.10.9 Microstructure Microstructure of concrete with RA differs from that of concrete with NA as concrete with RA presents two ITZ, one between NA and old cement matrix and another between old cement matrix and new cement matrix (Otsuki et al., 2003; Xiao et al., 2013). The old ITZ makes the concrete microstructure more fragile due to higher porosity and cracks, thus acting as the weakest link. The thickness of the new ITZ is of the same order of magnitude but thicker than the old ITZ (Xiao et al., 2013). Guedes et al. (2015) studied the effect of fine RA on the microstructure and the ITZ and found that the substitution of NA by RA from crushed concrete gave a higher porosity of ITZ and cracks but with apparently stronger interfacial bond if the level of substitution is limited. The ITZ affects the strength

102

Waste and Supplementary Cementitious Materials in Concrete

of concrete with RA depending on the water binder ratio of concrete with RA compared to the original concrete. In the case of high water binder ratio the old ITZ is stronger than the new ITZ and hence strength of concrete with RA is comparable to that of concrete with NA. However, in the case of a low water binder ratio, the old ITZ is weaker and the strength of concrete with RA is lower (Otsuki et al., 2003). The microstructure of concrete with RA could be improved by using surface saturated dry aggregates to reduce the micropores of concrete (Leite and Monteiro, 2016), coating of aggregates with pozzolanic materials which consume calcium hydroxide accumulated on the old attached mortar, and improve the microstructure of the ITZ (Kong et al., 2010) and by the addition of supplementary materials such as slag, silica fume, and metakaolin (Duan et al., 2013). Choi et al. (2016) coated the surface of low-quality RA with inorganic materials and managed to improve the ITZ that existed in the interface between coarse aggregates and the cement matrix and hence improved the adhesion between coarse RA and cement matrix and enhanced strength and permeability of concrete.

3.11

Use of recycled aggregates in self-compacting concrete

RAs have been investigated for their use in self-compacting concrete (SCC). The use of fine RA increases the flow spread and comparable L-box blocking ratio and segregation resistance (Fig. 3.15). Grdic et al. (2010) reported a comparable spread flow and a better resistance to segregation when RCAs are used at a substitution level of 50% and 100%. 870

Slump flow diameter (mm)

855

Series I Series II

840 825 810 795 780 765 750 735 0

25

50

75

100

Fine recycled aggregate (%)

Figure 3.15 Effect of recycled fine aggregates on the slump flow diameter (Kou and Poon, 2009).

Recycled aggregates

103

Kenai et al. (2014b) investigated six SCC mixes which were prepared with either 100% NA, 50% NA/50% RA, or 100% RA for both mixes with 15% natural pozzolan (NP) or without NP. The concrete mixes were cast with constant water to binder (w/b) ratio of 0.40 and total powder content of 495 kg/m 3 and 1.8% of superplasticizer by mass of binder materials was used. The experimental results showed that the substitution of 50% or 100% of NA by RA gives SCC with very comparable rheological properties to that of the reference SCC. The plastic viscosity of SCC mixture decreases with increasing the substitution level of NA by RA. Increasing NA substitution from 50% to 100% decreases the V-funnel flow time by 62%. The passing ability through L-box test is better for RA concrete than that for NA. This passing and filling abilities of the SCC mixtures with RA may be due to the change of the grading of aggregates during mixing. However, SCC with RA was less stable against bleeding. NP decreases the flowability of both SCC with NA and with RA. Omrane et al. (2017) studied four concrete mixes with different level of substitution of both coarse and fine NA by fine and coarse RA. The substitution levels were fixed at 0%, 50%, 75%, and 100%. The cement was also partially replaced by weight from 5% to 25% by NP. Table 3.4 summarizes the fresh properties SCC mixes. It was found that among the four tested mixtures, only the mix with 100% NA (NSCC) and the mix with 50% recycled coarse and fine aggregates (RSCC) have fulfilled all the SCC requirements of the slump, v-funnel, and J-Ring tests as is clearly shown in Figs. 3.16 3.18. The shear thickening has been found to increase with the increase of RA replacement level, and the flow behavior could be described using both the modified Bingham and the Herschel-Bulkley models (Singh et al., 2017). The increase in the flow index was about 17% for 100% RA concrete mix and was attributed to the higher levels of interparticulate friction. The compressive strength of SCC is slightly reduced when RAs are used. A decrease of 4% 9% is reported for 50% and 100% RCA substitution levels, respectively (Fig. 3.19). The decrease in compressive strength increases with the addition of fine RA and also depends on the original concrete grade (Kou and Poon, 2009). The splitting tensile strength also decreases with the increase of RA content. Drying shrinkage increases with increase of fine RA content but the decrease is lower the lower water/binder ratio (Fig. 3.20). Water permeability of SCC with RA increases with increase of RA content. The increase is mainly due to the capillary pores of the adhered old mortar in addition to the capillary pores of the new mortar (Grdic et al., 2010). Chloride diffusion also increases with the increase of RA content. The apparent chloride ions diffusion (Da) of RSCC mixes is much lower than that of NSCC mixes. Da of mixtures with NP is much smaller than that without NP for both NSCC and RSCC mixes. Da was 0.86 and 0.55 3 1028 m2/s for NSCC and RSCC mixes, respectively. However, the substitution of cement with

Table 3.4

Fresh properties of SCC (Omrane et al., 2017)

Mix description

Control (N) 5 NP 10 NP 15 NP 20 NP Control (R) SCC 5 NP 10 NP 15 NP 20 NP 25 NP

Slump test

L-box test

V-funnel test (s)

Sieve stability test (%)

T500 (s)

D (mm)

T200 (s)

T400 (s)

H2/H1 (%)

2.1 2.1 2.2 2.3 2.7 2 2.1 2.2 2.3 2.5 2.7

729 705 690 670 627 715 710 706 690 682 635

1.3 1.3 1.4 1.4

3.4 3.4 3.4 3.5

80 81 82.5 82

7.5 8.0 8.4 10.6

9.2 9.4 10.2 11.3

0.8 0.9 1.1 1.2 1.4

1.5 1.6 1.9 2.2 2.7

85 84.8 83 82.3 81

6.5 7.0 7.2 9.8 10.6

6.2 6.5 6.7 7.6 8.3

J-Ring D (mm)

DH (mm)

710.5 700 681 668

9.7 9.3 9.4 9.1

705555 700 697 676 669

9.6 8.6 8.9 9.3 9.2

Recycled aggregates

105

Figure 3.16 V-funnel flow time versus recycled coarse and fine aggregates content (%) (Omrane et al., 2017).

Figure 3.17 Slump flow test versus recycled coarse and fine aggregates content (%) (Omrane et al., 2017).

NP reduces Da (Figs. 3.21 and 3.22). The low chloride ions penetration of SCC with NP is due to the impermeability of the NP which prevents the passage of chloride ions.

106

Waste and Supplementary Cementitious Materials in Concrete

Compressive strength (MPa)

Figure 3.18 J-Ring versus recycled coarse and fine aggregates content (%) (Omrane et al., 2017).

Concrete compressive strength

60 50 40 30 20 10 0

E

P50 Type of concrete 2 days

7 days

P100

28 days

Figure 3.19 Effect of recycled aggregates on compressive strength (Grdic et al., 2010).

Omrane et al. (2017) measured the resistance to acid attack by immersion in a solution of 5% H2SO4. The monitoring of the mass was conducted for 3 months of immersion. For both type of concrete (NSCC and RSCC) during the first 4 weeks of attack, the results show the same deterioration trend. After 12 weeks the beneficial effect of incorporating NP is clear. SCC mixes with NP addition exhibits the lowest mass loss compared with control concrete (Fig. 3.23).

Recycled aggregates

107

1200

Drying shrinkage (x10–6)

Control-2 1000

RF25 RF50 RF75 RF100

800 600 400 200 0 0

20

40

60

80

100

120

Time (day)

Figure 3.20 Effect of recycled fine aggregates on drying shrinkage of SCC (Kou and Poon, 2009).

Figure 3.21 NP-content% versus apparent chloride-ion diffusion coefficient (Omrane et al., 2017).

3.12

Use of recycled aggregates in roller-compacted concrete

Roller-compacted concrete (RCC) is a special dry concrete with zero slump made from the same constituents as ordinary concrete but with low cement content. It is usually compacted like a soil. RCC is mainly used for the construction of massive structures such as dams or large horizontal surfaces like highway foundations. Its low cement content reduces the development of temperature in mass concrete and

108

Waste and Supplementary Cementitious Materials in Concrete

Total charge passed (coulombs)

2500 Series I Series II Series III

2000

1500

1000

500

0

Control

RF 25

RF 50

RF 75

RF 100/RF 100A

RF 100B

RF 100C

Mix notation

Figure 3.22 Effect of RA on chloride diffusion (Kou and Poon, 2009).

Figure 3.23 Change in mass of RSCC versus the immersion duration using 5% H2SO4 immersion (Omrane et al., 2017).

reduces thermal stresses. Two important dams were built recently in Algeria using RCC, one called Beni-Haroune was built in the 1990s with a capacity of 960 Mm3, a height of 118 m where 1.9 Mm3 of RCC was used, and the other called Koudiat-Asserdoun was built in 2010 with a capacity of 640 Mm3, a height of 121 m (Gasti, 2009). Mix design of RCC is similar to that of NA concrete. However, it is usually necessary to optimize the sand/gravel ratio and to search for an optimized water content. Good mechanical strength could be obtained with RA concrete. Mixes with comparable density were obtained using RA as compared with NA but compressive strength was reduced by 14% 32% (Gasti, 2009). Similar decreases were obtained when using the same RA for ordinary concrete with 34% decrease in compressive strength and 17% in splitting tensile strength.

Recycled aggregates

109

Debieb et al. (2009) investigated the performance of RCC with contaminated and virgin aggregates. They reported that RCC containing only RA (NRCC) is comparable in compactness with the RCC containing only NA (RRCC) but compressive strength is lower. The loss in compressive strength, splitting tensile strength, and modulus of elasticity were 30%, 56%, and 30%, respectively. This decrease in mechanical properties is mainly related to the nature of RA. The flexural strength of RCC is known not to be sensitive to the variations of the w/c ratio but rather to the nature of the aggregates (Quellet, 1998). The effect of contamination on mechanical properties was negligible. The durability tests showed an acceptable behavior in time and hence its possible use in the roadways construction like subbase. Fig. 3.24 shows the variation of water absorption by capillary for different concrete mixes with virgin and contaminated concrete. The swelling of concrete in water and in sulfates solution (Na2SO4-5%) is shown in Figs. 3.25 and 3.26. After 1 year of conservation in water, no significant swelling was observed for all concrete mixes and hence the RA and even the Sorptivity 0.09 0.08 0.07 0.06 0.05 0.04 0.03 0.02 0.01 0.00 NAC

Sorptivity (kg/m2 h0.5)

Initial absorption (kg/m2)

Initial absorption 0.09 0.08 0.07 0.06 0.05 0.04 0.03 0.02 0.01 0.00

NRCC NRCC-V NRCC-Cl NRCC-Su NRCCSw

Type of concrete

Figure 3.24 Water absorption by capillary of concrete (Debieb et al., 2009). 100

Swelling (µm/m)

NAC

75

NRCC RRCC-V

50

RRCC-Cl RRCC-Su

25

RRCC-Sw

0 0

50

100

150

200

250

300

Time (days)

Figure 3.25 Swelling concrete in water (Debieb et al., 2009).

350

110

Waste and Supplementary Cementitious Materials in Concrete

Swelling (µm/m)

350 300

NAC

250

NRCC

200

RRCC-V

150

RRCC-Cl

100

RRCC-Su

50

RRCC-Sw

– 0

50

100

150

200

250

300

350

Time (days)

Figure 3.26 Swelling concrete in sulfates solution (Na2SO4-5%) (Debieb et al., 2009).

polluted RA do not influence much the swelling of RCC in water. It seems that the energetic compaction of the concrete gives a lower permeability which prevents the swelling (Debieb et al., 2009). However, the conservation in sulfates solution causes a higher swelling for all the concrete-type RRCC (on average two times) than that of the reference concrete NRCC. The energetic compaction of concrete does not prevent additional swelling due to sulfates. Exceptionally for RRCC-Sw the gain in masse can exceed four times; the substitution of the ions Na21 by the ions Mg21 due to the Na2SO4 solution gives rise to an additional swelling which is added to primary swelling due to the SW (secondary ettringite), which favored the swelling of this type of concrete (Debieb et al., 2009).

3.13

Applications and case studies

Concrete with RA has been used for a long time, but mainly in roadwork and nonstructural applications such as kerbs and concrete blocks. The use of RA in structural components is scarcely reported. FIB (2004) stated that the use of RA is less than 1% of the amount of aggregates used in structural concrete. However, in some countries, the use of RA is high. Around 17% of the United Kingdom aggregate needs are already met from recycled material (Mineral Product Association MPA, 2013). Some applications for the construction of rigid pavement have been reported in the United States. In 2009 RAs obtained from concrete removed at the site were field tested in a lane at the O’Hare modernization project and compared with another lane side-by-side where NAs were used. Similar performances (workability, strength, and shrinkage) were obtained as compared to virgin aggregates and after 5 months monitoring, no difference in behavior between the two lanes was observed (Federal Highway Administration FHA, 2004). Choi and Won (2009) substituted totally the fine and coarse NA by coarse and fine RA in a section of a highway in

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Houston. Although the compressive strength and the modulus of elasticity were lower, the highway section with RA presented an overall good performance after more than 10 years of service life. Michigan has constructed 26 projects with 650 lane miles of Portland cement concrete pavements using recycled concrete aggregate (Federal Highway Administration FHA, 2004). In California, most concrete pavement removed from existing highways and streets is processed and reused as aggregate base. The concrete runways and aprons of the Denver Stapleton Airport demolition and redevelopment were crushed into aggregates and used for the redevelopment and building of the former airport site (Federal Highway Administration FHA, 2004). Loosemore (1994) reported the reuse of waste concrete from the construction of the great belt link by crushing it and sold it to a local contractor for the upgrading of local access tracks and roads. The construction of the west bridge involved the production and placing of some 480,000 m3 of concrete with an estimated waste of 1% arising from over ordering or concrete rejected for noncompliance with the specifications. Lauritzen and Jannerup (1994) described the selective demolition of approximately 350 houses in the Copenhagen area and the reuse of concrete and brick rubble for construction of new dams for a planned land reclamation Copenhagen Harbor project. Olsen (1994) described the construction of a 21/2 storey two-wing block of flats where recycled crushed concrete and crushed tiles used as aggregates in concrete from neighboring demolition sites were used as well as used structural steel and timber elements, bricks, and roof slates. Schulz (1994) reported on the German experience of manufacture of concrete blocks containing 30% of RA, and the use of 45% of coarse RA recovered from the old pavement in the first layer of the renewal of 17 km section of the A27 highway in Northern Germany. De Pauw (1994) gave some examples of recycling after natural disasters. The first example is a pilot recycling plant to produce building blocks set up by the Belgian Building Research Institute with support of the Belgian government, after the Chlef earthquake, Algeria in October 1980. The estimated debris was 700,000 tons. The second example concerns the installation of a recycling plant for debris, in region of Leninakan in Armenia after the December 1988 earthquake. The installation had a capacity of 120 t/h and the recycled material was primarily used for roadwork. Coarse RA from an old concrete pavement was used in 1991 92 for the 21 cm-thick bottom layer of a concrete pavement of 45 km of carriageway on the motorway Salzburg-Vienna in Austria (Sommer, 1994). However, there are few projects where RA was used in new concrete for construction projects such as in Germany where more than 480 and 1200 m3 of concrete with RA were used in 1998 for the Vilbeler Weg office building and the Waldaspirale residential building at Darmstadt, respectively (Vyncke, 2000). Also over 1500 m3 of concrete with RA issued from the demolition of a 12-storey office building in London was used for ready mixed concrete for foundation, floor slabs,

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structural columns, and waffle floors in the British research establishment (BRE) office building at Watford, England in 1996 using either C25 or C35 concrete (Vyncke, 2000). In Netherland, approximately 11,000 m3 of concrete with 20% of coarse RA was used for all concrete parts of a viaduct near Meppel in 1990. In Norway, concrete with 35% of coarse RA was used for the foundation and for half of the basement walls and columns for a new school at Sorumsand, outside the city of Oslo (Vyncke, 2000). In Belgium, 200,000 tons of RA were used for the construction of the largest ship lock in the world at the Antwerp harbor, and ready mixed concrete with 100% of coarse RA was used for the concrete skeleton of a demonstration “RecyHouse” project (Vyncke and Vrijders, 2010). Lafarge (2014) has signed a contract in Qatar which suffers a huge shortage of NA to provide 1.1 MT of RA for the construction of a new refinery which is considered as the first use of RA in this country. Hassan et al. (2016) summarized the Qatari experience where the infrastructure needs for the 2022 world cup is important, and the country suffers from shortage of local NA which is mostly imported from neighboring countries. They built in 2013 a single-storey (2.5 2 2.5 m in plan) full trial buildings. RAs were used to replace 50% of an imported NA in structural (C40) concrete in one of the buildings and the other building was a control constructed with 100% NA. The two buildings were let unoccupied and exposed to the severe Arabian Gulf environment. The buildings were designed to have the concrete exposed to compressive stresses (columns), flexural (roof slabs), and bending (cantilever). The buildings did not show any sign of deterioration and are being monitored through testing cubes and cores at 1, 3, and 10 years. The 1 year results showed comparable strength performance of concrete with NA or 50% RA but the water absorption and water permeability are higher for RA concrete.

3.14

Conclusions

RAs are accepted by most of the international standards to reduce the consumption of NA and contribute for more sustainable construction industry. Most countries are setting target for the reuse of CDW. The RAs have low densities and great capacity of water absorption as compared with NA mainly because of the cement gangue of old mortar which remains attached to the NA after crushing of the original concrete. The use of RA reduces the workability of concrete and reduces compressive and tensile strengths as well as the modulus of elasticity. However, the decrease in strength and the durability performance could be compensated by the use of SCMs and/or the increase of cement content. A well-designed mix with RA could produce a comparable concrete to that with NA if the substitution level of fine RA is limited. RAs are used successfully in SCC and RCC. The effect of aggregates contamination was little investigated and further research is needed to study the durability of concrete made with contaminated aggregates. Other research needs include structural performance under high temperature and fire, fatigue, shear strength, punching shear, seismic loading, prestressed

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concrete and long-term properties, and performance under aggressive environment and/or hot climate. Further research is also needed to investigate the early age shrinkage and restrained shrinkage. The development of analytical models for the prediction of the performance of concrete with RA is needed for structural design purposes of reinforced concrete elements especially under dynamic and seismic loads. Design guidelines need to be established.

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Further reading DCA 34, 1990. Recommendation for the Use of Recycled Aggregates for Concrete in Passive Environmental Class. Hrsg.: Danish Concrete Association Publication No. 34, Copenhagen (in Danish). DCA 34, 1995. Addition to Danish Concrete Association No. 34 for the Use of Recycled Aggregates for Concrete in Passive Environmental Class. Hrsg.: Danish Concrete Association, Copenhagen (in Danish). McGinnis, M.J., Davis, M., De La Rosa, A., Weldon, B.D., Kurama, Y.C., 2017b. Quantified sustainability of recycled concrete aggregates. Mag. Concr. Res. 69 (23), 1203 1211. Silva, R., de Brito, J., Dhir, R., 2015a. Comparative analysis of existing prediction models on the creep behaviour of recycled aggregate concrete. Eng. Struct. 100, 31 42.