materials

Article The Effect of Fine and Coarse Recycled Aggregates on Fresh and Mechanical Properties of Self-Compacting

Mahmoud Nili 1,2,* , Hossein Sasanipour 1 and Farhad Aslani 3,4 1 Department of , Bu-Ali Sina University, Hamedan 65178-38695, Iran; [email protected] 2 School of Engineering, Hamedan University of Technology, Hamedan 65169-13733, Iran 3 Materials and Structures Innovation Group, School of Engineering, University of Western Australia, Perth, WA 6009, Australia; [email protected] 4 School of Engineering, Edith Cowan University, Perth, WA 6027, Australia * Correspondence: [email protected]

 Received: 21 March 2019; Accepted: 1 April 2019; Published: 4 April 2019 

Abstract: Today, the use of recycled aggregates as a substitute for a part of the natural aggregates in concrete production is increasing. This approach is essential because the resources for natural aggregates are decreasing in the world. In the present study, the effects of recycled concrete aggregates as a partial replacement for fine (by 50%) and coarse aggregates (by 100%) were examined in the self-compacting concrete mixtures which contain air-entraining agents and silica fumes. Two series of self-compacting concrete mixes have been prepared. In the first series, fine and coarse recycled mixtures respectively with 50% and 100% replacement with air entraining agent were used. In the second series, fine recycled (with 50% replacement) and coarse recycled (with 100% replacement) were used with . The rheological properties of the self-compacting concrete (SCC) were determined using slump-flow and J-ring tests. The tests of compressive strength, tensile strength, and compressive stress-strain behavior were performed on both series. The results indicated that air-entraining agent and silica fume have an important role in stabilization of fresh properties of the mixtures. The results of tests indicated a decrease in compressive strength, modulus of elasticity, and energy absorption of concrete mixtures containing air entrained agent. Also, the results showed that complete replacement (100%) with coarse recycled material had no significant effect on mechanical strength, while replacement with 50% fine recycled material has reduced compressive strength, tensile strength, and energy absorption.

Keywords: self-compacting concrete; recycled concrete aggregates; fresh properties; mechanical properties

1. Introduction Nowadays, it is well known that preparing natural aggregates for concrete production—due to carbon dioxide consumption—is a severe threat of environment and should be logically minimized. On the other hand, the construction and demolition waste (CDW) in countries is growing. In this regard, little more than half a billion tons of annual waste generated in Europe, this amounts to 325 million and 77 million tonnes for the US and Japan respectively. Considering that China and India are now producing and using over 50% of the world’s concrete, as development continues their CDW will be important too [1,2]. It was reported by UEPG (European Aggregates Association) that aggregates consumption for producing of concrete was 2.5 billion tonnes in 2013. Figure1 illustrates the tonnes of aggregates produced per capita by countries. As shown, Finland produced about 16 tonnes per capita which ranks as the top producer amongst EU countries [3].

Materials 2019, 12, 1120; doi:10.3390/ma12071120 www.mdpi.com/journal/materials MaterialsMaterials 20192019, 12, 12, x, FOR 1120 PEER REVIEW 2 of2 of14 14

20 18 16 14 12 10 (Ton) 8 6 4

Aggregates perproduced capita Aggregates 2 0

Figure 1. Aggregates production (tonnes) per capita by EU countries [3]. Figure 1. Aggregates production (tonnes) per capita by EU countries [3]. Despite restrictions for preparing of aggregates, demands for new like self-compacted concreteDespite (SCC), restrictions due to for advantages preparing of of manufacture aggregates, demands and high fo efficiencyr new concretes at the final like self stage,-compacted have been concreteexpanded (SCC), around due theto advantages world [4–6 of]. manufacture The main benefits and high of SCC efficiency come backat the to final the stage, fact that have it canbeen be expandedeasily poured around into the the world [4–6]. ofThe highly main reinforced benefits of structures SCC come without back to any the vibration. fact that Decreasingit can be easilyconstruction poured into time, the maximizing formwork theof highly freedom reinforced of design structures work, and without improvement any vibration. in quality Decreasing of product constructionand working time, environment maximizing are the some freedom other of advantages design work of, and this improvement feature. Nowadays, in quality contractors of product are andencouraged working environment to use industrial are by-productssome other andadvantages also CDW, of this like recycledfeature. Nowadays, concrete aggregate contractors (RCA), are as encourageda partial replacement to use industrial for aggregates by-products inconcrete and alsomixtures CDW, like [7 ,recycled8]. It is clear, concrete due toaggregate mortar adhering(RCA), as to a recycledpartial replacement aggregates, for that aggregates the fresh andin concrete hardened mixtures properties [7,8] of. It concrete is clear, madedue to with mortar these adhering aggregates to recycledwere negatively aggregates, affected. that the For fresh instance, and hardened the workability, properties density, of concrete as well as made compressive with these strength, aggregates tensile werestrength, negatively and modulus affected. of For elasticity instance, (MOE), the wereworkability, reduced density [9]. The, densityas well of as CDW, compressive due to the strength, presence tensileof lower strength, density and remaining modulus cementof elasticity mortar (MOE), particles were attached reduced to[9] the. The aggregate, density of was CDW, lower due than to the that presencof naturale of lower aggregate density [10]. remaining However, when the mortar adhered particles mortar attached contact to in the RCA aggregate, is less than was 44%, lower the thanrecycled that of aggregate natural aggregate can be used [10] in. However, structural when concrete theelements adhered [mortar9]. Adding contact CDW in RCA aggregate is less led than to a 44%,decrease the recycled of compressive aggregate strength can be byused 12 in and structural 25 %, when concrete 25–30% eleme [11nts,12 ][9] or. 100Adding % NA CDW was aggregate substituted ledby to CDW a decrease aggregate of compressive [13–15]. However, strength no by significant 12 and 25 effect %, w washen seen 25– when30% [11,12] the coarse or 100 or % fine NA recycled was substitutedaggregate by was CDW applied aggregate to substitute [13–15] up. However, to 30 % of no coarse significant NA [16 effect–20] or was 20 %seen of finewhen NA the [21 coarse]. or fine recycledIt was alsoaggregate reported was that applied the slump to substitute of recycled up toaggregate 30 % of coarse concrete NA [16 (RAC),–20] or due 20 to % higher of fine waterNA [21]absorption,. angularity, and rough texture of CDW, was lower than that of conventional ones [22,23]. ForIt this was reason also reported of prevention that ofthe reducing slump of of recycled workability aggregate in RAC, concrete use of recycled (RAC), aggregates due to higher in saturation water absorption,surface drying angularity or spraying, and rough on recycled texture aggregates of CDW, was bysprinkler lower than system that of is conventional recommended one [12s ,[22,23]20,24,25. ]. ForCorinaldesi this reason and of Moriconi prevention (2011), of studiedreducing the of effect workability of both finein RAC, and coarse use of RCA recycled and also aggregates some mineral in saturationadditives surface on SCC dry properties.ing or spraying They showed on recycled that rubble aggregates powder by madesprinkler better system concrete is recommended flowability and [12,20,24,25]flow-segregation. Corinaldesi resistance and in Moriconi comparison (2011) with, studie fly ashd the and effect limestone of both powder fine and [26]. coarse RCA and also someContradictory mineral additive results weres on reportedSCC properties. for hardened They properties showed ofthat recycled rubble aggregate powder concrete.made better Some concreteresearchers flowability showed and that flow the- compressivesegregation resistance strength of in concrete comparison was increasedwith fly asash RCA and waslimestone used as powderreplacement [26]. for normal aggregates. These improvements were attributed to the rough texture in recycledContradictory aggregates results which were provided reported better for bonding hardened and properties interlocking of recycled between aggregate the cement concrete. paste and Somethe recycledresearchers aggregates showed [ 12that]. the compressive strength of concrete was increased as RCA was used as replacementHowever, for recycled normal concreteaggregates. aggregates These improvement may adverselys were impact attributed the mechanical to the rough properties texture in of recycledrecycled aggregates aggregate which concrete. provid Ited is better evident bonding that theand reduction interlocking of between compressive the cement strength paste of RACsand thecompensates recycled aggregates by adjusting [12]. the water to cement ratio, changing the procedure of mixing, treating theHowever, aggregate, r andecycled using concrete a mineral aggregates addition may [22]. Onadversely the other impact hand, the the mechanical result of different properties research of recycleddeclared aggregate that the substitution concrete. It ratio is evident of natural that aggregate the reduction by CDW of aggregate compressive had no strength negative of impact RACs on compensates by adjusting the water to cement ratio, changing the procedure of mixing, treating the

Materials 2019, 12, 1120 3 of 14 the splitting tensile strength compared to that for compressive strength [27], which may be due to the high bond strength between RCA and cement paste [28]. Modulus of elasticity of recycled aggregate concrete (RAC) specimens usually is less than that of conventional concrete, and it declines as the content of CDW aggregate in concrete grows. The causes for the decline in concrete’s MOE were due to the loss of concrete stiffness and porosity and also aggregate-cement paste bonding [22]. Most authors declared that RCA had a more negative impact on MOE than those for compressive strength [29,30]. The trend of curves of stress-strain are similar for both recycled and conventional concretes, however, a slight shift—due to differences MOE and ultimate strain—was observed in recycled ones. The shift is significant when the substitution rate is high. The longitudinal strain of the recycled concretes goes up with the percentage of recycled coarse aggregate used [30]. However, there are two main methods to enhance the properties of recycled concrete aggregates in order to improve concrete properties; 1) removing the adhered mortar, and 2) strengthening the adhered mortar. Several methods are used for removing the adhered mortar on RCAs, including physical and chemical treatment. Mechanical grinding, pre-soaking in water, and pre-soaking in acid are the common methods for removing the adhered mortar [31]. Improving the adhered mortar is another way to enhance the quality of RCAs. In this method by coating mineral admixtures on RCAs, such as silica fume, the interface transition zone can improve [32]. The high level of fineness and practically spherical shape of silica fume results in good cohesion and improved resistance to segregation. It is also very effective in reducing or eliminating bleed and this can give rise to problems of rapid surface crusting. This can result in cold joints or surface defects if there are any breaks in concrete delivery and also present difficulty in finishing the top surface (Cited by EFNARC) [33]. Additionally, it is well understood that silica fume, due to high pozzolanic activity, is an inevitable component when producing high strength concrete; silica fume effectively improves the structure of the transition zone, eliminates the weakness of the interfacial zone, reduces the number and size of cracks (cited by Nili et al.) [34]. Grdic et al. (2010) used high-quality rubble RCA by 0%, 50%, and 100% replacement for natural coarse aggregate in SCC mixtures. The results showed a minor loss in strength. When RFA was applied to substitute sand, the compressive strength was negatively influenced [35]. Fakitsas et al. (2012), surveyed the influence of internal curing applying saturated RA in SCC. All aggregates were plunged in water for three days and then surface dried for 12 hours before being used in the concrete mixture. The results declared that RA in SCC had shown to have a higher compressive strength compared to NA in SCC at ages of 28 and 90 days. This increase is attributed to internal curing of concrete by saturated RCA and therefore, utilization of saturated RCA may compensate for some of its other defects with strength development [36].

2. Research Significance The experimental study as outlined in this paper aims to promote the use of sustainable forms of structural self-compacting concrete incorporating recycled concrete aggregates and develop information on its fresh and hardened mechanical properties of SCC. In this study, the effect of recycled aggregates in addition to air-entrained admixture and silica fume on the properties of self-compacting concrete have been investigated. The aim is to reduce waste, reduce natural aggregate consumption in the concrete industry, and promote the widespread use of self-compacting concrete.

3. Experimental Design and Materials

3.1. Materials and Mix Proportions Ordinary (ASTM Type 1), and silica fume were used in this work. The physical properties of both natural and recycled aggregates are given in Table1. Limestone powder was also used to modify the viscosity of the SCC mixtures. The specific gravity of the limestone powder was Materials 2019, 12, 1120 4 of 14

Materials 2019, 12, x FOR PEER REVIEW 4 of 14 2.7. The amount of adhered mortar in RCA was measured using the methodology given by [9] and the usedpercentage to modify of adheredthe viscosity mortar of the was SCC calculated mixtures. using The Equation specific (1).gravity This of method the limestone consists powder of soaking was in 2.7.water Theand amount heating of adhered of the aggregate. mortar in RCA was measured using the methodology given by [9] and the percentage of adhered mortar was calculated using Equation (1). This method consists of soaking mi − m f in water and heating of the aggregate. M (%) = × 100 (1) c mi 푚푖−푚푓 Mc (%) = × 100 (1) 푚푖 where Mc (%) is the amount of adhered mortar in RCA, mi is the total mass of the RCA sample; mf is wthehere mass Mc (%) of theis the same amount NCA of (natural adhered coarse mortar aggregates) in RCA, 푚 sample.푖 is the total mass of the RCA sample; mf is the mass of the same NCA (natural coarse aggregates) sample. Table 1. Physical properties of NA and RCA. Table 1. Physical properties of NA and RCA Los Specific Water Adhered Specific Maximum Fineness Water Los AngelesAngeles Adhered Type of Aggregate GravityMaximum Fineness Absorption Mortar Type of Aggregate Gravity 3 Size (mm) Modulus Absorption AbrasionAbrasion Mortar (g/cm S) ize (mm) Modulus (%) (%) (g/cm3) (%) (%)(%) (%) NaturalNatural 2.66 2.6619 19- -1.21 1.2113.9 13.9 - - CoarseCoarse RCA RCA 2.52 2.5219 19- -5.04 5.0435.9 35.9 32.15 32.15 NaturalNatural 2.53 2.53- -3.79 3.793.70 3.70- -- - FineFine RCA RCA 2.46 2.46- -3.76 3.767.76 7.76- -- -

AsAs given given in in Table Table 1,1 ,the the water water absorption absorption of of coarse coarse and and fine fine recycled recycled aggregates aggregates is is 316% 316% and and 109%109% more more than than that that for for natural natural ones, ones, respectively. respectively. Furthermore, Furthermore, the the abrasion abrasion resistance resistance of of recycled recycled aggregateaggregate is is 164% 164% lower thanthan the the natural natural coarse coarse aggregate. aggregate. These These results, results, which which are due are to due the adheredto the adheredmortar, mortar, are in agreementare in agreement for the for results the results obtained obtained by other by other researchers researchers [37,38 [37,38], and], areand most are most likely likelyto conform to conform to EN1097-6, to EN1097 reporting-6, reporting the physicalthe physical properties properties of natural of natural and and recycled recycled aggregates aggregates [39 ]. [39]The. The gradations gradation ofs coarse of coarse and and fine fine aggregate aggregate and and limestone limestone powder powder are shownare shown in Figure in Figure2. 2.

100 90 Limestone powder 80 fine natural aggregate 70 fine recycled aggregate 60 50 coarse natural aggregate 40 coarse recycled aggregate 30

20 Passing Passing the sieve % 10 0 0.01 0.1 1 10 100 Sieve opening (mm)

Figure 2. Gradations of coarse and fine aggregate and limestone powder. Figure 2. Gradations of coarse and fine aggregate and limestone powder. Two types of superplasticizer agent with the commercial name of WBK50 and WRM (LG) were combinedTwo types and of used superplasticizer to adjust the workabilityagent with the of thecommercial self-compacting name of concretes. WBK50 and A rangeWRM of (LG) values were for combinedan adequate and slumpused to flow adjust is 550–850 the workability mm [33]. of the self-compacting concretes. A range of values for an adequate slump flow is 550–850 mm [33]. 3.2. Mix Properties and Procedure

3.2. MixIn P thisroperties research, and Procedure two series of SCC mixtures with water-(cement + Sf) ratios of 0.44 and cementitious material contents of 418 kg/m3 were prepared and labeled as I and II, respectively. In this research, two series of SCC mixtures with water-(cement + Sf) ratios of 0.44 and Table2 shows the mix proportions of the mixtures. As given, the fine and coarse recycled aggregate cementitious material contents of 418 kg/m3 were prepared and labeled as I and II, respectively. was used as 50 and 100% by volume replacements of natural aggregate, respectively. In Series I, the air Table 2 shows the mix proportions of the mixtures. As given, the fine and coarse recycled aggregate entraining agent (AEA), (0.03% by weight of cement) was used in concrete mixtures prepared with was used as 50 and 100% by volume replacements of natural aggregate, respectively. In Series I, the recycled aggregates. In Series II, silica fume was also added as a cement replacement (8% by weight). air entraining agent (AEA), (0.03% by weight of cement) was used in concrete mixtures prepared with recycled aggregates. In Series II, silica fume was also added as a cement replacement (8% by weight). Totally, eight mixtures were considered containing reference samples (S and SS). The

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Totally, eight mixtures were considered containing reference samples (S and SS). The specimens with 100% (by volume) coarse RCA replacement were labeled as S100C and SS100C in Series I and II, respectively. The other concretes in both series, which were labeled as S50f and SS50f, contained 50% (by volume) fine RCA as a partial replacement. The concretes which were produced with both fine and coarse RCAs were known S100C50f and SS100C50f. The mixing procedure was designed by trial and error as follows: the cement, limestone powder, fine aggregate, and half of the mixing water were mixed initially for 1 min, and then the remaining mixing water was mixed up with superplasticizer, and a little of it was added to the mixture, stirred for 3 min. Finally, the coarse aggregate and the rest of the water- superplasticizer were added and mixed for 3 min. It is noted that, in concrete mixture 1 Series I, AEA was added at the last step. In Series II, silica fume and 3 mixing water was mixed and then added to concrete mixtures. The fine and coarse recycled aggregates were pre-soaked for 24 h before being used in the mixtures. Pre-soaking is considered an effective way to separate impurities and obtain higher quality RCA [31].

Table 2. Mix proportions of the concrete.

SP Mix W/(C W Cement Sf FNA. CNA. FRA. CRA LP AEA Series (%) Code + Sf) (%) (kg/m3) S - 1172 335 - - 167 0.8 - S100C - 1160 - - 331 166 0.9 0.03 I 0.44 184 418 S50f - 580 332 580 - 166 0.9 0.03 S100C50f - 574 - 574 328 164 0.9 0.03 SS 33 1172 335 - - 167 0.9 - SS100C 33 1160 - - 331 166 1.0 - II 0.44 184 385 SS50f 33 580 332 580 - 166 1.1 - SS100C50f 33 574 - 574 328 164 1.2 - Sf: silica fume, FNA: fine natural aggregates, CNA: coarse natural aggregates. FRA: fine recycled aggregates, CRA: coarse recycled aggregates, LP: limestone powder. SP: superplasticizer, AEA: air-entraining agent.

3.3. Test Program and Procedures

3.3.1. Slump Flow and J-Ring The tests of slump flow and J-ring were carried out on the self-compacting concrete specimens according to EFNARK standard.

3.3.2. Compressive and Splitting Tensile Strength Testes The splitting tensile strength test was performed at 28 days on 100 × 200 mm2 cylindrical specimens. Cubic specimens of 100 mm were used for determination of compressive strength test which was performed at ages of 7, 28, and 91 days.

3.3.3. The Stress-strain Relationship Compressive strength stress-strain tests were performed at the age of 28 days on 100 × 200-mm cylindrical specimens. For this purpose, three capped samples were used in order to use their mean to plot stress-strain curves. Figure3 shows the setup instruments for stress-strain measuring: compression machine of ADR 2000 KN (ELE Company, England, UK), strain gauge, and data logger. Materials 2019, 12, 1120 6 of 14 Materials 2019, 12, x FOR PEER REVIEW 6 of 14

Figure 3. Compressive strength stress-strainstress-strain tests apparatus.

4. TestThe Results stress-strain and Discussion of the capped cylinder samples, at the age of 28 days, was measured via the system arranged in Figure3. The stress-strain curve of every mixture was the average of three This section presented the experimental results obtained in the laboratory and discussion for tested samples. properties of eight concrete mixtures. 4. Test Results and Discussion 4.1. Fresh Concrete Results This section presented the experimental results obtained in the laboratory and discussion for propertiesSeveral of trial eight and concrete error mixtures.efforts were made for preparing the convenient SCC mixtures. It was found that to avoid bleeding and segregation in concrete mixtures prepared with recycled 4.1.aggregates, Fresh Concrete AEA and Results silica fume must be used (Figure 4a–c). This important finding is surely an effective guidance contractors to prepare SCC mixtures made by fine and coarse RCAs. Several trial and error efforts were made for preparing the convenient SCC mixtures. It was found The results of the slump flow and J-ring tests are given in Table 3. The results indicate that use that to avoid bleeding and segregation in concrete mixtures prepared with recycled aggregates, AEA of the recycled aggregates in series I have reduced the slump flow. It is shown that replacing 100% and silica fume must be used (Figure4a–c). This important finding is surely an effective guidance of coarse and 50% of fine recycled aggregates with normal ones, S100C and S50f, led to 20 mm Materialscontractors 2019, 12 to, preparex FOR PEER SCC REVIEW mixtures made by fine and coarse RCAs. 7 of 14 reduction of slump flow compared to the reference sample S. Simultaneous use of recycled fine and coarse aggregate in the S100C50f has reduced the slump flow by 50 mm. However, the higher amount of superplasticizer in Series II compensated the reduction of slump flow of the coarse recycled concretes. The replacement of 50% fine aggregate in the SS50f suggests that fine RCA also has reduced slump flow. Increasing the superplasticizer content in the SS100S50f led to an increase of the slump flow without segregation. As given, the flow of all mixtures in both series satisfied the limits of EFNARC standard [33]. Figures 5a,b show the spread view of the mixtures after the slump flow test. As shown, no segregation and bleeding has occurred in the concrete mixtures. Figure 4. Concrete mixtures prepared with recycled aggregates: (a) concrete mixture without AEA and Figure 4. Concrete mixtures preparedTable with3. Fresh recycled properties aggregates: test results (a) concrete mixture without AEA Sf; (b) concrete mixture with AEA; and (c) concrete mixture with Sf. and Sf; (b) concrete mixture with AEA; and (c) concrete mixture with Sf. Slump T J-ring Whether Conforms SP T50 J-ring MixThe Code results Series of the slump flowFlow and J-ring testsfinal are given in TableHeight3. TheDifference results indicateto EFNARC that use [33] of The results of the J(%)-ring test showed (s )that, due to the(mm) presence of in this test, the measured the recycled aggregates in series (mm) I have reduced (s) the slump flow. It is(mm) shown that replacingGuidelines 100%? of diametercoarse S and had 50% been of fine decreased recycled0.8 765compared aggregates 3 to with the 31 normal slump 720 ones, flow S100C test in and all9 S50f, mixture led to (Fig 20 mmure Yes6 reductiona,b) [1]. Accordingof slumpS100C flowto the compared results 0.9 of to Tablethe 745 reference3, the 3height sample 32differences S. Simultaneous725 in the J-ring use 2 test of recycledfor all mixtures fine andYes are coarse less I thanaggregate S50f 10 mm. in It the is also S100C50f shown 0.9 has that 745 reduced there w2 theas no slump 33segr flowegation 650 by and 50 mm. bleeding However, 5 in any the of higherthe mixtures amountYes that of weresuperplasticizer S100C50f tested by the in J Series-ring 0.9 test II compensated ( Figure715 7). 4 the reduction 55 670 of slump flow of 8 the coarse recycled Yes concretes. The replacementSS of 50% 0.9 fine aggregate 680 2 in the SS50f19 suggests 630 that fine 5 RCA also has reduced Yes slump SS100C 1 685 2 23 570 3 Yes flow. Increasing II the superplasticizer content in the SS100S50f led to an increase of the slump flow without SS50f segregation. As 1.1 given, 665 the flow 3 of all mixtures25 580 in both seriessatisfied 5 the limits of Yes EFNARC SS100C50f 1.2 750 2 37 700 2 Yes standard [33]. Figure5a,b show the spread view of the mixtures after the slump flow test. As shown, no segregation and bleeding has occurred in the concrete mixtures.

(a)

(b) Figure 5. Slump flow tests (a) concrete mixtures series I, and (b) concrete mixtures series II.

Materials 2019, 12, x FOR PEER REVIEW 7 of 14

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Table 3. Fresh properties test results.

J-ring Slump Whether Conforms Mix T Final J-ring Height Series Sp (%) Flow T50 (s) to EFNARC [33] Code (s) (mm) Difference (mm) Guidelines? Figure 4. Concrete mixtures prepared with recycled aggregates: (a) concrete(mm) mixture without AEA andS Sf; (b) concrete mixture0.8 with 765 AEA; and 3 (c) concrete 31 mixture 720 with Sf. 9 Yes S100C 0.9 745 3 32 725 2 Yes I S50f 0.9 745 2 33 650 5 Yes S100C50fThe results of the J 0.9-ring test 715 showed that 4, due to 55 the presence 670 of rebar 8 in this test, Yesthe measured diameterSS had been decreased0.9 compared 680 to 2 the slump 19 flow 630test in all 5mixture (Fig Yesure 6a,b) [1]. AccordingSS100C to the results 1 of Table 685 3, the height 2 differences 23 in the 570 J-ring test 3 for all mixtures Yes are less II than 10SS50f mm. It is also shown 1.1 that 665 there was 3 no segregation 25 and 580 bleeding 5in any of the Yesmixtures that SS100C50f 1.2 750 2 37 700 2 Yes were tested by the J-ring test (Figure 7).

(a)

(b) Figure 5. Slump flow tests (a) concrete mixtures series I, and (b) concrete mixtures series II. Figure 5. Slump flow tests (a) concrete mixtures series I, and (b) concrete mixtures series II.

The results of the J-ring test showed that, due to the presence of rebar in this test, the measured diameter had been decreased compared to the slump flow test in all mixture (Figure6a,b) [ 1]. According Materials 2019, 12, 1120 8 of 14

Materials 2019, 12, x FOR PEER REVIEW 8 of 14 Materialsto the results2019, 12, of x FOR Table PEER3, the REVIEW height differences in the J-ring test for all mixtures are less than 10 mm.8 of 14 It is also shown that there was no segregation and bleeding in any of the mixtures that were tested by the J-ring test (Figure7). Slump Flow J-ring Slump Flow J-ring 800 800 Slump Flow J-ring Slump Flow J-ring 800 800 750 750 750 750 700 700 700 700 650 650 650 650

600 600

Diameter Diameter (mm) Diameter Diameter (mm)

600 600 Diameter Diameter (mm) 550 Diameter (mm) 550 550 S S100C S50f S100C50f 550 SS SS100C SS50f SS100C50f Mix S S100C MixS50f S100C50f SS SS100C SS50f SS100C50f Mix(a) Mix(b) (a) (b) Figure 6. Slump test flow diameter and J-ring flow diameters (a) series I, and (b) concrete mixtures Figure 6. Slump test flow diameter and J-ring flow diameters (a) series I, and (b) concrete mixtures series II. Figureseries II.6. Slump test flow diameter and J-ring flow diameters (a) series I, and (b) concrete mixtures series II.

(a) (b) (a) (b) Figure 7. JJ-ring-ring test test ( (a) concrete mixtures series I, and (b) concrete mixtures seriesseries IIII respectively.respectively. Figure 7. J-ring test (a) concrete mixtures series I, and (b) concrete mixtures series II respectively. 4.2. Properties of Hardened Concrete 4.2. Properties of Hardened Concrete 4.2.1. Compressive Strength 4.2.1. Compressive Strength 4.2.1. TheCompressive results of Strength compressive and tensile strength are shown in Table4. As given the compressive The results of compressive and tensile strength are shown in Table 4. As given the compressive strength of S100C, due to the replacement of 100% coarse RCA, diminished by 38.5%, 30.7%, and 25.2% strengthThe result of S100C,s of compressive due to the replacementand tensile strength of 100% are coarse shown RCA, in T diminishedable 4. As given by 38.5%, the compressive 30.7%, and compared to reference sample S, respectively, at the age of 7, 28, and 91. Moreover, the replacement of strength25.2% compared of S100C, todue reference to the replacement sample S, respectively, of 100% coarse at theRCA, age diminished of 7, 28, andby 38.5%,91. Moreover, 30.7%, and the 50% of fine RCA in S50f has reduced compressive strength by 27.1%, 24%, and 30.6% at the age of 7, 25.2%replacement compared of 50% to referenceof fine RCA sample in S50f S, has respectively, reduced compressive at the age strengthof 7, 28, by and 27.1%, 91. 24%Moreover,, and 30.6% the 28, and 91 days, respectively. The results indicate that the simultaneous use of fine and coarse RCA replacementat the age of of 7, 50% 28, ofand fine 91 RCAdays, in respectively. S50f has reduced The results compressive indicate strength that the by simultaneous 27.1%, 24%, anduse 30.6%of fine in S100C50f led to a reduction of compressive strength by 22.7% at the age of 91 days (Figure8a). It atand the coarse age of RCA7, 28 ,in and S100C50f 91 days, led respectively. to a reduction The ofresults compressive indicate strengththat the bysimultaneous 22.7% at the use age of offine 91 is noteworthy that air entraining agent is normally responsible for compressive strength reduction; anddays coarse (Figure RCA 8a). in It S100C50fis noteworthy led to that a re airduction entraining of compressive agent is normally strength responsible by 22.7% at for the compressive age of 91 however, the rule of this admixture on strength of recycled aggregate concrete is not so clear. Similar daysstrength (Figure reduction 8a). It ;is however noteworthy, the rulethat ofair this entraining admixture agent on isstrength normally of recycled responsible aggregate for compressive concrete is results were obtained by other researchers. They found that the main reasons for strength reduction strengthnot so clear. reduction Similar; however results were, the ruleobtained of this by admixture other researchers on strength. They of foundrecycled that aggregate the main concret reasonse foris were attributed to the higher porosity of recycled aggregate and the weak aggregate-matrix interface notstrength so clear. reduction Similar results were wereattributed obtained to theby otherhigher researchers porosity . ofThey recycled found thataggregate the main and reason the weaks for bond between recycled aggregate and mortar [40]. On the contrary, in series II, the compressive strengthaggregate reduction-matrix interface were attributed bond between to the recycledhigher porosityaggregate of and recycled mortar aggregate [40]. On theand contrary, the weak in strength of SS100C increased by 6.5%, 14%, and 28%, compared to SS sample at the ages of 7, 28, and 91 aggregateseries II, -thematrix compressive interface bondstrength between of SS100C recycled increased aggreg ateby 6.5%,and mortar 14%, and[40] .28%, On thecompared contrary, to inSS days, respectively. This result revealed the advantage effect of silica fume when used as a replacement seriessample II, atthe the compressive ages of 7, 28, strength and 91 of days, SS100C respectively. increased This by 6.5%,result 14%,revealed and the28%, advantage compared effect to SS of for cement. The other researchers also showed that utilization of mineral admixtures—like fly ash, samplesilica fumeat the when ages ofuse 7,d 28, as anda replacement 91 days, respectively. for cement. This The result other revealed researchers the advantage also showed effect that of silica fume, and ground granulated blast furnace slag—in the mix proportions led to an increase of silicautilization fume ofwhen mineral use dadmixtures as a replacement—like fly forash, cement. silica fume The, otherand ground researchers granulated also showedblast furnace that utilizationslag—in the of mineralmix proportions admixtures led— tolike an flyincrease ash, silica of compressive fume, and groundstrength granulated [41–43]. The blast resul furnacets also slagshowed—in thethat mix the proportions compressive led strength to an increase of SS50f of mixture compressive at the strength ages of [41 7, –28,43] .and The 91resul daysts alsowas showed that the compressive strength of SS50f mixture at the ages of 7, 28, and 91 days was

Materials 2019, 12, 1120 9 of 14 Materials 2019, 12, x FOR PEER REVIEW 9 of 14 decreasedcompressive by strength 31.6%, [4129.9%,–43]. Theand results22.1%, also respectively. showed that The the result compressive declared strength that the of SS50fcompressive mixture strengthat the ages of of SS100C50f, 7, 28, and 91which days wascontained decreased simultaneously by 31.6%, 29.9%, coarse and an 22.1%,d fine respectively. recycled aggregates, The result reduceddeclared about that the 26.6% compressive at the age strength of 91 days of SS100C50f, (Figure 8b). which contained simultaneously coarse and fine recycled aggregates, reduced about 26.6% at the age of 91 days (Figure8b). Table 4. Mechanical properties of self-compacting concrete Table 4. Mechanical properties of self-compacting concrete. Compressive Strength Splitting Tensile Strength Mix Code Series Compressive Strength (MPa) (MPa) Splitting Tensile(MPa) Strength (MPa) Mix Code Series 7 Days7days 28 Days28 days 91 Days 91 days 28 28 Days days S 38.7 46.3 50.7 3.4 S 38.7 46.3 50.7 3.4 23.8 S100C S100C 23.8 32.1 32.1 37.9 37.9 3.4 3.4 I I S50f S50f 28.228.2 35.2 35.2 35.2 35.2 3.2 3.2 S100C50f S100C50f 33.633.6 38.2 38.2 39.2 39.2 3.4 3.4 SS 33.8 46.4 47 4.3 SS 33.8 46.4 47 4.3 SS100C SS100C 3636 52.9 52.9 48.3 48.3 4.1 4.1 II II SS50f SS50f 23.123.1 32.5 32.5 36.6 36.6 2.9 2.9 SS100C50f SS100C50f 26.326.3 31.8 31.8 34.5 34.5 3.1 3.1

60 60 7 days 7 days 50 28 days 50 28 days 40 91 days 40 91 days

30 30

20 20

10 10

Compressive strength [MPa]Compressive Compressive strength [MPa]Compressive

0 0 S S100C S50f S100C50f SS SS100C SS50f SS100C50f Mix Mix (a) (b)

Figure 8. CompressiveCompressive strength results at 7 7,, 28 28,, and 91 days of ( a) Series I and (b) Series II.II. 4.2.2. Splitting Tensile Strength 4.2.2. Splitting Tensile Strength The results of the tensile strength test at the age of 28 days are illustrated in Figure9. As shown The results of the tensile strength test at the age of 28 days are illustrated in Figure 9. As shown the use of recycled aggregates had no significant effect on tensile strength in Series I. Replacing 50% of the use of recycled aggregates had no significant effect on tensile strength in Series I. Replacing 50% the fine RCA in the S50f has led to a slight reduction of 7%. In Series II with a 100% replacement of of the fine RCA in the S50f has led to a slight reduction of 7%. In Series II with a 100% replacement coarse RCA in SS100C, the tensile strength was reduced by 5.2%. In some studies, it is reported that of coarse RCA in SS100C, the tensile strength was reduced by 5.2%. In some studies, it is reported due to improvement in ITZ (interface transition zone) the recycled aggregates can affect a negligible that due to improvement in ITZ (interface transition zone) the recycled aggregates can affect a reduction in tensile strength [44,45]. However, the tensile strength of SS50f and SS100C50f specimens negligible reduction in tensile strength [44,45]. However, the tensile strength of SS50f and decreased by 31% and 27.2%, respectively. As shown, the air entrained agent had no negative impact SS100C50f specimens decreased by 31% and 27.2%, respectively. As shown, the air entrained agent on the tensile strength of the mixtures. This is an important issue which more study is necessary for had no negative impact on the tensile strength of the mixtures. This is an important issue which fully understanding the reasons. more study is necessary for fully understanding the reasons.

Materials 2019, 12, x FOR PEER REVIEW 10 of 14

Materials 2019, 12, 1120 5 10 of 14 Materials 2019, 12, x FOR PEER REVIEW Series 1 10 of 14 4 Series 2 5 3 Series 1 4 Series 2 2 3 1 2 Splitting tensilestrength[MPa] Splitting 0 0 100C 50f 100C50f 1 Type and percent of RCA

Splitting tensilestrength[MPa] Splitting 0 0 100C 50f 100C50f Figure 9. Tensile strength results at 28 days. Type and percent of RCA

4.2.3. Compressive Stress-strainFigure Behav 9. Tensileior strength results at 28 days. Figure 9. Tensile strength results at 28 days. 4.2.3.The Compressive stress-strain Stress-strain test results Behavior at 28 days are given in Table 5. Some properties, including the proportional4.2.3. Compressive strain test Stress (peer),-strain the maximumBehavior stress and the final strain, the energy absorbed in the ′ ′ intervalsThe stress-strainεc: (0 − εc) and test resultsεc: (0 − atεu) 28 and days the are MOE given are in also Table given5. Some in Table properties, 5. The results including showed the proportionalthat in allThe recycled strainstress- teststrain concrete (peer), test resultsmixtures, the maximum at 28with days stressthe are replacement and given the in final Table of strain, recycled 5. Some the energyaggregates, properties absorbed , theincluding energy in the the proportionalε ( − strainε0 ) testε (peer),( − ε 0the′ ) maximum stress and the final strain, the energy absorbed in the intervalsabsorptionc :in0 the intervalc and cεc:: (00 − εuc) andhas thedecreased MOE are compared also given to inthe Table reference5. The samples results showed (Figure that10a). ε : (0 − ε′ )′ ε : (0 − ε′ ) inIn all theintervals recycled interval concretec εc: (0 −c mixtures,ε uand), the cenergy withthe absorptionu replacementand the decreasedMOE of are recycled byalso replacing given aggregates, in recycled Table the 5. energy aggregates The results absorption except showed 0 infor the thatS100C interval in ( Figureall εrecycledc : 10(0b).− εconcretec) has decreased mixtures, compared with the toreplacement the reference of samplesrecycled (Figureaggregates, 10a). the In theenergy 0 ′ intervalabsorptionεc : (0 −in εtheu), interval the energy εc: ( absorption0 − εc) has decreased decreased bycompared replacing to recycledthe reference aggregates samples except (Figure for 10a). ′ S100CIn (Figurethe interval 10b). εc: (0 − εTableu), the 5. energyCompressive absorption stress- straindecreased curve bytest replacing results recycled aggregates except for S100C (Figure 10b). −4 ′ Energy absorption× 10 ′ Energy Absorption × Modulus of × 훆퐜 Table 5. Compressive stress-strain× 훆퐮 curve test results. 3 −4 3 Mix Code Series −3 (MJ/m ) −3 10 (MJ/m ) Elasticity 10 Table 5. Compressive′ stress 10-strain curve test results′ Energy훆퐜: (ퟎ Absorption− 훆퐜) Energy훆퐜: (ퟎ − Absorption훆퐮) Modulus(GPa) of Mix 0 −3 −4 3 0 −3 −4 3 Series εc × 10 × 10 (MJ/m ) −ε4 u× 10 × 10 (MJ/m ) Elasticity CodeS 2.18 ′ Energy713 absorption 0 × 10 2.61 ′ Energy924 Absorption 0 × Modulus38.8 of × 훆퐜 εc:(0−ε ) × 훆퐮 εc:(0−ε ) (GPa) S100C 2.33 591 c 3 4.17 1210−4 u 3 33.3 Mix Code Series −3 (MJ/m ) −3 10 (MJ/m ) Elasticity S I 2.18 10 713′ 2.61 10 924′ 38.8 S50f 1.69 292훆퐜: ( ퟎ − 훆퐜) 2.33 훆446퐜: ( ퟎ − 훆퐮) 30.3(GPa) S100C 2.33 591 4.17 1210 33.3 I S100C50fS50fS 2 1.69 2.18 540 292 713 3 2.33 2.61 865 446 924 30.334.938.8 S100C50fSSS100C 2.1822.33 62 5406 591 3.34 34.17 1120 8651210 34.932.333.3 I SS100CS50f 2.231.69 615 292 3.092.33 928 446 29.130.3 SS II 2.18 626 3.34 1120 32.3 SS50fSS100CS100C50f 1.68 2.23 2 362 615 540 2.77 3.09 3 671 928 865 29.139.834.9 II SS100C50fSS50fSS 2.17 1.682.18 396 362 626 2.48 2.773.34 485 6711120 39.821.432.3 SS100C50f 2.17 396 2.48 485 21.4 SS100C 2.23 615 3.09 928 29.1 II SS50f 1.68 362 2.77 671 39.8 Energy absorption - series1 SS100C50f Energy absorption 2.17 - series1 396 2.48 485 21.4 1400 Energy absorption - series2 1400 Energy absorption - series2

)

) 3 3 1200 1200 Energy absorption - series1 Energy absorption - series1 1000 1000

1400 Energy absorption - series2 1400 Energy absorption - series2

)

4

)

4

-

3 - 3 800 800

1200 1200

10

10 × × 600 600 1000 1000

400 400

4

4 -

- 800 800 10

20010 200

×

Energy absorption(Mj/mEnergy × Energy absorption(Mj/mEnergy 600 600 0 0 400 400 0 100C 50f 100C50f 0 100C 50f 100C50f

200 Type and percent of RCA 200 Type and percent of RCA Energy absorption(Mj/mEnergy Energy absorption(Mj/mEnergy (a) (b) 0 0 Figure0 10. Energy100C absorption50f in100C50f the intervals, (aε) ε (: (0−−εε0 )′ ), and0 (b)ε ε :100C((0−−εε0′ )). 50f 100C50f Figure 10. EnergyType and absorption percent of inRCA the intervals, (a) c :c 0 cc, and (b)Typec c: and0 percentuu . of RCA (a) (b) In Figure 11a, the stress-strain relationships of Series I specimens are shown. By replacing recycled ′ ′ aggregates, the modulusFigure 10. of Energy elasticity absorption (MOE) in has the decreased intervals, (a compared) εc: (0 − εc to), and the ( referenceb) εc: (0 − sampleεu). S. By

Materials 2019, 12, x FOR PEER REVIEW 11 of 14

MaterialsIn2019 Figure, 12, 1120 11a, the stress-strain relationships of Series I specimens are shown. By replacing11 of 14 recycled aggregates, the modulus of elasticity (MOE) has decreased compared to the reference sample S. By replacing 100% coarse RCA, MOE has decreased by 14% and by replacing 50% of the replacing 100% coarse RCA, MOE has decreased by 14% and by replacing 50% of the fine RCA, fine RCA, the MOE has declined by 22%. The MOE was also reduced by 10% in S100C50f, by the MOE has declined by 22%. The MOE was also reduced by 10% in S100C50f, by combining fine and combining fine and coarse recycled aggregates. coarse recycled aggregates.

60 60 S SS S100C 50 50 SS100C S50f SS50f 40 S100C50f 40 SS100C50f

30 30 Stress (MPa) Stress 20 (MPa) Stress 20

10 10

0 0 0.000 0.002 0.004 0.006 0.000 0.002 0.004 0.006 Strain Strain (a) (b)

FigureFigure 11. 1Compressive1. Compressive stress-strain stress-strain curves curves for for (a) ( Seriesa) Series I, (I,b )(b Series) Series II. II.

InIn Figure Figure 11 b,11b, the the stress-strain stress-strain curves curves of of Series Series II isII depicted.is depicted. The The use use of of coarse coarse RCA RCA in in SS100C SS100C reducedreduced the the MOE MOE by by 10%, 10%, while while utilization utilization of of fine fine RCA RCA in in SS50f SS50f led led to to a 23%a 23% increase increase of of MOE. MOE. Also, Also, thethe composition composition of of recycled recycled aggregates aggregates caused caused a sharpa sharp decline decline in in the the MOE MOE by by 34% 34% compared compared to to the the SS.SS. The The failure failure pattern pattern of of mixtures mixtures including including recycled recycled aggregate aggregate in in Series Series I isI is shown shown in in Figure Figure 12 1a.2a. ConsideringConsidering the the failure failure pattern pattern in this in series,this series, the pattern the pattern of cracks of in cracks the mixtures in the containingmixtures containing recycled aggregatesrecycled aggregates is vertical whileis vertical the crack while pattern the crack in thepattern reference in the sample reference isdiagonal sample is with diagonal an angle with of an approximatelyangle of approximately 45 degrees. 45 These degrees. differences These indifferences patterns ofinfailure patterns clarify of failure that cracks clarify passed that cracks within passed the recycledwithin aggregates. the recycled In aggregates. Series II, which In Series silica II, fume which was silica used fum in thee was mixtures, used in similar the mixtures, crack patterns similar were crack observedpatterns in were both referenceobserved andin bo recycledth reference specimens. and recycled This pattern specimens revealed. This that pattern silica fume revealed compensated that silica thefume weak compensated effect of the recycled the weak aggregates effect of as athe replacement recycled aggregates for natural aggregatesas a repla (Figurecement 12 forb). natural aggregates (Figure 12b).

Materials 2019, 12, 1120 12 of 14 Materials 2019, 12, x FOR PEER REVIEW 12 of 14

FigureFigure 12. 12. FailureFailure pattern pattern of ofmixtures mixtures in incompressive compressive stress, stress, (a) ( aSer) Seriesies I and I and (b ()b Series) Series II. II.

5. 5.Conclusions Conclusions AccordingAccording to to the the research carriedcarriedout out in in this this study, study, the the following following results results are presented are presented as research as researchachievements: achievements: (1)(1) UtilizationUtilization of ofrecycled recycled aggregates aggregates reduced reduced the the slump slump flow, flow, but but the the use use of ofhigher higher amounts amounts of of superplassuperplasticizerticizer could could prevent prevent reduction reduction of ofslump slump flow. flow. Also, Also, the the use use of ofrecycled recycled aggregates aggregates in in selfself-compacting-compacting recycled recycled concrete concrete showed showed acceptable acceptable passing passing ability ability in inthe the J-ring J-ring test. test. (2)(2) ReplacementReplacement of recycled of recycled aggregates aggregates in the inmixtures the mixtures including including air-entraining air-entraining admixture admixturereduced compressivereduced compressive strength. However, strength. However,no significant no significant reduction reduction of splitting of splitting tensile tensilestrength strength was observed.was observed. (3)(3) ReplacementReplacement of of100% 100% coarse coarse recycled recycled concrete concrete aggregates aggregates did did not not affect affect the the compressive compressive and and tensiletensile strength strength of of the the silicasilica fumefume mixtures. mixtures. Where Where the the fine fine recycled recycled aggregate aggregate negatively negatively affected affectedthe compressive the compressive strength strength and tensile and tensile strength strength of the RACof the ones. RAC ones. (4)(4) TheThe recycled recycled aggregates aggregates in inconcretes concretes containing containing air air-entrained-entrained admixture admixture cause cause a decrease a decrease in in compressivecompressive strength strength and and modulus modulus of ofelasticity. elasticity. Subs Substitutiontitution of of100% 100% coarse coarse RCA RCA in insilica silica fume fume specimensspecimens had had no no significant significant effect effect on on the the shape shape of ofthe the stress stress-strain-strain curve, curve, but but the the fine fine recycled recycled aggregatesaggregates caused caused a a decreasedecreasein in the the energy energy absorption absorption and compressiveand compressive strength strength of the specimens. of the (5) specimens.Crack inspection of the recycled specimens after compressive strength testing showed vertical (5) Crackcracks inspection which revealed of the recycled the failure specimens of the recycledafter compressive aggregate. strength Introducing testing silica showed fume vertical into the cracksrecycled which specimens revealed changed the failure the inclinedof the recycled crack pattern aggregate. with Introducing an angle ofapproximately silica fume into 45 ◦theand recycledsimilar specimens to those for changed the crack the patterns inclined of crack the reference pattern with samples. an angle of approximately 45° and (6) similarThepresent to those obtained for the crack results patterns regarding of the utilization referenceof samples. RCA, as a partial replacement for natural (6) Theaggregates, present obtained may lead results to regarding the fact that utilization recycled of aggregateRCA, as a partial concrete replacement is an environmentally for natural aggregates,friendly material. may lead to the fact that recycled aggregate concrete is an environmentally friendly material.

Materials 2019, 12, 1120 13 of 14

Author Contributions: Data curation: S.H., writing original draft and Supervision: N.M., Review and editing: F.A. Funding: This research received no external funding. Conflicts of Interest: The authors declare no conflict of interest.

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