Engineering Properties of Treated Recycled Concrete Aggregate

Construction and Building Materials 44 (2013) 464–476

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Construction and Building Materials

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Engineering properties of treated recycled concrete aggregate (RCA) forstructural applications

0950-0618/$ - see front matter � 2013 Elsevier Ltd. All rights reserved.http://dx.doi.org/10.1016/j.conbuildmat.2013.03.014

⇑ Corresponding author. Tel.: +60 0123707810; fax: +60 046576523.E-mail address: [email protected] (S. Ismail).

Sallehan Ismail ⇑, Mahyuddin RamliSchool of Housing, Building and Planning, Universiti Sains Malaysia, 11800 Pulau Pinang, Malaysia

h i g h l i g h t s

� The use of low concentration acid has significant to remove the loose adhered mortar on RCA surface.� The physical performance of RCA after acid treatment was improved and satisfied with specification requirement.� The amount of mortar loss is greatly influence with the molarity of acid.� The slump and density of concrete containing treated RCA is comparable with concrete containing with untreated RCA.� The use of treated RCA produced concrete with higher compressive strength as compared to untreated RCA.

a r t i c l e i n f o

Article history:Received 17 November 2012Received in revised form 17 February 2013Accepted 2 March 2013Available online 13 April 2013

Keywords:Recycled concrete aggregateLow-concentration acidTreatment

a b s t r a c t

One method to promote and encourage maximum recycled concrete aggregate (RCA) utilisation for struc-tural concrete applications is to minimise the adverse effects of RCA on concrete performance. The for-mulation of an appropriate recycling process in RCA production with improved properties is desirable.This study aims to develop a potential treatment of RCA by using low-concentration acid as an alternativemethod to produce high quality RCA for structural concrete applications. This work aims to study theeffect of using different molarities of acid solvent and age of treatment (soaking) on properties of RCA,as well as the influence of using this treated aggregate on the properties of concrete. The results showthat the use of different acid molarities to remove or minimise loose mortar particles attached on the sur-faces of RCA can significantly improves its physical and mechanical properties. In addition, the reductionof loose mortar that covers RCA particles can significantly improves surface contact between the newcement paste and the aggregate which subsequently resulted in a significant improvement in thestrength of concrete mechanical. However, the effectiveness of these treatment methods remains depen-dent on several factors that require further consideration.

� 2013 Elsevier Ltd. All rights reserved.

1. Introduction

In recent years, the accelerating urbanisation has led to exces-sive demolition work and construction activities, which conse-quently, resulted in the production of large quantities ofconstruction and demolition (C&D) waste, especially concretewaste. A huge amount of C&D waste has created a seriously signif-icant impact on the environment and society. The large-scale recy-cling of concrete waste was identified as the most feasible way tominimise the growing problem of waste disposal through landfills[1,2]. The application of recycled aggregates is important in provid-ing alternative material sources to reduce the dependence of theconstruction industry on natural aggregates. A critical shortage inthe sources of natural aggregates is becoming a worldwide prob-

lem, especially in the face of the development of major urban cen-tres [3,4].

The growing concern toward environmental preservation andsustainable development has led to the development of recyclingschemes for C&D waste. Producing and using recycled aggregatesare common practices in the construction industries of severalcountries. For example, the Construction Materials Recycling Asso-ciation (CMRA) has accounted for approximately 140 million ton-nes of concrete waste, which are recycled yearly in the UnitedStates [5]. The 2010 European Aggregates Association (UEPG) An-nual Review [6] reported recycled aggregates generated approxi-mately 5% of the production of aggregates in the European Union(EU). Based on the same report [6], Germany is the greatest pro-ducer of recycled aggregates, with a production of approximately60 million tonnes. The United Kingdom follows with approxi-mately 49 million tonnes; the Netherlands has approximately20 million tonnes; and France produces 17 million tonnes. In Aus-

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S. Ismail, M. Ramli / Construction and Building Materials 44 (2013) 464–476 465

tralia, more than 50% of the total concrete residue generated fromC&D activities is recovered for recycling, while the rest goes tolandfills [7]. Dosho [8] reported that Japan has reached approxi-mately a 98% rate for processing concrete waste to recycledaggregates.

Despite reports that construction waste constitutes a large por-tion of solid waste in Malaysia [9,10], the level of awareness to-ward recycling in production or application of recycledaggregates is still generally low [11]. Not surprisingly, several con-tractors have decided to dispose directly construction waste intolandfill areas [12] or through illegal means [13] without being fullyreused and utilised. One main factor that contributes to this situa-tion is the abundance of natural aggregate resources in Malaysia[14], which resulted in the construction industry being mostlydependent on the use of natural aggregates. In conjunction withthe 10th Malaysia Plan [15], the present Malaysian constructionsector is growing rapidly, with several large-scale projects beingstarted as part of the Malaysian vision of achieving a developedcountry status by 2020. The impact of the accelerating construc-tion growth indirectly requires a considerable high amount of pro-duction and consumption of natural aggregates. Accordingly,aggressive consumption will deplete such resource if proper plan-ning and control measures are not implemented [16]. Thus, thenext step of shifting toward the use of recycled aggregates couldreduce the dependence of the construction industry on naturalaggregates, and thus, maintain aggregate security and still ensuresustainable development [17].

The recycling of concrete waste into recycled concrete aggre-gate (RCA) by crushing concrete lumps into smaller particles hasbeen identified as a potential source of alternative aggregate forproduction of environmental friendly concrete [18]. However, theuse of RCA for concrete production is not simply applied becausethe properties of RCA are different from natural aggregates. Fur-thermore, the quality of RCA fluctuates when collected from differ-ent sources. In physical terms, distinctive differences are observedbetween the properties in which RCA is not only consist of originalaggregates, but also comprise of the remains of mortar (cementpaste) adhering to the aggregate surfaces. The presence of mortarsremain in the RCA is a main reason for deteriorated RCA quality ascompared to natural aggregates [19,20] because adhered mortar ischaracterised as porous [21–25] and presents numerous micro-cracks [23]. As a result, RCA are characterised as having lower den-sity, higher water absorption, and lower mechanical strength thanthe natural aggregates [21,26–29]. Consequently, when using RCAin production of new concrete, these characteristics of the aggre-gate may have adverse effect on interfacial bond between RCAand cement paste.

In the microstructure of concrete, the interface zone that exitsat the region between the aggregate and cement paste poses con-siderable importance because this zone governs the mechanicalstrength properties of concrete [30]. As indicated by Tam et al.[23], the presence of pores and cracks on old cement mortar at-tached at the interfacial transition zone (ITZ) of RCA forms a weaklink in microstructure of concrete that affects the ultimate strengthof concrete. In addition, the effects of using high porosity andwater absorption capacity characteristics of RCA would lead tolowering the effective water content for the hydration process be-cause the adhered mortar on the aggregate particle tends to absorba large amount of water during the initial mixing stage. This cre-ates a loose interfacial zone in the hardened concrete [2]. The com-pressive strength of recycled aggregate concrete (RAC) becomesunsatisfactory when a high percentage of RCA is used to replacenatural aggregate. The compressive strength of RCA seems to re-duce by 15% and 40% when natural aggregate is replaced by 50%and 100% RCA, respectively [31]. The compressive strength of con-crete containing 100% RCA is 6% lower than that of concrete con-

taining natural aggregate [32]. The compressive strength ofconcrete is reduced by 16% (compared with a control sample)when concrete is replaced with solely coarse and fine RCA [33].Most studies have indicated that the presence of residual mortarreduces RCA quality and consequently affects the compressivestrength of concrete.

The poor quality of RCA, which affects the performance of con-crete, imposes limitation on the widespread commercial use ofRCA especially in production of structural concrete. Hence, severalresearchers [34–37] have investigated various techniques andmethod that can enhance the physical properties of RCA. These in-volve the maximum removal of loose particles and old mortars at-tached to the original aggregate of RCA to attain qualitycomparable with that of natural aggregate. Some beneficial meth-ods proposed include thermal or heating method, microwave heat-ing method, heating then rubbing methods, and ultrasonic bathmethod. These methods minimise or totally remove mortars at-tached to the original aggregate of RCA. All these methods couldimprove the interfacial bond between RCA and new cement pastein new concrete, thus improving concrete performance. Thesemethods, however, require complicated mechanical equipmentand high energy consumption. Another potential treatment forRCA involves acid use, as demonstrated by Tam et al. [38]. In thismethod, low-concentration acid is used to remove the loose at-tached mortar of RCA from the original aggregate. They used vari-ous proportions of RCA, up to 30%, and treated them by soakingRCA in three different types of acid (hydrochloric acid, sulphuricacid, and phosphoric acid) at molarities 0.1 M for 24 h. In general,the benefit gained from the treatment significantly reduced thewater absorption of RCA by 7.27–12.17%. Consequently, the useof treated RCA in concrete mixtures have showed significantimprovements in concrete quality in compressive strength, flexuralstrength, and elastic modulus compared with those of concretewith untreated RCA. This method has great potential because it isinexpensive and could significantly improve RCA properties, thusincreasing concrete performance. Meanwhile, benefits from usinglow-concentration acid may not totally remove the adhered mortarof RCA but simply removes the loose adhered mortar on its surfaceand remain the strong bulk mortar, which can maximise the util-isation of this waste as a part of the aggregate particle for concrete.

The use of low-concentration acid for treatment of RCA involvescertain aspects that remain ambiguous. More research is requiredon the effect of different concentrations of acid solvent and ageof treatment (soaking) on RCA properties and concrete properties,which were not fully investigated by Tam et al. [38]. In addition,Tam et al. demonstrated that RCA treated with acid for concretehas a low proportion replacement level of natural coarse aggregateof up to 30% only. The present study aims to investigate the feasi-bility of using different concentrations of acid solvent and age oftreatment (soaking) on physical and mechanical properties ofRCA. The study is also involved in assessing the influence proper-ties of treated RCA on effect the fresh and hardened properties ofconcrete at high replacement ratio of up to 60%.

2. Material

2.1. Cement

Type I ordinary Portland cement was used as the main binder for the experi-ment with specific surface area of 1.0432 m2/g and specific gravity of 3.02. Typicalchemical compositions of the Ordinary Portland cement are tabulated in Table 1.

2.2. Aggregate

In this study, natural coarse aggregates were crushed granite with maximumsizes of 20 mm. The coarse RCA used in this study are generated from crushed wasteconcrete cubes, which were collected from debris area at concrete LaboratorySchool of Housing, Building, and Planning, USM Penang, by crushing with steel

Table 1Typical chemical compositions of ordinary Portland cement.

Materials Composition (%)

SiO2 Al2O3 Fe2O3 CaO MgO K2O SO3 P2O5 MnO TiO2 Others

Cement 16 3.6 2.9 72 1.5 0.34 3.1 0.06 0.03 0.17 0.31

466 S. Ismail, M. Ramli / Construction and Building Materials 44 (2013) 464–476

hammer. RCA were then put into a jaw crusher where it is broken down into re-quired sizes. After the crushing process, RCA were graded to the particular sizeusing a vibrator sieve to obtain aggregates with the maximum size of 20 mm. Thefine aggregates used were uncrushed quartzite natural river sand. The aggregateswere washed with water to remove any unwanted substances such as clay, dirt,dust, and were air-dried.

2.3. Acid

In this study a hydrochloric acid (HCl) being used for treating the RCA. This acidis prepared in three different acid molarities: 0.1, 0.5, and 0.8 M.

3. Experimental program

3.1. Acid soaking of RCA

The study include assessing the influence of different acid concentrations anddurations of treatment on the physical and mechanical properties of coarse RCA,as well as effects of using treated aggregate on concrete’s compressive strength.Three different acid concentrations with three different ages of treatment for RCAare proposed and compared. The method involves the application of hydrochloricacid (HCl) as acidic solvent in degradation action for removal of crumbs or loose ad-hered mortars attached to the original RCA aggregate. The selection with HCl indi-cates improved results in properties of recycled aggregate concrete and markedimprovements after pre-treatments, as reported by Tam et al. [38], due to its effec-tiveness in treating RCA. This method of acid treatment is adapted from Tam et al.[38]. The first procedure involves adding HCl to the sample size of RCA in plasticcontainer until the RCA surface is covered. Three types of acid molarity, 0.1, 0.5,and 0.8 M, of HCl were used in this study. The aggregates were immersed in acidicsolvents for 1, 3, and 7 days. The container was occasionally shaken to ensure amore efficient reaction of acid in the degradation bond of mortar adhered to the ori-ginal aggregate. After immersion based on age of treatment, the aggregates werewatering with distilled water and drained. Then the sample was sieved using a4.75 mm sieve to ensure that only the coarse aggregate were retained.

3.2. Mix design

Mix design of concrete was proportioned using the DOE method, which is cal-culated based on constant effective water/cement ratio of 0.41 for all concrete mix-tures to achieve target compressive strength of 50 MPa at the age of 28th day [39].The compositions of all constituents of concrete materials are shown in Table 2.Furthermore, the compositions of coarse aggregates for all concrete mixes are de-signed by replacing the natural coarse aggregate with various contents of treatedand untreated RCA at 15%, 30%, 45%, and 60% replacement by weight of the totalcoarse aggregate content. Thus, a total of nine batches of different types of concretemixtures were prepared, which comprise of treated RCA that were prepared basedon their different effects, various molarity of acid, and age of treatment. Meanwhile,another batch of concrete mix was prepared with untreated RCA and served as con-trol sample for comparison purpose. All tests were conducted to be compared withthese concrete properties. In order to maintain a concrete slump and avoid RCAabsorption of high amounts of water during mixing, RCA must be pre-wetted orpre-soaked before mixing, as suggested by previous studies [40,41]. The treatedRCA were soaked again with water for 24 h and drained to attain saturated surfacedry (SSD) conditions before use in concrete mixing. Natural coarse aggregates werealso used in this study to prepare SSD conditions for all mix proportions of concretemixtures.

Table 2Mix proportions.

Constituents Proportion (kg/m3)

15% 30% 45% 60%

Water 220 220 220 220Cement 537 537 537 537Sand 693 693 693 693

Coarse aggregateCrushed granite 782 644 506 368RCA 138 276 414 552

3.3. Method of mixing and curing of concretes

All concrete mixes in the study were mixed in accordance to sequences pre-scribed in BS1881-125 [42]. A drum mixer was used to prepare the concrete mixes.The first mixing procedure involved adding all coarse and fine aggregates into thedrum mixer and dry mixed for 30 s to allow aggregates to mix homogeneously. Sec-ondly, the first half portion of the mixing water was added into the mixer and themixing continued for another 2 min. The mixer was then stopped for several min-utes to facilitate the absorption of water into aggregates. The cement was addedand the mixer continued for another half minute. Finally, the remaining half ofthe mixing water was added and further mixing was performed for approximately2 min more. All hardened concrete specimens were cast in laboratory condition,demoulded at 24 h after casting, and then fully immersed in water at 25 ± 2 �C untilthe time of testing.

4. Testing

4.1. Determination of aggregate properties

Several tests are used to determine RCA properties before andafter treatment to ensure that the aggregates used are incompli-ance with standard requirements for concrete based on BS 882[43]. Basic properties, such density and water absorption of aggre-gates, were tested following BS 812-Part 2 [44]. In this test, RCAseparated into two sizes of particles: 20 mm and 10 mm. The par-ticle sizes of aggregates reportedly influences density and waterabsorption. The mechanical strength of aggregate was assessedby conducting crushing value and impact value tests. Both testmethods use 10–14 mm aggregate sizes for the test and weretested in accordance to BS 812-Part 110 [45] and Part 112 [46],respectively. The crushing and impact value are calculated byrecording fractions passing and retaining in a 2.36-mm sieve afterthe material underwent crushing and impact tests, respectively,based on standard weight of aggregate. This is expressed as a per-centage of the total weight. The assessments on chemical contentsof aggregate, such as chloride and sulphate contents, were con-ducted following guidelines stipulated in BS 812-Part 117 [47]and Part 118 [48], respectively. The pH values of the aggregateswere also determined in the present study.

4.2. Examination of microstructure of aggregate and concrete

The microstructure studies on RCA surface were conducted onthe untreated RCA and were compared with microstructure surfaceof treated RCA, which was treated in three different molarities ofHCl; (0.1, 0.5, and 0.8 M) for 1 day using a scanning electron micro-scope (SEM).

4.3. Determination of mortar loss

The procedure to determine the loss of adhered mortar on RCAincluded the following steps: (1) the coarse RCA was sieved to bedivided into two nominal different sample group sizes of 20 mmand 10 mm; (2) the procedure involves oven-drying the samplesize of coarse RCA used in the test for 24 h at 105 �C; (3) then,RCA samples were weighed at approximately 2 kg (M1) based onsample size. A total of 2 L of HCl was added based on their molarityand age of treatment in different plastic containers; (4) afterimmersion, the aggregates were washed with water and drained;(5) the aggregates were then placed on a tray and put in an ovenfor 24 h at 105 �C; (6) afterward, the sample was sieved using a


4.75 mm sieve to ensure that only the coarse aggregate were re-tained and weighed (M2); (7) the percent of adhered mortar losswas calculated based on the following expression:

% Adhered mortar loss

¼Mass of RCA ðM1Þ �mass of RCA after treatment ðM2ÞMass of RCA

ð1Þ

Fig. 1. Relationship between amount mortar loss and molarity of acid.

Fig. 2. Relationship between amount mortar loss and age of treatment.

4.4. Testing of fresh and hardened concrete

Three testing programs were designed to determine the effectof various content proportion of treated RCA on the low concentra-tion of acid in concrete, which determine concrete workability,density, and compressive strength. Slump tests of fresh concreteswere conducted to determine concrete workability immediatelyafter mixing. The slump test procedure was conducted in accor-dance with BS EN 12390-2 [49].

The 100-mm concrete cube specimens were moulded andcured. Each mix proportion was used for the determination of com-pressive strength, at ages of 3, 7, and 28 days, based on BS EN12390-3 [50]. The bulk density of hardened concrete was testedbased on BS EN 12390-7 [51]. All results on concrete properties,whether fresh or hardened, containing treated RCA were analysedand compared with concrete using untreated RCA, which act ascontrol specimens.

4.5. Statistical analysis of test data

Different parameters were used for statistical analysis usingSPSS version 16 for compressive strength data. This includes meanvalue, standard deviation, the difference in mean value, and onesample T-test. The difference between mean value effect fromcompressive strength of concrete containing various proportionsof treated and untreated RCA is the parameter used to indicateand calculate percentage improvement or deterioration in concretestrength. This mean difference indicates the gaps that were calcu-lated by subtracting the mean compressive strength of concretecontaining treated RCA from control specimen. A negative meandifferent indicated that compressive strength was lower than con-trol. A positive mean different indicated that compressive strengthexceeded control. The one sample T-test was performed to com-pare the means of samples to determine the statistical differencesin compressive strength of concrete containing various content oftreated RCA and the mean values of concrete with untreatedRCA. The test was performed with a 95% confidence level and thestatistical significance (p values) considered at 0.05 level of confi-dence was used to analyse the data. Hence, if the p values are high-er (>) than a = 0.05, no significant difference is observed in thestrength of the two samples, and vice versa.

5. Experimental results and discussion

5.1. Analysis of adhered mortar loss

Table 3 shows the variation of adhered mortar loss of RCA with re-spect to different molarities of acid and duration of exposure for

Table 3Percentage of mortar loss of RCA corresponding to different molarity of acid used and age

Description Size of aggregate Treated RCA with different molarity of

0.1 M HCl

1 Day 3 Days 7 Days

% Mortar loss 20 mm 0.56 0.41 0.4010 mm 0.80 0.66 0.86

treatment. In general, the results indicate that the use of low-con-centration acid is significant in reducing RCA mortar content. How-ever, mass loss is only in small amounts where the majority of theremaining bulk mortar was still firmly attached to the original RCAaggregate. In this case, mass loss is present; the amount weakenedmortar and other deleterious substance, such as dust, occur by dis-solving from the surface of RCA after acid treatment. The resultsshow that a linear correlation occurs between the amount of mortarloss with molarity of acid, which indicates that mortar loss is signif-icantly greater with an increase in acid molarity and vice versa. Theuse of acid at 0.8 M resulted in an almost 4–5% reduction in the mor-tar content compared with 3% and 1% when using 0.5 M and 0.1 Macid, respectively. The relationship between percentage of adheredmortar loss and molarity of acid for the recycled aggregate concreteis plotted in Fig. 1 with a correlation coefficient of R2 = 0.95. How-ever, minimal significance is observed in the relationship betweenloss of mortar paste and the RCA immersion time with acid wherethe correlation coefficient is R2 = 0.0083 (Fig. 2). Inconsistency oc-curs in percentage of mortar loss following age of treatment whencompared between different times of 1, 3, or 7 days.

5.2. Surface microstructure of recycled concrete aggregate

A scanning electron microscope (SEM) was used to study thedifference between microstructure on surface of untreated and

of treatment.

acid and ages of treatment

0.5 M HCl 0.8 M HCl

1 Day 3 Days 7 Days 1 Day 3 Days 7 Days

2.87 2.36 2.40 5.11 4.89 3.613.18 2.81 2.82 4.73 4.28 4.65


treated RCA. The results are summarised in Fig. 3. The surface un-treated RCA is considerably more porous and are covered with cer-tain amount of loose cement paste (crumbs) and other small

Fig. 3. Surface microstructures of untreated and treated RCA.

impurities, such as dust, which are loosely connected to their thebulk aggregate particle because of the crushing process (Fig. 3a).Similar results were observed by Katz [37]. Meanwhile, when com-paring Fig. 3b–d, the treatment of RCA at different molarities of HClat 0.1, 0.5, and 0.8 M respectively, significantly reduced the looseparticles on RCA surface and even made the surface clean and moreuniform. However, the results observed on RCA surface treatedwith 0.8 M (Fig. 3d) is slightly covered with small brittle particlesseveral microns small as compared with the surface treated withRCA at molarities of HCl at 0.1 and 0.5 (Fig. 3a and b, respectively).This may be due to the effect of increased molarity acid to 0.8 M.The acid not only removed the loose mortar pieces on RCA surface,but also possibly eroded the surface of the remaining bulk mortar,which are relatively more porous and weaker than the original RCAaggregate particle.

5.3. Properties of natural coarse aggregate, untreated coarse RCA, andtreated coarse RCA

The physical and mechanical properties of coarse natural aggre-gate (granite), coarse untreated RCA and treated coarse RCA arepresented in Table 4. Based on experimental results, the aggregatesindicate that RCA has deteriorated physical and mechanical prop-erties compared with natural aggregates. The particle density(oven dry condition) of RCA at 20 mm and 10 mm was found tobe 2.33 Mg/m3 and 2.23 Mg/m3, respectively. These figures arelower than the particle density of coarse natural aggregates at20 mm and 10 mm of 2.60 Mg/m3 and 2.58 Mg/m3, respectively.RCA is much more absorptive than virgin aggregate, which isapproximately 7.4 and 8 times higher relative to the aggregatesizes 20 mm and 10 mm, respectively, than coarse natural aggre-gate. The low specific gravity and high water absorption of recycledaggregate was due to residues of the old mortar attached to recy-cled aggregates, which are light and porous in nature, [2,27]. More-over, the results of the study on aggregate mechanical propertiesshowed that the aggregate crushing and impact value of RCA arerelatively higher as compared to natural aggregates. Therefore,RCA can be expected to have lower mechanical strength than nat-ural aggregates. A main factor that causes inferior properties ofRCA (less strength) as compared to natural aggregates is the re-moval of the light porous mortar attached to RCA during testing.The inferiority is characterised by being weaker than normalaggregates [21,26].

However, the physical properties of RCA were observed to im-prove after immersion in acid. This shows that acid treatmenteffectively removes a great portion of weak cement mortar andcertain loose particles from surface RCA, thus improving their qual-ity. Marked improvements in density, water absorption, andmechanical strength properties of RCA after acid treatments com-pared with untreated RCA are recorded in Table 4. The density ofRCA increases in varying concentrations of acid treatment. The re-sult also shows percentage improvement in RCA density, which ishigher for 10 mm aggregates than for 20 mm aggregates. The pres-ence of adhered mortar tends to be higher in smaller aggregatesizes as compared to coarser aggregates [20,21]. Thus, the loss ofmortar is relatively higher in small aggregates than in coarseraggregates. Because of the relationship between aggregate densityand absorption [52], the increase in RCA density results in the sig-nificant decrease in RCA water absorption (Fig. 4). The results indi-cate that this treatment significantly reduces the absorption of RCAwith reduction of between 1% and 28%. Particularly, the reductionin absorption is better for RCA treated with 0.5 M and 0.8 M HClthan in RCA treated with 0.1 M HCl. The removal of loose mortarssignificantly improved the mechanical strength of RCA. The test re-sults indicate that the crushing and impact values of RCA proper-ties decrease after treatment. Test results on aggregate pH

Table 4Properties of natural granite, untreated RCA, and treated RCA.

Properties of aggregate Sizes ofaggregate

Naturalgranite

UntreatedRCA

Treated RCA with molarity of acid and ages of treatment

0.1 M HCl 0.5 M HCl 0.8 M HCl

1 Day 3 Days 7 Days 1 Day 3 Days 7 Days 1 Day 3 Days 7 Days

Particle density – oven dry(Mg/m3)

20 mm 2.60 2.33 2.37 2.39 2.32 2.39 2.39 2.38 2.38 2.40 2.37

10 mm 2.58 2.23 2.24 2.27 2.26 2.30 2.34 2.28 2.30 2.35 2.27Water absorption (%) 20 mm 0.60 4.44 3.99 3.58 4.63 3.67 3.48 3.75 3.83 3.51 3.95

10 mm 0.70 5.58 5.50 4.77 5.33 4.82 4.48 4.66 4.65 3.94 5.01Agg. crushing value (%) 14 mm 24.32 29.15 28.02 27.39 28.86 28.73 27.95 28.68 28.34 28.14 28.8Agg. impact value (%) 14 mm 13.98 21.78 19.59 20.27 20.90 18.97 19.56 20.37 19.08 21.37 20.71pH aggregate Mixed 12.56 12.68 12.60 13.89 13.12 12.86 12.69 12.61 12.52 12.78Chloride content (%) Mixed 0.002 0.002 0.002 0.003 0.005 0.006 0.012 0.018 0.016 0.016Sulphate content (%) Mixed 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001

Fig. 4. Relationship between water absorption and oven dry density of RCA.


indicate that the treatment of RCA with acid does not lower thealkaline level of aggregate. Furthermore, the tests on chlorideand sulphur content of overall aggregates were investigated. Theresults indicate that a very low percentage of sulphur content ex-ists in affected aggregate samples. On the contrary, the percentageof chloride content is slightly higher in treated aggregates com-pared with untreated aggregates. The results show that percentchloride content tend to increase with increase in RCA acid molar-ity and treatment duration. However, the results show that thepercent of chloride content value in overall aggregate samples sat-isfy the specified limit of 0.05% in BS 882 [43].

5.4. Relationship of mortar loss with properties of RCA

Improvements in the physical and mechanical properties of RCAafter acid treatment have been determined. However, providingevidence that a close relationship exists between the increase inRCA properties after treatment and the increase in mortar loss,either from using different acid molarity concentrations or byincreasing treatment age, is difficult. The data presented in the re-sults are not consistent, as observed in this study. As reported in[53,35], a significant relationship affects the reduction in amountof adhered mortar and an increase in RCA properties. However,previous studies have demonstrated a method that can removesor totally eliminates the content of adhered mortar in RCA. Thepresent study only demonstrates the use of low concentrations ofacid to dissolve small portions of mortar, not the total removal ofadhered mortar. Therefore, the remaining amount of mortar causesunfavourable effects in RCA properties. In addition, heterogeneityin the quantity and quality of residual mortar in RCA occurs be-cause it was taken from various sources. Mortar properties are

greatly influenced by aggregate grain size, parent (original), con-crete strength, and crushing process [20,21,41,54].

5.5. Properties of concrete with treated and untreated RCA

The test results of slump, density, and compressive strength ofconcrete containing various mix proportions of untreated and trea-ted RCA is shown in Table 5.

5.5.1. Slump resultsThe slump tests results for the degree of workability of each

batch of mix are tabulated in Table 5 and are illustrated in Fig. 5.In general, the overall slump results indicate that no obvious differ-ences are observed between concrete mixes containing treatedRCA and untreated RCA. The research also reveals that the work-ability of concrete is significantly influenced by RCA content. A lin-ear decrease causes an increase in the addition of RCA in concrete.This may be attributed to the effects of the physical characteristicsof RCA. As indicated in this study, the properties of RCA are moreangular and more rough in the surface because of the presence ofadhered mortar. The angular and rougher surface of RCA particlescompared with normal concrete aggregates decreases the work-ability of the fresh concrete mix. Thus, workability is decreased,especially at higher concentrations. In addition, the presence ofporous adhered mortar in the RCA increases water absorption,hence, affecting the workability of the fresh mix.

5.5.2. Density of concreteThe density of hardened concrete containing various propor-

tions of treated and untreated RCA is illustrated in Fig. 6. In general,no obvious differences are observed in the density of concrete con-taining treated RCA and that containing untreated RCA. Moreover,it was observed that a loss in concrete density is accompanied byan increase in RCA replacement percentage. Such behaviour occursdue to the presence of porous adhered mortar attached to physicalproperties of coarse RCA. This lowers the specific gravity of coarseRCA in relation natural coarse aggregate. Thus, an increase in thereplacement content of coarse natural aggregate by RCA has signif-icant effect on the reduction of concrete density.

5.5.3. Compressive strengthThe compressive strength of concrete prepared with various

mix proportions at 15%, 30%, 45%, and 60% using treated and un-treated (normal) RCA and determined at 3, 7, and 28 days of curingare presented in Table 5. Meanwhile the statistical analysis datashowing mean difference and one sample T-Test analysis con-ducted by comparing concrete containing treated RCA and con-crete containing untreated RCA are shown in Table 6.

Table 5The results of slump, density, and compressive strength of concrete containing various mix proportions of untreated and treated RCA.

Series no. % Coarse RCA Slump (mm) Bulk density (kg/m3) Days of curing

3 days 7 days 28 days

fcm (MPa) STD fcm (MPa) STD fcm (MPa) STD

Control 15 70 2378 31.15 1.05 38.65 1.31 50.82 0.9830 60 2368 32.41 0.41 41.63 0.05 44.89 6.0445 50 2369 31.68 0.30 41.36 2.47 44.62 4.9460 40 2354 29.11 2.98 36.65 6.01 42.44 3.26

R0.1M1D 15 50 2393 34.00 0.45 38.69 3.69 53.96 3.6330 70 2404 37.23 0.36 43.55 2.12 55.99 2.1345 40 2435 35.37 2.18 40.12 0.51 54.43 2.9160 40 2347 32.40 1.23 35.21 2.89 40.61 4.76

R0.1M3D 15 50 2383 35.98 0.70 41.41 5.53 55.20 2.2330 40 2374 33.61 0.89 37.25 2.58 53.50 1.9445 30 2365 32.29 3.41 39.03 3.51 56.86 2.6960 35 2345 38.08 1.44 46.20 3.03 54.73 1.70

R0.1M7D 15 50 2388 35.06 2.80 45.45 2.62 50.52 1.0430 40 2383 38.12 2.06 43.09 4.18 48.86 1.6445 30 2380 35.72 3.28 44.61 1.58 45.78 1.4860 30 2346 30.03 1.35 33.34 5.43 39.96 0.45

R0.5M1D 15 80 2379 34.63 7.24 38.65 6.51 54.40 1.7430 65 2371 35.08 5.62 39.40 1.42 50.16 3.0545 40 2372 29.29 7.54 34.46 3.87 49.48 3.3960 30 2355 35.15 0.66 38.56 4.70 40.43 0.89

R0.5M3D 15 60 2376 34.02 2.49 41.90 1.11 45.00 3.9130 50 2374 34.71 0.49 40.89 1.37 46.92 9.7545 30 2378 34.39 0.74 42.14 2.65 51.35 2.0460 40 2348 38.27 2.26 48.31 0.74 53.19 1.61

R0.5M7D 15 50 2380 33.00 7.40 40.24 4.39 55.27 1.4730 40 2364 36.23 3.86 37.42 5.68 55.93 1.4445 40 2366 42.07 2.38 43.76 0.37 52.62 2.9860 40 2351 34.20 0.09 42.03 2.72 48.03 2.26

R0.8M1D 15 70 2384 28.83 1.15 33.67 2.42 49.12 2.2530 60 2366 33.79 2.57 35.91 3.32 49.94 1.0045 40 2356 37.26 2.57 40.23 3.24 50.33 4.0460 40 2359 33.65 4.99 40.69 2.72 47.52 4.38

R0.8M3D 15 70 2388 36.12 4.41 36.25 5.68 43.21 5.0830 60 2367 32.60 5.49 39.23 3.72 53.66 0.5745 70 2363 36.55 0.39 37.09 6.84 49.97 4.4660 35 2352 33.32 1.66 38.96 1.29 43.25 4.18

R0.8M7D 15 40 2383 36.67 5.62 36.42 4.56 52.91 2.2530 50 2362 27.38 4.60 32.97 9.11 49.91 1.9345 70 2358 37.48 3.99 34.47 2.93 53.68 5.8460 30 2349 29.83 4.20 40.00 3.01 46.01 4.8

Control: untreated RCA; R: treated RCA; 0.1,0.5 and 0.8M: molarity of HCl acid; 1,3 and 7D: duration of treatment.


Analysis of the compressive strength of concrete containing un-treated RCA (control specimens) indicates that compressivestrength on the age of 28 days is higher than that on the age of 3and 7 days. This is due to the increased amount of hydration prod-ucts produced on prolonged curing age. The results indicate thatconcrete containing low proportions of untreated RCA (control)at 15% only achieved the target, compressive strength of 50 MPaat the age of 28 days. The rest are below the target. The resultsindicate that when the content of untreated RCA exceeds 15%,which are 30%, 45%, and 60%, the compressive strength of concreteat 28 days was observed to decrease by 11.7%, 12.2%, and 16.5%,respectively, as compared to concrete with 15% untreated aggre-gate. This indicates that higher RCA replacement level results inlower concrete compressive strength. Similar trends were ob-served by other researchers [55]. The lack of improvement in con-crete compressive strength at higher RCA replacement levels mightbe explained by the low mechanical strength of RCA when com-pared than natural aggregate. This is due to the presence of adher-

ing mortar on surface RCA which is characterise porous and weakerthan the natural aggregate. Furthermore, the presence of loosemortar on the surface of RCA obstructs the bond between RCAand cement paste in concrete [37,38]. The increase in the amountof residual cement mortar on RCA creates a weak bonding betweenthe cement mortar and RCA, which crucially affects compressivestrength of concrete.

A comparison of the results in compressive strength of con-cretes at 3, 7, and 28 days of curing incorporated with 15% treatedand untreated RCA is presented in Fig. 7. The improvement in com-pressive strength of concrete containing treated aggregate as com-pared to untreated RCA is attained at earlier ages (at 3 days) ratherthan at the age of 28 days (Fig. 8). Furthermore, R0.5M7D concreteis shown to have the highest compressive strength at this level ofaggregate replacement with RCA. The compressive strength ishigher than that of the corresponding control concrete containinguntreated RCA, which had compressive strength of 55.27 MPa or8.76% higher than the control concrete at 28 days. The improve-

Fig. 5. Slump test results of concrete containing various proportions of treated and untreated RCA.

Fig. 6. Density of concrete containing various proportions of treated and untreated RCA.


ment in compressive strength was also indicated in another batchof concrete at 28 days of testing in types R0.1M3D, R0.5M1D,R0.1M1D, and R0.8M7D, which had improvements at 8.61%,7.04%, 6.17%, and 4.11%, respectively, compared with the controlconcrete. On the contrary, unfavourable results were indicated inconcrete types R0.8M3D, R0.5M3D, R0.8M1D, and R0.1M7D. Thevalue improvements for these types were negative or below thecontrol concrete.

For concretes incorporating 30% of untreated RCA and RCA trea-ted with acid, the variations in compressive strength at differentages of curing is shown in (Fig. 9). In general, not much improve-ment is observed in concrete strength at early ages of curing. Con-crete batches at the seventh day of curing were mostly below thestrength of the control concrete. This may attributed to the lowprogress of cement hydration process at early age. The negative va-lue of mean difference in strength is shown in Fig. 10. However, thepercentage improvement in compressive strength is greatly im-proved at later ages. On the 28 days, the overall concrete mixescontaining treated RCA indicated higher strength than the corre-sponding control specimens did. Concrete types R0.1M1D andR0.5M7D produced the highest compressive strength of 55.99and 55.93 MPa, respectively, or a 24.7% and 24.6% increment,respectively, in compressive strength as compared to the controlconcrete at 28 days.

For concrete mixes prepared with 45% of treated RCA (Fig. 11),the development of compressive strength at 3, 7, 28 days areslightly similar to concrete incorporating 30% of treated RCA. Thisindicates that the development of concrete strength with treatedRCA is slightly better on the third day of curing. However, minimalimprovement was observed on the seventh day of curing (Fig. 12).The compressive strength of treated RCA concrete was observed tobe higher than control concrete under prolonged curing durationsof 28 days (Fig. 12). Notably, the incorporation of treated RCA at45% did not show any significant negative impact on decreasingcompressive strength at 28 days as compared to the control con-crete. Most of the concrete mixes with treated RCA achieved com-pressive strength of up to or above 50 MPa at the age of 28 days.This shows that the use of treated RCA improves the compressivestrength of concrete at the age of 28 days by approximately 3–27% as compared to concrete containing untreated RCA. Addition-ally, the result demonstrated that R0.1M3D treated RCA concreteexhibited the highest compressive strength which is 56.86 MPaat 28 days. This result is the highest among overall concretes withtreated RCA specimens, not just in the 45% mix proportion batch.

The results for compressive strength of concretes with 60% oftreated RCA and untreated RCA on 3, 7, and 28 days are illustratedin Fig. 13. Based on this figure, the high proportion of RCA resultedin a low compressive strength of the concrete mixes produced.

Table 6One sample T-test analysis results for compressive strength.

Series no. % Coarse RCA Compressive strength


Mean different T-test Mean different T-test Mean different T-test

Sig. (2-tailed) P-value Sig. (2-tailed) P-value Sig. (2-tailed) P-value

R0.1M1D 15 2.85 0.008 0.004 0.03 0.988 0.494 3.14 0.273 0.13730 4.82 0.002 0.001 1.91 0.258 0.129 11.10 0.120 0.06045 3.69 0.099 0.050 �1.24 0.051 0.026 9.81 0.028 0.01460 3.28 0.044 0.022 �1.44 0.478 0.239 �1.83 0.574 0.287

R0.1M3D 15 4.83 0.007 0.004 2.76 0.478 0.239 4.38 0.077 0.03930 1.20 0.143 0.072 �4.38 0.099 0.050 8.61 0.016 0.00845 0.61 0.787 0.394 �2.33 0.369 0.185 12.24 0.016 0.00860 8.96 0.008 0.004 9.55 0.032 0.016 12.29 0.062 0.031

R0.1M7D 15 3.90 0.114 0.057 6.79 0.046 0.023 �0.30 0.750 0.37530 5.71 0.041 0.021 1.46 0.606 0.303 3.97 0.052 0.02645 4.04 0.166 0.083 3.25 0.070 0.035 1.16 0.307 0.15460 0.92 0.360 0.180 �3.31 0.402 0.201 �2.48 0.082 0.041

R0.5M1D 15 3.48 0.620 0.310 0.00 0.999 0.500 3.58 0.070 0.03530 2.67 0.496 0.248 �2.23 0.112 0.056 5.27 0.096 0.04845 �2.40 0.337 0.169 �6.90 0.091 0.046 4.86 0.292 0.14660 6.03 0.004 0.002 1.91 0.544 0.272 �2.01 0.060 0.030

R0.5M3D 15 2.86 0.185 0.093 3.24 0.037 0.019 �5.82 0.123 0.06230 2.30 0.015 0.008 �0.74 0.447 0.224 2.03 0.818 0.40945 2.71 0.024 0.012 0.78 0.662 0.331 6.74 0.029 0.01560 9.16 0.020 0.010 11.66 0.001 0.001 10.75 0.067 0.034

R0.5M7D 15 1.85 0.784 0.392 1.59 0.594 0.297 4.45 0.035 0.01830 3.82 0.229 0.115 �4.21 0.328 0.164 11.04 0.006 0.00345 10.39 0.017 0.009 2.41 0.632 0.316 8.01 0.164 0.08260 5.08 0.000 0.000 5.38 0.076 0.038 5.59 0.177 0.089

R0.8M1D 15 �2.32 0.073 0.037 �4.98 0.071 0.036 �1.70 0.321 0.16130 1.38 0.587 0.294 �5.73 0.247 0.124 5.05 0.088 0.04445 5.58 0.064 0.032 �1.13 0.606 0.303 5.72 0.134 0.06760 4.54 0.255 0.128 4.04 0.283 0.142 5.08 0.183 0.092

R0.8M3D 15 4.96 0.357 0.179 �2.41 0.540 0.270 �7.61 0.281 0.14130 0.19 0.970 0.485 �2.40 0.380 0.190 8.77 0.001 0.00145 4.87 0.036 0.018 �4.27 0.540 0.270 5.35 0.173 0.08760 4.20 0.048 0.024 2.31 0.090 0.045 0.81 0.769 0.385

R0.8M7D 15 5.52 0.231 0.116 �2.24 0.485 0.243 2.09 0.249 0.12530 �5.03 0.199 0.100 �8.66 0.242 0.121 5.02 0.046 0.02345 5.80 0.128 0.064 �6.89 0.055 0.028 9.06 0.115 0.05860 0.72 0.794 0.397 3.35 0.193 0.097 3.57 0.326 0.163

Fig. 7. Development of compressive strength of concrete mixtures incorporating15% replacement of coarse aggregate with treated and untreated RCA.

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R0.1M1DR0.1M3DR0.1M7DR0.5M1DR0.5M3DR0.5M7DR0.8M1DR0.8M3DR0.8M7D

Fig. 8. Comparisons of percentage improvement on compressive strength ofconcrete containing treated RCA relative to the control (0-axis) at 15% replacementof coarse aggregate.


Most of the concrete mixes produced did not achieve the targetcompressive strength of 50 MPa at the age of 28 days. The com-pressive strength of control concrete at 28 days only reached 85%


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of the design target (Fig. 13). As previously mentioned, the inverserelationship between RCA content and compressive strength isattributed to weaker RCA caused by poor physical quality of the ad-

hered mortar. However, concrete incorporating treated RCA led toa lower magnitude of decrease in the compressive strength of con-crete from the target strength as compared to concrete incorporat-ing untreated RCA. This is an evidence that the compressivestrength of almost all concretes containing treated RCA is higheras compared to concretes containing untreated RCA at all threetesting dates (Fig. 14). Furthermore, concrete incorporating treatedRCA (R0.1M3D and R0.5M3D) exhibited improved compressivestrength by 29% and 25.3% as compared to the control concreteat 28 days. Only two of these concrete types were able to achievethe target strength of 50 MPa. The remaining compressive strengthof concrete at 28 days, such as in types R0.5M7D, R0.8M1D, andR0.8M7D and R0.8M3D remains below the 50 MPa. However, theyare approximately 13.2%, 12%, 8.4% and 2% higher, respectively,than control concrete.

As overview, the findings from the compressive strength resultsanalysis indicate an improvement in the compressive strength ofconcrete using treated RCA as compared to concrete containing un-treated RCA. Concrete incorporating treated RCA, even at high pro-portions up to 60%, led to significant increases in compressivestrength as compared to untreated RCA concrete. The T-test analy-sis results of 28-day curing of concrete compressive strength indi-cate that incorporating treated RCA significantly affects

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compressive strength of the concrete mixes. Furthermore, the dataindicate that a statistically different compressive strength is ob-served in concrete using treated RCA compared with concreteusing untreated RCA. The P value is indicated to be below 0.05(P < 0.05).

The factor that contributes to the enhancement in concretecompressive strength is the use of low concentrations of acid at dif-ferent molarities for treatment. This significantly improves thephysical and mechanical properties of RCA by removing and reduc-ing the amount of loose cement paste and other impurities on RCAsurface. The improvement in the properties of RCA consequentlyreflects the improvement in concrete strength. In addition, the re-moval of loose particles on the physical surface of RCA may resultin a stronger contact at the interfacial zone between the cementpaste and the RCA. The interfacial bond between cement pasteand aggregate is known to be critical in concrete structures, andis a significant factor governing concrete strength development[56]. Thus, an increase in cement paste–aggregate interfacial bondstrength increases concrete strength, disregarding to some extentthe detrimental effect from the use of low-quality aggregate [2,56].

5.6. Compressive strength of concrete with treated RCA

In general, the results obtained from this study showed that theincorporation of treated RCA in concrete at coarse aggregatereplacement level of up to 45% provides optimum compressivestrength. However, determining the impression of a strong rela-tionship on the use of differing acid molarity or the impact of dif-ferent treatment ages on RCA is difficult. The results indicate thatinconsistencies and variations in compressive strength of concreteare due to overall testing impressions inclusive to mixing with var-ious proportions of treated RCA in concrete mixtures. The percent-age improvement of concrete strength at the age of 28 days, whichare indicated by the distinction mean of strength, show that thehighest compressive strength is achieved by using RCA that weretreated with acid molarities of 0.1 M and 0.5 M rather than0.8 M. This may be because the use of low concentrations of acidis less detrimental to the physical shape and surface of RCA. Theuse of acid molarity at 0.8 M is effective in removing loosely ad-hered mortar pieces on the RCA surface. However, at the same timeit might corrode the surface of the remaining mortar of RCA, mak-ing the surface tend to be brittle and fragile. This may interfere thegood interface and a strong bond between cement paste and aggre-gate particle. However, a more consistent improvement is also

demonstrated by the concrete using RCA treated in acid molarityat 0.8 M. In all three treatment periods (1, 3, and, 7 days), the trea-ted RCA concrete showed improvements in compressive strengthat the age of 28 days as compared to the control concrete, espe-cially when the coarse aggregate replacement ratio exceeds 15%.

The study on the effect of different soaking ages of RCA in lowconcentration acid seems insignificant. An extended period ofsoaking contributes to concrete strength. As indicated from the re-sults, the soaking of RCA of up to 3 days is sufficient to treat theRCA, giving it improved results in compressive strength. In othercases, some results did not indicate satisfactory improvement incompressive strength using treated RCA, such as in concrete typeR0.1M7D. The use of treated RCA with 0.1 M acid and 7 days oftreatment at various proportions of concrete mixtures did notshow much improvement in compressive strength compared withuntreated RCA, especially at the age of 28 days. Thus, one of themain factors that contribute to the inconsistency and unfavourableresults of compressive strength is that the properties of RCA arestrongly governed the presence of adhered mortar. As mentionedpreviously, the use of low concentrations of acid did not totally re-move bulk amount of mortar at aggregate particles. Therefore, theeffect of the existing attached mortar, which is characterised withlow-quality aggregate as opposed to natural aggregate, has unfa-vourable effects on properties of RCA. Therefore, the variation incompressive strength development of concrete is significantly gov-erned by RCA properties after treatment.

6. Conclusions

The following conclusions are drawn from the test results anddiscussions:

1. The use of low concentration HCl has the potential toremove the loose adhered mortar on RCA surface. The resultsshow a linear correlation between the amount of mortar losswith the increase of the molarity of acid. However, theimmersion time of RCA with acid did not have significantinfluence on the amount of mortar lost.

2. A microstructure study by SEM on RCA surface indicates thatthe surface of treated RCA has cleaner crumb and free fromloose particles as compared to untreated RCA. However,increasing acid molarity 0.8 M in treated RCA tends to resultin brittle and fragile particles on the mortar surface becausethe acid tends to have corrosive effects on the adheredmortar.

3. The properties of RCA have improved after treatment withacid immersion. The test results indicate marked improve-ments in density, water absorption, and mechanical strengthof RCA after acid treatments as compared to untreated RCA.The acid treatments can effectively remove a great portion ofweak cement mortar and certain loose substances from theRCA surface, and thus improving the physical properties ofRCA.

4. The use of a low-concentration acid seems safe and not det-rimental on RCA particles. The test results indicate that thechloride and sulphur contents of the acid remain withinthe limits of their respective standards.

5. No significant differences were observed in slump and den-sity results of concrete containing treated RCA as comparedwith concrete containing untreated RCA.

6. The test results indicate that the compressive strength ofconcrete containing untreated RCA decreases with increas-ing RCA content. Only the concrete containing 15% untreatedRCA met the target compressive strength of 50 MPa at28 days of curing, whereas the rest of the mixes fabricated


achieved results below that of the target. The inverse rela-tionship between RCA content and compressive strength isdue to the poor quality of RCA caused by the presence ofloose residual mortar on RCA surface. The presence of looseresidual mortar may obstruct the bond between RCA andcement paste.

7. The results demonstrate that treated RCA produced concretewith higher compressive strength as compared to untreatedRCA. The results indicate that incorporating concrete mixwith treated RCA at a proportion of up to 45% achieves theoptimum strength in the mix design of concrete compressivestrength. Most concrete batches containing treated RCA indi-cate an improvement in control and have achieved compres-sive strength of up to or above 50 MPa at 28 days.

8. The results in compressive strength indicate that increasingthe replacement content of natural coarse aggregate by RCAat 60% decreases the compressive strength of mix to belowthe target strength. However, incorporating treated RCAhas led to a significantly smaller reduction in the compres-sive strength of concrete compared with concrete with un-treated RCA. In addition, certain cases of concrete fabricatedusing treated RCA able to achieve target compressivestrength.

9. The findings from this research cannot specify or determinethe appropriate effect of using different molarities of acid orduration of the soaking age for treatment RCA, which indi-cates a main influence on concrete compressive strength.The inconsistency in the results of compressive strengthobtained for concrete containing various replacement levelsof RCA, is mainly caused by various intrinsic parameters inthe physical properties of RCA.

10. However, in general, the results show that the concrete con-taining RCA treated with acid with molarity of 0.1 M and0.5 M indicates the most substantial improvement in com-pressive strength as compared to concrete incorporatingRCA treated acid with molarity of 0.8 M. Meanwhile, thesoaking period of RCA in acid by not more than 3 days is suf-ficient for the treatment.

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Documents

Engineering Properties of Treated Recycled Concrete Aggregate