EMV mix design method for preparing sustainable self compacting recycled aggregate concrete subjected to chloride environment

Construction and Building Materials 199 (2019) 705–716

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EMV mix design method for preparing sustainable self compacting recycled aggregate concrete subjected to chloride environment Puja Rajhans a,⇑, Prashant Kumar Gupta b, Raju Kumar Ranjan a, Sarat Kumar Panda a, Sanket Nayak a a b

Department of Civil Engineering, Indian Institute of Technology (ISM), Dhanbad, India Department of Civil Engineering, Indian Institute of Technology Delhi, India

h i g h l i g h t s

g r a p h i c a l a b s t r a c t


Self compacting recycled aggregate

concrete (SCRAC) is being subjected to chloride environment.
Equivalent mortar volume (EMV) method for chloride resistance SCRAC.
Two stage mixing approach (TSMAsfc) for improving the chloride resistance.
Justification of improvement of properties through microstructural investigation.

Construction and demolition (C&D) wastes.

Self compacting recycled aggregate concrete subjected to chloride environment.

Two stage mixing approaches.

EMV method of mix design in conjunction with Nan Su mix design method.

100%

100% (T)

63.53% (EMV) 0%

Variation of electrical current with time passing through the SCRAC sample prepared with TSMAsfc having different percentage of RCA at 28 days of Improved interfacial transition zone

Densest paste

Improved ITZ and paste after following EMV mix design method along with TSMA sfc.

a r t i c l e

i n f o

Article history: Received 16 July 2018 Received in revised form 6 December 2018 Accepted 13 December 2018

Keywords: Recycled concrete aggregate RCPT Chloride ingress depth Migration coefficient Microstructure Elemental mapping

a b s t r a c t The present investigation is an effort to make sustainable self compacting recycled aggregate concrete (SCRAC) when the concrete is subjected to high probability of chloride ingress. Aproposed mix design method is employed in conjunction with Nan Su mix design method to study the chloride ions ingress of SCRAC. In this mix design method, the acceptable substitution of recycled concrete aggregate (RCA) depends on the residual mortar content (RMC) attached on the surface of RCA. The treatment on RCA is done by using a coat of sodium silicate along with silica fume to improve the properties of SCRAC mix. Finally, during mixing of ingredients different mixing approaches were followed to evaluate the chloride ion ingress depth, migration coefficient and microstructure of SCRAC. It is observed that SCRAC prepared with two stage mixing approach (TSMAsfc) along with proposed method of mix design resulted improved compressive strength and chloride resistance properties. The reason of improvement of SCRAC by filling of pores and cracks in interfacial transition zone (ITZ) and adjacent to it is justified through microstructural investigation. Further, elemental mapping is also carried out to know the presence of different elements which contributes for improving the strength in concrete. Ó 2018 Elsevier Ltd. All rights reserved.

1. Introduction The increase in population, rapid urbanization and the requirement of infrastructural development has led to the substantial growth of construction industry. In the necessity of making new structures, the old buildings are being demolished. Due to the ⇑ Corresponding author. E-mail address: [email protected] (P. Rajhans). https://doi.org/10.1016/j.conbuildmat.2018.12.079 0950-0618/Ó 2018 Elsevier Ltd. All rights reserved.

demolishing of old buildings, a large amount of debris is generated, which leads to various environmental pollutions. Environment is experiencing massive impact due to increased construction practices resulting emission of CO2 in the atmosphere, depletion of natural resources, generation of large amount of waste materials and difficulties in disposal of the same. In recent years, certain countries have considered the utilizations of construction and demolition (C&D) waste in construction of new infrastructure projects. Many researchers have justified the use recycled coarse aggregate

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Notation SGACNA b

Bulk specific gravity of ACNA

Bulk specific gravity of RCA SGRCA b SGCNA Bulk specific gravity of CNA b EMV V SCRAC Vol. of CNA in SCRAC-EMV CNA SCNAC V CNA Vol. of CNA in SCNAC EMV V SCRAC Total mortar vol. in SCRAC-EMV TMV Mortar volume in SCNAC V SCNAC MV SCRAC EMV V TCNA Total CNA in SCRAC-EMV EMV V SCRAC RMVin SCRAC-EMV RMV SCRAC EMV V FMV Fresh mortar vol. in SCRAC-E EMV V SCRAC ACNA in SCRAC-EMV mix. ACNA EMV V SCRAC Volume of RCA in SCRAC-EMV RCA 0 fC Designed compressive strength SGCNA Bulk specific gravity of CNA in dry compacted state DC EMV V SCRAC RCA in SCRAC-EMV mix in dry compacted state DCRCA SCRAC EMV WW Water in SCRAC-EMV

(RCA) from C&D waste for using in construction practice [1–4]. However, there are some drawbacks of this RCA for using in construction industry. The adhered mortar which is attached on the surface of RCA is highly porous in nature resulting high water absorption capacity. Moreover, the crushing and impact values of RCA are high which shows that RCA has lower strength than that coarse natural aggregate (CNA). Research works [5–8] on SCRAC are also published in open literature where RCA is suggested to be used as coarse aggregate. Self compacting concrete (SCC) maintains the homogeneity and fills the congested formwork without any need of external mechanical vibrations. SCC has three prime properties i.e., filling ability, passing ability and resistance to segregation. Researchers suggested that the mechanical and durability properties of SCC produced with RCA are enhanced by using admixtures like fly ash and silica fume [9–11]. The properties of SCRAC is further improved by adopting two stage mixing approach (TSMA) [1]. The durability properties of SCRAC is one of the most important properties of concrete, since it affects the service life and maintenance cost of the structures. The durability of concrete is strongly affected by the transport properties of the harmful parameter such as water, carbon dioxide (CO2), chloride, etc. through the concrete. The main agents leading to corrosion of the concrete structures are penetration of chlorides. It is also recommended in many literatures [12–16] that RCA can be used in concrete where the probability of occurrence of chloride ingress is high. Mohseni et al. [17] evaluated the impact of partial replacement of recycled coarse aggregate (RCA) on compressive strength, splitting tensile strength, water absorption and chloride ion penetration of the hardened composites and microstructural properties of self compacting concrete (SCC). They concluded that the potential replacement of such RCA can assist to the sustainability of the construction industry. Saravanakumar and Dhinakaran [18] investigated the durability properties of recycled aggregate concrete (RAC) with respect to its resistance to chloride ion penetration, sorptivity and acid attack resistance with substitution of different percentage of RCA. The results clearly stated that the replacement of CNA with RCA was very much possible and it was also eco-friendly. The open literature suggest different innovations for improving the quality of RCA, which results improvement in properties of

W SCNAC W

Water in SCNAC

EMV Cement in SCRAC-EMV W SCRAC C SCNAC WC Cement in SCNAC EMV W SCRAC Fine aggregate in SCRAC-EMV FA SCNAC W FA Fine aggregate in SCNAC EMV W SCRAC Superplasticizer in SCRAC-EMV SP Superplasticizer in SCNAC W SCNAC SP SCRAC EMV WF Flyash in SCRAC-EMV mix W SCNAC Flyash in SCNAC mix F CNA Bulk density of CNA b FA Bulk density of fine aggregate b SGRCA Bulk specific gravity of RCA in dry compacted DC SCNAC V DCCNA CNA in SCNAC mix in dry compacted state

q q

RMV

state

Residual mortar volume

RAC. The innovations are the development of advanced mixing approaches, methods of surface treatment and development of mix design methods for preparing the sustainable concrete from C&D waste. Different types of mixing approaches were adopted to improve the properties of RAC in which TSMA was firstly proposed by Tam et al. [19]. In this mixing approach, water was divided into two portions and added at different stages. This resulted enhanced properties of RAC than that of concrete prepared by using normal mixing approach (NMA) [19]. Further, Tam and Tam [20] diversified TSMA into two different mixing approaches i.e., TSMAs and TSMAsc. In TSMAs, silica fume were mixed with water and then added into RCA in the premix stage and referred as two stage mixing approach (silica fume) (TSMAs). However, in TSMAsc, silica fume, water and proportional amount of cement were added into RCA in the premix stage and referred as two stage mixing approach (silica fume and cement) (TSMAsc). It was observed that TSMAs and TSMAsc resulted best mechanical properties than that of other mixing approaches. Few literatures showed that the treatment of RCA is also an important technique to achieve better properties of RAC. Regarding the treatment of RCA, Shi et al. [21] used two different methods of treatment of RCA. In first method, RCA samples were treated with Pozzolana slurry and in second method, the samples were treated with CO2. It was observed that both the treatment method enhanced the mechanical and durability properties of RAC as both old and new ITZ got strengthened. Bui et al. [22] treated RCA with sodium silicate solution and silica fume for improving the properties of RAC. Compressive strength, splitting tensile strength, elastic modulus and direct tensile strength of RAC were improved after adopting treatment process. Wang et al. [23] used acetic acid solution for treating the RCA, where the acetic acid reacted with cement hydration products resulting 25% improvement in compressive strength. Guenyisi et al. [24] introduced four different aggregate surface treatment methods to improve the mechanical properties of SCC prepared by using 100% RCA. They concluded that fresh properties and mechanical properties of SCC were significantly improved by doing surface treatment of RCA. Ismail et al. [25] followed treatment technique for the RCA by using low concentration acid to produce high quality RAC for structural concrete applications. The resultshowed that the use of different acid molarities

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significantly improved the physical and mechanical properties of RCA. Open literature [26–28] presented that the concrete prepared by using RCA gave same target strength as of natural aggregate concrete (NAC) by introducing some changes such as increasing the cement content, adjusting the water cement ratio, varying the size of recycled aggregate etc. Fathifazl et al. [29] gave emphasis on improving the modulus of elasticity along with other mechanical and durability properties for concrete sample prepared by using RCA. In that study, it was considered that the adhered mortar content of RCA as the part of total mortar volume required for preparing the normal concrete mix which resulted reduction in new mortar required for preparing the concrete mix. Literature study revealed that, there wasa lack of research work in the domain of SCRAC when the concrete is subjected to chloride environment [30,31]. Investigation on SCRAC using equivalent mortar volume (EMV) method in conjunction with [32] mix design method by following different mixing approaches wasa potential scope for experimental investigation. In this context, the present investigation is an effort to obtain improved chloride resistance properties of SCRAC prepared with different mixing approaches by following EMV method in conjunction with [32] mix design method by replacing only CNA by RCA.

Table 2 Physical properties of OPC 43 grade cement. Sl. No

Characteristics

IS:8112-1989 specifications

Value obtained

1. 2. 3. 4.

Normal consistency (%) Initial setting time Final setting time Fineness (Retained on 90 mm) (%) Specific gravity Soundness(mm) Compressive strength (N/ mm2) 3 days 7 days 28 days

– 30 (minimum) 600 (maximum) 10

29 75 217 7

– 10 (maximum)

3.15 2.55 26.00

5. 6. 7.

23.00 33.00 43.00

35.59 45.48

Table 3 Physical properties of class F fly ash. S. No.

Physical properties

Value

1. 2. 3. 4.

Specific gravity Fines passing 150 m sieve (%) Fines passing 90 m sieve (%) Blaine’s fineness (cm2/gm)

2.13 99.60 97.20 3890

2. Experimental investigation Table 4 Physical properties of silica fume.

2.1. Materials Ordinary Portland cement (OPC) of 43 grade with a specific gravity of 3.15, classF fly ash and silica fume are used as cementitious material. OPC 43 grade cement conforms to IS: 8112-1989 and exhibits a minimum design strength of 23, 33 and 43 MPa at end of 3, 7 and 28 days of curing, respectively. The chemical compositions of cementitious materials are given in Table 1. The physical properties of cement, fly ash and silica fumeare presented in Tables 2–4, respectively. Limestone was used as CNA and river sand was used as fine aggregate. The RCAwas obtained from a demolished building of Bokaro, Jharkhand, India. The mineralogy of RCA is obtained by performing X-ray fluorescence (XRF) analysis. The chemical compositions of the RCA used in the present study are as given in Table 5. The physical properties of CNA, RCA, and fine aggregates are presented in Table 6.These properties of RCA are of good quality and can be used in preparing RAC [33]. Super plasticizer was used in order to achieve the flowability of SCC. Potable water was used for making all the concrete mixes. 2.2. Proposed mix design method for SCRAC-EMV In this proposed mix design method for preparing SCRAC-EMV mix, the total mortar volume required for preparing the SCRACEMV mix was equal to that of the mortar volume required for preparing self compacting natural aggregate concrete (SCNAC) mix. In order to prepare the SCRAC-EMV mix, first of all, the constituents of SCNAC mix was calculated by using [32] mix design method. Finally, depending upon RMC value, the maximum and minimum value of natural aggregate ratio (NAR) is decided. Using appropriate value of NAR and RMC value, subsequently volume of Table 1 Chemical composition of cementitious materials. Chemical compounds

Cement

Silica fume

Fly ash

CaO SiO2 Al2O3 MgO K2O Fe2O3

63.56 17.65 12.43 1.43 2.52 0.62

0.2 97.05 0.2 0.5 0.5 0.5

18.30 37.80 14.10 3.20 1.75 19.84

S. No.

Physical properties

Value

1. 2. 3. 4.

Particle size Specific surface area Bulk loose density Specific gravity

0.1 mm 20,000 m2/kg 240–280 kg/m3 2.15

Table 5 Chemical compositions of the RCA used. Compounds

(%) present

SiO2 Al2O3 Fe2O3 MgO CaO LOI Na2O K2O P2O5 MnO TiO2

64 4.76 2.11 1.96 14.35 9.13 0.77 0.52 0.33 0.05 0.19

RCA and CNA and hence weight is obtained. In addition to this, fresh mortar volume (FMV) is also calculated depending upon NAR. By knowing the FMV required for SCRAC-EMV and mortar volume of SCNAC, rest of other components can also be calculated for preparing SCRAC-EMV mix. 2.2.1. Determination of residual mortar content in RCA The method of determination of residual mortar content had been proposed by Abbas et al. [34]. The RCA sample werefirst washed in a tap water and kept for oven drying at 105 °C for 24 h. Then the oven dried RCA samples were placed in a 26 wt% sodium sulphate solution for 24 h. After 24 h of immersion, the sample prepared along with the solution were subjected to the process of freezing and thawing for five to six days continuously (16 h in a deep freezer at 17 °C and 8 h in an oven at 90 °C). Atthe last stage of freezing and thawing cycle, the samples were poured

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Table 6 Physical properties of aggregates (CNA, RCA and fine aggregates).

RMC ¼

S. No.

Aggregate Property

CNA

RCA

Fine aggregates

1. 2. 3.

Specific gravity Water absorption (%) Bulk density (kg/m3)

2.68 0.53 1250

2.46 4.62 1450

2.70 0.8 1500

 W RCA  W ACNA  100 W RCA

ðiÞ

where, WRCA is the oven drymass of RCA sample in gram before the test and WACNA is the oven dry mass of actual concrete natural aggregate after the complete removal of residual mortar in gram. 2.3. Mixture proportions

on 4.75 mm sieve so that the residual mortar is removed along with the solution. The sample was washed again with normal water to clean the remaining residual mortar. After washing, the aggregate samples were placed in an oven for another 24 h at 105 °C and further the weight of oven dried aggregate mass of actual concrete natural aggregate (WACNA) was measured. The residual mortar content (RMC) (%) was calculated by using the following equation.

Total four proportions were prepared, where three proportions were obtained by conventional [32] mix design method and one was of EMV method in conjunction with [32] mix design method. The first mix is the reference mix which contains 0% RCA and referred as SCRAC-0%. Second mix is prepared using 100% RCA and termed as SCRAC-100%. Third mix is prepared with the use of 100% treated RCA and designated as SCRAC-100% (T). A 10% concentration of sodium silicate solution was prepared and RCA was

Table 7 Mix design for M30grade of self compacting recycled aggregate concrete. Mix designation

Cement (kg/m3)

Fine aggregate (kg/m3)

SCRAC-0% SCRAC-100% SCRAC-100% (T) SCRAC-63.53% (EMV)

380 380 380 316.41

900 900 900 749.41

Coarse aggregate (kg/m3) CNA

RCA

646 – – 340.36

– 606 606 592.86

Cement + fly ash

Water + SP

Mixed for (30 s)

Mixed for (120 s)

Fine +RCA Mixed for (30s)

Fly ash (kg/m3)

Water (kg/m3)

SP (kg/m3)

132 122 122 109.91

219 219 219 182.36

2.8 2.8 2.8 2.33

Final Mix

(a) NMA Half water + half SP

Fine +RCA Mixed (60 s)

Mixed (60 s)

Remaining half water + Cement + fly ash half SP

Mixed (120 s)

Mixed (30 s)

Final Mix

(b) TSMA

RCA

Proportional (z %) Cement

Fine aggregate

7% silica fume Slurry (Mixed for30 s)

Mixed for 30 s

Mixed for 60 s

Half SP + half Half SP + half water (100-z)% cement water +fly ash

Mixed for 60 s

Mixed for30 s

Mixed for 120

(c) TSMAsfc Fig. 1. Flow diagram of different mixing approaches (a) NMA, (b) TSMA and (c) TSMAsfc [1].

Final Mix

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Data analyzer

(a) Experimental set up of RCPT

2.4. Mixing approaches In normal mixing approach (NMA), all the ingredients were added and mixed as per the flow diagram given Fig. 1(a). However, in two stage mixing approach (TSMA), mixing process was carried out by adding water in two different stages by dividing into two portions. The flow diagram of two stage mixing approach is shown in Fig. 1(b). Another proposed mixing approach, TSMAsfc i.e., two stage mixing approach (silica fume, fly ash and cement) was followed, where fly ash was replaced with certain percentage of silica fume. In this mixing approach, silica fume of 7% of the fly ash content was taken to prepare a silica fume slurry and then RCA was thoroughly mixed with it. Subsequently proportional amount of cement and water were added in premix stage and the process is followed as presented in Fig. 1(c). Both the RCA as well as CNA used for preparing the concrete mix were in kept in saturated surface dry condition (SSD). The SSD condition is the condition of RCA in which the pores of RCA are filled up with water and surface of RCA is in dry condition. 2.5. Test methods for properties of fresh SCRAC Different fresh properties of SCRAC were evaluated by following EFNARC [35] guidelines. These tests i.e., slump flow test, T50, Vfunnel, and J-ring were conducted for each of the various mixes by adopting three different mixing approaches. 2.6. Curing conditions

Concrete sample container (b) Enlarge view of concrete sample container

The nature of curing was normal curing. In normal curing, the specimens were cured in water tank having normal temperature of 27 °C ± 2 °C. 2.7. Test methods for properties of harden SCRAC

Fig. 2. Rapid chloride penetration test instrument.

immersed in it for 1 h at temperature around 27 ± 2 °C. After 1 h of immersion the RCA was taken out from sodium silicate solution and dried at room temperature for 4 h to attain dry wet condition. Further, the RCA samples were coated with silica fume and again kept for drying for 3–4 h at room temperature. The fourth and final mix is prepared with concept of equivalent mortar volume method. The substitution of RCA for EMV is taken as 63.53% and this mix is referred as SCRAC-63.53% (EMV). The mix proportions for the all above concrete mix are presented in Table 7. The calculation of ingredients of mix proportion of SCRAC mix using EMV method in conjunction with [32] mix design method is presented in detail in Appendix-A.

Compressive strength: After 7 and 28 days of curing, the test samples were tested in universal testing machine (UTM). The control mode of the press during compressive test is stress mode and the loading rate is 5150 N/s. Rapid chloride penetration test (RCPT):This test was performed to measure the penetration of ion through the SCRAC sample and conducted in accordance with ASTM C1202.RCPT instrument consists of two chambers, one chamber was filled with 3% sodium chloride (NaCl) and other was filled with 0.3 M sodium hydroxide (NaOH). The current passes through the concrete specimen and the temperature between the cells were noted at every 30 min for up to 6 h and total charge pass through the concrete specimen was calculated. For conducting RCPT test, a concrete disc having 100 mm diameter and 50 mm thickness was used as specimen.

Table 8 Fresh properties of SCRAC mixes prepared with different mixing approaches. Sample Mix

Mixing Approach

Slump flow (mm)

T50 (s)

V-funnel time (s)

J-ring (mm)

SCRAC-0%

NMA TSMA TSMAsfc

720 (4.36, SF2) 728 (3.61, SF2) 737 (2.65, SF2

4.5 (0.36, VS2) 4.3 (0.36, VS2) 3.8 (0.53, VS2)

8.0 (0.70, VF2) 7.6 (0.44, VF1) 7.5 (0.44, VF1)

8.0 (0.44, PA1) 7.8 (0.36, PA1) 7.5 (0.36, PA1)

SCRAC-100%

NMA TSMA TSMAsfc

699 (1.73, SF2) 715 (3.46, SF2) 726 (5.29, SF2)

4.8 (0.36, VS2) 4.5 (0.26, VS2) 4.2 (0.36, VS2)

9.9 (0.26, VF2) 9.5 (0.44, VF2) 9.0 (0.26, VF2)

8.8 (0.26, PA1) 8.2 (0.44, PA1) 8.0(0.66, PA1)

SCRAC-100% (T)

NMA TSMA TSMAsfc

680 (4.36, SF2) 692 (5.29, SF2) 692 (3.61, SF2)

5.0 (0.36, VS2) 4.5 (0.36, VS2) 4.5 (0.26, VS2)

10.7 (0.56, VF2) 10.0 (0.46, VF2) 9.8 (0.35, VF2)

9.5 (0.53, PA1) 9.0 (0.44, PA1) 8.5 (0.26, PA1)

SCRAC-63.53%(EMV)

NMA TSMA TSMAsfc

725 (4.36, SF2) 732 (1.73, SF2) 739 (2.65, SF2)

4.3 (0.26, VS2) 4.7 (0.36, VS2) 4.5 (0.26, VS2)

7.8 (0.44, VF1) 7.4 (0.26, VF1) 7.4 (0.44, VF1)

8.0 (0.35, PA1) 7.5 (0.44, PA1) 7.2 (0.53, PA1)

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the concrete disc. The ions affected part became white after the application of silver nitrate solution on the concrete. The chloride penetration depth was measured from the extent of the visible whitecolour. The penetration depth results obtained from this test are used in the following formula [36] to calculate the chloride migration coefficients. The chloride migration coefficient values of the concretes are determined at 14 and 28 days of curing.

Dnssm

" rffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi# 0:0239ð273 þ TÞL ð273 þ TÞLxd ¼ xd  0:0145 ðU  2Þt U2

ðiiÞ

where, Dnssm is the migration coefficient, 10( 1 2)m2/s, Tis the average temperature of the solution = 25 °C, L is the thickness of the concrete sample = 50 mm, U is the applied voltage = 60 V, xdis the average chloride penetration depth (mm) and tis the test duration time in hrs = 6hrs.

(a) 7 days

3. Results and discussion 3.1. Properties of fresh SCRAC

(b) 28 days Fig. 3. Variations of compressive strength of SCRAC having different percentage of RCA along with different mixing approaches.

The concrete sample was fixed between two chambers and the total charge was calculated to find out the penetrability. The full experimental set up with a test sample is presented in Fig. 2. Chloride penetration depth: After conducting the penetration test, the concrete disc was taken out from the apparatus and the concrete disc was split axially into two parts. Silver nitrate (AgNO3) solution of 0.1 M was sprayed on one of the fresh split surface of

The fresh properties of different SCRAC mixes are presented in Table 8 along with the uncertainty of the test results. The standard deviations of three sample test results and the category of fresh properties are presented in Table 8 within the bracket for each of the individual concrete mix. It is observed that the fresh properties parameters of concrete mixes are in the permissible range of EFNARC guidelines [35]. The concrete prepared with NMA shows minimum workability whereas the concrete prepared with TSMAsfc shows maximum workability for all the sample mix. Further, it is observed that the SCRAC 0% mix has maximum value of the fresh properties (slump flow, T50, V-funnel, and J-ring) than that of the SCRAC-100% and SCRAC-100% (T) mixes. This may be attributed due to effect of adhered mortar present in RCA leading to increase in surface roughness and water absorption capacity of RCA and makes SCRAC and SCRAC-100% (T) mix less workable. It is noticed that treated batches give lower slump value than that of the untreated concrete batches. Lower slump value of treated concrete batches is because of the use of sodium silicate and silica fume during treatment of RCA for preparing the mix. SCRAC-63.53% (EMV) mix shows almost comparable fresh property as that of SCRAC0% mix. The categories resulted for slump flow, T50, V-funnel and J-ring are SF2, VS2, VF2 and PA1, respectively, as per the

100%

100% (T)

63.53% (EMV) 0%

Fig. 4. Variation of electrical current with time passing through the SCRAC sample prepared with TSMAsfchaving different percentage of RCA at 28 days of curing.

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(a) 14 days

(a) 14 days

(b) 28 days

(b) 28 days Fig. 5. Charge passed through the concrete samples prepared with different percentage of treated and untreated RCA along with mixing approaches.

specifications of EFNARC guidelines [35]. The categories of concrete confirms for using in normal practice. 3.2. Properties of hardened SCRAC 3.2.1. Compressive strength The variations of compressive strength of at curing age of 7 days and 28 days are presented in Fig. 3(a) and (b), respectively. The error bar in the graph represents the variation of minimum and maximum value from the mean value. It is observed that the compressive strength of concrete from SCRAC-100% mix prepared with NMA shows lower strength than that of SCRAC-0% mix. This is due to the presence of pores and cracks in RCA resulting weaker ITZ. Further, these cracks and pores are filled in by adopting two stage mixing approach i.e., TSMAsfc. In TSMAsfc, silica fume slurry is mixed with RCA in premix stage. The silica presents in silica fume reacts with calcium hydroxide crystal and forms C-S-H gel which gives the strength. Further, the compressive strength of concrete from SCRAC-100% (T) mix is increased by 15.93% than that of SCRAC-100% mix after adopting TSMAsfc. This may be explained due to the treatment of RCA by using sodium silicate and silica fume. The sodium silicate is trapped inside the pores and reacts with portlandite of RCA and forms C-S-H gel. However, the compressive strength of concrete from SCRAC-63.53% (EMV) mix is increased by 21.69% than that of SCRAC-100% mix by using same mixing approach after 28 days of curing. This is because in the proposed mix design method the content of RCA is restricted to 63.53%

Fig. 6. Variation of chloride penetration depth of concrete samples prepared with different percentage of treated and untreated RCA by using different mixing approaches.

resulting reduction in pores and cracks and improvement in compressive strength. It is also observed that results of concrete prepared from SCRAC-63.53% (EMV) mix is nearly equal to the concrete prepared with SCRAC-0% mix.

3.2.2. Chloride ions ingress of SCRAC The flow of electric current depends on the presence of pores in the concrete and water to cement (w/c) ratio. Higher w/c ratio leads to higher porosity. However, the connectivity of the pores in concrete plays a pivotal role for flow of current and the ionic permeability. In case of chloride penetration, ionic diffusion takes place so it also dependent upon the moisture available in the sample. Moreover, the grading of aggregates also affects the resistivity of concrete. Well graded aggregates give higher degree of compactness and subsequently helps in reducing the porosity of the sample. The variations of flow of electric current with time interval of one minute for 360 min through the concrete specimens prepared using TSMAsfc at 28 days of curing are presented in Fig. 4. This plot is generated from the Giatech Perma2TM rapid chloride permeability instrument available at IIT(ISM) Dhanbad, India. It is observed from Fig. 4 that the flow of electric current is maximum in concrete prepared with SCRAC-100% mix. This is because of the presence of adhered mortar on the surface of RCA which has lots of minute cracks and pores. Further, an attempt is taken to minimize the flow

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(EMV) mix is reduced by 28% whereas chloride penetration depth is reduced by 28% than that of SCRAC-100% mix for TSMAsfc at 28 days of curing. The above observation is attributed due to the fact that usage of RCA is restricted only to 63.53% to that of 100% RCA in SCRAC-100% and SCRAC-100% (T) mixes. The presence of 36.47% of natural aggregate in SCRAC-63.53% (EMV)mix may have contributed to the segmentation of pores, resulting into considerable reduction in permeability and hence in chloride penetration depth and its migration coefficient. The lower is the value of migration coefficient, higher will be the resistance offered by the mix against the penetration of chloride ions.

3.3. Microstructural analysis

(a) 14 days

(b) 28 days Fig. 7. Chloride migration coefficients of different concrete mix with various percentage of treated and untreated RCA and following different mixing approaches.

of electric current by filling the pores and cracks in SCRAC-100% (T) mix. The flow of electric current of concrete sample prepared with SCRAC-63.53% (EMV) mix is lesser than that of concrete of SCRAC100% and SCRAC-100% (T) mixes. The electric flow is observed to be minimum in the concrete prepared with SCRAC-0% mix. The charge passed through the concrete sample having different percentage of treated and untreated RCA at the end of 14 and 28 days of curing are depicted in Fig. 5(a) and (b), respectively. The variations of chloride penetration depths and corresponding migration coefficients of the 14 and 28 days of concrete samples prepared with different percentage of treated or untreated RCA are presented in Figs. 6(a and b) and Fig. 7(a and b), respectively. It is observed from Fig. 5(a and b) that the charge passed through the concrete mix i.e., SCRAC-0% is minimum among all the other concrete mix. The charge passed through SCRAC-100% mix is maximum leading to higher ion penetration depth as well as higher migration coefficients and can be seen from Figs. 6(a and b) and 7(a and b), respectively. This may be due to usage of 100% of RCA into the mix resulting into higher permeability of the mix. However, these above observations is reduced for the SCRAC-100% (T) mix. As RCA used in this mix are treated with silica fume and sodium silicate leading to reduction in the permeability of the mix. This reduction is of 11% for charge passed, 28% for chloride penetration depth than that of SCRAC-100% mix for TSMAsfc. Furthermore, the charge passed through concrete mix i.e., SCRAC63.53% (EMV) is minimum than that of SCRAC-100% mix and SCRAC-100% (T) mix. The charge passed through SCRAC-63.53%

For justifying the reason of improvement of properties of SCRAC, microstructural investigation is carried out. After following the prescribed procedure of sample preparation for microstructural investigation, BSE images are generated through Electron probe micro analyzer (EPMA). The reason behind taking the BSE images is the intensity of electron backscattering, which is highly dependent on mean atomic number of the incidence compound. Hence, on a grey scale of the BSE image, brighter regions represent the compounds with higher mean atomic number and those with lesser mean atomic number are represented darker. Therefore, the un-hydrated (UH) products having higher mean atomic number appears brighter than those of hydrated products (C-S-H and CH). Further, the pores appear very dark due to its very low atomic number. The obtained BSE images of the concrete sample are presented in Fig. 8. The old adhered mortar present in concrete prepared with SCRAC-100% mix by using NMA are shown in Fig. 8(a) and (b). It is observed that this adhered mortar is having lots of pores and cracks at ITZ and area adjacent to it. The loose paste is observed in Fig. 8(a) and it is concluded by the presence of pores in mortar matrix which can be confirmed due to presence of some black areas in mortar and in ITZ of concrete prepared from SCRAC100% mix. Fig. 8(b) illustrates the quantity of unhydrated products available at the paste. It is seen from Fig. 8(c) that this unhydrated products reacts with water and forms hydrated products (C-S-H and CH) because the overall content of paste is less in SCRAC63.53% (EMV) mix. The concrete prepared from SCRAC-63.5% (EMV) mix by following TSMAsfc becomes dense as it contains 36.47% of natural aggregate and due to the addition of silica fume in the mix. The microstructure of concrete of SCRAC-63.53% (EMV) mix shows less pores as compared to SCRAC-100% mix and can be observed from BSE image. It is also important to access the properties of ITZ as this plays an important role in governing the strength of the concrete mix. It is seen that there are unfilled cracks adjacent to the ITZ of concrete prepared from SCRAC-100% mix in Fig. 8(b). However, in Fig. 8(c), these cracks are not observed for concrete prepared from SCRAC-63.53% (EMV) mix resulting stronger ITZ and improved properties. Elemental mapping of SCRAC 63.53% (EMV) mix is presented in Fig. 9. Fig. 9(a) represents the BSE image of an aggregate surrounded by mortar paste. Elemental mapping is carried out to know the spatial distribution of the strength contributing elements in this mix as it exhibits maximum strength. After comparing the distribution of these elements between the interface and in the bulk paste, it is observed that RCA mostly comprises of ‘Si’, ‘Al’ and ‘Fe’. This observation also agrees well with the chemical composition of RCA shown in Table 5.The distribution of ‘Si’, ‘Al’ and ‘Fe’ in sample are represented in Fig. 9(b–d), respectively. Furthermore, it is also observed that the presence of ‘Si’ is considerably high at ITZ and paste region which may be attributed due to application of TSMAsfc. Particularly, ITZ becomes stronger and less porous due to the presence of ‘Si’, ‘Al’ and ‘Fe’. Presence of ‘Si and

P. Rajhans et al. / Construction and Building Materials 199 (2019) 705–716

713

Interfacial transition zone

Loose paste

Pores Unhydrated cement paste

Pores

(a) Loose paste and pores of SCRAC100% mix prepared by using NMA. .

(b) ITZ, unhydrated cement paste and pores of SCRAC-100% mix prepared by using

Strongest interfacial transition zone

Densest paste

(c) Densest paste and strongest ITZ of SCRAC-63.53% (EMV) mix prepared by using TSMAsfc. . Fig. 8. Microstructural investigation of concrete prepared with different mixing approaches.

‘Al’ are also noticed with higher quantity in bulk paste which results dense paste. 3.4. Conclusion Large production of C&D waste in the urban areas leads to various environmental impacts. These materials are recycled and used as RCAin the production of concrete. In this investigation, sustainability of SCRAC which is subjected to chloride environment has been accessed. Based upon the experimental studies, following conclusions are drawn.
The content of RCA is restricted to 63.53% in the proposed mix design method as the percentage of RCA depends on the adhered mortar content on the surface of RCA. The fresh prop-

erties i.e., slump flow, T50, V-funnel and J-ring of the concrete are within the permissible range of EFNARC guidelines.
The compressive strength of SCRAC prepared with TSMAsfcis observed to be improved than that of the concrete prepared with NMA. Further, the concrete prepared with treated RCA i.e., SCRAC-100% (T) along with TSMAsfc results better compressive strength in comparison to the concrete prepared with untreated RCA. The compressive strength of SCRAC-63.53% (EMV) and SCRAC-100% (T) mixes are increased by 21.69% and 15.93%, respectively, than that of SCRAC-100% mix after adopting TSMAsfc. The results of concrete prepare with SCRAC-63.53% (EMV) mix is nearly equal to the concrete prepared with CNA.
The concrete prepared with treated RCA results 11% reduction for charge passed and 28% reduction for chloride depth than that of SCRAC-100% mix. The concrete prepared by following

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P. Rajhans et al. / Construction and Building Materials 199 (2019) 705–716

(a) BSE image of SCRAC-63.53% (EMV).

(c) Elemental mapping of aluminum.

(b) Elemental mapping of silica.

(d) Elemental mapping of iron.

Fig. 9. Various elemental mapping of the concrete prepared from SCRAC-63.53% (EMV) mix.

proposed mix design method i.e., SCRAC-63.53% (EMV) mix giveimproved performance in terms of current passed through concrete, chloride penetration depth and chloride migration coefficient than that of SCRAC-100%. The chloride penetration depth of SCRAC-63.53% (EMV) mix is reduced by 28%than that of SCRAC-100% mix.
Microstructural investigation shows that the ITZ gets stronger in concrete prepared by EMV method along with TSMAsfc. Elemental mapping shows the presence of strength contributing element in concrete which is prepared from SCRAC-63.53% (EMV) mix.
In nutshell, it is concluded that the present attempt for developing EMV mix design method for preparing SCRAC mix gives an opportunity to utilize RCA in concrete where the probability of occurrence of chloride ingress is high. Acknowledgements The authors would like to acknowledge the financial support for present work under HSMI/HUDCO R&D plan HSMI/R&D/ ISMD/2015-16.

Appendix. -A Explanation of proposed mix design method Determination of various constituents of SCRAC-EMV mix: Following conditions are satisfied in proposed method for SCRAC-EMV mix design.

V SCRAC TMV

EMV

¼ V SCNAC ; V SCRAC MV TCNA

V SCRAC TMV

EMV

¼ V SCRAC RMV ¼

EMV

EMV V SCRAC ACNA

EMV

¼ V SCNAC CNA

þ V SCRAC FMV þ

EMV

SCRAC ; V TCNA

EMV V SCRAC CNA

ð1Þ EMV

ð2Þ

Since, RCA consists of residual mortar and actual coarse natural aggregate present in it, V SCRAC ACNA

EMV

can be obtained as given below.

V SCRACEMV ¼ V SCRACEMV  ð1  RMCÞ  ACNA RCA

SGRCA b SGACNA b

ð3Þ

where, RMC is the residual mortarcontent of RCA sample. The ratio of fresh in SCRAC-EMV mix to that of SCNAC mix is defined as natural

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P. Rajhans et al. / Construction and Building Materials 199 (2019) 705–716

aggregate ratio (NAR). Substituting Eqs. (1) and (2) in Eq. (3) and rearranging we get the following equation.

V SCRAC RCA

EMV

V SCNAC  ð1  NARÞ CNA

¼

ð4Þ

SGRCA

b ð1  RMC Þ  SGACNA b

NAR ¼

V SCNAC CNA SCRAC EMV V RCA

EMV V SCRAC CNA

After obtaining the value of and from Eq. (4), the required weight of RCA and CNA can be obtained for preparing SCRAC-EMV mix. For finding the volume of fresh mortar required for preparing SCRAC-EMV mix, the residual mortar volume can be determined as given below.

V SCRAC RMV

EMV

¼ V SCRAC RCA

EMV

The maximum allowable RMC for SCRAC-EMV mix having 100% RCA content is obtained by rearranging the Eq. (11) as given below.

" RMC max ¼ 1  V SCNAC DCCNA 

 EMV

V SCRAC CNA

Maximum RMC in SCRAC-EMV mix:

 V SCRAC ACNA

EMV

ð5Þ

"

SGRCA b

EMV

¼ V SCNAC  V SCRAC MV RMV

ð6Þ

SGACNA b

SCRAC Subsequently, fresh mortar volumeV FMV given below.

V SCRAC FMV

#

EMV

is obtained as

EMV

ð7Þ

Now, weight of all the ingredients for preparing the SCRAC-EMV mix by proposed mix design method can be expressed as below.

W SCRAC RCA

EMV

¼ V SCRAC RCA

EMV

 SGRCA  1000 ; W SCRAC b CNA

¼ V SCRAC CNA

EMV

 SGCNA  1000 b

¼ W SCNAC  W SCRACEMV W W

V SCRACEMV FMV V SCNAC MV

ð8aÞ V SCRACEMV FMV V SCNAC MV ð8bÞ

W SCRACEMV FA

¼ W SCNAC FA



V SCRACEMV FMV V SCNAC MV

;W SCRACEMV SP

¼ W SCNAC SP



V SCRACEMV FMV V SCNAC MV ð8cÞ

W SCRACEMV ¼ W SCNAC  F F

V SCRACEMV FMV V SCNAC MV

ð8dÞ

NAR ¼

V SCNAC CNA are

The volume of and related to its corresponding dry compacted volume is as given below.

V SCRACEMV ¼ V SCRACEMV  RCA DCRCA

SGRCA DC SGRCA b

; V SCNAC ¼ V SCNAC CNA DCCNA 

SGCNA DC SGCNA b

ð9Þ

SCRAC EMV The maximum value of V DCRCA can be unit. Hence, first part of Eq. (9) is reduced as,

V SCRACEMV RCA

¼

SGRCA DC

ð10Þ

SGRCA b

ð1  RMCÞ V SCNAC DCCNA

ð13Þ

V SCRACEMV RCA

Substituting Eq. (13) in Eq. (6), the NAR is expressed as given below.

NAR ¼

V SCRACEMV AMV V SCRACEMV RCA

"

¼

1  ð1  RMCÞ 

SGRCA b

#

ð14Þ

SGACNA b

Mix proportion for preparing M30 grade of SCRAC is done by adopting EMV method in conjunction with [32] mix design method. Step wise evaluations of ingredients are shown as below.

Mix proportions for preparing SCNAC mix by using [32] mix design method are obtained as given below. Weight of cement ðW SCNAC Þ = 380 kg/m3; Weight of water C Þ = 195 kg/m3; ðW SCNAC W

Weight

of

coarse

Þ = 646 kg/m3; ðW SCNAC CNA

Weight

of

fine

natural

aggregate

aggregate(ðW SCNAC Þ) FA

Þ = 132 kg/m3; Weight of = 900 kg/m3; Weight of fly ashðW SCNAC F Þ = 2.8 kg/m3 and Air content = 2%. superplasticizerðW SCNAC SP Step: 2. Maximum allowable RMC for SCRAC-EMV mix.

"

SGCNA b SGRCA b

#

 100


 2:68  100 ¼ 32:45% RMC max ¼ 1  0:62  2:46 RCA where, V SCNAC = 2.46;SGCNA = 2.68. DCCNA = 0.62 (IS 10262:2009); SGb b Actual RMCmax is 48.6%. Hence, 100% replacement of CNA is not allowed.

Step: 3. Natural aggregate ratio ðNARÞ ¼ 

SCRACEMV V RMV SCRACEMV V RCA

¼


1  ð1  RMCÞ

SGRCA b

Substituting Eq. (10) and second part of Eq. (9) in Eq. (4) and assuming similar shape and size of CNA and RCA, the following expression is derived.

NARmin: ¼ 1 

ð12Þ

V SCRACEMV RMV

RMC max ¼ 1  V SCNAC DCCNA 

Minimum replacement ratio (NARmin) in SCRAC-EMV mix: EMV V SCRAC RCA

 100

SGRCA b

Step: 1.

EMV

; W SCRACEMV ¼ W SCNAC  C C

#

If the RMC determined after freezing and thawing actions is more than the RMCmax, it is not possible to use 100% RCA in SCRAC-EMV mix. In this condition, it is required to replace the RMV in RCA with CNA to compensate the requirement of total CNA in SCRAC-EMV mix compared to its companion SCNAC mix. The NAR is expressed as given below.

Putting the value of V SCRAC from Eqs.(3) into Eqs (5) we have ACNA

V SCRACEMV ¼ V SCRACEMV  1  ð1  RMCÞ  RMV RCA

SGCNA b



SGRCA b SGCNA b

ð11Þ

where, the value of V SCNAC DCCNA is obtained from Table 3 of IS 10262:2009 depending upon the maximum size of CNA and fineness modulus of fine aggregate used in preparing the SCRAC-E mix.

SGACNA b


 2:46 ¼ 1  ð1  0:486Þ  2:68 W SCRAC CNA

EMV

646 W SCRAC RCA 2:68  1000 RCA  SGb  1000

¼ NAR  V SCNAC ¼ 0:528 CNA ¼ V SCRAC RCA

EMV

¼ 0:241  2:46  1000 ¼ 592:86

EMV

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P. Rajhans et al. / Construction and Building Materials 199 (2019) 705–716

EMV W SCRAC ¼ V SCRAC CNA CNA 1000 ¼ 340:36 kg/m3.

EMV

 SGCNA  1000 ¼ 0:127  2:68  b

Step: 4.   EMV is calculated as The required fresh mortar volume V SCRAC RCA mention below.

V SCRAC FMV

EMV

¼ V SCNAC  V SCRACEMV ¼ 0:759  0:127 ¼ 0:632 MV RMV

where,

V SCRACEMV RMV

" ¼

V SCRACEMV RCA

 1  ð1  RMCÞ 


¼ 0:241 

1  ð1  :486Þ 

#

SGRCA b SGACNA b

 2:46 ¼ 0:127 2:68

Step: 5. Weight of water, cement, fine aggregate, superplasticizer and fly ash for SCRAC-EMV mix are calculated as given below. W SCRACEMV ¼ W SCNAC  W W

SCRACEMV V FMV

"

V SCNAC MV

¼ 219 

V SCRACEMV ¼ V SCRACEMV  1  ð1  RMCÞ  RMV RCA W SCRACEMV ¼ W SCNAC  C C

SCRACEMV V FMV

V SCNAC MV

W SCRACEMV ¼ W SCNAC  FA FA

SCRACEMV V FMV

W SCRACEMV ¼ W SCNAC  SP SP

SCRACEMV V FMV

W SCRACEMV ¼ W SCNAC  F F

V SCNAC MV V SCNAC MV

SCRACEMV V FMV

V SCNAC MV

¼ 380 

0:632 0:759

SGACNA b

¼ 900 

¼ 132 

#

SGRCA b

0:632 0:759

¼ 2:8 

¼ 182:36 kg/m3

¼ 316:416 kg/m3

0:632 0:759 0:632 0:759

0:632 0:759

¼ 749:41 kg/m3 ¼ 2:33 kg/m3

¼ 109:91 kg/m3

The authors whose names are listed immediately below certify that they have NO affiliations with or involvement in any organization or entity with any financial interest (such as honoraria; educational grants; participation in speakers’ bureaus; membership, employment, consultancies, stock ownership, or other equity interest; and expert testimony or patent-licensing arrangements), or non-financial interest (such as personal or professional relationships, affiliations, knowledge or beliefs) in the subject matter or materials discussed in this manuscript. References [1] P. Rajhans, S.K. Panda, S. Nayak, Sustainable self compacting concrete from C&D waste by improving the microstructures of concrete ITZ, Construct. Build. Mater. 163 (2018) 557–570. [2] P. Rajhans, S.K. Panda, S. Nayak, Sustainability on durability of self compacting concrete from C&D waste by improving porosity and hydrated compounds: a microstructural investigation, Construct. Build. Mater. 174 (2018) 559–575. [3] A. Gholampour, T. Ozbakkaloglu, Time-dependent and long-term mechanical properties of concretes incorporating different grades of coarse recycled concrete aggregates, Eng. Struct. 157 (2018) 224–234. [4] S. Shahidan, M.A.M. Azmi, K. Kupusamy, S.S.M. Zuki, N. Ali, Utilizing construction and demolition (c&d) waste as recycled aggregates (RA) in concrete, Proced. Eng. 174 (2017) 1028–1035. [5] F. Aslani, G. Ma, D.L.Y. Wan, G. Muselin, Development of high-performance self-compacting concrete using waste recycled concrete aggregates and rubber granules, J. Clean. Product. 182 (2018) 553–566. [6] M. Omrane, S. Kenai, E.H. Kadri, A. Aït-Mokhtar, Performance and durability of self compacting concrete using recycled concrete aggregates and natural pozzolan, J. Clean. Product. 165 (2017) 415–430. [7] R. Kurad, J.D. Silvestre, J. de Brito, H. Ahmed, Effect of incorporation of high volume of recycled concrete aggregates and fly ash on the strength and global warming potential of concrete, J. Clean. Product. 166 (2017) 485–502.

[8] K.C. Panda, P.K. Bal, Properties of self compacting concrete using recycled coarse aggregate, Proced. Eng. 51 (2013) 159–164. [9] N. Singh, S.P. Singh, Carbonation resistance and microstructural analysis of low and high volume fly ash self compacting concrete containing recycled concrete aggregates, Construct. Build. Mater. 127 (2016) 828–842. [10] D. Pedro, J. De Brito, L. Evangelista, Mechanical characterization of high performance concrete prepared with recycled aggregates and silica fume from precast industry, J. Clean. Product. 164 (2017) 939–949. [11] R. Sharma, R.A. Khan, Sustainable use of copper slag in self compacting concrete containing supplementary cementitious materials, J. Clean. Product. 151 (2017) 179–192. [12] Z.J. Grdic, G.A. Toplicic-Curcic, I.M. Despotovic, N.S. Ristic, Properties of selfcompacting concrete prepared with coarse recycled concrete aggregate, Construct. Build. Mater. 24 (7) (2010) 1129–1133. [13] J. Sim, C. Park, Compressive strength and resistance to chloride ion penetration and carbonation of recycled aggregate concrete with varying amount of fly ash and fine recycled aggregate, Waste Manage. 31 (11) (2011) 2352–2360. [14] R. Somna, C. Jaturapitakkul, A.M. Amde, Effect of ground fly ash and ground bagasse ash on the durability of recycled aggregate concrete, Cem. Concr. Compos. 34 (7) (2012) 848–854. [15] W.H. Kwan, M. Ramli, K.J. Kam, M.Z. Sulieman, Influence of the amount of recycled coarse aggregate in concrete design and durability properties, Construct. Build. Mater. 26 (1) (2012) 565–573. [16] Y.G. Zhu, S.C. Kou, C.S. Poon, J.G. Dai, Q.Y. Li, Influence of silane-based water repellent on the durability properties of recycled aggregate concrete, Cem. Concr. Compos. 35 (1) (2013) 32–38. [17] E. Mohseni, R. Saadati, N. Kordbacheh, Z.S. Parpinchi, W. Tang, Engineering and microstructural assessment of fibre-reinforced self-compacting concrete containing recycled coarse aggregate, J. Clean. Product. 168 (2017) 605–613. [18] P. Saravanakumar, G. Dhinakaran, Durability characteristics of recycled aggregate concrete, Struct. Eng. Mechan. 47 (5) (2013) 701–711. [19] V.W. Tam, X.F. Gao, C.M. Tam, Microstructural analysis of recycled aggregate concrete produced from two-stage mixing approach, Cem. Concr. Res. 35 (6) (2005) 1195–1203. [20] V.W. Tam, C.M. Tam, Diversifying two-stage mixing approach (TSMA) for recycled aggregate concrete: TSMAs and TSMAsc, Construct. Build. Mater. 22 (10) (2008) 2068–2077. [21] C. Shi, Z. Wu, Z. Cao, T.C. Ling, J. Zheng, Performance of mortar prepared with recycled concrete aggregate enhanced by CO2 and pozzolan slurry, Cem. Concr. Compos. 86 (2018) 130–138. [22] N.K. Bui, T. Satomi, H. Takahashi, Mechanical properties of concrete containing 100% treated coarse recycled concrete aggregate, Construct. Build. Mater. 163 (2018) 496–507. [23] L. Wang, J. Wang, X. Qian, P. Chen, Y. Xu, J. Guo, An environmentally friendly method to improve the quality of recycled concrete aggregates, Construct. Build. Mater. 144 (2017) 432–441. [24] E. Güneyisi, M. Gesog˘lu, Z. Algın, Effect of surface treatment methods on the properties of self-compacting concrete with recycled aggregates, Construct. Build. Mater. 64 (2014) 172–183. [25] S. Ismail, M. Ramli, Engineering properties of treated recycled concrete aggregate (RCA) for structural applications, Construct. Build. Mater. 44 (2013) 464–476. [26] I.B. Topcu, S. Senegel, Properties of concretes produced with waste concrete aggregate, Cem. Concr. Res. 34 (8) (2004) 1307–1312. [27] M.C. Limbachiya, T. Leelawat, R.K. Dhir, Use of recycled concrete aggregate in high-strength concrete, Mater. Struct. 33 (9) (2000) 574–580. [28] R.K. Dhir, M.C. Limbachiya, T. Leelawat, Suitability of recycled concrete aggregate for use in BS 5328 designated mixes. In Proceedings of the Institution of Civil Engineers, Struct. Build. 134 (3) (1999) 257–274. [29] G. Fathifazl, A. Abbas, A.G. Razaqpur, O.B. Isgor, B. Fournier, S. Foo, New mixture proportioning method for concrete made with coarse recycled concrete aggregate, J. Mater. Civil Eng. 21 (10) (2009) 601–611. [30] D. Wang, X. Zhou, B. Fu, L. Zhang, Chloride ion penetration resistance of concrete containing fly ash and silica fume against combined freezing-thawing and chloride attack, Construct. Build. Mater. 169 (2018) 740–747. [31] Q. Cao, Q. Gao, R. Gao, J. Jia, Chloride penetration resistance and frost resistance of fiber reinforced expansive self-consolidating concrete, Construct. Build. Mater. 158 (2018) 719–727. [32] N. Su, K.C. Hsu, H.W. Chai, A simple mix design method for self-compacting concrete, Cem. Concr. Res. 31 (12) (2001) 1799–1807. [33] B. González-Fonteboa, F. Martínez-Abella, Concretes with aggregates from demolition waste and silica fume. Materials and mechanical properties, Build. Environ. 43 (4) (2008) 429–437. [34] A. Abbas, G. Fathifazl, O.B. Isgor, A.G. Razaqpur, B. Fournier, S. Foo, Durability of recycled aggregate concrete designed with equivalent mortar volume method, Cem. Concr. Compos. 31 (8) (2009) 555–563. [35] EFNARC, Specifications and Guidelines for Self Compacting Concrete. European Association for Producers and Applicators of Specialist Building Products, 2005. [36] H. Du, H.J. Gao, S. Dai Pang, Improvement in concrete resistance against water and chloride ingress by adding graphene nanoplatelet, Cem. Concr. Res. 83 (2016) 114–123.