Influence of different curing conditions and water to cement ratio on properties of self-compacting concretes

Construction and Building Materials 237 (2020) 117570

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Influence of different curing conditions and water to cement ratio on properties of self-compacting concretes Morteza Nematollahzade a, Azim Tajadini b, Iman Afshoon c, Farhad Aslani d,e a

Department of Civil Engineering, University of Vali-e-Asr, Rafsanjan, Iran Department of Civil Engineering, Islamic Azad University Science & Research, Tehran (Construction Engineering and Management), Iran c Department of Civil Engineering, University of Vali-e-Asr, Rafsanjan, Iran d Materials and Structures Innovation Group, School of Engineering, University of Western Australia, Perth, WA 6009, Australia e School of Engineering, Edith Cowan University, Joondalup WA 6027, Australia b

h i g h l i g h t s
The strength variation in different curing conditions is more evident in the high W/C.
With increasing the W/C, the amount of particles is not hydrated and the pores have reduced the strength.
The durability tests showed the best performance in plastic curing and out-air curing conditions.
The microstructure study was also performed with SEM and EDS analysis.

a r t i c l e

i n f o

Article history: Received 19 July 2019 Received in revised form 18 October 2019 Accepted 8 November 2019

Keywords: Self-compacting concrete Curing condition Water to cement ratio Durability SEM EDS

a b s t r a c t Along with the water-to-cement ratio (W/C) as a key factor in the investigation of the properties of the concrete, the conditions and the time of curing also play a very important role on its performance. Therefore, in this research, the effect of different curing conditions such as water curing (wc), plastic curing (pc), out-air curing (oac), room-air curing (rac), wet burlap curing (wbc), out-air-curing compound (oacc) and room-air-curing compound (racc) has been investigated on the properties of self-compacting concrete (SCC) for three different W/C (0.35, 0.40 and 0.45). For this purpose, in addition to fresh concrete tests, compressive strength, splitting tensile strength, water absorption, capillary water absorption, electrical resistivity tests and scanning electron microscope (SEM) of surface morphology and energydispersive X-ray (EDS) analysis on the hardened concrete phase were investigated. The results showed that the compressive and splitting tensile strength test had the best outcome in conditions wc, pc, wbc, racc and rac, respectively, at all ages. However, strength at oacc and oac conditions behave differently by changing the W/C and ages. After 56 days, methods pc and wbc, which have the least amount of water absorption at different W/C. In this research, up to 24 h, the lower capillary water absorption test belongs to method pc, wbc, oacc, wc, racc, rac and oac, respectively. According to the results, by decreasing the W/C ratio, the amount of electrical resistance of samples increases and for high W/C ratio the influence of curing methods on this parameter is clearly. The microstructural observations confirm the results described above. Ó 2019 Elsevier Ltd. All rights reserved.

1. Introduction By the past two centuries, concrete has been intensively used as construction materials. Of course, today, its importance is more than any other time [1]. In order to overcome some disadvantages and weaknesses of concrete and also respect the standard

E-mail address: [email protected] (F. Aslani) https://doi.org/10.1016/j.conbuildmat.2019.117570 0950-0618/Ó 2019 Elsevier Ltd. All rights reserved.

principles of new construction in the present era, there is a great need to improve the performance of concrete. Self-compacting concrete (SCC) has been introduced as an improved model of concrete in the past decades. This kind of concrete is easily fitted into the mold and pass through the reinforcement and barriers without any specific compaction by the vibrator [2]. Elimination of mechanical vibration caused wholesome, calm, secure and improve surrounding at a construction site [3]. Some properties of fresh concrete such as passing ability, filling ability, viscosity and the characteristics of the hardened concrete

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and its durability have made it even more noticeable since the inception of its production in the early 1980s [4]. Due to the large amount of rebar in most of the precast concrete elements, SCC is the best solution for concreting these parts due to its fresh properties [5]. Moreover, because the low distant between reinforcements in some structures, mainly pre-tensioned bridges, vibrate concrete may not be surround the reinforcement bars, then using SCC can help to remove this problem [6]. SCC has become widely applied in the construction of tall walls, and it help to suitable filling in complex shaped elements. It should be noted that among the properties of hardened concrete, compressive strength plays a key role in choosing the mix design and construction of concrete [7]. Improvement of mechanical and durability properties of concrete depend on the conditions, duration and type of curing after concrete construction. After pouring fresh concrete into the mold and when the concrete is hardening, increasing the temperature and reducing the moisture content of the environment and even the wind blowing lead to evaporation of the concrete water. This will prevent the development and completion of the hydration process. On the other hand, reducing the evaporation rate of water and moisture, in addition to the positive effect on the process of obtaining strength, will undoubtedly have a good effect on the amount of shrinkage due to the drying, the permeability and abrasion resistance. Curing with keeping the moisture of concrete and increasing the available amount of water for the hydration process, will improve and accelerate the reaction of cement hydration which cause the strength and durability increment of concrete [8–10]. Various factors such as human error, perpendicularity of structural elements, water shortage or even the difficulty of accessing the place of construction and the distance away carrying water for curing, makes the curing processes completely inadequate. The ideal method for strength gaining and proper curing of concrete is to use water and keep it wet for 28 days. In this method, the saturation conditions for concrete are created by using a water pool or continuously spraying water on the surface of the concrete. Of course, in the construction industry, according to the conditions of implementation and high speed construction, use of wet burlap, plastic or polyethylene sheets and liquid curing materials are common. In some cases, curing materials that protect the concrete surface and prevent the evaporation of its water are used [11]. On the other hand, in many concrete structures, for preventing water evaporation and increasing the water holding capacity in concrete, manufacturers use hydrophilic materials which they are added at the time of concrete construction. These concretes are known as self-curing concretes [12,13]. However, in most projects, the curing process does not completely take place due to various reasons, such as lack of water at the workshop site, a lot of transportation from the place of extraction of water to its place of consumption, depreciation and wear of water transport vehicles, high speed of construction and etc. In such a situation, when concrete is removed from the mold, it is continuously exposed to temperature and ambient air for rest of life. Many researchers have studied the effect of different curing conditions on the properties and performance of concrete. Bingöl and Tohumcu [9] claimed that the use of mineral additives (silica fume and fly ash) and the steam curing method have a positive effect on the process of obtaining strength of samples compare to the air curing method. For fly ash groups, under steam curing the compressive strength ratio was 95% of that of standard water cured samples. All mixtures have decreased in compressive strength at air curing condition. When cement replacement by 5%, 10% and 15% of silica fume compressive strength reduction of 28%, 33% and 37%, respectively. Using 15% of silica fume in SCC through water curing method, had the best outcome in the compressive strength test.

Benli et al [10] assessed the effect of tap water curing, wet sack curing, air curing, and liquid paraffin wax curing on characteristics of SCC mortars after 3–180 days. They concluded that the control mixture was reduction of 15% at the longest period air curing. Of course, added 14% by weight of silica fume (SF) caused strength of all mixtures increased at 180 days in air curing. While the use of 10% and 6% C class fly ash (FA) and silica fume (SF) improves compressive strength by 3% compared to the control mixture in liquid paraffin wax curing. Investigations of Madduru et al [14] show that the optimal use of self-curing additives in SCC mortars, produces desirable mechanical and durability properties. They used two types of self-curing additives called Polyethylene Glycol 4000 and 200, with percentages of 0, 0.1, 0.5 and 1. In their research, three conditions including wet curing, self-curing and no curing were evaluated. For SCC mortars 1:1 with w/c = 0.34, compressive strengths have been increased 27.8% and 45.2% in case of 0.5% PEG 200 and 1.0% PEG 4000 respectively, compared that no cured specimens at 28 days. The results indicate that the use of the self-curing agent improves strength such as wet curing and has a positive effect on resistance of an acid attack. Only in the case of water absorption, curing of samples under self-curing show poor results than no curing samples. Zhao et al [15], indicated that when continuous full water curing condition, continuous full standard curing condition and continuous full room curing are used for curing of mixture up to the age of 3 and 7 days, the SCC can reach 54–59% and 86–87% of 28-days compressive strength. In a number of other studies, the effects of self-curing additives on different types of concrete have been investigated and the results indicate the desirable effect of the use of these materials [16–18]. For a long time, the use of atmospheric steam as a curing method has also been used to improve the process of obtaining strength and increase the amount of products and the rate of hydration, and the best temperature range is 65–85 °C [19,20]. Sajedi et al [21] believed that the positive effect of water curing on strengths of cement - slag mortars is more than the effect of air curing (room temperature). Using 500 kg/m3 cement or cement-slag caused 5.4% and 1.3% reduction of strength at 90 and 56 days, respectively. When specimens cured in air for 3 and 90 days, 7.7% and 48.7% strength loss recorded than those of the specimens cured in water. They claimed that using less binder and providing water curing would result in greater strengths. According to the results of their study, adding the percentage of cement and slag increases the sensitivity. Sajedi [22] reported that curing in air curing reduced the compressive strengths by 2.2% compared to the cure under heat curing. For water after heating curing, when 380 kg/m3 slag and 500 kg/m3 cement slag were used, 2.6% and 4.7% strength loss observed at 7 and 56 days, respectively. Thomas et al [23] examined the durability parameters of concrete with three percentages of recycled aggregate (20%, 50% and 100%) and 24 water-to-cement (W/C) ratios in different curing conditions, believe that the effect of the environment on these types of concrete depends on the cement paste. They report that the negative effect of marine environment curing conditions is either to reduce heat and eliminate moisture (incomplete hydration), or to utilize the porosity of recycled aggregates and to reduce the durability of concrete. Due to the fact that in addition to the curing conditions, the duration of this process is also important and has a significant effect on the mechanical properties of the concrete and the quality and speed of the hydration products, there is also a study on the effects of the curing time on the concrete performance. In this regard, Hiremath and Yaragal [24] studied the different curing conditions (ambient air, hot air, hot water and accelerated curing) and the duration of curing of 1, 3, 6, 9 and 12 h on reactive powder concrete, concluded that the best results

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is related to the conditions of hot water curing. When hot water curing time is 12 h, result show that about 7% and 38% increase compressive strengths versus accelerated curing and hot air curing respectively. In curing with a short duration (about 3 h), accelerated curing has the best and highest strength among different curing conditions. After this time, strength of samples under accelerated curing compared to hot air and hot water curing improve about 11% and 32%, respectively. In this research, we tried to study the properties of SCC by simulating different curing conditions that are commonly used in different workshop site projects. In this study, the results of scanning electron microscope (SEM) and energy-dispersive X-ray (EDS) spectroscopy confirming the improvement of microstructure and hydration products in all different curing conditions. 2. Research significance Several studies have been done on investigating the effect of duration and type of curing on the concrete specification. But these researches were conducted under specific conditions with laboratory facilities. Care should be taken to ensure that the working conditions and what happens in practice and in the workshop environments are often different due to the lack of facilities, the high speed of construction, the lack of proper access, and so on. Because different curing conditions affect the compressive strength of SCC [9] and the hydration process of this concrete due to the high volume of binder depends on the W/C ratio and curing conditions, this study investigates the effects of these parameters on SCC, at operational and practical workshops. 3. Experimental study In this research, three different of water-to-cement ratios (W/ C = 0.35, 0.40, 0.45) were used to construct SCCs mixtures. Then, the effect of different curing conditions such as water curing (wc), plastic curing (pc), out-air curing (oac), room-air curing (rac), wet burlap curing (wbc), out-air-curing compound (oacc) and room-air-curing compound (racc) on properties of the SCCs is investigated. In fact, these curing conditions are customary in different sites and workshops, and better model the actual curing conditions. Curing conditions with water are considered as the standard state and the results of other curing condition are compared with it. The reason for this is to examine the effects of other common practice situations in the workshops and introduces the best curing conditions for improving the quality of concrete in the projects. To evaluate the properties of fresh SCCs, according to the EFNARC [25], the slump flow, V-funnel and L-box tests have been performed. The compressive and splitting tensile strength, water absorption, capillary water absorption (sorptivity) and microstructural study (SEM image and EDS analysis) on hardened concrete samples were investigated and their results reported. 3.1. Materials 3.1.1. Cement For the production of samples, Portland Cement Type (II) (PC) was used as the main powder material accordance with ASTM

C150 [26] in this study. The chemical and physical characteristics of this PC are shown in Tables 1 and 2, respectively. 3.1.2. Aggregate The local river sand and gravel from around the city of Kerman Iran is used as fine and coarse aggregates in this research. These materials have the characteristics in accordance with the ASTM C33 [27]. The characteristics of these aggregates is given in Table 3. In Fig. 1, fine and coarse aggregate passing particles are compared with the upper and lower limits of ASTM C33 [27]. 3.1.3. Water In this research, drinking water was used to production of samples. This water is also used for curing conditions. It should be noted that the drinking water used in the process of this study is in accordance with the ASTM C94 [28]. 3.1.4. Superplasticizer In the production of SCC, high range water reducer or Superplasticizer (SP) are used to improve fresh concrete performance. The specifications of this SP and the permissible limits of the ASTM C494 [29] are given in Table 4. 3.2. Mix proportions In general, three SCC mixes with W/C of 0.35, 0.40 and 0.45 have been made. The three mixtures in this study are illustrated with the names SCC35, SCC40 and SCC45, respectively. For all mixtures, the amount of fine and coarse aggregate and the amount of binder is constant. But in order to achieve the proper performance and workability of the fresh concrete, in addition to the W/C ratio variability, the amount of SP also varies. Details of all mixtures are shown in Table 5. As shown in Table 5, the amount of fine and coarse aggregates are 880 and 750 kg/m3, respectively. The amount of binder is also estimated at 430 kg/m3 for all mixtures. The

Table 2 Physical properties of PC. Physical Properties Specific density (g/cm3) Specific surface area (cm2/g) Setting time (final) (min) Setting time (initial) (min) Autoclave Expansion (%) Compressive strength (kg/cm2)

3 days 7 days 28 days

PC 3.15 2900 170 120 0.1 220 275 380

Table 3 Physical properties of aggregates. Properties

Aggregate

Specific gravity Bulk density (kg/m3) Void content (%) Water absorption (%) Fineness modulus

Fine

Coarse

2.64 1580 42.46 1.35 2.21

2.78 1525 49.01 0.27 –

Table 1 Chemical properties of PC. Constituents

PC

Chemical compositions (%) SiO2

Al2O3

Fe2O3

CaO

MgO

Na2O

K2O

SO3

21.74

5

4

63.04

2

2.3

1

2.9

4

M. Nematollahzade et al. / Construction and Building Materials 237 (2020) 117570

100 90

Fine aggregate

80

Coarse aggregate

Percentage Pass(%)

70 60 50 40 30 20 10 0 0 µm

150 µm

300µm

600µm

1.18 mm 2.36 mm 4.75 mm

9.5 mm

12.5 mm

19 mm

Sieve size (mm) Fig. 1. Aggregate passing particles.

For wc method, samples are placed in a water tank at a temperature of 23 ± 2 °C. In fact, this model is the standard method proposed by the codes. For modeling of rac and oac conditions, the samples are placed after the removed from the molds in the room air and outside air from the laboratory until the test is performed. In wbc condition, such as the actual conditions of operation in the workshops (which are used for concreting and after the opening of the molds for better curing of the elements, they use a wet burlap), the samples are covered with a burlap in an out air, and they are carried out twice a day for watering. Another method used as one of the different curing conditions is plastic coating (pc). For racc and oacc conditions, 24 h after casting, the samples were removed from the molds, first, they are covered with liquid paraffin wax curing and then placed in the room and outside air laboratory, respectively. The various curing conditions investigated in this study are shown in Fig. 3.

Table 4 Properties of SP. Properties

Testing results

ASTM C494

Density (20 °C) PH (20 °C) Chlorine (ppm) Color

1.04 ± 0.02 6.5 850 Light Brown

0.938–1.146 5.4–7.4 2400 –

maximum nominal size of aggregate is 19.5 mm in all SCCs. All SCCs were made in the laboratory in 50 L pan mixer. The process of mixing materials and preparing SCCs is shown in Fig. 2. 3.3. Casting and curing specimens First, the molds are cleaned and lubricated so that they cannot be damaged or broken when the samples are removed from them. Then, concrete pouring in molds is performed after fresh concrete tests. The specimens are then covered with plastic sheets and placed in a laboratory environment at 23 ± 2 °C for 24 h. After this period, the molds are opened and the samples are removed and are placed under the desired curing conditions. The code, age, specification and number of samples used for hardened concrete tests are given in Table 6.

3.4. Testing methods 3.4.1. Fresh properties Fresh concrete tests are performed according to EFNARC [25], to check the flowability, passing ability and filling ability. In the slump flow test, the condition of flow ability of SCCs under its

Table 5 SCC mixtures properties. Mixes

PC (kg/m3)

Fine aggregate (kg/m3)

Coarse aggregate (kg/m3)

Coarse agg./total agg. Ratio

Water (kg/m3)

Water/binder .Ratio

SP (kg/m3)

SCC35 SCC40 SCC45

430 430 430

880 880 880

750 750 750

0.46 0.46 0.46

151 172 194

0.35 0.40 0.45

7.8 6.4 4.2

Fig. 2. Process of mixing materials and preparing SCCs.

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M. Nematollahzade et al. / Construction and Building Materials 237 (2020) 117570 Table 6 The code, age, specification and number of specimens. Test

Codes/Method

Ages

Specification of specimens

Total Numbers of specimens

Compressive strength Splitting tensile strength Water absorption Capillary water absorption

BS 1881: Part 116 ASTM C496 BS 1881: Part 12232 Hall [29]

Cubic – 100  100  100 mm Cylindrical – 100  200 mm Cube – 100  100  100 mm Cube – 100  100  100 mm

252 252 42 42

Electrical resistivity

Mendes et al [31]

7, 14, 28 and 56 days 7, 14, 28 and 56 days 0.5 h, 1 h, 5 h and 24 h 10, 30, 60, 300 min and 1, 3, 7, 14, 28 and 56 days 7, 14, 28 and 56 days

Cylindrical – 100  200 mm

168

Fig. 3. Various curing conditions of SCCs.

own weight is modeled in unobstructed environments. For this experiment, with the aid of the slump cone and evaluating the mean two perpendicular diameter of the concrete, amount of the slump flow is obtained. When this test is performing, the time that it takes for the SCC to reach circular borders with a diameter of 500 mm is recorded and reported as flow time (T500). If the value of this parameter is greater than 5 s, it indicates a high viscosity and, if less than 2 s, the amount of concrete viscosity is low. According to the Table 7, the slump flow test is classified into three classes SF1, SF2 and SF3. The viscosity, flowability and filling ability of SCCs when changing the cross section in the elements is also examined by testing the V-funnel. Of course, this test, simulates the conditions and capability of SCC to passing narrow sections in the absence of blockage and segregation. Table 7 shows the domain of the two classes VF1 and VF2 of the V-funnel test. In the L-box test, passing ability and cohesiveness of fresh concrete are carried out in the presence of reinforcing bars and other obstructions in the direction of concrete movement without segregation or blocking. To evaluate these specifications, we use the ratio of h1/h2 in the L-box test. In fact, in this ratio, h1 is a height of the SCC at the end of the horizontal section and h2 is in vertical section. The ratio of h1/h2 is calculated as the blocking ratio. PA1 and PA2 are the two classes of testing the L-box according to the regulations, which are given in Table 7. T200 and T400 times, which

show the ease of flow during the L-box test, are respectively the arrival time of fresh SCC at a distance of 200 and 400 mm from the gate of the vertical section of the test box. These two parameters can also be used to evaluate the filling capability [30]. 3.4.2. Hardened properties For compressive strength, three samples were used and the average of them were reported (Table 6). This experiment was carried out based on BS 1881: Part 116 [31]. Splitting tensile strength test accordance of ASTM C496 [32] and performed with three cylindrical specimens with 100 mm (diameter) and 200 mm (height) (Table 6). Two cubic specimens used for water absorption test conforming BS 1881: Part 12,232 [33]. After 28 days of curing the specimens, they dried in the oven for 72 ± 2 h and initial mass recorded. Then the specimens completely immersed in water, for evaluating the amount of absorbed water content. After these steps and at ages of 0.5 h, 1 h, 5 h, 24 h and 1, 3, 7, 14, 28 and 56 days, the mass of the specimens was measured again and the amount of water absorption percentage was reported. As shown in Table 6, two cubic samples were used to study the capillary water absorption in this investigation. For this experiment, the samples after being exposed to different conditions (until to 28 days) were placed in oven at 105 ± 5 °C in order to reach a constant weight. Then the four lateral faces were isolated

M. Nematollahzade et al. / Construction and Building Materials 237 (2020) 117570

with paraffin wax and the primary weight of the specimens were recorded accurately. In this case, the two opposite are free. These conditions allow water to flow through the path between the top and bottom surface of the sample. The results of this test was recorded at 0.5 h, 1 h, 5 h and 24 h. For this test, water absorbed Q (cm3), cross sectional area A (cm2) and time T (s) recorded and based on Eq.(1), sorptivity coefficient K (cm/s0.5) was calculated.

Q2

ð1Þ

A2 T

760

20

10

740

16

8

720

12

700 8

680

T500 (s)

Slump flow (mm)

K is measured using the slope of the linear relation Q/A and T. The test was conducted as per Hall’s method [34]. When examining the durability of concrete, one of the parameters that can be calculated in a non-destructive way, and even on the site, is electrical resistivity. Calculation of this parameter

V-final time (s)

K¼

allows engineers to judge the permeable/porous of the material that is effective in the transfer of moisture and ions. Resistance to chlorine ion penetration followed by corrosion resistance is directly related to electrical resistance. As with increasing electrical resistance, it also increases the resistance to chlorine ion and corrosion in concrete. Various manners such as single/one, two or four (Wenner’s method) electrode are used to carry out of this test [35]. In this research, the method proposed by the Mendes et al. [36] was used to carry out this test. The device used in this experiment consists of 4 electrodes with a spacing of 50 mm. The geometric correction factor of this device for cylindrical samples with a diameter of 100 mm and a height of 200 mm is equal to 0.75. Two specimens were used with saturated-dry-surface state, and electrical resistance was recorded at angles of 0, 120 and 360°. Then, the mean value of 9 electrical resistance recorded for the two samples was reported as the final electrical resistance.

4

660 640

0 SCC35

SCC40 Slump flow

6 4 2 0

SCC45

SCC35

SCC40

T500

SCC45

V-Funnel

(a) Slump flow and T500 time test.

(b) V-funnel time test. 2

T200 and T400 (s)

6

T500 (s)

5 4 y = 0.7468x - 1.7663 R² = 0.97

3

0.96

0.95

1.6

0.94

1.2

0.92

0.90 0.9

0.8

0.87 0.88

0.4

2

0.86

0 6

7

8

9

10

h1/h2

6

SCC35

V-Funnel time (s)

SCC40

T200

(c) Correlation between T500 and V-funnel time test.

SCC45

T400

h1/h2

(d) L-box test.

Fig. 4. Results of fresh tests of SCCs.

Table 7 Acceptance criteria for SCC according to EFNARC. Slump flow test

V-funnel test

L-box test

Slump flow classes

Slump flow (mm)

Viscosity classes

V-funnel times (s)

Passing ability classes

Blocking ratio (h2/h1)

SF1 SF2 SF3

550–650 660–750 760–850

VF1 VF2 –

8 9–25 –

PA1 PA2 –

0.8 with 2 bars 0.8 with 3 bars –

M. Nematollahzade et al. / Construction and Building Materials 237 (2020) 117570

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4. Test results

4.2. Hardened properties

4.1. Fresh properties

4.2.1. Compressive strength The compressive strength results of the SCC35, SCC40 and SCC45 mixes in different curing conditions at 7, 14, 28, and 56 days are shown in Fig. 6. Based on Fig. 6(a), it can be seen that for the W/ C of 0.45 at all ages, oacc method has the lowest compressive strength and the highest compressive strength belongs to wc. As the curing age increases, the difference between methods oac and oacc increases. Meanwhile, methods rac, racc and wbc have the same trend in gaining strength in all ages. Al-Gahtani [11] used curing compounds for curing of concrete and reported that these materials were effective in retaining the moisture required for the increase of denseness and strength of concretes. The range of compressive strength variations of SCC45 at 28 days is between 35.8 and 49 MPa. At an early age, there is little difference in the results of different curing conditions, but in older ages, differences in methods are more evident. As it is obvious (Fig. 6(a)), at older ages, both methods pc and wc show high strength than other methods. The use of plastic coatings for the curing of concrete, in addition to preventing the heat dissipation of the hydration phenomenon, caused positively effects and increases the rate of strength acquisition at an early age [37]. At age 28 and 56 days, wc method has 39.9% and 41.1% increase compressive strength compared to oacc method. Using water for curing compared to air curing or wrapped in a plastic sheet will increase compressive strength [38]. Applying the coating for curing is also more convenient than the air curing [39]. Fig. 6(b) shows the compressive strength results of SCC40 at different ages. By investigating the results, as shown in Fig. 6(b), the compressive strength variations for this design are between 43.4 and 54 MPa. The range of variations for SCC40 is more limited than SCC45, and this indicates the performance close to the different processing conditions. Method oacc at 7 and 14 days has the least compressive strength among all methods. However, as age increases, its amount also increases, and method oac has the smallest amount. Mohamed

According to the EFNARC [25], the allowed amount of slump flow for SCC is in the range of 550 to 850 mm. Fig. 4(a) shows that the results of this test for all three mixtures (SCC35, SCC40 and SCC45) are ranged in domain by the EFNARC [25]. By increasing the W/C, the flow ability and slump flow of the SCCs improve. This issue is more obvious for SCC45. According to Table 7 and Fig. 4(a), the SCC produced in Class SF2 are classified. When performing a slump flow test, the moment that fresh SCC is about to start moving, the viscosity is the factor that resists against movement. The T500 time or V-funnel time test evaluate this factor in fresh concrete. Based on Fig. 4(a) and the results obtained from the T500 time test, we can say that the viscosity of SCC35, SCC40 and SCC45 is appropriate and acceptable. The acceptable flow time for the Vfunnel is between 6 and 12 s according to the EFNARC [25]. Fig. 4(b) shows that the results of this experiment are in the range of 6.45 to 9.35 s, which adheres to the domain of the EFNARC [25] and indicates the appropriate flow time. By comparing the results of this experiment with Table 6, the concretes are made in class VF1/VF2. SCC35 has the most flow time, which is the reason for this phenomenon due to the lower W/C ratio. For a better comparison, T500 and V-funnel time test changes are shown in Fig. 4(c). Fig. 4(c) shows a good correlation between these two parameters (R2 = 0.97). EFNARC [25] considers the appropriate amount of blocking ratio for L-box test above 0.8. The results (Fig. 4(d)) show that SCC35, SCC40 and SCC45 have a ratio of 0.87, 0.90 and 0.95, respectively, which is greater than the minimum amount allowed (0.80). SCC35, SCC40 and SCC45, according to Table 7, are Class PA2. The results of T200 and T400 times for all mixtures are presented in Fig. 4(d). It is observed that an increase in the W/C ratio leads to an easy flow of SCCs and increases the filling ability. Fig. 5’s various tests have been used in present experimental study to investigate the fresh properties for mixes compositions.

Fig. 5. Sump flow and L-box test of SCCs.

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M. Nematollahzade et al. / Construction and Building Materials 237 (2020) 117570

[40], also reported that highest and lowest value of compressive strength belong to water and air cured samples, respectively. Bingöl and Tohumcu [9] claimed that loss of compressive strength is due to the evaporation of water and low humidity hydration is not completed. Compressive strength differences in SCC40 and methods rac, racc and wbc increase with age of samples. But for SCC45, this is exactly the opposite, and the strength difference

Fig. 6. Compressive strength of SCCs.

for these methods are evident at an earlier age. In method wc compared with method oacc, for the age of 7 and 14 days, 32.3% and 26% increased, respectively. Zhao et al [15] reported that, when the initial water-curing period increased, compressive strength of SCC at 28 days had more growth. According to Fig. 6(c), for SCC35, the lowest strength value is related to method oac. But as the age increases, the results of methods oac and oacc get closer together. In this water-to-cement ratio (0.35), the pc and wc methods also show the best strength at different ages. Of course, at 56 days, method pc approaches behavioral rac, racc and wbc and shows a higher difference than the 7th method (wc). The best curing conditions (wc) have a strength increase of about 28.4% and 22.5% at the age of 28 and 56 days, respectively, compared to the weakest curing condition (oac). This result is consistent with previous results [41]. For a better comparison, the results of the 28day compressive strength of SCC45, SCC40 and SCC35 in different curing conditions are given in Fig. 6(d). It is understood from Fig. 6(d) that the effect of curing conditions on high W/C ratio, more tangible and more specific. As shown in Fig. 6(d), SCC35 compared to SCC45, in oac, oacc, rac, racc, wbc, pc and wc methodes, increased by 32.9%, 39.7%, 30.3%, 30.4%, 29.2%, 19.3% and 22.8% respectively. These results indicate that oac, oacc, rac, racc and wbc methods are more sensitive to W/C ratio changes. The minimum compressive strength value of 28 days occurs in conditions oacc and water to cement ratio 0.45. 4.2.2. Splitting tensile strength The results of splitting tensile strength at different ages and the W/C ratio are shown in Fig. 7. In general, the behavior of the splitting tensile strength changes of SCC45, SCC40 and SCC35 are similar to the results of compressive strength. Based on Fig. 7(a), the range of variations in the results of the splitting tensile strength of SCC45 at different ages is 1.9 to 4.3 MPa. Changes in this parameter after 14 days are clearer than the rest of the ages. At 7 days of age, rac and racc behave closely together, and with increasing in age, their performance differences are increasing. For SCC45, the differences in wbc, pc and wc methods are more than other methods. Water curing as well as wrapped curing provide better results than air curing [37]. Method wc compared to methods pc, wbc, racc, rac, oacc and oac at 28 days of age has approximately 9.3%, 16.8%, 31.1%, 42.2%, 53.2% and 43.9% increases splitting tensile strength, respectively, and the best performance is belong to this method. At 28 and 56 days, the results vary between 2.6 and 3.9 MPa and 3 to 4.3 MPa, respectively. For the W/C ratio of 0.40, the behavior and performance of the strength of method wc exceeded the other methods (Fig. 7(b)). The range of splitting tensile strength variations in different ages and curing conditions is limited to 1 MPa to 1.4 MPa, which is less than SCC45. After 7 days, method oacc still has the lowest amount. Increasing age causes the method oac to become the least splitting tensile strength. Because, oac of the samples was not able to improve the strengths [22]. SCC40 at 28 days and method wc has a splitting tensile strength value of 4.3 MPa, which is reduced to 3.2 in method oac. At the same age (28 days), the increase in the splitting tensile strength value of method wc compared with methods pc, wbc, racc, rac, oacc and oac is 8.5%, 19.5%, 24.3%, 29.3%, 32% and 34.7%, respectively. By comparing these results with the same investigating as for SCC45, there are fewer values. By assessing the results presented in Fig. 7(b), it is seen that the effect of the type and conditions of curing is more pronounced and more specific at high age. Fig. 7(c) shows that the greatest difference in splitting tensile strength occurs at 14 days with a value of 1.4. But other ages (7, 28 and 56 days) have a difference of less than this value. SCC35 in method wc has the best performance compared to other meth-

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ods. This method (wc) has 42.2%, 43.6%, 35.2% and 35.1% increase in splitting tensile strength value compared to method oac (lowest value) at 7, 14, 28 and 56 days, respectively. Curing condition and its time has a significant effect on strength improvement [22]. Methods pc, wbc, racc, rac, oacc and oac, compared with method wc, show 6%, 13.6%, 17.4%, 24.6%, 30.3% and 35.2% reduction in splitting tensile strength at 28 days, respectively. Austin and

Robins [42] showed that wbc was the best and ac was the worst curing condition between 7 and 28 days. To accurately compare the results, SCC45, SCC40 and SCC35 splitting tensile strength at 28 days and different methods wc, pc, wbc, racc, rac, oacc and oac are shown in Fig. 7(d). Based on Fig. 7(d), SCC35 has 20.3%, 24.1%, 23.8%, 34.4%, 37.3%, 41.6% and 28% increase in splitting

Fig. 7. Split tensile strength of SCCs.

Fig. 8. Water absorption (%) of SCCs.

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tensile strength compared to SCC45 in methods wc, pc, wbc, racc, rac, oacc and oac, respectively. It can be concluded that the rate of change in the high ratio of W/C is more.

4.2.3. Water absorption Fig. 8 show the water absorption values (%) for the SCC45, SCC40 and SCC35, respectively. Based on these figures, methods pc, wbc, wc, racc, oacc, rac and oac, have the best results in the different W/C ratio, respectively. It can be seen from Fig. 8, that in different methods, water absorption decreases with decreasing water-to-cement ratio. In all ages and the ratio of W/C (0.45, 0.40 and 0.35), the difference between the results of methods pc, wbc and wc is more evident and clearer. The most changes in the water absorption parameter in all SCCs and curing conditions are for the first 30 min of the experiment. According to the results, changes in water absorption during the first 30 min are less than 3.6% for all three designs. Then, SCCs classified as poor based on initial water absorption values [43]. The maximum amount of water absorption for SCC45, SCC40 and SCC35 is obtained in

Fig. 9. Water absorption coefficient of SCCs.

method oac and is equal to 9.3%, 8.8% and 8.2%, respectively (at 56 days). While, Aprianti et al [43] claimed that when specimens first put in a hot water (60C for 24 h) for curing, then put in rac caused increase quality of microstructure and reduction of water absorption. By comparing the results, and according to Fig. 8(a), the water absorption rate at younger ages is increased faster for

Fig. 10. Electrical resistivity of SCCs.

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designs with a higher water to cement ratio (SCC45) at different curing conditions. At 28 days, SCC45, SCC40 and SCC35 in method pc compared to method oac have 1.9%, 2.3% and 2% water absorption reductions, respectively. In the ratio of water to cement 0.45, for different curing conditions, the range of variations in water absorption is between 1.7% and 2.7% after 56 days. Gill and Siddique [1] investigated water absorption of SCC incorporating metakaolin and rice husk ash. Their results indicated that porosity was decrease when the curing duration was increased. This phenomenon related to the pozzolanic reaction between calcium hydroxide and silica results in production of C-S-H gel, which further helps in filling the voids resulting in dense concrete. This is as shown in Fig. 8(c), with a decrease in W/C to 0.35, the range of water absorption changes decreases and ranges from 1.6% to 2.4%. This indicates the proper performance of the curing methods in the low water to cement ratio. Particularly methods pc and wbc, which have the least amount of water absorption. At 28 days, the amount and rate of water absorption decreases with reduction in water to cement ratio (Fig. 8(d)). SCC45, SCC40 and SCC35, the percentage of water absorption in all curing conditions at 28 days is between 5.7% and 8.6%. Based on Fig. 8(d), SCC45 performs relatively similarly in conditions oac, rac and oacc. But in SCC40 and SCC35, the water absorption rate is similar in all different curing conditions. 4.2.4. Capillary water absorption The results of the capillary water absorption test are presented in Fig. 9. The results show that by decreasing the ratio of water to cement, the amount of capillary absorption will decrease. By comparing the results of the three designs SCC45, SCC40 and SCC35, it is evident that changes in the water absorption coefficient in water to cement ratio 0.45 are more sensitive to different curing conditions. The variation in the sorptivity value in SCC45, SCC40 and SCC35 is between 0.09 and 2.90, 0.10–2.54 and 0.07–2.37 (104) cm/h0.5, respectively. Siad [44] reported that a suitable correlation between the growth of the strength and the reduction of sorptivity. When compressive strength improve due to increase pozzolanic

11

reaction with time, sorptivity was reduced [45]. In all SCCs and different methods of the curing, the minimum and maximum sorptivity values are related to conditions oac and pc, respectively. The results show that in the initial period test (0.5 h), the capillary water absorption coefficient in the pc method compared to oac method for SCC45, SCC40 and SCC35 decreased by 59.25%, 51.78% and 57.93%, respectively. But at the end period of the test (24 h), the difference between the two methods (pc and oac) is about 70%–80%, for all SCCs. Fig. 9 show that after 1 h from the start of the experiment, a sharp decrease in the amount of capillary water absorption coefficient is evident. In this experiment, the best results belong to method pc, wbc, oacc, wc, racc, rac and oac, respectively. Cakır and Akoz [46] reported that capillary water absorption of samples cured in water are higher than samples cured in humidity cabinet. 4.2.5. Electrical resistivity For testing electrical resistance, the resistance of the material to the flow of electricity is calculated. In fact, this parameter is the relationship between the applied voltage and the electricity current flows from the specimens. This parameter can be used to assess the possibility and amount of corrosion of reinforcement and durability of concrete. Various factors, such as W/C ratio, amount of aggregates, binder type, moisture, temperature, frequency and curing age, affect the electrical resistance of the samples [47]. Fig. 10 show the results of the electrical resistivity test. Based on the results obtained and Fig. 10(a–c), it is evident that the overall trend of the variation of the electrical resistance for all SCCs is similar in different curing conditions. According to the results, up to 28 days, the electrical resistance of various designs has a high rate of change. But from the age of 28 days to the age of 56 days, the rate of change in this parameter decreases. Vipulanandan and Amani [48] reported that increase curing duration caused increase the initial electrical resistivity of the cement composite as well as long term electrical resistivity. It is worth noting that the influence of curing methods on electrical resistivity of SCCs is clearly at the higher W/C. On the other hand, the effect of

Fig. 11. SEM images of SCC35 at different curing conditions. (A) wc, (B) pc, (C) wbc, (D) racc, (E) rac, (F) oacc and (G) oac.

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curing methods on electrical resistance of various mixtures at 56 days is quite clear. The results state that by increasing the W/ C ratio and age, the range of electrical resistance of samples also increases. As shown in SCC45, SCC40 and SCC35, the electrical resistivity changes are between 2.9 and 25.1, 2.8–28.5 and 3.4–3 4.4 kX.cm, respectively (from 7 to 56 days). The presence of porous in the concrete microstructure and water storage in these porous will increase the electrical conductivity in the more w/b ratio [49]. Shadkam et al. [50] also confirms that when the samples are cured in water, strength of SCC is usually better in the lower W/C ratio than conventional concrete. As can be seen from Fig. 10(a–c), the highest and lowest electrical resistivity values belong to methods pc and oac, respectively. Based on Fig. 10(d), by comparing conditions wc, rac, wbc, racc, oacc and pc with method oac, it is seen that the SCC45 has 37.8%, 24.4%, 12.1%, 16.9%, 20.4% and 22.4%, SCC40 has 19.4%, 25.1%, 16.5%, 20.2%, 12.9% and 12%, and SCC35 has 14.4%, 10.7%, 7.7%, 9.3%, 11.7% and 8.7% increase the electrical resistance value at age 28, respectively.

SCC35

4.2.6. Microstructural observation‘ In this part, the influence of different curing conditions on properties of SCC45, SCC40 and SCC35 after 28 days, has been studied by using scanning electron microscope (SEM) of surface morphology and EDS analysis. With studying the results of SEM and with the help of EDS, the presence of cracks and pores, the connection of the pores and the products of hydration are considered more. For a better comparison of the effects of different curing conditions, the SEM images each of the 7 curing methods for SCC35 are shown in Fig. 11. Based on Fig. 11(A), in method wc, the amount of C-S-H gel produced is high, but a continuous crack is also observed. In this method there is no specific pores or un-hydrated particles. Creating a dense gel due to increased hydration products, can improve compressive strength in this method. Fig. 11(B) shows that in method pc, in addition to some un-hydrated particles, small pores appear in the cement paste. It should be noted that in this method there is no clear and obvious cracks, but the amount of hydration products, and in particular C-S-H gel, is less than that of method wc. Reducing the amount of C-S-H gel and the presence of pores

SCC40

SCC45

wc method

rac method

oacc method

Fig. 12. SEM images of SCC35, SCC40 and SCC45 at different curing conditions (wc, rac and oacc).

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Fig. 13. EDS analysis of SCC35 at different curing conditions. (a) wc, (b) pc, (c) wbc, (d) racc, (e) rac, (f) oac and (g) oacc.

will cause loss of strength in this method. In method wbc, the number of pores is more and their size also large, and the amount of un-hydrated particles also increases compared to the wc/pc method Fig. 11(C). Based on the results obtained in Fig. 11(D), it can be said that in method racc, the amount of un-hydrated particles is very high and this factor, along with the number of pores,

continues the downward trend of strength. No clear cracks have been observed in samples cured with this method. The needle shaped ettringite (C6AS3H32) and deep or continuous cracks in Fig. 11(E), represent the incomplete hydatization process in rac method. In method oacc, large pores and high volumes of nonhydrated materials are the main reason for the loss of strength

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Fig. 13 (continued)

(Fig. 11(F)). As shown in Fig. 11(G), the hydration process is carried out in a small amount, and the un-hydrated particles and the increase in the production domain needle shaped ettringite caused a sharp drop in strength in method oac. Investigation by Madduru et al [14] shows that strong crystalline form of C-S-H gel, hexagonal plates of CH and minimum pores in the specimen without cracks observed in wc condition. While, ac condition caused cre-

ation of cracks, amorphous and poor crystalline form of C-S-H and more quantities of CH plates. Hiremath and Yaragal [24] believes that the microstructure of samples cured under heating condition was much different from wc and ac conditions. Based on SEM and EDS results the microstructure analysis showed that increase temperature caused increase quality of C-S-H products. In order to investigate the effect of W/C ratio, SEM images of wc,

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Fig. 13 (continued)

rac and oacc methods are presented in Fig. 12. Fig. 12 shows that with increasing the ratio of water to cement, the amount of particles is not hydrated and the pores in concrete are much higher. These factors have reduced the strength of concrete in a higher water-to-cement ratio. Concrete durability is also affected by these factors, and the negative effect of these factors on concrete performance is evident. Compared with method wc, it is observed that methods rac and oacc have larger pores and more un-hydrated particles. EDS analysis was carried out for SCC35 and in conditions wc, pc, wbc, racc, rac, oac and oacc, and the results are presented in Fig. 13 (a–g) for better investigation, respectively. In different curing methods, the presence of elements such as Si, Ca and Al affects the strength and durability of SCC35. Production of C-S-H/C-A-H and other products of hydration in the presence of such elements improves. According to Fig. 13, method wc has the highest Si/Ca ratio (0.54), which confirms its proper strength. In methods pc, wbc, racc, rac, oac and oacc, this ratio is also 0.39, 0.39, 0.38, 0.32, 0.31 and 0.29, respectively. It should be noted that by increasing the amount of Ca, the hydration products are reduced.

&

&

& 5. Conclusions In this research, the influence of different curing conditions and water to cement ratio on properties of self-compacting concretes was investigated. According to the obtained results, the following conclusions can be drawn: & Increasing the water to cement (W/C) ratio has a positive effect on the fresh properties of self-compacting concrete. All mixtures have good flow-ability and slump flow of SCCs equal to 690–740 mm. Based on the EFNARC and the results, the SCCs with water to cement ratio 0.35, 0.40 and 0.45 are in Classes SF2 (slump flow test), VF1/VF2 (V-funnel test) and PA2 (L-box test). & For different water to cement ratios and ages, water curing (wc), plastic curing (pc), wet burlap curing (wbc), room- air-curing compound (racc), room-air curing (rac), out-air curing (oac) and out-air-curing compound (oacc) conditions have the highest compressive strength, respectively. However, with decreasing W/C ratios, oacc condition show better strength compared to oac condition. Compressive strength of SCC45, SCC40 and SCC35 changes are between 35.8 and 49, 43.6–54 and 49.2– 60.2 MPa at different curing conditions. The results of splitting

&

tensile strength are quite similar to the results of compressive strength test. The rate of strength variation in different curing conditions is more evident in the high W/C ratio. Water absorption test show that SCC45, SCC40 and SCC35 have lower water absorption in methods pc, wbc, wc, racc, oacc, rac and oac, respectively. Amount of water absorption of SCCs in different curing conditions lower than 9% at 28 days. Of course in different curing conditions, water absorption decreases with decreasing W/C ratio. In all ages and the ratio of W/C (0.45, 0.40 and 0.35), the difference between the results of methods pc, wbc and wc is more evident and clearer. The results of the capillary water absorption test show that by decreasing the ratio of W/C, the amount of capillary absorption will decrease. Use of pc and wbc conditions cause capillary water absorption coefficient decreased 46–56% and 28–49%, respectively, compared to wc. By comparing the results of the three mixtures, it is evident that changes in the water absorption coefficient in W/C ratio 0.45 are more sensitive to different curing conditions. In this experiment, the best results belongs to method pc, wbc, oacc, wc, racc, rac and oac, respectively. Based on the results of the electrical resistivity test, it is evident that the overall trend of the variation of the electrical resistance for all SCCs is similar in different curing conditions. According to the results, up to 28 days, the electrical resistance of various designs has a high rate of change. But from the age of 28 days to the age of 56 days, the rate of change in this parameter decreases. SCC45, SCC40 and SCC35, the electrical resistivity changes are between 2.9 and 25.1, 2.8–28.5 and 3.4–34.4 kX. cm, respectively (from 7 to 56 days). It is worth noting that the influence of curing methods on electrical resistivity of SCCs is clearly in the higher W/C. Microstructure studies showed that reducing the amount of CS-H gel, the presence of pores, un-hydrated particles, needle shaped ettringite (C6AS3H32) and deep or continuous cracks are the main causes of the loss of strength in various conditions. However, these factors are more apparent in conditions rac and oacc. SCCs with low W/C ratio and cured in wc condition have dense structure compared to other curing condition. When W/ C ratio increase in different during conditions, the number of pores in paste cement increased, also. This factor have reduced the strength of SCC in a higher W/C ratio. The presence of Si, Ca and Al elements at different curing conditions is confirmed by the analysis of EDS. Lowest and highest Si/Ca ratio of wc, pc, wbc, racc, rac, oac and oacc conditions is 0.54, 0.39, 0.39, 0.38,

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0.32, 0.31 and 0.29, respectively. This matter indicates that when the concrete is cured without water and moisture, the amount of Ca in the concrete will increase and this phenomenon will cause a decrease in strength. Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. References [1] A.S. Gill, R. Siddique, Durability properties of self-compacting concrete incorporating metakaolin and rice husk ash, Constr. Build. Mater. 176 (2018) 323–332. [2] A. Khaloo, E.M. Raisi, P. Hosseini, H. Tahsiri, Mechanical performance of selfcompacting concrete reinforced with steel fibers, Constr. Build. Mater. 51 (2014) 179–186. [3] P. Rajhans, G. Chand, N. Kisku, S.K. Panda, S. Nayak, Proposed mix design method for producing sustainable self-compacting heat cured recycled aggregate concrete and its microstructural investigation, Constr. Build. Mater. 218 (2019) 568–581. [4] K. Ma, J. Feng, G. Long, Y. Xie, X. Chen, Improved mix design method of selfcompacting concrete based on coarse aggregate average diameter and slump flow, Constr. Build. Mater. 143 (2017) 566–573. [5] J.L. García Calvo, M.C. Alonso, L. Fernández Luco, M. Robles Velasco, Durability performance of sustainable self-compacting concretes in precast products due to heat curing, Constr. Build. Mater. 111 (2016) 379–385. [6] A.M. Ramezanianpour, Kh. Esmaeili, S.A. Ghahari, A.A. Ramezanianpour, Influence of initial steam curing and different types of mineral additives on mechanical and durability properties of self-compacting concrete, Constr. Build. Mater. 73 (2014) 187–194. [7] Sh. Mohd, P. Jagdish, M. Amjad, Effect of GGBFS on time dependent compressive strength of concrete, Constr. Build. Mater. 24 (8) (2010) 1469– 1478. [8] F. Sajedi, H.A. Razak, Effects of curing regimes and cement fineness on the compressive strength of ordinary Portland cement mortars, Constr. Build. Mater. 25 (2011) 2036–2045. [9] A.F. Bingöl, I. Tohumcu, Effects of different curing regimes on the compressive strength properties of self-compacting concrete incorporating fly ash and silica fume, Mater. Des. 51 (2013) 12–18. [10] A. Benli, M. Karatas, Y. Bakir, An experimental study of different curing regimes on the mechanical properties and sorptivity of self-compacting mortars with fly ash and silica fume, Constr. Build. Mater. 144 (2017) 552–562. [11] A.S. Al-Gahtani, Effect of curing methods on the properties of plain and blended cement concretes, Constr. Build. Mater. 24 (2010) 308–314. [12] M.S.R. Chand, P.S.N.R. Giri, G.R. Kumar, P.R. Kumar, Paraffin wax as an internal curing agent in ordinary concrete, Mag. Concr. Res. 67 (2) (2015) 82–88. [13] B.H. Nagaratnam, A. Faheem, M.E. Rahman, M.A. Mannan, M. Leblouba, Mechanical and durability properties of medium strength self-compacting concrete with high-volume fly ash and blended aggregates, Period. Polytech. Civil Eng. 59 (2) (2015) 155–164. [14] S.R.C. Madduru, S.N.R.G. Pallapothu, R.K. Pancharathi, R.K. Garje, R. Chakilam, Effect of self-curing chemicals in self compacting mortars, Constr. Build. Mater. 107 (2016) 356–364. [15] H. Zhao, W. Sun, X. Wu, B. Gao, Effect of initial water-curing period and curing condition on the properties of self-compacting concrete, Mater. Des. 35 (2012) 194–200. [16] A. Anantrao-Patil, M.R. Vyawahare, Comparative study on durability of selfcured SCC and normally cured SCC, Int. J. Sci. Res. Eng. Technol. 3 (8) (2014) 1201–1208. [17] A.S. Dieb, Self-curing concrete: water retention, hydration and moisture transport, Constr. Build. Mater. 21 (2007) 1282–1287. [18] M.S.R. Chand, P.S.N. Ratna-Giri, P.R. Kumar, G.R. Kumar, C. Raveena, Effect of self-curing chemicals in self compacting mortars, Constr. Build. Mater. 107 (15) (2016) 356–364. [19] S. Türkel, V. Alabas, The effect of excessive steam curing on Portland composite cement concrete, Cem. Concr. Res. 35 (2005) 405–411. [20] S. Mindess, J.F. Young, Concrete, Prentice Hall, 1981. [21] F. Sajedi, H.A. Razak, H.B. Mahmud, P. Shafigh, Relationships between compressive strength of cement–slag mortars under air and water curing regimes, Constr. Build. Mater. 31 (2012) 188–196. [22] Fathollah Sajedi, Effect of curing regime and temperature on the compressive strength ofcement-slag Mortars, Constr. Build. Mater. 36 (2012) 549–556. [23] C. Thomas, J. Setiéna, J.A. Polanco, A.I. Cimentada, C. Medina, Influence of curing conditions on recycled aggregate concrete, Constr. Build. Mater. 172 (2018) 618–625.

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