An investigation into the influence of superabsorbent polymers on the properties of glass powder modified cement pastes

Construction and Building Materials 149 (2017) 236–247

Contents lists available at ScienceDirect

Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat

An investigation into the influence of superabsorbent polymers on the properties of glass powder modified cement pastes Mahsa Kamali, Ali Ghahremaninezhad ⇑ Department of Civil, Architectural and Environmental Engineering, University of Miami, Coral Gables, FL 33146, United States

h i g h l i g h t s
Glass powders were shown to affect the absorption of SAP in pore solutions and in the cement pastes.
Addition of SAP decreased the electrical resistivity of the glass powder modified cement pastes.
The improvement in hydration with SAP was similar in the cement pastes with and without glass powders.

a r t i c l e

i n f o

Article history: Received 29 December 2016 Received in revised form 4 April 2017 Accepted 15 April 2017

Keywords: Superabsorbent polymers Cement paste Glass powder Absorption Hydration

a b s t r a c t This study examines superabsorbent polymer (SAP) absorption, mechanical strength, hydration, and electrical resistivity of glass powder modified cement pastes. The absorption of SAP was monitored using optical microscopy and shown to be higher when glass powders were used. Addition of SAP was found to improve hydration due to internal curing. The cement pastes with SAP exhibited a decreased compressive strength due to macrovoid formation. The glass powder modified cement pastes experienced a large reduction in electrical resistivity as a result of SAP addition; increased pore connectivity in these cement pastes is suggested as a possible cause of the reduction in electrical resistivity. Ó 2017 Elsevier Ltd. All rights reserved.

1. Introduction Autogenous shrinkage induced cracking is a critical issue in high performance cementitious materials [1–7]. In low water/binder ratio cementitious materials, the water in the mixture is gradually depleted during the hydration reaction and as a result, the relative humidity of microstructure is decreased [8,9]. When relative humidity in the pore structure of cementitious materials is decreased, the capillary pore pressure is increased, resulting in autogenous shrinkage in the solid skeleton of the microstructure. Due to mechanical constraint, the autogenous shrinkage generates tensile stress, which can cause crack formation in the cementitious materials at early age when the materials have a low tensile strength [10,11]. Internal curing to maintain high relative humidity inside the material with the use of an internal water reservoir has been shown to be a viable method to reduce autogenous shrinkage in cementitious materials [1,2,10,12–21]. Superabsorbent polymers ⇑ Corresponding author. E-mail address: [email protected] (A. Ghahremaninezhad). http://dx.doi.org/10.1016/j.conbuildmat.2017.04.125 0950-0618/Ó 2017 Elsevier Ltd. All rights reserved.

(SAP) have received increasing attention as an internal curing agent in recent years [2,10,17–21]. A key advantage of SAP is its versatility in size distribution and absorption/desorption characteristics, which allow it to be adapted to specific mix designs. Prior studies have shown improvements in the hydration of cementitious materials when SAP was used due to internal curing [19,22,23]. The potential of SAP to increase microstructure densification has been discussed in previous work [21,23–26]. The effect of SAP on the transport behavior was studied [18,19,27] and enhancement in the resistance to chloride permeability was indicated [18,19]. However, cementitious materials containing SAP have been found to exhibit a general reduction in compressive strength as a result of the formation of macrovoids due to SAP absorption in the fresh mixture [4,21,28–30]. It is important to note that the cement mix design and the physical and chemical characteristics of SAP strongly affect their influence on cementitious materials [4,7,18,20,29]. Supplementary cementitious materials (SCM) are commonly utilized in cementitious materials to improve their durability characteristics and extend their service life [31]. Utilization of waste glass powder as a viable supplementary cementitious material

237

M. Kamali, A. Ghahremaninezhad / Construction and Building Materials 149 (2017) 236–247

2. Experimental methods 2.1. Materials and sample preparation In this study a sodium polyacrylate SAP was used. The size distribution of SAP is depicted in Fig. 1a, indicating a median size of 200 lm. An SEM micrograph of SAP is shown in Fig. 1b. The size distribution was obtained by evaluating the SEM micrographs of about 100 particles using the ImageJ software. A type I/II Portland cement was used in the preparation of samples. In this study, two glass powders with different chemical compositions were used. GP-I is made of amorphous calcium aluminosilicate processed from waste glass fibers and GP-II is obtained from post-consumer recycled glass. The chemical compositions of the cement and glass powders are listed in Table 1. GP-I and GP-II had a similar median particle size of about 8.4 lm per manufacturer’s specifications. The absorption behavior of SAP is governed by the chemical characteristics of solutions such as ionic strength and pH [54– 56]. Ions, including Na+, K+, Ca2+ and OH, are present in the pore solution as a result of cement clinker dissolution during hydration. The addition of supplementary cementitious materials, such as glass powder, affects the pore solution chemistry, which influences the SAP absorption behavior in the cementitious mixtures. Such an effect has not been examined in the past; therefore, the interaction between SAP and the extracted pore solutions of glass powder modified cement pastes was evaluated in this paper. Fresh mixtures with a 0.36 water/binder ratio were prepared and used to extract pore solutions. Control cement paste without glass powder and cement pastes with 20%, by binder mass, replacement of cement with GP-I and GP-II were prepared. A

100

(a)

80

Percentage (%)

has received increased attention due to the rising cost of local virgin materials and the environmental impact of replacing cement in civil engineering applications [32–44]. Prior investigations have indicated that microscale size glass powders improve the durability characteristics of the materials [33,34,37,38,40,45–49]. The pozzolanic properties of glass powder with a microscale size distribution is responsible for the observed enhancement in the performance of cementitious materials [32,34,37,50,51]. A few studies examined the drying shrinkage of cementitious materials modified with glass powder [35–37,52]. Shayan and Xu [35,37] showed that the drying shrinkage of concrete modified with glass powder was acceptable. Sharifi et al. [52] indicated a decrease in drying shrinkage as a result of using glass powder, while Kara et al. [36] concluded an opposite trend. A few prior efforts studied the effect of SAP on the properties of cementitious materials blended with supplementary cementitious materials such as fly ash [25,53], silica fume [18,20] and ground granulated blast furnace slag [18,53]. However, studies on the influence of SAP on the behavior of glass powder modified mixtures do not exist in the literature. Knowledge of the effect of SAP on the performance of the glass modified mixtures is necessary for the design of such materials in internal curing applications. The aim of this study is to focus on this knowledge gap by studying how the addition of SAP influences the hydration, strength and transport properties of glass powder modified mixtures. The detailed interaction between SAP and the cement pastes modified with glass powder was studied. Hydration at early age was evaluated using semi-adiabatic calorimetry and at late ages using nonevaporable water content measurement. Electrical resistivity as a measure of the transport property of cementitious materials was assessed with electrochemical impedance spectroscopy (EIS). The change in the microstructural features arising from the addition of SAP was examined using scanning electron microscopy (SEM), X-ray diffraction (XRD), and thermogravimetric analysis (TGA).

60

40

20

0 0

50

100

150

200

250

300

350

400

Particle Size (μm) (b)

500 μm Fig. 1. (a) Cumulative size distribution of SAP particles. (b) Scanning electron micrograph image of SAP particles.

Table 1 Chemical compositions of cement, GP-I and GP-II. Composition (%)

Cement

GP-I

GP-II

SiO2 Al2O3 Fe2O3 CaO MgO Na2O K2O SO3 TiO2 B2O3 Loss on ignition (%) Median particle size (lm)

20.8 5 3.7 64.2 0.9 0.2 0.4 2.8 0.2

57.5 12.7 0.06 22.7 3.6 0.62 0.06 0.22 0.98 0–6 0.5 8.4

63.3 6.4 0.31 17.1 4.5 6.1 0.07 0.19 0.44 0–5 1 8.4

2.14

lignosulfonate-based superplasticizer (WRDAÒ 60, W. R. Grace & Co.-Conn.) at a concentration of 0.5%, by binder mass, was added to all cement pastes to improve workability. Water and binders were mixed at a slow speed for about 30 s followed by mixing at a medium speed for another 60 s. The pore solution was obtained by filtering cement pastes through a glass microfiber filter subject to a negative pressure in a filtration setup. To track the influence of changing pore solution chemistry on SAP absorption in each paste, the filtration process started at two different times corresponding to 0 and 50 min after the initial contact of water and binders. It should be noted that the filtration lasted for about 15–20 min and this can be accounted for in determining the actual time of the pore solution. The extracted pore solution was immediately stored in polypropylene bottles to avoid carbonation. The mix designs of the cement pastes cast in the experiments are listed in Table 2. Cement pastes were prepared with an effec-

238

M. Kamali, A. Ghahremaninezhad / Construction and Building Materials 149 (2017) 236–247

Table 2 Mix designs of the cement pastes used in the experiment. Mix design

Cement (%)

GP-I (%)

GP-II (%)

SAP (% cement)

Water/Binder

Ctrl Ctrl + SAP GP-I GP-I + SAP GP-II GP-II + SAP

100 100 80 80 80 80

0 0 20 20 0 0

0 0 0 0 20 20

0 0.3 0 0.3 0 0.3

0.3 0.36 0.3 0.36 0.3 0.36

tive water/binder ratio of 0.3. Control specimens without glass powders and specimens with 20%, by binder mass, replacement of cement with GP-I and GP-II were used. Cement pastes containing a 0.3%, by binder mass, addition of SAP were cast. In order to account for water absorption by SAP during mixing, additional water equal to a water/binder ratio of 0.06 was added to the cement pastes containing SAP to maintain the same effective water/binder ratio in all cement pastes. The estimated absorbed water by SAP was made based on the SAP absorption in the extracted pore solution, which is 20 g/gdry, as measured in our previous study [29]. The pore solution used to obtain this estimate of water absorption was obtained from a mixture with a water/ cement ratio of 0.5, while in the current study the pore solution was obtained from a mixture with a water/binder ratio of 0.36. However, in spite of potential variation in the accurate SAP absorption in the current water/binder ratio, the focus here is to understand the SAP absorption when glass powders are used in the mix design and the effect of SAP on the properties of the blended cementitious materials. It should be noted that the determination of additional water based on the flowability of mixtures has been suggested in some studies [4]. However, this method does not directly determine the absorbed water by SAP. The superplasticizer at a concentration of 0.5%, per binder mass, was added to the cement pastes to increase workability. For the cement pastes with SAP, dry SAP powder was dispersed in the binder by mixing for 3 min using a mixer. Then, the mixed binder and SAP were mixed with water. Cement paste cubes (50  50  50 mm) were cast according to ASTM C 109. The mixtures were poured in molds in two layers with each layer being tamped several times in accordance with ASTM C 109. Samples were sealed in double-layer polyethylene bags to protect them from evaporation. The cubes were removed from the molds after 24 h and immediately sealed again until testing.

2.2. SAP absorption 2.2.1. SAP absorption in pore solutions The absorption of SAP particles in the pore solutions extracted from cement pastes with and without glass powders was measured. The absorption of SAP particles was measured using optical microscopy. Dry SAP particles remaining on the sieve #40 (mesh width: 420 lm) were used in the experiment to have a more uniform distribution of SAP particle size. SAP particles were fully submerged in the solutions in a petri dish. Images of the SAP particles before and after absorption were taken using a micro camera with a resolution of 1280  960 pixel2. The absorption of SAP particles were monitored for about 30 min, after which point the absorption did not change. The petri dish containing the solution and SAP particles was sealed during the experiments and the seal was removed only for taking images. The image analysis software ImageJ was used to measure the change in the SAP particle size. The average measurement of six particles was evaluated and reported for each pore solution. The pH of the solutions was also measured using a pH meter.

2.2.2. SAP absorption in cement paste The absorption of SAP in the cement pastes was examined to study the interaction between SAP and the cementitious matrix. To this end, the size of macrovoids formed in the microstructure as a result of SAP absorption was measured. The size of macrovoids corresponds to the maximum absorption of SAP particles before the setting of the cementitious matrix. After setting, with continued hydration and water consumption, the relative humidity gradually drops, developing capillary forces which are the driving force for the desorption of SAP. Sections of the cement pastes with and without glass powders were prepared by cutting cement paste cubes using a saw. The sections of the cement pastes were imaged using a micro camera to include about 200–220 macrovoids from each cement paste to account for the statistical variation of the macrovoid size. 2.3. Fourier transform infrared spectroscopy (FTIR) The change in the chemical structure of SAP particles after absorption in the pore solutions was studied with FTIR. After absorption, SAP particles were dried in a vacuum oven at 40 °C for 24 h. A medium temperature was used for drying to prevent potential changes to the chemical structure of SAP. The FTIR analysis was performed using a Perkin Elmer Paragon 1000 FTIR with an ATR accessory in the transmission mode in the range of 650– 4000 cm1. 2.4. Semi-adiabatic calorimetry The hydration temperature of the cement pastes was evaluated using semi-adiabatic calorimetry. The hydration temperature measurement was carried out using a Grace AdiaCal calorimeter. To this end, cement pastes were mixed and about 300 g was immediately transferred into the instrument for testing. The time between the initial mixing and start of testing was minimized to less than five minutes. Temperature data was collected at a rate of 1/min. 2.5. Non-evaporable water content The hydration degree of the cement pastes at various ages was studied via measuring the non-evaporable water content of the cement pastes. The chemically bound water in the product of the reaction between water and binder is measured and used to determine the degree of hydration of cement pastes [50,57–59]. For sample preparation, cement paste pieces were ground into powder using a mortar and pestle. A small amount of the powder (5–7 g) with a particle size smaller than 250 lm was obtained by sieving and then dried at a temperature of 105 °C for about one day to remove capillary water from the cement paste powder. In order to determine the amount of chemically bound water in the cement paste powder, the powder was placed in a muffle furnace with a temperature of 1000–1100 °C for about three hours. The mass of the powder after initial drying (M1) and after ignition in the muffle furnace (M2) was measured using a balance with a resolution of

M. Kamali, A. Ghahremaninezhad / Construction and Building Materials 149 (2017) 236–247

0.0001 g. The following equation was used to obtain the nonevaporable water content per mass of binder (Wnew):

W new ¼

M1  M2 M

2

  c GPI;GPII  f LOIc þ f LOIGPI;GPII

ð1Þ

where LOIc and LOIGP-I,GP-II are the loss on ignition of the cement, and GP-I or GP-II, respectively, and fc and fGP-I,GP-II are the mass fraction in the binder of the cement, and GP-I and GP-II, respectively. The values of LOIc and LOIGP-I,GP-II are listed in Table 1. 2.6. TGA The calcium hydroxide (CH) content of the cement pastes was measured using TGA. TGA has been extensively utilized in the prior investigations to evaluate the CH content of cementitious materials [50,60–62]. The sample preparation consisted of grinding the hardened paste, passing it through the sieve #60, and vacuum drying it at 105 °C for 24 h. About 30–40 mg of the cement paste powder was analyzed in a Netzsch TG at a heating rate of 10 °C/min in a temperature range of 23–1000 °C. Mass reduction occurring between 400 °C and 500 °C is attributed to the conversion of calcium hydroxide into CaO and H2O. The amount of calcium hydroxide normalized with respect to the mass fraction of cement in the binder was determined as follows:

Calcium Hydroxide ðCHÞ ¼

74:1 M 18:0 f c M

ð2Þ

where M (mg) is the mass change corresponding to calcium hydroxide reaction, M (mg) is the initial sample mass, and f c is defined in Eq. (1). 2.7. XRD The phase composition of the hydration product in each cement paste was studied using XRD. This technique has been widely used to examine the phase composition of cementitious materials [63– 65]. The sample preparation for this test was the same as in TGA. The diffraction analysis was conducted with a Siemens 5000D Xray diffractometer. Samples were scanned at a rate of 1 deg/min and step size of 0.02 deg/step using a Cu Ka radiation source.

239

pre-wetted in a sodium chloride solution with a concentration of 1 mol was inserted between the sample surfaces and electrodes. The resistivity measurements were carried out with AC signals of 250 mV and a frequency range of 106 to 10 Hz using a Gamry Reference 600 potentiostat/galvanostat. The electrical resistivity q (X. m) was determined using the equation, q = RS/a, where R is the measured resistance (X) corrected for the resistance of the two pieces of wetted foam, a is the cube thickness (m), and S is the cube surface area in contact with the electrode (m2). Electrical resistivity of three replicates of each cement paste cube was measured and the average value was reported. 2.10. Scanning electron microscopy and elemental analysis The effect of SAP on the microstructure of the cement pastes at 28 days was examined using SEM. For SEM examination, cement paste pieces with a 5–10 mm thickness were fully soaked in acetone, vacuum oven dried at a temperature of 60 °C for 48 h, and then encapsulated in an epoxy. The polishing was carried out using SiC sand papers of grit sizes 180, 300, 600, and 1200 with ethanol as the polishing fluid. The surface of the samples was then polished using an abrasive medium consisting of a 1 mm diamond paste and ultrasonically cleaned in ethanol for 15 min. The samples were gold-palladium coated to prevent surface overcharging during the microscopic examination. The imaging was carried out in the backscatter mode (BSE) to permit the analysis of different constituents based on atomic number. Thus, pores appear as dark regions and the unhydrated cement particles are seen as the brightest phase in the images. This allows for the identification of the pores, which can be used to obtain quantitative characteristics such as porosity. SEM imaging was carried out using a JEOL JSM-6010PLUS/LA at the 15 kV accelerating voltage. Five images of each cement paste were taken to account for statistical variation inherent to the microstructure of cementitious materials. In order to quantify pore characteristics, images were segmented using the overflow method [69,70] in the image analysis software ImageJ. A cutoff limit was established for a pore area to avoid noises in the pore area analysis. Porosity was calculated as the percentage of pores’ area in each image. 3. Results and discussion

2.8. Compressive strength 3.1. Absorption of SAP in pore solution The compressive strength measurement was carried out using the cement paste cubes with and without SAP at 4 days, 7 days and 28 days of age. A SATEC material testing instrument was used for the compressive strength tests. Three replicate specimens were used and the average value was reported. 2.9. Electrical resistivity Morphological characteristics of pores and the chemistry of pore fluid in cement paste determine the electrical resistivity of the material. Thus, electrical resistivity provides insights into the microstructure of the cementitious materials and their resistance to the ingress of deleterious substances [66,67]. In this study, electrical resistivity measurement was conducted at three different ages (4, 7 and 28 days) using the EIS technique. This technique has proven reliable to obtain the electrical resistivity measurement of cementitious materials and avoids issues, including charge transfer resistance at electrodes, associated with the use of direct current [34,68]. In this test, the surface of cement pastes cubes was first dried and then the cubes were placed between two conductive plate electrodes. In order to ensure conductivity at the interface of the sample surface and electrodes, a piece of foam

The absorption of SAP particles in the pore solutions extracted 0 and 50 min after mixing, referred to as set 1 and set 2, is shown in Fig. 2. The pH of the pore solutions is listed in Table 3. Images showing the absorption of SAP particles in set 1 are illustrated in Fig. 3. It is seen that the absorption of SAP particles was higher in set 2 than in set 1. This increase in SAP absorption can be attributed to the higher pH level of set 2 than set 1, which results from increased dissolution of cement particles increasing the concentration of OH in the pore solutions over time. It is interesting to note the dynamic absorption behavior of SAP in the solutions. While the SAP absorption in the solution corresponding to GP-I was the lowest in set 1, it increased in set 2 and reached the highest absorption among the pore solutions. The absorption of SAP particles in the pore solutions is influenced by the pH and concentration of counterions, primarily Ca2+, Na+, and K+. The increase in pH in the pH range of the pore solution (13–13.5) results in the hydrolysis of the polymeric networks of SAP particles, reducing the stiffness and increasing the water absorption of SAP particles. On the other hand, the presence of counterions reduces the absorption due to the shielding effect and complexation, decreasing the repulsive forces between the

240

M. Kamali, A. Ghahremaninezhad / Construction and Building Materials 149 (2017) 236–247

Absorbed Diameter/Dry Diameter

3.5

(a) Set 1

Ctrl

3

GP-I GP-II

2.5 2 1.5 1 0.5 0

Absorbed Diameter/Dry Diameter

3.5

(b) Set 2

Ctrl

3

GP-I GP-II

2.5 2 1.5 1

GP-II modified pastes, respectively. It should be noted that the macrovoid size is calculated based on the diameter of an equivalent circle of the same area measured from 2D imaging. Assuming an average diameter of about 200 lm for the dry SAP, the ratio of absorbed to dry diameter of SAP is determined to be 3.85, 4.15 and 4.56 for the control cement paste and the GP-I and GP-II modified pastes, respectively. It is interesting to note the difference in the macrovoid size in different cement pastes and to compare this with the results of absorption in the extracted pore solutions. Comparison of the change in the size of SAP in the extracted pore solutions and cement pastes indicates the dynamic nature of SAP absorption in the cement pastes arising from dynamic evolution of the pore solution chemistry at early age. Larger SAP absorption in the cement pastes calculated from the macrovoid size measurement than in the extracted pore solutions can be observed. It is worth noting the difference in the macrovoid size in different cement pastes. The increase in the macrovoid size in the pastes with glass powders could be due to larger available water in these cement pastes since GP-I and GP-II are inert at early age and do not consume water. In addition to the effect of pH and counterion concentrations in the pore solution, the effect of mechanical constraint of the cementitious matrix could also influence the SAP absorption. An increase in the setting time of the GP-II modified paste relative to the control cement paste was observed (data not shown here). Thus, it is likely that SAP absorption was allowed to continue in this cement paste longer than in the control cement paste. The results of macrovoid size measurement discussed above help shed light onto the effect of supplementary cementitious materials on the behavior of SAP and are useful in the design of internal curing applications of blended cementitious materials.

0.5

3.3. FTIR 0 Fig. 2. Absorption of SAP particles in the pore solutions extracted (a) 0 min (set 1) and (b) 50 min (set 2) after initial mixing of binder and water. Ctrl, GP-I and GP-II correspond to the pore solution extracted from the control cement paste, cement paste with GP-I and the cement paste with GP-II, respectively.

Table 3 pH of the extracted pore solutions.

Extracted after 0 min (set 1) Extracted after 50 min (set 2)

Control

GP-I

GP-II

13.11 13.52

12.98 13.39

13.18 13.38

negatively charged polymeric networks of SAP [10,20,29,71]. Thus, these two opposing mechanisms affect the absorption of SAP particles in the pore solutions. It should be noted that the osmotic pressure also contributes to the SAP swelling behavior.

The FTIR spectra of SAP before and after absorption in the pore solutions corresponding to Ctrl, GP-I and GP-II in set 2 are plotted in Fig. 6. A broad peak between 2400 and 3600 cm1 is evident in all spectra, which is associated with O–H stretching indicative of hydrogen bonds in the SAP molecular structure. The peaks at about 1410 cm1 and 1570 cm1 correspond to carboxylates (C–O) [72]. A weak peak at about 766 cm1 is observed, which can be attributed to the amides of crosslinker. A peak at 878 cm1 appears in the spectra corresponding to SAP absorbed in the pore solutions, and this peak is more pronounced in the GP-II spectrum. This peak corresponds to the out-of-plane bending vibration of amines c (N–H), which can be attributed to the hydrolysis of amides from the crosslinker [72]. The appearance of this peak in the SAP after absorption indicates the potential change in the molecular structure of SAP in the pore solution, which could influence the SAP absorption behavior. 3.4. Semi-adiabatic calorimetry

3.2. Absorption of SAP in cement paste The size distribution of macrovoids formed as a result of SAP absorption in the microstructure of the cement pastes is shown in Fig. 4. Examples of macrovoids and an entrained air void in the cement pastes are also depicted in Fig. 5. Desorbed SAP was observed in most of the macrovoids selected for measurement. Macrovoids are differentiated from entrained air voids based on their morphology; entrained air voids exhibit a round morphology, but the macrovoids caused by SAP have an irregular shape. It is seen that macrovoids seem to be slightly larger in the cement pastes containing GP-I and GP-II than in the control cement paste. The average size of macrovoids was calculated to be 770 lm, 830 lm, and 912 lm in the control cement paste and GP-I and

The hydration temperature results of different cement pastes are shown in Fig. 7. It is seen that the GP-I and GP-II modified cement pastes showed a lower hydration temperature than the cement paste without glass powder. This is attributed to the effect of dilution, where less cement is available to participate in the hydration reaction at early age. It is seen that the GP-I modified cement paste exhibited a slightly earlier temperature peak compared to the GP-II modified cement paste. The earlier peak of the GP-I modified cement paste compared to the GP-II modified cement paste could be attributed to the difference in the chemical composition of GP-I and GP-II, and better dispersibility of GP-I than GP-II in the mixture. Even though both GP-I and GP-II have a similar median particle size, it was observed that GP-II had a small tendency to agglomerate compared to GP-I. It is noted that the

M. Kamali, A. Ghahremaninezhad / Construction and Building Materials 149 (2017) 236–247

(a)

241

(b)

Dry SAP particle

2 mm

Swollen SAP particle

Ctrl

(c)

(d)

Dry SAP particle

GP-I (e)

(f)

Dry SAP particle

GP-II Fig. 3. Images of dry and absorbed SAP particles in set 1 corresponding to (a, b) the control cement paste, (c, d) the cement paste with GP-I, and (e, f) the cement paste with GP-II. All images have the same magnification as Fig. 3a.

hydration temperature of Ctrl and Ctrl-SAP is similar and addition of SAP at the rate used here did not seem to influence the hydration temperature in the control cement paste. The addition of SAP slightly shifted the occurrence of the temperature peak in the cement paste with GP-I and to a lesser extent in the cement paste with GP-II. A potential explanation for the earlier peak in the GP-I and GP-II modified cement pastes with addition of SAP could be increased water absorption by SAP, thereby reducing the effective water/cement ratio in these cement pastes compared to the cement pastes without SAP, which accelerates hydration in the beginning hours of the contact between water and cement particles [73]. A reduction in the time corresponding to the hydration peak with decreased water/cement ratio was shown in [73]. The increase in SAP absorption in the GP-I and

GP-II modified cement pastes relative to the paste without glass powders was shown in Fig. 4. 3.5. Degree of hydration The results of non-evaporable water content (Wnew) measurement at different ages are shown in Fig. 8. An increase in Wnew with age is observed in the cement pastes as the hydration continues and more hydration products are formed in the cement pastes. It is observed that the GP-I and GP-II modified cement pastes demonstrated a reduced Wnew relative to the control cement paste. This is due to replacing 20% of cement with the glass powders in the modified pastes. Due to dilution there will be more water available for the cement in the pastes modified with glass powders and this is expected to improve hydration. In addition, glass powders can

242

M. Kamali, A. Ghahremaninezhad / Construction and Building Materials 149 (2017) 236–247

3.6. TGA

0.35

Ctrl, average macrovoid size = 0.770 mm GP-I, average macrovoid size = 0.830 mm GP-II, average macrovoid size = 0.912 mm

Distribution Probability

0.3 0.25 0.2 0.15 0.1 0.05 0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

More

Macrovoid Size (mm) Fig. 4. Size distribution of macrovoids in the control cement paste and the GP-I and GP-II modified cement pastes.

improve hydration through cement hydration enhancement as well as pozzolanic reaction. It is seen from the figure that the difference in Wnew between the control cement paste and the glass modified cement pastes is smaller than 20%, which is the cement replacement percent. This indicates an improvement in hydration in the cement pastes modified with glass powders. Hydration is seen to increase in the cement pastes with SAP due to the internal curing effect providing additional water during curing of the cement pastes. It is realized that the effect of SAP on the evolution of W new was similar in the cement paste without glass powders and the GP-I and GP-II modified cement pastes, as seen from the figure.

Ctrl

The results of the calcium hydroxide content measurement normalized with respect to the cement mass fraction of binder obtained from TGA are shown in Fig. 9. Cement pastes with SAP showed a higher calcium hydroxide content than the pastes without SAP except for the GP-I modified cement paste at the age of 28 days. It appears that the increase in the calcium hydroxide content at 4 days as a result of SAP addition is larger in the GP-I and GP-II modified samples than the sample without glass powders. The increase in the calcium hydroxide content in the cement pastes with SAP can be explained in light of increased hydration, as seen from the non-evaporable water content measurement depicted in Fig. 8. In addition, it has been suggested that the addition of SAP favors the nucleation of calcium hydroxide crystallites during the hydration of cement particles [74]. Esteves et al. [74] suggested that the interaction between Ca2+ and SAP, and possible entrapment of Ca2+ in the polymeric networks of SAP hydrogels, could play a role in increased production of calcium hydroxide in the cement pastes with SAP. It is realized that the GP-II modified cement paste exhibited a decrease in the calcium hydroxide content at 28 days compared to 4 days, which could be attributed to the pozzolanic reactivity of GP-II. It is interesting to note an opposite trend in the GP-I modified cement pastes with and without SAP. While the calcium hydroxide content of the GP-I modified cement paste with SAP decreased at 28 days, the calcium hydroxide content of the cement paste without SAP was increased. The calcium hydroxide content of the cementitious materials modified with pozzolanic materials consists of a contribution from the primary hydration reaction and a reduction due to the pozzolanic reaction consuming calcium hydroxide. Thus, it can be postulated that the higher calcium hydroxide content of the GP-I and GP-II modified cement pastes

GP-I Macrovoids

Air void

1 mm

1 mm GP-II

1 mm Fig. 5. Images of the SAP macrovoids in the microstructure of the control cement paste and the GP-I and GP-II modified cement pastes with addition of SAP. Example macrovoids and an example air void are indicated in the images.

243

M. Kamali, A. Ghahremaninezhad / Construction and Building Materials 149 (2017) 236–247

Transmittance (%)

Amide

Ctrl

GP-I

GP-II

Carboxylate (C-O)

Amine (N-H)

CH (g/g cement mass fraction of binder)

0.25 Before absorption

0.2

Ctrl Ctrl+SAP GP-I GP-I+SAP GP-II GP-II+SAP

0.15

0.1

0.05

0 4 days

3650

3150

2650

2150

1650

1150

650

Wavenumber (1/cm) Fig. 6. FTIR spectra of SAP before and after absorption in different pore solutions.

45

Ctrl Ctrl+SAP

Temperature (°C)

40

GP-I

28 days

Fig. 9. Ca(OH)2 content of the cement pastes at 4 days and 28 days of age.

pared to 4 days, reducing the calcium hydroxide content as seen from the figure. However, it appears that the enhancement in the primary hydration outweighed the reducing effect of the pozzolanic reaction in the GP-I modified cement paste without SAP at 28 days. Comparing the calcium hydroxide content of the GP-I modified cement paste with and without addition of SAP indicated the improved pozzolanic reactivity of GP-I with SAP addition.

GP-I+SAP 35

GP-II

3.7. XRD

GP-II+SAP 30

25

20 0

400

800

1200

1600

Time (min) Fig. 7. Heat of hydration curves of the cement pastes.

0.16

The XRD spectra of the cement pastes at 28 days are shown in Fig. 10. The peaks corresponding to CH at 2h of 18.00°, 34.10°, 47.12°, and 50.81° are observed in the spectra [75]. The peaks corresponding to CH are higher in the cement pastes with SAP except in the GP-I modified sample. The observed trend qualitatively agrees with the CH content measurements obtained from TGA presented in Fig. 9. The peaks in the 2h range of 29°-34° is attributed to tricalcium silicate (C3S) and dicalcium silicate (C2S) [75], which comprise the main constituents of the unhydrated cement particle. Comparing the XRD spectra, it is seen that no new phases were formed in the hydration product of the modified cement pastes. 3.8. Compressive strength

0.14 Ctrl

The results of the compressive strength tests at different ages are presented in Fig. 11. It is seen that at early age the use of GP-

Ctrl+SAP 0.10

GP-I GP-I+SAP

0.08

CH

C3S, C2S

CH

CH CH

GP-II

0.04 0.02 0.00

GP-II+SAP

GP-II+SAP

0.06

4 days

7 days

28 days

Fig. 8. Non-evaporable water content of the cement pastes at various ages.

than the cement paste without glass powders at 4 days was primarily due to an improvement in primary hydration as a result of the dilution effect and also potentially due to the seeding effect of fine GP-I and GP-II, providing more nucleation sites for the hydration products. The effect of pozzolanic reaction becomes more important in the modified cement pastes at 28 days com-

Intensity (Arbitraty Unit)

Wnew (g/g binder)

0.12

GP-II

GP-I+SAP

GP-I

Ctrl+SAP

Ctrl

10

20

30

40

50

60

2θ (Degree) Fig. 10. XRD spectra of the cement pastes with and without addition of SAP.

244

M. Kamali, A. Ghahremaninezhad / Construction and Building Materials 149 (2017) 236–247

Compressive Strength (MPa)

70 60 Ctrl Ctrl+SAP GP-I GP-I+SAP GP-II GP-II+SAP

50 40 30 20 10 0

4 days

7 days

28 days

Fig. 11. Compressive strength of the cement pastes at varied ages.

I and GP-II decreased strength since these pastes had a lower amount of cement to produce binding hydration product. The pozzolanic reaction does not notably contribute to hydration at early age. With continued curing, the compressive strength of the GP-I and GP-II modified cement pastes improved and this improvement was more noticeable in the GP-I modified cement paste. The improvement in compressive strength is due to the pozzolanic properties of GP-I and GP-II. Pozzolanic reaction occurs at a slower rate than the primary hydration reaction and it contributed to strength gain at later ages. At the age of 28 days, the compressive strength of the GP-I modified cement paste exceeded the compressive strength of the control cement paste. It is seen that the addition of SAP resulted in a reduction in the compressive strength of all cement pastes. The reduction in compressive strength is attributed primarily to increased stress concentrations due to the formation of macrovoids as a result of SAP absorption in the microstructure of the cement pastes.

pozzolanic activity of GP-I and GP-II. It is known that the pore morphological characteristics and pore solution chemistry significantly affect electrical resistivity in cement pastes; thus, electrical resistivity gives useful insights into the microstructure of these materials [68,76–78]. The pozzolanic reaction produces more calciumsilicate-hydrate (C-S-H) in the hydration product, resulting in enhanced densification. In addition, free ions in the pore solution have been shown to have higher binding to the C-S-H produced from the pozzolanic reaction, potentially reducing their mobility [79,80]. Refinement in pore structure and a decrease in ion mobility are the factors responsible for the increased electrical resistivity of the GP-I and GP-II modified pastes. It is observed that SAP addition resulted in a reduction of electrical resistivity in all cement pastes. This reduction is particularly more drastic in the GP-I and GP-II modified cement pastes. The effect of SAP on the microstructure consists of its effect on the capillary pores and macrovoid formation. The addition of SAP could reduce porosity of capillary pores due to increased hydration creating more solid hydration product. Although the macrovoids negatively affect the electrical resistivity due to increased porosity, its effect on electrical resistivity is expected to be small since macrovoids are not connected and are discretely dispersed in the microstructure. This can be realized by examining the influence of SAP on the control cement paste without glass powders, where a small reduction in electrical resistivity is observed. Thus, the macrovoids are not expected to be a key factor in the observed reduction in the electrical resistivity of the GP-I and GP-II modified pastes with addition of SAP. Although the macrovoids were shown to be slightly larger in the GP-I and GP-II modified pastes, the observed difference in the macrovoid size, and thereby increase in porosity, is not large so as to cause such a reduction in electrical resistivity. A potential explanation for this reduction could be suggested to be increased connectivity of the capillary pores in the GPI and GP-II modified pastes as a result of SAP addition. Next, microscopic examination will be presented to obtain insights into the influence SAP had on the microstructure of the cement pastes. 3.10. Scanning electron microscopy

3.9. Electrical resistivity The values of electrical resistivity at varied ages are illustrated in Fig. 12. It is observed that the GP-I and GP-II modified cement pastes had a lower electrical resistivity at early age, but their electrical resistivity was significantly improved at 28 days. The initial reduction in electrical resistivity at early age is attributed to the dilution effect. The observed improvement in electrical resistivity at late ages is due to microstructure improvement as a result of

70

Electrical Resistivity (Ω.m)

60 Ctrl Ctrl+SAP GP-I GP-I+SAP GP-II GP-II+SAP

50 40 30 20 10 0

4 days

7 days

28 days

Fig. 12. Electrical resistivity of the cement pastes at varied ages.

SEM micrographs of different pastes at 28 days are shown in Fig. 13. Examples of different constituents at the microscale are indicated in Fig. 13a. The cement pastes with SAP appear to be slightly more densified than the cement pastes without SAP. This is due to improved hydration when SAP is added as a result of internal curing generating more solid hydration product, which reduces the overall porosity. In order to obtain a quantitative comparison between the microstructure of the cement pastes, the total porosity determined using segmented SEM images is plotted in Fig. 14. The porosity calculation was based on the average of 5 images taken of random locations in the microstructure to account for the intrinsic variation in the microstructure of cementitious materials. It is seen that the overall porosity of the capillary pores is slightly decreased in the cement pastes with addition of SAP. In addition, there seems to be a small increase in the porosity of the GP-I and GP-II modified pastes relative to the control sample. It is noteworthy to compare the results of the electrical resistivity as shown in Fig. 12 with the porosity measurements. Although porosity as an overall parameter affects the transport properties, the electrical resistivity in cement pastes is strongly sensitive to the pore structure characteristics, such as pore connectivity and tortuosity [44,67,78,81]. Thus, the decreased electrical resistivity observed in the GP-I and GP-II modified pastes with addition of SAP could be rationalized in terms of increased connectivity of the capillary pores in these cement pastes. Accurate quantification of the connectivity of the capillary pores requires extensive imaging at high magnifications and was not pursued in this study.

M. Kamali, A. Ghahremaninezhad / Construction and Building Materials 149 (2017) 236–247

(a) Ctrl +SAP

Hydration product

Capillary pore

Unhydrated cement

245

(b) Ctrl

50 m

50 m

(c) GP-I+SAP

(d) GP-I

50 m

50 m

(e) GP-II+SAP

(f) GP-II

50 m

50 m

Fig. 13. SEM images of the cement pastes with and without addition of SAP at 28 days of age.

4. Conclusions

18 16

Porosity (%)

14 12 10 8

Ctrl Ctrl+SAP GP1 GP1+SAP GP2 GP2+SAP

6 4 2 0

Fig. 14. Porosity of the cement pastes at 28 days obtained from SEM images.

The effect of SAP on the mechanical strength, hydration evolution, electrical resistivity, and microstructural features of glass powder modified cement pastes was studied. The following conclusions were drawn:
SAP absorption showed a variable behavior at early age in the cement pastes with the maximum absorption being higher in the GP-I and GP-II modified pastes in comparison with the control sample. This was attributed to the evolving chemistry of the pore solutions as well as mechanical constraint of the cementitious matrix.
The cement pastes with addition of SAP were shown to have a higher degree of hydration due to the internal curing effect of SAP.
Formation of macrovoids as a result of SAP absorption decreased the compressive strength of the materials.

246

M. Kamali, A. Ghahremaninezhad / Construction and Building Materials 149 (2017) 236–247


Electrical resistivity was reduced in the pastes when SAP was added. This decrease was more pronounced in the GP-I and GP-II modified cement pastes.
SEM examination indicated a decrease in the porosity of the capillary pores in the cement pastes with addition of SAP. However, the increase in the connectivity of the capillary pore system in microstructure was suggested as a possible reason for the drastic reduction in the electrical resistivity of the GP-I and GP-II modified pastes when SAP is added.

Acknowledgements Some of the experiments as part of this study were performed in the Structures and Materials Laboratory and Environmental Engineering Laboratory at the University of Miami and it is hereby acknowledged. Marcelo Frota Bazhuni is thanked for his assistance with some of the sample preparation.

References [1] G.R. de Sensale, A.F. Goncalves, Effects of fine LWA and SAP as internal water curing agents, Int. J. Concr. Struct. Mater. 8 (2014) 229–238. [2] O.M. Jensen, P.F. Hansen, Water-entrained cement-based materials II. Experimental observations, Cem. Concr. Res. 32 (2002) 973–978. [3] K. Kovler, O.M. Jensen, Internal curing of concrete, state-of-the-art report of RILEM technical committee 196-ICC, 2007. [4] C. Schröfl, V. Mechtcherine, M. Gorges, Relation between the molecular structure and the efficiency of superabsorbent polymers (SAP) as concrete admixture to mitigate autogenous shrinkage, Cem. Concr. Res. 42 (2012) 865– 873. [5] P. Lura, O.M. Jensen, W.J. Weiss, Cracking in cement paste induced by autogenous shrinkage, (2009) 1089–1099. [6] A.B. Hossain, J. Weiss, Assessing residual stress development and stress relaxation in restrained concrete ring specimens, 26 (2004) 531–540. [7] V. Mechtcherine, M. Gorges, C. Schroefl, A. Assmann, Effect of internal curing by using superabsorbent polymers (SAP) on autogenous shrinkage and other properties of a high-performance fine-grained concrete: results of a RILEM round-robin test, (2014) 541–562. [8] J. Weiss, S.P. Shah, Shrinkage cracking of restrained concrete slabs, J. Eng. Mech. 124 (1998) 765–774. [9] D.P. Bentz, K.A. Snyder, Protected paste volume in concrete Extension to internal curing using saturated lightweight fine aggregate, Cem. Concr. Res. 29 (1999) 1863–1867. [10] O.M. Jensen, P.F. Hansen, Water-entrained cement-based materials I. Principles and theoretical background, Cem. Concr. Res. 31 (2001) 647–654. [11] P. Lura, O.M. Jensen, K. van Breugel, Autogenous shrinkage in highperformance cement paste: an evaluation of basic mechanisms, Cem. Concr. Res. 33 (2003) 223–232. [12] M.J. Krafcik, K.A. Erk, Characterization of superabsorbent poly (sodiumacrylate acrylamide) hydrogels and influence of chemical structure on internally cured mortar, Mater. Struct. 49 (2016) 4765–4778. [13] A.M.S.M.L. Nehdi, Effect of drying conditions on autogenous shrinkage in ultrahigh performance concrete at early-age, (2011) 879–899. [14] D. Cusson, T. Hoogeveen, Internal curing of high-performance concrete with pre-soaked fine lightweight aggregate for prevention of autogenous shrinkage cracking, Cem. Concr. Res. 38 (2008) 757–765. [15] M. S ß ahmaran, M. Lachemi, K.M.A. Hossain, V.C. Li, Internal curing of engineered cementitious composites for prevention of early age autogenous shrinkage cracking, Cem. Concr. Res. 39 (2009) 893–901. [16] A. Bentur, S. Igarashi, K. Kovler, Prevention of autogenous shrinkage in highstrength concrete by internal curing using wet lightweight aggregates, Cem. Concr. Res. 31 (2001) 1587–1591. [17] V. Mechtcherine, H.-W. Reinhardt, Application of Super Absorbent Polymers (SAP) in Concrete Construction, Springer, 2012. [18] H. Beushausen, M. Gillmer, M. Alexander, The influence of superabsorbent polymers on strength and durability properties of blended cement mortars, Cem. Concr. Compos. 52 (2014) 73–80. [19] M.T. Hasholt, O.M. Jensen, Chloride migration in concrete with superabsorbent polymers, Cem. Concr. Compos. 55 (2015) 290–297. [20] V. Mechtcherine, E. Secrieru, C. Schröfl, Effect of superabsorbent polymers (SAPs) on rheological properties of fresh cement-based mortars – development of yield stress and plastic viscosity over time, Cem. Concr. Res. 67 (2015) 52– 65. [21] D. Snoeck, D. Schaubroeck, P. Dubruel, N. De Belie, Effect of high amounts of superabsorbent polymers and additional water on the workability, microstructure and strength of mortars with a water-to-cement ratio of 0.50, Constr. Build. Mater. 72 (2014) 148–157.

[22] P. Lura, F. Durand, A. Loukili, K. Kovler, Compressive strength of cement pastes and mortars with superabsorbent polymers, in: Int. RILEM Conf. Vol. Chang. Hardening Concr. Test. Mitig. 20–23 August, 2006, pp. 117–125. [23] S. Igarashi, a Watanabe, O.M. Jensen, P. Lura, K. Kovler, Experimental study on prevention of autogenous deformation by internal curing using superabsorbent polymer particles, in: Int. RILEM Conf. Vol. Chang. Hardening Concr. Test. Mitig., (2006) 77–86. [24] O.M. Jensen, Use of superabsorbent polymers in construction materials, in: H. C.W. Sun, K. van Breugel, C. Miao, G. Ye (Eds.), Int. Conf. Microstruct. Relat. Durab. Cem. Compos., RILEM Publications, 2008, pp. 757–764. [25] K.S. Sikora, A.J. Klemm, Effect of superabsorbent polymers on workability and hydration process in fly ash cementitious composites, J. Mater. Civ. Eng. 27 (2015) 4014170. [26] D. Snoeck, L.F. Velasco, A. Mignon, S. Van Vlierberghe, P. Dubruel, P. Lodewyckx, N. De Belie, The effects of superabsorbent polymers on the microstructure of cementitious materials studied by means of sorption experiments, Cem. Concr. Res. 77 (2015) 26–35. [27] K. Farzanian, A. Ghahremaninezhad, The effect of capillary on the desorption of hydrogels in a porous cementitious material, Cem. Concr. Res. (2016). [28] A. Pourjavadi, S.M. Fakoorpoor, P. Hosseini, A. Khaloo, Interactions between superabsorbent polymers and cement-based composites incorporating colloidal silica nanoparticles, Cem. Concr. Compos. 37 (2013) 196–204. [29] K. Farzanian, K. Pimenta Teixeira, I. Perdiago Rocha, L. De Sa Carneiro, A. Ghahremaninezhad, The mechanical strength, degree of hydration, and electrical resistivity of cement pastes modified with superabsorbent polymers, Constr. Build. Mater. 109 (2015) 156–165. [30] Y. Wehbe, A. Ghahremaninezhad, Combined effect of shrinkage reducing admixtures (SRA) and superabsorbent polymers (SAP) on the autogenous shrinkage and properties of cementitious materials, Constr. Build. Mater. (2016). [31] B. Lothenbach, K. Scrivener, R.D. Hooton, Supplementary cementitious materials, Cem. Concr. Res. 41 (2011) 1244–1256. [32] N. Schwarz, N. Neithalath, Influence of a fine glass powder on cement hydration: comparison to fly ash and modeling the degree of hydration, Cem. Concr. Res. 38 (2008) 429–436. [33] M. Kamali, A. Ghahremaninezhad, Investigating the hydration and microstructure of cement pastes modified with glass powders, Constr. Build. Mater. 112 (2015) 915–924. [34] J.A. Jain, N. Neithalath, Chloride transport in fly ash and glass powder modified concretes – influence of test methods on microstructure, Cem. Concr. Compos. 32 (2010) 148–156. [35] A. Shayan, A. Xu, Performance of glass powder as a pozzolanic material in concrete: a field trial on concrete slabs, Cem. Concr. Res. 36 (2006) 457–468. [36] P. Kara, Performance of waste glass powder (WGP) supplementary cementitious material (SCM) – drying shrinkage and early age shrinkage cracking, 66 (2014). [37] A. Shayan, A. Xu, Value-added utilisation of waste glass in concrete, Cem. Concr. Res. 34 (2004) 81–89. [38] N. Schwarz, H. Cam, N. Neithalath, Influence of a fine glass powder on the durability characteristics of concrete and its comparison to fly ash, Cem. Concr. Compos. 30 (2008) 486–496. [39] Z. Bazant, G. Zi, C. Meyer, Fracture mechanics of ASR in concretes with waste glass particles of different sizes, J. Eng. Mech. 126 (2000) 226–232. [40] R.-U.-D. Nassar, P. Soroushian, Green and durable mortar produced with milled waste glass, Mag. Concr. Res. 64 (2012) 605–615. [41] M. Mirzahosseini, K.A. Riding, Influence of different particle sizes on reactivity of finely ground glass as supplementary cementitious material (SCM), Cem. Concr. Compos. 56 (2015) 95–105. [42] M. Mirzahosseini, D. Ph, S.M. Asce, K.A. Riding, M. Asce, Effect of combined glass particles on hydration in cementitious systems (2015) 1–13. [43] H. Maraghechi, S.-M.-H. Shafaatian, G. Fischer, F. Rajabipour, The role of residual cracks on alkali silica reactivity of recycled glass aggregates, Cem. Concr. Compos. 34 (2012) 41–47. [44] A. Pavoine, D. Harbec, T. Chaussadent, A. Tagnit-Hamou, L. Divet, Impact of alternative cementitious material on the mechanical and transfer properties of concrete, ACI Mater. J. 3 (2014) 251–261. [45] Y. Shao, T. Lefort, S. Moras, D. Rodriguez, Studies on concrete containing ground waste glass, Cem. Concr. Res. 30 (2000) 91–100. [46] R.-U.-D. Nassar, P. Soroushian, Strength and durability of recycled aggregate concrete containing milled glass as partial replacement for cement, Constr. Build. Mater. 29 (2012) 368–377. [47] Z. Wang, C. Shi, J. Song, Effect of glass powder on chloride ion transport and alkali-aggregate reaction expansion of lightweight aggregate concrete, J. Wuhan Univ. Technol. Sci. Ed. 24 (2009) 312–317. [48] M. Kamali, A. Ghahremaninezhad, Effect of glass powders on the mechanical and durability properties of cementitious materials, Constr. Build. Mater. 98 (2015) 407–416. [49] J. Flores, M. Kamali, A. Ghahremaninezhad, Electrical resistivity measurement to study alkali-silica-reaction cracking in mortar, in: Proc. ASCE Forensic Eng., Miami, 2015, pp. 230–241. [50] N. Neithalath, J. Persun, A. Hossain, Hydration in high-performance cementitious systems containing vitreous calcium aluminosilicate or silica fume, Cem. Concr. Res. 39 (2009) 473–481. [51] V. Vaitkevicˇius, E. Šerelis, H. Hilbig, The effect of glass powder on the microstructure of ultra high performance concrete, Constr. Build. Mater. 68 (2014) 102–109.

M. Kamali, A. Ghahremaninezhad / Construction and Building Materials 149 (2017) 236–247 [52] Y. Sharifi, I. Afshoon, Z. Firoozjaei, A. Momeni, Utilization of waste glass microparticles in producing self-consolidating concrete mixtures, Int. J. Concr. Struct. Mater. 10 (2016) 337–353. [53] D. Snoeck, O.M. Jensen, N. De Belie, The influence of superabsorbent polymers on the autogenous shrinkage properties of cement pastes with supplementary cementitious materials, Cem. Concr. Res. 74 (2015) 59–67. [54] Q. Zhu, C.W. Barney, K.A. Erk, Effect of ionic crosslinking on the swelling and mechanical response of model superabsorbent polymer hydrogels for internally cured concrete, Mater. Struct. (2014). [55] F. Horkay, I. Tasaki, P.J. Basser, Osmotic swelling of polyacrylate hydrogels in physiological salt solutions, Biomacromolecules 1 (2000) 84–90. [56] W. Siriwatwechakul, J. Siramanont, Behavior of superabsorbent polymers in calcium- and sodium-rich solutions, J. Mater. Civ. Eng. 976–980 (2012). [57] J. Chen, S.C. Kou, C.S. Poon, Hydration and properties of nano-TiO2 blended cement composites, Cem. Concr. Compos. 34 (2012) 642–649. [58] P. Hou, S. Kawashima, D. Kong, D.J. Corr, J. Qian, S.P. Shah, Modification effects of colloidal nanoSiO2 on cement hydration and its gel property, Compos. Part B Eng. 45 (2013) 440–448. [59] N. Schwarz, M. DuBois, N. Neithalath, Electrical conductivity based characterization of plain and coarse glass powder modified cement pastes, Cem. Concr. Compos. 29 (2007) 656–666. [60] P. Hou, K. Wang, J. Qian, S. Kawashima, D. Kong, S.P. Shah, Effects of colloidal nanoSiO2 on fly ash hydration, Cem. Concr. Compos. 34 (2012) 1095–1103. [61] S. Kawashima, P. Hou, D.J. Corr, S.P. Shah, Modification of cement-based materials with nanoparticles, Cem. Concr. Compos. 36 (2013) 8–15. [62] T. Kim, J. Olek, Effects of sample preparation and interpretation of thermogravimetric curves on calcium hydroxide in hydrated pastes and mortars, Transp. Res. Rec. J. Transp. Res. Board 2290 (2012) 10–18. [63] P. Chindaprasirt, C. Jaturapitakkul, T. Sinsiri, Effect of fly ash fineness on microstructure of blended cement paste, Constr. Build. Mater. 21 (2007) 1534– 1541. [64] P.K. Hou, S. Kawashima, K.J. Wang, D.J. Corr, J.S. Qian, S.P. Shah, Effects of colloidal nanosilica on rheological and mechanical properties of fly ashcement mortar, Cem. Concr. Compos. 35 (2013) 12–22. [65] M. Aly, M.S.J. Hashmi, A.G. Olabi, M. Messeiry, E.F. Abadir, A.I. Hussain, Effect of colloidal nano-silica on the mechanical and physical behaviour of waste-glass cement mortar, Mater. Des. 33 (2012) 127–135. [66] K.A. Snyder, C. Ferraris, N.S. Martys, E.J. Garboczi, Using impedance spectroscopy to assess the viability of the rapid chloride test for determining concrete conductivity, J. Res. Natl. Inst. Stand. Technol. 105 (2000) 497. [67] N. Neithalath, J. Weiss, J. Olek, Predicting Permeability of Pervious Concrete (Enhansed Porosity Concrete) from Non-Destructive Electrical Measurements, (n.d.).

247

[68] N. Neithalath, J. Weiss, J. Olek, Characterizing enhanced porosity concrete using electrical impedance to predict acoustic and hydraulic performance, Cem. Concr. Res. 36 (2006) 2074–2085. [69] H.S. Wong, N.R. Buenfeld, M.K. Head, Estimating transport properties of mortars using image analysis on backscattered electron images, Cem. Concr. Res. 36 (2006) 1556–1566. [70] Y. Gao, G. De Schutter, G. Ye, Z. Tan, K. Wu, The ITZ microstructure, thickness and porosity in blended cementitious composite: effects of curing age, water to binder ratio and aggregate content, Compos. Part B Eng. 60 (2014) 1–13. [71] A. Mignon, G.J. Graulus, D. Snoeck, J. Martins, N. De Belie, P. Dubruel, S. Van Vlierberghe, PH-sensitive superabsorbent polymers: a potential candidate material for self-healing concrete, J. Mater. Sci. 50 (2014) 970–979. [72] A. Mignon, D. Snoeck, D. Schaubroeck, N. Luickx, P. Dubruel, S. Van Vlierberghe, N. De Belie, PH-responsive superabsorbent polymers: a pathway to selfhealing of mortar, React. Funct. Polym. 93 (2015) 68–76. [73] J. Hu, Z. Ge, K. Wang, Influence of cement fineness and water-to-cement ratio on mortar early-age heat of hydration and set times, Constr. Build. Mater. 50 (2014) 657–663. [74] L.P. Esteves, I. Lukošiute, J. Cˇesniene, Hydration of cement with superabsorbent polymers, J. Therm. Anal. Calorim. 118 (2014) 1385–1393. [75] Joint Committee on Powder Diffraction Standards, JCPDS-International center for diffraction data (2000), n.d. [76] J. Jain, N. Neithalath, Electrical impedance analysis based quantification of microstructural changes in concretes due to non-steady state chloride migration, Mater. Chem. Phys. 129 (2011) 569–579. [77] Y. Bu, J. Weiss, The influence of alkali content on the electrical resistivity and transport properties of cementitious materials, Cem. Concr. Compos. 51 (2014) 49–58. [78] F. Rajabipour, C. Author, J. Weiss, Development of Electrical ConductivityBased Sensors for Health Monitoring of Concrete Materials Development of Electrical Conductivity-Based Sensors for Health Monitoring of Concrete Materials, (2007) 1–16. [79] S.M.H. Shafaatian, A. Akhavan, H. Maraghechi, F. Rajabipour, How does fly ash mitigate alkali–silica reaction (ASR) in accelerated mortar bar test (ASTM C1567)?, Cem Concr. Compos. 37 (2013) 143–153. [80] S.K. Wah, C. Co, M. Science, Effect of Pozzolanic Reaction Products on Alkalisilica Reaction, 21 (2006) 3–6. [81] S. Li, D.M. Roy, Investigation of relations between porosity, pore structures, and Cl- diffusion of fly ash and blended cement pastes, Cem. Concr. Res. 16 (1986) 749–759.