Research Article  Open Access
Qi Gao, Zhiming Ma, Jianzhuang Xiao, Fuan Li, "Effects of Imposed Damage on the Capillary Water Absorption of Recycled Aggregate Concrete", Advances in Materials Science and Engineering, vol. 2018, Article ID 2890931, 12 pages, 2018. https://doi.org/10.1155/2018/2890931
Effects of Imposed Damage on the Capillary Water Absorption of Recycled Aggregate Concrete
Abstract
Capillary water absorption of concrete is closely related to its pore structure, permeability, and durability. This paper intensively investigates the effects of imposed damage, including freezethaw damage and loading damage, on the capillary water absorption of recycled aggregate concrete (RAC). Freezethaw cycle test, loading test, and the experiment of capillary water absorption were carried out, respectively. The results demonstrate that the addition of recycled coarse aggregate (RCA) results in the increase in the capillary absorption behavior of RAC without imposed damage, and there exists a linear correlation between the behaviors of capillary water absorption and chloride penetration of RAC. The imposed freezethaw damage or load damage of RAC boosts with the increase of RCA replacement percentages after suffering the same freezethaw cycles or loading level. The imposed freezethaw damage and load damage further lead to the increase in the capillary water absorption of RAC, and the capillary absorption coefficient of RAC increases linearly with the increased RCA replacement percentages, after suffering the same freezethaw cycles or loading level. Furthermore, capillary absorption coefficient increases linearly with the growth of imposed freezethaw damage or load damage degree, which can be used to estimate the capillary absorption behavior of RAC exposed to the extreme environment.
1. Introduction
Construction and demolition waste (CDW) increased dramatically with the rapid development of the construction industry in the past few years, and the CDW will keep increasing at a high speed in China in the future [1, 2]. Traditional disposal of CDW is mainly the landfill and air storage, which requires more land occupation with a high cost. Due to the existence of hazardous substances in CDW, the traditional disposal of CDW also brings about a series of negative impacts on the environment, including soil, water, and atmosphere pollutions [3, 4]. Thereby, proposing an effective method to deal with the CDW is necessary. At the present stage, recycling waste concrete and bricks which account for about 80% of the CDW weight are the appropriate way to reduce the mass of CDW [2]. Recycled coarse aggregate (RCA) whose properties are similar to the natural coarse aggregate (NCA) can be produced through a series process of crushing and sieving, and the corresponding recycled aggregate concrete (RAC) is subsequently prepared, which can be used as the building materials. The properties of RAC have been investigated by the authors around the world, including the mechanical properties and some durability performance [5, 6]. Although the properties of RAC are inferior to the natural aggregate concrete (NAC), they can also be used in the engineering construction by the methods of mix optimization and design, such as increasing the amount of cement in the mix proportion.
Durability is the most important factor on the service life of concrete structures. Acting as the porous materials, water permeability is the main parameter of concrete durability, which is closely related to the carbonation, steel corrosion, freezethaw damage, and aggressive ions penetrations into concrete [7–9]. The high water permeability of concrete frequently results in the increase in the deterioration of concrete durability [10–12]. Water penetration into concrete mainly depends on the force of capillary absorption and hydrostatic pressure, whereas the watersaturated state is difficult to reach except for the concrete exposed to the condition of high hydrostatic pressure, such as the deep sea environment; consequently, almost all of the water penetration into concrete is mainly by the force of capillary absorption, and the test of capillary water absorption is developed to evaluate the permeability of concrete [13, 14]. The capillary absorption force is mainly provided by the surface tension and pore absorption of concrete, which can well reflect the number and distribution of pores in concrete [15]. Due to the aggressive ions penetrating into concrete mainly by the medium of water penetration, there exists a correlation between the water and aggressive ions penetrations into concrete [16]. For example, when the concrete is exposed to the wetdry environment (e.g., sea tidal zone), the capillary absorption provides the main driving force for the chloride and sulfate ions penetration into concrete.
Previous studies have investigated the capillary water absorption of NAC under various conditions. Wang, Bogas, and Hanžič have studied the capillary water absorption of NAC without imposed damage, and the results highlight that the mix proportion of concrete has an obvious effect on the capillary water absorption [15, 17, 18]. Furthermore, the capillary water absorption of NAC with imposed damage has also been investigated. Such as, Gonen presented the impact of freezethaw damage on the capillary absorption behavior of NAC [19], and Wang investigated the influence of applied loading on the capillary absorption behavior of NAC [20], which illustrates that the imposed freezethaw damage and load damage lead to the further increase in the capillary water absorption of NAC. The combination of capillary water absorption and imposed damage should be considered carefully in the evaluation and design of concrete durability.
A number of studies have been recently conducted to investigate the durability of RAC, and the focus was placed on chloride permeability, carbonation, freezethaw resistance, and so on, which highlights that the addition of RCA results in the decrease in the concrete durability [21–23]. However, there is currently a lack of adequate literature on the water permeability, especially for the capillary water absorption, of RAC. Attributing to the existence of the old mortar and interfacial transition zone (ITZ) with poor properties may lead to the increase in the capillary water absorption of RAC, considering the water penetration is frequently coupled with the freezethaw damage under cold condition, and RAC is inevitably exposed to the load application in the actual conditions, and the imposed damage may further increase the capillary water absorption of RAC. Consequently, the capillary water absorption of RAC with and without imposed damage should be investigated.
The aim of this paper is trying to experimentally investigate the capillary water absorption of RAC with and without imposed damage. Considering the practical service conditions, the effects of freezethaw damage and loading damage on the capillary water absorption of RAC were both investigated. Freezethaw cycle test, loading test, and capillary absorption experiment were carried out, respectively. Based on the testing results, the correlation between the capillary absorption behavior of RAC and RCA replacement percentages, as well as between the imposed damage and capillary absorption behavior of RAC, is established, which can be used to evaluate the capillary water absorption of RAC exposed to various conditions.
2. Experimental Program
2.1. Mixture Proportions and Concrete Specimens
Table 1 shows the properties of RCA and NCA, and the results confirm that the RCA has the inferior properties to NCA, due to the existence of old mortar which accounts for about 33% of the RCA weight. The packing density and apparent density of RCA are lower than those of NCA, and the RCA possesses the higher crushing value index compared with NCA. Particularly, the water absorption of RCA is about 5.3 times as high as that of NCA.

In order to investigate the effects of RCA replacement percentages on the capillary water absorption of RAC, different RCA replacement percentages are considered in the design of mix proportions, including 0%, 33%, 66%, and 100% of RCA to equivalently replace the NCA. Table 2 gives the specific mix proportions of RAC, and the specimen titled RAC0% is also named as NAC, and the specimen titled RAC33% presents the RCA replacement percentages are 33%. Polycarboxylate waterreducing agent produced in Shanghai was used, and all the slump values of various concrete mixes were kept around 90 mm by adjusting the amount of waterreducing agent in RAC. Attributing to high water absorption of RCA, the additional water was first mixed with the RCA to make the saturated surface dry, and the other binding materials, water as well as the waterreducing agent, were subsequently mixed to prepare the RAC. 100 mm cubes were used to measure the behavior of capillary water absorption, and the specimen with the size of 100 × 100 × 400 mm^{3} was prepared to determine the relative dynamic modulus of concrete after different freezethaw cycles.

RAC specimens after hardening were moved into a curing room, where the temperature was kept at (20 ± 2) °C and the relative humidity was above 95%, for 28 days. The tests of freezethaw cycles and loading were conducted to induce the damage on RAC specimens, and then the capillary absorption test was carried out to investigate the capillary water absorption of concrete with and without imposed damage.
2.2. Test of Capillary Water Absorption
The water penetration into concrete is mainly by the force of capillary absorption when the concrete is in a relatively dry state. Capillary water absorption test was carried out according to the ASTM C1585 [24]. RAC specimens were first dried in the drying oven for 24 h where the temperature was kept around 105^{°}C, and then the specimens were placed and cooled at room temperature. Finally, the capillary water absorption test was carried out, and the amount of absorbed water was determined at different time. Figure 1 describes the test of capillary water absorption and shows the SEM image of the capillary absorption pores of concrete. There exists a mass of capillary pores, as well as the porous characteristics of CSH, which provides the capillary absorption force for water penetration into concrete.
If the gravity is neglected, the capillary absorption behavior can be described in a simple way by the following equations. In Equation (1), ΔW stands for the mass increase (g) of absorbed water by the surface area titled S (S = 100 mm × 100 mm), g/m^{2}. A represents the coefficient of capillary absorption, g/(m^{2}·h^{0.5}), and it can be calculated by Equation (2) [25–27]. The amount of absorbed water and capillary absorption coefficient can well manifest the water permeability of cementbased materials, and the corresponding pores can be evaluated:
The penetrations of water and chloride are both related to the pore structure, number, and distribution in cementbased materials. To investigate the relationship between the water and chloride penetrations into RAC, the maximum chloride content was determined by the test of capillary salt absorption at 5% NaCl solution for 24 h, and the chloride diffusion coefficient was also obtained by the free diffusion test at 5% NaCl solution for 30 d, in terms of Fick’s second law.
2.3. Test of FreezeThaw Cycles
Accelerated freezethaw cycle test was carried out according to the Chinese Standard of “Testing code of concrete for port and waterway engineering” (JTJ 270), and one freezethaw cycle lasted for about four hours, and the core temperature of the concrete ranged from (8 ± 2) °C to (−17 ± 2) °C during one freezethaw cycle [28, 29]. RAC specimens were taken out from the setup of freezethaw cycles when the freezethaw cycles reached 0, 25, 50, and 75 times, respectively. The relative dynamic elastic modulus (E_{rd}) and mass loss were determined to quantitatively evaluate the imposed damage after different freezethaw cycles. Finally, the capillary absorption test of RAC with imposed freezethaw damage was conducted, and the testing process was the same as the description in Section 2.1.
2.4. Loading Test
To investigate the imposed load damage on the capillary water absorption of RAC, different loading levels were first applied on the RAC, and the loading rate was 0.05 mm/min. The target load value was, respectively, 0%, 40%, 60%, and 80% of ultimate compressive strength (f_{c}), and the target load was kept for 60 min to make the RAC specimens obtain enough load damage. Subsequently, the specimens were unloaded, and the imposed load damage was determined by an ultrasonic concrete tester, and then the test of capillary water absorption was conducted according to Section 2.2. Figure 2 illustrates the loading test and the testing method of imposed load damage. The is closely related to the cracks and pores development of cementbased materials, and it is frequently used in the performance evaluation of concrete with damage. The load damage degree can be determined according to Equation (3) by the change of the , where is the load damage degree, presents relative dynamic elastic modulus, %, and and are the sonic time with and without imposed load [30, 31]:
3. Results and Discussions
3.1. Capillary Water Absorption of RAC without Imposed Damage
The compressive strength after 28 d and 56 d was first determined, and the results highlight that the addition of RCA leads to the decrease in the compressive strength of RAC. As shown in Figure 3, 33%, 66%, and 100% of RCA replacements result in 3.7%, 7.5%, and 12.9% decrease in the compressive strength of RAC after 28 d curing, and the results become 3.1%, 6.4%, and 13.6% after 56 d curing (Table 3).
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(b)

Acting as the important parameters of concrete durability, the capillary absorption behavior is closely related to the composition, pore structure, and porosity of concrete. This section aims to investigate the capillary absorption behavior of RAC without any imposed damage. Figure 3(a) shows the capillary absorption curves of RAC with different RCA replacement percentages. The results reveal the amount of absorbed water rises with the increase of contact time with water, and the increased RCA replacement percentages result in the increase in the maximum amount of absorbed water of RAC. The capillary absorption coefficient increases with the rise of RCA replacement percentages; such as, the capillary absorption coefficient of RAC33%, RAC66%, and RAC100% is about 1.08, 1.14, and 1.28 times as high as that of NAC. Furthermore, Figure 3(b) highlights the correlation between the capillary absorbed behavior and the RCA replacement percentages, and the results show that the capillary absorption coefficient of concrete increases linearly with the rise of RCA replacement percentages, and the specific equation is given in Equation (4), where is the capillary absorption coefficient, g/(m^{2}·h^{0.5}), and is the RCA replacement percentages, %:
Figure 4 illustrates the mechanism of water penetration into RAC and NAC. The significant difference between the RAC and NAC is the existence of old mortar and ITZ, and the old mortar possesses the inferior properties compared with new mortar, which provides more passageways for the water penetration into RAC. As shown in Figure 4, the obvious flaws, cracks, and pores can be seen from the SEM images of old ITZ and old mortar. Moreover, due to the existence of old mortar attached to RAC, the total mortar content per unit volume increases with the increase of the RCA replacement percentages, which also provides more capillary absorption pores for the water penetration into RAC. Consequently, the addition of RCA results in the increase in the capillary water absorption of concrete.
3.2. Correlation between Chloride and Water Permeability of RAC
Chloride penetration is the main reason that leads to the steel corrosion in reinforced concrete, which significantly reduces the concrete durability and structural safety [32–34]. The chloride and water penetrations into concrete are both related to the pore structures of concrete, and the chloride penetration into concrete is mainly by the medium of water penetration. Moreover, the capillary absorption coefficient and chloride diffusion coefficient, respectively, represent the water and chloride penetration rates. Table 4 shows the capillary water absorption and chloride penetration parameters of RAC, and the results highlight that the addition of RCA results in the increase in the penetration amount and penetration rate of water and chloride.

To investigate the correlation between the penetration behaviors of chloride and water, the relationship between the maximum absorbed water amount and the maximum chloride content, as well as the capillary absorption coefficient of water and diffusion coefficient of chloride, is described in Figures 5(a) and 5(b), and the results show that they follow a linear relation. Figure 5 also presents the specific equations, where the W_{w,max} is the maximum amount of absorbed water, g/m^{2}; W_{c,max} is the maximum chloride content, %; D_{RAC} is the chloride diffusion coefficient, 10^{−12} m^{2}/s; and A_{RAC} stands for the capillary water absorption coefficient, g/(m^{2}h^{1/2}). The evaluation and measurement of water permeability are easier than those of chloride permeability of concrete, and the correlation presented in this section gives a fast and effective method to estimate the chloride permeability of RAC by the change of water permeability.
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(b)
3.3. Capillary Water Absorption of RAC with Imposed FreezeThaw Damage
Freezethaw damage frequently exists in concrete exposed to the cold condition, and it significantly reduces the impermeability, durability, and the service life of concrete [12, 35]. Gonen found that the freezethaw damage increases the capillary absorption behavior of NAC [19]. This section mainly investigates the effects of freezethaw damage on the capillary absorption behavior of RAC.
The mass loss and relative dynamic elastic modulus were first determined to present the freezethaw resistance of RAC, and the results are described in Figure 6. The mass loss of concrete increases with the increase of freezethaw cycles, and the addition of RCA results in the increase in the mass loss after the same freezethaw cycles; for example, the mass of RAC0%, RAC33%, RAC66%, and RAC100% after 75 freezethaw cycles decreases by 2.34%, 2.95%, 3.89%, and 5.45% compared with that without freezethaw attack. The relative dynamic elastic modulus (E_{rd}) of RAC decreases with the rise of freezethaw cycles, and the increased RCA replacement percentages result in decrease in the E_{rd} of concrete after the same freezethaw cycles; such as, the E_{rd} of RAC0% is 1.15, 1.78, and 5.01 times as high as that of RAC33%, RAC66%, and RAC100% after 75 freezethaw cycles.
The results mentioned above highlight that the RAC has the lower freezethaw resistance than NAC, and the freezethaw resistance decreases with the increase of RCA replacement percentages. Attributing to the existence of the old mortar adhered to RAC, the water adsorption of RAC increases with the increase of RCA replacement percentages, which leads to the RAC suffering more serious freezethaw expansion stress than NAC after the same freezethaw cycles. In addition, the cracks and pores in ITZ and old mortar of RCA are the weak points, which are easy to damage and aggravate the durability degradation of RAC. Consequently, the freezethaw damage of RAC increases with the increased RCA replacement percentage under the same condition of freezethaw cycles.
Capillary absorption curves of RAC after various freezethaw cycles are shown in Figure 7. The results highlight that the freezethaw damage results in the increase in the capillary water absorption of RAC. For example, the capillary absorption coefficient of NAC after suffering 75 freezethaw cycles is 0.94 times higher than that without freezethaw cycles, and the result is 6.29 times for RAC100%. As more cracks and pores are formed and developed with the increase of freezethaw cycles, more passageways are provided for the water penetration into concrete.
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(b)
(c)
(d)
By the mercury intrusion test (MIT), Table 5 gives the parameters of the pore structure of cement mortar with the w/c ratio of 0.5 after suffering different freezethaw cycles. It is remarkable that the amount of total porosity and the harmful pores quantity both rise with the increase of freezethaw cycles, which provides the passageway for the water penetration into concrete. Consequently, the absorbed water amount and capillary absorption coefficient of RAC both increase with the increase of freezethaw cycles.

As shown in Figures 7(a)–7(d), compared with the capillary absorption results of RAC with different RCA replacement percentages, it is easily found that the capillary absorption behavior of concrete increases with the increased RCA replacement percentages after the same freezethaw cycles, and the results become more obvious after suffering a large number of freezethaw cycles. Such as, the capillary absorption coefficient of RAC33%, RAC66%, and RAC100% is, respectively, 1.10, 1.21 and 1.37 times as high as that of NAC after 25 freezethaw cycles, and the result becomes 1.62, 3.61, and 4.81 times after 75 freezethaw cycles. It can be explained that the cracks and pores caused by the freezethaw damage rise with the growing of RCA replacement percentages after suffering the same freezethaw cycles. The higher water content and lowquality RCA both aggravate the property degradation of RAC under freezethaw cycles. The E_{rd} being closely related to the cracks and pores of concrete decreases by 21.4%, 31.7%, 55.8%, and 84.3% for RAC0%, RAC33%, RAC66%, and RAC100%, respectively, after 75 freezethaw cycles, as shown in Figure 6. Consequently, the capillary absorption behavior of RAC rises with the increase of RCA replacement percentages after the same freezethaw cycles. The results mentioned above highlight that the RAC has a higher capillary absorption behavior than NAC under the same condition of freezethaw cycles, and the increment becomes remarkable after suffering a large number of freezethaw cycles, which should be considered carefully in the durability design of RAC exposed to the cold environment:
Figure 8(a) shows the correlation among the suffered freezethaw cycles, RCA replacement percentages, and capillary absorption coefficient, which manifest the addition of RCA and suffered freezethaw cycles are found to have a negative effect on the capillary absorption behavior of RAC. For exploring the correlation between the imposed freezethaw damage and capillary absorption behavior of RAC, the relation between the E_{rd} and capillary water absorption coefficient is established, which shows that the capillary water absorption coefficient increases linearly with the decrease of E_{rd}, as shown in Figure 8(b). The specific equation can be seen in Equation (5), where the A_{RAC} and A_{RAC,0} is, respectively, the capillary absorption coefficient of RAC with and without imposed freezethaw damage, g/(m^{2}h^{1/2}); E/E_{0} stands for the relative dynamic elastic modulus, %; K^{FT}_{cor} presents the correlation coefficient, and it is closed related to the RCA replacement percentage; the K^{FT}_{cor} is 42 and 103 when the RCA replacement percentages are 0% and 100%, and K^{FT}_{cor} with different RCA replacement percentages can be calculated by the method of linear insertion.
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(b)
3.4. Capillary Water Absorption of RAC with Imposed Loading Damage
Through the observation of actual cracks development on the surface of RAC with different loadings, it can be seen that there existed some tiny cracks on the specimen surface when the applied loading reached 40%f_{c}, whereas the cracks continued to develop and the obvious cracks appear on the specimen surface when the applied loading reached 60%f_{c}; moreover, when the applied loading was 80%f_{c}, the width of crack became larger coupling with the spalling of concrete surface. Figure 9 shows the imposed load damage of RAC with various percentages of ultimate compressive strength. The results highlight that the increased loading results in the increase of damage degree of RAC, and the increasing range of load damage degree becomes more obvious when the applied loading is above 60%f_{c}. The damage level increases linearly with the growth of applied loading levels, and the increasing replacement percentage of RCA leads to the increase in the slope of fitting line. Such as, the damage level of RAC0% with the load of 40%f_{c}, 60%f_{c}, and 80%f_{c} is, respectively, 0.020, 0.066, and 0.143, and the results become 0.047, 0.108, and 0.199 for RAC100%.
As shown in Figure 9, the addition of RCA further results in the increase in the damage degree of RAC with the same loading, and the increasing range becomes more obvious with the increase of applied loading. For example, the damage degree of RAC33%, RAC66%, and RAC100% is about 1.25, 1.95, and 2.40 times as high as that of RAC0% when the applied loading is 40%f_{c}, and the results are 1.06, 1.31, and 1.40 times when the applied loading reaches 80%f_{c}. This could be attributed to the existence of RCA old mortar and ITZ with poor properties. On the one hand, the inferior properties of ITZ attached to RCA are easy to fail with the application of loading; on the other hand, the old mortar with a mass of initial damage cracks aggravates the property degeneration of RAC, which leads to the increase in the load damage degree of concrete with the addition of RCA.
Figure 10 presents the capillary absorption curves of RAC with different loadings, the results highlight that the applied loading leads to the increase in the capillary water absorption of RAC, and the growth of capillary water absorption becomes significant when the applied loading is above 60%f_{c}. Such as, the capillary absorption coefficient of RAC0% with the load of 0%f_{c,} 40%f_{c}, 60%f_{c}, and 80%f_{c} is, respectively, 973.5 g/(m^{2}h^{1/2}), 1073.6 g/(m^{2}h^{1/2}), 1265.0 g/(m^{2}h^{1/2}), and 1649.1 g/(m^{2}h^{1/2}), and the results are 1245.2 g/(m^{2}h^{1/2}), 1326.4 g/(m^{2}h^{1/2}), 1788.4 g/(m^{2}h^{1/2}), and 2513.8 g/(m^{2}h^{1/2}) for RAC100%. Comparing with the results in Figures 10(a)–10(d), the capillary absorption coefficient of concrete increases with the rise of RCA replacement percentages with the same loading; such as, the capillary absorption coefficient of RAC33%, RAC66%, and RAC100% is, respectively, 1.04, 1.11, and 1.24 times as high as that of RAC0% when the applied loading is 40%f_{c}, and the results become 1.09, 1.28, and 1.52 times when the applied loading reaches 80%f_{c}.
(a)
(b)
(c)
(d)
The results above highlight that the increased loading and RCA replacement percentages result in the increase in the capillary water absorption of concrete. This is attributed to the number of cracks rising with the increase of applied loading, which provides the passageways for water penetration into RAC; as a result, the applied loading increases the capillary water absorption of RAC. The cracks number and the mortar content per unit volume both increase with the rise of RCA replacement, which results in the capillary water absorption improvement of RAC with the same loading.
Figure 11 shows the relationship between capillary absorption coefficient and RCA replacement percentages with different loading levels, and the results manifest that the capillary absorption coefficient increases linearly with the rise of RCA replacement percentages with the same loading; however, the increased loading results in the increases in the slope of fitting line. To investigate the correlation between the capillary water absorption and imposed load damage, the relationship between the capillary absorption coefficient and load damage degree (D) is established, and the results are described in Figure 12:
The results highlight that the capillary absorption coefficient increases linearly with the rise of D; furthermore, the slope of fitting line grows with the increase of RCA replacement percentages. Equation (6) shows the specific equation, where the D is the load damage degree; and are, respectively, the capillary absorption coefficient of RAC without and with imposed loading damage, (g/m^{2}h^{1/2}); and stands for the correlation coefficient, and it is closely related to the RCA replacement percentages, the K^{ET}_{cor} is, respectively, 4480 and 6640 when the RCA replacement percentages is 0% and 100%, and K^{FT}_{cor} with the other RCA replacement percentages can be calculated by the method of linear insertion. Although the relationship between the capillary water absorption of RAC and imposed loading damage is established after unloading, the capillary water absorption of RAC with sustained loading can also be estimated by the value of damage degree with sustained loading using Equation (6).
This paper investigates the capillary water absorption of RAC with and without imposed damage, whereas there still has some shortcomings need to be solved in the further study. For example, if the source of RCA is much completed, the relation between the various sources of RCA and the capillary absorption behavior of RAC should be investigated. The method of improving the water permeability resistance of RAC should be also studied, such as by the waterproof treatment and mix optimization, which is necessary for the wide application of RAC in the engineering construction.
4. Conclusions
This paper investigates the capillary absorption behavior of RAC with different replacement percentages of RCA under normal, freezethaw cycles and loading conditions, respectively. Based on the results of this experimental work, the following conclusions can be drawn:(1)As the old mortar adhered to RCA possesses a low quality and the mortar content per unit volume of concrete increases with the growing of the RCA replacement percentages, the capillary water absorption of concrete increases with the increased RCA replacement percentages under normal condition. The capillary absorption coefficient and RCA replacement percentages follow a linear correlation. Furthermore, the addition of RCA results in the decrease in the compressive strength. There exists a linear relation between the capillary water absorption coefficient and chloride diffusion coefficient, as well as the maximum amount of absorbed water and chloride content, which provides an effective way to estimate the chloride permeability through the behavior of capillary water absorption of RAC.(2)Exposing to the condition of freezethaw cycles, the freezethaw resistance of concrete decreases with the increase of the RCA replacement percentage. The imposed freezethaw damage results in the increase in the capillary absorption behavior of RAC. Capillary water absorption of concrete increases with the rising of RCA replacement percentages after the same freezethaw cycles, and the increase becomes more obvious after suffering a large number of freezethaw cycles. Moreover, there exists a linear correlation between the capillary absorption coefficient and imposed freezethaw damage (E_{rd}).(3)Under the condition of applied loading, the imposed loading damage boosts with the increasing of applied loading, and the addition of RCA results in the increase in the imposed damage of concrete with the same loading level. The applied loading leads to the increase in the capillary water absorption of RAC, and the increasing range becomes more obvious with the applied loading above 60%f_{c}. Particularly, the capillary water absorption increases linearly with the growth of imposed loading damage, which can be used to estimate the capillary absorption behavior of RAC with imposed loading damage.(4)The addition of RCA and imposed damage both results in the increase in the capillary water absorption of concrete, which should be considered in the durability design. Considering the high capillary water absorption of RCA, they can act as the water storage materials used in the construction of sponge city.
Data Availability
The data used to support the findings of this study are available from the corresponding author upon request.
Conflicts of Interest
The authors declare that they have no conflicts of interest.
Acknowledgments
The authors wish to acknowledge the financial support from the National Natural Science Foundation of China (NSFC) (nos. 51438007 and 5161101205) and ChinaJapanese Joint Program sponsored by Ministry of Science and Technology in China (no. 2016YFE0118200).
References
 H. Yuan and L. Shen, “Trend of the research on construction and demolition waste management,” Waste Management, vol. 31, no. 4, pp. 670–679, 2011. View at: Publisher Site  Google Scholar
 J. Z. Xiao, Z. M. Ma, T. B. Sui, A. Akbarnezhad, and Z. H. Duan, “Mechanical properties of concrete mixed with recycled powder produced from construction and demolition waste,” Journal of Cleaner Production, vol. 188, no. 2, pp. 720–731, 2018. View at: Publisher Site  Google Scholar
 P. MercaderMoyano and A. RamãRezDeArellanoAgudo, “Selective classification and quantification model of C & D waste from material resources consumed in residential building construction,” Waste Management and Research, vol. 31, no. 5, pp. 458–74, 2013. View at: Publisher Site  Google Scholar
 N. Seror, S. Hareli, and B. A. Portnov, “Evaluating the effect of vehicle impoundment policy on illegal construction and demolition waste dumping: Israel as a case study,” Waste Management, vol. 34, no. 8, pp. 1436–1445, 2014. View at: Publisher Site  Google Scholar
 M. Cao, H. Zhang, and X. U. Ling, “Research progress on deformation performance of recycled concrete,” Materials Review, vol. 28, no. 1, pp. 106–109, 2014. View at: Google Scholar
 M. Safiuddin, U. J. Alengaram, M. M. Rahman, M. A. Salam, and M. Z. Jumaat, “Use of recycled concrete aggregate in concrete: a review,” Journal of Civil Engineering and Management, vol. 19, no. 6, pp. 796–810, 2013. View at: Publisher Site  Google Scholar
 T. Gonen and S. Yazicioglu, “The influence of compaction pores on sorptivity and carbonation of concrete,” Construction and Building Materials, vol. 21, no. 5, pp. 1040–1045, 2007. View at: Publisher Site  Google Scholar
 Rasheeduzzafar, “Influence of cement composition on concrete durability,” ACI Materials Journal, vol. 89, no. 6, pp. 574–586, 1992. View at: Publisher Site  Google Scholar
 Z. M. Ma, T. J. Zhao, J. Z. Xiao, and P. G. Wang, “Effect of applied loads on water and chloride penetrations of strain hardening cementbased composites,” Journal of Materials in Civil Engineering, vol. 28, no. 9, pp. 1–12, 2016. View at: Publisher Site  Google Scholar
 J. J. Shi and W. Sun, “Effects of phosphate on the chlorideinduced corrosion behavior of reinforcing steel in mortars,” Cement and Concrete Composites, vol. 45, pp. 166–175, 2014. View at: Publisher Site  Google Scholar
 M. Basista and W. Weglewski, “Chemically assisted damage of concrete: a model of expansion under external sulfate attack,” International Journal of Damage Mechanics, vol. 18, no. 2, pp. 155–175, 2009. View at: Publisher Site  Google Scholar
 W. Li, M. PourGhaz, J. Castro, and J. Weiss, “Water absorption and critical degree of saturation relating to freezethaw damage in concrete pavement joints,” Journal of Materials in Civil Engineering, vol. 24, no. 3, pp. 299–307, 2012. View at: Publisher Site  Google Scholar
 W. H. Dunagan, “Methods for measuring the passage of water through concrete,” Proceedings of the American society for Testing Materials, vol. 39, pp. 866–880, 1939. View at: Google Scholar
 Z. M. Ma, T. J. Zhao, and Y. D. Zhao, “Effects of hydrostatic pressure on chloride ion penetration into concrete,” Magazine of Concrete Research, vol. 68, no. 17, pp. 1–10, 2016. View at: Publisher Site  Google Scholar
 L. Hanžič, L. Kosec, and I. Anžel, “Capillary absorption in concrete and the Lucas–Washburn equation,” Cement and Concrete Composites, vol. 32, no. 1, pp. 84–91, 2010. View at: Publisher Site  Google Scholar
 H. J. Du, H. J. Gao, and S. D. Pang, “Improvement in concrete resistance against water and chloride ingress by adding graphene nanoplatelet,” Cement and Concrete Composites, vol. 83, no. 1, pp. 114–123, 2016. View at: Publisher Site  Google Scholar
 L. Wang and T. Ueda, “Mesoscale modeling of water penetration into concrete by capillary absorption,” Ocean Engineering, vol. 38, no. 4, pp. 519–528, 2011. View at: Publisher Site  Google Scholar
 J. A. Bogas, M. G. Gomes, and S. Real, “Capillary absorption of structural lightweight aggregate concrete,” Materials and Structures, vol. 48, no. 9, pp. 2869–2883, 2014. View at: Publisher Site  Google Scholar
 T. Gonen, S. Yazicioglu, and B. Demirel, “The influence of freezingthawing cycles on the capillary water absorption and porosity of concrete with mineral admixture,” KSCE Journal of Civil Engineering, vol. 19, no. 3, pp. 667–671, 2015. View at: Publisher Site  Google Scholar
 L. C. Wang and S. Li, “Capillary absorption of concrete after mechanical loading,” Magazine of Concrete Research, vol. 66, no. 8, pp. 420–431, 2014. View at: Publisher Site  Google Scholar
 W. H. Kwan, M. Ramli, K. J. Kam, and M. Z. Sulieman, “Influence of the amount of recycled coarse aggregate in concrete design and durability properties,” Construction and Building Materials, vol. 26, no. 1, pp. 565–573, 2012. View at: Publisher Site  Google Scholar
 H. B. Liu, J. Sun, and X. H. Cong, “A review of the durability of recycle aggregate concrete,” Applied Mechanics and Materials, vol. 744–746, pp. 1357–1360, 2015. View at: Publisher Site  Google Scholar
 J. Z. Xiao, D. Lu, and J. W. Ying, “Durability of recycled aggregate concrete: an overview,” Journal of Advanced Concrete Technology, vol. 11, no. 12, pp. 347–359, 2013. View at: Publisher Site  Google Scholar
 ASTM C1585, Standard Test Method for Measurement of Rate of Absorption of Water by HydraulicCement Concretes, ASTM International, West Conshohocken, PA, USA, 2013.
 S. A. Kelham, “A water absorption test for concrete,” Magazine of Concrete Research, vol. 40, no. 143, pp. 106–110, 1988. View at: Publisher Site  Google Scholar
 F. H. Wittmann, A. D. A. Wittmann, and P. G. Wang, “Capillary absorption of integral water repellent and surface impregnated concrete,” Restoration of Buildings and Monuments, vol. 20, no. 4, pp. 281–290, 2014. View at: Publisher Site  Google Scholar
 D. Wang, P. Yang, P. K. Hou, L. Zhang, Z. Zhou, and X. Cheng, “Effect of SiO_{2} oligomers on water absorption of cementitious materials,” Cement and Concrete Research, vol. 87, pp. 22–30, 2016. View at: Publisher Site  Google Scholar
 Z. M. Ma, F. Z. Zhu, and T. J. Zhao, “Effects of surface modification of silane coupling agent on the properties of concrete with freezethaw damage,” KSCE Journal of Civil Engineering, vol. 22, pp. 657–669, 2018. View at: Publisher Site  Google Scholar
 JTJ270, Testing Code of Concrete for Port and Waterway Engineering, Ministry of Communications of PRC, Beijing, China, 1998.
 F. Z. Zhu, J. Liu, and Z. L. Li, “Discussion on the influence of water content in concrete dynamic elastic modulus test,” Concrete, vol. 277, pp. 40–56, 2012. View at: Google Scholar
 Q. X. Luo and J. H. Bungey, “Using compression wave ultrasonic transducers to measure the velocity of surface waves and hence determine dynamic modulus of elasticity for concrete,” Construction and Building Materials, vol. 10, no. 4, pp. 264–270, 1996. View at: Google Scholar
 J. W. Ying, Chloride Ion Diffusion Law and Basic Characteristics of Recycled Aggregates Concrete, Doctoral dissertation, Tongji University, Shanghai, China, 2013.
 K. Thangavel and N. S. Rengaswamy, “Relationship between chloride hydroxide ratio and corrosion rate of steel in concrete,” Cement and Concrete Composites, vol. 20, no. 4, pp. 283–292, 1998. View at: Publisher Site  Google Scholar
 C. G. Berrocal, K. Lundgren, and I. Löfgren, “Corrosion of steel bars embedded in fibre reinforced concrete under chloride attack: state of the art,” Cement and Concrete Research, vol. 80, pp. 69–85, 2016. View at: Publisher Site  Google Scholar
 M. Saito, M. Ohta, and H. Ishimori, “Chloride permeability of concrete subjected to freezethaw damage,” Cement and Concrete Composites, vol. 16, no. 4, pp. 233–239, 1994. View at: Publisher Site  Google Scholar
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