Experimental Study on Tensile Creep of Coarse Recycled Aggregate Concrete
© The Author(s) 2015
Received: 2 March 2015
Accepted: 23 July 2015
Published: 15 September 2015
Previous studies have shown that the drying shrinkage of recycled aggregate concrete (RAC) is greater than that of natural aggregate concrete (NAC). Drying shrinkage is the fundamental reason for the cracking of concrete, and tensile creep caused by the restraint of drying shrinkage plays a significant role in the cracking because it can relieve the tensile stress and results in the delay of cracking occurrence. However, up till now, all research has been focusing on the compressive creep of RAC. Therefore, in this study, a uniaxial restrained shrinkage cracking test was executed to investigate the tensile creep properties caused by the restraint of drying shrinkage of RAC. The mechanical properties, such as compressive strength, tensile splitting strength, and Young’s modulus of RAC were also investigated in this study. The results confirmed that the tensile creep of RAC caused by the restraint of shrinkage was about 20–30 % larger than that of NAC.
As vast amounts of waste materials produced during the demolition of concrete structures create environmental pollution, recycling of construction wastes offers a practical alternative to protect the environment (Enad et al. 2013). Therefore, the use of concrete containing demolished concrete material is an important issue for reducing the environmental load. Because aggregate takes up nearly 70 % of concrete volume, the use of coarse recycled aggregate as a partial replacement for natural aggregate in the manufacturing of concrete has become a common practice. This concrete is called recycled aggregate concrete (RAC).
To encourage the usage of construction waste materials, many researchers have executed research on the mechanical characteristics of recycled aggregate (Soares et al. 2014a; Tavakoli and Soroushian 1996a; Valeria 2010) and the durability of recycled aggregate (Bravo et al. 2015; Ryou and Lee 2014; Sherif et al. 2015; Soares et al. 2014b). According to the studies of Domingo et al. (2009), Gholamreza et al. (2011), Rasiah et al. (2012), Tavakoli and Soroushian (1996b), and Xiao et al. (2014), the drying shrinkage of RAC is larger than that of NAC.
The drying shrinkage is the fundamental reason for the cracking of concrete, and cracks occur when the tensile stress caused by the drying shrinkage exceed the tensile strength of the concrete (Tao et al. 2012). Tensile creep plays a significant role in cracking of concrete because it can relieve the tensile stress and results in the delay of cracking occurrence (Garas et al. 2009). However, up till now, all research has been focusing on the compressive creep of RAC (Domingo et al. 2009; Gholamreza et al. 2011; Xiao et al. 2014).
Therefore, in this study, a uniaxial restrained shrinkage cracking test was executed to investigate the tensile creep properties caused by the restraint of the drying shrinkage of RAC. In a uniaxial restrained shrinkage cracking test, specimens were designed to generate cracks caused by the restraint of drying shrinkage. These specimens were also used to investigate tensile stress, tensile creep, and cracking age. The mechanical properties of RAC, such as compressive strength, tensile splitting strength, and Young’s modulus, were also investigated in this study.
2 Experimental Program
2.1 Mixture Proportions and Materials
Two different water-to-cement (w/c) ratios of 0.65 and 0.45, and types of coarse aggregate were used to create four different concrete mixtures. In Korea, when recycled aggregates are used for concrete, the design strength of 21–27 MPa is recommended (KMCT, 2005). However, to encourage the usage of recycled aggregates, the design strength of concrete larger than 27 MPa is included in this research.
Unit content (kg/m3)
Properties of aggregate.
Density SSD (g/cm3)
Dry density (g/cm3)
Absorption ratio (%)
2.2 Shape and Kind of Specimens
2.3 Testing Methods
All specimens were demolded after a day, moist-cured for 7 days, and then exposed to air. They were stored in a controlled environment, temperature of 20 ± 1 °C and relative humidity of 60 ± 5 %. The uniaxial restrained shrinkage cracking tests and drying shrinkage tests were started after 7 days and conducted in accordance with JIS A 1129 (2001) and JIS A 1151 (2002), respectively. A contact strain gauge (CSG) with a precision of 1/1000 was used to measure the strain. Compressive strength and splitting tensile strength tests were conducted in accordance with JIS A 1108 (1999a) and JIS A 1113 (1999b), respectively.
3 Results and Analysis
3.1 Mechanical Properties of Concrete
Mechanical properties of concrete.
f c (MPa)
f st (MPa)
E c (GPa)
f c (MPa)
f st (MPa)
E c (GPa)
f c (MPa)
f st (MPa)
E c (GPa)
f c (MPa)
f st (MPa)
E c (GPa)
3.2 Drying Shrinkage
3.3 Uniaxial Restrained Shrinkage Cracking Test
3.3.1 Cracking Age
Average value (cracking age)
3.3.2 Histories of Tensile Stress
3.3.3 Histories of Tensile Creep
For both w/c = 65 % and w/c = 45 % concrete, the compressive strength and splitting tensile strength of RC specimens containing coarse recycled aggregate at 28 days showed a decrease of about 20 % and about 10 %, respectively, compared to those of NC specimens containing 100 % natural aggregate at 28 days.
In w/c = 65 % concrete, the drying shrinkage at 60 days of RC specimens was about 20 % larger than that of NC specimens. In w/c = 45 % concrete, the drying shrinkages of NC specimens and RC specimens were almost the same.
The tensile stress of all concrete mixtures almost linearly increased with time, and the tensile stress of RC specimens showed about 10 % reduction compared to that of NC specimens.
According to previous studies, for compressive creep, creep deformation of RAC is 20–60 % larger than that of NAC. Based on the results of this study, for tensile creep due to restraint of shrinkage, the creep deformation of RAC is 20–30 % larger than that of NAC.
For cracking age, if the specimens have the same w/c ratio, the difference between NC specimens and RC specimens was very small. Although the tensile strength of the concrete with recycled aggregates is smaller than that of the concrete with natural aggregates, the cracking age was similar to each other, since the stress relaxation of the concrete with recycled aggregates caused by tensile creep is larger than that of the concrete with natural aggregates.
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