Recicled Agregate

Cement and Concrete Research 35 (2005) 1187 – 1194

Mechanical properties of recycled aggregate concrete under uniaxial loading
Jianzhuang Xiaoa,*, Jiabin Lia, Ch. Zhangb
b a Department of Building Engineering, Tongji University, Shanghai 200092, China Department of Civil Engineering, University of Applied Sciences Zittau/Gorlitz, D-02763 Zittau, Germany ¨

Received 17 June 2004; accepted23 September 2004

Abstract In this paper, the compressive strength and the stress–strain curve (SSC) of recycled aggregate concrete (RAC) with different replacement percentages of recycled coarse aggregate (RCA) are investigated experimentally. Concrete specimens were fabricated and tested with different RCA replacement percentages of 0%, 30%, 50%, 70% and 100%, respectively. Uniaxialcompression loading is applied in the experiments. Special attention of the analysis is devoted to the failure behaviour and the influences of the RCA contents on the compressive strength, the elastic modulus, the peak and the ultimate strains of RAC. Analytical expressions for the peak strain and the stress–strain relationship of RAC are given, which can be directly used in theoretical and numericalanalysis as well as practical engineering design of RAC structures. D 2004 Elsevier B.V. All rights reserved.
Keywords: Recycled aggregate; Concrete; Mechanical properties; Uniaxial loading

1. Introduction Recycling of waste concrete is beneficial and necessary from the viewpoint of environmental preservation and effective utilization of resources. For the effective utilization of waste concrete, itis necessary to use waste concrete as recycled aggregates for new concrete. To make this technology feasible, a significant amount of experimental works has been carried out. Various investigations mainly engaged in the processing of demolished concrete, the mixture design, the physical and the mechanical properties as well as the durability aspects. Most of the findings have been extensivelyreviewed and discussed by Nixon [1], Hansen [2,3] and ACI 555 Report [4]. It is shown that some properties of recycled aggregate concrete (RAC) may be generally lower than those of normal concrete (NC), but

* Corresponding author. Tel.: +86 21 65983422; Fax: +86 21 65986345. E-mail address: jzx@mail.tongji.edu.cn (J. Xiao). 0008-8846/$ - see front matter D 2004 Elsevier B.V. All rights reserved.doi:10.1016/j.cemconres.2004.09.020

they are still sufficient for some practical applications in Civil Engineering. The most important mechanical properties of RAC are the compressive strength, the tensile and the flexural strengths, the bond strength and the elastic modulus of such concrete. In particular, the stress–strain relation of RAC is especially important in theoretical and numericalanalysis as well as engineering design of RAC structures. The peak value of the stress–strain curve yields the compressive strength, and the area under the descending portion of the curve provides a measure of the toughness resistance of RAC. The descending portion of the stress– strain curve is essential when a RAC structure is subjected to impact, earthquakes, or fatigue loading. Manyinvestigations on the compressive stress–strain behaviour of natural aggregate concrete have been conducted and numerous stress–strain relationships have been developed [5]. In recent years, several investigations have also been performed for the stress–strain relation of recycled aggregate concrete. Henrichshen and Jensen [6] found that the stress–strain relationship for recycled aggregate concrete is1188

J. Xiao et al. / Cement and Concrete Research 35 (2005) 1187–1194 Table 2 Mix proportions of concrete (kg/m3) No. RCA Replacement percentage 0 30 50 70 100 W/C C S NCA RCA Mixing water 185 185 185 185 185

similar in shape to that of normal concrete. Thus structures made of recycled aggregate concrete can be designed according to the theory of plasticity just like structures made of...