Size effect on compressive behaviours of normal-strength concrete cubes made from demolished concrete blocks and fresh concrete

Abstract

This work presented in this paper contributes to a comprehensive research into structural elements containing demolished concrete blocks (DCBs) with a distinctly larger size than conventional recycled aggregates. In this research, 51 cubic specimens made from DCBs and fresh concrete (FC) with a replacement ratio of 30% were fabricated and tested under uniaxial compressive loadings. Two parameters were considered -the cube dimension and the characteristic size of DCBs. The influence of the two factors on the compressive behaviours of normalstrength concrete cubes made from DCBs and FC was examined in terms of the combined cubic compressive strength, the modulus of elasticity and the strain at peak stress. Based on the test results, a formula is presented to describe the relationship between the characteristic ratio (i.e. ratio of the characteristic size of DCBs to the cube dimension) and the combined cubic compressive strength of the specimens made from DCBs and FC, and a model is proposed to predict the combined cubic compressive strength of the specimens with various cube dimensions and characteristic ratios. The following results were obtained. In the case that the characteristic ratio is constant, the combined cubic compressive strength of the specimens made from DCBs and FC decreases significantly with an increase in cube dimension, and the effect of cube dimension on the combined strength accords with both the size effect law and the modified size effect law for conventional concrete. The effects of both the cube dimension and the characteristic size of DCBs on the specimen's modulus of elasticity and strain at peak stress are limited. In the case that the cube dimension is kept constant, the combined cubic compressive strength of the specimens made from DCBs and FC decreases gradually with an increase in characteristic ratio; the influence of cube dimension on this trend is very limited. Both the established formulae and the proposed model agree quite well with the test results.

Compressive behaviors of cubes and cylinders made of normal-strength demolished concrete blocks and high-strength fresh concrete

“…After that, core concrete of the waste components was broken into blocks by using simple tools such as pneumatic picks and hammers. Based on the experimental studies and actual practices conducted by the authors in the past six years [22][23][24][25][26][27], it is suggested that the best ratio of the characteristic size of DCBs to the short side of the specimen's (or structural member's) cross section ranges from 1/3 to 1/2, to ensure the casting quality of DCBs and FC combined concrete. In this way, the characteristic size of the broken DCBs was mainly ranging from 100 mm to 150 mm in this study (Fig.…”

“…At present, a large amount of waste concrete still ends up at disposal sites. In order to explore a more efficient approach to reuse the waste concrete directly as an acceptable structural material, some new kinds of structural members containing both fresh concrete (FC) and broken demolished concrete with distinctly larger size than conventional recycled aggregates (usually with a size of 640 mm) were proposed and investigated by the authors [22][23][24][25][26][27]. Here the term of ''broken demolished concrete'' refers to the demolished concrete blocks (DCBs, usually with a size of 100-300 mm) or demolished concrete segments (DCSs, usually with a size of >500 mm in length).…”

Discussion: Size effect on compressive behaviours of normal-strength concrete cubes made from demolished concrete blocks and fresh concrete

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Contribution by J. R. Martí-VargasBased on interest in using demolished concrete blocks (DCBs), the paper by Wu et al (2013) presents research on the uniaxial behaviours of cubic concrete specimens. The authors should be complimented for producing this detailed paper of interest for the discusser, who would like to offer some comments for the authors' consideration and response, mainly about the size effect on concrete compressive strength and concrete modulus of elasticity.

Regarding the effect of cube dimension on compressive strength, the authors found that compressive strength decreases if the cube dimension increases when DCBs are used.

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Compressive Behaviors of Prisms Made of Demolished Concrete Lumps and Fresh Concrete

“…A series of experimental studies on structural members (beams, columns, slabs, and walls) containing DCLs have now been carried out to examine the feasibility of such recycling [26][27][28][29][30][31][32]. Test results show that the mechanical properties and seismic performance of structural members containing DCLs are similar to or only slightly lower than those of such members containing FC alone.…”