Effect of pore structure and morphological characteristics of recycled fine aggregates from clay bricks on mechanical properties of concrete

Abstract

To boost the recycling rate of demolished clay bricks, recycled fine aggregates from clay bricks (RFCBs) can be feasibly used as sand substitute for preparing green concrete. In this study, the influence of pore structure and morphology characteristics of RFCBs on the mechanical and microstructural properties of concrete was explored. The porous structure and morphological features of RFCBs were quantitively assessed by mercury intrusion porosimetry (MIP), atomic force microscopy (AFM) and digital image analyser. The RFCBs effects on concrete were investigated regarding compressive strength, splitting tensile strength, elastic modulus, MIP and scanning electron microscopy (SEM). The RFCBs possessed elongated shape, rough surface texture, microcracks, and porous internal structure and showed more complex surface morphology than the natural fine aggregates (NAFs). Incorporation of RFCBs without additional water and with partially additional water achieved similar or increased compressive strength, while RFCBs with wholly additional water reduced the compressive strength compared to NAFs concrete. Furthermore, the complex surface morphology of RFCBs helped in improving the splitting tensile strength, but RFCBs with additional water imposed a deteriorated effect on the elastic modulus. MIP results of RFCBs concrete showed that the porosity and total pore volume increased but with better pore refinement. Overall, incorporation of RFCBs in concrete displayed better mechanical interlocking of the ITZ and the compactness of reaction rim than NAFs concrete, and consequently, the soft core and stiff shell of RFCBs could be formed in concrete.