Effectively reutilizing waste clay brick to prepare a novel green foam concrete base on a new two-step paste substitution method

Abstract

Waste clay brick is the most common demolition waste in China. Such numerous bricks are dumped in landfills, which cause great pressure to environment. Existing research reported that clay brick could partially replace aggregate or cement to prepare ordinary concrete, but only in a small amount, because of the weak flow spread, high water absorption, and low compressive strength of the mixtures. This work proposed an effective reutilizing technology of this waste to make high-strength foamed concrete (FC), in which discarded clay brick was rolled into clay brick powder (CBP) and then went through an innovative two-stage gelatinization replacement process. Totally 39 groups of 117 specimens were employed to investigate the influence of CBP dosage and water/cement (W/C) ratio on flow spread, water absorption, compressive behavior, and pore structure. Results show that the CBP dosage could rise to 12% without do harm to workability while the compressive strength of FC increased to 3.21 MPa (grew by 286% in maximum), the pore size distribution was measured as 89.57% in 0.50 to 1 mm range, and the porosity raised about 52.46%. Finally, the technologies of scanning electron microscope (SEM) and X-ray diffractometer (XRD) were used to analyze the microstructure and composition of specimen, confirming that the hydrates in CBP and FC blends primarily consisted of Ca(OH)2 and calcium silicate hydrate (C-S-H) gel. Pozzolanic reaction products formed in mixtures, including hydrates of calcium silicates (CSH), aluminates (CAH) and aluminosilicates (CASH), resulting in consumption of Ca(OH)2, which could make the microstructure denser and obtain stronger compressive strength growth at 28-day. This research can provide guidance and theoretical support for high utilization of waste clay brick to prepare FC green construction materials.