Study on preparation and performance of Brick-concrete recycled sand powder autoclaved aerated concrete

This research aims to prepare autoclaved aerated concrete (AAC) by using brick-concrete recycled sand powder (BCSP) as siliceous material. The effects of BCSP content (0∼100%), fineness(258∼452m2/kg), brick-concrete(B/C) ratio(10:0∼5:5), cement content(15∼23) and CaO-to-SiO2(Ca/Si) ratio (0.69∼0.94) on the performance of brick-concrete recycled sand powder autoclaved aerated concrete (BCSP-AAC) were studied by single factor test. Besides, the strength formation mechanism of BCSP-AAC was revealed by means of microscopic test. The results demonstrate that BCSP can be used as a single siliceous material to prepare AAC; Increasing the fineness can effectively stimulate the reactivity of BCSP, but if it is too large, it will cause agglomeration between the powders and hinder the gas generation of the aluminum powder. The optimum fineness is 374 m2/kg; B/C ratio is one of the key factors affecting the performance of BCSP-AAC. As the proportion of waste concrete in BCSP increases, the dry density of AAC gradually decreases, while the strength initially enhances then declines. The optimum B/C ratio is 7: 3; Ca/Si ratio is another key factor affecting the performance of BCSP-AAC, which directly affects the type, quantity and crystallinity of AAC hydration products. With the rise of Ca/Si ratio, the dry density of BCSP-AAC increases gradually, and the strength increases first and then decreases. The optimum Ca/Si ratio is 0.81. At this time, the tobermorite formed in BCSP-AAC exhibits a well-crystallized plate-like structure, and C-S-H gel intersperses in the gaps of tobermorite, forming a dense microstructure. Considering the dry density and compressive strength of BCSP-AAC, when the water-solid ratio is 0.65, the aluminum powder paste is 0.13 %, and the BCSP: quicklime: cement: desulfurization gypsum = 67: 13: 17: 3, a light BCSP-AAC with a dry density of 524kg / m3 and a compressive strength of 3.68MPa can be prepared.