Strengthening Effect of Nano-materials on the Compressive Strength and Microstructure of Recycled Brick Aggregate Concrete

To investigate the strengthening effect of different nano-materials on recycled brick aggregate concrete, this paper considered the influence of different nano-materials, different mixing amounts, and different mixing methods on the compressive strength and microstructure of recycled brick aggregate concrete. The results show that the 7-day, 14-day, and 28-day compressive strengths of recycled brick aggregate concrete increase to different degrees after adding nano-materials, but the improvement in early compressive strength is more obvious. The cubic compressive strength prediction model of three nanomaterial-reinforced recycled brick aggregate concretes is established using the compressive strength as the index. The optimum contents of nano-SiO2, nano-CaCO3, and nano-Al2O3 are 3 %, 2 %, and 3 %, respectively. Double-mixed nano-materials have a lower improvement effect on the compressive strength of recycled brick aggregate concrete at different ages than single-mixed nano-materials. The nanomaterials can not only promote the hydration reaction of cement but also fill the microcracks and micropores inside the concrete, making the structure denser and thereby improving the mechanical properties of recycled brick aggregate concrete. The 28-day compressive strength of recycled aggregate modified with nano-materials (nano-SiO2 and nano-Al2O3) concrete is higher than that of recycled aggregate concrete mixed with nano-materials. The early compressive strength of recycled aggregate modified with nano-Al2O3 concrete is lower than that of recycled aggregate concrete mixed with nano-Al2O3.