关键词: 花岗岩废料, 再生混凝土, 路面砖, 冻融损伤, 膨胀性应力

Abstract: 50 freeze-thaw cycles of recycled concrete pavement brick with granite waste were carried out by the slow freezing method. Based on the mass loss and compressive strength, the change rule of freeze-thaw resistance of recycled concrete pavement brick was studied. Based on the theory of volume expansion and osmotic pressure and combined with scanning electron microscope analysis, the microstructure, and hydration product composition of recycled concrete pavement brick before and after freeze-thaw were compared. The freeze-thaw damage mechanism was revealed from the perspective of microcrack accumulation and expansive stress. The slurry pore structure change model and the osmotic pressure model caused by slurry concentration difference were established. The results show that the mass loss rate and compressive strength loss rate of recycled concrete pavement brick with the optimal replacement rate of micro, fine and coarse aggregates of 20%, 30% and 50% (mass fraction) are 1.5% and 10.0% respectively, which is lower than reference group. But the utilization rate of granite waste is improved to a great extent and meets the basic requirements of experimental standards and road performance. The microscopic analysis results show that higher content of ettringite in the hydration products of slurry makes the microcracks of concrete enriched, and finally leads to the formation of macrocracks causing frost heave failure. The model reveals that the invasion of external water, resulting in volume expansion, and the expansive stress caused by osmotic pressure in the pores and gel pores are the real reasons for freeze-thaw damage.

Key words: granite waste, recycled concrete, pavement brick, freeze-thaw damage, expansive stress