Effects of air content and bubble parameters on frost resistance of recycled concrete in mild regions
Five groups of concrete ZS-0,PG-0,PG-3.5,PG-5.5,and PG-7.5 were prepared from recycled concrete in mild regions,and the effects of their air content and bubble parameters on frost resistance were studied.The results showed that when the air content was below 7.5％,the frost resistance of recycled concrete increased with the increase of the air content of the base concrete.When the air content is higher than 7.5％,the connection between pores has a significant negative impact on the strength of recycled concrete,which will gradually weaken the frost resistance of recycled concrete.Adding air entraining agent to the matrix concrete has a significant impact on the frost resistance of recycled concrete,and the frost resistance of recycled concrete shows a trend of increasing first and then decreasing with the increase of the air content of the matrix concrete.When the air content of the base concrete is 5.5％,recycled concrete has the strongest frost resistance,and its frost resistance is the same as that of ordinary concrete.When the air content of the concrete mixture is the same,the bubble characteristic parameters of recycled concrete have significant differences.When the air content is 5.5％,the bubble spacing coefficient varies greatly,the minimum is 247 μm and the maximum is 542 μm.
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