Performance And Improvement Measures Of Recycled Aggregate Concrete With Low Replacement Rate

Recycled aggregates technology has a great significance for saving resources, protecting the environment, and realizing the sustainable development of construction industry, moreover, it is also the hot spot that the domestic researchers focused on. At present, the domestic study of recycled concrete has not yet mature, and most researches are focused on the performance of recycled concrete with high aggregate replacement ratio, therefore, its theoretical results cannot systematically guide the actual production and engineering application. Recently domestic research in recycled concrete whose results cannot be applied to guide production is still immature and mainly based on performance research of recycled aggregate in high replacement ratio. Based on international and domestic research results and recent production process of recycled aggregate, this paper does a detail study on strength and durability of recycled concrete in low replacement ratio. The results of this paper might have great significance and value in application.Experiments of concrete compressing strength, axial compression strength, chloride penetration resistance, frost resistance, and carbonation resistance were performed by using water-binder ratio, replacement rate of recycled coarse aggregate, replacement rate of recycled fine aggregate and replacement rate of minerals as parameters. The changing rules of concrete strength and durability is observed considering different water-binder ratios, replacement ratios of recycled aggregate and replacement rates of mineral based on experiment results. According to the defects of recycled aggregate, modified experiments were performed to test the results of concrete compressing strength, axial compression strength, chloride penetration resistance, frost resistance, and carbonation resistance by socking recycled coarse aggregate with hydrochloric acid and PVA polymeride. According to the experiment, improvement of concrete strength and durability were observed by socking recycled coarse aggregate with hydrochloric acid and PVA polymeride. In consideration of poor crack resistance in early phase of recycled concrete, experiment to demonstrate the improvement in crack resistance of recycled concrete by adding Polypropylene fiber is performed.Compared with ordinary concrete, when the replacement rate of recycled coarse aggregate is below30%and water-binder is between0.40and0.48, the strength of recycled concrete reduces a bit while the durability increases. The strength of recycled concrete show some increase when water-binder is between0.56and0.60while strength and durability shows some decrease when the replacement ratio of coarse aggregate is beyond30%. When adding pulverized fuel ash into concrete with recycled coarse aggregate, chloride penetration resistance performance improves obviously, anti-frost property show no change and the carbonation resistance reduces a lot. When the mixture rate of pulverized fuel ash and mineral powder is both15%, the performance of chloride penetration resistance and anti-frost show increase evidently while the compressive strength is a bit lower. Concrete strength and durability are improved by using hydrochloric acid modification methods. When adding PVA polymeride, all other performance indexes are improved except for frost-resistance. When the replacement ratio of fine aggregate is below30%, strength and durability of recycled concrete is better than ordinary one. Mineral admixtures are not recommended to add to recycled fine aggregate concrete.