Preparation And Application Of Construction Waste Recycled Aggregate Concrete

With the acceleration of China’s urbanization process,the construction of large-scale infrastructure projects,the renovation of rural dilapidated houses,and the renovation of rural areas,China produces a large amount of construction waste every year.Among the construction wastes,waste concrete accounts for a large proportion.If the waste concrete is prepared into reusable sandstone resources,it can not only alleviate the deterioration of the ecological environment caused by the difficulty of handling a large amount of waste concrete,but also reduce the exploitation of natural mine resources.It fundamentally solves the problem of the depletion of natural aggregates and the destruction of the ecological environment by a large number of sand and gravel reclamation.This paper systematically studied the influence of recycled aggregate pretreatment technology on the properties of recycled aggregates.By adjusting the mixing ratio of different particle sizes of recycled aggregates and the replacement rate of recycled aggregates,combined with the development of special admixtures,the recycled aggregate concrete was prepared with good working performance and durability.Based on the characteristics of large water absorption rate and special surface properties of recycled aggregates,the influences of the pretreatment methods of saturated surface dry method and pure paste stone-wrapping method on the properties of recycled aggregates were studied.The pure paste stone-wrapping method can improve the structure of the interface layer between the coarse aggregate and the cement stone,increase the strength of the concrete which significantly improves the performance of the concrete.The aggregate after the saturated surface dry method has little absorption of the water in the cement paste when the concrete is mixed,thereby ensuring the working performance of the fresh concrete.The compressive strength of the recycled aggregate concrete treated with the pure paste stone-wrapping method at 7d and 28 d was slightly higher than that of the benchmark group,but the performance of the fresh concrete was poor.Saturated surface dry method can greatly reduce the water requirement of aggregate,and the fresh concrete has high fluidity and small slump loss.C40 grade concrete can be prepared by blending the saturated surface dry method with no more than 45% of recycled aggregates.When the amount of recycled aggregates do not exceed 45%,the amount of recycled aggregates would not adversely affect the strength of concrete.Therefore,the dry surface pretreatment of saturated aggregates is selected.Through the research on the properties of recycled aggregate concrete,we successfully developed a special additive product that can improve the properties of recycled aggregate.On the basis of the above research,based on the properties of recycled aggregate concrete,we systematically studied the influence of admixtures on the working performance and mechanical properties of recycled aggregate concrete,and developed a special type additive product that can improve the performance of recycled aggregate concrete.On the basis of determining the coarse aggregate pretreatment technology and the special admixture,the influence of the mixing ratio of different particle sizes of recycled aggregates on the working performance and mechanical properties of recycled aggregate concrete was systematically studied.Tests have shown that the performance of recycled aggregate concrete with a particle size of 5-10 mm and 10-20 mm in proportions of 1:9 and 5:5 can meet the working performance,mechanical properties and durability of concrete.Through comparison,it was found that when the mixing ratio of 1:9 is adopted,the concrete working performance,mechanical properties and durability performance were better.On the basis of determining the pretreatment technology of recycled aggregate,the special admixture,and mixing ratios of different particle sizes,by changing the replacement rate of overall recycled aggregate in the entire coarse aggregate system,the different performances recycled aggregate concrete under different replacement rates was studied,which including workability,mechanical properties,water resistance,chloride ion permeability,shrinkage.The results showed that when the replacement rate of recycled aggregate was not more than 45%,the durability indexes such as impermeability,carbonation resistance,shrinkage performance and resistance to chloride ion permeability of the recycled aggregate concrete with different amounts all met the requirements.On the basis of the above results of experimental study,C30 recycled aggregate concrete was used to cast the main structure of the office building of Lintong Plant of China West Construction North Co.,Ltd.,which became the first demonstration project of applying recycled aggregate concrete to the main structure in Shaanxi Province.