Preparation And Performance Study Of High Performance Recycled Aggregate Pervious Concrete

With the implementation of China's “sponge city” policy,the promotion and application of pervious concrete has developed rapidly.The use of recycled aggregate to prepare pervious concrete for pavement materials can reduce the consumption of primary resources,solve the environmental problems caused by construction waste,and improve the ecological environment,which has a good ecological,environmental and economic benefits and is a new type of environmentally friendly material.However,the use of recycled aggregate to prepare pervious concrete results in lower strength and severely limits its application.Therefore,how to improve the performance of recycled aggregate pervious concrete has important research significance.This project prepares high-performance recycled aggregate pervious concrete through three aspects: reinforcement of recycled aggregate,optimization of particle grading and mix design of recycled aggregate pervious concrete,so that the 28 d compressive strength reaches 30 MPa,the connected porosity is greater than 10%,and the water permeability coefficient is greater than 1 mm/s.The main conclusions of the study are as follows:(1)Reinforcement the recycled aggregate with cement paste mixed with silica fume and metakaolin and water-to-binder ratio of 0.3~0.5 can reduce the crushing value of recycled aggregate,increase the apparent density,but increase the water absorption rate.When the silica fume is added and the water-to-binder ratio is 0.35,the cement paste has the best reinforcement effect;the reinforced aggregate with different modulus of water glass solution can reduce the crushing value,water absorption and increase the apparent density,when the water glass modulus is 1.5,the reinforcement effect is best.Overall,both reinforcement methods improve the performance of recycled aggregates.(2)When the designed target porosity is 15%,the recycled aggregate pervious concrete is prepared by cement paste strengthening,water glass reinforced curing after mold and water glass reinforced molding integration.In summary,water glass reinforced curing after mold has the best effect.The 28 d compressive strength is 31.0MPa,the splitting tensile strength is 2.69 MPa,the water permeability coefficient is 1.9mm/s,and the connected porosity is 14.6%.(3)The recycled aggregate with a small particle size of 2.36~4.75 mm will be used to replace the aggregate of 4.75~9.5mm particle size in different proportions.As the substitution ratio increases,the mechanical properties and density of the pervious concrete first increase and then decrease.The water permeability coefficient and the connected porosity first decrease and then increase.When the substitution ratio is 25%,the performance of recycled aggregate pervious concrete is the best;when the replacement ratio is 50%,the performance of reinforced recycled aggregate pervious concrete is the best.Compared with the recycled aggregate pervious concrete,the mechanical properties of the reinforced recycled aggregate pervious concrete are better,and the water permeability coefficient and the connected porosity are reduced,which can meet the standard requirements.(4)The effect of the plane porosity and the equivalent pore size of the aggregate-grade pervious concrete was analyzed by Image-Pro Plus software.As the proportion of aggregates with small particle size increases,the average equivalent pore size decreases gradually,and the number of small pores increases;the aggregate of single particle size is more likely to form connected pores.The failure mode of recycled aggregate pervious concrete is mainly the destruction of aggregate interface and aggregate.By reinforced recycled aggregate,the crack and loose flaking of the pervious concrete can be reduced.For recycled aggregate pervious concrete,the ratio of small particles to aggregate replacement should not exceed 25%;for reinforced recycled aggregate pervious concrete,the replacement ratio should not exceed 50%.(5)The effects of water-to-binder ratio,water-reducing agent dosage and aggregate characteristics on the surface aggregates of thickness cement paste were studied.The thickness of the cement paste is applied to the mix design of the recycled aggregate permeable concrete by the fitting equation between the thickness of the cement paste and the amount of the water reducing agent stably wrapped on the aggregate surface.When the aggregate particle size is 4.75~9.5mm,the designed cement paste thickness is 0.519 mm,and the water-to-binder ratio is 0.35,the 28 d strength of the permeable concrete reaches 34.1MPa,and the water permeability coefficient is 0.79mm/s.The rheological behavior of cement paste was described by Herschel-Bulkley(H-B)model and numerically processed to obtain the rheological parameters of cement paste,and the relationship between rheological parameters and cement paste thickness was established.