Study On Basic Performance Of Rice Husk Ash Recycled Brick-concrete Aggregate Concrete

In recent years,the rapid progress of urban reconstruction and urban construction has led to the rapid add in the output of construction waste,the increasing demand for concrete,and the continuous growth of the demand for natural aggregate and cement.It is urgent to solve such problems as environmental pollution,resource depletion and other problems.The construction waste containing waste red brick and concrete is crushed and screened into recycled brick-concrete aggregate to prepare recycled concrete,which is one of the effective methods to realize resource utilization and relieve economic and environmental pressure.In order to develop environment-friendly concrete materials and increase the"green content"of cement,it has become a research hotspot to use high-quality mineral admixture to replace part of cement.Among them,rice husk ash obtained by burning rice husks contains a large amount of amorphous Si O₂.Because of its strong pozzolanic activity and micro-aggregate effect,small particle size and large specific surface area,rice husk ash is an ideal concrete admixture,which can replace cement as cementing material.Recycled aggregate has many defects and poor strength,which has brought some obstacles to the promotion and application of recycled concrete.But the addition of rice husk ash can enhance and modify concrete,improve its mechanical properties and durability,and make its internal structure more compact.At the same time,RHA can enhance the bond performance between concrete and steel bars,and prevent steel bars from corroding.The combination of recycled aggregate and rice husk ash can have a synergistic effect.Some pores and crack defects of recycled aggregate will be filled with rice husk ash,which can improve the compactness and performance index of recycled concrete.Therefore,rice husk ash recycled brick-concrete aggregate concrete has great research value and broad application prospects.The main research contents of this paper are included:（1）Study on raw material performance.The properties of raw materials for preparing RHA-RBCAC were tested.The X-ray fluorescence analysis,X-ray diffraction analysis,laser particle size analysis and microstructure of RHA were studied,and the activity index of cement mortar with RHA was tested.（2）Trial mix of concrete.Three mixing methods were used to prepare the 14-day cube compressive strength of RHA-RBCAC in partial mix proportions,so as to determine the variables and mixing methods for subsequent experiments.（3）Experimental study on basic mechanical properties of rice husk ash recycled brick-concrete aggregate concrete.Taking the RHA replacement rate r and the RBCA replacement rateρas variables,the cubic compressive strength f_cu,splitting tensile strength f_ts,flexural strength f_f,axial compressive strength f_c,elastic modulus E_c,Poisson’s ratioμand stress-strain curves of 20 groups of specimens were tested.And the effects of rice husk ash on f_cuand f_tsof NAC and RBCAC under different water-binder ratios,the relationship between f_cuof RHA-RBCAC and age were also tested.（4）Theoretical study on basic mechanical properties of rice husk ash recycled brick-concrete aggregate concrete.The relationship between f_ts,f_f,f_c,E_cand f_cuwas analyzed.The constitutive model of the ascending section of stress-strain curve was established.（5）Experimental study on durability of rice husk ash concrete.Through the freeze-thaw test,carbonization test and chloride ion penetration test of NAC and RBCAC containing rice husk ash,the effect of rice husk ash substitution rate on NAC and RBCAC was analyzed.（6）Experimental study on the bond performance between rice husk ash recycled brick-concrete aggregate concrete and steel bar.The effects of RHA replacement rate,RBCA replacement rate,steel bar diameter and bond length on the bond performance between RHA-RBCAC and steel bar were analyzed.The relationship between ultimate bond strength and cube compressive strength was discussed,and the ultimate bond strength calculation formula fitting and bond-slip constitutive relationship model analysis were carried out for each combination respectively.