Research On Failure Mechanism And Mechanical Properties Of Reinforced Brick Aggregate Recycled Concrete

China proposes to achieve carbon peak by 2030 and carbon neutral by 2060.This is of great significance to global environmental governance.And to achieve the"dual carbon"goal,we must promote prevention and control at the source.With the continuous advancement of urbanization in China,the waste clay bricks produced by the demolition of old buildings are increasing year by year,which gradually become an important source of urban solid waste.As a result,Recycling of waste clay bricks is an important direction to promote the sustainable development of construction industry.This is also an important measure to achieve the goal of"dual carbon".In this paper,broken and screened clay bricks were used as coarse aggregate to prepare recycled concrete,which not only realizes the effective utilization of construction waste,but also provides a new idea for the development of low-rise building materials.This paper mainly taked broken and screened brick aggregate as the object,and the optimal reinforcement method of brick aggregate was determined by studying the influence of chemical solution sodium silicate,silicone and cement wrapping on the basic indexes and appearance of brick aggregate,and combining with microscopic analysis.On this basis,the influence of brick aggregate substitution ratio and gel dosage on the mechanical properties of concrete was studied by using brick aggregate treated by different strengthening methods（brick aggregate RA-W,sodium silicate soaked brick aggregate RA-S,silicone soaked brick aggregate RA-Y,sodium silicate soaked paste-coated brick aggregate RA-SG and silicone soaked paste-coated brick aggregate RA-YG）as raw materials;the damage factor of brick aggregate was introduced to explore the correlation between the indexes of brick aggregate and the compressive strength of concrete.The main conclusions of this paper are as follows:（1）The physical and mechanical properties of natural aggregate,brick aggregate and strengthened brick aggregate are compared and analyzed.The results show that compared with natural aggregate,brick aggregate has poor gradation,poor crushing index,high water absorption,low apparent density and bulk density;The four strengthening methods can improve the basic indexes of brick aggregate to some extent,among which silicone soaking treatment can significantly reduce the water absorption,sodium silicate soaking and grouting after sodium silicate soaking can significantly improve the crushing indexes and significantly improve the compressive performance of concrete.（2）Through XRF,XPS and SRD tests on brick aggregate,the chemical composition differences between natural aggregate and brick aggregate were compared and analyzed.The oxide composition of brick aggregate was mainly Si O₂,and showed obvious element concentration phenomenon.SEM test results showed that the apparent structure of brick aggregate was improved by different strengthening treatments.Sodium silicate treatment can effectively fill the pores and micro-cracks on the surface and inside of brick aggregate,thus improving the density of brick aggregate;In addition,sodium silicate improved the apparent structure of brick aggregate and increased the roughness of its surface,which was conducive to the adhesion of cement slurry in brick aggregate.（3）Under different brick aggregate strengthening methods,the compressive strength of brick aggregate recycled concrete has a high linear relationship with replacement rate and gel dosage,and the overall trend is consistent.;When brick aggregate recycled concrete is compressed,the proportion of brick aggregate and interface damage in concrete fracture surface increases with the decrease of brick aggregate replacement rate and the increase of gel dosage;the strengthening method of brick aggregate is the key factor affecting the compressive strength of concrete,and the weakening degree of brick aggregate to the compressive strength of concrete decreases with the improvement of brick aggregate quality.Compared with ordinary concrete,the compressive strength of RA-SG specimens with 100%replacement rate only decreases by 3.1%.Taking the quality of brick aggregate as the strength factor of recycled concrete,the compressive strength calculation formula of ordinary concrete is modified,and the compressive strength calculation formula suitable for recycled concrete of brick aggregate is put forward.（4）Compared with the recycled concrete made from untreated brick aggregate,the splitting tensile strength of recycled concrete made from treated brick aggregate soaked in sodium silicate is improved;Compared with the amount of gel,the replacement rate of brick aggregate has a more significant influence on the splitting tensile strength of concrete.The static elastic modulus of brick aggregate recycled concrete is lower than that of ordinary concrete,and decreases with the increase of brick aggregate replacement rate,which is consistent with the law of compressive strength and splitting tensile strength of concrete.When the gel content is low,the axial compressive strength increases first and then decreases with the increase of brick aggregate replacement rate.