Study Of Coarse Aggregate’S Effect On Performance Of Concrete In Freeze–Thaw&Erosion Environment

Concrete is the most widely used building material in infrastructure construction,its production needs to consume a lot of sand,stone aggregate and other natural resources.Through the investigation of the coarse aggregate yard of the project site in the cold area of northwest China and the concrete structure of Bridges and culverts along the road,it is found that there are coarse aggregate that is easy to disintegrate and decompose.Therefore,experiments on mechanical properties,long-term properties and durability of concrete made from different kinds of coarse aggregates were carried out,in order to provide guidance for maximizing the utilization benefits and sustainable utilization of construction sand and stone resources in the Northwest dry cold saline soil area and similar environments in the "One Belt and One Road" infrastructure construction.In this paper,based on a highway bridge and culverts project in dry and cold saline soil area of Gansu Province,combined with the actual working climate environment and according to relevant test specifications,5 groups of concrete durability tests under the coupling action of freeze-thaw cycle and sulfate corrosion were carried out with 5 kinds of coarse aggregates and concrete with water-binder ratios of 0.31,0.35 and 0.41.Moreover,the influence of single factors such as freeze-thaw cycle and sulfate corrosion on the durability of 5 groups of concrete was studied.The influence of coarse aggregate on the performance of concrete was studied through the test analysis of the macroscopic indexes such as the appearance shape,quality and compressive strength of concrete at different test ages and the microscopic changes of pore structure and corrosion products.The main research contents of this paper are as follows:(1)SSH(dacite)is an acidic plutonic magmatic rock with dense rock structure and the best resistance to softening and disintegration.LBH(granite)belongs to acid plutonic magmatic rock,SMK(gabbro)belongs to neutral magmatic rock,and the pore space of rock sample increases successively.HYS(diabase)is a neutral magmatic rock with slightly higher degree of weathering and poor ability to resist softening and disintegration,while LFS(gneiss)is a basic granodiorite gneiss with higher microfracture development and the worst ability to resist softening and disintegration.(2)In freeze-thaw cycle test,the apparent damage of 5 groups of concrete decreases with the decrease of water-binder ratio.At the same water-binder ratio,the mass loss rate of HYS concrete was the highest,LFS concrete was the highest,SMK concrete and LBH concrete followed,and SSH concrete was the lowest.The change of compressive strength was consistent with the change of mass.The mass loss and compressive strength loss of HYS concrete and LFS concrete are the maximum at 0.41 water-binder ratio and the minimum at 0.31 waterbinder ratio,while the other three groups of concrete have little difference.(3)In the sulfate attack test,the apparent changes of concrete specimens in the 5 groups at the late stage of the test were more serious than that in the freeze-thaw cycle test.Salt erosion resulted in the loss of surface mortar and increased exposure of coarse aggregate.Compared with the freeze-thaw cycle test,the first stage is longer,and the quality of concrete in the five groups increases obviously.LFS concrete and HYS concrete deteriorated more seriously at 0.41water-binder ratio than at 0.31 water-binder ratio.Under the same water-binder ratio,SSH concrete has the highest compressive strength and the highest corrosion resistance coefficient,followed by SMK concrete and LBH concrete,HYS concrete is poor,and LFS concrete is the worst.(4)In the freeze-thaw corrosion coupling test,the apparent loss of HYS concrete and LFS concrete is more serious at 0.41 water-binder ratio,and the loose strength of the internal coarse aggregate decreases and the interfacial bonding strength between aggregate and cement mortar decreases.At the initial stage of the test of 5 groups of concrete specimens,the pores in the concrete specimens expand rapidly and more new pores are generated,and the number of small holes increases.The number of macropores decreased;At the late stage of freeze-thaw cycle,the pore expansion of LFS concrete is the largest,followed by HYS concrete due to the loose expansion of some coarse aggregate inside.The change trend of pore size of the five groups of concrete specimens is basically the same,and the decrease of concrete strength is related to the change of pore size.The reduction amplitude of concrete strength in 5 groups has nothing to do with the change of pores,but is related to the performance of coarse aggregate.(5)According to the experimental data of 5 groups of concrete in the laboratory,the concrete strength fitting analysis shows that under the action of freeze-thaw cycle,sulfate corrosion and freeze-thaw corrosion coupling,the durability of SSH concrete with different water-binder ratios is excellent,the durability of LFS concrete is the worst,and the durability of HYS concrete is generally poor.The durability of LBH concrete is good in freeze-thaw test,but average in corrosion test and freeze-thaw corrosion coupling test.The durability of SMK concrete is normal in freeze-thaw test,but good in corrosion test and freeze-thaw corrosion coupling test.The concrete A0(culvert wall),A1(pier),A2(abutment)and A3(box girder)at different structural parts of bridge and culvert in the actual engineering site is analyzed from the macro and micro aspects.It is found that A0 loses the most strength and suffers the most serious damage.A2 strength loss rate is higher;A3 strength does not decrease,and durability is the best,which is consistent with the results of indoor research,and provides a basis for indoor concrete research to guide practical engineering.