Experimental Study On Volume Stability And Durability Of High Strength Concrete Mixed With Expansion Agent

With the development of the society,all kinds of high-rise and super high-rise buildings have become more and more common,and the application of high strength concrete has been gradually promoted,but the high cracking sensitivity of high strength concrete has become an important factor affecting the structural strength and durability.To solve the problem of high strength concrete shrinkage crack,this article through to calcium sulphoaluminate expansion agent(CSA)-calcium oxide and magnesium oxide(MgO style)is obtained and is a kind of expansion agent according to 1:1 proportion expansion source expansion agent(hereinafter referred to as the CM expansion agent),and compared with single type magnesium oxide expansive agent,respectively,with 12% amount of replacing cement mixing proportion of concrete,the CM expansion agent in C40,C70,C100 three kinds of strength grade of concrete deformation properties,mechanical properties and water permeability resistance,frost resistance performance and resistance to chloride ion permeability.By means of X-ray diffraction(XRD)analysis and mercury injection(MIP)test,the phase composition and microstructure of concrete with this expansive agent were analyzed.The research results show that:Under the condition of sealing and curing at room temperature,free deformation of the test group with 12% CM expansive agent will occur in three stages: expansion,shrinkage and micro-expansion.Moreover,the higher the strength grade of concrete is,the smaller the expansion value will be in the expansion stage,but the smaller the shrinkage value will be in the contraction stage,and the larger the expansion energy will be in the later stage.The main reason is that the binding effect of the higher strength on the expansion energy in the early stage of high strength concrete and the lower water glue make the hydration degree of CSA expansive agent lower in the early stage,and then delay its expansion efficiency to the middle and late stage.And the higher the concrete strength grade,the lower the hydration degree of CM expansive agent in the early stage.Under the condition of 20 ? water raise,mixed 12% CM expansion agent group the restricted expansion rate greater than the experimental group with 12% magnesium oxide expansive agent,and mixing the CM high strength concrete expansive agent test group limited by the rapid development of the early stage of the expansion ratio,then gradually slow down,and high strength concrete strength growth trends are similar,so mixed CM high strength concrete expansive agent limit inflation growth regularity of experimental group and strength development rule has good coordination.But CM group its compressive strength than the mixing expansive agent,magnesia expansive agent test group and the blank group has the largest compressive strength,the main reason for the amount of replacing cement expansive agent makes the compactness of concrete is reduced,and further validation by mercury injection test,expansion agent is mixed CM group have larger porosity,and the compactness of concrete is relatively low.In durability test,the incorporation of 12% expansion agent can reduce the durability of concrete,but the reduction is small,and patients with CM expansion agent corresponding water penetration height,mass loss,the loss rate of relative dynamic elastic modulus,chloride ion and chloride ion penetration depth migration coefficient than mixed magnesia expansive agent group,the main reason for the amount of replacing cement mixing expansive agent reduces the compactness of concrete structure,and by mercury injection test,the group has a higher porosity mixed CM expansion agent,its density is low.However,the higher the strength grade of concrete is,the better its compactness is,the better its water permeability,frost resistance and chloride ion resistance are,and the higher the strength grade of concrete is,the less the adverse effect of CM expansion agent on the durability of concrete is.By mixing the CM concrete expansive agent group XRD test shows that different group of ettringite(AFt)in 3 d,7 d,28 d of the peak height change are different,C40 concrete experimental basic did not change,and C70,C100 high strength concrete experimental group has higher trend,known C40 concrete CSA expansive agent in the experimental group in the first 3 d has been basically completed reaction,and C70 high strength concrete,C100 patients because of its low water-binder ratio prompted a hydration delay phenomenon,CSA expansive agent and concrete strength grade,the higher the water-binder ratio,the lower expansion lag phenomenon is more obvious.According to the MIP mercury injection test,at the same age,the higher the concrete strength grade is,the lower the internal porosity of concrete will be,the less proportion of harmful pores will be,and the denser the structure will be.And CM,the mixed expansion agent can make the concrete internal porosity increases,the main reason for the reduced cement gel that generated inside the concrete expansion agent and dosage is large,the hydration products AFt crystal growth and generated continuously in the concrete internal pore,excessive expansion form expansion stress lead to the generation of micro cracks,leading to the increase of porosity.However,the higher the concrete strength is,the faster the early strength development is,and the less adverse effect of CM expansive agent on the early pore structure of concrete is.In addition,the test group with CM expansive agent has smaller maximum pore diameter and smaller pore structure in the later period,so that the concrete has better compactness.