Expansion Efficiency Of The Multi-expansion Sources Expansive Agent In High-strength Concrete

In this paper,two kinds of expansive agents,CA and MgO,are mixed in different proportions to obtain the multi-expansion sources expansive agent.On the basis of single expansion test of each expansive agent,the expansion property of the multi-expansion sources expansive agent in composite cementitious system and deformation and mechanical properties of high strength concrete mixed with this expansive agent are studied in consideration of the influence factors such as the dosage of expansive agent,the activity of the expansive agent of MgO and the temperature.And the hydration expansion mechanism of the multi-expansion sources expansive agent in the composite cementitious systems was studied by tests of chemical combined water,MIP,SEM and XRD.The results showed that:With the increase of the content,the expansion velocity of the CA expansive agent increases and the expansive stabilization period is shorter,while the expansion velocity of MgO expansion agent is not affected by the dosage,and the expansion of the CA expansive agent is far greater than the MgO expansive agent under the same dosage.In the case of admixture,the expansion velocity of the multi-expansion sources expansive agent slows down with the decrease of the content of CA expansive agent,the increase of the amount of MgO expansive agent.In addition,the expansion of the multi-expansion sources expansive agent obtained by a reasonable proportion is close to or even larger than the theoretical value.Under 20?temperature curing,the compressive and flexural strength of the test groups mixed with expansive agent is less than that of the blank group.The effect of CA expansive agent on strength is greater than that of MgO expansive agent,and when the temperature is rised to 40?,the flexural strength can be improved.It is well coordinated with the development of the rubber sand specimen mixed with CA:MgO=1:2 with multi-expansion sources expansive agent.Under the condition of sealing,the free deformation of the concrete with multi-expansion sources expansive agent is three stages,"expansion,shrinkage and reexpansion".And the specimen is in a expansive state all along.Under the dry condition,it successively experiences the four stages of"shrinkage,expansion,reshrinkage and reexpansion".And the specimen is in a shrinking state all along.Besides,the CA expansive agent will appear delayed expansion.The hydration of expansive agents can be promoted by increasing the curing temperature.Compared with MgO expansive agent,the effect of CA expansion agent is more obvious by the influence of temperature change.But in the case of single mixing,the high curing temperature?60??will cause the decomposition of AFt and the falling of expansion,while the multi-expansion sources expansive agent has no expansion falling which shows that the multi-expansion sources expansive agent has better temperature adaptability and is more suitable for the large volume and high strength concrete.From the microscopic tests,it can be seen that both crystalline AFt and Mg?OH?₂ are basically grown in the pores,and the change of curing temperature will cause the change of the microtopography of AFt and Mg?OH?₂.Under the curing at 20?,the porosity of the composite slurry will be increased by the introduction of the multi-expansion sources expansive agent.Under the curing at 60?,the multi-expansion sources expansive agent?CA:MgO=1:2 compound?can reduce the porosity of the composite slurry and increase the number of harmless pores,which in turn improves the pore structure of the cementitious system.