Experimental Study On Crack Resistance Of Internally Cured Concrete In Dry Areas With Large Temperature Differences

The climate in the western region of China is dry,with a large temperature difference between day and night,and the concrete is easy to crack during the construction period under the conditions of traditional external curing.The internal curing technology provides a new way to solve the problem of shrinkage and cracking of concrete,which can improve the curing efficiency and save the project cost.However,few existing studies have considered the early crack resistance of internal curing concrete under dry and large temperature diffrence environmental conditions,lacking the theoretical basis for the application of internal curing concrete in this environment.Therefore,this paper takes the environmental conditions of dry and large temperature difference in the western region of China as the test background,and adopts a research method combining macroscopic performance test and microstructure test.The effects of three internal curing materials,namely,Super Absorbent Polymer(SAP),Light Weight Aggregate(LWA)and Perforated Cenospheres(PCs),on the compressive strength,splitting tensile strength,early autogenous shrinkage and crack resistance of concrete were investigated.SEM and XRD were also used to observe the microscopic morphology and physical phase composition of concrete,and the evolution of pore characteristics was analyzed using MIP to explore the mechanism of the action of internal curing.Suggestions on the reasonable amount of internal curing materials are given,thus providing some guidance to the actual project.The main research contents and conclusions are as follows:(1)The effects of the type and content of internal curing materials on the basic mechanical properties of concrete were studied.The test results showed that the compressive strength of all groups of concrete increased with the growth of age under the dry and large temperature difference environment;at 28d,only the compressive strength of SAP group was higher than that of the reference group,and the concrete with 0.2%admixture was the highest.The damage to concrete by dry and large temperature difference environment was more sensitive reflected by the splitting strength,and there was no significant increase in the splitting strength of concrete in each group after 14d.At 28d,the splitting strength of SAP group was higher than that of the reference group and there existed a reasonable admixture of 0.2%;the splitting strength of 10%LWA admixture was the largest and increased by 7%compared to the reference concrete;the splitting strength of PCs group were all lower than that of the reference group.(2)The effects of the type and content of internal curing materials on the early shrinkage cracking of concrete were studied.The test results show that:internal curing can effectively reduce the early self-shrinkage of concrete under dry and large temperature difference environment,and the early autogenous shrinkage decreases with the increase of three internal curing materials,among which the autogenous shrinkage of concrete mixed with 30%LWA is reduced by 166%compared with the reference group;internal curing has a significant improvement on the crack resistance of concrete,among which the concrete mixed with 10%LWA has the strongest crack resistance.(3)The microstructure and physical phase composition of internal curing concrete were studied.The test results showed that under the dry and large temperature difference environment,the ettringite and Ca(OH)2 of the internal curing concrete increased significantly and the unhydrated cement clinker decreased significantly compared with the reference group;the pore structure refinement of the concrete with 0.3%content of SAP and 10%content of LWA was the most obvious and the concrete was more uniform and dense.(4)In the dry and large temperature difference environment,it is recommended to use 0.3%of SAP or 10%of LWA for concrete application in internal curing.0.3%of SAP and 10%of LWA not only meet the basic strength design grade requirements of concrete,but also improve the crack resistance of concrete to a large extent.