An Experimental Study On Physical And Mechanical Properties And Mass Transport Characteristic Of Self-compacting Concrete With Internal Curing

Internal curing can reduce the autogenous shrinkage of concrete,and increase the hydration degree of the cementitious materials in concrete.The internally cured concrete made with pre-wetted lightweight aggregates?LWAs?has a risk of segregation due to floating of LWAs in the process of vibration.Such risk can be reduced by applying the internal curing in self-compacting concrete,as it can avoid the vibration or rodding process.In this study,the internally cured self-compacting concrete with fine lightweight aggregates?F-LWAs?or coarse lightweight aggregates?C-LWAs?was prepared with the replacement level of 20% and 40% by volume of normal weight aggregates.The effect of internal curing on the properties of selfcompacting concrete was examined and compared between using fine and coarse LWAs.The effect of internal curing in concrete and mortar was also compared.The main work and conclusions are as follows:?1?The effect of internal curing using fine and coarse LWAs on the workability of selfcompacting concrete was examined.The flowability of concrete was largely reduced due the introduction of pre-wetted F-LWAs.The flowability of internally cured concrete using F-LWAs cannot meet the requirement for self-compacting concrete under the replacement level of 40%.The introduction of pre-wetted C-LWAs also reduced the flowabiltiy of concrete,with less effectiveness compared with F-LWAs.Both of these two types of LWAs increased the viscosity of concrete.The floating of LWAs in internally cured concretes did not occur in an improved static segregation resistance test.?2?The effectiveness of internal curing using F-LWAs and C-LWAs was evaluated in terms of the compressive strength,autogenous shrinkage,and transport properties.Results indicate that pre-wetted F-LWAs have a higher efficiency in reducing autogenous shrinkage of concrete than C-LWAs do.The internally cured concretes also showed lower compressive strengths when compared with concrete without internal curing.The compressive strength of the concrete internally cured using C-LWAs under the replacement level of 40% was approximately 13% lower than that of concrete without internal curing,and was the lowest one among all the mixtures.Internal curing using F-LWAs did not decrease the water sorptivity of concrete but improved the chloride resistance ability significantly.However,the concrete internally cured using C-LWAs showed higher rates of water absorption and chloride migration.All the mixtures with internal curing have lower water desorption rates than the concrete without internal curing.it is likely caused by the ink-bottle effect.?3?Scanning electric microscope imaging was conducted on F-LWAs and C-LWAs,along with their interfacial transition zones in concrete.It was found that there were less unconnected pores and a rougher surface in F-LWAs than in C-LWAs.Furthermore,the interfacial transition zones of F-LWAs was observed to be much denser than the one of C-LWAs.It was also found that the degree of hydration of fly ash around pre-wetted LWAs was higher than the one far away from pre-wetted LWAs.This could be due to the gathering of Ca?OH?₂,which could lead to the volcanic reaction with fly ash.?4?The distributions of internal curing water in mortar and concrete were simulated based on the hard core/soft shell model.The simulation results were used to be compared with experimental results.The comparison showed that there was a larger internal cured cement paste volume in mortar than in concrete due to the blocking effect of coarse normal aggregates on internal curing water transport.This may imply that the increase of coarse normal aggregates volume fraction would lead to the decrease of internally cured cement paste volume.