Study On Full-field Deformation Of Expansion Agent And Internal Curing For Shrinkage Compensation Of Cement Paste

Modern concrete,especially high performance concrete,has the characteristics of low water-binder ratio and high mineral admixture.At the same time,its deformation properties have changed.The proportion of early shrinkage of high performance concrete in total shrinkage deformation is increasing,which has become the main cause of shrinkage deformation cracks.In order to cope with this problem,shrinkage compensation methods such as internal curing and expansion agent have been developed.Although both methods have good shrinkage reduction effects,there are still some key problems to be solved,such as the transmission distance and the spatial distribution of internal curing water,the influence of expansive agent on the nonuniformity of cement paste,and so on.In this thesis,the shrinkage compensation of cement paste by internal curing is studied firstly.Through comparing the computed tomography(CT)gray data of SAP at different time,it shows that SAP has released most of the internal curing water within one day of hydration.By comparing the gray data of cement paste at different regions and different time,the transmission distance of internal curing water is analyzed.However,it is difficult for the X-CT equipment in this experiment to identify the internal curing water released into the cement paste due to the limited fluctuation of water cement ratio,bleeding effect,the noise in the original CT data and the early selfshrinkage effect.By comparing local autogenous shrinkage(LAS)at different positions and different time between the experimental group and the control group,it can be inferred that the internal curing water transports at least 35 mm within 18 hours of hydration,and the spatial distribution of the moisture content has clear gradient.Combining the water loss curve of SAP in saturated calcium hydroxide solution with LAS data,the additional water-cement ratio in each region are given.In order to completely eliminate the self-shrinkage of cement paste under this mix ratio,the watercement ratio should be increased by about 0.054.Secondly,the full-field deformation study of expansive agent for shrinkage compensation of cement paste is carried out.By comparing the deformation heterogeneity of expansive cement paste under different strain windows,it shows that the strain heterogeneity of expansive cement paste increases with the decrease of strain windows.By comparing the heterogeneity of deformation between cement pastes with and without expansive agent,it is shown that the addition of expansive agent can increase the heterogeneity of strain of cement paste.The effective expansion window of cement paste is defined based on the heterogeneity of strain.It is found that the effective expansion window of cement paste with water cement ratio of 0.3 and expansive agent content of 10% is less than 0.36 mm.