Influence Of Ettringite Decomposition And Reconstruction On The Volume Change Of Mortar

Delayed formation of ettringite is a potential deterioration of steam curing concrete,especially for mass concrete and pile concrete.Based on the production process of pile concrete,it can be divided into autoclave process and non autoclave process.However,even the maintenance temperature of non autoclave process is above 70?,reaching the decomposition temperature of ettringite.In this paper,the decomposition and reconstruction of ettringite under different environmental conditions are studied,and the influence of ettringite reconstruction process on the change of mortar volume is discussed.In this paper,pi42.5 cement is used as the main raw material to make mortar test block.Through XRD and DSC test and analysis,it is clear that under the premise of 100? steam curing and 70? steam curing and 1MPa steam pressure,the crystallization characteristics of secondary ettringite under two different curing conditions of fresh water and sea water with different proportion of mineral powder and ground quartz sand are different.Combined with the deformation measurement of mortar sample by laser rangefinder,the multi factor coupling condition is clear The relationship between ettringite reconstruction and concrete volume change is established.The results show that there is no ettringite in the mortar samples after steam curing at100 ? and 70 ? at 1MPa,and the ettringite reconstruction phenomenon appears in the mortar samples after 28 days in fresh water or sea water.In contrast,no obvious ettringite diffraction peak was found in the XRD patterns of pure cement mortar samples after 28 days of fresh water curing or sea water curing,but the endothermic peak appeared in the TG-DSC curve of the samples after 28 days of sea water curing at 60? ? 80?,which proved that ettringite reconstructed after 28 days of sea water curing,but the reconstructed crystal was incomplete and less.During the curing process of mortar specimens,the volume expansion of seawater curing for 28 days is slightly larger than that of fresh water curing,and the expansion of specimens with more mineral powder is slightly larger than that of pure cement specimens.The experimental results show that the presence of mineral powder makes the reconstruction of ettringite easier,and the seawater environment can accelerate the reconstruction of ettringite.