Study On The Effect Of Shrinkage-Reducing Agents On The Properties Of Cement-Based Materials

Yearly, more and more engineering problems are caused by the shrinkage of concrete. If unable to find effective solutions, the shrinkage has a severe impact on the performance and durability of the concrete structure. Therefore, many scholars have studied the shrinkage of concrete and put forward many useful methods, for example, optimizing the mixture ratio of concrete, strengthening the curing and applying fiber; in addition, one of the measures to reduce the early shrinkage of concrete is to mix shrinkage-reducing agents(SRA) in concrete in essence, but this measure has some shortcoming. Therefore, this paper studies the effect of shrinkage-reducing agents on the properties of cement-based material, especially the relationship between the shrinkage and the mass loss in detail. At the same time, the wind speed can increase the early shrinkage of concrete, so the thesis also studied the effect of SRA on the early shrinkage of concrete under the different wind speed, to provide more experimental data and theoretical support in use of the SRA in the practical engineering. The main conclusions of this thesis are as follows:(1) The critical micelle concentration of the SRA solutions was approximately4.10%; when the critical micelle concentration of the water reducing agent is1.29%, the changing rule of the surface tension of the solution with the increasing concentration of SRA is similar to the rule of only single mixing of SRA. Under the same conditions, the evaporation capacity of shrinkage-reducing agent solution is minimum, and the evaporation capacity of mixing shrinkage-reducing agent and water reducing agent is the largest. Under the different wind speed, the evaporation of solution with time is almost linear relationship, its evaporation rate is constant.(2) Under the same w/c ratio, the drying shrinkage of the mortar correspondingly decreased with the increasing dosage of SRA, the approximate exponential relationship between the drying shrinkage and mass loss of mortar is found. Under the same w/c ratio and the normal consistency, the dry shrinkage rate of mortar with shrinkage-reducing agents is minimum, the dry shrinkage rate of the baseline group is bigger, the dry shrinkage rate of mortar with SRA and water reducing agent is largest; under the normal consistency, the approximate linear relationship between the drying shrinkage rate and mass loss of mortar is found.(3)Whether the baseline concrete, the concrete with single water reducing agent, or, the concrete with water reducing agent and SRA, the greater the wind speed, the greater the early shrinkage of concrete; under the same wind speed, when the mass rate of concrete is same, the shrinkage rate of the concrete mixed with SRA and water-reducing agents is in between that of the concrete mixed with water-reducing agents and that of the benchmark concrete, which is an emergent property resulting from interactions among the surface tension of the concrete pore solution, the change of relative humidity caused by water evaporation, the delayed heat and the distribution of the concrete pore structure. Starting from the initial setting to120hours after the initial setting, the relationship between the early shrinkage of concrete and mass loss rate firstly presents the quadratic parabola and then presents approximate exponential relationship.