Experimental Research And Numerical Simulation On Early Age Shrinkage Of Cement-based Materials

The main issue studied in this paper is the early-age shrinkage of cement-based materials. Including the influence of mineral admixtures, superplastizers and progression agent on the early-age shrinkage of cement-based materials were studied. And the same time, the quantitative relationship between early shrinkage and Pore size distribution was also studied. A preliminary numerical simulation exploration of early shrinkage of concrete was carried on, looking for a bridge between the practical engineering and numerical simulation.All the experiment is measured by self-made equipment and CABR-NES deformation instrument developed by China Academy of Building Research Institute. The influences of mineral admixtures, superplastizers and progression agent on the early-age shrinkage of cement-based materials were studied, respectively. What’s more, further research about influence of superplastizer on early age drying shrinkage of cement paste with the same consistency was investigated. And the quantitative relationship between early shrinkage and Pore size distribution was and relative evaporation ratio also got. The results indicate fly ash reducing the early shrinkage of ordinary concrete, and the shrinkage decreases with the increasing of replacement ratio, but the effect is not so significant when the replacement ratio is above20%. Slag also reduces the early shrinkage of ordinary concrete, and the shrinkage decreases with the increasing of replacement ratio, but the effect is not so significant when the replacement ratio is below20%. Mixture with a combination of both fly ash and slag has lower shrinkage than mixture with fly ash. The use of progression agent could improve the workability of cement paste and cohesion. And it can prevent segregation of concrete and reduce the amount of cement in per cubic, and reduce the cost of concrete ultimately. But shrinkage tests showed The use of progression agent accelerate the shrinkage rate of concrete10hours after the initial setting, which may resulting in a larger shrinkage of concrete add with progression agent than the control mix. Results showed the addition of SP increased the early drying shrinkage greatly. The ratios of water evaporation and the total free water in mixtures added with SPs showed great differences. SPs fined the capillary pores of paste, and the pore volume of pore diameter within50nm was well consistent with shrinkage rate. The addition of SPs did not raise the capillary liquid surface tension. Results showed that the working together of pore volume of pore diameter within50nm and the ratio of water evaporation and the total free water could predict a tolerable shrinkage result of paste added with SP, and the elastic modulus could have an influence on the early shrinkage. These have never been proposed before. In order to do further research, the relationship of relative evaporation and early-age shrinkage of cement paste under different wind conditions were studied in this paper. The experiments show that cement-based material experience obvious expansion. In order to do further researches on the mechanism of the expansion, we designed some ordinary concrete mixtures and paste mixtures to do much more experiments, temperature probes were also used to make temperature compensation. From these experiments above, we exclude the influence of aggregate, the changes of cement composition, the addition of superplastizer (SP), the movement of aggregates and temperature changes from the source of the expansion. On the other hand, the content of free water and the particle size distribution of aggregate are related to the expansion. At last, a reliable method for simulating the early-age shrinkage of actual project by numerical simulation is studied preliminarily.In the end of the paper, some ideas based on the previous results were put forward. The quantitative relationship between early shrinkage of concrete and relative evaporation is also be studied. The numerical simulation and the practical engineering could be linked by the moisture diffusion surface factor. Through the humidity probe buried inside concrete specimens to get the humidity changes inside concrete, so we can study the quantitative relationship between humidity and shrinkage of concrete. And the humidity inside the concrete results of numerical simulation results can be compared with the actual experimental values, allowing for the numerical simulation results be corrected and improved.