Quantitative experimental study on time-varying characteristics of bleeding of cement-based grouting materials

Cement-based cementitious materials are the most common grouting materials for grouting engineering. This type of material has obvious water separation effect, and obtaining the quantitative formula of water separation thickness will be helpful to improve the calculation accuracy of slurry diffusion radius. By observing the water separation process of three admixtures, namely pyrophyllite powder (0%-35%), polyvinyl alcohol (0%-8%) and fly ash (0%-90%) in cement-based slurry, the water separating rate, stone formation rate, final water separation time and water separation thickness of the three admixtures were obtained. It is found that the water separation thickness of the slurry varies regularly with time to some extent, which is called the time-varying characteristic of water separation. In order to quantify the time-varying characteristic of water separation, the Pearl growth curve model and the power function model were introduced. The results show that all the three admixtures can reduce the water separation rate. Specifically, pyrophyllite powder has the greatest influence on the water separation rate of cement-based grouting materials, followed by fly ash, and finally polyvinyl alcohol. Meanwhile, all three admixtures can increase the stone formation rates. Besides, pyrophyllite powder can effectively shorten the final water separation time of the slurry, and the polyvinyl alcohol at a dosage of 1.5%-8.0%, as well as the fly ash at a dosage of 10%-60%, can shorten the final water separation time of slurry. Moreover, the change curves of the dosage of three admixtures are present in a “half-C” shape. Further, the data on water separation thickness were fitted and analyzed with the mathematical model. According to the goodness of fit R², the power function model is better than the Pearl growth curve model, and the change law of water separation thickness is more consistent with the power function model. Generally, the research results can provide important basic data for improving the grouting materials and perfecting the migration and diffusion theory of unsteady slurry.