Mechanism of attapulgite processed by calcination and grinding on hydration process and mechanical properties of cementitious materials

In this paper, the effects of attapulgite processed by two different methods, burning and grinding attapulgite (BGA) and grinding and burning attapulgite (GBA), on the macroscopic mechanical properties and microscopic hydration mechanism of cement paste were systematically studied. The application potential of these two materials in the field of cement-based materials was analyzed and evaluated. The results indicated that both BGA and GBA inhibited the hydration of cement to varying degrees at 7th day of age. Due to the competitive adsorption of water by the nanorod crystal structure of BGA and GBA, the amount of water used for cement hydration decreased, thus reducing the hydration degree of cement. The decrease of hydration product content increased the porosity and leaded to the decrease of mechanical strength. At the age of 28th days, due to the slow-release effect of the nanorod crystal structure and the pozzolanic effect, the macroscopic mechanical strength of the admixture ratio except for 20 % BGA all exceeded that of control paste. The mass generation of hydration products of the paste formed a dense micro structure and thus reduced the porosity. The structure and morphology of Calcium silicate hydrate (CSH) formed by BGA and GBA were distinctive by SEM-EDS at 28th days, because Ca/Si in CSH decreased to different degrees. In general, the performance of GBA on cement hydration kinetics and macroscopic mechanical strength was better than that of BGA at 7th and 28th day, and 20 % GBA was the optimal ratio of all mixture ratios.