Hydration Performance And Microstructural Stability Of Complex Cementitious Materials

Concrete batching using cementitious materials containing mineral admixture can not only comprehensively use solid industrial residues, but can also improve the performance of concrete. The stability and durability of complex cementitious materials containing mineral admixture have caught the attention of academic and engineer circles continuously. The hydration performance and microstructural stability of complex cementitious materials containing different rate of fly ash were investigated in this paper. The main content and results are listed as follows:(1) The incorporation of fly ash decreases the total hydration degree of the complex cementitious materials. The higher the content of fly ash is, the lower the reaction degree of itself is, on the contary, the higher the hydration degree of cement is. Curing at high temperature plays a significant role in the advancement of the total hydration degree in the early stage of the complex cementitious materials, and also increases the reaction degree of fly ash, but thwarts the further enhancement of total hydration degree in the later stage. Using the content of non-evaporable water to compare the relative hydration degree of cement in complex cementitious materials is feasible. Compared with the method based on the content of non-evaporable water, the method based on the content of Ca(OH)₂ can characterize the hydration degree of cement in complex cementitious materials more accurately and intuitively.(2) Adding fly ash means decline of cement content in complex cementitious materials, which leads to the decrease of Ca(OH)₂ content in hardened pastes. In the meanwhile, the alkalinity of pore solution in hardened pastes of complex cementitious declines slowly with hydration ages and reaches stability (above 12) at the age of 360 days. By replacing part of cement with fly ash, the early microstructure of hardened pastes of complex cementitious materials becomes loosened. As the hydration age increases, the microstructure of hardened pastes of the specimens with a appropriate fly ash content (35%) is improved substantially, and the parameters of pore structure are almost consistent with those of plain cement pastes at the age of 360 days. The early microstructure of hardened pastes of complex cementitious materials is improved significantly when they are cured at high temperature. (3) After leaching of soft water, the mass of complex cementitious materials reduces and its microstructure deteriorates in part. At the leaching duration of 180 days, hardened pastes with fly ash deteriorate a little more serious than plain cement pastes, but the incorporation of fly ash in proper ratios (20%) is helpful to hinder the deterioration trend of the hardened pastes'microstructure. After each leaching duration, the Ca(OH)₂ crystal exists in the hardened pastes of complex cementitious materials and the C-S-H gel doesn't decompose seriously. The microstructural stability of hardened pastes of complex cementitious materials isn't damaged severely during the 180 days'leaching duration.(4) When the fly ash content is below 65%, the hardened pastes of complex cementitious materials contain essential Ca(OH)₂ for microstructure stability. A moderate reduction of Ca(OH)₂ content has no effect on the stability of the hydration product and the microstructure of paste. Fly ash content, water to binder ratio, curing age, curing temperature and service environment are the major factors influencing the stability of the microstructure of hydration product and paste.