Jueshi Qian

Characterization and calorimetric study of early-age hydration behaviors of synthetic ye’elimite doped with the impurities in phosphogypsum

AbstractnTo better understand the influence of the impurities in phosphogypsum (PG) on the early-age hydration of calcium sulfoaluminate (CSA) cement manufactured with PG, the study prepared synthetic ye’elimite doped with fluorine (F) and phosphorus (P) and also synthesized ye’elimite with natural gypsum (NG) and PG. The acquired ye’elimite was characterized, and its early-age hydration within 24xa0h was investigated. Results demonstrate that F contributes to the crystallization and leads to the formation of large crystal synthetic ye’elimite. P and the simultaneous presence of F and P could stabilize C4A3

A novel evidence for the formation of semi-permeable membrane surrounding the Portland cement particles during the induction period

-c. Without the presence of gypsum, pure ye’elimite is much more active than synthetic ye’elimite doped with F and P, and synthetic ye’elimite prepared with NG is much more active than that prepared with PG. Although the presence of gypsum significantly boosts the hydration activity of synthetic ye’elimite doped with F and P and pared with PG, their hydration activity is still slightly lower. It is suggested that manufacture of alite-calcium sulfoaluminate cement and binary blends of CSA cement and Portland cement is an available way to boost the early-age hydration CSA cement manufactured with PG.

Surface treatment of cement-based materials with NanoSiO2

This letter presents strong novel evidence for the semi-permeable membrane surrounding Portland cement during the induction period. In the cement hydration, heat curve obtained through high-resolution differential scanning calorimetry under isothermal conditions, one main and some other smaller endothermic peaks were detected. These endothermic peaks are believed to be caused by the osmotic expansion that occurs after the semi-permeable membrane forms, not the precipitation of calcium hydroxide or the imbibition of water during the induction period.

Modification effects of colloidal nanoSiO2 on cement hydration and its gel property

A dense surface structure of cement-based material is favorable for its resistance to the impacts of environment. In this work, effectiveness and mechanisms of the surface treatment of cement-based materials with nanoSiO2 of different states, that is, colloidal nanoSiO2 (CNS) and the in situ formed nanoSiO2 gel through the hydrolysis of its precursor of tetraethoxysilane (TEOS), by brushing and soaking techniques, were investigated. Results showed that both CNS and TEOS are capable of reducing the liquid and gaseous transport properties of hardened cement-based materials, although at a different extent. It revealed that the pozzolanic reactivity and the filler effect of nanoSiO2 are the main causes for the refining of the threshold size and the reduction of volume of the capillary pores, and they finally lead to a linearly reduction of the transport property. From this study, it can be reflected that surface treatment of cement-based materials with nanoSiO2 would be an optimal alternative of making concrete structure more durable.