Modification of the MCM-41 mesoporous silica and its influence on the hydration and properties of a cement matrix

Recently, there has been a growing interest in materials that make it possible to reduce cement consumption in the concrete technology while improving the parameters of a final product. In this paper the validity of using, as an admixture to cement, the mesoporous silica of the MCM-41 structure type (MCM-41), modified with funcosil (hydrophobizing agent), triethanolamine, iron nitrate, and gluconic acid, has been analyzed. The effectiveness of the modification was evaluated on the basis of chemical and phase composition analysis, while the effect of admixtures on the cement matrix (CM) properties was additionally evaluated on the basis of selected physico-mechanical parameters and a hydration heat analysis. The results showed the quantitative effect of the modifications on the MCM-41 and CM composition. All the admixtures affected the rate and total amount of heat released during the hydration process. The presence of the triethanolamine and gluconid acid significantly delayed the main peak of the hydration process while the presence of the iron nitrate and gluconid acid decreased the total amount of heat released. Regardless of the maturation time, an increase in the CM compressive strength with the modified MCM-41 and a decrease in the percentage water loss during drying were observed. Only the gluconic acid modification caused a deterioration in the strength parameters. In conclusion, the use of the MCM-41 and its modifications in the production process of cement composites can positively affect the properties of the final product.