Effect of calcium-silicate-hydrate (C-S-H) nano-crystals on the hydration rate and early strength of microwave-absorbing cement mortar containing magnetite (Fe3O4) powder

Abstract

Fe3O4 powder (powdered magnetite) is a favorable absorbing material, which can effectively improve the microwave absorption and heating properties of the prepared cement mortar in engineering applications. However, its addition may have a certain degree of deterioration effect on the engineering performance of cement mortar. To reduce this effect, the calcium-silicate-hydrate nano-crystals (CSHN) were added to the mortar. The early hydration rate of Fe3O4 cement mortar (FC) was studied. Moreover, the early mechanical properties, physical and chemical properties, and pore structures of FC were investigated to characterize the effect of CSHN on the early strength evolution characteristics of FC from macroscopic and microscopic scales. In addition, the microwave heating efficiency and heat transfer ability of the FC were determined. The results showed that the CSHN could effectively increase the early hydration rate of the cement matrix to produce more hydration products, which could effectively improve the mechanical strength of FC. Within 1d, the compressive and flexural strength of FC could be improved by 99.4% and 101.4%, respectively. Meanwhile, the CSHN had a refining effect on the pore structures of FC, and it reduced the porosity of FC by 3.4% after curing for 7d. Due to the improvement of the pore structure properties of FC, its microwave absorption ability and heat transfer rate were increased, improving its microwave heating ability, correspondingly. Therefore, the CSHN was a favorable material, which could improve the early engineering performance and microwave heating ability of FC to some extent.