Effect of the Calcium-Silicon Ratio on the Properties of Composite Cementing Materials

Cement is the most commonly used inorganic cementing material in construction engineering owing to its stable performance; however, cement production requires a considerable amount of energy. To reduce energy consumption, inorganic cementing materials were prepared by solid waste to replace parts of the cement. In this experiment, composite cementing material was prepared by mixing ultrafine fly ash, lime and gypsum; then, this material was hydrated at a calcium-to-silicon (C/S) ratio of 0.6-2.2. The effects of various C/S ratios on the properties of the prepared composite cementing material were investigated. The results showed that when the C/S ratio was 1.6, the compressive and flexural strengths of the composite cementing material reached their maximum. With the increase of C/S ratio, the production of C–S–H gel and ettringite increased; the two products got interwoven, filling the pores of hydration products and increasing the strength of the cementing material. When the C/S ratio was 2.0, the carbonization rate of the cementing materials increased. Calcite coated the surface of the fly ash, preventing the pozzolanic reaction of the fly ash and reducing the overall strength of the material.