Zhenguo Shi

Factorial Design Method for Designing Ternary Composite Cements to Mitigate ASR Expansion

AbstractSupplementary cementitious materials (SCMs) have been successfully employed in binary or ternary cement blends to mitigate alkali-silica reaction (ASR). The determination of composition of binary or ternary composite cement to avoid deleterious expansion of concrete is usually based on a wide range of experiments, and it is time-consuming and costly. This paper introduces a factorial design method, combined with a ternary contour diagram, to correlate the compositions of ternary composite cements with ASR expansions with only seven batches of experiments. Based on the ternary contours, a safe composition range and dangerous composition range can be obtained. Moreover, the ternary contour diagram can also be used to analyze synergetic effects between any two components in the ternary composite cements. Finally, the efficiency of the factorial design method was verified by comparing the experimental and predicted expansions, and the results correlated very well.

Durability of Portland Cement Blends Including Calcined Clay and Limestone: Interactions with Sulfate, Chloride and Carbonate Ions

The durability has been investigated for mortars made from a pure Portland cement (CEM I) and five Portland cement – SCM blends, using a cement replacement level of 35 wt% and the following SCM’s: (i) pure limestone, (ii) pure metakaolin, (iii) metakaolin and limestone (3:1 w/w), (iv) metakaolin and silica fume, and (v) metakaolin, silica fume and limestone. The blends with metakaolin and silica fume employ a fixed ratio for these components which mimics the alumina-silicate composition of a 2:1 clay (i.e., montmorillonite). All mortars were demoulded after hydration for one day and cured saturated in water at 20 °C for 90 days prior to exposure. Expansions induced by sulfate attack, chloride profiles, and carbonation depths were measured to investigate the durability performances of the mortars. Porosity and pore connectivity were analysed before exposure by mercury intrusion porosimetry. The results show that mortars incorporating metakaolin, independent of additional silica fume or limestone, all exhibit very high resistance towards sulfate attack and chloride ingress, but are vulnerable to carbonation. The binary Portland cement – limestone blend is most susceptible to all types of studied chemical attacks, as expected. The pure Portland cement exhibits poor resistance to sulfate attack and chloride ingress, but high resistance to carbonation. The observed performances for the different blends can be explained based on their microstructure and phase assemblages. For example, the presence of metakaolin increases the chloride-ion binding capacity and enhances chloride resistance by the low pore connectivity present in the hydrated blends with metakaolin.