218 / 2022-06-10 14:49:25

Use of LC3 for Sustainable Urban Development

Marine clay; Microstructures; Durability; Sustainability

Marine clay, a low-grade kaolinitic clay widely existing in coastal areas, can be used to partially replace cement in concrete after calcination to reduce construction waste and embodied carbon in concrete. This research project investigated the sulfate resistance of mortars with 10 wt% and 20 wt% marine clay replacement ratios and varying kaolin contents. These mixes were exposed to 50 g/L Na₂SO4 solution after 28-day curing in saturated lime water. Marine clay from the construction sites was calcinated at 700 ℃ to ensure pozzolanic reactivity during hydration. Thermogravimetric analysis and X-ray diffraction were conducted to calculate the content of kaolinite and components of clay minerals in marine clay, respectively. The progressive deterioration of compressive strength and the relative length change of mortars were evaluated through compressive strength tests and length change apparatus. Results from this study could estimate the effects of marine clay on sulfate resistance and obtain an optimal cement replacement level with no significant strength reduction and length change.



The paper will also report the use of low-grade calcined clay (LCC), to produce low-carbon and lightweight strain-hardening cement composites (SHCC). The influence of LCC content (20, 40 and 60% by mass) on the hydration, microstructure, strength, ductility, shrinkage and embodied carbon of SHCC has been investigated. Pozzolanic reaction between LCC and cement hydration products has been observed, which results in significant pore refinement at 20% and 40% cement replacement. The density of SHCC containing LCC was only around 1600 kg/m3. The compressive strength, tensile strain, and tensile strength of SHCC mixtures containing 20% LCC were improved by 3.21%, 22.10%, and 32.28%, respectively. A continued increase in LCC substitution caused a decrease in the strength by the agglomeration of LCC and insufficient calcium hydroxide supply. Furthermore, a significant reduction in embodied carbon was achieved by replacing cement with LCC. Overall, this study shows that low-grade calcined clay has a high potential in producing low-carbon and lightweight SHCC.