Impact of low-grade limestone on mechanical and durability performance of binary blended cementitious systems

Limestone is used in many countries as an ingredient in Portland Limestone Cement (PLC). However, globally, codes suggest using cement-grade limestone as a partial cement replacement in PLC, which leads to a decrease in availability due to higher cement demand. Therefore, this work focused on the use of rejected low-grade limestone with different types of impurities (magnesium, silica, or clay) present in the limestone, making it unsuitable for cement production. The partial replacement of OPC was done with three types of low-grade limestone, and one cement grade limestone, in 5 %, 15 %, 35 % and 50 % proportions. The study showed that dolomitic and siliceous limestone show similar superplasticiser (SP) demand, while cement grade limestone required marginally more, and clayey limestone required a very high SP dosage. The mechanical performance of concrete with 5 % and 15 % replacement (across all) limestone was comparable to that of OPC concrete. With 35 % replacement, the strength was reduced due to dilution, and with 50 % replacement, the strength reduced drastically. Similar performance was seen with surface resistivity of concrete for up to 15 % replacement, and all the types of limestone performed comparably. The resistance to chloride ingress up to 15 % replacement showed that there is only a marginal increase in chloride migration coefficient compared to OPC, but with 35 % and 50 %, the chloride resistance was considerably compromised. Similar performance was seen with carbonation resistance. The capillary rise in the concrete, as per Water Sorptivity Index and water accessible porosity, also showed that up to 15 % replacement, irrespective of the type of limestone used, the performance was similar to OPC. Overall, it was concluded that low-grade limestone with impurities having high magnesium, silica, or clay content performed similarly to cement-grade limestone, and up to 15 % replacement, performed similarly to OPC concrete. • Three Low-grade and one cement-grade limestone were used as partial cement replacements (5–50 %). • Low-grade limestones containing higher magnesium, silica, or clay impurities can produce durable concrete. • 35 % replacement with low-grade limestone is suitable for low-strength structural concrete in mild environment. • A durability-index matrix classifies low-grade limestone concrete performance using multiple durability indicators. • Use of low-grade limestone improves resource efficiency and extends the service life of limestone mines.