Repurposing weathered Northern Ireland laterite as a supplementary cement replacement in low-carbon concrete

The UK generates ~80 million tonnes of ‘mineral waste’ annually. One of the most abundant low-value mineral wastes in Northern Ireland (NI) is weathered laterite (WL), as a by-product from basalt quarrying for the aggregate industry. Rather than sending WL to landfill , this research aims to investigate valorising WL as a low carbon SCM in Type II Portland cement (CEM-II)-based concretes . This approach is timely given the recently updated BS-8500[1], which permits the use of a wider range of SCMs for ternary binders . Furthermore, this resonates with UK Government and construction sectoral circular economy and net zero agendas. To maximise the pozzolanic activity and cementitious potential of WL, it was pre-processed involving oven drying at 110oC, crushing, pulverising (<63μm) and calcination at 700oC. The processed WL was then incorporated into a CEM-II -based concrete mixture at replacement levels of up to 50%, in accordance with BS EN 197-1 [2]. The mixtures were then subjected to compressive strength testing (fc) and ultrasonic pulse wave velocity (UPV) measurements after 7- and 28-days curing. Of the replacement mixtures considered, using 21% WL produced the highest 7-day and 28-day strengths, although these were 25% lower than strengths measured for CEM-II control mixtures. These results highlight WL’s potential as an SCM, which through design optimisation can be valorised further.