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Calcined clay plays an important role in the performance of limestone calcined clay cement (LC3) concrete. In this study, the performance of two different types of calcined clay produced from different calcination processes were investigated in chloride environment. The characteristics of the calcined clays, including mineral composition, chemical composition, particle size distribution, specific surface area and particle morphology, were evaluated. Based on the reactivity of the calcined clays, the compressive strength of concretes after up to 28 days of curing was adopted as the best measure to determine the appropriate replacement levels of Portland cement by LC3 to satisfy standards requirements for concrete in chloride environments. The chloride bulk diffusion test was conducted to investigate the performance of LC3 concretes in comparison with reference Portland cement concrete. Similar chloride diffusion resistance could be achieved by using the two different calcined clays in LC3 concrete. The performance of both LC3 concretes was much better than that of reference concrete. However, the Portland cement substitution rate for each calcined clay was governed by the compressive strength standard requirements.

The aim of this work is to investigate the carbonation resistance of limestone and calcined clay blended cement-based concrete. Two limestone and calcined clay concretes with an average 28 d compressive strength of about 36 MPa were considered. Limestone and calcined clay (with a ratio of 2 : 1) were blended with a general purpose (GP) cement. The GP cement substitution rates considered were 30% and 45%.A low-grade calcined clay was used with about 50% amorphous phase. Accelerated and natural carbonation tests were performed. Mercury intrusion porosimetry and X-ray diffraction were carried out, to assist in the analysis of the experimental results. Results show that the early-age compressive strength is only marginally affected by the limestone and calcined clay substitution up to 45% and a significant refinement of the pore structure was observed compared to the reference GP cement concrete. The resistance of concrete against carbonation reduces with increase in the GP cement substitution rate. Overall, this study shows that a limestone and calcined clay blend used as a simple substitution for GP cement in concrete can provide adequate protection against carbonation-induced steel reinforcement corrosion if the ordinary Portland cement content in the mix is at least 60%.

Ferronickel slag (FNS) which is also known as electric arc furnace slag is a byproduct of the production of ferronickel alloy. The production of FNS at Société Le Nickel (SLN) in New Caledonia is about 2 Mt per year with an existing stockpile of 25 Mt, which presents an excellent potential for concrete applications in the Pacific region. The possibility of using FNS from SLN as fine aggregate replacement in concrete is investigated. The low-carbon-concrete mix design includes 50% natural sand replacement by FNS sand and 25% ordinary portland cement substitution by fly ash. Microstructural analysis by scanning electron microscopy—energy dispersive X-ray spectrometer (SEM-EDS) of the interface transition zone (ITZ) of FNS sand shows that the excess in Portlandite weakening the ITZ of natural aggregate is absent in FNS sand ITZ. As a result, the resistance against chemically aggressive ions diffusion, water absorption, sorptivity, bulk and surface resistivity, and volume of permeable voids are significantly improved compared with the reference concretes due to the pozzolanic effect of FNS strengthening the ITZ. The substitution of 50% natural sand by FNS sand allows offsetting the detrimental effect of using fly ash on the concrete resistance against carbonation. All results show that using FNS sand in concrete can improve the concrete performance.