Fresh, mechanical, and microstructural properties of lithium slag concretes

Abstract

Lithium slag (LS) is a by-product of the lithium salt purification process, and this can be used as a partial replacement of cement for the production of green concrete by reducing carbon footprint associated with clinker production. The raw-LS is rich in aluminosilicate, containing 77.2 % of SiO2+Al2O3+Fe2O3, 31.6 % of amorphous phases, and the loss of ignition is 7.8 % at 750 °C, making it a suitable pozzolan by providing 4.8 times higher ion dissolution capacity at 1 day compared to class F fly ash (FA). In this study, fresh properties, mechanical, and microstructural properties of 0–60 % cement replaced LS concretes were thoroughly determined with a total binder content of 400 kg/m3 and water-binder ratio of 0.435, and the properties were compared with the same mix proportion of FA concrete. The results show that 20–60 % LS concrete mixes produced normal density concrete within the design slump of 125 ± 25 mm and air content of 2 ± 0.5 %. At 90 days, the average compressive strength, tensile strength, and elastic modulus of 40 % LS concrete were 58.6 MPa, 4.10 MPa, and 39 GPa, respectively, which are higher compared to 40 % FA concrete of 35.5 MPa, 3.0 MPa, and 31.1 GPa, respectively, revealing that LS concrete offers better mechanical strength. However, mechanical strengths decreased significantly beyond 40 % LS incorporation. The experimentally determined 28 days mechanical strengths of 40 % LS concrete were underestimated by ACI 318 and AS 3600 standard equations. The BSE-EDS on the ITZ of fine and coarse aggregate confirmed a consistent development of amorphous and amorphous intermediate hydration products in the development of mechanical properties of LS concrete mixes.