Sustainable Zero-Portland Cement Limecrete Produced from Binary Ground Granulated Blast Furnace Slag and Natural Hydraulic Lime as an Alternative to Standardised Concrete

Concrete, a ubiquitous material in modern construction, faces several fundamental issues, including the cement industry’s 8-10% anthropogenic CO2 emissions (CO2e), that can compromise its sustainability. Therefore, this paper explores novel material combinations of lower carbon binders. Performance issues considered were: volumetric stability; durability; characteristic strengths; environmental impacts; workability; and placement. To address these issues, innovative material combinations of Natural Hydraulic Lime (NHL) and Ground Granulated Blast-furnace Slag (GGBS) are suggested as promising alternatives to traditional cements. Recent changes to BS8500 have allowed for further ternary systems that use GGBS and calcium carbonate thereby giving increased importance to both as ingredients. Combining NHL5 and GGBS can enhance the sustainability of concrete by reducing CO2e, improving resistance to chemical attacks, and maintain overall structural integrity, whilst preserving desirable workability and aesthetic qualities. This research shows the peak mass replacement range of NHL and GGBS in the binary cementitious system at conventional concrete mix ratios, building upon and filling some of the empirical and data gaps. GGBS was used because of its low CO2e, direct cementitious qualities, and to reduce industrial waste. The NHL5 content in concrete was replaced at 10% and 20% increments up to 100% GGBS in concrete to assess the physical properties and mechanical performance. Analysis of compressive and flexural strengths at varying curing ages of 7,14, 28, 91 and 180 days, were conducted for the standard mix ratios of 1:1:2, 1:1:3, 2:1(1:2) and 2:1(2:1). Two curing conditions were examined at 91 days of curing, being submerged in water and in ambient conditions. Increased mechanical performance was produced using a 1:1:3 mix ratio, with the optimum replacement values occurring between 40-60% replacement for all ratios, with the optimal replacement value at 48% and carbon intensity point at 32%, representing the peak mass replacement range and points thus providing evidence and supporting the assertions made from thermodynamic models. The highest compressive and flexural strengths achieved at 31MPa and 2.0MPa by 1:1:3, water cured 40/60, and air cured 60/40, NHL/GGBS samples respectively, being significant gains in strength when compared to either the pure NHL or GGBS binder control concrete samples.