Low carbon sustainable building material: Maximizing slag potentials for improved lime mortar mechanical properties

Abstract

Prior to the 19th century discovery of Portland Cement (PC), Lime Based Mortar remained popular due to its flexibility, permeability and more importantly, associated low carbon emissions. However, lime’s characteristic delayed setting/hardening time, low mechanical strength, poor internal cohesion and some volumetric changes have overshadowed significance of its outstanding features particularly, flexibility, and consequently put its overall use into decline. This study therefore aims at integrating an industrial by-product, Ground Granulated Blast Furnace Slag (slag) with lime, in form of lime-slag mortar, with a view to addressing lime shortcomings for improved performance. The methodology involved mortars with the same Binder/Aggregate (B/A) mix ratio (1:3) using five separate volumetric compositions of ‘lime-slag’ binders (i.e. 1:1, 1:2, 1:3, 2:1 and 3:1). Physical properties of the mortars involving their Water/Binder (W/B) ratios, Air Contents and Bulk Densities were recorded. Comparative evaluations of the compositions in hardened state, involving mechanical characteristics, were carried out at specific intervals through a twelve-month curing period. These were partly monitored through assessments of the composites’ microstructural behaviours over a six-month period. Results of the investigation show that addition of slag to mortars facilitate slightly larger pores with increased porosity. These effects are however minimal (i.e. from 23.42% to 25.37% porosity) when slag content is at equal volumetric content with lime. Also, at this same volumetric composition, the results show beneficial effects of slag on the composite’s mechanical properties; while the flexural strength is increased by 50%, the compressive strength is improved by about 250%. Despite the improved mechanical characteristics, the composite exhibits comparable (with lime only) capacity for deformation absorptions, thus, preserving lime’s known fundamental flexibility property. This is important for material’s durability, and overall sustainable constructions.