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.

Pore Structure as a Determinant of Flexibility in Sustainable Lime-Cement Mortar Composites

“…Details of the microstructural characteristics evaluation (in respect of the total porosity, median pore diameter, bulk density and pore size distribution, using Mercury Intrusion Porosimetry (MIP) technique via AutoPore IV 9500 by Micrometrics (with pressure range up to 60000 psi)), mechanical properties assessment (using ELE AutoTest 2000 apparatus and INSTRON 3367) and some other relevant preliminary material testing (involving 'Carl Zeiss EVO 50' Scanning Electron Microscope and Laser Difractometry Xmastersize) are as documented in the previous studies [4], [28] and [38].…”

“…As shown in Table III, using the adopted B/A ratio (i.e., 1:3), mortars were prepared with increasing/decreasing cement contents. Mixing was done in the laboratory mixer of 30 litres maximum capacity as explained in previous studies [4], [28] and [38]. Three prismatic specimens of 40×40×160 mm was prepared for each mortar mix.…”