Enhancing the freeze thaw resistance of pozzolanic lime mortars by optimising the dewatering process

Abstract

Freeze–thaw weathering is commonly attributed to the premature degradation of lime mortars. This study is unique as it explores how the effect of incorporating pozzolanic brick dust, combined with the dewatering mechanism, can influence the resistance to freeze–thaw cycling. The combination of brick dust and hydrated lime constitutes a pozzolanic lime mortar with hydraulic character. Importantly, the addition of brick dust was shown to play a crucial role by modifying the pore structure of the mortar matrix, which affected the water transport kinetics, and durability. This rigorous investigation evaluates the freeze and thaw resistance of hardened young (7-day) and old (180-day) mortars in both dewatered and non-dewatered conditions. Quantitative analysis of the microstructure highlights the role of brick dust and dewatering in densifying the matrix, refining the pore structure, and enhancing the freeze and thaw resistance. The benefits of dewatered brick dust mortars were demonstrated as young-age dewatered mortars showed similar resistance to freeze and thaw compared to the older-age non-dewatered mortars. This was attributed to the reduction of the water/binder ratio due to dewatering. It has been successfully demonstrated that freshly mixed mortars can be enhanced on-site through the addition of brick dust and coupling with a substrate that promotes dewatering. Using this approach to produce mortars with greater freeze thaw resistance will improve longevity and reduce failure rates. Impact will be realised in mortars for both new build and conservation applications.