Natural hydraulic lime mortars for use in high temperature, high humidity climatic conditions : effect of calcitic fillers
Razali, Nadia Binti
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The widespread adoption of alternative binders are playing an increasing role in carbon dioxide (CO2) abatement in green construction and the repair of traditionally built structures. Natural Hydraulic Lime (NHL) has better environmental credentials than Portland Cement (PC) due in part to its lower calcination temperature and its ability to absorb CO2 during carbonation. However, NHL is more sensitive to climatic conditions during the setting and hardening processes and this is especially pronounced in high humidity climates. This research investigated the influence of various types of calcitic fillers (oyster shells, limestone, marble and precipitated calcium carbonate (PCC)) modifications to NHL mortars subjected to high temperature and humidity environments and evaluated the subsequent effect on early development of various chemical and physical properties. Primary mortar parameters such as moisture loss, pH, carbonation depth, flexural strength, compressive strength, sorptivity and microscopy analysis (SEM images) were studied. The results showed that the setting and hardening of those mortars with precipitated calcium carbonate worked most effectively in high humidity environments. The purity and crystallinity of the mineral ‘seeding’ materials was attributed to the positive benefits in the physical characteristics. Additionally, curing at higher temperatures greatly accelerated the hydration reaction of the mortar. It is evident from the findings that modified mortars can increase the performance especially in terms of carbonation rate, flexural strength, compressive strength and sorptivity. Whilst the precipitated calcium carbonate showed positive benefits in early stage setting reactions it did not significantly influence the long term physical characteristics of the mortars. This situation is meaningful for our understanding of modified lime mortars and the seeding materials. This research can be used to influence the specification and product design of NHL materials in high temperature and high humidity environments and this is especially important for its early stage use that has been traditionally associated with reduced set characteristics.