Long-Term Mechanical Properties and Durability of Lime-Spongilite Mortars

This paper presents a study on partial replacement of lime binder with fine spongilite with the purpose of exploring a new application of this natural material as lime mortar additive. Standard air lime mortars were made by incorporating from 0% to 40% of spongilite powder in replacement to lime and their mechanical performances, microstructure, and durability were determined. The spongilite powder showed similar pozzolanic activity as natural zeolite or waste brick powder predicting an improvement in the mechanical properties and durability of prepared mortars. As the replacement level in lime mortars increased, the amount of mixing water needed for the same mortar consistence decreased, and the performance properties of the mortars improved. The increase in strengths of mortars was manifested mainly in the long term of 180 and 365 days. The incorporation of fine spongilite led to the formation of slightly denser, more water absorptive, however, more frost resistant and salt crystallization resistant structure in air lime mortars. The effective use of spongilite powder as a supplementary material in air lime mortars was assessed to enhance their performance in building practice or to prepare feebly hydraulic mortars used in the past in constructions nowadays considered built heritage.