Abstract
The use of lime mortar to bind historic masonries exists over centuries. Traditionally natural additives are used in the manufacture of lime mortar to enhance mechanical and durability properties. In this research, the performance of natural hydraulic lime 3.5 (NHL 3.5) mortar was enhanced using neem gum as an additive added in different dosages of 0.1%, 0.2%, and 0.3% by weight of water. The modified NHL 3.5 mortar samples were subjected to fresh-state, mechanical, physical, and durability properties. The impact of organic inclusion in the hydraulic lime matrix on their mechanical and physical characteristics has been investigated. The results showed that organics in the lime matrix significantly increased the hydraulic lime's mechanical characteristics due to the organic's adhesive nature that solidifies on drying, which also bonded sand and lime particles together. Even though the organic inclusion increased the open total porosity, the strength and durability of lime mortar were enhanced because more micropores were in the range of 0.1-1.0 mu m, filling the gap between two consecutive lime particles in the mortar. Organic loading reduced the water absorption since the surfaces of the pores are coated with a layer of hydrophobic non-polar molecules of the admixture. The capillary rise is very much reduced with the addition of a hydrophobic admixture. The reduced capillary rise is due to the smaller pores in the modified NHL3.5 mortars due to the active conversion of 15% of macropores into micropores. That inhibited the capillary intake of water /salt solution. Analytical studies such as X-ray diffraction, TGA, and FTIR analysis have confirmed the new element formation in the organically modified NHL3.5 mortar due to the interaction of carbohydrates and fats with lime particles.