Artificial hydraulic lime mortar obtained by calcining limestone and siliceous waste materials

• Main Author: Zawawi, Rodiah
• Other Authors: Banfill, P. F. G.
• Published: Heriot-Watt University 2010
• Subjects: 690
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.547649

This study was carried out to produce an artificial hydraulic lime for the repair and conservation of historic masonry. Hydraulic lime mortar is preferred to cement mortar and pure lime mortar for conservation work because it can set and harden in wet condition as well as allowing the old wall to breathe. These characteristics create a repaired mortar which is compatible with natural stone and ancient brickwork, as well as being a more sustainable material. The study focused on the properties of an artificial hydraulic lime mortar obtained by burning a binary mixture of limestone and siliceous waste material. Five raw meals were prepared from five siliceous waste materials obtained as by products from other industrial processes (fly ash, glass cullet powder, silica sand, crushed rock dust, and spent oil shale) with the amount of silica varying between 3 and 16 per cent. The raw meals were burned in an electric furnace at 974oC for 7 hours. The mortar was prepared by mixing hot slaked lime putty (water/lime ratio about 1.6) and ‘Gowrie’ sand at a lime/sand ratio of 1:3 by weight. The limes and lime mortar was prepared and tested according to BS EN 459-2:2001. The investigations carried out on the products are free lime analysis, strength test and microstructure examination. The results show that the most promising hydraulic lime is glass cullet lime, followed by crushed rock lime. The glass cullet lime can be classified as feebly hydraulic. The optimum combination of silica with lime in the glass cullet lime is occurred at 10% silica raw meal. The hydration of silicates in the glass cullet lime mortar of 5% silica raw meal is completed in 28 days of curing. High strength but low lime oxide depletion in the crushed rock lime mortar shows the mortar hardens due to the hydration of silicates and the chemical reaction between silica and slaked lime. The results show that the silica in fly ash, spent oil shale and silica sand requires temperatures higher than 974 degree Celsius to achieve significant reaction with lime. The results suggest that hydraulic lime of appropriate performance can be produced using traditional kiln at low cost. Keywords: artificial hydraulic lime, mortar, siliceous waste, cullet, crushed rock