Use of particle packing methods for development of lime fly ash-based mortars for repair of heritage structures

Abstract

Lime is a sustainable alternative to cement as it requires less energy for production and it absorbs CO2 in the atmosphere for strength gain through carbonation. Non-hydraulic lime-based mortars have low strength and this can be enhanced using pozzolanic additions. However, densifying sand using particle packing theories in mortars for strength enhancement is one of the sustainable methods which is the main aspect of present study. In the current study, physico-chemical characteristics of two non-hydraulic lime binders Type-I and Type-II lime fly ash binders were prepared by replacing lime with fly ash from 0 to 30%. In addition, 5% gypsum was added to the binder mix for obtaining quicker setting. Two particle packing theories Modified Toufar Model (MTM) & J.D Dewar Model (JDD) and Indian Standard Codes (IS:650-2000 and IS: 383-2016) were considered for attaining different gradations of sand. Mix proportion 1:3 (Binder: Sand) lime-fly ash-based mortars were investigated for the flowability and compressive strength properties. The lowest minimum void ratio of 0.574 was attained for MTM proportioned sand. Compressive strengths of Type-I and Type-II lime fly ash-based mortars were highest for MTM particle packing sand with strengths 2.320 MPa and 0.738 MPa respectively after 28 days of curing. The compressive strengths were attained at 25% and 20% replacement levels of Type-I and Type-II limes with fly ash. The average flow values for Type-I and Type-II Lime fly ash-based mortars were obtained as 7.1 cm and 10.4 cm for MTM particle packing sand. From the study, it can be concluded that using Type-I lime fly ash-based mortar and MTM particle packing theory, repair mortars with reasonably good strength can be achieved.