DURABILITY STUDY ON COMMON BUILDING MATERIALS

Abstract

Use of stone masonry and the clay brick work in lime-mortar as building materials has a long history dating back to well before Roman times. Though the stone, brick and mortar are treated to be the durable building materials, many historical buildings and monuments made of these materials have shown signi-ficant signs of deterioration and distress due to the sharp rise in the environmental pollution in the recent past. Deterioration of building materials is the result of number of physical, chemical and biological factors in addition to the environmental conditions. Atmospheric pollutants include carbon dioxide, sulphur and nitrogen oxides, hydrogen sulphide, ammonia and particulate matter. The contaminants like salts, nitrates and carbonates are also equally responsible. These pollutants cause chemical deterioration and physical disintegration of building materials. The present study embodies the physical and chemical factors responsible for the decay of common building materials viz. marble, sand stone and lime-surkhi mortar, the materials extensively used in the construction of many monuments. The detailed investigation of the decay and durability characteristics of the above materials under different environmental gaseous pollutants have been taken up in this study. The physico-chemical studies have been carried out by immersion of specimens in the solutions of different concentra-tions of sulphuric, nitric and hydrochloric acid for different observation periods to simulate the effect of gaseous pollutants (iv) like sulphur oxides, nitrogen oxides and chlorine and chlorides respectively. In addition the sodium sulphate salt crystallisation test has also been conducted on all the materials to study resistance to freeze and thaw effect. The studies on these materials have clearly revealed the trends of decay of these material's under the respective environment considered. the durability of the materials is a physical phenomenon difficult to quahtify by any one paramter and hence physical properties like the weight loss, the water absorption and the compressive strength have all been investigated. The general trend found in all these cases is the progressive increase of weight loss, water absorption and the reduction in compressive strength with the decay of the respective material. A relation between the physical properties and the concentration of the solution and the immersion period for these three materials have been established. In Makrana marble the disintegration starts with the surface roughness proceeding towards the core with the cracks in the irregular pattern. The effect of the higher concentration of the acid solutions was drastic besides causing change in the colour of the marble which is undesirable. The disintegration of sand stone has been found to begin with the loss of cementing material both from the surface as well as along the bedding planes in the durability test. The cracks generally appear along the bedding plane, which deepen with the decay of the stone. The stone particles finally get separated (v) along the bedding planes. But, however, the sand stone stood well in all the acid environments. Initially the mortar showed somewhat different behaviour but with the prolonged exposure the decay was similar to marble but the resistance was very poor in case of durability test during which it completely disintegrated just after seven cycles only.