Chemical weathering of marbles has greatly increased during the past decades. The gaseous pollutants generated mainly by combustion of automobile, domestic, and industrial fuels have contributed significantly towards this increase. The weathering affects marble gradationally from outside inwards, producing three distinct zones. The success of a technique developed to provide cohesion to reduced and dislodged calcite crystals in the zone of weathering, by impregnation with resins which even permeate the inter-crystalline boundaries in the non-weathered region, is tested. As these weathered layers are quite thin and easily destructible, direct measurement of compressive strength is impossible. This property is, therefore, determined indirectly via Shore scleroscope hardness and specific gravity.
The impregnation increased the strength of the weathered zone up to 59% and of the unweathered region up to 24%. Corresponding values for permeability and capillarity, relative to untreated specimens, change inversely to strength changes as the pores receive relatively larger amounts of resin in the outer weathered region than in the unweathered region in depth. This phenomenon is substantiated by scanning electron microscopy (S.E.M.).
~TRODUCTION
The decay of natural stone due to the geologic process of weathering has been known for centuries. In relatively recent times WinNer, 1970; among others) methods have been developed to determine the rate of weathering and the characteristics of the weathered products. As the weathering degenerates the natural stone, many preservative treatments have been employed to arrest the continued weathering . developed a new technique for the preservation of stone statuary. His technique permitted impregnation of several centimeters depth into the stone; further, the density of the impregnant gradually decreased so that the pores in depth were only partially sealed to permit later breathing of the marble.