THERMODYNAMIC ANALYSIS OF DETERIORATION OF MARBLE AND CEMENT BUILDINGS FUNCTIONING AS HABITAT FOR TERRESTRIAL ALGAE

The phenomenon of secretion of organic acids, (primarily oxalic acid) from algae growing on buildings/monuments has been reported by some wo rkers. These secretions may cause rapid deterioration of building surf aces, In the present study, using thermodynamic data, the effect of aq ueous oxalic acid H2C2O4/C2O42- on the deterioration of marble and por tland cement has been estimated, Theoretically, for deterioration at n ormal pH, the equilibrium activity thresholds of H2C2O4 (ag) and C2O42 - (ag) are of the order of 10(-15)-10(-69) M. The required equilibrium activities being so low, the oxalic acid-induced deterioration of bui ldings seems to be spontaneous in natural environments. Theromodynamic calculations also show that cement buildings deteriorate faster than marble buildings, Moreover, the degree of C2O42- (ag) attack on buildi ngs increases with the fall in pH of the reacting medium.