Experimental tests on vapor and gas permeability of concrete boxes

The use of reinforced concrete (r.c.) in industrial plants presents new challenge in the design of gas containments. The r.c. has advantages in terms of costs, shape optimization and monolithicity, although its permeability to gas and vapor is a critical issue. The concrete has well-known performances for water containment (as dams or reservoir) but not for the vapor tightness, due to the natural porosity and physiological cracking due to shrinkage and low traction strength. Special additives can mitigate the problem of the natural cracking that is physiologic for non-prestressed concrete; nevertheless, coatings can solve this problem. The internal coating can produce proper insulation from vapor and gas, but it is difficult to survey and to repair. The external coating is characterized by opposite advantages. In this paper the effectiveness of four different type of the external coatings on the vapor tightness of concrete boxes is analyzed. The experimental test is developed considering small-scale boxes (a cube of 1,20 m side) with a thickness of about 10 cm. Four specimens of cubic concrete boxes made in vibro-compressed concrete are coated with four different layers. The tightness test is carried out by the application of an internal pressure given by blown nitrogen. The tests highlight the level of tightness of each treatment and highlights strength and drawbacks of each coating.