Direct method for improvement of durability of reinforced concrete structures

Simple methods for improvement of durability of reinforced-concrete or prestressed-concrete structures became commonly considered targets in the strategy of sustainable building. Promising method for durability improvement of concrete surface is application of controlled permeability formwork (CPF). The most spectacular results of casting concrete against CPF are significant changes in surface appearance comparing conventionally formed concrete: elimination of blowholes and other faults, darker colour, textured dull finish. The most of the recent tests have been done on specimens, therefore, testing of entire members behaviour has been undertaken now. Apart from different tests concerning basic properties of concrete surface - like hardness, abrasion resistance, tensile strength, resistance to water penetration and absorption, chloride diffusion - for the first time the influence of CPF on behaviour of structural members was investigated. Another group of the tests was focused on the possibility of reduction concrete cover. The considerable improvement of durability of concrete surface when formed against controlled permeability formwork (CPF) is evident, if compared with the same concrete formed against typical impermeable formworks made of impregnated plywood, steel, plastic foil. In the tests of reinforced concrete beams subjected to bending and shear the flexural stiffness of members formed against CPF was found noticeably greater than in case of traditional formwork, and the cracks appeared later. From durability point of view the smaller width of cracks is the significant result of such modified surfaces of concrete. The corrosion tests were done on specimens immersed in salt (NaCl) solution. It was stated that the kind of formwork had the crucial influence on the development of corrosion processes. In case of using CPF the values of polarization resistance were noticeably greater when compared with specimens formed against impermeable formwork in the period of 10 months of tests.