DURABILITY ASPECTS OF PRECAST PRESTRESSED CONCRETE. PART 2: CHLORIDE PERMEABILITY STUDY

A laboratory study was undertaken to investigate the good past performance of low water-cement ratio, heat-cured precast, prestressed concrete in highway bridges, parking garages, and other applications. The study included salt water ponding testing, AASHTO T 277 or ASTM C 1202 coulomb tests, compressive strength tests, and absorption and volume of permeable voids tests. Heat-cured, water-cured, and moist-cured concretes with water-cementitious ratio values of 0.46, 0.37 and 0.32 with and without silica fume were tested. Using the measured chloride contents, chloride diffusion coefficients were calculated and estimates of the time-to-corrosion were developed. The water-cement ratio was found to be the most important influence on the performance of the concrete, with low w/c, heat-cured conventional concretes having comparable performance to realistic silica fume concretes having 0.37 to 0.46 water-cementitious ratios. It was also found that the use of heat curing could reduce the permeability of AASHTO-grade, 0.46 w/c concrete by 40 to 50 percent. The addition of silica fume to concrete caused an increase in the absorption and volume of permeable voids in concrete, while heat curing was seen to decrease the absorption and volume of permeable voids in concrete.