| Precast, prestressed concrete members are in wide use due to their efficiencies in load carrying capacity and construction cost. These elements have normally had very good durability due to the low water cement ratios and high construction quality. The precast industry now uses chemical admixtures such as corrosion inhibitors and mineral admixtures such as ground granulated blast furnace slag (GGBFS). The effects of these materials on microstructure and on the relationship between microstructure and durability have not been fully examined.; In this study, the effects of accelerated versus standard moist curing, together with the addition of different chemical admixtures (a calcium nitrite corrosion inhibiting admixture and two types of high range water reducers) and different percentages of GGBFS were investigated. Differences in permeability and durability characteristics were related to differences in microstructure.; The microstructure of these concretes was analyzed quantitatively in terms of non-evaporable water content, volume of permeable voids and nitrogen porosimetry. Apparent diffusion coefficients from 90-day chloride penetration tests, air permeability and rapid chloride permeability characteristics were compared with behavior in rapid freeze-thaw and deicing salt scaling tests. In general, accelerated curing affected the microstructural and “macro” structural properties adversely compared to standard curing, although the extent of degradation was not substantial. The volume of small pores determined by nitrogen porosimetry were generally related to apparent diffusion coefficients and deicing-salt scaling (frost) resistance. |
