High performance concretes (HPC) are increasingly used in high-rise building columns. Some creep and shrinkage data of HPC has been published based on laboratory tests. Very few long term field results are available. During the construction of the new library of Concordia University (Montreal, Canada) in 1990, two pairs of circular 850 mm diameter reinforced, concrete columns made of lOO-MPa silica fume concrete and of 80.MPa non silica fume concrete were instrumented with vibrating wire extensometers. One column (called active column) of each pair was part of the structure; the other (called mockup column) was never loaded and used for shrinkage and thermal strain measurements. Strains and temperatures at different locations in concrete and in reinforcing bars as well as load in concrete were recorded for about 5 years. Data obtained on these HPC columns is presented in this paper. Creep, shrinkage, thermal expansion coefficient of the two field concretes are discussed. Stresses in concrete and in reinforcing bars are analyzed. Axial loads in active columns are calculated from experimental data and compared with the specified loads used in the structural design.

The diffusion mechanisms of chloride ions into ordinary and high performance mortars were studied. Four different mortar mixtures were tested. Test parameters included the water/binder ratio (0.25 and 0.45) and the use of silica fume. An ASTM type III cement was used in the preparation of the 0.25 water/binder ratio mortars while the 0.45 water/binder ratio mixtures were prepared with an ASTM type I. For all mixtures, the sand volume fraction was maintained constant at 50%. The diffusion properties of the mortars were studied according to two different experimental procedures. In a first series of tests, apparent diffusion coefficients were calculated from chloride ion profiles measured after a 12-month immersion period. In a second series, a migration test (where the chloride ion penetration is accelerated by the application of an electrical potential of 10 volts) was used to investigate the transport properties of the four mortars. All test results clearly show that the reduction of the water/binder ratio and the use of silica fume contribute significantly to the reduction of the chloride ion penetration. The consequences of these results on the long-term durability of high-performance concrete structures and, more specifically, on their ability to resist to reinforcing steel corrosion are discussed. The ability of the accelerated migration test to reliably predict the penetration of chlorides in cement-based materials after only a 14-day test period is also discussed.

In Japan high strength concrete was first achieved as early as the 1930s. Yoshida reported in 1930 that high strength concrete with 28-day compressive strength of 102 MPa was obtained. This result was obtained by a combination of pressing and vibrating processes without the use of any chemical and mineral admixtures. This method has been applied for production of high strength segments. In the 196Os, superplasticizers were developed in Japan and West Germany which were very effective chemical admixtures to decrease the water content in concrete. With the use of superplasticizers, it became possible to decrease the water to cement ratio while maintaining the workability of the concrete. This technique was applied very widely and many bridges, high-rise buildings, precast concrete members have been produced. In the 197Os, the combined use of superplasticizers and ultra-fine materials such as silica fume, finely ground blast furnace slag or anhydrous gypsum based additives were studied and has been applied to concrete structures until today. Finally, super high strength concrete greater than 120 MPa in compressive strength was achieved with selected materials and special techniques and this kind of concrete has been applied in other industries instead of in the construction industry. This paper summarizes the history and progress of the development of high strength concrete in Japan.

This investigation was performed to access the applicability of conventional maturity functions to high strength concretes incorporating silica fume and superplasticizer. Concrete specimens were allowed to cure under three temperatures simulating hot weather, laboratory, and cold weather conditions. Both linear and exponential strength-maturity functions predicted different values of strength for different concrete curing temperatures for the same value of maturity, as has been observed by other researchers. Of these two unctions, the exponential performed somewhat better in this regard for elatively low values of maturity. Concrete strength-gain behavior was influenced by the presence of silica ume and the high amount of super-plasticizer in the mixture. Strength-maturity equations already developed for normal strength concrete underestimated strength at low maturity ages and overestimated strength at high maturity. It is suggested that further studies should be done to evaluate such effects in those relationships.

Reinforced concrete columns are typically made with higher strength concrete than are the floor slabs that they support. In construction, the slab is usually cast continuous through the region of the slab-column joint. As a result, load in the column above the slab must pass through a layer of weaker slab concrete before reaching the column below the slab. The column-slab joint may be viewed as a “sandwich” column, with high strength concrete above and below a layer of lower strength concrete. In design, the effective column concrete strength is based on a special weighted average of the column and slab concrete strengths. Because of confinement, the slab concrete in the joint region is assumed to be capable of carrying stresses well in excess of its specified strength. This confinement is, in turn, affected by gravity loading of the slab. Existing design procedures are based on tests of slab-column joints in which no load was applied to the slabs. This paper presents the results of a series of tests on interior column-slab joints in which service level loads were applied to the slabs prior to loading the columns. The major conclusions of this study are: (1) tests of sandwich slab-column joints with unloaded slabs consistently overestimate the strength of the connection and (2) the AC1 3 18-89 provisions for interior column-slab joints are unconservative for high ratios of column to slab strength and/or high ratios of slab thickness to column size.