International Concrete Abstracts Portal

Ground granulated blast furnace slag may show very high strength in the presence of proper alkaline activators. However, the high cost and short supply of alkalies restrict the application of such cementitious materials. This paper reports on an investigation of some practical ways to increase the reactivity of blast furnace slag. Experimental results indicate that for moisture curing at 50 C, the addition of either four percent Na 2SO 4 or four percent flake calcium chloride can significantly increase the strength of lime- slag mixtures consisting of 80 percent slag and 20 percent hydrated lime. The measurements of change in Ca(OH) 2 content with times in the hardened pastes show that the addition of activators accelerates the early reaction, but does not affect overall reactivity. Strength improvement in Na 2SO 4 pastes is due to the formation of ettringite (AFt), while the presence of CaCl 2 favors the formation of C 3A.Ca(OH) 2.12H 2O. At the same time CaCl 2 partially replaces the Ca(OH) 2 in C 3A.Ca(OH) 2.12H 2O and forms a solid solution of C 3A.Ca(OH) 2.12H 2O - C 3A.CaCl 2.10H 2O in CaCl 2 pastes.

Small-angle neutron and X-ray scattering techniques are being used in a systematic study of the development of concrete microstructure on the nanometer scale (1 to 1000 nm) as a function of the addition of fly ash, silica fume, or other pozzolanic materials. These methods yield direct measures of the fractal aspects of the material microstructure, including volume- and surface- fractal exponents and structure parameters within the calcium-silicate-hydrate gel. These variables are being evaluated for use in a classification system of microstructures. In the first phase of the program, the emphasis has been on the characterization of silica fume products both as separate phases and after reaction in concrete. The combination of small-angle scattering with a fractal interpretation scheme has been found to provide a resilient and powerful probe of the undisturbed statistically-significant microstructures in cementitious systems.

The increasing construction of high-rise buildings in recent years had led to a demand for lightweight, high-strength concrete. In this study, the compositions of the matrix and the air void structure of aerated mortar containing silica fume were investigated as the basis for manufacturing lightweight, high-strength concrete. Mortars made with cement containing silica fume and fine or ultra-fine silica stone powder, having a particle size between that of cement and silica fume, were tested; the properties of cement paste in fresh and hardened conditions were improved. The compressive strength and the air void structure of prefoamed aerated mortars were determined and their relationship studied. Based on the results, it was confirmed that lightweight, high-strength concrete could be made with an effective combination of aerated mortar containing silica fume and lightweight coarse aggregate.

SP-153 In 1995, CANMET, in association with ACI, U.S.A. Electric Power Research Institute, Canadian Electrical Association, and several other organizations in Canada and the United States, sponsered the Fifth International Conference on fly ash, ferrous and nonferrous slags, and silica fume was held. The two volume proceedings of the Fifth CANMET/ACI Conference contains 62 papers from 23 countries.

Various accelerated test methods have been proposed for the assessment of sulfate resistance of cements. A majority of these methods measure the expansion of mortar prisms in sulfate solution. Differences in test procedure can have a significant effect on the expansion observed and may possible affect the ranking of cement types. The different performance in sulfate solutions of cements containing different slag percentages and water- cement ratios and the lesser influence of different slag alumina contents have been reported previously. This paper summarizes data from various test works which demonstrate the effect on expansion of variations in the following test parameters: aggregate- cement ratio (at constant water-cement ratio), specimen shape, initial curing period, specimen compaction, initial curing deficiencies, early carbonation, concentration of sulfate solution, and type of sulfate solution. The first three of these parameters had comparatively little influence on expansion; the remainder had more significant influences on expansion. Sieving mortar for test specimens from production concrete provided a useful and comparable method of assessment. The test programs were principally concerned with slag cement blends, but as any test method had to be applicable to all types of cement, a number of sulfate-resisting portland cements were tested. The wide range of expansion characteristics suggest that a "typical" control SRPC may not be easily defined.