International Concrete Abstracts Portal

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.

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.

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.

The properties of mortar and concrete using the mineral admixture consisting of red mud and finely ground silica were investigated in order to use effectively an industrial byproduct from a chemical factory. This paper reports on the effects of five mixing ratios of red mud to finely ground silica on flow value and air content of fresh mortar, compressive strength, resistance to chloride penetration, and sulfate resistance of hardened mortar compared with those of plain mortar. Secondly, the compressive strength and the drying shrinkage of concrete specimens cured at 20 C in water and a steam chamber at the maximum temperature of 65 C were investigated on the concrete using the admixture consisting of five percent red mud and five percent finely ground silica and 10 percent finely ground silica only. The substitution was 10 percent of cement. The flow value of mortars tends to decrease with an increasing rate of red mud content, when the substitution of the mineral admixture for cement is 50 percent. The air content of fresh mortar becomes maximum when the mixing ratio of red mud and finely ground silica is equal. The compressive strengths of mortars containing red mud are lower than that of plain mortar at each age. The mortars containing finely ground silica exhibit higher strength from seven to 28 days. The resistance to chloride penetration and the sulfate resistance of the mortars are clearly improved by the use of this mineral admixture. The compressive strength of concrete at each age using red mud as a single admixture increases slightly when compared to concrete using the admixture consisting of red mud and finely ground silica. The drying shrinkage of the concrete using this admixture is higher than that of plain concrete, and the shrinkage is slightly reduced by the adoption of steam curing.

Describes the results of an experimental study carried out on concretes incorporating high volume of ground granulated blast furnace slag. The slag content in cement ranged from 50 to 95 percent by weight of the total cementitious materials; the fineness of slag ranged from 4000 to 8000 cm 2/g. A large number of test specimens were subjected to the determination of heat of hydration and amount of chemically combined water in cement paste, adiabatic temperature rise, compressive strength, static modulus of elasticity, and rate of carbonation in concrete. The following results were obtained. 1. The strength development of high blast furnace slag content concrete is more highly influenced by the curing temperature than that of slag free concrete. 2. For compressive strengths below 5 MPa, the compressive strength developed quickly with increasing slag content in the range of 70 to 95 percent, regardless of fineness of slag. 3. The strength of high blast furnace slag content concrete is strongly related to the amount of effective combined water, especially at the early ages. 4. The correlation between the compressive strength and the maturity is higher on the maturity of the basic temperature of 0 C than that of -10 C. 5. The maximum adiabatic temperature rise (K) of concrete mixture decreased with increasing ground blast furnace slag content, especially in the range of more than 70 percent. 6. It is very useful to utilize the high fineness slag (such as 8000 cm 2/g), because the adiabatic temperature rise per unit compressive strength decreases with increasing fineness of slag. 7. The depth of carbonation of high blast furnace content concrete is proportional to the square root of age similar to that of ordinary portland cement concrete. Using this relationship, the progress of carbonation in field exposure can also be predicted.