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.

When using high-strength concrete in large structures, it is important to minimize generation of thermal stresses during hydration of cement and to minimize variation of concrete properties. The proper workability is also very important. A research program is underway with the above aspects in mind to optimize the requirements of high strength, low heat generation, and pumpability, using both the newly developed low heat cement (LSC) with high content of finely ground blast furnace slag and the high-range, water-reducing admixture. This paper describes the test results on fundamental properties, pumpability, and thermal stress reduction effects on high-strength concrete of 60 MPa, using this type of low heat cement. The following results were obtained. 1. The heat generation of LSC is remarkably lower than conventional low heat cement (blended cement: FMKC). When using LSC, the thermal stress was reduced by 60 percent compared to concrete using normal portland cement. 2. The quality of concrete manufactured in the concrete plant was comparatively uniform. 3.Pressure loss during pumping was three to four times larger than ordinary concrete. However, it was verified that after pumping, the quality of concrete using LSC showed satisfactory workability and had less variation compared to the quality of concrete using FMKC. 4. From results mentioned above, by selecting proper high-range, water-reducing admixture, the use of LSC is considered to be a solution for reducing cracks due to hydration in high-strength concrete while maintaining suitable workability and sufficient strength development.

In a program covering a wide range of mixtures, three portland cements and two ground granulated blast furnace slags (GGBS) were used to investigate the relationship between alkali content and ASR expansion. Length changes were monitored, for several years, on concrete prisms made with a reactive natural aggregate. The prisms were moist cured at 20 C and 38 C. Storage at 38 C was found to be an accelerated test which correlated will with storage at 20 C. At 20 C, the rate of expansion was some four times slower than at 38 C. Nonetheless, there was very good consistency between the two temperatures in classifying mixtures either expanding or nonexpanding. Current indications are that the magnitudes of ultimate expansions are independent of temperature. The mixtures containing GGBS tolerated much greater alkali contents in the concrete without expansion. This effect was more pronounced for higher proportions of GGBS. The results of the program are discussed in this paper in relation to various rules which have been proposed to take advantage of the effectiveness of GGBS in preventing ASR.

A new variety of applications are being found for fly ash. It is increasingly important to determine the structural properties of fly ash particles, especially for increasing use in composites, such as polymer matrix and cast metal matrix composites. In this paper, selected properties of precipitator fly ash and cenosphere fly ash were directly measured; other properties were indirectly estimated from the experimental measurements on the properties of composites containing fly ash. The properties studied included sphericity of fly ash particles, wall thickness, the ratio of wall thickness to diameter, and modulus. The data generated on properties of fly ash have been compared with other filler or reinforcement materials, such as glass microspheres, Al 2O 3 , SiO 2, and SiC particles. The results show that the deviation of cenospheres from sphericity is virtually independent of diameter. The ratio of wall thickness to diameter of cenospheres is about 0.1 and tends to decrease with increasing particle diameter. The calculated values of effective modulus of fly ash from the property measurements on metal matrix-fly ash composites are in the range of 140 to 310 GPa, which are of the same order of magnitude as of general ceramics and glasses. The morphology of precipitator and cenosphere fly ash particles studied using scanning electron microscope is discussed. The implications of the morphology and properties of fly ash on its utilization, especially in micro and macro composites, including cements, are also discussed.

A test program was conducted to establish criteria for a performance- based specification of concrete quality, as a opposed to a prescriptive specification, for a major project in South Africa. Concretes containing different combinations of portland cement, fly ash, ground granulated blast furnace slag, and silica fume were prepared over a range of water/binder (W/CM) ratios. The samples were stored in water for three days to simulate the probable effects of site curing practice. Each concrete was then subjected to three different tests: air permeability and water sorptivity, both conducted in an "Autoclam," and a rapid chloride conductivity test. Time constraints prevented the preparation of a performance specification, but the results were used to prescribe a W/CM ratio and binder type. The results of the investigation also provide the basis for future evaluation of the site concrete by conducting similar tests on cores extracted from the structure. It was established that specifying only on the basis of concrete strength is insufficient to insure a high potential durability.