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.

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.

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.

Conventional limestone concrete airfield pavements are prone to spalling as a result of jet blast from vertical take-off and landing aircraft. This paper describes a research program to develop jet blast resistant pavement quality controls containing alternative cementitious materials and aggregates. The concretes were evaluated by subjecting slabs to simulated Harrier jet engine blast, using thermal imaging and video cameras to record surface temperatures, spall times, and spalled areas. Slag and fly ash as partial cement replacement materials produced moderate increases in the surface temperature and exposure time at which spalling initiated. Fly ash aggregates produced substantial improvements in spalling resistance under simulated Harrier conditions, particularly when used to replace both the fine and coarse natural aggregates. The spalling mechanism was associated with differential thermal expansion, as opposed to the release of water vapor and the dehydration of cementitious compounds. Spalling observed during field exposure was attributed to laitance and brushing of the surface, which also suffered from drying shrinkage cracking.