International Concrete Abstracts Portal

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.

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.

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.