Presents a study on high-early-strength cements based on calcium sulfoaluminate, C 4A 3S. These cements can be produced at temperatures about 300 C lower than normal portland cement and can also be synthesized using industrial process wastes and byproducts, such as fly ash, blast furnace slag, chemical gypsums, and other waste materials containing reactive sulfate and alumina. Cements designed to contain C 4A 3S, Beta-C 2S, and CS or C 4A 3S, calcium sulfosilicate, C 5S 2S, and CS have been synthesized using (a) pure analytical reagent (AR) calcium carbonate or commercial limestone as the source of CaO; (b) fly ash, blast furnace slag, bauxite, clay, or alumina as the source of Al 2O 3 and SiO 2; and (c) natural gypsum, phosphogypsum, or desulfogypsum as the source of sulfate. Ettringite, C 6AS 3H 32, generated by the hydration of C 4A 3S and CS is responsible for the high early strength of these cements. The hydration of the silicate phase and the presence of C 5S 2S contribute to ultimate strength. These ettringite-containing cements do not expand and, in fact, have dimensional stabilities similar to portland cement. In these types of cements, durability problems may arise from the poor resistance of ettringite to carbonation. Due to the higher resistance to carbonation of another calcium sulfoaluminate hydrate, monosulfate (C 4ASH 12), the investigation has been extended to a composition which included brownmillerite, C 4AF, whose presence promotes the conversion of ettringite to monosulfate during hydration.

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.

Presents the results of research performed in developing and using flowable fly ash slurry which is classified as a Controlled Low Strength Material (CLSM) as defined by ACI Committee 229 for underground facility construction and abandonment. The mixture proportions for the CLSM described in this paper used fly ash as a primary ingredient. The fly ash was produced at Wisconsin Electric's Port Washington Power Plant as a byproduct of burning coal from Pennsylvania. Port Washington Power Plant has four 80 MW electric generating units that were brought in service between 1935 and 1949. Additional ingredients included portland cement, water, and conventional fine and coarse aggregates. Information is also included on the compressive strength, electrical resistivity, thermal conductivity, and compatibility with plastics used in the manufacture of underground electric cable jackets and natural gas lines. The results indicate that CLSM fly ash slurry is an excellent material for backfilling trenches and filling abandoned underground facilities.

The use of blast furnace slag aggregate (BFSA) is not new, but its application in the production of high-performance concrete (HPC) is nonexistent at least, in Australia. This paper presents the results of a preliminary optimization of the high-strength concretes made using BFSA, normal sand, portland cement, ground granulated blast furnace slag (GGBFS), condensed silica fume (CSF), and a proprietary superplasticizer. The paper also describes some additional characteristics of the optimized concretes. In all, 15 types of concretes were made. The properties examined were workability, density, compressive strength, elastic modulus, shrinkage, and water penetration. The maximum strength achieved using the slag aggregate was 107 MPa, which placed the slag aggregate concrete well into the very high strength range of concretes. The workability was found to be unaffected by the use of the slag aggregate. The tensile strength of the concrete was relatively high (5.4 Mpa); the shrinkage was found to be lower than concretes produced with normal aggregates, as was the water penetration and absorption. Of particular importance, the elastic modulus was found to be markedly lower than that of concretes made with normal aggregates. It is concluded that the slag aggregate can be used successfully in the production of high-performance, high-strength concrete.

The sensitivity of strength and deformation of high-strength concrete incorporating silica fume to variations in strain rates were studied experimentally and compared with those of normal strength concrete (without silica fume). The observed phenomena in the experiments were qualitatively interpreted according to an assumed mechanism of strain rate sensitivity of concrete. The differences of the material structure between high-strength concrete with silica fume and normal strength concrete without silica fume are discussed in this paper; emphasis is placed on the change of pore structure and moisture content due to the incorporation of silica fume for high-strength concrete and its influence on the rate sensitivities to strength and deformation of concrete. In particular, the Stefan Effect is believed to play a very important role in the case of rate sensitivity. In general, it was found that high-strength silica fume concrete is more sensitive to the variation of strain rate than normal strength concrete as far as strength and deformation in compression are concerned. However, in tension, this rate sensitivity is less pronounced.