International Concrete Abstracts Portal

Presents the results of exploratory experiments using AFBC ash to produce a new kind of expansive cement. The principles for design of the compositions and theoretical consideration are discussed. The tests were carried out to examine the XRD pattern and the pozzolanic activity of the AFBC ash used. The expansive properties of this cement and its effects on porosity, pore structure, heat evolution, setting time, resistance to chemical attack, leaching effect, and strength of hardened cement paste are analyzed in detail. A kind of warm-pressed AFBC ash expansive cement product is also presented. The present results indicate that the sulfoaluminate of AFBC ash can be used as an expansive component. This kind of expansive cement could be used to chemically induce compressive stress in the mortar and thereby reduce the size and amount of shrinkage cracks that frequently occur in portland cement concrete during drying. The results suggest an economically and environmentally acceptable approach.

As focus increasingly shifts to protecting the environment through recycling of industrial byproducts and wastes, as well as conserving energy and resources, corresponding restructuring of conventional production technology and practices has become imperative. Because of these considerations, mixtures of kiln dust and fly ash were hydrothermally treated and calcined to produce a new type of beta-C 2S rich cement. Fly ash, which is the most abundantly generated industrial byproduct, is still largely disposed of as waste; kiln dust is the waste product of the cement industry, vast quantities of which are discarded due to its high alkali content. The former is composed of alumino-silicate glass, while the latter has a composition similar to that of partially calcined cement raw meal. This study demonstrates that it is possible to produce C 2S cement of dequate 28-day strength by suitably proportioning fly ash and kiln dust. The results of variations in factors such as the CaO:SiO 2 ratio and two different precalcination treatments are presented. Prehydration-dehydration (sintering at 950 C) processes were specially applied for the production of this cement, in contrast to the direct calcination method in the presence of a mineralizer. The cement was constituted of beta-C 2S and calcium aluminates. The formation of these minerals in relation to the clinkering sequence is discussed. The cement is sufficiently hydraulic, and its strength development largely depended on the CaO:SiO 2 ratio of the raw mix and the precalcination process.

Bagasse is the fibrous residue of sugar cane, which is burned for energy leaving various types of ashes as waste residue, of which grate ash is found to be the most suitable for use in concrete. Grate ash shows poor chemical reactivity with portland cement, making it not very effective as a pozzolan. It can, however, be used as a fine aggregate constituent of concrete. Five grades of concrete were tested, ranging from 20 to 60 MPa, to compare the performance of grate ash concrete with that of normal concrete. The use of the ash alone as fine aggregate gave harsh concrete with low workability and poor cohesion. This was improved by blending about 25 percent normal concrete sand with the ash. Bleeding was comparable with, if not generally less than, that of normal concrete. Grate ash concrete, in particular the lower strength mixes, had 10 to 18 percent higher initial drying rates and would, therefore, require more stringent curing precautions than normal concrete. Rates of strength development were comparable in the two concretes. Compressive strengths of over 80 MPa were achieved after one year with the high-strength ash concrete mixtures. But, for a given strength, the grate ash concrete requires more cement than normal concrete. In comparison with normal concrete, grate ash concrete had similar shrinkages, slightly lower modulus of elasticity, and about 40 percent lower creep deformations. For equivalent strengths, the two concretes showed similar durability properties, in terms of their resistances to mechanical abrasion, water absorption, chloride diffusion, and carbonation. However, due to the porosity of the grate ash particles, the concrete had a much better resistance to freezing and thawing attack than normal concrete, even though all concretes were non-air-entrained.

Presents the results of a study of the influence of ground fly ashes on workability and strength of mortars. Fly ash (T0) was obtained from the thermoelectric power plant of Andorra-Teruel (Spain). Samples of (T0) fly ash were ground using a laboratory ball mill for 10, 40, and 60 minutes (T10, T40, and T60). This process crushed spherical or spheroidal fly ash particles so that the morphology of the particles was substantially modified and the fineness notably increased. Mortars were prepared by replacing from 15 to 60 percent of cement by fly ash. Curing time, curing temperature, and fly ash amount influenced the strength of mortars. Curing times longer than seven days showed significant differences among fly ashes, with compressive and flexural strengths decreasing in the order T60 > T40 > T10 > T0. Increasing the curing temperature from 20 to 40 C produces a rise of compressive strength that exceeds control mortars when T60 and T40 fly ashes were used. It is concluded that the use of ground fly ashes improves the strength of mortars compared with strengths obtained with normal fly ash, but high replacement percentages of ground fly ash adversely affect workability.

The individual binding capacity of fly ash in lime bearing systems and gypsum on its own is well established. This study was aimed at utilizing gypsum as phosphogypsum and industrial lime in conjunction with high volume fly ash to develop a cost-effective cementitious binder product by advantageously utilizing the individual binding capacity of the materials. The materials were first fully characterized chemically and mineralogically to evaluate their potential as building material components. Different mixture proportions were tested. Compressive strength data of different mixtures at one day, 3, 7, 14, 21, and 28 days are presented. These are correlated with the hydration properties at corresponding ages studied by means of XRD, SEM/EDXA, and DTA. The discussion relates to the roles of the individual components in the development of strength properties. Products with an interlocking microstructure and compressive strengths of over 12 MPa after 28 days of hydration are described. The cost effectiveness and possible applications of cementitious products that can be developed with such a system are also described.