International Concrete Abstracts Portal

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.

SP-153 In 1995, CANMET, in association with ACI, U.S.A. Electric Power Research Institute, Canadian Electrical Association, and several other organizations in Canada and the United States, sponsered the Fifth International Conference on fly ash, ferrous and nonferrous slags, and silica fume was held. The two volume proceedings of the Fifth CANMET/ACI Conference contains 62 papers from 23 countries.

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 water-to-cementitious materials ratio (W/CM) is recognized as an important variable in understanding and controlling the quality of concretes containing pozzolan powder additives, such as fly ash. This paper presents part of a study to determine a correct way to evaluate the contribution of fly ash to concrete strength as is usually indicated by the W/CM ratio. A rational mathematical model of the form W/CM = W/(C + K * FA) is presented, in which W, C and FA are water, cement, and fly ash contents per m 3 of concrete, respectively. K is a pozzolan efficiency factor based on comparing the compressive strength of two concretes having the same workability and the same amount of cement. An experimental program was conducted to demonstrate the use of the proposed W/CM ratio model and corresponding K values. The variables studied were class and addition level of fly ash and slump, strength, and age of concrete. Results show that the model describes and considers the influence of fly ash on the rheological properties of fresh concrete and on the strength of hardened concrete. The model is also suitable for use as an equivalent to Abram's law to account for modern day powder additives.

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.