International Concrete Abstracts Portal

Introduces some experimental results on the application of ASTM Class C (high lime) fly ash from Thailand to reduce shrinkage of cement paste. Measurement of both autogeneous and drying shrinkage were conducted on cement paste samples. Parameters varied in the autogeneous shrinkage test were type of fly ash (two samples of Class C fly ash, from the same source, with different chemical composition, and a sample of Class F fly ash), cement replacement percentage (0 percent, 30 percent, and 50 percent), curing condition (seal and submerged), and curing period. For autogeneous shrinkage specimens, flexural strength, compressive strength, and setting time were tested to compare the mixtures containing Class C fly ash with those containing Class F fly ash and with those without any fly ash, to derive some basic information for judging the suitability of the Class C fly ash as a pozzolan. From the test results, it was found that Class C fly ash was effective for reducing autogeneous shrinkage and improving flexural strength. The effect was due to expansion which occurred in the samples containing Class C fly ash. For the tested range, the higher the replacement percentage, the more effective the fly ash becomes. Class C fly ash which contained higher SO 3 content was more effective than that with the lower SO 3 content for reducing shrinkage. Water curing was more effective than sealed curing since the expansion process required water; specimens with longer water curing periods showed smaller shrinkages. The pozzolanic activity index of the tested Class C fly ashes was higher than that of the tested Class F fly ash; therefore, higher 28-day compressive strength was observed in paste with the Class C fly ash than in paste with the Class F fly ash. Setting times of pastes with the Class C fly ash were generally shorter than that of the paste with the Class F fly ash. The Class C fly ash also proved to be effective for reducing drying shrinkage, as indicated by comparison of specimens made with and without Class C fly ash. Longer curing periods reduced the drying shrinkage of specimens with and without fly ash.

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.

A new variety of applications are being found for fly ash. It is increasingly important to determine the structural properties of fly ash particles, especially for increasing use in composites, such as polymer matrix and cast metal matrix composites. In this paper, selected properties of precipitator fly ash and cenosphere fly ash were directly measured; other properties were indirectly estimated from the experimental measurements on the properties of composites containing fly ash. The properties studied included sphericity of fly ash particles, wall thickness, the ratio of wall thickness to diameter, and modulus. The data generated on properties of fly ash have been compared with other filler or reinforcement materials, such as glass microspheres, Al 2O 3 , SiO 2, and SiC particles. The results show that the deviation of cenospheres from sphericity is virtually independent of diameter. The ratio of wall thickness to diameter of cenospheres is about 0.1 and tends to decrease with increasing particle diameter. The calculated values of effective modulus of fly ash from the property measurements on metal matrix-fly ash composites are in the range of 140 to 310 GPa, which are of the same order of magnitude as of general ceramics and glasses. The morphology of precipitator and cenosphere fly ash particles studied using scanning electron microscope is discussed. The implications of the morphology and properties of fly ash on its utilization, especially in micro and macro composites, including cements, are also discussed.