International Concrete Abstracts Portal

Canada Centre for Mineral and Energy Technology (CANMET) has an ongoing project dealing with the role of supplementary cementing materials in concrete technology. As a part of this program, a new type of concrete known as high-volume fly ash concrete has been developed. In this type of concrete, the water and cement (ASTM Type I) contents are kept very low, about 115 and 155 g/m 3, respectively, and the proportion of low-calcium fly ash in the total cementitious materials content is about 56 percent. This type of concrete has excellent mechanical properties and durability characteristics. In spite of very good properties shown by the high-volume fly ash concrete, one concern about the use of this type of concrete is its performance at early ages due to its low cement content and the slow reaction process of fly ash. This can be an obstacle for the use of this type of concrete when compressive strengths over 10 MPa at one day are needed or when proper curing cannot be provided for a long period of time. One way to improve the early-age properties of this type of concrete is to use ASTM Type III portland cement. Therefore, a study was undertaken to develop engineering data base on the high- volume fly ash concrete using ASTM Type III cement. Concrete mixtures were made using ASTM Type III portland cement from a source in the U. S. A. and three low-calcium fly ashes also from source in the U. S. A. A reference mixture (without fly ash) was also made for comparison purposes. The use of ASTM Type III cement instead of Type I cement noticeably improved the early-age strength properties of the high-volume fly ash concrete incorporating the fly ashes investigated in this study; this was done without having any detrimental effect on long-term properties of the concrete. The one- day compressive strengths were about 5 to 8 MPa higher than those of the high- volume fly ash concrete made with the same fly ash and Type I cement. The use of Type III cement also shortened slightly the setting time of the high-volume fly ash concrete. Durability characteristics and drying shrinkage of high- volume fly ash concrete made with ASTM Type III cement were no different than those for the concrete made with Type I cement.

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.

The strength development of blends of five cements with various levels of a fly ash, two blast furnace slags, a ground limestone, and a dried chalk dust was determined using EN 196 mortars and, for selected materials, concretes. Three of the cements were based on normal portland cement (OPC) clinkers and two on a high-early-strength (HES) mineralized clinker. At the same specific surface area and SO 3 content, the HES clinker gave cements with strengths 5 to 10 MPa higher than those based on equivalent normal clinker at all ages from one to 56 days. This allows the use of significant levels of fly ash, slag, or other less reactive materials in blends giving similar early strengths to normal portland cements. The early strengths of the blends with the ground limestone and the lower surface area HES cement were higher than expected. The finer chalk dust gave significant contributions to strengths with all the base cements, particularly at early ages. The effect was greater with the lower surface area cements and those based on HES clinker. It is concluded that the acceleration of hydration by the fine calcium carbonate is particularly strong with cements based on the mineralized clinker.

The concept of highly-flowable concrete was developed from the transformation of underwater concreting ideas to the concreting of structures on land. Therefore, the general properties of highly-flowable concrete are similar to those for concreting under water. The viscosity of highly-flowable concrete is high so that segregation of the coarse aggregate from the concrete can be eliminated. The slump flow of highly-flowable concrete is greater than 600 mm so as to increase its flowability. The slump flow is defined as the diameter of slumped concrete. The distinctive feature of the mixture is that a larger proportion of fine material is used in it. The high viscosity and large amount of fines increase its resistance to segregation. In the method of mixture proportioning of highly-flowable concrete proposed by the authors, a high-range, water-reducing admixture (HRWRA) is used to increase the slump flow. Furthermore, a segregation-reducing agent is used to minimize the segregation, although a large proportion of fines somewhat increases the viscosity of concrete. Limestone powder, which is a relatively low reactive material, is used to reduce the heat of hydration and shrinkage. In the proposed method of mixture proportioning, it is possible to choose the required average strength, water content, and fine aggregate-total aggregate ratio to suit special and particular conditions of concrete structures under various environmental conditions.