International Concrete Abstracts Portal

An expansive grout, based on Class H cement, an expan- sive admixture consisting essentially of plaster of paris (calcium sulfate hemihydrate), and a Class C fly ash, was proportioned for use underground. Specimens of this grout, and of five modified versions of it, were tested to determine the effects of using two ther fly ashes, with or without silica fume, on compressive strength, volume change, phase composition, and microstructure. Properties were monitored to 960-days age. Up to 365-days age, specimens of the mixture modified with Class F fly ash had lower compressive strengths and generally more expansion than did those of the original composition. At ages of 90 days and greater, the same was true of samples prepared with a second Class C fly ash. Substitution of silica fume for 5 or 10 percent of the cement gave higher early strength, but the combination of the second Class C fly ash and 10 percent silica fume gave the lowest strengths at ages of 90 days and greater. Despite the substitutions, properties were markedly similar, compressive strength from all modifications exceeded 90 MPa at 365 days, and phase composition and microstructures became more similar with time.

This paper describes an investigation of the use of industrial by-products such as bottom ash and silica fume with high silica content, as the admixture for mortar and concrete. The bottom ash used for this investigation was ground in a ball mill. At first, basic tests using mortars were conducted. Subsequently, the concretes containing different proportions of the two by-products were tested for strength development under accelerated curing, drying shrinkage, and water permeability. The results of the mortar strength tests indicate that the proper amount of ground bottom ash is about 5 percent if used to replace cement or 10 percent if used in addition to cement, and that of silica fume is approximately from 5 to 10 percent if used to replace cement and from 10 to 15 percent if used in addition to cement. When steam curing and autoclave curing are used, the concretes containing ground bottom ash and silica fume have higher early compressive strength than concrete without these materials. The coefficients of water permeability of the concretes using ground bottom ash and silica fume are lower than those of concrete without these materials. Paticularly, the water-tightness of silica fume concrete improved remarkably, although the concrete has a little higher drying shrinkage in comparison with concrete without silica fume. The use of these materials in amount of 5 to 10 percent to replace cement is effective for the improvement of concrete properties.

The paper presents the results of a laboratory investigation into the effects of subjecting concretes (made from OPC and blends of OPC and slag) to adiabatic temperature cycles. The adiabatic cycle is similar to that which concrete at the centre of a large mass would undergo during the first few days after placing. Concretes with two different cement contents (300, 450 kg/m3) were made with slag replacement levels of 50% and 70% by mass of cementitious material. The properties investigated were: adiabatic temperature rise, compressive and tensile strength development and modulus of elasticity. Tests were carried out at ages between 1 day and 6 months.

Blast-furnace slags cooled at different rates were used to study the effect of fineness, mixing method and content of slag on the strength development of blended-slag mortar. Test results indicated that the strength development of air-cooled slag was better than expected, even though it was less effective than that of water quenched. When the intergrinding method was compared with the separate batching method, the latter needs a longer mixing time to reach a comparable quality. The slump and bleeding were reduced as the amount of slag increased at low water to cementitious mix ratio. Alkali activated the reaction of slag. However, excessive alkali might cause flash setting of the fresh mortar. The diffusion process seemed to govern the cementitious reaction of slag and which, in turn, tended to retard the hydra-tion of cement. Therefore, the optimum slag content depended upon the age of cement mortar.

This paper describes a study of the full exploitation of the inherent hydraulic behavior of granulated blast-furnace slag. An attempt was made by laboratory tests and by actual concrete practices to improve the properties of conventional slag cements and develop a high quality binder. Granulated blast-furnace slag pulverized and classified by an industrial mill (Blaine fineness 850 m2/kg> was mixed with ordinary portland cement and semi-crushed granulated blast-furnace slag sand aggregate with the addition of a high-range water-reducing admixture. Workability, strength, and resistance to freezing and thawing cycles, mechanical abrasion and chemical attacks were determined. Microstructures were measured by SEM, and mercury intrusion and nitrogen adsorption porosimetries. Major findings of the research include: 1 . Workable mixtures with ultra-highly pulverized blast-furnace slag can be obtained with the addition of high-range water-reducing admixtures (HRWRA) and have less bleeding. 2. Use of ultra-highly pulverized blast-furnace slag is effective in getting a very dense and uniform structure of the hydrated paste and shows superior characteristics with high-strength concrete having more than 100 MPa, as compared to the straight portland cement high-strength concrete. 3. Densification and reduced calcium hydroxide caused by the hydration of slag remarkably improve the resistance to acid and sulfate attack as well as other characters.