International Concrete Abstracts Portal

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.

Because of increasing annual production volumes of fly ash, large volume applications, such as aggregate production, are beneficial in solving the disposal problem of fly ash while making economical use of a mineral resource. Aggregates have been produced from high calcium fly ash of Soma Thermal Power Plant and their engineering properties measured. For high volume utilization of fly ash, aggregate production involving pelletization and pressing into specially designed molds has been carried out successfully. Mechanical property and durability tests were conducted on the cured lightweight fly ash aggregates; five percent by weight lime addition to fly ash showed the best performance. It was also shown that different shapes of aggregates can be produced using the pressing technique.

Presents results of five-year exposure tests on the long term properties of concretes containing fly ash (FA), blast furnace slag (BFS), and silica fume (SF). Four kinds of concretes with and without a mineral admixture (OPC concrete, FA 30 percent concrete, BFS 50 percent concrete, and SF 10 percent concrete) were prepared. After 28 days of initial curing, they were exposed to different environments for five years. Compressive strength, pulse velocity, depth of carbonation, and chloride ion penetration of concrete were determined at various intervals of exposure time. From the results, it was found that under the indoor exposure condition, influences of initial curing conditions on the long term strength development of concrete were especially pronounced for FA 30 percent concrete and BFS 50 percent concrete, but that under the outdoor exposure conditions, its influence was considerably reduced due to the supply of rainfall during the outdoor exposure. On the other hand, SF 10 percent concretes showed some reduction in compressive strength when they were initially cured in water for seven days and then continuously air-dried indoors for a long period. The depth of carbonation of BFS 50 percent concrete and FA 30 percent concrete was much greater than that of the corresponding OPC concrete and SF 10 percent concrete when they were exposed indoors or outdoors for five years. Furthermore, all mineral admixtures used in this study were found to be equally efficient in preventing chloride ions from intruding into concretes under a marine environment.

It is necessary for concrete engineers to get more information on the ion movement through and in concrete for the development of new technologies, such as cathodic protection, desalination, and re-alkalization for reinforced concrete members. In concrete members with these treatments, various ions should be moved through and in concrete members. The movement of ions could influence concrete properties and steel reinforcing bars. Ground granulated blast furnace slag, fly ash, and silica fume have been recognized as high quality mineral admixtures for concrete. Since structures built with these materials might eventually be subjected to electro-migration processes, a set of experiments to assess the effects of these pozzolans were devised. In this study, considering the conditions mentioned above, the movement of several kinds of ions through hardened mortar with mineral admixtures was investigated. As ions, Na +, K +, and Cl - were selected because the ions were closely related to alkali-aggregate reaction or chloride attack. As mineral admixtures, ground granulated blast furnace slag, fly ash, and silica fume were used. Also, the influences of water-to-binder ratio on the movement of ions were investigated. Electrochemical cells were used for the experimental work; the current was applied to a cell in the range between 0.1 A/m 2 and 10.0 A/m 2. Analyzing the data from the experimental work, the following conclusions were obtained. 1. The electromigration of ions through mortar are reduced with the addition of admixtures. 2. The electromigration of ions increases with the water-to-binder ratio. 3. The electromigration of ions is closely related to the pore size distribution of mortar and paste.