International Concrete Abstracts Portal

A rapid-hardening cement was made by blending mixtures of high- alumina cement (HAC) and ground granulated blast furnace slag (GGBS). The addition of slag alters the course of hydration reactions in HAC. A chemical compound 2CaO.Al 2O 3.SiO 2.8H 2O (gehlenite hydrate or stratlingite), only seen in plain HAC in small amounts, readily forms and becomes the main stable hydrate in the blended cement concretes in the temperature range of 5 to 38 C, replacing the metastable hydrates which lead to loss of strength in HAC through the conversion reaction. The properties of mortars and concretes made with this cement were assessed in a series of durability studies carried out by the Building Research Establishment. Mortars made with the blend have shown excellent sulfate resistance. Concrete specimens were compared with those from HAC concretes of similar proportions, following exposure for two years in aggressive sulfate, marine, and soft acid water environments. The findings, at this relatively early stage, are very encouraging. Longer term tests will be carried out at five and 10 years. Concretes made with the blend have shown a greater tolerance of high water-cement ratio mixtures in forming stable products with reduced temperature rises and enhanced durability in terms of their excellent sulfate, seawater, and soft acid water resistance.

The use of blast furnace slag aggregate (BFSA) is not new, but its application in the production of high-performance concrete (HPC) is nonexistent at least, in Australia. This paper presents the results of a preliminary optimization of the high-strength concretes made using BFSA, normal sand, portland cement, ground granulated blast furnace slag (GGBFS), condensed silica fume (CSF), and a proprietary superplasticizer. The paper also describes some additional characteristics of the optimized concretes. In all, 15 types of concretes were made. The properties examined were workability, density, compressive strength, elastic modulus, shrinkage, and water penetration. The maximum strength achieved using the slag aggregate was 107 MPa, which placed the slag aggregate concrete well into the very high strength range of concretes. The workability was found to be unaffected by the use of the slag aggregate. The tensile strength of the concrete was relatively high (5.4 Mpa); the shrinkage was found to be lower than concretes produced with normal aggregates, as was the water penetration and absorption. Of particular importance, the elastic modulus was found to be markedly lower than that of concretes made with normal aggregates. It is concluded that the slag aggregate can be used successfully in the production of high-performance, high-strength concrete.

Describes chemical attack caused by a high concentration CaCl 2 solution and its preventive measures by the addition of a mineral admixture. Changes which occur in mechanical strengths and chemical properties in mortars with and without fly ash, blast furnace slag, and silica fume when immersed in a 30 percent CaCl 2 solution at different temperatures were investigated. Portland cement mortars seriously deteriorated at early ages of exposure to a high concentration CaCl 2 solution, its deterioration being associated with cracking and spalling on the surfaces of specimens. On the other hand, 10 percent silica fume and 50 percent blast furnace slag mortars showed a good resistance to calcium chloride attack, although 30 percent fly ash mortars slightly deteriorated at late ages of exposure. X-ray diffraction and differential thermal analysis indicated that the deterioration of portland cement mortars cause by the chemical attack of a high concentration CaCl 2 solution was attributed primarily to both the dissolution of calcium hydroxide and the simultaneous formation of a complex salt in the mortar. Thus, the combined effect of a decrease in calcium hydroxide content and a reduced chloride ion permeability by the addition of a mineral admixture effectively improved the resistance of mortar to calcium chloride attack.

Describes test results obtained on the heat of hydration, strength development, hydration products, pore structure, and combined water of blended cements with high fineness and large amounts of ground granulated blast furnace slag (GGBS) and discusses the relationship between them, comparing them with ordinary portland cement (OPC) and blended cement with smaller amounts of GGBS. The following conclusions were drawn from this study. 1. The heat of hydration of blended cement with over 70 percent content of GGBS reduces significantly. The blended cement incorporating a large amount of GGBS with high fineness can have the properties of lower heat of hydration and relatively high compressive strength required for massive concrete generally used in Japan. 2. The blended cement with high fineness and high content of GGBS results in a more compact pore structure than OPC due to the formation of finer hydration products.

In Japan, the use of blast furnace slag is a specified measure for reducing alkali-silica reaction (ASR) expansion in concrete. Most of the studies on the effect of blast furnace slag on reducing ASR expansion have been carried out with mortar tests; few studies have been carried out on the relationship between expansions in mortar and concrete. The studies on concrete containing different contents of reactive aggregate and blast furnace slag have been very limited. A proper method for estimating the effect of slag on reducing expansion has not been established. In this study, the expansion characteristics of mortar made using reactive aggregate and slag cement and the effect of replacement of portland cement by slag to reduce the expansion of concrete due to ASR were investigated. The effect of blast furnace slag for reducing expansion due to ASR is described from the viewpoint of dilution, stabilization, and immobilization of alkali. The pessimum conditions of expansion in concrete containing different reactive aggregate contents were studied. The expansion of concrete with 100 percent reactive fine aggregate was the largest. In addition, in the concrete with 100 percent reactive coarse aggregate and 50 percent slag, the limit value of total alkali content was estimated, as 8.0 kg/m 3 without considering the alkali content in slag, and as 9.0 kg/m 3 when the alkali content in slag is taken into consideration.