International Concrete Abstracts Portal

The increasing construction of high-rise buildings in recent years had led to a demand for lightweight, high-strength concrete. In this study, the compositions of the matrix and the air void structure of aerated mortar containing silica fume were investigated as the basis for manufacturing lightweight, high-strength concrete. Mortars made with cement containing silica fume and fine or ultra-fine silica stone powder, having a particle size between that of cement and silica fume, were tested; the properties of cement paste in fresh and hardened conditions were improved. The compressive strength and the air void structure of prefoamed aerated mortars were determined and their relationship studied. Based on the results, it was confirmed that lightweight, high-strength concrete could be made with an effective combination of aerated mortar containing silica fume and lightweight coarse aggregate.

Ferrocement is a form of reinforced concrete using closely spaced multiple layers of mesh and/or small-diameter rods completely infiltrated with, or encapsulated in, mortar. The presence of wire mesh reinforcement in ferrocement improves crack resistance, ultimate strength, and toughness. In recent years, due to increased awareness of the need for conservation of non- renewable tropical forest resources, increased consideration is being given to the use of ferrocement as a substitute for wood. In this paper, mechanical properties of thin ferrocement plates (10-mm thickness) made of cement mortar mixed with silica fume as a matrix and two kinds of wire mesh as reinforcement were investigated. The effects of the reinforcement arrangements on strength and deformational characteristics of ferrocement in direct tension and simple bending were studied experimentally. Test results indicate that ferrocement containing silica fume has higher workability and did not segregate in fresh state. The tests show higher ultimate strength, as well as toughness, compared with the normal ferrocement.

The first two abrasion-erosion concrete repair projects in the United States that used silica fume (SF) concrete started in 1983. One was the stilling basin rehabilitation of the Kinzua Dam, in northwestern Pennsylvania. The other was the Los Angeles River low-flow channel rehabilitation project (completed in 1985). The first known application of SF concrete (SFC) addressing cavitation resistance occurred in 1985, also at the Kinzua Dam, but for a sluice repair. This paper largely summarizes long term performance information relating to the 1983 to 1985 SFC placements. Other, more recent, SFC projects in which abrasion-erosion or cavitation was a concern are mentioned. Also presented are two mixtures featuring portland cement with ground granulated blast furnace slag and SF that were recently used in a very severe environment. Overall, after up to 10-1/2 years in service, the various SFCs are performing very well. The 1983 Kinzua Dam stilling basin SFC wear after 10-1/2 years is only a small fraction of that seen in previously utilized concretes. For the Los Angeles River SFCs, all of the three different SFC mixtures that were employed are performing comparably as of March 1994. Overall erosion was uniform and to an estimated 4 to 12 mm depth. The 1985 Kinzua Dam sluice repair concrete showed no evidence of cavitation damage by 1994.

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.