International Concrete Abstracts Portal

High strength lightweight aggregate concretes are usually produced using special artificial aggregates together with mineral and chemical admixtures. Using natural lightweight aggregates instead of processed artificial aggregates can significantly reduce cost of such concretes. Turkey has rich reserves of volcanic tuff and pumice stones. In Turkish standards highest strength classes for lightweight tuff and pumice concretes are 30 and 16 MPa, respectively. In this research selected samples of these lightweight rocks were used to produce high strength lightweight aggregate concretes. The binding medium was made of portland cement, silica fume and superplasticizing admixture. For each concrete mixture properties such as workability, unit weight, compressive strength at various ages, as well as splitting tensile strength, modulus of elasticity and thermal conductivity values were determined to find the optimum quantities of materials to be used. Tests show that it is possible to produce a natural lightweight aggregate concrete with a 28-day compressive strength of 55 MPa, a dry unit weight in the range of 1700-2100 kg/m3 and coefficient of thermal conductivity value of about 0.55 W/m2 K. Mathematical equations based on experimental results were obtained by regression analyses. The equations are useful for optimizing concrete mixtures for specified unit weight and compressive strength.

As part of a comprehensive research project on the durability of on and offshore concrete structures in the Persian Gulf, a simulation laboratory has been made use of. The present study consists mainly of nine month exposure tests in the tidal and atmospheric zone conditions in the laboratory. Concrete specimens containing different supplementary materials, namely; silica fume, blast - furnace slag, diatomous earth and trass, have been thoroughly investigated. The tests conducted include, compressive strength, volume changes, half cell potentials, carbonation, and chloride diffusion, all at different ages. With respect to the alternate cycles of wetting and drying the superior preformance of silica fume was followed by the diatomous earth pozzolan. However all concrete mixtures containing natural and artificial pozzolans showed better performance when compared with the plain portland cement control concrete mixtures.

The purpose of this study was to determine the water permeability of high slag content concrete(HSCC) incorporating large amounts of ground granulated blast-furnace slag (GGBS) of high fineness. The main variables are the replacement level of slag, the fineness of slag and the type of chemical admixtures. The slag content in cement ranged from 0 to 95 percent by weight of total cementitious materials and the fineness of slag ranged from 404 to 1200 m2 /kg. Within the range of this study, the following results were obtained: 1 . The coefficient of water permeability of high slag content (HSC) concrete increased as the content of ground granulated blast-furnace slag(GGBS) was increased. However the water tightness of HSC concretes could be improved by utilizing high fineness slag within the range of 1200 m2/kg, and was further improved by utilizing an air entraining and high range water reducing (AEHW) admixture. 2. Both the total porosity and mean diameter of pores increased by raising the slag content, but decreased as the fineness of slag increased. The water permeability of HSC concretes was closely related to the porosity, with the diameter over the certain threshold value, rather than to the mean diameter of pores.

Effect and mechanism of natural zeolite(NZ) on preventing expansion due to ASR are studied in this paper. The reduction of deleterious expansion by NZ is compared with that of three other cementitious materials: silica fume(SF), fly ash(FA), and blast-fhrnace slag(BFS). The order of effectiveness is SF>NZ>FA>BFS. When 30% zeolite blended cement with an alkali content of 1.82% NazO equivalent is used in concrete, there will be no damage from ASR even ifall the aggregates are reactive. The suppression of ASR by NZ is related to its fineness. The required dosage of NZ is about 20% at a surface area of 7000 cm2/g, and decreases to 15% at 9000 cm’lg with the same effect. Pre-heating of NZ at 500 ‘C increases the preventive effectiveness. The suppressing mechanism of NZ on ASR is decreasing the alkali ion concentration in the pore solution in concrete through ion exchange, adsorption, and pozzolanic reaction of NZ. So the formation of alkali silicate is prevented and the interface is improved.

SP-178 This Symposium Publication contains the proceedings of the Fourth CANMET/ACI/JCI International Conference held in Tokushima, Japan, in June 1998. Sixty-two refereed papers were accepted for presentation at this conference and for this publication.