International Concrete Abstracts Portal

In order to reduce the density for load bearing structural members and to improve the strength properties a new binder matrix has been investigated (1, 2). The binder matrix is composed of cement, variable amounts of condensed silica fume, high range water reducer and air entraining agent. The use of heavy duty grade expanded clay as lightweight aggregate in combination with artificially introduced air voids in the concrete was found to be ad-vantageous. With these combinations it was possible to attain an air content up to 40 % of the concrete volume and density / com-pressive strength values ranging from 1.1 t/m3 / 10 MPa to 1.8t/m3 60 MPa. The main properties of such lightweight concrete were investigated including strength and density, bond of embedded steel, modulus of elasticity and length change. In this paper the main results are presented and discussed. It can be concluded that cement-condensed silica fume blends can be used for the production of low density high strength lightweight concrete for structural use.

A low heat of hydration blended cement for structural applications has been developed. This cement is composed of 50 percent of a Canadian cement, CSA Type 20, (ASTM Type II), 35 percent of a slowly reactive slag, and 15 percent of condensed silica fume. The heat of hydration measured at 20°C of this blended cement is 30 percent lower than that of the pure Type 20 cement whereas the 28 d compressive strength of standard mortars is about the same. The peak temperature of an insulated mass of concrete having a 28 d compressive strength of 30 MPa is reduced from 44.4°C to 34.4°C when using this composition instead of the Type 20 cement. A microstruc tural study has shown th at when using this blended cement the CSH formed is ve ry dense and amorpho us-like.

Early-age strength development of concrete in which part of the portland cement has been replaced by low-calcium fly ash tends to be slow, because fly ash acts as a relatively inert component during this period of hydration, though at later ages it contributes significantly to strength development. It was considered that the problem of low early-age strength of portland cement-fly ash concrete could be overcome by the incorporation of small amounts of condensed silica fume, a very fine and more rapidly reactive pozzolan. This report presents the results of an investigation on the early-age strength development of concrete incorporating 30% low-calcium fly ash, and to which small amounts of condensed silica fume have been added. The amounts of the fume ranged from 0 to 20% by combined weight of the portland cement plus fly ash. A total of thirty 0.06-m3 concrete mixtures with water-(cement + fly ash) ratios ranging from 0.40 to 0.80 were made; 240 cylinders were tested in compression and 180 prisms were tested in flexure. A supplementary series of six concrete mixtures was made to deter-mine the effect of silica fume and fly ash on the long-term strength development of concrete. Test data showed that the incorporation of condensed silica fume increased the compressive strength of concrete at all ages as compared with the compressive strength of the control concrete (70% portland cement + 30% fly ash). At 7 days, the loss of compressive strength due to the partial replacement of cement by fly ash was completely overcome by the addition of 10% condensed silica fume for concretes with water-(cement + fly ash) ratios ranging from 0.40 to 0.60; 15 to 20% was required for concretes with higher water-(cement + fly ash) ratios, At 28 days, regardless of the water-(cement + fly ash) ratio, the effect was generally achieved with less than 5% silica fume addition. The laterage strength development of portland cement-fly ash concrete did not appear to be impaired by the use of condensed silica fume indicating availability of sufficient lime for the fly ash pozzolanic activity.

SP79 It's a virtual encyclopedia of what mineral by-products do to concrete--and why. 1196 pages of essential information in 62 clearly defined, easy reference chapters. Key subjects include: effects on durability, fiber reinforced concrete, fly ash, pozzolans, sulfate resistance and concrete workability. With the rapidly increasing usage of by-product additives in concrete, every designer and builder needs the answers which these volumes provide.

Granulated blast furnace slag and low-calcium fly ashes have long been used as portland cement additives or as mineral ad-mixtures in concrete. With the addition of high-calcium fly ash, rice husk ash, and condensed silica fume to the list of traditional mineral admixtures, a scientific approach for characterization and evaluation of all industrial byproducts which are suitable for use as admixtures in concete is needed. Since it is not the source of origin or the chemical composition of a mineral admixture but the mineralogical composition and particle characteristics which determine its contribution to concrete behavior, in this review the entire area is treated as a unified discipline. This approach seems to provide a better basis for explaining the similarities and differences in behavior between mineral admixtures originating from either the same or different sources. Mineralogical compositions, particle characteristics, current production rates, and utilization of major pozzolanic and industrial byproducts available in the United States and Canada are included. Mechanisms by which the use of these byproducts in portland cement concrete can improve engineering properties are discussed, and examples of data from field and laboratory investigations are given.