International Concrete Abstracts Portal

Fly Ash, Silica Fume, Slag, and Natural Pozzolans in Concrete: Proceedings of the Third International Conference presents the latest technological advances in the use of these extremely valuable mineral by products. This two-volume set of 83 papers explores in detail how you can conserve energy and resource while increasing your profitability. The first volume contains papers dealing with fly ash and natural pozzolans, and the second volume details the use of condensed silica fume and ferrous and non-ferrous slags. Note: The individual papers are also available as .pdf downloads.. Please click on the following link to view the papers available, or call 248.848.3800 to order. SP114

Many marine and hydraulic structures must be constructed and repaired while submerged under water. Frequently, this requires placement of relatively thin (0.5 m or less) layers of concrete to fill voids in exposed surfaces or submerged formwork. Concretes placed underwater should flow readily and with little segregation and resist erosion from underwater currents. The hardened concrete should achieve excellent adhesion to underlying surfaces and develop high strengths. To achieve the desired performance, the concrete should contain a moderate amount of anti-washout admixture, a cement content of approximately 350 kg/m3, 25 kg/m3 of silica fume to enhance durability, and 18 kg/m3 fly ash to improve workability of the fresh concrete. A hard, natural gravel, representing approximately 54 percent of the aggregate content, should be used for wear resistance, and with the lowest possible w/c (0.41 ñ 0.03, typically) consistent with placement requirements, to maintain strengths. Prior to the actual field placement, several rheological and mechanical properties should be determined to insure proper placability, homogeneity, and therefore increase the success probability and cost effectiveness of site trials and subsequent actual field placements.

Blast furnace slags and pulverized fly ash have been used extensively as additives to ordinary portland cement (OPC) to make low-permeability pastes with adequate long-term strengths. These properties are a consequence of phase development in the matrix that proceeds nonuniformly because the OPC clinker and blending agent react at different rates. Also, sheaths of hydration products forming around anhydrous grains inhibit reaction. This complicates our interpretation of the properties of blended cement systems because phases observed as products on laboratory time scales are not necessarily representative of the steady state assemblages. The aqueous chemistry is also subject to time-dependent changes since solution composition is related to that of the coexisting solids. In some applications, it is necessary to predict long-term physicochemical properties. This can be achieved through modeling, based on sound scientific principles, and using as much information as realistic from immature systems. Paper describes progress in model development and verification.

Traditionally, the utilization of granulated blast-furnace slag (BFS) is based on activation with alkalies released from the hydration of portland cements (PC). In Finland, a special type of alkaline admixture was introduced some years ago for activation of BFS. In the present paper, some experiences based on the activation of a Norwegian BFS with this admixture are reported. To investigate the hydraulicity of the slag, the slag was ground to three different levels of Blaine fineness (420, 540, and 640 mý/kg) and hydrated at five different levels of curing temperature (20 to 60 C). For comparison, a Finnish slag and a Norwegian blended portland cement with 10 percent fly ash were also included in the test program. The test results demonstrate that increasing curing temperature and fineness of the slag significantly accelerate the strength development (more so at early ages than later on). Thus, at 60 C the slag with 640 mý/kg of fineness and a water-cement ratio of 0.33 reached a compressive strength of approximately 40 MPa after a curing period of 4 hr. After a curing period of 72 hr, the heat of hydration of the slag cements was only about 60 percent of that of the modified portland cement.

Presents results of research work on the evaluation of physical-chemical properties of fly ashes and their influence on physical and mechanical properties of cement mortars. Two types of fly ash were examined: a low-calcium and a high-calcium. Variability of chemical composition with grain size of the fly ashes was analyzed. When testing the influence of physical and mechanical activation (fly ash grinding process) on hydraulic activity of the two types of fly ash, it was found that grinding had an activating effect on the high-calcium fly ash. Consequently, cements containing ground high-calcium fly ash were comparable in strength to pure portland cement. The main factor affecting strength properties was the formation of ettringite and its stabilization in the structure of hardened mortars and pastes.