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Silica fume
About: Silica fume is a research topic. Over the lifetime, 10177 publications have been published within this topic receiving 173857 citations.
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TL;DR: In this paper, the effect of silica fume on bond and anchorage characteristics of reinforcing bars in high performance concrete was investigated and the validity of the upper limit of 70 MPa (10,000 psi) imposed by the American Concrete Institute (ACI) Building Code 318-95 on the concrete compressive strength for determination of development length was evaluated.
Abstract: Little research is reported in the literature on the effect of pozzolans such as silica fume on structural behavior of reinforced concrete, namely on bond and anchorage characteristics of reinforcing bars in concrete. The objectives of the study were to investigate the effect of silica fume on bond and anchorage characteristics of reinforcing bars in high performance concrete, to study the validity of the upper limit of 70 MPa (10,000 psi) imposed by the American Concrete Institute (ACI) Building Code 318-95 on the concrete compressive strength for determination of development length, and to evaluate the reliability of the empirical equation of Orangun, Jirsa, and Breen in estimating the bond strength of deformed bars embedded in high strength concrete. Sixteen beam specimens were tested. Each beam was designed to include two bars in tension, spliced at the center of the span. The splice length was selected so that bars would fail in bond, splitting the concrete cover in the splice region, before reaching the yield point. The beams were loaded in positive bending with the splice in a constant moment region. The variables used were the percentage replacement by weight of cement by silica fume, casting position, and the superplasticizer dosage. Test results indicated that replacement of 5-20% of the cement by an equal weight of silica fume resulted in an average 10% reduction in bond strength regardless of casting position or the superplasticizer dosage used.
64 citations
TL;DR: In this paper, three mineral admixtures, namely blast furnace slag, silica fume and metakaolin, were used to synthesize binary alkali activated binders whose major volumetric fraction was waste fly ash.
Abstract: Waste fly ash, referred in literature also as “weathered”, represents a major management issue for coal-fired power plants. The low qualification of this relevant fraction of produced fly ash is not adequate for recycling in structural concrete. Non-structural applications may represent an economically feasible solution to maximize the recovery of coal fly ash from power plants. A potentially valuable recycling track may be represented by alkaline activation for the production of sustainable precast elements based on geopolymeric binders. In this work, three mineral admixtures, namely blast furnace slag, silica fume and metakaolin, were used to synthesize binary alkali activated binders whose major volumetric fraction was waste fly ash. Three curing temperatures (20, 40, 60 °C) were also considered. Early age kinetics and properties development were assessed by means of strength development and ultrasonic pulse velocity. Residual compressive strength after exposure at high temperature was also assessed in order to highlight typical geopolymeric thermal resistance which is generally observed for higher value raw materials. Furthermore, microstructural analysis was carried out by means of scanning electron microscopy. Silica fume exhibited an increasing detrimental effect (formation of agglomerates/partial foaming) with early age curing temperature, while blast furnace slag and metakaolin revealed to be effective admixtures without strict need of higher curing temperatures.
64 citations
31 Mar 2021
64 citations
TL;DR: In this article, the results indicated that the water permeability coefficient and connected porosity decreased as the amount of binder used increased and increased with increasing aggregate size, while the compressive, splitting tensile, and flexural strength increased as binder usage increased and decreased with the increase of aggregate size.
Abstract: Specimens were prepared by altering parameters such as aggregate sizes, binder materials, and the amounts of binder used and were subsequently tested by using permeability, porosity, mechanical strength, and soundness tests. The results indicated that the water permeability coefficient and connected porosity decreased as the amount of binder used increased and increased with increasing aggregate size. In the mechanical strength test, the compressive, splitting tensile, and flexural strengths increased as the amount of binder used increased and decreased with the increase of aggregate size. Highly viscous binder enhanced compressive strength, water permeability, and the resistance to sulfate attacks. In the mechanics and sulfate soundness tests, the mix proportion of alkali-activated slag paste used in this study exhibited a superior performance than the Portland cement pervious concrete (the control) did, but the difference in water permeability between the two types of concrete was insignificant. The mix proportions of cement paste containing 20% and 30% silica fume exhibited less mechanical strength than the control did. Moreover, compared with the control, the cement paste containing silica fume demonstrated poor resistance to sulfate attacks, and the difference in the water permeability between such specimen and the control was not noticeable.
64 citations