Silica fume

About: Silica fume is a research topic. Over the lifetime, 10177 publications have been published within this topic receiving 173857 citations.

Densified silica fume: particle sizes and dispersion in concrete

Abstract: Dry densified silica fume is by far the most common form of silica fume used in current concrete practice; the alternative, slurried silica fume has become unavailable in many places. Densified silica fume as commonly supplied consists of particles of sizes up to several millimeters, which are generally not dispersable into individual silica fume spheres. Densified silica fumes from some sources can be dispersed by moderate ultrasonic treatment into small clusters or chains of spheres; others resist such treatment and mostly remain as large agglomerates. Under conventional concrete mixing, substantial contents of agglomerates almost always remain in the concrete. Thus the assumption that the densification process is somehow ‘reversible’ is not generally warranted. The sizes of undispersed agglomerates remaining in concrete after mixing often exceed the sizes of Portland cement particles, thus limiting any potential benefits attributed to the fine particle filler effect. Large undispersed grains appear to always undergo chemical reaction in concrete, but such reactions may induce ASR damage only under especially unfavorable circumstances.

Mechanical properties and frost resistance of silica fume concrete

Abstract: Freeze-thaw tests were carried out on air-entrained and non-air-entrained concrete prisms containing different dosages of condensed silica fume (CSF). Six concrete mixes were made incorporating 0, 5 and 10% CSF as partial replacements for OPC. The performance of the concrete prisms exposed to 210 cycles of freezing and thawing was assessed from weight, length, resonance frequency and pulse velocity measurements of the test specimens before and after freezing and thawing. Tests were also conducted to determine the compressive and flexural strengths and the static modulus of elasticity. Although the control concrete gave better durability factors (92%) than those obtained for the CSF concrete (85%), the physical appearance of the CSF prisms exhibited less scaling.

Phase Composition of Hydrated DSP Cement Pastes

Abstract: Cement pastes densified with small particles (DSP) containing up to 48% silica fume by weight of cement, and hydrated to up to 180 d at room temperature, have been analyzed using TMS-GPC, TGA, and 29 Si NMR to quantitatively estimate the amount of unreacted cement, Ca(OH) 2 , and residual silica fume, respectively. Using a mass balance approach, the CaO/SiO 2 and H 2 O/SiO 2 molar ratios of the C-S-H in the samples were calculated. For samples containing silica fume, the values of CaO/SiO 2 lie between 0.9 and 1.3, depending on the degree of hydration and silica fume content, whereas for samples without silica fume they were 1.6. Silicate polymerization analysis using TMS-GPC suggests that the molecular structure of the C-S-H is similar to that formed in conventional hydration. No cross-linking species were found, but the fraction of higher polymers (above octamer) increases as the CaO/SiO 2 ratio decreases