Silica fume

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

Chemical activation of calcium aluminate cement composites cured at elevated temperature

Abstract: The influence of sodium sulfate, as an activator, on the hydration of calcium aluminate cement (CAC)–fly ash (FA)–silica fume (SF) composites was investigated. Different mixes of CAC with 20% pozzolans (20% FA, 20% SF and 10% FA + 10% SF) were prepared and hydrated at 38 °C for up to 28 days. The hydration products were investigated by XRD, DSC and SEM. The results showed that sodium sulfate accelerated the hydration reactions of calcium aluminate cement as well as the reactions of FA and SF with CAH10 and C2AH8 to form the stratlingite (C2ASH8). The later reactions prevent the strength loss by preventing the conversion of CAH10 and C2AH8 to the cubic C3AH6 phase. The acceleration effect of Na2SO4 on the reactivity of fly ash was more pronounced than on the reactivity of silica fume with respect to reaction with CAH10 and C2AH8 phases.

Powder Additions to Mitigate Retardation in High-Volume Fly Ash Mixtures

Abstract: This article describes how high-volume fly ash (HVFA) concrete mixtures are attractive from a sustainability viewpoint, they are sometimes plagued by long delays in finishing, producing a performance that is unacceptable to contractors. Isothermal calorimetry studies are conducted to examine excessive retardation in HVFA mixtures based on both Class C and Class F fly ash. In addition to quantifying the retardation, the calorimetric curves are also used to evaluate the performance of mitigation strategies based on various powder additions. Powder additions examined in the present study include an aluminum trihydroxide, calcium hydroxide, cement kiln dust, condensed silica fume, limestone, and a rapid-set cement. The addition of either 5% calcium hydroxide or 10% of the rapid-set cement by mass of total solids (powders) is observed to provide a significant reduction in the retardation measured in mixtures based on either class of fly ash for the material combinations examined in this study. Thus, these two powder additions may provide viable solutions to mitigating excessive retardation, extending the use of HVFA mixtures in practice.

Properties of silica fume concrete and mortar

Abstract: The properties of silica fume concrete was studied. Various properties of silica fume cocnrete, including slump, air-content, compressive strength, flexural strength, permeability, and permeable void volume were investigated, and the effect of the silica fume replacement ratio of cement is described. The effects of aggregate content and graduation, water-binder (cement plus silica fume), and superplasticizer dosage rate also are discussed. In this investigation, silica fume-binder ratios ranged from 0.00 to 0.40, water binder ratios from 0.41 to 0.47, aggregate binder ratios from 1.0 to 4.0, and superplasticizer binder ratios from 0.01 to 0.05.

Ultrasound monitoring of setting and hardening process of ultra-high performance cementitious materials

Abstract: A novel specially designed ultrasonic monitoring apparatus (UMA) for in-situ continuous studying of the early age hydration process of cementitious materials was developed. Utilizing UMA, the early microstructure formation process was systematically investigated for ultra-high performance cementitious materials made with various mineral admixtures (fly ash, slag and silica fume), fine and coarse aggregates, different volume fraction of steel fiber (0, 1%, 2% and 3%). The influence of curing temperature (20, 40, 60, 80 and 90 °C) was also studied. The results show that four stages can be clearly identified during the microstructure formation process of ultra-high performance cementitious materials with sand, aggregate or steel fiber: pre-dormant stage, dormant stage, acceleration stage, and deceleration stage, while only the last three stages occur for the one without fillers and reinforcement. Curing temperature, mineral admixtures, fillers and reinforcement addition have great impact on microstructure formation process. Hydration reaction rate is obviously promoted with an increase in curing temperature. Silica fume addition also accelerates the microstructure formation, while the reverse phenomenon is observed when fly ash and slag are incorporated. Steel fiber addition retards the microstructure formation, especially in high volume fraction of fiber.