Silica fume

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

Dispersion of Short Fibers in Cement

Abstract: The degree of dispersion of short microfibers in cement, as assessed by electrical resistivity measurement for the case of electrically conductive fibers at a volume fraction below the percolation threshold, is improved by the use of admixtures (namely, silica fume, acrylic particle dispersion, methylcellulose solution, and silane) and fiber surface treatment (such as ozone treatment). Acrylic particle dispersion is more effective than latex particle dispersion.

Precast, prestressed pedestrian bridge : World's first Reactive Powder Concrete structure

Abstract: Spanning 197 ft (60 m), this precast, prestressed pedestrian/bikeway bridge in Sherbrooke, Quebec, is a post-tensioned open-web space truss containing no conventional steel reinforcement. Made up of six prefabricated match-cast segments, it was manufactured using Reactive Powder Concrete (RPC), a cement based material proportioned with sand, cement, and powders of silica fume (microsilica), and quartz, with fine steel fibers added to enhance ductility. In the top and bottom chord member, the RPC has a compressive strength of 29,000 psi (200 MPa). For the web member diagonals, RPC was confined in stainless steel tubes, attaining improved ductility and a compressive strength of 50,000 psi (350 MPa). An extensive program monitoring bridge deflections and forces in the prestressing tendons has been implemented to provide information on long-term performance of RPC.

Analysis of calcium leaching behavior of plain and modified cement pastes in pure water

Abstract: The calcium ion leaching behavior of cement pastes modified with a high-alkali fine glass powder, silica fume, and fly ash, exposed to deionized water, is reported in this paper. Porosity enhancement in pastes subjected to leaching is attributed both to the dissolution of calcium hydroxide (CH) as well as decalcification of C–S–H gel. A methodology that combines the measured porosity increase along with the CH and C–S–H contents remaining after leaching for a particular duration is developed to separate the porosities created due to CH and C–S–H leaching. In order to quantify the influence of leaching on the amounts of Ca ions remaining in the CH and C–S–H phases, solid–liquid equilibrium curves for calcium are developed for the unleached and leached pastes. Leaching depths are also calculated using the CH contents of the leached and unleached specimens. All the modified pastes show better leaching resistance than the plain paste. In addition to the microstructure densification, the lower Ca–Si molar ratio in modified pastes that reduces the equilibrium liquid Ca ion concentration contributes to this observation. For the glass powder modified paste, the presence of higher alkali content in the pore solution further reduces the dissolution of CH due to common ion effect, thus providing it with the highest leaching resistance. Fly ash and silica fume modified pastes demonstrate leaching resistance in between those of the plain and glass powder modified mixtures.

Pozzolanic properties of fine and coarse color-mixed glass cullet

Abstract: Mixed glasses of different colors are economically difficult to reuse for the fabrication of new glass products but their use in cement-based materials is a promising way to recycle this material. This paper deals with the pozzolanic activity of mixed glass cullet, by evaluating the pozzolanic behavior of a large range of glass particle sizes, from less than 40 μm (540 m2/kg) up to 2.5 mm (2.2 m2/kg). Five different classes of glass are assessed separately, in terms of compressive strength tests on mortars, consumption of lime (TG), morphology (SEM) and composition of hydrates (EDX and X-ray fluorescence). The results show that the pozzolanic activity increases with glass fineness and that, compared to a reference material without glass, equivalent or superior compressive strength can be obtained when using up to 40% of glass of 540 m2/kg fineness. A transition fineness around 30 m2/kg (140 μm) is highlighted, for which the pozzolanic activity becomes substantial. However, a slight but significant pozzolanic activity is detected for coarse particles (>1 mm), as confirmed by the consumption of Ca(OH)2, the formation of C–S–H-like hydrates and an increase of 10% (5 MPa) in the compressive strength compared to an inert admixture. The chronology of the reaction (pozzolanic and alkali-reactive) for coarse glass particles is discussed.