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Silica fume particles viewed in a transmission electron microscope. Silica fume, also known as microsilica, (CAS number 69012-64-2, EINECS number 273-761-1) is an amorphous (non-crystalline) polymorph of silicon dioxide, silica. It is an ultrafine powder collected as a by-product of the silicon and ferrosilicon alloy production and consists of ...
Often, the concept also refers to the ratio of water to cementitious materials, w/cm. Cementitious materials include cement and supplementary cementitious materials such as ground granulated blast-furnace slag (GGBFS), fly ash (FA), silica fume (SF), rice husk ash (RHA), metakaolin (MK), and natural pozzolans. Most of supplementary cementitious ...
The flow table test or slump-flow test is a method to determine consistency of fresh concrete. Flow table test is also used to identify transportable moisture limit of solid bulk cargoes. [ 1 ] It is used primarily for assessing concrete that is too fluid (workable) to be measured using the slump test , because the concrete will not retain its ...
The maximum replacement ratios are generally defined as for Portland-fly ash cement. Portland silica fume cement. Addition of silica fume can yield exceptionally high strengths, and cements containing 5–20% silica fume are occasionally produced, with 10% being the maximum allowed addition under EN 197–1. However, silica fume is more usually ...
GGBS cement also produces a smoother, more defect-free surface, due to the fineness of the GGBS particles. Dirt does not adhere to GGBS concrete as easily as concrete made with Portland cement, reducing maintenance costs. GGBS cement prevents the occurrence of efflorescence, the staining of concrete surfaces by calcium carbonate deposits.
High-strength concrete is made by lowering the water-cement (W/C) ratio to 0.35 or lower. Often silica fume is added to prevent the formation of free calcium hydroxide crystals in the cement matrix, which might reduce the strength at the cement-aggregate bond.
The ability of a concrete to chloride binding is related to the cement type, being higher for blended cements containing silica fume, fly ash or furnace slag. Being the modelling of chloride penetration in concrete particularly complex, a simplified correlation is generally adopted, which was firstly proposed by Collepardi in 1972 [8]
The atomic (or molar) ratio Ca/Si, CaO/SiO 2, or C/S, and the number of water molecules can vary and the above-mentioned stoichiometry may differ. Many pozzolans may also contain aluminate , or Al(OH) 4 − , that will react with calcium hydroxide and water to form calcium aluminate hydrates such as C 4 AH 13 , C 3 AH 6 or hydrogarnet , or in ...