Showing papers on "Silica fume published in 1983"

Pore solution composition and chloride binding capacity of silica-fume cement pastes

Abstract: Samples of the capillary pore solution, associated with hardened cement pastes containing various proportions of silica-fume and sodium chloride, have been expressed at different stages of curing and analysed to determine concentrations of dissolved ions. The results indicate that partial replacement of Portland cement by increasing percentages of silica-fume causes a regular decrease in alkalinity of the pore solution and a reduction in the chloride-binding capacity of the material. Possible implications regarding the level of corrosion protection afforded to embedded steel are considered.

Effects of Microsilica (Silica Fume) on Pore-Solution Chemistry of Cement Pastes

Abstract: Pore solutions expressed from hydrated Portland cement pastes containing up to 30% microsilica (silica fume) as replacement for cement were analyzed. The presence of microsilica enhances early concentrations of alkalies and hydroxyl ions, but after 1 day the effect is reversed, and the concentrations of these ions are progressively reduced to very low values. Alkali reduction seems more pronounced for pastes of higher water content, and low levels of microsilica replacement (5 or 10%) exert substantially greater than proportional effects.

Light-weight cementitious product

Abstract: A glass-fiber reinforced light-weight cementitious product having a density of less than 85 pounds per cubic foot, a high tensile strength and a high compressive strength, when cured, and hence, suitable for structural articles in which such properties are required. The product is formulated from a mixture in which the aggregate comprises substantially equal parts by weight of fly ash cenospheres and silica fume.

Mechanical Properties, Durability, and Drying Shrinkage of Portland Cement Concrete Incorporating Silica Fume

Abstract: Portland cement is a highly energy intensive material, therefore, considerable effort is being made to find substitutes for partially replacing cement in concrete. Silica fume, a byproduct in the manufacture of ferrosilicon and silicon metal is one possible substitute. Results are given of a preliminary investigation to determine the strength, freezing and thawing characteristics, and drying shrinkage of concrete incorporating various percentages of silica fume. Eighteen 0.06-m3 air-entrained concrete mixes were made incorporating 0 to 30% silica fume as a partial replacement for cement. Some mixes were proportioned to have constant slump with water to cementitious materials ratio (W/C + S) ranging from 0.64 to 0.84 whereas others were proportioned to have a constant W/C + S of 0.40; the latter incorporated a superplasticizer. Cylinder and prism specimens were cast for determining the mechanical properties and durability of concrete. Test data indicate that silica fume when used in concrete as a partial replacement for cement performs as a highly efficient pozzolanic material. Notwithstanding the extreme fineness of silica fume (20 000 m2/kg) and, hence, its high water demand, the compressive strength of constant slump concrete incorporating up to 30% silica fume is comparable with or higher than the strength of control concrete. Superplasticized concrete mixes having a W/C + S maintained at 0.40 indicate some increase in compressive strength at all ages regardless of the percentage of silica fume. Concrete prisms incorporating 0 to 15% silica fume (W/C + S = 0.40) perform satisfactorily when subjected to 300 cycles of freezing and thawing; however, prisms incorporating 20 to 30% silica fume and large dosages of superplasticizer show excessive expansion and relatively low dynamic moduli after 300 cycles. The drying shrinkage of concrete incorporating silica fume is generally comparable with that of control concrete regardless of the W/C + S.

The use of fly ash, silica fume, slag and other mineral by-products in concrete

Abstract: Portland cement is a highly energy-intensive product, and therefore, in an energy-hungry world considerable efforts are being made to find substitute materials for the partial replacement of cement in concrete Some of the most promising substitutes or supplementary cementing materials are high- and low-calcium fly-ashes, ferrous- and non-ferrous slags and condensed silica fume This paper presents a state-of-the-art review on the use of these mineral by-products in concrete, and the role of these materials in the less developed countries The physical and possolanic properties of the supplementary cementing materials are outlined, and their effect on the properties of fresh and hardened concrete discussed Particular emphasis is placed on the use of condensed silica fume, a relatively new addition to the family of supplementary cementing materials The contribution of superplasticizers to achieving high-strength concrete incorporating fly-ash and silica fume is mentioned Reference is made to the currently available specifications for these materials both in North America and Europe, and their limitations discussed The advantages and limitations in the use of supplementary cementing materials as separately batched ingredients at a ready-mixed concrete plant, versus the use of blended cements are discussed, and North American trends in this field are mentioned briefly It is emphasized that additional quality control measures are needed when fly-ash, slag and silica fume are incorporated in ready-mixed concrete This is especially so when chemical admixtures are also incorporated in concrete made with supplementary cementing materials (Author/TRRL)

Concrete additive admixture containing microsilica and concrete produced therewith

Abstract: A multicomponent additive comprises microsilica which has been stabilized by means of one or more water reducing agents alone or in combination. This mixture is especially of advantage as additive to cement and mortar and results in an improvement of plasticity, workability and strength as compared to usual cements and mortars. The additive can be mixed with water whereupon more microsilica is added for formation of a slurry.

Preparation of aqueous dispersion of silica fume

Abstract: PURPOSE: To reduce transportation and handling costs and to enable stable weighing of silica fume by handling silica fume in the form of concentrated slurry by mixing with a dispersant and water. CONSTITUTION: Slurry of silica fume is prepd. by mixing silica fume with ≥0.5 wt% and ≤40wt% dispersant (basing on the weight of the silica fume) such as one derived from naphthalene sulfonic acid condensed with formaldehyde, melamine sulfonic acid condensed with formaldehyde, or one derived from polycarboxylic acid salts, etc. together with water. Uniform mixture is obtd. by mixing said slurry with cement, etc. COPYRIGHT: (C)1985,JPO&Japio

Modification of Bell Canyon Test (BCT) of 1-FF Grout.

Abstract: : Bell Canyon Test (BCT) 1-FF grout was developed as a candidate material for use in repository sealing applications and was actually used in two field tests in New Mexico. This grout and modifications of it were made in the laboratory and tested or examined for workability, compressive strength, restrained expansion, permeability, phase composition, and microstructure. Most of these were done to an age of 1 year. Compressive strength and expansion data were determined beyond this age (960 days). Modifications included use of three other cements, two other fly ashes, a silica fume, different water contents, and different amounts of expansive additive (plaster). Each cement and mineral admixture was characterized by conventional chemical and physical tests as well as by X-ray diffraction examination. In general, the results indicated that the modifications to the basic BCT-1-FF grout produced other grouts that were as good as it. An exception to this was the grout mixture (M-8-C) made with shrinkage compensating expansive cement; it has an excessive flow time (20 sec). Another grout mixture (M-9-C) also had excessive flow time and lower strength. It was thought that these problems could be solved with more modification to these two mixtures. (Author)

Abrasion-Erosion Evaluation of Concrete Mixtures for Stilling Basin Repairs, Kinzua Dam, Pennsylvania.

Abstract: : The resistance to abrasion-erosion of several concretes made with different coarse aggregates, with and without silica fume as a mineral admixture, was evaluated, Testing was done in accordance with the Corps of Engineers standard test method. Initially, concretes made with a limestone coarse aggregate (available near the project site) and with two gabbros (from New York and Virginia) were prepared and tested. Although the gabbros were thought to be harder than the limestone, testing revealed very little difference in abrasion-erosion resistance among the three aggregates. The two gabbros did not show a great enough improvement to justify the increased transportation costs necessary for their use. A polymer portland-cement concrete (epoxy-modified concrete) was also prepared using the limestone aggregate. This material showed very little improvement on abrasion-erosion resistant--certainly not enough improvement to justify the high cost of the epoxy product. High-strength concretes (fc 7500 psi) made using the limestone aggregate and one of the gabbros and containing silica fume and a high-range water reducing admixture showed improved abrasion resistance. Very high strength silica-fume concretes (fc = 14,000 psi) showed excellent abrasion-erosion resistance. Cores taken from the fiber-reinforced concrete overlay presently in the Kinzua stilling basin were also tested. The cores showed very high abrasion losses, which agrees well with the apparent poor performance of the material in the prototype. (Author)

Production of ultrafine silica powder

Abstract: PURPOSE: To enable the arbitrary control of the specific surface area of fine silica powder, and to obtain fine silica powder having excellent dispersibility and transparency, by decomposing a volatile silicon compound in a flame at a high reaction temperature. CONSTITUTION: A volatile silicon compound such as silicon tetrachloride, etc. is supplied to a flame together with hydrogen gas and air, etc. and burnt and decomposed at a reaction temperature higher than the melting point of silica to obtain fine silica powder. The specific surface area and the dispersibility of the silica powder can be conrolled mainly by the reaction temperature, and the fine control of the above properties are carried out by adjusting the concentration of the silicon compound in the feed gas, the ratio of oxygen, the ratio of hydrogen, etc. COPYRIGHT: (C)1984,JPO&Japio

Modification of Bell Canyon Test (BCT) 1-FF grout. Final report

Abstract: Bell Canyon Test (BCT) 1-FF grout was developed as a candidate material for use in repository sealing applications and was actually used in two field tests in New Mexico. This grout and modifications of it were made in the laboratory and tested or examined for workability, compressive strength, restrained expansion, permeability, phase composition, and microstructure. Most of these were done to an age of 1 year. Compressive strength and expansion data were determined beyond this age (960 days). Modifications include use of three other cements, two other fly ashes, a silica fume, different water contents, and different amounts of expansive additive (plaster). Each cement and mineral admixture was characterized by conventional chemical and physical tests as well as by x-ray diffraction examination. In general, the results indicated that the modifcations to the basic BCT-1-FF grout produced other grouts that were as good as it. An exception to this was the grout mixture (M-8-C) made with shrinkage compensating expansive cement; it had an excessive flow time (>20 sec). Another grout mixture (M-9-C) also had excessive flow time and lower strength. It was thought that these problems could be solved with more modification to these two mixtures. 6 references, 24 figures, 7more » tables.« less

Natural ground stabilization work of excellent durability

Abstract: PURPOSE:To raise the durability of the natural ground by spraying a cement mortar prepared by mixing specific weight amounts of a slurried superfine powder and a high performance plasticizer with cement on the surface of the natural ground. CONSTITUTION:A superfine powder of silicon, silica fume, etc., having an average grain size of 1mum or less, is slurried with 30% or more water/superfine powder weight ratios before carried to construction site. The 100pts.wt. cement, 5-50pts.wt. the slurried superfine powder, and 10pts.wt. (at most) a high performance plasticizer composed primarily of a salt of melamine sulfonate-formaldehyde condensate are mixed together with a water-cement ratio of 20-60 to form a cement mortar. A formwork is set on the slope, reinforcing bars are arranged in the formworks, and the cement mortar is sprayed on them.