Showing papers on "Silica fume published in 1984"

The hydration of tricalcium silicate in the presence of colloidal silica

Abstract: Reactions of colloidal silica fumes with calcium hydroxide or hydrating tricalcium silicate (C3S) have been studied using calorimetry, chemical analyses, and scanning electron microscopy. Silica fume reacts immediately with calcium hydroxide forming a colloidal calcium silicate hydrate (C-S-H) similar to that formed by the hydration of C3S. When excess silica is present it reacts with C-S-H already formed to produce a new, highly polymerized C-S-H, having a very low C/S ratio (1.0). Silica fume accelerates the hydration of C3S, reduces the amount of calcium hydroxide formed by reacting with it, and slightly lowers the C-S-H ratio of the C-S-H formed by hydration. When large amounts of silica fume are present the formation of calcium hydroxide may be entirely suppressed and a highly polymerized C-S-H is formed. Silica fume is considered a good model for reactive pozzolans used in concrete.

Light-weight aggregate

Abstract: A light-weight aggregate, for use in production of light-weight structural products, composed of a self-hardening fly ash, a surfactant foam, and optionally an accelerator and additives. The self-hardening fly ash is preferably class C fly ash formed by the combustion of sub-bituminous coal from the Power River Basin. The surfactant foam is preferably an anionic sulfate surfactant foam. The accelerator is preferably an extract of silica fume dust. The additives may include magnesium and boron compounds, other fly ashes, light-weight fillers, polymers, cement and magnesium silicate and like materials.

Rapid set lightweight cement product

Abstract: A lightweight cement product formed from a mixture comprising cement, condensed silica fume, flyash, cenospheres, finely divided crystalline silica particles, epoxy emulsion, curing agent, accelerator and water which hardens in less than one hour to produce articles with a density less than 90 pounds per cubic foot and a tensile strength of at least 600 psi and a compressive strength of at least 6000 psi after curing for 1 day at 60° C.

The Uniformity and Influence of Silica Fume from a U.S. Source on the Properties of Portland Cement Concrete

Abstract: Silica fume is formed during the manufacture of ferrosilicon in electric submerged-arc furnaces. The use of silica fume has been evaluated in portland cement concrete. Thirty samples of silica fume, each collected on consecutive days from SKW Alloys, Inc. in Calvert City, KY, were analyzed for routine quality control tests of a pozzolan. Six of these samples, representing the variations of the routine tests, were tested for complete ASTM Specification for Fly Ash and Raw or Calcined Natural Pozzolan for Use as a Mineral Admixture in Portland Cement Concrete (C 618) conformance. Laboratory mixtures of air-entrained and nonair-entrained concrete, containing a representative sample of silica fume, were cast for compressive strength (1 to 120 days), drying shrinkage, and time of set. Although a classification for silica fume is not currently contained in ASTM C 618, all of the samples tested were found to conform when compared to the requirements of this standard, with the exception that the water requirement was excessive. Concrete mixtures containing only 24 kg/m3 (40 lb/yd3) of silica fume showed slightly high shrinkage at 64 weeks of drying with the lower cement content mixtures relative to control mixtures. The silica fume mixtures showed 120 to 180% higher compressive strength at 120 days in lean mixtures, 110 to 120% higher compressive strength in richer mixtures. This amount of silica fume was found to have no effect on initial set of concrete and had only a slightly longer final set.

The Chemical Environment in Cements

Abstract: The alkalinity of Portland cements is responsible for precipitation and low solubility of many radwaste species. The sources of alkalinity are evaluated and two chemical models, based on experimental and theoretical data presented enabling the effect of blending agents (PFA, silica fume, etc.) to be evaluated and the alkalinity of the system at longer ages predicted. The data take the form of a solubility model which is applicable to non-heat generating wastes.

Very High Strength Cement for Very High Strength Concrete

Abstract: During 1984 summer, an experimental concrete column was cast in a 26-story high-building using a 100 MPa silica fume concrete Only the coarse aggregate was selected specifically for this concrete The cement used was an ordinary type 1 Portland cement The super-plasticizer was a naphthalene base The field conditions were among the most unfavourable, the transportation was about 3/4 of an hour The placing lasted 15 minutes However, after 1 h 00 the slump of this concrete having a water/cementitious ratio of 025 was still higher than 100 mm so that the concrete was placed without any problems

Corrosion of Steel in Concrete: Some Fundamental Aspects of Concrete with Added Silica

Abstract: Silica, which is a waste product of the ferrosilicon industry, has been used as an additive to concrete. This silica-fume material consists of minute spherical silica particles with pozzol...

Resistance to Freezing and Thawing of Silica Fume Concrete

Abstract: The resistance to freezing and thawing of a concrete containing silica fume that was used during the construction of an experimental section on highway A25 in Montreal was done according to ASTM Test for Resistance of Concrete to Rapid Freezing and Thawing (C 666). The original mix was modified so that silica fume replaced three times its weight of cement. The use of silica fume did not create any particular problems as far as the air content and slump were concerned except perhaps that slightly higher losses were observed during the transportation in comparison to the regular mix. The 28- and 91-day compressive strength results proved that silica fume has been more active than three times its cement weight. The tests show that the resistance to freezing and thawing of the silica fume concrete was far superior to the plain concrete used for the completion of the project. The length increase and the absorption of the silica fume concrete were about or less than half of those observed with the regular mix. The durability factor of the silica fume concrete was 83 at the end of the test whereas the regular mix durability factor was only 68.

Lubricating system composition for extrusion of polyvinyl chloride resin binder

Abstract: A lubricating system composition for the extrusion of polyvinyl chloride resin conduits is provided by treating silica fume particles at least in part with a lubricant to form a premix additive for polyvinyl chloride extrusion compounds whereby the resulting product has unique and particularly advantageous physical characteristics which makes possible the reduction in wall thickness and an increase in loading of calcium carbonate to effect a material reduction in cost of manufacture

Optimized High Strength Mortars: Effects of Chemistry, Particle Packing, and Interface Bonding

Abstract: High strength mortars have been prepared utilizing optimized particle packing, reactive substituents to modify the chemistry- and addition of superplasticizers. Otherwise the processing techniques were conventional. The compressive strengths of one prototype material after curing at temperatures from 38 C to 250 C were above 70 MPa. The strengths were particularly high at 175 C (195 MPa) where excellent bonding had developed; one chemically modified material reached 245 MPa. The specimens cured at 175 and 250 C (after a lower temperature precure) developed their strengths rapidly, having reached essentially full strength by 7 days. At lower curing temperatures the strength increased with time, apparently still increasing at 56 days (106 MPa) for the materials cured at 38 C. Modified mixtures were prepared using different proportions of silica fume, MgO, different ratios of sand to fine components, and different sand mineralogy and other admixture proportions for rheological optimization. Microhardness, dynamic Young’s modulus, density, and permeability were measured in addition to strength. Matrix chemistry and sand mineralogy and proportions affected the strength. Matrix-aggregate bond was very important. The above types of cementitious materials have potential importance for applications where they may be exposed to extreme conditions and to temperature cycling.

High Strength Concrete and Mortars in High Temperature Environments

Abstract: A number of new materials are presently being introduced for application in high temperature environments. Though some of these are old materials fabricated with new methods or processes, many are actually new. This paper focuses on the use of high strength concretes or mortars for application to high temperature environments, such as furnaces or boilers for coal gasification and similar processes requiring high pressure and temperature. This paper reports the results of an investigation on the high temperature performance of mortar of different strengths incorporating 0%, 8% and 16% of condensed silica fume (CSF). The experiments described have been carried out to compare the performance of different strength level mortars with different CSF contents. Generally speaking, it was found that low strength mortar with CSF is less susceptible to strength loss after high temperature exposure than mortar without CSF. On the other hand, high strength mortar with CSF seems to be more sensitive to high temperature than high strength mortar without CSF since it retains only 65% of its room temperature strength after heating to 3200C as compared to regular high strength mortar which retains 95% of its room temperature strength. Though there may be a possible practical problem in using high strength CSF concrete, this shown loss of strength in high strength CSF concrete upon heating may prove very important in giving us insight into the fundamental mechanisms of strengthening concrete with CSF. An explanation is hypothesized on the observed behavior of high strength CSF concrete, which will produce a theory for one of the ways in which CSF strengthens portland cement paste. It is theorized that the CSF touohens the portlandite in high strength paste, but after heating to 320 C, the CSF particles which have been converted to C-S-H have lost their ability to toughen the portlandite.

The Variability of Condensed Silica Fume from a Canadian Source and Its Influence on the Properties of Portland Cement Concrete

Abstract: Condensed silica fume is formed during the manufacture of ferrosilicon in electric submerged-arc furnaces. The use of condensed silica fume has been evaluated in portland cement concrete. Thirty-two samples of condensed silica fume, each collected on consecutive days, were analyzed for chemical and physical routine quality control tests of pozzolan. Eight of these samples, representing the variations of the routine tests, were tested for complete ASTM Specification for Fly Ash and Raw or Calcined Natural Pozzolan for Use as a Mineral Admixture in Portland Cement Concrete (C 618) conformance. All of the samples tested were found to conform to ASTM C 618 with the exception that the water requirement was excessive. Concrete mixtures were evaluated with a fixed quantity of 24 kg/m3 (40 lb/yd3) of condensed silica fume. The low portland cement content mixtures show slightly higher shrinkage after 64 weeks of drying; the rich mixtures have the same shrinkage. Compressive strengths were more than 30% higher than control mixtures having low cement contents and were more than 10% higher than control mixtures having higher cement contents. This amount of condensed silica fume was found to have no effect on the time of set relative to control mixtures containing the same portland cement content.

Microsilica Concrete: A Technological Breakthrough Commercialized

Abstract: With the advent of microsilica concrete, a new generation of high to ultra high strength and high durability concretes have become commercially feasible and are now being specified and used internationally. Microsilica concrete is produced by incorporating microsilica (beneficiated condensed silica fume) additives in conventional concrete mixes, using conventional materials and equipment. Flowing microsilica concretes with strengths as high as 17000 psi have become field realizable, also benefiting by durability improvements expressible by factors, not percents. Properties of microsilica concrete are reviewed, and property improvements qualitatively linked to a much refined micropore structure of the binder phase. Some recent and rapidly developing field and laboratory experience both in the U.S. and overseas are presented.

Formed amorphous silica

Abstract: PURPOSE: Formed amorphous silica which is obtained by forming primary crystals of apparently crystal-like amorphous silica having a specific shape and size, thus being suitable for a thermally insulating material, because of its light wight and high mechanical strength. CONSTITUTION: Carbon dioxide is brought into contact with calcium silicate crystals such as wollastonite in the presence of water to effect conversion into amorphous silica and fine particles of calcium carbonate, then the product is treated with acid to separate the amorphous silica from the calcium salt. Thus, apparently crystal-like amorphous silica is obtained in the form of primary particles which have the crystalline habit of the calcium silicate, about 1W500μm length and about 50ÅW1μm thickness where the length is more than 10 times the thickness. The resultant amorphous silica primary particles are subjected to dehydrative forming and drying to effect the entangling of amorphous silica primary particles with one another irregularly and three-dimensionally to give the objective formed amorphous silica. COPYRIGHT: (C)1984,JPO&Japio