Showing papers on "Silica fume published in 1988"

Alkali-silica reaction in concrete

Abstract: History, the reaction, cracking and pessimum behaviour effect of mix proportion and constituents upon expansion effect of applied stress upon the mechanical properties structural effects and implications and repair diagnosis GGBS, PFA and silica fume testing aggregates and cement aggregate combinations for their reactivity minimizing the risk of expansion in new construction.

Quantitative characterization of the transition zone in high strength concretes

Abstract: Synopsis The microstructure of the transition zone in high strength concretes, with and without silica fume, was characterized. Backscattered electron (bse) imaging combined with quantitative image...

Concrete Incorporating High Volumes of ASTM Class F Fly Ash

Abstract: This paper gives results of an investigation undertaken to develop additional data on mechanical properties, and freezing and thawing resistance of high-volume Class F fly ash concrete made with ASTM Types I and III cements. A series of eight concrete mixtures involving twelve batches, each 0.06 m3 in volume, were made at a water-to-cementitious materials ratio of 0.32 ± 0.01. The fly ash-to-(fly ash + cement) ratio was 0.56. The cement content of the mixtures was 154 kg/m3. All mixtures were air-entrained and superplasticized. The mixtures incorporated Type I and Type III cements, various combinations of as-received fly ash, beneficiated fly ash, and condensed silica fume. From the test results, it is concluded that high-volume fly ash concrete has excellent mechanical properties and satisfactory resistance to repeated cycles of freezing and thawing. The use of ASTM Type III cement appears to be essential when high strengths at early ages are required. For concretes made with ASTM Type I cement, the use of beneficiated fly ash, and beneficiated fly ash and condensed silica fume, does little to enhance the properties of concrete compared with “as received” fly ash. For concrete made with ASTM Type III cement, the benefits of using beneficiated Class F fly ash and condensed silica fume are not clear.

Silica-fume (microsilica) concrete in bridges in the united states

Abstract: This paper reviews silica-fume-concrete (SFC) use in bridges in the United States. Although the focus is on bridge-deck overlays, other bridge-related applications are discussed, including full-depth decks, approach slabs, and piles. The reasons for using SFC include providing a chloride barrier, developing high early strength, achieving high ultimate strength, obtaining abrasion resistance, and improving bond strength. The concretes, representing silica-fume dosages between 5 and 15.5 percent, were placed successfully, although some difficulties were encountered. These difficulties, along with their solutions, are discussed. One silica-fume-concrete feature that required particular attention was the need to take measures to prevent plastic shrinkage cracking. An attempt is made to characterize the performances of the concretes, which are generally acceptable and encouraging. Further experimental work with silica-fume concrete is being done, and the material is now being specified in bridges.

Fire Endurance of High-Strength Concrete Slabs

Abstract: In recent years, use of high-strength concrete ranging in compressive strength from 8000 to 15,000 psi has become more prevalent. Concrete structures, such as high-rise buildings, are now using these materials. Most recently, the use of silica fume as a supplementary cementitious material has developed for design of higher strength concrete mixtures. The objective of this investigation was to develop fundamental information on the behavior of high-strength concrete at elevated temperatures using realistic test specimens. Scope of the work included a review of available literature on performance in fire tests of specimens fabricated fron high-strength concrete mixtures, with and without silica fume. The literature review was followed by laboratory tests of 3 x 3 x 0.33 ft slab specimens with embedded reinforcement. Specimens were exposed to elevated temperatures and monitored for temperature rise and physical integrity. Tests were conducted at the Fire/Thermal Technology Section of Construction Technology Laboratories, Inc. (CTL). Results of fire tests performed on the slab specimens show no measurable difference in performance of high-strength concretes and conventional strength concretes.

Preparation and characterization of high and low CaO/SiO 2 ratio “pure” C–S–H for chemically bonded ceramics

Abstract: A type of solidified “pure” C–S–H (calcium silicate hydrate) has been prepared by hydrating mixtures of synthesized Ca3SiO5(C3S) and silica fume at very low water/solid (w/s) ratios (< 0.15). The mechanical properties (splitting tensile strength), stoichiometry, and microstructure of hydration products have been investigated. Results are reported here in which 12.03%−41.56% (by weight) silica fume was added to C3S. It has been found that the strength of the materials with CaO/SiO2(C/S) molar ratio of 1.5 is comparatively higher than that of the others, after curing from 1 day to 28 days. The homogeneity and rheology are of direct importance to the formation of the calcium silicate bonding, which influences greatly the mechanical properties. The hydrates are primarily C–S–H with only small amounts of Ca(OH)2. The compositions of the solidified C–S–H are (1.33–1.37) CaO·SiO2. (1.02–1.21) H2O and (1.40–1.19)CaO·SiO2.(0.68–0.91)H2O for mixtures of C/S = 1.5 and 0.83, respectively. The characterization of the chemically bonded materials by Wn (nonevaporable water), density, x-ray diffraction, and scanning electron microscopy (SEM) studies has been carried out. The relationships between these characteristics and the strength are discussed.

Dry-Mix Silica Fume Shotcrete in Western Canada

Abstract: This article discusses the rapid advances in shotcrete technology with the incorporation of silica fume and the development, properties, and field application of dry-mix silica fume shotcrete in western Canada. Describes its use in major tunneling, mining, rock slope stabilization, marine, and rehabilitation projects.

Cement additive containing superplasticizer and bentonite

Abstract: A cement additive contains a superplasticizer, an inorganic strength increasing agent such as calcium sulfate or silica fume and bentonite.

Polyamide fibers, microsilica and Portland cement composites and method for production

Abstract: A hardened cementitious composite produced using conventional mixing techniques, including a microsilica-cement mixture and randomly distributed discontinuous polyamide fibers is described. Other mix ingredients used in forming the composite are superplasticizer, water and possibly aggregates and fly ash substituting for part of the Portland cement. The microsilica particles are essential in dispersing the fibers during the regular mixing, and in enhancing the fiber-cement interfacial bond. Microsilica also reduces the alkalinity of the matrix and helps in increasing the durability of polyamide fibers in the alkaline environment of cement. With their close spacing and superior bond to the matrix of the composite, the polyamide fibers are highly effective in increasing the ultimate tensile and flexural strength and in improving the ductility and toughness of the material.

Resistance to chloride ion penetration of concretes containing fly ash, silica fume, or slag. final report

Abstract: The effects of two pozzolanic admixtures, fly ash and silica fume, and a ground-granulated blast furnace slag on the chloride ion intrusion of concretes prepared with low water-to-cementitious material ratios (w/c) (0.35 to 0.45) were investigated. Results of the rapid permeability test (AASHTO T 277) showed that the resistance of concrete to the penetration of chloride ions increases significantly as the w/c is decreased for the same proportion of solid ingredients. Usually, concretes with pozzolans or slag exhibited higher resistance to chloride ion penetration than the control concretes containing portland cement as the cementitious material. Results of the 90-day ponding test (similar to AASHTO T 259), which was conducted with 0.40 w/c concretes only, indicated minimal chloride content at depths below 3/4 in (19 mm) for all the test concretes. Strength values for all concretes made with the pozzolans and slag at 90 days were in excess of 5,000 psi (34.5 MPa), which is satisfactory.

Resistance to Chloride Ion Penetration of Concretes Containing Fly Ash, Silica Fume, or Slag

Abstract: The effects of two pozzolanic admixtures, fly ash and silica fume, and a ground granulated blast furnace slag on the chloride ion intrusion of concretes prepared with low water to cementitious material ratios (w/c) (0.35 to 0.45) were investigated. Results of the rapid permeability test (AASHTO T 277) showed that the resistance of concrete to the penetration of chloride ions increases significantly as the w/c is decreased for the same proportion of solid ingredients. Usually, concretes with pozzolans or slag exhibited higher resistance to chloride ion penetration than the control concretes containing portland cement as the cementitious material. Results of the 90 day ponding test (similar to aashto t 259), which was conducted with 0.40 w/c concretes only, indicated minimal choride content at depths below 3/4 inch (19 mm) for all the test concretes. Strength values for all concretes made with the pozzolans and slag at 90 days were in excess of 5,000 psi (34.5 Mpa), which is satisfactory (a).

The properties and performance of high strength silica fume concrete

Abstract: Silicafume (SF) has been used as a partial replacement for cement in concrete and experiments have been carried out to measure the durability of the mixes. The SF mixes were made with 20% SF replacement of cement and waterlcement (wlc) ratios of 0.3 and 0.46. Three different curing conditions were used to simulate different site conditions and tests were carried out at 3,28 and 90 days after casting. The following properties were measuredfor the two SF mixes and the two control (OPC) mixes for each of the ages and curing conditions: corrosion rate of embedded steel by linear polarisation, electrical resistivity, carbonation depth, water vapour permeability, chloride permeability, oxygen permeability and porosity from helium and mercury intrusion. Samples were also investigated by thermogravimetric analysis. The resulting data matrix was analysed by using the method of analysis of variance to quantify the effect of the SF on the properties tested and their sensitivity to age and curing. It was also analysed by multiple regression to identify major effects of one property on another. It was concluded that SF will reduce the corrosion rate and that the major contributing factor is the substantial increase in resistivity that the SF causes. This increase in resistivity was found to be highly sensitive to cold curing in the short term but this effect was not permanent. The cause of the increase in resistivity is believed to be the depletion of calcium hydroxide which is caused by the pozzolanic activity of the SF. The analysis also indicated that the SF reduces the porosity in the .01-.15)1m size range and that this has a major influence on the durability.

Method for adding silica fume to dry shotcrete mixture

Abstract: A method for adding silica fume to a dry shotcrete mixture wherein the silica fume is added together with the water supplied to the dry mixture in the spray nozzle.

Method of shotcreting

Abstract: A method of shotcreting in which cement and sand are mixed in a bin (1) and piped to a nozzle (5) by means of compressed air (4). A slurry of water and silica fume is added to the cement and sand in the nozzle (5) from a tank (9) via a water line (8).

Freeze-Thaw Durability of Wet-Mix and Dry-Mix Shotcretes with Silica Fume and Steel Fibres

Abstract: This investigation was undertaken to study the freeze-thaw durability of wet-mix and dry-mix shotcretes when tested according to ASTM Test Method for Resistance of Concrete to Rapid Freezing and Thawing (C 666) Procedure A. Parameters of the air voids system were determined using ASTM Recommended Practice for Microscopical Determination of Air-Void Content and Parameters of the Air-Void System in Hardened Concrete (C 457-82). The effect of substitution of condensed silica fume for part of the cement was studied for plain shotcrete mixes as well as for mixes containing steel fibres. It was concluded that excellent durability was achieved in nonfibre and steel fibre shotcrete mixes manufactured by both the wet-mix and dry-mix shotcrete processes when approximately 13% of the cement was replaced with silica fume. After 300 cycles of freeze-thaw, excellent durability factors exceeding 95% were achieved in both wet-mix and dry-mix shotcretes having total air contents in the range of 4.5 to 6.5% and spacing factors in the range of 0.27 to 0.31 mm. Substantial increases in compressive strength were also realized during the period of freeze-thaw testing. Flexural strength and toughness of the samples were also not significantly affected by the freeze-thaw cycling.

Repair, Evaluation, Maintenance, and Rehabilitation Research Program: Evaluation of Concrete Mixtures for Use in Underwater Repairs.

Abstract: : Concrete mixtures were evaluated to determine which were most suited for placement underwater in thin lifts The concretes were proportioned to have good workability, good abrasion erosion resistance, and good resistance to washing out of the cement paste High-range water reducers (HRWR) were used to increase the workability and permit the use of low water cement ratios (W/C) to increase the resistance to abrasion erosion Low W/C, silica fume, and antiwashout admixtures (AWA) were used to increase the resistance to washout A washout test was used to determine the relative amount of cement paste lost when the concrete is exposed to a large volume of water The two-point workability test was used to evaluate the relative workability properties of each mixture The slump and air content were also measured for most of the mixtures The test method for abrasion erosion resistance of concrete (underwater method) was used to determine the abrasion erosion resistance of each mixture The results of these tests were used to determine the combination of materials necessary to produce concrete with the desired properties Significant correlations that exist between the two-point measurements and washout measurements were examined The effects that W/C, HRWR's, AWA's, fly ash, and silica fume have upon washout resistance and abrasion-erosion resistance were examined

Odot experience with silica-fume concrete

Abstract: Two bridge-deck-overlay projects placed in 1984 and 1987 are the basis for Ohio's specifications on the use of silica fume; they are reviewed along with a full-depth silica-fume structure placed in 1987. Data on mixing, placing, curing, compressive and flexural strengths, resistance to freezing and thawing, and permeability are presented. An assessment of these results shows that Ohio's 15 percent by mass of cement silica-fume requirement could be reduced, retaining high compressive and flexural strengths, good resistance to freezing and thawing, and favorable permeability characteristics. At present silica-fume-modified concrete appears to be a satisfactory and cost-competitive method of extending the life of bridge decks.

Evaluation of pullout test for estimating shear, flexural, and compressive strength of fiber reinforced silica fume concrete

Abstract: The use of pullout strength of steel fiber reinforced concrete (SFRC) to evaluate the shear, flexural, and compressve strength of SFRC containing a condensed silica fume is discussed. First, the effect of fiber reinforcement and silica fume addition on pullout strength was investigated with different apex angles of the concrete frustrum. Then the correlations between the pullout strength of steel fiber reinforced concrete and shear strengths were obtained for three types of shear test methods. In addition, compressive strength and flexural strength were also correlated with the pullout strength. The test results show the addition of fiber reinforced and silica fume significantly improves the pullout strength. The regression analysis of the test data shows that a close correlation exists between the shear strengths and the pullout strength of the steel fiber reinforced concrete. The magnitude of pullout strength is found to be approximately the same order as that of indirect shear strength.

Lightweight cement composition

Abstract: PURPOSE: To obtain the title composition capable of preparing exterior and interior building materials without using asbestos by mixing cement, a lightweight aggregate, an inorg. aggregate consisting of a spherical aggregate and a superfine-grain aggregate, a reinforcing fiber, and a cellulosic admixture. CONSTITUTION: (A) One hundred pts.wt. cement (e.g., portland cement and blast- furnace cement), (B) 5-100pts.wt., preferably 5-50pts.wt., lightweight aggregate [inorg. hollow (porous) grains such as fly ash having ≤2mm, preferably 0.1-2mm, grain diameter and ≤0.5, preferably 0.1-0.4, bulk density], (C) 5-100pts.wt., inorg. aggregate (superfine-grain aggregate contg. micro silica, for example, consisting essentially of a spherical aggregate having 1-100μm grain diameter, and contg. 1-20wt.% grains having 0.01-1μm diameter), (D) 0.2-10pts.wt., reinforcing fiber (the org. fiber, pulp, fibrous wollastonite, etc., having 1-100μm diameter and 3-20mm length), and (E) 0.1-10pts.wt., preferably 0.5-5pts.wt., cellulosic admixture (methylcellulose, etc.) are mixed to obtain the lightweight cement composition. COPYRIGHT: (C)1989,JPO&Japio

Microsilica and concrete durability

Abstract: Results from experiments to determine the effects of microsilica on concrete freeze-thaw resistance and on the permeability to chlorides and subsequent early corrosion rates of steel in the concrete are described. The results to date show that air-entrained microsilica concretes pass laboratory freeze-thaw tests and demonstrate reduced chloride permeability and corrosion rates. ASTM C 666 testing was performed on concretes with no entrained air, below-normal entrained air, and normal air-entrainment levels on numerous mix designs with and without microsilica slurry additions. In all cases, properly air entrained microsilica mixes behaved as well as or better than control mixes. When air entrainment was not added, all mixes failed. Chloride permeabilities were determined using AASHTO 277. Results show that silica fumes significantly reduced chloride permeability. Concrete resistivity measurements were performed using the A. C. impedance method. Microsilica significantly increased concrete resistivity over that of the control concretes, indicating that macrocell corrosion should be reduced. Corrosion-rate measurements show reduced rates (essentially noncorroding) for silica-fume concretes at 0.43 and 0.5 water-cement ratios, whereas some controls have gone into corrosion. Chloride analyses are to be performed to determine whether reduced permeability, increased electrical resistivity, or a combination of the two is responsible for the better corrosion performance.

Method for reinforcing concrete or mortar, hydraulic composite material and reinforcing additive

Abstract: PURPOSE: To obtain an inexpensive concrete, capable of providing a high strength, durability and density and improved in handling by filling interstices between closely filled cement particles with inorganic solid particles and particles without high water absorptivity. CONSTITUTION: Inorganic solid particles (B) having 0.01-0.5μ particle diameter and particles (C) having a continuous particle size distribution of 0.1-15μ particle diameter without high water absorptivity are filled in interstices (H) between closely filled cement particles having 0.15-100μ grain diameter to reinforce a concrete or mortar. Mineral fine powder, e.g., silica fume or silica flour, is suitable as the above-mentioned particles (B). Particles without high water absorptivity, e.g., clay, blast furnace slag, zeolite, fly ash, lime or quartzite, is suitable as the intermediate particles (C) and particles having latent hydraulicity or pozzolan activity are especially preferred. COPYRIGHT: (C)1990,JPO&Japio