Showing papers on "Silica fume published in 1993"
TL;DR: The linearity between the volume resistivity change and the compressive stress was good for mortar containing carbon fibers together with either methylcellulose or latex as dispersants as discussed by the authors.
Abstract: Electrically conducting concrete, as provided by the addition of a short carbon fibers (0.2-0.4 vol.%) to concrete, can function as smart structure material that allows non-destructive electrical probing for the monitoring of flaws. The electrical signal is related to an increase in the concrete's volume resistivity during crack generation or propagation and a decrease in the resistivity during crack closure. The linearity between the volume resistivity change and the compressive stress was good for mortar containing carbon fibers together with either methylcellulose or latex as dispersants. However, the linearity was poor for mortar containing carbon fibers together with both methylcellulose and silica fume, as this mortar required a minimum compressive stress for crack closure, whereas the other two mortars did not.
349 citations
TL;DR: The results of a series of tests of the physical properties and durability of pastes, mortars, and concretes made with silica fume replacements for part of the portland cement were presented in this paper.
Abstract: The results are presented of a series of tests of the physical properties and durability of pastes, mortars, and concretes made with silica fume replacements for part of the portland cement: silica fume reduced the permeability of cement pastes and concretes; silica fume reduced the size of pores and total porosities of both cement and concretes; silica fume reduced the leachable calcium hydroxide contents of cement pastes; silica fume reduced the level of alkalies leached from the pastes; silica fume improved the resistance of ASTM C 441 Pyrex mortar bars to deleterious expansion; silica fume provided resistance superior to that of a sulfate resistant portland cement in ASTM C 1012 tests for sulfate resistance; and silica fume provided resistance to freezing and thawing to a series of high-strength, non-air-entrained concretes.
230 citations
TL;DR: In this paper, carbon black was introduced as an alternative microfiller to silica fume, which was found to be effective in modifying the basic concrete-matrix strength relationship.
201 citations
TL;DR: In this paper, a fire test was conducted on 2 specimens, one of high strength concrete and the other of normal strength concrete, and it was found that the length of the path for moisture to escape also has a significant influence on the spalling of high-strength concrete.
Abstract: A fire test was conducted on 2 specimens, one of high strength concrete and the other of normal strength concrete. At the time of test, sepcimen strengths were 27 and 105 MPa respectively. Details of the beam slabs and the specimens are described. The specimens were tested after 3.5 months of drying in an indoor environment. Explosive spalling was observed in high strength concrete while no spalling occurred in the normal strength concrete. However, spalling in the high strength concrete was confined to a region with 75 mm cover to steel. It was also found that the length of the path for moisture to escape also has a significant influence on the spalling of high-strength concrete.
179 citations
TL;DR: In this paper, the use of short pitch-based carbon fibres (0.5% by weight of cement, 0.189 volume % (vol%) of concrete), together with a dispersant, chemical agents and silica fume, in concrete with fine and coarse aggregates, resulted in a flexural strength increase of 85%, flexural toughness increase of 205, a compressive strength increase, and a material price increase of 39%.
153 citations
TL;DR: In this paper, the influence of silica fume on impedance behavior of hydrating cement has been carefully investigated, and the results demonstrate that impedance measurement is very sensitive to changes in hydration kinetics and microstructure development due to the presence of Silica Fume.
118 citations
Patent•
07 Jun 1993
TL;DR: A low cost cement composition that can be admixed with water and hydrothermally closed cured to give acid-resistant products of high compressive strength consisting essentially of, in parts by weight, 1 to 1.5 parts of a calcium oxide material containing at least about 60% CaO, 10 to 15 parts of pozzolanic material and 0.025 to 0.075 parts of an alkali metal catalyst and building materials made therefrom as well as the method of making such building materials by closed curing as discussed by the authors.
Abstract: A low cost cement composition that can be admixed with water and hydrothermally closed cured to give acid-resistant products of high compressive strength consisting essentially of, in parts by weight, 1 to 1.5 parts of a calcium oxide material containing at least about 60% CaO, 10 to 15 parts of pozzolanic material containing at least about 30% by weight amorphous glass or vitreous silica, and 0.025 to 0.075 parts by weight of an alkali metal catalyst and building materials made therefrom as well as the method of making such building materials by closed curing.
104 citations
Journal Article•
TL;DR: In this paper, the authors discuss the properties and limitations of fly ash, slag, condensed silica fume and rice-husk ash in the production of ready-mixed and precast concretes.
Abstract: Environmental problems associated with waste product disposal, resource conservation considerations, and the cost of portland cement will demand the increasing use of of fly ash, slag, condensed silica fume and rice-husk ash in the production of cement and ready-mixed and precast concretes. This article discusses this issue, the properties and limitations of these materials, and the effects that this will have on concrete properties. It is noted that North American trends indicate preference for the separate batching of these materials at concrete-batching plants rather than the intergrinding with portland cement clinker at a cement plant. This, however, is not advised in developing countries. It is also noted that recent developments in chemical admixtures, especially the introduction of superplasticizers, will increasingly facilitate the incorporation of supplementary cementing materials in concrete. Technology transfer needs are also noted.
103 citations
TL;DR: In this article, the amount of unreacted cement, Ca(OH) 2, and residual silica fume was quantitatively estimated using TMS-GPC, TGA, and 29 Si NMR.
Abstract: Cement pastes densified with small particles (DSP) containing up to 48% silica fume by weight of cement, and hydrated to up to 180 d at room temperature, have been analyzed using TMS-GPC, TGA, and 29 Si NMR to quantitatively estimate the amount of unreacted cement, Ca(OH) 2 , and residual silica fume, respectively. Using a mass balance approach, the CaO/SiO 2 and H 2 O/SiO 2 molar ratios of the C-S-H in the samples were calculated. For samples containing silica fume, the values of CaO/SiO 2 lie between 0.9 and 1.3, depending on the degree of hydration and silica fume content, whereas for samples without silica fume they were 1.6. Silicate polymerization analysis using TMS-GPC suggests that the molecular structure of the C-S-H is similar to that formed in conventional hydration. No cross-linking species were found, but the fraction of higher polymers (above octamer) increases as the CaO/SiO 2 ratio decreases
81 citations
TL;DR: In this article, the properties of silica fume concrete were investigated, including slump, air-content, compressive strength, flexural strength, permeability, and permeable void volume.
Abstract: The properties of silica fume concrete was studied. Various properties of silica fume cocnrete, including slump, air-content, compressive strength, flexural strength, permeability, and permeable void volume were investigated, and the effect of the silica fume replacement ratio of cement is described. The effects of aggregate content and graduation, water-binder (cement plus silica fume), and superplasticizer dosage rate also are discussed. In this investigation, silica fume-binder ratios ranged from 0.00 to 0.40, water binder ratios from 0.41 to 0.47, aggregate binder ratios from 1.0 to 4.0, and superplasticizer binder ratios from 0.01 to 0.05.
76 citations
01 Jan 1993
TL;DR: In this article, the authors examined the microstructural characteristics of the interfacial region around aggregate particles in concrete and explored the influence of this interfacial zone on some of the properties of concrete such as the compressive strength, the water transport capacity, and the diffusion of ions into concretes prepared with and without mineral additives.
Abstract: This is a report of a study that examined the microstructural characteristics of the interfacial region around aggregate particles in concrete. The study also explored the influence of this interfacial zone on some of the properties of concrete such as the compressive strength, the water transport capacity, and the diffusion of ions into concretes prepared with and without mineral additives. The literature review is described, as well as the materials and the experimental methods. The micro-characteristics of the interfacial zone in portland cement mortars and concrete are described, as well as the effects of the interfacial zone on diffusion of ions in concrete. The effects of mineral additives on the cement paste-aggregate interfacial zone in concrete, and the influence of pozzolans on the interfacial zone in relationship to the transport of water and the diffusion of ions in concrete are covered. The study also covered the effects of silica fume and metakaolinite on the interfacial zone with respect to the strength of mortars.
TL;DR: In this paper, a chemical and microstructural study has been carried out on Portland cement mortars with and without silica fume subjected to magnesium sulfate attack, and it was concluded that the decalcification of the CSH plays a major role in the deterioration process.
01 Jan 1993
TL;DR: In this paper, the authors examined the microstructural characteristics of the interfacial region around aggregate particles in concrete and explored the influence of this interfacial zone on some of the properties of concrete such as the compressive strength, the water transport capacity, and the diffusion of ions into concretes prepared with and without mineral additives.
Abstract: This is a report of a study that examined the microstructural characteristics of the interfacial region around aggregate particles in concrete The study also explored the influence of this interfacial zone on some of the properties of concrete such as the compressive strength, the water transport capacity, and the diffusion of ions into concretes prepared with and without mineral additives The literature review is described, as well as the materials and the experimental methods The micro-characteristics of the interfacial zone in portland cement mortars and concrete are described, as well as the effects of the interfacial zone on diffusion of ions in concrete The effects of mineral additives on the cement paste-aggregate interfacial zone in concrete, and the influence of pozzolans on the interfacial zone in relationship to the transport of water and the diffusion of ions in concrete are covered The study also covered the effects of silica fume and metakaolinite on the interfacial zone with respect to the strength of mortars
TL;DR: In this paper, the microstructure of the transition zone between aggregate and cement paste, and the effect of silica fume, slag, fly ash and latex (EVA) aggregate coatings were investigated by means of AC impedance measurements.
TL;DR: In this article, short carbon fibers were found to exhibit volume electrical resistivity of 103-105Omega cm and contact resistivity between the cured concrete and stainless steel at zero contact pressure.
Abstract: Concrete containing 0.2-0.4 vol.% short carbon fibers was found to exhibit volume electrical resistivity of 103-105Omega cm and contact resistivity (between the cured concrete and stainless steel) of 103-106Omega cm at zero contact pressure. Increasing the contact pressure from 0 up to 0.05 MPa was sufficient to lower the contact resistivity to a minimum value. Increasing the fiber content to >0.4 vol.% did not decrease the contact resistivity, but decreased the volume resistivity. The values of the volume and contact resistivities depended on the non-fiber additives (i.e., latex, methylcellulose and silica fume) needed for fiber dispersion. Using latex gave a higher volume resistivity (1 × 105Omega cm) and a lower contact resistivity (5 × 103Omega cm2) than methylcellulose and silica fume; the high volume resistivity was due to the large proportion of latex used; the low contact resistivity was due to the lack of adherent on the surface of fibers protruding from the concrete containing latex.
TL;DR: In this paper, granulated tyre rubbers were incorporated in Portland Type 1 cement pastes to improve the mechanical properties of these composites, including compressive, diametral tensile, and flexural strength under freezing and thawing cycles.
Abstract: Organic polymers or fibres in ordinary Portland cement matrices have been shown to improve the mechanical properties of these composites. Such industrial wastes as fly ash and silica fume have been successfully incorporated into cement. Based on these results and the disposal problem of waste tyres, granulated tyre rubbers were incorporated in Portland Type 1 cement pastes. Results from preliminary experiments in compressive, diametral tensile, and flexural strengths under freezing and thawing cycles are reported
TL;DR: In this article, an investigation of cement composite behavior showed that a flexural strength in excess of 28 MPa (4080 psi) can be achieved in normal cement paste by incorporating an optimum amount of silica fume and 11.5% by volume of natural wollastonite micro-fibres.
TL;DR: In this article, an experimental investigation into the ultimate strength of concrete under triaxial laoding was conducted, where several mixes were used with strength ranging from normal strength concrete to very high-strength concrete.
Abstract: Results are presented from an experimental investigation into the ultimate strength of concrete under triaxial laoding. Several mixes are used with strength ranging from normal strength concrete to very high-strength concrete. Other parameters in the mixes were the use of silica fume and type of crushed coarse aggregate with the 3 types of aggregates studied. A 2-parameter model for the failure envelope for confined concrete was adopted. Empirical expressions for the failure envelope were derived for normal strength concrete and very high-strength concrete with and without silica fume. A simple lower bound expression for the ultimate strength of concrete under confinement is presented for any grade of concrete.
TL;DR: In this paper, the microstructure of very low porosity cement and cement-silica fume paste systems was investigated by A.C. impedance spectroscopy (ACIS), and the theoretical relationship between ACIS parameters and the structure of porous materials was confirmed for these systems.
TL;DR: In this article, a study of the behavior of fiber reinforced high strength semilightweight concrete is presented, where the workability, behavior under compression, splitting tension, flexure, and shear.
Abstract: This study of the behavior of fiber reinforced high strength semilightweight concrete investigated the workability, behavior under compression, splitting tension, flexure, and shear. Silica fume and high-range water-reducing admixtures were used to obtain the high strength. The lightweight aggregate used was made of expanded shale. The primary independent variables were fiber content and fiber length. Study results showed that the silica fume can be successfully used to obtain high strength. The brittleness of silica fume concrete can be overcome by using fibers. The addition of fibers provides a significant increase in young's modulus. splitting tensile strength, and shear strength. Strength increase is also considerable under flexure. In all cases, fibers provide substantial improvement in ductility.
Journal Article•
TL;DR: In this article, the authors demonstrated that all three forms of silica fume, uncompacted, compacted low density, and compacted high density, can be readily batched, mixed, and applied in both the dry and wet-mix shotcrete processes.
Abstract: The details are described of a study that demonstrated that all the three forms of silica fume, uncompacted, compacted low density, and compacted high density, can be readily batched, mixed, and applied in both the dry- and wet-mix shotcrete processes. In the wet-mix shotcrete process, incorporating silica fume in the mix resulted in signigicant increases in achievable thickness of build-up compared to plain portland cement shotcrete. In the dry-mix shotcrete process, silica fume use in the mix resulted in substantial increases in achievable thickness of build-up compared to the plain portland cement shotcrete. These and other study findings are presented and discussed.
TL;DR: In this article, the authors investigated the synergistic effect of a ternary system of portland cement, fly ash and silica fume on the performance of concrete mortars, and found that the superplasticizer is more effective in increasing the flow as well as strength than in the case of mortars without mineral admixture.
TL;DR: In this paper, the microstructures of the partially carbonated slices were examined by transmission electron microscopy, and in the case of the OPC the silicate structure was investigated by 29Si NMR.
Abstract: Slices of hardened pastes of OPC and an OPC/silica fume blend of the same water: solids ratio of 0·5 were carbonated in air for 116 days at a fixed relative humidity. The blended paste slices were found to have carbonated less overall, and to a lesser depth, than the OPC slices. The microstructures of the partially carbonated slices were examined by transmission electron microscopy, and in the case of the OPC the silicate structure was investigated by 29Si NMR.
Journal Article•
TL;DR: In this paper, a study of the behavior of fiber reinforced high strength semilightweight concrete is presented, where the workability, behavior under compression, splitting tension, flexure, and shear.
Abstract: This study of the behavior of fiber reinforced high strength semilightweight concrete investigated the workability, behavior under compression, splitting tension, flexure, and shear. Silica fume and high-range water-reducing admixtures were used to obtain the high strength. The lightweight aggregate used was made of expanded shale. The primary independent variables were fiber content and fiber length. Study results showed that the silica fume can be successfully used to obtain high strength. The brittleness of silica fume concrete can be overcome by using fibers. The addition of fibers provides a significant increase in young's modulus. splitting tensile strength, and shear strength. Strength increase is also considerable under flexure. In all cases, fibers provide substantial improvement in ductility.
TL;DR: The effects of alumino-silicate clays on the fracture properties of cement-based materials are reported in this article, where two clays, illite and kaolinite, were used to replace 20% of Type I portland cement in different mixtures.
TL;DR: In this article, an a.c. impedance technique was applied to the investigation of crack growth mechanisms in portland cement and cement-silica fume pastes, mortars and cementwollastonite micro-fiber reinforced systems during compressive loading.
TL;DR: In this article, densified silica fume agglomerates of 40-100 μm size persisted in the concrete, and in the presence of high alkali levels acted like reactive aggregate.
Abstract: Densified silica fume was incorporated in concrete mixes, containing various alkali contents, at the rate of 10% silica fume replacing 20% cement by mass. The cast specimens were steam-cured at 75°C and were examined by scanning electron microscopy, X-ray diffraction and thermal analysis soon after steam curing (1 day), and after periods of28 days and 1 year of external exposure. Mortars with and without silica fume were made with the same cement as that used in the concretes, and their pore solutions were expressed at different ages for the determination of their chemical compositions. The results show that the silica fume is very effective in removing alkali from the pore solution. However, densified silica fume agglomerates of 40-100 μm size persisted in the concrete, and in the presence of high alkali levels acted like reactive aggregate. Nevertheless, the silica fume was very effective in reducing the concrete expansion caused by a reactive granite aggregate, although it added slightly to the expansi...
TL;DR: In this article, the long-term effectiveness of condenser silica fume against asr is questioned by a number of workers, based on expansion tests on concrete containing csf and reactive aggregates, and on the chemistry of the pore solution extracted at different time intervals from equivalent cement-csf pastes.