Showing papers on "Cement 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.

Photocurable ionomer cement systems

Abstract: A dental cement system containing a photocurable ionomer, reactive powder and water undergoes both a conventional setting reaction and a photocuring reaction. The cement system can provide a long working time and can be cured on demand by exposure to an appropriate source of radiant energy. The surface of the cement cured in this manner is then hard enough to allow subsequent clinical procedures to be performed, while the ongoing chemical-cure "setting" reaction hardens the remainder of the cement.

Modelling the Incongruent Dissolution of Hydrated Cement Minerals

Abstract: Hydrated calciumsilicates are the main constituents of hydrated Portland cements. Their chemistry will strongly influence the longterm behaviour of a concrete system envisioned in use in radioactive waste repositories. Experimental data show that hydrated calciumsilicates dissolve incongruently, depending on the calcium/silicon ratio of the solid. A model that simulates the incongruent dissolution behaviour of these hydrated calciumsilicates is presented. In the model the hydrated calciumsilicates are represented as a mixture of two congruently soluble components. The dissolution of the particular components is described using the concept of variable activities in the solid state. Each component's activity in the solid state is obtained from a large body of solubility data by applying the Gibbs-Duhem equation for nonideal mixtures. Using this approach a simplified set of equations, which describe the solubility of the components as a function of the calcium / silicon ratio of the solid, is derived. As an application, the degradation of a standard portland cement in pure water and in a carbonate-rich groundwater is modelled.

Impedance measurements on cement paste

Abstract: Les mesures sont faites pendant le durcissement du ciment apres 1, 14 ou 25 fours d'hydratation; on etudie l'influence de la frequence

A new gas permeameter for measuring the permeability of mortar and concrete

Abstract: Synopsis A permeability cell for measuring the permeability of mortar and concrete to gas is described. The problems encountered and overcome during the development of the cell are discussed. The cell is designed to test 25 mm diameter mortar samples but can also be used for 50mm diameter concrete specimens. Specimens of heights between 10 and 50mm can be tested. Measurements using the new cell are highly repeatable and reproducible. The cell is very sensitive to the influence of water/cement ratio, age and replacement of cement by pulverized-fuel ash. It can be used to obtain permeability profiles through the depth of a concrete element in order to evaluate the influence of different curing conditions or curing compounds.

Bioerodable implant composition

Abstract: An improved bone cement is comprised of a particulate biocompatible calcium phosphate ceramic and particulate resorbable calcium salt dispersed in a cross-linked biodegradable polyester matrix. The polymer/salt-particle composite exhibits good biomechanical strength/modulus characteristics with surgically acceptable cure times. When used for sustained release of biologically active agents in a physiological environment, controlled release of biological agents that are mixed into the composite can be achieved as the cement biodegrades. When used for bone/implant fixation, or as a filler or cement for bone repair, gradual biodegradation of the cement composite permits, under suitable circumstances, eventual replacement of the cement with developing bone tissue.

Reinforced bone cement, method of production thereof and reinforcing fiber bundles therefor

Abstract: The distribution of short, fine, reinforcing fibers homogeneously throughout surgical bone cement is accomplished by adding the fibers in the form of bundles of several hundred fibers with the fibers bonded to each other with an adhesive binder that is soluble in the liquid monomer component of the bone cement. The fiber bundles are either premixed with the powdery polymer bead component of the bone cement followed by addition of the liquid monomer or the polymer and liquid are premixed into a viscous liquid and the fiber bundles are gradually added with stirring to the viscous liquid. In either case, as the adhesive binder dissolves in the liquid monomer the individual fibers are freed and continued stirring mixes the fibers homogeneously throughout the cement mass.

Cement composition curable at low temperatures

Abstract: A blended hydraulic cement composition, curable at low temperatures, including temperatures below the freezing point of water, is composed of portland cement, slag, pozzolans including metakaolin, and admixtures including potassium carbonate and water reducing compositions. The cement is particularly useful in producing concrete compositions which achieve high strength in a brief period of time, and continue curing at ambient temperatures, and temperatures below the freezing point of water.

Grouting composition comprising slag.

Abstract: A grouting composition, a method of grouting and a formation so grouted are disclosed. The composition comprises a very small particle size slag, an equal or greater weight of water and the optional components cement, alkali silicate, anionic dispersant, a source of orthophosphate ions, sodium hydroxide and sodium carbonate. The grout is particularly adapted to the treatment of "tight" or low permeability formations being low in viscosity and having controllable set time and hardening time as well as high strength upon hardening. Being based on slag, a byproduct, the grout is economical.

Synthetic class C fly ash and use thereof as partial cement replacement in general purpose concrete

Abstract: A synthetic Class C fly ash results from a substantially homogeneous blend of about 40-60% by weight of a Class F fly ash and about 60-40% by weight of cement kiln dust (CKD). This new fly ash can replace about 25-50% by weight of portland cement in conventional formulations with coarse and fine aggregate for making general purpose concrete and particularly ready-mix concrete with comparable compressive strength and like properties.

Influence of curing at different relative humidities upon compound reactions and porosity in Portland cement paste

Abstract: The reduction in relative humidity within drying concrete depends mainly on the depth from the exposed surface, exposure duration, temperature and environmental humidity; this limits hydration and coarsens pore structure, thus impairing durability. OPC paste, of 0.59 water/cement ratio, was cured for 2 days and then exposed to controlled relative humidity environments. After 14 and 90 days exposure, hydration of the individual compounds was measured using quantitative X-ray diffraction and thermogravimetry. Methanol adsorption was used to monitor porosity and gel formation. Even a small drop in relative humidity below 95% r.h. significantly limited cement hydration. Gel porosity increased with amount of hydration and, for a given level of hydration, decreased with drying. Curing below 80% r.h. produced a coarsened pore structure with a large-diameter porosity three times greater than that obtained with saturated curing.

Rheological models for cement pastes

Abstract: Shear stress and shear rate data obtained for cement pastes were correlated by means of different rheological models. Pastes were prepared from a commercial Portland cement 325 at different water/cement ratios ranging from 0.34 to 0.42. Tests were performed at 25°C using a rotating coaxial cylinder viscometer. The investigation was accomplished by means of a hysteresis-cycles procedure. On the basis of the goodness of fit, the Herschel-Bulkley model seemed to be very effective for application to cement pastes.

Hydraulic cement and composition employing the same

Abstract: A hydraulic cement is formed from a Class C fly ash, an alkali metal activator, and citric acid. Mortar and concrete compositions can be prepared with this hydraulic cement. The cement is particularly useful in producing mortar and concrete compositions that achieve high strengths in a short time, in particular, a mortar having a strength of at least 2500 psi in 24 hours, when cured at room temperature.

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.

Properties of Fiber Reinforced Concrete: Workability, Behavior Under Long-Term Loading, and Air-Void Characteristics

Abstract: This paper presents the results of an experimental invesigation of the behavior of steel fiber reinforced concrete. The properties investigated were: setting times, slump and air content loss with time, creep and shrinkage, and air-void characeristics including bubble size distribution. To compare the behavior of fiber reinforced concrete with plain concrete, all of the proceding properies were also investigated for plain concrete mixtures of similar composition. Two mixture proportions with cement contents of 611 and 799 lb/yd sup 3 (363 and 474 kg/m sup 3) were investigated. The lower cement content that was used with a water-cement ratio of 0.4 resulted in a highly workable medium-strength concrete. The compressive strength was in the range of 6000 psi (41 MPa). The higher cement content, wih a 0.3 water-cement ratio, resulted in a relatively stiff concrete with an average compressive strength of 7000 psi (48 MPa). High-range water reducers and air-entraining admixtures were used for all the mixtures. Collated 50 mm long steel fibers with hooked ends were used for the fiber concrete. The experiments were conducted using the appropriate ASTM standards. The air-void characteristics were studied using the linear traverse method. The results indicate that setting times are about the same for both concretes. Fiber concrete has lower slump and air content; the rate of loss of these parameters with time is also higher. Shrinkage of fiber reinforced concrete is slightly less, but it undergoes slightly more creep deformations. In the area of aid-void characteristics, the specific surface of air bubbles is lower for fiber reinforced concrete, and it has relatively less number of chord-intercepts in the 0 to 0.002-in. (0 to 0.05-mm) range.

Welan gum in cement compositions

Abstract: Cement compositions, i.e., mortar, structured concrete, pre-cast concrete, and oilfield cement, comprising 0.01-0.9% (wt/wt) welan gum are described.

Cement/gypsum composites based cellulose-I

Abstract: Composite materials based on cement or gypsum materials reinforced by mixing with cellulosic fibers grafted with silylating agents. Processes for preparing these reinforced composites are also disclosed.

Strength and Durability Considerations Affecting Mix Proportioning of Concrete Containing Fly Ash

Abstract: The results of a 3-year study on the properties of concrete containing fly ash are presented. Both the fresh and hardened properties are reported of concrete made using Type 1 cement, river gravel, natural sand, and fly ashes from several sources. The mixtures were proportioned to have similar slump and a constant cementitious content by weight. It is shown that concrete containing fly ash can be proportioned having equal strength properties and adequate durability when a suitable ASTM C 618 Class C or F fly ash is used. Test data on over 1600 laboratory and field specimens tested for freeze-thaw resistance, flexural strength, compressive strength, creep, shrinkage, and abrasion resistance are presented. Fly ash contents ranging from 0 to 35 percent by weight of portland cement were used with both Class C and Class F fly ashes. Guidelines for the selection of materials and their proportions for producing concrete containing fly ash to meet existing highway specifications for concrete are presented.

Influence of sulphate source on Portland cement hydration

Abstract: Synopsis Cements were synthesized by blending a Type I low alkali Portland cement clinker with sulphate salts. A quantitative X-ray diffraction method was developed to measure the rate at which the C3A and C4AFphases in these cements were consumed in pastes hydrated at 23°C. The initial high rate of aluminate phase consumption was influenced significantly by the rate of solubility of the sulphate source, and especially the rate at which it released CaSO4 into solution. Interground gypsum was far more effective than interblended gypsum in controlling aluminate hydration. Better control of the initial aluminate hydration generally led to higher 28-day paste strengths.