Showing papers on "Cement published in 1989"

Materials science of concrete

Abstract: Prediction of a Portland Cement's Properties from its Chemical and Mineralogical Compositon. Tricalcium Silicate Hydration: A Historical Overview. Thermodynamics of Hydration Reactions. Tricalcium Silicate Hydration: A Historical Overview. Influence of Initial and Boundary Conditions on Moisture Transport in Hydrated Cement Systems. Ionic Interactions in Cement-Based Materials: Importance of Physical and Chemical Interactions in Presence of Chloride or Sulfate Ions. Mechanisms of Frost Damage. Early-Age Flexural Strength: The Role of Aggregates and Their Influence on Maturity Prediction. Drying stresses and Internal Relative Humidity in Concrete.

Modification of the Bogue calculation

Abstract: The Bogue calculation gives low results for alite and inaccurate ones for the other phases in Portland cement clinkers, largely because the compositions of the phases differ markedly from those of ...

Pozzolanic and Cementitious by-Products in Concrete--Another Look

Abstract: Updates of a 1983 critical review on pozzolanic and cementitious by-products for use in concrete are presented in this paper. The by-products included in this report are fly ash, granulated blast-furnace slag, and condensed silica fume. Recently available worldwide statistics on production and utilization rates of these mineral admixtures are given. New information is presented on their physical and chemical characteristics, structure, and reactivity of the glassy phase, mechanisms by which concrete properties are enhanced, and engineering properties of concrete containing siliceous by-products. A special emphasis is given to durability aspects of concretes incorporating fly ash, blast-furnace slag, or condensed silica fume. Finally, the status of standard specifications and test methods is reviewed, and the contribution of siliceous by-products to make concrete an environment-friendly material of construction is emphasized.

Set retarded cement compositions and methods for well cementing

Abstract: Set retarded cement compositions for cementing across a zone or zones in a well having enhanced compressive strength and rapid gel strength development after placement. The cement compositions are comprised of hydraulic cement, sufficient fresh water to form a pumpable slurry, a set retarder comprising a copolymer of 2-acrylamido, 2-methylpropane sulfonic acid and acrylic acid having an average molecular weight below about 5000 and any other desired additives. Methods of cementing utilizing the cement composition also are provided.

Near-surface characteristics of concrete: prediction of carbonation resistance

Abstract: The relationship between the intrinsic permeability and the Carbonation of concrete is examined. It is shown that the Figg air index test, which is portable, cheap and simple to operate, can be used to predict directly the potential resistance of concrete to carbonation. The water/cement ratio and degree of moist curing are the main factors influencing the quality of concrete in terms of its carbonation resistance.

Bond effects in high-strength silica-fume concretes

Abstract: The strengthening effects in high-strength silica-fume concretes were evaluated in terms of water-reducing effect associated with the reduction in water requirement in the silica fume system and in terms of an inherent effect that reflects the increase in strength of the silica-fume concrete over a similar water/cement ratio concrete without silica fume. The inherent effect was found to be as important as the water-reducing effect, and it is suggested that its origin is in the improved aggregate-matrix bond. This enhanced bonding is associated with the formation of a dense microstructure in the transition zone of the silica-fume concrete.

Injection of Fine Sands with Very Fine Cement Grout

Abstract: The use of very fine cement grouts for injection into fine to medium sands has been proposed recently to circumvent problems associated with the permanence and toxicity of chemical grouts and the inability of ordinary cement grouts to permeate soil formations finer than coarse sand. The results of a laboratory investigation conducted on a commercially available very fine cement grout indicate that this grout has better flow properties and bleed characteristics than ordinary portland cement grputs. Very fine cement grouts with a water‐to‐cement ratio as low as two can permeate several feet into well‐compacted fine sands with D15 in the range of 0.15 mm. The groutability ratio is not a universally applicable criterion, and experimental evidence suggests that the grain‐size distribution of the fine sand, and especially the amount of fines in the sand, may control the grouting operation. The granulometry of the fine sand influences the effectiveness of the grouting operation in terms of permeability and strength.

Cement composition for extrusion

Abstract: A cement composition for extrusion which is produced by incorporating, into cement mortar, 3 to 15 weight % of crushed pulp fiber, 0.2 to 1 weight % of at least one member selected from an alkylcellulose and a hydroxyalkylalkyllcellulose, and a 2% water solution having a viscosity of 80,000 cps or more allows for reduced production costs by reducing the loads of the binder material using a pulp fiber without carcinogenicitic asbestos fiber. Furthermore, it allows for excellent extrudability and provides the moldings with workability such as nailing and sawing.

Bioerodable implant composition comprising crosslinked biodegradable polyesters

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, evantual replacement of the cement with developing bone tissue.

Particle Size Distribution and Rate of Strength Development of Portland Cement

Abstract: The fineness of a portland cement is a key factor in determining its strength development characteristics. A simple one-parameter fineness characterization such as a Blaine value or a sieve residue is often inadequate for a precise evaluation of the influence of fineness on the strength development of cement, especially when comparing cements ground with different grinding equipment. Information on the whole particle size distribution (PSD) of the cement must be used. A mathematical model relating PSD to strength, based on comparison of cements made from the same basic materials (clinker and gypsum) but ground to different PSD, is presented. The model assumes that at a given time of hydration all particles have reacted to the same depth from the original surface. Integrating over the total PSD will give the degree of hydration for a specific size distribution. From a correlation between strength and degree of hydration, differences in degree of hydration can be converted into relative strengths. The applicability of the model is demonstrated by two examples. The first example compares two cements which are ground to different finenesses in the same mill. The second example compares two cements which are ground to the same specific surface area in two different mill systems, bringing about cements with PSDs of different shape. The depth of reaction values found to give the best description seems to be proportional to the square root of time of reaction, indicating a diffusion-controlled hydration reaction.

Fibres and material comprising same

Abstract: Synthetic fibre bundles designed for use in concrete, mortar or cement, the bundles comprising about 10-10,000 filaments per bundle, the filaments consisting essentially of a polyolefin such as polypropylene or polyethylene, a polyolefin derivative, a polyester, a polyamide or a mixture of the foregoing and having a length of about 1 to about 30 mm, a mean transverse dimension of about 5 to about 50 νm and an aspect ratio of about 100 to about 1000, the individual filaments having a surface tension which allows them to become substantially homogeneously dispersed in a concrete, mortar or paste with conventional mixing in conventional concrete mixing equipment; cement-based concretes, mortars and pastes comprising the fibre bundles, and a method of producing the fibre bundles and the cement based materials.

Compressive strength of municipal sludge ash mortars

Abstract: Sludge ashes produced by the incineration of municipal sewage wastes are becoming increasingly difficult to dispose of in landfills, and there is a resulting increase of interest in disposal by inorporation in building materials. In the present study, a comprehensive test program was developed to examine the potential for using the ash as a fine aggregate in mortar. The strength characteristics of mortars prepared from sludge ash with addition of fly ashes (both Classes C and F) and varying amounts of cement and lime were cured under standard laboratory conditions for periods of 1, 3, 7, 14, and 28 days before testing for compressive strength. The results indicate that the addition of sludge ash adversely affects the strength behavior of mortars. Although partial substitution of sludge ash with fly ash gave improved results, strengths were always less than those obtained from control mortars using sand. Addition of fly ashes also improves mortar workability. The addition of lime in place of cement reduces strength.

Analyses of the gaseous species in halide-activated cementation coating packs

Abstract: The partial pressures of equilibrium gaseous species in pack-cementation diffusion processes using pure condensed Al(l), Cr(s), and Si(s) metals activated by various halide salts under Ar or reducing environments which contain different amounts of hydrogen have been calculated. The analyses indicate that the presence of hydrogen gas in the system does not significantly alter the equilibrium partial pressures of gaseous species for a pack containing Al at unit activity. In general, the partial pressures of CrCl2 and SiCl2 are higher in a chloride-activated pack than in a fluoride-activated pack. Therefore, the codeposition of Cr or Si with Al is possible when a chloride salt is used as the activator with a masteralloy of composition dilute in Al. The addition of hydrogen to the gas phase decreases the partial pressure of Cl2 and thereby the partial pressures of CrCl2 and SiCl2. However, the presence of hydrogen and the formation of hydrogen halides and metal hydrides could increase the kinetics of the transporting processes, particularly for the coatings of Cr and Si. The study also indicates that the vapor pressures for the volatile chlorides of Fe are significantly higher than those for Ni or Co, so that displacement reactions leading to the loss of Fe from the substrate are expected for coating processes involving high halide activities.

Solidification of hazardous substances‐a TGA and FTIR study of Portland cement containing metal nitrates

Abstract: Type I Portland cement samples containing the soluble nitrates of the priority pollutant metals chromium, lead, barium, mercury, cadmium and zinc have been investigated using thermogravimetric and fourier—transform infrared techniques (including diffuse reflectance). The major vibrational bands and thermal stability of the carbonate, sulfate, silicate, water and nitrate species are tabulated and discussed in comparison to uncontaminated Portland cement. The solubility and volatility of mercury in cement and the effect of metal nitrate concentration on the silicate condensation process is discussed. Although results suggest that retardation of cement setting by Zn and Pb salts occurs by limiting hydration, the chemistry of the two processes is distinctly different.

Cement, method of preparing such cement and method of making products using such cement

Abstract: A cement based on blast-furnace slag and fly ash, characterized in that the cement is a homogeneous dry particulate mixture in ready-to-use form, which comprises blast-furnace slag having a specific surface area of 500-650 m 2 /kg and fly ash in a weight ratio in the range of 20/80-60/40, and further comprises the following components in the amounts indicated, calculated on the total mixture: at least 2% by weight of portland cement clinker and 2-12% by weight of sodium silicate (calculated as Na 2 O+SiO 2 ).

Comparative studies of the carbonation of hydrated cements

Abstract: A method is described to determine the depth of carbonation of cement paste cylinders using a thermoanalytical method. Depth-profiled thermogravimetry has been used to determine the extent and kine...

Some factors affecting the strength of the cement-metal interface.

Abstract: A manufacturing technique to increase the bonding between bone cement and metal prostheses has been assessed in the laboratory by "push-out" tests, and the effects of contamination of the cement and of the prosthesis with blood and intramedullary contents have been studied. The technique, known as pre-coating, increases bond strength; this increase is preserved after contamination of the cement which does, however, cause some lowering of interface shear strength. The implications for clinical practice are discussed.

Beneficiated Fly Ash: Hydration, Microstructure, and Strength Development in Portland Cement Systems

Abstract: A study of the effects of beneficiation on the performance and properties of fly ash from Lingan Generating Station, Nova Scotia, has been conducted in this paper. A pilot scale high-efficiency air classifier was used successfully to separate the fly ash into product grades with nominal sizes of -45µm, -10µm, and -45/ + 10µm. Overall recovery of the -45µm fraction from the raw ash was 66 percent. Beneficiation was found to generally improve the quality of the fly ash by increasing both the glass content and the proportion of spherical particles. The raw fly ash and the process fractions were all acceptable pozzolans complying with the requirements of CSA Standard A23.5-M1982. Beneficiated ashes showed improved pozzolanic activity, reduced water demand, and enhanced ability to reduce alkali-aggregate reactivity. In ASTM C 109 mortars, approximately twice the quantity of the -45aem fraction compared to the raw ash could be substituted for portland cement without loss of strength at 28d. This indicates that considerable cement savings would be realized from beneficiation of the ash. The -10aem fraction was an even more effective pozzolan with improved strength development and higher ultimate strength (110 percent of control). The hydration of control and portland cement-fly ash pastes (85:15 and 70:30) was investigated at w/c = 0.5 and curing ages from 2 hr to 28 days. In the early stages of hydration, fly ash substitution increased both the rate and extent of ettringite precipitation. At 28 days, the major ions in pore solutions were Na+, K+, and OH- with concentrations similar to the control. Mechanisms for the apparent net depletion of Na+ and K+ with increasing curing age are discussed in terms of a general theory of the chemistry of pore fluids. In general, the ash-containing systems showed less dissolved total alkali than the control. The pore structures of the portland cement-fly ash pastes were investigated by mercury intrusion porosimetry and their permeability to water at 500 psi. While permeability was not uniquely related to the pore structure parameters, it is clear that the fly ash particles in the pastes serve to close the pore structures in a way that generally restricts water intrusion. Whether this is attributable to reduced permeability of the matrix material (possibly as a result of improved nucleation and phase growth) or increased tortuosity remains to be established.