Showing papers on "Cement published in 1984"

The diffusion of ions through water-saturated cement

Abstract: The interdiffusion of l− and Cl− ions and the tracer diffusion of Cs+ ions in watersaturated Ordinary Portland Cement have been measured at 30° C as a function of water/ cement ratio at fabrication. The diffusion was strongly influenced by the water/cement ratio in an approximately exponential manner and the Cs+ ions were significantly less mobile than the other ions. Diffusion measurements and electrical conductivity measurements have also been made as a function of temperature and reveal that significant irreversible changes in pore structure were induced on heating. The implications of the observations for the diffusion mechanism and the probable pore structure of the cement paste are discussed.

Changes in the structure of hardened cement paste due to high temperature

Abstract: The investigation performed was aimed at explaining explaining experimentally the changes occurring in the microstructure and phase composition of cement pastes during their exposure to heat in the temperature range 20–800°C. The investigation was performed by means of the following methods; thermal analysis, X-ray diffraction analysis, infrared spectroscopy analysis and mercury porosimetry. During the investigation observations were made regarding the behaviour of the following phases in pastes exposed to heat: Ca(OH)2, CaCO3, C−S−H, non-evaporable water and micropores. From an analysis of the experimental results, temperature ranges of the following changes were determined in the structure of the investigated paste: additional hydration of unhydrared cement grains, recrystallization and carbonization of Ca(OH)2, deformation and transformation of C−S−H phases, non-linear changes in the distribution of pore diameters and total porosity.

Set delayed cement compositions and methods of using the same

Abstract: Set delayed cement compositions capable of being retained in pumpable fluid states for long time periods and then activated to set into hard masses and methods of using such compositions for cementing zones at remote locations are provided. The compositions are comprised of hydraulic cement, water, one or more hydratable gel forming materials and one or more methylenephosphonic acid derivative set delaying agents.

Effect of specimen and crack sizes, water/ cement ratio and coarse aggregate texture upon fracture toughness of concrete

Abstract: Synopsis Tests were performed on cement mortar and concrete beams, in two stages, with a view to studying the influence of several specimen and mix variables upon the fracture behaviour of concrete. On the basis of the results from the first stage of tests, in which a single water/cement ratio and type of coarse aggregate were used, a simple formula was established to estimate the fracture toughness of concrete in terms of specimen dimensions, maximum aggregate size and notch depth, together with the mix compressive strength and modulus of elasticity (determined from separate standard cylinder tests). It was found to predict, with sufficient accuracy, the results from the second stage of tests in which, besides variation of the type of coarse aggregate and water/cement ratio, some of the specimen sizes were outside the range used in the first series.

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.

Heat deformations of cement paste phases and the microstructure of cement paste

Abstract: The paper presents the results of an experimental investigation of the influence of thermal deformations of phases present in hardened cement paste on its microstructure. For the observation of the thermal deformation course in the range of temperature20–800°C, a method of complex thermal analysis (DTA, DTD, TD) was employed. The microstructure of heated cement pastes was observed by both optic and electron microscopes.

Curing characteristics of wood particles from nine northern Rocky Mountain species mixed with portland cement [Cement hydration, Idaho].

Abstract: On presente une technique permettant de caracteriser l'effet inhibiteur du bois sur le durcissement du ciment Portland. Cette technique est appliquee a 9 especes de bois du nord de l'Idaho. Les resultats montrent que les systemes bois-ciment-eau sont tres sensibles a l'espece de bois consideree

Cement Shrinkage and Elasticity: A New Approach for a Good Zonal Isolation

Abstract: Characterization of cement bonding performance required the set up of new pieces of laboratory equipment. The evaluation of cement bonding property has been performed under controlled temperature and pressure curing conditions, and was proved to be reproducible with a very small dispersion of results. Shear bond has been tested through mechanical and hydraulic means, and related to other parameters such as volumetric shrinkage development, stress-strain relationships, permeability, and compressive strength. A laboratory and field experimental program has been conducted to compare the bonding capability of standard cement compositions with that of cement modified with a bonding agent. Laboratory and field results are in perfect accordance.

The electrical response characteristics of setting cement paste

Abstract: Synopsis The objective of the work presented in this paper is to investigate the changes in the electrical properties of cement paste during the first 24 hours after gauging with water. It is demonstrated that the electrical response characteristics of setting cement paste can be used as an effective means of studying the progress of cement hydration and for monitoring structuralchanges occurring within the paste

Effects of supercritical carbon dioxide on well cements

Abstract: Due to the widespread manifestation of large scale miscible CO/sub 2/ enhanced recovery projects, particularly in West Texas and Gulf Coast regions, considerable concern has developed regarding the performance and/or durability of hydrated cement located across producing and injection intervals in CO/sub 2/ related wells. It is known that carbonation affects the microstructure of cement affecting both porosity and compressive strength. The CO/sub 2/ reactivity of a cement is characterized not only by its chemical composition, but also by the properties of the CO/sub 2/ medium itself, that is, partial pressure, temperature and relative humidity. However, a clear understanding of this phenomenon and its effects on portland cement is still not completely substantiated, giving rise to contradictory opinions in this particular area of research. This led to the need and development of a laboratory program for examining the effects of supercritical CO/sub 2/ on preset cement, as well as the influence of carbonation on the early stages of the cement hydration process. This article presents the findings of a comprehensive study which show that after prolonged exposure to CO/sub 2/ under supercritical conditions, the hydration products formed in the hydration of common portland cement undergo decomposition into calcium carbonate andmore » a siliceous residue. Cement samples exposed to the lower extremes (temperature and pressure) of a supercritical CO/sub 2/ environment exhibited greater reactivity under dynamic conditions as compared to static conditions, while increasing CO/sub 2/ pressure increased the degree of reaction regardless of the carbonation conditions employed.« less

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.

Bonding in wood fibre-cement composites

Abstract: Much has been written about the mechanical properties of wood-fibre reinforced cement composites (WFRC), but little has been reported on their response to moisture or how the composite materials are bonded. The present observations are consistent with the hypothesis that hydrogen bonds and/or hydroxide bridges play a major role in the mechanical performance of wood fibre-cement composites.

Cement metering system

Abstract: For use in preparing cement to cement a well, a cement metering system is set forth. The preferred and illustrated embodiment incorporates flow meters measuring water delivered to a cement jet mixer for cement and water into a slurry. A downstream density meter is included. A second water line dilutes the slurry to adjust the density downwardly to the desired slurry density controlled by the control system. The control system includes a data formatting circuit connected to the various transducers which converts the data so that the density required for the slurry is obtained. As desired, the data can be totalled by integrating over a period of time and shown on the data display. Volume flow rate of the controlled density slurry and bulk volume of dry cement may be determined.

Non-expansive, rapid setting cement

Abstract: An ettringite-producing hydraulic cement especially adapted to the high speed production of carbon dioxide resistant cement board produces essentially all of its potential ettringite within about 20 minutes after it is mixed with water. The cement is non-expansive and sets within about 25 minutes at a temperature of from about 65°F to about 150°F.

High modulus polyethylene fiber bundles as reinforcement for brittle matrices

Abstract: A process for producing bundles of high modulus polyethylene fibers for reinforcement in composites wherein the matrix is a brittle material such as cement, concrete, plaster of Paris or the like. The process involves passing high modulus polyethylene yarn through high pressure nip rolls to deform the individual filaments and to form a loosely adhering unitary mass or bundle of filaments which is then chopped into short lengths for use as fibrous reinforcement in composites. In a preferred embodiment, the yarn is twisted prior to being passed through the nip rolls.

Origin of Secondary Porosity and Cement Distribution in a Sandstone/Shale Sequence from the Frio Formation (Oligocene): Part 2. Aspects of Porosity Modification

Abstract: Petrographic, SEM, and chemical analyses of closely spaced samples from a core of sandstone and shale (Oligocene Frio Formation, Brazoria County, Texas) reveal a mechanism for secondary porosity development. Maturation of organic and inorganic materials in the shale produced a solvent solution which, upon expulsion, resulted in zoned reservoir quality in the adjacent sandstone. Framework grain dissolution (secondary porosity) originated at the sandstone/shale contact zone (near the solvent source). Aluminum in this zone was not conserved by the process but instead was removed by mobile, shale-derived organic complexers. The production of these complexers (ligands) appears to be essential to the process of framework grain dissolution. Aluminum removal elevated the silica a tivity and resulted in precipitation of authigenic quartz cement. Secondary porosity was developed to a lesser extent farther away from the shale. Imported aluminum from the contact zone and a failure to complex aluminum adequately resulted in kaolinite precipitation. This sink for silica prohibited quartz precipitation. This general process of framework grain dissolution is probably common in sandstone/shale sequences. In summary, secondary porosity development is accentuated by: (1) high initial permeability, (2) increased relative thickness of shale to sandstone, (3) increased organic content in the shale, and (4) abundant soluble grains (potential secondary pores).

Cellulose fibers for cement reinforcement

Abstract: Cellulose fibres such as wood pulp are made more suitable for reinforcement of cement products by a treatment which reduces their swelling in aqueous and alkaline mediums. The fibres are dispersed in water, allowed to swell, and impregnated with a solution of a titanium and/or zirconium chelate compound. After drying, the fibres are heated to react the chelate compound(s) with the hydroxyl groups on the cellulose fibres, preferably to produce cross-linking between hydroxyl group residues. The treated fibres are more stable in cement media, and, despite their increased hydrophobicity, are dispersible in cement slurries to give good web formation in the manufacture of cement products such as sheet. They impart improved flexural strength and modulus to cement products compared with untreated cellulose reinforcing fibres.

Process for placing cement composition having high strength

Abstract: A process for placing a cement composition having high strength is provided. The process comprises the steps of adding a viscosity increasing agent, vacuum de-bubbling under reduced pressure and allowing the de-bubbled cement composition to be hardened. At the vacuum de-bubbling step, relatively large foams present in the cement composition are removed and only fine bubbles are left in the composition. The strength of the cement composition is remarkably improved by the removal of large bubbles.