Showing papers on "Cement published in 1975"

A characterization of polymethylmethacrylate bone cement.

Abstract: Polymethylmethacrylate cement is characterized in terms of chemical composition, handling characteristics, and physical properties; the dough time, setting time, handling time, and temperature rise were found to be most affected by environmental temperature and kneading of the dough mass. As the set material ages, the residual monomer content gradually decreases and the strength increases. A volume shrinkage of up to 5 per cent was observed. The porosity, which is increased by rapid mixing, may reach 10 per cent. The mechanical properties of the cement approximate those of polymethylmethacrylate denture base material. Some variability encountered in the handling qualities of the cement could be attributed only to the variability of different batches.

The conversion of high alumina cement

Abstract: Synopsis High alumina cement (HAC) concrete suffers from a conversion reaction in which the metastable calcium aluminate hydrate compounds change to more stable compounds. This reaction takes place at a rate which depends upon a number offactors including temperature, water/cement ratio, stress and the presence of ‘releasable’ alkalis in the aggregate. As a result of the reaction, the concrete will lose strength and the strength will reach a minimum at various times depending upon conditions of storage; thereafter there may be a small increase in strength. The strength at this minimum, S, expressed as a percentage of the one-day strength depends upon the rate, R, at which the conversion reaction takes place, and upon the water/cement ratio. An empirical relationship for laboratory-prepared specimens is S = (− 37·8 logeR + 39·5) − 100(w/c − 0·4). However, this cannot be used for unknown concretes until a reliable method of determining the original water/cement ratio of HAC concrete is available. Rapidly co...

Siliceous ashes and hydraulic cements prepared therefrom

Abstract: Siliceous compositions are prepared from naturally occurring plant materials (particularly rice hulls and rice straw) which have relatively high silica concentration by controlled incineration of the plant material to preserve the original cellular structure of the material and to prevent formation of crystalline forms of silica so that the silica in the product (which may contain from about 49% to about 98% silica remains in the amorphous state; the novel silica containing compositions find utility as a constituent of novel hydraulic cement compositions of high strength and acid resistance, useful in the preparation of mortar and concrete.

Use of polymethylmethacrylate to enhance screw fixation in bone.

Abstract: Pull-out testing of screws inserted into cement and bone under various conditions showed that the cement-screw complex was significantly stronger when the screw was placed in soft cement and the cement was allowed to polymerize without further manipulation. When screw fixation in osteoporotic bone was reinforced with cement, the bone was the weakest component in the system. Fixation under these conditions should be enhanced by increasing the area of contact between the cement and bone. By cooling the cement to prolong its working time, it could be injected with a syringe in such a way that maximum endosteal and periosteal contact was provided.

Cotton-cement articles

Abstract: A cotton reinforced, cementitious, hydrated product is made by combining on a dry basis between about 25 and about 75 wt. % Portland cement, between about 1 and about 15 wt. % cotton fiber, between about 3 and about 30 wt. % inorganic filler and preferably between about 10 and about 40 wt. % silica with water to form an aqueous slurry. The slurry is formed into desired shapes such as sheets or slabs and cured by autoclaving to produce the desired product.

Carbon Isotopes and Limestone Cement

Abstract: Most marine limestones have about the same δC 13 as marine carbonate sediments, about 0 per mil versus the PDB isotopic standard. Because the limestones are half cement, the cement too must have δC 13 of about 0 per mil. In contrast, limestones lithified by contact with vadose or phreatic meteoric waters, as in Bermuda, have strongly negative δC 13 . This suggests that most limestones in the geologic record are cemented, at least mainly, by a different process that takes place during burial diagenesis. Pressure solution is important in transferring CaCO 3 from “donor” sites along stylolites and microstylolites to “receptor” sites in pores. Shales may also be important donors for limestone cements.

New and Conventional Engineering Uses of Fly Ash

Abstract: Successful uses of pozzolanic fly ash for modification of a highly plastic clay, and of natural and stabilized fly ashes to effect economy in road construction, are described. Three fly ashes collected in dry, moist, and sludge states were investigated in detail for modification of a highly plastic clay. Laboratory investigations were conducted to determine suitability of natural fly ash for structural fill, and lime and cement stabilized fly ashes for base course construction. Field trial sections were constructed and performance tests made to evaluate technical and economic feasibility. Laboratory and performance data on trial sections indicate that: (1) It is possible to modify a highly plastic clay with a pozzolanic fly ash to provide stable subgrades; (2) structural fills of compacted pozzolanic fly ashes gain strength with time and are lighter and stronger than clay or sand fills; and (3) base courses of cement stabilized fly ashes can be constructed with available equipment.

Effect of Various Accelerating Chemical Admixtures on Setting and Strength Development of Concrete

Abstract: A study of the rate of hardening of concretes which contain inorganic accelerators demonstrates the superior performance of calcium chloride. However, there are significant changes in the compressive strength of concretes at various ages when accelerators are employed. Calorimetric studies of cement mortars show the advantages as an accelerator that calcium chloride maintains over other inorganic salts. Also, calorimetric tests demonstrate what appears to be different mechanisms of acceleration between different kinds of accelerators. Differential thermal analysis (DTA) techniques were applied to a study of the effect of calcium chloride and calcium formate on the early stages of hydration of a cement. DTA patterns show definite differences between the function of the accelerators.

Magnesia cement composition, process of its manufacture, and composite comprising same

Abstract: A magnesia cement composition comprising active magnesia, magnesium sulfate, and pulp or a mixture of pulp and fibrous glass When hardened, this composition yields a crack-free low-shrinkage material Valuable composite boards are obtained by lamination from the hardened composition and core materials such as cellular concrete, plywood, plastic foam, gypsum plaster board, and cemented excelsior board

Void free electrical cement-concrete

Abstract: Electrical insulation grade concrete is prepared by mixing the aggregate and cement with an excess of water and thereafter vacuum deaerating and vacuum dehydrating the resulting mixture.

Method of simultaneously strengthening the surface of a borehole and bonding cement thereto and method of forming cementitious pilings

Abstract: An improved method of consolidating the surface of a borehole in an incompetent formation and simultaneously strengthening the bond between the surface of the borehole and cement placed in the borehole is achieved by forcing an aqueous solution of a multivalent cation salt into the formation, thereafter forcing an alkali metal silicate solution which has a pH less than 12.0 containing at least 12% by weight silica into the formation, and thereafter forcing an aqueous cement slurry containing at least 2% by weight of a water soluble multivalent cation salt to contact the surface of the borehole. A cementitious piling intimately bonded to the formation is prepared by filing the stabilized borehole with an aqueous cement slurry and allowing the cement to harden.

High alumina cement concrete

Abstract: Temperature Dependence of Compressive Strength of Conversion. 22 Dec 2016. Heat-resisting concrete 1500 oC Refractory Concrete using high alumina cement HAC. Concrete slump 180 – 200 mm Cube compressive

Dimensional behavior of curing bone cement masses

Abstract: The curing of bone cements is accompanied by release of polymerization heat and, hence, by a temperature rise of the curing cement mass. This temperature rise causes expansion of enclosed air bubbles and evaporation of the volatile monomer. An overall expansion of 3 to 5 vol % has been mentioned in the literature. It has often been stated that this expansion favours the fixation of metal endoprostheses in the marrow cavity of bone. To check for the influence of this expansion on linear dimensions of the cured cement mass we filled stainless steel cylinders with a precision bore of 22,000 ± 0,005 mm and a length of 120 mm with bone cement. After curing of the cement in a environment of 37°C the resulting cement rod was released from the cylinder and the diameter of the rod was measured at 37°C. The influence of the “foaming effect” on the transverse dimensions of the rods was studied by curing the cement at 37°C and 2 atm air pressure in a high-pressure-vessel. This method of curing eliminates porosity in the cement almost completely, so that curing shrinkage is to be expected rather than expansion of the cement mass. The results indicate that a volumetric expansion of the cement during curing of cylindrical rods in laboratory experiments, can be accompanied by a linear diametrical shrinkage of the cement mass. The explanation of this phenomenon is to be sought in the fact that the volumetric expansion takes place at a time when the cement is still plastic; by the formation of gas bubbles, the cement is forced in longitudinal direction into the cylinder and when the temperature of the mass has passed through a maximum, the cooling of the cement mass results in a thermal shrinkage of approximately 0.4% linearly. Extrapolating this laboratory result to a clinical situation one might doubt whether the overall expansion of bone cements during curing will result in a permanent positive pressure on the walls of marrow cavity and whether it will contribute to a better fixation of endoprostheses than in the case of a, still hypothetical, nonporous cement.

Pozzolans - a review

Abstract: The occurrence, availability, and use of natural pozzolans and fly ash, their effects on the properties of concrete and the state of our knowledge regarding their chemical and physical action are discussed. The need for research on high-lime fly ashes and for extending the use of fly ash in cement blends is proposed.

High early strength cement

Abstract: A high early strength cement composition is disclosed which is capable of providing sufficient compressive strength within 2 to 24 hours to enable one to use it in highway or airport runway patching. The cement also exhibits satisfactory ultimate strength, that is, strength after 28 or more days of curing. The high early strength cement comprises a mixture of portland cement, calcium aluminate, and calcium sulfate in certain specified proportions.

Apparatus for manufacturing concrete panels with surface pattern decorations

Abstract: An apparatus for manufacturing concrete panels with surface decoration patterns thereon said surface decoration patterns being formed by finishing material containing color cement or pigments or other coloring materials The apparatus comprises a mortar hopper having a mortar outlet opening and a mortar shoot extending downward from beneath the outlet opening of the hopper A molding surface is positioned below the mortar shoot and the mortar shoot extends to the molding surface Color mortar containers are disposed above the mortar shoot to discharge color mortar materials contained therein A mixing means incompletely mixes the mortar with the color mortar materials on the mortar shoot, a mixed mortar inverting descent guide plate is connected to the lower end of the mortar shoot and a vibrator is attached to the mortar shoot The mortar layer which is obtained with color patterns produced through the incomplete mixing carried out by the mixing means is laid on the molding surface by the relative movement between the mixed mortar inverting descent guide plate and the molding surface

Fifty year properties of concrete

Abstract: Compressive strength, unit weight, and volume changes of concrete for ages up to 50 years have been determined. Variables included are types of cement and coarse aggregate, mix proportions, consistency, methods of placement, and storage conditions. Over 2500 concrete cylinders, 132 concrete expansion prisms, and several thousand mortar cylinders and briquets were made in 1910, 1923, and 1937 for this program. Earlier reports on these tests were published in 1931, 1943, and 1961. Under outdoor storage in Madison the compressive strength of concrete made with coarsely ground cements having high C2S contents generally increased as the log cf the age out to 50 years, but concrete made with finer cements having relatively low C2S contents appeared to reach maximum strength at ages between 10 to 25 years and showed some retrogression thereafter.

Strength and Related Properties of Brick Masonry

Abstract: Sixteen important controllable variables in the strength of conventional brick masonry are related in 10 equations for strength in compression, flexure, and shear. Axial compressive strength of standard brick masonry prisms is a function of the compressive strengths of brick and mortar and quality of workmanship. The compressive strength of brick is a function of unit size and shape, raw material, manufacturing process and degree of burning. Compressive strength of mortar is a function of cement, lime, water and air content, curing condition and batch life. Flexural strength of brick masonry is a function of brick-mortar bond, joint thickness, and mortar cement content. Bond strength of brick to mortar is a function of mortar flow, air content, and exposure time, and brick suction and surface condition. Shear strength of brick masonry is a function of brick-mortar bond strength, compressive stress and coefficient of internal friction.

Exposed aggregate finishing method for concrete

Abstract: An exposed aggregate finishing method for concrete. The method comprises coating the inside faces of a form for concrete with a cement setting retarder, drying, coating the dried faces with a synthetic organic polymer coating material which is soluble in an aqueous alkaline solution of cement, but is insoluble in water; and drying the coated faces. Alternatively, the method may be carried out by coating the inside faces of the form for concrete with the mixture of the cement setting retarder and the organic polymer coating material and drying the coated faces. Concrete is thereafter placed in the concrete form, the form removed and the surface of the molded concrete washed to make the surface rough.

Early strength cements

Abstract: An early strength hydraulic cement is disclosed in which a clinker rich in C12 A7 and poor in CA or C3 A interground with Portland cement clinker, the resultant early strength cement including at least 10% by weight of C12 A7 with a majority of the balance being calcium silicates and including at least 10% by weight of C3 S.

Economical, finely controlled cement production

Abstract: Method and apparatus for manufacturing portland cement characterized by a plurality of steps. First, there is introduced into the feed end of a rotary kiln at a first rate a first mixture containing calcareous material for the cement; and at a second rate a second mixture including at least one of argillaceous material and siliceous material for the cement. Either or both mixtures may be coarsely ground. Next, there is introduced into the combustion zone of the kiln at a third rate a third mixture and a fuel, the third rate of the third mixture being complementary with the second rate of the second mixture and the first rate of the first mixture so as to form a balanced cement clinker for the cement, the cement clinker being discharged from the discharge end of the kiln for further processing into the desired final form of the cement. Also disclosed are more specific embodiments including respective sampling and analysis procedures at a plurality of points in the kiln system and the respective altering of proportions of the mixtures to maintain an exceptionally high degree of on-line control over the quality of the final cement clinker; the admixture of the first and second mixtures with slurry for a combination process that has the advantages of both the wet and dry processes; the manufacture of special purpose cement; and the specific apparatus and advantages.

Hydrothermal cement and method of cementing well bores

Abstract: A hydrothermal cement composition consisting essentially of (a) a polyvalent metal ion source, (b) water, and (c) a hydratable silica source wherein the silica becomes available for chemical combination with the polyvalent metal salt upon application of heat. A method of cementing a string of pipe in a bore hole including the steps of preparing such a cement composition, pumping the cement composition into the annular space between the string of pipe and the walls of the bore hole, and allowing the cement to set due to the temperature of the bore hole or by passage of time or both.

Shrinkage-compensating portland cement concrete and mortar compositions

Abstract: This invention pertains to improved shrinkage compensating portland cement concrete and mortar compositions comprising essentially an expansive portland cement, mineral aggregate, from about 5 to about 25 percent based on cement weight of a styrene-butadiene-1,3 copolymer having a styrene to butadiene weight ratio of about 30:70 to 70:30, water and certain minor amounts of nonionic and anionic surfactants, and a foam depressant. When properly restrained by either external restraints or internal restraints in the form of ordinary reinforcement or fibers of various lengths, these compositions possess improved mechanical and physical properties such as compressive and flexural strengths and unexpectedly enhanced freeze-thaw resistance. Such compositions are particularly suited for use in the construction of crack-free structures.