Showing papers on "Cement published in 1977"

Antibiotic-loaded acrylic cement

Abstract: Laboratory experiments and clinical investigations have confirmed the various claims made originally by Buchholz and Engelbrecht (1970) that antibiotic-loaded acrylic cement releases the antibiotic into the surroundings in useful concentrations. Palacos R cement released higher concentrations than CMW, Simplex and Sulfix brands of cement and over longer periods. Concentrations of gentamycin and fucidin were sufficient to penetrate dead cortical bone. These conclusions need to be assessed with animal studies, mechanical testing and clinical results before the ideal place of antibiotic-loaded acrylic cement is established.

Properties of Blended Cements Madefrom Rice Husk Ash

Abstract: Rice husk ash containing silica in a highly reactive form is found to be an excellent ingredient for making either lime-rice husk ash or portland-rice husk ash cements. Properties of both types of cements were investigated by standard ASTM test procedures. Portland-rice husk ash cements containing up to 50% ash showed compressive strengths which were considerably higher than the control portland cements even at early ages of 3 and 7 days. Test data is presented to show that a unique property of the cements containing rice husk ash is their good resistance to dilute organic and mineral acids.

Dental cement containing poly(carboxylic acid), chelating agent and glass cement powder

Abstract: A poly(carboxylate) cement pack comprising a water soluble poly(carboxylic acid) having a relative viscosity of from 1.05 to 2.00, a chelating agent and a cement powder which will react with the poly(carboxylic acid) in the presence of the chelating agent and water to give a plastic mass which rapidly hardens to form a poly(carboxylate) cement.

Methods of preparing iron oxide mortars or cements with admixtures and the resulting products

Abstract: A mortar or cement composition is provided which is adapted for being mixed with water and thereafter set. The composition comprises cement mixed with iron oxide in a ratio of about 1:4. At least one admixture is added from a group consisting of functional water-reducer admixtures, thickener admixtures and defoamer admixtures. The functional water reducer admixture is used to increase the density of the mortar or cement without substantially retarding the setting thereof and without entraining substantial amounts of air. The defoamer admixture is added to reduce air content of the mortar or concrete and to increase the density thereof. The thickener is adapted to inhibit bleeding of water from the mortar or cement. The method of the invention involves making a mortar or cement composition which comprises adding to cement and iron oxide at least one admixture selected from the group consisting of functional water-reducer, thickener, and defoamer admixtures. The thickener admixture may be added to enhance pumpability of the mortar or concrete and the defoamer admixture is used to compensate for the air entrained by the thickener admixture.

Portland cement manufacture

Abstract: Waste matter is incinerated in a combustion zone external to a rotary cement kiln. The resulting gaseous product is taken up in effluent gas from the cement making process in contact with calcareous material. At least some of the combustion zone bottom ash is combined in the eventual standard Portland cement by firing it in the kiln with the clinker-forming materials. The combustion zone can for instance be a fluidized bed combustor. The combustion zone can be a zone through which the clinker-forming materials pass at a temperature such that the waste matter ignites.

The mechanical properties of bone cements

Abstract: The mechanical properties of a number of commercially available bone cements have been investigated. Tests were carried out on specimens in compression, in bending and in tension. Using the compression test as a standard, the effects of the following variables were studied: the addition of antibiotics, strain rate, environmental temperature, and age. It was concluded that age, temperature and rate of straining have a marked effect on the strength of the cement, while the addition of small quantities of antibiotics only marginally weakens the cement.

Admixtures and method for accelerating the setting of portland cement compositions

Abstract: A method of and compositions for accelerating the setting time of portland cement compositions are disclosed. Certain admixtures, comprising water-soluble carbonates and α-hydroxy carbonyl compounds, are employed as accelerators. Preferred accelerators further comprise water-soluble organic compounds having a plurality of hydroxyl groups. The concentration of admixture relative to cement necessary to achieve acceleration depends upon the identity of the admixture, the water-cement ratio, and the amount and type of aggregate in the composition, among other factors.

Hydraulic cement composition

Abstract: A hydraulic cement composition containing a hydrogenation product of an oligosaccharide, such as a hydrolyzate of starch, cellulose or hemicellulose, having an average molecular weight of 300 to 3,500, as an agent for improving the properties of the cement.

Fiber reinforcing composites comprising portland cement having embedded therein precombined absorbent and reinforcing fibers

Abstract: Fibre reinforced composites of cementitious materials or gypsum are reinforced with pre-combined mixtures of strong reinforcing fibres eg, glass or steel, and water absorbent fibres, eg, cotton Examples of composites are cement pipes, wall boards, etc

Catalyst and its method of preparation

Abstract: A catalyst comprising 10 to 30 wt.% of nickel as nickel oxide, 20 to 60 wt.% of calcium as calcium oxide, 10 to 70 wt.% of aluminum as aluminum oxide and containing less than 1 wt.% of silicon dioxide. The catalyst is prepared by using: as the starting material for the nickel component, fine particles of nickel oxide obtained by heating a nickel compound which is decomposed to nickel oxide by heating at a temperature in the range of 400° to 800° C in the presence of oxygen; as the starting material for the calcium component, calcium oxide per se or a calcium compound which is decomposed to calcium oxide by heating and; as the starting material for the aluminum component, alumina cement of a high purity. The catalyst is prepared by mixing and kneading the starting materials with water, molding the same, then keeping the catalyst composition under a highly humid atmosphere at a temperature in the range of 5° to 35° C for longer than one day for hydrating and hardening the cement and thereafter sintering the same at a temperature in the range of 550° to 1200° C.

Treating wells to mitigate flow-after-cementing

Abstract: This specification discloses a method of treating a well drilled into the earth. In carrying out this method there is formed a lightweight thixotropic cement slurry that is comprised of a low density calcined shale cement, attapulgite and water, in ratios to provide a pumpable slurry that has zero water separation. This lightweight thixotropic cement slurry having zero water separation is placed in a well and allowed to set.

The strength of acrylic bone cements and acrylic cement-stainless steel interfaces

Abstract: The strength and fracture toughness of a surgical acrylic bone cement have been evaluated in air, saline solution, and a blood serum, and little effect of environment was observed. Second phase dispersions of either barium sulphate or glass spheres were found to have significant effects upon the strength and fracture surface energy. In the first composite, a decrease in strength and fracture surface energy may be explained in terms of the formation of voids around the barium sulphate particles and tearing of material between them; in the second composite, an increase in strength and fracture surface energy occurred through a crack front-glass sphere interaction effect. The occurrence of subcritical crack growth in the acrylic bone cement composites was investigated, and crack velocity-stress intensity factor diagrams were constructed for the purposes of fracturesafe design.

Inorganic cement grouting system for use in anchoring a bolt in a hole

Abstract: In an inorganic cement grouting system for use in anchoring a reinforcing member such as a rock bolt in a hole, e.g., in a mine roof, by the reaction of the mixed components of the system so as to form a hardened grout around the reinforcing member, the two separate components of the system are: (1) a slush or sludgy mass of a particulate inorganic cement, e.g., an hydraulic cement, and a liquid which is nonreactive therewith, preferably a hydrocarbon, and (2) a liquid, e.g., water, which is reactive with the cement; and sand is present in the cement slush and/or the reactive liquid. The sand is graded to the extent that the deviation from the median particle size is more than about ± 20, and usually more than about ± 30, percent; and particles larger than about 600 microns constitute no more than about 10 percent, and preferably about 5 percent or less, of the total volume of the sand. The inorganic cement constitutes more than 10 percent, and the weight of the sand is no more than about 80 percent, of the total weight of the two components. The two components preferably are delivered into the hole separately, e.g., from separate feeding conduits or, more preferably, in separate compartments of a frangible package, which is broken by the penetration and rotation of the reinforcing member. Graded sand produces a grout having a higher shear strength than that produced from uniform sand, and the substantial absence of particles larger than about 600 microns facilitates packaging and insertion of the reinforcing member into the package.

Experimental Carbonate Cementation: Salinity, Temperature and Vadose-Phreatic Effects

Abstract: Experimental carbonate cementation under various conditions of temperature, solution composition and physical environment of cementation resulted in cements analogous to their natural counterparts reported in the literature. Scanning electron microscopic (SEM), optical microscopic, and chemical analyses of these experimental cements confirm and provide additional criteria for distinction between cements formed 1) in NaCl fresh and marine waters, 2) at various temperatures, and 3) in phreatic and vadose environments. The morphology of a cement crystal is a function of the growth rates of its various faces and of variation of these rates with time. Growth rate is dependent on nucleation rate, temperature, supersaturation state, crystal structure, and presence of various ions in solution. These factors are not necessarily independent. In our experiments the morphology of the cement crystals formed in fresh water did not differ significantly from those formed from NaCl solution except in size, whereas, cement crystals precipitated in the presence of Mg++ ion were morphologically different from those obtained from the other solution compositions. Crystal size varies directly with temperature, supersaturation, and NaCl content of the solution. Increasing temperature and NaCl content of a solution appear to result in increasing crystal size of calcite cements. Three-sided pyramidal crystals of calcite formed in salt- and fresh waters are exact replicates of Mg-calcite cement reported from marine environments, indicating that the composition of the cement may not be inferred from morphology alone.

Effect of Cement Composition on Corrosion of Reinforcing Steel in Concrete

Abstract: The tricalcium aluminate present in portland cement is known to be effective for chloride removal and can thus provide protection against steel corrosion. Contradictions are found in the literature with regard to the minimum tricalcium aluminate content of a cement which is desirable to prevent corrosion of reinforcing steel in concretes exposed to chlorides. A review of published experimental data and some theoretical considerations are presented to show that not only the amount of tricalcium aluminate present but also its crystallographic type and the source of chloride are necessary factors in predicting the corrosion behavior of steel in reinforced concrete.

Method of cementing

Abstract: A cement composition is provided containing portland cement; calcium sulfate hemihydrate; urea; one or more retarders selected from the group consisting of a water soluble salt of a lignosulfonic acid, a low molecular weight hydroxypolycarboxylic acid and sodium, potassium, and lithium salts thereof, and an alkaline hexametaphosphate; and as optional ingredients, calcium chloride and/or a condensation product of mononaphthalene sulfonic acid and formaldehyde; said ingredients being present in amounts effective to provide a cement which will set within a desired period of time at temperatures below about 80° F down to below freezing, e.g. 32° F, to provide a monolithic mass having adequate strength and which also has a sufficient pumping time, i.e., setting time, at higher temperatures, i.e., above about 80° F, so that it can be transported, i.e., pumped at such elevated temperatures without prematurely setting up.

Cements and concretes which contain them

Abstract: The invention is directed to a cement composition comprising (1) 10-30% of an alkaline-earth mineral substance such as a slag or cement having a base of calcium aluminate or a calcined alkaline-earth oxide, (b) 14-56% of a constituent of a grain size of 100 A to 0.1 micron selected from silica, chromium oxide, TiO 2 , ZrO 2 and Al 2 O 3 , and (c) 14-56% of an inert filler of a grain size from 1 to 100 microns, the sum of (b) + (c) representing from 70 to 90% of the cement. Concrete mixtures which employ the inventive cements display superior properties.

The solidification of cement

Abstract: This article describes the development of strength resulting from chemical reactions between cement constituents and added water. The main features of the hydration and development of strength of portland cement and high-alumina cement are described in terms of a comparison between the two types. Both cements are comparable with respect to their system of oxides, their hydraulic properties, and their ultimate strength. The products of hydration and their proportions in the hardened paste of portland cement are considered. It is noted that the reaction between cement and water is exothermic and that under typical conditions the temperature of a paste may rise by tens of degrees. The problems caused by this phenonemon are discussed. The study of the microstructure of the hydrates by electron microscopy shows that the gel fibrils consist of fine hollow tubes. The essential features of the hydration of portland cement and in particular the growth of the fibrillar calcium-silicate-hydrate gel material that is an important factor in the development of strength, is discussed. Since cements (and concretes in general) can develop large compressive strength during hydration, it is usually necessary to reinforce concrete beams or to subject them to prestressing or postressing in compression by the inclusion of stretched steel wires or rods. The prospects for useful modification with the well-developed crystaline hydrates of high-alumina cements are uncertain. With the irregular fibers of portland cement some improvement might be expected if, for example, the fibers could be made less regular and more intricately woven.

Method of cementing

Abstract: A cement composition is provided containing portland cement; calcium sulfate hemihydrate; an alkali metal nitrate; one or more retarders selected from the group consisting of a low molecular weight hydroxypolycarboxylic acid and sodium, potassium, and lithium salts thereof, and an alkaline hexametaphosphate; and as optional ingredients, calcium chloride and/or a condensation product of mononaphthalene sulfonic acid and formaldehyde; said ingredients being present in amounts effective to provide a cement which will set within a desired period of time at temperatures below about 80° F down to below freezing, e.g. 32° F, to provide a monolithic mass having adequate strength.

Inorganic cement grouting system for use in anchoring a bolt in a hole and compartmented package for use therewith

Abstract: In a method of anchoring a reinforcing member such as a rock bolt in a hole, e.g., in a mine roof,wherein two separate components of an inorganic cement grouting system are mixed, preferably in the hole, e.g., by the rotation of the reinforcing member, whereby the components react to form a hardened grout around the reinforcing member, the two components of the system delivered into the hole are: (1) a slush or sludgy mass of a particulate inorganic cement, e.g., an hydraulic cement, and a liquid which is nonreactive therewith, preferably a hydrocarbon, and (2) a liquid, e.g., water, which is reactive with the cement; and a particulate aggregate such as sand preferably is present in the cement slush and/or the reactive liquid. The inorganic cement constitutes more than 10 percent, and the weight of any aggregate present is no more than about 80 percent, of the total weight of the two components. The two components preferably are delivered into the hole separately, e.g., from separate feeding conduits or, more preferably, in separate compartments of a frangible package, which is broken by the penetration and rotation of the reinforcing member. The cement composition in slush form and controlled aggregate content impart lubricity to the system for easy insertion and rotation of a reinforcing member, and make the cement component and the combined components pumpable through small-diameter passageways, while permitting the development of an adequate pull strength in the hardened grout formed around the reinforcing member when the mixed components react.

Porous acrylic cement.

Abstract: The use of acrylic bone cement has a number of shortcomings, viz., high curing temperatures that can cause thermal necrosis, release of toxic monomer, and a less than perfect cement-to-bone bond. However, by modifying the cement composition through the addition of a soluble, nontoxic filler such as sucrose or tricalcium phosphate which does not impair the workability of the material during surgery, a significant improvement in the performance of the cement can be achieved. Because the filler replaces part of the acrylic components, less heat is generated during curing while the filler itself acts as a heat sink. Also, less monomer, proportional to the amount replaced by the filler, diffuses from the implant site. Upon elution of the filler, a porous cement will be obtained provided that a critical minimum percentage loading is exceeded so that the filler crystals will make physical contact with each other. The value of this percentage depends on both crystal modification and size. In the 125–175 μm sucrose crystal size range, the critical minimum percentage lies in the range of 20–28 wt % loading. Above 30%, the interconnecting pore size increases sharply to a value which allows good tissue ingrowth into the pores. The introduction of filler and pores causes a drop in strength, but the diametral tensile strength of modified cement containing up to 40% pores and sucrose lies between .7 and 1.5 kg/mm2, respectively, which is still in the same range as that of bone.