Compressive Strength Of Specimens Research Articles

Residual bond strength of polymer adhesive anchored reinforcement subjected to high temperatures

The results are presented of an experimental project into the residual strength characteristics of polymer adhesives used in anchoring steel reinforcement bars, following exposure to elevated temperatures. The adhesives tested were polyester resin and epoxy resin grouts. Two types of experiment were undertaken designed to investigate the residual bond strength as well as the compressive strength of specimens. For the bond strength determination, pull-out tests were carried out on 150 mm cubes. Compressive tests were undertaken on small cylindrical specimens. All specimens were exposed to different temperatures in pre-heated ovens and then allowed to cool down to normal laboratory temperatures prior to testing. In the bond tests, two types of failure were observed: splitting and slipping. Splitting of the cubes occurred in specimens exposed to temperatures below about 200° C, and the adhesive characteristics were in general enhanced. Slipping failures, by pulling through the adhesive, were obtained in specimens exposed to higher temperatures than about 200°C, and both the residual bond and compressive strengths were observed to diminish with increasing temperature. Additionally, the texture of the adhesive had changed, losing its cohesiveness. Based on this observation, an approach for assessing thein situ bond capacity of anchors is proposed.

Analysis of Delamination Initiation in Postbuckled Dropped-Ply Laminates

The compression strength of dropped-ply, graphite-epoxy laminated plates for the delamination mode of failure is studied by analysis and corroborated with experiments. The nonlinear response of the test specimens is modeled by a geometrically nonlinear finite element analysis. The methodology for predicting delamination is based on a quadratic interlaminar stress criterion evaluated at a characteristic distance from the ply drop-off. The compression strength of specimens exhibiting a linear response is greater than the compression strength of specimens with the same layup exhibiting a geometrically nonlinear response. The analyses for both linear and nonlinear response show that severe interlaminar stress gradients occur in the interfaces at the drop-off because of the thickness/stiffness discontinuity. However, these interlaminar stress distributions are altered in the geometrically nonlinear response such that, with increasing load, their growth at the center of the laminate is retarded while their growth near the unloaded supported edge is increased.

Influence of production factors on the strength of ceramic materials

1. It is experimentally shown that the 95% aluminum oxide-base ceramic has the highest compressive strength among the materials considered, σc=3100 MPa, which is almost 15 and 30% more than the similar characteristics for cast STL-10 pyroceram and 13v technical glass, respectively. 2. The difference between the axial compressive, tensile, and pure bend strengths of specimens cut from sections and parts of chemically resistant porcelain and ceramic VIII produced by forming of a plastic mixture and slip casting in gypsum molds is from 25 to 40%. At the same time the difference between the compressive strength of specimens of ceramic VIII oriented at a right angle in cutting from the nozzle type part produced by slip casting in a gypsum mold reached 60%. 3. The axial compressive strength of the investigated ceramics increases with an increase in aluminum oxide content and decreases with an increase in silicon dioxide content. The bend strength of the ceramics may be increased by 15–80% by selection of the optimum machining conditions and firing temperature of the sections and by decreasing the porosity of the material. 4. The spread in experimental values of the strength of aluminum oxide-base ceramic materials under bending conditions, conditionally characterized by the sample variation coefficient, may be decreased to 8–12% by decreasing the porosity of the material and also by selection of the optimum machining conditions.

The effects of mixing capsule geometry on the early compressive strength of dental amalgam.

Three dental amalgams were mixed in a number of different mixing capsules. Compressive strength specimens were prepared using a clinically relevant technique and tested at 1 h and 7 days. The results showed that the early compressive strength of an alloy was influenced by the mixing capsule, and suggested that internal capsule geometry may be an important contributory factor in capsule performance. With one exception, there was a marked difference between the compressive strengths produced under the present method and those reported by manufacturers under test conditions laid down in standards specifications.

Compressive strength of radiation-induced polymer impregnated autoclaved lime-rich clay

Factors affecting the radiation-induced polymer impregnation of autoclaved lime-rich clay specimens have been investigated. The monomer used is acrylic acid and it was found that the amount of monomer absorbed by the autoclaved specimens increases with increase of acrylic acid concentration and with impregnation time. The degree of polymer incorporation at a fixed γ-irradiation dose of 20 kGy increased with impregnation time of monomer up to 5 hr and also with monomer concentration. An improvement in the compressive strength of the polymer-impregnated autoclaved specimens was observed, and was found to depend mainly on the degree of polymer incorporation. The compressive strength of the autoclaved impregnated specimens was twice the value of the unimpregnated at a degree of polymer incorporation of 12%. The effect of γ-irradiation dose on the degree of polymer incorporation and on the compressive strength of the specimens was also investigated. Infrared and scanning electron microscopic studies of the polymer impregnated specimens were carried out.

A Study of Cement and Concrete Correlation

Abstract American specifications for portland cement require the crushing of mortar cubes for compressive strength of cement and the breaking of cylinder specimens for compressive strength of concrete. It has been assumed that there is a reasonable correlation of mortar and concrete strengths. This has been questioned. A preliminary study of sixty samples showed a significant correlation but indicated a very low order of confidence. A more extensive research was undertaken, which is reported in this paper. This research involved 42 job cement samples and twelve repetitions of a monitor cement. Each of the cements in mortar was subjected to the standard 3, 7, and 28-day strength tests, a repeat of the 28-day test, and two accelerated strength tests. The corresponding cements were tested in cylinders of ready-mixed concrete, sampled at both the batching plant and at the job site. Test specimens of these concretes were broken at seven days and at 28 days. Concrete from the job site was also tested after autogenous curing for two days. The same cements were used in two additional concrete batches at the research laboratory, the first using job mix proportions and the second using a standard formulation. Both batches for each cement used job sand and gravel. These latter concretes were tested after standard curing for 7 and 28 days, and other cylinders after accelerated curing under two different sets of conditions. Much information was obtained concerning the cements, the five mortar tests, the five concrete tests, and their many relationships—mortar/mortar, concrete/concrete, and mortar/concrete. Results were subjected to recognized statistical analysis. The paper includes 25 tables of data, 13 tables of processed information, and 18 figures. An evaluation of the testing laboratories indicated an acceptable level of competency; an analysis of the cement and concrete variations showed normal good levels of operation. These two factors provided limitations but also gave validity to the conclusions that have been drawn from the research.

Alteration in concrete properties depending on conditions and setting period after hydrothermal treatment

The ultimate compressive strengths of specimens exposed to hydrothermal treatment increase steadily during hardening under moist conditions. Hardening in extremely moist conditions (in wet chips, for example) is particularly effective. After 14 days hardening in an atmosphere with a humidity of 95% and a temperature of 18–22°C, the strength of the concrete rises by 16–28% and can reach standard values. Where the hardening temperature is about 8–15°C, conditions of maximum moisture should be obtained so that the rate of increase of the strength will be of the same order. Determinations of water absorption give a picture of the structural changes in concrete for various types of conditions during hardening. When the concrete dries out, its open porosity increases by 10–30%. Hardening in moist conditions after hydrothermal treatment raises the frost resistance of concretes without additives. Hardening in the air has no beneficial effect. Concretes containing a complex plasticizer (sulfite liquor) or an air-entraining agent (air-entraining resin) also exhibit a frost resistance several times greater than additive-free concretes after hydrothermal treatment. If concretes are to attain their design properties after hydrothermal treatment, the most important factor is the provision of a very humid atmosphere for hardening in the initial stage. The duration of such a stage is about 14 days.

Processing Studies on Pure Oxide Bodies

The results of some studies on the effect of (1) ball-milling time, (2) granulating by “slugging,” and (3) dry pressing of pure oxide ceramic bodies are presented. When the compressive strength of specimens of single-component bodies was plotted against ball-milling time (in revolutions), minima in the curves were found between 30,000 and 50,000 revolutions. For a multicomponent body of the porcelain type and one of the oxide porcelain type, when the same data were plotted, maxima in the curves were found between 30,000 and 40,000 revolutions. Granulating by slugging provided 30% greater compressive strength, 1.5% less shrinkage, and 1% less absorption in the specimens as compared with specimens formed from ungranulated material. High-pressure forming, preferably by hydrostatic pressure, was desirable; however, there appeared to be an optimum pressure for the physical properties of each material.

The relationship between compressive strength and age for soils stabilized with four types of cement

Summary: The relationships between unconfined compressive strength and age up to 28 days have been determined for soil-cement specimens made with a sand, a silty clay and a clay, stabilized with four different cements. A comparison has also been made of the effects on compressive strength of coating test specimens with wax and of placing them in a humid atmosphere during the curing period. High-alumina cement was found to give the highest strength after 24 hours, wirh all three soils, but afier 28 days it gave lower strengths than the other cements. Rapid-hardening cement was found to give strengths 20-40 lb per sq. in. greater than normal Portland cement with the two cohesive soils, while super-rapid-hardening cement generally gave strengths about 40 lb per sq. in. lower than those obtained with the other two Portland-type cements. The setting of normal Portland and rapid-hardening cement mixed with the sand was retarded for seven days, due to an organic impurity, but the setting of high-alumina cement was not affected. The addition of lime, or calcium chloride (e.g. in super-rapid-hardening cement) was found to reduce the retardation, the latter being the most effective. The action of calcium chloride in this respect was confirmed with three other soils containing deleterious organic matter. Coating test specimens with paraffin wax during the curing period was found to result in considerably smaller differences in moisture content among similar specimens in a batch than was obtained by storage in a humid atmosphere. This was accompanied by a reduction in the differences in the unconfined compressive strength of specimens only in the case of the sand-cement. The average limits of error of the mean compressive strengths based on ten independent measurements were calculated to be between ±10 and ±20 lb per sq. in. for strengths ranging between 200 and 400 lb per sq. in.

PLASTIC MAGNESIA CEMENTS1

Preparation of the Cement.—Crystalline magnesite from Washington was crushed to three sizes—to pass a No. 6 sieve but retained on a No. 10; between a No. 10 and a No. 30 and to pass a No. 60 sieve. These sizes were burned separately in an electric rotary kiln at 600°, 650°, 700°, 800°, and 900°C. Tests of the Cement.—The cement was tested in three flooring mixes in which the MgO was 35.0, 42.5 or 50.0% by weight, and in three stucco mixes in which the MgO was 11, 22 or 33% by weight. Tensile and compressive strength specimens were broken at 24 hours, 7 and 28 days. The coefficient of expansion was determined at 48 hours, 4, 7, 28 and 90 days. Other properties determined were time of set, consistency, soundness, fineness and effect of density of the chloride solution used. Results.—The property of the calcined cement is materially affected by the size of ore, temperature and duration of burning. The rate of reaction of MgO with chloride materially decreases with increased temperature of burning. Decreasing the concentration of the magnesium chloride solution (down to 22° Bé) accelerates the set of freshly calcined magnesite and retards the set of magnesia which has become hydrated to a considerable extent through exposure. Exposure to moisture before using as well as increasing the consistency of the mixture lengthens the setting lime. A composition which expands excessively and warps or buckles is not necessarily “unsound,” but one which disintegrates within a comparatively short time may be considered as such. Used in this sense, “unsoundness” is believed to result from the presence of free magnesia which hydrates after the mixture has hardened, and not from the presence of lime. Therefore, soundness is not a property of the magnesia alone but depends upon the extent to which it reacts with the magnesium chloride, water, or carbon dioxide before hardening takes place and upon the amount of hydration which subsequently occurs. The steam or cold water tests are unsatisfactory as accelerated tests for soundness of magnesia mixtures. Under the conditions of these tests, the best material with regard to setting time and strength was produced at a temperature of 800°C. However, the magnesia burned at 650°C and which gave comparatively very low strength when gaged with a 22° Bé solution of magnesium chloride, gave excellent strengths when gagrd with more concentrated solutions. Materials tested with 22° Bé solution and giving satisfactory results would not necessarily be satisfactory with a higher or lower concentration. It seems that general specifications should also include limits corresponding with tests in which higher and lower concentrations are used. No relation was found between the volume change and any other property of the magnesia. Tests of any particular mixture are no indication of the behavior of the same magnesia in other mixtures. However, the laboratory tests indicate that the leaner mixtures undergo less change in volume than the richer ones. Furthermore, a number of strict comparisons between laboratory and field tests indicate that the laboratory tests of volume changes as made are no index to the behavior of the material under actual service. The lean mortar mixture proved to be the most suitable of any used for testing magnesia, and in this case the tensile strength furnished as much, if not more, information than the compressive strength.