Showing papers on "Compressive strength published in 1995"

Stress-Strain Model for Confined High-Strength Concrete

Abstract: A stress-strain model for confined high-strength concrete has been developed and calibrated against the test results from 50 large-scale high-strength concrete tied columns tested under concentric loading The effects of the concrete compressive strength, tie yield strength, tie configuration, transverse reinforcement ratio, tie spacing, and longitudinal reinforcement ratio are accounted for in the proposed stress-strain model The determination of the strength and ductility of confined concrete is based on the computation of the effective confinement pressure, which depends on the stress in the transverse reinforcement at maximum strength of confined concrete, and on the effectively confined concrete area A method is proposed to compute the stress in the transverse reinforcement at maximum strength of confined concrete

Effect of curing on the compressive strength, resistance to chloride-ion penetration and porosity of concretes incorporating slag, fly ash or silica fume

Abstract: This paper reports an investigation in which the performance of slag, fly ash, and silica fume concretes were studied under four different curing regimes. The water-cementitious materials ratio of all the concrete mixtures was kept constant at 0.50, except for the high-volume fly ash concrete mixture, for which the ratio was 0.35. The concrete specimens were subjected to moist curing, curing at room temperature after demoulding, curing at room temperature after two days of moist curing, and curing at 38 °C and 65% relative humidity. The compressive strength was determined at various ages, and the resistance to chloride-ion penetration was measured according to ASTM C 1202 at different ages up to 180 days. Mercury intrusion porosimetry tests were performed on the 28-day old mortar specimens for comparison purposes. The results indicate that the reduction in the moist-curing period results in lower strengths, higher porosity and more permeable concretes. The strength of the concretes containing fly ash or slag appears to be more sensitive to poor curing that the control concrete, with the sensitivity increasing with the increasing amounts of fly ash or slag in the mixtures. The incorporation of slag or silica fume, or high volumes of fly ash in the concrete mixtures, increased the resistance to chloride ions and produced concretes with very low permeability.

Shear vs. Tensile Bond Strength of Resin Composite Bonded to Ceramic

Abstract: Since the mode of failure of resin composites bonded to ceramics has frequently been reported to be cohesive fracture of either ceramic or resin composite rather than separation at the adhesive interface, this study was designed to question the validity of shear bond strength tests. The reasons for such a failure mode are identified and an alternative tensile bond strength test evaluated. Three configurations (A, conventional; B, reversed; and C, all composite) of the cylinder-on-disc design were produced for shear bond strength testing. Two-dimensional finite element stress analysis (FEA) was carried out to determine qualitatively the stress distribution for the three configurations. A tensile bond strength test was designed and used to evaluate two ceramic repair systems, one using hydrofluoric acid (HF) and the other acidulated phosphate fluoride (APF). Results from the shear bond strength tests and FEA showed that this particular test has as its inherent feature the measurement of the strength of the ...

Compressive and tensile failure of inclined well bores and determination of in situ stress and rock strength

Abstract: In this paper we investigate the occurrence of compressive and tensile failures of arbitrarily inclined well bores under a wide variety of stress conditions. The principal assumptions in this analysis are that the rock is isotropic and that it deforms elastically to the point of failure. As has been shown by previous investigators, for a given stress state and well bore orientation, it is straightforward to predict the orientation of the failures around the well bore as well as whether failure is likely to occur depending on such parameters as rock strength and borehole fluid pressure. However, as the stress state is almost never known in situ, we demonstrate how observations of compressive and tensile wall failures in inclined holes can be used to constrain in situ stress orientations and magnitudes if there are independent data on the magnitude of the least principal stress from either leak-off or microfrac tests and on the formation pore pressure. We further demonstrate how once the stress state is determined, it is possible to assess both an upper bound on the effective in situ rock strength and the degree to which increasing the borehole fluid pressure (or mud weight) can reduce the likelihood of borehole failure. Through application of this methodology to an inclined well bore in an area of complex faulting in the Gulf of Mexico, we illustrate how it is possible to utilize observations of borehole failures to determine the magnitude and orientation of the stress tensor in areas such as offshore sedimentary basins where drilling inclined well bores is quite common.

Strength, durability and shrinkage characteristics of cement stabilised soil blocks

Abstract: The paper outlines results of a comprehensive investigation undertaken to assess the influence of soil characteristics and cement content on the physical properties of stabilised soil blocks. The dry density, compressive and flexural strength, durability and drying shrinkage of over 1500 block tests are outlined in the paper. Experimental results are compared with current specifications and used to develop empirical guidelines for cement content requirements for a range of soil plasticity characteristics. An empirical relationship between compressive and flexural strength is proposed as a simple means of field assessment.

Limits on strength and deformation properties of jointed basaltic rock masses

Abstract: A study of strength and deformation measurements for basaltic rocks, along with consideration of the influence of fracturing using a rock mass classification system, documents the range of brittle response for basaltic rock masses. Although basalts vary widely in composition and other physical factors, many of the properties of a basaltic rock mass appear to vary within a factor of about 10. Typical values of strength parameters for intact basalt at ambient temperature (20°C) and negligible confining pressure are Young's modulus, 78±19 GPa; Poisson's ratio, 0.25±0.05; tensile strength, −14.5±3.3 MPa; unconfined compressive strength, 266±98 MPa; and conhesion, 66 MPa. Corresponding values for a basaltic rock mass that incorporate the weakening effects of scale are deformation modulus, 10–40 GPa; Poisson's ratio, 0.3; tensile strength, −0.1 to −2.5 MPa; uniaxial compressive strength, 10–90 MPa; and cohesion, 0.6–6 MPa. A measured deformation modulus for ambient pressure in the vertical direction, 20 GPa, is 1.5–3 times larger than that in the horizontal directions, 13.5 and 6.5 GPa, reflecting strength anisotropy due to column or block geometry for one particular basalt. Values of tensile and cohesive strength for the basaltic rock mass are generally one to two orders of magnitude lower than corresponding values for intact basalt. The shear strength of joints appears to vary considerably from flow to flow.

HPC Strength Prediction Using Artificial Neural Network

Abstract: An artificial neural network of the fuzzy-ARTMAP type was applied for predicting strength properties of high-performance concrete (HPC) mixes. Composition of HPC was assumed simplified, as a mixture of six components (cement, silica, superplasticizer, water, fine aggregate, and coarse aggregate). The 28-day compressive strength value was considered as the only aim of the prediction. Data on about 340 mixes were taken from various recent publications. The system was trained based on 200 training pairs chosen randomly from the data set, and then tested using remaining 140 examples. A significant enough correlation between the actual strength values and the values predicted by the neural network was observed. Obtained results suggest that the problem of concrete properties prediction can be effectively modeled in a neural system, in spite of data complexity, incompleteness, and incoherence. It is demonstrated that the approach can be used in multicriterial search for optimal concrete mixes.

Evaluation of density and strength of Norway spruce wood by near infrared reflectance spectroscopy

Abstract: The non-destructive evaluation of wood properties by Near Infrared Reflectance Spectroscopy (NIR) has been assessed. The surfaces of specimens of clear wood (Picea abies) were NIR-scanned, and the results compared to such properties as moisture content, density, compression strength and chemical and biological degradation. In addition, the NIR-scans of clear wood specimens were compared to the bending strength of the structural timber from which it had been cut. The NIR dependency of surface roughness was investigated and found to be of minor importance.

Impact Behavior of Plain Concrete Loaded in Uniaxial Compression

Abstract: The uniaxial stress-strain response has been measured for air-dried plain-concrete cylinders, nominally 100 mm in diameter and 250 mm long, loaded in compression at both a slow static rate of about 10 microstrains per second and a much higher impact rate of between 5 and 10 strains per second. Design concrete strengths of 30 and 50 MPa were tested. Static loading was carried out in a hydraulic testing machine, and a guided free-falling mass was used for impact loading. The impact and static responses are compared to provide some insight into the behavior of concrete during hard-impact loading. Differences in behavior are identified for various strength and deformation characteristics. Although the maximum strength and corresponding axial strain, the energy-absorption capacity at failure, and the secant modulus all increase during impact loading, the initial tangent modulus does not appear to change very much. Other characteristics such as volumetric strain and Poisson’s ration are also studied. A simple physical model is used to help explain observed changes.

Laboratory Investigation of Compacted No-Fines Concrete for Paving Materials

Abstract: In this study the physical and engineering characteristics of various no-fines concrete mixtures are investigated. No-fines concrete mixtures subjected to impact compaction are studied under unconfined compression, indirect tension, and static modulus of elasticity; and the results are interpreted as functions of mixture proportions. The effect of impact-compaction energies, consolidation techniques, mixture proportions, curing types, and testing conditions on physical and engineering properties are presented. The abrasion characteristics and resistance to freezing and thawing of no-fines concrete are also discussed. It was found that the strength of no-fines concrete is strongly related to its mixture proportion and compaction energy. A sealed compressive strength of 20.7 MPa (3,000 psi) can readily be achieved with an aggregate cement ratio of 4.5:1 or less and a minimum compaction energy of 165 J/m 3 (4,303 ft-lb/cu ft). The splitting tensile-compressive relationship followed a pattern similar to that ...

High strength and high density intraluminal wire stent

Abstract: An intraluminally implantable stent is formed of helically wound wire. The stent has a generally elongate tubular configuration and is radially expandable after implantation in a body vessel. The wire includes successively formed waves along the length of the wire. When helically wound into a tube, the waves are longitudinally nested along the longitudinal extent of the stent so as to form a densely compacted wire configuration. After radial expansion the stent maintains high radial compressive strength and wire density to retard tissue ingrowth.

Mechanical properties of hydroxyapatite formed at physiological temperature

Abstract: The mechanical properties of monoliths of calcium-deficient and carbonated hydroxyapatite formed by dissolution-precipitation reactions at 38°C have been determined. Particulate solid reactants were mixed at liquid-to-solid weight ratios of 0.11 and 0.2 and pressed into various configurations on which mechanical tests were carried out. Testing was performed on wet had formed. Calcium-deficient hydroxyapatite produced at a liquid-to-solids ratio of 0.11 exhibited a tensile strength as high as 18 MPa, an average compressive strength of 174 MPa and a Young's modulus of 6 GPa. These values were lower when a larger proportion of water (liquid-to-solid 0.2) was used in sample preparation. However, the compressive strengths of calcium-deficient hydroxyapatite prepared at 38°C are comparable to the compressive strengths of sintered hydroxyapatite containing an equivalent total porosity. Carbonated hydroxyapatite showed mechanical properties inferior to those exhibited by calcium-deficient material. These differences appear to be related to the microstructural variations between these compositions.

Innovations in acrylic bone cement and application equipment.

Abstract: A new bone cement was developed with the purpose of reducing the adverse biological effects during cementation of implants. This bone cement is characterized by lower exotherm, low release of monomer, low residual content of monomer, and retained physical properties. The essential innovation was substitution of half of the methylmethacrylate (MMA) in the monomer with long chain, high molecular weight, less volatile, and less soluble methacrylates (n-decylmethacrylate, isobornyl-methacrylate), as well as alteration of the accelerator system to a mix of dihydroxypropyl-p-toluidine and N,N-dimethyl-p-toluidine. The powder contains butyl-methacrylate-MMA copolymers. These measures lower the glass-transition temperature, and permit more complete mixing in an integrated package, mixing, and delivery system consisting of a vacuum packed, double chamber pouch. The porosity was reduced to about 2% and the largest voids measured 0.1 mm. The polymerization exotherm was reduced to 58 °C. The compressive strength was 82 MPa, the four-point bending strength 55 MPa, the flexural modulus 2.24 GPa, the tensile strength 32 MPa, and the shear strength 36 MPa. The fracture toughness was 0.89 MPa √cm. These mechanical properties together with the fatigue life were on level with manually mixed, conventional PMMA bone cements. © 1995 John Wiley & Sons, Inc.

Compressive behavior of materials: Part II. High performance fibers

Abstract: The primary focus of this paper is on the axial compression behavior of high performance polymeric and carbon fibers. Seven test methods used for determining the compressive strength of single fibers have been reviewed. Various micromechanical models proposed in the literature to understand the compressive failure in single filaments and in other anisotropic systems have been discussed and analyzed. The results of various approaches to influence the compressive strength of polymeric fibers have been summarized. Possible reasons for the variation in the compressive strength of pitch and PAN-based carbon fibers have also been addressed.

Effect of particle variation on wear rates of posterior composites.

Abstract: Purpose To evaluate the relationship between filler size, shape, mechanical properties and wear resistance of posterior resin composite was evaluated. Materials and methods Six UDMA/TEGDMA-based experimental resin composites consisting of different types of filler particles were investigated. These included four sized spherical fillers, (9.88 microns, 2.01 microns, 0.62 micron, 0.20 micron) and two irregular, (9.46 microns, 1.97 microns). Property measurements consisted of hardness and compressive strength. Wear resistance was evaluated by a three-bodied in vitro wear test. Results The composites containing the smallest sized spherical particle exhibited maximum mechanical strength and maximum wear resistance. The composites containing the largest spherical particle exhibited minimum wear resistance. There were no significant differences amongst those containing similar sized fillers regardless of particle shape. However, differences between the 0.20 microns spherical filled composite and other composites were statistically significant. SEM analysis showed that only the larger sized filler exhibited some exfoliation after wear testing. The smaller size spherical filler exhibited better mechanical strength and substantially higher wear resistance.