Showing papers on "Compressive strength published in 1988"

Behavior of Laterally Confined High‐Strength Concrete under Axial Loads

Abstract: The empirical results of a test program studying the effects of rectilinear confinement in highstrength concrete subjected to a monotonically increasing compressive axial load was reported. Twentyf...

Engineering Properties of Concrete Affected by Alkali-Silica Reaction

Abstract: A detailed study of the effects of alkali-silica reaction (ASR) on the engineering properties of concrete such as compressive and tensile strength, elastic modulus, and pulse velocity is presented. Two types of reactive aggregate - a naturally occurring Beltane opal and synthetic fused silica - were used. The tests wee carried out at 20 C and 96 percent relative humidity (RH). The results showed that losses in engineering properties do not all occur at the same rate or in proportion to the expansion undergone by the ASR-affected concrete. The two major properties affected by ASR were flexural strength and dynamic modulus of elasticity. Compressive strength was not a good indicator of ASR, but the flexural strength proved to be a reliable and sensitve test for mointoring ASR. Nondestructive tests like dynamic modulus and pulse velocity were also able to identify deterioration of concrete by ASR. The data indicate that critical expansion limits due to ASR would vary depending on the type and use of a concrete structure.

Strength and stiffness of ships' plating under in-plane compression and tension

Abstract: New data curves are presented describing the behavior of imperfect rectangular plates under uniaxial or biaxial longitudinal and/or transverse compression and tension. The data curves, developed by a combination of nonlinear finite element analysis and regression analysis of a large body of test results, provide a definition not only of plate strength (maximum load-carrying capacity) but also of effective stress-strain relationships throughout the tensile and compressive strain ranges, from which plating "effective widths" and "effective breadths" may be determined. In addition to mean plate stiffness and strength, upper and lower-bound stress-strain and strength curves are described.

Prediction of the compressive strength of vertebral bodies of the lumbar spine by quantitative computed tomography.

Abstract: The ultimate compressive strength of 36 thoracolumbar vertebrae was determined experimentally. In addition, the trabecular bone mineral content was measured by single energy quantitative computed tomography. The areas of fractured endplates were also determined by computed tomography. The results show that a linear relationship exists between the compressive strength and the product of bone density and endplate area. These data allow an in vivo prediction of vertebral body strength using a noninvasive method with a standard error of estimate amounting to less than 0.95 kN.

Residual Strength of a Carbon/Epoxy Composite Material Subjected to Repeated Impact:

Abstract: The residual tensile and compressive strengths of specimens cut from composite plates subjected to repeated impact at various energy levels were measured. The 16-ply quasi- isotropic composite plates were 2 mm thick, fabricated from Hercules AS4/3501-6 car bon/epoxy prepreg. Impact energy level and number of impacts were found to be major factors influencing strength degradation. However, strength degradation was limited to the region near the impact point.

Coal Measures mudrocks: composition, classification and weathering processes

Abstract: British Coal Measures mudrocks are dominantly non-marine, mature sediments with a high average clay minerals content of over 75%. A geological classification based on quartz content does not differentiate the dominant durable mudrocks from the non-durable types and overconsolidated clays in the formation. A uniaxial compressive strength greater than 3.6MN/m 2 with a three cycle slake durability value of over 60% is suggested as an appropriate division between durable and non-durable mudrocks of this age. Physical breakdown, which acts as a control on chemical weathering triggered by pyrite oxidation, is considered to be governed by incidence of sedimentary structures, slaking and expandable mixed-layer clay content. Shear strength reduction during post-glacial weathering can be significant. A tentative fully weathered effective stress peak strength for the weakest mudrocks and clays is deduced to be φ′ = 22°( c ′ = 0). Colliery tip investigations indicate that chemical weathering effects on the shear strength of the mudrocks are small. A diagenetic rank factor applies both to peak shear strength and slake durability of mudrocks excavated from UK coal mines.

Mechanical properties of concrete at low temperature

Abstract: Laboratory studies were conducted on concrete compressive and splitting tensile strength, modulus of elasticity, and Poisson's ratio and on the local bond strength between concrete and steel under ...

Experimental verification of a microbuckling model for the axial compressive failure of high performance polymer fibres

Abstract: A previously derived theoretical compressive strength for fibres composed of uniaxially oriented and extended polymer chains was compared with the measured strengths of several high performance fibres. For failure initiated by elastic microbuckling of polymer chains or fibrils, the maximum fibre strength is predicted to be equal to the minimum longitudinal shear modulus of the fibre. An excellent linear correlation between measured strengths and torsion moduli was obtained for four liquid-crystalline polymer fibres and high modulus graphite fibres. The correlation shows that measured strengths are 30% of the corresponding torsion moduli for all these fibres. A high modulus, high strength polyethylene fibre exhibited a compressive strength-torsion modulus ratio that was lower than the value 0.3 obtained for the other fibres examined in this study.

Failure of compression-loaded multi-directional composite laminates

Abstract: An analytical and experimental investigation of the failure of selected compression-loaded composite laminates is described. A general nonlinear theory is presented for predicting a laminate's compressive strength and failure mode. The theory includes the effects of out-of-plane ply waviness, inplane fiber waviness, and fiber scissoring. A simple compressive test technique is used to obtain the experimental data. The analytical and experimental results show good agreement for theta less than 45 deg and show excellent agreement for theta not less than 45 deg. The dominant compression failure modes for the laminates in this study were found to be interlaminar shearing, inplane matrix shearing, and matrix compression.

Mechanical properties of polycrystalline diamonds

Abstract: The room temperature mechanical properties of polycrystalline diamonds, i.e. tensile strength, transverse rupture strength, compressive strength, impact strength, fracture toughness, and elastic constants, have been determined. The applied test techniques are described and the results compared with those obtained by other authors. The fracture mode under the present experimental conditions was primarily transgranular. A grain size dependence, where strength increases with decreasing grain size, has been found. Fracture toughness was found to go through a maximum for grain sizes between 10 to 30 μm. The modulus of elasticity increases with increasing grain size. An influence of cobalt content on strength and modulus of elasticity has been found, while no significant influence on toughness could be determined. Increasing the cobalt content increases strength, but has the inverse effect on the modulus of elasticity. The results of strength, toughness, and elastic constants measurements are discussed ...

Sensitivity in Shear Strength of Longitudinally Reinforced Concrete Beams to Fracture Energy of Concrete

Abstract: The size effect in shear strength of longitudinally reinforced beams is studied by means of a nonlinear fracture mechanics model. According to the actual theoretical study, structure size should be normalized to an intrinsic length parameter of the concrete. This length parameter is proportional to the fracture energy G//F of the concrete. It is found that the shear strength of a concrete beam may be equally sensitive to G//F as to the tensile strength of the concrete. It is concluded that G//F should be measured during experimental studies of the shear strength of beams and the punching strength of slabs. A simple method for considering the intrinsic length parameter in existing shear strength formulas is proposed.

SettingTime and Strength of Concrete Using the Impact-Echo Method

Abstract: Tests were performed to evaluate the feasibility of using the impact-echo method to determine setting time and to monitor strength development of concrete. In the impact-echo method, the test object is subjected to point impact and the surface displacement is monitored at a point adjacent to the impact. From the measured displacement waveform and the thickness of the object, the P-wave velocity is determined. Changes in the P-wave velocity with time reveal information about the development of mechanical properties as the concrete matures. The results are discussed of setting-time tests on concrete mixtures of two water-cement ratios both with and without set-controlling admixtures. The results are also discussed of tests that examined the relationship between P-wave velocity, as determined by the impact-echo method, and the compressive strength of concrete. It is concluded that the impact-echo method is a promising nondestructive technique for monitoring the development of mechanical properties in concrete from initial setting to ages of several days.

Strength evaluation of recycled-aggregate concrete byin-situ tests

Abstract: Coarse and fine aggregates generated from crushed concrete products for new concrete can be generally accepted only when the properties of recycled aggregate concrete, in addition to the relationships between different properties of such a concrete, are well understood. The results of an experimental investigation into the relationship of compressive strength to ultrasonic pulse velocity and to rebound number is presented in this paper. It has been observed that for the water-cured concrete the strength-pulse velocity relationship is influenced by the use of the recycled aggregate. For the same value of the pulse velocity, the strength of recycled aggregate concrete is higher than that for the natural aggregate concrete. On the other hand, the strength-rebound number relationship is not affected by the aggregate type used. The combined method of pulse velocity and rebound number for strength estimation is also evaluated.

A Strength Criterion for Anisotropic Rocks

Abstract: Two intrinsically anisotropic phyllites obtained from Chamera hydro-electric project site in the Himalayan region were tested in high pressure triaxial apparatus at confining pressures up to 70 MPa and specimen orientations varying from 0 to 90 degrees with respect to the direction of major principal stress. On the basis of these experimental results and the available triaxial data on various anisotropic rocks, a simple strength criterion has been proposed. The strength predictions made on the basis of the proposed criterion show a good agreement with the experimental results. In contrast to the various existing theories, i. e. ; Walsh-Brace theory, single plane of weakness theory, variable coefficient of internal friction and cohesive strength theory and McLamore-Gray theory, the proposed criterion takes into account all the types of anisotropies resulting from 'cleavage', 'bedding-planes' and multiple sets of discontinuities, and has been found valid for jointed rocks as well. Another additional advantage is that the minimum input data requirement is only of two triaxial test results at a single orientation (i.e., beta = 90˚) and uniaxial compressive strength at different orientations. This test data is adequate for strength prediction at any confining pressure and specimen orientation.

Properties of Fiber Reinforced Concrete: Workability, Behavior Under Long-Term Loading, and Air-Void Characteristics

Abstract: This paper presents the results of an experimental invesigation of the behavior of steel fiber reinforced concrete. The properties investigated were: setting times, slump and air content loss with time, creep and shrinkage, and air-void characeristics including bubble size distribution. To compare the behavior of fiber reinforced concrete with plain concrete, all of the proceding properies were also investigated for plain concrete mixtures of similar composition. Two mixture proportions with cement contents of 611 and 799 lb/yd sup 3 (363 and 474 kg/m sup 3) were investigated. The lower cement content that was used with a water-cement ratio of 0.4 resulted in a highly workable medium-strength concrete. The compressive strength was in the range of 6000 psi (41 MPa). The higher cement content, wih a 0.3 water-cement ratio, resulted in a relatively stiff concrete with an average compressive strength of 7000 psi (48 MPa). High-range water reducers and air-entraining admixtures were used for all the mixtures. Collated 50 mm long steel fibers with hooked ends were used for the fiber concrete. The experiments were conducted using the appropriate ASTM standards. The air-void characteristics were studied using the linear traverse method. The results indicate that setting times are about the same for both concretes. Fiber concrete has lower slump and air content; the rate of loss of these parameters with time is also higher. Shrinkage of fiber reinforced concrete is slightly less, but it undergoes slightly more creep deformations. In the area of aid-void characteristics, the specific surface of air bubbles is lower for fiber reinforced concrete, and it has relatively less number of chord-intercepts in the 0 to 0.002-in. (0 to 0.05-mm) range.

Fabrication and properties of metal matrix composites based on SiC fibre reinforced aluminium alloys

Abstract: Composites made with Al–7 wt-%Si alloys and discontinuous Nicalon SiC fibres were prepared by compocasting followed by squeeze casting. This technique gives rise to macroscopically homogeneous materials with, however, some segregation of the fibres in the eutectic phase, especially for the lowest volume fractions. The SiC fibres appreciably improve wear resistance, hardness, and compressive strength of the matrix, both in the as cast and heat treated conditions. An analysis of the compressive test results is given based on the mixture rule modified to apply for discontinuous randomly oriented fibre composites. However, it is shown that agreement between predictions and experimental results can only be obtained by considering the increase of the strength of the matrix as a result of the presence of the fibres. This increase is discussed in terms of structural changes and residual stresses created during cooling resulting from the difference in the coefficients of thermal expansion of the components...

Strength and Durability Considerations Affecting Mix Proportioning of Concrete Containing Fly Ash

Abstract: The results of a 3-year study on the properties of concrete containing fly ash are presented. Both the fresh and hardened properties are reported of concrete made using Type 1 cement, river gravel, natural sand, and fly ashes from several sources. The mixtures were proportioned to have similar slump and a constant cementitious content by weight. It is shown that concrete containing fly ash can be proportioned having equal strength properties and adequate durability when a suitable ASTM C 618 Class C or F fly ash is used. Test data on over 1600 laboratory and field specimens tested for freeze-thaw resistance, flexural strength, compressive strength, creep, shrinkage, and abrasion resistance are presented. Fly ash contents ranging from 0 to 35 percent by weight of portland cement were used with both Class C and Class F fly ashes. Guidelines for the selection of materials and their proportions for producing concrete containing fly ash to meet existing highway specifications for concrete are presented.

Reinforced laminated beam

Abstract: A reinforced laminated beam provides reinforcement in the locations where maximum tension occurs on such beams, generally at the lower portions of the beam, by the addition of a layer of high tensile strength material between successive layers or laminations of wood. A thin layer of high tensile strength material, preferably a strip of aluminum alloy with a tensile yield strength of approximately 41,000 psi and a thickness of 0.064-inch, which is continuous across the width and length of the beam, is adhesively fixed between the bottom two laminations of wood, thereby producing a significant increase in the carrying capacity of the beam, while providing no obstacle to the sawing or other working of the beam in the field. Reinforcing material also may be added between other lower laminations for additional reinforcement, this being particularly useful for deep beams having a large number of laminations. The carrying capacity of a beam may be still further strengthened by the addition of a reinforcing strip between the two upper laminations in a beam, such upper reinforcing layer being useful where, because of the increase in the tensile strength at the lower laminations, the weaker area in the beam now has become the compressive strength of the upper laminations.

Relationship among fatigue strength, mean grain size and compressive strength of a rock

Abstract: Fatigue tests carried on three sets of samples having different mean grain sizes revealed that fatigue strength is a function of mean grain size of the rock. Samples having smaller grain size show higher value of fatigue strength. Graywacke samples from Flagstaff formation having mean grain sizes of 1.79 mm, 1.35 mm and 0.93 mm showed fatigue strengths of 87%, 88.25% and 89.1% respectively. Since the mean uniaxial compressive strength also varied with varying grain size, i. e. higher mean strength value for samples having finer grain size; the fatigue strength of a rock also shows a converse relation with mean uniaxial compressive strength.

Geotechnical properties of cemented volcanic soil

Abstract: A volcaniclastic formation, known as Cangahua, found in the Andes of Ecuador and Colombia is focused on. The deposit is composed of moderately cemented fine sand and silt‐sized particles. A pronounced linear correlation is shown between strengh, in terms of both uniaxial compressive and Brazil tensile strengths, and the dry unit weight of the deposit. The tensile strength is unusually high for soil, being between 18 and 29% of the uniaxial compressive strength. Brazil tensile, uniaxial compressive, and triaxial strength characteristics depend on the initial void ratio and degree of saturation. As the saturation declines from 90 to 40%, test results show a fourfold increase in tensile strength. Moreover, increasing degrees of saturation cause a shift from brittle to ductile failure. Slope failures in Cangahua develop from fractures which initiate at zones of high tensile stress. Material properties such as tensile strength and fracture toughness play an important role in explaining and evaluating slope fai...

Influences of interfacial bonding strength and scatter of fibre strength on tensile behaviour of unidirectional metal matrix composites

Abstract: The influences of interfacial bonding strength and scatter of strength of fibres on tensile behaviour of unidirectional metal matrix composites, whose matrix has low yield stress in comparison to the strength of fibres, were studied using the Monte-Carlo simulation technique using two-dimensional model composites. The following results were found. The strength of composites increases with increasing bonding strength, especially when the bonding strength exceeds the shear yield stress of the matrix and then remains nearly constant. The strength of composites is very sensitive to bonding strength when the scatter of fibre strength is large, but not when it is small. The fracture mode varies from non-cumulative to cumulative with increasing scatter of fibre strength for both cases of weak and strong interfacial bondings. The fracture surface becomes irregular when bonding strength becomes low and scatter of fibre strength becomes large. The applicability of the Rosen and Zweben models and the rule of mixtures to predict the strength of composites was examined.

Compressive Strength of Composite Sandwich Panels After Impact Damage: An Experimental and Analytical Study

Abstract: The effect of low speed impact on the compressive strength of graphite/epoxy sandwich panels was examined experimentally and analytically. Various impactor sizes and impact energy levels were used. Impact damage was found to decrease the compressive strength of panels in this investigation by up to 33%. The use of film adhesive as an interply layer was found to reduce the extent of damage and increase the residual compressive strength. A one-parameter model to predict compressive failure of impact damaged panels is presented. The theoretical predictions are in good agreement with experimental results. Some of the factors affecting the panel behavior are also discussed.

Mechanical strength of trabecular bone at the knee.

Abstract: Interest in the biomechanical properties of trabecular bone has expanded in response to the problems related to total and partial joint replacement with the knee joint constituting a main focus of attention. This relatively recent development has left a number of fundamental problems unanswered, especially related to the machining, storage and testing of trabecular bone specimens. Nevertheless, these studies have contributed to the understanding of the mechanical function of trabecular bone. Regarding the role of trabecular bone at the knee joint, the following conclusions may be emphasized (conclusions drawn from the author's previous studies (I-X) are shown in italics): (1) Trabecular bone is almost exclusively responsible for the transmission of load at the proximal tibial epiphysis from the knee joint to the metaphysis. The peripheral shell surrounding the epiphysis is not composed of cortical bone and plays a negligible role in load transmission. (2) The compressive strength and stiffness of trabecular bone is primarily dependent upon the apparent density, trabecular architecture and the strength of the bone material. Direct and indirect sources suggest that the true material strength of trabecular bone is less than that of cortical bone. The epiphyseal trabecular architecture, featuring a marked polarity with alignment of primary trabeculae at right angles to the joint surface, is responsible for functional anisotropy which points to the axial compressive properties as the more important mechanical parameters. (3) Tensile and shear properties are of special relevance to mechanical loosening of implants. These properties may be derived from the apparent density, and a close empirical relation to the axial compressive strength and stiffness is suggested. (4) The foam-like structure of trabecular bone is the basis for the large energy absorptive capacity. (5) The pattern of axial compressive stiffness and strength at the normal proximal tibia differs little among individuals. Supporting the medial tibial plateau is a large high strength area with maximal strength centrally and slightly anteriorly, while laterally there is a restricted area of relatively high strength posteriorly with a lower maximal value than medially. Bone strength is significantly reduced within ten millimeters of the subchondral bone plate, and this reduction continues distally at the lateral condyle. At both condyles strength is reduced towards the periphery with very low values being obtained at the margins of the condyles and at the intercondylar region. Absolute bone strength values are influenced by the level of physical activity.(ABSTRACT TRUNCATED AT 400 WORDS)

In vitro characterization and biomechanical optimization of a biodegradable particulate composite bone cement.

Abstract: We have developed a biodegradable particulate composite bone cement and used in vitro and in vivo methods for studying its suitability for orthopaedic applications. The composite matrix consists of gelatin, water, and sodium salicylate. The particulate phase is made up of powdered and particulate (355-600 microns diameter) tricalcium phosphate. Paraformaldehyde (0.1% to 0.5% by weight) is used as a matrix cross-linking agent. The effects of incubation time, particulate volume fraction, density of the individual particles, water content, concentration of crosslinking agent, and freeze-drying on the unconfined compressive strength and modulus of the particulate composite were measured. Compressive strengths of 7 MPa and moduli of 65 MPa could be achieved. Mechanical properties depended critically upon the water content of the particulate composite, with values of strength and modulus decreasing rapidly outside a range of 10-14% of specimen dry weight. High-density tricalcium phosphate particulate produced cement with twice the strength found with porous particulate. In a companion study we document in vivo performance of this particulate composite in an animal model system.