Showing papers on "Compressive strength published in 1991"
TL;DR: Experimental techniques commonly used for high strain-rate testing of concrete in compression, together with the methods used for measurement and recording of stress and strain, are critically assessed in the first part of this paper as discussed by the authors.
Abstract: Experimental techniques commonly used for high strain-rate testing of concrete in compression, together with the methods used for measurement and recording of stress and strain, are critically assessed in the first part of this paper. The physical capability of each loading method is discussed and some consideration is given to the definitions used for specifying the loading rate. The second part reviews the dynamic compressive strength (mostly uniaxial rather than bi- or triaxial) of plain concrete, while in the third part a review on deformation behaviour indicates that uncertainty and disagreement exist concerning changes in axial strain at high strain rates.
1,167 citations
TL;DR: In this paper, the surface of sisal fibres has been modified by mercerization and silane treatment to improve adhesion characteristics and moisture resistance, which is most effective in reducing moisture uptake of fibres in humid environments.
405 citations
TL;DR: It is suggested that the reduced rate of polymerization may allow for increased flow of the material, decreasing the contraction stress in the filling, and thus allow for greater bonding strength to dentin and diametral compressive strength.
Abstract: — The aim of this study was to investigate the effect of reduced rate of polymerization on the marginal adaptation of a composite resin inserted in dentin cavities treated with a simplified Gluma system. The effect on bonding strength to dentin and compressive strength was also investigated. The light intensity of the polymerization unit was lowered by the use of a transformer, and thus the rate of polymerization of the composite resin. When the resin was irradiated for 30 s at 110 V followed by 30 s at 220 V, the marginal adaptation was significantly improved. This condition resulted in acceptable values of bonding strength to dentin and diametral compressive strength. It is suggested that the reduced rate of polymerization may allow for increased flow of the material, decreasing the contraction stress in the filling.
291 citations
TL;DR: Investigation of the relationship between the mechanical properties of trabecular bone in tension and compression found strength, ultimate strain and work to failure was significantly higher in tensile testing than in compressive testing.
237 citations
TL;DR: In this paper, an analytical model based on the compatibility of deformations and equilibrium of forces is presented to predict the stresses and deformations in concrete beams strengthened with fiber composite plates epoxy-bonded to the tension face of the beams.
Abstract: Analytical models based on the compatibility of deformations and equilibrium of forces are presented to predict the stresses and deformations in concrete beams strengthened with fiber composite plates epoxy-bonded to the tension face of the beams. The models are given for beams having rectangular and T cross sections. A parametric study is conducted to investigate the effects of design variables such as plate area, plate stiffness and strength, concrete compressive strength, and steel reinforcement ratio. The moment versus curvature diagrams for various combinations of these variables are plotted and compared. The results indicate that bonding composite plate to a concrete beam can increase the stiffness, yield moment, and flexural strength of the beam. The method is particularly effective for beams with a relatively low steel reinforcement ratio.
209 citations
TL;DR: In this article, the properties of high-strength lightweight concrete up to 100 MPa with a corresponding density of 1865 kg/sq m were investigated and the shape of the ascending part of the stress-strain curve was more linear than that of lightweight concrete with low to medium strength.
Abstract: Information is presented on the mechanical properties of high-strength lightweight concrete up to 100 MPa with a corresponding density of 1865 kg/ sq m. Five different types of lightweight aggregates were investigatged and the strength of the aggregate appears to be the primary factor controlling the strength of the high strength lightweight concrete. The tensile/compressive strength ratio appears to be lower for high strength lightweight concrete than that for high strength normal weight concrete, and the elastic modulus, which varied from 17.8 to 25.9 GPa, is much lower than that of normal weight concrete. For the high strength lightweight concrete, the shape of the ascending part of the stress-strain curve was more linear than that of lightweight concrete with low to medium strength.
182 citations
TL;DR: In this article, six different sandstone units were studied to investigate and quantify the relationship between their mechanical properties (compressive strength, tensile strength, Young's modulus, Poisson's ratio), petrographic characteristics, and engineering index properties.
Abstract: Six different sandstone units were studied to investigate and quantify the relationship between their mechanical properties (compressive strength, tensile strength, Young's modulus, Poisson's ratio), petrographic characteristics, and engineering index properties. Sandstones investigated included the Sharon sandstone, the Juniata sandstone, the Morgantown-Grafton sandstone, and three Berea sandstone units. These sandstones were tested for percent absorption, density, slake durability, total pore volume, uniaxial compressive strength, tensile strength, Young's modulus, and Poisson's ratio. Petrographic characteristics studied included grain size, grain shape, grain sorting, packing density, packing proximity, degree of grain interlocking, and mineral composition. The data were analyzed statistically to determine the quantitative relationships between various properties.
Results indicate that compressive strength, tensile strength, and Young's modulus values for the sandstones studied are closely related (r>0.7) to their density, percent absorption, total pore volume, and type of grain-to-grain contacts. Generally, sandstones with higher densities, lower percent absorption, lower total pore volume, and higher percentage of sutured contacts exhibited higher values of compressive strength, tensile strength, and Young's modulus. For Poisson's ratio, however, inverse relationships were observed with compressive strength and Young's modulus. Based on these results, equations were developed for predicting mechanical properties from values of density, percent absorption, total pore volume, and percent sutured contacts.
163 citations
TL;DR: In this paper, the authors investigated the validity and accuracy of these alternate relations and found that the splitting tensile strength is not proportional to the 0.5 power of compressive strength, and proposed a 0.69 power relation as an alternative to the ACI 318 relation.
Abstract: The 0.5 power relation adopted by ACI Committee 318 predicting the splitting tensile strength of concrete from its compressive strength has been investigated. Research has consistently indicated that the relation in the Building Code Requirement does not agree particularly well with test results. Consequently, researchers have proposed alternative relations. The research for this paper investigated the validity and accuracy of these alternate relations. Tensile strength preditions from these relations were compared with test results assembled from various sources. It was found that the splitting tensile strength is not proportional to the 0.5 power of compressive strength. Although most of the alternate relations appear to be good, the assembled test data revealed that 0.69 is the most accurate power relation. Thus 0.69 power relation is proposed as an alternative to the ACI 318 relation.
146 citations
135 citations
TL;DR: A possible bone substitute material for dental treatment was developed and tested and a composition was found which showed neutral pH, short setting time, and relatively high compressive strength.
129 citations
TL;DR: A survey of the behavior of reinforced concrete subjected to dynamic loading is presented in this paper, where the authors consider the impact of different strain rates on the performance of a reinforced concrete structure.
Abstract: A survey of the behavior of reinforced concrete subjected to dynamic loading is presented. Provisions for seismic design in current design codes have been developed on the basis of results obtained from static tests. Realistic methods of design should take into consideration the strain‐rate‐dependent properties of reinforced concrete in order to accurately predict the behavior of a reinforced concrete structure subjected to dynamic loads. The response of reinforced concrete materials and elements to different strain rates is reviewed and discussed. As rate of loading increases, concrete compressive strength, steel yield strength, and flexural capacity of reinforced concrete member also increase. The increase in flexural capacity of individual members as a result of high strain rates, if significant, may shift the failure mode of a structure from a preferred ductile manner to a less desirable brittle mode.
01 Jan 1991
TL;DR: In this paper, coupled shear conductivity tests have been performed on natural joints in magmatic, metamorphic and sedimentary rocks and the results showed that joint conductivity increases or decreases with ongoing shear, depending on the joint/rock properties and the stresses applied.
Abstract: Coupled shear conductivity tests have been performed on natural joints in magmatic, metamorphic and sedimentary rocks. Conductivity, normal and shear displacements and stresses were recorded. Whether joint conductivity increases or decreases with ongoing shear, depends on the joint/rock properties and the stresses applied. The uniaxial compressive strength, joint compressive strength, joint roughness coefficient, normal stress acting across the joint and shear displacement are anticipated to be the major parameters and a first attempt of quantification is undertaken
TL;DR: In this paper, a hybrid composite (CARALL) consisting of thin layers of carbon fiber/ epoxy prepreg sandwiched between aluminium sheets was developed, and it was shown that this class of materials offers higher modulus, higher tensile strength and lower density than 2024-T3 alloy in the longitudinal direction.
TL;DR: In this paper, an experimental study of the compressive failure of T800/924C carbon-fibre/efoxy composite laminates was performed and the critical failure mechanism observed was microbuckling of the 0° plies.
TL;DR: It was found that, over the period of 24 h to 4 months, some materials, namely those based on polyacrylic acid, maintained or even showed a slight increase in their strength, whereas others based on copolymers of acrylic acid first increased in strength, but thereafter showed deterioration.
Abstract: Summary
This study investigated whether long-term changes occur in the compressive strength of a number of glass ionomer restorative materials, in view of the fact that little information is available from the manufacturers, and any variations with time might affect suitability for clinical use.
It was found that, over the period of 24 h to 4 months, some materials, namely those based on polyacrylic acid, maintained or even showed a slight increase in their strength, whereas others based on copolymers of acrylic acid first increased in strength, but thereafter showed deterioration. In one case the strength decreased by nearly 50% compared to that at 24 h.
TL;DR: In this article, four-point bending and pinned-end buckling tests were carried out on scaled specimens of 25, 50 and 100 plies and showed a significant decrease in strength with increasing specimen size.
TL;DR: In this paper, the authors examined the mechanical aspects of the microbond pull-out technique for measuring fiber/resin interfacial shear strength and determined the origins of the consistent variability in bond strength results.
TL;DR: In this paper, the compressive strength of ground granulated slag concretes was investigated and the results showed that 1-day and 28-day compressive strengths ranged from 20.4 to 38.9 MPa and from 45.5 to 59.6 MPa, respectively.
TL;DR: In this paper, the Brazilian test is valid for materials which exhibit brittle failure and the continual δ model and β model created on the basis of the effective tensile stress are proposed.
Journal Article•
TL;DR: In this paper, the authors investigated the relationship between concrete compressive strength and its splitting tensile strength, especially at early ages, and examined the applicability of existing relations between these properties.
Abstract: The paper reports on investigation of the relationship between concrete compressive strength and its splitting tensile strength, especially at early ages, as well as the examination of the applicability of some of the existing relations between these properties to concrete at early ages. Analyses of test results show that the compressive strength and the spliltting tensile strength are related, and an increase in one, in general is similarly reflected in an increase in the other. The commonly accepted 0.5 power relationship between the compressive strength and the spliltting tensile strength was found to be inaccurate at all ages. In fact the tensile strength was found to be proportional to the 0.79 power of the cylinder compressive strength. An alternate relationship between the tensile strength and the compressive strength is proposed. Tables of results and figures supporting these observations and conclusions are included.
TL;DR: In this article, the effects of confinement and compressive strength of concrete on the local bond stress-slip characteristics of deformed bars were investigated and it was shown that, as far as the bondsplitting cracks are restrained by reinforcing bars crossing these cracks, confinement of concrete has insignificant effects on local bond behavior.
Abstract: Slippage of the beam reinforcement at beam-column connections is an important cause of damage to reinforced concrete frames under static and dynamic loads. This paper summarizes the results of an experimental study on the effects of confinement and compressive strength of concrete on the local bond stress-slip characteristics of deformed bars. The test data indicate that, as far as the bond-splitting cracks are restrained by reinforcing bars crossing these cracks, confinement of concrete has insignificant effects on the local bond behavior. The ultimate bond strength, however, increases proportionally with the square root of concrete compressive strength. An empirical model was develped for local bond stress-slip relationship of deformed bars in confined concrete.
TL;DR: In this paper, the estimated point-load strength values of specimens of varying sizes and also the values corrected to a standard thickness of 50 mm have been used to estimate the uniaxial (unconfined) compressive strength.
Abstract: Point-load strength (Is) as a measure for the determination of rock strength and for estimating uniaxial (unconfined) compressive strength (UCS) are described and both put together and used for rock strength classification of brittle and hard rocks. The estimated point-load strength values of specimens of varying sizes and also the values corrected to a standard thickness of 50 mm, and the resultant point-load strength values (Is-50) have been used to estimate the uniaxial (unconfined) compressive strength which correlates well with actual recorded uniaxial (unconfined) compression test results. Using graphical and mathematical relationships between the observed and estimated UCS and Is values, a conversion factor of 16 is obtained for estimating uniaxial (unconfined) compressive strength values from point load strength results. A nomogram for computing point-load strength index and a system for the classification of rock material are presented.
TL;DR: In this paper, a phenomenological model describing the interaction of bombarding ions in the plasma and coating ions, whose mobility is restricted by their position on the substrate or previously deposited layers of the coating, was proposed.
Abstract: Compressive stress in hard plasma vapor deposition coatings — up to values of several gigapascals — is found to be strongly dependent on the process parameters, especially on the energy of ion bombardment on the growing film. Increasing energy usually causes increasing stress. Internal stress influences all other coating properties, e.g. adhesive strength, microhardness and wear resistance. A detailed knowledge of the origin of this stress is therefore of great significance, particularly for practical applications. Experimental work was performed with various coating and substrate materials and various coating processes (d.c. sputtering, r.f. sputtering, arc ion plating) to determine the interrelationships. The creation of internal stress can be explained by a phenomenological model describing the interaction of bombarding ions in the plasma and coating ions, whose mobility is restricted by their position on the substrate or previously deposited layers of the coating. The validity of the model is demonstrated by good agreement with experimental results for both crystalline and amorphous coatings.
TL;DR: In this article, the authors present the results of an experimental investigation into the relationship between the elastic modulus, Poisson's ratio, and the cylinder compressive strength of concrete, especially at early ages.
Abstract: The paper presents the results of an experimental investigation into the relationships between the elastic modulus, Poisson's ratio, and the cylinder compressive strength of concrete, especially at early ages. The applicability to concrete at early ages of some of the existing relations between these properties was also examined. Tests were performed on 4 different concrete mixes using conventional 6 x 12-in.-cylinders. Test results were obtained for ages ranging from 6 hr to 28 days. Analyses of test results show that the compressive strength and the elastic modulus are related, and an increase in one is, in general, similarly reflected in an increase in the other. Poisson's ratio was found to be insensitive to both the age and the richness of concrete mix and did not change appreciably with compressive strength development.
TL;DR: In this paper, the strength of a short composite steel-concrete beam column is affected by variations in the strengths of concrete and steel, the cross-sectional dimensions of concrete, the placement of steel section and reinforcing bars, and the strength model itself.
Abstract: The strength of a short composite steel-concrete beam column is affected by variations in the strengths of concrete and steel, the cross-sectional dimensions of concrete and steel section, the placement of steel section and reinforcing bars, and the strength model itself. The effects of these factors on the variability of the ultimate strength of square short composite beam columns in which steel shapes are encased in cast-in-place concrete are studied. The results indicate that the specified concrete strength, the structural steel ratio, and the end eccentricity ratio influence the probability distribution properties of short composite beam-column strength. The end eccentricity ratios of 0.5 or less are critical since they have a very significant effect on the beam-column strength. As expected, the beam columns with slenderness ratios near the ACI Building Code upper limit for short columns produce lower strengths than the corresponding cross sections.
TL;DR: In this article, a wide-ranging investigation of the abrasion resistance of concrete is reported and the influence of water/cement ratio, curing, workability, maximum aggregate size and the constituent materials is discussed.
Abstract: Results of a wide-ranging investigation of the abrasion resistance of concrete are reported and the influence of water/cement ratio, curing, workability, maximum aggregate size and the constituent materials is discussed. Various other tests, namely compressive strength, rebound hardness and permeation (initial surface absorption, intrinsic permeability and vapour diffusivity) are examined for their ability to predict the abrasion resistance of concrete. The initial surface absorption test is recommended for this purpose.
01 Jan 1991
TL;DR: In this article, an analysis of both elastic and plastic microbuckling of unidirectional composites under remote axial and shear loading is presented, and the effects of fiber misalignment and inclination of the band are included.
Abstract: The dominant compressive failure mechanism of modern fibre composites is microbuckling. This is demonstrated in the form of a fracture map. For polymer matrix composites microbuckling is a plastic event. An analysis is presented of both elastic and plastic microbuckling of unidirectional composites under remote axial and shear loading. The effects of fibre misalignment and inclination of the band are included. We find that a simple rigid-perfectly plastic analysis suffices for plastic microbuckling; it demonstrates that the axial compressive strength increases with decreasing fibre misalignment, increasing shear strength of the matrix, and decreasing remote shear stress. Finally, a calculation is performed of the remote axial and shear stress required to propagate an existing microbuckle. We find that the axial propagation stress is typically less than the shear yield stress of the matrix material.
TL;DR: Comparisons of physical and mechanical properties, as well as anatomical comparisons by others, indicate that the calf spine is a good model of the young non-osteoporotic human spine and thus useful for the testing of spinal instrumentation.
TL;DR: In this paper, the use of microwave energy as a source of heat to accelerate the curing of ordinary Portland Cement mortar was investigated, and the microwave treatment did not alter significantly the compressive strength of the samples compared to samples cured at 20 degrees Celsius.
TL;DR: In this paper, the authors investigated the relationship between concrete compressive strength and its splitting tensile strength, especially at early ages, and examined the applicability of existing relations between these properties.
Abstract: The paper reports on investigation of the relationship between concrete compressive strength and its splitting tensile strength, especially at early ages, as well as the examination of the applicability of some of the existing relations between these properties to concrete at early ages. Analyses of test results show that the compressive strength and the spliltting tensile strength are related, and an increase in one, in general is similarly reflected in an increase in the other. The commonly accepted 0.5 power relationship between the compressive strength and the spliltting tensile strength was found to be inaccurate at all ages. In fact the tensile strength was found to be proportional to the 0.79 power of the cylinder compressive strength. An alternate relationship between the tensile strength and the compressive strength is proposed. Tables of results and figures supporting these observations and conclusions are included.