Showing papers on "Compressive strength published in 1994"
TL;DR: The strength of intact rock is made up of two components: the intrinsic strength, or cohesion; and the frictional strength as discussed by the authors, and it is generally assumed that cohesion and friction are mobilized at the same displacements such that both components can be relied on simultaneously.
1,207 citations
TL;DR: In this article, the authors presented two models allowing to predict the packing density of a particle mix, derived from the Mooney's suspension viscosity model, and made a selection of mixes with the help of the Solid Suspension Model, and tests are performed in order to verify that the mix obtained is definitely optimal.
681 citations
01 Jan 1994
TL;DR: In this article, the authors proposed a structural model for high-tech Geopolymer K-Poly(sialate-siloxo) binders, which is similar to that of zeolites and feldspathoids.
Abstract: Geopolymer cement, high-alkali (K-Ca)-Poly(sialate-siloxo) cement, results from an inorganic polycondensation reaction, a so-called geopolymerisation yielding three dimensional zeolitic frameworks. High-tech Geopolymer K-Poly(sialate-siloxo) binders, whether used pure, with fillers or reinforced, are already finding applications in all fields of industry. These applications are to be found in the automobile and aeronautic industries, non-ferrous foundries and metallurgy, civil engineering, plastics industries, etc. Geopolymer cement hardens rapidly at room temperature and provides compressive strengths in the range of 20 MPa, after only 4 hours at 2 0°C, when tested in accordance with the standards applied to hydraulic binder mortars. The final 28-day compression strength is in the range of 70-100 MPa.The behaviour of geopolymeric cements is similar to that of zeolites and feldspathoids; they immobilize hazardous materials within the geopolymeric matrix, and act as a binder to convert semi-solid wastes into adhesive solids. Their unique properties which include high early strength, low shrinkage, freeze-thaw resistance, sulphate resistance and corrosion resistance, make them ideal for long term containment in surface disposal facilities. These high-alkali cements do not generate any Alkali-Aggregate-Reaction. Preliminary study involving 27 Al and 29 Si MASNMR spectroscopy and the proposed structural model, reveal
615 citations
TL;DR: In this article, a simple method is proposed whereby the strength enhancement provided by axial compression is separated from the concrete component of shear strength and considered to result from arch action.
Abstract: Aspects relating to the shear strength of circular and rectangular columns under seismic loading are presented An examination of existing design equations reveals wide differences in predicted responses Particular emphasis is placed on models capable of representing the interaction between flexural ductility and shear strength A simple method is proposed whereby the strength enhancement provided by axial compression is separated from the concrete component of shear strength and considered to result from arch action The strength of the concrete component is reduced as flexural displacement ductility increases Prediction of shear strength from the proposed and alternative methods are compared with results from a wide range of tests of columns failing in shear The proposed method is shown to provide significantly improved correlation with experimental results Conservative modifications are made to enable the method to be used for design
515 citations
TL;DR: In this article, a new technique for seismic strengthening of concrete columns is presented, which requires wrapping thin, flexible high-strength fiber composite straps around the column to improve the column's ductility and strength.
Abstract: Bridge failures in recent earthquakes such as the 1989 Loma Prieta earthquake have attracted the attention of the bridge engineering community to the large number of bridges with substandard seismic design details. Many concrete columns in bridges designed before the new seismic design provisions were adopted have low flexural ductility, low shear strength, and inadequate lap length for starter bars. These problems, compounded by flaws in the design of structural systems, have contributed to the catastrophic bridge failures in recent earthquakes. In this paper, a new technique for seismic strengthening of concrete columns is presented. The technique requires wrapping thin, flexible high-strength fiber composite straps around the column to improve the confinement and, thereby, its ductility and strength. Analytical models are presented that quantify the gain in strength and ductility of concrete columns externally confined by means of high-strength fiber composite straps. A parametric study is conducted to examine the effects of various design parameters such as concrete compressive strength, thickness and spacing of straps, and type of strap. The results indicate that the strength and ductility of concrete columns can be significantly increased by wrapping high-strength fiber composite straps around the columns.
484 citations
TL;DR: The split Hopkinson pressure bar (SHPB) is widely used to determine the dynamic compressive strength of ceramics and ceramic composites as mentioned in this paper, however, extreme caution needs to be exercised while testing these high-strength composites at high strain rates.
Abstract: The split Hopkinson pressure bar (SHPB) is being widely used to determine the dynamic compressive strength of ceramics and ceramic composites. However, extreme caution needs to be exercised while testing these high-strength ceramics at high strain rates. The highest strain rate at which ceramics can be tested using an SHPB without violating the underlying assumptions is found to be in the range of 2500-3000/s. It is also shown that at very high loading rates, dispersion in the transmitted pulse can lead to discrepancies in measuring the dynamic failure strength of ceramics.
422 citations
TL;DR: In this paper, the authors evaluated the mechanical properties of a kaolinite/fiber soil composite by a series of laboratory unconfined compression, splitting tensile strength, three-point bending, and hydraulic conductivity tests.
Abstract: The mechanical properties of a kaolinite/fiber soil composite were evaluated by a series of laboratory unconfined‐compression, splitting‐tension, three‐point‐bending, and hydraulic‐conductivity tests. The inclusion of randomly distributed fibers significantly increased the peak compressive strength, ductility, splitting tensile strength, and flexural toughness of kaolinite clay. The increase in strength and toughness was a function of fiber length and content, and the water content of the composite. Increasing fiber content increased the compressive and tensile strength, and the toughness index of kaolinite clay, with the effect being more pronounced at lower water contents. The contribution of fibers to peak compressive and tensile strengths were reduced, and ductility increased, with increasing fiber length. The fiber inclusion increased the hydraulic conductivity of the composite and the increase was more pronounced at higher fiber contents. Despite the increase, the hydraulic conductivity of the compo...
391 citations
TL;DR: Compared measurements of the tensile and compressive yield strengths, and yield strains, of trabecular bone specimens taken from 38 bovine proximal tibiae suggest that failure parameters based on strains may provide more powerful and general comparisons of the failure properties for trabECular bone than measures based on stress.
333 citations
TL;DR: In this paper, the behavior of large-scale high-strength concrete columns confined by rectangular ties under concentric loading was studied, and important gains in strength, toughness, and ductility were recorded for the concrete core of well-confined columns.
Abstract: This paper presents an experimental study of the behavior of large‐scale high‐strength concrete columns confined by rectangular ties under concentric loading. Effects of key variables such as the concrete compressive strength, the tie yield strength, the tie configuration, the transverse reinforcement ratio, the tie spacing, the longitudinal reinforcement ratio, and the spalling of the concrete cover are studied in this research program. The behavior of high‐strength concrete columns is characterized by the sudden separation of the concrete cover, leading to a loss of axial capacity before the lateral confinement becomes effective. After the concrete is completely spalled, important gains in strength, toughness, and ductility are recorded for the concrete core of well‐confined columns.
307 citations
TL;DR: Small but significant decreases in modulus suggest that initial yielding involves microstructural damage (as opposed to plastic slip) of individual trabeculae and also indicate that the tensile and/or the compressive yield strain of (bovine tibial)trabecular bone is less than 0.5%.
01 Jan 1994
TL;DR: In this article, the authors describe several fracture processes specific of polymers, which are determined experimentally by the mode and time profile of loading, stress-and strain controlled loading yields different behavior as well as loading in tension, compression or shear (torsion).
Abstract: Fracture analysis is complicated for polymers since, besides of temperature and time dependence, there are involved effects from plastification, chain orientation and adiabatic temperature rise. It is the aim of this section to describe several fracture processes which are specific of polymers. Fracture behavior is determined experimentally by the mode and time profile of loading. Stress- and strain controlled loading yields different behavior as well as loading in tension, compression or shear (torsion). Compressive strength is higher than tensile strength; shear strength is the lowest one.
TL;DR: In this paper, the early hydration period of pastes containing metakaolin was investigated using isothermal calorimetry and conductivity, and differential thermal analysis, X-ray diffraction, and Fourier transform infrared spectrometry were used to follow the consumption of calcium hydroxide (CH) and identify the products of reaction.
TL;DR: In this article, empirical equations were proposed to represent the complete stress-strain relationships of unconfined and confined high-strength concretes with compressive strength exceeding 10 kip/in2 (69 MPa).
Abstract: A series of compression tests were conducted on 3 × 6 in (76·2 × 152·4 mm) cylindrical specimens using a modified testing method that gave the complete stress–strain behaviour for high-strength concrete with or without tie confinements. Empirical equations are proposed to represent the complete stress–strain relationships of unconfined and confined high-strength concretes with compressive strength exceeding 10 kip/in2 (69 MPa). Various parameters were studied and their relationships were experimentally determined. me proposed empirical stress–strain equations are compared with actual cylinder tests under axial compression, and are found to agree well.
TL;DR: In this paper, a joint factor J f has been developed to account for the number of joints per metre length, inclination of the sliding joint and the shear strength along this joint.
TL;DR: In this article, the authors examined and compared the very different stress-strain results of polycarbonate produced from four types of mechanical testing, namely, uniaxial compression, plane strain compression and simple shear.
Abstract: Polymeric materials subjected to large strains undergo an evolution in molecular orientation. The developing orientation and corresponding strengthening are highly dependent on the state of strain. In this paper, we examine and compare the very different stress-strain results of polycarbonate produced from four types of mechanical testing: uniaxial compression, plane strain compression, uniaxial tension, and simple shear. These tests produce different states of orientation within the material and, in the case of simple shear, the principle axes of orientation rotate during the deformation. The ability of the recent constitutive model of Anuda and Boyce (1992) to predict the observed behavior is evaluated. The model has been incorporated into a finite element code in order to properly simulate the material behavior during the inhomogeneous deformations of tension (cold drawing) and simple shear. The material properties of the model are obtained from the uniaxial compression test and the model is then found to be truly predictive of the other states of deformation demonstrating its fully three dimensional capability. The disadvantages of the tensile and simple shear tests for obtaining the data needed to accurately quantify the large strain material behavior of polymers are shown and discussed.
TL;DR: In this paper, a simple model of an array of interacting, dynamically growing wing cracks is used to simulate the rate-dependent dynamic damage evolution and subsequent brittle failure of solids under compression.
Abstract: A simple model of an array of interacting, dynamically growing wing cracks is used to simulate the rate-dependent dynamic damage evolution and subsequent brittle failure of solids under compression. The validity of the model is discussed. Parameters which identify the overall failure by the coalescence of compression-induced, interacting, tensile microcracks are calculated in closed form, and relations between microstructure and the corresponding rate dependency of the overall response are examined in some detail. It is shown that the experimentally observed change in the compressive failure stress with increasing strain rate, may be considered to be a consequence of the generation and dynamic growth of interacting, compression-induced, tensile microcracks. Examples of brittle failure in uniaxial stress and uniaxial strain conditions, respectively, produced in the Hopkinson compression bar and normal plate-impact experiments, are discussed in terms of this model.
TL;DR: The methacrylate-modified glass ionomers of this study did not exhibit a decrease in compressive strength, modulus and diametral tensile strength as a result of prolonged storage in water at oral temperature, and could be indicated for use in applications where they are in contact with oral fluids under physiological conditions.
TL;DR: The physical origin of surface stress is discussed in this article, where a general functional form of the dependence of the adsorbate-induced surface stress on the coverage is proposed based on these considerations.
Abstract: The physical origin of surface stress is discussed. Based on these considerations a general functional form of the dependence of the adsorbate‐induced surface stress on the coverage is proposed. Experimental data on the adsorption of oxygen, sulfur, and carbon on Ni(100) are in agreement with this proposition. It is shown further that the p4g reconstruction of the Ni(100) surface upon carbon deposition is caused by the compressive stress induced by the carbon atoms. Recent results on CO on Ni(100) are, however, at variance with the simple reasoning concerning all aspects of the induced surface stress—the sign, the magnitude, as well as the coverage dependence.
TL;DR: In this paper, the authors investigated the influence of the water/cement ratio (i.e., the compressive strength of the concrete) on rate effects in the behavior of concrete under tensile stress.
Abstract: In the context of an international co-operation project between the University of Delft (The Netherlands) and the LCPC, an experimental study was made of rate effects in the behaviour of concrete under tensile stress. Very high speed tests (\(\dot \sigma \) between 1 and 80 GPa s−1) were carried out in Delft on a Hopkinson bar, and quasi-static tests (\(\dot \sigma \) between 5×10−5 and 5×10−3 GPa s−1) were carried out by the LCPC on a hydraulic press. This investigation had two objectives. 1. To verify on a mini-concrete (diameter of the largest particles 10 mm) a result obtained with a micro-concrete (diameter of the largest particles 2 mm) in the course of a previous study. Rate effects are produced by the presence of pore water in the material. 2. To investigate the influence of the water/cement ratio (i.e., the compressive strength of the concrete) on these rate effects. The three main conclusions that can be drawn from this study are (i) it is indeed the presence of pore water in the concrete which is at the origin of rate effects where this materials is concerned, (ii) the effect of speed on the tensile strengthf1 increases with the water/cement ratio, and (iii) in absolute value, the increase in strength (ftdyn-ftstat) seems to be independent of the water/cement ratio.
TL;DR: In this paper, the effect of moisture condition on the strength of mature cores obtained from well-cured elements is investigated by reviewing available literature and performing regression analyses of data from tests of 727 core specimens.
Abstract: In accordance with the provisions of American Society for Testing and Materials (ASTM) C 42-90 and American Concrete Institute (ACI) 318-89, it is current practice to either dry concrete core specimens in air for 7 days or soak them in lime-saturated water for at least 40 hours before they are tested. In this paper, the effect of moisture condition on the strengths of mature cores obtained from well-cured elements is investigated by reviewing available literature and performing regression analyses of data from tests of 727 core specimens. Tests show that the compressive strength of a concrete specimen is influenced both by moisture content changes that are uniform throughout the specimen volume and moisture content gradients between the surface of the specimen and interior. The air-drying and soaking periods specified in ASTM C 42-90 and ACI 318-89 are too short to cause a uniform change of moisture content throughout the volume of the core. The effect of these treatments is to create a moisture gradient that artificially biases the test result. The strength of air-dried cores is on average 14 percent larger than the strength of soaked cores. The strength of cores with a negligible moisture gradient is on average 9 percent larger than the strength of soaked cores. These general average values are constant for concretes with strengths ranging from 2,200 to 13,400 psi. However, the strength ratios for any particular mix may differ appreciably from these general average values.
TL;DR: Hydroxyapatite composite resin is a promising material which possesses superior mechanical strength and the biological property of achieving direct contact with bone in a new type of bioactive bone cement.
TL;DR: In this article, an experimental investigation was conducted to investigate the behavior of composite columns subjected to simulated seismic loading conditions, and the results of the test program indicate that encased composite columns possess exceptional cyclic strength and ductility if buckling of the longitudinal reinforcement is inhibited.
Abstract: An experimental investigation was conducted to investigate the behavior of composite columns subjected to simulated seismic loading conditions. Eight two‐thirds‐scale specimens were tested, each consisting of a structural steel shape encased in reinforced concrete. The parameters studied in the test program included the degree of concrete confinement required to achieve adequate ductility under cyclic loading, effectiveness of flange shear studs for enhancing flexural stiffness and strength, concrete compressive strength, and the shear resistance mechanism of the composite column. The results of the test program indicate that encased composite columns possess exceptional cyclic strength and ductility if buckling of the longitudinal reinforcement is inhibited. The encased steel shape was found to provide the primary resistance to transverse shear during overloading, with the shear studs not effective in enhancing the flexural resistance to lateral loading. The specimen flexural capacity under combined axia...
TL;DR: Nanophase Fe-28Al-2Cr powder was obtained by ball milling and consolidated by shock wave compaction Fully-dense well-bonded compacts were produced with a diameter of 32 mm and a thickness of [approx]6 mm as discussed by the authors.
Abstract: Nanophase Fe-28Al-2Cr powder was obtained by ball milling and consolidated by shock wave compaction Fully-dense well-bonded compacts were produced with a diameter of 32 mm and a thickness of [approx]6 mm The grain size in the compacts was [approx]80 nm In tension, the nanophase intermetallic is brittle with a failure strength ([sigma][sub f] = 065 GPa) comparable to a coarse-grained intermetallic with similar composition In compression, the nanophase material exhibits superplastic-like flow during room temperature quasistatic deformation to true strains greater than 14 The compressive flow strength is 21 GPa and no macroscopic strain hardening is observed This behavior is compared to the coarse-grained material that has a yield strength of 025 GPa, displays significant work hardening and little tension-compression anisotropy TEM examination of the nanophase material before and after deformation shows a refinement of the microstructure during deformation The microstructure refines to [approx]10 nm grains surrounded by amorphous material
TL;DR: In this article, it was shown that the various proposals for assessing the value e0 of the strain at the peak of the compressive strength of concrete appear sufficiently precise, at maximum, for a limited range of strengths, and the new formula in this paper seems to perform much better when applied to the experimental data obtained in the very wide range of strength possible today.
Abstract: The increasing interest in the strain behaviour of concrete is not restricted to everyday mean compressive strengths but now extends to very high values. In this paper it is shown that the various proposals for assessing the value e0 of the strain at the peak of the compressive strength of concrete appear sufficiently precise, at maximum, for a limited range of strengths, This had led us to estimate e0 for a wide range of strengths, and the new formula in this paper seems to perform much better when applied to the experimental data obtained in the very wide range of strengths possible today.
TL;DR: In this article, the authors reported the results of an experimental investigation into the properties of hardened concrete containing chemically treated expanded polystyrene beads and showed that the strength, stiffness, and chemical resistance of polystructure aggregate concrete of a constant density were affected by the water to cement ratio.
Abstract: This paper reports the results of an experimental investigation into the properties of hardened concrete containing chemically treated expanded polystyrene beads. The results showed that the strength, stiffness and chemical resistance of polystyrene aggregate concrete of a constant density were affected by the water to cement ratio. Drying shrinkage after 84 days of drying for polystyrene concretes, having 10 mm coarse aggregate and a nominal density of 1300 kg/m3, were 730 and 655 microstrains. Empirical equations were developed to relate the strength and pulse velocity and to predict the modulus of elasticity from its strength.
TL;DR: In this article, the authors summarized recent developments in the laser spallation technique for measuring the tensile strength of planar thin film interfaces using a Doppler interferometer.
Abstract: This paper summarizes recent developments in the laser spallation technique for measuring the tensile strength of planar thin film interfaces. In this technique, a laser-produced compressive stress pulse in the substrate, reflecting from the coating's free surface, pulls the interface in tension and leads to its failure if the tensile amplitude is high enough. Earlier, the critical stress amplitude that accomplishes the removal of the coating was determined through a computer simulation of the process. Recently, the technique was modified so that the interface stress can be determined directly by recording the coating or substrate free-surface velocities using a Doppler interferometer. The recorded surface velocity is related to the interface stress via an elastic wave mechanics simulation. Interface strengths of several metal/ceramic, ceramic/ceramic and ceramic/polymer systems are summarized from our recent efforts. In addition, two developments, the first a novel interferometer to record velocities fro...
TL;DR: In this article, the authors present results from four high strength concrete specimens, 3 non-prismatic and 1 prismatic, tested under constant axial load and cyclic lateral loads simulating earthquake forces, and comparison is made with similar specimens of normal strength concrete.
Abstract: The paper presents results from 4 high strength concrete specimens, 3 nonprismatic and 1 prismatic, tested under constant axial load and cyclic lateral loads simulating earthquake forces, and comparison is made with similar specimens of normal strength concrete. Concrete strength varied between 4500 and 8500 psi. Relevant provisions of the ACI Building Code are evaluated in light of the test data. Increase in the lateral steel contents resulted in an almost proportional increase in ductility and energy-absorption capacity of confined high strength concrete, just as in the case of normal strength concrete. The required amount of confining steel appears to be proportional to the strength of concrete for a certain column performance if the axial load is measured in terms of Po rather than as a fraction of f'c Ag. Comments are made on the useable compressive strain.
TL;DR: In this paper, a total of 15 shear critical reinforced concrete beams without and with shear reinforcement (web) were tested in a stiff testing facility, and complete load-midspan deflection curves, including the post-peak portion, were obtained.
Abstract: A total of 15 shear critical reinforced concrete beams without and with shear reinforcement (web) were tested in a stiff testing facility, and complete load-midspan deflection curves, including the post-peak portion, were obtained. The experimental variables were the concrete compressive strength, shear span-to-depth ratio, and the amount of shear reinforcement. For the range of variables tested, the results indicate that shear reinforcement (web) improves the shear ductility index of reinforced concrete beams of normal as well as high-strength concrete. High strength reinforced concrete beams with a/d of 3 show a plastic post-peak response when shear reinforcement provided is about twice the minimum reocmmended by the ACI Building Code. These and other findings are presented.