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[en] Tsinghua University started to test the biaxial and triaxial compressive concrete strength and deformation since 1983. Test results of biaxial and triaxial compressive concrete strength are analyzed. A concrete failure criterion is suggested and is compared with others. Biaxial compressive stress-strain relationships under different load ratios are investigated. (orig./HP)
[en] A type of cost-effective and very high strength concrete (VHSC) with 28-day compressive strength of 100-150MPa is developed for applications in concrete-encased steel composite column constructions. This paper experimentally investigates the structural behaviour of VHSCencased steel composite columns based on a series of pure compression and eccentric compression tests. It is found that such high-strengthcomposite column exhibits brittle post peak behaviour and low ductility but with acceptable compressive resistance. Throughout the tests, the main failure of VHSC encased column under compressive load is brittle spalling of concrete followed by local buckling of the reinforcement bars. The splitting and slippage may occur between concrete and steel section due to bending downward action. The confinement effect by the shear stirrups designed based on normal reinforced concrete codesmay not be sufficient. Composite column subjected to initial flexural cracking due to end moment load with large eccentricity may experience degradation in the stiffness and ultimate resistance so that plastic design resistance may not be achieved. Analytical studies show that the N-M interaction model based on current design codes may over-predict the combined resistance of the composite columns. Therefore, a modified elastic-plastic design approach based on strain compatibility is developed to evaluate the compressive resistance of concrete encased composite columns. The validation against the test data shows a reasonable and conservative estimation on the combined resistance of VHSC encased composite columns. (Author)
[en] Highlights: • Zircon up to 10 g/100 g metakaolin improved microstructure and mechanical properties. • No new phases were formed upon the addition of zircon. • Zircon didn't participate in geopolymerization reaction. • Zircon entered between polysialate networks and formed a rigid microstructure. • Higher content of zircon (15 g/100 g kaolin) lowered the compressive strength.
[en] A procedure is described for determining the compressive (crushing) strength of a right cylindrical specimen of graphite at room temperature. Specimen dimensions are given as is a description of different parts of the testing machine. A formula is included for calculating the compressive strength from the test results
[en] It has long been assumed that basal dislocations were responsible for the deformation of layered, crystalline solids. Herein we make the case that, with the notable exception of some metals that kink, ripplocations - not basal dislocations - are the operative micromechanism. The reasons are: i) clear evidence for c-axis strain at multiple length scales including in transmission electron microscopy images; ii) strong influence of confining pressure on the compressive strengths of poly-, and especially single crystals; iii) ripplocations are a topological imperative if the layers are to move relative to each other, without breaking the in-plane bonds.
[en] Nuclear graphite is a type of quasi-brittle material, in which the ratio of the tensile strength to the compressive strength is higher than that of ceramic and hard rock materials. In this case, it is difficult to achieve a perfect splitting mode when the Brazilian splitting test is used to measure the tensile strength of such materials, leading to significant measurement errors. In this study, a ring compression test for measuring the tensile strength of the nuclear graphite material was proposed, and related principles and experimental verification were presented. The results showed that a regular tensile failure mode can be achieved using ring compression tests, and the tensile strength of nuclear graphite can be accurately measured. Furthermore, it was found that the accuracy obtained from ring compression tests was much higher than that from Brazilian splitting tests.
[en] The compressive strength, flexural strength, porosity and electrical resistivity properties of cement mortars with nano-Fe2O3 and nano-SiO2 are studied. Amorphous silica is the main component of pozzolanic materials due to its reaction with calcium hydroxide formed from calcium silicate (C3S and C2S) hydration. The pozzolanic reaction rate is not only proportional to the amount of amorphous silica but also to the surface area available for reaction. Subsequently, fine nano-Fe2O3 and nano-SiO2 particles in mortars are expected to improve mortar performance. The experimental results showed that the compressive strength of mortars with nano-Fe2O3 and nano-SiO2 particles were lower than those obtained with the reference mortar at seven and 28 days. It was shown that the nano-particles were not able to enhance mechanical strength on every occasion. The continuous microstructural progress monitored by mercury intrusion porosimetry (MIP) measurements, pore-size distribution (PSD), total porosity and critical pore diameter also confirmed such results.
[es]Se estudia la resistencia a compresión y flexión, porosidad y resistividad eléctrica de morteros de cemento con nano-Fe2O3 y nano-SiO2. La sílice amorfa reacciona con el hidróxido de calcio formado en la hidratación del C3S y C2S. La tasa de reacción puzolánica es proporcional a la cantidad de sílice amorfa y la superficie disponible para la reacción, esperando que las partículas finas de nano-Fe2O3 y nano-SiO2 mejoren las propiedades de los morteros. Los resultados experimentales han mostrado que la resistencia a compresión a siete y 28 días de morteros con partículas de nano-Fe2O3 y nano-SiO2 era, en ocasiones, inferior a la obtenida con el mortero de referencia. Se muestra que las nano-partículas no siempre son capaces de mejorar la resistencia de los morteros. Las medidas mediante porosimetría de intrusión de mercurio (PIM) de la distribución de tamaño de poro (DTP), porosidad total y diámetro de poro crítico confirmaron estos resultados.
[en] Methods based on propagation of stress wave phenomena indicate particularly useful in diagnosis of non-metallic materials. The aim of this research is to demonstrate that ultrasonic measurement can produce satisfactory results in predicting certain mechanical properties of standing Aquilaria malaccensis tree. The mechanical information is very important to diagnose the condition inside the trunk. The experiment has been conducted on agarwood samples using a pulse compression ultrasonic system. The apparatus equipped with exponential horn 54 kHz piezoelectric normal probe. Through transmission method of longitudinal ultrasonic wave has been used throughout this experiment to measure velocity of ultrasonic signal through the sample. The result showed that the ultrasonic technique can be used in diagnosing of wood-based samples. (author)
[en] This research aimed to use of bagasse ash as a cement replacement in high-strength recycled aggregate concrete (HS-RAC). Crushed limestone was replaced with 100% recycled concrete aggregate (RCA) and the ground bagasse ash (GBA) was used to partially replace ordinary Portland cement (OPC) at 20, 35 and 50%wt of binder to cast HS-RAC. The results indicated that the replacing of crushed limestone with RCA had a negative impact on the properties of the concrete. Increasing the amount of GBA in HS-RAC resulted in a decrease in density and an increase in the volume of permeable pore space. The concrete mixtures prepared with 20%wt GBA replacement of OPC promoted greater the compressive strength than the conventional concrete (CT concrete) at 90 days or more. HS-RAC with GBA (up to 50%) was more durable in terms of chloride ion penetration resistance, although it had lower compressive strength than the CT concrete.
[es]En esta investigación se utilizó ceniza de bagazo como sustituto del cemento en hormigón de alta resistencia con áridos reciclados (HS-RAC). La piedra caliza fue sustituida por un árido 100% reciclado de hormigón y la ceniza de bagazo molida (GBA) en diferentes porcentajes (20, 35 y 50% en peso del material cementante) fue utilizada para reemplazar parcialmente al cemento Portland para producir hormigón de tipo HS-RAC. Los resultados indicaron que la sustitución de la piedra caliza molida por áridos de hormigón reciclado tiene un efecto negativo en las propiedades del hormigón. Aumentar la cantidad de GBA en el HS-RAC redujo la densidad e incrementó el volumen del espacio de los poros permeables. Las mezclas de hormigón preparadas reemplazando 20% en peso del cemento Portland por ceniza de bagazo molida presentaron mayor resistencia a la compresión que el hormigón convencional a los 90 días o más. El HS-RAC con GBA (hasta 50%) tuvo una durabilidad mayor que el hormigón convencional en términos de resistencia a la penetración de iones de cloruro, a pesar de tener una menor resistencia a la compresión.