Effect of coarse aggregate size and matrix quality on ITZ and failure behavior of concrete under uniaxial compression

Effects of coarse aggregate size and water/cement (w/c) ratio of the matrix on the formation of interfacial transition zone (ITZ) and subsequently on the failure process of concrete under uniaxial compression were studied. For this purpose, a series of experiments were designed and carried out on mortars with two different w/c ratios containing single spherical steel aggregates of different sizes. The ITZ properties and the failure process of concrete were investigated through tensile strength tests both before and after compressive preloading, stress-axial strain, stress volumetric strain and stress-lateral strain measurements. It was observed that ITZ becomes critical for larger aggregates and lower w/c ratio mortar matrices. The negative effect of smooth surface texture of the aggregate and the large difference between aggregate and matrix moduli of elasticity on the properties of ITZ is of paramount importance for low w/c ratio composites. The effect of reduced bond properties of ITZ relative to its matrix was reflected in the lower critical stress levels for the low w/c ratio composites with larger aggregates

Effect of coarse aggregate size on interfacial cracking under uniaxial compression

The effects of aggregate type and size are important parameters in the formation of interfacial transition zone (ITZ) structure and subsequently in the failure process of concrete. The influence of surface, rigidity and size of aggregates and water/cement (w/c) ratio of the matrix on bond strength at the ITZ and the interrelationship between the bond and the matrix in the failure process of concrete under uniaxial compression were studied. For this purpose a series of experiments were designed and carried out on mortars (with two different w/c ratios) containing single spherical steel aggregates. The ITZ properties and the failure process of concrete were investigated by means of tensile and compressive strength, and stress-volumetric strain measurements. It was observed that the effect of aggregate properties (high modulus of elasticity, smooth surface texture and size) on the weakness of ITZ and the failure process of concrete are of paramount importance for low w/c ratio composites. The effect of reduced bond properties was reflected in lowered critical stress levels for the low w/c ratio composites with larger aggregates

Dynamics and structure of planar gravity currents propagating down an inclined surface

Planar, Boussinesq, compositional gravity currents formed by the release of a fixed volume of heavier fluid from a closed lock and advancing on an inclined no-slip bottom surface in a reservoir with a horizontal free surface are investigated based on 3-D large eddy simulation. The initial region containing the lock fluid has a rectangular shape. Simulations are conducted for bottom slope angles, theta, between 0 degrees and 60 degrees. The running length of the inclined bottom was sufficiently long to allow a detailed study of the evolution, front dynamics and structure of the current during the latter stages of the deceleration phase (front velocity reduces with time). Results show that currents advancing over inclined surfaces with theta > 10 degrees are characterized by the formation of an intensified mixed vortex (IMV) at the back of the head. The IMV forms faster and its coherence, circulation, and size increase monotonically with increasing bottom slope angle. The paper discusses how the buoyancy in the head varies with varying bottom slope angle and with time. In particular, for theta >= 30 degrees, the current reaches a regime where the total buoyancy of the head and IMV is close to a constant and the value of this constant increases with increasing theta. During this regime, the head mainly loses buoyancy to the IMV. For theta >= 40 degrees, a close to linear decay of the head buoyancy with time is observed during the later stages of this regime. Simulation results show that, while for relatively small bottom slope angles most of the sediment is entrained beneath the head, for theta > 20 degrees the IMV has a much larger capacity to entrain the sediment compared to the head region past the initial stages of the propagation of the current. This means that sediment entrainment patterns of currents propagating over highly inclined surfaces are qualitatively very different from the widely studied case of currents propagating over horizontal surfaces. The paper also discusses the different regimes observed in the temporal evolution of the front velocity and the applicability of theoretical models derived based on the data obtained for relatively small bottom slope angles and a relatively short evolution of the current to describe the evolution of currents propagating over large bottom slope angles and/or at large times after the start of the deceleration phase. While it is found that mixing increases monotonically with increasing theta, the largest total kinetic energy for a given front position is observed for theta = 30 degrees-40 degrees. Results also show that the largest magnitude of the bed friction velocity is induced for theta = 30 degrees-40 degrees, which means that the currents with the largest capacity to entrain sediment are those with the largest rate of increase of total kinetic energy with the propagation distance. Published by AIP Publishing

Assessing the ITZ microcracking via scanning electron microscope and its effect on the failure behavior of concrete

The influence of aggregate size and water-to-cement (w/c) ratio of the matrix on the structure of interfacial transition zone (ITZ) and the interaction between the ITZ and the matrix on the failure process of concrete under uniaxial compression were studied. The ITZ microcracking and the failure process of concrete were investigated experimentally by means of compressive and indirect tensile testing, stress-volumetric strain measurements and microscopic analyses on the model concrete containing single spherical steel aggregate with three different w/c ratios. At low w/c ratios, the rigid and smooth surface texture aggregates made by the ITZ have a significant structural difference compared to the mortar. This was more pronounced for larger aggregates. Higher structural differences between the mortar matrix and ITZ in low w/c ratio composites resulted in accelerated ITZ microcracking at high stress level. The effect of condensed microcracking in a narrower ITZ was reflected in the lower critical stress levels for the low w/c ratio composites with larger aggregates

Forced hydraulic jump on non-protruding rough beds

Baffle blocks and sills are commonly used to stabilize the location of a hydraulic jump and shorten its length. However, corrugations or prismatic roughness elements may be effective alternatives to them. In the present study, experiments were performed to determine the effects of corrugations and prismatic roughness elements on fundamental characteristics of jump such as length, tailwater depth, and energy dissipation capacity. Corrugations were placed to cover the entire length of the basin. Prismatic roughness elements were placed in two different arrangements as strip and staggered. The results showed that the length of jump was reduced about 35% by corrugations, 40% by strip roughness, and 35%-55% by staggered roughness. The tailwater depth reduction was 20% for corrugations, 5%-13% for strip roughness, and 7%-15% for the staggered roughness compared to classical jump. The roughness elements induce 3%-10% more energy dissipation than that of classical jump

Bed shear stress and sediment entrainment potential for breaking of internal solitary waves

We investigate the interaction of strongly non linear internal solitary waves (ISWs) with boundaries having different slopes by means of high-resolution 3D large Eddy Simulations (LES). Releasing a volume of fresh water into a stratified ambient fluid, three different breaking mechanisms are produced: plunging, collapsing and surging breakers. The different shoaling dynamics affect the ISW evolution over the sloping boundary, inducing different effects on the bottom. In order to investigate the effects of the ISW breaking on the inclined surface, we calculate the bed shear stress and estimate the local flux of sediments entrained from the bed. We analyze the relationship between the breaking criteria and the related effects on the sloping surface. Although plunging breakers are expected to induce significant effects within the fluid, causing larger amount of mixing and fluid entrainment, the effects on the bottom are totally opposite. The collapsing breaker mechanism, indeed, generates boundary layer separation, which in turn induces whirling instabilities. Results show that the ISW interaction with the inclined surface occurs in its close proximity for collapsing breaker mechanism, which explains why the largest bed shear stresses and sediment re-suspension are predicted in the simulation where a collapsing breaker mechanism is observed

Effect of ground perlite incorporation on the performance of blended cements

Perlite is a volcanic rock that contains relatively high amounts of SiO2 and Al2O3. Due to its proper chemical composition and glassy structure, it can be used as a pozzolanic addition in blended cements. In this study, ground perlite was used as a cement replacement material in blended cements. Several mortar mixes were prepared to investigate the performance of those cements. The results showed that perlite incorporation caused early age strength losses when compared to the control mortars containing only portland cement; however, the difference between them decreased in time due to the pozzolanic reactions. The strengths of the blended cements were still within the limits of the EN standards. Moreover, it was observed that use of ground perlite increased the durability of portland cement mixes

Impact of the terrorist bombings of the Hong Kong Shanghai Bank Corporation headquarters and the British consulate on two hospitals in Istanbul, Turkey, in November 2003

Background. The authors sought to estimate the impact of the terrorist bombings of the Hong Kong Shanghai Banking Corporation headquarters and the British consulate in Istanbul, Turkey, on November 20, 2003, on two nearby hospitals, in terms of epidemiologic outcomes, resource utilization, and time course of emergency needs

Impact of the terrorist bombings of the Neve Shalom and Beth Israel synagogues on a hospital in Istanbul, Turkey

Objectives: The authors sought to estimate the impact of the open-air mass-casualty terrorist bombings of the Neve Shalom and Beth Israel Synagogues in Istanbul, Turkey, on November 15, 2003, on the American Hospital (AH) in terms of resource utilization, epidemiologic outcomes, and time course of emergency needs. Methods: A retrospective descriptive study using data from hospital records of injured survivors who used the emergency department at AH on November 15, 2003, to determine the number and percentage of injured survivors who were hospitalized, received operative care, had specific injury types, had an Injury Severity Score 16, died, and arrived within certain time intervals. Results: AH received 69 (91 %) injured survivors from the scene, of which nine (12 %) were hospitalized and three (4 %) received operative care. Starting four hours after the initial blast, seven (9 %) injured survivors were transferred to AH from other hospitals, of which five (7 %) were hospitalized and four (5 %) received operative care. Of the 49 injured survivors from the scene with documented injuries, 43 (88 %) had injuries to the head or face, 42 (86 %) had lacerations, five (10 %) had fractures, one (2 %) had a penetrating eye injury, one (2%) had a serious intracranial injury, and none had primary blast injuries. Four (5 %) injured survivors at AH had an Injury Severity Score greater than or equal to 16, and none died. Conclusions: Seventy-six injured survivors used the emergency department at AH, including a delayed wave of injured survivors transferred from other hospitals. The majority of injured survivors with documented injuries had non-life-threatening lacerations of the head or face, and relatively few injured survivors were hospitalized or received operative care