A comparative study of concrete behavior during compression testing and water jet erosion (original) (raw)
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The Importance of Erosion Concrete Tests for Hydraulic Surfaces
2018
The population growth requires improvements in water availability for consumption, food and energy. There are many challenges to achieve this. However, in many cases, one solution resolves all needs: reserving the water for supply, irrigation of crops and energy generation. In particular, the current demand for clean energy generation has encouraged some governments to invest in the construction of new hydropower plants. This scenario results in building a dam and its appurtenances. The concept of accumulating water for human use dates back to antiquity, but it was only during the 19th century that the technological development allowed the advent of hydropower plants. Since then, ongoing efforts on this field have developed technologies and the systematic construction of dams. More recently, there has been an increasing concern regarding the safety of dams. In Brazil, the safety legislation began to operate only in 2010. Malfunctioning of dams can lead to failure and even to catastrophic consequences. When an accident occurs, not only are the costs for repairing high, but it also compromises operation and the environment. A dam failure may be related to a poor performance of the spillway. Erosion is one of the main causes of spillways failure. In this sense, it is essential to characterize the composition and resistance of the concrete to be used in the spillway. Cavitation and water solid mixture are among the main causes of erosion that put spillways into risk. Cavitation is the formation of bubbles within the liquid, if the vapor pressure is reached. Once the pressure rises, the bubbles implode and eventually cause damage, noise, vibration and pressure fluctuation. Water solid mixture causes erosion by the impact of particles. The particles are carried in the flow, and it is especially important, because the damage is irreversible and progressive. The objective of this paper is to show the importance of testing concrete samples to erosion before using them in prototype. The concrete samples are submitted to erosion due to cavitation and water-solid mixture. The tests were performed at the Laboratory of Hydraulics and Fluid Mechanics at Unicamp, Brazil. The method for evaluating cavitation erosion resistance is based on the use of a high velocity cavitating jet. The other method, for evaluating water solid mixture erosion resistance, is based on the use of a mixing tank, where an impeller propels solid particles in the water over the sample. In both cases, the erosion resistance is associated with the mass loss of the sample through time. The results highlight the erosion that can occur in prototypes and the importance of testing concretes before construction or repairing of concrete spillways.
A combined CFD-experimental method for abrasive erosion testing of concrete
Journal of Hydrology and Hydromechanics
Serious damage may occur to concrete hydraulic structures, such as water galleries, spillways, and stilling basins, due to the abrasive erosion caused by the presence of solid particles in the flow. This underlines the importance of being capable in providing characterization of the concrete from the point of view of its vulnerability to abrasive erosion, in order to improve the design of the structure and the material selection. Nevertheless, the existing apparatus for concrete abrasive erosion testing are either far from allowing realistic simulation of the actual environment in which this phenomenon occurs, or show a large degree of complexity and cost. An alternative method has been developed with the aid of Computational Fluid Dynamics (CFD). CFD was first employed to verify the effectiveness of a new laboratory equipment. Afterwards, a parameter has been introduced which, by successful comparison against preliminary experiments, proved suitable to quantify the effect of the fl...
A New Testing Method to Investigate the Compacting Behaviour of Fresh Concretes Under Impact Loading
Experimental Mechanics, 2006
This paper presents a new instrumented Proctor test using a Hopkinson bar which allows for the original measurement of forces and velocities during the impact loading on soft fresh concrete samples. For this purpose, the specific points of using low impedance Nylon bar as well as the two-point measurement method to recover coupled waves are discussed. The whole test consists of successive impacts of low velocity (less than 3 m/s) exerted on the compressible specimen of a fresh concrete. The proposed original measurement allows for a quantitative comparison of the behaviour of the fresh concrete submitted to quasi-static and impact compaction. It shows that impact compaction is more efficient than quasi-static case. However, the increase of the impact velocity seems to reduce the efficiency. There exists probably an optimal loading path. The further understanding of the behaviour of fresh concrete under low velocity impact should be an interesting way to improve the industrial compacting process. Keywords Fresh concrete. Compaction. Proctor test. Hopkinson bars Nomenclature C Celerity of the elastic waves E Young's modulus S b Cross-sectional area of the bars (A Strain measured by a strain gauge A (o Output strain at the interface between the output bar and the specimen V o Output velocity at the interface between the output bar and the specimen S e Cross-section h ? Initial length h Current length M Mass > Apparent density > = M/(S e h) A i Input stress at the interface between the impact bar and the specimen A o Output stress at the interface between the output bar and the specimen N Number of successive impacts
The use of non-destructive tests to estimate Self-compacting concrete compressive strength
MATEC Web of Conferences, 2018
Until now, there are few studies on the effect of mineral admixtures on correlation between compressive strength and ultrasonic pulse velocity for concrete. The aim of this work is to study the effect of mineral admixture available in Algeria such as limestone powder, granulated slag and natural pozzolana on the correlation between compressive strength and corresponding ultrasonic pulse velocity for self-compacting concrete (SCC). Compressive strength and ultrasonic pulse velocity (UPV) were determined for four different SCC (with and without mineral admixture) at the 3, 7, 28 and 90 day curing period. The results of this study showed that it is possible to develop a good correlation relationship between the compressive strength and the corresponding ultrasonic pulse velocity for all SCC studied in this research and all the relationships had exponential form. However, constants were different for each mineral admixture type; where, the best correlation was found in the case of SCC with granulated slag (R 2 = 0.85). Unlike the SCC with pozzolana, which have the lowest correlation coefficient (R 2 = 0.69).
Behavior of Concrete in Water Subjected to Dynamic Triaxial Compression
Journal of Engineering Mechanics, 2010
To understand the behavior of concrete material in ambient water, a series of triaxial compressive tests of concrete cylindrical specimens ͑ 100ϫ 200 mm͒ was conducted on a large scale triaxial machine. The acting pattern of water, confining pressure, loading strain rate, and moisture content were chosen as test parameters. The water acting patterns on concrete were directly divided into mechanical loading and real water loading according to whether the specimens were directly exposed to water or not. The confining pressure ranged from 0-8 MPa and the strain rate included 10 −5 / s, 10 −3 / s, and 10 −2 / s. By testing dry and saturated specimens, the effect of moisture on concrete strength was also examined. The test results indicated that the compressive strengths of both dry and saturated concrete increase obviously with the confining pressure under mechanical confining pressure. However, the effect on the strengthened dry concrete specimens is more significant. The strength of dry concrete under real water loading decreased remarkably, even less than its uniaxial strength, whereas the compressive strength of the saturated concrete specimen under real water loading is close to its uniaxial compressive strength. The strength of concrete increases with strain rate, and this phenomenon becomes more apparent under water loading.
The mechanical behaviour of concrete when subjected to impact or blast has still many aspects requiring further study. Dam concrete is characterized by large coarse aggregates, hence large specimen sizes are needed in order to study a representative volume of the material. Exploiting an innovative equipment, based on Hopkinson bar techniques, the dynamic behaviour of concrete of 64 mm maximum aggregate size has been investigated. Direct dynamic compression tests have been performed on medium and large size cylindrical samples. Full stress-strain curves have been obtained, which have allowed the estimation of fracturing energies and of the relevant dynamic increase factor. The experimental campaign has also included a reference standard concrete in order to highlight the peculiarity of the dam concrete at high strain rates and to validate the transition of this type of testing to very large specimens.
Brief Overview and Comparison between Destructive and Non-Destructive Concrete testing
The Introduction to Engineering (NGN 110 ) course walks freshman engineering students at AUS through the various engineering fields and demonstrations of some applications of each field. This lab report illustrates the two of the prominent methods of concrete testing: Destructive using hydraulic compression, and Non-Destructive using the Schmidt hammer, to which students were introduced in their Civil Engineering Lab.
DYMAT 2009 - 9th International Conferences on the Mechanical and Physical Behaviour of Materials under Dynamic Loading, 2009
This paper concerns the concrete behavior under extreme loading situations (ballistic impacts, penetration). During such loadings, concrete material is subjected to very high-intensity triaxial stress states. For the purpose of reproducing such stress levels with well-controlled loading paths, static tests have been conducted on concrete samples using a triaxial press offering very high capacities (stress levels of around 1 GPa). This paper is devoted to experimental results which show that the concrete strength in uniaxial compression after 28 days of ageing, f c28 , is a very poor indicator of the high-pressure mechanical response of concrete. From the composition of a reference ordinary concrete (f c28 = 29 MPa), two other concretes have been produced with f c28 equal to 21 MPa and 57 MPa, respectively. Besides, to evaluate the effect of the saturation ratio, Sr, tests have been conducted on both dried samples, wet samples and saturated samples. The results show that contrary to what is observed in simple compression, when placed under high confinement, concrete behaves like a granular stacking. There is no more effect of the cement matrix strength whereas the concrete saturation ratio exerts a major influence.
Destructive and Non-destructive Testing of Concrete Structures
The estimation of mechanical properties of concrete can be carried out by several methods; destructive and non-destructive. In this context, the crushing of the samples is the usual destructive test to determine the concrete strength. The rebound hammer test and the ultrasonic device are used in the field of non-destructive tests to determine respectively the compression strength and the ultrasonic pulse velocity (UPV) in the concrete. In this work, eight concrete compositions were used to prepare cylindrical specimens (16 cm x 32 cm) by varying the water/ cement ratio and the cement dosage. An experimental study was conducted to determine the compressive strength of concrete by destructive (compression) and non-destructive (rebound hammer) tests at different ages (7, 14 and 28 days). In addition, the influence of several factors on the modulus of elasticity determined by pulse velocity test was investigated. These factors mainly included the age of concrete and the water/ cement ratio. The results showed that the difference between the resistance values obtained by destructive and non-destructive methods decreases with increasing age of concrete. The dynamic modulus of elasticity increases with the curing time of the concrete until the age of three months. In addition, a simplified expression has been proposed to estimate the rebound number from the value of the dynamic modulus of elasticity determined by pulse velocity test.
Effect of the water/cement ratio on concrete behavior under extreme loading
International Journal for Numerical and Analytical Methods in Geomechanics, 2009
This study focuses on identifying concrete behavior under severe triaxial loadings (near field detonation or ballistic impacts). In order to reproduce high stress levels with well-controlled loading paths, static tests have been carried out on concrete samples by mean of a very high-capacity triaxial press (stress levels on the order of 1 GPa). It is a longstanding fact that the water/cement ratio (W/C), upon entering the concrete composition, is a major parameter affecting the porosity and strength of the cement matrix of hardened concrete. The objective of this article is to quantify the effect of this ratio on concrete behavior under conditions of high confinement. From the composition of a reference 'ordinary' concrete (i.e. W/C = 0.6), two other concretes have been produced with W/C ratios equal to 0.4 and 0.8, respectively. This article presents experimental results and their analysis regarding the effect of water/cement ratio (W/C) on concrete behavior under high confinement. It shows that when placed under high confinement, concrete behaves like a granular stacking composed of concrete without any influence from the level of cement matrix strength.