Concrete is undoubtedly the most important and widely used construction material of the late twentieth century. Yet, mathematical models that can accurately capture the particular material behavior under all loading conditions of significance are scarce at best. Although concepts and suitable models have existed for quite a while, their practical significance is low due to the limited attention to calibration and validation requirements and the scarcity of robust, transparent and comprehensive methods to perform such tasks. In addition, issues such as computational cost, difficulties associated with calculating the response of highly nonlinear systems, and, most importantly, lack of comprehensive experimental data sets have hampered progress in this area. This paper attempts to promote the use of advanced concrete models by (a) providing an overview of required tests and data preparation techniques; and (b) making a comprehensive set of concrete test data, cast from the same batch, available for model development, calibration, and validation. Data included in the database 'http://www. baunat.boku.ac.at/cd-labor/downloads/versuchsdaten' comprise flexure tests of four sizes, direct tension tests, confined and unconfined compression tests, Brazilian splitting tests of five sizes, and loading and unloading data. For all specimen sets the nominal stress-strain curves and crack patterns are provided.
Summary The research presented in this paper deals with the numerical analysis of projectile impact on regular strength concrete (RSC), high‐strength concrete (HSC), and engineered cementitious composites (ECC) using the Lattice Discrete Particle Model (LDPM). The LDPM is chosen in this study as it naturally captures the failure mechanisms at the length scale of coarse aggregate of concrete, and its capabilities include the accurate depiction of both intrinsic and apparent rate effects in concrete, as well as fiber reinforcement effects. The model is used to predict the experimental impact response performed by four independent testing laboratories, and for each data set the model parameters are calibrated and validated using a combination of uniaxial compression, triaxial compression, uniaxial strain compression, and dogbone tests. In the first study, perforation experiments on RSC and HSC for varied impact velocities are carried out, and the exit velocity is compared with the available experimental data. The second study focuses on ECC, where multiple impact of steel and plastic fiber reinforced concrete panels are explored. A third investigation is performed on four RSC panels with varied thicknesses and subjected to the same impact velocity. In this instance, the model is used to predict the penetration depths for the different cases. Finally, in the last study, the response of large‐thickness infinite panels of sizes ranging from 300 mm to 700 mm under projectile impact is considered. Copyright © 2016 John Wiley & Sons, Ltd.
The recent increase in structural developments worldwide, has given rise to the consumption of natural aggregates and energy hence generating a vast amount of construction and demolition waste. Natural aggregates occupy 60-75 percent in volume of the concrete matrix. It is beneficial to recycle construction and demolition waste, for construction activities. One such material retained from construction sites is waste concrete, which can be used to produce recycled concrete aggregates (RCAs). Recycling waste concrete produces a substitute to natural aggregates and preserves the environment by reducing waste disposal at landfills and conserving energy. The use of recycled concrete aggregates has piqued the interest of many researchers by utilization of a full or partial substitution to that of natural aggregates in concrete mixtures. Over the last decade, a significant volume of literature has been published discussing the properties and microstructure of recycled concrete aggregates and its response when used in a new concrete mix. Within this paper a brief history of RCAs is outlined together with statistics on the quantity of concrete waste produced, recycled and its practical applications. A comparison between the RCA and natural aggregate properties are discussed on a microscopic level, such as the density and water absorption capacities. Further to this, a summary of the mechanical and durability parameters are discussed such as compressive, tensile and flexural strengths together with chloride ion penetration. Several pre-treatment methods such as: acid treatment and the use of fine mineral fillers are also discussed. Finally, the conclusions and gaps are stated.
Abstract. Aggregate size effect is among several important factors that affect concrete mechanical behavior. In this study, this effect is investigated numerically, and the obtained results are compared with the gathered experimental data that are recently performed at Politecnico di Milano and the Joint Research Center of Ispra, Italy. Since concrete is a rate-dependent material, different types of static and dynamic experiments are carried out to study the aggregate size effect on concrete response. The Lattice Discrete Particle Model (LDPM), a three-dimensional mesoscale discrete model, is employed to simulate concrete mechanical response. LDPM simulates concrete at the level of coarse aggregate pieces and is capable of characterizing strain localization, distributed cracking in tension and compression and to reproduce post peak softening behavior. The parameters governing different aspects of LDPM from concrete mixture design to the meso-scale mechanical constitutive law are calibrated and used in the validation process.
This paper investigates the calibration and validation of a new ultra highperformance concrete (UHPC) named Cortuf using LDPM-F, the Lattice Discrete Particle Model for ¿ber reinforced concrete. The LDPM-F is a discrete meso-scale model that can accurately describe the macroscopic behavior of concrete in elastic, fracturing, softening, and hardening regimes. LDPM-F has been verified extensively through the analysis of a variety of experimental tests and can reproduce with great accuracy the response of concrete under uniaxial and multiaxial stress states in compression and tension, and under both quasi-static and dynamic loading conditions. The model is calibrated herein by simulating: (1) unconfined and confined compression tests as well as 3-point bending tests on plain Cortuf and (2) single fiber pull-out tests. Afterward, quasi-static compression and tensile validation and prediction experiments were performed. The numerical results are compared to the experimental results both graphically and through failure modes.
The Lattice Discrete Particle Model (LDPM), a meso-scale model for concrete, was extensively calibrated and validated in previous research for quasi-static loading conditions. In this paper, LDPM is used to investigate the time-dependent behavior of concrete for high strain rates with the main objective of (1) assessing the role of apparent and intrinsic rate effect mechanisms on the macroscopic concrete response; and (2) demonstrating LDPM predictive capabilities under dynamic loading conditions. The LDPM formulation is extended to incorporate rate-dependent fracture mechanisms associated with the interpretation of fracture processes as thermally activated phenomena and governed by the classical Maxwell-Boltzmann theory. According to this approach, the LDPM meso-scale strength and toughness are assumed to be functions of the meso-scale strain rate. The model is calibrated and validated on the basis of experimental data available in the literature and obtained through (a) reinforced and unreinforced unconfined compression tests; and (b) Hopkinson bar tests in tension and compression. Analysis of the numerical results shows the ability of LDPM to simulate accurately the dynamic response of concrete under a large variety of loading conditions. Furthermore, in this study, LDPM is used to perform simulations of projectile impacts on regular strength concrete (RSC) and high strength concrete (HSC). Perforation and penetration experiments on RSC and HSC for varied impact velocities are carried out and the exit velocities are compared to available experimental data. In general, LDPM replicates successfully the behavior of concrete for penetration and perforation events and it is able to capture accurately the main features of concrete response in terms of projectile deceleration as well as fracture patterns. IntroductionAs a result of increased concerns regarding public safety in recent years, the resistance of infrastructure to impact and penetration has become an emerging research focus in the cement and concrete industry. Under extreme loading scenarios, such as earthquakes, impacts, and explosions, concrete experiences strain rates orders of magnitude higher than those relevant to classical laboratory tests for strength and toughness measurements. Consequently, under these conditions, the correct design of concrete structural elements requires a better understanding of time-dependent mechanical behavior of concrete at high strain rates. Typical experimental observations on regular strength concrete report an increase of macroscopic mechanical properties such as, Young's modulus, compressive strength, tensile strength, and fracture energy, for increasing strain rate (Bischoff and Perry, 1991;Dilger et al., 1984;Mainstone, 1975). In most cases, rate effect is quantified through the Dynamic Increase Factor (DIF) defined as the ratio between the dynamic property of interest and the associated quasi-static value. The evolution of DIF with strain-rate is often approximated through a bilinear curve in which the second line...
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