Characterization of Vibration Effects on the Internal Structure and Strength of Regular and High Strength Recycled Concrete

There is a need for more in depth understanding of the consolidation effect of concrete on its durability, especially in tropical climates. During placement of fresh concrete in molds vibration is required to prevent quality problems such as honeycombs and desegregation. Nevertheless, precise monitoring of concrete vibration time has been avoided by construction professionals. This results in concrete durability reduction of appropriately designed concrete due to variation in aggregate settlement, air void content and change in water to cement ratio. In this study, the effects of vibration time on concrete strength, aggregate segregation, and physical properties were experimentally investigated on regular and high strength recycled concrete. The optimum vibration times are to be determined as a tool for construction professionals to address concrete consolidation issues associated with improper vibration time. The study reports on the test results of regular and high strength recycled concrete with a vibrating table and a rod vibrator for varying vibration times. The result of vibration on the internal structure is also studied as aggregate packing greatly affects concrete durability. It was concluded that an ideal vibration time period for recycled concrete should be based on a combination of concrete properties affecting durability instead of a specific property as vibration of concrete significantly affects concrete strength, porosity, density, viscosity, aggregate segregation, and consolidation. Ideal vibration period for recycled regular and high strength concrete provided the best combination of compressive and splitting tensile strengths, consolidation of aggregate particles, aggregate packing, and air void content to enhance the overall durability of material

Intermediate Temperature Fracture Resistance of Stone Matrix Asphalt Containing Untreated Recycled Concrete Aggregate

The sustainable alternative of blending natural limestone aggregates (NAs) with recycled concrete aggregate (RCA) was investigated in this research in order to encourage the utilization of recycled concrete in heavy traffic paving applications. The Marshall Mix design method was used to optimize mix designs containing 0%, 10%, 35% and 50% RCA. Single-edge notched beam (SENB) and semi-circular bending (SCB) tests were then applied and the fracture energy and fracture toughness determined. The tests were conducted at intermediate temperatures (5 °C, 15 °C, 25 °C) and varying notch depths (0.2H, 0.3H and 0.4H). Fracture energy and toughness did not consistently follow the behaviour of mixes with only NA; however, it was determined in this study that a RCA content between 10% and 35% would achieve peak loads, fracture energies and fracture toughness values comparative to a virgin mix

Characterization of concrete failure behavior: a comprehensive experimental database for the calibration and validation of concrete models

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.Austria. Ministry of Environment, Youth and FamilyAustria. National Foundation for Research, Technology and DevelopmentUnited States. Dept. of Transportation (Grant No. 20778

Numerical Simulation of Quasi-Static and Dynamic Experiments of Standard and Dam Concrete

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