In this study, the fresh properties of self-compacting concrete (SCC) incorporating ground waste glass (GWG) as cementing material were experimentally investigated. GWG was used as a partial replacement for cement at replacement levels of 0, 5, 10, 15, 20, 25 and 30% by weight. Reducing the consumption of cement in construction is a major issue in terms of economic performance. Such reduction would also contribute to the environment by lessening the harmful impact of the manufacturing process. Concrete mixtures containing different levels of GWG were prepared with the water to cementitious materials ratio of 0.51. The examined properties included workability, wet density, air content and setting time. Workability of the fresh concrete was determined by using the slump flow, visual stability index, V-funnel, J-ring, L-box and GTM screen stability tests. The results indicate that there is a slight decrease in the wet density of self-compacting ground waste glass concrete (SCGWGC) of nearly 1.37% with the increase of GWG content. The conclusion is that using GWG significantly increases the workability of SCC mixtures. As the GWG increases, the slump flow also increases at a constant amount of water and super-plasticizer, but the concrete flow time decreases. The results showed that it is possible to successfully produce SCC with GWG as cement replacement.
Recently, increasing traffic in urban areas has led to a dramatic increase in collisions between speeding vehicles and structural columns. An impact applies a greater force to a column than its regular static or dynamic load because of the mass acceleration effect of the vehicle. Vehicle impact can cause catastrophic damage to structural columns and ultimately cause them to collapse; therefore, an in-depth study of their structural resistance to vehicle impact is needed. This paper reports the behavior of a reinforced concrete (RC) compression member or column under a lateral impact load. The study quantitatively assessed the columns' resistance capacity and developed an impact-resistance capacity evaluation procedure. Because it is extremely difficult and costly to experimentally perform a parametric study for column impact scenarios, this analytical study was carried out using LS-DYNA, a commercial explicit finite element (FE) analysis program that simulates the effects of a high strain rate from impact or blast loading on structural and material behavior. The parameters used for this case study were cross-section shape variation, impact load angle, axial load magnitude ratio, concrete compressive strength, longitudinal and lateral reinforcement ratios, and slenderness ratio. Using the analysis results, an impact resistance capacity evaluation procedure using a probabilistic approach is proposed.
This paper presents an experimental investigation on the response of reinforced concrete (RC) beams with the use of ultra-high toughness cementitious composite (UHTCC) in the tension zone. Two parameters, the longitudinal reinforcement ratio and the depth of UHTCC layer, were varied. The failure mechanism, flexural behavior, interface per-formance, and cracking pattern were compared between RC and RC/UHTCC beams as well as between RC/UHTCC beams with different depths of the UHTCC layer. The experimental results revealed that the yielding load was improved apparently for beams with a reinforcement ratio of 0.67%, and the macro wide cracks in concrete turned into multiple tight cracks in the UHTCC layer depending on the prominent crack dispersion capacity of the UHTCC. However, RC/UHTCC beams with 1.0% and 1.73% reinforcement ratios showed shear-interface debonding failure prior to the yielding of reinforcement, and the failure resulted from the accumulated interface crack extension up to the support and the crush of concrete. Moreover, the theoretical analysis indicates that the interface cracking strength and ultimate interface bonding strength are related with the reinforcement ratio and UHTCC depth. The tensile stress difference of reinforcement in the UHTCC layer plays a controlling role in the interface debonding between concrete and UHTCC. The present study provides significant insights for the engineering application of hot-casting RC/UHTCC composite beam.
Changes in temperature and relative humidity affect splitting tensile strength of concrete but the mechanisms are left unknown. This study aimed to clarify the mechanism through experiments using control mortar specimen and concrete specimens with two types of coarse aggregate of different shrinkage behavior mixed with the control mortar. Specimens were shaped in a thin plate for a faster equilibrium with the ambient drying conditions. Dying of different temperatures or relative humidities were maintained till the mass of specimens become constant. Then length changes, mass changes and splitting tensile strength were determined. It was shown that changes in strength of control mortar became more significant as drying conditions became severer while the change was not always monotonic. Compared with existing studies on shrinkage of cement pastes, the shrinkage of mortar specimens was supposed to be affected by the changes in strength of cement paste and by increase in strength as a result of multiple crack formation that occur due to fine aggregates. Changes in strength of concretes were affected by the change in mortar strength particularly at a relative humidity ranging from 0.80 to 0.43, where effects of fine cracks due to restraint of aggregate were imposed and strength reduction became more significant when coarse aggregate with a lower shrinkage was used. The restraining effect of coarse aggregate was confirmed also during heating higher than 40°C resulting in reduction of strength. It was concluded that the changes in strength of concrete during drying were mainly affected by both changes in mortar strength and restraint of coarse aggregate.
This paper presents an alternative fuzzy logic approach to localization of cracks on a concrete surface. The exact locations of cracks are especially needed in the case of comparison between the results of numerical analyses and experiments. The proposed method is based on the fact that cracks can be considered as highlands which has to be trekked along the ridge. The problem is similar to human perception and decision making. For this reason, the use of fuzzy logic for the purpose of classification is appropriate. The whole procedure of the so-called climber method is given. The results show the capability of the proposed method to localize cracks, advantages and the possible range of application of the proposed method are discussed.
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