Strengthening and repair of steel-concrete composite girders using CFRP laminates

The use of advanced composite materials for rehabilitation and repair of deteriorating infrastructure has been embraced worldwide. The conventional techniques for strengthening of substandard bridges are costly, time consuming and labor intensive. A total of 38 specimens made of steel and carbon fibers were prepared and tested to investigate the possibility of galvanic corrosion. Two simulated aggressive environments and three different amounts of epoxy coating were used. Potentiodynamic polarization and galvanic corrosion tests were conducted. The results of the experiments showed the existence of galvanic corrosion however the rate of such corrosion could be decreased significantly by epoxy coating. A total of 21 specimens made of S 5 x 10 A36 steel beams were prepared and tested to determine the effectiveness of CFRP patch on fatigue life of notched beam. The results showed that not only CFRP patch tends to extend the fatigue life of a detail more than three times, but also it decreases the crack growth rate significantly. To investigate the effectiveness of the epoxy bonded CFRP sheets in repair and retrofit of composite girders, a total of six large-scale steel-concrete composite girders made of W 14 x 30 A36 steel beam and 7.5 cm. thick by 91 cm wide concrete slab were prepared and tested. Three different numbers of CFRP layers and three different damage level in Range were considered. The retrofitting test results showed that epoxy bonded CFRP Sheet increased the ultimate load carrying capacity of composite girders and the behavior can be conservatively predicted by traditional methods. The repair test results showed that epoxy bonded CFRP sheet could restore the ultimate load carrying capacity and stiffness of damaged steel-concrete composite girders. The ultimate capacity of the repaired beam was predicted by traditional methods of analysis of steel-concrete composite beams, which was fairly conservative. Guidelines and procedures for design of Steel-Concrete-CFRP composite girders were developed to assist practicing engineers. The design considers the elastic and fully plastic behavior of the composite girders while is taking into account the different modes of failure. A design example is also given to illustrate the benefit of this retrofitting technique

Nonlinear Regression Prediction of Mechanical Properties for SMA-Confined Concrete Cylindrical Specimens

In order to achieve active confinement in concrete elements, researchers have recently employed smart materials called shape memory alloys (SMA). Several empirical relationships have been widely used to predict the behavior of confined concrete. To develop more accurate relations for predicting the behavior of concrete actively confined with SMA spirals, it is necessary to obtain new relations for determining the peak compressive stress and the corresponding strain in addition to the ultimate stress and strain. For this purpose, existing data from 42 specimens of plain concrete cylindrical specimens confined with SMA spirals and subjected to uniaxial compression were collected. Then, by using MATLAB and SigmaPlot software, nonlinear regression analyses were conducted to obtain the optimum relations. The best equations were selected using multiple error criteria of root mean square error (RMSE) and R-squared (R2). Finally, the accuracy of the proposed relations was compared to the existing relations for active concrete confinement which showed better accuracy

Enhancing Mechanical Behavior and Energy Dissipation in Fiber-Reinforced Polymers through Shape Memory Alloy Integration: A Numerical Study on SMA-FRP Composites under Cyclic Tensile Loading

Conventional fiber-reinforced polymers (FRPs) have a relatively linear stress–strain behavior up to the failure point. Therefore, they show brittle behavior until the failure point. Shape memory alloys, in addition to having high ductility and good energy dissipation capability, are highly resistant to corrosion and show good performance against fatigue. Therefore, using the SMA fibers in the production of FRPs can be a suitable solution to solve the problem of the brittle behavior of conventional FRPs. SMA fibers can be integrated with a polymeric matrix with or without conventional fibers and create a new material called SMA-FRP. This study investigates the effect of using different volume fractions of conventional fibers (carbon, glass, and aramid) and SMA fibers (NiTi) in the super-elastic phase and the effect of the initial strain of SMA fibers on the behavior of SMA-FRP composites under cyclic tensile loading. Specimens are designed to reach a target elastic modulus and are modeled using OpenSees (v. 3.5.0) finite element software. Analyzing the results shows that in the SMA-FRP composites that are designed to reach a target elastic modulus, with an increase in the volume fraction of SMA fibers, the maximum stress, residual strain, and strain hardening ratio are reduced, and the ability to energy dissipation capability and residual stress increases. It was also observed that increasing the percentage of the initial strain of SMA fibers increases the maximum stress and energy dissipation capability and reduces the residual strain and yield stress. In the investigation of the effect of the type of conventional fibers used in the construction of composites, it was found that the use of fibers that have a larger failure strain increases the maximum stress and energy dissipation capability of the composite and reduces the strain hardening ratio. In addition, increasing the elastic modulus of conventional fibers increases the residual strain and residual stress of the composites

Effect of magnetized water on foam stability and compressive strength of foam concrete

It has been widely reported that the use of magnetized water to mix concrete can increase the workability of fresh concrete and its hardened strength. Meanwhile, the use of foam concrete in construction industry is gaining popularity because of its excellent properties, such as low self-weight and excellent thermal insulation properties. But the foam stability and relatively low compressive and splitting tensile strength of foam concrete are still the main challenges for engineers to use this material. This study intends to evaluate the influence of magnetized water on the foam stability, compressive strength, splitting tensile strength, water absorption and micro structure of foam concrete. A total of 9 mixes were prepared with water that passed through a permanent magnetic field for 1, 5 and 10 times at flow speeds of 0.75 m/s, 1.75 m/s and 2.75 m/s, respectively. The test results indicate that the foam stability, compressive and splitting tensile strength of foam concrete are significantly improved by using magnetized water, whereas the water absorption of hardened foam concrete decreases slightly

Application of statistical analysis to evaluate the corrosion resistance of steel rebars embedded in concrete with marble and granite waste dust

In recent years, the production of waste materials has increased due to the growth of industrial activities around the world. Therefore, recycling and reusing these waste materials for different applications would make a tremendous contribution to waste elimination and sustainable building construction. The objective of this paper is to investigate the effect of marble and granite waste dust (MGWD) as a result of marble and granite stone processing on concrete properties. To achieve this purpose, a total of 15 mixes were prepared with up to 30% of MGWD cement replacement. After 28-day immersion of specimens in lime-saturated water, they were placed in a NaCl solution with 3.5% by weight for 90 days. Then, splitting tensile and compressive strength, scanning electron microscopy (SEM), open circuit potential (OCP) and electrochemical impedance spectroscopy (EIS) tests were performed alongside a statistical analysis. The mechanical results indicate that utilizing MGWD as cement replacement at a maximum amount of 20% does not notably influence the mechanical properties of concrete. The OCP assessment revealed that using 10% of granite and 10% of marble waste dust instead of cement enhances the corrosion resistance of steel rebars embedded in concrete, and also increases the potential compared to the other tested concrete mixes

Effect of magnetized water on the fresh, hardened and durability properties of mortar mixes with marble waste dust as partial replacement of cement

In this research, the simultaneous effect of marble waste dust (MWD) and magnetized water (MW) on the fresh, hardened and durability properties of mortar mixes were investigated. A total of 10 mortar mixes using different cement replacement ratios of MWD (0%, 10%, 20%, 30 and 40%) with regular tap water (RTW) and MW were prepared and tested. The standard consistency and setting characteristics, dry density, compressive and tensile strengths, water absorption and resistance to the acid attack of specimens were examined. The results showed that the fresh, hardened and durability properties of mortar mixes were improved by using MW. The results also revealed that the mortar mixes with either RTW or MW and 10% MWD as cement replacement displayed the most improvement in the hardened and durability performance compared to other mixes. However, using higher amounts of MWD leads to a lower strength and durability performance of the mortar mixes due to more porous microstructure