Utilization of Demolished Waste as Coarse Aggregate in Concrete

Demolishing concrete building usually produces huge amounts of remains and wastes worldwide that have promising possibilities to be utilized as coarse aggregate for new mixes of concrete. High numbers of structures around the world currently need to be removed for several reasons, such as reaching the end of the expected life, to be replaced by new investments, or were not built by the local and international standards. Maintaining or removal of such structures leads to large quantities of concrete ruins. Reusing these concrete wastes will help in saving landfill spaces in addition to more sustainability in natural resources. The objective of this study is to investigate the possibility of using old recycled concrete as coarse aggregate to make new concrete mixes, and its effect on the evolution of the compressive strength of the new concrete mixes.  Core samples for demolished concrete were tested to determine its compressive strength. The core test results can be thought of as aggregate properties for the new concrete. Then, the compressive strength and splitting tensile strength of the new recycled aggregate concrete (RAC) were determined experimentally by casting a cubes and cylinders, respectively. It was found that the evolution of compressive strength of recycled aggregate concrete is similar in behavior to the concrete with natural aggregate, except that it is about 10% lower in values. It was also seen that water absorption for recycled aggregate is noticeably higher than that for natural aggregate, and should be substituted for in the mix design

Behavior of reinforced concrete deep beam with web openings strengthened with (CFRP) sheet

Deep beams are used in various applications in reinforced concrete (R.C.) structures. There have been continuous efforts to enhance and improve the performance of these crucial elements in (R.C.) structures by using several strengthening techniques such as using the carbon fiber-reinforced polymer (CFRP). However, by exploring the literature, none of the previously conducted experimental tests have studied the propagation of cracks beneath the (CFRP) sheets. In this research, the propagation of the first diagonal crack, which takes place beneath the (CFRP), is investigated by modeling sixteen (R.C.) deep beams with different opening sizes. Two shear span/ depth ratios (a/h) are studied numerically using the finite element analysis tool (ABAQUS). All models are validated using the concrete damage plasticity (CDP) model, and their results are found similar to the experimental results obtained by other authors. Results show that the Finite Element models catch the real behavior of the (R.C.) deep beams. In addition, the (CFRP) sheets are found to enhance the failure load capacity as well as the flexural crack remarkably. Moreover, the (CFRP) increases the load required to cause the first diagonal crack for models with (a/h) equals 0.9, while there is a slight change in this load for models with (a/h) equals 1.1

The effect of shape memory alloys on the ductility of exterior reinforced concrete beam-column joints using the damage plasticity model

Using shape memory alloys (SMA) bars can significantly enhance the ductility of exterior reinforced concrete joints, where they can replace the conventional steel reinforcement. This research focuses on studying the effect of using SMA on the ductility capacity of exterior reinforced concrete beam-column joints at different column axial load levels. Finite element analysis was carried out and compared with the experimental results from the literature for verification purposes, and both were compared with theoretical solutions. The results show that the use of SMA bars can improve the ductility of reinforced concrete joints noticeably, without losing load capacity. The finite element method was successful in capturing the large strain and superelastic behavior of SMA bars

Simple equations for predicting the rotational ductility of fiber-reinforced-polymer strengthened reinforced concrete joints

Achieving a certain limit of rotational ductility in retrofitted reinforced concrete (R.C) joints is very important in the design of earthquake-resistant structures. Strengthening of R.C joints using wraps of fiber-reinforced polymers (FRP) is a common attractive technique and has an effect on the ductility of such joints. This study focuses on developing simple conceptual equations to predict the ductility of exterior reinforced concrete (R.C) beamcolumn joints as a function of the applied FRP. The equations are derived based on statistical regression through parametric study using results from a high-fidelity finite element model created using ABAQUS. The validated model includes material and geometric nonlinearities, in addition to the use of realistic nonlinear contact behavior between FRP and concrete. The proposed simple equations can be used as an initial conceptual design step for checking the adequacy of R.C beam-column joints in seismic design of R.C buildings. The proposed equations consider FRP, relative column-to-beam inertia, and transverse reinforcement in the beam and joint as the main parameter. This study defines the types of failure based on the ductility, and it develops the equations for ductile and brittle failures for both CFRP-strengthened joints and non-strengthened joints. This research confirms quantitatively the effectiveness of using CFRP to increase the ductility in most cases of the R.C beamcolumn joints. However, contribution of the CFRP is limited for some cases