EXPERIMENTAL CHARACTERISTICS OF RUBBERIZED CONCRETE

One of the construction industry’s main interest is using innovative materials to facilitate construction, extend service life, and minimize maintenance and rehabilitation costs. Recycling waste tire rubbers into conventional concrete materials constitutes one of the biggest challenging issues in modern concrete technology, which can significantly relieve critical environmental issues. However, the compressive strength reduction caused by the added rubber aggregates, albeit with significant ductility enhancement, has limited its application in concrete structures. The present study aimed at attaining the optimum ratio of crumb rubber ratio with minimal reduction in compressive strength to be used in large scale elements in which the ductility constitutes a critical design parameter. Different rubberized concrete mixes with different percentages of crumb rubber (CR) and different treatment were investigated. The main parameters were the type of crumb rubber (course or fine), the percentage of replacement (5%, 10%, 20%, and 30%), the treatment conditions (treated with NAOH, or without treatment), and using silica fume as partial replacement of cement. The test data were analyzed considering the workability, the compressive, tensile, and flexural strengths. The results revealed that the most appropriate concrete mix is using a 20% treated fine crumb rubber, with silica fume incorporation

Prediction of Axial Compressive Strength of Hybrid Reinforced Concrete Columns under Static Loading

Steel corrosion is thought to be one of the primary causes of the inadequate durability of concrete buildings in the maritime environment. Because of this, adopting Fiber-Reinforced Polymer (FRP) bars in harsh settings has attracted a lot of attention for its appealing mechanical properties as well as to prevent corrosion issues. But because there hasn't been much research in this area, we don't fully understand how fiber-reinforced polymer (FRP) bars behave when they are compressed. This work's goal is to assess the expected axial compressive strength of columns when hybrid reinforcement is used in place of steel reinforcement. Hybrid bars are steel bars surrounded by a cover shell of Glass or Carbon FRP (hybrid-steel) for longitudinal reinforcement and/or transverse reinforcement. 17 column specimens were included in an experimental study program that was created.The specimens were tested to failure with an axial loading condition. The parameters studied were the type of fibers, the percentage of steel in the hybrid reinforcement for longitudinal main reinforcement ρL(0.96, 0.44, and 0.25), the ratio of the web reinforcement (internal ties), the proportion of fiber in the hybrid bars, as well as the columns' cross sections' rectangularity. Based on the data, mathematical models were devised and assessed to forecast the load bearing capability of the column. The findings indicate that hybrid reinforced concrete columns have acceptable levels of dependability index in general

Development of A New Local Mineral Admixture for Enhancing Concrete properties

Proceeding from the saying of our God almighty on his book, the holy Qur'an: "Then ignite for me, O Hāmān, (a fire) upon the clay (From which bricks are made) and make for me a tower....". Therefore, this paper presents an investigation on, using calcined ball-clay (CBC) as mineral pozzolanic admixture for concrete production. CBC is obtained from calcination processes for local ball-clay at specified conditions. To evaluate ball-clay calcination process, various temperatures (600–900 ºC) and burning durations (2, 3 and 4 hours) are used and the optimum temperature and burning time for calcination are assessed by strength activity index at age of 28 days. The hardened properties development of concrete mixtures containing 0%, 10%, 15% and 20% CBC as cement partial replacement are analysed in terms of compressive strength at 7, 28, 90 and 180 days, water absorption, ultra-sonic pulse velocity and electrical resistivity. In addition, microstructure by XRD of the cement pastes incorporating CBC was studied. The results showed that the optimum calcination process to obtain CBC are carried out at temperature 800 °C for 4 hours. The replacement of cement by 10% of CBC is an optimal dosage for concrete mixtures since it achieved an increase of compressive strength by 28% as compared with control one. Therefore, adding CBC can lead to a beneficial utilization of natural local resources, which reduces energy consumption and minimizes CO2 footprint during the manufacturing of cement concrete, thus, concrete can become an eco-friendly and sustainable material

Structural performance of axially loaded FRP-confined rectangular concrete columns as affected by cross-section aspect ratio

Wrapping of concrete column using Fiber Reinforced Polymer (FRP) sheets can significantly improve their structural behavior. The aspect ratio of the cross section plays an important role on the efficiency of the applied strengthening technique. This research aimed, experimentally and analytically, to study the effect of aspect ratio on the obtained gain in strength and structural ductility. Also, the effect of both type and configuration of FRP wrapping is discussed. The obtained experimental results showed that the value of the aspect ratio has a significant effect on the gain in strength but it has no obvious influence on the obtained ductility. Moreover, based on the experimental results of 16 specimens concerning the load carrying capacity of FRP-confined specimens, a study to address the applicability of the analytical models (Egyptian code EC, American Concrete Institute ‘ACI’ code) proposed to predict the nominal compressive strength of rectangular columns confined with FRP sheets is presented in this research. Furthermore, this research introduces a modified model to deal with the FRP partial wrapping system. However both the examined models (ACI and EC) haven’t introduced any analytical models to predict the strength of RC columns confined partially with FRP wrapping sheets. The model proposed by ACI code showed an underestimation in predicting the nominal compressive strength, however that proposed by EC showed somewhat an acceptable estimation but inaccurate. Also, the modified expression suggested by the author dealing with columns confined with partially wrapped FRP sheets is examined in this research. Keywords: Fiber Reinforced Polymer (FRP), Wrapping, Confinement, Aspect rati

Fatigue behavior of RC T-beams

The objective of this research is to study the fatigue performance of reinforced concrete (RC) T-beams strengthened in shear with Carbon Fiber Reinforced Polymer (CFRP) composite. Experiments were conducted on RC beams with and without CFRP sheets bonded on their web surfaces and subjected to static and cycling loading. The obtained results showed that the strengthened beams could survive one million cycles of cyclic loading (=50% of maximum static load) with no apparent signs of damage (premature failure) demonstrating the effectiveness of CFRP strengthening system on extending the fatigue life of structures. Also, for beams having the same geometry, the applied strengthening technique can significantly enhance the cycling load particularly, in case of beams provided with U-jacket sheets. Moreover, although the failure mode for the different beams was a brittle one, the strengthened beams provided with U-jacket sheets approved an acceptable enhancement in the structural ductility