This paper involves an experimental investigation to study the behavior of short rectangular columns cast with hybrid concrete, to compare the strength, stiffness and toughness provided by the hybrid structural system and the results collected may be used as basic data for future development of design models for this combination of materials. Seven columns were cast and tested under concentric loading; the variables studied included the diameter of steel bars for both longitudinal and lateral reinforcement. The dimensions of rectangular columns were: 100 mm x 200 mm x 740 mm high. Two columns were cast as full conventional concrete and full reactive powder concrete columns acted as control specimens. The remaining five were cast as hybrid columns having the conventional concrete at the core and surrounded by a 40 mm thickness of reactive powder concrete, with 1% micro steel fiber. The combination of these two types of concrete into the hybrid concrete columns was very useful because it enhanced the ultimate capacity of the columns with respect to the conventional concrete in about 179% compared to the enhancement produced due to using the reactive powder concrete alone which was 203%, therefore, it was concluded that using this hybrid concrete combination in concrete industry would be more economical than the use of reactive powder concrete; moreover, based on the mode of failure observed, it would be safer to use the hybrid structural system because of the destructive type of failure for columns cast with conventional concrete. Increasing the diameter of the main reinforcement gave an average increase in the percentage of the failure load with respect to the conventional concrete column of about 179% compared to the increase in the diameter of the ties which gave an average increase of 185%; which leads to the conclusion that the effect of lateral reinforcement was more pronounced than the effect of the longitudinal reinforcement in hybrid columns, due to the increase in confinement produced by both the reactive powder concrete cover in the hybrid concrete columns and the ties represented by the lateral reinforcement.
Transportation of toxic elements from air, water and soil is the main reason for agriculture crops pollution. Therefore, fast detection of heavy metals is very important for ensuring the quality and safety of crops. Laser-induced breakdown spectroscopy (LIBS), coupled with univariate and multivariate analysis, was applied for quantitative analysis of Cr, Pb, Cu and Cd in twelve kinds of rice available in local markets. Qualitative and quantitative analysis of the samples were achieved by using the locally developed LIBS set up equipped with Q-switched Nd: YAG laser and optical spectrum analyzer. Atomic absorption spectrometry (AAS) was used not only to validate the analysis results but also to establish the essential calibration curves. Distribution pattern of detected metals and possible contamination sources were analyzed by radar plot and multivariate statistics including PCA. In this study, harmful metals have been analyzed in all samples. The average content for harmful metals were 0.040 mg/kg for chromium (VI), 0.051 mg/kg for lead, and 0.041 mg/kg for copper and 0.043 mg/kg for cadmium.
In huge reinforced concrete structures, it is often difficult to distribute the reinforcing bars, especially at the connection regions, to keep the spacing between bars within the minimum acceptable limits as recommended in the global specifications standard, by using the common methods such as, overlapping or welding, therefore, a new method for bonding was introduced, using mechanical joints and electro fusion bonding method, and comparing these methods with the maximum strength of reinforcing bars without joints and the failure location within maximum strength limits outside the joints.
This paper deals with the experimental investigation on torsion in hybrid reinforced concrete beams cast with conventional concrete (CC) at the core surrounded by reactive powder concrete (RPC) at the periphery. Hybrid concrete is usually used in structural members to resist flexure, shear and torsion. Four reinforced concrete beams are cast and tested with dimensions: width 100mm, height 200mm and length 1500mm and the cross-sectional areas of the core in the specimen studied were (20×120) mm and (40×140) mm, respectively. All beams were cast and tested to failure by using two opposite cantilevers steel arms, which contribute to transferring the torque to the central part of the beam. One of the beams was of RPC. The second beam was CC only and the others were hybrid beams. Experimental data on ultimate capacity, cracking torsional loads, failure pattern and twisting angle for each of the beams were obtained. The experimental results show that the ultimate torsional strength value of hybrid beams was higher than conventional concrete beams by about (23.7-50.0) % and about (25.8-10.0) % lower than reactive powder concrete beam depending on the thickness of RPC.
This research discusses experimentally the shear strain of the reinforcement concrete hybrid beams composed of reactive powder concrete (RPC) at the peripheral and conventional concrete (CC) at the core beams under torsional strength tests. Shear strain is usually represented by (), which is explained as the tangent of the angle and is be like the length of deformation at its maximum divided by the length of perpendicular in the plane of the force application. Twelve reinforced concrete beams are tested having the following dimensions: 100, 200 and 1500mm as width, height and length respectively with thickness of the RPC concrete were 40 and 20mm. The beams were cast and tested to failure in torsion by using two opposite cantilevers steel arms that contribute to transferring the torque to the centre of the beams. Two control (CC and RPC) beams were poured, and the ten other beams were all poured as hybrid ones. Experimental data of the three strain gauges locations in the middle of the beams in one of the side surface face, to calculate shear strain (). The percentage of shear strain at ultimate torsion capacity was reduced by about 76% for RPC (RP) to CC (NC) beams and 63% for hybrid beam (H1) to CC (NC) beam.
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