Civil Engineering

ABSTRACT Corrosion of steel reinforcements is one of the most serious defects of reinforced concrete. A lot of money and efforts are needed for repairing corrosion of RC structures. Corrosion of steel in RC columns may lead to complete or partial failure of the building. Consequently, the issue of solving the problem of corrosion of steel rebars in RC columns is very demanding. In this paper the behavior of RC columns reinforced by GFRP bars is studied and compared to the behavior of the traditional steel reinforced columns. The study includes most of the parameters those may affect the behavior of the GFRP reinforced columns. This included replacing steel stirrups by GFRP sheets in two forms, warping the longitudinal reinforcement of the column, and warping the column from the outside. Also the reinforcement percentage was taken as a variable. Ultimate load, axial shortening, and strains in the longitudinal reinforcements were recorded for each test specimen. Data were analyzed and conclusions and design recommendations were drawn.

This paper presents a focused study on using different methods to enhance the ultimate capacity of flexural behavior in RC slabs. Four RC specimens were casted with common compressive strength and reinforced with steel mesh. Specimens were strengthened with different methods such as usage of GFRP sheets, carbon fibers laminate strips and near surface mounted steel rebars. All specimens were subjected to two-point loading setup. Load was increased from zero to failure load. First crack was recorded and crack pattern was observed. The behavior of strengthened specimens was compared to that of the control specimen to judge the efficiency of the used techniques. Test results showed that the used techniques were effective in enhancing the behavior of the strengthened slabs by noteworthy values.

The aim of this study is to investigate the influence of adding nano-silica particles, on the properties of fresh and hardened cement mortar through measurements of workability, compressive and flexure strengths in addition to measuring by SEM analysis. Nano-silica particles with size of 19 nm have been used as a cement addition by 1, 3, 5, 7 and 10 % by weight of cement content. Results indicated that the cement mortar workability decrease with increasing nano-silica addition. On the other hand, the percentage of 7 % of nano-silica recorded as optimum percentage in compressive and flexure strength measured for cement mortar mixed with the nano-silica. The improvement in compressive and flexure strength measured as 55.7 % and 46.9 % respectively, compared with the conventional mortar, especially at early ages. In addition, the scanning electron microscope (SEM) analysis of the microstructures showed that the nano silica filled the cement paste pores, more homogeneity for cement paste and interfacial zone, by reacting with calcium hydroxide crystals forming more calcium silicate hydration.

This paper presents a focused study on properties of porous concrete to widen its application to structural engineering. Mechanical properties like compressive strength, indirect tensile strength, flexural strength and physical properties like density, permeability and porosity are studied. To determine those parameters, twenty-seven cubes, cylinders and prisms were tested. Also, three polymer impregnated porous concrete slabs were tested under pure bending moment to study the efficiency of selected resin to integrate particle of concrete to achieve a new generation in using porous concrete in structural engineering. Three different cement content specimens of porous concrete were considered, studied cement contents are 200 kg/m 3 , 300 kg/m 3 and 400 kg/m 3. The results show that, increasing the cement content can increase the compressive strength, indirect tensile strength and flexural strength. Density of porous concrete is less than conventional concrete by 21% but permeability factor recorded higher value compared to conventional concrete by sixteen times. Increasing the cement content has no significant effect on either ultimate load or maximum deflection of polymer impregnated porous concrete slabs but the results recorded an achievement to use this concrete in structural engineering applications and give an easy way to cast special concrete like polymer concrete without special tools.

—High performance traditional and optimized lightweight fibrous concrete was investigated by using steel fibers and glass fiber reinforced polymer (GFRP) sheet, double action of Fibers. Basically, fibers could controlled the cracking of concrete, crack propagation and crack width. However, using fibers capable of enhancing failure mode of concrete to semi-ductile or ductile mode. Experimental work was consist of two phases, the first phase was focused on cast traditional fibrous concrete specimens in addition to control specimens to compare obtained results. These specimens were cubes, cylinders and prisms, which were tested after seven, fourteen and twenty eight days. Three percentages of round crimped (corrugated) steel fibers (0.5%, 1% and 1.5%) were used to get the optimum percentage. The second phase was concerned with cast lightweight concrete specimens by using the obtained optimum percentage of steel fibers. Specimens were cast by using waste lightweight sand bricks as an coarse aggregate (replacement percentage 50% of actual weight). The effect of strengthening with external GFRP sheet was studied for traditional and lightweight concrete specimens. The results confirmed that, steel fibers and GFRP sheet (external strengthening) increased the studied mechanical properties with competitive values in comparison to traditional concrete.

— It's very important for environmental issue to use disposal of waste tires. Rubber from waste tires used for partial replacement of fine aggregate in traditional concrete, the resulting product called crumb rubber concrete (CRC). Concrete mixes containing waste crumb rubber untreated/treated with replacement percentages (3% and 6%) of fine aggregate were studied and those mixes were compared with traditional concrete mix to investigate the behavior of untreated CRC and optimized treated CRC. It's worth to be mention that, chemical agent succeeded to treat and increase the bonding chain between crumb rubber and concrete. On the other hand, reinforced concrete beams were cast with the same percentages of fine aggregate replacement (3% and 6% treated crumb rubber). Furthermore, two reinforced concrete beams were cast with three layers, the lower concrete layer cast with traditional concrete but the middle and upper layers were cast with treated CRC to studying flexural strength and bond efficiency, also, control RC beam with traditional concrete was cast for comparison. It was concluded that, compressive strength effected by positive value by increasing treated crumb rubber percentage. CRC shows reduction in the density of concrete in comparison to traditional concrete. By increasing rubber percentage, slump values decreased.

Relatively recent materials, such as fiber reinforced polymer (FRP), have been used to strengthen circular short columns. Six circular columns were cast with 200mm diameter and having length of 1300mm. The first group, was three unreinforced concrete columns. The second group, was three reinforced concrete columns with six bars having diameter of 12mm, however, stirrups with 8mm diameter and spacing 150mm. Low compressive strength concrete was used with 200kg/cm 2 strength after twenty eight days. External glass fiber reinforced polymer (GFRP) sheet were used in the circumferential direction to confine circular columns by strips or jacket mode. Columns were tested under an axial load after twenty eight days. The study was conducted to compare GFRP strengthened columns (strips or jacket) with control specimens (columns). Theoretical study was incorporated to verify the experimental results and investigate the effect of strength reduction factors in ACI design equations on experimental results. Test results revealed that, the two techniques significantly enhanced the capability of the low compressive strength columns to carrying axial load for both reinforced and unreinforced columns. The achieved conclusions confirmed that, the studied techniques capable of increasing the vertical load capacity of deficient columns with significant values.

Stratified Slab consist of two or more types of concrete; in particular, of composite materials consisting of High Strength Concrete (HSC) and Normal Strength Concrete (NSC). This study had the effect of delay time overlap between two concrete mixes (15 minutes and 60 minutes). An experimental program was conducted to investigate the flexural behavior of two HSC/NSC slabs that had subjected to double static loads. The most important achievement conclusion is the success of the idea of casting different strengths concrete layers using a short time (60 minutes) interval to improve the flexural behavior of the slab. Keywords-Composite Slab, Multi-Layers Concrete, High Strength Concrete, Effect of Cold Joint. I. INTRODUCTION The usage of HSC has been risen in the past decades, to enhance structural element and retain the volume of structural elements. The usage of the NSC may lead to larger volumes of concrete, which results miss leading in the cost of structure. On the other hand, the usage of only HSC may lead to over estimated cost to an ordinary structure. As a result, the concept of using NSC with HSC or any advanced concrete to obtain the benefits of two materials is developed. The lower layer was cast by NSC (25MPa) to reduce the cost, but the upper layer of compression zone was cast by HSC (60MPa) to enhance the behavior of concrete slabs in both flexural and deformation. A lot of studies had the impact of the time delay when casting the second layer of concrete on its mechanical properties [1], [2], [3], [4], [5], [6]. Their results indicated that when cast the second layer of concrete at early age (about 1 hour), the compressive, flexural, and split tensile strengths decreased by neglected ratios. so, this study will show the flexural behavior for composite sections (HSC/NSC) by taking short time lap (15minutes and 60minutes) between casting the two layers. The two times was chosen to study which of them satisfy the good bond between the two layers.

This paper represents an experimental study to investigate the axial behavior of reinforced concrete (RC) columns which reinforced with steel or Basalt Fiber Reinforced Polymer (BFRP) bars. Three reinforced concrete columns with 2000 mm high and of square cross-section 200mm width were tested under compression loading test up to failure. The key parameters considered in this study were: reinforcement type, centric or non-centric load with small eccentricity of 5cm. The study gives a clear result for judge the capability of using BFRP in RC columns.

This paper represents the effect of post tensioning system on reinforced concrete slab. Three slabs were tested to ensure the system capacity of post tensioning by two techniques. The first specimen is a reference slab reinforced with traditional steel bars system, the second one is cast with an embedded duct (two holes) in slab to install post tensioning basalt fiber reinforced polymer bars (BFRP). Finally, the last one as first specimen but enhanced with external post tensioning BFRP bars. These systems have a fixed level of post tensioning 10% of bar stress. Cast slabs with a rectangular cross-section of 500 mm width, 120 mm depth and an overall span of 3000 mm and were tested under the effect of pure bending moment. The results showed a conservative achievement for post tensioning RC slabs with 10% level of stress.

This paper investigates the structural performance of concrete beams reinforced with steel and fiber-reinforced polymer (FRP) bars that having large rectangular openings. An experimental study was conducted on three FRP steel reinforced concrete (FSRC) beams using basalt FRP (BFRP) bars. The FSRC beams were consisted of one beam without openings served as a reference beam; one beam with non-reinforced openings and one beam with reinforced openings. All beams were tested under the effect of two line loads bending test up to failure. Based on the test results, it was found that the presence of opening produces earlier cracks at opening locations. These cracks increased and propagate continuously with the increasing in applied load and lead to earlier failure. Compared to similar beams without openings, the presence of non-reinforced and reinforced openings was found to produce reductions in strength of up to 75% and 63%, respectively.

This study aims to present a model suitable for analyzing reinforced concrete slabs fabricated by stratified concrete using finite element method. Stratified Concrete consist of two or more types of concrete; in particular of composite materials consisting of High Strength Concrete (HSC) (60MPa) and Normal Strength Concrete (NSC) (25MPa). A nonlinear three-dimensional finite element analysis has been used to conduct an analytical investigation on the overall behavior of reinforced concrete stratified slabs. ANSYS computer program version 15 is utilized in the analysis. The two layers of concrete were idealized by using the 8-node isoperimetric brick elements in ANSYS assuming good bond between them, while the reinforcement was modeled as link element by assuming perfect bond between the concrete and steel reinforcement. The numerical analysis includes material nonlinearity due to concrete cracking in tension, nonlinear stress strain relations of concrete in compression, crushing of concrete and yielding of steel reinforcement. The validity of the adopted models was verified through comparison with the one experimental slab, and the agreement has proven to be good.

In the recent years, the demands on new generation of modern concrete as a results of the industry revolution become important matter. One of these concrete is polymer impregnated no-fines concrete. The scope of this study is to study the fresh and hardened characteristics of selected concrete. The experimental work was done by producing eighteen samples prepared by three different mixing proportions (the samples mainly consists of cement, water and polyester) as a fix proportions but coarse aggregate weight as a variable parameter to obtain the optimal percentage. The failure mechanism was observed and classified, in addition to the density of concrete and voids percentage were taken into consideration. The results show that, the increasing of coarse aggregate weight within the no-fines mixture lead to increase the density along with increasing the compressive, indirect tensile and flexural strength for the samples.

This paper presents a focused study on using different methods to enhance the ultimate capacity of flexural behavior in RC slabs. Four RC specimens were casted with common compressive strength and reinforced with steel mesh. Specimens were strengthened with different methods such as usage of GFRP sheets, carbon fibers laminate strips and near surface mounted steel rebars. All specimens were subjected to two-point loading setup. Load was increased from zero to failure load. First crack was recorded and crack pattern was observed. The behavior of strengthened specimens was compared to that of the control specimen to judge the efficiency of the used techniques. Test results showed that the used techniques were effective in enhancing the behavior of the strengthened slabs by noteworthy values.

Residential housing is one of the major priorities in Egypt. The cost of apartment in different regions can charge the person over budget money and per disability of people the slums appears with uncivilized environment. Construction material like cement consumes a lot of energy to produce final product which make an additional burden on state economy. This paper presents a simple technique to build low-cost housing by using new materials abundantly available in nature with low cost to improve sustainability and green energy. The compressive strength of compressed stabilized earth building bricks depends upon the soil type, amount of stabilizer and the compaction pressure used to form the bricks with dimension of 25x12x6cm. Experimental program was carried out on specimens and seven tests were applied. Each test consists of five masonry prisms assemblage cast with stabilized bricks. These tests are compressive strength, shear strength, in-plane tensile strength, and flexural tensile strength. The results are encouraging and promising to use these bricks in green constructions as low cost housing and national projects. A comparative study approved the cost effectiveness of using the stabilized bricks, as a load bearing wall system, instead of using the traditional skeleton structures by about 34% in case of one story building.