JOURNAL OF CONCRETE RESEARCH
Year:2016 | Volume:8 | Issue:2|Papers Count:10

Pozzolanic materials is one of the strategies to improve strength and durability of concrete. Pozzolanic reactions lead to filling the voids in the concrete and reduces porosity and permeability and thereby increase the durability and strength of concrete. Zeolite is a natural pozzolan is abundant in Iran and is easily extracted and processed. Therefore, in this study, Effect of zeolite on resistance and permeability of concrete with different grades of cement has been investigated. For this purpose, tests of strength, capillary water absorption, determination chloride ion profiles and X-ray diffraction (XRD) was conducted on specimens. In making specimens, various of cement content and different percentages of zeolite and water-cement ratio was used. The results show that addition of zeolite on concrete increased resistance and decreased permeability of specimens compared to the reference concrete. Also results of XRD and SEM images obtained from the tests show that microstructures of specimens containing zeolite, has a greater density than the zeolite without it.

Recent researches have shown that use fiber in concrete can increase the flexural, tensile, and abrasion resistance. On the other hand Self-Compacting Concrete is a high flowable homogenous concrete which can eliminate several common problems in normal concretes by means of its compaction under its own weight. The above properties of self compacting concrete facilitate the fabrication of concrete structural members with congested reinforcement.On the other hand, in the past two decades application of nano-technology has significantly revolutionized human knowledge. Using nano silica particles as a product of pozolanic reaction, can strongly improve the permeability of concrete. Thus concrete having the properties of both self compacting concrete and fiber reinforced concrete with strengthened micro matrices can improve the fabrication of durable structures with high performance level. In this research, the combined effect of nano-silica particles and fibers type (steel, polypropylene and glass) on mechanical properties (compressive, tensile and flexural strength, modulus of elasticity), rheological behavior (L-box, slump flow and T50) and also the durability of Self-Compacting concrete were evaluated using water absorption and Rapid Chloride Penetration Test (RCPT). Furthermore, XRD test has been used.For this purpose, forty mixtures in A, B, C and D series representing 0, 2, 4 and 6 percent of nano silica particles replacing cement content were cast. Each series involved three different fiber type and content.0.2, 0.3 and 0.5% volume for steel fiber, 0.1, 0.15 and 0.2% of volume for polypropylene fiber and finally 0.15, 0.2 and 0.3% of volume for glass fiber. The results show that the combined usage of optimum percent of fiber and nano silica particles will improve the mechanical properties and durability of self-compacting concrete.

When the concrete loses its moisture, shrinkage and volume reduction is happen and eventually cracks create and deformations in the concrete are increased. If the reinforcement concrete member be bounde, strain caused by condensation cause cracking member and increases the deformation member with time. This phenomenon is due to the rapid evaporation of water in the concrete, occurs because of the wind and temperature rise. One of the main reasons for the decrease in strength and durability of concrete are cracks. In this study evaluated the effect of fibers by different volumes on reduce cracking that created by, shrinkage plastic on concrete slabs. Plastic shrinkage experiments in a greenhouse by using mold that was designed for this purpose. The parameters in this study are, the percentage of fiber volume to volume of concrete and concrete strength. Finally, the effect of polymer fibers on plastic shrinkage cracking of concrete was investigated and discussed.

Concrete is one of the most important structural materials which is produced from proportional mixture of cement, aggregates, water and admixtures. Compaction of the concrete is one of the factors that make it difficult to use, particularly in the structures with high reinforcement steel bars. In cases such as foundation of bridges, bottom of the columns of skyscrapers and ets, vibration of concrete for compaction is almost impossible. To solve this problem we can use self-compacting concrete which causes complete compaction and also increases casting velocity. This kind of concrete is produced with superplasticizer and other admixtures. This Article examines the effect of the addition of nanosilica on mechanical properties and Durability parameters self-compacting concrete in sulfate destructive environment. For this purpose, in laboratory studies we have used some tests such as compressive strength and permeability. The results show that the addition of nanosilica could effect on mechanical properties of self compacting concrete, also increase the durability of concrete against sulfate destructive factor that reduce the compressive strength at later stages. Nanosilica reduces the porosity in hydration cement by filling the pore space between the larger particles at the nano-scale and greatly reduced permeability.

In present study, linear attenuation coefficient of concretes containing different percentages of lead slag and silica fume against gamma-ray emitted from Cs-137 and Co-60 sources were measured using experimental and Monte Carlo simulation procedures. Moreover, compressive strength of concretes and ultrasonic pulse wave velocity test were determined as well. Two series of concrete mixes were designed and casted. The first series contained different percentages of 0, 25, 50, 75, and 100 lead slag replaced with natural sand. In the second series 10% silica fume replaced by cement weight was added to all mixes of the first series. The results showed positive effect of lead slag and silica fume on concrete shielding properties against gamma-ray such that specimens containing 100% lead slag and silica fume gained a very suitable compressive strength of 62 MPa, and exhibited highest shielding to gamma-ray. Relatively Good agreement was also observed in the trend of the results between the experimental and Monte Carlo simulation methods.

Elastic and inelastic performance of structure members can be evaluated by Bending moment–axial force interaction surfaces in a non - linear process. The use of composite shear wall structures is common method in the past two decades. In this research, this kind of surfaces are being introduced for the first time to be utilized in composite shear walls, which can be used in analyzing and designing without the need to non - linear analysis. Composite shear walls used for high-rise buildings, offer more lateral stiffness, bending resisting moment, Energy dissipation and ductility in comparison with other ordinary walls. Here, a simple, efficient and expeditious method is presented for nonlinear analysis of reinforced concrete structural members, based on fiber method concepts. One of the considerable advantages of this method is its high speed in nonlinear analysis of structural members that makes it distinctive from the others. The OpenSees software is used for modelling the discussed shear walls.

Most of ordinary bridge decks are made of reinforced concrete and often deteriorate at a rapid rate in rough operational environments. The rapid deterioration of the deck often impacts other critical components of the bridge. Another disadvantage of the concrete deck is its increased weight in long-span bridges. Therefore, it is essential to examine new materials and innovative designs using hybrid system consisting conventional materials such as concrete and steel with FRP plates which is also known as composite deck. Since these decks are relatively new so it would be useful to evaluate their performances in more details. The present study is dedicated to Hat-Shape composite beam with concrete slab. The structural performance of deck was evaluated by nonlinear finite element method and numerical results have been compared with published experimental results where possible. After ensuring the validity of numerical modeling of composite deck, parametric studies has been done; such as using steel rebar in concrete slab, changing the angle of webs of Hat-Shape Section, modeling RC sections to match strength and stiffness of Hat-Shape composite beam and altering the GFRP Material into steel and aluminum. It was found that the behavior of this type of composite beams can be considered with numerical methods without executing costly experiments. Using rebar in concrete slab can increase ultimate load capacity of composite beam by 45 %. Also strength-to- weight ratio of the beam increased by changing the GFRP Material to aluminum by 51%.

The most common method of strengthening columns with FRP is confining their external environment. Confining is effective for compression members and use for increase load carrying capacity or for increase ductility. The main target in this research is investigation strengthening of RC columns with multi directional FRP composites. For this purpose first, 3 available experimental specimens were modeled in ABAQUS software. So, accuracy of this modeling proved, by Comparison and proximity the result of experimental and software. Then 18 analytical specimens were modeled with considering variables such fiber gender, direction of composites layers and percent of longitudinal steel of column section, in ABAQUS software. Analytical specimen divided to the two groups, half of them with 2 percent longitudinal steel and the other half with 4 percent steel. In every group were considered a specimen without strengthening, four specimens confined with CFRP sheets and four specimens confined with GFRP sheets. Beside specimens of every group strengthened with composite layers in different directions 0, 0, 0 degrees and 90, 0, 90 degrees and -45, 45, 0 degrees and -45, 45, 90 degrees. The finite elements analysis results of these specimens shows that multi directional FRP composites increases 1.34 to 2.77 times the axial load carrying capacity of strengthened columns and 5.5 to 13 time their ductility. Strengthening by FRP composites with layers in direction of -45, 45, 0 degree, is good method for increasing the ductility of columns. Also effect of strengthening the specimens with two percent steel section are 8 to 16 percent more than specimens with four percent steel section.

In many cases concrete shear walls have openings for architectural reasons.opning cause some changes in shear capacity, stiffness and behaviour of reinforced concrete walls. In this study, finite element models are developed by Abaqus software to compare the effect of area and position of opening on shear capacity of concrete shear wall with regular openings. The experimental results on concrete shear walls with two bands of openings by Aguda are used to verify the analytical models. After verification; some specimens with one and two bands of opening are designed similar to qualification of Agudas experiments. Nonlinear finite element analysis of reinforced concrete walls is performed using damage plasticity model. Results further confirm that compressive area of wall play an important role on shear capacity of structural concrete walls and parameters of area and position of opening can effect on compressive area. Comparison of results are also showed that the position of opening is more effective on shear capacity of concrete shear walls.

Today improvement the behavior of fiber-reinforced concrete in concrete technology is one of the most common methods. Adding fiber to concrete causes strength growth, improve the stress - strain and will increase ductility. Steel fibers, polypropylene and glass fibers used are most commonly. In this study, concrete water-cement ratio of 0.45 and 400kg/m3 cement content and percentages of steel fiber and polypropylene were built both separately and in combination as well. The results of compressive and tensile strength and stress-strain tests has showed that by adding different percentages of fiber at the age of seven days there has not been much change but the sample compressive and tensile strength of 28 days old has been increased. The greatest strength growth was related to the samples containing 1 percentage of steel fibers. According to stress-strain curves, the strength of thoughness has been significantly improved and have gotten formed the behavior of samples. Then for better comparison of results and improve short-term strength by adding Silica fume two examples were built. The results have showed that adding Silica fume causes the strength parameters improved.