JOURNAL OF CONCRETE RESEARCH
Year:2015 | Volume:7 | Issue:2|Papers Count:9

Lightweight Concrete is one of the most important materials in the construction of concrete structures. The main disadvantages of lightweight concrete are their low compressive, flexural and tensile strength. To solve this problem, fibers can be used to reinforce concrete. Fibers reinforced lightweight concrete can be used as an excellent building material in the construction of structural /nonstructural elements. In this study the mechanical properties of fibers reinforced lightweight concrete precast panels and their suitability for use in manufacturing precast building elements have been studied experimentally. The results show that fiber reinforced lightweight concrete has sufficient compressive and flexural strength and also suitable ductility and it can be used for construction of precast structural/nonstructural elements.

Investigating non-linear behavior of structures in order to evaluating vulnerability and determining performance level of existing structures is very important. Because of deep beams dimensions and also cost and time limitation and complexity of applying boundary conditions in lab, it is better to use software and non-linear analysis. In this paper the behavior of deep beams with lightweight and normal concrete and shear length to height ratio of 0.5, 1, 1.5 and 2 and also height of 30, 45, 60 and 90 centimeters is studied using Abaqus software. Results of non-linear analysis show that normalized shear strength decreases with increase in height in both groups of beams and this decrease can be seen in all shear length to height ratios. Comparing experimental results with truss methods available in codes shows that all methods are conservative in small height beams and safety margin reduces with increase in height. Results are non-conservative in CSA method in shear length to height ratio of 0.5 and in normal concrete, and with increase in shear length to height, predicted shear strength by CSA method is much more than strength obtained from analysis.

Today, we see frequent use of self-consolidating concrete (SCC) because of its special fresh and hardened properties in civil projects. These properties are depend on numerous parameters such as paste content and composition and aggregates volume and its grading. Hence, aggregates as an inexpensive material, can play an important role in concrete production. Since an increase in aggregates properties results in reduction of cement paste which is used to fill up the voids, therefore this paper proposes a method to approach a proper aggregates grading zone with lesser voids content by using uniformity coefficient and coefficient of gradation in soil mechanics. From the results, it can be seen that there is a direct and inverse correlation between uniformity coefficient, coefficient of gradation and void content, respectively. The presented grading zone shows that all the concluding aggregate proportions satisfy all fresh and hardened properties and will lead to produce SCC.

In this study, the effect of bacterial nanocellulose, in three levels (control, powder and gel) as a reinforcement for fiber- cement composites was investigated. Also, 6 and 7 wt% of bagasse fibers were used for composite manufacturing. Mechanical and physical properties of composites including modulus of rupture (MOR), modulus of elasticity (MOE), fracture toughness (FT), internal bonding strength (IB), and ware absorption (WA) after 2 and 24h emersion in water were measured. Results showed that composites made with cellulose gel had higher bending strengths, internal bonding strength and fracture toughness. Combination of 7% bagasse fiber content and cellulose gel reduced water absorption of composites. In these composites, internal bonding was increased and less empty spaces remained for water penetration probably due to uniform distribution of fibers and cellulose gel within the cement matrix. XRD analysis showed that peaks corresponding to main hydration products such as CSH and calcium hydroxide had higher intensities in composites containing bacterial cellulose gel. Results obtained from freeze-thaw cycling test showed that composites containing cellulose gel had the higher internal bonding strength compared with other two composites after 20 cycles. In this study, fiber-cement composites produced from 7% bagasse fiber and bacterial cellulose gel have been selected as the optimum treatment.

With limited material resources and fragile environment, the need to recycle materials is inevitable. Waste from construction and demolition has good potential for recycling. These materials are usually abandoned or buried in the ground without being efficiently used. Retrieve them, while solving environmental problems will also be conservation for limited natural resources. Construction waste can be separated after crushing, screening, and grading and then can be used as aggregate in concrete construction. In the recycling industry, what will be remained after recycling old tires are rubber powder and steel wires. Therefore, the use of steel wire in the concrete in addition to solving environmental problems, improve the mechanical properties of concrete too. In this study the role of recycled steel fibers in concrete containing recycled aggregates have been investigated. Rates of replacement of this type of aggregate with coarse natural aggregate are: 0%, 50% and 100%. The amount of fibers used in the mix design is 0.5%of concrete volume. The results showed that the addition of steel fibers in concrete with recycled aggregate, low resistance can be recovered.

Due to the high usage of concrete in construction, civil engineers try to decrease the defects of concrete and increase the benefits of it by using some methods. One of these methods is adding additive materials in order to achieve mentioned target. Undoubtedly in the usage of these materials engineers should pay attention to economic issues, decreasing costs of project and their availability. Most of these additive materials used in concrete, are chemicals and albeit they improve some properties of concrete they have some negative effects on other features of it.In this investigation an herbal additive material is used in concrete, this herbal material is the powder of the leaves of a plant named Mahur or Khargushak)Verbascum Thapsus) that grows in the mountains naturally. The experimental results of specimens in this investigation indicate that adding this herbal material during concrete mixing increases compressive strength up to 12% and tensile strength 20% to 25%. Due to the significant increase in tensile strength of concrete by adding the powder of Mahur additive, the surficial cracks of concrete decrease. By the way the amount of used cement in order to reach to a specific strength decreases.

Many reinforced concrete buildings in the world and Iran, have a life of over several decades And many reasons have been damaged. According to the Replacing these buildings will lead to high costs and is no economic and Environmental feasibility and Due to the need Increasing engineers and construction industry Professionals to strengthen, repair and rehabilitation of concrete structures, Several different methods have been proposed for this issue. One method of strengthening is the approach of using a special concrete With high capabilities. one of these concretes is HPFRCC. Experimental Studies have been carried lately about strengthening with HPFRCC on beams, Columns, slabs and other Structural elements and the strength of this concrete Has been confirmed in strengthening. High performance fiber reinforced cement composite (HPFRCC) is a material that is composed of a cement-based matrix and short composite and steel fibers. that Indicate multiple cracking under tensile stress and because of high bonding strength, HPFRCC used as a repair material. However, the mechanical performance of a RC member repaired with HPFRCC has yet been investigated sufficiently. In this paper, is used layers of HPFRCC (HPFR CC patching) in different thickness for deficient RC slabs Flexural Strengthened and numerical Study HPFRCC layers on this slabs with Finite Element.

In order to select the most suitable concrete for the construction of high-rise buildings, method of analytic hierarchy process (AHP) based on expert knowledge has been used.Investigating alternative contain designing structure, costs, quality, time and easy to do. In order to closer examination and get documented results, six types of concrete (with or without vibration) for a 21-storey building in the city of Babolsar is running with normal concrete is studied. Structures with the software ETABS modeling was investigated. These structures, based on listed criteria, the Analytical Hierarchy Process and Expert Choice software was evaluated. The results suggest that By using low weight concrete, and self compact low weight concrete, weight of the building reduced to %12.5 in comparison to normal, and self compact concrete and to 4.9% in comparison to high strength, and self compact high strength concrete. By using high strength, and self compact high strength concrete, the cost of consumed bar is reduced to 18.9% in comparison to normal, and self compact concrete and to 7.8% in comparison to low weight concrete. According to all criteria evaluated in this study, High strength self compacting concrete is primarily importance to construction high-rise is located.

EPS concrete is a type of lightweight concrete that can be produced by replacing the normal aggregate with expanded polystyrene (EPS), either partially or fully, depending upon the requirements of density. Expanded polystyrene (EPS) concrete is good energy-absorbing material and is used in building as partition blocks and floor leveling. However, due to the light weight of EPS beads and their hydrophobic surface, EPS concrete is prone to segregation during casting, which results in poor workability, homogeneity and lower strength. The present study was designed to investigate the effects of mix design parameters such as percentage of EPS instead of aggregate, silica fume (SF), air entraining agent (AEA) on compressive strength and homogeneity. In this research, 16 concrete mix designs with W/CM equal to 0.4 and density about 770 kg/m3 were made. The results of this research show that using silica fume and air entraining agent can decrease segregation of EPS grains and improve bonding between EPS and cement paste, so the concrete mixture will have more homogeneity and compressive strength. In this research, production cost of mix designs was calculated. Economical investigation show that although using SF and AEA in EPS concrete increases cost of concrete up to maximum %20, it increases compressive strength even up to %262.