Behavior of Confined Concrete using Prestressing Skew Bars

This paper presents the results of an experimental study on the biaxial compression behavior of concrete prism confined using pre-stressed bars. The pre-stressed bars could provide passive confinement stress, that preventing the lateral strain of the prism from increasing leading to an increase in both the initial modulus of elasticity and prism compressive strength. The confined concrete had a higher compressive strength that was directly proportional to the confinement bar pressing force and lower ductility than the plain prisms. The concrete initial modulus of elasticity is directly proportioned to the confinement lateral pressure of the prestressing bar and inversely proportion with the spacing between prestressing bars. It was simple to find out that the best pre-stressing stress was 10 N/mm2, also the compressive strength of the confined concrete with pre-stressed skew bars was greater than the compressive strength of the unconfined concrete by more 3.3 times.

Experimental Study on Light Weight Concrete Using Coconut Shell and Fly Ash

Aggregates provide volume at low cost, comprising 66% to 78% of the concrete. With increasing concern over the excessive exploitation of natural and quality aggregates, the aggregate produced from industrial wastes and agricultural wastes is the viable new source for building material. This study was carried out to determine the possibilities of using coconut shells as aggregate in concrete. Utilizing coconut shells as aggregate in concrete production not only solves the problem of disposing of this solid waste but also helps conserve natural resources. In this paper, the physical properties of crushed coconut shell aggregate were presented. The fresh concrete properties such as the density and slump and 28 days compressive strength of lightweight concrete made with coconut shell as coarse aggregate were also presented. The findings indicate that water absorption of the coconut shell aggregate was high about 24% but crushing value and impact value were comparable to that of other lightweight aggregates. The average fresh concrete density and 28days cube compressive strength of the concrete using coconut shell aggregate 1975kg/m3 and 19.1 N/mm2 respectively. It is concluded that crushed coconut shell is suitable when it is used as a substitute for conventional aggregates in lightweight concrete production. Keywords: Coarse Aggregate, Cement, Concrete, Fly Ash, Coconut shell Aggregate, Water, Compressive Strength, Workability, Fine Aggregate.

“Effect of Hydroxyapatite Nanoparticles On Compressive strength and Flexural strength of Dental Composites Using Taguchi Method”

Several composite materials are being used in biomedical and dental field with their immense applications to repair and transform various organs in human body. Recent advances suggest that Hydroxyapatite is one of the most reliable and widely used inorganic composite in dentistry. Desirable applications of Hydroxyapatite are achieved by utilizing variety of hydroxyapatite and their composites. This study was conducted to evaluate the compressive & flexural strength. Cylindrical specimens (n=9) for compressive strength & rectangular shaped specimens (n=9) for flexural strength were made according to manufacturer’s recommendations. Dental composite is using quartz, silica, and alumina glass as filler for a long time. Taguchi optimization technique keeps the experimentation within limit giving valid product in the calculating of compressive and flexural strength optimization. The goal of the work is to detect the best combination of composite materials. Keywords: Hydroxyapatite, Compressive Strength, Flexural Strength, Taguchi’s optimization method.

Effect of freeze and thaw cycle on the mechanical properties of engineered cementitious composites with un-oiled fibers containing liquid and solid polymers

Nowadays, the application of the engineered cementitious composites(ECC) is expected to highly develop. Due to the lack of access to oiled- polyvinyl alcohol (PVA) fibers in many parts of the world, the implementation of the ECC has contained many difficulties. In this study, to increase the mechanical properties of ECC with the use of un-oiled PVA fibers, the polymers of styrene butadiene rubber (SBR), and ethylene vinyl acetate (EVA) were taken into account to resolve the abovementioned issue. Herein, also in order to enhance the tensile and flexural properties of ECC, the cement was replaced by polymers. Accordingly, a total of 7 mix designs were planned to conduct the proposed tests. The compressive strength, uniaxial tensile strength, and three-point bending tests were performed on the ECC at their 28-day age with consideration of the freeze and thaw cycle. The results of this research illustrated that the use of polymers can enhance the tensile and flexural properties of the ECC with un-oiled PVA fibers. The tensile strain in this study increased by more than 3% after the application of the polymers. Furthermore, the compressive strength increased by more than 47 MPa, and the deflection at the mid-span reached more than 9 mm in the bending test. However, the results showed that the use of polymers was effective on the freeze and thaw cycle and almost preserved the mechanical properties of the ECC. SBR latex has higher compatibility with the ECC in comparison with EVA powder.