Recycled Plastic Fibers for Minimizing Plastic Shrinkage Cracking of Cement Based Mortar

The development of new construction materials using recycled plastic is important to both the construction and the plastic recycling industries. Manufacturing of fibers from industrial or post-consumer plastic waste is an attractive approach with such benefits as concrete performance enhancement, and reduced needs for land filling. The main objective of this study is to investigate the effect of plastic fibers obtained locally from recycled waste on plastic shrinkage cracking of ordinary cement based mortar. Parameters investigated include: Fiber length ranging from 20 to 50 mm, and fiber volume fraction ranging from 0% to 1.5% by volume. The test results showed significant improvement in crack arresting mechanism and substantial reduction in the surface area of cracks for the mortar reinforced with recycled plastic fibers compared to plain mortar. Furthermore, test results indicated that there was a slight decrease in compressive strength of mortar reinforced with different lengths and contents of recycled fibers compared to plain mortar. This study suggests that adding more than 1% of RP fibers to mortar, can be used effectively for controlling plastic shrinkage cracking of cement based mortar, and thus results in waste reduction and resources conservation

The Efficiency of the PQ4R Strategy in Understanding the Mathematical Proof among the Primary School Female Students

The purpose of the study is to examine the efficiency of the PQ4R strategy in understanding the mathematical proof among primary school female students. To achieve the purpose of the study, the analytical approach is used. The sample of the study consists of 40 female students divided into two groups, one is experimental and the other is control, with each group consisting of (20) students. As for the validity and reliability of the study instrument, they are validated as required by a group of highly respective validators. The results of the study show that there is an efficiency of the teaching strategy using (PQ4R) in improving the understanding of mathematical proof for female primary school students. DOI: 10.7176/JEP/11-16-09 Publication date:June 30th 202

An experimental and analytical investigation of reinforced concrete beam-column joints strengthened with a range of CFRP schemes applied only to the beam

This paper investigates the experimental and analytical behaviour of beam-column joints that are subjected to a combination of torque, flexural and direct shear forces, where different Carbon Fibre Polymer (CFRP) strengthening wraps have been applied only to the beam. These wrapping schemes have previously been determined by the research community as an effective method of enhancing the torsional capacities of simply supported reinforced concrete beams. In this investigation, four 3/4-scale exterior beam-column joints were subjected to combined monotonic loading; three different beam wrapping schemes were employed to strengthen the beam region of the joint. The paper suggests a series of rational formulae, based on the space truss mechanism, which can be used to evaluate the joint shear demand of the beams wrapped in these various ways. Further, an iterative model, based on the average stress-strain method, has been introduced to predict joint strength. The proposed analytical approaches show good agreement with the experimental results. The experimental outcomes along with the adopted analytical methods reflect the consistent influence of the wrapping ratio, the interaction between the combined forces, the concrete strut capacity and the fibre orientation on the joint forces, the failure mode and the distortion levels. A large rise in the strut force resulting from shear stresses generated from this combination of forces is demonstrated and leads to a sudden-brittle failure. Likewise, increases in the beams’ main steel rebar strains are identified at the column face, again influenced by the load interactions and the wrapping systems used

Tensile behavior of fiber-reinforced DSP cement.

The mechanisms responsible for the improvement in tensile strain capacity of fiber reinforced densified small particles (FR-DSP) cement containing high volume fraction of discontinuous steel fibers, randomly distributed throughout the matrix were investigated. Existing micromechanical models based on energy principles were further improved for predicting the tensile strain capacity of the composite, which is highly dependent on the properties of the fiber matrix interface. The debonding and pullout behavior of a single steel fiber from cement based matrices was examined using a specially designed apparatus which provides simultaneous results on total fiber displacement versus load in addition to monitoring the fiber displacement at the free end. In this apparatus the fiber goes through the entire specimen, which made it possible to determine the point of complete debonding. To control the embedment length, a plastic tube was inserted around the fiber. The described method coupled with an appropriate analyses provides a quantitative determination of interfacial properties which are relevant to toughening of brittle materials through fiber-reinforcement. The technique was used on a high strength cement-based matrix (DSP), and on an ordinary strength cement matrix. Other parameters investigated included fiber embedment length, fiber volume fraction in the cement matrix, and matrix surface effect. A model was proposed for analyzing the debonding process in single fiber pullout tests. The model provides a simple and direct way of estimating the debonding energy and the frictional bond strength of the fiber/matrix interface, by evaluating the part of the area under the pullout curve corresponding to pure debonding. The results indicate that: (1) the dense DSP matrix has significantly improved interfacial properties as compared to the ordinary strength matrix; (2) the major energy of pullout in both systems is due to sliding; and (3) both the debonding energy and sliding energy increase with fiber embedment length. These results are important for understanding the role of steel fibers in improving the tensile properties of high performance fiber reinforced composites. The results obtained from uniaxial tension tests on FR-DSP containing small amount of main reinforcement confirmed an increase in the elastic and inelastic strains of the composite as predicted from previous models.Ph.D.Civil EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/104424/1/9527578.pdfDescription of 9527578.pdf : Restricted to UM users only

Crack Width Analysis of Steel Fiber Reinforced Concrete Elements

<p>The article investigates the effectiveness of steel fiber reinforcement in RC concrete members in regard to ordinary reinforcement. The advantages and disadvantages of different shapes of steel fibers are discussed. The algorithm for calculating crack width based on EC2 and Rilem methodologies is presented. A comparison of theoretical and experimental crack widths has been performed. The relative errors of crack width predictions at different load levels were defined.</p><p>Article in Lithuanian</p