The effect of adding polypropylene fibers; with different shapes and volume fractions; on the compressive strength, modulus of rupture, load-deflection curve and flexural toughness (equivalent flexural strength ratio) of concrete was investigated. Crimped and twisted polypropylene fibers were used with 0.0%, 0.2%, 0.4% and 0.6% volume fractions. It was found that the compressive strength, flexural strength and the equivalent flexural strength ratio of concrete increased about 11%, 25% and 40% respectively by adding 0.6% volume fraction of twisted polypropylene fiber. In addition; it was found that the contribution of polypropylene fiber to the flexural strength and flexural toughness was more effective when twisted polypropylene fiber was added comparing to crimped polypropylene fibers. The experimental results were used in numerical example using FAARFIELD program to explore the airfield pavement thickness reduction resulted from polypropylene fiber incorporation.

Dynamic anti-plane characteristic is investigated theoretically on two dissimilar piezoelectric media with an interfacial crack subjected to time-harmonic incident anti-plane shearing in this paper. The formulations are based on the method of complex variable and Green’s function. Dynamic stress intensity factors at the crack’s tip are obtained by solving boundary value problems with the methods of conjunction and crack-division technique. The calculating results are plotted to show how the frequencies of incident wave, all kinds physical parameters of two dissimilar piezoelectric materials, applied electric loads and the dimension of the interfacial crack influence upon the dynamic stress intensity factor (DSIF). And some of the calculating results are compared with other published documents.

Federal aviation administration rigid and flexible iterative elastic layered design (FAARFIELD) software program became the exclusive approved method for airport pavement thickness design adopted by federal aviation administration (FAA) in the United States after the advisory circular AC150/5320-6E “Airport Pavement Design and Evaluation” was issued in September 2009. In this paper, a sensitivity analysis was conducted to investigate the effect of FAARFIELD input parameters on the required thickness of the airport rigid pavement. The input parameters studied are: concrete flexural strength (modulus of rupture, MOR), the subgrade reaction modulus, K, subbase layers and air traffic mix .Each evaluated input parameter was varied within its recommended range to study its effect on the required thickness of the airport pavement. It was found that the concrete modulus of rupture is the most sensitive parameter on the required thickness.

This paper presents the experimental investigation carried out to study the behavior of polypropylene fiber reinforced concrete (PPFRC) under compression and flexure. Crimped polypropylene fibers and twisted polypropylene fiber were used with 0.0%, 0.2%, 0.4% and 0.6% volume fractions. The influence of the volume fraction of each shape of polypropylene fiber on the compressive strength and flexural strength is presented. Empirical equations to predict the effect of polypropylene fiber on compressive and flexural strength of concrete were proposed using linear regression analysis. An increase of 27% in flexural strength was obtained when 0.6% volume fraction of twisted polypropylene fiber was added. It was also found that the contribution of fiber in flexural strength is more effective when twisted fibers were used. The compressive strength was found to be less affected by polypropylene fiber addition.

An analytical model for compressive stress-strain curve of polypropylene fiber reinforced concrete (PPFRC) was proposed. The polypropylene fiber used was 60-mm long twisted fiber with aspect ratio of 120. The fiber was added in three volume fractions 0.2%, 0.4% and 0.6%. Tow concrete mixtures with varying water-cement ratio were used. The accuracy of the proposed model was evaluated by comparing the area under stress-strain curves for experimental and analytical model. The results showed good agreement between the experimental and analytical curves. In addition; empirical equations were proposed to quantify the effect of polypropylene fiber on compressive strength, strain at peak stress, and toughness of concrete in terms of fiber volume fraction.