This paper determines the effect of steel, glass, and nylon fibers on the compressive strength and ultrasonic pulse velocity (UPV) of fiber reinforced concrete. The influence of different fiber types, fiber volume fraction, and water to cement ratios on the compressive strength of fiber reinforced concrete was tested using the compression test machine (CTM) and ultrasonic pulse velocity tester. Experiments were carried out at different ages on more than 100 cylindrical specimens. A comparison between the experimental results and equations available in the literature for prediction of compressive strength in terms of UPV was conducted to better evaluate the accuracy of available methods, when the type and volume fraction of fibers change. A new empirical equation that accounts for the presence of different types of fibers and fiber volume fraction is proposed to better estimate the compressive strength of steel, glass, and nylon fiber reinforced concrete.

This chapter has been prepared with the hope that its readers will become interested in lightweight concrete (LWC). Therefore, after a brief background of lightweight concrete, different types of LWC will be introduced and then LWC made of lightweight aggregates (LWA) will be specifically discussed. Compressive strength and density of LWC are the main points of interest in this chapter. In addition to conventional compression test, a nondestructive test (NDT) method will be used to assess the compressive strength of a variety of lightweight concrete mixes. A case study has been designed and conducted including an experimental program on the LWC made of expanded glass aggregate. The experimental program includes about 150 specimens, incorporating different unit weight for the entire specimens. In the end, it can be observed that the properties of LWC depend on the properties of the used LWA, and therefore for each specific type of lightweight aggregate, a brand new equation will be required for prediction of concrete compressive strength. The author hopes that the present chapter and the discussed case study on LWC would attract the attention of researchers to the importance of LWC in the future of construction industry.

Using fibers in concrete, has been recognized as a practical method to improve concrete properties such as reduction in crack development and higher resistance against impact and abrasion. Dry cementitious material exhibits very high electrical resistivity. However, fibers can significantly decrease the electrical resistivity of concrete which affects its insulating nature and has negative effects on concrete properties such as durability and also in special cases such as rail road ties production. In this paper the effect of steel, glass, and nylon fiber on the electrical properties of Fiber Reinforced Concrete (FRC) is investigated. Six different fiber volume fractions (Vf) (0.10% vol., 0.25% vol., 0.50% vol., 0.75% vol., 1.00% vol., 1.50% vol.) and several water-to-cement ratios (w/c) were considered as the main variables in the present study. In order to test the electrical properties of FRC, 100 mm × 200 mm cylinders were casted, cured and tested. The four point technique was used for measuring the surface electrical resistivity of concrete after curing in water for 3, 7, 28, and 44 days. Additionally, the compressive strength of each specimen was determined experimentally using the Compression Test Machine. The results revealed that the electrical resistivity of FRC decreases with an increase in fiber content but different types of fibers have different electrical effects on concrete. The effects of different volume fractions of three fiber types, together with different concrete mix proportions are presented and discussed.

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In the present study, a non-destructive testing method was utilized to assess the mechanical properties of lightweight and normal-weight concrete specimens. The experiment program consisted of more than a hundred concrete specimens with the unit weight ranging from around 850 to 2250 kg/m3. Compressive strength tests were performed at the age of seven and twenty eight days. Ultrasonic Pulse Velocity (UPV) was the NDT that was implemented in this study to investigate the significance of the correlation between UPV and compressive strength of lightweight concrete specimens. Water to cement ratio (w/c), mix designs, aggregate volume, and the amount of normal weight coarse and fine aggregates replaced with lightweight aggregate, are the variables in this work. The lightweight aggregate used in this study, Poraver®, is a product of recycled glass materials. Furthermore, the validity of the current prediction methods in the literature was investigated including comparison between this study and an available expression in the literature on similar materials, for calculation of mechanical properties of lightweight concrete based on pulse velocity. It was observed that the recently developed empirical equation would better predict the compressive strength of lightweight concrete specimens in terms of the pulse velocity.

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