The toughness of fiber reinforced concretes (FRC) was characterized from notched beam tests. The tests were performed under CMOD control in a servo-hydraulic machine to obtain the stable response of both the unreinforced concrete and the FRC. Several toughness measures were defined in terms of the experimentally obtained load versus crack opening (CMOD) curves. They give a better indication of the fundamental behavior of the concrete, avoid the problems associated with the approach based on the deflection of unnotched beams, and are amenable to the incorporation of serviceability considerations (for example, crack widths). The effect of specimen size on toughness was found to be significant in both the matrix- and fiber-dominated regimes of the FRC behavior. In general, toughness increases with specimen size and needs to be accounted for in the characterization. The study was conducted on beams of a 70 MPa compressive strength silica fume concrete, with and without high-strength hooked steel fibers. It was found that the incorporation of a low volume fraction (one percent) of steel fibers is sufficient to significantly decrease the brittleness of high-strength concretes.

The issue of how the method of determining midspan deflection in ASTM C 1018 toughness tests influences first-crack strength, first-crack deflection, toughness indices, and residual strength factors is addressed in this paper by comparing results obtained using the method now required in the current standard, which is based on net midspan deflection determined as the nominal midspan deflection minus the average of the deflections measured at the beam supports, with corresponding same specimen results based on nominal midspan deflection only which was not explicitly excluded in earlier versions of the standard. The problem of dealing with the portion of load-deflection relationship immediately after first crack when it is unstable is discussed. The range of test specimens for which comparative data are reported includes a series of third-point-loaded 500 x 150 x 150 mm beams with three different steel fibers ranging in length from 18 mm to 63 mm; a second, smaller series of 350 x 100 x 100 mm beams allowed for assessment of the effects of beam size and fiber alignment. Fiber contents varied from 20 to 75 kg/m 3 (0.25 to 0.94 percent by volume). Also included was a series of 350 x 100 x 100 mm beams with a single type of fibrillated polypropylene fiber of length 38 to 64 mm in amounts of 0.5 to 0.75 percent by volume. The results illustrate the extent to which the ASTM C 1018 parameters I 5, I 10, I 20, R 5,10, and R 10,20 are effective in distinguishing the performance of the various fiber reinforced concretes (FRC) mixtures in terms of fiber type, geometry, and amount. The index I 5 was found to be least effective. A case is made for greater emphasis on use of residual strength factors, especially R 10,20, when employing the test to specify and control the quality of FRC.

One of the possible factors inhibiting the wider application of fiber concretes is the fact that to characterize the engineering properties of fiber concrete, both cubes/cylinders and prisms have to be cast and tested, in addition to the determination of workability. This paper shows that with the use of superplasticizer, the slump test can be used to give guidance on the flowability characteristics of the fresh fiber concrete. The advantage of the slump test is that it is easy to carry it out in the field, apart from its simplicity and convenience. The paper further shows that the equivalent cube strength obtained from the broken pieces of a flexural test can adequately represent the compressive strength of fiber concretes. It is thus shown that it is possible to characterize the engineering properties of fiber concretes from only one set of prisms of about 100 x 100 x 500 mm size. Apart from first crack load, modulus of rupture, and fracture toughness properties, the prisms can be used to give additional information as appropriate, such as shrinkage and expansion, and through pulse velocity, internal microcracking. It is suggested that by rationalizing the approach to testing, it is possible to reduce not only the cost and inconvenience associated with different sizes of test specimens, but also to enhance the relevance of some of the information obtained from such testing.

Recent natural disasters involving high wind events have demonstrated the fact that building envelopes, including structural walls and roofs, can lose structural integrity as a result of penetration by missile objects. Because of this, there is heightened interest in the testing of components and cladding that are used as a part of building envelopes of habitable structures. A large missile impact test has been designed and is being evaluated in laboratories around the country. The test, discussed in this paper, is suitable for laboratory or field applications and is currently undergoing scrutiny by the ASTM Task Force of Committee E6, Performance of Buildings. Adoption of the test by the South Florida Building Code came in the wake of Hurricane Andrew in 1992. The test has been applied to numerous types of wall systems and building products, including a fiber reinforced cellular concrete panel which is designed to be used as an alternate to masonry infill construction, architectural precast, demising walls, and security fencing. Additional tests of the missile impact resistance of fiber reinforced cellular concrete involving the use of large caliber ballistics are also discussed. The high energy impact resistance of fiber reinforced systems is demonstrated and discussed.

With the objective of understanding the reinforcing mechanisms of fibers in steel fiber reinforced concrete, the adherence between the fiber and the matrix was studied by conducting pullout tests of fibers from a cementitious matrix. In this paper, the effect of factors such as loading rate, inclination of fibers, and number of fibers have been investigated. An innovative measurement system was developed for high rates. It was experimentally obtained that by increasing the rate of loading, both pullout resistance and slip at peak were increased. Peak pullout force presents a higher rate sensitivity for a higher number of fibers. The lower the number of fibers, the higher the slip at peak rate sensitivity. Regardless of the number of fibers, a higher rate sensitivity for inclined fibers was observed.