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.

Describes the construction of two simple impact machines, one small with a capacity of 100 Joules and the other large with a capacity of 1000 Joules, designed to conduct impact tests on fiber reinforced mortars and concretes in the uniaxial tensile mode. During a test, the applied load, accelerations, and velocities are measured such that with a proper analysis scheme, the raw data can be analyzed to obtain fundamental material properties under impact loading. Carbon, steel, and polypropylene micro-fiber reinforced mortars and steel fiber reinforced concrete were tested; it was demonstrated that the proposed technique is a simple and rational method of obtaining meaningful material properties. In general, fiber reinforced composites were found to be more impact resistant than their unreinforced counterparts, with the improvements found to be proportional to the fiber volume fraction. In addition, both the unreinforced matrix as well as fiber reinforced composites were found to be stress-rate sensitive, but the extent of sensitivity observed was smaller than usually reported in the literature for cement-based materials under uniaxial tensile loading.

The prime consideration in minimizing concrete cracks in the field is to maximize the early (six hour) tensile strength development in order to resist the volume reduction due to rapid water loss. This paper describes a test method, which simulates field conditions, for measuring direct tensilestrength soon after initial set at six hours. The prototype direct tensile test described presents an effort to quantify results as a measure of crack resistance. In this investigation, three different types of concrete mortar fractions were evaluated: 1) plain, 2) polypropylene fibers mixed in the batch, and 3) the same fiber bur roughened by intergrinding with cement for better mechanical bond. Results of tensile testing indicate that the process of intergrinding fibers with cement improves the tensile strength of similar mortar reinforced with smooth fibers by 63 percent. Comparing the ground fiber results to a plain (no fiber) mortar mixture shows almost three times higher direct tensile strength. Based on this exploratory work on early tensile strength testing, it appears to be a viable method to arrive at quantifiable values, which will lead to a better understanding of the concrete cracking phenomenon and its control.

The usefulness of fiber reinforcement in improving the cracking resistance of cement-based materials under restrained shrinkage conditions is indisputable. In fact, in many instances, this may be the sole reason of adding fibers to concrete. In spite of this general recognition, there is no universally accepted technique of demonstrating or quantifying the effectiveness of fibers under the conditions of restrained shrinkage. This paper describes a newly developed technique in which prismatic specimens with a linear restraint along the longitudinal axis are subjected to a drying environment such that conditions of uniaxial tension are generated. The specimen cracks under these conditions; if fiber reinforcement is present, the influence of fibers on the cracking pattern can be established. Results with seven types of fibers are presented. Based on the observations of the crack patterns, a "fiber efficiency factor" is proposed which appears to be an appropriate basis for characterizing the fibers.

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.