Experimental determination of crack resistance characteristics of fiber reinforced concrete
The samples of fiber reinforced concrete with different fiber concentration, types of fiber, class of concrete were tested. The values of the critical stress intensity factors were determined as well as the strength characteristics of fiber-reinforced concrete of various compositions. Tests were carried out by bending the beams of 400x100x100 mm with a cut. Critical stress intensity factor was determined with the help of the value of the breaking load. The regularities of the influence of the type and concentration of fibers on the strength characteristics of the fiber reinforced concrete were stated. The authors identified key properties of steely and polypropylene fibers and offered their comparison. From these experiments we obtained data for further use in theoretical studies of fiber reinforced concretes structures. This research revealed common patterns of change in the properties of fiber reinforced concrete, depending on the composition. The advantages of different types of fibers were discussed. Valid formula for determining the critical stress intensity factor was found. Adding fiber in different concentrations to the concrete mix increase the tensile strength 3.5-4.5 times for steel fibers and 2-2.5 times for polypropylene fibers. Polypropylene fiber addition leads to decrease in compressive strength of the concrete of up to 8 %, the steel fibers addition, on the contrary, to increase in the compressive strength of concrete up to 20 %. Increase in tensile strength is observed mostly for low-strength concrete. In order to ensure uniform distribution of fibers in the volume of concrete specific methods should be applied.