DEFORMABILITY AND CRACK RESISTANCE OF REINFORCED CONCRETE AND FIBER CONCRETE BEAMS

Abstract

The work presents the results of the study of deformability and crack resistance of reinforced concrete beams with additional steel fiber reinforcement. Beam samples of three series were produced (three in each series): series I ― beams made of ordinary concrete; II series ― steel-reinforced concrete beams; III series ― beams of combined section, in which the lower zone (0.5 from the height of the beam) is made of steel fiber concrete, and the upper zone is made of ordinary concrete. One sample of each series was made from one batch. At the same time, material samples were made from the same batch. Fiber, the total volume of which was 1% of the volume, was uniformly added to the composition of the concrete mass for the II and III series of samples during mixing. The load was applied in increments of 1 ton. Deformations were determined using strain gauges, watch-type indicators with a division value of 0.01 mm in the middle of the beam span. At each stage, a certain amount of time was required to read the instruments, find and fix the cracks, as well as to measure the length and width of their opening using a Brinell tube. The tests showed that the deformability of the beams of the three series and the character of the crack formation are significantly different from each other. Moreover, the series III beam with combined reinforcement occupies an intermediate position in terms of these characteristics. Thus, by the end of the tests, the reinforced concrete beam (series I) had 19 cracks, the fiber concrete beam (series II) ― 28, the beams with combined reinforcement (series III) ― 23. At the same time, the maximum final crack opening width for beams I, II, III series was 0.8 mm, 0.1 mm (one crack) and 0.1 mm (two cracks), respectively. Cracks in a fiber concrete beam are much smaller in width. And the maximum length of the cracks here turned out to be the largest ― 31.3 cm, while in the beams of the I and III series this value was 25.5 cm and 20.4 cm, respectively.
 The analysis of the given results shows that the best indicators of crack resistance are revealed by beams with full dispersion reinforcement. The use of fiber allows you to change the nature of the destruction process. Unlike ordinary concrete, in which this process occurs almost instantaneously, in fiber concrete there is no brittle failure, and the beam continues to resist the load, and the nature of the failure changes from brittle to viscous.