Fracture Toughness Of Concrete Research Articles

Fracture energy for three point bend tests on single edge notched beams: Proposed evaluation

The research in fracture mechanics of concrete is reviewed in an attempt to reconcile the different, and sometimes contradictory, approaches for evaluation of the fracture energy, Gf. An improved method to measure Gf for beams in three point bending is presented. This method is expected to provide a more reliable characterization of the fracture toughness of concrete.

Influence of aggregate size on fracture toughness of concrete

Employing an extension of the splitting tensile by using a notched cylinder specimen, we have studied effects of initial notch length and maximum aggregate size on fracture toughness of concrete. Experimental results show that maximum aggregate size does influence ductility, with increasingly ductile behavior associated with increasing aggregate size. The results also support previous work in that initial notch length and maximum load do not yield a constant value for fracture toughness, whereas maximum linear load and initial notch length minimize the effects of slow crack growth and do produce a more constant value.

The fracture toughness of concrete under impact loading

The fracture toughness of plain concrete, high strength concrete, and concrete reinforced with fibrillated polypropylene fibers was studied. Single-edge notched beams, of dimensions (l×w×d) 1400×100×125 mm, were loaded dynamically in 3-point bending, using an instrumented drop weight impact machine. Fracture energies and dynamic fracture toughness (K ID) values were determined, using three different drop heights of the impact hammer. It was found that, for all three types of concrete, K ID increased with increasing drop height; the fracture toughness values under impact loading were much higher than those obtained in static tests. There were also dramatic increases in the fracture energies under impact loading.

Fracture toughness testing by means of the SECRBB test specimen

The single edge crack round bar in bending (SECRBB) test specimen is a practical test specimen for determining the fracture toughness of concrete. The specimens used in this study were prepared from standard 100 mm and 150 mm diameter cylinders with notch depth ratios within the range 0.2 <aD < 0.5. These specimens were more compact than the SECRBB specimens used by earlier researchers (with other materials) with support span/diameter ratios of only 1.5 and 1.67 for the smaller and larger diameter cylinders respectively. Thus an experimental expression was developed which gave K1P values for both cylinder sizes and hence fracture toughness results were determined.The SECRBB test geometry was used to evaluate the fracture toughness of a number of mixes. The effect of maximum coarse aggregate size was studied with inconclusive results — the fracture toughness was reduced for maximum aggregate sizes of 5 mm and 20 mm compared to the results obtained using 10 mm maximum aggregate size. The effect of adding crimped steel fibres in the mix was also investigated. The fracture toughness increased with increasing fibre content but the increase was only half that obtained from other test geometries. This variation was probably due to the method of manufacture of the specimens and it appears that the fracture toughness of steel fibre reinforced concrete may be sensitive to the method of specimen preparation.

The effect of test specimen size on the fracture toughness of concrete

The effect of test specimen size on the fracture toughness of plain concrete determined by means of the compact compression test geometry was investigated. The test specimens ranged from 100×100×100mm to 100×400×400× (width × depth × length). It was concluded that the fracture toughness increased with increasing test specimen size — the increase was negligible for the smaller specimens and was approximately 20% for the largest specimens tested. It was also concluded that the effect if self-weight was an important factor in the case of the larger test specimens and this effect must be taken into account in determining the fracture toughness. The results confirm some other recent test results in this area of study.

Fracture toughness testing by means of the compact compression test specimen

Synopsis The paper describes an experimental and numerical study of the compact compression test specimen for determining the fracture toughness of concrete. A range of cubes and prisms was used in the study and the best results were achieved by means of the double-notched 100 mm and 150 mm cubes. The fracture toughness of the concrete used in the study was 0·5 MN/m3/2 and the results were shown to be independent of the test specimen geometry.

Effect of specimen and crack sizes, water/cement ratio and coarse aggregate texture upon fracture toughness of concrete

Synopsis Tests were performed on cement mortar and concrete beams, in two stages, with a view to studying the influence of several specimen and mix variables upon the fracture behaviour of concrete. On the basis of the results from the first stage of tests, in which a single water/cement ratio and type of coarse aggregate were used, a simple formula was established to estimate the fracture toughness of concrete in terms of specimen dimensions, maximum aggregate size and notch depth, together with the mix compressive strength and modulus of elasticity (determined from separate standard cylinder tests). It was found to predict, with sufficient accuracy, the results from the second stage of tests in which, besides variation of the type of coarse aggregate and water/cement ratio, some of the specimen sizes were outside the range used in the first series.

Notch sensitivity and fracture toughness of concrete

Whether rules based on fracture mechanics or classical mechanics should be used as a basis for design and analysis depends on the notch sensitivity as well as the fracture toughness of the material. Therefore, information about these properties of all structural materials is important. Experiments were undertaken to investigate the notch sensitivity and fracture toughness of concrete with different types, volumes, sizes and strengths of aggregate. The investigation, which was carried out on small flexural specimens with notches of lengths up to 25 mm, indicates that both mortar and concrete are notch sensitive materials although not as sensitive as neat cement paste. If the assumption is valid that the fracture of neat cement paste is governed by the established theory of linear fracture mechanics, however, it appears that this theory is not applicable to small-size members of mortar and concrete. Light-weight concrete appears to have about the same fracture properties as neat cement paste.