13th International Conference on Fracture June 16–21, 2013, Beijing, China -2- radius, for both plain and reinforced mortars. Finally, the J-integral results are also correlated with the impact energy of unnotched prismatic bars having the Charpy dimensions. 2. Materials and Experimental Procedure The mortar mixture used in the present study was composed of Portland cement PC 32, washed dry sand and tap water, in the proportions of 1:1: 0.4, respectively. The sand had fineness modulus of about 3.33, a maximum particle size of 2 mm and an apparent density of 1.6 g/cm3. As to the production of the reinforced mortar, sisal fibers, in an amount of 3% to the cement weight, were added to the mixture in two different lengths, namely 25 and 45 mm. The fibers had average mechanical properties of 670 MPa tensile strength, 4% elongation and 30 GPa elastic modulus. Compressive strength of the materials was determined making use of cylindrical specimens (50 mm in diameter and 100 mm in length) which were cast from the plain and reinforced mortar mixtures. The specimens were loaded at room temperature (23 ºC) in a universal testing machine with a cross-head speed of 10-5 m/s. In order to determine the load-displacement (P-δ) curves of the materials, notched prismatic specimens (50x50x300 mm) with 270 mm loading span were submitted to three point bending with a test speed of 2x10-5 m/s at room temperature. The specimens were cast from the plain and fiber reinforced mortar mixtures containing a 25 mm deep parallel sided notch with 0.5, 1, 1.5, 2 and 2.4 mm root radius. Unnotched specimens with identical geometry were also tested in three point bending. Impact testing was carried out on unnotched prismatic specimens (10x10x50 mm), using a low capacity Charpy type impact machine appropriate for low toughness brittle materials. 3. Results and Discussion 3.1. Compressive Strength The tests pointed that the plain mortar specimens loaded in compression suffered a highly unstable mode of failure, whereas the fiber-reinforced mortars exhibited a more stable behavior, characterized by larger deformations with a gradual drop in the applied load. Table 1 presents the compressive strength calculated from the ultimate load. From this table it can be verified that the presence of sisal fibers has a deleterious influence on the strength level. Moreover, this influence turns out to be more significant for the long fibers in comparison with the shorter ones. This can be attributed to a decrease in the mortar’s density, associated with an increase in its porosity [5-6]. However, it should be mentioned that the specimen integrity was preserved over a wider deformation range in the presence of longer fibers. Table 1. Compressive strength of the plain and reinforced mortars Mortar Compressive Strength (MPa) plain 28 ± 1 reinforced with 25 mm sisal fibers 25 ± 1 reinforced with 45 mm sisal fibers 22 ± 1
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