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R. A. Khushnood et alii, Frattura ed Integrità Strutturale, 34 (2015) 534-542; DOI: 10.3221/IGF-ESIS.34.59 539 addition of reinforcing CRBF particles. Both the flexural strength as well as fracture toughness have been observed to increase due to nano/micro modifications as revealed form the curves given in Figure 5. Most of the formulations offering maximum resistance in flexure contain CRBF particles in the content of 0.2 to 0.5 wt% of cement. Based on experimental load-CMOD curves, modulus of rupture as well fracture toughness were evaluated. Modulus of rupture is defined as maximum surface stress at the failure of specimen in three point bending test given by σ=(3P m L)/(2wh 2 ) where ‘P m ’ is the maximum applied force on the prism at the instant of failure, ‘L’ is the effective span, “w” is the prism width while “h” is considered as the height of specimen under the point of load application. Fracture toughness has been divided into two classes’ first crack toughness and ultimate toughness. First crack toughness corresponds to area under load-CMOD curve till the onset of first crack in vicinity of 6mm deep notch while the ultimate toughness corresponds to area under the load-CMOD curve till the extent of complete failure in accordance with the Rilem Recommendations and ASTM C 1018 [26]. Figure 5 : Typical load-CMOD curves for cement composites with and without CRBF particles additions Figure 6 : Modulus of rupture of the cement composites with CRBF particles inclusions. Figure 7 : Fracture toughness of the cement composites with CRBF particles inclusions. The average modulus of rupture of cement composite samples along with fracture toughness are reported in Figures 6 & 7 respectively. The results demonstrated significant increase in the flexural strength as well as the fracture toughness of cement composites with CRBF addition. The trend of increment is ascending till the percentage addition of 0.2 wt% but beyond this content it has been shifted to the descending order. The optimum content of addition is revealed to be 0.2 wt% as observed from the plotted bar charts which is slightly more than 0.08 wt% commonly believed as an optimum level of CNTs induction [5]. The results demonstrated that an addition of CRBF particles by 0.2wt% improved the