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R. A. Khushnood et alii, Frattura ed Integrità Strutturale, 34 (2015) 534-542; DOI: 10.3221/IGF-ESIS.34.59 540 flexural resistance measured in terms of MOR by 69.9% while an increment of 46.4% and 61.2% was achieved in first crack and ultimate fracture toughness respectively. On further addition of CRBF particles, the values tend to decrease due to relatively high proportion of inerts inclusion as observed by Konsta et al. while dealing with the case of CNTs additions [5]. The value of optimum content varies with the type of carbonized additive. Micro-Cracking Patterns The FESEM micrographs of fractured high performance cementitious matrices displayed in Figure 8 revealed that the induction of nano/micro carbonaceous inerts remarkably interrupted the straight and smooth trajectory of crack as attained in case of pristine cement matrix. The plain cement paste (Figure 8a) showed major cracks usually pass through dense hydration products in a relative straight direction. The cement composites with nano/micro heterogenic particles showed a number of fine cracks with occasional branch and considerable discontinuity. The entire phases of crack arresting phenomena were successfully observed through microscopic visuals. Figure 8: Micro-cracking pattern in plain (a) and CRBF reinforced (b) cementitious composites. On addition of CRBF particles, major signs of crack pinning and crack deflection were observed in complicating the straight crack paths. Due to the angular shape of CRBF particles, the crack gets diverted from its original trajectory in case of encounter. Such crack deflections or crack contouring result in the requirement of an extra energy input to further propagate the crack along a different path and consequently enhanced fracture toughness of the reinforced cementitious matrix is attained. C ONCLUSIONS t is concluded that we can synthesize carbonized particles from agricultural residue and they can be effectively used in cement matrix to enhance the fracture properties and to refine microstructure. The dependence of the particle shape on toughening is critical and angular grains are needed to produce effective crack-bridging. In our case, from what observed by means of micro-graphical obervations, we believe that carbonized bagasse particles contouring by the crack, crack pinning and crack diversions are the mechanisms which can explain the increase of toughness in the composite samples. A CKNOWLEDGEMENTS he authors are grateful to Dr. Guastella Salvatore (DISAT, Politecnico di Torino) for FESEM and EDX analysis, to Dr. Mauro Giorcelli (DISAT, Politecnico di Torino) for Raman analysis, to Dr. Stefano Broggio (Mapei S.p.A.) for providing super-plasticizer and to Dr. Fulvio Canonico (Buzzi Unicem S.p.A.) for supplying cement. Rao Arsalan Khushnood and Sajjad Ahmad wish to acknowledge the PhD study grant of Higher Education Commission, Pakistan (Ref no. HRDI-UESTPs/HEC/2012/36). I T