This paper gives a report on a fracture mechanics study of legal strength concrete with compressive strength up 80 MPa.. 6 mixes were selected, designed to achieve a slump above 100 mm and strength up to 80 MPa.. The investigation used tiered levels of silica fume(0, 10%, 20% by weight of cement) and two coarse aggregate proportions of local aggregate (0.48, 0.65 by volume) In each case, compressive strength, splitting tensile strength, flexural strength fracture energy Gr and Fracture process zone Cr were determined. A test method for determining fracture energy Gr and process zone length Cr, defined by the size effect wide is generalized theory, has been proposed. It allows the use of specimenc of the different size and shape but with same notch length. This paper proposes test und data analysis procedures. The results obtained by the Size effect law (SEL) apparently follow the trend of fracture energy increasing as the compressive strength of the concrete increases. On the other hand, process zone length or decrease considerably with increase in strength. The Bazant's size effect taw gives a very good account of the size dependency of flexural strength for both normal and high strength concrete. As observed in the size effect curve, the fracture behavior of the HSC seems to be more brittle than that of the normal strength concrete. Linear classic fracture mechanics (LEFM) is applicable to HSC in the normal size range than nonlinear fracture mechanics.