New Determination Method For Softening Curve Of Massive Concrete

Concrete in today’s world is mostly used as building materials, andnow its fracture and damage research is a hot issue in mechanical study ofconcrete. The softening curve and fracture energy are two key concepts inconcrete fracture mechanics. The determination of softening curve andfracture energy of concrete is very important to concrete fracturemechanics study.Wedge-splitting specimen which has relatively small ratio of weightto volume and relatively long ligament can avoid influence of self-weighton experimental results. Therefore wedge-splitting test is an ideal methodfor testing the fracture properties of mass concrete. The fictitious crackmodel (FCM) has been proved to be an appropriate model for simulatingfracture processes in concrete structures. A new optimization method wasemployed in the inverse analysis for determing the softening curve ofmass concrete. It is based on an evolutionary algorithm (EA) includingneighbourhood attraction for convergence improvement. Based on the wedge-splitting test results, FCM and EA, tri-linear softening curves ofdam concrete and wet-screened concrete were obtained by inverseanalysis procedure.Based on the results of the softening curves of dam concrete andwet-screened concrete by inverse analysis, the following conclusionswere achieved:(1) With the increase of compressive strength, the tensile strengthf tand the fracture energyG_Fincrease firstly and tend to be stableafterward, and the maximum crack opening widthw_c tends to be aconstant.(2) With the increase of coarse aggregate size, thew_c and theG_Fboth increase, but thef treduces and then increases.(3) The of dam concrete and wet-screened concrete by theinverse analysis all exist size effect. The both increase and then tendto be stable with increase of specimen size, which shows boundary effect.The influence of the specimen size on the is insignificant.(4) The and of fully-graded dam concrete is smaller thanthat of the corresponding wet-screened concrete, respectively. With theincrease of specimen size, the differences of and between thedam concrete and wet-screened concrete increase and then tend to bestable.(5) The softening curves determined by the inverse analysis method are in substantial agreement with those by the direct tension test methodwhen the specimen size is small. However, the difference between theresults of two methods increases with the increase of specimen size.