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In this paper, twenty-nine three-point bending beam specimens made of ultra high strength concrete (cube compressive strength of about 125 MPa and cylinder compressive strength of about 105 MPa) incorporating Ultra Fine Ground Granulated Blast-furnace Slag (UFGGBS) were tested. The depths of the beam specimens range from 75 mm to 300 mm. The fracture energy calculated by Hillerborg’s work-of-fracture method, Bazant’s size effect method, and Karihaloo–Nallathambi’s effective crack method, as well as two empirical formulas of Bazant and Becq-Giraudon and of CEB-FIP Model Code 1990 were investigated and compared on the basis of the tested specimens. It was found that the results from the different methods were different from one another. In addition, the authors introduce a nonlinear regression method based on the effective elastic crack model to calculate the fracture energy. It is shown that the proposed method shows good tolerance on the scattered test data, and thus leads to a more consistent fracture energy value. [ABSTRACT FROM AUTHOR]

Abstract: This paper examines the applicability of support vector machine (SVM) based regression to predict fracture characteristics and failure load (P max) of high strength and ultra high strength concrete beams. Characterization of mix and testing of beams of high strength and ultra strength concrete have been described briefly. Methodologies for evaluation of fracture energy, critical stress intensity factor and critical crack tip opening displacement have been outlined. Support Vector Regression (SVR) is the extension of SVMs to solve regression and prediction problems. The main characteristics of SVR includes minimizing the observed training error, attempts to minimize the generalized error bound so as to achieve generalized performance. Four Support Vector Regression (SVR) models have been developed using MATLAB software for training and prediction of fracture characteristics. It is observed that the predicted values from the SVR models are in good agreement with those of the experimental values. [Copyright &y& Elsevier]

• Development and analysis of 3D numerical mesoscale model is presented. • Realistic aggregate geometric shapes and placing algorithms are discussed. • Cohesive contact can be used successfully to model Interfacial Transition Zone. • Transgranular fracture in UHSC can be observed under static uniaxial compression. • Damage can initiate in any of the three phases and subsequently progress. Ultra High Strength Concrete (UHSC) is a composite material of which the fracture and damage behavior is highly dependent on its constituent phases. Damage and fracture behavior of UHSC is markedly different from the Normal Strength Concrete (NSC) due to its brittle behavior and crushing through the aggregate. This complex behaviour and influence of properties of constituent phases to the mechanical properties of UHSC cannot be understood using conventional testing on materials. To better understand this complex fracture behavior and influence of the phases, a different approach is required. Mesoscale modelling where concrete is modelled as a three-phase material which consists of aggregates, mortar and Interfacial Transition Zone (ITZ), can be considered as a potential method to address these issues. In this paper, development of mesoscale models of concrete using various shapes of aggregates and methods of intersection checks and placing algorithms are presented. Accurate material model selection for the constituent phases and efficient meshing methods are also discussed. Fracture and damage behavior of UHSC under uniaxial compression is investigated using the developed mesoscale models. Transgranular fracture of UHSC under uniaxial compression was modelled successfully and found that the damage initiation can occur in any of the three phases in mesoscale. Effect of various parameters on the damage behavior of UHSC is discussed and the feasibility of using this powerful tool of mesoscale modelling is discussed with the challenges. [ABSTRACT FROM AUTHOR]