A reformulation of a multi-axial failure criterion for the concrete

The research of a failure criterion for concrete under multi-axial stresses is a very important task because of the numerous civil engineering applications. Nowadays several concrete failure tests are available in literature and various criteria have been proposed. A multi-axial failure criterion for the concrete founded on a simple physical basis, has been proposed by one of the authors. In this paper a sharper foundation of this criterion is given. The hardened cement paste (hcp), the binder of all the aggregate particles, is responsible of the concrete strength. Consequently, a preliminary average evaluation of the stresses, occurring, when the concrete is loaded, into the various phases components, and particularly in the hcp, is necessary to analyse the failure. To that end, the paper revolves around the analysis of the thermal behaviour of the concrete at its early stage of setting. It is shown that the heat production during the cement hydration process, is responsible to produce clearances among the various particles and the surrounding hcp that, in turn, the consequent statically determined structure of the concrete. Validation of this result comes out by analysing the elastic moduli and the thermal expansion coefficients. The micro-macro failure condition of Como & Luciano thus receives a sounder physical basis.