Issue 10

B. Chiaia et alii, Frattura ed Integrità Strutturale, 10 (2009) 29-37; DOI: 10.3221/IGF-ESIS.10.04 36 In fact, as F ( w ) is a relative stress normalized with respect to the compressive strength f c , a comparison between all the cement-based composites, under uniaxial and multi-axial compression, is possible. Higher values of A F are attained in concretes capable of maintaining high loads after failure (i.e., in the case of ductile materials). Obviously, the maximum ductility A F,max = 2mm is reached in the case of plastic behaviour [ F ( w ) = 1= const. ]. The areas A F computed by Eq.(6) for the tested specimens (Tab. 2) are also reported in the histogram of Fig. 8b. In all cases, A F is between A F,max = 2 mm and the lower limit A F,min = 0.61 mm, corresponding to the normal and self- consolidating concretes without any confinement (Fig.8b). To be more precise, A F,min is obtained by substituting Eqs.(4) (with a = 0.320 mm -2 and b = -1.12 mm -1 ) into Eq.(6). At  3 = 1MPa, for the specimens made of SC and NC (i.e., NC1, SC1, SC1b) the values of A F range between 1.39 mm and 1.46 mm (Fig.8b) , and do not differ substantially from those measured for Sismabeton ( A F  1.56 mm) without confinement. C ONCLUSIONS rom the results of an experimental campaign performed on NC, SC and Sismabeton cylinders under uniaxial and multi-axial compression, the following conclusion can be drawn: - In normal and self-consolidating concrete, fracture toughness in compression increases in the presence of an active confinement. - During the post-peak stage, the ductility of Sismabeton is comparable with that of NC or SC at 1MPa of confining pressure. - In compression, the performance of fiber-reinforced composites can be quantified by the distributed confining pressure generated by the fibers. The presence of an active confinement can improve the mechanical behaviour of concrete and, consequently, its durability. Thus, further researches should be developed in order to introduce new sustainability indexes, which take into account fracture toughness, both in tension and compression. A CKNOWLEDGEMENTS he authors wish to express their gratitude to the Italian Ministry of University and Research (PRIN 2006) and to Fondazione Cassa di Risparmio di Alessandria for financing this research work, and also to Buzzi Unicem S.p.A. for its technical support. R EFERENCES [1] M. A. Mansur, M. S. Chin, T. H. Wee, ACI Structural Journal, 94-6 (1997) 663. [2] K. H. Khayat, P. Paultre, S. Tremblay, ACI Materials Journal, 98-1 (2001) 371. [3] UNI EN 1998-1:2005. Eurocodice 8 – Design of structures for earthquake resistance - Part 1: General rules, seismic actions and rules for buildings, (1998) 229 [4] UNI EN 1992-1-1:2005. Eurocodice 2- Design of concrete structures- Part 1-1: General rules and rules for building, (1992) 225. [5] N. Ganesan, J. V. Ramana Murthy, ACI Materials Journal, 87-3 (1990) 221. [6] G. Pons, M. Mouret, M. Alcantara, J. L. Granju, Materials and Structures, 40-2 (2007) 201. [7] CEB (Comite Euro-International du Beton), “CEB-FIP Model Code 1990”, bulletin d'information n°203-205, Thomas Telford, London, UK (1993). [8] J. G. M. van Mier, , Fracture Processes of Concrete: Assessment of Material Parameters for Fracture Models. CRC Press, (1996) 448. [9] D. C. Jansen, S. P. Shah, ASCE Journal of Engineering Mechanics, 123-1 (1997) 25. [10] A. P. Fantilli, H. Mihashi, P. Vallini, ACI Materials Journal, 104-5 (2007) 501. [11] P. Jamet, A. Millard, G. Nahas, Int. conference on concrete under multiaxial conditions, Toulouse (1984) 133. [12] S. J. Foster, J. Liu, S. A. Sheikh, ASCE Journal of Structural Engineering, 124-12 (1998) 1431. F T