Issue 40

S. K. Kourkoulis et alii, Frattura ed Integrità Strutturale, 40 (2017) 74-84; DOI: 10.3221/IGF-ESIS.40.07 75 which are then filled by a proper white cement paste [1]. However it has been observed that under specific loading conditions the adhesion between the cement paste and marble is sometimes not adequate permitting gradual or abrupt slip of the reinforcing bar from the body of the restored element, a phenomenon known as “pull-out”. Taking into account that the construction of specimens in the form of structural elements of classical monuments is a difficult and costly task, an alternative experimental protocol was recently designed [2, 3], permitting laboratory investigation of the pull-out phenomenon (Fig.1). The specimens were made of Dionysos marble blocks drilled centrally throughout their length. The hole was filled with a cementitious material and a threaded titanium bar was driven into the hole while the filling material was still liquid. The experiments were implemented after a 28-day curing period. Using a properly designed metallic supporting system the marble was fully restricted (Fig.1c) and the bar was pulled-out under displacement-control mode (Fig.1d). Figure 1 : (a) , (b) Typical pull out specimens; (c) , (d) The experimental set up [2, 3]. The data obtained by the AE sensors during a typical pull-out experiment are somehow “chaotic” as it is seen in Fig. 2, where the AE recordings’ duration is plotted (in conjunction to the marble-bar relative slip and also the force imposed by the frame) versus time. A direct interpretation of these data is difficult, especially concerning the sources of the emissions. In the direction of gaining a better insight it was considered that the AE technique should be first applied on specimens of simple geometry made of a single material. The protocol described here has proven that classifying the acoustic sources in such elementary tests is indeed a useful tool for the identification of the sources of acoustic signals in complex structures. Figure 2 : Time variation of the duration of AE recordings, the LVDT (in touch with the bar’s lowest end) indications and the load [3]. T HE EXPERIMENTAL PROTOCOL The materials he Alfas stone is a natural building material, quarried near the village of Alfas in the island of Crete. It was used as building material for quite a few monuments in Crete, both classical and modern, like for example the primary school at Scordilo village, built in 1884 (Fig.3a). Recently, during the construction of the Rethymnon-Ancient Eleutherna road, 128 ancient graves were discovered, all of them sculpted by Alfas stone. Nowadays Alfas stone is extensively used for the restoration of several monuments of great historical and cultural significance such as the T (a) (b) (c) (d)