• stone
• stone buildings
• physical-mechanical characterization
• cultural heritage
• stone materials

This Ph.D. work is not only a scientific and technical research, but also a contribute for the conservation purposes on Historical and Cultural Heritage.
Building Stones represent a cultural and typical element of each territory and are a very powerful tool for the transmission of testimonies. The city of Florence, due to the immense artistic heritage, was admitted into the World Heritage List in 1982 by UNESCO.
The main purpose of this work was to provide a starting database for the physical and mechanical characterization of the main Building Stones used in Florence through the centuries.
Samples for laboratory tests have been taken from the historical quarries of Pietraforte, Pietra Serena, Pietra Bigia, Verde Prato, Rosso Cintoia and Alberese. On these samples physical and mechanical determinations has been done according to two different standards: UNI EN Standards and ISRM Suggested Methods.
Physical and mechanical properties determined for Pietraforte, Pietra Serena, Pietra Bigia, Verde Prato and Rosso Cintoia, were porosity (Φ), density (ρ), imbibition coefficient (IC), water absorption at atmospheric pressure, water absorption by capillarity (Aw), uniaxial compressive strength (UCS), indirect tensile strength (σt) and ultrasonic velocities (UsV).
Alberese was not historically used as construction material, but as material for the production of lime, therefore analysis were made using X-Ray diffraction, calcimetry and FT-IR spectroscopy.
Physical properties results are in line with the few sporadic data reported in literature.
Following UNI EN Standards, the results obtained for mechanical properties show the highest UCS values for Pietraforte with Tb parallel laminations and Pietra Serena (between 95 MPa and 100 MPa) and the lowest for Pietra Bigia and Pietraforte with Tc convolutions (between 50 and 70 MPa). Verde Prato has low UCS average value ( ̴ 55 MPa) due to intense micro-fracturing of the material, instead Rosso Cintoia presents quite high values ( ̴ 90 MPa). Likewise, the highest σt values were found for Pietraforte with Tb parallel laminations and Pietra Serena (between 5 MPa and 6 MPa) and the lowest for Pietra Bigia and Pietraforte with Tc convolutions (between 2 MPa and 3 MPa).
Following ISRM Suggested Methods the highest UCS values were determined for Pietraforte with Tb parallel laminations ( ̴ 120 MPa) and the lowest for Pietra Bigia and Pietraforte with Tc convolutions (between 55 MPa and 70 MPa). The highest σt values were found for Pietraforte with Tb parallel laminations ( ̴ 7 MPa) and the lowest for Pietra Bigia and Pietraforte with Tc convolutions (between 2 MPa and 4 MPa).
Shape and size specifications of the samples are different for UNI EN Standards and ISRM Suggested Methods and for this reason, results obtained with the two different standards, are not directly comparable with each other.
It is very difficult to predict, for these materials, the value of σt starting from the value of UCS, by assuming σt 1/10 σc, as suggested in literature. Our results are always lower, in order of about 1/20.
The determination of UCS, from the elastic rebound index (Schmidt Hammer) does not appear to be in line with UCS results obtained in laboratory; this may be due to the fact that in situ the alternating surfaces of the rock (JCS) were measured, with the aim of recreating the situation we find on the Building Stones in place, instead in laboratory samples have standard dimensions and conditions.
The decrease between oven-dried and water-saturated samples in UCS is between 20% and 40% for the materials analysed. In literature this decrease is assumed to be about 30%.
There is an increase in UsV in water saturated samples, compared to dry samples, varying between 300 m/s and 600 m/s, with peaks up to 1500 m/s. This phenomenon is very important in a context of Cultural Heritage preservation, because during the in-situ measurement on various historical monuments, it is usual that rocks, exposed to humidity, can retain a percentage of water not always determinable. This, according to the results obtained in this work, can imply an increase of UsV and can false the in-situ UsV determination.
The analyses performed on Alberese limestone, specifically on Sasso Alberese variety used to produce calcina dolce, are in line with those available in literature.