Freeze thaw fracturing in building granites
Abstract Four types of granite widely exported and used in construction around the world were subjected to 280 accelerated freeze thaw test cycles, conducted as stipulated in European standard UNE EN, 12371, 2001 to ascertain their petrophysical response. The techniques used to characterise the granite before and after freeze thaw induced microcracking included vacuum water absorption, ultrasonic P wave pulse velocity and ultrasonic S wave pulse velocity, mercury intrusion porosimetry and polarised optical and fluorescence microscopy to quantify the type of microcracks developing (inter intra or transcrystalline) and identify the associated mineral phases: quartz, feldspar and biotite. The linear crack density (number of cracks per millimetre) was calculated based on the microscopic data collected. Young's modulus was likewise found before and after the freeze thaw cycles. The chief ice crystallisation mechanism was involved in microcracking and hence deterioration was ice segregation. In all four granites, ultrasonic propagation velocities and strength parameters declined with the development of freeze thaw induced microcracking. More intercrystalline microcracks were developed in the early cycles, while larger numbers of intracrystalline microcracks were found at the end of the test. The results of this study can be applied to other granites with similar characteristics and whose microcracks are generated with same mechanisms of frost damage. Upon conclusion of the cycles, Zarzalejo granite exhibited the largest number of microcracks, with a linear crack density of 3.9, as well as the highest rise in microcracking. Colmenar Viejo ended the freeze thaw test with the fewest number of microcracks and a post test linear crack density of 2.3, denoting greater freeze thaw resistance. The smallest increase in the number of microcracks was found for Cadalso de los Vidrios granite. The microscopic and microporosity findings reported in this paper revealed the existence of freeze thaw test induced microcracking which, while barely affecting mechanical stability (Young's modulus) did cause damage.