Exfoliation microcracks in building granite. Implications for anisotropy

Abstract

Granite is found in many world heritage monuments and cities. It continues to be one of the most widely used stones in today's construction, given its abundance, uniformity and durability. Quarrymen traditionally cut this rock along its orthogonal slip planes, where splitting is easier. Ranked by ease of splitting, these planes are rift, grain and hardway. Granite is traditionally quarried along the rift plane where coplanar exfoliaton microcracks coalesce developing a flat surface. This splitting surface minimizes the cost and effort of subsequent hewing. Rift plane was predominantly used on the fair face of ashlars in heritage buildings worldwide. Determining the petrographic and petrophysical behaviour of these three orthogonal splitting planes in granite is instrumental to understanding decay in ashlars and sculptures. The decay of building granite is different in each splitting plane. Alpedrete granite was the stone selected for this study based on the orientation and distribution of exfoliation microcracks and the characterisation of their implications for the anisotropy of petrophysical properties such as ultrasonic wave propagation, capillarity, air permeability, micro-roughness and surface hardness. Inter-and intracrystalline microcrack length and spacing were also measured and quantified. The findings show that the splitting planes in Alpedrete granite are determined by the orientation of exfoliation microcracks, which as a rule are generally straight and intracrystalline and determine the anisotropy of the petrophysical properties analysed. Splitting planes are the orientation that should be applied when performing laboratory tests for the petrographic and petrophysical properties of building granite.

Experimental Study on Temperature Change and Crack Expansion of High Temperature Granite under Different Cooling Shock Treatments

“…These main cracks extended through the hole to the edge, which was more pronounced with the decrease of the cooling shock temperature under the same rock temperature conditions. The anisotropy of granite affected the propagation of cracks [36], and we could also observe the extension of the main crack. Generally, the cracks on the outer boundary of granite were wider, the crack gradually narrowed in the direction of the hole, and as the rock temperature increased, the cooling shock temperature decreased, and the width of the crack also increased.…”

The Forerunners on Heritage Stones Investigation: Historical Synthesis and Evolution

“…Stones from several kilometers far-away quarries were used (Figure 4) for the construction of megalithic structures. These early quarries had optimal cleat spacing and exfoliation microcracks for the extraction of blocks with the appropriate dimensions [74].…”

Elastic Anisotropy and Internal Structure of Rocks from the Uranium Ore Occurrences of the Litsa Ore Area (Kola Region, Russia)

“…The location of a weakly permeable ore body in permeable host rocks means a ban on the use of the in-situ leaching method [1]. Ultrasonic methods of nondestructive analysis are commonly used to measure the elastic properties of rocks (including anisotropy index) [2].…”