Characterisation of the tensile performance of bonding agents for the restoration of heritage dimension stone from southeast Australia

Abstract Through this research, we measure the direct tensile strength of three important southeast Australian heritage dimension stones and compare the results with published values. The three stones are Sydney Sandstone, Victorian Bluestone and South Australian Black Granite. This information is crucial for stone masons when they are selecting and cutting stone for construction projects, as they need to ensure that the stone they use and the repair will be strong enough to withstand the loads and stresses it will be subjected to in its final location. Results show that direct methods of testing provide tensile strengths that are 30–63% of the indirect methods. When the direct tension to compressive strength ratio is considered, results of 2–7% are calculated for these stones. This is significantly less than the typically assumed 10% for intact rock. Three masonry bonding agents have been selected to determine their capacity to re-bond the dimension stone. Highly variable results were achieved, with re-bonded tensile strengths ranging from 6% to 104% of the intact strength. This variability is most likely related to the heterogeneity of the stones and the surface preparations. Based on these outcomes, it is recommended that stone masons carefully consider the product that is used for restoration works and that test samples be prepared to confirm capacities. KEY POINTS Direct tension testing has been completed on Sydney Sandstone, Victorian Bluestone and South Australian Black Granite dimension stones. Direct tension results have not been previously published for these stones. Direct methods of testing provide tensile strengths that are 30–63% of the indirect methods on these stone types. When the direct tension to unconfined compressive strength ratio is considered, results of 2–7% are returned for these stones. This is significantly less than the typically assumed 10%. The performance of bonding agents on each of the stones provides variable results suggesting that careful selection of products is required and, if possible, test samples be prepared to confirm bond capacities.