No rapid testing method is available to determine the type of weathering and the weathering resistance of aggregates and rocks. The current testing methods are time consuming (1 to 3 month). It is needed to achieve a simple and rapid testing method to determine the main weathering properties of rocks and aggregates within maximum one week.
The objective of the project is development of a fast and simple testing method to determine the weathering properties of rocks and aggregates.
The methodology is based on laboratory testing, in situ comparisons and to a lesser extent, theoretical compilation of existing data, in particular the work of F. de Quervain on sustainability rocks in Switzerland.
Tests for resistance to weathering are not the same for ornamental rocks and aggregates in European standardisation. Weathering resistance tests require much time and work. This is particularly the case for the freeze-thaw-test, which consists of 240 cycles and can last about a year.
An automated method based on the solubility of sodium sulphate was developed in this research. The presence of an unstable phase was a key difficulty to establish the testing method. A metastable phase composed of Na2SO4w7H2O was discovered by Hamilton et al in 2008 that corresponds to the unstable phase observed in this study. The test conditions were adapted to this metastable phase. It is especially the conditions for temperature range which must be between -4 °C and + 30 °C. Additional research and further developments are needed to refine the method.
The fundamental principle of this new testing method is based on the variation of solubility of sodium sulphate as a function of the temperature.
The automated method developed in this study uses a thermos-cryostat, an external reactor, a mixer as well as racks to support the different types of samples and containers for small aggregates.
The tests conducted in this study showed that a correlation between the freeze-thaw test and this new method could be possible. On the other hand, significant differences were observed with the test according to F. de Quervain. An easy or simple correlation with the test according to F. de Quervain does not appear to be possible with this new method.
Uniaxial compression tests on cylindrical samples subjected to freeze-thaw cycles, cycles of crystallization of sodium sulphate according to F. de Quervain and of cycles of crystallization with this new method showed linear strength loss depending on the number of cycles. No significant loss of mechanical resistance is observed for inalterable rocks.
Test of crystallisation according to EN 12370 showed that this test was not suitable for testing some molasse sandstone used as ornamental rocks in Switzerland. Tests were conducted on grit and ballasts of different petrographic composition.
Aggregates and railway ballasts composed of frost-sensitive rocks showed strong damages after being tested with the new method.
In summary, this new procedure for testing the weathering resistance developed in this work provides a fully automated testing method of resistance to weathering and saves a very significant time compared to traditional