Engineering properties and durability of limestones used in Persepolis complex, Iran, against acid solutions

The main weathering mechanisms threatening Persepolis rocks are acid attack coming from acid rains and bio acids produced by lichens. The Persepolis complex in Fars Province, Iran is built almost entirely with two Mesozoic limestones including Dariyan and Ilam formations. The durability of limestones against acid solutions is one of the most significant factors for determining the stability of these stones in monuments. This study mainly describes the durability of these stones against acid solutions. Another purpose of this study was to evaluate the intact rock and in situ strength of limestones used in Persepolis and its quarries. For these purposes, intact rock samples from the ancient quarries of the monument were selected and their petrographic characteristics, as well as physical and mechanical properties (density, porosity, water absorption, UCS, point load strength, Brazilian tensile strength, and P-wave velocity), were determined. Then, a slake durability test was carried out, with up to 15 cycles in hydrochloric and sulfuric acid solutions. The Dariyan limestone had a lower durability index against both acidic solutions than the Ilam limestone. This is mainly due to the higher porosity and water absorption of Dariyan limestone, and the yellow gypsum-patina layer formed on this stone in the monument is another indication of its higher reaction tendency with sulfuric acid. Schmidt hammer rebound test was carried out on Persepolis limestones and fresh rocks of its ancient quarries in order to determine the strength changes in the monument stones compared to intact rocks from ancient quarries. Although both limestones showed nearly equal Schmidt hammer rebound numbers in the quarries, the Dariyan limestone in Persepolis showed lower Schmidt hammer values than the Ilam limestone. Lower strength properties and the durability of Dariyan limestone are the main reasons that have led to its higher deterioration in the monument compared to Ilam limestone.