Bioconsolidation of calcarenite for cultural heritage conservation: Effects of application methods on mechanical and petrophysical properties

Bioconsolidation is an eco-friendly technique that uses carbonatogenic bacteria to improve the adhesion of weathered stone materials. Although its efficacy in consolidating sand and healing cement has been demonstrated, a systematic evaluation of its application methods and effectiveness in improving mechanical properties remains limited, particularly in the context of Cultural Heritage conservation. In this study, we investigated the potential of bioconsolidation for the restoration of calcarenite, a highly porous rock, under laboratory conditions. This work was prompted by conservators at the Parco Archeologico di Cerveteri e Tarquinia to explore the use of bioconsolidation as a non-invasive intervention in ancient Etruscan hypogeal tombs in the Necropolis of Tarquinia, Italy, a UNESCO World Heritage Site. These tombs were carved from a calcarenite known as Macco . We assessed the carbonatogenic activity of Lysinibacillus fusiformis 3.20 bacterial strain examining multiple bioconsolidation application methods on the Macco . We measured petrophysical and mechanical properties, including uniaxial unconfined compressive strength, porosity and seismic wave velocity, before and after bioconsolidation. Our results demonstrate significant improvements in material strength and cohesion, with differences observed between the treatments. The spray treatment led to higher mass gain, but comparatively lower mechanical reinforcement compared to the immersion method. Overall, our findings support the use of bioconsolidation as a conservation technique for calcarenite and other weathered, porous rocks.