The expansion of thin marble slabs, known as bowing, is a spectacular and often observed behaviour of calcitic marbles. The result of this phenomenon is frequently the removal and replacement of those panels as a precaution, which is a significant economic factor. In a previous study, promising results were obtained on the possibility to mitigate and prevent bowing by treating marble with solutions of diammonium hydrogen phosphate (DAP) to form hydroxyapatite with consolidating properties. Based on these ecourafing results, in the present paper a systematic study is presented on 5 different marble varieties. The treatment is based on application of a solution of DAP to induce formation of new calcium phosphate phases inside micro-cracks and on the marble surface. So formed calcium phosphates have been found to restore mechanical properties of weathered marble by re-establishing cohesion among calcite grains. In the present study, the application of DAP was performed on unweathered and artificially bowed calcitic marble slabs, in addition to naturally bowed marble panels, taken from the library (SUB) in Göttingen. This enables to see if the bowing of the marble slabs can be reduced or even be stopped. Besides the bowing behaviour, the thermal dilation of the varieties and their directional dependency was examined. The tests were performed under dry and wet sample conditions for thermal cycles from 20°C up to 90°C, particularly with regard to the irreversible residual strain under unweathered conditions, as well as weathered and treated with the DAP and unweathered and consolidated. The grain to grain cohesion was tested by means of ultrasonic velocities for all samples before and after the artificial bowing, as well as after the consolidation and subsequently after the final bowing cycles. All investigations have been performed according to the specific directional dependency of the varieties under consideration of the maximum and minimum expansion direction.
Marble bowing: Prevention by the application of Hydroxyapatite - A systematic study
Enrico Sassoni;
2020
Abstract
The expansion of thin marble slabs, known as bowing, is a spectacular and often observed behaviour of calcitic marbles. The result of this phenomenon is frequently the removal and replacement of those panels as a precaution, which is a significant economic factor. In a previous study, promising results were obtained on the possibility to mitigate and prevent bowing by treating marble with solutions of diammonium hydrogen phosphate (DAP) to form hydroxyapatite with consolidating properties. Based on these ecourafing results, in the present paper a systematic study is presented on 5 different marble varieties. The treatment is based on application of a solution of DAP to induce formation of new calcium phosphate phases inside micro-cracks and on the marble surface. So formed calcium phosphates have been found to restore mechanical properties of weathered marble by re-establishing cohesion among calcite grains. In the present study, the application of DAP was performed on unweathered and artificially bowed calcitic marble slabs, in addition to naturally bowed marble panels, taken from the library (SUB) in Göttingen. This enables to see if the bowing of the marble slabs can be reduced or even be stopped. Besides the bowing behaviour, the thermal dilation of the varieties and their directional dependency was examined. The tests were performed under dry and wet sample conditions for thermal cycles from 20°C up to 90°C, particularly with regard to the irreversible residual strain under unweathered conditions, as well as weathered and treated with the DAP and unweathered and consolidated. The grain to grain cohesion was tested by means of ultrasonic velocities for all samples before and after the artificial bowing, as well as after the consolidation and subsequently after the final bowing cycles. All investigations have been performed according to the specific directional dependency of the varieties under consideration of the maximum and minimum expansion direction.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
