Novel treatments based on hydroxyapatite for the conservation of historical concrete: a preliminary experimental study.

Given the enormous abundance of existing concrete structures, the maintenance, rehabilitation and treatment of ageing structures is a remarkable issue. Due to the lack of previous studies in this field, there is an urgent need to develop a systematic methodology and proper materials that can be used in the treatment of structural defects. The long-term performance of concrete buildings depends on the interactions with the environment, the use of the structure, the design, the structural defects and the quality of materials. By considering all these aspects together, it is possible to estimate the pathology of the building and to successfully design its rehabilitation. There is also a need for scientific research to better understand the behavior of historical concrete in order to identify the correct path of suitable and lasting solutions. For these reasons, the improvement of historical concrete buildings, should be constantly researched in depth. This study aims at identifying the performance that results from the formation of the calcium phosphates ideally hydroxyapatite, HAP [1], by using it as a consolidant for cement-based materials. Three ammonium dihydrogen phosphate-based solutions have been investigated. The method is based on the application of aqueous phosphate solution for the formation of HAP, the most stable CaP phase, on concrete specimens. The experimental campaign has been divided into a first chemical characterization, and secondly a mechanical one. Regarding the chemical characterization, FTIR test, calcimetry test, SEM analysis, EDS analysis, Mercury Intrusion Porosimetry (MIP), were performed. The mechanical characterization was carried out by the Young’s modulus determination, abrasion test, double punch test, bending test and compression test.