Magnesium phosphate-based cements containing Halloysite nanotubes for cracks repair

The repair of damaged cement structures represents an important area of the construction field, with dramatic structural and economic impact. Among all the available repair materials, magnesium phosphate cements (MPCs) are commonly used for their fast setting and hardening, low shrinkage and excellent bonding to aged concrete surfaces. In this work, a new material made of MPC doped with Halloysite nanotubes was developed for the repair of cement-based structures, in particular of cultural heritage interest. Halloysites were introduced in the composite for a twofold reason: i) to enhance the mechanical properties of MPCs; ii) to provide slow delivery of active molecules. Here, Halloysites were loaded with an antimicrobial agent, sodium salicylate, to achieve anti-fouling protection properties. The composites were thoroughly characterized to get a complete overview of the physico-chemical features of the repair material and to unravel the effect of the inorganic nanotubes by means of X-ray diffraction, scanning electron microscopy, FT-IR spectroscopy, thermogravimetry, porosimetry and mechanical testing. The incorporation of Halloysites in MPCs improves the handling and mechanical properties of the cements and allows for the release of active molecules from the cement matrix. Some preliminary applications of the composite were conducted in a real case study, demonstrating that it can be effectively used for crack repair and that the use of Halloysites as nano-carriers confers additional specific protection through the slow delivery of anti-fouling molecules from MPCs.