TECHNICAL UPDATES:

The main project activity is the development, characterization and optimization of some conservation prod­ucts and techniques to preserve historic concrete. The developed conservation products and techniques for concrete consolidation and corrosion inhibition are: impregnation treatments by using a surfactant-assisted route, calcium oxalate-based impregnation treatments, smart nanostructured materials for corrosion inhibition, multifunctional treatments combining C-S-H gel formation and superhydrophobic per­formance and a self-healing system based on the natural enzyme-assisted biomineralization mechanism. These materials have been optimized by using a multi-scale modelling approach and relevant parameters, such as penetration depth of the products into the concrete, have been improved. Moreover, they have been all validated in laboratory and they are now testing on the selected case studies right now.

Another activity performed was focused on the investigation of cement formulations, including inorganic additives, to be used as coating or as a repair material for microcracks and their optimization in order to produce a multi-functional treatment to increase the reinforcement of concrete, to trigger the formation of additional C-S-H gel at the interphase, to increase the interfacial bond strength and to release corrosion inhibitors. From the results of this study, three different pastes were developed: a fluid cement paste suitable as a coating to remedy delamination problems, a viscous cement paste optimized for repairing small cracks (< 5 mm) and a repair mortar formulated to repair bigger (5-10 mm) cracks. All these formulations were evaluated to test their adhesion to the substrates, durability, struc­ture, phase composition and the effect of the halloysite nanotubes on cement hydration kinetics. The optimized formulations have been tested by the project’s partners on the selected case studies. The laboratory validation consisted in the execution of different types of tests: for everyone, impregnation treatments to put in evidence colour changes, penetration depth, mechanical strengths, porosity, water vapor permeability, water absorption coefficient and surface’s hardness. For the superhydrophobic products, additional tests were carried out, like static and dynamic contact angle, water absorption at low pressure and sponge test. Also, the changes in the microstructure and texture after the treatment have been analysed using a fibre optics microscope. Corrosion inhibitors have been preliminary validated using steel bars in contact with a simulated concrete pore solution: electrochemical, morphological and structural studies have been performed. Moreover, these products have been tested together with the impregnation treatment in the reinforced mortars. Last, but not least, also some bio-mineral treatments have taken place: the evolution of the crack width after the application of the treatment is being followed by Optical microscopy. The modification of the hydric properties and the superficial hardness of the mortars have been analysed.

Representative mock-up samples, with similar composition and structural properties to the selected concrete case studies have been prepared. Considering the high number of monuments, the different ageing procedures to be performed and the test programmed to study the validation of the products, 6 mix designs were executed. Mock-up specimens have been physically and chemically aged using, when it was possible, the same decay processes performed in the Ordinary Portland Cement mortars already developed. The validation of the optimized products has taken place on both sound mock-ups and in aged samples.