Technical updates

June 2020 | M30


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.

In September 2019, after the laboratory validation, the validation of products and technologies on the monuments selected as case studies has started.

Before the application of the products, a cleaning intervention was necessary in order to prepare the concrete surface areas selected for in-situ validation. The presence of contaminants, patinas, biofilms, previous treatments or even graffiti to be removed was evaluated and this information was used to define the best protocols for the removal of the most frequently found detrimental layers on the monument’s surfaces. In order to define specific cleaning protocols, some study visits was done to collect some specific samples, to evaluate the chemical nature of the materials to be removed and to perform preliminary tests on the areas selected for the in-situ validation activities. These studies were first conducted at the IX Fort Monument in Kaunas (Lithuania), in the Warsaw Srodmiescie Station (Poland), and in the interior wall of the War Memorial tower in Torricella Peligna (Italy). The analysis of the surfaces showed that the sites presented scenarios typically observed by conservators in concrete monuments. The following conservation issues were addressed: the removal of detrimental materials/coatings, the removal of synthetic varnish (vandalism and/or coatings/re-paintings), the removal of biofilms, the removal of corrosion layer from metal reinforcing bars and the use of enzyme solutions for the removal of natural organic grime. The defined protocols comprise formulations that are already used for the treatment of stone artefacts and innovative low environmental-impact formulations used for the first time on concrete surfaces.

In order to organize the in-situ validation activities, protocols for the application of InnovaConcrete products and performance evaluation were defined: the definition of a proper methodology to be followed for the products application was defined with the contribution of products developers.

Regarding the in-situ validation, the partners responsible for the monuments have overseen the products application that should be performed by restorers or people with experience in this field: this is important to avoid an inappropriate application. The same partners have also to select the areas to be treated with the InnovaConcrete products and this selection must be done in agreement with the Italian National Research Centre (CNR) that will conduct the in-situ characterization. Due to weather conditions, the in-situ validation activities have been anticipated in some case studies, including Warsaw Srodmiescie Station (Poland), IX Fort Monument in Kaunas (Lithuania), Centennial Hall in Wroclaw (Poland) and War Memorial Tower in Torricella Peligna (Italy). The products already validated at laboratory scale have been applied in the areas selected for the validation. In particular, the products application in the IX Fort Monument in Kaunas (Lithuania), in the Warsaw Srodmiescie Station (Poland) and in the War Memorial Tower in Torricella Peligna (Italy) was conducted at the end of 2019; in the case of the Centennial Hall in Wroclaw (Poland), the products application was performed in January 2020.

CNR is monitoring the treated surfaces since the application and curing of products (T0), but also after 4 months (T4) and after 8 months (T8). Specifically, the in-situ characterization performed by CNR started in the monuments where the InnovaConcrete products have been already applied. The first measurements have been conducted at T0 after application and curing of the products.

In addition, the monitoring of cracks to be treated with the InnovaConcrete products has already started in the selected monuments. Two cracks monitoring systems were defined: a contactless type system, based on 3D scanning and image processing, was installed inside the War Memorial Tower in Torricella Peligna and inside the Centennial Hall in Wroclaw while a system, based on contact sensing by means of a wire crack meter with integrated datalogger and wireless connection to the Data Acquisition Unit, was installed on top of the Śródmieście Raylway Station, in Warsaw. Both systems are managed remotely to monitor 5-6 cracks in each monument. The data acquisition and the processing started between the end of August and half September 2019 and it will continue for six months before and (at least) six months after the application of products to treat the cracks.

The InnovaConcrete researchers will be able to see some results from the product in-situ application supposedly at the end of 2020.

INNOVACONCRETE project is not focused only on the development of new product to preserve concrete heritage, but also to let people understand the importance of this kind of heritage, essential for the development of 20th-century architecture and engineering and often not considered as cultural heritage or buildings to protect. For this reason, the project is putting in place some strategies to raise awareness and foster the social appreciation of this heritage.