The project was born to develop, characterize and improve some conservation products and techniques to preserve historic concrete. To reach this objective the project counts different stages. Firstly the development of a “Multi-scale modelling” has been useful to implement necessary activities needed to achieve the following set of goals: computationally-driven design of new impregnation treatments based on the formation of C-S-H gel; computationally-driven design of new multifunctional treatments, combining C-S-H gel formation and superhydrophobic performance made of micro-pattern structures decorated by plasma spraying; computationally-driven design of enzyme-assisted self-healing treatments.
During the project six families of products—some of them with variations for different applications—and a plasma device have been developed and optimized with input from the theoretical models, laboratory validation results and recommendations from the partners in charge of in situ application.
Two different products have been designed and optimized: a consolidant used as a solvent-less product to maximize the production of silica-rich C-S-H gel, in line with the structure predicted by theoretical models; and a consolidant used to enhance the effectiveness on carbonate-rich substrates (e.g. heavily carbonated concretes or those with predominant calcareous aggregates) and incorporates a hydrophobic agent. Two types of nanocarriers have been developed and optimized for their incorporation into the consolidants. The first type is based on size-tunable mesoporous silica nanoparticles loaded with a benzotriazole-Ag complex, designed with a dual function: (1) to gradually release the inhibitor in response to pH and (2) capture chloride ions. The second type is based on layered double hydroxides loaded with “green” inhibitors and is specifically designed to capture chloride ions and release the inhibitor in their presence. The changes in physical properties of the consolidants was minimal after incorporation of nanocarriers, and the models predicted a non-significant impact on their penetration. Three different cement-based repair mortars with varying viscosity, workability and setting times have been developed by modifying the aggregate granulometry and the proportions of halloysite nanotubes, micro-silica, superplasticizers or cellulose ethers. The mortars have been designed to repair different type of damages on the concrete structure: (1) a fluid paste to apply as coating for delamination problems and surface reinforcement. (2) Am injectable mortar to heal small cracks (< 5 mm). (3) A plastic mortar to heal larger cracks (5-10 mm). Additional studies have been started to exploit the capacity to load the nanotubes with corrosion inhibitors. A hydrophobic impregnation product has been designed by modifying the formulation of the consolidant, incorporating alkylsiloxane/alkylalkoxysilane as hydrophobic agents and nano-SiO2 to produce a nano-roughness—both requirements to promote a superhydrophobic surface. The results from the theoretical models were used to design a sol with physical properties that enhance its penetration into smaller pores without compromising the consolidant effect.
A functional portable atmospheric plasma device, designed for application of the hydrophobic sol has been developed. The device provides a stable plasma under typical working conditions and has been designed considering ease of use and safety for the operator. The device has been tested in laboratory and in situ, demonstrating that the plasma treatment is able to create a superhydrophobic surface while minimizing product uptake and crates a regular roughness without the need to incorporate nano-silica.
Plus, a product based on the enzymatic activity of the alkaline phosphatase (ALP) present in the bacteria colonizing historic concrete has been designed. The formulation, containing PMMA, calcium polyphosphate and amorphous CaCO3 nanoparticles, was designed to obtain a product with reasonable costs and applicability in situ by common techniques. The working principle exploits the activity of naturally-occurring bacteria to fill the concrete cracks with calcite and calcium phosphate. The bio-mineralization models were used to predict the crack-sealing capacity of the materials. After validation on artificially aged mortars and mockup specimens, all of the products were sent to partners and validated in different case studies.
The products developed during the InnovaConcrete project have been applied and validated on the monuments identified as case studies. The treatments were performed on selected areas that differ for composition, state of conservation and environmental conditions. The proposed monitoring strategy for the products characterization has been successfully applied to evaluate the products performances in different environmental conditions. The monitoring lasted in time at least two years and it involved European research groups formed by the project partners using different instrumentations devoted to measure the same characteristics parameters: color changes, water absorption, hardness, cohesion/compactness and rebar corrosion. The results of this European inter-comparison are absolutely an innovative tool to test the products performance. The effect of different locations and of different concrete materials was evaluated also involving the interest of other stakeholder in the sector and of the citizens.