Dessi Koleva d.a.koleva@tudelft.nl
Nano-materials with tailored properties for self-healing of corrosion damages in reinforced concrete
Summary:
Corrosion of steel and thus induced degradation of reinforced concrete, subjected to aggressive environment, represents a great concern in relation to infrastructure durability. Achieving sustainability and durability in construction, maintenance or repair of reinforced concrete structures would require proper design and criteria, based on a multi-functional approach, including concrete and steel reinforcement as main materials, considering their properties and performance with operation.
The project will integrate the following main activities:
The project will integrate the following main activities:
1. Improving reinforced concrete performance by incorporating nano-scale materials with tailored properties i.e. core-shell polymer vesicles or micelles in the cement-based system.
2. Parallel investigation of the material properties of the concrete matrix and the steel reinforcement, as well as the interactions at the steel/cement paste interface, in the presence of tailored nano-polymers.
3. Focusing on materials behavior in natural and corroding conditions (chloride or carbonation induced reinforcement corrosion), thus achieving an integrated approach to multidisciplinary research (electrochemistry, concrete material science, polymer materials).
To this end, the focus of this proposal is theoretical and experimental research on a thoroughly innovative for the field of civil engineering application of novel materials and the establishment of a new method for corrosion control in reinforced concrete, using an autonomous self-healing mechanism.
The project is carried out by Delft University of Technology. Industrial partners who have shown their interest are
ENCI BVand KOAC.NPC
The project is carried out by Delft University of Technology. Industrial partners who have shown their interest are
ENCI BVand KOAC.NPC
Current Overview: Aiming at establishing novel approaches to corrosion control, this project represents a non-traditional investigation, involving the application of polymeric nano-aggregates in reinforced concrete. The emphasis is on self-healing of corrosion damages in reinforced concrete, by tailoring the material properties of both steel and concrete via initially admixed micelles and/or vesicles. The nano-aggregates are not meant to have inhibiting effects on corrosion initiation in the sense that organic inhibitors work for example, but to release certain compounds i.e. so called “active substance”, which would modify the pore solution and the steel/cement paste interface in a way, so that restoration of the original environment takes place (e.g. release of alkaline compound which would restore pH). The release of “active substance” is foreseen to be triggered by changes in pH. The proposed and investigated self-healing mechanism is schematically presented further below in Fig.1.
Preliminary research has been conducted with several types of nano-aggregates – micelles, vesicles and hybrid aggregates (in model solutions, in cement pastes and in mortar).1-4
Reported results: The properties of the bulk cement-based matrix, containing PEO113-b-PS218 core-shell micelles with concentration of 0.5 g/l mixing water (which is 0.006 wt. % per mortar weight), were previously investigated in plain (not reinforced) and in reinforced mortar specimens.1-3 It was found out that even a very low concentration of the micelles induces significant reduction of porosity (about 2 times at early hydration stages) and water permeability K [m/s] (approximately 6 orders of magnitude) of the matrix. The recorded coefficient of NaCl permeability, however, was quite different for both micelles-containing and micelles-free groups. For the former (micelles-containing) group, permeability increases in the presence of NaCl (KNaCl = 1.1 e-10 m/s), while it decreases for the latter (micelles-free) group (KNaCl= 6.09 e-9 m/s). For the micelles-free mixture, NaCl permeability is reduced, compared to water permeability, due to well-known chloride binding mechanisms, morphological and structural modifications of the bulk matrix.5,6 For the micelles-containing specimens, although similar binding mechanisms and structural alterations should be taking place in the presence of NaCl, permeability increases as a result of “shrinkage” of the polymer shell (polyethylene oxide, PEO) of the micelles.7 In the latter case, although NaCl permeability was lower, compared to mixtures without micelles, the remaining question is whether corrosion resistance of the steel reinforcement in the modified matrix will be increased, compared to the micelles-free specimens. The previously reported results3,4 show a decreased corrosion initiation and propagation in the micelles-modified matrix. Further, tests on carbon steel in model alkaline solutions, where hybrid aggregates were added in a concentration of 4.9.10-4 g/l (hybrid formations, synthesized through a layer-by-layer adsorption of oppositely charged ployelectrolytes (PDADMAC (poly(diallyldimethyl ammonium chloride)/ PAA Poly(acrylic acid)/PDADMAC on CaO crystals) also resulted in improved corrosion resistance of the steel electrodes.8
Most recent outcomes: The above mentioned preliminary investigations did not fully reveal whether the nano-aggregates were indeed present at the steel/cement paste interface and/or on the steel surface (considering the nano-size of the formations and the variety of cement hydration/corrosion products on the steel surface). To this end and in order to minimize the influence of the surrounding cement matrix, the focus of a very recent investigation was on the effect of polymeric nano-aggregates on the steel corrosion performance in model solutions, simulating the pore solution of the bulk cementitious matrix9. The morphological observation and surface analysis confirmed that the micelles are present on the steel surface and would be expected to result in a more uniform and compact layer i.e. to increase barrier properties and corrosion resistance respectively. X-ray photoelectron spectroscopy revealed that the product layers on the surface of steel electrodes, treated in micelles-containing medium exhibit more homogeneous and protective α – Fe2O3 and/or Fe3O4, whereas the product layers of steel, treated in micelles-free solution exhibit more hydrated FeOOH, FeO and FeCO3 which is prone to chloride attack. Therefore, the “barrier effect” along with the composition of the product layers on the steel surface (in addition to the very low concentration of the micelles i.e. 0.0024 wt. % PEO113-b-PS70 micelles) denote for the initially increased corrosion resistance of the steel in chloride-containing cement extract in the presence of micelles.
Fig.1. Self-healing of the bulk cementitious matrix, the steel/cement paste interface and the steel surface after carbonation or chloride-induced corrosion.
