Maria Adelaide Pereira Gomes de Araújo

Simulation-Aided Design of Tubular Polymeric Capsules for Self-Healing Concrete

Polymeric capsules can have an advantage over glass capsules used up to now as proof-of-concept carriers in self-healing concrete. They allow easier processing and afford the possibility to fine tune their mechanical properties. Out of the multiple requirements for capsules used in this context, the capability of rupturing when crossed by a crack in concrete of a typical size is one of the most relevant, as without it no healing agent is released into the crack. This study assessed the fitness of five types of polymeric capsules to fulfill this requirement by using a numerical model to screen the best performing ones and verifying their fitness with experimental methods. Capsules made of a specific type of poly(methyl methacrylate) (PMMA) were considered fit for the intended application, rupturing at average crack sizes of 69 and 128 μm, respectively for a wall thickness of ~0.3 and ~0.7 mm. Thicker walls were considered unfit, as they ruptured for crack sizes much higher than 100 μm. Other types of PMMA used and polylactic acid were equally unfit for the same reason. There was overall good fitting between model output and experimental results and an elongation at break of 1.5% is recommended regarding polymers for this application.

Screening of Different Encapsulated Polymer-Based Healing Agents for Chloride Exposed Self-Healing Concrete Using Chloride Migration Tests

The service life of steel reinforced concrete in aggressive marine environments could be increased substantially by embedding a self-healing mechanism that ensures autonomous healing of cracks upon their occurrence. Previous proof-of-concept experiments have shown that the incorporation of encapsulated polymer-based healing agents (HAs) counts as a very appropriate way to achieve this goal. Over the years, several polymer-precursor-capsule systems have been developed in that perspective at our laboratory. Cementitious materials containing either commercial or in-house developed encapsulated HAs have been subjected to preliminary feasibility tests (water absorption, permeability tests, etc.). However, these experiments did not yet allow for a fast and straightforward assessment of the self-healing efficiency (SHE) in relation to the expected durability and service life performance of the material. This approach would have many advantages when having to select the most suitable polymer-precursor-capsule system for a particular concrete application. In this paper, a modified chloride migration test based on the one prescribed in NT Build 492 has been proposed to support the development of self-healing concrete for marine environments. Four polymer-based HAs have been screened that way, i.e. an in-house developed high-viscosity polyurethane (PU) precursor, a commercial low-viscosity PU precursor, the same commercial PU precursor with addition of accelerator and benzoyl peroxide (BPO), and an in-house developed 2-component acrylate-endcapped precursor + cross-linker. For now, a highly repeatable SHE value of 100% could only be obtained for the second option.

Screening Encapsulated Polymeric Healing Agents for Carbonation-Exposed Self-Healing Concrete, Service Life Extension, and Environmental Benefit

By incorporating encapsulated polymers in concrete, cracks can be healed autonomously upon occurrence. This is of high value for steel reinforced concrete structures subject to carbonation-induced corrosion. This paper presents the results of a rapid colorimetric screening test to assess the carbonation resistance of self-healing concretes containing encapsulated polymer-based healing agents. Four systems were tested for inhibition of further carbonation near artificially induced cracks (width: 300 μm). Next, the time to steel depassivation was assessed probabilistically in comparison with cracked concrete. With an adequately working pressurized PU precursor, the concrete would remain repair-free for at least 100 years. Subsequent life cycle assessment in SimaPro showed a potential environmental benefit (72–78%) for the ten CML-IA baseline impact categories which is mainly due to the service life extension possible with a properly working self-healing concrete.

Design and testing of tubular polymeric capsules for self-healing of concrete

Polymeric healing agents have proven their efficiency to heal cracks in concrete in an autonomous way. However, the bottleneck for valorisation of self-healing concrete with polymeric healing agents is their encapsulation. In the present work, the suitability of polymeric materials such as poly(methyl methacrylate) (PMMA), polystyrene (PS) and poly(lactic acid) (PLA) as carriers for healing agents in self-healing concrete has been evaluated. The durability of the polymeric capsules in different environments (demineralized water, salt water and simulated concrete pore solution) and their compatibility with various healing agents have been assessed. Next, a numerical model was used to simulate capsule rupture when intersected by a crack in concrete and validated experimentally. Finally, two real-scale self-healing concrete beams were made, containing the selected polymeric capsules (with the best properties regarding resistance to concrete mixing and breakage upon crack formation) or glass capsules and a reference beam without capsules. The self-healing efficiency was determined after crack creation by 3-point-bending tests.

Multiple self-repair of concrete cracks by encapsulated methyl methacrylate

Among all investigated approaches to obtain self-healing properties in concrete, autonomous healing of cracks through release of embedded polymer-based healing agents, seems a very promising approach. However, a suitable healing agent is needed to assure that also upon multiple crack formation, all cracks can be healed. For this purpose methyl methacrylate seems a suitable agent as it can create a very strong bond with the cementitious matrix. This will assure that after autonomous crack repair, later cracks appear at another location, where the self-healing mechanism is still intact and can thus still cause release of healing agent. As some problems with regard to the methyl methacrylate healing agent were found in previous research, these were tackled within this study by following three different approaches. The most promising approach(es) were selected for further use with regard to self-healing of concrete.