Urs Buegger, M.Sc.
Pockelsstraße 3
38106 Braunschweig
Telephone: 0531/391 94358
Research project:
Experimental evaluation of self-healing and crack management of engineered cementitious composites (ECCs)
The longevity of reinforced concrete structures under service conditions depends largely on their ability to withstand environmental influences. In its uncracked state, concrete generally provides good protection for the embedded rebar against the ingress of corrosion-inducing media such as chlorides. Cracks in concrete structures are, however, unavoidable and create a primary path for such media to reach the steel and initiate corrosion. Corrosion initiation as well as corrosion progression depend on several factors such as crack width and concrete cover, for which current construction codes have explicit provisions to provide the desired level of durability. Nonetheless, corrosion remains a leading cause for the degradation of structures resulting in a premature end of their service life. With the continuing innovation in the field of cementitious materials comes the necessity to consider other factors that influence durability such as crack tortuosity, crack spacing, and the ability of cracks to self-heal, which are not considered in current codes.
The focus of this research project lies on engineered cementitious composites (ECCs) with PVA fibers. ECCs have a much larger binder content than regular concrete mixes, have no coarse aggregates, and contain a considerable amount of polymer fibers (around 2 Vol-%). This leads to unique mechanical properties such as a strain hardening response under load and a much larger total strain capacity than regular concrete. The inclusion of PVA fibers in ECCs also promotes a distributed cracking pattern with many small and very tortuous cracks. In addition to that, ECCs have the ability to self-heal these cracks after they form. This is largely due to the low water/binder ratio that leaves a significant amount of unhydrated binder in the matrix. Once a crack appears, the binder reacts with water that is absorbed through the crack to form new reaction products, effectively closing the crack.
The goal of this project is to show that the use of engineered cementitious composites (ECCs) can significantly extend the service life of a structure. ECCs exhibit not only high matrix density in the uncracked state, but also significant self-healing capacity after cracks appear, providing high resistance against the permeation of corrosion-inducing media after cracking. These properties make ECCs highly suitable for structures exposed to aggressive environments as well as retrofitting damaged structures. In newly built structures, it can allow for a significant reduction of the concrete cover while maintaining a high level of durability. When used as a retrofitting material, it can re-establish a strong barrier against corrosive media without adding a lot of self-weight.
The research will focus on evaluating the self-healing behaviour on a microscopic level using X-ray µCT to analyze cracking and self-healing under different exposure and loading conditions. The goal is to visualize and quantify the ability of PVA-fiber reinforced ECCs to re-establish the durability properties after cracking.