HEALCON PROJECT

The project 'HEALCON - Self-healing concrete to create durable and sustainable concrete structures' is an integrated project within EUs 7th Framework Program. The overall objective of the project is to design, develop, test, apply and evaluate self-healing methods for concrete structures.

With this newsletter we want to inform you about the progress made within the project. In case you are interested to receive more information, you can consult the HEALCON website (www.healcon.eu) or e-mail our contact person ( This email address is being protected from spambots. You need JavaScript enabled to view it. ).

 

Figure 1. Overview of the general organization of the project

 STANDARDIZATION ACTIVITIES

Within the HEALCON project, a series of laboratory tests has been developed and recommended to evaluate self-healing at lab-scale. The test procedures are designed to quantify the extent of the recovery of water tightness (sealing) and the recovery of mechanical properties (healing). The test methods are adapted from common techniques used in mortar testing and can be applied in a wide variety of self-healing cementitious materials.

Steps towards standardization of testing self-healing mortar at lab scale have been taken with co-operation of NEN (Netherlands Standardization Institute). Up to now, a pre-standard document has been written and we are waiting for the results of a round robin test to evaluate the reproducibility of the different test proposed.  

Figure 2. Different crack permeability tests developed (left: capillary water absorption test – right: water flow test

 LARGE SCALE TESTING

Two large scale lab units have been designed in order to demonstrate the efficiency of the healing technologies developed, using the monitoring techniques tested in prior stages of the project. The design includes both, the mix design of the concrete to be used and the design (dimensions and reinforcement) of the lab units: a beam and a slab. For both the beam and slab, a reference unit without self-healing technology will be cast. Furthermore, these elements will be monitored by means of NDT (Non-Destructive Testing) measurements in order to evaluate the self-healing process.

Several self-healing agents have been tested at laboratory scale and are up-scaled to be used in large scale testing:

-          Biogenic healing agents: Incorporation of bacteria in concrete can enhance crack-healing by production of CaCO3, as a result of their metabolic activity and of subsequent chemical reactions including the metabolic products. The CaCO3 precipitating bacteria and nutrients are added into the concrete matrix during the process of mixing (encapsulated or not, depending on the type of bacterial healing agent used). Upon cracking, the bacteria around the crack will precipitate CaCO3 (in situ) to heal the cracks. Ureolytic (spores of an axenic culture of Bacillus sphaericus encapsulated in micro-capsules and a non-axenic mixed ureolytic culture not encapsulted) as well as non-ureolytic bacteria (Bacillus cohnii) are investigated. Non-ureolytic bacteria that are alkali-resistant spores of Bacillus have been successfully incorporated in expanded clay particles. These Liapor particles serve as healing agent reservoirs for protection and immobilization of the biogenic healing agent.

-          Superabsorbent polymers: Superabsorbent polymers (SAPs) or hydrogels are three-dimensional, crosslinked polymeric networks that are not soluble but which can absorb large quantities of water. Within the HEALCON project, synthetic superabsorbent polymers with improved swelling and pH sensitiveness have been developed in order to seal the crack more efficiently.

-          Elastic polymeric healing agents: Self-healing based on an encapsulated precursor of a flexible polymer resulted in a stiffness regain of 35% and a very effective sealing of healed cracks, both against capillary water absorption and flow due to hydrostatic pressure, reducing both practically to the level of sound concrete. This healing agent will not yet be incorporated in the large elements because encapsulation trials are still ongoing.

 

NTD MEASUREMENTS

Non-destructive testing (NDT) techniques are able to characterize material properties of small mortar and concrete specimens. For a reliable characterization of the healing efficiency of self-healing concrete at lab-scale, acoustic emission and vibration analysis as well as the ultrasonic transmission technique were adjusted and modified. Large-scale and in-field tests, scheduled for 2016, have to show their final suitability and efficiency. Additional NDT applications can still broaden the assortment.

Figure 3. Acoustic emission measurements during a crack width controlled 3P-bending experiment at TU Munich to test self-healing efficiency
(Image source: Kathrin Flohr, Master thesis)

Fully automatic periodic monitoring with wireless sensors installed on site can also be conducted. The measurement nodes are battery operated and suited for independent outdoor operation rated for up to 4 years. Attached sensors measure environmental parameters such as temperature and humidity of both the test sample and the surrounding air.

The health of the concrete samples is monitored using electrical sensors, measuring the impedance of the material across a broad frequency spectrum, as well as static potentials between the reinforcement metal and embedded electrodes. This allows detecting moisture ingress into the material as well as the onset of reinforcement corrosion based on the recorded data. Any measured data is transmitted to a base station, which in turn uploads all measurements to a cloud based database server, where fully automatic post-processing and analysis will occur.

Alert thresholds can be set to automatically notify operators in real time if the measurements suggest any new developments within the measured samples.

   

Figure 4. Concrete prisms with corrosion potential being measured between reinforcement simulation wire and surrounding salt liquid (Immersed reference electrode not shown) (left), Wireless impedance measurement device connected to electrodes embedded in concrete prisms (center) and monitoring network prototype installation setup for impedance and potential measurements on concrete prisms in climate chamber (right).

Consortium

Coordinator:

 

Universiteit Gent

Belgium

Partners:

 

Avecom N.V.

Belgium

Technische Universiteit Delft

The Netherlands

Acciona Infraestructure S.A.

Spain

Technische Universitaet Muenchen

Germany

Technologie-Transfer-Initiative GmbH

Germany

Teknologian Tutkimuskesk VTT OY

Finland

Cowi A/S

Denmark

Teknologisk Institut DTI

Denmark

INNCEINNMAT S.L.

Spain

Fescon OY

Finland

Devan Micropolis

Portugal

 
This project has received funding from the European Union’s Seventh Framework Programme
for research, technological development and demonstration under grant agreement no 309451.
Saturday the 21st. © 2013 Universiteit Gent.