Eirini Tziviloglou

Bio-Based Self-Healing Concrete: From Research to Field Application

Cracks are intrinsic concrete characteristics. However, cracking can endanger the durability of a structure, because it eases the ingress of aggressive gasses and liquids. Traditional practices tackle the problem by applying manual repair. Scientists inspired by nature have created self-healing concrete able to self-repair as a result of the metabolic activity of bacteria. Various research groups have studied bio-based self-healing concepts over the last decade. Although the metabolic pathways of different bacteria can vary, the principle is essentially the same: a bio-based healing agent is incorporated into fresh concrete and when a crack appears in hardened concrete the bacteria become active, precipitate limestone and seal the open crack. Bio-based self-healing concrete technology targets the recovery of the original performance of concrete by regaining water tightness lost by cracking. Along these lines, bio-based repair systems have also been developed to protect existing structures by applying materials that are more concrete-compatible and environmentally friendly than existing repair materials. All these innovative concepts have shown promising results in laboratory-scale tests. Steps have been taken towards the first full-scale outdoor applications, which will prove the functionality of this new technology.

Self-healing mortar with pH-sensitive superabsorbent polymers: testing of the sealing efficiency by water flow tests

Superabsorbent polymers (SAPs) have potential to be used as healing agent in self-healing concrete due to their property to attract moisture from the environment and their capacity to promote autogenous healing. A possible drawback, however, is their uptake of mixing water during concrete manufacturing, resulting in an increased volume of macro-pores in the hardened concrete. To limit this drawback, newly developed SAPs with a high swelling and pH-sensitiveness were developed and tested within the FP7 project HEALCON. Evaluation of their self-sealing performance occurred through a water permeability test via water flow, a test method also developed within HEALCON. Three different sizes of the newly developed SAP were compared with a commercial SAP. Swelling tests in cement filtrate solution indicated that the commercial and in-house synthesized SAPs performed quite similar, but the difference between the swelling capacity at pH 9 and pH 13 is more pronounced for the self-synthesized SAPs. Moreover, in comparison to the commercial SAPs, less macro-pores are formed in the cement matrix of mixes with self-synthesized SAPs and the effect on the mechanical properties is lower, but not negligible, when using high amounts of SAPs. Although the immediate sealing effect of cracks in mortar was the highest for the commercial SAPs, the in-house made SAPs with a particle size between 400 and 600 μm performed the best with regard to crack closure (mainly CaCO3 precipitation) and self-sealing efficiency, after exposing the specimens to 28 wet–dry cycles. Some specimens could even withstand a water pressure of 2 bar.

Selection of Nutrient Used in Biogenic Healing Agent for Cementitious Materials

Biogenic self-healing cementitious materials target on the closure of micro-cracks with precipitated inorganic minerals originating from bacterial metabolic activity. Dormant bacterial spores and organic mineral compounds often constitute a biogenic healing agent. The current paper focuses on the investigation of the most appropriate organic carbon source to be used as component of a biogenic healing agent. It is of great importance to use an appropriate organic source, since it will firstly ensure an optimal bacterial performance in terms of metabolic activity, while it should secondly affect the least the properties of the cementitious matrix. The selection is made among three different organic compounds, namely calcium lactate, calcium acetate and sodium gluconate. The methodology that was used for the research was based on continuous and non-continuous oxygen consumption measurements of washed bacterial cultures and on compressive strength tests on mortar cubes. The oxygen consumption investigation revealed a preference for calcium lactate and acetate, but an indifferent behaviour for sodium gluconate. The compressive strength on mortar cubes with different amounts of either calcium lactate or acetate (up to 2.24% per cement weight) was not or it was positively affected when the compounds were dissolved in the mixing water. In fact, for calcium lactate the increase in compressive strength reached 8%, while for calcium acetate the maximum strength increase was 13.4%.

Influence of Microfiber Additive Effect on the Self-healing Behavior of Engineered Cementitious Composites

This paper investigates the self-healing behavior of Polyvinyl Alcohol Engineered Cementitious Composites (PVA-ECC) with the addition of other microfibers, including steel fiber and rock wool fiber. Four-point bending tests were used to precrack ECC beams at the age of 7 and 28 days, respectively. The precracked samples were then cured in water to promote the occurrence of self-healing and in air for control. The addition of microfibers helps tighten the crack width greatly, resulting in enhanced flexural stiffness for the water cured samples. Furthermore, the additive effect also promotes larger extent restoration of deflection capacity, despite much lower initial deflection capacity for the mixtures 2a and 3a. The self-healed samples were also examined under light microscope and environmental scanning electrical microscope (ESEM) to reveal the products of self-healing.