Potential of bacteria-based repair solution as healing agent for porous network concrete

POTENTIAL OF BACTERIA-BASED REPAIR SOLUTION AS

HEALING AGENT FOR POROUS NETWORK CONCRETE

V. Wiktor, S. Sangadji, H.M. Jonkers and E. Schlangen

Delft University of Technology, Faculty of Civil Engineering & Geosciences, Section of Materials & Environment - Microlab, Stevinweg 1, 2628 CN Delft, the Netherlands

Keywords: concrete, self-healing, cracks, bacteria-based system, porous network.

ABSTRACT

Bacterially induced calcium carbonate precipitation has received considerable attention for its potential application in enforcing or repairing construction material. The mechanism of bacterially mediated calcite precipitation in those studies is primarily based on the enzymatic hydrolysis of urea. Besides calcite precipitation, this reaction mechanism leads also to the production of ammonium ions which may result in excessive environmental pressure.

More recently, bacterially mediated calcite precipitation thanks to metabolic conversion of calcium lactate has been successfully applied in self-healing concrete. This concept is also now considered for the development of bio-based repair system for concrete structures.

The bio-based repair system as presented in this paper is a liquid-based system which transports the bio-based agent into concrete. This paper presents the recent advances on the development of the bacteria-based repair system and especially its possible application as healing agent in porous network concrete.

To assess the repair capacity of the system the bacteria-based solution is injected into porous cores, and the production of the biomineral in time is monitored by X-ray micro-tomography. In parallel, water permeability testing is conducted before and after the injection of the bacteria-based solution to determine the sealing efficiency of the system. The precipitate is analyzed with FTIR and thermal analysis for identification and quantification. Finally, at the end of the healing period, polished sections of injected specimens are observed with ESEM/EDS to analyze and locate precipitated biominerals.

FTIR results coupled with thermal analysis and ESEM observations showed that CaCO3 has been formed in pores after 21 days, with increased amount after 28 days.

Moreover, the evidence that CaCO3 precipitation was indeed mediated by bacteria

has been found with observations of bacteria imprints on Ca-based minerals.

It can be concluded that the bacteria-based repair system can successfully be injected as healing agent into porous network concrete.

1. INTRODUCTION

Porous network concrete, a novel concept of self-healing concrete which imitates bone morphology, has recently been developed [1]. This concrete is composed of a porous core surrounded by a concrete structure. Upon crack formation, the healing agent (chemical-, bio-, or cement-based) can easily be distributed through the porous network to the crack location.

This paper investigates the possible application of bacteria-based repair system as healing agent for porous network concrete.

2. MATERIALS

2.1. Bacteria-based system

The bacteria-based system is a liquid-based system which transports a bio-based agent into concrete. The bio-based agent consists of concrete compatible bacteria and feed which produces calcite-based minerals resulting in decreased porosity. The preparation and composition of solutions (solution A&B) is as described by Wiktor and Jonkers [2].

2.2. Porous core

The goal of this study is to investigate the feasibility of injecting a bacteria-based solution into porous network concrete. Therefore, several parameters are tested and due to the high number of specimens required, the experiment is conducted only on the porous core used in porous network concrete. Porous cores are prepared as described by Sangadji and Schlangen [1]. The porous cores are then cut in smaller specimen of 3cm high.

3. METHODS

The experiment is designed over 5 series as shown in Figure 1. Tests are performed 3, 7, 14, 21 and 28 days after injection and 2 replicates are used per time and series except for series D (only 28 days is tested).

Control series

Control series

Series

Series ““AA””

1 time injection sequencing sol A, sol B

Series

Series ““BB””

1 time injection with mixing nozzle

Series

Series ““CC””

As series “A” but 3 times injection

Series

Series ““DD””

As series “A” but only food (no bacteria)

Concrete carbonation vs. induced CaCO3precipitation

Best injection procedure? Several injection needed? Necessity of alkaliphilic bacteria     1 time injection, tap water Control series Control series Series Series ““AA”” 1 time injection sequencing sol A, sol B

Series

Series ““BB””

1 time injection with mixing nozzle

Series

Series ““CC””

As series “A” but 3 times injection

Series

Series ““DD””

As series “A” but only food (no bacteria)

Concrete carbonation vs. induced CaCO3precipitation

Best injection procedure? Several injection needed? Necessity of alkaliphilic bacteria     1 time injection, tap water

Figure 1: Experimental approach of the study

To assess the repair capacity of the system the bacteria-based solution is injected into porous cores, and the production of biominerals in time is monitored by X-ray micro-tomography. In parallel, water permeability test is conducted before and after the injection of the bacteria-based solution at regular time interval to determine the sealing efficiency of the system. When possible, sampling of the mineral is performed by gently scrapping the surface of the core and FTIR analysis is performed for identification. Finally, at the end of the healing period, polished sections of injected specimens are observed with ESEM/EDS to analyze and locate biominerals.

4. RESULTS

The results for water permeability test showed sparse data and no significant difference is observe between the series. However, the specimens are very porous, and based on theoretical calculations the maximum volume of CaCO3 which can be

formed in these conditions is less than 1% of the total porosity. This explains why the water permeability test results are not relevant in the present case.

Processing of CT-scan data showed that 3 days after injection ~6% of the material volume corresponds to new material. This percentage decreases to ~2% after 7 days and stays constant until 28 days. Even though bacteria start to grow within the first 24h, they cannot yet produce that high volume of CaCO3. This means that after 3

days mainly the solution that has been injected into the porous core is detected with this technique. With time the solution dries out so that its volume decreases. As a conclusion, it is very hard to distinguish between food (organic precipitates) and converted food (biominerals) with CT-scan analysis.

a b d c a b d c

Figure 2: ESEM pictures of polished sections – (a)  Series  “C”  at  21  days:  Ca-based mineral at the surface of cement matrix, (b) zoom in of (a), bacteria imprints in Ca-based minerals (pink arrows), (c) control  series  at  14  days,  (d)  series  “D”  at  28  days. Observations of polished sections with stereomicroscope and ESEM showed that for series containing food (A, B, C and D) the bonding between the epoxy and the specimen is not good (Figure 2a). Considering that during the preparation of the polished sections the grinding was performed with water and that each specimen has been in contact with the grinding paper and water for 45 min, it can be concluded that the food dissolved resulting in holes what then appears as bad bonding between epoxy and the matrix. However,   this   “de-bonding”   can   serve   as   indicator   of   the   presence of food, and help to locate CaCO3 formed due conversion of food by

For series “A”, small Ca-based crystals are observed 21 days after injection. After 28 days less debonding and more Ca-based crystals are noticed suggesting that their formation could be due to bacterial activity.

Similar observations are made for series “B”, and FTIR and DSC/TG analysis on precipitate scrapped from the edge of the specimen at 21 days showed that the precipitate is composed in majority of Ca-lactate, and to a lower extent (~10%) of Calcium carbonate which strongly suggest that bacteria are active at 21 days. However it seems that less crystals are formed in series “B” compared to series “A”. Observations for series “C” showed similar results as in series “A” but with a more pronounced debonding. This is explained by the fact that 3 injections have been made for series “C” compared to 1 for series “A” resulting in more food. Bacteria imprints are observed in different locations at 21 and 28 days (Figure 2a, b) and FTIR analysis confirmed the presence of CaCO3 in the scrapped precipitate. This

constitutes the evidence that bacteria are already active at 21 days leading to the formation of CaCO3.

Finally, the observations at 28 days of series “D” were similar to the control specimen besides some debonding, which is explained by the presence of the food (Figure 2c, d). This also means that in this case no bacteria induced CaCO3 formation is noticed

and therefore, alkaliphilic bacteria are an essential part of the system.

5. CONCLUSIONS

CT-scan results pointed out that this technique is not appropriate for this type of experiment as it is really hard to distinguish between food which has been initially injected and food which has been converted in CaCO3.

However, FTIR results coupled with thermal analysis and ESEM observations showed that CaCO3 has been formed in pores after 21 days, with increased amount

after 28 days. Moreover, evidence that CaCO3 precipitation was indeed mediated by

bacteria has been found with observations of bacteria imprints on Ca-based minerals. Finally, multiple injections of the solutions in sequence appear to be most efficient for CaCO3 precipitation.

It can be concluded that the bacteria-based repair system can successfully be injected as healing agent into porous network concrete. Nevertheless, the system needs to be further optimized in order to increase the CaCO3 formation capacity and

the crack healing efficiency should be assessed by injection into porous network concrete beams.

ACKNOWLEDGEMENTS

Authors would like to thank the Technology Foundation STW for the financial support for the project 11342 and the Ministry of National Education, the Government of the Republic of Indonesia for its financial support in the form of scholarship for S. Sangadji.

REFERENCES

[1] S. Sangadji, E. Schlangen, Self-healing of Concrete Structures - Novel approach using porous network concrete. Journal of Advanced Concrete Technology. 10 (2012) 185-194.

[2] V. Wiktor, H.M. Jonkers, Application of bacteria-based repair system to damaged concrete structures, Proceedings of the 2nd International Workshop on Structural Life Management of Underground Structures, Daejeon, 2012, pp. 31-34.