Bio-based repair method for concrete

Abstract

The invention provides a process for the bio-based reparation of a concrete element having an element surface with cavities, comprising applying a first liquid with a first composition and a second liquid with a second composition to the element surface of the concrete element to provide a combined product to the cavities, wherein the first composition and the second composition are selected to provide gel formation in the cavities after application of one or more of the first liquid and the second liquid to the element surface, wherein the first composition and the second composition are also selected to provide bacterial material, a calcium source, and a nutrient for bacteria in the cavities after application of the first liquid and the second liquid to the element surface, wherein the first liquid at least comprises sodium silicate and wherein the second liquid at least comprises the calcium source.

Claims

1. A process for the bio-based reparation of a concrete element having an element surface with cavities, the process comprising applying a first liquid with a first composition and a second liquid with a second composition to the element surface of the concrete element to provide a combined product to the cavities, wherein the first composition and the second composition are selected to provide gel formation in the cavities after application of one or more of the first liquid and the second liquid to the element surface, wherein the first composition and the second composition are also selected to provide bacterial material, a calcium source, and a nutrient for bacteria in the cavities after application of the first liquid and the second liquid to the element surface, wherein the first liquid at least comprises sodium silicate in an amount of 0.5-20 wt. %, wherein the second liquid at least comprises the calcium source, wherein the nutrient comprises (i) a nitrate compound, (ii) a yeast extract, and (iii) one or more of a lactate and a gluconate, and wherein both the first liquid and the second liquid comprise water.

2. The process according to claim 1, wherein the molar ratio between silicate and calcium is in the range of 0.05-5.

3. The process according to claim 1, wherein the first liquid comprises sodium silicate in an amount of 0.5-20 wt. %, wherein the first liquid has a pH of at least 11, and wherein the second liquid comprises calcium nitrate in an amount of 10-75 wt. %.

4. The process according to claim 1, wherein the second liquid comprises calcium nitrate.

5. The process according to claim 1, wherein first the first liquid comprising the sodium silicate is applied to the element surface and subsequently the second liquid comprising the calcium source is applied to the element surface.

6. The process according to claim 1, wherein the bacterial material is selected from the group consisting of a bacterium, a lyophilized bacterium and a bacterial spore of a bacterium.

7. The process to claim 6, wherein the bacterium is selected from the group consisting of aerobic bacteria and anaerobic bacteria.

8. The process according to claim 6, wherein the bacterium is selected from the group consisting of bacteria that can form a phosphate or a carbonate precipitate in an alkaline medium.

9. The process according to claim 6, wherein the bacterium is selected from the group of genera consisting of Planococcus, Bacillus and Sporosarcina.

10. The process according to claim 6, wherein the bacterium is a denitrifying bacterium.

11. The process according to claim 1, wherein the second liquid is applied to the element surface within 0.5 h after applying the first liquid to the element surface, or wherein the first liquid is applied to the element surface within 0.5 h after applying the second liquid to the element surface.

12. The process according to claim 1, wherein the first liquid and the second liquid are applied to the element surface by spraying the liquids on the element surface.

13. The process according to claim 1, wherein the element is comprised by a building or a civil engineering structure.

14. The process according to claim 3, wherein the second liquid comprises calcium nitrate in an amount of 25-55 wt. %.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings in which corresponding reference symbols indicate corresponding parts, and in which:

(2) FIG. 1 schematically depicts some aspects of the invention. The drawing is not necessarily on scale.

(3) FIGS. 2-4 shown ESEM (Environmental Scanning Electron Microscope) and EDS (Energy Dispersive X-ray Spectrometry (EDS)) graphs of some results of the method of the invention:

(4) FIG. 2: ESEM observation of a polished section of concrete beam treated with (A) bacteria-based solutions, and (B) tap water (control), as well as a polished section of concrete beam treated with bacteria-based solutions, after reloading;

(5) FIG. 3a-3c: ESEM observation of the polished section (location deeper in the crack compared to FIG. 2);

(6) FIG. 4: Elemental analysis (EDS) of the mineral formed along the crack wall;

(7) FIG. 5: Effect of curing condition on the repair efficiency, with PD indicating the permeability decrease;

(8) FIG. 6: Comparison of the sealing efficiency of the repair system with and without extra calcium in its composition. NC refers to no Ca.sup.2+ in the repair solution and C refers to Ca.sup.2+ in the repair solution with PD indicating the permeability decrease;

(9) FIG. 7: Influence of sequence order on the crack-sealing efficiency of the bio-based repair system, with PD indicating the permeability decrease.

(10) FIG. 8: Comparison of the durability of the repair with calcium lactate and calcium nitrate. The permeability is tested by measuring the permeability decrease (PD). The two left bars indicate the first test and the two right bars the second test. Ca-L refers to the presence of calcium lactate in the repair solution and CaN refers to calcium nitrate in the repair solution;

(11) FIG. 9: Quantification by thermogravimetry of calcium carbonate produced in the repair system with calcium acetate or calcium nitrate as calcium source. The CaCO.sub.3 production (PCaCO.sub.3) was measured with either calcium acetate (Ca-A) or with calcium nitrate (CaN) as calcium source;

DETAILED DESCRIPTION

(12) FIG. 1 schematically shows embodiments and variants of a process for the bio-based reparation of a concrete element 200 having an element surface 210 with cavities 220. The process comprises applying a first liquid 111 with a first composition and a second liquid 112 with a second composition to the element surface 210 of the concrete element 200 to provide a combined product to the cavities. As indicated above, the first composition and the second composition are selected to provide gel formation in the cavities 220 after application of one or more of the first liquid 111 and the second liquid 112 to the element surface 210. As also indicated above, the first composition and the second composition are also selected to provide bacterial material, a calcium source, and a nutrient for bacteria in the cavities 220 after application of the first liquid 111 and the second liquid to the element surface 210, wherein the first liquid 111 at least comprises the sodium silicate and wherein the second liquid 112 at least comprises the calcium source.

(13) To this end, a kit of parts 100 may be provided, comprising a first container 110 and a second container 120, wherein the first container 110 contains a silicate, especially sodium silicate, and wherein the second container 120 contains a calcium source, such as calcium nitrate, wherein one or more of the containers further contain bacterial material and a nutrient for bacteria. Optionally, more containers can be used. For instance, such further container(s) may comprise bacterial material and a nutrient for bacteria. FIG. 1 schematically depicts two variants. For instance, the kit of part may already contain liquids in the containers, which can directly be applied to the element surface 210, for instance by spraying and/or coating. In an alternative variant, the containers contain dry material, or very viscous material, and the contents of the containers are to be combined with liquid, such as water (indicated with the arrow with H.sub.2O). This can in an embodiment be added to the containers. However, alternatively the content of the containers is provided to further containers to which the liquid is added. Note however that before applying to the element surface 210, the components are not mixed in such a way that the calcium source and the silicate are in the same liquid. At least two liquids, the first liquid 111 and the second liquid 112, and optionally further liquids, are applied to the element surface 210, wherein one or more liquids contain the sodium silicate and one or more other liquids contain the calcium source. The other ingredients, i.e. the nutrient and the bacterial material can be available in one or more of the containers. The first liquid may be applied first to the cavity/cavities 220, and thereafter the second liquid, or the other way around, or simultaneously.

EXAMPLES

Experiment 1

Injection of Bacteria-Based Solution in Cracked Concrete Beam

(14) Aim of the test: Evaluation of the crack repair efficiency of bacteria-based repair system

(15) Description: Optimized repair solution is used in this experiment; calcium nitrate replaces calcium lactate as source of calcium in solution B.

(16) The system is therefore composed of (see also the table below):

(17) Solution ASodium-silicate 34.9%48.5 g/L (alkaline buffer), Sodium-gluconate125 g/L (Carbon source for bacteria growth), yeast extract1 g/L (vitamins essential elements for bacterial growth), alkaliphilic bacteria1.610.sup.8 spores/L. Solution BCalcium-nitrate500 g/L (Nitrate source for bacteria growth using denitrification pathway and Calcium for CaCO.sub.3 precipitation), yeast extract1 g/L (vitamins essential elements for bacterial growth), alkaliphilic bacteria1.610.sup.8 spores/L.

(18) TABLE-US-00001 Ingredient Concentration (g/L) Solution A - Na-gluconate + Na-silicate Na-gluconate 125 pH = 11.5 Na-silicate 34.9% 48.5 Yeast extract 1 Bacterial spores 8 10.sup.8 spores/g powder --> (powder) 0.2 1.6 10.sup.8 spores/L Solution N - Ca-Nitrate Ca-Nitrate 500 pH = 6 Yeast extract 1 Bacterial spores 8 10.sup.8 spores/g powder --> (powder) 0.2 1.6 10.sup.8 spores/L Solution A - Concentration Silicate = 0.139 mol/L Solution N - Concentration Ca.sup.2+ = 2.12 mol/L

(19) Eight porous network concrete beams are used for this experiment as follow: 4 beams for control with 1 tap water injection, 2 are cured in wet chamber (RH=95%) and 2 in dry atmosphere (lab, RH=25%) 4 beams to be injected 1 time with optimized bacteria-based solution, 2 are cured in wet chamber and 2 in dry atmosphere (lab) during the repair. Initial loading of the beams is performed to induce a crack. Water permeability test is performed after cracking of the beam and 28 days after injection. The repair of the crack is monitored weekly by observation with stereomicroscope. After 28 days, 1 replicate of each series is re-loaded to assess mechanical properties recovery and further prepared for polished section. The other replicate is kept for further curing and a final permeability test is performed after 100 days.

(20) The recovery of the beam properties (sealing, initial stiffness and ultimate strength) 28 days after repair was determined. The recovery % is calculated according to equation (eq. 1):

(21) $\begin{array}{cc}\mathrm{Recovery}\left(\%\right)=\frac{\mathrm{Xf}-\mathrm{Xi}}{\mathrm{Xi}}*100& \left(\mathrm{eq}.1\right)\end{array}$ Where Xf=value after 28 days (permeability, stiffness or strength) Xi=initial value, before repair (permeability, stiffness or strength)

(22) The results showed that the control exhibits only a limited decrease in the permeability value while the crack is completely sealed after the treatment with the bacteria-based system. It was also observed that the recovery of the initial stiffness is better for the specimen treated with the bacteria-based solutions, according to the invention, suggesting a good cohesion of the repair material with the initial mortar matrix. Less clear conclusion can be drawn from the results of ultimate strength as the beams used are reinforced with a steel bar. Therefore, in that case we are not testing the concrete itself but more the loading capacity of the steel bar. The evaluation of the repair efficiency with CaNO3 as calcium source is indicated in the table below, with the values indicating the recovery efficiency:

(23) TABLE-US-00002 Sealing Initial stiffness Ultimate strength Control 8.91 45.23 80.42 Bacteria-based system 100 93.11 88.12

(24) The observation of polished sections after reloading of the beam is presented on FIG. 2. Calcium-based mineral, most probably calcium carbonate, along the crack wall can be observed. It should be stressed that the crack has been re-opened due to the reloading of the beam. However, this observation combined with results from water permeability test suggests that the newly formed mineral indeed bridged the crack. In addition, ESEM observations of the control specimen show that the crack remains empty (see FIGS. 3a-3b).

(25) FIG. 3c presents the ESEM observation of the polished section deeper in the crack. It can clearly be seen that Ca-based mineral is formed on top of the mortar matrix (along the crack wall). Elemental analysis of this mineral is shown in FIG. 4. We also noticed the presence of less dense material mainly composed of calcium and silicon. This can be attributed to the gel which is formed upon the mixing of solution A and solution B and also takes part in the repair of the crack.

(26) Further, FIG. 5 depicts the effect of curing condition on the repair efficiency. The results show that the curing condition seems to have no effect on the repair with the bacteria-based solution; while the permeability decrease for the control is significantly improved when the specimen is exposed to high relative humidity. This is due to higher carbonation rate of the concrete. References i-ii refer to a control and references iii-iv refer to a test with bacteria; references i and iii refer to 25 relative humidity (RH-25%) and references ii and iv refer to a relative humidity of 95% (RH-95%). However, the observation of polished sections after reloading of the control beam cured in wet conditions (95% RH) shows an empty crack. The decrease in permeability could then be attributed a high carbonation rate at the interface porous core/concrete matrix, which decrease somehow the crack width at that location. On the other hand, the ESEM pictures of the specimen treated with the bacteria-based solution and cured in the same environment (95% RH) shows significant mineral production along the crack wall.

(27) Conclusion: It can be concluded that the treatment with the bacteria-based repair system significantly improved the material properties, especially in term of crack sealing as after 28 days no leaking of the crack is observed. Moreover, evidence that the crack sealing is indeed due to Ca-based mineral formed in the crack has been found with ESEM observation of cross section of the crack. Newly formed mineral is observed along the crack wall for the specimen treated with bacteria-based solution, while for the control specimen the carbonation results in the formation of calcium carbonate within the concrete matrix.

Experiment 2

Evaluation of the CaCO3 Production Capacity and Determination of the Optimum Silicate/Calcium Ratio

(28) Aim of the test: Fine tuning of the optimum silicate/calcium molar ratio in combination with kinetic and quantification study of CaCO.sub.3 production.

(29) Description: Solutions with various Silicate/Ca molar ratios (0.2<NaS/Ca<0.5) are prepared (NaS is sodium silicate).

(30) TABLE-US-00003 concentration salt in NaS in molar ratio NaS/Ca Calcium salt solution N solution A 1:5 1:4 1:3 1:2 Ca-nitrate 500 g/L 48.5 g/L 1n 2n 3n 4n [Ca(NO.sub.3).sub.25H.sub.2O] Time 1 week -w 1 -w 1 -w 1 -w 1 2 weeks -w 2 -w 2 -w 2 -w 2 4 weeks -w 4 -w 4 -w 4 -w 4 6 weeks -w 6 -w 6 -w 6 -w 6 8 weeks -w 8 -w 8 -w 8 -w 8

(31) The pH and the oxygen concentration in solution are monitored first daily and then weekly to follow the bacterial activity. In parallel solutions are weekly sampled and observed with light microscope to detect biomineral formation.

(32) After 1, 2, 4, 6, and 8 weeks the precipitate & gel is separated by filtration on a sintered-glass filter (pore size 10-16 m), washed with demi-water, dried at 35 C., grinded, weight and further analyzed with FTIR and DSC/TG for identification and quantification respectively.

(33) In case of significant CaCO.sub.3 formation, the precipitate will be analyzed with ESEM to possibly observe bacteria imprints.

(34) Results: From the evolution of the oxygen concentration in solution and the pH respectively as a function of time and silicate/calcium molar ratio it can be seen that the oxygen concentration in solution decreases faster as the silicate/calcium ratio increases suggesting that higher ratio promotes bacteria activity. This can be also correlated with the higher pH value for higher silicate/calcium molar ratios. Moreover, for a same ratio the pH remains constant over 7 days, this means that the system is well buffered due the presence of silicate.

(35) The observation with light microscope shows the mineral formation increases with the silicate/calcium molar ratio. This result combined with the oxygen measurements suggests that the mineral is formed due to bacterial activity.

(36) The infrared results combined to thermal analysis show the presence of amorphous calcium carbonate which tends to progressively crystallize into calcite after 2 weeks. Moreover, the structure of the calcium-silicate hydrates is less ordered at 2 weeks compared to 1 week, which could mean that calcium ions can be more accessible for CaCO.sub.3 precipitation.

(37) Conclusion: The results showed that the silicate/calcium ratio has great influence on the mineral formation kinetic, and also probably on its production capacity suggesting the existence of an optimum ratio for the bio mineral formation.

Experiment 3

Experimental Evidence that Extra Calcium (in the Feed) Works Better than the Calcium of the Concrete Alone

(38) The purpose of introducing calcium in the feed in the composition of the repair system is twofold: First, it ensures, by chemical reaction with the silicate compound in solution A (i.e. the solution comprising sodium silicate), the formation of a gel inside the crack or the porosity of the concrete-based material. This gel allows a rapid sealing of the crack (within few hours) and optimum environment for bacteria to precipitate calcium carbonate. This is a relevant feature of this system and is of importance as the bacterial induced precipitation alone is a rather slow process (several weeks). By the time the gel becomes too weak, substantial amount of calcium carbonate has been precipitated by bacteria to seal the crack or fill the porosity of the material. Second, it ensures that enough calcium is available and distributed within the whole crack volume or porosity of the concrete-based material for the formation of substantial amount of calcium carbonate (sealing/filling mineral).

(39) Besides the necessity of extra calcium for the gel formation, to show that calcium of the concrete alone is not enough for a good repair, the crack sealing efficiency of the repair system with and without extra calcium has been compared. The crack sealing efficiency is reflected by the difference in water permeability before and 28 days after application of repair system.

(40) The results have shown (FIG. 6) that when no calcium (NC) is added in the composition of the repair system, the crack is only partially sealed with a water permeability decrease of 68%. On the other hand, when extra calcium (C) is added in the repair system the crack is fully sealed as the permeability decreased 100% meaning that the crack was not leaking anymore and that substantial amount of filling material has been produced.

Experiment 4

Impregnation of an Element

(41) The repair system is composed of two solutions: Solution A, silicate-based solution having an alkaline pH (>10) Solution B, Calcium-based solution exhibiting a pH of 4-6.

(42) If solution B is first applied on the concrete-based material, which is alkaline (pH>9), it may lead first to a rapid deterioration of the material due to the rapid dissolution of the hydrates of the cement paste. Indeed, the pH difference between solution B and the concrete-based material is such that application first of solution B instead of solution A might be similar to an acid attack.

(43) For this reason, solution A, which has a similar pH to the concrete-based material, may especially be applied first. Then when solution B is applied right after, it reacts immediately with solution A forming a gel. As the silicate-based compound also acts as a buffer, the pH after reaction with solution B remains alkaline. Therefore the repair system applied in this sequence is not detrimental for the concrete-based material while the reverse order would be.

(44) The effect of the sequence was also tested. FIG. 7 compares the crack-sealing efficiency of the repair system when solution A (silicate-based solution having an alkaline pH (>10)) or solution B (Calcium-based solution exhibiting a pH of 4-6) is applied first. The initial water permeability is measured before application of the repair system. Another test is performed 2 weeks after application of the repair system on cracked concrete specimen. The permeability decrease after permeability test 1 is calculated as follow:

(45) $P_{\mathrm{decrease}}\left(\%\right)=\frac{P_0-P_1}{P_0}100$

(46) Where P.sub.0 is the initial permeability value (before application of the repair system), and P.sub.1 is the permeability value of permeability test 1 (after application of the repair system).

(47) The results show that the water permeability was reduced of at least 77% 2 weeks only after application of the repair system. Similar crack-sealing efficiency is observed when solution A is applied first or when solution B is applied prior to solution A.

Experiment 5

The Advantages of Calcium Nitrate Over Other Calcium Sources

(48) The advantage of calcium nitrate over other calcium sources is double: First, calcium nitrate is a highly soluble salt. Therefore, far more calcium can be added to the repair system when calcium nitrate is used compared for instance to calcium acetate and calcium lactate which are respectively 3.5 and 15 less soluble in water. Second, nitrate can also be used by the bacteria (denitrification) to mediate calcium carbonate precipitation when oxygen is limited as for instance deep inside a crack.

(49) The advantage of calcium nitrate over other calcium sources, such as calcium lactate or calcium acetate, has also been shown experimentally through water permeability test (FIG. 8) and quantification of calcium carbonate produced in the repair solution (FIG. 9). In each case, better performance of the repair system is obtained when calcium nitrate is used as calcium source.

(50) FIG. 8 compares the crack-sealing efficiency of the repair system with calcium lactate or calcium nitrate. The water permeability test 1 (left) is performed after application of the repair system on cracked concrete specimen. Another water permeability test (test 2) (right) is performed on the same specimens two weeks at least after the permeability test 1 to evaluate the durability of the repair. The crack sealing efficiency is reflected by the permeability decrease as 100% of decrease in the permeability value means that no water is dripping from the crack and therefore that the crack is completely sealed. If the permeability decrease is <100%, then the crack is only partially sealed as water can still drip from the crack.

(51) The permeability decrease after permeability test 1 is calculated as follow:

(52) $P_{\mathrm{decrease}}\left(\%\right)=\frac{P_0-P_1}{P_0}100$

(53) Where P.sub.0 is the initial permeability value (before application of the repair system), and P.sub.1 is the permeability value of permeability test 1 (after application of the repair system).

(54) The permeability decrease after permeability test 2 is calculated as follow:

(55) $P_{\mathrm{decrease}}\left(\%\right)=\frac{P_0-P_2}{P_0}100$

(56) Where P.sub.0 is the initial permeability value (before application of the repair system), and P.sub.2 is the permeability value of permeability test 2 (2 weeks at least after permeability test 1).

(57) The results show that, when calcium lactate is used as calcium source in the composition of the repair, the crack appears to be completely sealed after permeability test 1 but is leaking again after permeability test 2. The complete sealing of the crack in permeability test 1 is probably due to the gel formation while after permeability test 2, the gel has become weaker and not enough calcium carbonate has been precipitated by bacteria to fully seal the crack.

(58) On the other hand, with calcium nitrate more calcium is brought to the system which results in more calcium carbonate being formed. This is reflected by 100% in permeability decrease in test 1 and test 2.

(59) The amount of calcium carbonate which can be produced in the repair system when calcium nitrate or calcium acetate is used has been quantified by thermogravimetric analysis. The results (FIG. 9) show that 60 mg of calcium carbonate is produced with calcium nitrate while it is 4 times less with calcium acetate (14 mg). From the other experiments, it is learned that the use of calcium nitrate is better than calcium lactate. From this experiment it is learned that the use of calcium nitrate is better then the use of calcium acetate. Hence, especially at least calcium nitrate is available in the repair solution.