Concrete self-healing strategies Prof. dr. ir. Nele De Belie Magnel Laboratory for Concrete Research – Department of Structural Engineering I. DIFFERENT STRATEGIES FOR CONCRETE SELF-HEALING Magnel Laboratory for Concrete Research One of the “coolest” biomimetic applications: self-healing concrete Nature : not designed to withstand everything In case of failure : ‣ Rapid & autonomous detection ‣ ‘massive’ & efficient action ‣ “after” as strong as “before” ‣ ‘inexhaustable’ ‣ cheap Magnel Laboratory for Concrete Research 3 One of the “coolest” biomimetic applications: self-healing concrete Nature : not designed to withstand everything In case of failure : ‣ Rapid & autonomous detection ‣ ‘massive’ & efficient action ‣ “after” as strong as “before” ‣ ‘inexhaustable’ ‣ cheap Magnel Laboratory for Concrete Research 4 Strategies for concrete self-healing 1. Autogenous healing 2. Improved autogenous healing 3. Stimulated autogenous healing 4. Autonomous healing by bacteria 5. Autonomous healing by encapsulated polymers Magnel Laboratory for Concrete Research Strategies for concrete self-healing Autogenous healing (a) Crystallization: precipitation of CaCO3 (b) Blockage by impurities and products (c) Further hydration & pozzolanic activity (d) Expansion of C-S-H Autogenous healing © N. ter Heide & precipitation of CaCO3 Magnel Laboratory for Concrete Research Strategies for concrete self-healing Improved autogenous healing: fibre reinforcement to restrict crack width ECC (Victor Li): cracks < 60 µm Magnel Laboratory for Concrete Research Strategies for concrete self-healing Stimulated autogenous healing: hydrogels + fibres to limit crack width Enhance precipitation of CaCO3 Block cracks Stimulate further hydration Magnel Laboratory for Concrete Research Hydrogels or superabsorbing polymers Hydrogel swelling de-swelling Sealing of the crack Binder hydration, CaCO3 precipitation and healing 500 times their own weight (50 times own volume) Impression of swelling absorption by hydrogels (D. Snoeck, UGent) Magnel Laboratory for Concrete Research Hydrogels Magnel Laboratory for Concrete Research Strategies for concrete self-healing Stimulated autogenous healing: alkali activation Stimulate further hydration & pozzolanic activity Magnel Laboratory for Concrete Research Hydration of cement and slag in slag-blended pastes (E.Gruyaert) Scanning Electron microscopy (BSE) αcementt initial volume of cement - anhydrous volume cement at time t Pores CS(A)H (hydration products) initial volume of cement CH αslagt initial volume of slag - anhydrous volume slag at time t acement Unhydrated slag Unhydrated cement initial volume of slag 2 days 2 years CP0 55% 74% CP50 78% 94% CP85 28% 91% aslag 2 days 2 years CP50 28% 72% CP85 4% 39% Magnel Laboratory for Concrete Research Strategies for concrete self-healing Autonomous healing: bacteria Enhance precipitation of CaCO3 (Block cracks: carrier) Magnel Laboratory for Concrete Research Strategies for concrete self-healing Autonomous healing: encapsulated polymers Seal cracks completely (and restore mechanical properties) Magnel Laboratory for Concrete Research II. HYDROGEL STRATEGY SEALING AND SUBSEQUENT HEALING Ongoing PhD of Didier Snoeck Magnel Laboratory for Concrete Research Hydrogel swelling capacity in different solutions SAP B: a crosslinked potassium salt polyacrylate (∅ 476.6 ± 52.9 µm) - vacuum drying with silica gel - add fluid and filter after one day - determine retained water ΔV demineralised water [g / g SAP] 283.2 (±2.4) ΔV cement slurry [g / g SAP] 58.4 (±1.7) Swelling time [s] 120 Difference ΔV: 1) screening effect cations; 2) complex formation Ca2+ with carboxylate groups new cross-links Magnel Laboratory for Concrete Research 16 Experiments at the Neutron Line of PSI SNOECK D, STEUPERAERT S, VAN TITTELBOOM K, DUBRUEL P, DE BELIE N. (2012). Visualization of water penetration in cementitious materials with superabsorbent polymers by means of neutron radiography. Cement and Concrete Research, 42(8):1113-21. NEUTRA beam line at the Paul Scherrer Institute Magnel Laboratory for Concrete Research Self-sealing properties of SAP Self sealing of a cracked specimen SAP block the crack Possible to measure absorption of large SAP Swelling SAP Magnel Laboratory for Concrete Research Self-healing: Mortar sample composition polycarboxylate superplast PVA fibres (volume fraction Vf) SAP (1-2 m-% of cement) OPC: 571 kg/m³ FA: 685 kg/m³ Silica sand 0/2: 456 kg/m³ Water: 332 kg/m³ Stored at 20°C and 90% RH for 28 d Crack formation F/2 F/2 u F/2 F/2 Magnel Laboratory for Concrete Research 19 Overview of variable combinations Specimen prism cylinder Code REF P90 P60 B1 B90 B60 B2 REF B1 B2 Vf 2 2 2 2 2 2 2 1 1 1 m% SAP 0 0 0 1 1 1 2 0 1 2 Cracking 4 point bending 4 point bending 4 point bending 4 point bending 4 point bending 4 point bending 4 point bending Splitting Splitting Splitting Prisms: 160.40.15 mm³ Cylinders: ∅ 78 mm, height 20 mm Curing Wet/dry cycles RH > 90% RH = 60% Wet/dry cycles RH > 90% RH = 60% Wet/dry cycles Permeability Permeability Permeability Number 3 3 3 3 3 3 3 5 3 4 Curing for 28 d Repeat four-point bending test Magnel Laboratory for Concrete Research 20 Typical stress/strain curve Multiple cracking + strain hardening Preloading Bending stress [MPa] [2] Reloading 6 [3] [1] [8] [7] [9] 4 [4] [6] 2 [5] 0 0 Regain in stiffness = 1 2 Strain [%] 3 4 [5 6] [ 4 5] [0 1] [4 5] Regain in peak load = Regain first-cracking strength = [8 ] [ 4 ] [2] [ 4] Regain in multiple crack formation = [7 9 ] [1 3] Regain strength = [6] [1] Magnel Laboratory for Concrete Research 5 [7 ] [ 4 ] [1] [ 4] Bending ductility Multiple cracking enhanced by SAP Large ductility 7.5 mm thickness 9 mm vertical displacement Crack widths: 5-150 µm Bending ductility, 9 mm vertical displacement Magnel Laboratory for Concrete Research Regain of mechanical properties Wet/dry cycles: m% SAP ↑ → σfc ↓ healing ↑ Magnel Laboratory for Concrete Research Regain of mechanical properties Only with SAP: Healing at RH>90% and RH=60% ! Magnel Laboratory for Concrete Research Microscopic observations 0 µm < total closure < 30 µm < partial < 150 µm < no closure Wet/dry cycle without SAP 100 RH>90% with SAP RH=60% with SAP 60-90% RH without SAP Percentage closure [%] 80 60 40 20 0 0 50 100 150 Initial residual crackwidth [µm] Magnel Laboratory for Concrete Research 200 Self-healing of crack with SAP Before After Composition of white crystals? → ThermoGravimetric Analysis Self-healing of a 138 µm crack Hydration products Precipitation of CaCO3 Magnel Laboratory for Concrete Research Water permeability of healed samples decreases a lot by SAP addition m% SAP B ↑ coarsening of the matrix SNOECK, D., VAN TITTELBOOM, K., STEUPERAERT, S., DUBRUEL, P., DE BELIE, N. (2012) Self-healing cementitious materials by the combination of microfibres and superabsorbent polymers. Journal of Intelligent Material Systems and Structures, online. Magnel Laboratory for Concrete Research Water uptake in specimens Water uptake ↓ with SAP 18 REF - CRA Total water uptake [l/m²] 16 14 1B - CRA 12 1C - CRA 10 8 2C - CRA 6 REF - UNC 4 2 1C - UNC 0 0 0,5 1 1,5 2 Root of time [√(h)] Total water uptake after 4 hours and uptake in time Magnel Laboratory for Concrete Research III. MICROBIAL STRATEGY BIODEPOSITION OF CALCIUM CARBONATE Magnel Laboratory for Concrete Research Biotechnology in conservation Calcite Bioconcept Microbial deposition of a protective CaCO3 layer Magnel Laboratory for Concrete Research Mechanism of microbiologically induced carbonate precipitation Microbiology Precipitation parameters Metabolism [dissolved inorganic carbon] pH [Ca 2+ ] Cell wall nucleation site If [Ca 2+ ]*[CO32-] > Ks : precipitation occurs Magnel Laboratory for Concrete Research UGent research on concrete: Mechanism Example of a nitrogen conversion process: Hydrolysis of urea CO(NH2)2 + H2O Cell wall: Precipitation parameters CO32+ 2NH4+ [dissolved inorganic carbon] pH nucleation site Negatively charged De Muynck, W., Belie, N. & Verstraete, W. (2010). Microbial carbonate precipitation in construction materials: a review. Ecological Engineering, 36 (2), 118-136. De Muynck, W., Cox, K., Belie, N. & Verstraete, W. (2008). Bacterial carbonate precipitation as an alternative surface treatment for concrete. Construction and Building Materials, 22, 875-885. Magnel Laboratory for Concrete Research NH4+ CO32- UREA Magnel Laboratory for Concrete Research Precipitation of carbonate crystals Thin sections, SEM pictures of A) reference; biodeposition with B) CaCl2 and C) with Ca acetate Magnel Laboratory for Concrete Research Precipitation of carbonate crystals Microbial mediation of precipitation Magnel Laboratory for Concrete Research Bacteria for self-healing Carrier • porosity • pore size distribution • strength • compatibility Concrete activity survival (spores) workability strength PhD / postdoc of Jianyun Wang permeability Magnel Laboratory for Concrete Research Self-healing systems based on different carriers used + Wang, J.Y., Van Tittelboom, K., De Belie, N., Verstraete, W. (2012). Use of silica gel or polyurethane immobilized bacteria for self-healing concrete. Construction and building materials, 26, 532–540. Magnel Laboratory for Concrete Research 37 Porous carrier: Bacteria immobilized on diatomaceous earth (DE) Particle size: 4μm to 15μm Wang, J.Y., De Belie, N., Verstraete, W. (2012). Diatomaceous earth as a protective vehicle for bacteria applied for self-healing concrete. Journal of Industrial Microbiology and Biotechnology, 39, 567–577. Magnel Laboratory for Concrete Research 38 Specimens with DE immobilized bacteria and nutrients Influence on 28d strength 80 2 Tensile strength(N/mm) 2 Compressive strength(N/mm) 8 6 4 2 0 60 40 20 0 reference DE 5 DE 5N DE 5BN reference DE 5 DE 5N DE 5BN DE slightly increases the strength DE with bacteria and nutrients will not decrease the strength Magnel Laboratory for Concrete Research 39 Crack making (0.15mm~0.17mm) Immersion (40 days) H2O urea + Ca2+ Magnel Laboratory for Concrete Research 40 In water Partly filled crack In deposition medium Completely filled crack R DE5 DE5N DE5BN Magnel Laboratory for Concrete Research 41 •Water penetration resistance increased due to the precipitation specimen Aluminum foil water •Water absorption of the specimens with DE immobilized bacteria decreased 50% ~ 70%. 1 2 Water absorped (g/cm ) DE,W DE,M 0.8 DEBS,W DEBS,M 0.6 0.4 0.2 0 0 50 100 150 200 250 300 350 Time (h) Magnel Laboratory for Concrete Research 400 42 SEM SEM images of the precipitation in cracks of DE+BS Based on EDS, the precipitation was CaCO3 Magnel Laboratory for Concrete Research 43 IV = II + III Self-healing by bacteria encapsulated in hydrogels Hydrogel Distinct properties: 1) High water absorption and retention capacity; 2) Moisture uptake from the air; Magnel Laboratory for Concrete Research 44 Encapsulation process Bacteria Polymer solution wet-dry cycles 28d Test procedure 2% of cement (w/w) wet-dry cycles 28d Magnel Laboratory for Concrete Research 45 Bacterial spores keep viable after immobilization 25 Urea decomposed (g/L) After UV After UV+FG+VD After UV+FG After UV+FD+VD 20 urea decomposed after 48h by free spores urea decomposed after 48h 15 urea decomposed after 24h by free spores 10 urea decomposed after 24h 5 0 S H HY HU HYU HS HYS Magnel Laboratory for Concrete Research HUS HYUS 46 Healing with biohydrogel after 0, 7, 14 days Maximum crack width healed… With hydrogel only: 184μm With biohydrogel: 507μm Magnel Laboratory for Concrete Research 47 Crack healing ratio: (Wi-Wf)/Wi 100 90 Healing ratio (%) 80 70 R 60 N H 50 HYU 40 HYUC 30 HSYU 20 HSYUC 10 0 0-50 50-100 100-150 150-200 200-250 250-300 Initial crack width ranges (μm) 300-350 350-400 400-700 Crack healing ratio in the bacterial series was much higher compared with R series: (50% ~ 100%) / (1% ~ 7%) Magnel Laboratory for Concrete Research 48 SEM Hydrogel remains CaCO3 precipitation Magnel Laboratory for Concrete Research 49 X-ray Tomography (3D) Before After All Precipitation precipitation inside R Volume ratio: 0.5% R+ bio-hydrogel Volume ratio: 2.2% Magnel Laboratory for Concrete Research 50 V. CONCLUSIONS - hydrogels stimulate autogenous healing in fibre reinforced concrete; cracks of around 150 µm can be sealed immediately and then healed - with hydrogels, healing can be obtained without liquid water - CaCO3 precipitation by immobilized bacteria can provide autonomous crack healing, but bacteria need water to become active - hydrogels can be used to protect the bacteria and provide humidity; cracks of 500 µm can be healed in 14 days time Magnel Laboratory for Concrete Research SECEMIN Magnel Laboratory for Concrete Research 52 FP7 Marie Curie Action: Training network for self-healing materials: from concept to market FP7 NMP: Self-healing concrete to create durable and sustainable concrete structures Magnel Laboratory for Concrete Research 53 With special thanks to: PhD students and postdocs; technical staff; FWO, IWT, SIM-Flanders, BOF, EC for financial support Magnel Laboratory for Concrete Research
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