Early Carbonation of Concrete to Improve Sustainability and Durability

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1 Early Carbonation of Concrete to Improve Sustainability and Durability Yixin Shao Department of Civil Engineering McGill University Montreal, Quebec, Canada

2 Early Carbonation Technology Immediate (carbonation + rehydration) After preset (hydration + carbonation + rehydration)

3 Sustainable Concrete by Carbonation Emission reduction through carbon dioxide uptake during carbonation reaction CO 2 emitted from cement production will be used in concrete products through curing Improvement in durability of concrete Densification of surface by CaCO 3 Elimination of Ca(OH) 2 A durability solution

4 Cement Solution Carbonation 10g cement in 400g liter CO 2 /min ID Maximum possible CO 2 uptake in a cement solution carbonation Hydr ation (h) Carbon ation (h) Theoretical maximum (%) Experimental Mass gain Titration TG Average A ± ± ±0.3 A ± ± ±2.1 A ± ± ±1.0 A ± ± ±1.8

5 Precast concrete products Dry cast concrete (blocks, pavers, pipes) Zero slump with vibration compaction Cement=320kg/m 3 w/c=0.36 Fc = 40 MPa (28d) Wet cast concrete (beams, slabs) High slump (158 mm) with vibration cast Cement=450kg/m 3 w/c = 0.4 and SP/c = 0.5-1% Fc=80MPa (28d)

6 (I) Dry-cast concrete The carbonation curing procedure: Initial hydration (18h) Carbonation 5bar) Rehydration with water compensation (27d) CO 2 uptake=8-10%

7 Durability: Freeze-Thaw Cycling (ASTM C1262) Freeze-thaw cycle in 3% NaCl solution for 6h -18C and 18h 22C

8 Durability: Air Permeation

9 Durability: Ettringite Sulphate Attack (ASTM C 1012)

10 Durability: Thaumasite Sulfate Attack Cement paste 25mm-cubes (w/c=0.36) Hydrated OPC and PLC, carbonated OPC and PLC 18h hydration 4h carbonation - 27d rehydration Sulfate exposure condition: Fully submerged in 5% MgSO 4 solution at 4 C CO 2 content CaCO 3 content

11 6 months exposure 10 months exposure

12 Durability: Weathering Carbonation Shrinkage (Concrete)

13 average mortar bar expansion (%) Durability: Alkali Silica Reaction Effect of early carbonation curing on ASR expansion of mortar bar containing Spratt aggregates (ASTM C1260) CO2 uptake = 14% in 2h carbonation and 17% in 18h carbonation reactive above 0.20 % inconclusive zone between 0.10 % non-reactive up to 0.10 % age (d) moist reference dry reference 2h carbonation at 1 bar 18h carbonation at 1 bar max innocuous limit (%) min deleterious limit (%)

14 (II) Wet-cast concrete The carbonation curing procedure: In-mold initial hydration (5h) Demold fan drying (5h) Carbonation 5bar) Rehydration in moisture room (27d) CO 2 uptake=12-14%

15 Compressive strength

16 Mass loss due to corrosion Effect of carbonation on Rebar corrosion: After 50 cycles One cycle (7d): 3d in 3.5% NaCl solution 4d oven

17 Chloride content after 50 cycles One cycle (7d): 3d in 3.5% NaCl solution 4d oven 60C

18 ph Distribution in Carbonated Concrete PH distribution CO 2 uptake: 14% PH recovers after 28 days subsequent hydration Carbon content reduces along depth Region Depth 1-day ph 28-day ph CO 2 Uptake I 0~10mm % II 10~20mm % III 20~30mm % IV 30~50mm %

19 Pore volume and size (MIP) Cement paste at 1 year 13% 22% 7nm 20nm Porosity Pore size

20 Pore size distribution Cement paste at 1 year

21 Surface resistivity (AASHTO TP95)

22 Full-scale carbonation blocks Carboclave process for blocks curing Boehmers block plant in Ontario, Canada 5 autoclaves are turned into 5 carboclaves (0.5 bar) CO 2 is a recovered gas from ethanol production Daily capacity: 25,000 blocks

23 Carbonated Blocks NW NW-25% NW-HS Compressive strength, 1-day, (MPa) Autoclave 26.3 ± ± 4.1 Carboclave 36.2 ± ± ± 4.5 Carbon dioxide uptake, (%) Carboclave Carbon dioxide uptake per block, (g) Carboclave NW: Normal weight blocks NW-25%: Normal weight blocks with 25% GGBF slag NW-HS: Normal weight high strength blocks

24 Carbonation in a non-pressure chamber Steam strength=17mpa, Carbonation strength=37mpa Carbon dioxide uptake=200g/block

25 Conclusions Early carbonation technology can be used to reduce carbon emission and improve concrete durability. For concrete carbonation, the CO 2 uptake can reach 10-30% based on cement content. Carbonation-cured concretes are more resistant to freeze-thaw cycling, sulfate attack, weathering shrinkage, ASR expansion and chloride penetration. Carbon dioxide captured from cement kiln can be beneficially utilized in concrete carbonation curing to have a closed-loop production.