Using Carbon Dioxide as a Beneficial Admixture in Ready-Mixed Concrete

Transcription

1 NRMCA 215 International Concrete Sustainability Conference May 13, 215 Using Carbon Dioxide as a Beneficial Admixture in Ready-Mixed Concrete Sean Monkman CarbonCure Technologies, VP Technology Development Mark MacDonald CarbonCure Technologies, Director of Research Doug Hooton University of Toronto, Department of Civil Engineering 1

2 Cement Production And CO 2 Emissions 4%.65 t CO 2 6% Specific CO 2 emissions Calcination Clinker 865 kg CO 2e / t Cement 65 kg CO 2e / t.25 t additions Combustion 1.13 t Raw Material.75 t clinker.75 t clinker.1 t coal 2

3 Carbonation Of Freshly Hydrating Cement C3S (alite) + 3H 2 O 3Ca 2+ + SiO 2 + 6OH - C2S (belite) + 2H 2 O 2Ca 2+ + SiO 2 + 4OH - Ca(OH) 2 + H 2 O Ca OH - + H 2 O CO 2 (g) CO 2 (aq) CO 2 (aq) + H 2 O H 2 CO 3 (aq) H 2 CO 3 (aq) HCO - 3 (aq) + H + HCO - 3 (aq) CO -2 3 (aq) + H + Dissolution (Ca 2+ Supply) + CO 2 Dissociation (CO 3-2 Supply) = Ca +2 (aq) + CO 3-2 (aq) CaCO 3 (s) Precipitation (CO 2 Storage) 3

4 Schematic Of Gas Delivery System Integration With Ready-mix Truck Truck 2 - Mixing drum 3 - CO 2 tubing or water line 4 - Connec<on to gas supply 5 - Gas manifold 6 - Control box 7 - Telemetry 8 - CO 2 supply 4

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6 Trial summary Trial one o One truck o CO 2 applied at the wash rack, three doses. Trial two o Two trucks o CO 2 during batching and at the wash rack Tes<ng o Slump, temperature, isothermal calorimetry o Compressive strength (1, 3, 7, 28, 56, 91 days) o Resis<vity 6

7 Metrix Mix Design (kg/m 3 ) Cement, 212, 9% Slag, 53, 2% Sand, 959, 42% Stone, 18, 47% 25 MPa plain mix 2 mm aggregate 2% slag 7

8 Trial 1 outline Sample Code Condition Age at injection (min) CO 2 Dose (%bwc) Slump (inches) Mix Temperature ( C) 141 Control CO CO CO One truck, sequential dosing of CO 2 after the control specimen was taken. Slump was decreasing, temperature was increasing 8

9 Trial 1 Calorimetry - Power Normalized Power (a.u.) Control 141 CO2 142 CO2 143 CO Time After Mixing (hours) 9

10 Trial 1 Calorimetry - Energy Energy (J/g cement) Control 141 CO2 142 CO2 143 CO Time After Mixing (hours) 1

11 Trial 1 - Early compressive strength 3 Compressive strength (MPa) % 17% 117% 112% 126% 116% 16% 115% 1 day 122% 3 day 7 day Control CO2-1 CO2-2 CO Compressive Strength (psi) 11

12 Trial 1 - Later compressive strength 5 121% 7 Compressive strength (MPa) % 97% 15% 13% 28 day 115% 59 day Control CO2-1 CO2-2 CO Compressive Strength (psi) 12

13 Bulk Resistivity (Ω m) and Chloride Penetration Risk Test Age (days) Batch Control CO CO CO Control Moderate Low 142 CO2 Moderate Low The resistivity ranges as relating to chloride ion penetrability levels described in ASTM C122 suggest there was no change in the risk of chloride penetration 143 CO2 Moderate Low 144 CO2 Moderate Low 13

14 Strength benefit conclusions Age (days) Avg Control 142.1% CO % CO % CO2 1% 1% 1% 1% 1% 16% 19% 17% 18% 97% 115% 117% 112% 15% 13% 122% 126% 116% 115% 121% Strength benefit of last condition was maintained across the test period. Can the results be repeated? Is there more industrially viable approach? 14

15 Trial 2 outline Sample Code Condition Age at injection (min) CO 2 Dose (%bwc) Slump (inches) Mix Temperature ( C) 81 Control CO CO CO CO Sequential dosing of CO2 after the control was taken in first truck, dosing during batching in second truck. Slump was decreasing, temperature was increasing 15

16 Trial 2 Calorimetry - Power Normalized Power (a.u.) Control 81 CO2 82 CO2 83 CO2 84 CO Time After Mixing (hours) 16

17 Trial 2 Calorimetry - Energy 25 2 Energy (J/g cement) Control 81 CO2 82 CO2 83 CO2 84 CO Time After Mixing (hours) 17

18 Strength - CO2 during batching Compressive Strength (MPa) % 126% 121% 115% 118% Compressive Strength (psi) 1 day 3 day 7 day 28 day 56 day Test Age 18

19 Trial 2 - Early compressive strength 3 4 Compressive Strength (MPa) % 17% 16% 16% 112% 111% 1 day 18% 3 day 19% 7 day 115% Compresive Strength (psi) Control CO2-1 CO2-2 CO2-3 Batch 19

20 Trial 2 - Late compressive strength Compressive Strength (MPa) % 85% 13% 11% 116% 16% 28 day 17% 56 day 111% 91 day 17% Compresive Strength (psi) Control CO2-1 CO2-2 CO2-3 Batch 2

21 Strength benefit conclusions Age (days) 81 Control 82.1% CO2 83.3% CO2 84.6% CO2 85.3% CO % 1% 1% 1% 1% 1% 99% 17% 16% 14% 85% 13% 16% 112% 111% 11% 116% 16% 18% 19% 115% 17% 111% 17% 114% 126% 121% 115% 118% 115% Best results from CO2 during batching Resistivity results and chloride risk conclusions were reinforced 21

22 Mechanism Strength benefit associated with nano- CaCO 3 formation. Acceleration in calorimetry associated with nucleation Like an admixture, there are cement sensitivities Subject of further investigation 22

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24 Environmental Impact CO 2 utilization is modest, doses are small However a consistent strength benefit can o Allow a price premium on a stronger mix o Allow mix design optimization If the mix design is reformulated for increased SCM usage then the carbon footprint of the mix is decreased. 24

25 Durability Study Commenced Oct 214 Strength Compressive and flexural Exposure Freeze-thaw durability, salt scaling Chloride Permeability RCPT, bulk diffusion test Shrinkage Service life carbonation testing Abrasion testing 25

26 Durability Study Pore Solution Chemistry - ph Paste samples made specifically for pore solution expression. Carbonation had essentially no impact on ph. We do not necessarily expect increased corrosion potential due to CO 2 addition, even at 1.7% bwc. ph %.6% 1.% 1.5% 1.7% CO2 Uptake (%bwc) 26

27 Ready-mix pilot program 27

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29 Trial Feb 215 Design: 3 24 hrs and 6 28 days Compressive Strength (MPa) % 117% 113% 116% Control CO Test age (days) Compressive Strength (psi) 29

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