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Sustainability – Going Green
Thomas Van Dam, Ph.D., P.E.Principal
Annual Concrete Conference 2021Thursday, December 9, 2021
Suddenly, Sustainability Is All The Rage• Politicians come and go, but scientific facts
remain– The Arctic continue to melt and sea levels are rising– As I write this, it is snowing hard in the U.P.
• The Biden administration is emphasizing climate change and social equity– Climate change is a focal point in infrastructure bill
• Sustainable solutions are of increasing interest to governmental agencies and industry
• Sustainability is important in Minnesota
Climate Change• Changes in global climate from human
activities are occurring– Supported by historical observation and climate
modeling• Optimistic models predict substantial climate
change over the next century– Rate of change dependent on human activities– Long life of emitted heat-trapping, greenhouse
gases and slow feedback functions of atmospheric systems drive climate change
Certainty“It is unequivocal that human influence has warmed the atmosphere, ocean and land. Widespread and rapid changes in the atmosphere, ocean, cryosphere and biosphere have occurred”
IPCC, 2021: Summary for Policymakers. In: Climate Change 2021: The Physical Science Basis
UncertaintyThe degree of change is uncertain as many variables are important and as yet, undefined
Changes in Global Surface Temperatures Relative to 1850-1900 (IPCC 2021)
IPCC, 2021: Summary for Policymakers. In: Climate Change 2021: The Physical Science Basis
Global Surface Temperature Increases Compared to 1850-1900
IPCC, 2021: Summary for Policymakers. In: Climate Change 2021: The Physical Science Basis
Projected Sea Level Rise
The Sustainability Triple Bottom LineSustainable practices are simply good engineering
And not just GHG emissions or environmental impacts
Sustainable Solutions Require Life-Cycle Thinking
Long-life designOptimized design
Reduced energyBlended cementsAlternative cements
EfficiencyCaCO3 mineralization
Work together tominimize GHG emissions
RecyclingCarbonation
Challenges In Front of Us• Change is difficult
– Must ween ourselves from business as usual• Traditional cement and concrete are
carbon intensive• Designs and materials are dictated by past
experience and “conservatism” in codes and specifications
DON’T BE SAD – INNOVATE!
There is Hope!• New policies and initiatives are focused on
sustainability– New infrastructure bill– State and local initiatives
• The cement and concrete industry is focused on change– PCA’s Net Zero by 2050– ACI, ASTM and others
• Organizations and associations are responding to the need to innovate– ACPA, APWA, ASCE, etc.– Others (e.g., Breakthrough Energy)
What Can We Do?
• Stay educated – This is really important• Adopt life cycle thinking• Wise use of materials• Consider the use phase • Verification
What Can We Do? A LOT!
Hydraulic Cement and Concrete Mixtures• Hydraulic cement concrete is humankind’s most
used material after water– Approximately 1 yd3/person/year– Civilization is built on it– 5%-8% of global GHG emissions
• Large economic, environmental, and social impacts– 88.5 million metric tons of cement manufactured in
the U.S. in 2019– In 2018, linked to 0.6% of US GHG emissions
Materials and Mixtures• Material extraction, production, transportation• Mixture batching and concrete plant operations• Focus is often on cradle to gate
– Assumption is long-life is not compromised
GHG Emissions Associated With Concrete at the Gate• ~1.5% from acquiring and processing raw
materials• ~89% from cement manufacturing
– ~37% from burning fuel– ~46% from calcination
• ~9.5% from making concreteNet result: for every pound (kg) of U.S. made typical
ASTM C150 Type I cement, about 0.94 lbs (kg) of GHG emissions are released
Total GHG Emissions Embodied in Concrete
Typical concrete at the gate:0.26 tons CO2 /yd3 concrete0.23 tons CO2 from portland cement
Cement
GravelSandWater
Elements of PCA’s Net Zero by 2050• Clinker optimization
– Production enhancements– Sequestration
• Cement optimization– Blended portland cements– Alternative cements
• Concrete optimization– Reduced cementitious materials content– Longevity
• In-service and end-of-life carbonation– For structural concrete, small but still significant
Clinker Optimization• Reduce GHG emissions during production
including– Make kilns super efficient– High efficiency grinding mills– Fuels including waste fuels and plasma
• Carbon dioxide sequestration– Kiln flue gas has high CO2 concentration…typically
about 25 mol% vs 14% for coal-fired power plant vs 0.033% in atmosphere
– Excellent opportunity to sequester CO2
Cement Optimization• Replace clinker with supplementary
cementitious materials (SCMs)– Obtained as blended cement (ASTM
C595)– Blend at concrete plant
• Replace clinker with ground limestone– ASTM C595 Type IL blended cement
can have up to 15% limestone– On-going work to look at higher
limestone content
Supplementary Cementitious Materials (SCMs)• Fly ash
– Collected from flue gases of coal burning power plant
• Slag cement– From iron blast furnace
• Natural pozzolan– Calcined clay, volcanic ash,
ground pumice, etc.
Alternative SCMs• Reclaimed coal ash
– From landfills and ponds– Mix of fly ash and bottom ash– Often requires processing
• Ground glass pozzolan• SCM produced from carbon dioxide
sequestration
ASTM C595 Blended Cements
• Produced by cement manufacturers• Type IP(X), Type IS(X),
and Type IT (X)(Y)– Blended with pozzolan, slag cement,
limestone or ternary blend• Type IL will reduce carbon footprint by 8 to 10
percent with little impact on behavior• Can be designated as moderate sulfate
resistance (MS), high sulfate resistance (HS), moderate heat (MH), or low heat (LH)
LC3 Cement
LC3 is a family of cements,the figure refers tothe clinker content
• 50% less clinker• 40% less CO2• Similar strength• Better chloride resistance• Resistant to alkali silica reaction
0
20
40
60
80
100
PC PPC30 LC3-50 LC3-65
Mas
s pro
port
ion
(%)
GypsumLimestoneCalcined clayClinker
0
10
20
30
40
50
60
70
Com
pres
sive
stre
ngth
(MPa
)
1 day
7 days
28 days
90 days
K. Scrivener, 2020
PC LC3-50
Alternative Cements• Alternative cements are available
– e.g., calcium sulfoaluminate cements, calcium aluminate
– Alkali-activated hydraulic cements– Geopolymers
• Specialty applications• No scenario exists in which sufficient
alternative cements are available for large-scale replacement of portlandcement Provis, van Deventer, 2014
Reduce Cementitious Content in Concrete• Maximize aggregate content through use of optimized aggregate grading
Tarantula curved based on Tyler Ley et al.
Common Fallacy: Increasing Cement Content Does Not Increase Strength
Based on Taylor and Wilson
Real Data from Project NEON
0
100
200
300
400
500
600
700
800
900
06/14/17 08/03/17 09/22/17 11/11/17 12/31/17 02/19/18 04/10/18 05/30/18 07/19/18 09/07/18 10/27/18
3-Da
y Av
erag
e Fl
exur
al S
tren
gth
(psi)
Date Placed
3-Day Average Flexural Strength
AE532 AE703FA• 500 pcy• 611 pcy
Project NEON Concrete
0
200
400
600
800
1000
1200
1400
1600
06/14/17 08/03/17 09/22/17 11/11/17 12/31/17 02/19/18 04/10/18 05/30/18 07/19/18 09/07/18 10/27/18
28-D
ay A
vera
ge F
lexu
ral S
tren
gth
(psi)
Date Placed
28-Day Average Flexural Strength
AE532 AE703FA
Reducing GHG Emissions by Minimizing Cement Content and Increasing SCMs
376
564
0
100
200
300
400
500
600
0 25 50Percent Replacement with SCMs
Poun
ds C
O2/
yd3
What About CO2 Sequestration Through Carbonation?• It is a real thing• Anderson, et. al. 2019. “Carbonation as a
method to improve climate performance for cement based materials.” Cement and Concrete Research (2019)
• Paper quantifies uptake of CO2 by concrete through carbonation– Ca(OH)2 + CO2 →CaCO3 + H2O– C-S-H also undergoes carbonation– Uses Fick’s law
How Much Carbonation Occur in a Typical U.S. Concrete?• Depends on exposure and quality of concrete
– Is climate wet or dry? Is it exposed to rain?
• Quality of concrete– In the paper is related to strength, but it is permeability that matters– Related to w/cm
• In general, dry concrete that is permeable (low strength) will have a higher degree of carbonation than wet concrete that has low permeability (high strength)
Applying This to a Typical U.S. Pavement
• Assume 564 lbs/cy pure portland cement mix with a compressive strength of 4000 psi that is exposed to rain– Note that less carbonation would occur if less cement and/or
SCMs were used• The amount of CO2 sequestered through carbonation is
calculated to be between 0.2-0.3 lbs/ft2 of surface area in 50 years– Roughly 14,000-20,000 lbs per lane-mile, or equivalent to 700 to
1000 gallons of fuel consumed
Pounds CO2 Sequestered Over Time per Lane-Mile
0
5000
10000
15000
20000
25000
0 10 20 30 40 50 60
lbs S
eque
ster
ed/L
ane-
Mile
Time (Years)
F’c = 3,600-5,100 psi
F’c = > 5,100 psi
Preservation Through Diamond Grinding Increases Carbonation• Rate of carbonation decreases with time
– Roughly 45% of carbonation over 50 years occurs by Year 10
• Diamond grinding creates a “fresh” surface with more surface area for carbonation
• Grinding every 10 years will more than double the amount of sequestered CO2
• Overlaying concrete with asphalt will shut out atmospheric CO2 and terminate sequestration
Pounds CO2 Sequestered Over Time per Lane-Mile
0
5000
10000
15000
20000
25000
30000
35000
40000
45000
50000
0 10 20 30 40 50 60
lbs S
eque
ster
ed/L
ane-
Mile
Time (Years)
Range with grinding every 10 years
Range without grinding
Diamond Grinding is Close to Carbon Neutral• Diamond grinding every 10 years results in 17,400 to 25,300 lbs
of additional CO2 being sequestered over 50 years per lane-mile– This is equivalent to 870 to 1,270 gallons of diesel fuel consumed over
50 years• Four diamond grindings consumes between 1,000 and 1,600
gallons of diesel– 250-400 gallons per lane-mile of grinding
• Improved vehicle fuel efficiency due to improved smoothness results in greater than net zero GHG emissions
Assessing Sustainability• Use of unbiased, factually-based tools/resources
to assess life cycle impacts are essential– There is A LOT of greenwashing going on– It is only through standardized assessment can we
know if we are doing the right thing• An LCA method meeting ISO standards is the best
way to assess environmental impact– Request EPDs– Stay informed– Seek help as needed
Nice Story, But…? VERIFY• Assessment tools should be used to
evaluate the economic, environmental, and social impacts of alternatives over the life cycle
• Tools for environmental impact assessment are currently under development– Environmental product declarations– FHWA LCA tool– eLCAP in California– Athena Pavement LCA
“Trust, but verify”
Some Current Initiatives
• MnROAD low carbon paving mixtures– In cooperation with NRRA– 16 test cells evaluating various carbon-
reduction strategies• Identification and elimination of barriers
restricting carbon reduction strategies– Funded by Breakthrough Energy Foundation
• Many other Federal and State efforts
Summary
• Sustainable concrete practices are available for all concrete structures at all phases of life
• Sustainability requires a life cycle perspective• Strive to optimize your cement and concrete• Use rigorous verification to avoid “greenwashing”• As an industry, the future is bright
