www.sgh.com

Boston Society of Architects

Concrete Selection

and Sustainable Choices

Alec Zimmer, PE, LEED AP

Simpson Gumpertz & Heger

28 January 2014

What is “Green” Concrete?

• A balancing act:

– Managing optimal use of concrete

– Meeting performance objectives

– Doing least harm to the environment and

society

– Providing durability and resilience

2

ACI Committee 130 – Sustainability of Concrete

• Mission: Develop and report information on the

sustainability of concrete.

• Goal: To produce relevant and timely educational

products and sessions covering the three pillars of

sustainability (environmental, social and economic.)

• Currently drafting ACI 130R: Guide to Concrete

Sustainability

3

ACI Committee 130 – Sustainability of Concrete

• “The purpose of designing for sustainability is to reduce impacts on environment, society, and economy. Fulfillment of the requirements for sustainability presumes that all aspects of design, construction, use, demolition of a structure and recycling and disposal of concrete that are relevant for environment and society are taken into account. This is achieved through evaluating and verifying performance of concrete, concrete component, or structure. A concrete structure should be designed so that it can satisfy the requirements regarding serviceability, safety, durability, robustness, performance and aesthetics in a well-balanced manner throughout its design service life.”

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ACI Committee 130 – Sustainability of Concrete

• Subcommittees

– 130-A Materials

– 130-B Production / Transportation / Construction

– 130-C Structures in Service

– 130-D Rating Systems / Sustainability Tools

– 130-E Design / Specification / Codes / Regulations

– 130-F Social Issues

– 130-G Education / Certification

– 130- H Global Climate Change (proposed)

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What are the drivers for “greener” concrete?

• Primarily LEED Certification – “LEED Certifiable” projects

• Green Globes does not seem to carry brand recognition that LEED carries

• Limited opportunities for traditional concrete to play a major role in earning LEED credits – Regional Material Credits

– Recycled Material Content Credits

– Innovative Design Credits

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How has greener concrete typically been made?

• One ton of cement yields roughly 0.89 tons of CO2

• Typically through the use of pozzolans (supplementary cementitous materials)

– Fly Ash (ASTM C618, Grade C or F)

• By-product of coal fired power plants

• May require significant processing depending on grade of coal and point of precipitation in exhaust stream

– Ground Granulated Blast Furnace Slag (aka Slag Cement, ASTM C989, Grade 100 or 120)

• By-product of steel production

• Requires processing

• Limited availability

– Silica Fume (ASTM C1240)

• Can yield very high strength concrete, but difficult to work with

• Limited availability

– Rice Hull Ash, Natural Pozzolans

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How has concrete been “greened” in the past?

• For interior construction for walls, elevated slabs (where

finish is not an issue), beams, and columns:

– Fly ash: 15% min. and 25% max. replacement

– GGBFS: 25% min. and 35% max. replacement

– Silica Fume: 5% max. replacement

• For foundations (when rate of strength gain is not

critical):

– Fly ash: 25% min. and 35% max. replacement

– GGBFS: 35% min. and 50% max. replacement

– Silica Fume: 5% min. to 10% max. replacement

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What are benefits to fly ash?

• Environmental Benefits

– About 62 million tons produced annually (as of 2009)

– 43% recycled / diverted from waste stream

– Balance landfilled

– Reduction in embodied CO2 content in concrete

• Performance Benefits

– Improved workability

– Reduced permeability

– Reduced heat of hydration

– Reduced shrinkage and cracking (if cured properly)

– Improved long-term strength gain

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What are drawbacks to fly ash?

• Materials Issues – Tacitly promotes use of coal-fired power plants

– Shortages • Impending closure of Brayton Point in Somerset, MA

• Transportation issues

• Pressure to burn municipal waste in combination with coal

– Proposed EPA ruling (2010) to regulate coal combustion byproducts as hazardous waste

– Lower burning temperatures lead to higher LOI

• Construction Issues – Extended set time, slower strength gain

– Difficulty in finishing concrete flatwork due to reduction in bleed water

– Limitations on content in aggressive exposures

– Controversy over interaction of fly ash and flooring

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LEED Recycled Materials Credit

• 1 Credit: Recycled materials comprise 10% of total

material cost

• 2 Credits: Recycled materials comprise at least 20% of

total material cost

• Pre-consumer recycled material at ½ that of post-

consumer recycled material

• SCM’s contribute an almost negligible amount to the

total material cost of any project. (<<1%)

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What can designers do today?

• Look for LEED Innovative Design Credits.

• Use concrete efficiently

– Bubble deck for slabs

– High strength rebar

• Avoid “over cementing” concrete mixes

• Increase coarse aggregate size where appropriate

• Improve aggregate gradation to reduce cement paste volume

• Consider using interground limestone filler to reduce portland cement in paste

– PCA is promoting up to 15% portland cement replacement

– History of use in Europe, starting to use in US pavements

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Photo by Bill Bradley

Photo by PCA

What are the hurdles to greener concrete?

• Inertia among designers and contractors

– Ignorance of proper curing practices

– Rushed construction schedules

• Limited availability of high quality fly ash

• Resistance to high fly ash substitution rates

• Mix design coordination with ready mix suppliers

– Experimentation and trial batching

– Multiple sources of aggregates required

– Hard to do on an open bid project

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www.sgh.com

Boston Society of Architects

Concrete Selection

and Sustainable Choices

Mark D. Webster, PE, LEED AP BD+C

Simpson Gumpertz & Heger

28 January 2014

Some Success Stories

The David Brower Center, Berkeley, CA

Slag replaces 50% of the cement in slabs, columns, and walls, and 70% of the cement in the mat foundation.

Structural Engineer: Tipping Mar + associates; Archi­tect: Wallace Roberts & Todd; image: WRT/Solomon E.T.C.)

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Monolithic Slab, Hawaii

57% replacement of cement with Class F fly ash, 1,000-yr design life

Article in July 2000 issue of Concrete International by P.K. Mehta and W.S. Langley

Some Success Stories

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Wayland H.S. Field House

Unreinforced concrete slab, joints 10 to 12 ft apart Engineer: Simpson Gumpertz & Heger

Some Success Stories

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Adapted from: Methods, Impacts, and Opportunities in the Concrete Building Life Cycle, J. Ochsendorf, et al., MIT

Concrete Sustainability Hub, August 2011

Concrete in Commercial Buildings

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141

7 7

Concrete Building Total Weight 156 psf

Concrete

Rebar

Structural Steel

Steel Deck

Other

conc+rebar=95% of weight

rebar/conc=5%

conc+rebar=67% of weight

rebar/conc=2%

54

1

15

2 10

Steel Building Total Weight 82 psf

Adapted from: Methods, Impacts, and Opportunities in the Concrete Building Life Cycle, J. Ochsendorf, et al., MIT

Concrete Sustainability Hub, August 2011

Carbon Emissions in Commercial Buildings

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14.4

4.3

6.6

Concrete Building Total Emissions 25 lb CO2e/sf

Concrete

Rebar

Structural Steel

Steel Deck

Other

conc+rebar=74% of emissions

rebar/conc=30%

conc+rebar=20% of emissions

rebar/conc=14%

5.5

0.8

12.4

4.4

8.8

Steel Building Total Emissions 32 lb CO2e/sf

Carbon Emissions in Commercial Buildings

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-

5.0

10.0

15.0

20.0

25.0

30.0

35.0

baseline 30% Fly Ash 30% Fly Ash + 10% Less Steel

baseline 30% Fly Ash 30% Fly Ash + 10% Less Steel

Concrete Building Steel Building

lb C

O2

e/s

f

Other

Steel Deck

Structural Steel

Rebar

Concrete

17% reduction

19% reduction

5% reduction

5% reduction

Alphabet Soup: PCRs and EPDs

• Product Category Rules: Product-specific rules about

how to conduct the life-cycle assessment for “apples-to-

apples” comparisons.

• Environmental Product Declarations: Environmental

impacts report developed using PCRs.

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PCR for Concrete: Reporting

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PCRs and EPDs

• Will allow purchasers to compare environmental

performance of competing suppliers.

• Will allow specifiers to specify minimum environmental

performance.

• For concrete, currently specify strength, durability; what

about maximum CO2e/cy?

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LEED v4

• Currently available for use

• LEED 2009 phased out in June 2015

• Credit: Building Life-Cycle Impact Reduction

– Option 4: Whole Building LCA

– 3 points!

– Conduct LCA of structure and enclosure demonstrating at least

10% reduction relative to a baseline building in at least three

environmental impacts, including GWP

– How to define baseline?

• Need a national materials database like the Portfolio Manager for

energy

• Baseline = 100% cement mix?

• Then could meet requirements for concrete building just by using

30% fly ash!

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LEED v4

• Credit: Environmental Product Declarations

– Option 1: EPDs for 20+ different products from 5+ manufacturers

(1 point)

– Option 2: 50% of products in building with demonstrated impact

reductions below industry average (1 point)

– structure + enclosure cannot exceed 30% of value of compliant

products

– products sourced within 100 miles worth double

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LEED v4

• Credit: Product Disclosure and Optimization: Sourcing of

Raw Materials

– Option 1: Reporting: Publicly released sustainability reports from

raw material suppliers for 20+ different products from 5+

manufacturers (1 point)

– Option 2: Leadership: Meet certain sustainability criteria, such as

recycled content, for 25% of products (1 point)

– structure + enclosure cannot exceed 30% of value of compliant

products

– products sourced within 100 miles worth double

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LEED v4

• Credit: Product Disclosure and Optimization: Material

Ingredients

– Option 1: Material Ingredient Reporting (1 point)

• Report chemical inventory to 0.1% for 20+ different products from

5+ manufacturers (1 point)

– Option 2: Optimization (1 point)

• 25% of materials satisfy certain sustainability programs

– Option 3: Supply Chain Optimization (1 point)

• 25% of materials have documented supply chain safety and

environmental impact processes in place

– structure + enclosure cannot exceed 30% of value of compliant

products

– products sourced within 100 miles worth double

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What does the future hold?

• Use EPDs to specify environmental performance

• More LCA, driven by LEED

• New LCA tools, integrated into Revit, e.g. Tally

• New technologies such as carbon sequestration

• Wider acceptance of high-volume SCMs

• New types of SCMs

• New types of cement

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