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Specifying Sustainable Concrete
Lionel Lemay, PE, SE, LEED AP
Colin Lobo, PhD, PE
Instructions
- Everyone is muted
- Webinar is being recorded
- Type questions in the question box
- Download the handouts in the gotowebinar control panel
- Credit for course
- Based on attendance.
- Quiz – In follow-up e-mail. 10 attempts to get 70% or higher.
- Certificate – Download once you pass the quiz.
NRMCA Super Sponsors
About the Course
Learning Units
- AIA-CES SSC-101 (1LU/HSW - 1 PDH - 0.1 CEU)
Learning Objectives
- Understand the difference between performance-based specification and
prescriptive specifications
- Discover how performance-based specifications can improve performance
and lower environmental impact of concrete structures.
- Learn how to implement performance-based specifications in projects.
- Demonstrate the importance of balancing structural and architectural
performance of concrete with green building strategies.
Case Study: Rowan, San Francisco
- Zigzagging concrete exoskeleton
- Stands out from other buildings
- Negates the need for interior columns
- Maximizing the interior space for residents
- Concrete on the project used high volumes of slag cement and fly ash to reduce environmental footprint
Portland cement 208 kg/m 3 (350 lb/yd 3 )
Slag cement 178 kg/m 3 (300 lb/yd 3 )
Silica fume 30 kg/m 3 (50 lb/yd 3 )
Coarse aggregate 1068 kg/m 3 (1800 lb/yd 3 )
Fine aggregate 712 kg/m 3 (1200 lb/yd 3 )
Water 178 kg/m 3 (300 lb/yd 3 )
Air content 6%
Is This Concrete Sustainable?
50% portland cement replacement! Is this Sustainable Concrete?
High Early Strength Concrete
Mass Concrete
Influence of Project Specifications
• Sustainability criteria should have
minimum impact on performance
or service life of concrete
• Specifications should not restrict
concrete from being sustainable
Concrete Performance
• Performance of concrete materials
are based on performance
indicators measured by standard
test methods with defined
acceptance criteria stated in
contract documents and with no
restrictions on the parameters of
concrete mixture proportions
Performance Based Specification
- Specifier defines performance requirements
- Consider qualifications of concrete producer and contractor
- Producer and contractor ensure right mixture is designed, delivered and installed
- Submittals include pre-qualification tests
- Field acceptance tests determine if concrete meets performance criteria - Not all tests are conducive to field testing
- Instructions outlining what happens when concrete does not meet performance criteria
Problems with Prescription?
• Does not assure required performance
• Prevents mixtures from being optimized
• No incentive
– Quality
– Innovation
• Contradicts sustainability initiatives
• Responsibility is unclear
Typical Specification
Typical Specification
Example Specification (Hybrid)
Interior Building Column
• Maximum w/cm = 0.
• Min. Cem matls = 640 lb/yd^3 (380 kg/m 3 )
• Maximum fly ash = 15% by mass of CM
• Specified strength ƒ’ c = 4000 psi (28 MPa)
• Max. Slump = 4 in. (100 mm)
Solution 1 - prescriptive
- Start with water – 295 lb/yd 3
- w/cm 0.
- CM - 740 lb/yd 3
- Strength = 7000 psi (48 MPa)
- Specified = 4000 psi (28 MPa)
- Paste volume = 31%
- High heat of hydration
- High shrinkage
- High creep
440 kg/m^3
175 kg/m^3
Performance Specifications
General Guidelines
- Do not limit material ingredients that are permitted
in standards
- Do not try to control means and methods such as
early age strength and slump
- Do not limit Global Warming Potential or Carbon
Footprint for each mix, but establish a carbon
budget for the entire building
- TIP: Download guide spec
- TIP: Download whole build LCA example
Specifications and Sustainability
Specification Provision
Impacts
Sustainability Performance Cost
Restrictions on Type and source of
cement ↓^ ↕^ ↑
Not permitting cements conforming to
ASTM C1157 and ASTM C595 ↓^ ↔^ ↔
Restriction on cement alkali content ↓ ↔ ↑
Restriction on type and source of
aggregates ↓^ ↔^ ↑
Specifications and Sustainability
Specification Provision
Impacts
Sustainability Performance Cost
Restrictions on characteristics of aggregates ↓ ↔ ↑
Minimum content for cementitious materials ↓ ↕ ↑
Restriction on quantity of SCM ↓ ↓ ↑
Restriction on type and characteristics of SCM ↓ ↓ ↑
Specifications and Sustainability
Specification Provision
Impacts
Sustainability Performance Cost
Restriction on type or brands of
admixtures ↔^ ↓^ ↑
Same class of concrete for all members ↓ ↔ ↑
Requiring higher strength than
required for design ↓^ ↔^ ↑
Invoking maximum w/cm when not
applicable ↓^ ↔^ ↑
Concrete Mixture Requirements
Application (^) _Aggregate SizeNominal Max. Exposure Class f’c_*
Interior slabs and beams 19 mm (3/4 in.)^ F0, S0, P0, C^
28 MPa (4,000 psi) Interior Columns 19 mm (3/4 in). F0, S0, P0, C0 (^) (5,000 psi)35 MPa
Footings 38 mm (1-1/2 in.) F0, S1, P0, C1 (^) (4,000 psi)28 MPa Exterior slabs and beams 19 mm (3/4 in.)^ F3, S0, P0, C^
35 MPa (5,000 psi)
- Specify strength at age (more than 28 days)
- Specify Exposure Class (ACI 318)
- Additional criteria (permeability, shrinkage, etc.)
Plant Qualification
• NRMCA Concrete Plant Certification
– Alternate Approval - DOT
• NRMCA Green-Star Plant Certification
(optional)
Personnel Qualification
• NRMCA Certified Concrete Technologist
Level 2
• NRMCA Certified Plant Manager
• NRMCA Certified Delivery Professionals
• Alternate Personnel Qualifications
What About Embodied Carbon?
• Do not specify carbon footprint for each
mix (application)
• Specify a carbon budget for all the
concrete on the project
• Permit more flexibility to meet other
performance criteria
Establishing a Carbon Budget
Shear Walls: 6,000 psi
Columns: 8,000 psi
Floors 2-18: 5,000 psi
Floors B2-1: 5,000 psi
Basement Walls: 5,000 psi
Mat Foundation: 6,000 psi
Concrete Strengths
Example: Proposed Building in Northeast U.S.
Download at www.nrmca.org/sustainability
NRMCA Industry Wide/Average EPD
Download at www.nrmca.org/sustainability
NRMCA Eastern Region Benchmark Mixes
