Performance-based Specifications: the Key to Optimising Concrete’s Contribution

to the Climate Change Challenge

Dr. Mark Richardson

UCD School of Architecture, Landscape & Civil Engineeringp g g

8th May 2009

Institiúid na gCóras Domhanda

An Coláiste Ollscoile Baile Átha CliathEarth Systems Institute

University College Dublin

Web: www.ucd.ie/earthEmail: esi.admin@ucd.ie

Concrete is ....

“Concrete is dull grey stuff”

“It has got to be good to be taken for granted”be ta e o g a ted

Concrete is ....

Aggregate

Cement

…. just add water

Reinforced concrete: backbone of the world’s infrastructureinfrastructure

Reinforced concrete: backbone of the world’s infrastructureinfrastructure

High strength

Low cost

Robustness

Local availability

Versatility

Durability ???

Key issues: Durability and Sustainability

Over 0.25 million deficient

concrete bridges in the

230 – 930 kg CO2 per

tonne of cement g

United States 46 – 212 kg CO2 per tonne

of concrete of concrete

World Resources Institute

Cement 3.8%

Key issues in respect of the energy and climate change challenge:climate change challenge:Durability and Sustainability of Concrete InfrastructureInfrastructure

Efficiency

S ffi i Sufficiency

(Adrian Campbell, ARUP, 2009)

Performance-based Specification of C t th k t D bilit d Concrete: the key to Durability and Sustainability

• Cements and secondary cementitious materials

f f d bl• Specification of durable concrete - prescription

• Specification of durable concrete - performance

• Addressing the energy and climate change

challenge

Cements and secondary cementitious t i lmaterials

• Portland Cement = Clinker + minor additions

• Blended cements = Clinker + other major

component + minor additions

• Examples of major componentsp j p

» Limestone

» Blastfurnace slag (GGBS)Blastfurnace slag (GGBS)

» Fly Ash (PFA)

Cement production

Finely ground clinker + Gypsum = cement

Limestone rock + Shale + Energy (1500oC) = clinker

27 distinct cements are recognised in Europe 27 distinct cements are recognised in Europe

Significant variety of Significant variety of

cement chemistries

available to be

harnessed in matching

the demands of

durability with just the

right capacity of material

properties

Efficiency, sufficiency

Type Designation Secondary Constituent

Embodied CO2

(kg/tonne)(kg/tonne)

CEM I CEM I 930

CEM II CEM II/A-L, LL Limestone 6-20% 880 – 750

CEM II/A-V PFA 6-20% 870 – 750CEM II/A V PFA 6 20% 870 750

CEM II/B-V PFA 21-35% 730 – 610

CEM II/B-S GGBS 21-35% 740 – 620

CEM III CEM III/A GGBS 36-65% 610 – 360

CEM III/B GGBS 66-80% 340 - 230CEM III/B GGBS 66-80% 340 - 230

Same effect can be achieved by adding PFA or GGBS at the mixer

British Cement Association

Specification of durable concrete -i tiprescription

P i t th 1970’ th i it ifi ti f • Prior to the 1970’s the priority was specification of

strength

• From the 1970’s it was recognised that durability

should be specified also

• Both factors are specified by prescription

• The prescriptive parameters are minimum strength,

minimum cement content, and maximum water/cement

ratio

Chronology

Formalised as ‘Durability Grade’ Concept

Strength implies min. cement content and max w/c

Weakness in Prescriptive Approach

Does not prioritise durability over strength• Does not prioritise durability over strength

• Does not explicity address sustainability and embodied CO2 issue2

• Likelihood of over-specification, rather than provision of sufficiency – high safety factor but potentially wasteful of resourcesresources

• Assumption of constant high standard of site practice in respect of curing

“Durable and sustainable concrete:

buy one, get one free”

(Prof. Ravindra Dhir, Dublin, 2008)

Specify performance: efficiency, sufficiency

Specification of durable concrete -fperformance

Explicit Durability Design and Specification of durable concrete by performancedurable concrete by performance

• Quantify durability threat

• Define service life

• Quantify level of acceptable deterioration

• Determine required material parameters

Example of quantifying the threat: Example of quantifying the threat: Chloride ingress and corrosion of reinforcementChloride ingress and corrosion of reinforcementChloride ingress and corrosion of reinforcementChloride ingress and corrosion of reinforcement

• Electrochemical • Electrochemical process of corrosion is initiated if the chloride level at the chloride level at the reinforcement exceeds a critical level

• Chlorides migrate into concrete from exposure to seawater exposure to seawater or de-icing salts

• Electrochemical cell

• Anode

• Cathode

• Electrolyte• Electrolyte

Electrochemical cell in reinforced concrete

Method for Determination of Required Material ParametersParameters

Combination of

Performance test methods

P di ti d l f d t i ti Predictive models of deterioration

Lifetime Safety Factor Method

P ⎨R(t) - S(t) < 0⎬T < Pf max T = tmean

td = γt tg

Performance-related design

• Quantify critical chloride level at reinforcement (C x, t )

• State required service life (t)

• Estimate durability ‘load’ from chloride source (C sn )y ( sn )

• Specify cover to reinforcement (x)

• Solve for required material parameter of chloride resistance

• Chloride penetration model based on Fick’s Second Law of Diffusion for the non-steady state condition in a Crank’s error function solution to Fick’s Law

⎟⎟⎞

⎜⎜⎛ ⎪

⎬⎫⎪

⎨⎧ x

fCC 1( ) ⎟⎟

⎟

⎠⎜⎜⎜

⎝ ⎪⎭⎬

⎪⎩⎨−=

tDerfCC

ca

sntx2

1,

Solve to ascertain minimum value of material parameter (Dca)

• Specify concrete based on a performance requirement of the required value of Dcathe required value of Dca

• Allow producer to use their skill to provide concrete with a sufficient value of Dca

• Test finished product (“what gets measured gets done”)

(ECOserve 2006)

Recent developments in Ireland

• Specifiers’ practice is heavily influenced by explicit advice in standards documents

• Typically national standards permit the use of up to 70% • Typically national standards permit the use of up to 70% GGBS with Portland cement (CEM I)

• Irish cement producers have responded to the CO2 issue p p 2

by replacing dominance of CEM I (930 kg CO2 / tonne) by Limestone cement CEM II/A-LL or fly ash cement CEM II/A-V (both c.810 kg CO2 / tonne) / ( g 2 / )

• The National Standards Authority of Ireland have moved swiftly with the industry to update National Standards for y y pconcrete

• To date the NSAI have modified the national standard to permit combinations of 50% GGBS with standard to permit combinations of 50% GGBS with CEM II/A-LL and CEM II/A-V

• Following further research at UCD, using perfomance-based arguments, a proposal is currently being considered by the NSAI to increase currently being considered by the NSAI to increase this to 70% GGBS with CEM II/A-LL and CEM II/A-V

• The swift response of the NSAI will assist in meeting the energy and climate change challenge but current practice is potentially limited by being current practice is potentially limited by being rooted in the prescriptive specification approach

• More can be achieved with performance-based specifications.

Addressing the energy and climate change challengechange challenge

• Golden opportunity for Ireland as we roll out NDP infrastructure NDP infrastructure

• Durability

• Sustainability

• Efficiency

• Sufficiency

Addressing the energy and climate h h llchange challenge

• Smart technology: we have the basis of the technology, it just needs development

UCD Earth Systems Institute

• Smart policy: we must provide the research data th t ill f ilit t

Systems InstituteMeeting the Challenge of

Climate Change that will facilitate an editorial shift in standards documents from

i i

Climate Change

prescriptive to performance-based specifications

Key UCD Message

• The Innovation Imperative: Productivity growth in the Irish economy has slowed to close to zero. The only way to rediscover productivity growth and be able only way to rediscover productivity growth and be able to sustain it is by innovation and the embedding of the knowledge society.

• The Energy and Climate Change Imperative: We have hugely demanding energy and emission reduction obligations – the only way to meet them is through the use of markets and innovation.

• The Earth Systems Institute response to these imperatives We will be an engine showing how to imperatives - We will be an engine showing how to use research and innovation – smart technology and smart policy - to regain competitiveness and productivity generate jobs and meet our energy and productivity, generate jobs and meet our energy and climate change obligations

Addressing the energy and climate h h llchange challenge

• Smart technology: we have the basis of the technology, it just needs development

• Smart policy: we must provide the research data th t ill f ilit t that will facilitate an editorial shift in standards documents from

i iprescriptive to performance-based specifications

UCD Earth Systems InstituteMeeting the Challenge of Climate Change Meeting the Challenge of Climate Change

Seminar Series

In collaboration with

Comhar Sustainable Development Council, Environmental Protection Agency, Forfás, Geological Survey of Ireland,

Marine Institute, Met Éireann, Sustainable Energy Ireland & Teagasc

Further details on the seminar series is available at www.ucd.ie/earth

A paper and podcast of this seminar will be available on the ESI website soon, please join the online ESI mailing list for such notifications

ESI email: esi.admin@ucd.ie

UCD Earth Systems InstituteMeeting the Challenge of Climate Change Meeting the Challenge of Climate Change

Seminar Series

Next week...Seminar #20Next week...Seminar #20

Friday 15th May 2009

Royal College of Physicians, 12.30pmRoyal College of Physicians, 12.30pm

Dr. Brendan WilliamsUCD School of Geography, Planning & Environmental Policy

f fShaping the Dublin of 2020: meeting future challenges for managing the urban environment

Further details available at www.ucd.ie/earth