Alternatives for Specifying Concrete

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Alternatives for Specifying Concrete

• By Wally Rooke, P.Eng.
• Executive Director,
• Manitoba Ready Mix Concrete Association

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CSA A23.1-04 4.1.2 Alternatives for
Specifying Concrete

• Probably the most significant change within the
  Standard since it will affect the way most
  concrete is managed in the Specification, during
  the Submittal stage and within the batch plant.

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CSA A23.1-04 4.1.2 Alternatives for
Specifying Concrete

• Alternative Methods are given in Table 5
• and elaborated in Annex J

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Table 5 Alternatives

• Two Alternatives are given (rather than 3)
  Common option is deleted, leaving
• Performance
• Prescription
• The choice by the Owner depends on who is
  expected to take responsibility for the concrete.

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Table 5 Prescription mixes

• When the Owner assumes responsibility for the
  concrete.
• The Owner shall specify all mix proportions
• Including quantities (kg/m3) of aggregates,
  cementing materials, admix water range of air
  slump range etc

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Table 5 Prescription mixes

• The Contractor shall plan construction based on
  Owners mix proportions.
• obtain approval for any mix changes
• identify to the Owner any anticipated problem
  or deficiencies with mix parameters related to
  construction.

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Table 5 Prescription mixes

• (a) The Producer shall assure all materials
  comply with CSA requirements
• (b) Assure that the concrete is batched according
  to the mix design provided
• (c) Identify to the Contractor any anticipated
  problems or deficiencies with mix parameters in
  construction

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Table 5 Performance Mixes

• Selected when the Owner wishes the
• Producer to take responsibility
• for the concrete.

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Table 5 Performance Mixes

• Specific responsibilities of the Owner,
  Contractor and Supplier are spelled out.

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Table 5 Performance Mixes

• The Owner shall specify
• Strength, MPa
• Durability Class of exposure Table 1
• Other performance criteria such as chloride ion
  permeability, lineal shrinkage etc. any
  pre-qualification/verification criteria
• Quality management requirements Annex J
• Industry certification requirements plant
• Any other concrete property

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Table 1 Class of Exposure

• There are 5 broad classes of exposure
  Chloride (C)
• Frost (F)
• No exposure (N)
• Agricultural (A)
• Sulphate (S)
• With sub-categories, A1, A2 etc in each (except
  N).

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Table 1 Class of Exposure

• Listing by Owner of Class of Exposure
  automatically refers the Producer to Table 2
  Requirements for classes of exposure
• For each class, Table 2 lists max w/cm
  ratio Min strength _at_ 28 days (56
  days for Class S)
• Air Content category
• Curing type for extreme exposures,
  chloride ion permeability

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Table 2 Requirements for Class of Exposure

• These requirements, together with any special
  requirements, are the Performance criteria the
  Producer must meet with the mix design he
  develops for the project.
• Note there are no constraints on such things as
  minimum cement content (except 265 kg/m3 for
  industrial floors) or flyash limits.

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• Since the Producer is taking responsibility, it
  is up to him to meet the given Performance
  criteria using materials with which he is
  uniquely familiar and experienced.
• The resulting mix design remains confidential
  unless a special Confidentiality Agreement is
  signed with Owner

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Table 5 Performance Mixes

• Contractor shall
• provide satisfactory evidence that the mix
  proportions selected will produce the quality
  specified.
• Thats a quote from a recent spec and it
  embodies the essence of a Performance
  specification.

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Table 5 Performance Mixes

• Contractor shall
• Work with Producer to assure plastic mix meets
  placing and hardened requirements
  negotiates appropriate slump
• Submit documentation showing owners
  pre-qualification needs are met
• Prepare and implement a QC plan and provide
  documentation in advance and during work

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Table 5 Performance Mixes

• The Producer shall
• Certify plant and materials meet CSA A23.1
• Certify his mix design satisfies Clause 4.3
• Certify delivery satisfies Clause 5.2
• Certify the concrete complies with Performance
  spec
• Prepare and implement QC plan
• If specified, certify Certification is met

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Plant certification has been available for over
20 years in Manitoba. Guide may be reviewed _at_
www.mrmca.com
Plant Certification Guide Checklist for Ready
Mixed Concrete Production Facilities May
2007
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Performance Mixes

• The details of the Producers mix design remain
  proprietary information
• BUT
• in return, the Producer must be able to document
  in advance that his mix meets the performance
  criteria for strength etc.

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Statistical spreadsheet program and Guide
available _at_ www.mrmca.com
Stats Program developed by RMCAO
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Producer inputs test data
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Statistical analysis determines if recorded
strengths satisfy CSA A23.1 criteria
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Annex J

• Performance option clarifies the roles and
  responsibilities of specifying various mix design
  parameters as well as defining who is assuming
  responsibility for the concrete mix proportions.
• Effective Performance spec states Performance
  criteria in terms verifiable by Standard tests

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Performance criteria

• Concrete in Plastic state uniformity
• placeability
• workability
• finishability
• set time
• These characteristics are of primary interest to
  Producer, Contractor and subcontractors

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Performance criteria

• Concrete in Hardened state
• Compressive, flexural or tensile
  strength or E value rate
  of strength development
• durability
• volume stability
• appearance
• surface texture
• geometric requirements (Flatness/Levelness)

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Annex J, 3.4.4

• Challenge is to state Performance requirements
  that can be satisfied and be measured.
• Without a comprehensive and reliable
  verification process, the owners Performance
  requirements cannot be verified at the
  appropriate time and the process is not workable.

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J.4 Roles Responsibilities

• Given for Owner, his Designer,
  Contractor Concrete Supplier

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J 5.3.2 Quality Management

• Verification of concrete quality (QA) is the
  Owners responsibility
• Contractor must have QC plan appropriate to the
  complexity of project
• In Performance spec, a higher level of
  responsibility is placed on the Contractor and
  all suppliers and subcontractors.

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J 5.3..3 Component of spec

• Must include pre- and post-qualifiers to allow
  Owner to place reliance of the Contractor, his
  suppliers and subs.
• Pre-qualifiers such as experience
  mix design performance record proposal
  evaluation QC plan other criteria

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Contract documents

• Plans Specs must clearly articulate roles
  and responsibilities of all parties
• Terms conditions of interaction between
  parties
• Clear definitions of Performance and
  point of delivery
• Pre- post-qualifiers
• Performance criteria and test methods
• Penalties and dispute resolution mechanisms

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J. 5.3.4 Verification Process

• Spec will require an effective QA QC process
  to verify and assure Performance criteria are met
• Subjective criteria must be defined in some
  measurable way
• Responsibility for some defects such as random
  cracking may overlap between designer and
  contractor.

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