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Title: Concrete Quality Assurance: How Concrete is Specified and Supplied To Meet Construction Specifications


1
Concrete Quality AssuranceHow Concrete is
Specified and Supplied To Meet Construction
Specifications
Prepared By Prof. Marcia C. Belcher Construction
Engineering Technology University of Akron
2
Design Criteria And Quality is Specified by ACI
(American Concrete Institute)
  • ACI is a technical and educational society with
    30,000 members and 93 chapters in 30 countries.
  • ACI has
  • more than 400 technical documents for the best
    use of concrete
  • conducts over 150 educational seminars each year
  • has 13 different certification programs for
    concrete practitioners
  • See http//www.concrete.org/certification/cert_pro
    g.asp

3
ACI Manual of Concrete Practice
  • ACI standards and reports are prepared by
    committees
  • The committees gather annually to revise/update
    the manual

4
ACI Committees
  • Areas of
  • materials and properties of concrete
  • construction practices
  • inspection
  • pavements and slabs
  • structural design analysis
  • structural specifications
  • special products and processes

5
American Concrete InstituteBox 19150, Redford
StationDetroit, Michigan 48219-0150 or go to
www.concrete.org
  • A complete catalog of ACI publications is
    available free of charge

6
Building Code Requirements for Reinforced Concrete
  • The ACI code has no legal status unless adopted
    by building code governing bodies, i.e..
  • Uniform Building Code (UBC)
  • Building Officials and Code Administrators (BOCA)
  • International Building Code (IBC)

7
Building Code Requirements for Reinforced Concrete
  • The ACI code provides minimum requirements
    necessary for public safety
  • Designer may require higher standards in project
    specification (see Structural Notes Handout)
  • Lower, standards are not permitted

8
Building Code Requirements for Reinforced
(Structural) Concrete
  • Sections include
  • mixing and placing
  • formwork
  • embedded pipes, construction joints
  • slab systems
  • walls
  • footings
  • precast concrete
  • prestressed concrete
  • strength evaluation of existing structures
  • seismic design provisions

9
Drawings Specifications
  • For quality control, ACI requires that the
    supplier provide results from 30 28-day
    compressive breaks for the mix design
  • The average strength and standard deviation must
    meet criteria ACI R5-3 (handout discussion to
    follow)
  • Definition Standard deviation is the average
    distance from the mean of all samples.

10
Standard Deviation Of The Results
A normal distribution of data means that most of
the samples in a set of data are close to the
"average," while relatively few samples tend to
one extreme or the other.
The standard deviation tells you how tightly all
results are clustered around the mean. When the
samples are pretty tightly bunched together and
the bell-shaped curve is steep, the standard
deviation is small. When the examples are spread
apart and the bell curve is relatively flat.
11
Example Specification of Concrete
  • Handout for EMS Project
  • The project specification for an EMS Facility in
    Wadsworth requires that all concrete conform with
    ACI Chapter 5, Concrete Quality, Mixing and
    Placing.
  • On the foundation details, the engineer has
    specified 3500 psi concrete.
  • The supplier has submitted the test results from
    the proposed mix design as follows (see handout)

12
Example In Handout
Break 28-Day Compressive Strength (psi) Break 28-Day Compressive Strength (psi)
1 3800 16 3452
2 3965 17 3313
3 3865 18 3490
4 3987 19 3800
5 3700 20 3700
6 3854 21 3800
7 3755 22 3700
8 3498 23 3377
9 3527 24 3789
10 3865 25 3588
11 3800 26 3589
12 3854 27 3270
13 3755 28 3167
14 3965 29 3279
15 3865 30 4798

Average 3705.6 Standard Deviation
503.8 psi
13
ACI R5-3 Approval of Mix Design(Handout)
  • If 30 consecutive tests (meaning samples from
    same mix from same job) are submitted
  • Calculate s (503.8 psi)
  • Calculate fc of results (3705.6 psi)
  • Calculate the required average compressive
    strength for the job ACI 5.3.2
  • Greater of fcr fc 1.34s
  • fcr fc 2.33s 500
    (psi)

14
ACI R5-3 Approval of Mix Design
  • For our project, the required strength is the
    greater of
  • fcr fc 1.34s
  • 3500 1.34(503.8) 4175.1 psi
  • fcr 3500 2.33s 500
  • 3500 2.33(503.8) 500 4173.8
  • MIX DESIGN DOES NOT MEET SPECIFICATION ACI
    REQUIREMENTS

15
Approval of Mix Design
  • Often, suppliers do not have the data available
    for a particular mix
  • Some basis for decision making is needed to
    approve or reject a mix design

16
Approval of Mix Design
  • When sufficient data are not available, ACI table
    5.3.2.2 may be used as a tool to proportion an
    adequate mix.

17
Approval of Mix Design
  • The required average strength for the mix can be
    determined from this table
  • Proportions can then be selected to achieve the
    required strength.
  • Lab trial batches tested for average compressive
    strength _at_ 28-days
  • Several field samples of mix (if available) to
    prove compressive strength _at_ 28 days.
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