Concrete Quality Assurance: How Concrete is Specified and Supplied To Meet Construction Specifications Prepared By: Prof. Marcia C. Belcher Construction Engineering Technology University of Akron

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. u 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

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

ACI Committees u Areas of: –materials and properties of concrete –construction practices –inspection –pavements and slabs –structural design & analysis –structural specifications –special products and processes

American Concrete Institute Box 19150, Redford Station Detroit, Michigan or go to A complete catalog of ACI publications is available free of charge

Building Code Requirements for Reinforced Concrete u 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)***

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

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

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

Standard Deviation Of The Results 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. 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.

Example: Specification of Concrete Handout for EMS Project: u The project specification for an EMS Facility in Wadsworth requires that all concrete conform with ACI Chapter 5, Concrete Quality, Mixing and Placing. u On the foundation details, the engineer has specified 3500 psi concrete. u The supplier has submitted the test results from the proposed mix design as follows: (see handout)

Example In Handout Break28-Day Compressive Strength (psi) Break28-Day Compressive Strength (psi) Average: Standard Deviation: psi

ACI R5-3: Approval of Mix Design (Handout) u If 30 consecutive tests (meaning samples from same mix & from same job) are submitted: –Calculate s (503.8 psi) –Calculate f’c of results ( psi) –Calculate the required average compressive strength for the job: ACI Greater of: f’ cr = f’ c s f’ cr = f’ c s – 500 (psi)

ACI R5-3: Approval of Mix Design u For our project, the required strength is the greater of: f’ cr = f’ c s = (503.8) = psi f’ cr = s – 500 = (503.8) – 500 = MIX DESIGN DOES NOT MEET SPECIFICATION & ACI REQUIREMENTS

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

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

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