Ct-17 Quality Control

Concrete Technology Quality Control

Harza Engineering Company

Purpose ■

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To assure placement of consistent, uniform concrete in the work To minimize variation in concrete properties such that the concrete will perform in a predictable manner To achieve maximum economy in the work

Where does quality control begin? ■

It begins in the production of materials used in concrete (sampling and testing): Portland cement  Pozzolan  Coarse and fine aggregates 

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Uniformity of concrete production will be no greater than the uniformity of materials used in that concrete

How does quality control continue? ■ ■ ■

Handling and stockpiling Batching and mixing Sampling and testing fresh concrete Slump  Air content  Unit weight  Temperature 

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Transporting and placing the freshly mixed concrete

How do we measure quality control? ■

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The most common measurement is the uniformity of the compressive strength specimens determined from statistical concepts (ACI 214) These same statistical concepts can also be applied to test results on materials used in the concrete, on the fresh concrete, and on other properties of the hardened concrete.

Primary criteria for application of statistical concepts ■

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The primary criteria for application of statistical concepts is that the data to be analyzed has been developed from random sampling, and At least 30 consecutive test results are available for analysis.

Normal distribution curve

Level of acceptance

Standards of Concrete Control

(General Construction Testing) ACI 214 ■ ■ ■ ■ ■

Excellent: Std. Dev. below 2.76 MPa Very Good: Std. Dev. of 2.76 to 3.45 MPa Good: Std. Dev. of 3.45 to 4.14 MPa Fair: Std. Dev. of 4.14 to 4.83 MPa Poor: Std. Dev. above 4.83 MPa

Within-test variation

Standards of Concrete Control

(Field Control Testing) ACI 214 ■

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Excellent: Coefficient of variation below 3.0 percent Very good: Coefficient of variation of 3.0 to 4.0 percent Good: Coefficient of variation of 4.0 to 5.0 percent Fair: Coefficient of variation of 5.0 to 6.0 percent Poor: Coefficient of variation above 7.0 percent