Concrete Technology

Harza Engineering Company

Quality Control

Purpose

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

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

Transporting and placing the freshly mixed concrete

How do we measure quality control? 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

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

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