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1.11 USE OF TEST RESULTS

1.11 USE OF TEST RESULTS. Causes of Variations CUSUM Multi-variate Systems. Daily variations in concrete supplied to site:. Changes in cement Changes in aggregate Changes in batching control Changes in temperature. Variations in concrete between successive batches (loads):.

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1.11 USE OF TEST RESULTS

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  1. 1.11 USE OF TEST RESULTS • Causes of Variations • CUSUM • Multi-variate Systems

  2. Daily variations in concrete supplied to site: • Changes in cement • Changes in aggregate • Changes in batching control • Changes in temperature

  3. Variations in concrete between successive batches (loads): • Changes in water content • Changes in haul times

  4. Sampling variations within a load • Changes in aggregate content between two samples taken from the same load. • Operator error, e.g. effect of sampling from the end of a load.

  5.   Testing variations • Variations in the position of the aggregate in the cubes. • Operator error, e.g. changes in loading rate, dirt on the platens etc.

  6. 1.11 USE OF TEST RESULTS • Causes of Variations • CUSUM • Multi-variate Systems

  7. Simple Quality Control

  8. CUSUMTarget mean = 29

  9. Cusum Charts

  10. Extending CUSUM • CUSUM methods only work well when most of the concrete from a given plant is of basically the same type. • If there are many different mixes being made there will be insufficient data to work the system on all of them. • In order to overcome this the strengths of the plain cement mixes can be adjusted using strength-w/c relationships to fit them all to a single model. • Adjusting results from mixes with cement replacements or admixtures is, however, very unreliable.

  11. 1.11 USE OF TEST RESULTS • Causes of Variations • CUSUM • Multi-variate Systems

  12. Current Trends • Computer systems also permit the use of other factors that affect strength, e.g. aggregate grading, temperature, etc. to be combined with the data on the mix ingredients and used to develop a single model for strength. • A model of this type can be used to show when an unexpected deviation from predicted strengths has occurred and remedial action is needed.

  13. Spreadsheet for Predictive Model

  14. Predictor Variables • w/c • Cement content • Cement type/replacements • Aggregate content • Aggregate Grading • Aggregate type • Slump • Temperature • Haul Time • Plant

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