Original sample lesson · allow approximately 10–15 minutes
By the end of this lesson
Separate water-cementitious ratio from workability, then choose a defensible quality-control response.
A concrete batch looks stiff at discharge. Adding water seems like the fastest way to restore flow, but the quality-control decision starts with the batch record. Water changes both consistency and the water-cementitious ratio. Slump is an observation about fresh concrete; it is not a direct measurement of strength or the ratio.
Consider an original teaching batch containing 600 lb of cementitious material and 240 lb of total mixing water. Its water-cementitious ratio is 240 ÷ 600 = 0.40. If an extra 30 lb of water is added without any other change, the ratio becomes 270 ÷ 600 = 0.45. The concrete may flow more easily, while its qualified performance has also changed.
Check 1: A batch is proportioned with 550 lb of cementitious material and 198 lb of batch water. The aggregates carry 11 lb of free surface moisture, and 33 lb of water is added at the truck before discharge. What is the water-cementitious ratio of the concrete as delivered?
Total mixing water includes the added water and the contribution from aggregate surface moisture. Aggregate below the saturated-surface-dry condition may absorb water instead. That is why a moisture measurement and a batch correction belong together. Recording a new moisture result without changing the batch settings leaves the error in the product.
A useful inspection sequence is to check the specified limits, verify the batch quantities and moisture correction, identify permitted adjustments, then document the action. Keep the limits for water, admixtures and elapsed time separate. Do not infer that a passing slump result means every mixture requirement has been met.
Check 2: A batch passes its slump check. What does that establish?
After this checkpoint, explain the decision in your own words: what changed in the material, what changed in the record, and what evidence permits the batch to proceed? This is the same read–apply–check rhythm used throughout the full course.
Check 3: A new sand-moisture result is higher than the value used by the batch controls. What should happen next?
Take it into your study session
Write a one-sentence explanation of the principle, then describe a situation where the wrong answer would create a problem. Revisit the questions tomorrow without looking at the explanations first.
Continue with PCI Level I
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