Concrete quality control Flashcards
What is concrete quality control?
Testing and analysis of concrete properties to ensure they meet specified standards, accounting for material variations and production processes.
When should concrete samples be taken for testing?
Randomly from different batches.
At least once per day of placing.
Every 50 m³ per concrete grade.
What are the key tests for fresh and hardened concrete?
Fresh: Slump test (workability).
Hardened: Compressive strength (cube test).
How is compressive strength calculated?
Strength (MPa)= Load(N)
Cross-sectional area (mm²)
What is a normal distribution in concrete testing?
A bell-shaped curve where most results cluster around the mean, with symmetry and defined standard deviation (variability).
How does standard deviation relate to quality control?
Low SD: Tight control (results near mean).
High SD: Poor control (results widely scattered).
Define Specified Characteristic Strength (SCS).
The 28-day strength where ≤5% of results fall below it (e.g., 30 MPa means 95% of tests ≥30 MPa).
What is Target Average Strength (TAS)?
The design strength (mean) set ~1.645 SD above SCS (typically SCS + 8 MPa). Ensures 95% compliance.
How is strength used in structural analysis calculated?
Design strength=
0.67×SCS/ 1.5
What are the acceptance criteria for in-situ concrete?
Average core strength ≥80% of SCS.
No single core <70% of SCS.
What are the acceptance criteria for test results?
Individual results: ≥ SCS – 3 MPa.
Mean of 3 consecutive results: ≥ SCS + 2 MPa.
What is the Cusum technique?
A plot of cumulative differences between test results and TAS to track trends (positive slope = exceeds TAS; negative = below TAS).
What steps are involved in practical quality control?
Set TAS for each grade.
Design mixes.
Sample/test production.
Statistically evaluate.
Accept/reject.
Remediate if needed.
