--- title: "Quality control of concrete at site" subject: "Concrete Technology and Masonry Structure" chapter: 5 key: "semester_5/concrete_technology_and_masonry_structure:quality-control-at-site" source: https://www.bctengineer.com/q/semester_5/concrete_technology_and_masonry_structure/quality-control-at-site site: BCT Engineering --- # Quality control of concrete at site Concrete Technology and Masonry Structure · Chapter 5: Testing of concrete and quality control - Asked in: 2079 Bhadra, 4 marks; 2078 Bhadra, 2 marks; 2076 Ashwin, 4 marks; 2075 Chaitra, 4 marks; 2073 Shrawan, 4 marks; 2072 Kartik, 4 marks; 2069 Chaitra, 4 marks; 2068 Chaitra, 8 marks; 2068 Baisakh (old course), 5 marks; 2067 Ashadh (old course), 5 marks; 2066 Chaitra (old course), 2 marks (asked 11 times) - Video: [Quality Control of Concrete On Site (Part 1)](https://www.youtube.com/watch?v=jJvdpvpt15k) — PublicResourceOrg - Answer checked by Claude Sonnet 5.5 on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_5/concrete_technology_and_masonry_structure/quality-control-at-site - Whole chapter: https://www.bctengineer.com/md/semester_5/concrete_technology_and_masonry_structure/chapter-5 ## Question How would you maintain quality control of concrete at site (measures and steps for quality control, including quality assurance and the standard process in each stage of concrete production / construction)? ## Short answer Key measures: test materials (cement, aggregates, water) per IS standards; batch by weight accurately; control slump and w/c ratio; place and compact without segregation; cure for specified period; sample and test cubes at 28 days; accept if mean of four consecutive results meets IS 456 Table 11 limits and no individual falls below fck-3 MPa. ## Answer Quality control (QC) is the set of checks that ensure the concrete meets the specified strength and durability; quality assurance (QA) is the planned system (documents, responsibilities, audits) that gives confidence that QC is done. IS 456 (Cl. 15 and 16) sets the sampling and acceptance rules. #### 1. Planning and quality assurance - A QA plan with job specifications, drawings, method statements, responsible persons and test records. - Trained staff, calibrated equipment, a site laboratory, and an approved mix design (IS 10262) with trial mixes. #### 2. Materials - **Cement:** check manufacturer's test certificate, date of manufacture, storage on a dry raised platform (IS 456, Cl. 5.7), use in the order received; test for setting time, fineness and strength as needed. - **Aggregates:** sieve analysis, silt and organic content, moisture correction, flakiness; stored separately on clean hard floor (IS 383). - **Water:** potable, pH not below 6; limits on chloride and sulphate (IS 456 Cl. 5.4). - **Steel and admixtures:** approved grade, no loose rust, test certificates. #### 3. Batching and mixing - Batch by weight (by volume only for small works; IS 456, Cl. 10), with an accuracy of $\pm2\%$ for cement and water and $\pm3\%$ for aggregates. - Mix in a mechanical mixer for the minimum time (usually 2 minutes); correct for moisture in aggregate. #### 4. Fresh concrete control - Slump or compacting factor on every batch, and the temperature (IS 456 Cl. 7). - Check the w/c ratio; no extra water at site. #### 5. Transport, placing and compaction - Prevent segregation, limit free fall to 1.5 m, and place before initial set (30 min to 2 hours). - Compact with needle vibrators; clean formwork, proper cover blocks, check bar spacing and cover before concreting. #### 6. Curing and protection - Cure properly (IS 456 Cl. 13.5) and keep records; follow hot/cold-weather rules (Cl. 14). #### 7. Sampling, testing and acceptance - Sample at the point of placing: 1 sample for 1 to 5 m$^3$, 2 for 6 to 15, 3 for 16 to 30, 4 for 31 to 50 and 1 extra for each additional 50 m$^3$ (IS 456 Cl. 15.2). - Three 150 mm cubes per sample, tested at 28 days; the sample strength is the mean of three (Cl. 15.4). - Accept using Table 11: the mean of 4 consecutive results must be at least the larger of $f_{ck}+0.825s$ and $f_{ck}+4$ (M20 and above; $f_{ck}+3$ for M15), and every result must be at least $f_{ck}-3$ N/mm$^2$. - If the cubes fail, carry out NDT or core tests and, if needed, load tests (Cl. 17). #### 8. Records and statistical control Daily records of mix, tests and weather; control charts of cube strength; the standard deviation is monitored and the mix is adjusted. Non-conformities are reported and corrected. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. Quality assurance differs from quality control in that QA is: A. The testing of cubes only B. The planned system (documents, responsibilities, audits) giving confidence QC is done C. The batching of materials D. The curing of concrete Answer: B. QC are checks; QA is the planned system behind them. (Key point: QC vs QA) 2. Batching accuracy for cement and water, and for aggregates, is: A. +-2% and +-3% B. +-5% and +-5% C. +-3% and +-2% D. +-10% and +-10% Answer: A. Cement and water +-2%, aggregates +-3%. (Key point: Batching accuracy) 3. For 16 to 30 m^3 of concrete, how many samples are taken (IS 456 Cl. 15.2)? A. 1 B. 2 C. 3 D. 4 Answer: C. 1 for 1-5, 2 for 6-15, 3 for 16-30, 4 for 31-50 m^3. (Key point: Sampling frequency) 4. Acceptance by Table 11 requires every individual result to be at least: A. f_ck + 3 B. f_ck + 4 C. f_ck D. f_ck - 3 Answer: D. Every result >= f_ck - 3, and mean of 4 >= f_ck + 0.825s (or f_ck + 4). (Key point: Acceptance) ## Related in Concrete Technology and Masonry Structure - [Quality control at site; slump test](https://www.bctengineer.com/question.md?key=semester_5%2Fconcrete_technology_and_masonry_structure%3Aqc-and-slump-test) — Concrete Technology and Masonry Structure, chapter 3 - [Role and quality of water in concrete](https://www.bctengineer.com/question.md?key=semester_5%2Fconcrete_technology_and_masonry_structure%3Awater-role-quality-impurities) — Concrete Technology and Masonry Structure, chapter 1, asked 3× - [Field testing of cement quality](https://www.bctengineer.com/question.md?key=semester_5%2Fconcrete_technology_and_masonry_structure%3Acement-field-tests) — Concrete Technology and Masonry Structure, chapter 1, asked 2× - [Preventive measures against corrosion](https://www.bctengineer.com/question.md?key=semester_5%2Fconcrete_technology_and_masonry_structure%3Acorrosion-preventive-measures) — Concrete Technology and Masonry Structure, chapter 6, asked 3× - [Measures of workability; role of w/c ratio](https://www.bctengineer.com/question.md?key=semester_5%2Fconcrete_technology_and_masonry_structure%3Aworkability-measures-wc-role) — Concrete Technology and Masonry Structure, chapter 3 - [In-plane, out-of-plane failure and remedial measures](https://www.bctengineer.com/question.md?key=semester_5%2Fconcrete_technology_and_masonry_structure%3Ain-plane-out-of-plane-remedial) — Concrete Technology and Masonry Structure, chapter 9 ## Related in other subjects - [Asphalt concrete construction and quality control](https://www.bctengineer.com/question.md?key=semester_7%2Ftransportation_engineering_ii%3Aasphalt-concrete-construction) — Transportation Engineering II, chapter 3, asked 5× - [Quality; QA vs QC; site engineer steps](https://www.bctengineer.com/question.md?key=semester_7%2Fproject_engineering%3Aquality-qa-qc-site-engineer-steps) — Project Engineering, chapter 4 - [Differentiate quality control and assurance](https://www.bctengineer.com/question.md?key=semester_7%2Fproject_engineering%3Aqa-vs-qc-differentiate) — Project Engineering, chapter 4 - [Construction steps of cement concrete pavement](https://www.bctengineer.com/question.md?key=semester_7%2Ftransportation_engineering_ii%3Acc-pavement-construction-steps) — Transportation Engineering II, chapter 3