Quality Assurance
Quality Assurance of Concrete
Testing for physical properties of every incoming batch aggregate are done not only at internal laboratory according to standard method and procedure but also external third party laboratory as specified interval. Nominal maximum size of 9.5 mm and 19 mm coarse aggregate are commonly available for general mix proportion and nominal maximum size of 25 mm and 37.5 mm can be applied as project required.
Type-1 Ordinary Portland Cement is mainly used in concrete production. Cement mortar tests are regularly performed for every incoming cement at internal laboratory. Monthly physical quality testing of current using cement is done in order to assure the quality. Also, chemical properties of each batch cement can be available from cement test certificate of manufacturer/supplier. Cement stored at warehouse over three months is retested for use of concrete production.
Water analysis test is conducted at external laboratory at every six months. Usually, water is kept in clean and free fom undesirable particle, injurious amount of sewage, oil, acid and other deleterious matters.
Cool water can be available and applied for concrete temperature purpose as special requirement of construction projects.
- Retarder
- Superplasticizer
- High range water reducing admixture (polycarboxylate ether polymer base)
- Air- Entrained admixture
- Waterproofing admixture
- Slump retention admixture
Most of chemical suppliers are Grace, Sika and BASF. Quality assurance certificate of each incoming batch can be available from chemical supplier. Specific gravity test of every incoming chemical admixture is done as an internal quality checking.
- Testing of Fresh Conerete
- Workability/ Slump test
- Unit weight test
- Air content test by pressure
- Temperature test of fresh concrete
- Concrete setting test
- Concrete Sampling, Making and Curing of Specimens
Every batch of concrete supplied will be mixed thoroughly and performed required fresh concrete tests before delivery to construction sites. Slump test and specimen making will be responsible of concrete supplier. Six number of cube or cylinder specimens are collected per 100 cubic meter or as per customer site requiremet.
- Testing of Hardened Concrete
In order to monitor and control concrete quality, in-house concrete specimens are tested compressive strength at the age of 3 days, 7 days and 28 days or as required.
- Acceptance Criteria of Concrete (ACI 318)
- Every arithmetic average of any three consecutive strength tests equals or exceeds specified strength fc’.
- No strength test falls below specified strength fc‘ by more than 3.5 MPa when fc‘ is 35 MPa or less or by more than 0.10 fc‘ when fc‘ is more than 35 MPa.
Batching load cells and all testing equipment will be calibrated by external labs or in-house labs at appropriate intervals.
All quality control records are maintained according to respective retention.