The scope of this procedure covers best practices and checks for carrying out prior to and during the site batching of concrete.
Checks prior to commencement of concrete batching activity:
Basic constituents of concrete viz. cement, coarse and fine aggregates shall comply with the contract specifications.
In case of large projects and where specified, a laboratory will be set up at site for conducting tests on materials and to ensure the quality of product.
Availability of potable water and power shall be ensured.
In case of supply failure alternative arrangements shall also be planned.
Verify the type of admixture if required to be added. If required receive approval from Engineer’s representative.
Handling and Storage of Materials
Special care shall be taken for proper storage of basic materials in order to avoid contamination.
Unless otherwise specified, the following measures shall be taken for proper handling and storage of these materials:
Cement (in bulk)
The silos shall be weatherproof and the mechanism will be cleaned regularly in accordance with manufacturer’s manual.
The air filter will be cleaned after every delivery.
Care shall be taken to use stored cement in the order of delivery.
Care shall be taken to minimize the contact of cement with air.
The silo shall be painted white and wherever possible, shaded from sun.
Aggregates
Storage of aggregates shall be on clean; permanent clean hard-standing laid to fall for drainage.
Different sizes of aggregates shall be separated from each other in bins or compartments with rigid dividing walls extending high enough to prevent different aggregates from being mixed during batching.
In hot climates either shading or sprinkling clean water is required to reduce that fines and dust have not built up at the lower levels.
If this has occurred, contaminated aggregates shall be removed and washed or replaced with clean material.
If aggregates are wet stockpiles shall be frequently inspected to make sure that fines and dust have not built up at the lower levels.
If this has occurred, contaminated aggregates shall be removed and washed or replaced with clean material.
Admixtures
Storage of admixture shall be as per the manufacturer’s recommendations.
The containers shall be leveled to indicate the contents, batch number, date of manufacture, shelf life and any other requirements for storage.
Water
Water shall be stored as cool as possible, particularly if it has been supplied by road tanker or shallow wells.
Wherever possible, storage tanks shall be sited below ground. If this is not possible, they should be at least be shaded from the sun and painted white.
Tank to be covered properly to prevent the growth of algae.
For cooling of water even site cooling towers can be used which reduces the temperature up to 10°C or ice can be used.
Batching Plant
Batching and mixing plant shall be painted white and kept clean.
If possible, mixing and batching plant shall be shaded from the sun.
Provision shall be made to prevent dust accumulating in the plant and immediately before it is used each day (or after any substantial interruption in concreting) it shall be flushed out with water.
Feed belts and weigh batchers shall be protected from the wind so that cement can’t be blown away.
Ensure the accuracy of all weighing and measuring equipment falls within + 3% unless specified otherwise calibrate plant as necessary.
Batching by volume
Prepare gauge boxes or similar standard containers of a size such that complete filling is necessary when proportioning materials.
Clear written instructions will be provided to the Plant operator on quantities of all materials to be batched and batching sequence for each mix required.
Priming of internal drum of mixer to be done at the time of loading the first batch of materials.
Mix ingredients for sufficient time as specified to ensure uniform distribution of materials.
Check the zero reading when hopper is empty.
Check the speed of mixer drum once a week and adjust to that given in the manufacturer’s manual.
Regular maintenance of moving parts shall be done in accordance with the manufacturer’s manual.
Transport the concrete with minimum delay so that it is placed before it comes hardened and difficult to place and compact.
Following documents may be appropriate as a minimum requirement:
- Test certificates of cement, aggregates, water and admixtures
- Mix design details
- Calibration record of all equipments of batching plant