Quality control of ready-mixed concrete can be divided into three components,
1. Forward Control,
2. Immediate check and
3. Check afterwards.
Forward control and the resulting corrective actions are essential aspects of quality control. Forward control includes the following.
• Control of purchased material quality
• Control of material storage
• Mix design and mix design modification
• Transfer and weighing equipment: the manufacturer must be able to demonstrate that a documented calibration procedure is in place. The use of elector-mechanical weighing and measuring systems, i.e. load cells, flow meters, etc., is preferable to purely mechanical systems, i.e. knife edge and lever systems.
• Plant mixers if present and used truck mixers must be in an operational condition.
Immediate control refers to immediate action to check the quality of the concrete produced or that of deliveries that follow closely. It includes the production control and the product control.
a) Production control:
The production of concrete in each factory must be systematically monitored.
This is to ensure that all concrete supplied is in accordance with these requirements and with the specifications that form the basis of the agreement between producer and buyer.
Each load of mixed concrete must be inspected before shipment and before unloading.
The workability of the concrete must be continuously monitored during production and any corrective measures taken.
For each load, written, printed or graphical records shall be made of the mass of the grouped materials, the estimated draft, the total amount of water added to the load, the number of the delivery note for that load and the time the concrete was set. loaded into the truck.
Routine inspections are carried out on the condition of installations and equipment, including vans.
b) Product control:
Concrete mixes are randomly sampled and tested for workability and, if applicable, plastic density, temperature and air content. If significant deviations from the target values are found, corrective measures must be taken.
It is important to keep the water-cement ratio constant at the correct value. The amount of water added should be adjusted to compensate for any observed variations in moisture content in the additives.
Due to this variation, appropriate adjustments must also be made in masses of the aggregates (see IS 456). Any change in water content due to a change in aggregate classification should be accommodated by forward control through appropriate adjustments to the mixture design.
Retrospective control deals with those factors that influence the control of production.
Retrospective control can refer to all properties of materials or concrete, such as aggregate quality, slump, or air volume, but is particularly associated with a cube strength of 28 days, as it is by nature not a property that can be measured before or at the time of , manufacturing.