There is no direct way to assess the compressive strength of concrete when it is in fresh stage. Hence it is very difficult to judge the quality of concrete in its fresh stage. So we need to take various steps to ensure quality of the concrete.
Following are some of the important processes to be followed in site level to achieve high quality concrete:
1.Approval of design mix:
Approval of design mix and initial batching plant inspection is must before approving concrete companies or concrete suppliers for a project.
Design mix has to be approved by Structural Consultants for every grade of concrete. Grade wise approved copy should be available with all the concerned engineers.
The same should consist of permissible limits of properties of ingredients and their quantities. Since there are minor variations possible in quantities, permissible limits of variations have to be listed in the approved copy. The design mix has to be revalidated periodically, say once in three or six months and also at the times of change in source of ingredients.
2. Batching plant inspections:
Initial stage inspection for approving the supplier and periodic inspections to concrete batching plants have to be done from the site execution or quality team. Following are the points to be cross checked while going for these inspections;
- Check material source & related documents
- Stacking conditions – ingredients should be stacked on proper concrete floor - should not be on soil, should not get mixed with each other
- Machinery status – Working conditions of all the machineries to be checked
- Automatic batch reports – these are very important. These reports show exactly what is going in the concrete. If the automated system is not installed, then the manual reports would be produced which can have errors.
3.Batch sheet / Cycle data:
For every vehicle of RMC computerized Batch sheet should be checked along with delivery Chelan against the design mix.
In batching sheet following aspects has to be cross checked –
- Batching quantities,
- water cement ratio,
- Admixtures,
- batch time,
- vehicle arrival & unloading time,
- Water level in vehicle’s water tank
4. Slump Test:
In concrete testing slump test is important part to assess the Workability of concrete; it is done to assess how easy to handle the concrete.
To achieve homogeneous and fully compactable concrete we need to get the workability right. So Slump test is must for every load of concrete.
5. Concrete cubes – for testing of Compressive strength of concrete:
Achieving highest concrete compressive strength is the aim of entire concreting activity. Hence proper cubes have to be prepared at the time of concreting in required numbers.
The curing for these cubes can be done in two ways – first is as per Codes & second is as per site curing conditions. For the purpose of contractual requirements cubes has to be cured as per standard codes. To assess actual strength of concrete poured in the structure, curing has to be done same way like how the actual structure’s curing is done.
6.Avoid addition of Water:
There is a tendency of workers to add extra water in RMC vehicle if in case concrete becomes little stiff. This practice has to be avoided at all costs.
Adding excess water may create segregation or higher porosity. This will reduce the Durability concrete.
7.Temperature:
Checking the concrete temperature also equally important to ensure nothing is going wrong. If there is some issue with chemical reaction, temperature of concrete may go beyond the permissible limits.
8.Transporting:
Transporting of concrete can be done by pumping, conveyor belts or by manual carrying. At the time of transportation segregation has to be avoided.
9.Placing, Compacting & Finishing:
Highest importance has to be given for placing and compacting when comparing with everything else in concreting process.
I can’t stress enough…. 100% compaction is must.
Surface finishing has to be achieved as per required specifications.
10.Curing:
All the concretes have to be cured continuously for 7 days & periodically for next 21 days.
Conclusion:
Achieving high quality concreting is the primary importance for all the constructions. Above listed steps will help you to achieve the same.
