PQC stands for Pavement Quality Concrete, which is a type of concrete used for constructing roads and highways. PQC is different from building concrete, which is used for foundations, columns, beams, slabs and other load-bearing elements. In this blog post, we will discuss what is the grade of PQC and how it is determined.
What is PQC?
PQC is cement concrete made with large size aggregates (20 mm and 10 mm) in accordance with IRC specifications and laid over a dry lean concrete (DLC) sub-base. DLC is a low-strength concrete layer that provides a uniform support to the PQC layer. PQC can withstand heavy loads and has high flexural strength. It also has low permeability and good durability.
How is the grade of PQC determined?
The grade of PQC refers to its compressive strength at 28 days after curing. The compressive strength is measured by testing standard cubes or cylinders of concrete in a laboratory. The grade of PQC depends on several factors, such as:
- The type and quality of cement used
- The water-cement ratio
- The type and dosage of chemical admixtures used
- The quality and gradation of aggregates used
- The mixing, transporting, placing, compacting and curing methods.
According to IRC:15-2002, the minimum grade of PQC for highway pavements should be M40 (40 MPa or N/mm2). However, higher grades may be required depending on the traffic intensity, climatic conditions and design life of the pavement.
How to design a mix for PQC?
The mix design for PQC should be done as per IRC:44, which provides guidelines for selecting the materials and proportions for achieving the desired grade of PQC. Some of the important steps involved in mix design are:
- Determine the target mean strength based on the specified grade and standard deviation
- Select suitable materials such as cement, aggregates, admixtures etc.
- Conduct trial mixes with different water-cement ratios to obtain workability and strength values
- Choose the optimum water-cement ratio that gives adequate workability and meets the strength requirement
- Calculate the quantities of materials required per cubic meter of concrete.
The mix design should also consider other factors such as shrinkage control, temperature control, durability etc.
Conclusion
Pavement Quality Concrete (PQC) is a special type of concrete used for road construction. It has high strength, low permeability and good durability. The grade of PQC depends on its compressive strength at 28 days after curing. The mix design for PQC should be done as per IRC specifications to achieve the desired grade.
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