Saving money with Bulk Bags of Cement

Making the choice between purchasing Ready Mix Concrete or mixing on site can seem complicated, balancing up material cost, labour and equipment required. Cement in bulk sacks have been available for many years but users are often put off by what appears to be limited or no cost saving against the standard 25kg bag of cement.

This blog post will explain in high level detail why using bulk bags of cement can prove to be a worthwhile consideration. 

Cement Strength

Most people would be forgiven for believing that "cement is cement!" but the truth is that is not the case. Varying degrees of cement strength exists which varies the requirement for cement in the concrete mix. 

The typical bag of cement that you will find in most DIY stores or Builders Merchants is a 32.5N cement, sold in a 25kg paper or plastic bag, from brands such as Blue Circle, Mannok, Cemex etc. 

The bulk cement sold by Red Stag Materials, in a 1.5 tonne tote bag contains a 52.5R cement, which is a stronger, faster setting cement.

Both cement types are suitable for most general concrete work and can mixed into sand/gravel, sand/crushed aggregate or crushed rock fines/aggregate mix compositions.

Understanding Mix Designs

In order to explain this in an easily explainable way, it is easiest to provide a worked example.

C25/30 concrete a medium-strength mix (30 MPa at 28 days), is often used for structural purposes like foundations and floor slabs. The cement content required depends on the cement type and water-cement ratio.

In this example, we will calculate, by rule of thumb, the cement requirements for making a C25/30, often known as 30N concrete and assuming a water cement ratio of 0.5, which is a typical value for achieving workability and strength.

Using 52.5R Cement

• Target Strength: 30 MPa
• Cement Strength: 52.5 MPa
• Cement Content = 30 x 0.5 x 1 divide by 52.5 = 286 kg/m3 

Using 32.5N Cement

• Target Strength: 30 MPa
• Cement Strength: 32.5 MPa
• Cement Content = 30 x 0.5 x 1 divide by 32.5 = 462kg/m3

This means that using 52.5R cement requires a lot less cement to achieve the same strength than if using 32.5N cement.

Key Considerations

• It's always advisable to produce a trial mix first to ensure the correct strength and workability. 
• The quality of sand and aggregates used will impact strength. Dirty or clay bound materials will impact strength.
• Smaller aggregates sizes will require a greater cement content.
• Maintain a close eye on the water cement ratio.

To achieve the best possible mix design for structural integrity, cost effectiveness and workability, it is advisable to seek the professional opinion. 

Difference between 52.5n and 52.5R

Technical Difference between 52.5N and 52.5R