Concrete Pavers' Compressive Strength in Relation to Durability

For years in South Africa, there has been heated debate concerning compressive strength as a measure of durability for concrete paving blocks.  To a certain degree, there has been an increase in durability associated with high compressive strengths.  However, specifying a high compressive strength paving block, is definitely not a guarantee of high durability. 

In the Western Cape, the majority of concrete pavers have been manufactured using a "single concrete" method.  What this simply means, is that the paving block is made up of 1 type of mix design.  Manufacturers have had to try to combine the following characteristics with 1 concrete type:

  • Compressive strength
  • Acceptable durability
  • Colour consistency
  • Texture consistency
  • Economy

The negatives that can result from this type of manufacture, is that somewhere along the chain of requirements, a compromise will have to be reached.

An alternative (and in use worldwide) method of manufacture is a paving block manufactured with a topping or face mix.  This paving block has a structurally sound concrete "base mix" with a topping mix comprising of a high cement content, carefully selected  high quality aggregates and pigment if a coloured paving block is required.

The advantages of this method of manufacture, is that the base mix can be designed for what it is intended for:  to be a structurally sound base having adequate mechanical strength.  The aesthetics do not matter since the base will never be seen.  The face mix is consistent in texture and colour, which is also designed to have a high durability or abrasion resistance factor.

Do not be mislead by claims that this is purely a cost reducing exercise.  The fact is that it takes slightly longer to manufacture topped pavers, requiring more specialized equipment and greater expertise.  
 
To summarise, a 25mpa paving block having an adequate abrasion resistance factor, can be used in most heavy duty applications.  Where exceptionally high point loads are expected (container depots, warehouses to store heavy steel sections etc) a specifier may wish to install a 35 mpa paving block.  Insisting on a higher strength block will only add to the cost of the job without increasing performance. The end result will be a functionally and aesthetically superior paving block at the lowest possible cost.

From an Environmental Perspective:

In the production of aesthetic concrete pavers, pigments and premium aggregates are very often used.  Most of C.E.L.'s premium aggregates come from further away than standard aggregate sources.  For many of C.E.L.'s range of special products, we utilize aggregates from Vredendal, Worcester, Saldanha and soon, from as far as Namibia.  Chinese manufacturers supply most pigments, used for colouring concrete in South Africa.  Colouring a paver's base also serves no purpose.  Simply from an energy perspective, it makes very little sense to waste valuable resources for the structure, which will never be seen.