NEW SANS 1058 STANDARD ON CONCRETE BLOCK PAVERS IMMINENT:

The new strength test, which is based on the European system of tensile splitting, will replace the existing method which relies on testing the compressive strength of pavers.

CMA director, John Cairns, says the existing strength test is being changed because of the crucial role that shape and size play in determining the strength of a paving block.

“The current standard only defines what the strength should be - an average compressive strength of 25MPa for most applications - but makes no reference to shape or thickness. In today’s paving market, in which diversity in the shape and size of paving blocks is considerable, a more reliable testing method is now a matter of urgency.

“Our research has shown that a paving block is not crushed under load, rather it breaks due to either a point load or a line load. Pavers are also worn down gradually through abrasion.

“The tensile test deals with the former, and an abrasion test based on an Australian/New Zealand abrasion testing model, with the latter. Both will form part of the new SANS 1058 standard.

“We conducted extensive research on the relationship between the compressive strength and the tensile splitting tests, and this resulted in a thickness factor being taken into account in the new standard.

“Tensile splitting involves two knife edge pressure points and, more importantly, takes the relationship of load and area into account. The test also reflects the conditions under which a block performs far more accurately.

“Our research showed that a standard block, which measures 200 x 100mm and which passes the compressive test will appear to lose 40% of its strength if the same block is cut in half and then tested,” notes Cairns.

Cairns says the South African concrete block paving manufacturers also require an abrasion standard. None currently exists.

“We have found there is no relationship between compressive strength and abrasion resistance. There are currently two classes of block on the market, one rated at 25 MPa and the other at 35 MPa. At the time of its introduction it was thought that the block with the higher compressive strength would offer higher abrasion resistance properties. This has proved to be incorrect.

“Our charts show that even a block of 59 MPa can have very poor abrasion resistance while a block of only 25 MPa can have excellent abrasion resistance.

“We have investigated all forms of abrasion resistance testing systems around the world and Nicholas Papenfus, an independent consultant, completed a thesis on many of them. In the end the Australian/New Zealand model proved to be the most suited to in situ performance conditions.

“Our tests have shown that even a low-grade block with a good topping layer can offer high abrasion resistance. So topping layers do more than offer a choice of colour.

“We are also investigating and will probably introduce a water absorption test into SANS 1058. In Europe it was introduced to prevent blocks from shattering when frozen. We don’t have that problem in South Africa but there are other reasons for its applicability and these are durability related.

“Overall we believe that compressive strength doesn't really test paving block performance effectively and we believe that pavers are less likely to fail if they have passed the tensile splitting test. It’s more appropriate to actual loading conditions and takes shape into account because we found that different shapes will give different results with the same concrete.

“We believe that the new SANS 1058 will be good for the consumer. Concrete paving blocks will be rated according to the new standard and this will provide the consumer with the means of being able to compare the performance of the various pavers on the market with far more accuracy,” concludes Cairns.

This busy intersection in Randfontein, which is subjected to an almost continual pounding by heavy trucks and other traffic has been resurfaced with hard- wearing, abrasion-resistant concrete block pavers. Considerable quantities of grit fall from trucks onto the intersection which exacerbates abrasion wear. Concrete pavers are far more durable than bitumen and this is why they were chosen for this and other intersections countrywide.

An intersection in Randfontein on the same road as the adjoining picture where concrete block pavers (eight years old) with inadequate abrasion resistance properties for this type of loading and volume of traffic should be replaced with pavers with much higher abrasion resistance properties. This type of mis-specification will be easily avoided when the revised SANS 1058 is implemented.