TWELVE-MONTH IMPLEMENTATION WINDOW FOR REVISED PAVING STANDARD:

The revised standard was drafted jointly by SABS and the CMA (Concrete Manufacturers Association), and replaces the old compression-based standard with three new performance measurement techniques, tensile splitting, abrasion testing and water absorption.

According to Hamish Laing, CMA director, SANS 1058 2010 will be good for property owners and developers as it provides them with the means of comparing the performance of the various pavers on the market with far more accuracy.

“A revised standard was required because of the crucial role that shape and size play in determining the strength of a paving block. The old standard only defined what the compressive strength should be - an average of 25MPa for most applications - but made no reference to shape or thickness. Compressive strength doesn't really test paving block performance effectively and 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.

“Furthermore, the considerable diversity in shape and size of CBPs in today’s paving market called for a more relevant performance-based testing regime. Prior to making our recommendations on the revised standard, we conducted research which showed that paving blocks are not crushed under load, rather they break up either through excessive point or line loads. Moreover, we found that pavers which pass the compressive strength test may have a poor abrasion resistance. The tensile splitting test deals with the former, and of course the abrasion test, based on an Australian/New Zealand abrasion testing model, with the latter.

“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 revised standard.

“The tensile split test involves two knife edge pressure points and, more importantly, takes load and area into account. It 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 appears to lose 40% of its strength if it is cut in half and then re-tested.

“We also found there is no relationship between compressive strength and abrasion resistance. In the past it was thought that higher compression equated to higher abrasion resistance. However, this has subsequently proved to be false. In fact we found that blocks of 59MPa can have very poor abrasion resistance whereas those of only 25MPa can have excellent resistance. Subsequent tests demonstrated that even low-grade blocks with a good topping layer can offer high abrasion resistance, proving that topping layers do more than offer colour variation,” advises Laing.

The CMA investigated all forms of abrasion resistance, testing systems around the world, and in the end opted for the Australian/New Zealand model which proved to be best suited to in situ performance conditions.

Laing says the water absorption test also forms part of SANS 1058 2010 because CBPs with low absorption rates tend to offer better durability.

“The absorption test was first introduced in Europe to prevent blocks from shattering when frozen and although we don’t experience that problem in South Africa, durability is closely allied to strength and abrasion resistance.

“We strongly recommend that both private and public specifiers adopt the revised standard as soon as possible beacause most CMA producer members are already geared to test their products in accordance with it. Moreover, two accredited laboratories, one belonging to the SABS and the other to CMA member, Soilcon, are on hand to perform independent tests, should the need arise,” concludes Laing.

A new paving block abrasion testing machine manufactured locally.

These concrete block pavers have been tested for abrasion resistance on the new abrasion testing machine.

DATE :  April, 2010
ISSUED BY :  David Beer Communication Consultants
FOR :  Concrete Manufacturers Association 
ENQUIRIES:   Hamish Laing (011) 805 6742
David Beer (011) 478 0239 or 082 880 6726.  Email: bigsky@ibi.co.za