Development of UK standards for precast concrete paving and kerbs

Development of UK standards for precast concrete paving and kerbs

Budge, Clive

Introduction

The current British Standards for paving and kerbs are as follows:

Products:

BS 6717: Part 1: 1993 Precast concrete paving blocks: specification for paving blocks

BS 7263: Part 1: 1994 Precast concrete flags, kerbs, channels edgings and quadrants: specification

Design:

BS 7533: Part 1: 1992 Guide for structural design of pavements constructed with clay or concrete blocks

Construction

BS 7533: Part 3:1997 Pavements constructed with clay, natural stone or concrete pavers: code of practice for laying precast concrete paving blocks and clay pavers for flexible pavements

BS 7533: Part 4: 1998 Pavements constructed with clay, natural stone or concrete pavers: code of practice for the construction of pavements of precast concrete flags or natural stone slabs

BS 7533: Part 6: 1999 Pavements constructed with clay, natural stone or concrete pavers: code of practice for laying natural stone, precast concrete and clay kerb units.

The natural progression of the UK standards for paving products in recent years has been inhibited by the standstill agreement during the preparation of European Standards. Consequently, these have reached the stage where they are close to being ‘past their sell-by date’. In 1999, the BSI Committee (B/507) decided that, as European Standards were still a long way from implementation, the UK should adapt its current versions and publish them as replacements for the three products (block, flag and kerb). An application was then made to CEN for derogation of the standstill on the British Standards on the basis that their replacement would follow the CEN Standards. This was quickly granted and for the past year or more there has been a great deal of work to adapt the European drafts for publication as British Standards.

The major difference between existing British Standards and their forthcoming European counterparts is that the former are prescriptive whereas the latter are performancebased. Revised British Standards are following the latter approach and the new Standards have no prescribed product dimensions. Instead, existing flag and kerb sizes are put forward as designated units, and familiar products will continue to be available. However, the method of performance measurements will be unfamiliar to many users, as the performance classes and different requirements in the standards reflect the different applications of the products. The inclusion of a ‘no performance determined’ option for slip/skid, abrasion and freeze/thaw reflects the content of the forthcoming harmonised European Standards.

Strength

A splitting strength is established for blocks, while flag and kerb continue to use bending strength, albeit with a modified test. The tests all derive material strengths rather than unit strengths. A minimum strength is specified for block and kerb, whereas flag has two strength classes.

Slip/skid resistance

The pendulum test is used in conjunction with a polishing regime specified in BS 7932: 1998 Method for determination of polished paver value to give unpolished and polished test values. The lower of these provides the slip/skid resistance value for the products and the standard allows for performance classes.

Abrasion resistance

The wide-wheel (70mm) abrasion test is adopted, with the specimen being held against the rotating wheel for one minute while abrasive material is fed into the interface (Figure 3). The resulting abraded area is shown in Figure 4. Performance of the product is defined by the chord length of the groove and the three products have different performance requirements.

Freeze/thaw durability

The existing standard for paving blocks specifies a minimum cement content to ensure durability. In the flag and kerb standard, this is defined by limits on water absorption (Figure 5). The new standards have a freeze test performance requirement, and product specimens are subject to freeze/thaw cycling in the presence of a saline solution.

Type testing and production control

The new standards contain requirements for type-testing new products and specify the continuing production controls for all products covered by the Standard. The standard replacing BS 6717 : Part 1: 1993 will retain the existing number and BS 7263: Part 1: 1994 will be replaced by Part 1 for flags and Part 3 for kerbs. Publication is expected before the end of 2000. The European Standards continue to progress, although a publication date cannot yet be predicted. However, the revised British Standards will have a life of at least three years.

Information about paving design can be found in Interpave’s Design handbook and a new publication on the installation of paving products is expected to be published later in the year. For more information, phone Interpave on +44 (0) 116 253 6161 or visit www.paving.org.uk.

Clive Budge, Interpave

Copyright The Concrete Society Sep 2000

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