Published in 2021, BS 7533-101 provides recommendations and guidance on the design of pavements surfaced with modular paving units. This new standard serves as an update to the existing BS 7533 series by consolidating several design standards into one document.
This affects the design of all modular paving in the UK.
The use of concrete blocks, clay pavers, stone setts, and concrete and stone slabs or flags and kerb units has significantly increased since the original standards were published.
Public sector improvement schemes have increased their hard landscaping and the cost of the products has become more competitive. Therefore, a comprehensive portfolio of design standards will provide consistency and promote their further use.
Over time the provisions contained within the previous pavement standards have become obsolete and the many versions caused confusion amongst designers and installers, leading to a risk of errors and premature failure. Revising and updating the parts of the BS 7533 series on design - and consolidating seven parts into the one - BS 7533-101 - has simplified the design process for users and will reduce significant errors, also making the products and pavements significantly more durable.
To learn more about the changes, read our article 'The structural pavement design standard series has been updated'
Since the launch of BS 7533-101, we have run both a webinar and podcast exploring its importance to the built environment. To support you further, we have asked the experts behind the standard to answer your frequently asked questions.
Sustainability and Net Zero
Question 1: How is concrete considered a low carbon material?
Answer: Many material comparison studies have been conducted over the years to monitor this, such as Hammond (2011), the University of Bath Carbon database, and many others. We have all heard about the claim that concrete emissions make 6-8% of the world’s CO2 emissions. It should be noted that those figures over-estimate the carbon load for concrete in the UK, which only makes around 1.5% of the UK’s carbon emissions (around 25% only of the global impact average).
The reason that concrete continues to have a major impact on global CO2 emissions is that it is used in such high quantities - around 30,000Mt per year. However, in the past decade, the UK has managed to halve concrete CO2 levels, and UK cement and concrete are continuing to progress rapidly towards net zero.
Safety
Question 2: On the importance of tonal contrast of blister tactile paving (the different messaging associated with buff and red coloured) - does BS 7533-101 provide guidance on this or refer out to the relevant guidance in other standards?
Answer: Although not specified in BS 7533-101, there are requirements in BS 8300 to be followed to obtain sufficient contrast in adjoining pavement surfaces. This is to ensure the safety of pedestrian users and cyclists.
In particular, the information on light reflection should be obtained for the stone concerned when wet as well as dry. It is not easy to optimize the contrast in both circumstances and it may be prudent to think through this matter before deciding on the main aspects of the colour scheme to avoid re-design from being necessary.
Question 3: In Sweden, tests are being carried out on a shock-absorbent mix that absorbs more than 80% of the impact of a fall. A safer surface would encourage older people to take more exercise, improving physical and mental health. Should this new mix laid on pedestrian pathways be given priority?
Answer: To provide a correct response we should point out that the scope of BS 7533-101 is to address a specific type of pavement design: modular paving. The modules which comprise the pavement are limited by the scope of the standard to those described in European product norms - BS EN 1338, BS EN 1339, BS EN 1340, BS EN 1341, BS EN 1342, and BS EN 1343.
The type of pavement the question refers to comprises a homogenous surfacing material, namely rubber crumb, and stone aggregate bound together with bitumen. Relevant BSI documents exist for this type of pavement. Whilst there is sometimes new research into manufacturing paving modules and other construction industry modular elements using rubber crumb there is - to the best of our knowledge - no standards existing to address this hypothetical application.
Technical Details
Question 4: In BS 7533-101, Bound System A details that for this system the paver should be deeper than its width. Could you explain the reason for this in more detail? There aren't many pavers that are deeper than they are wide unless the unit is used on its side.
Answer: Firstly, a clarification, clause 6.4.2 states that Bound System A should be used only for setts and pavers having depth not less than width.
It does not state that they should always be deeper than width, only that they should not be shallower. Even so, for natural stone setts, it is sometimes necessary to design with setts that are deeper than their width, in the highest traffic categories.
The need for setts in Bound System A to be no less deep than their width and sometimes deeper than their width in higher traffic categories can be explained as Bound System A may be laid over a bituminous bound asphalt concrete base (AC) or an unbound base layer, to which the bedding mortar does not adhere, and the setts are also not strongly adhered to the bedding mortar. The base, therefore, provides less support in compression than with Bound System B and a relatively weak connection in tension.
When the pavement is subjected to purely static, vertical loading the jointing mortar is subjected to shear forces and the ability to resist those forces is directly proportional to the depth of the joint; in short, deeper is better.
When the pavement is subjected to dynamic loading, the reaction of the setts is to rotate about a horizontal axis; the jointing mortar is again subjected to shear forces but also to extremes of stress and strain in the top and bottom regions of the joint. Just as we might consider the mechanical advantage provided by levers, the deeper the sett is in relation to its width, the better the reduction in stress and strain at the top and bottom of the joint. This is also why pavement surfaces sometimes buckle and lift when overloaded and we can say that pavements generally fail up, not down.
Whilst pre-cast concrete and clay pavers are more often shallower than their width, a relatively few being square or deeper as standard, natural stone setts can be manufactured having an infinite variety of dimensions, and setts having a depth greater than width are not unusual.
Question 5: With increased flooding events likely going forward, what are the recommendations for avoiding the washout of the jointing and laying course? BS 7533-101 seems to indicate that unbound is hard-wearing, but we have increasing issues of the material being washed out requiring full relaying.
Answer: If the bedding and jointing are in accordance with BS 7533-101, washout can be avoided if the surface is sealed. Drainage of the sand is also essential to avoid this from occurring.
Do you have any questions about BS 7533-101 that you would like to ask the experts? Get in touch with our Customer Relations Team here - cservices@bsigroup.com. You can also add BS 7533-101 to your collection today.
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