4.1 Introduction to Clause 4: Understanding the Pavement as a Complete System
BS 7533-102 Clause 4 covers the key considerations that influence how modular paving should be assessed, designed and constructed, including ground conditions, foundations, drainage and the choice between bound and unbound paving systems.
Throughout this series, we have broken down the individual parts of Clause 4 and presented them in a more practical, user-friendly format. Supporting guidance and links have also been included where they help explain individual topics in greater detail.
Bound and Unbound Paving Systems
One of the fundamental considerations when constructing paving is whether the pavement will use a bound or unbound construction system.
Unbound paving systems are often easier to lift and repair, particularly where future access beneath the pavement may be required. However, they will normally require more maintenance than bound construction.
Rigid or bound paving systems provide greater stiffness and, in some situations, can support the use of thinner paving units. However, they can also be more susceptible to cracking where the base, bedding or anticipated loading has not been properly considered.
The construction method should therefore be selected as part of the overall pavement design rather than being considered in isolation.
Supporting Thin Paving Slabs and Flags
Thin slabs and flags — particularly porcelain, natural stone and concrete paving units — benefit from full, compatible bonding to a sound reinforced concrete base.
This provides continuous support beneath the paving and helps reduce the risk of:
- Breakage;
- Rocking paving units; and
- Uneven edges
However, the construction of a reinforced concrete slab is a highly skilled operation in its own right and requires careful planning and design.
Mortar bedding over a granular base — sometimes described as bound over unbound construction — can also improve support and stability when it is correctly specified and installed.
Reinforcement Does Not Replace Good Foundations
Reinforcement can also form part of the pavement construction.
The use of alkali-resistant geosynthetic or stainless-steel mesh within the bedding layer can help resist cracking. However, reinforcement should not be viewed as a solution for poor ground preparation, inadequate drainage or insufficient foundation construction and compaction.
For areas that will be subjected to vehicle loading, plant or concentrated stabiliser loads, the pavement should be designed for its actual intended use rather than selected solely on the appearance or thickness of the paving unit.
Assess the Subgrade First
The condition of the ground beneath the pavement remains fundamental to the performance of every construction system.
Geosynthetic mesh installed over a firm, stable and properly assessed subgrade, following appropriate assessment such as the boot test and subgrade assessment, and within subsequent foundation layers can help mitigate creep or lateral movement while providing additional structural integrity.
The key principle throughout Clause 4 is that no single paving component works independently.
The paving unit, bedding, base, sub-base, reinforcement, drainage and underlying ground all need to work together as a complete pavement structure. The following sections of this Clause 4 series examine each of these areas in greater detail.
