Vanstone Precast (Pty) Ltd

General Design of Block Paving

General and comprehensive guidelines to concrete block paving (CBP) is available from the CMA: www.cma.org.za Follow the link to Publications:

• Book 1. Introduction to Paving;
• Book 2. Design Aspects;
• Book 3. Specification and Installation;
• Book 4. Site Management and Laying;
• Books 5&6. Training Manual for the Laying of CBP

See also: Introduction for Engineers

Design Aspects Particular to Permeable Paving

Permeable Concrete Block Paving (PCBP) is both road and the stormwater system. The porous paving and road foundation replace elaborate storm water systems including catchpits, massive pipes, canals and outlet structures. All or part of the surface is made permeable, and the water is allowed to infiltrate. While collecting under the surface it absorbs the flood, infiltrates the ground and the (much reduced) excess is drained away.

Permeable paving is not simply a standard road foundation with permeable paving on top. The road foundation must be permeable as well. The two basic components of PCBP therefore are: 1) porous paving blocks and 2) a porous road foundation.

Vanstone Aqualock and Aqua Random are specific Permeable Paving Blocks. As such they are equipped with special openings between blocks and also with wider than ordinary joints to let water through.

To help with the choice of road base, bedding and filler materials for successful permeable paving, the following guidelines are given.

Base Course for Permeable Paving

The Base Course in Permeable Paving serves a dual purpose: 1) It supports the paving blocks and 2) It acts as a collector of the water that penetrate the paving. It has to be both strong and porous. From the base course the water is either let into the underground or retained for a while to absorb flood. It is then drained into a small bore pipe system. A hybrid of the two is also a possibility. See: Introduction for Engineers

Recommended Material for Base Course

The base course has to be both structurally strong and properly porous. It has been found that single size crushed stone is both widely available and suitable for Permeable Paving. The size of the stones must be such that clogging by finer material from above or below does not happen. Geotextile may be used as a separator to prevent intermixing of layers.

Thick base courses may be constructed in two layers with the bottom one say 38mm stone and the top one 25mm stone.

Layer Thickness

Normal road foundation design considerations will determine in the first place the (minimum) foundation layers and thicknesses required for structural integrity.

Storm water design will determine the required holding volume of the base course. For single size crushed stone, the void volume is on average a third of the total volume. With this in mind the following can be played around with:

• Layer thickness
• Combining base and subbase
• Infiltration and/or drainage
• Permeable paving area: full or partial

Bedding and Filler Sand for Permeable Paving

Single grade large size sand is not suitable as it will compromise interlock. Without interlock, paving blocks act individually and the bearing capacity is drastically reduced.

After many experiments and practical experience, it was found that the best performing sand for both filling and bedding is clean 2mm – 5mm crusher sand containing no fines. For standard sieve sizes this may be translated to between 1.18mm to 4.75mm (no fines), which also works well.

For bedding sand only, larger sizes up to 9mm may be used with smaller sizes down to about 2mm but no fines.

For filler sand only, neither sizes larger than 6mm nor fines are permitted.

Some Examples:

Small Capacity with Full Infiltration:	Small Capacity with Drainage:
Large Capacity with Full Infiltration:	Large Capacity with Drainage: