Although the engineering benefits of the technique are accepted in principle, factors such as price and the slow pace of manually laid projects deter contractors from including block paving in their tenders. Increasingly tight deadlines and the occasional problem of repetitive strain injury with manual laying means that the industry is turning to the benefits of machine-laid block paving. The much faster production rates obtainable have become an important factor during the past few years.

The benefits of machine-laid block paving

Aesthetic considerations and low maintenance costs, in conjunction with a life of well over 25 years, are sufficient justification to convince architects, engineers and clients that block paving is a practicable alternative to other materials. With their resistance to concentrated loads, concrete blocks are ideal for airports and ports and, unlike asphalt, are undamaged by fuel and hydraulic oil spillages.

In ports, pavements often experience differential settlement because of the varying nature of fill materials and here paves offer a serviceable pavement without cracking: if settlement or rutting occurs, blocks can be removed, repairs rapidly made to the base and the same units rein stated. Studies show that the initial costs of laying block paving fail to take into account the long-term economic benefits.

The authors consider that block paving is less expensive than asphalt over a 25-year period. The laying method represents a major component of lifetime costs and cost studies demonstrate that machine-laid block paving for large commercial and industrial areas is very competitive.

The benefits of machine-laid paving will be realised if:

• project management is systematic and efficient
• a proficient, experienced team is employed
• the right specialized laying machines are selected

Manual vs machine

With hand-laying, it is difficult to maintain exact joint widths. Some operatives will lay the blocks loose and others tight, making it difficult to control pavement directions. A 10,000m2 project can be completed by four qualified labourers in 50 days.

Using a dedicated self-propelled paving machine and with good site organisation, the same laborers can complete the same project in nine days. If the equipment is purchased, subsequent unit costs will be reduced and competitiveness should be improved. Manual laying will there fore be restricted to just a few square metres per day and confined to edge detailing and areas where using machinery is difficult or impossible.

Optimising machine laying

In ideal circumstances, automatic laying machines can achieve four cycles per minute, ie. 240 cycles/h. Shaped concrete blocks such as Uni-Coloc (L-shaped), Xenex (cruciform) and rectangular blocks in herringbone pattern are ideal for machine laying as they can be palletised in the laying pattern.

With a 1.32x1.32m layer (l.742m2) Operating at 2 cycles/min, output is around 209m2/h. Evidence available to the authors confirms that such productivity rates are achievable. For example, New Zealand contractor Mirage Paving laid on average at least 900m2 in eight hours with one expert machine team and a paver layer size of about 1m2 while completing the Tranz Rail Freight Terminal in Christchurch, New Zealand during 1998.

Complex hardscaping -- CAD to construction

It is now possible to incorporate complex patterns of multi-coloured blocks of different shapes and sizes into a single pavement in the factory. The blocks can be manufactured according to the laying pattern, colour and mix of sizes in a forming station, divided into the corresponding laying units and packed for sequential delivery to site.

To make the best use of mechanical laying, the manufacturer has to supply the blocks to site in the necessary laying patterns and colour mix, including the edges. This increases manufacturing costs but reduces laying time.

As a result:

• the customer does not have to pay a premium for sophisticated paving patterns
• projects will be completed quicker, resulting in further savings.

Such factory prefabrication with subsequent division into laying units will be indispensable if the new industrial protection directives from Europe are applied consistently.

The change from production to site-processing

Intensive promotional and technical activity has highlighted the aesthetic, physical, and commercial advantages of block paving. The paving industry continues to invest in production facilities and methods but these have not yet been matched on site. The weakest link is still on-site laying, particularly at airports, ports, superstore car-parks and even roads, where time is crucial.

One of the leading manufacturers of concrete block paving is Marshalls. Mark Bushell, block paving commercial manager, comments: "While machine laying has been around for some time, it seems the market is ready to take on board the real benefits. Firstly, we are working more closely with everyone in the supply chain. By coming together at design stage, machine-laid block paving is effectively integrated into the programme. And, with new health and safety legislation on the horizon, the technique offers benefits such as reduced fatigue and less repetitive strain injury."

Manufacturers are solving technical problems associated with block paving -- such as cement and colour inconsistencies -- using available technology and materials. However, trends towards shorter deadlines and the difficulty of finding skilled workers for "dirty" industry are moving the emphasis towards the on-site laying process. Major impediments to speedy machine laying of concrete block paving in are:

• Use of void packs (800 by 800mm packs with gaps to receive the forklift)
• Laying machines capable of processing up to 1.6sq m per layer, offering double the efficiency, are available and general contractors need to be made aware of this.

From Interlocking Concrete Pavement brochure, ICPI Bauma tour.

The effects of technology

In the construction industry, it is generally true that the more technology applied on site, the lower the costs.

Unfortunately, many subcontractors wrongly assume that better quality laying and the use of technology on site increases finished cost. In fact, the opposite is the rule, as accuracy is improved, laying is cheaper and the health problems connected with block paving are avoided. All this, in turn, speeds completion.

Machine-laid paving is growing, but significant progress will be possible only if all in the paving chain work together.

Who buys the machines?

If paving projects are to take into account economic and health and safety considerations and use dedicated machines, the question is who will supply them and how will they be financed. The best route is to award tenders to subcontractors that have the machines necessary to complete the project on time, but many labour-only subcontractors cannot afford the capital outlay. On top of this, many machine suppliers will not provide the equipment because of the financial risk associated with under-capitalised companies. Furthermore, the contractor with the lowest bid will generally be unable to generate sufficient funds to invest in expensive machines.

Suitable support by the paver producer or general contractor would reduce the problem of the labour-only subcontractor unable to pay for the equipment needed to complete the job. Block-paving producers wanting to sell their products may wish to play a greater role in providing finance for purchase, rental or lease programmes and financing facilities for contractors.

At least three possibilities exist:

First, the concrete block supplier and/or the general contractor will supply the equipment needed for "labour-only" contractors. Second, large established labour-only contractors and pavement-laying contractors with in-house surfacing divisions purchase the equipment and the paving. Third, contractors become general "surfacing" contractors and prepare the base using a similar approach to that of asphalt, but substitute the surface course with machine-laid concrete block paving.

Conclusions

• Block paving is a cost-effective alternative to asphalt and in-situ concrete
• Mechanical laying avoids the health and safety problems of continuous manual laying
• About 900m2 can be laid by machine in a 10-hour day
• Although initial costs may be higher with block paving, long-term maintenance and replacement costs are lower
• A huge selection of complex and attractive surfaces is available.