Clay pavers are making a solid comeback as a preferred paving material, both for small and large projects. And not just because of the attractive appearance of clay paving (»1). Nowadays, a major reason is concern about the environment and stormwater management: Impervious surfaces like asphalt paving cause stormwater either to run off into rivers and streams, contributing to pollution and erosion, or to flow into drainage systems that combine raw sewage and rainwater, thus increasing the volume and cost of sewage treatment. Permeable pavements allow more water to penetrate into the soil, to stop falling water tables by ground water recharge. Public or commercial surfaces like paved streets, driveways and commercial parking places, as well as residential driveways, terraces and patios can reduce the impervious surface footprint to meet local stormwater requirements and also open the way for a larger house footprint. Access for underground repairs is permitted. Project costs for drainage and retention systems are reduced.
Convincing features of clay pavers are their natural, everlasting colours, as they come in a wide choice of terracotta shades, various reds, yellows, blue or brown, blends or shades.
The city council of Amsterdam, Netherlands, commissioned a research institute to investigate what the best paving material for their slow traffic streets and pavements is. The outcome of this study was clay pavers. Studies in the Netherlands showed the average lifetime of a clay paver to be 125 years, although 250 years is not rare. Taking all this into account, clay pavers naturally boast an excellent carbon footprint! Earlier, for aesthetic reasons, Amsterdam had chosen clay pavers as the preferred material in all 30 km/h zones. The results of this study acknowledged the correctness of that decision. The breaking load and tensile strength of clay pavers are sufficient to bear heavy traffic. Their chemical resistance, thermal shock and freeze-thaw resistance are also excellent.
In the Netherlands, sales of clay pavers have doubled over the past ten years (»2), mainly as a result of gaining market shares from concrete pavers. For this reason, many facing brick manufacturers have switched over to producing pavers instead.
Moulded clay pavers
Clay pavers can be extruded or machine moulded. As compared to extruded clay pavers, moulded pavers show various advantages:
› As a result of moulding process, moulded pavers get a nice soft shape without sharp edges, and a very natural appearance. Furthermore, the moulding process easily allows giving the pavers chamfered edges (“English-edges”) (»3). Alternatively, “waterstruck” bricks can be made on the same machine
› As a raw material, leaner clay or shale mixes can be used than in the extrusion process, and a much higher sand fraction of up to 30% is possible
› A content of, for instance, 25 to 30% fine sand (63 – 250 µm) to the clay body ensures superior skid resistance
Moulded pavers can have distance holders or nibs on all sides (»4), to achieve the desired permeability of the final pavement. The use of nibs and chamfered edges also reduces possible chipping. The moulding process allows all kinds of special shapes to be produced. If required, these special shapes can be produced simultaneously on the same press as the main stream product, to secure the same properties and colour as the standard product.
In the Netherlands, many ways of mechanical paving have been developed, to reduce the strenuous labour involved in manual paving. The majority of pavers are now laid with the help of mini caterpillar cranes with a vacuum grab: The grab lifts approx. 1 m² pavers at a time and lays these precisely onto the prepared sand bed (»5). The pavers have been pre-set into the required herringbone or elbow pattern. This pre-setting can be done on site by means of a compact, movable and dedicated machine, with some manual assistance, or already at the factory. At the factory, usually several robots set the pavers some ten layers high in the required pattern onto a timber pallet (»6).
De Boer Machines
De Boer Machines in the Netherlands has been supplying brick and paver moulding machines for more than 75 years (»7). Many machines have been developed and installed all over the world. Production capacities range from 2 000 to 40 000 units per hour. Thanks to the versatility and flexibility of the machines, various sizes of pavers as well as specials can be produced on one machine. If required, colour staining and surface texturing can be realized with the machine.