A Projection Report On The Effect Of Geometric Properties (shape) On The Strength Of Interlocking Paving Stone

    A special type of concrete paving block is the ‘spalling-free’ block. These blocks not only have a chamfer but a strongly reduced horizontal area over the upper centimeters. The objective of this reduced horizontal area is to strongly reduce the spalling of edges due to direct contact between adjacent blocks. Therefore these spalling-free blocks are especially suited for concrete block pavements with very narrow joints between the blocks and for pavements that exhibit great deflections under the heavy traffic loadings.     (Encarta, 2010).
The specifications for concrete paving blocks (Dutch, 1985) concrern the materials, the manufacturing, the dimensions and dimensional tolerances, and the quality (Strength, durability, etc.).
The properties of concrete paving blocks are determined on the one hand by the material concrete and on the other hand by the manufacturing process (pouring concrete in steel moulds and then heavy vibratory compaction).
2.4    Laying Patterns
Burnt clay bricks as well as rectangular and some shaped concrete paving blocks can be installed in several laying patterns (Bonds). The most important laying patterns are shown in figure 2.3.
However, most of the shaped concrete paving blocks fit together in only one way, which means that these blocks have to be laid either in herringbone bond or in stretcher bond. The laying pattern affects both the structural behaviour (Strength) of a small element pavement and the ‘creep’ (horizontal displacements in the direction of traffic) of the elements due to the traffic loadings. In this respect herringbone bond is more favourable than stretcher bond. Furthermore concrete paving blocks are more faovurable than burnt clay bricks because of the narrow joints that can be realized due to the smaller shape and dimensional tolerances of concrete blocks (Houben, 1998).
By applying different laying pattenrs, the bond can also be used for functional reasons, for instance for traffic guidance, on traffic junctions, parking lots and squares. When applying concrete paving blocks, the different functions of paved areas can be pointed out by applying blocks with a different colour.
Nowadays on traffic lanes mostly herringbone bond B is applied, and on parking lots and industrial yards usually herringbone bond A. for temporal small element pavements normally a basket weave bond is applied because of the high production rates during construction (which limits the labour costs). Concrete tiles can be installed in basket weave bond, stretcher bond and diagonal bond (Figure 2.4).
Generally the stretcher bond is applied on footways and bicycle tracks, with this type of bond there are no continuous longitudinal joints, resulting in a better interlock between the concrete tiles.
The relatively weak basket weave bond is only applied on very lightly loaded pavements (footways and paths), sometimes for esthetical reasons.
There are, for aesthetical reasons, some applications on squares. Besides the common uncolored (grey) concrete tiles also coloured tiles are applied sometimes for esthetical reasons but also for functional reasons. The best example of this is the wide scale use of red-coloured concrete tiles for bicycle tracks (Wikipedia, 2012).
The herringbone bond B (concrete blocks) as well as the diagonal bond (concrete tiles) requires especially shaped elements (so called bishop’s mitre, element A in figure 2.3) to realize a straight pavement edge along the edge restraint.
Figure 2.4: Types of laying patterns for burnt clay bricks and concrete blocks.
2.5    Manufacturing of Interlocking Paving Blocks 
Interlocking pavers are manufactured by machinery in factories. They consist of both fine and coarsely grained aggregate, along with cement compounds. The ingredients are put through pressure and vibration courses, which produce a strong, durable concrete that can then be molded into various shapes and designs. (Paver, 2012).
Manufacturing of pavers is done on two types of machines. In general the first being more popular, more productive, cost effective, yielding high strength product is through Block making machines, the movements are controlled through hydraulics and the compaction is done through eccentric weight vibrators. The other choice is of Hydraulic press machines that deny each of the above mentioned advantages still common in few countries because of their low capital demand. There is no vibration to move the material in the mould thus voids may remained present.