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

CHAPTER TWO
2.0.    LITERATURE REVIEW
2.1    Preamble
An interlocking concrete paver is a pre-cast piece of concrete or brick commonly used in exterior landscaping applications. Interlocking paving blocks are installed over a compacted stone sub-base and a leveling bed of sand. Concrete paving stones can be used for walkways, paths, pool decks and driveways and airport or landing docks (Paver, 2012).
When one thinks of interlocking paving stones, one often get the idea of dog bone shape stones that fit together like a jigsaw puzzle that is not the case at all. The interlocking comes from the fact that each stone cannot move independently from its neighbor, in fact, there are two important aspects of an interlocking paving stone work which keeps pavers interlocked. The first is sand, as simple as this might seem, the sand creates the interlock, not any sand though it must be a sharp angular sand. If one fills the joint between the pavers with sand, each particle will be round and will then be able to move independently of the stone next to them. Pavers are made with a small ridge on the side of each one so there is space for the sand. If properly done, one will observe that when pavers are being lifted, the whole surface lifts not just one paver. The fact that the whole surface moves together demonstrates the sand holding the pavers together (Thomas, 1997).
The second importance is the edge restraints (the border that is holding the pavers together). Since they are sitting on sand and not mortal; if the edge is not held firmly in place, they could start to spread apart, in doing this, it is required that a well leveled sand bed layer must be prepared so as to ensure alignment and flatness as one paver will not be higher than the other or else it could create larger opening between the pavers that would eventually be so wide that there would no longer be friction between the stones (Houben, 2003).
2.2    Structure of Interlocking Paving Blocks
The structure of a paving block consists the various components of a small element pavement structure that especially the top layer (consisting of small elements and sand – filled joints), the bedding layer and last but not least the necessary edge restraints. Fig 2.1 and 2.2 gives the structure and load bearing mechanism respectively.
Instead of connecting the pavers or elements by pouring grout between the joints as one would with tiles, sand particles or quarry dust are spread over the pavers and tamped down. The sand stabilizes the interlocking pavers, yet allows for some flexibility. In this way also the permanent deformations of a small element, relative to adjacent elements, are limited. This type of paverment structure will absorb stress such as small earthquakes, freezes and thaws, and slight group erosion by shifting each tile slightly. Therefore, they will not crack or buckle like concrete. Most people do not realize that paving stones are several times stronger than concrete. Concrete is hard and “brittle” and thus prone to cracking (Sambawa, 2003).
Concrete cannot be repaired without leaving “scar” marks but paving stones can be easily replaced should the need ever arise.
Most importantly paving stones add beauty and aesthetics to environment and value to homes. There are so many different types of paving stones, colors, textures, shapes, sizes, patterns and designs that they can blend in and greatly enhance the beauty of any home or building (Paver, 2012).
2.3    Various Shapes of Interlocking Paving Blocks:
In principle, two types of paving blocks can be distinguished, i.e ‘rectangular’ blocks (with a rectangular or hexagonal horizontal cross section) and shaped (non-rectangular or dentated) blocks with profiles in the horizontal and or vertical direction.
Figure 2.2 gives an overview of the most widely used block shapes the main features of the distinguished categories A, B and C are:
i.    Category A: Shaped blocks with geometrical interlock at all sides
ii.    Category B: Shaped blocks with geometrical interlock at two sides
iii.    Category C: Rectangular blocks
Figure 2.2: Categories of block shapes.
    From observations, the categories B and some parts of A are widely used and most of the paving blocks are manufactured with a chamfer (Reduced top surface). Furthermore coloured blocks are applied more and more, not only for esthetical reasons but also for functional reasons (Traffic guiding).
    Depending on the laying pattern, specific auxiliary blocks are necessary, for example half blocks for herringbone bond A and stretcher bond A and so-called bishop mitres for herringbone bond B (see figure 2.2a). shaped blocks mostly require more types of auxiliary blocks than rectangular blocks, such as blocks to realize a straight edge at the start or end of the block pavement and blocks to realize curves. (Wiki Pedia, 2012).