The important features to be incorporated, compared to regular brick masonry, are control joints, band beams and joint reinforcements. These factors are to be provided failing which the block masonry is bound to result in random cracking due to shrinkage and moisture movements. These factors are discussed below.
1. Control Joints
Concrete has higher coefficient of expansion than brickwork. In order to control thermal movements, these joints are built as continuous and vertical. Further, to minimise cutting of units, they are to be located at change of sections. These joints may be shrinkage joints and expansion joints. The shrinkage joints are continuous vertical joints approximately 18 mm thick. These joints are later raked and caulked. Expansion joints are located at spacing of 45–60 m in suitable locations. These joints are filled with joint filers, which are compressible materials that close the gap but allow movement.
2. Bond Beams
Bond beams are similar to lintels which are to be provided on top of openings or top of walls such as compound walls. This is constructed using special channel-shaped units which are reinforced and filled with concrete. It serves as a structural element as that of a lintel to control cracks on top of openings.
3. Joint Reinforcement
For crack control, horizontal joint reinforcements in the form of minimum two No. 9 gauge wires at intervals can be used. As they are expensive, they are not generally provided. When used as load-bearing walls with RCC slabs resting on the walls, the top three courses at least should be provided with joint reinforcement (Fig. 16.12).
Figure 16.12 Load-bearing wall
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