Different types of basic hollow blocks used in construction are discussed in Section 9.6.1. Additional hollow block units are given in Fig. 16.9 Now the construction features are explained.
1. Construction of Walls
A mortar bed is spread on the foundation concrete and levelled to have a uniform thickness everywhere. The corner block is first placed and positioned accurately. Mortar is applied to the other end and one block is positioned to the end and aligned. The level of the course is checked after placing a few blocks. If necessary, the blocks are tapped with additional mortar such that the mortar thickness is 2 cm below and on the ends. The first course is checked to be in plumb before planning second and additional courses.
As done in brick laying, the successive courses are laid in such a manner so as to break the joints vertically. For vertical joints the mortar is applied to the projection at the sides of the block. As followed for the first course, the courses are built starting from the corners only. Every time, the verticality and horizontality are checked. All the four vertical edges of the final block and the edges of the opening are covered with mortar and pushed in position. The face of the masonry may be pointed by running a tool. The type of joint recommended are weathered, V-shaped or concave, such that the joints shed off water easily.
2. Construction of Columns
Columns are used wherever a large pressure to be transferred through large bearing surface. The columns may form an integral part of the wall or it can be a separate unit. The columns are made of standard stretcher and corner blocks or other special shapes are used. For better stability, the hollows within the blocks may be filled with plain or reinforced concrete (Fig. 16.10(a)).
Figure 16.10 Pilasters and piers
3. Construction of Window and Door Openings
Blocks with hole (jamb) near the opening should be filled with concrete and wooden plugs (Fig. 16.10(b)). The door or window frames are screwed to the wooden plugs. It is also fixed in the lintel with small dowels of mild steel. Under the base of the window or door, a course of solid concrete block masonry is laid which is extended into the adjacent walls up to a distance of at least 30 cm on either side. Lintels are also of hollow channel-shaped sections which can be filled with concrete and provided with steel reinforcement at their bottom.
4. Construction of Reinforced Walls
This is made by providing vertical reinforcement in the hollow with concrete (Fig. 16.11). In order to increase the strength of the wall, reinforcement is provided at the horizontal joints. Because of this provision, expansion cracks which may occur due to moisture and change of temperature may be reduced. Further, two horizontal bars of 6 mm diameter are placed on each on the face of the wall. Instead of steel rods, welded steel mesh may be used wherever needed (Fig. 16.11).
Figure 16.11 Jamb details for 200 mm thick hollow block wall
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