Blocks

Blocks

Blocks are larger than bricks as it requires both hands to lift it for laying. Moreover, they can be laid more quickly which means it is larger than bricks. Therefore, it is less versatility in laying especially when building up ends, corners, and curves. Blocks are also intended to be plastered. Blocks are categorized into two types, which is clay blocks and concrete blocks. However, concrete blocks are widely used in construction industry.

Clay blocks are commonly extruded hollow units (Refer to figure 1). The monolithic clay block wall provides a unique combination of thermal insulation and heat storage. The natural air conditioner ensures a relatively constant indoor temperature as well as protection from the heat. (Refer to figure 2). The standard sizes for wall blocks are also shown in figure 1. Material used in manufacturing the blocks is usually the same as clay bricks. Clay blocks are dense, hard and brittle after firing. This caused difficulties in cutting and fixing them.

Figure 1

Figure 2

The following data is the minimum average compressive strength of clay blocks:

-1.4 N/mm² for non-load bearing wall or partitions
-2.8 N/mm² for facing and common blocks
-2.8 N/mm² for loadbearing internal walls

On the other hand, concrete blocks are primarily used as a building material in the construction of walls. A concrete block is one of several precast concrete products used in construction. Concrete blocks are found in either dense or lightweight. One of the advantages of using lightweight blocks is its easier to handle and quicker to lay. Next, the air in the lightweight blocks provides better sound and thermal insulation. Furthermore, these lightweight blocks result in lighter foundations and structural members. Moreover, they can be cut and chased with hand tools and hold nails as well as screws without plugs. Thus, it is mostly used in internal wall partitions.

Concrete blocks are divided into three types which are solid blocks, hollow blocks and cellular blocks. There are no formed holes or slots in solid blocks. Conversely, hollow blocks have cavities that can pass through whereas cellular blocks have cavities that cannot pass through. The sizes of the typical work are shown in table 1.

Table 1 BS 6073 Work Sizes for Manufacture of Concrete Block 

The minimum crushing strength of concrete blocks is shown in Table 2.

	Concrete density1 , kg/mm3	Strength, N/mm2
Dense aggregate	1500 – 2000	2.8 – 3.5
Lightweight aggregate	700 – 1500	2.8 – 10.5
Autoclaved aerated	400 – 900	2.8 – 7.0

¹ weight of block divided by overall volume

Table 2

To prevent shrinkage cracks, the use of blocks with low drying (reversible) shrinkage is important. It is also vital to take necessary precautions described for calcium silicate brickwork. Thermal conductivity of blocks depends on the density. Lightweight concrete blocks have better thermal insulation. Besides, it has good fire resistance property.

The durability of those factory-made blocks is commonly good. The blocks made with dense aggregate and having a compressive strength at a minimum of 7 N/mm² can be used for external walls and below the ground level as damp-proof courses. The bonding pattern and quality of workmanship is essential for its good appearance. The appearance of concrete block work is also depends on the quality of blocks and the mortar used.