In recent times, we have seen a drastic transition from brick masonry to concrete block masonry due to its numerous advantages such as fire resistance, good acoustic performance, cost-efficiency, and strength.
In this article, we'll discuss the standard specifications of hollow and solid concrete blocks such as dimensions, classification, physical requirements, drying shrinkage, moisture movement, water absorption, curing, and drying.
Contents:
1. General Specifications
Hollow and solid concrete blocks shall be sound and free from cracks, broken edges, honeycombing, and other defects that would interfere with the proper placing of block or impair the strength or performance during construction.
2. Dimensions and Tolerances
The concrete block units shall be made in sizes and shapes to fit different construction needs. They include stretcher, corner, double corner or pier, jamb, header, bullnose, and partition block, and concrete floor units.
The concrete block—hollow (open or closed cavity) or solid shall be referred to by its nominal dimensions. The nominal dimensions of the concrete blocks are given below:
Length : 400, 500 or 600 mm
Height : 200 or 100 mm
Width : 50, 75, 100, 150, 200, 250 or 300 mm
In addition to the blocks mentioned above, blocks shall be manufactured in half lengths of 200, 250, and 300 mm to correspond to the full-lengths. The tolerance in the length of the units shall not be more than +/- 5 mm and maximum variation in height and width of the unit, not more than +/- 3mm.
3. Classification of Concrete Blocks
The hollow concrete blocks shall be classified in the following four types:
1. Grade ‘A’
These are used as load-bearing units and shall have a minimum block-density of 1500 kg/m3. The concrete blocks shall be manufactured for minimum compressive strengths of 3.5, 4.5, 5.5, and 7.0 N/mm2 respectively, at 28 days.
2. Grade ‘B’
These are also used as load-bearing units and shall have a block density of 1500 kg/m3 but not less than 1000 kg/m3. These shall be manufactured for minimum compressive strengths of 2.0, 3.0, and 5.0 N/mm2 respectively, at 28 days.
3. Grade ‘C’
These grades of concrete blocks are used as non-load bearing units and shall have a block density of less than 1500 kg/m3 but not less than 1000 kg/m3. These shall be manufactured for minimum average compressive strength of 1.5 N/mm2 at 28 days.
4. Grade ‘D'
The solid concrete blocks shall have a block density of not less than 1800 kg/m3. These shall be manufactured for minimum compressive strengths of 4.0 and 5.0 N/mm2, respectively.
4. Compressive Strength and Density
The average compressive strength and density of eight blocks shall not be less than as specified in Table-1 below-
Table-1: Compressive Strength and Density of Concrete Blocks
5. Drying Shrinkage
The drying shrinkage of the blocks (average of three blocks), when unrestrained, shall not exceed 0.1%.
6. Moisture Movement
The moisture movement (average of three blocks) shall not exceed 0.09%.
7. Water Absorption
The water absorption (average of three blocks) shall be not more than 10% by mass.
8. Face Shell and Web Thickness
The face shells and webs shall increase in thickness from the bottom to the top of the unit. Depending upon the core molds used, the face shells and webs of the concrete blocks shall be flared and tapered or straight tapered. The thickness of the web shell and face shell should not be less than the values given in Table-4.
| Nominal block length and width | Face shell thickness | Thickness of web | Total web thickness per course in any 200 mm of walling |
| Min. | Min. | Min. | |
| 100 or less | 25 | 25 | 25 |
| Over 100 to 150 | 25 | 25 | 30 |
| Over 150 to 200 | 30 | 25 | 30 |
| Over 200 | 35 | 30 | 38 |
9. Curing and Drying
The blocks shall be cured in a curing yard or in an immersion tank and shall be kept in a moist condition for 14 days. When the blocks are cured in an immersion tank, the water of the tank shall be changed at least every four days.
After curing, the blocks shall be dried in the shade before being used for work. They shall be stacked with void-face horizontal to facilitate the passage of air. The blocks must be allowed to complete their initial shrinkage before they are used for construction.
FAQs
The nominal dimensions of the concrete blocks are:
Length : 400, 500 or 600 mm
Height : 200 or 100 mm
Width : 50, 75, 100, 150, 200, 250 or 300 mm
The maximum variation in the length of the units shall not be more than +/- 5 mm and maximum variation in height and width of the unit, not more than +/- 3mm.
The drying shrinkage of the blocks (average of three blocks), when unrestrained shall not exceed 0.1%.
The moisture movement (average of three blocks) shall not exceed 0.09%.
The water absorption (average of three blocks) shall be not more than 10% by mass.
Read More
Types of Concrete Blocks or Concrete Masonry Units Used in Construction