45 Questions
What is the primary purpose of First Class Bricks?
For pointing, exposed face work in masonry structures, flooring and reinforced brick work
What is the maximum water absorption percentage allowed for Second Class Bricks?
16-20% of its dry weight
What is the minimum crushing strength required for Second Class Bricks?
7.0 N/mm2
What is the main characteristic of Third Class Bricks?
They are soft and light-coloured
What is the recommended use of Fourth Class Bricks?
For foundation and floors in lime concrete and road metal
According to ASTM C62, what grade of bricks is intended for use in areas subjected to frost action?
Severe Weathering (SW)
What is the main factor that determines the durability of bricks?
All of the above
Why are highly absorptive bricks problematic?
They can cause efflorescence and other problems in the masonry
What is the purpose of grading bricks according to properties related to durability?
To determine their resistance to weathering
What happens to brick if silica is present in excess?
It becomes brittle and weak
What is the primary function of alumina in clay?
To absorb water and make clay plastic
What happens if lime is present in excess in clay?
It causes the brick to melt and lose its shape
What is the effect of magnesia on the brick?
It affects the colour and makes the brick yellow
What is the primary function of iron oxide in clay?
To impart red colour on burning
What is the result of burning bricks at a high temperature (more than 800°C)?
Red bricks are obtained
What is the effect of excess ferric oxide on the brick?
It makes the brick dark blue
What is the result of improvements in brick manufacturing?
More efficient brick plants with improved quality
What is clay?
One of the most abundant natural mineral materials on earth
What is the first phase of the manufacturing process?
Mining and storage of raw materials
What is the purpose of storing sufficient quantities of raw materials?
To ensure continuous brick production regardless of weather conditions
What is the purpose of blending the clays?
To produce more uniform raw materials and control color
What is the purpose of size reduction machines?
To break up large clay lumps and stones
What is the purpose of the pug mill?
To mix the raw materials with water
What is the range of water mixed into the clay in the stiff-mud process?
10 to 15 percent
How many principal processes are there for forming brick?
3
What is the purpose of tempering?
To produce a homogeneous, plastic clay mass
What is the sixth and final phase of the manufacturing process?
De-hacking and storing finished products
What is the maximum percentage of holes allowed in a solid brick?
25 per cent
What is the minimum crushing strength required for a good brick?
10 N/mm2
What is the purpose of silica in brick making?
It enables the brick to retain its shape
What is the maximum percentage of water absorption allowed for a good brick?
20 per cent of its dry weight
What is the characteristic of a good brick in terms of its size and shape?
Uniform size and plane, rectangular surfaces
What is the function of alumina in brick making?
It is not a main ingredient in brick making
What is the characteristic of a good brick in terms of its texture and compactness?
The surfaces should not be too smooth
What should be the sound produced when two good bricks are struck together?
A metallic sound
What should be free from in the brick earth?
Stones, kankars, organic matter, saltpetre, etc.
What happens when bricks come in contact with moisture?
Water is absorbed and the alkalis crystallise
What is the recommended way to remove efflorescence from a brick?
Dry brush it away
What is usually found in clay as a sulphate?
Calcium, magnesium, sodium, potassium or iron
What happens when carbon is present in the clay and insufficient time is given during burning?
The sulphur causes the formation of a spongy, swollen structure in the brick
What is the effect of a large proportion of free water in clay during drying?
The clay shrinks considerably
What is the effect of combined water in clay during burning?
The clay shrinks
What is the effect of using water containing small quantities of magnesium or calcium carbonates during burning?
The brick becomes decoloured
Why is it important to remove efflorescence before rendering or plastering a wall?
To prevent the salts from reappearing later
What is the result of insufficient oxidation of carbon and sulphur during burning?
The brick becomes decoloured by white blotches
Study Notes
Classification of Bricks
- First class bricks: recommended for pointing, exposed face work, flooring, and reinforced brick work
- Second class bricks: permitted to have small cracks and distortions, higher water absorption (16-20%), and crushing strength of at least 7.0 N/mm2; recommended for hidden masonry works and centering of RCC structures
- Third class bricks: under-burnt, soft, and light-coloured; used for building temporary structures
- Fourth class bricks: over-burnt, distorted, and brittle; used for foundation, floors, and road metal in lime concrete
Strength and Durability
- Clay building bricks are graded according to properties related to durability and resistance to weathering, including compressive strength, water absorption, and saturation coefficient (ASTM C62)
- Three available grades: severe weathering (SW), moderate weathering (MW), and negligible weathering (NW)
- Absorption is an important property that determines the durability of bricks
- Highly absorptive bricks can cause efflorescence and other problems in the masonry
Characteristics of Good Bricks
- Size and shape: uniform, plane, rectangular surfaces with parallel sides and sharp straight edges
- Colour: uniform deep red or cherry colour, indicative of uniformity in chemical composition and thoroughness in burning
- Texture and compactness: surfaces should not be too smooth, and brick should have a precompact and uniform texture
- Hardness and soundness: hard, with a metallic sound when struck together
- Water absorption: should not exceed 20% of its dry weight when kept immersed in water for 24 hours
- Crushing strength: should not be less than 10 N/mm2
- Brick earth: should be free from stones, kankars, organic matter, saltpetre, etc.
Ingredients of Good Bricks
- Silica: enables brick to retain its shape, imparts durability, and prevents shrinkage and warping
- Alumina: absorbs water, renders clay plastic, and prevents cracking on drying
- Lime: normally constitutes less than 10% of clay, reduces shrinkage, causes silica to melt on burning, and lowers fusion point
- Magnesia: affects colour, makes brick yellow or softens clay at a slower rate
- Iron: imparts red colour, improves impermeability and durability, and lowers fusion point
- Sulphur: usually found in clay as sulphate, can cause spongy structure and decolouration of brick if not properly oxidized during burning
- Water: can cause shrinkage during drying and burning, and affect brick's strength and hardness
Manufacturing of Bricks
- Fundamentals of brick manufacturing have not changed, but technological advancements have improved efficiency and product quality
- Phases of manufacturing: mining and storage, preparing raw materials, forming, drying, firing and cooling, and de-hacking and storing finished products
- Raw materials: clay, shale, and fire clay are mined and stored in separate areas to facilitate blending and control colour
- Preparation: large clay lumps and stones are broken down and mixed to control particle size and produce a homogeneous, plastic clay mass
- Forming: three principal processes - stiff-mud, soft-mud, and dry-press; stiff-mud process involves mixing water with clay to produce plasticity
This quiz covers the different types of bricks used in construction, including their characteristics, uses, and required specifications.
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