The maximum surface drying time (min) for class A type plastic emulsion paint as per the Indian standard is
As per IS 15489 : 2004:
1. Maximum Surface drying time for class A and Class B type plastic emulsion paint is 45 minutes.
2. Maximum Surface drying time for class C and Class D type plastic emulsion paint is 90 minutes.
3. Maximum Hard drying time for class A and class B type plastic emulsion paint is 240 minutes.
4. Maximum Hard drying time for class C and class D type plastic emulsion paint is 480 minutes.
The limiting value of water absorption (%) for a class 25 Brick as specified in the Indian Standard (IS 3495) is:
The bricks, when tested in accordance with the procedure laid in IS 3495 ( Part 2) : 1992 after immersion in cold water for 24 hours, water absorption shall not be more than 20 percent by weight up to class 12'5 and 15 percent by weight for higher classes.
The phenomenon of internal cracking (separation of fibres) in timbers due to drying stresses is called as:
Honeycombing – During drying, internal stresses cause various radial and circular cracks to develop in the interior portion of the wood resembling a honeycomb texture.
Internal Stressing- The basic cause is always an internal tensile stress perpendicular to grain that exceeds the maximum strength of the wood.
Heart Rot - Heart rot is generated in the trees when fungi attack the heartwood through its newly formed branch. This type of fungi makes the tree hollow by consuming heartwood. This defect is known as heart rot.
The ___________ timber which is resinous & catches fire easily.
Depending upon the ease with which Indian timbers can be seasoned, they are divided into three groups, namely, non- refractory timbers, moderately refractory timbers and highly refractory timbers.
1. Non-refractory timbers can be rapidly seasoned without any trouble. They can be seasoned even in the open air and sun. Examples are deodar, simul, etc.
2. Moderately refractory timbers have tendency to split and to crack during seasoning. They are therefore to be protected against rapid drying conditions. Examples are mango, rosewood, sissoo, teak, etc
3. Highly refractory timbers are likely to be damaged severaly during seasoning. They are difficult to season. Examples are axle wood, hopes, laurel, sal, etc.
With respect to fire resistance, timber is classified as refractory timber and non-refractory timber. The refractory timber is non-resinous and it does not catch fire easily. Examples of refractory timbers are sal, teak, etc. The non-refractory timber is resinous and it catches fire easily. Examples of non- refractory timbers are chir, deodar, fir, etc.
Note: The cost of seasoning of timber will naturally depend on the thickness of timber and type of timber with respect to seasoning. It will be more for highly refractory timbers and less for non- refractory timbers.
In which classification the fat lime falls?
Classification of Lime as a Building Material for use in Construction as per IS 712-1973 is as Follows:
1. The Class A lime are the hydraulic lime, that undergoes setting under the action of water. These are used for the construction of structures like arches and domes.
2. Class B is semi-hydraulic in nature. They are limited to small area work, like in masonry constructions.
3. Class C are called as fat lime. Another name for the same is quick lime or white lime or non-hydraulic lime. These are used for works like whitewashing, as a final coat for plastering etc. It is also used in the making of masonry mortar with the help of an additional pozzolanic material.
4. Class D is categorized for lime that is of magnesia or dolomite origin. For finishing works of plastering and white washing, the class D lime can be used
5. Kankar lime is the lime that is categorized under the class E. This lime is produced by the burning of lime nodules that are mainly found in the black soils, that constitutes silica. This forms to be hydraulic in nature. The main application of Kankar lime is in masonry mortar.
6. The siliceous dolomite lime is grouped under the class F lime. This is mainly used in the finishing coat of plaster or for its undercoat.
The chemical reaction that occurs when cement is mixed with water is known as
1. Portland cement is a hydraulic cement, hence it derives its strength from chemical reactions between the cement and water. The process is known as hydration. It is the reaction (series of chemical reactions) of cement with water to form the binding material. In other words, in the presence of water, the silicates (C3S and C2S) and aluminates (C3A and C4AF) form products of hydration which in time produce a firm and hard mass - the hydrated cement paste.
2. Segregation is the “Separation of constituent materials in concrete.”
3. Bleeding is a form of segregation in which water present in the concrete mix is pushed upwards due to the settlement of cement and aggregate. The specific gravity of water is low, due to this water tends to move upwards. Bleeding ordinarily occurs in the wet mix of concrete.
Among the more common varieties of timber namely sal, mango and deodar,
1. Sal is strongest
2. Mango is least durable
3. Deodar is lightest
Of the statements:
Sal: Wood is hard, close grained, heavy and durable. It is used in bridge construction, ship building, piling etc. it is not suitable for ornamental work.
Mango: Wood is of inferior quality. It is coarse and open grained. The wood is readily attacked by white ants and decays on exposure to wet atmosphere, that's why it is least durable among these three.
Deodar: It is a timber tree providing soft wood having well defined grains, It is highly durable and has distinct annual rings.
The increased rate of strength gain of rapid hardening cement is achieved by:
1. Rapid hardening of cement can be obtained by fine grinding of clinker thus increases the surface area of the cement particles which turn increases the rate of hydration of cement that leads to decrease in setting time of cement.
2. Rapid hardening cement is similar to Ordinary Portland cement (OPC) but with higher tri-calcium silicate (C3S) content and finer grinding. It gains strength more quickly than OPC, though the final strength is only slightly higher. This type of cement is also called as High Strength Portland Cement (HSPC). The one-day strength of this cement is equal to the three-day strength of OPC with the same water-cement ratio.
Portland cement is heavier than water by about:
Specific Gravity of Portland cement is 3.15 which represents its weight of about 3.15 times as that of water for the same volume.
Which of the following represent the crushing strength (MPa) for the good quality stone that are used in the construction of buildings?
Characteristics of good building stones are:
Which of the following is determined with the help of Le Chatelier’s device?
Le chatelier’s device is used to determine soundness of cement. This test is performed in the standard apparatus prescribed as per IS: 5514-1969 to check the pressure of the impurities in the cement. Cement is said to be sound when the expansion is below 10 mm.
Abrasion resistance: Los Angeles Abrasion test
Strength test: Standard compression test
Chemical Resistance: By ASTM method.
The type of mortar which is used for the construction works carried out in water-logged area is ________.
Depending upon the nature of civil Engineering works suitable of master should be selected or recommended. For Example – The cement mortar is used where a mortar of high strength and water resisting properties is required such as underground structures, water saturated soils, etc.
Loose mortar is used where brick work is done on less importance work
Mortar having high w/c ratio possess low strength, that’s why it is not used in waterlogged areas.
With increase in moisture content, the bulking of sand
The increase in moisture of sand increases the volume of sand. The reason is that moisture causes film of water around sand particles which results in the increase of volume of sand. For a moisture content percentage of 5 to 8 there will be an increase in volume up to 20 to 40 percent depending upon sand. If the sand is finer there will be more increase in volume. This is known as bulking of sand. When the moisture content of sand is increased by adding more water, the sand particles pack near each other and the amount of bulking of sand is decreased.
Graphical representation of bulking of sand is shown below:
In a shape test of aggregate, which one the following gives the correct slot for flakiness index for a material passing 50 mm sieve and retained on 40 mm sieve?
Mean dimension = (40 + 50)/2 = 45 mm
Slot for flakiness index =
An aggregate is known as cyclopean aggregate if its size is more than:
Which of the following rocks are formed under the influence of heat or pressure or both, from pre-existing rocks?
Rocks which are formed by consolidation of sediments of Pre-existing rocks under the mechanical, chemical or organic activities of the wind, running water etc are sedimentary rocks.
Rocks which are formed under the influence of heat, pressure or both from pre-existing rocks are called Metamorphic rocks
Rocks which are formed by the direct solidification of magma either on the surface or below it are called Igneous Rock.
Based on the following rocks and minerals, select the correct statement.
Quartz, shale, basalt, granite, marble, gypsum, mica
Out of the Given rocks and minerals
1. Quartz is mineral
2. shale is the sedimentary rock and argillaceous rock.
3. Basalt is a siliceous rock and igneous rock
4. Granite is igneous rock and unstratified rock.
5. Marble is calcareous and metamorphic rock.
6. Gypsum is a calcareous rock.
7. Mica is a mineral
Match List I with List II and select the correct answer in respect of brick earth by using the options given below the list:
D. Oxide of iron
1. Provides plasticity
2. Provides bondage to clay particles
3. Provides hardness
4. Prevents shrinkage
Functions of Various Ingredients:
Silica: It enables the brick to retain its shape, imparts durability, and prevents shrinkage and warping. Excess of silica makes the brick brittle and weak on burning. A large percentage of sand or uncombined silica in clay is undesirable. However, it is added to decrease shrinkage in burning and to increase the refractoriness of low alumina clays.
Alumina: Absorbs water and renders the clay plastic. If alumina is present in excess of the specified quantity, it produces cracks in brick on drying. Clays having exceedingly high alumina content are likely to be very refractory.
Lime: Normally constitutes less than 10 per cent of clay. Lime in brick clay has the following effects:
1. Reduces the shrinkage on drying.
2. Causes silica in clay to melt on burning and thus helps to bind it.
3. In carbonated form, lime lowers the fusion point.
4. Excess of lime causes the brick to melt and the brick looses its shape.
5. Red bricks are obtained on burning the sun dried bricks at considerably high temperature (more than 800°C). Buff-burning of bricks results due to high lime content.
Magnesia: rarely exceeding 1 per cent, affects the colour and makes the brick yellow. In burning, it causes the clay to soften at slower rate than does lime and reduces warping.
Iron: Iron oxide constituting less than 7 per cent of clay imparts the following properties:
1. Gives red colour on burning when excess of oxygen is available and dark brown or even black colour when oxygen available is insufficient. However, excess of ferric oxide makes the brick dark blue.
2. Improves impermeability and durability.
3. Tends to lower the fusion point of the clay, especially if present as ferrous oxide.
4. Gives strength and hardness.
Rapid Hardening cement should have surface area not less than (in mm2/gm × 102):
Surface area for following cements is given below:
Heart rot is a defect in timber which is formed:
Heart rot is a fungal disease that causes the decay of wood at the center of the trunk and branches. Fungi enter the tree through wounds in the bark and decay the heartwood.