The material having particles of size varying from 0.06 mm to 0.002 mm is known as Silt.
An aggregate is known as cyclopean aggregate if its size is more than 75 mm.
The maximum size of a coarse aggregate is 75 mm and minimum 4.75 mm.
The maximum Size of the fine aggregate is 4.75 mm and minimum 0.075 mm.
The main objects of compaction of concrete are – 1.To eliminate air holes, 2.To achieve maximum density, 3.To provide initiate contact between the concrete and embedded materials.
Gypsum is added for – Controlling setting time
A concrete having a slump of 6.5 cm is said to be Plastic.
For road pavements the cement generally used is – Rapid hardening cement
Non-uniform compaction may cause the concrete – Porous, Non-homogenoeus, Reduced strength
Los Angles machine is used to test the aggregate for – Abrasion resistance
If fineness modulus of sand is 2.5, it is graded as Fine sand.
Continuous grading is not necessary for obtaining a minimum of airvoids.
The omission of a certain size of aggregate is shown by a straight horizontal line on the grading curve.
The omission of a certain Size of aggregate in concrete increases the workability bit also increases the liability to segregation.
Transport of concrete by pumps is done for a distance Of – 400
For given water content workability decreases if the concrete aggregates contain an excess of – Thin particles, Flat particles, Elongated particles, Flaky particles
The light weight aggregates are obtained from – Volcanic source
According to the petro-logical characteristics concrete aggregates are classified as heavy weight normal weight and light weight.
According to the shape of the particles concrete aggregates are classified as rounded irregular, angular and flaky
According to the surface texture of the particles the concrete aggregates are classified as glassy, smooth, granular, rough, crystalline, honey combed and porous.
Segregation is responsible for – 1.Honey-combed concrete, 2.Porous layers in concrete, 3.Surface scaling in concrete, 4.Sand streaks in concrete
After casting an ordinary cement concrete on drying – Shrinks
For quality control of Portland cement, the test essentially done is – Setting time, Soundness, Tensile strength, Consistency
The size of fine aggregates does not exceed 4.75 mm.
The weight of ingredients of concrete mix is taken in kilograms.
Water and Aggregates are measured in litres.
The finished concrete is measured in cubic metres.
20 bags of cement make one tonne.
The risk of segregation is more for – 1.Wetter mix, 2.Larger proportion of maximum size aggregate, 3.Coarser grading
The ratio of the length to breadth of a wooden float is 7.5.
The proportion of the ingredients of concrete mix, is in conformation to arbitrary method of proportioning – 1:1:2, 1:2:4, 1:3:6, 1:2:8.
Slump test is done for – Concrete
Proper batching ensures – Economy, Durability, Workability, Strength
Proper proportioning of concrete ensures – 1.Desired strength and workability, 2.Desired durability, 3.Watertightness of the structure, 4. Resistance to water
The bulk density of aggregates does not depend upon – Size and Shape of the container
The total water is the free water and the amount actually absorbed by the aggregates.
Batching error means inaccuracy in the quantity of Aggregates, Cement, Water
M 150 grade of concrete approximates – 1:1:2 mix
Addition of pozzolana to cement causes – 1.Reduction in permeability, 2.Loss of heat of hydration, 3.Reduction in bleeding, 4.Increase in curing time
Lime in excess causes the cement to expand and disintegrate.
Silica in excess causes the cement to set slow .
Alumina in excess reduces the strength of the cement.
Magnesium oxide in excess remains in free state and makes the cement unsound.
Workability of concrete is measured by – Slump test
Internal friction between the ingredients of concrete is decreased by using – More water and coarse aggregates
For the construction of cement concrete floor, the maximum permissible size of. aggregate is 10 mm
Construction Joints are provided – 1.Where B.M. and S.F. are small, 2.Where the member is supported by other member, 3. At 18 m apart in huge structures, 4.In concrete wall at sill level of windows.
The process of proper and accurate measurement of concrete ingredients for uniformity of proportion is known – Batching
Higher workability Indicates unexpected increase in the moisture content & deficiency of sand.
If the concrete mix is dry, the slump is zero.
Concrete mix having zero slumps is unsuitable for high strength.
To construct a massive dam the type of cement you will use is – Low heat cement
Grading of sand causes great variation in – 1.Workability of concrete, 2.Strength of concrete, 3.Durability of concrete, 4.Handing and placing of concrete
Shrinkage in concrete can be reduced by using – 1.Low water cement ratio, 2.Less cement in the concrete, 3.Proper concrete mix, 4.Presaturated aggregates
Ordinary concrete is not used for concrete grade – M 400
Water required per bag of cement is 35kg.
The process of hardening the concrete by keeping its surface moist is known as – Curing
Curing a concrete for long period ensures better volume stability, Strength, Water resistance.
While compacting the concrete by a mechanical vibrator the slumps should not exceed 5.0 cm.
Workability of concrete for given water content is good if the aggregates are rounded aggregate.
Bulking of sand is caused due to formation of a thin film of surface moisture.
Fine sand bulks more than coarse sand.
With 10% moisture content by weight the bulking of sand is increased by 50%.
The volume of fully saturated sand is equal to the volume of dry and loose sand.
For compacting plain concrete road surface of thickness less than 20 cm we use Screed vibrator.
Segregation is necessary for a workable concrete.
Consistency does not affect the workability of concrete.
If the slumps increases workability decreases.
If the concrete mix is dry the slumps are maximum.
The grade of concrete not recommended by IS : 456 is M 500.
According to water-cement ratio law the strength of workable plastic concrete – 1.Depends upon the amount of water used in the mix, 2.Does not depend upon the quality of cement mixed with aggregates, 3.Does not depend upon the quantity of cement mixed with aggregates.
In single size aggregates bulk density is least.
C.R.R.I charts are used to obtain a relationship between strength of Concrete and Water cement ratio.
Specified compressive Strength of concrete is obtained from cube tests at the end of 28 days.
An aggregate is said to be flaky If its least dimension is less than – 3/5th mean dimension
Too wet concrete may cause – Weakness of concrete, Excessive laitance, Segregation, Lower density
The strength of concrete decreases as the water cement ratio increases.
If the water cement ratio is less than 0.45, the concrete is not workable and causes honey – combed structure.
Good compaction by mechanical vibrations increases the strength of concrete.
The degree of grinding of cement is called Fineness.
The process of changing cement paste into hard mass is known as Setting of cement.
The heat generated during chemical reaction of Cement with water is known as Heat of hydration.
Tri-calcium aluminate (GA) – Generates less heat of hydration
Slump test of concrete is a measure of its – Consistency
Saw dust can be rendered chemically inert by boiling it in water containing – Ferrous sulphate
High percentage of C3S and low percentage of C2S cause rapid hardening.
Low percentage of C3S and high percentage of C2S contribute to slow hardening.
Low percentage of C3S and high percentage of C2S provide greater resistance to chemical attack.
Permissible compressive strength of M 150 concrete grade is 200 kg/cm²
Pozzolana cement is used with confidence for construction of – Dams, Massive foundations, Abutments, R.C.C. structures
The ratio of various ingredients (cement, sand, aggregates) in concrete of grade M 200 is – 4: 2 : 1
Separation of water or water sand cement from a fresh concrete is known as – Bleeding
An ordinary portland cement when tested for its fineness, should not leave any residue on IS. sieve No. 9 more than – 10%
The cement whose strength is a little lower than the ordinary cement during the first three months but attains afterwards the same strength is known as – Low Heat Portland cement
Sand stones may be divided into calcareous, siliceous and ferruginous sand stones.
Concrete using sand stones cracks due to excessive shrinkage.
Very hard and close grained crystalline lime stones are suitable aggregates but provide low strength.
Broken bricks produce a concrete having good fire resisting qualities.
The grade of concrete M 150 means that compressive strength of a 15 cm cube after 28 days is 150 kg/cm².
Water cement ratio is the ratio of – Volume of water to that of cement or Weight of water to that of cement
Efflorescence in cement is caused due to an excess of – Alumina, Iron oxide, Silica, Alkalis
The diameter of the Vicat plunger is 10 mm and its length varies from 40 mm to 50 mm.
Water enables chemical reaction to take place with cement.
Water lubricate is the mixture of gravel sand and cement.
Only a small quantity of water require for hydration of cement.
Strength of concrete structure largely depends upon its workability.
Joints in concrete structures are provided – 1.To minimize the necessary cracking, 2.To reduce the tensile stresses likely to be developed due to evaporation of water, 3.To minimize the change in the dimensions of the slab.
The conditions applicable to water cement ratio law are – 1.Internal moisture conditions on hydration continue till complete strength is gained, 2.Concrete specimens need to be of same age, 3.Concrete specimens need to be of same size.
High temperature – Decreases the strength of concrete
The bulk density of aggregates is generally expressed as – kg/litre
The aggregate containing moisture in pores and having its surface dry is known as Saturated Surface Dry Aggregate.
While designing an air entrained concrete – water cement ratio is reduced, proportion of aggregates is reduced, an allowance for the entrained air is made, strength of the concrete is reduced.
The most useless aggregate is one whose surface texture is – Glassy
The maximum thickness of concrete floor of a cement warehouse is 25 cm..
The type of aggregates is suitable for high strength concrete and for pavements subjected to tension is – Irregular aggregate
The top diameter, bottom diameter and the height of a slump mould are — 10 cm, 20 cm, 30 cm
Workability of concrete mix with low water cement ratio is determined by – Compaction factor test
Permissible Compressive Strength of M 200 concrete grade is 250 kg/cm².
For concreting tunnel linings transportation of concrete is done by – Pumps
The final operation of finishing floors is known as – Trowelling
For an ordinary Portland cement – Initial setting time is not less than 30 minutes
The operation of removing humps and hollows of uniform concrete surface is known as screeding.
The compaction of concrete improves – Density, Strength, Durability
Water cement paste hardens due to hydration.
During hardening cement binds the aggregates together.
Cement provides strength, durability and water tightness to the concrete.
To prevent segregation the maximum height for placing concrete is 100 cm.
For the construction of cement concrete dams the maximum permissible size of the aggregates is 40 mm.
The commercial names of white and coloured cement in India are Colocrete, Rainbow cement, Silvicrete add Snow cement.
To obtain a very high strength concrete use very fine grained – Granite
The aggregate Impact value of the aggregate used in – 1.Buildlng concrete is less than 45, 2.Road pavement concrete is less than 30, 3.Runway concrete is less than 30.
The maximum percentage of chemical ingredient of cement is that of – Lime
An Increase in water content must be accompanied by an Increase in cement content.
Angular and Rough aggregates reduce the workability of the concrete.
Large size aggregates increase the workability due to lesser surface area.
The slump of the concrete mix decreases due to an increase in temperature.
To hydrate 500 kg of cement full water needed is 130 kg.
The bottom and top ends of slump mould are parallel to each other.
The axis of the mould is perpendicular to the end faces.
The Internal surface of the mould is kept clean.
For construction of structures in sea water the cement generally preferred to use is – Portland pozzolana cement
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