Testing of Sand Quality at Construction Site for Concrete

There are different methods for testing of sand quality at construction site for concrete construction. Quality of sand is as much of importance as other materials for concrete.

Aggregate most of which pass through 4.75 mm IS sieve is known as fine aggregate. Fine aggregate shall consists of natural sand, crushed stone sand, crushed gravel sand stone dust or arable dust, fly ash and broken brick (burnt clay).

It shall be hard, durable, chemically inert, clean and free from adherent coatings, organic matter etc. and shall not contain any appreciable amount of clay balls or pellets and harmful impurities e.g. iron pyrites, alkalis, salts, coal, mica, shale or similar laminated materials in such form or in such quantities as to cause corrosion of metal or affect adversely the strength, the durability or the appearance of mortar, plaster or concrete.

The sum of the percentages of all deleterious material shall not exceed 5%. Fine aggregate must be checked for organic impurities such as decayed vegetation humps, coal dust etc.

Testing of Sand Quality at Construction Site for Concrete

Following are the tests for sand at construction site:

1. Organic impurities test – this test is conducted at the field, for every 20 cum or part thereof.

2. Silt content test – this is also a field test and to be conducted for every 20 cum.

3. Particle size distribution – this test can be conducted at site or in laboratory for every 40 cum of sand.

4. Bulking of sand – this test is conducted at site for every 20 cum of sand. Based on bulking of sand, suitable water cement ratio is calculated for concrete at site.

1. Silt Content Test of Sand

The maximum quantity of silt in sand shall not exceed 8%. Fine aggregate containing more than allowable percentage of silt shall be washed so as to bring the silt content within allowable limits.

2. Grading of sand

On the basis of particle size, fine aggregate is graded into four zones. Where the grading falls outside the limits of any particular grading zone of sieves, other than 600 micron IS sieve, by a total amount not exceeding 5 percent, it shall be regarded as falling within that grading zone.

IS Sieve	Percentage passing for
	Grading Zone I	Grading Zone II	Grading Zone III	Grading Zone IV
10 mm	100	100	100	100
4.75 mm	90 – 100	90 – 100	90 – 100	90 – 100
2.36 mm	60 – 95	75 – 100	85 – 100	95 – 100
1.18 mm	30 – 70	55 – 90	75 – 100	90 – 100
600 micron	15 – 34	35 – 59	60 – 79	80 – 100
300 microns	5 – 20	8 – 30	12 – 40	15 – 50
150 microns	0 – 10	0 – 10	0 – 10	0 – 15

Sand shall not contain any harmful impurities such as iron, pyrites, alaklies, salts, coal or other organic impurities, mica, shale or similar laminated materials, soft fragments, sea shale in such form or in such quantities as to affect adversely the hardening, strength or durability of the mortar.3. Deleterious materials in sand:

The maximum quantities of clay, fine silt, fine dust and organic impurities in the sand / marble dust shall not exceed the following limits:

(a) Clay, fine silt and fine dust when determined in accordance within not more than 5% by mass in IS 2386 (Part-II), natural sand or crushed gravel sand and crushed stone sand.

(b) Organic impurities when determined in colour of the liquid shall be lighter in lighter in accordance with IS 2386 (Part –II) than that specified in the code.

4. Bulking of sand:

Figure: Bulking of sand test

Fine aggregate, when dry or saturated, has almost the same volume but dampness causes increase in volume. In case fine aggregate is damp at the time of proportioning the ingredients for mortar or concrete, its quantity shall be increased suitably to allow for bulkage.

Table below gives the relation between moisture content and percentage of bulking for guidance only.

Moisture content (%)	Bulking percentage (by volume)
2	15
3	20
4	25
5	30

What is Efflorescence on Brick Masonry, Its Causes and Treatment Techniques?

What is Efflorescence on Brick Masonry?

We know that efflorescence is a fine, white, powdery deposit of water-soluble salts left on the surface of masonry as the water evaporates. These efflorescent salt deposits tend to appear at the worst times, usually about a month after the building is constructed, and sometimes as long as a year after completion. 

Efflorescence on brick masonry is a white and sometimes brown green or yellow powdery substance observed in winter season. It is produced as result of mixing soluble salts and water.

The salt would deposit on brick masonry and manifest itself as efflorescence after water evaporates. The color of the efflorescence is based on the type of salt that creates it.

Efflorescence might disappear in summer occasionally but it frequently remains through the year. Figure shows efflorescence on masonry wall.

What are the Causes of Efflorescence?

The condition in which efflorescence occurs is unique and all conditions should be met otherwise brick masonry would not suffer from it.

There are three main conditions that offer excellent condition for efflorescence formation on brick masonry wall. The conditions are explained in the following section:

• Masonry brick wall should contain soluble salts and the salt might be in masonry brick, mortar, adjacent soil and backing material
• Water should present in brick masonry wall and need to be in contact with soluble salt to dissolve it.
• Brick masonry wall shall possess pore structure to permit the migration of soluble salt to the surface where water may evaporate and leave the salt.
• These conditions should be present for the efflorescence to occur.

What the Sources of Materials Causing Efflorescence?

In the above discussion, materials causing the occurrence of efflorescence on brick masonry wall is discussed.

It is considerably important to specify their sources because it might help the decrease of efflorescence through control material sources.

The sources materials namely soluble salt and water are explained below:

Source of Soluble Salt on Brick Masonry

There are several sources of salts for instance brick masonry, block masonry, mortar constituents including cement, sand, lime and admixture, grout components involve cement, sand, aggregates and admixtures, contacting soil and ground water.

It should be known that salts may be produced because of reactions between different constituents of brick masonry walls. All soluble salts are capable of producing efflorescence, for instance, carbonates silicate, sulfate, and chloride.

It is worth mentioning that efflorescence produced by chloride might be washed away by water because chloride is substantially soluble in water.

Source of Moisture on Brick Masonry

The major source of moisture is rain water specifically wind driven rain water that lead to penetrate considerable water quantity into the wall. Leakage of moist air from the interior of the structure is another source of moisture in brick masonry wall.

What are the Detrimental Effects of Efflorescence on Brick Masonry Building?

Generally, efflorescence does not lead to structural deterioration of brick masonry. However, it distorts aesthetic view of the structure and if the problem maintain for long time, it would be required to investigate and tackle the source of moisture to prevent efflorescence formation.

It should be known that, efflorescence could be generated in short time after construction completion and the term used for this case is bloom efflorescence. The bloom efflorescence is formed few months after the completion of masonry building construction and it would not last for long time.

Therefore, it would not be necessary to take any action in this case because bloom efflorescence is washed away by rain water. Apart from bloom efflorescence, it would be required to investigate the problem and cut the moisture source to prevent the formation of efflorescence.

How to Control Efflorescence on Brick Masonry?

As discussed previously, efflorescence is occurred if three aforementioned conditions are met. However, when these conditions are controlled then the efflorescence can be avoided.

• Decline soluble salts
• Design and construct masonry structure properly to prevent water penetration
• Execute construction suitably to avoid paths through which moisture travels

It should be remembered that, efflorescence cannot be eliminated completely. That is why the next section will be about the removal of efflorescence.

How to Remove Efflorescence from Brick Masonry?

Inevitably, efflorescence is formed on the surface of brick masonry wall due to natural or man-made reasons. The removal of efflorescence is conducted using one of the following methods:

• Dry brush
• Rinsing with water or other acceptable liquid
• Hand washing
• Sand blasting
• Utilize special chemical cleaner
• Ordinary chemical cleaner such as muriatic

There are number of factor that controls the selection of efflorescence removal. For example, if the salt is soluble, it is recommended to apply dry brush. Hand washing is recommended to choose for small efflorescence batches.

It should be known that the removal and cleaning of the efflorescence on masonry surface would not solve the problem. So, it is required to seal the wall to tackle the problem permanently.

Tests on Cement at Construction site

The following are the quality tests on cement at construction site:

• Adulteration test
• Color test
• Presence of lumps
• Temperature test
• Float tests
• Strength test
• Setting test
• Date of packing

Cement Adulteration Test

The cement should feel smooth when touched or rubbed in between fingers. If it is felt rough, it indicates adulteration with sand.

Color Test of Cement

The color of the cement should be uniform. It should be grey colour with a light greenish shade.

Presence of Lumps

The cement should be free from any hard lumps. Such lumps are formed by the absorption of moisture from the atmosphere. Any bag of cement containing such lumps should be rejected.

Temperature Test of Cement

If hand is inserted in a bag of cement or heap of cement, it should feel cool and not warm.

Float Test

If a small quantity of cement is thrown in a bucket of water, the particles should float for some time before it sinks.

Strength of Cement Test

A block of cement 25 mm ×25 mm and 200 mm long is prepared and it is immersed for 7 days in water. It is then placed on supports 15cm apart and it is loaded with a weight of about 34 kg. The block should not show signs of failure.

The briquettes of a lean mortar (1:6) are made. The size of briquette may be about 75 mm ×25 mm ×12 mm. They are immersed in water for a period of 3 days after drying. If cement is of sound quality such briquettes will not be broken easily.

Setting Test

A thick paste of cement with water is made on a piece of glass plate and it is kept under water for 24 hours. It should set and not crack.

Date of Packing:

Strength of cement reduces with time, so it is important to check the manufacturing date of the cement. Generally, the cement should be used before 90 days from the date of manufacturing.

BRICKWORK CHECK LIST FOR SITE ENGINEERS

While on site, a site engineer must ensure that the brickwork is going on as per quality requirements. Some of the general requirements of quality of brickwork are mentioned below. Use this as a checklist while executing brickwork.

1. The thickness of joint in brick masonry should not exceed 1 cm.
2. The face joints should be raked to a depth of 15 mm by raking tool when the mortar is still green so as to provide proper key for plaster or pointing.
3. Brickwork should be taken up in layers not exceeding one meter height at a time.
4. Check that the brick work is in plumb.
5. Check that the brick courses are in level.
6. Check the quality of bricks with specific reference to

• Strength
• Efflorescence
• Dimensional accuracy
• Water absorption

7. Check that no brick bats are used as queen closer.
8. Check strength of mortar by scratching with sharp instrument like screw driver.
9. Check quality of sand in mortar. (Test for fineness modulus and silt content).
10. Check mixing of mortar whether done by hand or by machine, whether mixing is done on a proper platform.
11. Check bonding of cross wall with long walls.
12. Check arrangements for curing.
13. Check reinforcement in brick partition wall, whether provided.
14. Whether soaking of bricks done or not.
15. Check general quality of works with reference to lines, levels, thickness and trueness of the joints.
16. Whether brick corners are provided properly by a proper brick closer and not by pitting brick bats.
17. Whether top courses in plinth, in window sill and below RCC slab and parapet are provided with brick on edge.
18. Whether joints of brick work are filled with mortar fully, check especially vertical joints.
19. Whether raking of green joints done or not.
20. Check type of scaffolding and whether tied and braced properly.
21. Whether holes left in the brick work while execution for supporting scaffolding are filled with concrete and not with dry bricks.

Airport Engineering : Objective Questions with answers

1. As per ICAO recommendation, minimum width of safety area for instrumental runway should be a) 78 m

b)  150 m

c)   300 m

d)  450 m

Ans: c

2. As per ICAO, for A, B, and C type of airports, maximum effective, transverse and longitudinal grades in percentage respectively are 

a) 1.0, 1.5 and 1.5

b)  1.0, 1.5 and 2.0

c)   1.5, 1.5 and 2.0

d)  2.0, 2.0 and 2.0

Ans: a

3. As per ICAO recommendation, the rate of change of longitudinal gradient per 30 m length of vertical curve for A and B type of airports is limited to a maximum of 

a) 0.1 %

b)  0.2%

c)   0.3 %

d)  0.4%

Ans: a

4. Assertion A : The ratio of arriving and departing aircrafts influences the airport capacity: Reason R :Landing operation is generally given priority over the taking off operation. Select your answer based on the coding system given below:

a)   Both A and R are true and R is the correct explanation of A

b)  Both A and R are true and R is not the correct explanation of A

c)   A is true but R is false.

d)  A is false but R is true.

Ans: a

5. An airport has 4 gates. If the weighted average gate occupancy time is 30 minutes and gate utilisation factor is 0.5, then the capacity of the gate will be 

a) 1 aircraft per hour

b)  2 aircrafts per hour

c)   4 aircrafts per hour

d)  16 aircrafts per hour

Ans: c

7. The capacity of parallel runway pattern depends upon

a)   weather conditions and navigational aids available

b)  lateral spacing between two runways and weather conditions

c)   lateral spacing between two runways and navigational aids available

d)  lateral spacing between two runways, weather conditions and navigational aids available. 

Ans: d

8. The engine failure case for determining the basic runway length may require 

a) only clearway

b)  only stop way ,

c)   either a clearway or a stopway

d)  either a clearway or a stopway or both

Ans: d

9. The minimum width of clearway is

a)   50 m

b)  100 m

c)   150 m

d)  250 m

Ans: c

10. If the monthly mean of average daily temperature for the hottest month of the year is 25° C and the monthly mean of the maximum daily temperature of the same month of the year is 46° C, the airport reference temperature is 

a) 32°C

b)  35.5°C

c)   48°C

d)  25°C

Ans: c

11. Consider the following statements regarding iCAO recommendation for correction to basic runway length

1.The basic runway length should be increased at the rate of 7 percent per 300 m rise in elevation above the mean sea level.

2.The basic runway length after having been corrected for elevation should be further increased at the rate of 1 percent for every 1°C rise in airport reference temperature above the standard atmospheric temperature at that elevation.

3.The runway length after having been corrected for elevation and temperature should be further increased at the rate of 20% for every 1 percent of effective gradient.

Of these statements

a)   1 and 2 are correct

b)  2 and 3 are correct

c)   1 and 3 are correct

d)  1,2 and 3 are correct

Ans: a

12. The total length of a runway is 1000 m. The elevation at distance 0,200 m, 400 m, 600 m, 800 m and 1000 m are 100.0 m, 99.2 m, 101.0 m, 101.8 m, 101.4 m and 101.0 m respectively. The effective gradient of runway will be. 

a) 0.10%

b)  0.26%

c)   0.43 %

d)  0.65%

Ans: b

13. The length of runway under standard conditions is 2000 m. The elevation of airport site is 300 m. Its reference temperature is 33.05°C. If the runway is to be constructed with an effective gradient of 0.25 percent, the corrected runway length will be 

a) 2500 m

b)  2600 m

c)   2700 m

d)  2800 m

Ans: c

14. As per ICAO, the minimum basic runway length for A and E type of airport will be 

a) 1500 m and 600 m

b)  2100 m and 750 m

c)   1500 m and 750 m

d)  2100 m and 600 m

Ans: d

15. Zero fuel weight of an aircraft is:

a)   equal to empty operating weight

b)  equal to maximum landing weight

c)   less than empty operating weight

d)  equal to sum of empty operating weight and the maximum pay load. 

Ans: d

17. The cruising speed of the aircraft is 500 kmph. If there is a head wind of 50 kmph, then the air speed and ground speed of the aircraft respectively will be 

a) 450 kmph and 500 kmph

b)  500 kmph and 450 kmph

c)   450 kmph and 450 kmph

d)  500 kmph and 500 kmph

Ans: a

19. As per ICAO, for airports serving big aircrafts, the crosswind component should not exceed 

a) 15 kmph

b)  25 kmph

c)   35 kmph

d)  45 kmph

Ans: c

20. Calm period is the percentage of time during which wind intensity is less than 

a) 4.8 kmph

b)  6.4 kmph

c)   8.0 kmph

d)  9.6 kmph

Ans: b

21. For determining the basic runway.length, the landing case requires that aircraft should come to a stop within p % of the landing distance. The value of p is 

a) 40 %

b)  50%

c)   60%

d)  75%

Ans: c

22. According to ICAO, all markings on the runways are

a)   Yellow

b)  White

c)   Black

d)  Red

Ans: b

23. Runway threshold is indicated by a series of parallel lines starting from a distance of 

a) 3 m from runway end

b)  6 m from runway end

c)   10 m from runway end

d)  15m from runway end

Ans: b

24. The width and interval of transverse centre line bars along the extended centre line of runway, in approach lighting system are

a)   3 m and 30 m

b)  4.2 m and 30 m

c)   4.2 m and 50 m

d)  3 m and 45 m

Ans: b

25. In Intrumental landing system, the middle markers are located

a)   along the  extended  centre  line  of runway end

b)  about  1  km. ahead of the runway threshold

c)   at the runway threshold

d)  about 7 km.  ahead of the runway threshold

Ans: b

26. The size of landing area for multiengined helicopters operating under 1FR conditions is 

a) 22.5 m x 22.5 m

b)  30 m x 30 m

c)   22.5 m x 30 m

d)  60 mx 120 m

Ans: d

27. The centre to centre spacing of heliport lighting along the periphery of landing and take off area should be

a)   2.5 m

b)  5.0 m

c)   7.5 m

d)  10.0 m

Ans: c

28. The slope of the obstruction clearance line from the boundary of the heliport should be 

a) 1:2

b)  1:5

c)   1:8

d)  1:40

Ans: c

29. Assertion  A  :  Airport capacity during IFR conditions is usually less than that during VFR conditions. Reason R: During clear weather condition (VFR), the aircrafts on final approach to runway can be spaced closer during poor visibility conditions.

Select your answer based on the coding system given below:

a)   Both A and R are true and R is the correct explanation of A

b)  Both A and R are true but R is not the correct explanation of A

c)   A is true but R is false

d)  A is false but R is true

Ans: a

30. Assertion A: The width of a taxiway is smaller than the runway width. Reason R:The speed of the aircraft on a taxiway is greater than that on runway. Select   your   answer   based   on   coding system given below

a)   Both A and R are true and R is the correct explanation of A

b)  Both A and R are true but R is not the correct explanation of A

c)   A is true but R is false

d)  A is false but R is true

Ans: c

31. For supersonic transport aircraft, the minimum turning radius of taxiway is 

a) 60 m

b)  120 m

c)   180 m

d)  240 m

Ans: c

33. As per UK design criteria, if LCN of aircraft is between 1.25 to 1.5 times the LCN of pavement, then the number of movements allowed are 

a) Zero

b)  300

c)   3000

d)  Unrestricted

Ans: b

34. Which of the following is an example of failure in flexible pavements ? 

a) Alligator cracking

b)  Mud pumping

c)   Warping cracks

d)  Shrinkage cracks

Ans: a

35. The main disadvantage of angle nose out parking configuration of aircraft is that the

a)   aircraft rear loading door is far away from terminal building.

b)  hot blast is directed  towards the terminal building

c)   overall apron area required is more

d)  all the above

Ans: b

36. Which of the following is used for servicing and repairs of the aircraft ? 

a) Apron

b)  Hanger

c)   Terminal building

d)  holding apron

Ans: b

37. The slope of the transitional surface for A, B and C type of runway shall be 

a) 1:5

b)  1:7

c)   1:10

d)  1:12

Ans: b

38. The length of clear zone for none instrument runway of a small aircraft is 

a) 150 m

b)  300 m

c)   600 m

d)  750 m

Ans: b

39. In approach areas of runways equipped with instrumental landing facilities any object within 4.5 km distance from runway end shall be considered as an obstruction if its height is more than

a)   20 m                         

b)  30 m

c)   45 m

d)  51 m

Ans: b

40. Maximum gross take-off weight of an aircraft is

a)   equal   to   the   maximum   structural landing weight

b)  less  than  the  maximum   structural landing weight

c)   more than the maximum  structural landing weight

d)  equal to the empty operating weight plus the payload 

Ans: c

41. Consider the following statements: Wind rose diagram is used for the purposes of

1.  runway orientation

2.  estimating the runway capacity

3.  geometric design of holding apron 

Of these statements

a)   1 and 2 are correct

b)  2 and 3 are correct

c)   1 and 3 are correct

d)  1 alone is correct 

Ans: d

42. Which of the following factors are taken into account for estimating the runway length required for aircraft landing?

1.  Normal maximum temperature

2.  Airport elevation

3.  Maximum landing weight

4.  Effective runway gradient

Select the correct answer using the codes given below Codes: 

a) 1,2,3 and 4

b)  1,3, and 4

c)   2 and 3

d)  1,2 and 4 

Ans: d

43. In an airport, if 4 groups of 5 gates each located well-separated are considered for traffic and the future to present traffic ratio is 3, then the total requirement of future gates will be 

a) 32

b)  36

c)   44

d)  68  Ans: b

44. Castor angle is defined as the angle

a)   formed by the longitudinal axis of the aircraft and the direction of movement of the nose gear

b)  between the direction of wind and the longitudinal axis of the runway

c)   between the true speed of the aircraft and the crosswind component

d)  between the horizontal and the fuselage axis 

Ans: a

45. The runway length after correcting for elevation and temperature is 2845 m. If the effective gradient on runway is 0.5 percent then the revised runway length will be 

a) 2845 m         

b) 2910 m          

c) 3030 m      

d) 3130 m  

Ans: c