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Civil Eng Formulas + Buildings Short > concrete technology > Flashcards

concrete technology Flashcards

1
Q

characteristics and specifications of OPC

A
  • Lime saturation Factor is limited between i.e. 0.66 to 1.02.
  • Free lime-cause the Cement to be unsound.
  • Percentage of (AL2O3/Fe2O3) is not less than 0.66.
  • Insoluble residue not more than 1.5%.
  • Percentage of SO3 limited by 2.5% when C3A < 7% and not more than 3% when C3A >7%.
  • Loss of ignition -4%(max)
  • Percentage of Mg0-5% (max.)
  • Fineness -not less than 2250 cm2/g.
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2
Q

Rapid hardening Portland cement

A
  • It is firmer than Ordinary Portland Cement
  • It contains more C3S are less C2S than the ordinary Portland cement.
  • Its 3 days strength is same as 7 days strength of ordinary Portland cement.
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3
Q

Low heat Portland cement

A
  • Heat generated in ordinary Portland cement at the end of 3days 80 cal/gm. While in low heat cement it is about 50cal/gm of cement.
  • It has low percentage of C3A and relatively more C2S and less C3S than O.P. Cement.
  • Reduce and delay the heat of hydration. British standard ( B S. 1370 : 1974 ) limit the heat of hydration of this cement.
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4
Q

Sulphate resisting Portland cement

and super sulphated cement

A

• Maximum C3A content by 3.5% and minimum fineness by 2500 cm’/g.
• Firmer than ordinary pot land cement.
• Sulphate forms the sulpha-aluminates which have expensive properties and so causes disintegration of concrete.
SUPER SULPHATED
• For this cement, the silage as obtained from blast furnace is used
• The clinkers of cement are ground with about 60 to 65 percent of slag.
• Its strength in early days is less and hence it required longer curing period. It proves to be economical as slag, which is a Waste product, is used in its manufactures.

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5
Q

Pozzolanic cement

A
  • As per Indian standard, the proportions of Pozzolana may be 10 to 25 % by weight. e.2. Burnt clay, shale, Fly ash.
  • This Cement has higher resistance to chemical agencies and to sea water because of absence of lime.
  • It evolves less heat and initial strength is less but final strength is 28 days onward equal to ordinary Portland cement.
  • It possesses less resistance to the erosion and weathering action.
  • It imparts higher degree of water tightness and it is cheap.
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6
Q

White Portland cement

A
  • Grey colour of O.P. cement is due to presence of Iron Oxide. Hence in White Cement Fe,,O, is limited to 1 %. Sodium Alumina Ferrite (Crinoline) NavAlF6 is added to act as flux in the absence of Iron-Oxide. •: • It is quick drying, possesses high strength and has superior aesthetic values and it also cost lee than ordinary Cement because of specific requirements imposed upon the raw materials and the manufacturing process.
  • White Cement are used in Swimming pools, for painting garden furniture, moulding sculptures and statues etc.
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7
Q

Coloured Portland

A
  • The Cement of desired colour may be obtained by mixing mineral pigments with ordinary Cement.
  • The amount of colouring material may vary from 5 to 10 percent. If this percentage exceeds 10percent, the strength of cements is affected.
  • The iron Oxide in different proportions gives brown, red or yellow colour. The coloured Cement are widely used for finishing of floors, window sill slabs, stair treads etc.
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8
Q

Expansive cement

A
  • This type of cement is produced by adding an expanding medium like sulphoaluminate and a stabilising agent to the ordinary cement.
  • The expanding cement is used for the construction of water retaining structures and for repairing the damaged concrete surfaces.
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9
Q

High alumina cement

A
  • This cement is produced by grilling clinkers formed by calcining bauxite and lime. It can stand high temper lures.
  • If evolves great heat during setting. It is therefore not affected by frost
  • high resistance in case of chemical corrosion
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10
Q

Bogue’s compound values

A

C3s - 30-50 %
C2S : 20-45 %
C3A : 8-12%
C4AF : 6-10%

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11
Q

Calcium hydroxide in cement

A

It constitutes 20 to 25 per cent of the volume of solids
The calcium hydroxide also reacts with sulphates present in soils or water to form calcium sulphate which further reacts with C3A . This is known as sulphate attack.

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12
Q

Compressive strength test of cement

A
  • This test is carried out to determine the compressive strength of cement.
  • The mortar of cement and sand is prepared in ratio 1:3.
  • Water is added to mortar in water content p/4 +3.
  • The mortar is placed in moulds.The test specimens are in the form of cubes and the moulds are of metals.For 70.6 mm and 76 mm cubes ,the cement required is 185gm and 235 gm respectively.
  • Then the mortar is compacted in vibrating machine for 2 minutes and the moulds are placed in a damp cabin for 24 hours.
  • Then are submerged in clean water for curing.
  • The cubes are then tested in compression testing machine at the end of 3days and 7 days.
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13
Q

consistency of cement

A
  • Take 300 gm of cement and add 30 percent by weight or 90 gm of water to it.
  • Fill the mould of Vicat apparatus and the gauging time should be 3.75 to 4.25 minutes.
  • Vicat apparatus consists of aneedle is attached a movable rod with an indicator attached to it.
  • There are three attachments: square needle,plungerand needle with annular collar.
  • The plunger is attached to the movable rod.the plunger is gently lowered on the paste in the mould.
  • The settlement of plunger is noted.If the penetration is between 5 mm to 7 mm from the bottom of mould,the water added is correct.If not process is repeated with different percentages of water till the desired penetration is obtained.
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14
Q

Setting time test of cement

A
  • Square needle is attached to moving rod of vicat apparatus.
  • The needle is quickly released and it is allowed to penetrate the cement paste.In the beginning the needle penetrates completely.The procedure is repeated at regular intervals till the needle does not penetrate completely.(upto 5mm from bottom)
  • Initial setting time =<30min for ordinary Portland cement and 60 min for low heat cement.
  • The cement paste is prepared as above and it is filled in the Vicat mould.
  • The needle with annular collar is attached to the moving rod of the Vicat apparatus.
  • The needle is gently released. The time at which the needle makes an impression on test block and the collar fails to do so is noted.
  • Final setting time is the difference between the time at which water was added to cement and time as recorded in previous step,and it is =<10hours.
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15
Q

Soundness test of cement

A
  • The purpose of this test is to detect the presence of uncombined lime in the cement.
  • It is covered at top by another glass plate. A small weight is placed at top and the whole assembly is submerged in water for 24 hours.
  • The distance between the points of indicator is noted.The mould is again placed in water and heat is applied in such a way that boiling point of water is reached in about 30 minutes. The boiling of water is continued for one hour.
  • The mould is removed from water and it is allowed to cool down.
  • The distance between the points of indicator is again measured.The difference between the two readings indicates the expansion of cement and it should not exceed 10 mm.
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16
Q

bulking of sand

A

5-8 % water content

increase in volume 20-40 %

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17
Q

Guniting

A

method used for repairing of concrete work

1:3 mixture of cement sand

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18
Q

calcination

A

heating of lime to redness in open air

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19
Q

hydraulicity

A

property of lime by which it sets or hardens where there is no free air circulation

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20
Q

quick lime

A

CaO obtained from calcination.

capable of slaking in presence of water

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21
Q

Fat lime

A

high calcium lime, pure lime, rich lime or white lime
it slake vigorously and volume can be increased 2~2.5 times
Impurity < 5%

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22
Q

Hydraulic lime

A

also called as water lime as it sets under water

it contains clay and some amount of ferrous oxide

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23
Q

poor lime

A

clay > 30%

it slakes very slow

24
Q

slump and compaction factor values and their application

A

~0 (0.78) - road vibrated by power
25-75(.85) - roads by hand operated
50-100(.92) - manual compacted flat slab
100-150(.95)- congested RCC

25
Q

tests required for workability of concrete

A
  1. slump test
  2. Vee-Bee test
  3. Compaction factor test
  4. Flow test
26
Q

Slump test equipment

A

Dtop =10 cm
Dbott = 20 cm
Height = 30 cm

27
Q

Slump requirement for various purpose

A 
10 ~ 25    Concrete to be vibrated
20 ~ 40   Road construction
25 ~ 50   Mass concrete
50 ~ 100  Beams and slabs
75 ~ 120  Impermeable work
80 ~ 150  Normal RCC
28
Q

lightweight concrete density and aggrigates

A

500~ 1500 kg/m3

coke-breeze, cinder, slag

29
Q

use of gypsum and its quantity in cement

A

to control setting time of concrete
slow down hydration process
3~ 4% in OPC
2.5% in rapid hardning

30
Q

effect of Allumina in cement

A

low clinkering temprature and quick setting

31
Q

sulphate resisting portland cement

A

C3A is < 5%

used in canal lining, culverts

32
Q

water % used in finding setting time, soundness, compressive test

A

setting time: 0.85p

soundness: 0.78p
compressive: p/4 +3%

33
Q

compressive and tensile test conditions for cement

A 
tensile :briquettes
comp : cube 70.6 mm 
1:3 cement mortar
temp 25~29
relative humidity : 90%
34
Q

concrete grades and nominal mix ratios

A

M10 - 1:3:6
M15 - 1:2:4
M20 - 1:1.5:3
M25 - 1:1:2

35
Q

when vibrators should be used for compaction of concrete?

A

when slump <50

to avoid seggrigation

36
Q

after grinding , cement is sieved through IS sieve no ?

A

sieve no 9

90 micron

37
Q

strength reduced by air entrainment

A

10~15%

38
Q

colocrete

A

colored cement

39
Q

IS code required for aggrigates

A

IS 383 -1970

40
Q

partical size of coarse aggrigates and fine aggrigates

A
  1. 75 - 75 mm :CA

0. 075- 4.75 mm : FA

41
Q

flackyness and elongation of aggrigates

A

d < 0.6 D , flacky

d > 1.8 D , elongated

42
Q

value of finness modulus for fine sand in concrete

A

2.2 to 2.6

43
Q

effect of Na2Co3 and NaHCo3 in setting time of concrete

A

Na2CO3 accelerate the setting and NaHCO3 retards

44
Q

calcium chloride CaCl2 effect on setting time

A

accelerator

45
Q

30% excess of water will result in strength drop

A

50% drop

46
Q

specification of concrete can be lifted by pump to what height

A

H < 50 m
slump 50 ~ 80
w/c 0.5 ~ 0.65

47
Q

what is trowelling

A

final operation of finishing of concrete surface

48
Q

What is Lime saturation factor

A

TheLime Saturation Factoris a ratio of CaO to the other three main oxides. Applied to clinker, it is calculated as: LSF=CaO/(2.8SiO2+ 1.2Al2O3+ 0.65Fe2O3)

49
Q

Various methods of applying preservation to timber are:

A

Various methods of applying preservation to timber are:

(i) Surface application
(ii) Soaking
(iii) Hot and cold process
(iv) Boucherie process
(v) Diffusion process
(vi) Pressure or pneumatic process
(vii) Fuel cell or Bethel process
(viii) Empty cell process

50
Q

Ferro-cement

A
  1. The term Ferro-cement implies the combination of ferrous product with cement. Generally this combination
    is in the form of steel wires meshes embeded in a Portland cement mortar.
  2. Ferro-cement reinforcement is assembled into its final desired shape and plastered directly. There is no
    need for form work. Minimum two layers of reinforcing steel meshes are required.
    Properties :
  3. Its strength per unit mass is high.
  4. It has the capacity to resist shock load.
  5. It can be given attractive finish like that of teak and rose wood.
  6. Ferro cement elements can be constructed without using form work.
  7. It is impervious.
51
Q

Polymer concrete :

A

 The mechanical properties and durability of concrete can be improved by filling the pores, voids and cracks
by using polymers with concrete.
 Polymer concrete composities are obtained by processing polymeric materials with some or all of the
ingredients of the cement concrete composition.
 A polymer concrete can be classified depending upon the process by which the polymeric materialic materials are incorporated in concete.
(a) Polymer concrete or resin concrete (PC)
(b) Polymer impregnated concrete (PIC)
(c) Latex modified concrete (LMC)
Styrene, methyl – mathacrylic, vinyl chloride, epoxy polyvinyl acetate, styene butadine copolymer latex etc.
are commonly used polymers. The polymer concrete is very effective in repairing damaged concrete structural
members.

52
Q

Revibration:

A

The delayed vibration of concrete, already placed and compacted is
known as revibration. When successive top layers are vibrated, some vibration is
transferred to bottom layers. It is beneficial since the quality of concrete improves as
the entrapped air and water escape and also the rearrangement of particles takes
place.

53
Q

Nuclear concrete

A

Nuclear concrete : Due to its excellent characteristics for neutron and gamma-ray attenuation, the ease of construction and a relatively low initial as well as maintenance costs, make concrete the most suitable material for radiation shielding. The concrete
primarily used for radiation shielding may be called as nuclear concrete.
To design nuclear concrete for effective radiation shielding, it is desirable to understand the type
of radiation and the effective resulting hazards. In the electromagnetic waves category,
the high-energy, high frequency waves known, as X-rays and gamma rays are the only ones that require shielding for the users. These waves are similar to light rays but have higher energy with greater penetrating power.
Although both X-rays and gamma-rays are highly energy penetrating, they can be adequately absorbed by an appropriate thickness of specially constructed nuclear concrete shield.

54
Q

Lean or poor Lime

A

Lean or poor Lime:
It consists of CaO +MgO 80 to 85% with MgO less than 5%
and clayey impurities > 7 % in the form of silica, alumina and iron oxide.
It sets on absorbing CO2 from atmosphere.
Characteristics.
1. Slaking requires more time and so it hydrates slowly. Its expansion is less than that of fat lime.
2. It makes thin paste with water.
3. Setting and hardening is very slow.
4. The colour varies from yellow to grey.
Uses: It gives poor and inferior mortar and is recommended for less important structure.

55
Q

Hydraulic Lime:

A

Hydraulic Lime: it is a product obtained by moderate burning (900° – 1100°C) of raw limestone which contains:
-small proportions of clay (silica and alumina) 5 – 30 per cent
-and iron oxide in chemical combination with the calcium oxide content (CaO + MgO 78 – 80% with MgO less than 5%).
In slaking considerable care is required to provide just sufficient water, since an excess of water would cause the lime to harden.
Depending on the percentage of clay present these are classified further as, feebly, modrately and eminently hydraulic limes.

It sets under water. Feebly hydraulic lime has less than 5–10 per cent of silica and alumina and slakes slowly, after few minutes
(5 to 15). The setting time is twenty one days.
It is used in damp places and for less important structures.

Moderately hydraulic lime has 10 – 20 percent of impurties,
slakes sluggishly after 1–2 hours.
The setting time is seven days.
It is used in damp places.

Eminently hydraulic lime has clayey impurites 20 – 30 per cent and slakes with with difficulty.
Its initial setting time is 2 hours.
It is used in damp places and for all structural purposes.

56
Q

Pure, Rich of fat lime:

A

Pure, Rich of fat lime: It is soft lime (CaO + MgO more than 85% with MgO less than 4%) obtained by
the calcination of nearly pure limestone, marble white chalk, oolitic limestone and calcareous tufa.
Also known as white washing lime should not have impurities of clay and stones, more than 5 per cent.
Fat lime is nearly pure calcium oxide and when it is hydrated with the required amount of water the solid lumps fall to a soft fine powder of Ca(OH)2 and the high heat of hydration produces of cloud of steam.
It sets on absorbing CO2 , from atmosphere.
Characteristics
1. Slaking is vigourous and the volume becomes 2-3 times.
2. It sets slowly in contact with air, and hence is not suitable for thick walls or in wet climate.
3. If kept under water a fat lime paste does not lose its high plasticity and consequently does not set
and harden.
4. Sp. gr. of pure lime is about 3.4.

Uses: Fat lime finds extensive use in making mortar, matrix for concrete, base for distemper and in white
wash, manufacturing of cement, and metallurgical industry.

Civil Eng Formulas + Buildings Short (16 decks)

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