Sunday, August 20, 2017

Types of Ready Mix Concrete Plants

Types of Ready Mix Concrete Plants


There are various types of ready mix concrete plants which most of them designed for specific locations or circumstances. Moreover, there are standard ready mix concrete plants but these are usually modified to accommodate for certain situations.

Ready-mix concrete is concrete that is manufactured in a factory or batching plant, according to a set recipe, and then delivered to a work site by truck mounted in–transit mixers. This results in a precise mixture, allowing specialty concrete mixtures to be developed and implemented on construction sites.

Concrete that are produced as per established procedures in batching plants and after that delivered to construction site by truck on which transit mixture is mounted is called ready mix concrete. In this article, various types of ready mix plant, which are categorized based on the type of mixer, is described.


Types of Ready Mix Concrete Plants

Following are the different types of ready mix concrete plants and their mixing actions.
Dry batch concrete plant
 Wet batch concrete plant
 Half-wet batch concrete plant
 Combination batch concrete plant

Dry Batch Ready Mix Concrete Plants

This type of ready mix concrete plant produces uniform concrete mix through the mixing action of the truck mixer. The mixing action is basically a twofold mechanism. Consider the complex movement of already well mixed plastic concrete in the drum.
At the beginning, neglect the blade action, then rotation of the drum and both concrete internal friction of the concrete and its friction against drum inside surface make the concrete appears to move up the right hand wall of the drum as shown in below picture.
Cross Section of Track Mix Action - constructionway.blogspot.com
Cross Section of Track Mix Action

There are two factors which affect the height that the concrete can climb up before gravity surpasses it and make it to fall. Firstly, drum surface linear velocity which based on its angular velocity and the inside diameter of the drum. Concrete falling point is increased with increasing linear velocity. Secondly, concrete workebility which its decline leads to rise concrete falling point.
It is observed that, at speed of 22-27 rpm (normal speed is 10-14 rpm), the concrete spins full contact with the drum surface hence concrete falling will no longer exist. This may lead to create problems because substantially efficient local mixing will be lost if concrete falling point is avoided.


Wet Batch Ready Mix Concrete Plants

There are various types of wet batch systems and the wet batch system is plant based mixer. This means that different component of concrete mixture such as cement, aggregate, and water is mixed in the system.
Comparatively, the output of wet batch concrete plant is greater than dry batch concrete plant that is why it is frequently seen as large plants. Moreover, the wet batch concrete plant is necessary in the case mortar production is required. There are different mixers sizes that range from 0.8 m to 6 m and the largest mixer drum can adequately mix about 6 m plastic concrete in around forty five seconds.
Furthermore, there are several factors for example, required to output, predominant type of mixes
supplied, plant geometry, available space, initial and entire life expenses, upon which specific mixer is decided to be chosen.


Types of Wet Batch Mixer and its Mixing Action


Following are the available different types of wet batch mixers and its mixing action:

Rotating Drum Mixer

◑ Rotating drum, freefall mixing action, none tilting.
◑ Rotating drum, freefall mixing action, tilting.

Fixed Trough Mixers

◑ Fixed mixing trough within which spiral blades revolve on horizontal shafts
◑ Fixed mixing trough within which paddles rotate on twin horizontal shafts

Pan Mixers

Fixed horizontal pan in which mixing paddles travel around an annular channel
 Fixed horizontal pan in which mixing paddles travel around an annular channel while revolving about their own axis
 Fixed horizontal pan in which the mixing blades traverse the entire pan floor with a planetary motion
◑ Fixed horizontal pan in which two sets of mixing paddles travel around an annular channel in
opposite directions
 Horizontal pan rotating beneath a stationary motor unit carrying paddles, the axes of rotation being non-coincident.

Reversing Drum Mixers

 System of fixed blades and shovels within a non-tilting rotating drum giving a combined freefall and compulsory mixing action.

Continuous Mixers

 Fixed trough mixer with twin rotating shafts and paddles angled at about 20° arranged to produce a continuous mixing action.

Half-Wet Batch Ready Mix Concrete Plant


Half wet system includes premixing of sand, cement, and water to make slurry, after that, the slurry and aggregate are added to the truck. Not only does the half-wet system decrease wear and tear on central mixer units but also substantially decline the time of batching.

Combination Batch Ready Mix Concrete Plants


Both dry batch and wet batch system is combined in this type of batching plant, and most of concrete is mixed in dry leg bur small mixers with 0.8-2 m is employed to deliver concrete to the customer.

>>Types of Ready Mix Concrete Plants<<

Monday, August 7, 2017

Level and Leveling

Level and Leveling

Elevation measurements involve measurements in vertical plane. It is also known as leveling. It may be defined as the art of determining the elevations of given points above or below a datum line or establishing given points of required heights above or below the datum line.


OBJECT AND USES OF LEVELING


As stated in the definition of leveling, the object is

 to determine the elevations of given points with respect to a datum

➋ to establish the points of required height above or below the datum line.

Uses of leveling are...

➊ to determine or to set the plinth level of a building.

➋ to decide or set the road, railway, canal or sewage line alignment.

➌ to determine or to set various levels of dams, towers, etc.

 to determine the capacity of a reservoir.

TERMS USED IN LEVELING

Before studying the art of leveling, it is necessary to clearly understand the following terms used in leveling:

☞ Level Surface: A surface parallel to the mean spheroid of the earth is called a level surface
and the line drawn on the level surface is known as a level line. Hence all points lying on a
level surface are equidistant from the center of the earth. Figure 15.1 shows a typical level
surface.
A level surface - constructionway.blogspot.com
A level surface

☞ Horizontal Surface: A surface tangential to level surface at a given point is called horizontal
surface at that point. Hence a horizontal line is at right angles to the plumb line at that point.
Vertical and horizontal lines - constructionway.blogspot.com
Vertical and horizontal lines

☞ Vertical Line: A vertical line at a point is the line connecting the point to the center of the
earth. It is the plumb line at that point. Vertical and horizontal lines at a point are at right
angles to each other.

☞ Datum: The level of a point or the surface with respect to which levels of other points or
planes are calculated, is called a datum or datum surface.

☞ Mean Sea Level (MSL): MSL is the average height of the sea for all stages of the tides. At
any particular place MSL is established by finding the mean sea level (free of tides) after
averaging tide heights over a long period of at least 19 years. In India MSL used is that
established at Karachi, presently, in Pakistan. In all important surveys this is used as datum.

☞ Reduced Levels (RL): The level of a point taken as height above the datum surface is known
as RL of that point.

☞ Benchmarks: A benchmark is a relatively permanent reference point, the elevation of which
is known (assumed or known w.r.t. MSL). It is used as a starting point for leveling or as a
point upon which to close for a check. The following are the different types of benchmarks
used in surveying:

⒜ GTS benchmarks
⒝ Permanent benchmarks
⒞ Arbitrary benchmarks and
⒟ Temporary benchmarks.

 GTS Benchmark: The long form of GTS benchmark is Great Trigonometrical Survey
benchmark. These benchmarks are established by national agency. In India, the department
of Survey of India is entrusted with such works. GTS benchmarks are established all
over the country with highest precision survey, the datum being mean sea level. A bronze
plate provided on the top of a concrete pedastal with elevation engraved on it serves as
benchmark. It is well protected with masonry structure built around it so that its position
is not disturbed by animals or by any unauthorised person. The position of GTS
benchmarks are shown in the topo sheets published.

 Permanent Benchmark: These are the benchmarks established by state government
agencies like PWD. They are established with reference to GTS benchmarks. They are
usually on the corner of plinth of public buildings.

 Arbitrary Benchmark: In many engineering projects the difference in elevations of
neighbouring points is more important than their reduced level with respect to mean sea
level. In such cases a relatively permanent point, like plinth of a building or corner of a
culvert, are taken as benchmarks, their level assumed arbitrarily such as 100.0 m,
300.0 m, etc.

⒟ Temporary Benchmark: This type of benchmark is established at the end of the day’s
work, so that the next day work may be continued from that point. Such point should be
on a permanent object so that next day it is easily identified.

LEVELLING INSTRUMENTS

A level is an instrument giving horizontal line of sight and magnifying the reading at a far away distance.
It consists of the following parts:

A telescope to provide a line of sight
A level tube to make the line of sight horizontal and
A levelling head to level the instrument.

The following types of levels are available:

Dumpy level
 Wye (or, Y) level
 Cooke’s reversible level
 Cushing’s level
 Tilting level and
 Auto level.

Dumpy Level

It is a short and stout instrument with telescope tube rigidly connected to the vertical spindle. Hence the
level tube cannot move in vertical plane. It cannot be removed from its support. Hence it is named as 
dumpy level. The telescope rotates in horizontal plane in the socket of the leveling head. A bubble tube is attached to the top of the telescope.
Dumpy level - constructionway.blogspot.com
Dumpy level

1. Telescope
2. Eyepiece
3. Shade
4. Objective end
5. Longitudinal bubble tube
6. Transverse bubble tube 
7. Bubble tube adjusting screws
8. Diaphragm adjusting screws
9. Focusing screws
10. Foot screws
11. Upper parallel plate
12. Foot plate (Trivet stage)

Telescope is a tube with object glass and eyepiece. Object glass can be adjusted using the focussing screw before sighting the graduated staff held on the object. Eyepiece can be adjusted by rotating it to see that parallel is removed and cross hairs appears distinctly. Eyepiece once adjusted needs no change as long as the same person takes the readings.

Level tube is a glass tube with slightly curved shape provided over the level tube. The tube is filled with ether or alcohol leaving a little air gap, which takes the shape of a bubble. The air bubble is always at the highest point. The level tube is fixed with its axis parallel to telescope tube, so that when bubble is centred, the telescope is horizontal. The tube is graduated on either side of its centre to estimate how much the bubble is out of centre. The glass tube is placed inside a brass tube which is open from top and on lower side it is fixed to telescope tube by means of capston headed nuts. The bubble tube is
adjusted with these nuts, if it is out of order.

Leveling head consists of two parallel plates with three foot screws. The upper plate is known as tribratch plate and the lower one as the trivet. The lower plate can be screwed on to the tripod stand.
By adjusting the screws the instrument can be leveled to get perfect horizontal line of sight. Dumpy level is to be fitted to a tripod stand to use it in the field. The tripod stand consists of three legs connected to a head to which the lower plate of level can be fitted. The lower side of the legs are provided with metal shoes to get good grip with ground. Show below typical level stands.
leveling stands (adjustable and non-adjustable) - constructionway.blogspot.com
leveling stands (adjustable and non-adjustable)

Wye or Y-Level

In this type of level, the telescope is supported in two Y-shaped supports and can be fixed with the help of curved clips. Clips can be opened and telescope can be reversed end to end and fitted. The advantage of this level is some of the errors eliminated, if the readings are taken in both the direction of telescope.


Cooke’s Reversible Level

In this instrument the telescope is supported by two rigid sockets into which telescope can be introduced from either end and then screwed. For taking the readings in the reversed position of telescope, the screw is slackened and then the telescope is taken out and reversed end for end. Thus it combines the rigidity of dumpy level and reversibility of Y-level.


Cushings Level

In this reversing of telescope end for end is achieved by interchanging the eyepiece and the objective piece since both collars are exactly the same.


Tilting Level

In this, telescope can be tilted through about four degrees with the help of a tilting screw. Hence bubble can be easily centered. But it needs centering of the bubble before taking every reading. Hence it is useful, if at every setting of the instrument number of readings to be taken are few.


Auto Level

The auto-level or the automatic-level is a self aligning level. Within a certain range of tilt automatic leveling is achieved by an inclination compensating device. The operational comfort, high speed and precision are the advantages of this instrument.

LEVELING STAFF

Along with a level, a leveling staff is also required for leveling. The leveling staff is a rectangular rod having graduations. The staff is provided with a metal shoes at its bottom to resist wear and tear. The foot of the shoe represents zero reading. Leveling staff may be divided into two groups:

1. Self reading staff
2. Target staff

1. Self reading staff : This staff reading is directly read by the instrument man through telescope. In a metric system staff, one metre length is divided into 200 subdivisions, each of uniform thickness of 5 mm. All divisions are marked with black in a white background. Metres and decimetres are written in red colour. The following three types of self reading staffs are available:
Self-reading staff - constructionway.blogspot.com
Self-reading staff

(a) Solid staff: It is a single piece of 3 m.

(b) Folding staff: A staff of two pieces each of 2 m which can be folded one over the other.

(c) Telescopic staff: A staff of 3 pieces with upper one solid and lower two hollow. The
upper part can slide into the central one and the central part can go into the lower part.
Each length can be pulled up and held in position by means of brass spring. The total
length may be 4 m or 5 m.


2. Target staff: If the sighting distance is more, instrument man finds it difficult to read self reading staff. In such case a target staff shown in below picture may be used. Target staff is similar to self reading staff, but provided with a movable target. Target is a circular or oval shape, painted red and white in alternate quadrant. It is fitted with a vernier at the center. The instrument man directs the person holding target staff to move the target, till its center is in the horizontal line of sight. Then target man reads the target and isrecorded.
Target staff - constructionway.blogspot.com
Target staff

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Wednesday, July 5, 2017

Costing for Plastering Cement Motar

සිමෙන්ති බදාම කපරාරුවකට යන පිරිවැය සොයමු.

Costing for Plastering Cement Motar

Costing for Plastering Cement Motar

තෙත් බදාම මිශ්‍රනයකින් 1cub සෑදීමට වියළි සිමෙන්ති සහ වැලි (C:S) ඕනෑම අනුපායකට 1.35 cub වැය වේ.

සිමෙන්ති මිශ්‍රන අනුපාත :- 1:2, 1:3, 1:4, 1:5, 1:6 etc.

එක් එක් සිමෙන්ති මිශ්‍රන අනුපාත සාමාන්‍යයෙන් පහත පරිදි විවිධ වැඩ සඳහා යොදාගනී.

 Masonry Works --------- 1:6 to 1:8
  Plastering Masonry ----------- 1:3 to 1:4
  Plastering Concrete -------- 1:3
  Pointing -------------- 1:2 to 1:3

දැන්, සිමෙන්ති මිශ්‍රන අනුපාතය 1:2 ක් වූ තෙත් බදාම 1cub සෑදීමට අවශ්‍ය වියළි ද්‍රව්‍ය ගනණය කරමු.

(C:S = 1:2)

C = 1.35 × 1/3 = 0.45 cub
S = 1.35 × 2/3 = 0.9 cub


සිමෙන්ති වෙලඳපොලේ විකිනීමට අැත්තේ 50 kg බෑග් වශයෙනි. සිමෙන්ති කොට්ටයක පරිමාව 1.23 ඝනඅඩි (cft) වේ.  ∴  ඉහත අැති සිමෙන්ති කොට්ට ප්‍රමාණය

= (0.45 × 100) / 1.23 = 36.58 bag

ප්‍රවාහනයේදී සහ ගොඩ ගැසීමේදී සිදුවන නාස්තිය වෙනුවෙන් සිමෙන්ති සඳහා 5% වැලි සඳහා 10% ක් එකතු කරන්න.

එවිට, 
C = 36.58 + (36.58 × 5/100) = 38.4 bag

S = 0.9 + (0.9 × 10/100) = 0.99 cub

වෙනත් මිශ්‍රණ අනුපාත මඟින් තෙත් බදාම 1 cub සදාගැනීමට යන වියළි අමුද්‍රව්‍ය ප්‍රමාණයන් ඉහත පරිදිම සොයාගත හැක.

1:2 මිශ්‍රණ අනුපාතයම යොදාගෙන ඝනකම අඟල් 1/2 ක් වූ 100 වර්ග අඩි, කපරාරුවක් සඳහා අවශ්‍ය සිමෙන්ති සහ වැලි අනුපාත සොයමු.

මෙම Squar එකෙහි දිග, පළල අඩි 10 බැගින් වේ, ඝනකම අඟල් භාගයකි.

= (10 × 10 × 1/2)/12       (අගයන් තුනම එක එ්කකයක් බවට පත් කිරීමට 12 බෙදා අැත.)
= 100/24 ඝනඅඩි     (ඝනඅඩි, cub කිරීමට 100 න් බෙදා අැත.)
=1/24 cub

∴ අවශ්‍ය සිමෙන්ති = 1/24 × 38.4 = 1.6 bag //
            අවශ්‍ය වැලි = 1/24 × 0.99 = 0.04 cub //

තවත් මේවැනි ලිපියකින් හමුවෙමු.😁😁 මෙම විෂයට කැමති ඔබගේ මිතුරන්ටද අපගේ blog අඩවිය ගැන දැනුවත් කරන්න, ඔබගේ අදහස් කමෙන්ට් මඟින් ලබා දෙන්න.😇😇😇

Wednesday, May 10, 2017

Uses of Cement

Cement


Cement is a commonly used binding material in the construction. The cement is obtained by burning a mixture of calcarious (calcium) and argillaceous (clay) material at a very high temperature and then grinding the clinker so produced to a fine powder. It was first produced by a mason Joseph Aspdin in England in 1924. He patented it as portland cement.

read more about cement;

Cement

uses-of-cement-constructionway.blogspot.com
uses-of-cement

Types of Cement


In addition to ordinary portland cement there are many varieties of cement. Important varieties are briefly explained below;...

 White Cement; The cement when made free from colouring oxides of iron, maganese and chlorium results into white cement. In the manufacture of this cement, the oil fuel is used instead of coal for burning. White cement is used for the floor finishes, plastering, ornamental works etc. In swimming pools white cement is used to replace glazed tiles. It is used for fixing marbles and glazed tiles.

 Coloured Cement; The cements of desired colours are produced by intimately mixing pigments with ordinary cement. The chlorium oxide gives green colour. Cobalt produce blue colour. Iron oxide with different proportion produce brown, red or yellow colour. Addition of manganese dioxide gives black or brown coloured cement. These cements are used for giving finishing touches to floors, walls, window sills, roofs etc.

 Quick Setting Cement; Quick setting cement is produced by reducing the percentage of gypsum and adding a small amount of aluminium sulphate during the manufacture of cement. Finer grinding also adds to quick setting property. This cement starts setting within 5 minutes after adding water and becomes hard mass within 30 minutes. This cement is used to lay concrete under static or slowly running water.

 Rapid Hardening Cement; This cement can be produced by increasing lime content and burning at high temperature while manufacturing cement. Grinding to very fine is also necessary. Though the initial and final setting time of this cement is the same as that of portland cement, it gains strength in early days. This property helps in earlier removal of form works and speed in construction activity.

 Low Heat Cement; In mass concrete works like construction of dams, heat produced due to hydration of cement will not get dispersed easily. This may give rise to cracks. Hence in such constructions it is preferable to use low heat cement. This cement contains low percentage (5%) of tricalcium aluminate (C₃A) and higher percentage (46%) of dicalcium silicate (C₂S).

 Pozzulana Cement; Pozzulana is a volcanic power found in Italy. It can be processed from shales and certain types of clay also. In this cement pozzulana material is 10 to 30 per cent. It can resist action of sulphate. It releases less heat during setting. It imparts higher degree of water tightness. Its tensile strength is high but compressive strength is low. It is used for mass concrete works. It is also used in sewage line works.

 Expanding Cement; This cement expands as it sets. This property is achieved by adding expanding medium like sulpho aluminate and a stabilizing agent to ordinary cement. This is used for filling the cracks in concrete structures.

 High Alumina Cement; It is manufactured by calcining a mixture of lime and bauxite. It is more resistant to sulphate and acid attack. It develops almost full strength within 24 hours of adding water. It is used for under water works.

 Blast Furnace Cement; In the manufacture of pig iron, slag comes out as a waste product. By grinding clinkers of cement with about 60 to 65 per cent of slag, this cement is produced. The properties of this cement are more or less same as ordinary cement, but it is cheap, since it utilise waste product. This cement is durable but it gains the strength slowly and hence needs longer period of curing.

 Acid Resistant Cement; This cement is produced by adding acid resistant aggregated such as quartz, quartzite, sodium silicate or soluble glass. This cement has good resistance to action of acid and water. It is commonly used in the construction of chemical factories.

 Sulphate Resistant Cement; By keeping the percentage of tricalcium aluminate C3A below five per cent in ordinary cement this cement is produced. It is used in the construction of structures which are likely to be damaged by alkaline conditions. Examples of such structures are canals, culverts etc.

 Fly Ash Blended Cement; Fly ash is a byproduct in thermal stations. The particles of fly ash are very minute and they fly in the air, creating air pollution problems. Thermal power stations have to spend lot of money to arrest fly ash and dispose safely. It is found that one of the best way to dispose fly ash is to mix it with cement in controlled condition and derive some of the beneficiary effects on cement. Now-a-days cement factories produce the fly ash in their own thermal stations or borrow it from other thermal stations and further process it to make it suitable to blend with cement. 20 to 30% fly ash is used for blending.

Fly ash blended cements have superior quality of resistance to weathering action. The ultimate strength gained is the same as that with ordinary portland cement. However strength gained in the initial stage is slow. Birla plus, Birla star, A.C.C. Suraksha are some of the brand mame of blended cement.

Properties of Ordinary Portland Cement


Chemical properties; Portland cement consists of the following chemical compounds:

There may be small quantities of impurifies present such as calcium oxide (CaO) and magnesium oxide (MgO).

When water is added to cement, C3A is the first to react and cause initial set. It generates great amount of heat. C3S hydrates early and develops strength in the first 28 days. It also generates heat. C 2S is the next to hydrate. It hydrates slowly and is responsible for increase in ultimate strength. C4AF is comparatively inactive compound.


Physical properties; The following physical properties should be checked before selecting a portland cement for the civil engineering works. IS 269–1967 specifies the method of testing and prescribes the limits:

 Fineness

 Setting time

 Soundness

 Crushing strength

Fineness; It is measured in terms of percentage of weight retained after sieving the cement through 90 micron sieve or by surface area of cement in square centimeters per gramme of cement. According to IS code specification weight retained on the sieve should not be more than 10 per cent. In terms of specific surface should not be less than 2250 cm²/gm.

Setting time; A period of 30 minutes as minimum setting time for initial setting and a maximum period of 600 minutes as maximum setting time is specified by IS code, provided the tests are conducted as per the procedure prescribed by IS 269-1967.

Soundness; Once the concrete has hardened it is necessary to ensure that no volumetric changes takes place. The cement is said to be unsound, if it exhibits volumetric instability after hardening. IS code recommends test with Le Chatelier mould for testing this property. At the end of the test, the indicator of Le Chatelier mould should not expand by more than 10 mm.

Crushing strength; For this mortar cubes are made with standard sand and tested in compression testing machine as per the specification of IS code. The minimum strength specified is 16 N/mm² after 3 days and 22 N/mm² after 7 days of curing.

Physical Tests on Cement


Soundness Test; It is conducted by sieve analysis. 100 gms of cement is taken and sieved through IS sieve No. 9 for fifteen minutes. Residue on the sieve is weighed. This should not exceed 10 per cent by weight of sample taken.

Setting Time; Initial setting time and final setting time are the two important physical properties of cement. Initial setting time is the time taken by the cement from adding of water to the starting of losing its plasticity. Final setting time is the time lapsed from adding of the water to complete loss of plasticity. Vicat apparatus is used for finding the setting times [Ref. Fig. 1.5]. Vicat apparatus consists of a movable rod to which any one of the three needles shown in figure can be attached. An indicator is attached to the movable rod. A vicat mould is associated with this apparatus which is in the form of split cylinder.

vicat-apparatus-constructionway.blogspot.com
vicat-apparatus

Before finding initial and final setting time it is necessary to determine water to be added to get standard consistency. For this 300 gms of cement is mixed with about 30% water and cement paste prepared is filled in the mould which rests on non porous plate. The plunger is attached to the movable rod of vicat apparatus and gently lowered to touch the paste in the mould. Then the plunger is allowed to move freely. If the penetration is 5 mm to 7 mm from the bottom of the mould, then cement is having standard consistency. If not, experiment is repeated with different proportion of water fill water required for standard consistency is found. Then the tests for initial and final setting times can be carried out as explained below:

Initial Setting Time: 300 gms of cement is thoroughly mixed with 0.85 times the water for standard consistency and vicat mould is completely filled and top surface is levelled. 1 mm square needle is fixed to the rod and gently placed over the paste. Then it is freely allowed to penetrate. In the beginning the needle penetrates the paste completely. As time lapses the paste start losing its plasticity and offers resistance to penetration. When needle can penetrate up to 5 to 7 mm above bottom of the paste experiment is stopped and time lapsed between the addition of water and end if the experiment is noted as initial setting time.

Final Setting Time. The square needle is replaced with annular collar. Experiment is continued by allowing this needle to freely move after gently touching the surface of the paste. Time lapsed between the addition of water and the mark of needle but not of annular ring is found on the paste. This time is noted as final setting time.

Soundness Test; This test is conducted to find free lime in cement, which is not desirable. Le Chatelier apparatus shown in Fig. 1.6 is used for conducting this test. It consists of a split brass mould of diameter 30 mm and height 30 mm. On either side of the split, there are two indicators, with pointed ends. The ends of indicators are 165 mm from the centre of the mould.
Le Chatelier’s apparatus-constructionway.blogspot.com
Le Chatelier’s apparatus

Properly oiled Le Chatelier mould is placed on a glass plate and is filled completely with a cement paste having 0.78 times the water required for standard consistency. It is then covered with another glass plate and a small weight is placed over it. Then the whole assembly is kept under water for 24 hours. The temperature of water should be between 24°C and 50°C. Note the distance between the indicator. Then place the mould again in the water and heat the assembly such that water reaches the boiling point in 30 minutes. Boil the water for one hour. The mould is removed from water and allowed to cool. The distance between the two pointers is measured. The difference between the two readings indicate the expansion of the cement due to the presence of unburnt lime. This value should not exceed 10 mm.


Crushing Strength Test; For this 200 gm of cement is mixed with 600 gm of standard sand confirming to IS 650–1966. After mixing thoroughly in dry condition for a minute distilled potable

water p/4+ 3 percentage is added where P is the water required for the standard consistency. They are
 
mixed with trowel for 3 to 4 minutes to get uniform mixture. The mix is placed in a cube mould of 70.6 mm size (Area 5000 mm²) kept on a steel plate and prodded with 25 mm standard steel rod 20 times within 8 seconds. Then the mould is placed on a standard vibrating table that vibrates at a speed of 12000 ± 400 vibration per minute. A hopper is secured at the top and the remaining mortar is filled. The mould is vibrated for two minutes and hopper removed. The top is finished with a knife or with a trowel and levelled. After 24 ± 1 hour mould is removed and cube is placed under clean water for curing.

After specified period cubes are tested in compression testing machine, keeping the specimen on its level edges. Average of three cubes is reported as crushing strength. The compressive strength at the end of 3 days should not be less than 11.5 N/mm² and that at the end of 7 days not less than 17.5 N/mm².

Uses of Cement



 Cement is used widely for the construction of various structures. Some of them are listed below:

 Cement slurry is used for filling cracks in concrete structures.

 Cement mortar is used for masonry work, plastering and pointing.

 Cement concrete is used for the construction of various structures like buildings, bridges. water tanks, tunnels, docks, harhours etc.

 Cement is used to manufacture lamp posts, telephone posts, railway sleepers, piles etc.

 For manufacturing cement pipes, garden seats, dust bins, flower pots etc. cement is commonly used.

 It is useful for the construction of roads, footpaths, courts for various sports etc.


Monday, April 17, 2017

Types of Lime Used in Construction

Types of Lime Used in Construction

Lime


It is an important binding material used in building construction. Lime has been used as the material of construction from ancient time. When it is mixed with sand it provides lime mortar and when mixed with sand and coarse aggregate, it forms lime concrete.
Types of Lime Used in Construction
limestone

Types of Limes and their Properties


The limes are classified as fat lime, hydraulic lime and poor lime:

Fat lime:

It is composed of 95 percentage of calcium oxide. When water is added, it slakes
vigorously and its volume increases to 2 to 2 ¹/₂ times. It is white in colour. Its properties are:

 hardens slowly
 has high degree of plasticity
 sets slowly in the presence of air
 white in colour
 slakes vigorously

Hydraulic lime:

It contains clay and ferrous oxide. Depending upon the percentage of clay present, the hydraulic lime is divided into the following three types:

Feebly hydraulic lime (5 to 10% clay content)
Moderately hydraulic lime (11 to 20% clay content)
Eminently hydraulic lime (21 to 30% clay content)

The properties of hydraulic limes are:

Sets under water 
Colour is not perfectly white
Forms a thin paste with water and do not dissolve in water.
Its binding property improves if its fine powder is mixed with sand and kept in the form of heap for a week, before using.

Poor lime:

It contains more than 30% clay. Its colour is muddy. It has poor binding property. The mortar made with such lime is used for inferior works.

IS 712-1973 classifies lime as class A, B, C, D and E.

 Class A Lime: It is predominently hydraulic lime. It is normally supplied as hydrated lime and is commonly used for structural works.

 Class B Lime: It contains both hydraulic lime and fat lime. It is supplied as hydrated lime or as quick lime. It is used for making mortar for masonry works.

 Class C Lime: It is predominently fat lime, supplied both as quick lime and fat lime. It is used for finishing coat in plastering and for white washing.

 Class D Lime: This lime contains large quantity of magnesium oxide and is similar to fat lime. This is also commonly used for white washing and for finishing coat in plastering.

✖ Class E Lime: It is an impure lime stone, known as kankar. It is available in modular and block form. It is supplied as hydrated lime. It is commonly used for masonry mortar.


Tests on Limestones

The following practical tests are made on limestones to determine their suitability:

 Physical tests
 Heat test
✒ Chemical test
✒ Ball test


 Physical tests ; Pure limestone is white in colour. Hydraulic limestones are bluish grey, brown or are having dark colours. The hydraulic lime gives out earthy smell. They are having clayey taste. The presence of lumps give indication of quick lime and unburnt lime stones.

 Heat test ; A piece of dry stone weighing W1 is heated in an open fire for few hours. If weight of sample after cooling is W2, the loss of weight is W2 – W1. The loss of weight indicates the amount of carbon dioxide. From this the amount of calcium carbonate in limestone can be worked out.

 Chemical test ; A teaspoon full of lime is placed in a test tube and dilute hydrochloric acid is poured in it. The content is stirred and the test tube is kept in the stand for 24 hours. Vigourous effervescence and less residue indicates pure limestone. If effervescence is less and residue is more it indicates impure limestone.

If thick gel is formed and after test tube is held upside down it is possible to identify class of lime as indicated below:

Class A lime, if gel do not flow.
Class B lime, if gel tends to flow down.
Class C lime, if there is no gel formation.


 Ball test ; This test is conducted to identify whether the lime belongs to class C or to class B. By adding sufficient water about 40 mm size lime balls are made and they are left undisturbed for six hours. Then the balls are placed in a basin of water. If within minutes slow expansion and slow disintegration starts it indicates class C lime. If there is little or no expansion, but only cracks appear it belongs to class B lime.


Uses of Lime

The following are the uses of lime in civil works:

☑☄

 For white washing.
 For making mortar for masonry works and plastering.
 To produce lime sand bricks.
 For soil stabilization.
 As a refractory material for lining open hearth furnaces.
 For making cement. 
  
Types of Lime Used in Construction

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