55152d16bec1e53f7f2bc1aae730e014dd00585c Construction, Final Account & Tender

Monday, November 6, 2017

BAR BENDING SCHEDULE FOR RCC BEAM

BAR BENDING SCHEDULE FOR RCC BEAM


We will take one simple example for reinforcement quantity calculations for a concrete beam. Consider a beam of clear length of 6550mm, 250mm wide by 450mm depth. It consists of 2-20 and 1-12 diameter bars at top, 2-25 and 1-20 diameter bars at the bottom. Diameter of stirrup is 10mm spaced at 150mm/200mm/150mm center to center. Clear cover to reinforcement provided is 25mm and lap length is 45d.
Drawing Detail of main beam (MB16)-constructionway.blogspot.com
Drawing Detail of main beam (MB16)

main deam 16 drawing detail-constructionway.blogspot
main deam 16 drawing detail

Now we will calculate the length of reinforcement based on shapes of reinforcement required for reinforced concrete beam in above example.
We will start with top reinforcement,
bar mark, 92
Bar shape of 92 is as shown below:
92, bar mark-bar shape-constructionway.blogspot.com
92, bar mark-bar shape
Length of 92 = clear distance on drawing detail + bend length
= 2150 + 200 = 2350
Bend length = consider as 200mm
Bar mark, 93
Bar shape of 93 is as shown below:
93, bar mark-bar shape-constructionway.blogspot.com
93, bar mark-bar shape
Length of 93 = clear distance on drawing + 2 (lap length*)
 = (6500 - 2 x 2150) + 2 x 550
= 3300
*lap length = 45d = 45 x 12 = 540 = consider as 550mm
We will start with Bottom reinforcement,
Bar mark, 94
Bar shape of 94 is as shown below:
94, bar mark-bar shape-constructionway.blogspot.com
94, bar mark-bar shape
where can be take 6000mm (6m) full bar and 90º bend bar
Length of 94 = Bend length + lap length* + balance length of full bar
= 200 + 1150 + (6000-{200+ 1150})
200 + 1150 + 4650 = 6000
*lap length = 45d = 45 x 25 = 1125 = consider as 1150mm
&
Length of 90º bend bar = bend length + balance length of beam
= 200 + (6500 - 4650- 20) = 1830
Bar mark, 95
Bar shape of 95 is as shown below:
95, bar mark-bar shape-constructionway.blogspot.com
95, bar mark-bar shape
Length of 95 = 6500 - (2 x 300 + 2 x 200)
= 5500
Length of Stirrups
Bar mark, 96
Stirrups are spaced at 150mm/200mm/150mm center to center. Stirrups are provided between walls or support for a beam.
section x-x of main beam 16-constructionway.blogspot.com
section x-x of main beam 16
No. of stirrups required for given beam = 6500/200 = 33
Length a = 450 – 2 x 25 – 10 = 390mm
Length b = 250 – 2 x 25 – 10 = 190mm
Therefore length of one stirrup = 2 x (390 + 190) + 90* = 1250 mm
Where 90mm is the minimum hook length as per IS 2502 – Table – II.

Bar Bending Schedule for RCC Beam

Bar Bending Schedule for RCC Beam-constructionway.blogspot.com
Bar Bending Schedule for RCC Beam


Formula for weight of bars :-Formula for weight of bars



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Saturday, November 4, 2017

Precast Concrete Construction Technology

Precast Concrete Construction Technology


As the name suggest, precast concrete is prepared by casting and curing the concrete in a mold under specific circumstances. The concrete is totally manufactured in a factory by adopting special construction techniques. When the concrete is fully hardened and prepared, it is sent to the final construction site. Precast concrete construction has become very popular in some countries like the USA, SriLanka, UK etc.

There are many different types of precast concrete forming systems for architectural applications, differing in size, function, and cost. Too many building elements are manufactured in precast concrete yard.

Following are the precast concrete Members.

➟ Railway Sleepers
➟ Bridge Beam
➟ Paving Slab
➟ Beam (tie beam, main beam)
➟ Road and Bridge Components
➟ Column
➟ Footing
➟ PC Pipes
➟ PC Piles
➟ SBS slab (include 't' beam, soffit block)
➟ Pergolas
➟ Stairs, etc...

precast concrete yard-constructionway.blogspot.com
precast concrete yard

precast column unloading by crane-constructionway.blogspot.com
precast column unloading by crane

precast column erection-constructionway.blogspot.com
precast column erection

precast building first stage-constructionway.blogspot.com
precast building first stage

precast main beam-constructionway.blogspot.com
precast main beam
  
precast wall-constructionway.blogspot.com
precast wall



The advantages and disadvantages of precast concrete:

Advantages are :


1. Precast concrete is produced in a factory with advanced construction techniques.


2. The materials used in precast concrete production are easily obtainable.

3. The construction procedure is very fast, which ultimately saves time.

4. It possesses better thermal insulating characteristics.

5. Precast members are totally fire-proof and sound-proof.

6. Precast members are lightweight and can be transported easily to the job site.

7. Formwork is not required in such construction.

8. If necessary, precast members can be separated and reused in other structure.

9. It is economical & can be take profit.


Disadvantages:


1. It requires careful supervision and more skilled workers for producing the members.

2. Uniform spacing between beams are required in the structure, which can become difficult.

3. Some members are broken up and wasted during the time of transportation from the factory to the construction site.

4. The molds that are used for casting are little costly, so the construction will be economical when a lot of members are produced.


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Wednesday, November 1, 2017

Preparing and Placing of Concrete

Preparing and Placing of Concrete


The following steps are involved in the concreting:
Batching
 Mixing Transporting and placing Compacting

Batching

The measurement of materials for making concrete is known as batching. The following two methods of batching is practiced:

(a) Volume batching
(b) Weight batching

(a) Volume Batching

In this method cement, sand and concrete are batched by volume. A gauge box is made with wooden plates, its volume being equal to that of one bag of cement. One bag of cement has volume of 35 litres. The required amount of sand and coarse aggregate is added by measuring on to the gauge box. The quantity of water required for making concrete is found after deciding water cement ratio. For example, if water cement ratio is 0.5, for one bag of cement (50 kg), water required is 0.5 × 50 = 25 kg, which is equal to 25 litres. Suitable measure is used to select required quantity of water.

Volume batching is not ideal method of batching. Wet sand has higher volume for the same weight of dry sand. It is called bulking of sand. Hence it upsets the calculated volume required.

(b) Weight Batching

This is the recommended method of batching. A weighing platform is used in the field to pick up correct proportion of sand and coarse aggregates. Large weigh batching plants have automatic weighing equipments.

Mixing

To produce uniform and good concrete, it is necessary to mix cement, sand and coarse aggregate, first in dry condition and then in wet condition after adding water.

The following methods are practiced:

(a) Hand Mixing
(b) Machine Mixing

(a) Hand Mixing

Required amount of coarse aggregate for a batch is weighed and is spread on an impervious platform. Then the sand required for the batch is spread over coarse aggregate. They are mixed in dry condition by overturning the mix with shovels. Then the cement required for the batch is spread over the dry mix and mixed by shovels. After uniform texture is observed water is added gradually and mixing is continued. Full amount of water is added and mixing is completed when uniform colour and consistancy is observed. The process of mixing is completed in 6–8 minutes of adding water. This method of mixing is not very good but for small works it is commonly adopted.

(b) Machine Mixing

In large and important works machine mixing is preferred. Figure 3.2 shows a typical concrete mixer. Required quantities if sand and coarse aggregates are placed in the drum of the mixer. 4 to 5 rotations are made for dry mixing and then required quantity of cement is added and dry mixing is made with another 4 to 5 rotations. Water is gradually added and drum is rotated for 2 to 3 minutes during which period it makes about 50 rotations. At this stage uniform and homogeneous mix is obtained.
concrete-mixer-constructionway.blogspot.com
concrete-mixer

Transporting and Placing of Concrete

After mixing concrete should be transported to the final position. In small works it is transported in iron pans from hand to hand of a set of workers. Wheel barrow and hand carts also may be employed. In large scale concreting chutes and belt conveyors or pipes with pumps are employed. In transporting care should be taken to see that seggregation of aggregate from matrix of cement do not take place.

Concrete is placed on form works. The form works should be cleaned and properly oiled. If concrete is to be placed for foundation, the soil bed should be compacted well and is made free from loose soil.

Concrete should be dropped on its final position as closely as possible. If it is dropped from a height, the coarse aggregates fall early and then mortar matrix. This segregation results into weaker concrete.

Compaction of Concrete

In the process of placing concrete, air is entrapped. The entrapped air reduces the strength of concrete up to 30%. Hence it is necessary to remove this entrapped air. This is achieved by compacting the concrete after placing it in its final position. Compaction can be carried out either by hand or with the help of vibrators.

(a) Hand Compaction:

In this method concrete is compacted by ramming, tamping, spading or by slicing with tools. In intricate portions a pointed steel rod of 16 mm diameter and about a metre long is used for poking the concrete.

(b) Compaction by Vibrators:

Concrete can be compacted by using high frequency vibrators. Vibration reduces the friction between the particles and set the motion of particles. As a result entrapped air is removed and the concrete is compacted. The use of vibrators reduces the compaction time. When vibrators are used for compaction, water cement ratio can be less, which also help in improving the strength of concrete. Vibration should be stopped as soon as cement paste is seen on the surface of concrete. Over vibration is not good for the concrete.

The following types of vibrators are commonly used in concreting:
 Needle or immersion vibrators
Surface vibrators Form or shutter vibrators➟ Vibrating tables.

Needle vibrators are used in concreting beams and columns. Surface vibrators and form vibrators are useful in concreting slabs. Vibrating tables are useful in preparing precast concrete elements.

read more articles :

>> Building and Construction Terms Dictionary

>> Level and Leveling

>> Stairs and Composing Parts of Staircases

Tuesday, October 31, 2017

How to Draw Walls - Chief Architect Premier X6 - Sinhala

How to Draw Walls - Chief Architect Premier X6 - Sinhala

මේ කියන්න යන්නේ ඉගෙන ගන්නවනම් හොද පැත්තක් ගැන, ඒ තමයි අලුතෙන් හදන ගෙවල් වලට ප්ලෑන් අදින එක, මේ වැඩ QS කෙනෙක් නැත්නම් ඉංජිනේරුවෙක්/ architect සැලසුම්ශිල්පියෙක් තමා කරන්නේ. නැත්තන් රජයේ පිළිගත් සමාගම් තියෙනවා මේ වැඩ කරලා දෙන, උදාහරණයක්‌ විදියට DDN DESIGN (PVT) LTD , නාරා කියලත් කොම්පැණි එකක් තියෙනවා. හැබැයි සමාගමක් මාර්ගයෙන් ප්ලෑන් එක ඇන්දොත් රුපියල් පනස්දාහක්,හැටදාහක්වත්  යයි (අවමය).

මේ කට්ටිය ඔයාලගේ ඉඩමට ඇවිත් මැනලා බලනවා ඉඩමේ වට ප්‍රමාණය එහෙම. ඊළගට අවට තියෙන ගොඩනැගිලි, බෑවුම්, වතුර බැහල යන කානු වගේ ඒවත් බලනවා. ඊළගට ඉඩමේ පසේ ස්භාවය ගැනත් එයාලා බලනවා. එව්වා සේරම බලලා තමයි ඔයාගේ අදහසුත් අරගෙන හදන්න යන නිවසේ ප්ලෑන් එක අදින්නේ.

එහෙම අදින සැලැස්මේ, හදන්න යන ගෙදර බේස් වලවල් ගාන, ෆවුන්ඩේෂන් එක දාගන්නේ කොහොමද, කොච්චර යටට හාරලා අත්තිකාරම් බදින්න ඕනිද කියලා ඉදන්, ගේ හදලා ඉවර උනාම එහි ඇතුලේ ගෘහ භාණ්ඩ තියන්න ඕනි ආකාරය ගැනත් විස්තර තියෙනවා. ඒ කියන්නේ ගේ වැඩ ඉවර වුනාම පේන විදින ත්‍රිමාණ රූප වලින් ඉල්ලගන්නත් පුලුවන්.

ඊට පස්සේ ඕකත් අරං යන්න ඕන ඉඩම පිහිටි නගරසභාවට හෝ ප්‍රදේශීය සභාවට. එතනදී වරිපනම් ගාස්තු එහෙම ගෙවලා, තව අවශ්‍ය ලියකියවිලි එහෙම දීලා ප්ලෑනට අනුමැතිය ගන්න ඕනි. ඒ වැඩේට සතියක් දෙකක් යයි සමහර විට. කොච්චර ලොකු ඉදිකිරීම් සමාගම් අදින ප්ලෑන් උනත් පොඩි පොඩි අතපසුවීම් තිබිලා අනුමත වෙන්නේ නැතිව ආපසු එන්නත් ඉඩ තියෙනවා. එහෙම උනොත් ඒ ප්ලෑන් එකේ තියෙන නිවැරදි කල යුතු තැන් මොනාද කියලා බලලා, ආයේ ප්ලෑන් එකත් අරං ඒක ඇඳපු අය ලගටම ගිහිං ඒවා නිවැරදි කරලා වැඩේ අනුමත කරගන්න. ඒත් මේ කතාව ඔය පර්චස් 4,5 හේ ගමේ හදන ගෙවල් වලට එච්චර වැදගත් නෑ.


පාර්ට් ටයිම් ජොබ් එහකට හොඳ සබ්ජෙක්ට් එකක්, මාසයක් වගේ අරගෙන හොද වැඩක් කරල දුන්නොත් බය නැතිව 70,000 ක් වගේ ඉල්ලන්න ඇහැකි
පහල තියෙනවා නේද පොඩි ප්ලෑන් එකක්, මේ වගේ එකක් 10,000 කට වගේ කරන්න පුලුවන්
මම හොඳ ප්ලෑන් එකක් පස්සේ දාන්නම් මෙතනටම ඈ,
එ්ත් ප්ලෑන් අදින්නනම් ඉඩමක පාද බෙදන ඒවා එහෙම දැනගෙන ඉන්නත් ඕන
simple-drawing-constructionway.blogspot.com
simple-drawing

හරි, මම මෙතන Chief Architect Premier ගැන තමයි දිගට කතා කරන්න යන්නේ


Chief Architect Premier X6 පරිගණකයෙහි ඉස්ථාපනය කර ගැනීම.

පියවර 1. පහළ ලින්ක් ඒකෙන් ගිහින් Torrent ෆයිල් ඒක Download කරගන්න.(32-bit & 64-bit file size  450 MB)



පියවර 2. භාගත කර ගත් ( Chief Architect Premier X6 version 16.0.3.41 [32-64Bit] Incl Activator - [MUMBAI-TPB] නමින් අැති ෆෝල්ඩරය ) Torrent ෆයිල් ඒක විවෘත කර ගන්න.

පියවර 3. තමාගේ PC ඒකට ගැළපෙන Bit සංස්කරණය අැතුළත් සෙටප් ෆයිල් මත ඩබල් ක්ලික් කර සාමාන්‍යය පරිදි ස්ථාපනය කර ගන්න. (තවමත් වැඩසටහන ධාවනය නොකරන්න.)

පියවර 4. ඉන් පසුව Activator ෆෝල්ඩරය තුළ අැති ෆයිල් ඒක Run කරන්න. විමසන පාස්වර්ඩ් ඒක ලෙස countryboy යන්න දී ඒයද අවසන් කරගන්න.

පියවර 5. දැන් Desktop ඒක මත අැති පහත අාකාර වු අයිකනය ඩබල් ක්ලික් කර විවෘත කර ගන්න.
Chief Architect Premier X6 Sinhala Laesson
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බිත්ති අදින අකාරය.

Chief Architect මගින් අලුත් ප්ලෑන් ඒකක් අැදීමේදී File>>New Plane යන අාකාරයට ගොස් අලුත් ප්ලෑන් ඒකක් ලබාගත හැක. සැලසුමක් නිමාර්ණය කරන විට මුලින්ම පිටත බිත්ති (Exterior Wall) අැද ගත යුතුය. බිත්ති අැදීමට කලින් ඊට අදාල සැකසුම් කිරීම සදහා Default Settings ඩයලොග් බොක්ස් ඒක තුළින් Wall යන්න තෝරා ගත යුතුය. ඒම බිත්ති අතරින් Exterior Wall යන්න තෝරා ගෙන Edit බට්න් ඒක කළ විට ඊට අදාළ සැකසුම් වෙනස් කර ගන්නට හැක. මේහිදී General යටතේ අැති Foundation wall තේරීමෙන් අත්තිවාරම සහිතව බිත්තිය නිර්මාණය කර ගත හැක. Thickness යටතෙන් බිත්තියේ ඝනකම සකස් කර ගන්නට පුලුවන.

පරිමාණයට බිත්ති අැදීම.

මිනුම් ලබා දෙමින් බිත්තියේ ප්‍රමාණය සැකසීමට නම් මුලින්ම අවශ්‍ය බිත්තිය සිලෙක්ට් කර ගත යුතුය. දැන් දිග පෙන්වන පරිමාණයක් බිත්තිය අසල මතු වෙයි. දැන් ඒය තුළට අවශ්‍ය මිනුම් ලබා දිය යුතුය. අඩි වලින් මිනුම් දක්වන්නේ නම් මිනුමට පසුව උඩු කොමා ලකුණක්ද(') , අගල් වලින් මිනුම් දක්වන්නේ නම් මිනුමට පසුව උඩු කොමා ලකුණූ දෙකක්('') ද සටහන් කිරීමෙන් අනතුරුව Enter යතුර තද කළ යුතුය. ඒවිට දුන් අගයන් අනුව ඒම රේඛාව වෙනස් වන අතර අනෙක් රේඛාවල ප්‍රමාණයද උචිත පරිදි වෙනස් වේ.

අවශ්‍ය වෙනස් කම් කිරීම.

අදින ලද Wall ඒකක යම් වෙනස් කමක් කර ගැනීමට නම් මුුුලින්ම Architectural Features ටූල් බාර් ඒක මත අැති Select Objects අයිකන් ඒක තේරීය යුතුය. දැන් අදින ලද Wall ඒක මත ක්ලික් කළ යුතුය.දැන් අදින ලද Wall  ඒක සිලෙක්ට් කර ගැනීමෙන් පසුව කොටු ලකුණ සහිත අයිකන් තුනක් ඒහි දෙපස සහ මැදින් මතු වේ. දෙපස අැති අයිකන් ඒකක් මතට මයිස් පොයින්ටරය ගෙන ගිය විට දෙපසට ඊතල ලකුණු දෙකක් අැති අයිකනයක් සේ මවුස් පොයින්ටරය වෙනස් වේ. දැන් ඒවා ක්ලික් කර පිටතට හෝ අැතුළට අැද බිත්තියේ දිග වෙනස් කර ගත හැක. බිත්තිය තිබෙන තැන වෙනස් කර ගැනීමට නම් රේඛාවේ මැදින් අැති කොටු ලකුණ වෙත ගොස් කැමති තැනකට අැද දැමිය හැක.

සැලසුම 3D view ඒකකින් බැලීම.

අදින ලද සැලසුමක් ත්‍රිමාණ අාකාරයට බැලීම පිණිස Cameras and Navigation මෙනු බාර් ඒකට පිවිසිය යුතුය. ඒහි අැති Full Camera අයිකන් ඒකෙහි දකුණු පසින් තිබෙන ඊතල ලකුණ ක්ලික් කළ යුතුය. දැන් ලැබෙන මෙනු ඒකෙන් Perspective Floor Overview (පර්ස්පෙක්ටිව් ෆ්ලෝ ඕවර්වීව්) යන්න තේරිය යුතුය. මෙවිට ත්‍රිමාණ රූප පෙනෙන වින්ඩෝ ඒක විවෘත වෙයි. ත්‍රිමාණ වින්ඩෝ ඒකට අදාළ ටැබ් ඒක වසා දැමූ විට මෙම සැකසුමෙන් ඉවත් වීමට පුලුවණ.


ඒහෙනම්!, තවත් පාඩමකින් මුණ ගැහෙමු.


Monday, October 30, 2017

Compressive Strength of Cylindrical Concrete Specimens

Compressive Strength of Cylindrical Concrete Specimens



Scope

The test method covers the determination of compressive strength of cylindrical concrete specimens , such as molded cylinders and drilled cores. It is limited to concrete having a unit weight > 800 kg/m3
Compressive Strength of Cylindrical Concrete Specimens

Apparatus

 Weights and weighing device.
 Tools and containers and pans for mixing, or mixer.
 A tamper (circular in cross-section) (16 mm in diameter and 600 mm in length).
 Testing machine.
 Three cylinders (150mm in diameter and 300mm in height).

Procedure

1. Follow the same steps as (Specific Gravity and Absorption of fine Aggregate) in order to preparea fresh concrete mix.

2. The cylinder also must be clean, lightly oiled, well fixed with the base.

3. Filling the specimens will be also in three layers, roding each layer by (25) strokes
using the circular section rod.

4. All other steps are the same as in
 Flow Table Test for Fresh Concrete.

5. The test specimens must be tested in the moist condition with a rate of loading
(0.14-0.34) MPa.

Calculation

1. Calculate the compressive strength of the specimen by dividing the maximum load
carried by the specimen during the test by the average cross-section area.

2. If the specimen length to diameter ratio is less than(1.8), correct the result obtained
by multiplying the appropriate correction factor shown in following table :



Note:-
Factor are applicable for normal concrete strengths (from13.8-14.4) MPa.


Sunday, October 29, 2017

Specific Gravity and Absorption of fine Aggregate

Specific Gravity and Absorption of fine Aggregate

Scope

This test method covers the determination of Bulk and Apparent Specific Gravity and Absorption of fine aggregate.

Exposing the fine aggregate to a gently moving current of warm air
Exposing the fine aggregate to a gently moving current of warm air

Materials:-
l kg of sand is used using sample splitter.

Apparatus


 A balance having capacity of 1kg or more sensitive to 0.1gm Pycnometer - A flask or other suitable container into which the fine aggregate sample can be introduced. It is usually of 500cm3 capacity. Mold - a metal mold in the form of a frustum of a cone with dimensions as follows: 37mm inside diameter at the top, 90mm inside diameter at the bottom and 75mm in height. Tamper - A metal tamper weighing 340±15gm and having a flat circular tamping face 25mm in diameter. Electrical Oven. A container suitable to submerge the sample with water.

Preparation of the test Specimen


1. Obtain approximately 1kg of the fine aggregate using sample splitter.

2. Dry it in a suitable pan or vessel to constant weight at 110°C. Allow it to cool to a comfortable handling temperature, cover with water by immersion and permit to stand for 24 hours.

3. Decant excess water with care to avoid loss of fines, spread the sample on a flat nonabsorbent surface exposed to a gently moving current of warm air.

4. Stir frequently to get homogeneous drying until achieving the saturated surface dry condition. Use cone test for surface moisture.

5. Hold the mold firmly on a smooth nonabsorbent surface with the large diameter down. Place a portion of partially dried fine aggregate loosely in the mold by filling it to over following and heaping additional materials above the top of the mold.

6. Lightly tamp the sand into the mold with 25 light drops of the tamper. Each drop should start about 5mm above the top surface of the sand. Permit the tamper to fall freely under gravitational attraction on each drop.

7. Adjust the surface, remove loose sand from the base and lift the mold vertically. If surface moisture is still present the sand will retain the molded shape. When the sand slumps slightly, it indicates that it has reached S.S.D condition.

Procedure

1. Weigh 500gm of the S.S.D sample.

2. Partially fill the pycnometer with water. Immediately put into the pycnometer 500gm saturated surface dry aggregate.

3. Then fill with additional water to approximately 90%of capacity.

4. Roll; invert the pycnometer to eliminate all air bubbles.

5. Adjust its temperature to 23±1.7 °C by putting the pycnometer in a water bath for an hour.

6. Bring the water level in the pycuometer to its calibrated capacity.

7. Determine the total weight of the pycnometer, specimen and water.

8. Remove the fine aggregate from the pycnometer, dry to constant weight at temp. 
110±5 C, cool in air at room temperature for one hour, and weigh.

9. Determine the weight of the pycnometer filled to its capacity with water at 23 o C

Calculations

1. Calculate the bulk specific gravity as follows:-
Bulk sp. gr. = A / ( B + S – C )

(Meaning of Symbol)⇒ 
A: Weight of oven —dry specimen in air, (gm).
B: Weight of pycnometer filled with water, (gm)
S: Weight of the saturated surface-dry specimen. (500 gm)
C: Weight of pycnometer with specimen and water to calibration mark, (gm).

2. Calculate the bulk specific gravity (SSD) as follows:

Bulk sp. gr.(SSD) = S / ( B + S – C )

3- Calculate the apparent Specific Gravity as follows:-

Apparent sp. gr=. A / ( B + A - C )

3-Calculate the percentage of absorption as follows:-
Absorption = [ ( S – A) / A x] 100


The fine aggregate is still damp
The fine aggregate is still damp

The fine aggregate is SSD condition
The fine aggregate is SSD condition

Discussion

 Comment on the results.
 Compare the results with the typical values.
 How can the percentage of absorption affect on a concrete mix?

read more articles:-

>> The Slump of hydraulic Cement Concrete - Concrete Slump Test

>> Compressive Strength Test of Concrete Cubes

>>  Specific Gravity and Absorption of fine Aggregate

>> Splitting Tensile Strength of Cylindrical Concrete Specimens

Friday, October 27, 2017

Compressive Strength Test of Concrete Cubes

Compressive Strength Test of Concrete Cubes

The Compressive Strength of Cubic Concrete Specimens

Compressive strength of concrete: Out of many test applied to the concrete, this is the utmost important which gives an idea about all the characteristics of concrete. By this single test one judge that whether Concreting has been done properly or not.

The compression machine-constructionway.blogspot.com
The compression machine

Scope

The test method covers determination of compressive strength of cubic concrete specimens. It consists of applying a compressive axial load to molded cubes at a rate which is within a prescribed range until failure occurs. The compressive strength is calculated by dividing the maximum load attained during the test by the crosssectional area of the specimen.

Apparatus

➾ Weights and weighing device. Tools and containers for mixing. Tamper (square in cross section) Testing machine.
 Three cubes (150 mm side)

Procedure

1: Prepare a concrete mix as mentioned in (read this test) with the proportions suggested
Such as: 1: 2: 3 with w/c = 55% by mechanical mixer.

2
: Prepare three testing cubes; make sure that they are clean and greased or oiled
thinly.

3
: Metal molds should be sealed to their base plates to prevent loss of water.

4
: Fill the cubes in three layers, tamping each layer with (35) strokes using a tamper,
square in cross-section with 2.54 cm side and 38.1 cm length, weighing 1.818 kg.

5
: While filling the molds, occasionally stir and scrape together the concrete
remaining in the mixer to keep the materials from separating.

6
: Fill the molds completely, smooth off the tops evenly, and clean up any concrete
outside the cubes.

7
: Mark the specimens by a slip of paper on which is written the date and the
Specimen identification. Leave the specimens in the curing room for 24 hours.

8
: After that open the molds and immerse the concrete cubes in a water basin for
7 days.

9
: Before testing, ensure that all testing machine bearing surfaces are wiped clean.

10: Carefully center the cube on the lower platen and ensure that the load will be
applied to two opposite cast faces of the cube.

11: Without shock, apply and increase the load continuously at a nominal rate within
the range of ( 0.2 N/mm2.s to 0.4 N/mm2.s ) until no greater load can be
sustained. On manually controlled machines, as failure is approached, the
loading rate will decrease, at this stage operate the controls to maintain, as far as
possible, the specified loading rate. Record the maximum load applied to each
cube.


Note:
When the cubes are surface dry, or have not been cured in water, immerse them in water, for a minimum of 5 minutes, before testing. They must be tested while they are still wet.

Type of failure

Record any unusual feature in the type of failure. Refer to fig: 1.1 for examples of satisfactory failure and to fig: 1.2 for examples of some unsatisfactory failures. Note: Unsatisfactory failures are usually caused by insufficient attention to the details of making and testing specimens, such as bad molds, bad made specimens or misplacement of cubes in the testing machine or machine fault.

satisfactory Failure-constructionway.blogspot.com
Fig: 1.1 satisfactory Failure

Unsatisfactory Failure-constructionway.blogspot.com
Fig: 1.2 Unsatisfactory Failure

Note

Minimum three specimens should be tested at each selected age. If strength of any specimen varies by more than 15 per cent of average strength, results of such specimen should be rejected. Average of three specimens gives the crushing strength of concrete. The strength requirements of concrete.

Calculations

Size of the cube =15cm x15cm x15cm

Area of the specimen (calculated from the mean size of the specimen )=225 cm
²

Characteristic compressive strength(f ck)at 7 days =

Expected maximum load =fck x area x f.s

Range to be selected is …………………..

Similar calculation should be done for 28 day compressive strength

Maximum load applied =……….tones = ………….N

Compressive strength = (Load in N/ Area in mm =……………N/mm²

=……………………….N/mm
²

Report

a) Identification mark

b) Date of test

c) Age of specimen

d) Curing conditions, including date of manufacture of specimen

f) Appearance of fractured faces of concrete and the type of fracture if they are unusual


Result

Average compressive strength of the concrete cube = ………….N/ mm (at 7 days)

Average compressive strength of the concrete cube =………. N/mm (at 28 days)


Compressive strength of concrete at various ages

The strength of concrete increases with age. Table shows the strength of concrete at different ages in comparison with the strength at 28 days after casting.

Compressive strength of concrete at various ages

Compressive strength of different grades of concrete at 7 and 28 days


Compressive Strength of Different Grades of Concrete at 7 and 28 Days


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