Monday, 9 October 2017

Dumpy level

Dumpy level is an optical surveying leveling instrument consisting a telescope tube firmly secured in two collars fixed by adjusting screws to the stage by the vertical spindle. The telescope can rotate only in a horizontal plane. Relative elevation of different points of a surveying land is determined with dumpy level.

Use of Dumpy Levels

The dumpy level is mainly used in surveying for the following purposes:

To determine relative height and distance among different locations of a surveyingland.To determine relative distance among different locations of a surveying land.

Advantages of Dumpy Level

Simple construction with fewer movable parts.Fewer adjustments to be made.Due to the rigidity of dumpy levels, it retains its two adjustment for a long time.High optical power.

Disadvantages of Dumpy Level

Civil Engineers may be find it difficult in making accurate measurements.Difficulty in using.

Monday, 2 October 2017

Segregation

Segregation is the separation of the different materials of concrete. A good concrete is one which is homogeneous in nature.If a sample of concrete exhibits a tendency for separation of say, coarse aggregate from the rest of the ingredients, then, that sample is said to be showing the tendency for segregation. Such concrete is not only going to be weak; lack of homogeneity is also going to induce all undesirable properties in the hardened concrete.

There are considerable differences in the sizes and specific gravities of the constituent ingredients of concrete. Therefore, it is natural that the materials show a tendency to fall apart. 

Segregation may be of three types — firstly, the coarse aggregate separating out or settling down from the rest of the matrix, secondly, the paste or matrix separating away from coarse aggregate and thirdly, water separating out from the rest of the material being a material of lowest specific gravity. A well made concrete, taking into consideration various parameters such as grading, size, shape and surface texture of aggregate with optimum quantity of waters makes a cohesive mix. Such concrete will not exhibit any tendency for segregation. The cohesive and fatty characteristics of matrix do not allow the aggregate to fall apart, at the same time, the matrix itself is sufficiently contained by the aggregate. Similarly, water also does not find it easy to move out freely from the rest of the ingredients. 

The conditions favourable for segregation are, as can be seen from the above para, the badly proportioned mix where sufficient matrix is not there to bind and contain the aggregates. Insufficiently mixed concrete with excess water content shows a higher tendency for segregation. Dropping of concrete from heights as in the case of placing concrete in column concreting will result in segregation. When concrete is discharged from a badly designed mixer, or from a mixer with worn out blades, concrete shows a tendency for segregation. Conveyance of concrete by conveyor belts, wheel barrow, long distance haul by dumper, long lift by skip and hoist are the other situations promoting segregation of concrete. 

The most important method of concrete compaction is Vibration. Only comparatively dry mix should be vibrated. When a too wet a mix is excessively vibrated, it is likely to get segregated. Vibration also to be continued just for required time for optimum results. If the vibration is continued for a long time, particularly, in too wet a mix, it is likely to result in segregation of concrete due to settlement of coarse aggregate in matrix. 

Concrete is used with very high slump now a days particularly in RMC. The slump value required at the batching point may be in the order of 150 mm and at the pumping point the slump may be around 100 mm. At both these points cubes are cast. One has to take care to compact the cube mould with these high slump concrete. If sufficient care and understanding of concrete is not exercised, the concrete in the cube mould may get segregated and show low strength. Similarly care must be taken in the compaction of such concrete in actual structures to avoid segregation.


In case of floors or pavement finishing, with a view to achieve a smooth surface, masons work too much with the trowel, float or tamping rule immediately on placing concrete. This immediate working on the concrete on placing, without any time interval, is likely to press the coarse aggregate down, which results in the movement of excess of matrix or paste to the surface. Segragation caused on this account, impairs the homogeneity and serviceability of concrete. The excess mortar at the top causes plastic shrinkage cracks.  


So it can be concluded that the tendency for segregation can be remedied by correctly proportioning the mix, by proper handling, transporting, placing, compacting and finishing. If segregation is observed, it is advisable to remixing for a short time which would make the concrete again homogeneous. As mentioned earlier, a cohesive mix would reduce the tendency for segregation. For this reason, use of certain workability agents and pozzolanic materials greatly help in reducing segregation. The use of air-entraining agent appreciably reduces segregation. 
Segregation is difficult to measure quantitatively, but it can be easily observed at the time of concreting operation. The pattern of subsidence of concrete in slump test or the pattern of spread in the flow test gives a fair idea of the quality of concrete with respect to segregation.

Pumpable Concrete

Pumpable concrete is that type of  concrete which can be pushed through a pipeline for construction. It is made in such a manner that its friction at the inner wall of the pipeline does not become very high and that it does not wedge while flowing through the pipeline. It is very important to have a clear understanding of what happens to concrete when it is pumped through pipeline to any study of concrete pumping. Pumpable concrete emerging from a pipeline flows in the form of a plug which is separated from the pipe wall by a thin lubricating layer consisting of cement paste. The water in the paste is hydraulically linked with the interparticle water layer in the plug. 

The pressure generated by the flow resistance must not be greater than the pump pressure rating for maintaining continuous plug movement.  However, if the concrete is too saturated at higher w/c ratio, the concrete at certain pump pressures may be such that water is forced out of the mix, creating an increase in flow resistance and a possible blockage. In other words, a very stiff concrete is not pumpable and also a concrete with high w/c ratio is also not pumpable. It is interesting to note that if a concrete is pumpable, it is implied that it is a good concrete. 


High-Performance concrete

Recently a new term has come in the field of concrete technology “High Performance Concrete” or HPC. The properties of HPC are.
  • ·     High Workability
  • ·     High Strength
  • ·     High Modulus of Elasticity
  • ·     High Density
  • ·     High Dimensional Stability
  • ·     Low Permeability and
  • ·    Resistance to Chemical Attack

There is a little controversy between the terms high-strength and high performance concrete. High-performance concrete is also, a high-strength concrete but it has a few more attributes specifically designed as mentioned above. It is, therefore, logical to describe by the more widely embracing term “High Performance Concrete” (HPC).

In normal concrete, relatively low strength and elastic modulus are the result of high heterogeneous nature of structure of the material, particularly the porous and weak transition zone, which exists at the cement paste-aggregate interface. By densification and strengthening of the transition zone, many desirable properties can be improved many fold. A substantial reduction of quantity of mixing water is the fundamental step for making HPC. With reduction of w/c ratio strength concrete will increase. But reduction in w/c ratio to less than 0.3 will greatly improve the qualities of transition zone to give inherent qualities expected in HPC. 

Use of silica fume is also found to be necessary to improve the qualities of transition zone.Silica fumes becomes a necessary ingredient for strength above to 80 MPa. The best quality fly ash and GGBS may be used for other nominal benefits. Inspite of the fact that these pozzolanicmaterials increase the water demand, their benefits will out weigh the disadvantages. The crux of whole problem lies in using very low w/c ratio, consistant with high workability at the time of placing and compacting. Neville opines that the lowest w/c ratio that could be used is 0.22.


Only with the use of superplasticizer, w/c ratio in the range of 0.25 to 0.3 can be adopted and a high slump is possible to achieve. Therefore, use of appropriate superplasticizer is a key material in making HPC. The associated problem is the selection of superplasticizer and that of cement so that they are compatible and retain the slump and rheological properties for a sufficiently long time till concrete is placed and compacted.

























Cement Mortar

Mortar is a material used in masonry construction to fill the gaps between the bricks and blocks used in construction. Mortar is a mixture of sand, a binder such as cement or lime, and water and is applied as a paste which then sets hard.

Puzzolana Portland cement and sulphate-resisting cement form mortar which are used for constructions exposed to aggressive and waste waters. Cement mortars are used for plastering, rendering smooth finishes and damp proof courses. 

The mix proportions of cement mortar are given in Table below 


Preparation:-Manual mixing is applied for Small quantities of mortar; mechanical mixers are used for large quantities. 

For manual mixing,sand is sieved, cleaned with water to remove dirt and dust and dried. This dry sand is laid uniformly, on a pucca platform, over which cement is uniformly spread. The whole mass is then thoroughly mixed with spades till it becomes uniform in colour. A depression is then made in the middle of the mix and required quantity of water is added. The dry mix from the sides is moved and placed on the edges of the depression formed till the water is completely absorbed by the mix. The wet mix is then worked with spades to give a uniform consistency to the mortar.

For mechanical mixing the calculated quantity of cement, sand and water are fed into the cylindrical container of the mixer. A rotar with blades, inside the container, rotates and thoroughly mixes the ingredients. 
  
Precautions:-Basic property of Cement mortar should be uniformity and workability. It should be consumed within 30 minutes from the instant of adding water to the mix. The bricks, stones and blocks should be fully saturated in water before laying. The masonry and plastered or pointed surface should be kept completely wet by sprinkling water for at least 7 days. 

Sunday, 1 October 2017

ORDINARY PORTLAND CEMENT

Cement is one of the most important base products of construction industry and Ordinary Portland cement or OPC is by far the most important type of cement. Prior to 1987, there was only one grade of OPC [which was governed by IS 269-1976]. After 1987 higher grade cements were introduced. The OPC was classified into three grades, namely..

1.   OPC-33 Grade
2.   OPC-43 Grade
3.   OPC-53 Grade


These classifications are based on the strength of the cement at 28 days when tested as per IS 4031- 1988. If the 28 days strength is not less than 33N/mm2, it is called 33 grade cement, if the strength is not less than 43N/mm2, it is called 43 grade cement, and if the strength is not less then 53 N/mm2, it is called 53 grade cement. But the actual strength obtained by these cements at the factory are much higher than the BIS specifications.

The physical and chemical properties of different types of  OPC are shown in Table below.


It has been possible to upgrade the qualities of cement by using high quality limestone, modern equipments, closer on line control of constituents, maintaining better particle size distribution, finer grinding and better packing. Generally use of high grade cements offer many advantages for making stronger concrete. Although they are little costlier than low grade cement, they offer 10-20% savings in cement consumption and also they offer many other hidden benefits. One of the most important benefits is the faster rate of development of strength. In the modern construction activities, higher grade cements have become so popular that 33 grade cement is almost out of the market. Table shows the grades of cement manufactured in various countries of the world.

The manufacture of OPC is decreasing all over the world in view of the popularity of blended cement on account of lower energy consumption, environmental pollution, economic and other technical reasons. In advanced western countries the use of OPC has come down to about 40 per cent of the total cement production. In India for the year 1998-99 out of the total cement production i.e., 79 million tons, the production of OPC in 57.00 million tons i.e., 70%. The production of PPC is 16 million tone i.e., 19% and slag cement is 8 million tons i.e., 10%. In the years to come the use of OPC may still come down, but all the same the OPC will remain as an important type for general construction.


RHEOLOGY

Originated from a Greek word “rheo” which means “flow” and “logia” which means “study” Rheology is the study of flow of matter in liquid, soft solid or solid state under conditions in which they respond to plastic flow other deforming elastically when a external force is applied. 

Rheological properties of a cement mix means deformation of hardened concrete and placing and mixing of freshly mixed concrete.The mechanical behaviour of hardened cement paste,which exhibits both elastic and inelastic deformations, can be expressed in rheological terms.

Factors Affecting Rheological Properties:- 

1. If the amount of coarse aggregate in a concrete mix is more the desirable amount the voids cannot be filled with the available mortar, which will lead to loss of cohesion and mobility. Such a mix is termed harsh and requires a great amount of effort to place and compact. On the other hand, an excessive amount of fine aggregate or entrained air in a concrete mixture will greatly increase the cohesion and render the concrete difficult to move.

2. Slump test is the measure of consistency of concrete mix or it is an indicator of relative water content of the mix. An increase in the water content or slump above that required to achieve a workable mix produces greater fluidity and decreased internal friction. Thus, a water content more than that needed will not improve the rheological properties of concrete. But very low slump with decrease the workability of a concrete mix making it impossible to place is some areas.

3. Elevated temperature, use of rapid hardening cement, cement deficient in gypsum and use of accelerating admixtures, increase the rate of hardening which reduce the mobility of concrete.

4. The rough and highly angular aggregate particles will result in higher percentage of voids being filled by mortar, requiring higher fine aggregate contents and correspondingly higher water content. Similarly an angular fine aggregate will increase internal friction in the concrete mixture and require higher water contents than well rounded natural sands.

5. A well graded aggregate gives good workability. Gap graded aggregate affects void system and workability. These effects are greater in fine aggregate.

6. An increase in the maximum size of aggregate will reduce the fine aggregate requirement to maintain a given workability and will thereby reduce the surface area to be wetted and hence the cement content necessary for a constant water/cement ratio .

7. The admixtures which have significant effect on the rheology of concrete are plasticizers and super-plasticizers, air-entraining agents, accelerators and retarders.Lignosulphate salt based plasticizers (0.15%) reduce the water content by 10% without any detrimental effect. Super-plasticizers and plasticizers prevent the formation of flocculated structure by changing the inter-particle attraction/repulsion.
With proper attention to the rheological properties can increase work efficiency and reduce the material cost as well as the cost of construction

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Monday, 14 August 2017

IS codes for civil engineering.

* IS: 456 – code of  practice for plain and reinforced concrete.
* IS: 383 – specifications for fine & coarse aggregate from natural sources for concrete.
* IS: 2386 – methods of tests for aggregate for concrete.
* IS: 2430 – methods of sampling.
* IS: 4082 – specifications for storage of materials.
* IS: 2116 – permissible clay, silt & fine dust contents in sand.
* IS: 2250 – compressive strength test for cement mortar cubes.
* IS: 269 – specifications for 33 grade OPC.
* IS: 8112 – specifications for 43 grade OPC.
* IS: 12269 – specifications for 53 grade OPC.
* IS: 455 – specifications for PSC (Portland slag cement).
* IS: 1489 – specifications for PPC (Portland pozzolana cement).
* IS: 6909 – specifications for SSC (super sulphated cement).
* IS: 8041 – specifications for RHPC (Rapid Hardening Portland cement).
* IS: 12330 – specifications for SRPC (sulphate resistant portland cement).
* IS: 6452 – specifications for HAC for structural use (high alumina cement).
* IS: 3466 – specifications for masonry cement.
* IS: 4031 – chemical analysis and tests on cement.
* IS: 456; 10262; SP 23 – codes for designing concrete mixes.
* IS: 1199 – methods of sampling and analysis of concrete.
* IS: 516 – methods of test for strength of concrete.
* IS: 13311 – ultrasonic testing of concrete structures.
* IS: 4925 – specifications for concrete batching plant.
* IS: 3025 – tests on water samples.
* IS: 4990 – specifications for plywood formwork for concrete.
* IS: 9103 – specifications for concrete admixtures.
* IS: 12200 – specifications for PVC water bars.
* IS: 1077 – specifications for bricks for masonry work.
* IS: 5454 – methods of sampling of bricks for tests.
* IS: 3495 – methods of testing of bricks.
* IS: 1786 – cold-worked HYSD steel rebars (grade Fe415 & Fe500).
* IS: 432; 226; 2062 – mild steel of grade I.
* IS: 432; 1877 – mild steel of grade II.
* IS: 1566 – specifications for hard drawn steel wire fabric for reinforcing concrete.
* IS: 1785 – specifications for plain hard drawn steel wire fabric for prestressed concrete.
* IS: 2090 – specifications for high tensile strength steel bar for prestressed concrete.
* IS: 2062 – specifications for steel for general purposes.
* IS: 226 – specifications for rolled steel made from structural steel.
* IS: 2074 – specifications for prime coat for structural steel.
* IS: 2932 – specifications for synthetic enamel paint for structural steel.
* IS: 12118 – specifications for Polysulphide sealants.

Tuesday, 8 August 2017

A good civil engineer should know many basics and Topics

1)- BUILDING MATERIAL AND CONSTRUCTION

Lab test of Rock,Brick,Cement,Aggregate,Concrete etc

ex.

sand + Cement = Mortar

Mortar + Coarse aggregate = Concrete

Different Test of Brick

1) Crushing strength test by UTM in lab

Standard result are 10.5N/mm2 (1st class) 7.5(2nd class) 3.5(3rd class)

Stand. Size of brick- 19x19x9

2)- Water absorption test - Not more than 20% Of water by Wt. If immersed in water for 24hr - 1st class

Not more than 22% water- 2nd class & 24% - 3rd class

Many other test of brick- Hardness test,Toughness test.

English,Fleming,strecher & Header bond of brick masonary.

CONCRETE

Strong in Compression & weak in tension (i.e we provide steel bar)

Grade(Nominal mix)- M10- 1:3:6 M15- 1:2:4 M20- 1:1.5:3 M25- 1:1:2

Know about admixture

Geo-technical engg.

Index properties of soil, Phase diagram of soil, Classification of soil

 

Saturday, 29 July 2017

Highway Engineering MCQs





Question No. 01

Group index method of design of flexible pavement is

(A) A theoretical method

(B) An empirical method based on physical properties of sub-grade soil

(C) An empirical method based on strength characteristics of sub-grade soil

(D) A semi empirical method

Answer: Option B

Question No. 02

Which of the following is considered to be the highest quality construction in the group of black top pavements?

(A) Mastic asphalt

(B) Sheet asphalt

(C) Bituminous carpet

(D) Bituminous concrete

Answer: Option D

Question No. 03

Los Angeles testing machine is used to conduct

(A) Abrasion test

(B) Impact test

(C) Attrition test

(D) Crushing strength test

Answer: Option A

Question No. 04

When the width of car parking space and width of street are limited, generally preferred parking system is

(A) Parallel parking

(B) 45° angle parking

(C) 65° angle parking

(D) 90° angle parking

Answer: Option A

Question No. 05

When the bituminous surfacing is done on already existing black top road or over existing cement concrete road, the type of treatment given is

(A) Seal coat

(B) Tack coat

(C) Prime coat

(D) Spray of emulsion

Answer: Option B

Friday, 28 July 2017

UNIT WEIGHT


01. Concrete 25 kN/m3
02. Brick 19 kN/m3
03.  Steel 7850 Kg/m3
04. Water 1000 Lt/m3
05. Cement 1440 Kg/m3
06. 1Gallon  4.81 Litres
07. Link 8″ = 200mm
08. 1 Hectare 2.471 acr(10000m2)
09. 1  Acr 4046.82m2 = 100 cent

Unit conversation

CONCRETE GRADES:
M5 = 1:4:8
M10= 1:3:6
M15= 1:2:4
M20=  1:1.5:3
M25= 1:1:2

CLEAR COVER TO MAIN REINFORCEMENT:
1.FOOTINGS : 50 mm
2.RAFT  FOUNDATION.TOP : 50 mm
3.RAFT FOUNDATION.BOTTOM/SIDES : 75 mm
4.STRAP BEAM  : 50 mm
5.GRADE SLAB : 20 mm
6.COLUMN : 40 mm
7.SHEAR WALL : 25  mm
8.BEAMS : 25 mm
9.SLABS : 15 mm
10.FLAT SLAB : 20 mm
11.STAIRCASE  : 15 mm
12.RET. WALL : 20/ 25 mm on earth
13.WATER RETAINING STRUCTURES :  20/30 mm

WEIGHT OF ROD PER METER LENGTH:
DIA WEIGHT PER METER
6mm = 0.222Kg
8mm = 0.395 Kg
10mm = 0.616 Kg
12mm = 0.888  Kg
16mm = 1.578 Kg
20mm = 2.466 Kg
25mm = 3.853 Kg
32mm = 6.313  Kg
40mm = 9.865 Kg

1bag cement-50kg
1feet-0.3048m
1m-3.28ft
1sq.m-10.76sq.f t
1cu.m-35.28cu.ft
1acre-43560sq.ft
1hectare-2.47acre

DESIGN MIX:
M10 ( 1 : 3.92 : 5.62)
Cement : 210 Kg/ M 3
20  mm Jelly : 708 Kg/ M 3
12.5 mm Jelly : 472 Kg/ M 3
River sand : 823 Kg/ M  3
Total water : 185 Kg/ M 3
Fresh concrete density: 2398 Kg/M 3

M20 ( 1 : 2.48 :  3.55)
Cement : 320 Kg/ M 3
20 mm Jelly : 683 Kg/ M 3
12.5 mm Jelly :  455 Kg/ M 3
River sand : 794 Kg/ M 3
Total water : 176 Kg/ M  3
Admixture : 0.7%
Fresh concrete density: 2430 Kg/ M 3

M25 ( 1 : 2.28 :  3.27)
Cement : 340 Kg/ M 3
20 mm Jelly : 667 Kg/ M 3
12.5 mm Jelly :  445 Kg/ M 3
River sand : 775 Kg/ M 3
Total water : 185 Kg/ M  3
Admixture : 0.6%
Fresh concrete density: 2414 Kg/ M 3
Note: sand 775  + 2% moisture, Water185 -20.5 =
164 Liters,
Admixture = 0.5% is  100ml

M30 ( 1 : 2 : 2.87)
Cement : 380 Kg/ M 3
20 mm Jelly : 654 Kg/ M  3
12.5 mm Jelly : 436 Kg/ M 3
River sand : 760 Kg/ M 3
Total water :  187 Kg/ M 3
Admixture : 0.7%
Fresh concrete density: 2420 Kg/ M 3
Note:  Sand = 760 Kg with 2% moisture
(170.80+15.20)

STANDARD CONVERSION FACTORS
INCH = 25.4 MILLIMETRE
FOOT =  0.3048 METRE
YARD = 0.9144 METRE
MILE = 1.6093 KILOMETER
ACRE = 0.4047  HECTARE
POUND = 0.4536 KILOGRAM
DEGREE FARENHEIT X 5/9 – 32 =  DEGREE
CELSIUS
MILLIMETRE= 0.0394 INCH
METRE = 3.2808FOOT
METRE =  1.0936YARD

Physical test on cement.

(a) 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.

(b) 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 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.

 

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 7mm 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.

 

(c) Soundness Test:

This test is conducted to find free lime in cement, which is not desirable. Le Chatelier apparatus shown in  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.

 

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.

 

(d) 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 P4+ 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.

 

 

Low cost housing

Low Cost Housing is a new concept which deals with effective budgeting and following of techniques which help in reducing the cost construction through the use of locally available materials along with improved skills and technology without sacrificing the strength, performance and life of the structure.

There is huge misconception that low cost housing is suitable for only sub standard works and they are constructed by utilizing cheap building materials of low quality.The fact is that Low cost housing is done by proper management of resources.Economy is also achieved by postponing finishing works or implementing them in phases.

Building Cost

The building construction cost can be divided into two parts namely:

Building material cost : 65 to 70 %

Labour cost : 65 to 70 %

Now in low cost housing, building material cost is less because we make use of the locally available materials and also the labour cost can be reduced by properly making the time schedule of our work. Cost of reduction is achieved by selection of more efficient material or by an improved design.

 

Areas from where cost can be reduced are:-

1) Reduce plinth area by using thinner wall concept.Ex.15 cms thick solid concrete block wall.

2) Use locally available material in an innovative form like soil cement blocks in place of burnt brick.

3) Use energy efficiency materials which consumes less energy like concrete block in place of burnt brick.

4) Use environmentally friendly materials which are substitute for conventional building components like use R.C.C. Door and window frames in place of wooden frames.

5) Preplan every component of a house and rationalize the design procedure for reducing the size of the component in the building.

6) By planning each and every component of a house the wastage of materials due to demolition of the unplanned component of the house can be avoided.

7) Each component of the house shall be checked whether if it’s necessary, if it is not necessary, then that component should not be used.

Cost reduction through adhoc methods

 

Foundation

Normally the foundation cost comes to about 10 to 15% of the total building and usually foundation depth of 3 to 4 ft. is adopted for single or double store building and also the concrete bed of 6″(15 Cms.) is used for the foundation which could be avoided.

It is recommended to adopt a foundation depth of 2 ft.(0.6m) for normal soil like gravely soil, red soils etc., and use the uncoursed rubble masonry with the bond stones and good packing. Similarly the foundation width is rationalized to 2 ft.(0.6m).To avoid cracks formation in foundation the masonry shall be thoroughly packed with cement mortar of 1:8 boulders and bond stones at regular intervals.

It is further suggested adopt arch foundation in ordinary soil for effecting reduction in construction cost up to 40%.This kind of foundation will help in bridging the loose pockets of soil which occurs along the foundation.

In the case black cotton and other soft soils it is recommend to use under ream pile foundation which saves about 20 to 25% in cost over the conventional method of construction.

 

Plinth

It is suggested to adopt 1 ft. height above ground level for the plinth and may be constructed with a cement mortar of 1:6. The plinth slab of 4 to 6″ which is normally adopted can be avoided and in its place brick on edge can be used for reducing the cost. By adopting this procedure the cost of plinth foundation can be reduced by about 35 to 50%.It is necessary to take precaution of providing impervious blanket like concrete slabs or stone slabs all round the building for enabling to reduce erosion of soil and thereby avoiding exposure of foundation surface and crack formation.

 

Walling

Wall thickness of 6 to 9″ is recommended for adoption in the construction of walls all-round the building and 41/2 ” for inside walls. It is suggested to use burnt bricks which are immersed in water for 24 hours and then shall be used for the walls

 

Rat – trap bond wall

It is a cavity wall construction with added advantage of thermal comfort and reduction in the quantity of bricks required for masonry work. By adopting this method of bonding of brick masonry compared to traditional English or Flemish bond masonry, it is possible to reduce in the material cost of bricks by 25% and about 10to 15% in the masonry cost. By adopting rat-trap bond method one can create aesthetically pleasing wall surface and plastering can be avoided.

 

Concrete block walling

In view of high energy consumption by burnt brick it is suggested to use concrete block (block hollow and solid) which consumes about only 1/3 of the energy of the burnt bricks in its production. By using concrete block masonry the wall thickness can be reduced from 20 cms to 15 Cms. Concrete block masonry saves mortar consumption, speedy construction of wall resulting in higher output of labour, plastering can be avoided thereby an overall saving of 10 to 25% can be achieved.

 

Soil cement block technology

It is an alternative method of construction of walls using soil cement blocks in place of burnt bricks masonry. It is an energy efficient method of construction where soil mixed with 5% and above cement and pressed in hand operated machine and cured well and then used in the masonry. This masonry doesn’t require plastering on both sides of the wall. The overall economy that could be achieved with the soil cement technology is about 15 to 20% compared to conventional method of construction.

 

Doors and windows

It is suggested not to use wood for doors and windows and in its place concrete or steel section frames shall be used for achieving saving in cost up to 30 to 40%.Similiarly for shutters commercially available block boards, fibre or wooden practical boards etc., shall be used for reducing the cost by about 25%.By adopting brick jelly work and precast components effective ventilation could be provided to the building and also the construction cost could be saved up to 50% over the window components.

 

Lintels and Chajjas

The traditional R.C.C. lintels which are costly can be replaced by brick arches for small spans and save construction cost up to 30 to 40% over the traditional method of construction. By adopting arches of different shapes a good architectural pleasing appearance can be given to the external wall surfaces of the brick masonry.

 

Roofing

Normally 5″(12.5 cms) thick R.C.C. slabs is used for roofing of residential buildings. By adopting rationally designed insitu construction practices like filler slab and precast elements the construction cost of roofing can be reduced by about 20 to 25%.

 

Filler slabs

They are normal RCC slabs where bottom half (tension) concrete portions are replaced by filler materials such as bricks, tiles, cellular concrete blocks, etc.These filler materials are so placed as not to compromise structural strength, result in replacing unwanted and nonfunctional tension concrete, thus resulting in economy. These are safe, sound and provide aesthetically pleasing pattern ceilings and also need no plaster.

 

Jack arch roof/floor

They are easy to construct, save on cement and steel, are more appropriate in hot climates. These can be constructed using compressed earth blocks also as alternative to bricks for further economy.

 

Ferrocement channel/shell unit

Provide an economic solution to RCC slab by providing 30 to 40% cost reduction on floor/roof unit over RCC slabs without compromising the strength. These being precast, construction is speedy, economical due to avoidance of shuttering and facilitate quality control.

 

Finishing Work

The cost of finishing items like sanitary, electricity, painting etc., varies depending upon the type and quality of products used in the building and its cost reduction is left to the individual choice and liking.

 

Basic steps of Stadd-pro

In this blog I am going to discuss about STAADPRO as it is mostly use and better user Interface the steps involved are elaborated in following lines :

1. Creating a project file with suitable file name.
2. Fixing the units.
3. Creating the Geometry by JOINT   COORDINATES and MEMBER INCIDENCE command.
4. Applying the member properties as per codal provision and self judgement.
5. Providing support to the structure.
6. Using definition command for loads .
7. Applying loads on floors and other structural components.
8. Providing output units.
9. Defining the codes.
10. Print support reaction command after  perform analysis.
11. Defining design code i.e., IS 456 or IS 13920
11. Design commands as per respective codes
12 .Finally design and result output.

Compression Test of concrete block.


The Compression Test is a laboratory test to determine the characteristic strength of the concrete but the making of test cubes is sometimes carried out by the supervisor on site. This cube test result is very important to the acceptance of insitu concrete work since it demonstrates the strength of the design mix.

The procedure of making the test cubes is as follows:

150 mm standard cube mold is to be used for concrete mix and 100 mm standard cube mold is to be used for grout mix.

Arrange adequate numbers of required cube molds to site in respect with the sampling sequence for the proposed pour.Make sure the apparatus and associated equipment are clean before test and free from hardened concrete and superfluous water .

Assemble the cube mold correctly and ensure all nuts are tightened.Apply a light coat of proprietary mold oil on the internal faces of the mold.Place the mold on level firm ground and fill with sampled concrete to a layer of about 50 mm thick.

Compact the layer of concrete thoroughly by tamping the whole surface area with the Standard Tamping Bar. (Note that no less than 35 tamps / layer for 150 mm mold and no less than 25 tamps / layer for 100 mm mold).Repeat Steps 5 & 6 until the mold is all filled. (Note that 3 layers to be proceeded for 150 mm mold and 2 layers for 100 mm mold).

Remove the surplus concrete after the mold is fully filled and trowel the top surface flush with the mold.Mark the cube surface with an identification number (say simply 1, 2, 3, etc) with a nail or match stick and record these numbers in respect with the concrete truck and location of pour where the sampled concrete is obtained.

Cover the cube surface with a piece of damp cloth or polythene sheeting and keep the cube in a place free from vibration for about 24 hours to allow initial set .Strip off the mold pieces in about 24 hours after the respective pour is cast. Press the concrete surface with the thumb to see any denting to ensure the concrete is sufficiently hardened, or otherwise de-molding has to be delayed for one more day and this occurrence should be stated clearly in the Test Report.

Mark the test cube a reference number with waterproof felt pen on the molded side, in respect with the previous identification number.Place the cube and submerge in a clean water bath or preferably a thermostatically controlled curing tank until it is delivered to the accredited laboratory for testing.

Different test conduct on Stones to select the appropriate stone for construction purpose.

Stones form one of the most important building materials in civil engineering. Stones are derived from rocks, which form the earth's crust and have no definite shape or chemical combination but are mixtures of two or more minerals. The mineral is a substance which is formed by the natural inorganic process and possesses a definite chemical combination and molecular structure. They are strong, durable and descent in appearance.

The main uses of stone as a building material are:

As a principal material for foundation of civil engineering works, and for the construction of walls, arches, abutments and dams.In stone masonry in places where it is naturally available.As coarse aggregate in cement concrete (crushed form of rock).

Tests which are to be conducted on stones for selecting it as a building material.

Acid Test: Acid test is used to investigate how much atmospheric action can be resisted by stone.  In this test 100 grams of stones in chipped form are kept in a 5% solution of hydrochloric acid or sulphuric acid. After 3 days stones in chipped form are taken out and dried. If the edges of stones are sharp as earlier, it indicates that stone can resist weathering actions.

Smith's Test: This test is used for finding out the presence of soluble matter in stones. In this test few sample of stones are place in a glass or test-tube filled with clean water. Stones are kept in water for 1 hour. After this the glass or test-tube is vigorously shaken. Due to presence of earthy material and clay impurities water is converted to dirty water. Slightly cloudiness of water will prove that the stones are good and durable. If water becomes too dirty, it indicates that stone contains too much soluble impurities and it is not suitable for construction.

 
Crushing Strength: Crushing test is used to investigate the compressive strength of stone. In this test stone is cut into cubes of dimension 40mm. Sides of cube are finely dressed and finished. Cubes of stones are then kept in water for 72 hours. Then 5mm thick layer of plywood or plaster of paris is applied on the load bearing surface. Load is applied axially on load bearing surface using universal testing machine or crushing testing machine until cracks appear on the stone or stone starts crushing.
     Crushing strength of the stone is the maximum load at which it crushes divided by the area of the load bearing surface. 

Water Absorption Test: In this test, 50 grams of stones in chipped form are places in an oven at 105 degree celsius for 3 hours then cooled at room temperature. Weight of stones is then taken (W1). Then stones are places in distilled water for 3 days. After 3 days weight of stones is taken (W2).

     Percentage '%' of water absorption should not exceed 15%, otherwise stone is not suitable for construction.

Crystallization Test: 4 cubes of stone with dimension 40mm are taken. Stones are dried for 3 days and weighed. Then stones are immersed in 14% solution of Sodium Sulfate (Na2SO4) for 2 hours. After this stones are dried at 100 degree Centigrade  and weighed. Difference in weight is noted .Process of drying, weighing, immersion and reweighing is repeated at least 5 times. Each time, change in weight is noted and it is expressed as a percentage of original weight.

PERCENTAGE OF WEAR SHOULD NOT EXCEED 2% FOR GOOD STONE.

Hardness Test: This test is carried out to determine the hardness of stone. First weight of specimen is taken (W1). The specimen is filled in a test cylinder of diameter 25 mm and height 25 mm. Then cylinder is placed in Dorry's testing machine and force of 12.50 N is applied. The disc of testing machine is rotated at 28 revolutions per minute.During the rotation of the disc, coarse sand of standard specification is sprinkled on the top of disc. After 1000 revolutions specimen is weighed (W2).

Impact Test: This test is carried out to determine the toughness of stone. This test requires an 'Impact Testing Machine'. In this test stones are filled in test cylinder of diameter 25 mm and height 25 mm. The cylinder is placed on machine and steel hammer of weight 20 N is allowed to fall on the specimen in cylinder. The height of first fall is 1 cm, height of second fall is 2 cm and so on. The height at which specimen breaks is recorded. If specimen breaks at 'n cm' then 'n' is the toughness index of stone.  
Microscopic Test: In this test specimen of stones is placed under microscope and various properties are studied such as grain size, texture of stone, pores, veins, shakes etc.

Attrition Test: This test is carried out to test the resistance to abrasion (ability to withstand grinding action)  of stone. This test is carried out in 'Attrition Test Machine'. In this test specimen of stone is weighed (W1). Then stones are transferred to drum and drum is inclined to 30 degree to the horizontal. Then stones are revolved ate 2000 revolution per hour for 5 hours. After this stones are sieved on a 2 mm sieve. Stones retained on sieve are weighed (W2) and loss in weight percentage gives the percentage of wear. 

Friday, 30 June 2017

Effect of Maximum size of Aggregate on Strength of CONCRETE

Earlier it was thought that the use of larger size aggregate leads to higher strength.This was due to the fact that the larger the aggregate the lower is the total surface area and, therefore, the lower is the requirement of water for the given workability. So, a lower water/cement ratio can be used which will result in higher strength of Concrete.

However, later it was found that the use of larger size aggregate did not contribute to higher strength as expected from the theoretical considerations due to the following reasons.. 

1. The larger maximum size aggregate gives lower surface area for developments of gel bonds which is responsible for the lower strength of the concrete.

2. Secondly bigger aggregate size causes a more heterogeneity in the concrete which will prevent the uniform distribution of load when stressed.


When large size aggregate is used, due to internal bleeding, the transition zone will become much weaker due to the development of micro-cracks which result in lower compressive strength. 
Generally, high strength concrete or rich concrete is adversely affected by the use of large size aggregate. But in lean mixes or weaker concrete the influence of size of the aggregate gets reduced. It is interesting to note that in lean mixes larger aggregate gives highest strength while in rich mixes it is the smaller aggregate which yields higher strength. 

The Fig.  below shows the influence of maximum size of aggregate on compressive strength of concrete..






Following Figure depicts the influence of size of aggregate on compressive strength of concrete for different w/c ratio.