ONLINE CIVIL ENGINEERING

ELECTIRC CONE PENETRATION TEST ON SOIL

2023-05-17T15:40:00.000-07:00

One of the advanced techniques in Soil Investigation is Electric Cone Penetration Test (ECPT). It is a widely used geotechnical investigation technique that involves measuring the resistance of soil to a penetrating cone. ECPT test is essential in determining the soil’s strength and consistency, which are critical factors in designing foundation structures, embankments, and retaining walls. Here, we will discuss the concept of ECPT, its procedure, and its applications in geotechnical engineering.

CONCEPT:-

ECPT involves inserting a cone-shaped probe, known as a penetrometer, into the soil at a constant rate. The penetrometer measures the electrical resistance of the soil as it penetrates. The resistance is directly proportional to the soil's strength, which is an excellent indicator of soil properties.

The electric cone penetrometer is an electrical device that calculates soil resistance and pore pressure, which is the pressure of fluids in the soil. The probe consists of a pointed tip, followed by a cylindrical section, and then a conical section. The conical section has a base area of 10 cm2, and the apex angle is 60 degrees. The cylindrical section is used to measure pore pressure and has small holes for fluid entry.

The information gathered during an ECPT can be extremely helpful in determining the density, strength, and other geotechnical characteristics of the soil or substance being examined. It aids in assessing the load-bearing capacity, soil behavior, and potential risks related to slope stability, foundation design, and other geotechnical projects by engineers and geotechnical specialists.

CONCLUSION:-

To gain a thorough understanding of the subsurface conditions at a specific site, the ECPT is frequently utilized in conjunction with other geotechnical experiments and investigations.

CONCRETE

2020-04-26T02:13:00.002-07:00

CONCRETE a composite material which consists of materials like cement, sand, aggregate, water and admixtures.

ADVANTAGES: - i) Concrete is economical

ii) Ability to cast into any shapes

iii) Durable

iv) Low maintenance

v) High strength.

CONCRETE

TRANSPORTION:- Transportation of concrete from mixing plant to the construction site .care should be while transporting so that no any loss of ingredients occurs.

For manual mix or site mix wheel borrow is used for and for RMC (Ready Mix concrete) Transit mixture is used.

CONCRETE MIX:-Concrete mix ratios are the proportions of concrete components such as cement, sand, aggregates and water. These mix ratios are decided based on type of construction, cost efficiency and availability of materials.

VOLUMETRIC MIX is concrete mix which is mixed by volume of material, rather than weight. Volumetric Concrete is typically mixed on-site in volumetric concrete mixers, which are self-contained portable batch plants. These specialist trucks contain all the requisite concrete ingredient materials (sand, aggregate, cement, and water).

DESIGN MIX is the process of designing a concrete based on requirement of strength, workability by determining relative proportions of different ingredients (cement, coarse aggregate, sand, water and admixture) as economically as possible.

Typically design mix is done is certified 3^rd party testing labs by taking different mix propositions in hit and trail basis and checking their results for workability and strength keeping in eye the economical parameter.

PLACING OF CONCRETE:- Placing-Concrete should be placed as early as possible to formwork.as per IS code it should be placed in 3 hrs from the time of batching of concrete in plant. Care should be taken while placing as to ensure there is no loss of workability of concrete.

Placing of concrete is done by transit mixture, concrete pump ,Boom pleasure, chute etc.

CONCRETE PUMP BOOM PLACER CHUTE

VIBRATION- after concrete is placed in there position compaction is to be done. Compaction educed air from the concrete and make it dense so to achieve proper strength. If compaction is not done properly then honeycomb occurs which reduces strength of the concrete.

Compaction is done by Needle vibrator, Surface vibrator, External vibrator and Table vibrator.

CURING is the way to maintain adequate moisture content & temperature in concrete at early to achieve designed strength.

Curing is done by Ponding, Moist curing (Gunny bags), Chemical curing.

CEMENT CONCRETE FLOORING

2020-04-21T03:07:00.000-07:00

Cement concrete flooring is one of the most common types of flooring used in both in residential as well as public buildings.

• Advantages

1. It is non-absorbent in nature.

2. It is very useful for water stores.

3. High Durability.

4. Smooth in nature and pleasing in appearance.

5. Good wearing Properties.

6. Easy to maintain

7. Economical

•But it requires proper attention while laying as defects in carelessly made floor cannot be rectified easily.

• They are used for very low maintenance cost and long life.

• For achieving more abrasion value metallic or chemical hardener is mixed, which is called ironite or chemical hardener flooring.

POINTING of BRICK WALLS

2020-04-19T03:29:00.001-07:00

Definition: - Pointing is the art of finishing the mortar joints in exposed brick or stone masonry with suitable cement or lime mortar.

Objective: -

Protection of masonry joins from weather effects
When workmanship in masonry works is of very good quality and the aesthetic view of exposed well maintained masonry joints is desirable, their walls with points is used (without any plaster or other finishing).

Building with Pointing Surface

PLASTERING

2020-04-18T21:39:00.000-07:00

Definition: - Plastering is the process of covering rough walls and uneven surfaces in the construction of houses and other structures with mortar or plaster.

Objective: -

Protection layer of masonry wall (from weather effects or any third party etc)
Provides good aesthetic view by providing flat and neat surface.
It’s a base layer for other activities like painting, putty or tiling etc.

Materials for Plastering: -

Basic Info of Plastering:-

• Ceiling Plastering- 6mm [1:3 or 1:4 –Cement : Sand]

• Inside Plastering-12mm [1:4 to 1:6-Cement : Sand]

• External Plaster-18mm [12mm (1:6)+6(1:4)] or 20mm [15mm (1:6)+5mm(1:4)]

• Before plastering surface is roughened by hacking.

• Plastering is cured for 7 days.

Wall & Ceiling Plastering

CONSTRUCTION OF ROOF SLAB

2018-12-14T06:22:00.001-08:00

Construction of any roof slab comprises of these following steps..

1.Staging:-After completion of Columns upto Roof Beam Bottom Construction of Roof Slab is stats. The First stage is Staging. Staging is noting but erection of staging forms on which shuttering of Roof Slab or Beam will rest. Staging can be made of different type of materials starting wooden to metal parts, which hold is shuttering. Staging should be stable and firm to hold the load of the slab.It should be firm enough so that during concreting it should properly hold the concrete & shuttering so that shuttering do not bulge of settle.

2.Shuttering:- Shuttering is started after completion of staging. Plywood or metal any type of shuttering are used base on the load of slab. During shuttering proper alignment and level of shuttering is checked. Shuttering is properly sealed to avoid slurry lickage which will lead to honeycomb structure or segregation of concrete. Demolding agent are used in shuttering for smooth finishing of concrete surfaces and easy stripping of shuttering boards.

3. Reinforcement:- Reinforcement the third step is construction of roof slab. It can be started after completion of shuttering or it can be done together with shuttering for beams also. Reinforcement placement to be properly checked according to the BBS or Approved Bad Bending Schedule. Diameter of rods, length, spacing, lap length, no of chairs and location of rods to be properly checked before concreting.

4.Concreting:- After completion of Shuttering, Reinforcement Concreting of Slab is started. Concreting is to be properly done as per design with proper vibration (Surface & Needle Vibrator) for avoiding segregation. Extra care to be given for maintaining proper slump during concreting. No bleeding and creep should be there. After concreting Surface of Slab is finished by manual or mechanical means.

5. Curing:- Curing to be done by making ponds/ carry over the slab. Slab to be cured for 21 days.

6. De-shuttering:- De-shuttering is to be done after slab reaches its design strength ie. after 21 days. If quick setting cement or admixture is used during concreting shuttering can be removed earlier as per the specification of the chemical.

CONSTRUCTION OF RETAINING WALL

2018-12-08T01:07:00.001-08:00

A retaining wall is a structure designed and constructed to resist the lateral pressure of soil, when there is a desired change in ground elevation that exceeds the angle of repose of the soil.

Construction of Concrete Retaining wall:-Following are steps in Construction of RCC retaining wall..

Excavation:-First Excavation of Wall base is done & it is well compacted via mechanical means and with sprinkling of adequate water.
PCC:- Plain Cement Concrete of Grade M-10 to M-15 is laid over compacted earth. This PCC acts as a base for the retaining wall
Reinforcement: & Shuttering- Reinforcement is tied as per drawings and specifications and shuttering is paced for concreting as per required shape of the wall.Before erection of shuttering they are properly oiled for smooth surface.
Concrete:- After Completion of Shuttering Concreting is done.Before concreting the joint of PCC and RCC are properly hacked, cleaned and treated with joining chemical.Concrete is then poured into shuttering with proper vibration. Normally M-25 or higher grade of concrete is used for Construction of retaining walls.During Concreting construction and expansion joints are provided for avoiding cracks in Construction Joints. Then the concrete is properly cured.
Backfilling:- The final activity in construction of a retaining wall is backfilling of the wall. During backfilling it is to be ensured that there is no void in any layer of filling. Compaction checks in every layer of filling is to be checked.

PAVEMENT QUALITY CONCRETE FOR ROADS

2018-12-03T05:37:00.001-08:00

Pavement Quality Concrete is a concrete which is used now a days for most type of Road Contraction works. Generally it is designed in High Grade (M-35 to M-50) and designed for 32mm size aggregates and low slump.

Materials Required:- The Following materials are required for Construction of PQC Road..

Ordinary Portland Cement (IS 269), Portland Pozzolana Cement (IS 459) & Portland Slag Cement (IS 1489) Can be used for PQC.
Crushed Aggregates with Max size 32mm can be used as per IS:383.
Clean Coarse river sand to be used for PQC conforming to IS:383.
Water conforming to IS:456-2000 to be used for PQC. In case of hot water concrete plant should have a arrangement for water cooling.
Different types of admixtures conforming to IS:6925 & IS:9103 to be used for PQC.

Procedure:-

For concrete road or rigid pavements, the concrete shall be laid in alternate panels to avoid development of shrinkage & thermal cracks.
The base shall be sprayed with water to ensure no moisture is drawn from the concrete.
If specified in the drawing, polythene sheet shall be spread on the entire area to limit the loss of moisture from the concrete. polythene sheet of 125 micron (with Lap of 300mm) shall be overlapped at the junctions.
In case continuous casting is desired, the same can be carried with saw cutting arrangement of the concrete pavement.
Such pavement shall be cut to 1/3rd the depth at every 6m within 24 Hours after laying the concrete. Any deviation in this can result in irregular formation of cracks.

Construction & Expansion Joints:-

A typical constriction joint consist of placing a stopper across the length & width without affecting the spacing or placing of rebar’s. Necessary holes shall be made in the stopper for ensuring the same. All stoppers shall be applied with form release agents and removed as soon as concrete attains final set.

The concrete surface shall be made rough by chipping the same with chisel immediately after de-shuttering.
For expansion joints, additional MS bar ( Dowel Bar ) shall be provided at half the depth of the pavement with 50 % of the length of the rod in the previous concrete & remaining in the next pour.
Expansion joints of 25mm (or More) width and half of depth of pavement to be provided after required concrete length (as instructed in drawing or technical specifications) .
Construction joints of 12mm to be provided after required length.
One end of the MS bar shall be coated with grease & covered in plastic sleeve for easy movement.
If required as per drawing, an expansion board made of bitumen impregnated fibre or polystyrene shall be placed at the expansion joint area.
Tie bars as shown in drawing shall be inserted at the longitudinal joints where load transfer is minimal.

Concreting:-

Concrete of minimum M-35 grade shall be used for laying the pavement.
Concrete shall start only after all arrangements for laying were in place including crack preventive measures & curing mechanism.
Concrete shall be differed in windy or rainy weather.
Necessary protective covers and its spreading mechanism without disturbing the texture shall be made available for every pour.
Concrete slump shall be controlled to 50mm & placement shall start from one end.
Concrete shall be spread evenly & rough levelled using wooden screeds.
The levelled concrete shall be vibrated by surface mounted vibrators and finished to rough texture.
Slump should be 15 to 45mm for placing of this concrete.

Curing:-

Curing of completed pavement shall start immediately after concrete final setting.
Initial curing shall be carried by covering the surface with wet hessian & latter by ponding

Joint Sealing:-

Joints to be sealed with bitumen sealant of Grade-A of IS-1834 in every expansion and construction joints.

Testing:-

Cubes (For Compressive Strength) & Beams (For Flexural Strength) to be taken for each 150 cum of concrete .If the volume of concrete done in one day is less than 150 cum, still 6 cubes & 6 Beams to be taken.
These cubes & beams to be tested in 7 & 28 days of concreting and checked as per specifications.(Average strength of 3 cubes (28 days result) not to be less than Required Strength).
Core test shall be carried out in case of failure of Cube or Beams as per engineer in charge.

COMPRESSIVE STRENGTH OF CEMENT

2018-10-04T00:28:00.001-07:00

Compressive Strength of Cement is the capacity of taking compressive loads of cement.

It is determined by compressive strength test on mortar cubes compacted by means of a standard vibration machine. Standard sand (IS:650) is used for the preparation of cement mortar. The specimen is in the form of cubes 70.6mm*70.6mm*70.6mm.

APPRATUS:-

1. Cube Mould of size 70.6mmX70.6mmX70.6mm (As per IS:10080)

2. Vibration Machine (As per IS: 10080)

3. Compression Testing Machine

4. Measuring Cylinder

5. Balance

PROCEDURE:-

1. Environmental condition for cement testing should be of temperature 27± 2⁰ C.

2. Take 200 g of cement and 600 g of standard sand and mix them dry thoroughly.

3. Add (P/4+3)X8 [ P is % of water required for preparing paste of standard consistency] to the dry mix of cement and sand and for a time of 3 to 4 minutes mix them properly si that they form a mix of uniform colour. If the mix is not homogeneous after 4 minutes reject the mix and do the procedure again.

4. Clean the cube moulds of cement thoroughly and place them the vibrating machine. It should be hold properly in position by clamps provided on the machine..

5. Fill the mould with entire quantity of mortar using a suitable hopper attached to the top of the mould for facility of filling and vibrate it for 2 minutes at a specified speed of 12000±400 per minute to achieve full compaction.

6. Remove the mould from the machine and keep it in a place with temp of 27±2⁰C and relative humidity of 90% for 24 hours.

7. After 24 hrs remove the cube from the mould and immediately submerge in fresh clean water in temperature controlled cube curing tank where its temp. is kept in 27±2⁰C. They should be submerged in waster till testing.

8. Prepare at least 9 cubes in the manner explained .

9. Place the test cube on the platform of a compressive testing machine so that the cubes central line and central line of platform coincides. No packing materials to be used between the cubes and loading plates.

10. At the rate of 35 N/mm²/minute apply the load steadily and uniformly.

11. 3 Cubes to be tested on completion of 3,7 and 28 days of testing and to be reported as shown below.

CALCULATIONS:-

Compressive Strength = P/A

[ P=Maximum load applied to the cube. (N)

A=Cross sectional area (Calculated from the mean dimensions) (mm²) ]

Compressive strength is reported to the nearest 0.5 N/mm²
Specimens that are manifestly faulty, or that give strengths differing by more than 10% from the average value of all the test specimen should not be considered.
Test three cubes for compressive strength for each period of curing.

REPORTING OF RESULTS:-

Test result of Cement Cube Testing is reported as following..

CONSISTENCY OF CEMENT

2018-09-27T01:38:00.000-07:00

Consistency is defined as the amount of water that can be added to cement to produce a plastic paste of cement and the ingredients of of concrete.

The standard consistency of a cement paste is defined as that consistency which will permit the Vicat Plunger to penetrate to a point 5 to 7 mm from the bottom of the Vicat mould.

APPARATUS:-

1. Vicat apparatus conforming to IS: 5513 – 1976
2. Balance, whose permissible variation at a load of 1000g should be +1.0g
3. Gauging trowel conforming to IS: 10086 – 1982

PROCEDURE:-

1. Prepare a paste of weighed quantity of Cement with a weighed quantity of potable or distilled water, taking care that the time of gauging is not less than 3 minutes, nor more than 5 min, and the gauging shall be completed before any sign of setting occurs. The gauging time shall be counted from the time of adding water to the dry cement until commencing to fill the mould. Fill the Vicat mould E with this paste, the mould resting upon a non-porous plate. After completely filling the mould,smoothen the surface of the paste, making it level with the top of the mould. The mould may be slightly shaken to expel the air.

2. Place the test block in the mould, together with the non-porous resting plate, under the rod bearing the plunger; lower the plunger gently to touch the surface of the test block, and quickly release, allowing it to sink into the paste.This operation shah be carried out immediately after filling the mould.

3. Prepare trial pastes with varying percentages of water and test as described above until the amount of water necessary for making up the standard consistency as defined above is found.

CALCULATION:-

Prepare trial pastes with varying percentages of water and test as described above until the amount of water necessary for making up the standard consistency i.e. the vicat apparatus shows a reading of 5 to 7mm.

Sample table for calculation and representation of results for standard consistency of cement is shown below.

DRY LEAN CONCRETE FOR ROADS

2017-07-19T23:02:00.000-07:00

DLC or Dry Lean Concrete is cement concrete with low slump value to be laid for rigid pavement over sub-base and rolled & compacted by mechanical means.

· Ordinary Portland cement, Portland PozzolanaCement or Portland Slag Cement be used for DLC.

· Coarse aggregate shall consist of Clean, hard, strong, dense, non-porous and durable pieces of crushed stone or crushed gravel and shall be devoid of pieces of disintegrated stone, soft, flaky, elongated, very angular or splintery pieces. The maximum size of the coarse aggregate shall be 25 mm.

· The fine aggregate shall consist of clean, natural sand or crushed stone sand or a combination of the two and shall conform to IS : 383. Fine aggregate shall be free from soft particles, clay, shale, loam, cemented particles, mica, organic and other foreign matter.

· The coarse and fine aggregates may be obtained in either of the following manner:

(i) In separate nominal sizes of coarse and fine aggregates and mixed together intimately before use.

(ii) Separately as 25 mm nominal single size, 12.5 mm nominal size graded aggregates - and Fine

Aggregate of crushed stone dust or sand or a combination of these two.

AGGREGATE GRADATION FOR DRY LEAN CONCRETE:-

Sl No	Sieve Sizes	Percentage passing the sieve by weight
1	26.50 mm	100%
2	19.00 mm	80-100%
3	9.50 mm	55-75%
4	4.75 mm	35-60%
5	600.00 micron	10-35%
6	75.00 micron	0-8%

· Water for mixing and curing of concrete shall be clean and free from injurious amounts of oil, salt, acid, vegetable matter or other substances harmful to the finished concrete.

· The mix shall be proportioned with a maximum aggregate cement ratio of 15 : 1.

· The minimum cement content is 150 kg/cu.m. of concrete.

· The average compressive strength of each consecutive group of 5 cubes made shall not be less than 10 MPa at 7 days. In addition, the minimum compressive strength of any individual cube shall not be less than 7.5 MPa at 7 days.

· The batching plant shall be capable of proportioning the materials by weight, each type of material being weighed separately. The cement from the bulk stock shall be weighed separately from the aggregates. The batching and mixing shall be carried out preferably in a forced action central batching and mixing plant having necessary automatic controls to ensure accurate proportioning and mixing. Other types of mixers shall be permitted subject to demonstration of their satisfactory performance during the trial length. The type and capacity of the plant shall be got approved by the Engineer before commencement of the trial length. The (weighing balances shall be calibrated by weighing the aggregates, cement, water and admixtures physically either by weighing with large weighing machine or in a weigh bridge. The accuracy of weighing scales of the batching plant shall be within ± 2 per cent in the case of aggregates and ±1 per cent in the case of cement and water.

· Plant mix lean concrete shall be discharged immediately from the mixer, transported directly to the point where it is to be laid and protected from the weather by covering the tippers/ dumpers with tarpaulin during transit. The concrete shall be transported by tipping trucks, sufficient in number to ensure a continuous supply of material to feed the laying equipment to work at a uniform speed and in an uninterrupted manner. The lead of the batching plant to paving site shall be such that the travel time available from mixing to paving.

· Lean concrete shall be laid/placed mechanically /manually. The concrete shall be laid in one layer in an even manner without segregation, so that after compaction the total thickness is as specified. The laying of the two- lane road sub-base may be done either in full width or lane by lane. Preferably the lean concrete shall be placed and compacted across the full width of the road, by constructing it in one go or in two lanes running forward simultaneously.

Rolling & Compaction; Spreading of DLC

· The compaction shall be carried out immediately after the material is laid and leveled with 8 -10 Tonne Static Roller. In order to ensure thorough compaction which is essential, rolling shall be continued on the full width till there is no further visible movement under the roller and the surface is closed.

· As soon as the lean concrete surface is compacted, curing shall commence. Curing shall be done by covering the surface by gunny bags/hessian, which shall be kept continuously moist for 7 days by sprinkling water.

· The minimum dry density obtained shall be 97% of the dry density achieved during trial length construction and the density achieved at the edges (i.e. upto 0.5m from the edge) shall be not less than 95% of the MDD.

BRICKS

2017-07-15T02:01:00.001-07:00

Brick is one of the oldest building material that continues to be a most popular and leading construction material because of being cheap, durable and easy to handle and work with. Fly Ash & Clay bricks are used for building-up exterior and interior walls, partitions, piers, footings and other load bearing structures.

Shape of a brick is rectangular and its size can be conveniently handled with one hand. Brick may be made of burnt clay or mixture of sand and lime or of Portland cement concrete.

Dimensions of a brick are interrelated as below:

Length of brick = 2 × width of brick + thickness of mortar

Height of brick = width of brick

Size of a standard brick (also known as modular brick) should be 19 × 9 × 9 cm and 19 × 9 × 4 cm.

When placed in masonry the 19 × 9 × 9 cm brick with mortar becomes 20 × 10 × 10 cm.

Classification of Bricks

On Filed Practice

Clay bricks are classified as first class, second class, third class and fourth class based on their physical and mechanical properties.

First Class Bricks

1. These are thoroughly burnt.

2. The surface should be smooth and rectangular, with parallel, sharp and straight edges and square corners.

3. These should be free from flaws, cracks and stones.

4. These should have uniform texture.

5. No impression should be left on the brick when a scratch is made by a finger nail.

6. The fractured surface of the brick should not show lumps of lime.

7. A metallic or ringing sound should come when two bricks are struck against each other.

8. When immersed in water, water-absorption should be less than 20%.

9. The crushing strength of the brick should not be less than 10 N/mm2. This limit varies with different Government organizations around the country. Uses: First class bricks are recommended for pointing, exposed face work in masonry structures, flooring and reinforced brick work.

Second Class Bricks are supposed to have the same requirements as the first class ones except that

1. Small cracks and distortions are permitted.

2. A little higher water absorption of about 16–20% of its dry weight is allowed.

3. The crushing strength should not be less than 7.0 N/mm2.

Uses: Second class bricks are recommended for all important or unimportant hidden masonry works and cantering of reinforced brick and reinforced cement concrete (RCC) structures.

Second Class Bricks are under burnt. They are soft and light-coloured producing a dull sound when struck against each other. Water absorption is about 25 per cent of dry weight.

Uses : It is used for building temporary structures.

Third Class Bricks are over burnt and badly distorted in shape and size and are brittle in nature.

Uses: The ballast of such bricks is used for foundation and floors in lime concrete and road metal.

CEMENT PAINT

2017-07-13T06:59:00.001-07:00

Cement paint is an economical exterior wall finish that enhances the decor of buildings. It is resistant to fungus and algae and protects buildings from varying weather conditions.

Waterproof cement paint is an exterior coating made in powder form with Portland cement as its base. It binds chemically to any porous masonry surface producing an attractive and smooth, non-chalking, anti-fungus durable surface.

Advantages
• Provides a durable, hard & waterproof surface
• Does not rub, flak or peel off when applied as per instruction
• Hygienic and resistant to climatic changes
• Easy to use
• Excellent heat and light reflector
• Ideal coating for exteriors of houses, factories etc
• Available in myriad shades

Cement Paint Applied Surfaces

TECHNICAL ASPECTS:

1.Process of Manufacturing:-

Cement Paint is a mixture of Portland or white cement and lime with additions of mineral extenders, accelerator and water repellent substances. A typical formulation is as follows;

Sl No	Items	Percentage
1	White / Port land cement	50-60%
2	Lime	10-15%
3	Calcite /Titanium Dioxide	10-15%
4	China Clay	10%
5	Calcium Chloride	2-5%
6	Calcium /Aluminium stearate	5-10%
7	Alkali Resistance Pigment	3- 5%

2.Process

The ingredients in powdered form are weighed and charged in the ball mill for grinding and mixing property. After obtaining the desired fineness, the products are packed in drum or any suitable container. For getting different shades as per Indian Standard, trial batches are to be carried out in small quantity in pot mill before taking up the bulk production

CREEP OF CONCRETE

2015-02-20T08:58:00.001-08:00

Creep of concrete is the continued deformation with time under applied load. Sometimes it is defined as increase in strain in concrete with time under sustained stress. This is also known as plastic flow or time yield. The rate of creep decrease with time and the creep strains at five years are taken as terminal values. Creep increases rapidly with the stress, loading at an early age of concrete, broken ballast, soft and porous aggregate, poorly graded and improperly compacted concrete. The deformation of hardened concrete is shown in Fig. below.

The Causes of Creep are.

Closer of internal voids of Concrete
Viscous flow of the cement paste inside concrete
Flow of water out of the cement gel inside concrete.

In reinforced concrete structures it is of advantage since it causes better distribution of stresses. For example in a R.C.C. column there is a reduction of stress in concrete and a corresponding increase of stress in steel due to creep. As another example creep relieves the high stressed portions of concrete in a continuous beam and increases the stress in the adjacent less stressed portion. Creep causes large deformations and deflections and is undesirable.

RHEOLOGY

2015-02-19T07:13:00.001-08:00

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.

ORDINARY PORTLAND CEMENT

2015-02-18T04:05:00.001-08:00

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..

OPC-33 Grade
OPC-43 Grade
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.

HYDROPHOBIC CEMENT

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For construction in places of high humidity and frequent rainfall, Hydrophobic Cement or Waterproof Cement is used.It is obtained by grinding ordinary Portland cement clinker with water repellent film-forming substance such as oleic acid, and stearic acid. The water-repellent film formed around each grain of cement, reduces the rate of deterioration of the cement during long storage, transport, or under unfavourable conditions. The film is broken out when the cement and aggregate are mixed together at the mixer exposing the cement particles for normal hydration. The film forming water-repellent material will entrain certain amount of air in the body of the concrete which incidentally will improve the workability of concrete. This cement is most used In places where we get plenty of rainfall in the rainy season had have high humidity in other seasons.Due to this weather conditions Ordinary cement gets deteriorated and loses some if its strength,whereas Hydrophobic Cement does not lose any strength and very effective for construction in these type of areas.

Other than entraining a small quantity of air bubbles the properties of hydrophobic cement is nearly the same as that ordinary Portland cement . The hydrophobic cement is made actually from ordinary Portland cement clinker. After grinding, the cement particle is sprayed in one direction and film forming materials such as oleic acid, or stearic acid, or pentachlorophenol, or calcium oleate are sprayed from another direction such that every particle of cement is coated with a very fine film of this water repellent material.These materials protects the cement from bad effects of weather during transportation and storage. Due to adding of additional materials he cost of this cement is nominally higher than ordinary Portland cement.

DESIGN FLOOD

2015-02-11T06:43:00.002-08:00

The flood adopted for design of hydraulic structures is called Design flood. Any hydraulic structure is generally made safe against the maximum flood possible in the catchment. Smaller structures such as culverts, storm drainage systems can be designed for relatively small floods (i.e., more frequent floods) as the consequences of a higher than design flood may only cause temporary inconvenience and some repair works without any loss of life and property. However, failure of structures such as spillway would cause huge loss of life and property and, therefore, such structures should be designed for relatively more severe floods having relatively larger return period. The table below provides guidelines for selecting design floods. The terms PMF and SPF in the Table below have the following meaning...

PMF or probable maximum flood is the extreme large flood that is physically possible in a region as a result of severe most (including rare ones) combination of meteorological and hydrological factors.

SPF is the standard project flood that would result from a severe combination of meteorological and hydrological factors. Usually, SPF is about 40 to 60% of PMF.

General Guidelines for designing floods is as following…

Sl No	Structure	Recommended design flood
1.	Spillways [storage more than 60 Mm³]	(a) PMF determined by unit hydrograph and probable maximum precipitation (PMP) (b) If (a) is not applicable or possible, flood frequency method with T = 1000 years to 5000 years
2.	Permanent barrage and minor dams [capacity less than 60 Mm³]	(a) SPF determined by unit hydrograph and standard project storm (SPS) which is usually the largest recorded storm in the region (b) Flood with a return period of 100 years.(a) or (b) whichever gives higher value.
3.	Pickup weirs	Flood with a return period of 100 or 50 years,depending on the importance of the project
4.	Aqueducts (a) Waterway (b) Foundations and free board	Flood with T = 50 years Flood with T = 100 years
5.	Project with very scanty or inadequate data	Empirical formulae

CEMENT MORTAR

2015-02-09T07:46:00.000-08:00

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.

High-Performance concrete

2014-10-10T05:47:00.001-07:00

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 pozzolanic materials 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 0.22^7.9
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.

PUMPABLE CONCRETE

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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. Fig- 1 below shows the concrete flow under pressure.

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. Fig.2 illustrates such a condition. 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.

Effect of Maximum size of Aggregate on Strength of CONCRETE

2014-10-08T00:02:00.001-07:00

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..

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

GEL/SPACE RATIO

2013-10-06T21:16:00.001-07:00

As propounded by Duff Abrams many research workers commented on the validity of water/cement ratio law. They have focused on a few of the limitations of the water/ cement ratio law and argued that Abrams water/cement ratio law can only be called a rule and not a law because Abrams’ statement does not include many qualifications necessary for its validity to call it a law. Some of the limitations are that the strength at any water/cement ratio depends on the following things…

   1.Degree of hydration
   2.Chemical and Physical properties
   3.The temperature at which the hydration takes place
   4.Air content (in case of air entrained concrete)
   5.the change in the effective water/cement ratio and the formation of fissures and cracks due to bleeding or shrinkage

Instead of relating the strength to water/cement ratio, the strength can be more correctly related to the solid products of hydration of cement to the space available for formation of this product. Powers and Brownyard have established the relationship between the strength and gel/space ratio. This ratio is defined as the ratio of the volume of the hydrated cement paste to the sum of volumes of the hydrated cement and of the capillary pores.
Power’s experiment showed that the strength of concrete bears a specific relationship with the gel/space ratio. He found the relationship to be 240 x3, where x is the gel/space ratio and 240 represents the intrinsic strength of the gel in MPa for the type of cement and specimen used.
The strength calculated by Power’s expression holds good for an ideal case.
The fig. below shows the relationship between strength and gel/space ratio. It is pointed out that the relationship between the strength and water/cement ratio will hold.

RUNOFF

2013-10-02T00:07:00.001-07:00

When soil in is infiltrated to full capacity and excess water from rain, melt-water or any other precipitation flows over the land is called runoff or surface runoff.

After satisfying the requirements of evapotranspiration, interception, infiltration into the ground, and detention storage, precipitation (or rainfall) drains off or flows off from a catchment basin as an overland flow (or surface runoff which includes precipitation falling on the stream system too) into a stream channel. Part of the infiltrating water moves laterally through the upper layers of the soil and returns to the ground surface as interflow or subsurface runoff at some place away from the point of infiltration into the soil. Part of the infiltrating water percolates deep into the ground and joins the ground water storage. When water table intersects the stream channels of the catchment basin, some ground water may reach the surface or join the stream as ground water runoff, also called base flow or dry-weather flow. Thus, the runoff from a catchment includes surface runoff, subsurface runoff and base flow. The surface runoff starts soon after the precipitation and is the first to join the stream flow. Subsurface runoff is slower and joins the stream later. Depending upon the time taken by the subsurface runoff between the infiltration and joining the stream channel, it may be termed as prompt subsurface runoff or delayed subsurface runoff. The groundwater runoff is the slowest in joining the stream channel but, is responsible in maintaining low flows in the stream during dry season. Based on the time interval between the precipitation and runoff, the runoff is categorized as direct runoff (that enters the stream immediately after precipitation i.e., surface runoff and subsurface runoff) and base flow (i.e., ground water runoff). Runoff, thus is the response of a catchment to the precipitation reflecting the combined effects of the nature of precipitation, other climatic characteristics of the region, and the physiographic characteristics of the catchment basin.

The chief characteristics of the precipitation that affect the stream flow are
1.Type,
2.Intensity,
3.Duration
4.Areal distribution of precipitation over the catchment,

Precipitation in the form of rainfall is quicker to appear as stream flow than when it is in the form of snow. For the surface runoff to start, the intensity of rainfall (or precipitation) must exceed the infiltration capacity of the soil which decreases with the increase in the duration of rainfall. It is, therefore, obvious that a longer duration rainfall may produce higher runoff even if the intensity of rainfall is less but, of course, exceeding the infiltration capacity of the soil. Heavy rainfalls in the downstream region of the catchment will cause rapid rise in the stream levels and early peaking of the discharge. A rare occurrence of uniformly distributed rainfall may result in increased infiltration and, therefore, increased subsurface runoff and base flow resulting in slow rise in levels and delayed peaking of the discharge. Likewise, antecedent higher soil moisture conditions at the time of precipitation would hasten the rise in the stream levels.

HYBRID CROPPING

2013-09-28T07:21:00.001-07:00

By the term Hybrid we mean an offspring of parents belonging to different characteristic groups of the same genetic group. Plant and animal breeders have developed special techniques for producing hybrids artificially in laboratories, zoos, and farms.

Hybrids generally tend to be sterile. Even if they can produce, the first generation offspring may resemble their parents but next generation may not. The second generation usually shows different combination of the characteristics of the original crossbred parents.

Growing of a crop with hybrid seeds is called hybrid cropping. The hybrid seeds may unite the desirable traits of both parents. For example, a gardener may crossbreed an ornamental large flower with a sweet-smelling variety to produce a hybrid variety of large aromatic flowers.
The hybrid seeds have what is called hybrid vigour i.e., they generally tend to be large, faster-growing and healthier than their parent. This fact has been exploited commercially in the cultivation of corn (maize), potatoes, cotton, and several varieties of flowers. However, the hybrid seeds are very costly and, therefore, cannot be adopted on a mass scale in the country. Hybrid seeds, however, appear more promising for glasshouse cultivation of plants.