Plasticizer charts - Admixtures used in RCC

Admixtures	Functions	Typical compounds	Application	Disadvantages
Accelerating admixtures or accelerators	More rapid gain of strength or higher early strength. More rapid setting.	Calcium chloride Calcium formate Triethanolamine  (TEA) Soluble inorganic salts Sodium nitrite Sodium sulphate Sodium aluminate Sodium silicate	1. Normal rate of strength development at low temperature. 2. To counter retarding effects 3. Shorter stripping times. 4. Plugging of pressure leaks. 5. Sprayed concreting.	1. Possible cracking due to heat evolution. 2. Possibility of corrosion of embedded effects reinforcement.
Retarding admixtures or retarders	Delayed setting	Soluble carbohydrate derivatives: starch Hydroxylated carboxylic acids, Inorganic retarders Sugars	1. Maintain workability at high temperatures. 2. Reduce rate of heat evolution. 3. Extend placing times, e.g., ready-mixed concrete. 4. Prevent cold joint formation.	May promote bleeding.
Water-reducing accelerators	Increased workability with faster gain of strength.	Mixtures of calcium chloride and lignosulfonate.	Water reducer with faster strength development.	Risk of corrosion.
Water-reducing retarders	Increased workability and delayed setting	Mixtures of sugars or hydroxylated carboxylic acids and lignosulfonate.	Water reducer, with slower loss of workability.
Air-entraining agents	Entrainment of air into concrete.	Aluminum powders, Natural wood resins, fats, lignosulfonates, alkyl sulfates, sodium salts of petroleum, sulfonic acids.	Enhanced durability to frost without increasing cement content, improvement in workability, lowered permeability and cellular concrete.	Careful control of air content, water-cement ratio, temperature, type and grading of aggregate and mixing time is necessary.
Damp-proofing or water-proofing agents	1. Water-repellent, i.e. prevention of water from entering cap 2. Reduced water permeability of concrete.	Potash soaps, calcium-stearate, aluminium-stearate, butylstearate, petroleum	1. Reduced permeability. 2. Enhanced durability. 3. Increased freeze-thaw resistance. 4. Reduced drying shrinkage. 5. Reduced surface staining. 6. Water tightness of structures without using every low water-cement ratio.	1. Not efficient under high hydrostatic pressure. 2. Requires low water-cement ratio and full compaction.
Plasticizers (water reducers)-8 to 15 percent water reduction	Higher flowability	Hydroxylated carboxylic acid derivatives Calcium and sodium lignosulfonates.	1. Higher workability with strength unchanged. 2. Higher strength with workability unchanged. 3. Less cement for same strength and workability.	Certain special types of cements like sulphate resistant cement (low C3A content) and expansive cement do not perform well.
Superplasticizers (Super-water reducers) – 15 to 30 per cent water reduction	Greatly enhanced workability.	Sulfonated Melamine formaldehyde resin, sulfonated naphthalene-formaldehyde resin, Mixtures of saccharates and acid amides.	1. Water reducer, but over a wider range. 2. Facilitate production of flowing or self-leveling concrete	1. Tendency to segregate. 2. Flowability is not long lasting. 3. During hot weather the workability retention period decreases fast.

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Irrigation - Civil Engineering

Irrigation

Civil Engineering

Types of Irrigation
Flow Irrigation					Lift Irrigation
Perennial Irriagation	Direct Irrigation	Inundation Irrigation	Storage Irrigation	Combined Storage and Diversion scheme	(well irrigation)
(The water required is supplied to the crop through out the year)	(diversion scheme) (or) (River canal irrigation) (Water is directly diverted to canal without storing)	(The irrigation is carried out by deep flooding)	(storage scheme) (or) (Tank irrigation) (Water is stored in dam (or) reservoir)	(Water is stored in dam (or) reservoir and then diverted to canal)	(Subsoil water is lifted to the Surface and conveyed to agricultural fields.)

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All study of Irrigation in Civil Engineering in Exam point of view 

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Irrigation and its all study

CHAPTER HIGHLIGHTS

☞ Introduction
☞ Types of irrigation
☞ Methods of irrigation
☞ Water requirements of crops
☞ Irrigation efficiencies
☞ Irrigation requirements of crops
☞ Crop seasons
☞ Water logging and drainage

Garret's diagram

It gives the graphical method of designing the channel dimensions based on Kennedy's Theory.

 

The diagram has discharge plotted on the abscissa and the ordinates on the left indicate the slope and on the right water depth in the channel and critical velocity (Vo).

Kennedy's theory

R.G. Kennedy studied a number of sites at Upper Baro Doab System (now in Punjab) for carrying out investigations about the velocity and depth of channels.

According to him, Critical velocity (Vo) is the mean velocity that will just keep the channel free from sitting and scouring and related it to depth.

Modified critical Velocity, 

Vo=0.55md0.64

Where, d = depth of the channel (m), m = Critical velocity ratio (V / Vo) (For sand m = 1.1 to 1.2, for finer sand other than standard m = 0.9 to 0.8)

Further, the Critical Velocity ratio (CVR) is the ratio of actual velocity (Va) to critical velocity (Vc) in the channel.

Now If,

CVR > 1 Va > Vc Scouring will occur.

CVR < 1 Va < Vc Silting will occur

CVR = 1 Va = Vc There will be no silting and scouring

For calculating velocity, He used Kutter's formula and Manning's formula.

Kutter formula

• `V=\left[\frac{\frac1N+\left(23+\frac{0.00155}S\right)}{1+\left(23+\frac{0.00155}S\right)\frac N{\sqrt R}}\right]`

where, R = hydraulic radius

S = slope or gradient

Manning Formula

• `V=\frac1NR^\frac2{3}\sqrt S`

Meandering

• A meander is formed when moving water in a stream erodes the outer banks and widens its valley and the inner part of the river has less energy and deposits what it is carrying.
• A wave phenomena.
• A Meandering river is a river that contains many bends throughout its length.

Causes of Meandering

• Extra turbulence generated by the excess of river sediment during floods.
• Size and grade of sediments that make up the river bed.
• Valley slope.
• Bed slope and side slope of the channel.

• Main cause is Extra turbulence generated by the excess of river sediment during floods.

Meander Parameters:

Meander Length (ML) - The tangential distance between the crests or trough of a mender in plan view.

Meander belt width (MB) - Distance between top and bottom portion of successive crests and trough of a member in plan view.

Meander ratio - Ratio of meander belt width to meander length.

Tortuosity or sinuosity -  Ratio of archual length (length along the channel) to the direct axial length.

Head Sluices (or Canal Head Regulator):

• A head sluices or canal head regulator (CHR) is provided at the head of the off-taking canal, and serves the following functions:
• It controls the entry of the silt in the canal.
• It regulates the supply of water entering the canal.
• It prevents the river floods from entering the canal.

Silt Ejectors (or Silt extractors): 

• These are the devices that extract the silt from the canal water after the silted water has traveled a certain distance in the off-take canal. 
• These works are, therefore, constructed on the bed of the canal, and a little distance downstream from the head regulator.

Under-Sluices (or Scouring Sluices): 

• The under sluices are the openings that are located on the same side as the off-taking canal and are fully controlled by gates, provided in the weir wall with their crest at a low level. 
• Their main functions are:
• It helps in controlling the silt entry into the canal.
• It scours the silt deposited on the river bed above the approach channel.
• It passes the low floods without dropping the shutter of the main weir.
• It preserves a clear and defined river channel approaching the regulator.

Divide Walls: 

• Divide wall is a masonry or concrete wall constructed at the right angle to the axis of the weir. 
• Its main objective is to form a still and comparatively less turbulent water pocket in front of the canal head regulator so that the suspended silt can be settled down 
• which then later be cleaned through the scouring sluices from time to time.

As per Lacey’s formula, the relation between discharge, Q, and the wetted perimeter is given as:

P=4.75√Q

For a rectangular channel, wetted perimeter P is given as:

P = B + 2 × y

Where y is the depth of flow.

If the channel is very wide the P ≈ B (as y ≪ B)

According to Lacey's theory, the following formulae has been given below:

Velocity of flow, V	V=(Qf2140)1/6
Hydraulic mean depth, R	R=52V2f
Area of the channel section, A	A=QV
Wetted perimeter, P	P=4.75Q−−√
Bed Slope, S	S=f5/33340Q1/6$\frac{{\mathrm{<br><br>}}^{}}{}$

The drainage water intercepting the canal can be classified in the following ways:

i) By passing the canal over the drainage

a) Aqueduct

b) Syphon aqueduct

ii) By passing the canal below the drainage

a) Superpassage

b) Syphon

iii) By the drain through canal ⇒ 

• a) level crossing
• b) inlets and outlets

Tile drains or under drains

They are located at suitable depths below the ground surface above the impervious soil (clay) which prevent natural percolation of water and usually covered with coarse sand or bajri.

They are preferably placed in a soil of medium or high permeability.

The Tile drains permit deep root development by lowering the water table.

Tile drains have their outlets in natural as well as artificial channels.

Gravitational water at the head of the tile drain is under pressure due to head of water above it.

Drainage coefficient

Drainage coefficient is the rate at which water is removed by a drain.

It is expressed as depth of water in cms or meters to be removed in 24 hours from the drainage area.

It depends on rainfall, type of soil, type of crop, degree of surface drainage etc.

Its recommended value is 1 % of the average annual rainfall to be removed per day.

As per Lacey’s Theory, Normal scour depth is given by :

Case 1: If river width equal to the regime width of 4.75 √Q ; Q is the Discharge

R=C(Qf)13$R=C{\left(\frac{Q}{f}\right)}^{\frac{1}{3}}$

${\frac{\mathrm{<br>}}{}}^{}$

${\frac{\mathrm{`V=\backslash left(\backslash frac\{Qf^2\}\{140\}\backslash right)^\backslash frac16`}}{}}^{}$

Where, C is constant, generally taken 0.473.

Q = Design flood discharge and

f = Silt factor and it is given as   

f = 1.76 √d; d is particle size in mm

Case 2: For all other values of actual width of river the normal scour depth is given as:

R=c(q2f)13$\mathrm{R}=\mathrm{c}{\left(\frac{{\mathrm{q}}^2}{\mathrm{f}}\right)}^{\frac{1}{3}}$

Where,

C = 1.35 and q is the discharge per unit width.

Further,

Maximum scour depth Smax = K × R

Where, K = 2 (Constant for piers)

It is a phenomenon in which the productivity of land gets affected due to the high water table leading to flooding of the root zone of the plants and making the root zones of the plants ill-aerated.

• Over and intensive irrigation
• Seepage of water from the adjoining lands
• Impervious obstruction
• Inadequate surface drainage
• Inadequate natural drainage
• Heavy rains
• Submergence due to floods High water table

Lift irrigation:

• Irrigation with which water is supplied to the system by water-lifting devices is called pumping/mechanical/lift irrigation (by means of mechanical water-lifting devices).
• It has high operating costs. 
• It has fewer problems with waterlogging.

Extensive irrigation:

• These systems are more costly to build and to maintain.
• Irrigation service provided to end-users is often limited to only two to three irrigations per season.
• These systems often have fewer problems with waterlogging and salinity and provide incentives for the conjunctive use of ground and surface water.

Intensive irrigation

• This system uses a large amount of water, labour, and resources for a small area in order to increase production and yield.
• More prone to waterlogging as no limit to the amount of irrigation water.

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