Gravitational water:

• Percolates through the soil under gravity
• Pore water pressure at GWT = 0
• Soil above GWT is saturated by capillary action (pore water pressure is tensile and negative = -ϒwh)
• Above GWT – impervious formation above- local saturation
• Water occurring at local saturation – perched water

Held water:

• Water held in soil pores other than gravity.

Types of Held Water:

Structural Water

• Remains in the crystal structure of soil minerals chemically, cannot removed by normal drying (105-110⁰C)

Hygroscopic Water

• Removed by normal drying, replaced back

• Capillary Water
• Due to surface tension

Height of Capillarity = 4T/ϒwd

Note:

Soil Suction: in case of capillary tube, water above WT has a ‘-‘ pressure, soil remains in a state of reduced pressure, known as soil suction (P_F = log₁₀(h_c))

Permeability:

• Flow of water through interconnected voids.

Darcy’s Law :

Laminar flow:

• Flow follows a well-defined path and doesn’t cross the path of other particles (Re ≤ 2000)

Turbulent flow:

• Fluctuates with the time both in magnitude and direction (Re ≥ 2000)

v ∝ i

v = ki

q = vA = Aki

therefore, q= Aki

Seepage Velocity:

Seepage Velocity > Avg. Velocity (v = q/A; v_s = q/A_s)

q = v*A = v_s*A_s

v_s =v* A/A_s

     = v V/v_s

     = v/n

     = ki/n

K = cd² * (e³/(1+e)) * (ϒ_w/μ)

K ∝ c

K ∝ (1/μ) 

{(K_T/K₂₀) = (μ₂₀/μ_T)}

K ∝ e

K ∝ T (temp^r)

Note:

• Impurities (salts, alkalis) increases, K decreases
• Entrapped air, k decreases

Determination of coefficient of Permeability:

(A) Laboratory Method:

Constant Head Method (k > 10^-4)

• Coarse grained soil
• Constant head of water at supply tank
• Vol. of water flowing out of permeameter per unit time = q

H= head water level – tail water level

k_stone > k_soil

From Darcy’s law

q = Aki

   = Ak h/L  

 Where L = soil specimen ht.

Therefore,

k = qL/Ah

= qL/(A*h*t)   

Where,

k = (k1+K2+ ………………Kn)/n

Falling head method (10^-7 <K< 10^-4)

• Undisturbed sample
• Fine-grained soils
• A standpipe of area ‘a’ above the cylinder
• Variable head (h1 to h2) at time t

 rate of change of head = -dh/dt

Acc. Darcy’s Law

q = A*k*i

a*v = A*k*i

-a* (dh/dt) = A*k* (h/L)

After Integrating from 0 to t and from h1 to h2;

K = 2.303*(q/A) *(L/t) *log₁₀(h1/h2)

Note:

• soil in the permeameter should be fully saturated.

Determination of Coeff. Of Permeability (Field):

(B) In-situ method:

• More reliable than the lab method

(a) Pumping test (pumping out)

• Continuous pumping from test well and observation in bore wells (observation well) till steady state.
• Min. two observation wells
• Well should penetrate full depth of water-bearing strata

Confined Aquifer – upper and lower surface impervious

Unconfined Aquifer- no overburden lying over them, top most water-bearing strata.

Unconfined Aquifer:

Observation wells – (r1 and r2 apart test well)

Ht. of observations wells – (z1 and z2)

i = dh/dr

z =ht. of water level at a distance, r

A= 2π*r*z

Darcy’s law;

q = kAi

   = 2π*r*z* dh/dr

On integrating;

K = {2.303*q*log10(r2/r1)}/ {π*(z_z² – z₁²)}

If only one observation well;

K= {2.303*q*log10(R/rw)}/ {π*(H² – hw²)}

R = Radius of influence

H = depth to the bottom of the aquifer from WT

Rw = radius of the test well

Hw = ht. of water in the test well

 Confined Aquifer:

r, r1, r2 – same as above

z.z1.z2 – ht. from the bottom impervious layer (same as above)

b= spacing between two layers

i= dz/dr

A = 2π * r* b

q= kAi

= k * dz/dr * 2π*r*b

On integrating,

K = {q*log10(R/rw)}/ {2.727*b*(h – hw)}

R = 3000*d*√k, R in m

d = draw down, m

k= Coeff. of permeability, m/sec

(b) Bore Hole Test

Constant head method:

• Water    is allowed to flow through the bottom of the bore
• Low end of the casing should not be less than 5d from the top and bottom of the stratum.
• Water level in borehole = constant

Therefore, k = q/(2.7*d*h)

Where d = dia. of well

H = head above GWT

Variable head method:

• Drop from h1 to h2
• For D ≤ 1.5 m

k = (πd/11t) * log(h1/h2)

• For D > 1.5 m

K= (πd²/81t) * log (2L/d) * log (h1/h2)

Insitu measurement of seepage velocity:

• Two trial pits A & B
• Dye inserted in A
• Observe in t time in B

h= level diff. between A and B

i = h/AB

v_s (seepage velocity) =AB/t

We know;

v_s =ki/n

Therefore,

AB/t =(k*h)/(n*AB)

k = (AB²*n)/(t*h)

Permeability on layered deposit:

h= h1+h2

q= q1+q2

q = kz * A * h/(h1+h2)

= k1*A*h1/h1

=k2*A*h2/h2

Therefore,

k =(h1+h2)/{(h1/k1)+(h2/k2)}

In direction of bedding;

i = i1 =i2

q = q1+q2

A*k_x*i = A*k1*i + A*k2*i

k = (k1*h1+k2*h2)/(h1+h2)

The post SOIL MECHANICS: Permeability, Determination of Coefficient of Permeability, Lab Method & Field Method, Confined & Unconfined Aquifer appeared first on OnlineEngineeringNotes.

White Wash

Preparation of lime wash:

• Lime wash shall be prepared from pure fat lime. i.e., fresh stone white lime.
• The lime shall be thoroughly slaked with water on the spot and stirred to make thin cream (app. Add 1 kg of lime to the 5 Liters of water)
• Allowed to stand for a period of 24 hours and then s screened through a clean coarse cloth.
• For 10 Cubic decimeters of the cream, add 40 grams of gum.
• Indigo (Neel) up to 3 grams per kg of lime dissolved in water shall then be added and stirred well.

Preparation of surface:

– For new work; the surface shall be thoroughly brushed free from mortar droppings and foreign matter.

–  For old work; all loose particles and scales shall be scrapped off and holes in plaster, as well as patches of less than 50 cm2 area, shall be filled up with mortar of the same mix.

– If any efflorescence is observed on the surfaces, the deposits should be brushed, clean, and washed.

– The surface shall then be allowed to dry for at least 48 hours before whitewashing is done.

Application:

• The whitewash shall be applied with moon brushes to the specified number of coats.
• The operation for each coat shall consist of a strike of the brush given from the top to downwards and another from the bottom to upwards, and similarly from left to right and right to left horizontally constitutes a coat.
• Wait until the previously applied coat is dried for the next coat.
• 3 or more coats for newly plastered surfaces for obtaining a smooth and uniform finish.
• For old work; after the surface has been prepared, a coat of whitewash shall be applied over the patches and repairs, then a single coat or two or more coats of whitewash as stipulated should be applied to present a uniform finish through which the plaster patches do not appear.
• No signs of cracking and peeling over the dried surface.
• The washing on the ceiling should be done prior to that on the walls.

Protection measures:

• Doors, windows, floors, articles of furniture, etc., and such other parts of the building not to be whitewashed, shall be protected from being splashed upon.
• Splashing and dropping, if any shall be removed by the contractor at his own cost and the surfaces cleaned.
• Damages if any to furniture and fixtures shall be recoverable from the contractor.

Distemper Work

Preparation of paint:

• The washable distemper powder shall be stirred slowly in clean water using 0.6 liters of water per kg of distemper or as specified by the manufacturer.
• Warm water is preferably be used.
• It shall be allowed to stand for at least 30 minutes (or if practicable overnight) before using.
• Frequently stirred and shaken before and during use to obtain even consistency.
• Only a sufficient quantity of Distemper shall be mixed for an actual one day’s work.

Preparation of surface:

• Surfaces should be thoroughly brushed or sandpapered smooth and made free from loose mortar and foreign particles before distempering.
• Pitting in plaster shall be made good with Plaster of Paris mixed with color to be used.
• The surface shall then be rubbed down again with fine grade sand/paper and made smooth.
• Single Coat distemper shall be applied initially over the patches.

Application:

• For new work, the treatment shall consist of a priming coat of whiting followed by the application of two or more coats of distemper till the surface shows an even color.
• Plastered surface/POP surface should be properly cleaned with hot water-based primer and rectification of defects in plaster/POP surface with broken edges shall be done by using a proper color putty paste as per manufacturer’s specifications.
• With proper distemper brushes in horizontal strokes followed by immediate vertical ones, known as one coat.
• The subsequent coats shall be applied only after the previous coat has dried.
• The finished surface shall be mixed to finish one room at a time.
• The application of a coat in each room shall be finished in a single operation & no work shall be started in any room, which cannot be completed on the same day.
• The brushes shall be washed with hot water and hung down to dry after completion of each day’s work. Old brushes should not be used. t be used.

Waterproof Cement Paint Work

Preparation of paint:

• Only fresh paint shall be used, hard or set paint shall not be used.
• The container, which must be stored in a dry place shall be made loose by rolling and shaking the container before opening
• Cement paint shall be mixed with water in two stages first by mixing 2 parts of paint with 2 parts of water by volume to have a uniform solution.
• Gradually add the cement paint to the water and not vice-versa.
• Further add 1 part of water to the mix and stirred properly to obtain workable, uniform, and consistent liquid as per the manufacturer’s specifications.
• Enough and minimum quantities of cement paint mixed to be used within 1 hour, otherwise it sets.
• The lids of cement paint shall be kept tightly closed when not in use, as by exposure to the atmosphere the cement paint rapidly becomes air set due to hygroscopic qualities.

Preparation of surfaces:

• Before the application of paints, all duct, and foreign materials shall be removed from the surface by use of a wire brush.
• All holes, cracks, and abrasions shall be filled with plaster of Paris, properly prepared and applied, and smoothed off to match adjoining surfaces.
• Any loose or uneven areas of any major cracks or defects in the concrete or plaster background shall be cut out and made good and the repairs allowed to dry thoroughly.
• Efflorescence if seen, removed by dry brushing.

Application:

• The freshly mixed paint shall be frequently stirred during application and no mixture (paint) shall be used after an hour. Of mixing
• A vertical stroke with another horizontal stroke comprises one coat.
• Paint solution shall be applied to the surface with a hairbrush/roller in a number of coats to get a uniform finish.
• After the first coat of the paint has hardened, it shall be cured with water at least 24 hours before the second coat is applied.
• Similarly, the required number of coats shall be given to get an even and uniform shade.
• Left and keep damp for 7 days.
• The final painted surface shall exhibit a uniform and good finish appearance.

Enamel Paint

Application of paint:

• The primer and paint shall be of approved quality and of approved manufacturers like Asian paints, Nerolac, Jensolin, Berger British Paints, Jhonson, and Nicholson or equivalent brand approved by the engineer.
• These materials shall be ready mixed and in sealed tins with the manufactures name, color and instruction clearly painted in the container.

Preparation of surfaces:

• All surfaces to be painted shall be planned and thoroughly sandpapered, first by using N0. 120 Sand Paper.
• Ordinary putting shall fill up nail’s holes, cracks, or other inequalities.
• Putting shall be made up of 2 parts of best quality whiting (absolutely DEAD STONE LIME), 1 part of white lead mixed together in linseed oil and kneaded (3 oz. of linseed oil to 1 lb. of whiting).
• A primer coat shall be locally applied before putty in holes, cracks, etc.
• The putty/paste fillers shall be of approved quality and shall be applied to the surfaces with a knife or other sharp-edged tools after the priming coat as well as after each undercoat.
• After the surface is dry, it shall be sandpapered by using No. 60 sandpaper.
• Surfaces so prepared shall be painted with one coat of primer. The primed surface when dry shall be sandpapered by using No. 100 Sandpaper.
• The primed surface so prepared shall be painted with one coat of selected enamel using a bristle brush. The paint shall be applied in the thinnest possible layers with parallel strokes.
• Care shall be taken to ensure the surfaces are free from dust and other foreign material before priming or enameling the surfaces.
• No paint shall splash on the floor, walls, jambs, sill, or other parts of buildings.

Application:

On Wood Work:

• After preparing and after the priming coat has been applied, the top coat shall be applied.
• The primed surface so prepared shall be painted with one coat of selected enamel using a bristle brush and not horse hair ones.
• The paint shall be applied in the thinnest possible layers with parallel drawings, no flowing down shall not be allowed.
• Spray Paintings for the false ceiling and acoustic materials such as thermo cole, perforated acoustic tile, soft board, etc.
• The engineer prior to commencement of work shall approve a sample of workmanship.

On Metal Surfaces:

• The paint shall be continuously stirred in the containers so that its consistency is kept uniform throughout.
• The painting shall be laid on smoothly by means of crossing and laying off.
• The crossing & laying off consists of covering the area with paints, brushing the surface hard for the first time, and then brushing alternatively in opposite directions, two or three times, and then finally brushing lightly in a direction at right angles to the same.
• The full process of crossing and laying off will constitute one coat and no brush marks shall be left after the laying off is finished.
• Paints used shall be brought to the required consistency by adding suitable thinner.
• Surface to be painted shall be clean, dry, smooth, and adequately protected from dampness.
• Each coat shall be applied in sufficient quantity to obtain complete coverages, shall be well brushed and evenly worked out over the entire surfaces and into all corners, angles, and cervices, and allowed to dry thoroughly.
• Second coat shall be a suitable shade to match the final color.
• Allow at least 48 hours of drying time between coats for interior and 7 days for exterior work.
• Finished surfaces shall be protected from dampness and dust until completely dry and shall be uniform, of approved color, smooth and free from defective brushing and clogging.
•  Edges of paints adjoining other materials or colors shall be made sharp and clean without any overlapping.

(e) Chapra Polish

Preparation of Polish:

• The Chapra polish shall be made by mixing Chapra granules, thinner, and spirit.
• The chapra should completely dissolve in the spirit and the thinner should be used to obtain the required consistency.

Preparation of surfaces:

• Before application of Chapra polish, the timber surface shall be thoroughly sandpapered to obtain a smooth surface and all the dust shall be removed from the surface.
• A coat of primer of chalk powder mixed with resin or ready-made approved putty shall be applied and sandpapered to fill in the voids and joints.

Application:

• Over the primed surfaces, the Chapra polish of approved quality shall be applied with smooth cotton cloth with firm rubbing and spread evenly.
• Use good quality and perfectly clean cloth.
• Chapra wood finish shall be reapplied at least three times, after sand papering with fine sand paper to get the final finish and best result.

The post Paintings: types of paints, specifications for various types of painting, Whitewash, Distemper, Cement Paint, Enamel, Chapra Polish appeared first on OnlineEngineeringNotes.

Shear strength of soil is the resistance to deformation by continuous shear displacement of soil particles by the action of shear stresses.

Shear stresses > Shear Strength, failure takes place

• Failure may be sinking of footing or movement of a wedge of soil behind a retaining wall forcing it to move or slide.
• Shear strength is due to friction between particles, interlocking, and cohesion.
• Principal plane – shear stress = 0
• Normal stresses acting on Principal Planes are called Principal Stresses.
• Critical stress values and Obliquities generally occur on major and minor principal planes (two-dimensional solution)

Mohr-Coulomb failure theory:

Coulomb – 1776

Mohr – 1900 (extended Coulomb’s theory)

The theory states that:

1. Materials essentially fail in shear. the critical shear stress causing shear failure depends upon the properties of the material as well as normal stress on the failure plane.
2. The shear strength is equal to shear stress at failure on a potential plane.
3. In a material subjected to three-dimensional principal stress (Ϭ1, Ϭ2, and Ϭ3), the intermediate principal stress Ϭ2 doesn’t have any influence on the strength of the material.

Mathematically,

τ = f(Ϭ)

τ = shear stress

Ϭ= normal stress

MOHR’S STRESS CIRCLE 

Ϭ – Normal stress

τ -Shear stress

Ϭ1- major principal plane

Ϭ3- minor principal plane

α = Inclination to major plane

Resolving the forces horizontally;

Ϭ3*BC = Ϭ*AC Sinα – τ *AC Cosα

Vertically;

Ϭ1*AB = Ϭ*AC Cosα + τ *AC Sinα

Dividing both sides by AC;

Ϭ3*Sinα = Ϭ*Sinα – τ *Cosα – (i)

And,

Ϭ1*Cosα = Ϭ* Cosα + τ *Sinα- (ii)

Multiplying (i) by Cosα and (ii) by Sinα and subtracting (i) from (ii)

Cosα*Sinα (Ϭ1-Ϭ3) = τ (Sin²α + Cos²α)

Therefore,

τ = {(Ϭ1-Ϭ2)Sinα}/2 – (iii)

Substituting τ in eqⁿ (i)

Ϭ3 Sinα = Ϭ Sinα – {(Ϭ1-Ϭ3)*Sin2α*Cosα}/2

Or, Ϭ3 = Ϭ – {(Ϭ1-Ϭ3)*2Cos²α}/2

Or, Ϭ3 = Ϭ – (Ϭ1-Ϭ3)*Cos²α

Or, Ϭ = Ϭ3 + (Ϭ1-Ϭ3)* Cos²α

Or, Ϭ = Ϭ3 + (Ϭ1-Ϭ3)* {(1+Cos2α)/2}

           = Ϭ3 + {(Ϭ1-Ϭ3)/2} + {(Ϭ1-Ϭ3)/2} *Cos2α

Therefore,

Ϭ = {(Ϭ1+Ϭ3)/2} + {(Ϭ1-Ϭ3)/2} *Cos2α – (iv)

MOHR’S CIRCLE

Values of Ϭ, τ for α are plotted, locus of all the points gives a circle known as Mohr Circle

OE – Normal Stress (inclined at α)

ED – Shear Stress (inclined at α)

A – Minor Principal Stress

B – Major Principal Stress

These plane intersects at A (pole)

Principle Planes inclined to the Co-ordinate Axis :

Draw MN//BP (P = Pole) (Major Plane)

                   Similarly NO//AP           (Minor Plane)

                   OM//P’P  (P’ = Pole of inclined Plane)

                   P’X = τ; OX = Ϭ_n   (for inclined)

Angle of Obliquity:

Relation between Ф and α :

Coulomb failure criterion:

Τ_f = C + Ϭ_nf * tanФ (linear function)

Mohr failure criterion :

Τ_f = f (Ϭ_nf)  (Unique function)

Mohr-Coulomb failure Criterion :

θ= 45 + Ф/2

References:

1. Terzaghi, Karl, Peck, R.B & John, Wiley (1969) Soil mechanics in engineering practice, New York.
2. Arora , K.R (2008), Soil mechanics and foundation engineering, Delhi: Standard Publisher Distribution

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Concrete

• Artificially built-up Stone with Cement, Water, Aggregates with or without Admixtures

Constituents of Concrete:

Aggregates = (60-70) %

Water = (7- 15) %

Cement = (14-21) %

Air = (0 – 3) %

Properties of Concrete:

• Air Content
• Fluidity
• Strength
• Setting Time
• Durability

Types of Concrete:

• Based on Binding Materials
• Cement Concrete
• Lime Concrete

• Based on Design
• Plain Concrete (no reinf.)
• Reinforced Concrete
• Prestressed Concrete (High Compressive Stress are artificially induced before use)

• Based on Density
• Light Weight Concrete (18 KN/M³) (i.e., by using pumice from volcanoes or bloated aggregates)
• Normal Weight Concrete (24 KN/M³)
• Heavy Weight Concrete (32 KN/M³)

Boated Aggregates?

• Slightly Salted and lightly smoked

Cement

Composition of Cement Clinker:

Tricalcium Silicate (C₃S) – 40%

• Cement hydrates more rapidly
• Generates more heat of hydration
• Develops high early strength
• Possesses less resistance to Sulphur Attack

Dicalcium Silicate (C₂S) – 32 %

• Cement hydrates slowly
• Generates less heat of hydration
• Provides good ultimate strength
• More resistance to sulphate attack

Tricalcium Aluminate (C₃A) – 10.5 %

• Reacts fast with water
• Generates a large amount of heat of hydration when reacts with water.
• Causes initial setting of cement

• First compound which reacts with water

Tetra Calcium Alumino Ferrite (C₄AF) – 9 %

• Poor cementing value
• Reacts slowly with water
• Generates small heat of hydration

Types of Cement:

Ordinary Portland Cement (OPC)

• Common type of cement
•  Resistance to dry shrinkage and cracking
• Less resistance to chemical attack
• Shouldn’t be used for construction work exposed to sulphate

Rapid hardening Portland Cement (RHPC)

• High early strength cement
• Lighter than OPC
• Shouldn’t be used for massive concrete structures

Low Heat Portland Cement (LHPC)

• Low percentage of tri-calcium silicate
• High percentage of di-calcium silicate
• Hydrates slowly
• Less lime than OPC
• Possesses less compressive strength
• Widely used in retaining walls
• Shouldn’t be used for thin concrete structures

Sulphate Resisting Portland Cement (SRPC)

• Percentage of C₃A kept below 5%
•  Resisting power against sulphates
• Used for structures subjected to severe alkaline conditions such as canal linings, culverts, etc.

High Alumina Cement (HAC)

• 35% of Alumina
• Sets slowly
• Obtained higher ultimate strength in a short period of time.
• Used for structure subjected to the action of Sea water, chemical plants and furnaces.

Blast Furnace Slag Cement (BFSC)

• Made by intergrading of OPC clinker and granulated blast furnace slag.
• Cheaper than OPC
• Develops low heat of hydration
• Has less early strength
• Frequently used in dams, abutments, and retaining walls.

Colored Cement (CC)

•  prepared by adding (5-15) % of a suitable coloring pigment before the Cement is finally ground.
• Commercial term used is colocrete.
• Used for the finishing of floors, external surfaces, decorative concrete, aesthetics, etc.

Portland Pozzolana Cement (PPC)

Made by intergrinding of OPC clinker and pozzolana

• Pozzolana Materials are a silicious material containing clay up to 80%.
• 30% of Pozzolana added to OPC
• Used for hydraulic structures as dams, weirs

Aggregates

Aggregates = Boulder (> 200 mm)

                        Cobble (80 – 200 )mm

Properties of Aggregate:

• Strong
• Chemically inert
• Hard
• Durable

Types of Aggregates:

• Natural Aggregates = sand, gravel, crushed stone, crushed rock etc.
• Artificial aggregates = furnace clinker, coke – breeze, saw dust, foamed slag

(A) Based on size

                              (0.002 – 0.06) mm – silt

                              < 0.002 mm – clay

(ii)Coarse Aggregates: (4.75 – 75) mm

Max. size of Coarse < (1/4) * min. dia. of PCC

                                    < (1/5) * min. dia. of RCC

(iii) Cyclopean Aggregates: (> 75 mm)

(iv) All- in Aggregates:

• Consists of different fractions of fine & coarse aggregates

• Not used as an aggregate for making high-quality concrete.

Based on type of Rock

• Aggregates from Igneous Rock
• Aggregates from Sedimentary Rock
• Aggregates from Metamorphic Rock

Based on Strength

• Hard Aggregates
• Soft Aggregates

Based on Shape

• Rounded (33 % void, good workability, low strength due to poor interlocking)
• Flaky (least diameter < 0.6 mean diameter)
• Elongated (Greater diameter > 1.8 mean diameter)
• Angular ((38 – 45) % void, less workability, high strength due to best interlocking)
• Irregular ((35 – 37) % void, low workability, average strength due to average interlocking)

Based on Surface Texture

• Glassy
• Smooth
• Granular
• Rough
• Crystalline
• Honey combed
• Porous

Based on surface moisture

• Very Very Dry
• Dry
• Saturated Surface Dry
• Wet or Moist

Properties of Aggregates:

Crushing Value:

• It is the value which shows resistance of an aggregate to  the crushing under any gradually applied compressive load.

Impact value:

• Resistance to sudden shock/impact
• Used as alternative to crushing value
• Know quality of aggregates

Abrasion Value:

• Resistance to wear
• Rotated in cylinder with some abrasive charges
• By Los-Angeles machine

Soundness :

• Resistance to effect of hydration of cement & weather

Water

• Insufficient water – harsh & unworkable concrete
• Excess water – bleeding & segregation
• Presence of CO3, HCO3^—of Na– adversely affect on the setting time of cement
• Presence of CaCl2 -accelerates setting & hardening of Cement (restricted to 1.5% by wt. of Cement)

W/C Ratio: (Experiment by Duffs Abrahms known as w/c ratio law)

• Law is valid only when concrete is of workable plasticity
• Strength depends on w/c and not on C/A ratio
• Strength  1/(w/c)
• w/c < 0.45: – concrete is not workable/honey combed

Workability:

• ease and homogeneity in mixing, placing, compacting, finishing

Factors affecting Workability:

Water Content

• Increases with water content

Size of Aggregates

• Large size aggregates more workable than small size

Shape of Aggregates

• Round shape more workable than flaky, angular & elongated

Surface texture of Aggregates

• Smooth texture more workable than rough

Grading of Aggregates

• Continuous lean concrete mix more workable

Air entraining Agents

• Increases the workability (bubbles produced)

Temperature

• Reduces at high temperature

Admixtures

Admixtures are used for accelerating or retarding initial set and strength, can be positive or negative, either chemical or mineral.

• Air- entraining Admixtures, Retarding and Water reducing Admixtures, Accelerating Admixtures, Water Proofing Admixtures, Pozzolanic Admixtures, Coloring/Pigment Admixtures

The post Concrete Technology: Cement, Aggregate, Water (W/C, Workability), Admixtures appeared first on OnlineEngineeringNotes.

Physical Properties: Identified by visual observation & Hand tools

Chemical Properties: Identified based on the effect of different chemicals

Thermal Properties: Effect of Heat

Types of Building Materials

Stone

Stone is the naturally available construction material and is obtained from a quarry, process of extracting stones by excavating, wedging, heating & blasting is called quarrying and is composed of different minerals and with different processes.

Classification of stones:

Geological Classification:

Igneous Rocks

• Solidification of molten mass above or below the earth’s surface.

• Crystalline glossy or fussed texture

• Ex: – Granite, Basalt, Diorite, Trap dolerite, Syenite, Pegmatite, Gabbro etc.

Sedimentary Rocks

• Gradually deposition of sand, clay, debris, etc. by the action of rain, wind, sun etc.
• Stratified
• Ex: – limestone and sandstone, conglomerate, gypsum, dolomite, magnesite, chalk, shale, kankar,Tripoli, diatomite, etc.

Metamorphic Rocks

• Change in texture or mineral composition of rocks under heat and excessive pressure
• Ex: – marble, Gneiss, Quartzite, Slate, Schist, etc.

Physical classification:

Stratified Rocks:

• Distinct layers which can be separated
• E.g.: limestone, slate, and sandstone.

Unstratified Rocks:

• No sign of strata
• E.g.: granite, marble, etc.

Chemical classification:

Silicious Rocks

• Silica as the main constituents
• E.g.: granite, quartzite, gneiss etc.

Argillaceous Rocks

• Clay or Alumina as main constituents
• E.g. of silicious rock: slate, laterite, kaolin, etc.

Calcareous Rocks

• Lime or calcium
• E.g.: limestone, marble, etc.

Important building stones:

1. Granite

• mainly composed of quartz, felspar, mica

What is Feldspar?

“Feldspar is no other than silicate of aluminum with varying amounts of potash, soda, or lime.

• Sp. Gravity -= 2.64
• Compressive strength = 70 – 130 MN/m²
• color depends on felspar – brown, grey, green, pink
• Offer high resistance to weathering
• Easily polished and worked
• Used for the external facing of buildings

2. Slate

• Argillaceous rock
• Alumina + sand /carbonate of lime
• Sp. Gravity = 2.8
• Compressive strength = 60-7- MN/m²
• Grey/dark blue color
• Hard, tough, fine-grained
• Used in cisterns
• Slate as tiles, an excellent roof covering material.

3. Gneiss

• Gneiss:
• A silicious rock
• Composed of quartz and felspar
• More easily worked than granite
• Used for street paving

4. Sandstone

• Silicious sedimentary rock.
• Composed of quartz, lime, and silica
• Sp. Gravity = 2.65- 2.9
• Compressive strength = 35 -40 MN/m²
• White, grey, brown, pink, etc.
• Strong and durable
• Used for ashlar works, moldings, carvings, etc.

5. Limestone

• Sedimentary rock of calcareous variety
• Sp. Gravity = 2.6
• Brown, yellow, dark grey colors
• Used large quantities in blast furnaces
• Used as stone masonry for walls.

6. Marble

• Metamorphic rock of calcareous variety
• Sp. Gravity = 2.7
• Very hard, ornamental work, takes a fine polish
• Carving, decoration
• Kankar
• Impure limestone containing 30 % alumina & silica
• Used for foundations of buildings

7. Laterite

• Laterite contains a high percentage of iron oxide.
• Porous and cellular structure
• Sp. Gravity = 2 -2.2
• Laterite blocks are suitable for light roads, and inferior buildings.
•  a very good road metal

8. Moorum

• Decomposed laterite
• Deep brown or red color
• Used in  garden walks & paths

9. Quartzite

• Siliceous sandstones
• Strong, durable, used as road metal/ railway ballast

Bricks

Bricks are construction materials made by moulding the tempered clay to a suitable shape and size which is in a plastic condition, dried in sun, and burnt in a kiln or clamp.

Other constituents are lime, magnesia, sodium, potassium, manganese, and Iron oxide.

Excess of Alumina,Silica & Lime

Alumina – brick crack/warp on drying

Silica – brick brittle and weak

Lime –  brick to melt and distort during burning

Alkaline salt – efflorescence

Manufacture of Bricks:

Preparation of Brick clay

• Earth left for atmospheric action for a few weeks after digging called weathering.

• 1.5 – 2.5 m³ of brick soil – 1000 bricks

• Tempered in pug mills

• Process of mixing clay, water, and other ingredients is known as Kneading.

Moulding bricks:

• Handmade bricks superior to machine-made bricks

• Drying of Bricks:
• Bricks are arranged in rows on their edges on a slightly raised ground called hacks.

• Burning of bricks:
• Clamp burning = 60 % out-turn
• Kiln burning = 80 – 90 % out-turn
• Takes 24 hrs. at 1000 – 1200 ⁰c.
• Cool for 12 days

Classification of Bricks:

1. First Class:

• Well burnt, smooth, even surface, rectangular, uniform reddish.
• Water absorption (≤ 20 %) at 24 hrs.
• Min. crushing strength = 10.5 MN/m²

2. Second Class:

• Slightly overburnt, rough, no perfect rectangle
• Water absorption (≤ 22 %)

3. Third Class:

• Under burnt, soft, easily broken
• Water absorption (≤ 25 %)

4. Jhama bricks

• Over burnt, irregular, dark bluish color

What is the size of the Brick?

•  Size of Brick = (19 cm * 9 cm * 4 cm)

                          Or (19 cm * 9 cm * 9 cm)

• Sp. Gravity = 2

• For 1 m³ of brick masonry = 550 machine-made bricks

                                                  500 handmade bricks

Special Bricks:

Squint bricks: construction of acute and obtuse squint quoins

Paving bricks: used for street pavements

Round bricks: circular pillars

Perforated & Hollow: Partitions walls

Refractory Bricks: withstanding temperature, low Coeff. of expansion & contraction.

• Acid Bricks: (fire Bricks & silica bricks)
• Basic Bricks: ( Dolomite bricks, Magnesite bricks and bauxite bricks)
• Neutral Bricks: (Chrome bricks, chrome-magnesite Bricks, spinel Bricks)

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Pre-fabrication

Pre-fabrication is the practice of assembling the components of a building other than the building sites, i.e., in the factory or a manufacturing site, and transporting either complete assemble or semi-assembled to the construction site where the structure is located.

This method controls the construction cost by economizing the wages, time, and materials.

The pre-fabrication is done in two stages

1. Manufacturing under factory conditions
2. Erection of structures at locations

Broadly stages are classified as:

1. Casting
2. Curing
3. Transportation and erecting

Advantages:

• The need for formwork, scaffolding & shuttering is reduced.
• Construction time is reduced.
• Quality control is easier in a factory than on a construction site.
• Congestion in the site is minimized.
• Time spent due to bad weather at the construction site is minimized.
• Less wastage.

Disadvantages:

•  Great attention is required while joining the pre-fabricated section to avoid joint failure.
• Leakage from the joint is possible if not properly jointed.
• High transportation cost is required for the transportation of bulky & voluminous sections.
• If the prefabricated section is heavy then a crane is required at the site.
• Local jobs are lost
• Can’t hide cable wiring, it can be expensive.

Commonly used pre-fab material in Nepal:

Fiber cement Board:

• These are the sandwich panel of two fiber-reinforced cement sheets enclosing a lightweight core composed of Portland cement, binder, and aggregate.

• The panel has a tongue & groove joining system that facilitates rapid construction with minimum effort.

• The board has a low water absorption rate.

• Thickness 50 to 75 mm, width 2’ & height varies from 8’ to 10’.

PUF Panel

• PUF panel consists of the prefabricated sandwich panel made of GI sheet and polyurethane between them.

• The PUF panel are interlocked with each other by a cam lock system or through a tongue & groove arrangement.

• PUF is generally used for roofs & it is the newest type of roofing panel.

•  It has a beautiful appearance.

• PUF panel are available in standard width of 1 m and various thickness 50,60,80,120,150 & 200 mm.

Rockwool Panel

• Rockwool panel consists of a prefabricated sandwich panel of GI sheet on both sides.

• Insulation against sound in this type of panel is remarkable.

• They are used in wall.

EPS Panel

• EPS panel is made by using thermocol/expanded polystyrene covered by a metal sheet on both sides.

• Expanded polystyrene (EPS) is a lightweight cellular paper material consisting of a small hollow spherical ball.

• EPS panel requires light installation & has a short construction period.

• It is low cost, can bear a high load, is moisture-proof, sound-insulating & heat insulating.

Visually there are not a lot of differences between a prefab house and a house made of bricks & stones. pre-fab buildings look the same as any ordinary houses.

Prefab houses are comfortable, portable, and durable in the long run.

The beauty of prefab houses is that they take far less time to build than concrete houses. The prefab materials required to build the house are manufactured at the factory and then assembled at the site.

• The material used to construct walls in a prefab house are lighter than bricks.so, living in an earthquake-prone zone with fears of our own house crumbling down on us, a prefab house should do little damage.
• People have this misconception that prefab houses are only temporary when actually the prefab house is an excellent permanent alternative to the traditional house we have.
• Prefab houses are also certified fireproofs, waterproofs, weatherproofs & earthquake resistant.

The drawbacks: –

•  once the house is installed it can’t be painted over or plastered with the wallpaper of your choice.
• Also, because it’s a thin wall, the wiring inside the house can’t be hidden.
• Another drawback of a prefab house is the money factor, it can be fairly expensive, and a lot of materials have to be imported thus resulting in a high price.
• With prefab s house with 3- bedroom, total 5 room can take one to the half-month of construction.
• The initial construction phase is similar to that of a concrete house, it has a foundation & strong steel structure, the only difference is instead of bricks prefabs are installed in the wall.
• Price per square foot is from Rs 2000 to 3500.

Advantages:

• Safe
• Earthquake proof
• Fire proof
• Weather proof
• Quick assembly
• Durable & potable
• Short construction period

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• During the bending of simply supported structures, the upper portion is subjected to compressive stresses, while the lower portion is subjected to tensile stresses.
• The permissible tensile stress in concrete is about one-tenth of the permissible compressive stress, therefore the tensile stresses in the structure are taken care of by the steel.
• Such a combination of concrete and steel is known as reinforced cement concrete (RCC) & structure is known as reinforced concrete structures.

Note: for the same cross-section of steel to that of concrete, tensile strength is 300 times, while compressive strength is 30 times that of concrete.

There are three types of steel reinforcement bars:

• Mild steel and medium tensile steel bars
• Deformed bars
• Cold twisted bars

What are deformed bars?

Deformed bars have projection and check the slipping of bars, developing a great bond.

Note:

1. when we used cold twisted bars instead of normal mild steel bars, it increased yield stress by about 50%. Hence save reinforcing material by 33%.
2. The pitch of projection in the deformed bar is in the range of (90-120) mm.
3. Size of bars = 5,6,8,10,12,16,20,22,25,32,36,40,45 and 50 mm.

Design methods of RCC structures:

Working Stress Method

1. This method is known as a modular ratio or elastic method.
2. Most popular and common method.
3. The moment and forces acting on a structure are obtained from the actual values of service loads.
4. The stresses in concrete and the reinforcing steel are restricted to only a fraction of their true strengths in order to provide an adequate factor of safety.

i.e., FOS _(conc) = 3

        FOS _(steel) =1.78-1.80

Limit State Method

• This method is known as the plastic method.
• It is designed to withstand safely all loads throughout its life.
• It also satisfies serviceability requirements such as excessive deflections, cracking, vibrations, etc.

Ultimate Strength Method

• This method is also known as the load factor method.
• In this method true margin of safety is exactly known.
• It is based upon results obtained from experiments depicting true behaviors of structures.

Working Stress Philosophy

• Traditional method used for a reinforced concrete design where it is assumed that concrete is elastic, steel and concrete act together elastically and the relationship between loads & stresses is linear right up to the collapse of the structures.
• The elastic theory assumes a linear variation of strain and stress from zero at the neutral axis to a maximum at the extreme fiber.

Assumptions:

•  A section that is plane before bending remains plain after bending (Bernoulli’s Assumptions)
• Within the elastic limit the bond between steel and concrete is perfect
• The tensile strength of concrete is ignored.
• The stress in concrete varies linearly from zero at its neutral axis and maximum at its extreme fiber. i.e., concrete is elastic.

• The modular ratio ‘m’ has the value (280/_cb) where _cb is the permissible compressive stress in bending. its unit is N/mm² or mpa.

Drawbacks:

• Concrete is not actually elastic. The inelastic behavior of concrete is even shown in low stresses. i.e., the distribution of actual stress in concrete is not described by triangular shape.
• Since the factor of safety is on the stresses under working loads, there is no way to account for different degrees of uncertainties associated with different types of loads. With elastic theory, it is impossible to determine the actual factor with respect to loads.
• It is difficult for shrinkage and creeps’ effects by using the working stress method.

Limit state philosophy:

• Limit state philosophy has originated from ultimate or plastic design.
• The object of design is to achieve an acceptable probability that a structure will not become unserviceable in its lifetime for the use for which it is intended, i.e., it will not reach a limit state.
• A structure with appropriate degrees of reliability should be able to withstand safely all loads and also satisfy the serviceability requirements, such as limitations on deflections and cracking.

The most important of these above limit states which must be examined in design are as follows:

Limit state of collapse:

• The collapse limit states or ultimate limit states concern the safety of people and/or the safety of the structures
• When collapse limit states violate, it implies failure in the sense that a clearly defined limit state of structural usefulness has been exceeded.
• The ultimate limit state :
• Flexure
•  compression
• Shear, and
• Torsion

Limit states of serviceability:

• The serviceability limit states concern the functioning of the structure or structural members under normal use, the comfort of people, or the appearance of the construction world.

The factors  and l called partial safety factors in the limit state concept of design of reinforced concrete structures.

References:

1. Reinforced Concrete Limit State/ A.K. Jain

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Project management is the application of knowledge and skills along with experiences and associated with various processes and methods to achieve specific project objectives within agreed parameters and according to project acceptance. It is constrained to a finite time scale and within budget.

Project management also involves identifying and managing risks, careful resources management, smart budgeting, and clear communications among different stakeholders and team networks.

The purpose is to plan and manage the project to the successful completion of its listed goals and deliverables.

What is marketing?

Marketing is a complete set of processes that involves researching, promoting, selling, and distributing products or services. i.e., marketing is not other than getting potential clients or customers interested in the products or services.

The project life cycle

The project life cycle is a time frame. It includes the steps required for managers to successfully manage a project from start to the finish.

It includes 5 phases

• Initiating
• Planning
• Executing
• Monitoring/controlling
• closing

Setting project objectives & goals

Setting up project objectives means the clear, precise, and measurable steps needed for achieving the set goals. Objectives are very specific that typically have a time-bound schedule for completion.

Whereas goals are broad vision and direction and almost align with the company mission, vision, and culture.

For example:

Goals: Being a top-grossing company over the next 5 years

Objectives: Increasing sales by 5% p.a.

Goals are always SMART:

• Specific
• Measurable
• Attainable
• Relevant
• Timely

Network model: CPM & PERT

CPM (Morgan R. Walker,1957)

In the Critical Path Method, networks, the whole project consists of a number of clearly recognizable jobs called activities.

The Critical Path Method (CPM) is a network technique to deal with large and complex projects.

Activities are usually the operations, which take time to carry out and on which resources are expended. It is used for a repetitive type of project, which take a fairly accurate estimate of time for completion of each activity can be made. This technique is useful to determine how best to reduce the time required to perform production, maintenance, and construction. It helps to minimize the direct and indirect costs of a project.

The main characteristics of CPM are:-

1. CPM is activity-oriented.
2. CPM times are related to cost.

Terms associated with CPM:

1. Critical Path

It is the longest path on a network that does not allow any delay. If any delay on the critical path brings a delay in the project. The activities lying on the critical path are known as critical activities.

• Total project time/critical time

This is the total duration of time of all the activities falling on the critical path and gives the total project duration of the network.

• Activity and Events

Activity consumes time and resources while the event is the instant of time. Activity is denoted by an arrow and event is denoted by a circle, triangle, etc.

The beginning and end of activities are the events.

• Head & Tail Event

Head event represents the end of a project. i.e. it lies at the end of an arrow and is the last event of the project. therefore, there is only one head event.

The tail event represents the beginning of a project.it lies at the start of an arrow and is the first event of the project. Therefore, there is only one tail event.

• Dual role event

All the intermediate events other than head and tail events become dual role events. Intermediate events will be at the head of the arrow or at the tail of the arrow hence these are called dual role events.

• Non-critical activity

Activities that do not lie on the critical path are non-critical activities. The delay on non-critical activity can be permitted which does not delay the overall project.

• Dummy activities

An activity on a network that neither consumes resources nor time is called a dummy activity. Also called redundant activities. It helps to maintain the logic of the network and is denoted by the dotted line.

Calculation of CPM Network

Rules: Forward & Backward Pass

While calculating the Earliest Expected Time/Earliest Finish time for the occurrence of an event, we started from the initial event and ended with the last event. This is called a forward pass.

EFT=T_Eⁱ+t^ij

Where T_Eⁱ =Earliest Start Time

For calculating the Latest allowable Time/Latest Start Time for the occurrence of an event, we started from the end event and arrived at the initial event. This is called backward pass.

LST=T_L^j-t^ij

Where T^j_L=Latest Finish Time

Types of float

Float means a certain range within which an activity’s start time or its finish time may fluctuate without affecting the completion time of the project.

1. Total float

It is the difference between the Latest start time the and Earliest start time or the Latest finish time and the Earliest finish time.

• Free float

It is the difference between the Earliest finish time and the Earliest start time for its successor activity. therefore, it affects proceeding activities.

Numerically, FF=TF-slack of head events

• Independent float

It is the excess time available when proceeding activities finish as soon as possible and succeeding activities start as early as possible. It affects only particular activities.

Numerically, IF= FF-slack of a tail event

• Interfering float

The difference between total float and free float is called Interfering float.

Numerically, I_{f =} TF-FF = slack of head event

Q. A project schedule has the following characteristics

1. Construct Network Diagram
2. Compute the earliest event time and latest event time
3. Determine the critical path and total project duration
4. Compute the total and free float for each activity

Solution:

1.

2. Earliest Event Time

Forward Pass                                                                  

EFT=T_Fⁱ + t^ij

          = EST + d

EFT = max (Tⁱ_F + t_ij)

Backward Pass

LST = T^j_L – t^ij

       = LFT – d

LST = min (T^j_L – tⁱ)

3.

Critical Path : 1-2-3-5-6-7-8-9 (longest Duration Path)

 Total Project Duration = 3+4+0+3+4+6+4 = 24

4.

TF & FF (As above table)

PERT

The program evaluation and review technique is a project planning and controlling process for projects having uncertainties and is considered useful for research & development types of projects. For example, developing and launching a missile, installation of machinery, r & d of products, marketing & advertising.

It is a logical sequence of activities but the time required for each activity is not certain.

Therefore, there associated three times and the expected duration of an activity is the weighted average of the three-time estimates. Three types of time estimates used in PERT are:

1. Optimistic time

The shortest possible time for the completion of activities if everything goes well as expected. It is denoted by t_o.

• Pessimistic time

The longest possible time for completion of activity if everything goes wrong and is unexpected. It is denoted by t_p.

• Most likely time

The other time most likely to occur and is between optimistic time and pessimistic time is known as most likely time and is denoted by t_l.

Expected/average time (t_e) = (t_o+t_p+4t_l)/6

Gantt Chart (Henry Gantt,1900)

This is a graphical representation of various activities involved in a project. It has two coordinates. The horizontal ordinates or bar represents the duration of time taken. The vertical abscissa represents different types of activities.

The bar is divided into two parts longitudinally. The top portion indicates the progress of activities and the bottom portion indicates the duration.

Gantt charrt is also known as a bar chart.

Milestone chart

Milestone charts are the modification of a bar chart. The key events are identified and arranged in chronological order but not in a logical sequence.

Each event is numbered and a keynote is provided with it.

The key events are known as milestones.

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The deformation of soil is a natural and physical phenomenon. Civil Engineering structures built on soils such as buildings, dams, bridges, roads, rails, etc. transmit load over a large area of soil through foundations or substructures. Soil tends to deform with the settlement or fail in shear. Therefore, the resistance to deformation of the soil is its bearing capacity. This resistance to deformation depends on various factors such as water content, bulk density, angle of friction, and the manner of application of loads.

Bearing capacity

The supporting power of soil is called the bearing capacity of the soil. In other words, the load or pressure developed under the foundation without introducing any damaging movement in the foundation and in the supporting structure is called the bearing capacity of the soil. It depends upon the grain size of the soil, the size, and the shape of the footing. The bearing capacity of soil increases with the decrease in the area of the footing.

Types of bearing capacity

1. Ultimate bearing capacity

It is defined as the gross pressure intensity at the base of the foundation at which the soil fails in shear. It is denoted by q_f. Gross pressure intensity at the bed of footing is due to weight of the superstructure including self-weight of footing and overburden pressure due to earth fill and is denoted by q.

• Net ultimate bearing capacity

It is the minimum net pressure intensity at the base of the foundation causing shear failure of soil. It is denoted by q_nf.

q_nf=q_f–gD

Where, D= depth of soil

Net pressure intensity is the difference between gross pressure intensity and original over burden pressure.It is denoted by q_n.It is given by the equation.

q_n=q-gD

gD= overburden pressure

• Safe bearing capacity

The maximum pressure which soil can carry safely without the risk of shear failure. It is obtained by adding net safe bearing capacity plus original overburden pressure. It is denoted by q_s.

q_s= q_nf/F + gD

• Net safe bearing capacity

It is the net ultimate bearing capacity divided by factor of safety.

q_ns = q_nf/F

• Allowable bearing capacity

Allowable bearing capacity is the loading intensity at which neither the soil fails by shear nor excessive settlement. It is used for designing of any structure.

Factor Influencing Bearing Capacity

There are various factors influencing the bearing capacity of the soil. The bearing capacity varies over a range for cohesive and cohesion-less soil. The physical features of foundation such as type of foundation, size of foundation, depth of foundation and shape of foundation significantly affect the bearing capacity. The amount of total and differential settlement is one of the main controlling factors for the bearing capacity of soil. The relative density in the case of granular soil and consistency in the case of cohesive soil play a deceive role in influencing the bearing capacity. The physical as well as engineering properties of soils such as density, cohesion and friction, position of water table and original stresses are the main factors governing the soil bearing capacity.

Factors influencing bearing capacity of soils

• Types of soil (coarse grained soil has greater bearing capacity than fine grained soil)
• Physical features of the foundations (types, size, shape, depth, rigidity)
• The amount of total and differential settlement
• Physical properties of soil (grain size)
• Position of water level (WT)
• Fluctuation in the level of ground water table
• Structural arrangement of soil

References

1. Terzaghi, Karl, Peck, R.B & John, Wiley (1969) Soil mechanics in engineering practice, New York.
2. Arora , K.R (2008), Soil mechanics and foundation engineering, Delhi: Standard Publisher Distribution

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