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Showing posts from February, 2020

Types of paints

1. Aluminium paint Very finely grained aluminum suspended in either quick drying spirit varnish or slow drying oil varnish. Then spirit or oil evaporates and a thin film of aluminum formed Advantages: Visible in darkness Resist heat to certain degree Iron and steel are protected from corrosion by this paint Posses high covering capacity 1 litre cover 200sqm Give good appearance to surface Impervious to the moisture Posses high electrical resistance Uses:- for painting gas tanks, hot water pipes, marine pipes, oil storage tank, radiator etc 2. Anticorrosive paint Consists of oil and strong drier. A pigment such as chromium oxide or lead or red lead, zinc chrome is taken and after mixing it with some quality of five sand it is added to paint. Advantages: Cheap Leave for long duration Appearance of paint is black 3. Asbestos paint Peculiar type of it is added on the surfaces which are exposed to acidic gases and steam 4. Bituminous paint Prepare

Workability of concrete

Workability  is used to describe the ease or difficulty with which concrete is handled, transported and placed between the forms with minimum loss of homogeneity. It is not a proper definition of workability as a physical property of concrete alone irrespective of a particular type of construction can be defined as the amount of useful internal work necessary to produce full compaction. Measurement of workability: 1) Slump test: Measure consistency of concrete which gives indication of workability Applicable for aggregates size < 38mm If aggregate size is larger than 38mm the concrete is wet sieved through 38mm screen to exclude aggregate particle bigger than 38mm 2) Compacting factor test: This test is designed primarily for laboratory More precise or sensitive than slump test Useful for concrete mixes of medium and low workability as are normally used when concrete is to be compacted by vibration such dry concretes are insensitive of slump test For concrete

Methods to find EVAPORATION: (Determine)

1. Class 'A' Evaporation Pan: This Pan has been developed by U.S. weather bureau and it is a standard pan having a diameter of 1210mm and depth of 255mm Class A pan will have maximum evaporation This Pan is normally made of unpainted G.I sheets. In areas, subjected to heavy corrosion Monel metal  is used. Monel metal is an alloy of alloy of 'Ni' and 'Cu' with high tensile strength and resistance to corrosion Pan coefficient for class 'A' pan = 0.7 2. ISI evaporation pan This is a modified form of class 'A' evaporation pan in which diameter is 1220mm and depth 255mm.  This pan is made of Copper sheet having a thickness of 0.9mm Top of the pan is covered with hexagonal wire netting in order to prevent any type of disturbances to water and in order to ensure that uniform temperature is maintained during day and night Pan coefficient for ISI pan = 0.8 3. Colorado sunken-pan The main advantage of this pan is that it creat

Approximate estimate

The following are the method used for preparation of approximate estimates Plinth area method Cubical contents method Unit base method Plinth area method The cost of construction is determined by multiplying plinth area with plinth area rate. The area is obtained by multiplying length and breadth (outer dimensions of building) As per IS 3861-1966, the following areas include while calculating the plinth area of building Area of walls at floor level Internal shafts of sanitary installations not exceeding 2.0m^2, lifts, air-conditioning ducts etc. Area of barsati at terrace level (barsati means any covered space open on one side constructed on one side constructed on terraced roof which is used as shelter during rainy season Porches of non cantilever type Areas which are not to include: Unenclosed balconies Architectural bands, cornices etc. Domes, towers projecting above terrace level Box louvers and vertical sun breakers Cubical contents method This m

Detailed estimate

The preparation of detailed estimate consists of working out quantities of various items of work and then determine the cost of each item. This is prepared in two stages: 1) details of measurements and calculation of quantities: The complete work is divided into various items of work such as earth work, concreting, brickwork, R.C.C, plastering etc. The details of measurements are taken from drawings and entered in respective columns of prescribed performa. The quantities are calculated by multiplying the values that are in numbers column to depth column as shown below: Details of measurements form 2) Abstract of estimated cost: The cost of each item of work is worked out from the quantities that already computed in the details measurement form at workable rate. But the total cost is worked out in the prescribed form is known as abstract of estimated form. 4% of estimated cost is allowed for petty supervision, contingencies and unforeseen items. Abstract of estimate form

Prestressed concrete

According to the ACJ committee of prestressed concrete the prestressed concrete is one in which there have been introduced internal stresses of such magnitude and the distribution that, the stresses resulting from the external loading can be counterbalanced upto desired degree Necessity of very high strength steel and concrete for the prestressed concrete 1. Steel (1000-2000)N/mm²    Due to various losses a large stress value is lost. Only due to creep and shrinkage strain, l m    = 0.0008   l m   due to  creep and shrinkage = 0.0008 × E s = 0.0008 × 2×10^5 = 160   N/mm² Total l m       of stress is about 200-300 N/mm² But total l m    of stress > 10 to 20% of initial prestress. So initial prestress should be in the range of 1000 N/mm² to 2000N/mm² 2. Concrete  To bear high bearing stress due to very high stress in steel To bear high value of bond stress in case of pretensioned prestress concrete To keep the  l m   due to creep and shrinkage minimum Types of pr

Qualities of a good building stone

1. Crushing strength : for good structural stone, should be greater than 100   N/ mm 2 Granite - 75 to 127N/ mm 2   Basalt - 150 to 185 N/ mm 2 Diorite - 90 to 150 N/ mm 2 Laterite - 1.80 to 3.10  N/ mm 2 Limestone - 54 N/ mm 2 Sandstone - 64 N/ mm 2 Shale - 0.20 to 0.60 N/ mm 2 Slate - 75 to 207 N/ mm 2 Gneiss - 206 to 370 N/ mm 2 2. Percentage wear For good building stone, wear should be equal to or less than 3% If it is equal to 3%, the stone is just tolerable 3. Appearance Good building stone, should be of uniform colour and free from clay holes, spots of other colour etc Stones which are used to face work, should be decent in appearance and they should be capable of preserving their colour uniformly for a long time 4. Durability Good building stone should be durable Various factors: chemical composition, texture, resistance to atmospheric and other influences, location in structure etc ✓✓[Effects] Alternate condition of heat and cold due


Concrete = cement+sand+pebbles or crushed rock+ water Properties of concrete: (a) Concrete has tendency to shrink under following conditions: There is initial shrinkage of cement concrete which is due to loss of water through forms, absorption by surface of forms Shrinkage of cement concrete takes place during hardening which can be minimized by proper curing (b) It has tendency to be porous. It can be avoided by following precautions: There should be proper grinding and consolidation of the aggregates. The minimum water cement ratio should be adopted Ingredients of cement concrete Cement Aggregates Water Admixtures ✓ Aggregates These are inert materials form bulk of cement concrete Aggregates should be hard, durable and clean Aggregates should be completely free from lump of clay, organic and vegetative matter because these reduce the adhesion of concrete Aggregates are classified as coarse aggregates (>4.75mm) and fine aggregates (<4.75mm)

Clay mineralogy

All the clay minerals are found to consist of two fundamental building blocks. They are Silica tetrahedral unit Octahedral unit 1. Silica tetrahedral unit:   In this unit, flux oxygen atoms encloses silica at the center of the tetrahedral geometry such that all the oxygen present at the base of the tetrahedron lies in single common plane and is being shared between two tetrahedral unit. Net charge present over silica tetrahedron unit is -1 This unit is represented symbolically as trapezium. 2. Octahedral unit: In this unit, six hydroxyl atoms enclose aluminium, magnesium or iron at the center of octahedron geometry. If aluminum is present at each unit, it is termed as 'Gibbsite unit'. If magnesium is present at the center it is termed as 'Brucite unit' and if iron is present at the center it is termed as 'Ferrite unit'. Each hydroxyl unit is shared in between 3 octahedron units. Net charge present over Gibbsite unit is +1 This u

Specification of bolted joints

Specification of bolted joints: 1. Diameter of bolts: Few large diameter bolts cost less than one of some capacity with fsmall diameter Shear capacity of bolts is directly proportional to the square of diameter 2. Spacing of bolt holes       Pitch (p) :- It is center to center distance of two consecutive bolts in a row. [ Row is line of bolts in direction parallel to direction of stress Mini pitch:- there is a limit on minimum pitch to prevent bearing failure of members between two bolts Efficient installation of bolts :- pitch should not be greater than 2.5d ( d= nominal diameter of bolts Maximum pitch:- maximum limit on pitch is to reduce joint length and to have uniform stress in bolts (In short length joint force in bolts will be redistributed by plastic action) For tension member:- lesser of 16t or 200mm (t= thickness of plate) For compression member:- lesser of 12t or 200mm (t= thickness of plate) For compression members transmitting force through

Bolted connections

Bolt is designed as a metal pin with head at one end and a shrank threaded at other end to receive a nut. Bolt length = distance from behind bolt head to end of bolt Grip length = distance from behind bolt head to back of nut/washer Washer distributes the clamping pressure and prevent the threaded portion from bearing on connecting pieces Washers are made of hard Steel/carburized steel If bolted connection is subjected to vibration then nuts must be locked in position Holes made for bolting may be either drilled or punched Fabricator's prefer punched holes due to simplicity but drilled holes are better Punching reduces ductility and toughness Note:- IS:800 limits use of punching only in material for which f y  < 360MPa and thickness doesn't exceed (5600/f y ) In cyclic loaded joints punching should be avoided for plates of thickness greater than 12mm Advantages of bolted connections: Less erection time Less excited labour required Overall cost i


Foundation is that part of structure through which load is finally transmitted to the soil. The failure of foundation is due to Settlement of soil which is called settlement failure or progressive failure Sliding or slipping of foundation or soil such failure is called shear failure or sudden failure Guidelines for selection of foundation: If structural load is less then shallow foundation may be provided. If swelling pressure is high & differential free swell value is more than 35% then shallow footing is not adequate either raft foundation or deep foundation should be provided. If footing area is more than 40% of plinth area then either raft foundation or combined footing may be provided. If structural load is heavy and soil is loose then either raft foundation or pile foundation (deep) should be provided. If structural load is less but top 3 to 4m soil is loose followed by stiff soil then deep foundation may be provided. If structural load is heavy and fou

Introduction to estimation and costing

Definition of estimation and costing Estimating is the technique of calculating or computing the various quantities and the expected expenditure to be incurred on a particular work or project. In case the funds available are less, the estimated cost of the work is done in part or by reducing it or specifications are altered, the following requirements are necessary for preparing an estimate. Drawings like plan, elevation and sections of important points. Detailed specifications about workmanship & properties of material etc Standard schedule of rates of the current year Need for estimating and costing Estimates give an idea of the cost of the work and hence its feasibility can be determined i.e. whether the project could be taken up with in the funds available or not. Estimate gives an idea of time required for the completion of work Estimate is required to invite the tenders and Quotations and to arrange contract. Estimate is also required to control the expend

Properties of soil

Soil mass is a three phase system that comprises of sand, water and air that do not occupy separate spaces but are blended with each other resulting in the formation of complex material properties of which depends upon relative proportion of these constituents. Volume of voids = volume of air + volume of water 1. Water content (moisture content) (% moisture) Water content is defined as the ratio of weight of water to the the weight of solids present in the given soil mass. Water content of fine grained soils is more than that of coarse grained soils. 2. Void ratio (e) It is defined as the ratio of volume of voids to the volume of solids present in given soil mass e = vol. of voids / vol. of volume of solids e > 0 (there is no upper limit for void ratio) 3. Porosity (%voids) (n) Porosity is defined as the ratio of volume of voids to the volume of soil of the given soil mass. The relation between void ratio and porosity is  4. Degree of saturati