Compaction Factor Test – Workability of Concrete

Compaction Factor Test – Workability of Concrete

Compaction Factor Test is designed in such a way that it can be used only in laboratory but in some cases, it can be used for field concrete tests. The compacting factor test has been developed at the Road Research Laboratory in United Kingdom. This test is one of the most accurate test performed in order to determine the workability of concrete.

The apparatus of compaction factor test is shown below.

COMPACTING FACTOR TEST APPARATUS

COMPACTING FACTOR TEST APPARATUS

 

Dimension of the Test Apparatus is given below.

Compaction Factor Test Apparatus

 

This test works on the principle of determining the degree of compaction achieved by a standard amount of work done by allowing the concrete to fall through a standard height. The degree of compaction, called the compacting factor is measured by the density ratio i.e., the ratio of the density actually achieved in the test to density of same concrete fully compacted.

Procedure of Compacting Factor test:

  1. Prepare a concrete mix in the ratio of 1:2:4
  2. With the help of a trowel, fill the freshly prepared concrete in the top upper of the apparatus. The concrete should be filled to the brim of the hopper and level it of with trowel.
  3. Now open the trap of the upper hopper, so that the concrete falls in the lower hopper.
  4. After all concrete falls from the upper hopper to lower one. Then again open the trap of the lower hopper. Let the concrete falls on the cylinder.
  5. Now take the weight of the cylinder in which concrete had felled. Let this weight be “The weight of partially compacted concrete (W1)“.
  6. Empty the cylinder.
  7. Now again, fill concrete in the cylinder in three layers with 25 blows for each layer using tamping rod. Fill concrete to the top of cylinder and scrape excess concrete above the brim.
  8. Now take the weight of the cylinder in which concrete we filled. Let this weight be “The weight of fully compacted concrete (W2)“.

The compacting factor of concrete can be found out using the formula,

 

= (Weight of Partially Compacted Concrete W1)/(Weight of Partially Compacted Concrete W2)

 

Compacting Factor test Or Slump Cone Test. Which is Best?

  1. This test is more accurate and sensitive than the slump cone test.
  2. In this test, Concrete mixes of very low workability can be tested out. Where in slump test it is difficult and it gives inaccurate results for dry mix.

 

 

Retaining Walls – Types, Design, Stability

Retaining Walls – Types, Design, Stability

Retaining walls may be defined as a wall built to resist the pressure of liquid, earth filling, sand, or other granular material filled behind it after it is built. It is commonly required in the construction of hill roads, masonry dams, abutments and wings walls of bridges and so on. Depending upon the site conditions, type of material to be retained and the height of the wall to be constructed, retaining wall may be built in dry Stone masonry, stone masonry, brick masonry, plain cement concrete and reinforced cement concrete.

Types of Retaining Walls:

Some of the types of Retaining Walls are,

  1. Gravity Retaining walls
  2. Cantilever Walls
  3. Counterfort walls
  4. Buttress Walls

 

Dry Stone Retaining Walls:

This is the simplest form of retaining wall. The stability of such walls depends upon the arrangement of stones in the wall and the friction between the individual stones. The stones used in the wall should be of large size and roughly hammer-dressed so as to ensure maximum bedding area. The wall should have a minimum top width of 60 cm. and the front face should have a batter varying from 1 in 4 to 1 in 3. The batter of I in 4 is adopted for walls lesser than 4.5 m in height. In principle, the height of dry stone masonry wall should be restricted to 6 m. For walls above 4.5 m in height, the upper 4.5 m of the walls is usually built of dry rubble stone masonry and the portion below this height is built with mortar.

The stones used in the wall construction are laid at right angle to the face baller. A proper bond is maintained and the front and the rear faces of the wall are nicely bonded with the hearting. The filling immediately behind the wall should consist of stone chips gravel or similar granular material and not earth. 75 to 100 mm. square weep-holes should be provided in the wall at 2m c/c vertically and horizontally to drain off the water from the filling behind. The wall has been shown in figure 943 on page (252).

Dry Stone Pitching or Revetment:

It is generally provided to protect the slopping face of an earthen cutting or embankment from erosion. Stones used, should be perfectly sound and roughly cut to fit in the shape of the pitching. In case of channels and dams, pitching should be carried at least 90 cm. above the high flood level and to ensure its stability, the toe should be prevented from slipping by suitable construction. The slopes of embankment should not be steeper than 1:1, a slope of 1½ : 1 being usually adopted. The thickness of pitching varies from 30 cm. to 75 cm. Selected stones are tightly hand packed and all the interstices are filled up with smaller pieces of stone and wedged up tight. Every stone in pitching is laid flat and no projecting stones are allowed.

Breast walls:

They are stone walls provided to protect the slopes of cutting in natural ground from the action of weather. The section of wall to be adopted depends upon the height of wall, the nature of the backing and the slope of cutting. The front and back batters of the wall vary from 1 in 4to 1 in 2 (1in horizontal : 4 or 2 vertical), with the minimum top width of 60 cm.

Retaining Walls

Brick Masonry, Stone Masonry or Plain Concrete Retaining Walls:

These walls are also provided to support earth, loose stone, coal etc. The wall acts as one mass to resist the thrust from the backing and is much more stronger than dry stone masonry wall. The stability of the wall depends entirely upon its dead weight. They are designed on the assumption that masonry or concrete is not subjected to any tensile stresses. In order that the walls may be stable they have to be very thick in section and as such they are seldom constructed for heights beyond 6 m. The top width of masonry walls and concrete walls should not be less than 60 cm. and 45 cm. respectively. The bottom width of the walls varies with the height.

It is necessary to have proper drainage of the retaining wall from consideration of structural safety and stability.

The backing material is drained by providing 50 to 75 mm. square weep holes at every 2 m. c/c vertically and horizontally.

The lowest weep hole is keep 300 mm. above the ground level. In order to prevent blockage of the weep holes, a 450 mm. thick layer of stone chips, gravel or similar granular material should be placed behind the wall right from footing upto its top (covering the full area of the back of wall) simultaneously with the filling of backing material.

Weep Holes

Design Of Retaining Walls:

The thrust from the backing which tends to overturn the wall or causes it to slide, is the deciding factor in the selection of the section and type of the wall. There are many conditions upon which thrust exerted by the backing depends, such as cohesion of the soil, dryness of the backing material, the manner in which the material is filled against the wall and so on. There are various theories by the help of which the value of thrust under different conditions can be worked out. Having known the thrust, the section of the wall is so designed that the self weight is sufficient to resist the tendency of the thrust to slide the wall and the bottom width of the wall is such that the resultant force (resultant of the weight of wall and pressure of filling behind) lies within the middle third of the base. This condition is necessary to prevent the tendency of thrust to overturn the wall and to ensure that there is no tension at the wall base. It is equally essential to ascertain that the maximum stress at the toe of the wall does not exceed the safe bearing capacity of the soil.

Calculation of Earth Pressure:

The thrust due to the backfilling, which may be assumed to be earth, is generally calculated by Rankine’s Theory. The theory is based on the assumption that the backing material or earth consists of cohesionless granular particles. The formulae derived from this theory under different conditions of back filling are given below:

Case 1 : Walls with earth levelled with the top of wall.

(a). Horizontal pressure per sq. m. (ph) at a depth of (h) metre below the levelled top is given by the
formula :

(b). Total horizontal pressure (P) at a depth of (h) metre per metre length of wall is given by the
formula :

Acting at h/3 metre from the base.

Case 2 : In case of surcharged retaining wall or wall retaining earth filled at slope of a° to the horizontal, the formula giving lateral earth pressure (ph) is given by :

 

acting parallel to the surcharge slope of the filling.

Total pressure (P) at depth of h metre per metre length of wall is given by the formula :

 

Conditions of Stability of Retaining Walls:

A satisfactory retaining wall must meet the following requirements for ensuring its stability :

(1). The wall should be structurally capable of resisting the pressure applied to it.

(2). The section of the wall should be so proportioned that it will not overturn by the lateral pressure.

(3). The wall should be safe from consideration of sliding, i.e., the wall should not be pushed out by the lateral pressure.

(4). The weight of wall together with the force resulting from the earth pressure acting on it, should not stress its foundation to a value greater than safe bearing capacity of the soil on which it is founded.

(5). It is important to prevent accumulation of water behind a retaining wall. The backing material should be suitably drained by providing weep holes as detailed earlier.

(6). As far as possible, long masonry retaining walls should be provided with expansion joints located at 6 to 9 metre apart.

 

 

 

Concrete Curing – Methods – Curing of Concrete

Concrete Curing – Methods – Curing of Concrete

What is Curing:

It may be defined as the operation of keeping a freshly placed concrete moist during a specified period after its finishing to ensure complete hydration of cement particles or other cementing material for obtaining a properly hardened concrete.

The concrete starts attaining its strength immediately after its setting is completed, and it continues to gain strength there after along with time. About 90% of concrete strength is attained in the first 28 days and its value is generally known ad design strength. Development of the concrete strength is primarily due to hydration of cement which takes place only in the presence of water. It is therefore necessary that water in the capillaries in prevented from evaporating. For proper hydration of cement particles in a freshly placed and compacted concrete, a proper environment of humidity and temperature needs be maintained. This process is called ‘curing’

Curing of Concrete

To achieve proper curing of concrete, the following requirement should be fulfilled.

(a) Maintenance of adequate water content in the concrete which is essential for the hydration of cement particles.

(b) Maintenance of uniform temperature in the whole mass of the concrete.

(c) Maintenance of the concrete temperature above the freezing point in cold climatic regions.

(d) Protecting a freshly placed concrete structure from damages.

 

Object of curing:

If a freshly place concrete is left in air, it attains a strength of about 50% of the concrete cured for 14 days. This is due to the face that hydration of cement takes place only in the presence of water in the pores. The rate of hydration is maximum at saturation pressure, i.e. when all the voids are fully filled with water. As the time passes on, the vapour pressure in the capillaries is reduced and hence the rate of hydration and subsequently the rate of development of strength is reduced. It is therefore essential to prevent even a small of water during the process of hardening even if the water cement ratio is above 0.5 in the mix. In addition of the strength development, it also affects the following qualities of the concrete:

(i) It improves the wearing and water resisting qualities of the cement concrete.

(ii) It improves the durability and impermeability of the concrete structure.

(iii) It reduces the shrinkage.

 

Methods of Curing Concrete:

There are various methods of curing and adopt ion of a particular method depends upon the climatic conditions and the nature of the work. The commonly adopted method of curing concrete may be broadly divided into four categories:

1. Water

2. Membrane

3. Steam

4. Miscellaneous methods.

1.Water curing:

This method is considered the best method of curing because it  satisfies all the necessary requirements of curing i.e. continuance of hydration elimination of shrinkage and controlling the heat of hydration. Water curing may be done by the following methods.

(a) Water immersion method:

In this method, the concrete structure is kept immersed for a specified period, is called water immersion method of curing. Precast concrete structural items, are normally cured by this method.

(b) Water ponding method:

In this method, the surface are of the structure is divided into a number of suitable sized rectangles, having their bunds of clay and the ponds thus formed are filled in with water, is called water ponding method. The filling of water in these ponds is done twice or thrice a day depending upon the climatic conditions. This is the most efficient method of curing. It is suitable for the structures having horizontal surfaces such as floors, roof slabs, road and airfield Pavements. The only disadvantage of this method ¡s that it becomes difficult to remove the clay after curing and thus surface becomes muddy.

(c) Water spraying method.

In this method, the surface of concrete structure is kept moist by spraying water at regular intervals. Water may be either sprayed from the performed plastic box or sprinkled on the top surface to allow it to rundown between the from work and the concrete surface.

(d) Water moist covering method.

In this method, in which wet covering such as wet gunny-bags, hessian cloth, jute mattings, etc. are wrapped around vertical surfaces of the structures for keeping the concrete moist. This is most suitable for vertical columns.

2. Membrane curing.

In this method, the wetted concrete surface is covered by a layer of water proof material to prevent the evaporation of water from the concrete, is called membrane curing. This method is adopted in places where there is an acute shortage of water and curing method is not found economical. The membranes which may be either is solid or liquid form are generally known as sealing compounds. Bituminised water proof papers, bitumen emulsions, wax emulsion, plastic films, etc. are the common types of membranes used.

Bitumen curing membrane is applied over the surface for curing only after curing the structure for 24 hours with gunny bags. Loose water is dried from the surface and then liquid asphalt is sprayed throughout. The moisture in the concrete thus preserved is quite enough for curing purposes.

Disadvantages:

  1. It is not efficient as compared with water curing method because in this case the rate of hydration is slow.
  2. The strength of the concrete is less as compared with the concrete cured by water.
  3. In case, the membrane is damaged, the curing is adversely affected.

 

3. Steam curing:

In this method, concrete structure is kept in steam to accelerate the hydration of cement particles. The development of strength of concrete is accelerated if the concrete is subjected to higher temperature due to higher rate of hydration. This method is suitable for the structures which are to be loaded at an early date. Steam curing the structures which are to be loaded at an early date. Steam curing is adopted for prefabricated concrete members, stored in a chamber, at ordinary pressure and temperature. In this method, heating is even throughout even if the space between the stacked precast concrete products is very small. The heat is transferred to the concrete by condensation of steam of the surface along-with the release of latent heat in the steam. In steam curing the temperature of steam should be restricted to 75°C as in the absence of proper humidity (about 90%) the concrete dries up soon. In case of hot water curing, temperature may be raised to 100° to 110°C. At these temperatures, the developed strength is about 70% of the 28 days strength just within 4 to 5 hours.

Demerits:

Though the concrete develops the strength very soon, the following are the demerits of the method.

(i) There is 55% reduction in the bond strength of an R.C.C. structure.

(ii) Due to rapid drying and cooling, cracks may develop.

(iii) The method is unsuitable if the concrete contains high alumina cement.

 

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Hand Mixing Of Concrete

Hand Mixing Of Concrete

The process of mixing the various ingredients of concrete by manual labour, is called hand mixing of concrete. Hand mixing of concrete may be resorted to at small projects which require limited quantity of concrete. Now-a-days machine mixing of concrete is almost done and only in exceptional cases, mixing concrete by hand may be permitted. It may be noted that in hand mixing more cement is required as compared to machine mixing of concrete for obtaining the concrete of same strength. Method of mixing concrete by hand may also be necessitate if the mixer fails to work due to mechanical defects and concreting operation is to be completed. The hand mixing of concrete may be done as detailed below:

hand mixing of concrete

(i) Depending upon the quantity of concrete to be mixed, either construct a suitable platform of bricks with lean concrete or obtain iron sheets of suitable size.

(ii) Spread the required quantity of fine aggregates (sand) on the platform and then spread the required quantity of cement uniformly over the sand layer.

(iii) With the help of shovels, mix the sand and cement in dry state till a mixture of uniform colour is obtained.

(iv) Spread the sand cement mixture once again uniformly on the platform and then spread the required quantity of the coarse aggregates and mix the mixture in dry state thoroughly.

(v) On obtaining a uniform coloured mix with sand, cement and coarse aggregates, make a depression in the centre of the mixed materials.

(vi)  Add 75% of the required quantity of water (based on the water-cement ratio) in the depression and turn the mix towards the middle, with the help of hands or shovels. The mixture is mixed thoroughly till a uniform colour and consistency is obtained.

(vii) Add the remaining quantity of water and continue the mixing process till a concrete of uniform consistency is obtained.

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Chemical Classification of Rocks

Chemical Classification of Rocks

The Chemical Classification of Rocks are,

(a) Siliceous rocks : These rocks have silica (and, quartz and flint) as their principal constituent and are very hard and durable, unaffected by weathering. Chief types of siliceous rocks are Granites, Traps, Quartzite and Sandstones.

(b) Calcareous rocks : Calcium carbonate or lime is the main constituent of these rocks. Crystalline and compact types are hard and durable. Clay is very often found mixed in such rocks. Marbles and limestone are calcareous rocks.

(c) Argillaceous rocks : Rocks of the clayey types which are more or less composed of alumina mixed with small quantities of other minerals. Slates and laterites belong to this group.

Chemical Classification of Rocks – Also see geological classification of rocks

WaterProofing Concrete, Walls and Floors

WaterProofing Concrete, Walls and Floors

A badly made concrete cannot be made waterproofing, to the penetration of water by any admixtures. The first requisite for waterproofing concrete, is to obtain a dense concrete with well-proportioned non-porous aggregates, and with low water/cement ratio (0.54 or less) so as to have a minimum of air voids. Normally all concretes are porous, and these pores have to be reduced to make the concrete, as far as possible, impermeable to Water.

Methods of making good concrete as detailed. It is often beneficial to use a slightly excessive proportion of fines. A small increase in cement content over that used for ordinary concrete is also advantageous as with more of cement less of water is required for the Same workability. The following methods can be used for further waterproofing.

(a) Concrete and masonry surfaces can be made waterproof by giving three alternate coats of alum and soap solutions. 10 grams of alum is dissolved in one litre of hot water, and 50 grams soap is dissolved in one litre of hot water. The hot alum solution is applied first and worked, in with a stiff’ brush immediately followed by hot soap solution. The solutions are applied with an interval of about 24 hours between alternate coats.

Recent experiments have indicated that a cement plaster (even 1:6) can be made waterproof by mixing the cement mortar in a 1 per cent soap solution instead or ordinary water. “Sunlight” soap was used in the experiment.

Soap solutions act as lubricants and also form insoluble fillers by reaction with cement and may be applied while he concrete is still green.

Walls can be effectively treated against moisture penetration by these methods.

water proofing concrete

(b) Addition of fully slaked (hydrated) white lime in the following proportions will also make the concrete water-proof. Lime paste occupies about twice the bulk of paste made with equal weight of cement and is therefore very efficient in void filing ; but the mixture must be of dense concrete.

1:2:4 concrete — 10% of the weight of dry cement

1:2.5:5 concrete —15%  of the weight of dry cement

The addition of hydrated lime increases workability but it is nevertheless an adulterant and where strength is a primary consideration the use of higher cement content should be preferred for increasing workability and achieving impermeability. (Some of the experiments have shown that addition of a small quantity of hydrated lime slightly increases the strength of a concrete, but there are conflicting views about this point.) Increase of workability permits a slight reduction in water content, which in turn reduces permeability.

Make concrete rich to have at least 15.to 20 percent excess cement over sand and 20 per cent excess mortar over coarse aggregate. A 1:1.5:3 mix with water/cement ratio of about 0.40 will make the concrete practically water-proof.

Rendering with mortar consisting of cement, hydrated lime and sand in the proportions 1:3:10, 12mm thick will also make concrete waterproof.

(e) The form-work should be removed as soon as practicable and the concrete surface rubbed smooth and washed. A mixture of cement and sand of proportions 1:1.5 with some waterproofing compound should be worked into the pores and over the whole surface in such a manner that no more material is left on the concrete face than is necessary to fill the pores completely.

(d) Concrete floors may be treated during concreting operation with. dry cement sprinkled over the surface and worked in with a steel trowel on the initial set of the concrete.

(e) As regards surface application of a water-proofer the method depends on the quality of the concrete. If pores are very small, silt or fine clay may fill them. Boiled linseed oil, paraffin, or varnish, can be brushed on the surface when the concrete has been well cured and has dried. Two or three coats may be applied allowing each to dry before the next application. A coat or two of bitumen or coal tar makes the surface impermeable to water ; concrete must be perfectly dry and dust free ; a thin priming coat (of bituminous material) should be given to ensure bond. 50 to 60 litres per 10 sq. m of bitumen are required.

(f) Bituminous Mastics are generally laid on horizontal surfaces and also toweled on vertical surfaces. They are used either hot or cold. (An asphalt lining has the disadvantage that it insulates the floor from the beneficial effects of saturation, thus increasing the tendency to develop cracks, the asphalt is liable to fail ultimately over such cracks and construction joints).

(g) Proprietary compounds such as Pudlo, Medusa, Ceresit or Ironite are used according to the manufacturers’ instructions, not exceeding 1.5 kg/50 kg (one bag) of cement.

Inert materials used include finely divided chalk, Fuller’s earth and talc, all of which Consist of very fine particles. They assist in making the concrete dense, especially if the aggregate is deficient in fines.

(h) Treatment with silicate or soda.

(i) One kg of washing soda dissolved ¡n 30 litres of mixing water will make a cement mortar water-proof.

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Civil Engineering Terms and Definitions

Civil Engineering Terms and Definitions

Some of the basic Civil Engineering Terms and Definitions are listed below,

Arcade : A series of arches with their supporting columns or piers.

Arris : The meeting of two surfaces producing an external angle.

Base: Base is immediately above plinth. A building having no plinth, immediately above footings.

Basement or Basement Storey or Cellar : Part of a building (usually a storey) below ground level,

Bat: Part of a brick.

Baiter : The slope away from you of a wall or timber piece, etc.

Bay : The space between two piers, columns or projections.

Bay window: A window projecting outward from a wall and reaching up to the ground.

Bevel: Any inclination of two surfaces other than 90 deg. (either greater or less),

Blocking Course : A course of stones (or only one stone) placed on the top of a course to add to its appearance and also to prevent the cornice from overturning.

Bressummer : Joist embedded in concrete; beam over verandah posts on which purlins of sloping roofs rest. Also means a beam which carries a wall.

Brick core : Brickwork filled in between the top of a lintel and the soffit of a relieving arch.

Brick flogging: Brickwork filled in between wooden posts or studs (for making a wall).

Bull’s eye : A circular or oval opening in a wall.

Buttress: A projection of masonry built into the front of the wall to strengthen it for lateral stability against thrust from an arch, roof, or wind pressure.

Flying Buttress : A detached buttress or pier of masonry at some distance from a wall, and connected therewith by an arch or portion of an arch, so as to discharge the thrust of roof or vault, on some strong point.

Chamfer: To cut off, in a small degree, the angle or arris formed by two faces, usually at an angle of 45 deg.

Chase : A recess made inside of a wall to accommodate pipes or electric Wiring, etc.

Composite Building : A building of which part is masonry and part is either open or framed ; or a building of which part is open building and part is framed building. .

Coping: The capping or covering placed upon the exposed top of a wall (or parapet), usually of stone, to throw off and prevent the rain-water soaking in to it.

Corbel: One or more courses of brick projecting from a wall like a cornice), generally to form a support for wall plates, etc. A brick should not project more than 1/4 beyond the lower course.

Counterfort: Is a projection of masonry built into the back of the wall.

Cowl: A hood shaped top for a chimney; a ventilating top of a sewage pipe. .

Cross Wall: An internal weight bearing wall built into another wall to the full height thereof.

Dormer Window : A small vertical window built in a sloping roof.

Dowel: A pin or peg let into two pieces of stone or wood for joining them ; a cramp iron.

Drip : Part of a cornice or projecting sill etc., which has a projection beyond other parts for throwing off rain-water.

Efflorescence: The formation of a whitish loose powder or crust, on the surface of brick walls. .

Extrados: The outer surface of an arch.

Frog: Is a small recess on the top surface of a brick, made while moulding, usually embossed with the initials of the contractor. It forms a key for the mortar and also reduces the weight of the brick.

Gable : The entire end wall of a building. (The term is generally used for the triangular end wall of a sloping roof.)

Haunch : That part of an arch lying midway between the springing and the crown.

Herring-bone work: Masonry work (generally in floors) in which the bricks are laid slanting in opposite directions. .

Hydroscopic: A substance that attracts water from the air.

Intrados: The inner surface of an arch.

Lambs : The two sides of doors, windows or other openings between the back of a  and, the chowkat or frame. The portions of the openings outside the frame are called Reveals.

Joggle : A dowel or stub tennon joint by means of which one piece of stone or timber is fitted to another.

Keystone : The uppermost or central voussoir of an arch.

King closer: A brick cut lengthwise so that one end is nearly half the width of the other, They are used in the construction of jambs.

Lobby : An open space surrounding a range of chambers, or seats in a theatre ; a small hall or waiting room.

Mantel: The facing and shelf (usually ornamental) above a fire place.

Mastic : A preparation of bitumen used for water proofing and damp proofing, etc.

Mat finish : A term applied to surface finishing (generally painting) which is free from gloss or polish (not shining),

Mezzanine floor : An additional (low storey) floor, gallery or balcony erected between the floor and ceiling of any storey.

Mosaic : Small pieces of stones, glass,. etc. (generally of different colours) laid in cement mortar to form artistic patterns for flooring and dados, etc.

Mullion : An upright (piece) in any framing ; a division piece between the sash of a frame.

Oriel Window: An upper storey window projecting outward from a wall (and which does not reach up to the ground, as distinguished from a bay-window).

Party Wall: A wall erected on a line between adjoining property owners and used in common.

Pedestal: A base or support, as for a column or statue, and generally of a bigger size.

Pilaster : A right-angled column or projection from a pier or wall; a square pillar made generally to support a concentrated load.

Pillar : A detached vertical support to some structure; a solid portion of a wall between window openings and other voids.

Plinth : The portion of the external wall between the level of the street and the level of the floor first above the street.

Queen closer: A brick cut lengthwise into two so that each piece is half as wide as the full brick.

Quoin brick : A brick forming a corner in brickwork ; it has one end and one side exposed to view.

Recs: A depth in the thickness of a wall.

Refractory materials : The term “refractory” is applied to various heat resisting materials such as, lire-bricks, furnace linings.

Reveal: A vertical side of a window or door opening from the face of the wall to the frame. (See lambs).

Skew-back: That (inclined) part of a pier or abutment from which an arch springs.

Sleeper Walls : Low walls erected at intervals between the main walls to provide intermediate supports to the lowest floor.

Soup header :A brick header not extending the full length of a brick into a wall, usually half a brick.

Soffit : The lower horizontal face of anything ; the under face of an arch where its thickness is seen.

Spall:  Bat or broken brick; stone chips,

Spandrel or Spandril: The space between the top of a masonry arch and the roof, beam or carriageway, etc.

Spandrel Wall : A wall built upon the extrados of an arch up to the top level of the roof or beam, etc.

Splay: An oblique surface (bevel or chamfered), as of the jambs of a doorway or Window ; of which one side makes an oblique angle with the other.

Springing line : A line of intersection between the intrados and the supports of an arch.

Spring points: The points from which the curve of an arch springs.

Springer: The voussoir placed next to the skew-back in an arch.

Squint Bricks: Bricks used for forming acute or obtuse corners in brick masonry.

Striking : The releasing or lowering of centering of arches or lintels.

String course :. A horizontal (usually ornamental) course projecting along the face of a building (usually introduced at every floor level or under Windows or below parapets) for imparting architectural appearance to the structure and also keeping off the rain water.

Throating:  Term used for making a channel or groove on the under side of string courses copings, cornices or sun-shades, etc., to prevent rain water from running inside towards the walls.

Underpinning : The process of supporting the. existing structure for renewing or repairing the lower Walls or foundations.

Vault : An arched masonry structure (with series of arches).

Veneered Wall: In a wall in which the facing material is merely attached to and nor properly bonded into the backing.

Voussoir : The wedge shaped structure component of a stone arch.

Weathering: Action of sun and rain on structures or soils.

The Civil Engineering terms and definitions will be updated regularly.

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Damp Proof Course – Damp Proofing

Damp Proof Course

One of the following specifications may be adopted for a damp proof course, according to the type of the construction and the nature of the ground:

(j) Two courses of dense bricks in 1. : 3 cement mortar. Bricks should have a water absorption of not more than 4.5 per cent. It is advantageous to leave the vertical joints unfilled as moisture rises through the mortar joints.

(ii) A layer of well burnt bricks soaked in hot tar and pitch will suit for cheap class buildings.

(iii) Non-porous stone slabs about 50 mm thick laid for the full width of the walls over a bed of cement mortar.

(iii) Two layers of non-porous slates laid to break joint, each layer being bedded and set solidly in cement mortar 1: 3.

(iv) 12 mm cement plaster 1 : 2 with some water proofing compound laid above the plinth masonry with one or two thick coats of hot coal tar applied over the mortar after the mortar has fully dried. Dry sharp sand should be sprinkled over the hot tar. Five per cent of Pudlo by weight of cement can be used for water proofing the mortar. .

(v) For 40 to 50 mm cement concrete 1 : 2 : 4. Two coats of asphalt or hot coal tar should be applied over the cement concrete when the concrete has been fully cured and dried. A coat of 7 asphalt mixed with 3 parts of clean sharp sand may be laid 6 min thick over the concrete. A layer of tough asphalt about 10 mm thick is often used instead of hot asphalt, Mastic asphalt in one or two layers is generally considered best where hydraulic pressure is encountered. The asphalt used should not melt or soften in the hottest days and should not get squeezed out due to pressure of the masonry over it.

The damp proof course should be laid flush with the floor surface and should not be carried across doorways or other openings. The upper layer of cement concrete floors should be continued over such openings and should be laid at the same time as the floors. The asphalt or tar layer should be laid under the concrete at the Openings. Where concrete is laid on bitumen or tar, the surface of the bitumen or tar must be sprinkled with dry sand.

The position of the damp proof course is also an important factor and it should be laid at such a height that it is above the normal level to which water splashes from the ground when it is raining. A damp proof course should not be less than 15 cm above the highest level of the ground. In Northern India plinths are usually kept 45 to 60 cm above ground level for good class buildings under normal conditions.

Test for Stones

Test for Stones

Some of the simple test for stones are listed below,

(a) Crushing test for stones: The crushing strength of a stone greatly depends upon its texture and specific gravity. A stone of even texture arid of specific gravity greater than 2.7 can take heavy loads. Safe compressive loads on stones should be taken not more than one-tenth of the crushing loads determined by cube test. Stones generally begin to crack or split under about half of their crushing loads.

(b) Porosity or absorption test : Porous stones such as coarse grained sandstones should not be used. A good building stone should not absorb more than 5 per cent of its weight of water after 24 hours immersion. Any stone absorbing more than 10 per cent or having specific gravity less than 25 should be rejected.

(c) Structure test : Small pieces of the stone are kept for about an hour in a glass of water and then shaken vigorously. 1f the water gets dirty it shows the stone particles are not properly cemented together.

(d) Acid test : A small sample is immersed into 1 per cent solution of hydrochloric acid and kept for about seven days. During this time the solution is frequently agitated. If the sample has still maintained its edges and corners as sharp as before, the stone will weather well. If a drop of weak sulphuric or hydrochloric acid on a piece of stone causes effervescence, the stone contains chalk and is poor in weathering qualities unless it is marble.

(e) Hardness test for stones: may be tested by scratching with a penknife, which should not make an impression on a hard stone.

(f) Toughness : may be tested by breaking the stone under a hammer. A hard and tough stone is required for road mental.

These are the simple tests.

Grading of Aggregates – Aggregate Grading

Grading of Aggregates

Grading of Aggregates is one which is made up of stones of different sizes, ranging from large to small (inclusive of sand) so as to have minimum of air voids (and that will have maximum density) when mixed together. In grading of aggregates, the voids in the mixed aggregate would be minimum when the sand is just sufficient to fill the voids in the coarse aggregate. Voids in the coarse aggregate are filled in by sand and voids in the sand are filled in by cement. Mix that occupies the least volume is the densest and will produce the best results. The volume of the coarse aggregate is generally taken as twice that of the fine aggregate, but variations of its proportions may be made within the limits of 1.5 to 3 times the volume of the fine aggregate to Suit the size and grading to secure dense and workable concrete. Grading is of great importance since it affects workability of concrete and hence density and strength.

The proportion of voids to volume of well graded sand is 30 to 35 per cent and that of coarse aggregate between 30 and 45 per cent. This should represent the amount of cement required to fill the interstices in the sand and the amount of sand required to fill the interstices in the coarse aggregate. But it has been realized that when sand is added to coarse aggregate the particles of latter are separated by grains of sand so increasing the original volume of voids. To allow for this and to obtain workability, ten per cent extra sand and fifteen per cent extra cement to the percentage of voids in aggregate and sand are usually provided to arrive at the proportions of different materials for a particular mix.

In grading of aggregates, well graded sand from coarse to fine has less voids than fine sand. The lesser the voids the better is the quality of sand for use in cement concrete, provided there is no silt in sand.

Grading of Aggregates

The combined aggregate when mixed with the required quantity of cement and water, should give a good workable concrete which can be readily placed in position without segregation. The proportion of fine to coarse aggregate should be such as will give maximum workability with minimum of water. Mixtures with a deficiency of fine materials will be harsh, hard to work and difficult to finish. A little more sand makes the concrete more fluid without extra water. Too much of sand will increase porosity of the concrete and need more cement. Mixes having a larger coarse aggregate require less water and less cement.

For concrete works to be water-roof, a dense mix should be aimed at with small size of aggregate. As little of cement as possible consistent with the required strength of the resulting concrete has to be used for purposes of economy.

While a drying water evaporates and leaves air voids, cement expands in the process and occupies some of the air voids.

Excess of fine materials need more cement and more water. A small amount of very fine material (silt and clay) passing 75-micron (No. 200 BS) sieve may improve the workability of the concrete, but an excess causes reduction in strength. The material passing through 150-micron (No. 100 BS) sieve must not exceed 10 per cent. Crusher dust in broken stone is injurious when present more than 10 per cent. Clay particles although less injurious, but should not be more than 5 per cent.

Nominal mix is the proportion of cement, sand and broken stone; all the three measured separately by volume (dry materials).

Real mix is the proportion of cement to a mixture of sand and stones by volume. Sand and stones when mixed together will occupy less volume than when measured separately.

Field mix. The proportion of wet sand and stones taken to make particular nominal mix is called a “field mix.”