A temporary structure use in building operations to support platforms for workmen, structural materials essential require during construction at raise heights ( > 1.5 m ) is refer as scaffolding.

It is very useful in construction, demolition, repair and maintenance works carry on various civil engineering structures such as buildings, bridges, dams, tanks etc. This type of arrangement is provide either on one or both the sides of the walls. In case of ordinary works. These may be erect on one side only but must be provide on both sides if work is of superior quality. The height should be adjust with the progress of the work.

Brick-layer’s scaffolding

This is also refer as single scaffolding. This type of scaffolding consists of bamboos and poles except platforms. In this case, single row of standards ( i.e. vertical members ) are driven into the ground. The distance between two standards varies from 1.5 m to 2.0 m. The standards are driven about 1.2 m to 1.5 m away from the main face of the wall. Standards may be place in tubs or barrels fill with sand or earth in case these can not be driven into the ground. Sand or earth is fill in order to make the standard strong against any movement or slipping.

The standards are, then, connect to each other by longitudinal horizontal members ( i.e. ledgers ) at every vertical rise of 1.2 to 1.5 m. They are provide on the building side and are secure by rope lashings. After this, the put logs ( i.e., transverse horizontal members ) are place at a horizontal distance of 1.2 m to 1.5 m such that on one side they are support on ledgers and on the other are held in the holes provide in the wall. They are fix to ledgers by rope lashings.

After this, cross braces and guards boards etc. are fix for increasing the strength and to guard against materials at working level respectively.

The platform is raise higher and higher during the progress of the work, if need be. When the work is complete, the arrangement is remove and the holes are fill with soil as soon as the standards are remove.

Mason’s scaffolding

This is also refer as double scaffolding. It is stronger than brick layer’s scaffolding. This type of scaffolding is mainly use for stone masonry, superior brick work and surface finishing of costly structures. The arrangement is similar to the brick layer’s scaffolding. The only difference is that in this case two rows of standards are use.

The standards in the first row are driven at a distance of 15 cm from the face of the wall whereas those of second row are driven at a distance of 1.2 to 1.5 m away from the wall face. The put logs are support at the ends on both the ledgers. In this case, holes are not provide in the wall to support the putlogs. In some of the cases, instead of diagonal braces, indicate supports ( i.e., raking shore or shoring ) are provide to increase the resistance of the scaffold from slipping away from the wall face.

Tabular scaffolding

This type of scaffolding is also refer as steel scaffolding. In this case, wooden members are replace by steel tubes and rope lashings are substitute by special coupling at junctions and joints.

The diameter of the steel tube varies from 4 cm to 6.5 cm and its thickness is about 5 mm. The standards are space at a distance of about 3 m. Each one is weld to a base plate which may be circular or square in plan. The plate has holes so that it can be spike to a concrete or timber base in order to form a rigid foundation for scaffolding. Ledgers are space at 1.8 m vertically apart. The length of putlogs i.e., short steel tubes varies from 1.2 to 1.8 m in length. No holes are require in the wall for bearing the putlogs because these have special end of fit into the joints in the wall face.

This type of scaffolding has several advantages and therefore is generally prefer over other ordinary timber scaffolding. The advantages are :

• Suitable for any height.
• Economical in long run inspite of its higher initial cost.
• It can be rapidly erect and dismantle.
• It is durable.
• Strong as compare to other types.
• Possesses fire resisting qualities.
• Use for painting the walls and underside of roofs etc. if it is mount on bogie wheels.

The building stones are to be test for their different properties. Following are such tests for the building stones :

Acid test

In this test, a sample of stone weighing about 0.50 to 1 N is taken. It is place in a solution of hydrochloric acid having strength of one percent and it is keep there for seven days. The solution is agitate at intervals. A good building stones maintains its sharp edges and keeps its surface free from powder at the end of this period. If edges are broke and powder is form on the surface, it indicates the presence of calcium carbonate and such a building stones will have poor weathering quality. It is natural that this test cannot be apply to the limestones. This test is usually carry out on the sandstones.

Attrition test

This test is done to find out the rate of wear of stones which are use in road construction. The results of test indicate the resisting power of building stones against the grinding action under traffic. Following procedure is adopt :

• The sample of stone is broken into pieces of about 60 mm size.
• Such pieces, weighing 50 N, are put in both the cylinder of Deval’s attrition test machine. The diameter and length of cylinder are respectively 200 mm and 340 mm.
• The cylinders are close. Their axes make an angle of 30 degree with the horizontal.
• The cylinders are rotate about horizontal axis for 5 hours at the rate of 30 R.P.M.
• After this period, The contents are taken out from the cylinders and they are pass through a sieve of 1.50 mm mesh.
• The quantity of material which is retain on the sieve is weight.
• The percentage wear is work out as follows :

Crushing test

The compressive strength of stone is found out with the help of this test.

The sample of stone is cut into cubes of size 40 mm X 40 mm. The sides of cubes are finely dress and finish. The minimum number of specimens to be test is three. Such specimens should be place in water for about 72 hours prior to test and thereafter test in saturate condition.

The load-bearing surface is then cover with plaster of Paris or 5 mm thick plywood. The load is apply axially on the cube in a crushing test machine. The rate of loading is 13.72 N/mm2 per minute. The crushing strength of the stone per unit area is the maximum load at which its sample crushes or fails divide by the area of the bearing face of the specimen.

Crystallisation test

In this test, at least four cubes of stone with side as 40 mm are taken. They are dry for 72 hours and weight. Then immerse in 14 percent solution of Na2SO4 for 2 hours. They are dry at 100 degree celsius and weight. The difference in weight is note. This procedure of drying, weighing, immersing and reweighing is repeat at least five times. Each time, the change in weight is note and it is express as a percentage of original weight.

It is to be note that the crystallisation of CaSO4 in pores of stone causes the decay of stone due to weathering. But, as CaSO4 has low solubility in water, it is not adopt in this test.

Freezing and thawing test

The specimen of stone is keep immerse in water for 24 hours. It is then place in a freezing mixture at -12 degree celsius for 24 hours. It is then thaw or warm at atmospheric temperature. This should be do in shade to prevent any effect due to wind, sun rays, etc. Such a procedure is repeat several times and behavior of stone is carefully observe.

Hardness test

To determine the hardness of a stone, the test is carry out as follows :

• A cylinder of diameter 25 mm and height 25 mm is taken out from the sample of stone.
• It is weight.
• Then, it is place in Dorry’s testing machine and press with a pressure of 12.50 N.
• The annular steel disc of machine is then rotate at a speed of 28 R.P.M.
• During the rotation of disc, the coarse sand of standard specification is sprinkle on the top of disc.
• After 1000 revolutions, the specimen is taken out and weight.
• The coefficient of hardness is found out from the following equations :

Impact test

To determine toughness of a stone, the impact test is carry out in page impact machine as follow :

• A cylinder of diameter 25 mm and height 25 mm is taken out from the sample of stone.
• It is place on cast-iron anvil of machine.
• A steel hammer of weight 20 N is allow to fall axially in a vertical direction over the specimen.
• The height of first blow is 1 cm ; that of second blow is 2 cm; that of third blow is 3 cm; and so on.
• The blow at which specimen breaks is note. If it in nTh blow, n represents the toughness index of stone.

Microscopic test

In this test, the sample of stone is subject to the microscopic examination. The thin sections of stone are taken and place under the microscope to study various properties such as :

• Average grain size;
• Existence of pores, fissures, veins and shakes;
• Mineral constituents;
• Nature of cementing material;
• Presence of any harmful substance;
• Texture of stone; etc.

Smith’s test

This test is perform to find out the presence of soluble matter in a sample of stone. The few chips or pieces of stones are take and they are place in a glass tube. This tube is take fill with clear water. After about an hour, the tube is vigorously stir or shaken. The presence of earthy matter will convert the clear water into dirty water. If water remains clear, the stone will be durable and free from any soluble matter. On the other hand, if the water becomes dirty, it will indicate that the stone contains too much of soluble earthy and mineral matters.

Water absorption test

Following procedure is adopt for this test :

• From the given sample of stone, a cube weighing about 0.50 N is prepare. Its actual weight is record. Let it be W1 N.
• The cube is then immerse in distill water for a period of 24 hours.
• The cube is taken out of water and surface water is wipe off with a damp cloth.
• It is weight again. Let its weight be W2 N.
• The cube is suspend freely in water and its weight is record. Let it be W3 N.
• The water is boil and cube is keep in boiling water for five hours.
• It is then remove and surface water is wipe off with a damp cloth. Its weight is record. Let it be W4 N.

For certain types of works like water storage tanks, reservoirs, basement walls, roofs, swimming pools, sewage units, etc., the impermeability of concrete is absolutely essential. In general, it can be state that if concrete is make dense and free from cracks, it is watertight. The dense concrete can be obtain by closely adhering the following water proof cement concrete essentials :-

• Using a high class Portland cement of guaranteed quality.
• Taking extreme care to adopt correct grading and proportioning of the sand, aggregate and cement.
• Using clean and non-porous aggregates.
• Mixing thoroughly to the right consistency using the right amount of water.
• Placing, tamping and curing carefully.
• Making use of suitable water-proofing compound.

The cement concrete to a certain extent may be make impermeable to the water by using hydrophobic cement. All the flat roofs in the modern age are generally construct of R.C.C. It becomes necessary to give some treatment of water-proofing to such roofs.

Following are the four methods adopt for water-proofing of R.C.C. flat roofs :

Finishing

For ordinary buildings of cheap construction, the finishing of roof surface is done at the time of laying cement concrete. The finishing of flat roof is carry out in cement mortar of proportion 1 : 4 i.e., one part of cement to four parts of sand by volume.

Bedding concrete and flooring

In this method, the surface of R.C.C. slab is keep rough and on this surface, a layer of concrete is lay. The concrete may be brickbats line concrete ( 1 : 2 : 4 ) on brickbats cement concrete ( 1 : 6 : 12 ). The thickness of the concrete layer is about 100 mm. The surface of the bedding concrete is provide by a suitable flooring such as tiles, terrazzo, Indian patent stone, etc. A convex joint is provide at the junction of parapet wall and roof.

Mastic asphalt and jute cloth

In this method, a layer of hot mastic asphalt is lay on the roof surface. The jute cloth is spread over this layer. Then one more layer of mastic asphalt is apply so that the jute cloth is sandwich between the two layers of mastic asphalt. The sand is then sprinkle over the entire surface of roof. For better grip, the lead sheets are insert at the junction of parapet wall and roof.

Use of water-proofing compounds

Some of the water-proofing compounds like pudlo, Impermo, etc., are available in the market and when such a compound is add to the cement during construction, it prevents seepage, leakage and damp cause by the capillary absorption of the moisture in cement, mortar and concrete. The quantity of water-proofing compound to be add is also very small, say 2% and thus a bag of cement will require only about 10 N of such compound.

Both is the arrangement of bricks in each layer so as to avoid the continuity of vertical joints in any two adjacent courses, both on the face and inside of a masonry structure. As well as In this, English Bond and Flemish bond mostly use in the construction of the walls.

English Bond and Flemish Bond are discuss are below :-

English Bond

• A queen closer must be place after the quoin header in the header course for breaking the continuity of vertical joints.
• Every alternate header in the header course should be centrally place over a stretcher.
• There should be no continuous vertical joints except at stop ends.
• The wall shall show same appearance on both faces when its thickness is equivalent to multiple of half bricks.
• Wall shall show stretcher on the face and header on the back or vice-versa if its thickness is equivalent to odd multiple of half bricks.
• The hearting of the thicker walls should consists of only headers.
• The joints in the header course should be made thinner than those in the stretcher course because twice the number of joints are provide in the heading course than in the stretching course.

Flemish Bond

• The stretchers and headers are lay alternately on the front and the back faces in the same course.
• The header in every course is in the center of a stretcher of the underlying or overlying courses.
• Queen closer are provide after every quoin headers in alternate courses to break the continuity of vertical joints in successive layers.
• Brick bats are use in walls having thickness equal to an odd number of half bricks.

Masonry is the art of construction of building units ( stones, bricks, precast concrete blocks ) which are bond together with mortar. In stone masonry, only stones are use which are obtain from rocks that may be igneous, sedimentary ( sandstone and limestone ) or metamorphic ( states and marbles ). For building purposes, mainly limestones and sandstones are use. Joints in Masonry Wall are provide in masonry are :

Joints in Masonry wall in building construction

Butt or Square joint

It is form by placing the square surface of one stone against that of another.

Rebate or Lap joint

It prevents movement between the arch voussoirs. It is adopt to secure a water-tight joint.

Tongue and Groove joint

Groove joint is not commonly use. It consists of a tongue or projection that works along one edge of a stone which fits into the corresponding groove in the adjacent stone. It in some cases, is adopt as an alternative to the rebate joint in flat arches and between the horizontal slabs forming the landings of stone staircases. Groove joint is also known as joogle joint and should not be confuse with mortar joggle joint.

Rusticate joint

Lower storeys of buildings, plinths and quoins are, in some cases, emphasis by the use of stone blocks which have their edges sunk below the general face. The word rusticate is use for such a type of masonry. It gives massive appearance to the structure.

Saddle joint

It is use in cornices and at such places where water is to be divert away from the joint. The saddle in this case is bevel backward from the front edge.

Joggle joint

The mortar joggle joint is use for the end joints of ashlar when the stone blocks have a small bed and for cornice stones.

Dowel Joint

Dowels are provide at the joints in those stones that are liable to become displace. These are either of slate or gun metal ( alloy of copper and tin ). The length is 2t or 3t where t is the thickness of end section is square, the size of which varies from 25 mm to 50 mm.

Cramp joint

In this, the joints are reinforce with either metal or slate cramps. Cramp is a piece of non-corrosive metal e.g. gunmetal, 22.5 cm to 45 cm long, 6 mm to 13 mm thick and 25 mm to 50 mm wide with ends that are turn down from 2 cm to 4 cm. It must be fit in tightly, after which it is grout and cover with either asphalt or cement.

Plug joint

It is not use now-a-day. in this, a hole is sunk of dovetail shape in the sides of adjacent stones and after placing the adjacent stone, a common space for the plug is form. It is fill with cement grout to form a cement plug. Molten lead was poured in early stages to form a lead plug and is not now use.

Bed joint or Tables joint

In this a joggle is form in the stone bed to prevent lateral movement of stones. The height of the projection varies from 3 cm to 4 cm and the width is 0.34 times the breadth of the stone.

Detail in Substructure and Superstructure in the construction of the building https://civilcrews.com/substructure-and-superstructure/