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The compressive strength of each prepared brick / block was analysed at the age of 3, 7, 14 and 28 days using a compressive test machine by applying a crushing load.   Brick / Blocks of thickness 75 mm or more when tested for compressive strength shall comply with the following The average crushing strength of 10 bricks shall be not less than 7.0 N/mm 2 The average crushing strength of 10 blocks shall be not less than 2.8 N/mm2                   (The coefficient of variation for the sample shall not exceed 20% )

Spacer bars are used to maintain covering between the same layer reinforcement bars of the reinforcement work. When two layers of the top or bottom reinforcement layer, spacer bars are applied between them. In this case, most of the time use a 25 mm diameter piece of reinforcement bar as a spacer bar.

In normal circumstances, the ambient temperature does not fall below 15 C, ordinary Portland cement is used, and adequate curing is done, following period is acceptable. Part of Structure The minimum period for removing formwork Sides of foundations, columns, beams and walls 24 hours   Under sides of slabs of up to 4.5 metre span 7 days   Under sides of slabs of above 4.5 metres span and under sides of beams and arches up to 6 metres span 14 days   Under sides of beams and arches over 6 metres   span and up to 9 metres span 21 days Cantilever slabs and beams   21 days Domes, shells and other structures of special nature As per written instructions of officer-in-charge. The officer-in-charge may however extend the periods noted where necessary by giving written instructions to the...

   Concrete mix ratio=  1:1:2  [Cement: Fine Aggregate: Coarse Aggregates] Unit Weight of Cement=  1440 kg/m³ Shrinkage Factor or Factor of Safety to Counter Shrinkage (Dry Volume / Wet Volume)=  54%,  (Range  54 to 57% ). For  1 m³ Wet Concrete : Total Volume of Dry Concrete=  1 m³ Dry Concrete + 54% = 1 m³ + 0.54 m³ =  1.54 m³ . Total Ratio = 1+1+2 = 4 Total Parts of Cement for 1m³  Concrete= (Ratio of Cement/Total Ratio of Concrete)x1.54 = (1/4)x1.54=  0.385 m³ So, Total volume of Cement= 0.28x Unit Weight of Cement= 0.385 m³x 1440 kg/m³=  554.4 kg Number of Cement Bags= 554.4/50=  11.088  Bags 

   Concrete mix ratio=  1:2:4  [Cement: Fine Aggregate: Coarse Aggregates] Unit Weight of Cement=  1440 kg/m³ . Shrinkage Factor or Factor of Safety to Counter Shrinkage (Dry Volume / Wet Volume)=  54%,  (Range  54 to 57% ). For  1 m³ Wet Concrete : Total Volume of Dry Concrete=  1 m³ Dry Concrete + 54% = 1 m³ + 0.54 m³ =  1.54 m³ . Total Ratio = 1+2+4 =  7 Total Parts of Cement for 1m³  Concrete= (Ratio of Cement/Total Ratio of Concrete)x1.54 = (1/7)x1.54=  0.22 m³ So, Total volume of Cement= 0.28x Unit Weight of Cement= 0.22 m³x 1440 kg/m³=  316.8 kg . Number of Cement Bags= 316.8/50=  6.336  Bags

   Concrete mix ratio=  1:1.5:3  [Cement: Fine Aggregate: Coarse Aggregates] Unit Weight of Cement=  1440 kg/m³ . Shrinkage Factor or Factor of Safety to Counter Shrinkage (Dry Volume / Wet Volume)=  54%,  (Range  54 to 57% ). For  1 m³ Wet Concrete : Total Volume of Dry Concrete=  1 m³ Dry Concrete + 54% = 1 m³ + 0.54 m³ =  1.54 m³ . Total Ratio = 1+1.5+3 =  5.5 Total Parts of Cement for 1m³  Concrete= (Ratio of Cement/Total Ratio of Concrete)x1.54 = (1/5.5)x1.54=  0.28m³ So, Total volume of Cement= 0.28x Unit Weight of Cement= 0.28 m³x 1440 kg/m³=  403.2 kg . Number of Cement Bags= 403.2/50=  8.064  Bags ≈  8 Bags

Normally speaking, we mention that  1 cube is 2.83  m³ 1  feet (ft )  = 0.3048 m 1 unit = 100 cubic feet (ft ³)  = 2.83 cubic metre ( m³) Normally we mention in Sri Lanka 1 Tractor load = 0.75 cube 1 Dipper (medium) load = 3 cube

Proportioning by volume The internal dimension of boxes for measuring aggregate shall be 400 mm × 350 mm × 250 mm (0.035  m³) the unit of measurement for cement shall be a bag of 50 kg.  (0.039  m³) Specified mix Equivalent grade Quantities per 50 kg bag of cement Fine aggregate Coarse aggregate Approx water content in litres 1:1:2 30 0.035 m³ (1 box) 0.07 m³  (2 box) 20 1:1.5:3 25 0.053 m³  (1.5 box) 0.105 m³  (3 box) 22.5 1:2:4 20 0.07 m³  (2 box) 0.14 m³  (4 box) 25 1:3:6 10 0.105 m³  (3 box) 0.210 m³  (6 box) 35 1:4:8   0.14 m³  (4 box) 0.28 m³  (8 box) 40

How many days of curing should be done for plastering Technically, though it depends on the specifications of the cement used, mortar achieves almost 60-70% of its strength within the first seven days. After 28 days, 95% strength has been achieved.  Therefore, in theory, curing may be done for 28 days. But this isn't practical. However, it's a good idea to make sure that the curing process is carried out properly for at least 7 days . How frequently curing should be done for plastering It is entirely dependent on the climatic conditions at the site. In hot and low-humidity climatic situations, it is recommended that a hessian cloth or something similar be used to cover the plaster surface to retain wetness and prevent water loss due to hydration. In theory, water should constantly be present on the surface to  promote strength development. I recommend curing at least three times  per day under usual conditions. Hessian cloth Curing for plastering

The mortar shall consist of Portland cement and sand, each complying with the respective standard and mixed in the proportions specified. Cement mortar must be used on the work within two hours of mixing. Mortar that has been unused for more than two hours will be rejected and removed from the work site.   work cement sand Mortar for masonry 1 5 up to 8 as may be specified Mortar for plastering 1 3 up to 4 as may be specified(3 for plastering of concrete surface) Mortar for pointing 1 3

 

The sand may be naturally occurring like river sand, pit sand or offshore sand. All sand types shall be hard, durable, clean and free from adherent coatings such as clay. It must be free of dangerous substances such as pyrites, salts, coal or other organic impurities, mica, shale, or similar laminated materials, as well as flaky or elongated particles in amounts or forms that could negatively impact the motor's strength, durability, or hardness.

The storage sheds must be weatherproof, with no flooding possibilities on the flooring. The width of stacks should not be more than 4 bags or 3 m. The bags must be put on wooden planks and joints at least 100 to 200 mm above the floor. The distance between the stacks and the outer walls should be maintained at 600 mm. cement bags should be stacked closely together to minimize air circulation. To minimize lumping under pressure, cement bags should not be stacked higher than ten bags. The stack must be thoroughly covered in thick polythene sheets, canvas sheets, or any other appropriate waterproof sheeting. When removing cement bags for use the 'first in, first out' rule should be followed. When storing cement for an extended period of time, identify each stack of cement bags with the date of receipt to determine the age of the cement.

The internal dimension of  the gauge box for measuring aggregate is 400 mm x 350 mm x 250 mm (which is 0.035 m³ and corresponds to the volume of a 50 kg bag of cement and dry volume sand is used for proportioning) The internal dimension of the gauge box for measuring cement is 400 mm x 350 mm x 290 mm (This volume is equal to a 50 kg bag of cement)         GAUGE BOX