BT ROADS
Grade III ( CC roads) and Grade V(BT roads) will be used
GSB grade –III Material Proportion for mixing( approximate)
12 mm – 60%, 6mm & dust – 40%
Loose thickness - 128 mm (100 mm compacted)
Wet mix macadam Material Proportion for mixing( approximate)
40mm -25% , 20mm – 15% , 12 mm – 20%, 6mm & dust – 40%
Loose thickness - 132 mm (100 mm compacted)
Bituminous macadam Grading II (thickness 50mm to 75mm)
Material Proportion for mixing( approximate)
20mm – 20% , 12 mm – 40%, 6mm & dust – 40%
Loose thickness - 142 mm (100 mm compacted)
Dense Bituminous macadam (DBM)Grading II (thickness 50mm to 75mm)
Material Proportion for mixing( approximate)
20mm – 20% , 12 mm – 30%, 6mm & dust – 50%
Loose thickness - 147 mm (100 mm compacted)
Material Proportion for mixing( approximate)
12 mm – 30%, 6mm 25 %,Dust – 45%
Loose thickness - 149 mm (100 mm compacted)
Semi- Dense Bituminous Concrete
Material Proportion for mixing( approximate)
12 mm – 30%, 6mm 40 %,Dust – 30%
Loose thickness - 148 mm (100 mm compacted)
Gradation for SDBC
Sieve Layer Layer
S.No Designation Thickness Thickness
in mm 40 mm 25 mm
1 2 7 7
1 19.00 100
2 13.20 90-100 100
3 9.50 70-90 90-100
4 4.75 35-51 35-51
5 2.36 24-39 24-39
6 1.18 15-30 15-30
7 0.300 9-19 9-19
8 0.075 3-8 3-8
Bitumen 4.5% 5.0%
Fine aggregates(sand): Aggregates Passed on 4.75mm sieve is called fine aggregates
Fine aggregate conforming to Grading Zone IV shall not be used in
reinforced cement concrete
Fineness modulus(FM) : Fine sand - 2.20 to 2.60, medium sand: 2.60 to 2.90
Coarse sand -2.90 to 3.20.FM more than 3.20 not suitable for concrete
GRADES of concrete
Nominal mixes concrete : M 5 to M 20 ( M denotes the strength of concrete)
M5 - 1:5:10
M 7.5 – 1:4:8
M 10 – 1:3:6
M 15 – 1:2:4
M 20 – 1:1.5:3
Designed Concrete mixes : M-25 to M- 50
Water to cement ratio (W/C) ratio is the ratio of water (w) to cement (c) used in a concrete
mix.
Generally varies from 0.40 and 0.60 depends upon the grade of concrete mix..
Formula to Calculate the water-cement ratio
To calculate the water-cement ratio, divide the weight of water by the weight of cement.
For ratio of 0.50. : Water / 50 kg = 0.50, . Water = 0.50 x 50 = 25 liters.
Similarly, for a ratio of 0.40: Water = 0.40 x 50. Water = 20 liters.
The use of excess water in concrete not only produce low strength but increases
shrinkage and decrease durability and density.
Lesser the water cement ratio more will be the strength
Slump test is used to test the workability of concrete
Procedure:
Concrete is filled in three layers and each layer is temped 25 times
with 16mm dia steel rod.
Mould is completely filled with concrete and top surface is to be finished neatly.
Immediately after filling is completed top surface to be leveled
The cone is slowly and carefully lifted vertically
The decrease in height of the slumped concrete is called slump.
Requirement of Slump: CC pavements – 0 -25 mm( Not more than 40mm)
Foundations and Light reinforced structures – 10 – 40 mm
Normal reinforced structures – 50 – 90 mm
Material calculations
One bag of cement (50 Kgs) equal to 1.226 cft (0.0347 cum)
1 cum = 35.3147 cft 1 Cum of cement = 1440 kgs i.e. 28.80 bags
Material shall be measured using with gauge box equal to one bag of cement
(size 30 cm x30 cm x 40 cm) in volumetric mixes
Material required for one cum of wet concrete
Grade of Aggregate Sand in Cement Cement in
concrete in cum (cft) Cum(cft) in MT bags
M 7.5 (1:4:8) 0.90 (32 ) 0.45 (16) 0.162 3.24 bags
M10 (1:3:6) 0.90 (32) 0.45 (16) 0.230 4.6 bags
M 15 (1:2:4) 0.90 (32) 0.45 (16) 0.275 5.50 bags
M 20 0.90 (32) 0.45 (16) 0.341 6.82 bags
(1:1.5:3)
M 30 0.90 (32) 0.45 (16) 0.406 8.13 bags
General Observations
Min. curing period of concrete – 7days
Cover to reinforcement – Footings- 50mm, Columns – 40mm,Slab-20mm,Beam-25mm
Lapping of reinforcement – 40 d in tension, 50d in compression. ( Dia of reinforcement)
Hook length for stirrups – 9d ( Dia of reinforcement)
Cement should be used within three months of manufacture
Removal form work : Walls, columns and vertical sides of beams – 16 to 24 hours.
Slabs spanning less than 4.50m -7days,Span more than4.50m -14 days
Core tests; Cores shall be procured as per part -4 of IS:1199 and Tesing as per IS:516
Min. three cores to be taken for testing. Average strength of three cores
shall not be less than 85% and strength of individual core shall not be less
than 75% of required strength.
REBOUND HAMMER TEST as per (IS:13311(Part 2): Min. nine reading to be taken
