CONCRETE WORK FOR BRIDGES AND CULVERTS
GENERAL
This section includes the quality control requirements for imparting prestress to structural members by stressing of wires/strands/tendons/cables with jacks of required capacity and holding them between approximately designed anchorages fixed internally or externally to the members.
MATERIALS:
CEMENT
The quality control requirements such as cement identification, storage, sampling and testing of cement shall be as per, IRC: 112 and MoRTH Specifications for Road and Bridge works.
AGGREGATE
Components |
Maximum nominal size of coarse aggregate (mm) |
RCC well curb |
20 |
RCC/PCC well steining |
40 |
Well cap/pile cap |
20 |
Solid type piers and abutments |
40 |
RCC work in girder, slabs wearing coat, kerb, approach slabs, hollow piers and abutments, pier/abutment caps, piles |
20 |
PSC work |
20 |
WATER
The quality control requirements, sampling and testing of water used for mixing of concrete and curing shall be as per, IRC: 112 and MoRTH Specifications for Road and Bridge works.
ADMIXTURES
STEEL REINFORCEMENT
REQUIREMENTS FOR CONCRETE
1. GRADE OF CEMENT
Table: Types and grades of concrete
Types of concrete/Grade designation |
Characteristic compressive strength in 28 days (MPa) |
||
Ordinary concrete |
Standard concrete |
High performance concrete |
|
M15 M20 |
M15 M20 M25 M30 M35 M40 M45 M50 |
- - - M30 M35 M40 M45 M50 M55 M60 M65 M70 M75 M80 M85 M90 |
15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 |
The minimum grades of concrete and corresponding minimum cement content and maximum water/cement ratios for different exposure conditions shall be as (Ref: Table 14.2 of IRC: 112).
Requirement of concrete for different exposure conditions using 20 mm aggregate
Exposure condition |
Maximum water- cement ratio |
Minimum cement content, kg/m3 |
Minimum grade of concrete |
Moderate |
0.45 |
340 |
M25 |
Severe |
0.45 |
360 |
M30 |
Very severe |
0.40 |
380 |
M40 |
Extreme |
0.35 |
400 |
M45 |
Table : Requirement of concrete exposed to sulphate attack
Class |
Concentration of Sulphates as SO3 |
Type of cement |
Min. cement content kg/m3 |
Min. water cement ratio |
Min. grade of concrete |
||
In soils |
In ground water, gm/l |
||||||
Total SO3 % |
SO3 in 2:1, Water: Soil extract, gm/l |
||||||
1 |
Traces |
<1 |
<0.3 |
OPC, PPC or PSC |
280 |
0.5 |
M25 |
2 |
2.0 to 0.5 |
1.0 to 1.9 |
0.3 to 1.2 |
OPC,PPC or PSC, SRPC |
330 |
0.5 |
M25 |
3 |
0.5 to 1.0 |
1.9 to 3.1 |
1.2 to 2.5 |
SRPC, PPC |
330 |
0.5 |
M25 |
PSC |
350 |
0.45 |
M30 |
||||
4 |
1.0 to 2.0 |
3.1 to 5.0 |
2.5 to 5 |
SRPC |
370 |
0.45 |
M35 |
5 |
>2.0 |
>5.0 |
>5.0 |
SRPC with protective coating |
400 |
0.4 |
M40 |
NOTE: OPC-Ordinary Portland cement, PPC-Portland Pozzolana cement, PSC-Portland Slag cement, SRPC-Sulphate Resistant Portland cement.
For concrete made with PPC, PSC or mineral admixtures, the setting time and rate of gain of strength are different from those for concrete made with OPC alone.
MIX DESIGN
Table : Current margin for initial design mix
Concrete Grade |
Current Margin (MPa) |
Target mean strength (MPa) |
M 15 |
10 |
25 |
M20 |
10 |
30 |
M25 |
11 |
36 |
M30 |
12 |
42 |
M35 |
12 |
47 |
M40 |
12 |
52 |
M45 |
13 |
58 |
M50 |
13 |
63 |
M55 |
14 |
69 |
M60 |
14 |
74 |
M65 |
15 |
80 |
M70 |
15 |
85 |
M75 |
15 |
90 |
M80 |
15 |
95 |
M85 |
16 |
101 |
M90 |
16 |
106 |
Concrete grade |
Total quantity of dry aggregates by mass per 50 kg of cement to be taken as the sum of individual masses of fine and coarse aggregates (kg) |
Proportion of fine to coarse aggregate (By mass) |
Maximum quantity of water for 50 kg of cement (Litres) |
|
PCC |
RCC |
|||
M15 |
350 |
|
25 |
- |
M20 |
250 |
25 |
22 |
Table : Requirements of Consistency
Sl. No. |
Type |
Slump (mm) at the time of placing of concrete |
1 |
Structures with exposed inclined surface requiring low slump concrete to allow compaction. |
25 |
2 |
Plain cement concrete. |
25 |
3 |
RCC structure with widely spaced reinforcements like solid columns, piers, abutments, footings, well steining. |
40-50 |
4 |
RCC structure with fair degree of congestion of reinforcement such as pier and abutment caps, box culverts, well curb, well cap, walls with thickness greater than 300 mm. |
50-75 |
5 |
RCC and PSC structure with highly congested reinforcements such as deck slab girders, box girders, walls with thickness less than 300 mm. |
75-125 |
6 |
Under water concreting through tremie for bottom plug, cast in situ piling etc. |
150-200 |
NOTE: Where the concrete is to be transported through transit mixer and placed using concrete pump, the optimum consistency during placement for the items of work of Sl. Nos. 1 to 3 can be considered ranging from 75 mm to 150 mm, subject to satisfying the other essential criteria of strength, durability etc., and approval of the Engineer.
DESIGN OF FORMWORK
Sl. No. |
Component of structure |
Period |
1 |
Walls, piers, abutments, columns and vertical faces of structural members |
12 to 48 hours as may be decided by the Engineer. |
2 |
Soffits of slabs (with props left under) |
3 days |
3 |
Props left under slabs |
14 days |
4 |
Soffits of girders (with props left under) |
7 days |
5 |
Props (left under girders) |
21 days |
READY MIXED CONCRETE
ACCEPTANCE CRITERIA
Table : Acceptance criteria for concrete
Test |
Code |
Criteria |
Requirement |
Compressive strength |
IRC:112 |
Mean strength from any group of four consecutive non- overlapping samples |
Shall exceed specified characteristic compressive strength +3 MPa. |
Strength of any sample |
Shall not be less than specified characteristic compressive strength -3 MPa. |
||
Flexural strength |
IRC:112 |
Mean strength from any group of four consecutive non- overlapping samples |
Shall exceed specified characteristic flexural strength +0.3 MPa. |
Strength of any sample |
Shall not be less than specified characteristic flexural strength -0.3 MPa. |
||
Density (Fresh & hardened) |
IRC:112 |
Mean strength from any group of four consecutive non- overlapping samples |
Shall not be less 97.5% of specified value. |
Chloride content |
IS:14959 |
- |
Shall not exceed, for: i) PSC : 0.10% ii) RCC (Exposure: -severe to extreme) : 0.20% iii) RCC (Moderate) : 0.30% |
Durability (Rapid Chloride Ion Permeability test) |
ASTM C1202 |
- |
Shall not exceed, for: i) Extreme : 800 Coulombs ii) Very severe: 1200 Coulombs iii) Severe : 1500 Coulombs |
If the concrete is deemed not to comply as per the above criteria, the structural adequacy of the bridge elements affected shall be investigated and any consequential action as needed shall be taken.
RELATED CODES :
1.IRC:87-Guidelines for the design and erection of false work for road bridges.
2.IRC:112-Code of practice for concrete road bridges.
3.IS:516-Methods of tests for strength of concrete.
4.IS:1199-Methods of sampling and analysis of concrete.
5.IS:2751-Code of practice for welding of mild steel plain and deformed bars for reinforced concrete construction.
6.IS:4926-Code of practice for ready-mixed concrete.
7.IS:9013-Method of making, curing and determining compressive strength of accelerated cured concrete test specimen.
8.IS:9417-Recommendations for welding cold worked bars for reinforced concrete construction.
9.IS:10262-Guidelines for concrete mix design proportioning.
10.IS:12594-Hot-dip zinc coating on structural steel bars for concrete reinforcement.
11.IS:13620-Fusion bonded epoxy coated reinforcing.
12.IS:14959-Determination of water soluble and acid soluble chlorides in mortar and concrete - method of test.
(Part 1)-Fresh mortar and concrete.
13.ASTMC1202-Standard test method for electrical indication of concrete’s ability to resist chloride ion penetration.
14.MoRTH-Specification for Road and Bridge works (5th revision).
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