Morth 1700 Structural Concrete
Morth 1700 Structural Concrete
Morth 1700 Structural Concrete
1700
Structural Concrete
Section 1700 Structural Concrete
1701 DESCRIPTION
The work shall consist of furnishing concrete mixes, transporting and placing structural
concrete including fixing formwork and temporary works etc. and incidental construction in
accordance with these Specifications and in conformity with the lines, grades and
dimensions, as shown on the drawings or as directed by the Engineer.
1702 MATERIALS
Table 1700-1
* For high strength concrete, design parameters may be obtained from the specialized
literature and experimental results.
2
Structural Concrete Section 1700
Table 1700-2 For Bridges With Prestressed Concrete or those with Individual
Span Lengths More than 60 M or those that are Built with
Innovative Design/Construction.
Table 1700-3 For Bridges other than those Mentioned in Table 1700-2 and for
Culverts and other Incidental Construction
3
Section 1700 Structural Concrete
The cement content shall be as low as possible but not less than the quantities specified
above. In no case shall it exceed 450 kg/cu.m of concrete.
1703.4 If the Contractor so elects, the Engineer may permit the use of higher grade
concrete than that specified on the drawing, in which event the higher grade concrete shall
meet the specifications applicable thereto without additional compensation.
Prior to the start of construction, the Contractor shall design the mix in case of “Design Mix
Concrete” or propose nominal mix in case of “Nominal Mix Concrete”, and submit to the
Engineer for approval, the proportions of materials, including admixtures to be used. Water-
reducing admixtures (including plasticisers or super-plasticisers) may be used at the
Contractor’s option, subject to the approval of the Engineer. Other types of admixtures
shall be prohibited, unless specifically permitted by the Engineer.
4
Structural Concrete Section 1700
The mix shall have the consistency which will allow proper placement and consolidation in
the required position. Every attempt shall be made to obtain uniform consistency. Slump
test shall be used to measure consistency of the concrete.
The optimum consistency for various types of structures shall be as indicated in Table
1700-4, or as directed by the Engineer. The slump of concrete shall be checked as per
IS:516.
Table 1700-4
However, notwithstanding the optimum consistency indicated under Sl. No. 1 to 3, the
situation at hand should be property assessed to arrive at desired workability with the
adjustment in admixture in each case where the concrete is to be transported through
transit mixer and placed using concrete pump. Under these circumstances, the optimum
consistency during placement for the item of mark from Sl. No. 1 to 3 can be considered
ranging from 50-100 mm this is, however, subject to satisfying the other essential criteria
of strength, durability, finishing in trial mix design stage and approval of the Engineer.
5
Section 1700 Structural Concrete
The target mean strength of specimen shall exceed the specified characteristic
compressive strength by at least the “current margin”.
i) The current margin for a concrete mix shall be determined by the Contractor
and shall be taken as 1.64 times the standard deviation of sample test results
taken from at least 40 separate batches of concrete of nominally similar
proportions produced at site by the same plant under similar supervision,
over a period exceeding 5 days, but not exceeding 6 months.
ii) Where there is insufficient data to satisfy the above, the current margin for
the initial design mix shall be taken as given in Table 1700-5 :
Table 1700-5
The initial current margin given in Table 1700-5 shall be used till sufficient data is available
to determine the current margin as per sub-clause (i) above.
The Contractor shall give notice to the Engineer to enable him to be present at the making
of trial mixes and preliminary testing of the cubes. Prior to commencement of trial mix
design, all materials forming constituents of proposed design mix should have been tested
and approval obtained in writing from the Engineer. Based on test results of material,
draft mix design calculation for all grades shall be prepared taking into account the
provisions in the Contract Technical Specifications, guidelines of IS:10262 IRC:SP:23,
IRC:21 and submitted to the Engineer for approval. Prior to commencement of concreting,
6
Structural Concrete Section 1700
trial mix design shall be performed for all grades of concrete, and trial mix which has been
found successful should be submitted by the Contractor and approval obtained. During
concreting with the approved Trial Mix Design, if source of any constituents is changed,
the mix design shall be revised and tested for satisfying the strength requirements.
The initial trial mixes shall generally be carried out in an established laboratory approved
by the Engineer. In exceptional cases, the Engineer may permit the initial trial mixes to be
prepared at the site laboratory of the Contractor, if a full fledged concrete laboratory has
been established well before the start of construction, to his entire satisfaction. In all cases
complete testing of materials forming the constituents of proposed Design Mix shall be
carried out prior to making trial mixes.
When the site laboratory is utilized for preparing initial mix design, the concreting plant
and means of transport employed to make the trial mixes shall be similar to that proposed
to be used in the works.
Test cubes shall be taken from trial mixes as follows. For each mix, set of six cubes shall
be made from each of three consecutive batches. Three cubes from each set of six shall
be tested at an age of 28 days and three at an earlier age approved by the Engineer. The
cubes shall be made, cured, stored, transported and tested in accordance with these
Specifications. The average strength of the nine cubes at 28 days shall exceed the specified
characteristic strength by the current margin minus 3.5 MPa
7
Section 1700 Structural Concrete
Requirements for nominal mix concrete unless otherwise specified, shall be as given in
Table 1700-6.
Concrete shall meet any other requirements as specified on the drawing or as directed by
the Engineer. Additional requirements shall also consist of the following overall limits of
deleterious substances in concrete :
8
Structural Concrete Section 1700
The Contractor shall submit the following information for the Engineer’s approval :
In proportioning concrete, the quantity of both cement and aggregate shall be determined
by weight. Where the weight of cement is determined by accepting the manufacturer’s
weight per bag, a reasonable number of bags shall be weighed separately to check the
net weight. Where cement is weiged from bulk stock at site and not by bag, it shall be
weighed separately from the aggregates. Water shall either be measured by volume in
calibrated tanks or weighed. All measuring equipment shall be maintained in a clean and
serviceable condition. Their accuracy shall be periodically checked.
It is most important to keep the specified water cement ratio constant and at its correct
value. To this end, moisture content in both fine and coarse aggregates shall be determined
as frequently as possible, frequency for a given job being determined by the Engineer
according to the weather conditions. The amount of mixing water shall then be adjusted to
compensate for variations in the moisture content. For the determination of moisture content
in the aggregates IS:2386 (part III) shall be referred to. Suitable adjustments shall also be
made in the weight of aggregates to allow for the variation in weight of aggregates due to
variation in their moisture content.
Materials for pumped concrete shall be batched consistently and uniformly. Maximum
size of aggregate shall not exceed one-third of the internal diameter of the pipe.
9
Section 1700 Structural Concrete
The grading of aggregates shall be continuous and shall have sufficient ultra fine materials
(material finer than 0.25 mm). Proportion of fine aggregates passing through 0.25 mm
shall be between 15 and 30 percent and that passing through 0.125 mm sieve shall not be
less than 5 percent of the total volume of aggregate. Admixtures to increase workability
can be added. When pumping long distances and in hot weather, set-retarding admixtures
can be used. Fluid mixes can be pumped satisfactorily after adding plasticisers and super
plaslicisers. Suitability of concrete shall be verified by trial mixes and by performing pumping
test.
1705 ADMIXTURES
As the selection of an appropriate concrete admixture is an integral part of the mix design,
the manufacturers shall recommend the use of any one of their products only after obtaining
complete knowledge of all the actual constituents of concrete as well as methodologies of
manufacture, transportation and compaction of concrete proposed to be used in the work.
Admixtures/additives conforming to IS:6925 and IS:9103 may be used subjected to
approval of the Engineer. However, admixers/additives generating Hydrogen or Nitrogen
and containing Chlorides, Nitrates, Sulphides, Sulphates and any other material likely to
adversely affect the steel or concrete shall not be permitted.
The size (maximum nominal) of coarse aggregates for concrete to be used in various
components shall be as given Table 1700-7.
Table 1700-7
Components Maximum Nominal Size of Coarse
Aggregate (mm)
i) RCC well curb 20
ii) RCC/PCC well steining 40
iii) Well cap or Pile Cap 40
Solid type piers and abutments
iv) RCC work in girder, slabs wearing 20
coat, kerb, approach slab, hollow
piers and abutments, peir/abutment
caps, piles
v) PSC Work 20
vi) Any other item As specified by the Engineer
10
Structural Concrete Section 1700
Maximum nominal size of aggregates shall also be restricted to the smaller of the following
values :
The proportions of the various individual size of aggregates shall be so adjusted that the
grading produces densest mix and the grading curve corresponds to the maximum nominal
size adopted for the concrete mix.
1707 EQUIPMENT
All measuring devices of the equipment shall be maintained in a clean and serviceable
condition. Its accuracy shall be checked over the range in use, when set up at each site
and thereafter periodically as directed by the Engineer.
The accuracy of the measuring devices shall fall within the following limits :
11
Section 1700 Structural Concrete
Concrete shall be mixed either in concrete mixer or in a batching and mixing plant, as per
these specifications. Hand mixing shall not be permitted. The mixer or the plant shall be
at an approved location considering the properties of the mixes and the transportation
arrangements available with the Contractor. The mixer or the plant shall be approved by
the Engineer.
Mixing shall be continued till materials are uniformly distributed and a uniform colour of the
entire mass is obtained, and each individual particle of the coarse aggregate shows
complete coating of mortar containing its proportionate amount of cement. In no case
shall mixing be done for less than 2 minutes. It shall be ensured that the mixers are not
loaded above their rated capacities and shall be operated at a speed recommended by
the Manufacturer.
Mixers which have been out of use of more than 30 minutes shall be thoroughly cleaned
before putting in a new batch. Unless otherwise agreed to by the Engineer, the first batch
of concrete from the mixer shall contain only two thirds of the normal quantity of coarse
aggregate. Mixing plant shall be thoroughly cleaned before changing from one type of
cement to another.
12
Structural Concrete Section 1700
Ready mix concrete will be proportioned and mixed off the project site and delivered to the
construction site in a freshly mixed and unhardened state, conforming to IS:4926 shall be
allowed with the approval of the Engineer.
The method of transporting and placing concrete shall be approved by the Engineer.
Concrete shall be transported and placed as near as practicable to its final position, so
that no contamination, segregation or loss of its constituent materials takes place. Concrete
shall not be freely dropped into place from a height exceeding 2 m.
The equipment for transporting and placing concrete shall have means for discharging
concrete without segregation.
When concrete is conveyed by chute, the plant shall be of such size and design as to
ensure practically continuous flow. Slope of the chute shall be so adjusted that the concrete
flows without excessive quantity of water and without any segregation of its ingredients.
The delivery end of the chute shall be as close as possible to the point of deposit. The
chute shall be thoroughly flushed with water before and after each working period and the
water used for this purpose shall be discharged outside the formwork.
Pipelines from the pump to the placing area shall be laid with minimum bends. For large
quantity placements, standby pumps shall be available. Suitable air release valves, shutoff
valves etc shall be provided as per the site requirements. The pumping of concrete shall
precede pumping of priming mix i.e. rich mix of creamy consistency, to lubricate the concrete
pump and pipelines. Continuous pumping shall be done to the extent possible. After
concreting, the pipelines and accessories shall be cleaned immediately. A plug spung
ball shall be inserted at the end near the pump and shall be forced through the pipeline by
either water or by air pressure. The pipes for pumping shall not be made of material
which have adverse effect on concrete. Aluminum alloy pipelines shall not be used.
13
Section 1700 Structural Concrete
All formwork and reinforcement contained in it shall be cleaned and made free from standing
water, dust, snow or ice immediately before placing of concrete.
No concrete shall be placed in any part of the structure until the approval of the Engineer
has been obtained.
If concreting is not started within 24 hours of the approval being given, it shall have to be
obtained again from the Engineer. Concreting then shall proceed continuously over the
area between the construction joints. Fresh concrete shall not be placed against concrete
which has been in position for more than 30 minutes unless a proper construction joint is
formed.
Concrete when deposited shall have a temperature of not less than 5oC, and not more
than 40oC. It shall be compacted in its final position within 30 minutes of its discharge
from the mixer, unless carried in properly designed agitator, operating continuously, when
this time shall be within 1 hour of the addition of cement to the mix and within 30 minutes of
its discharge from the agitator. It may be necessary to add retarding admixtures to concrete
if trials show that the periods indicated above are unacceptable. In all such matters, the
Engineer’s decision shall be final.
Concrete shall be thoroughly compacted by vibration or other means during placing and
worked around the reinforcement, tendons or duct formers, embedded fixtures and into
corners of the formwork to produce a dense homogeneous void-free mass having the
required surface finish. When vibrators are used, vibration shall be done continuously
during the lacing of each bath of concrete until the expulsion of air has practically ceased
and in a manner that does not promote segregation. Over vibration shall be avoided to
minimize the risk of forming a weak surface layer. When external vibrators are used, the
design of formwork and disposition of vibrator shall be such as to ensure efficient
compaction and to avoid surface blemishes. Vibrations shall not be applied through
reinforcement and where vibrators of immersion type are used, contact with reinforcement
and all inserts like ducts etc., shall be avoided. The internal vibrators shall be inserted in
an orderly manner and the distance between insertions should be about one and half
times the radius of the area visibly affected by vibration. Additional vibrators in serviceable
condition shall be kept at site so that they can be used in the event of breakdown.
Mechanical vibrators used shall comply with IS:2502, IS:2506, IS:2514 and IS:4656.
14
Structural Concrete Section 1700
Construction joints shall be avoided as far as possible and in no case the locations of such
joints shall be changed or increased from those shown on the drawings, except with the
express approval of the Engineer. The joints shall be provided in a direction perpendicular
to the member axis.
Location, preparation of surface and concreting of construction joints shall conform to the
additional specifications given in Appendix 1700/I.
When it is necessary to deposit concrete under water, the methods, equipment, materials
and proportions of mix to be used shall be got approved from the Engineer before any
work is started. Concrete shall contain 10 percent more cement than that required for the
same mix placed in the dry to compensate the loss due to wash.
Concrete shall not be placed in water having a temperature below 5oC. The temperature
of the concrete, when deposited, shall not be less than 16oC, nor more than 40oC.
Coffer dams or forms shall be sufficiently tight to ensure still water conditions, if practicable,
and in any case to reduce the flow of water to less than 3 m per minute through the space
into which concrete is to be deposited. Coffer dams or forms in still water shall be sufficiently
tight to prevent loss of mortar through the joints in the walls. Pumping shall not be done
while concrete is being placed, or until 24 hours thereafter. To minimise the formation of
laitance, care shall be exercised not to disturb the concrete as far as possible while it is
being deposited.
All under water concreting shall be carried out by tremie method only, using tremie of
appropriate diameter. The number and spacing of the tremies should be worked out to
ensure proper concreting. The tremie concreting when started should continue without
interruption for the full height of the member being concreted. The concrete production
and placement equipment should be sufficient to enable the underwater concrete to be
completed uninterrupted within the stipulated time. Necessary stand-by equipment should
be available for emergency situation.
The top section of the tremie shall have a hopper large enough to hold one full batch of the
mix or the entire contents of the transporting bucket as the case may be. The tremie pipe
shall not be less than 200 mm in diameter and shall be large enough to allow a free flow of
concrete and strong enough to withstand the external pressure of the water in which it is
suspended, even if a partial vacuum develops inside the pipe. Preferably, flanged steel
pipe of adequate strength for the job shall be used. A separate lifting device shall be
provided for each tremie pipe with its hopper at the upper end. Unless the lower end of the
15
Section 1700 Structural Concrete
pipe is equipped with an approved automatic check valve, the upper end of the pipe shall
be plugged with a wadding of gunny sacking or other approved material before delivering
the concrete to the tremie pipe through the hopper so that when the concrete is forced
down from the hopper to the pipe, it will force the plug (and along with it any water in the
pipe) down the pipe and out of the bottom end, thus establishing a continuous stream of
concrete. It will be necessary to raise slowly the tremie in order to allow a uniform flow of
concrete, but it shall not be emptied so that water is not allowed to enter above the concrete
in the pipe. At all times after placing of concrete is started and until all the required quantity
has been placed, the lower end of the tremie pipe shall be kept below the surface of the
plastic concrete. This will cause the concrete to build up from below instead of flowing out
over the surface and thus avoid formation of layers of laitance. If the charge in the tremie
is lost while depositing, the tremie shall be raised above the concrete surface and unless
sealed by a check valve, is shall be replugged at the top end, as at the beginning, before
refilling for depositing further concrete.
When depositing concrete in hot weather, precautions shall be taken so that the temperature
of wet concrete does not exceed 40oC while placing. This shall be achieved by stacking
aggregate under the shade and keeping them moist, using cold water, reducing the time
between mixing and placing to the minimum, cooling formwork by sprinkling water, starting
curing before concrete dries out and restricting concreting as far as possible to early
mornings and later evenings. When ice is used to cool mixing water, it will be considered
a part of the water in design mix. Under no circumstances shall the mixing operation be
considered complete until all ice in the mixing drum has melted.
16
Structural Concrete Section 1700
The Contractor will be required to state his methodology for the Engineer’s approval when
temperatures of concrete are likely to exceed 40oC during the work.
Concreting operations shall not commence until adequate arrangements for concrete curing
have been made by the Contractor.
Curing and protection of concrete shall start immediately after compaction of the concrete
to protect it from :
Sea water shall not be used for curing. Sea water shall not come into contact with concrete
members unless it has attained adequate strength.
The concrete should be kept constantly wet for a minimum period of 14 (fourteen) days
after concreting except for rapid hardening cement concrete where it can be reduced to 5
(five) days. Water should be applied on surfaces after the final set. Curing through watering
shall not be done on green concrete. On formed surfaces, curing shall start immediately
after the forms are stripped. The concrete shall be kept constantly wet by ponding or
covered with a layer of sacking, canvas, hessian or a similar absorbent material.
After placing and during the first stages of hardening concrete shall be protected from
harmful effects of sunrays, drying winds, cold, running water, shocks, vibrations, traffic
including construction traffic etc.
17
Section 1700 Structural Concrete
Where steam curing is adopted, it shall be ensured that it is done in suitable enclosure to
contain the live steam in order to minimize moisture and heat losses. The initial application
of the steam shall be after about four hours of placement of concrete to allow the initial set
of the concrete to take place.
Where retarders are used, the waiting period before application of the steam shall be
increased to about six hours.
The steam shall be at 100 percent relative humidity to prevent loss of moisture and to
provide excess moisture for proper hydration of the cement. The application of steam
shall not be directly on the concrete and the ambient air temperature shall increase at a
rate not exceeding 5oC per hour until a maximum temperature of 60oC to 70oC is reached.
The maximum temperatures shall be maintained until the concrete has reached the desired
strength.
When steam curing is discontinued, the ambient air temperature shall not drop at a rate
exceeding 5oC per hour until a temperature of about 10oC above the temperature of the
air to which the concrete will be exposed, has been reached.
The concrete shall not be exposed to temperatures below freezing for at least six days
after curing.
Curing compounds shall be continuously agitated during use. All concrete cured by this
method shall receive two applications of the curing compound. The first coat shall be
applied immediately after acceptance of concrete finish. If the surface is dry, the concrete
shall be saturated with water and curing compound applied as soon as the surface film of
water disappears. The second application shall be made after the first application has
set. Placement in more than two coats may be required to prevent streaking.
1714 FINISHING
Immediately after the removal of forms, exposed bars or bolts, if any, shall be cut inside the
concrete member to a depth of at least 50 mm below the surface of the concrete and the
18
Structural Concrete Section 1700
resulting holes filled by the removal of form ties and all other holes and depressions,
honeycomb spots, broken edges or corners, and other defects, shall be thoroughly cleaned,
saturated with water and carefully pointed and rendered true with mortar of cement and
fine aggregate mixed in the proportions used in the grade of concrete that is being finished
and of as dry as consistency as is possible to use. Considerable pressure shall be applied
in filling and pointing to ensure thorough filling in all voids. Surfaces which have been
pointed shall be kept moist for a period of twenty four hours. Special pre-packaged
proprietary mortars shall be used where appropriate or where specified in the drawing.
All construction and expansion joints in the completed work shall be left carefully tooled
and free from any mortar and concrete. Expansion joint filler shall be left exposed for its full
length with clean and true edges.
Immediately on removal of forms, the concrete work shall be examined by the Engineer
before any defects are made good.
1715 TOLERANCES
1716.1 Concrete shall conform to the surface finish and tolerance as prescribed in
these Specifications for respective components.
1716.2 Random sampling and lot by lot of acceptance inspection shall be made for
the 28 days cube strength of concrete.
1716.2.1 Concrete under acceptance shall be notionally divided into lots for the purpose
of sampling, before commencement of work. The delimitation of lots shall be determined
by the following :
19
Section 1700 Structural Concrete
ii) At least one cube forming an item of the sample representing the lot
shall be taken from concrete of the same grade and mix proportions
cast on any day.
iii) Different grades of mixes of concrete shall be divided into separate
lots.
iv) Concrete of a lot shall be used in the same identifiable component of
the bridge.
1716.2.3 Test specimen and sample strength : Three test specimens shall be
made from each sample for testing at 28 days. Additional cubes may be required for
various purposes such as to determine the strength of concrete at 7 days or for any other
purpose.
The test strength of the sample shall be the average of the strength of 3 cubes. The individual
variation should not be more than + 15 percent of the average. If variation is more, the test
results of the sample are invalid.
Table 1700-8
Quantity of Concrete in work, m3 No. of samples
1–5 1
6 – 15 2
16 – 30 3
31 – 50 4
51 and above 4 plus one additional sample for each
additional 50 m3 or part thereof
20
Structural Concrete Section 1700
When both the following conditions are met, the concrete complies with the specified
compressive strength:
When the concrete does not satisfy both the above conditions, cores shall be extracted
from the representative hardened concrete. Area for compression test in accordance with
the method described in IS:1199 and tested whether the concrete satisfies the compressive
strength.
The quantity of concrete represented by the test results include the batches from which the
first and last samples were taken, together with all intervening batches.
The total chloride and sulphuric anhydride (SO3) content of all the constituents of concrete
as a percentage of mass of cement in the mix shall not exceed the values given in this
section of the Specifications.
Where minimum density of fresh concrete is specified, the mean of any four consecutive
samples shall not be less than the specified value and any individual sample result shall
not be less than 97.5 percent of the specified value.
Where minimum density of hardened concrete is specified, the mean of any four consecutive
samples shall not be less than the specified value and any individual sample result shall
not be less than 97.5 percent of the specified value.
21
Section 1700 Structural Concrete
The concrete should pass the following test if it is properly compacted and is not considered
permeable :
1718 RATE
The contract unit rate for structural concrete shall cover costs of all materials, labour, tools,
plant and equipment required for mixing, transporting and placing in position, vibrating
and compacting, finishing and curing as per this Section or as directed by the Engineer,
including all incidental expenses, sampling and testing, quality assurance and supervision.
Unless mentioned separately as an item in the Contract, the contract unit rate for concrete
shall also include the cost of providing, fixing and removing formwork required for concrete
work as per Section 1500.
22
Structural Concrete Section 1700
23