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Precautions in concreting_ CD Structures

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Precautions in concreting_ CD Structures Powered By Docstoc
					    PRECAUTION IN
CONCRETING, TESTING OF
CONCRETE AND DESIGN OF
    CD STRUCTURES
                   By

    Dr. P. Srinivasa Rao
           Associate Professor
     Department of Civil Engineering
     J N T U College of Engineering
         Hyderabad – 500 072.
             INTRODUCTION
In order to adopt uniform standards and to assist
the field engineers in providing cross drainage
works, type designs and estimates of culverts of
probable spans and heights for rural roads.
    Culverts
    Small Bridges
    Minor Bridges

           Geometric Standards
   Formation width for rural roads (ODR) and
    Village roads (VR) is 7.5 m.

    Culvert                           L < 6 m.
    Small Bridge (on rural road) L = 6 m to 30 m
    Minor Bridge                      L = 60 m.
        Overall width of CD works
  Type of     For 7.5 m Roadway        For 6.0 m Roadway
   Cross             width                    width
 Drainage
  Works       Overall    Carriageway   Overall    Carriageway
              width, m        m        width, m        m

 Culverts       7.5          6.6         6.0          5.5


 Small and      6.4          5.5         6.0          5.5
  Minor
  Bridges

Submersible     7.5          6.6         6.0          5.5
  Bridges
                Design Loading
IRC class A Loading with impact:

Wearing Coat :

   Road is with Bituminous surface :   20 mm

   For submersible structures Arch :   75 mm
    Vented causeways
Name Plates and Numbering of Culverts

   0.6 m High Guard Stone
   Number of Culvert
   Description of Type
   Direction of Flow
   Pipe Culverts:
   Two Guard Pillars of 400 x 400 x 600 mm
Culverts are designated in the form of fraction
Numerator denotes the no. of kilometer
Denominator denotes kilometer wise serial no.
of structure
11/3 3rd culvert between 11th and 12th km.
IRC 7 “Recommended practice for no. of
bridges and culverts”.
Size of letter < 100 mm high.
IRC 30 “Standards letters and numerals of
different heights for use on highway signs”.
 Design of Culverts (Hydraulic Aspects)
Waterway area      A = Q/10.9
                   Q = Catchment area in hectares

Hydraulic Data:

a)   Catchment area of the stream in hectares
b)   Cross-section of the stream at proposed crossing
     along with L-section of road up to 200 m
c)   L-section of nalla about 200 m upstream and 200 m
     down stream
d)   High flood level (HFL)
e)   Road top level (RTL)
      Minimum span and clearance

Clear waterway of slab culvert is minimum 1.5
m and dia of pipe incase of pipe culvert is 1000
mm (900 mm internal dia)

         Span, m        Vertical Clearance,
                                mm
         1.0 and 1.5            150
         2.0 and 2.5            300
         3.0 and 4.0            450
         5.0 and 6.0            600
       Types of Culvert

RCC Pipe Culvert
RCC Slab on Masonry or Plain Concrete
Abutment
RCC Box Types Culvert
Arch Culvert
Cut Stone Slab Culvert
Stone Masonry Scupper
Vented Causeway
Submersible Bridge
                 Height of Culvert
 Minimum Height of the formation level of the road from
 the bed level (pipe culvert)

   Diameter ( Pipes), mm            Height of Formation, m
For 1000 mm (900 mm internal dia)            1.75
            For 1200                         2.15


 Minimum height in slab culvert will be 1.775 m.
 Height of abutment                     1.5 m.
 Thickness of RCC deck slabs            0.2 m.
 Wearing coat                           0.075 m.
               Pipe Culvert
Catchment Area (Hectares)    Diameter of Pipe (mm)

        Up to 10                 1000 single row

        10 to 20                 1200 single row

        20 to 50            1000 or 1200 (2 to 3 rows)

        50 to 60              1000 or 1200 (4 rows)
Diameter of Pipe:
  From inspection and maintenance point of view, a
  min. of 900 mm (internal ) diameter is recommended.
  600 mm and 750 mm may also be used in exceptional
  situations.
  300 mm and 450 mm dia, used for irrigation and
  agriculture are to be considered as mere buried conduits
  and not as culverts.
  The height of embankment on account of geometric
  consideration of the road is more than 5 m but the
  catchment area of the stream is less than 40 hectares.
  It would be economical to provide pipe culvert with 2
  rows or 4 rows of pipes.
Advantages of Pipe Culvert:

   Speed of construction

   Good Quality of Factory produced pipes

   Pipe culvert can be constructed in 15 days.

   The only time consuming and costly item is
    stone masonry headwall.
Design Aspects:
   The pipes shall be conform to IS 458 – 1989
   Laying of pipes IS 783 – 1985

Structural Design of Pipe Culvert Requires:

   Calculation of probable maximum load on the pipe
   Inherent strength of pipe
   Selection of bedding for the pipe
   Load factor of a pipe depends on different
   conditions of bedding as well as laying of pipes.
Type A:
    Concrete cradle bedding for pipes of 1000 mm dia and
    above and those with fills higher than 4 m.
    Minimum compressive strength 20 Mpa

Type B:
   Height of fill between 0.6 and 4 m.
    It consist of a continuous layer f compacted sand or
     moorum with minimum thickness of 75 mm below the
     pipe.
    The fill material shall be free from clay lumps retained on
     75 µ sieve.
Jointing of Pipe:

   Caulking of space shall be between 13 to 20 mm
    according to the dia of the pipe.

   The collar shall be properly placed over the joint of
      the pipe to cover the joint evenly.

   Caulking material shall be a wet mix of cement and
    sand in the ratio of 1 : 2.
              RCC Slab Culvert

Catchment area and span requirement:

For catchment area more than 60 hectares, RCC slab culvert
offer an economical proposal.
      Catchment Area in         Clear Span of Culvert, m
          Hectares
           Up to 15                       1.5
            16 to 25                      2.0
            26 to 50                      3.0
            51 to 75                      4.0
           76 to 100                      5.0
          101 to 125                      6.0
   126 to 200 (deep channels)             6.0
: Minimum Depth From Lowest Bed Level
Minimum depth from lowest bed level to soffit is 1.5
m.

Detailing:
    In case of simply supported slabs
    Crank alternate bars at 1/7 span for 4 m span and
      above.
    For 3 m span one bar in every 4 bars is to be bent.
    Alternatively cranking may be avoided.
Foundation Concrete:

   For masonry abutment and Return        M10 or M15

   If the foundation level is below water table 10 % excess
    cement should be added.

   The thickness of footing below abutment should be
    minimum 200 mm.
In case of pipe culvert:
   It is not necessary to provide concrete bedding below the
   entire length and width of pipe.
   A moorum cushion consolidated to 200 mm thickness is
   adequate below pipe.
   300 mm wide M15 concrete bedding is necessary at all
   the joints of pipes.
   The guide lines gives in IS 783-1985 should be followed.
Return wall or Wing wall:

   Length of return and splayed wing wall are found to be
    better than straight returns.

   Straight returns are easy for construction.

   Layout and construction of wing wall is also difficult.

   Therefore it is proposed to provide straight Return
    walls for culverts.
                   Length of Return
Normally the length of return should be 1.5 times height of abutment
above lowest bed level.

 Height of formation at               Length of Return, m
abutment above bed level,
           m
             2.5                               3.75

         2.5 to 3.0                        3.75 to 4.5

             3.5                               5.25

              4                                  6
Expansion Joints:

 Expansion gap may not be provided up to 3 m span.


 The top abutment cap and the face of dirt wall are
    however coated with a layer of bitumen.
For Span 3 to 6 M:
 Pre-moulded bituminous sheet such as shalitex board of
    12 mm thickness may be provided.
   In the parapet wall it is desirable to provide a vertical
    joint in the masonry wall at the location of end of deck
    slab.
   Parapet wall have three parts,
    The central part over deck portion and two sides parts
    over return walls.
   Corresponding joint is also necessary in the coping over
    parapet wall
   Tar paper (bearing) should be provide on all supports of
    deck span up to 10 m span.
Weep Hole and Water Spout:

Weep Holes :

   To prevent building up of hydrostatic pressure
    behind abutments and wing walls.
   Not necessary in small span culverts.
   Height of abutment and Return over bed level
     is > 2 m.
   These should be provided 150 mm above low water
    level or ground level whichever is higher.
In case of stone masonry these are 150 mm dia or
80x150 mm size in 1:20 slope should be provided at
required intervals.


For 5 M and 6 M Span:

Water spout or 100 mm dia should be provided in the
centre of the slab on either side of the deck.
                Cost of culverts
Height 2.4 to 3.2 m., Spans 1.5 to 2.5 m.
           Items                Percentage of Total Cost
Excavation and dewatering                5 – 10
etc.
Foundation concrete                      10 – 15

Stone masonry substructures              40 – 50
(piers,    abutments,  caps,
returns, coping, etc.)
RCC deck slab                            15 – 20

Parapet wall and wearing coat            5 - 10
Items 1, 2 and 3 constituting 75 % of the total
cost governed by followed parameters
    Height (H) from the top of foundation to the top of
    slab
    Over all width (W) and length of the Returns.

Items 4 and 5 consisting 25 % of overall cost.
    Span of culvert (L)
    Width of culvert (W)
In case of culvert the span is not a function of height.
Hence, cost of culvert can not be calculated on the
basis of span.
Mix Design Considerations

   The design of concrete mixes is partly art and
partly science as with the cooking of good food.
Concrete is forever ; make it that way.
   Both good and bad concrete can be prepared from
exactly the same constituents cement, aggregate ,
water.
   It is the mix proportions the „know – how‟ and
the „do-how‟ that makes the difference.
Design mix concrete is preferred to nominal
mix. If design mix concrete cannot be used for
any reason on the work for grades of M 20 or
lower, nominal mixes may be used with the
permission of engineer-in-charge, which,
however, is likely to involve a higher cement
content.
It refers selection of the mix ingredients and
their ratios.
Criteria for selection:
  Strength of Concrete
  Workability must be the appropriate for the placing
  conditions.
  Durability.
                  DURABILITY CRITERIA
Exposure      Plain Concrete       R.C.C                   Minimum Grade of Concrete
               Min.Cement Max. W/C Min.Cement     Max. W/C       Plain R.C.C
               Kg/m3               Kg/m3



Mild              220      0.60    300          0.55             -        M20

Moderate          250      0.60    300          0.50           M15        M25

Severe            260      0.50    350          0.45           M20        M30

Very severe       280      0.45    375          0.45           M20        M35

Extreme           300      0.40    375          0.40           M25        M40
Exposure            Description                   Min.    Min.      Min.    Max.
Category                                          Grade   Cover   Cement    Free
                                                          (mm)    (kg/m3)   w/c.
                                                                            ratio

  Mild        Protected against weather or
               aggressive conditions, except       M 20    20*      300      0.55
                  if located in coastal area

 Moderate     Sheltered from severe rain or
                    freezing whilst wet, or
                Exposed to condensation and
                 rain, or Continuously under
               under water, or In contact with     M 25    30       300      0.50
               or bured under non-aggressive
                    soil or ground water, or
            Sheltered from saturated „salt air‟
                         in coastal area
  Severe    Exposed to severe rain, alternate
                  wetting and drying or
              occasional freezing whilst wet
                or severe condensation, or
               completely immersed in sea          M 30   45 **     320      0.45
                water, or In contact with or
               buried under aggressive sub-
                   soil or ground water
Exposure           Description             Min.    Min.      Min.    Max.
Category                                   Grade   Cover   Cement    Free
                                                   (mm)    (kg/m3)   w/c.
                                                                     ratio


  Very     Exposed to sea water spray,
 Severe    corrosive fumes or severe
           freezing whilst wet, or In
           contact with or buried under    M 35     50      340      0.45
           aggressive sub-soil or
           ground water


Extreme    Member in tidal zone, or
           members in direct contact
           with liquid/ solid aggressive   M 40     75      360      0.40
           chemicals.
 Workability of Concrete
Placing conditions             Degree of      Slump
                              workability     (mm)
Blinding concrete ;
Shallow sections;              Very low     < 25 or C.F
Pavements using pavers ;                    0.75 to 0.80
Mass concrete ;
Lightly reinforced sections
in slabs, beams, walls,
Columns, Floors;                 Low          25 – 75
Hand placed pavements
;Canal lining;
Strip footings.
Heavily reinforced
Sections in slabs,             Medium        50 – 100
Beams, walls, columns,                       75 -100
Slip form work ;
Pumped concrete‟
Trench fill; Inisitu piling      High       100 – 150
Tremie Concrete.               Very high       200
     Assumed Standard Deviation (IS 456 – 2000)
Grade of                    Assumed Standard Deviation
Concrete                            (N/mm2)
      M 10
      M 15                                  3.5
      M20
      M25                                   4.0
      M30
      M35
      M40                                   5.0
      M45
      M50

        The above values correspond to the site control having proper
storage of cement; weigh batching of all materials control addition of
water regular checking of all materials, aggregate gradings, and the
moisture content.
   SUGGESTED VALUES OF THE STANDARD DEVIATION (SP 23)

Grade of Concrete   S D for different degrees of control in N/mm2
                    Very Good          Good                     Fair
M10                 2.00               2.30                     3.30
M15                 2.50             3.50                      4.50
M20                 3.60             4.60                      5.60
M25                 4.30             5.30                      6.30
M30                 5.00             6.00                      7.00
M35                 5.30             6.30                      7.30
M40                 5.60             6.60                      7.60
M45                 6.00             7.00                      8.00
M50                 6.40             7.40                      8.40
M55                 6.70             7.70                      8.70
M60                 6.80             7.80                      8.80
                DATA SHEET FOR MIX DESIGN

Please indicate the following for the Mix Design Desired   :

Name of the organization                                   :

Address :

1.      Type of work for which the Mix is used             :

2.      Required Grade of Concrete                         :

3.      Is it for RCC/PCC/PSC/PRECAST                      :

4.      Will the cement be obtained from single            :

        source/Different sources
5.    Cement Storage                                 :
      Fresh / Careful / Proper
6.    Will the cement be tested Regularly /          :
      occassional / No
7.    Will the Moisture content of aggregate         :
      measured at site regularly / occasional / No
8.    Is water content controlled / left to mixer    :
      operator
9.    Is the Supervision Frequent / Intermittent         :
      /occassional
10.   Any field test facilities available at site    :
      Yes / No
11.   Batching by weight / Volume                      :
12.   Nominal Maximum size of Aggregate                :
13.   Is Coarse Aggregate in single size / Graded /    :
      Multiple size.
14.   Minimum cement content                           :
15.   Limitation on maximum w/c ratio                  :
16.   Quantum of reinforcement light / medium / heavy:
17.   Grade of cement & manufacturer’s name            :
18.   Environmental exposure                           :
      Mild / moderate / severe / very severe / extreme :
19.   Size of aggregate used                           :
      i. 10mm & 12mm only
      ii. 12mm/10mm       20mm only
      iii. 12mm/10mm      20mm 40mm only
20.   Any requirement in workability                   :
      High / Medium / Low
      slump --------
Water Content :
      Almost every property of concrete is adversely affected by an
      increased water content , so increase water alone is generally frowned
      upon limits are placed on the water/cement ratio.
      The designer of the mix used on site will choose his water content for
      the required workability.
      Maximum aggregate size.
      The aggregate shape.
      The cement type or source
      and the admixture if one is being used.
      Smaller the maximum size of the aggregate the higher the water
      content needed.
              FINE AGGREGATE
IS Sieve                 Percentage passing for
Designation   Grading   Grading     Grading       Grading
              Zone 1    Zone 11     Zone 111      Zone 1V
10mm           100      100          100            100
4.75mm         90-100   90-100       90-100         95-100
2.36mm         60-95    75-100       90-100         95-100
1.18mm         30-70    55-90        70-100         90-100
600micron      15-34    35-49        60-79          80-100
300 micron     5-20     8-30         12-40          15-50
150 micron     0-10     0-10         0-10           0 -15
Aggregate type and Grading :
   Zone –I represents coarsest sand.
   Zone-IV represents Finest Sand.
   Zone – II & Zone – III represents medium
   fineness.
   When finer fines of fine aggregate particles,
   generally 600 micron passing are in high
   percentage, the surface area of aggregates
   increases per unit weight.
   Larger surface area will require more cement
   paste.
 Using Crushed Sand (Rock Sand or Robo
  Sand)
     Making concrete with stone dust gives a
  requisite strength compared to that made with
  sand. Hence use of stone dust may be
  recommended.
     Use of stone dust as fine aggregate slightly
  increases the cement content as water
      requirement is more.
Silt Content :
    The maximum quantity of silt in sand shall
not exceed 8 %.
Bulking :
    Fine aggregate, when dry or saturated, has
almost the same volume but dampness causes
increase in volume.
    In case fine aggregate is damp at the time of
proportioning the quantity shall be increased
suitably to allow for bulkage.
 Moisture       Bulkage % age
Content % age    (by volume)
    2                15
    3                20
    4                25
    5                30
                Graded Stone Aggregate or Gravel
IS Sieve      Percentage Passing (by weight) for
Designation   nominal size of
              40 mm           20 mm 16 mm        12.5 mm
75 mm         100             --         --      --

37.5mm        95 to 100       100         --              --

19 mm         30 to 70        95 to 100   100             --

16 mm         --              --          95 to 100       100

11.2mm--                 --         --          90 to 100

9.5mm         10 to 35        25 to 55    30 to 70        40 to 85

4.75 mm       0 to 5          0 to 10           0 to 10              0 to 10
Single Sized ( Ungraded ) Stone Aggregate or Gravel
 IS Sieve      Percentage Passing (by weight) for Gravel
 Designation    Nominal size of
               40 mm 20 mm 16 mm               12.5 mm     10mm


 63mm               100        --         --               --     --

 40mm               85-100   100          --               --       --

 20mm               0-25      85-100      100              --      --

 16 mm              --         --         85-100           100      --

 12.5mm             --         --         85-100           100     --

10 mm               0-5        0-20       0-20             0-20   85-100

 4.75mm             --         0-5        0-5              0-5    0-20

 2.36mm        --                    --            --             0-5
Test on Cement

1.       Consistency

2.       Initial setting time             > 30 minutes

          Final setting time              < 600 minutes.

3.       Specific gravity                  2.8 to 3.15

4.       Compressive strength of cement at 28 days

                 33 grade          33 N/mm2

                 43 Grade          43 N/mm2

                 53 Grade          53 N/mm2
Test on Sand


1.     Specific gravity
W1                        empty bottle
W2                        empty bottle + (1/3 to 2/3 Sand)
W3                        empty bottle + (1/3 to 2/3 Sand) + Water
W4                        empty bottle + Water


                              w2-w1
Specific gravity =
                          (w2-w1) – (w3-w4)
2.     Fineness Modulus (using sieve analysis)
       < 2.6              Fine sand
       > 2.6 to 2.9       Medium sand
       > 2.9              Coarse sand.
Tests on coarse aggregate.

1.      Specific gravity

2.      Fineness Modulus

        40mm, 20mm, 10mm,4.75,2.36,1.18mm,600,300,150microns

        fineness modulus > 8.0    40mm   aggregate

                           > 7+   20mm   aggregate

                           > 6+   10mm   aggregate

                           > 5+   4.75mm aggregate
MIX DESIGN PROCEDURE


1.   Assume water content for given materials.
2.   Assume water/cement ratio for given mix grade.
3.   From water/cement ratio, find the cement content required for
     given    mix grade.
4.   Assume the percentage of sand for given materials & for designed
     workability.
5.   Find the sand content from the below relation .
      980 =    Water + Cement           +        Sand
                Sp. Gravity of cement       % sand x Sp.gravity Sand
6.   Find the aggregate content.
      980 = Water + Cement              +      Coarse Aggregate
                    Sp. Gravity of cement    % sand x Sp.gravity CA
1.   SIZE OF AGGREGATE          WATER EQUIREMENT

                        FOR 1M3

     10 mm                     190 Litres.

     20 mm                     175 Litres.    Approximately

     33 mm                     168 Litres.

     40 mm                     160 Litres.

     The concrete will be less durable and weaker due to the

     increase in the water content than required to maintain

     workability.

     Use less water for mixing more water for curing.
2.   % SAND IN MIX DESIGN IF AGGREGATE IS 20mm

     Fineness Modulus of Sand   % of Sand

     ≤ 2.7                      34 %

     2.7 to 3.0                 35 %

     > 3 ≤ 3.3                  38 %

     > 3.4                      40 %

      3.5                       41 %

      3.6                       42 %

      3.7                       43 %

      3.8                       44 %
           Approximate Cement Content
                for 1 M3 Concrete

Grade of        Design           Nominal
Concrete        Mix              Mix
                ( Kgs)           ( Kgs)

M 15            280 (5.6 bags)   330 (6.6)

M20             330 (6.6)        400 (8.0)

M25             350 (7.0)        475 (9.5)

M 30            370 (7.4)        ------

M40             400 (8.0)        ------
    Quality Assurance Measures

In order that the properties of the
completed structure be consistent
with the requirements and assumptions
made during the planning and
the design, adequate quality assurance
measures shall be taken
  Comparison of in-situ and standard
          cube strengths

Member type   cube strength as % Typical 28-day in-situ
              equivalent wet of standard cube strength
               Average                  Likely range
  Column         65%                     55%-75%
   Wall          65%                     45%-95%
   Beam          75%                     60%-100%
   Slab          50%                     40%-60%
      Quality Assurance Measures
                         (Contd..)

How it can be achieved ?
   Proper design
   Use of adequate materials and components
   Proper Workmanship
   Proper care during the use
   Timely maintainance and repair
       Testing of Green Concrete

 Slump test
 Compacting factor Test
 Vee-Bee Consistency Test
 Flow Test
 Measurement of Air Content
 Setting time of concrete
 Analysis of fresh concrete Segregation, Bleeding, Setting
  time, Pumpability, w/c ratio
     Testing of Hardened concrete

   Compressive strength test
   Tensile strength test
   Analysis of Hardened concrete
   Abrasion Resistance Test
    Why Non-Destructive Testing ?

   A growing number of Concrete structures,
   especially those of recent origin, have
   shown signs of deterioration may be due to
       - increased use of cement replacements
          and admixtures
       - decline in standards of workmanship
       - bad construction supervision
    TESTING AND EVALUATION OF
       IN-SITU CONCRETE AND
      CONCRETE STRUCTURES

VISUAL OBSERVATIONS
FIELD DATA AND RECORDS
NON-DESTRUCTIVE TECHNIQUES
CORE EXTRACTION & TESTING
SUPPLEMENTARY LABORATORY TECHNIQUES
LOAD TESTING
         Surface hardness methods
            (Rebound Hammer)

Factors influencing test results
Cement type and content
Coarse aggregate type
Compaction
Surface type
Age, rate of hardening, curing
Moisture condition
Stress state and temperature
 TESTING AND EVALUATION OF IN-SITU
CONCRETE AND CONCRETE STRUCTURES
CORE EXTRACTION AND TESTING
CRACK DEPTH AND
PROPOGATION
VISUAL SIGNS ON
CONCRETE
STRENGTH TEST
MODULUS OF ELASTICITY
TEST
DENSITY
CONCRETE AFTER
CRUSHING USED FOR
CHEMICAL ANALYSIS AND
OTHER LABORATORY TESTS
                 STEPS OF CORE TESTING
                   (IS 516,1199,456)
   Select diameter of core equal to 3 MSA
   Drill Core ( minimum three numbers)
   Prepare , Cap and Store (L/D ratio between 1-2)
   Test the core for Compressive Strength
   Apply correction if L/D ratio is less than 2( as per IS-516)
   Convert core strength to equivalent cube strength
    (multiply by 1.25)
   Check strength as per IS-456 criteria
Thank You

				
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