inspection,good construction practices,workmanship and codal provisions

INSPECTION,GOOD CONSTRUCTION

PRACTICES AND CODAL PROVISIONS

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INSPECTION AND GOOD CONSTRUCTION PRACTICES

• An inspection procedure should be set up covering Materials,Records,Workmanship and construction,

• Tests on materials as per Standards,• Use of suitable quality assurance schemes,• Immediately after stripping the formwork,all concrete

shall be carefully inspected and any defect shall be rectified before concrete is hardened.

• To ensure proper performance,it is necessary that each step of concreting is inspected as the work proceeds.

GOOD CONCRETE

• Concrete in the fresh state should be cohesive,so that it can be transported and placed without segregation.

• Many properties of concrete are related to

its compressive strength:

1 Density

2 Impermeability

3 Impact-resistance

4 Abrasion-resistance

The compressive strength of concrete is dependent on W/Cratio of concrete.

28-day compressive W/C ratiostrength of concrete 43-grade 53-grade (N/mm2) cement cement 30 0.47 0.55 35 0.42 0.50 40 0.37 0.45 45 0.35 0.41 50 0.30 0.37 55 0.28 0.33 60 - 0.32

The W/C ratio also controls the permeability

of concrete.

The construction should result in satisfactory strength,serviceability and long-term durability.

QUALITY ASSURANCE

Qualily assurance in construction relates to:

1 Proper design.

2 Use of satisfactory materials and components.

3Proper workmanship in the execution of works and finally,

4 Proper care during the use of the structure

including timely maintenance and repair..

The job of Q.C and Q.A would involve quality audit of both the inputs & outputs.

INPUTS in the form of materials for concrete,WORKMANSHIP in all stages of batching,mixing,transportation,placing,

compaction and curing & the related plant,

machinery and equipment resulting in the form of concrete in place.

The Quality assurance Plan shall include:

a)Test reports and manufacturer,s certificate

for materials,concrete mix design details;

b) Pour cards for site organization & clearance for concrete placement;

c)Record of site inspection of workmanship,field tests;

d) Non-conformance reports, change orders;

e)Quality control charts& statistical analysis.

QUALITY CONTROL CHARTS ARE

RECOMMENDED WHEREVER THE

CONCRETE IS IN CONTINUOUS

PRODUCTION OVER CONSIDERABLE

PERIOD.

STANDARD DEVIATION

Standard Deviation is a good measure of Q.C. GOOD control means lower S.D (say 3 or 4 N/mm2). At least 30 test results should be used to calculate Standard Deviation. Each test result is average of 3 cube test results at 28 days.

CALCULATION OF S.D S.D= Root mean square deviation X X/ X-X/ ( X-X/)2

1. 20 -1 12. 21 0 03. 22 21 1 1 n=54. 24 3 95. 18 -3 9 ---------- 20 S.D=[20/(5-1)]1/2

=2.27N/mm2

WORKMANSHIP & CODAL PROVISIONS

• Concrete supplied by RMC plants shall be preferred.

• The grading of coarse aggregate should be controlled by obtaining the coarse aggregate in different size fractions & blending them in right proportions to satisfy the grading limits prescribed in IS 383.

The grading of coarse & fine aggregates should be

Checked as frequently as possible.

IS: 383 REQUIREMENT FOR COMBINED GRADING

IS sieve Size

40 mm MSA

20 mm MSA

16 mm MSA

12.5 mm MSA

40 mm 95-100

20 mm 30-70 95-100

16 mm 90-100

12.5 mm 90-100

10 mm 10-35 25-55 30-70 40-85

4.75 mm 0-5 0-10 0-10 0-10

It is important to maintain the W/C at its correct value.

For this,moisture content of coarse &fine aggregates should be determined as frequently as possible.

MIXING OF CONCRETE

• The mixing time should be at least

2 minutes in a drum mixer.

• For more efficient mixers(in a batching & mixing plant or in an RMC plant),the mixing time may be about ½ minute.

(Manufacturer”s recommendation may be

followed)

PLACING OF CONCRETE

The concrete shall be placed & compacted

in its final position as early as possible & before initial setting of concrete.

Care should be taken to avoid displacement of reinforcement or movement of formwork

Max. free fall of concrete may be 1.5m.

CONCRETE ADMIXTURES

The dosages of retarders,plasticizers & superplasticizers shall be restricted to 0.5,1.0 and 2.0% respectively,by weight

of cementitious materials,unless a higher

value is agreed upon between the

manufacturer & the constructer based

on performance test.

COMPACTION OF CONCRETE

Concrte should be thoroughly compacted.

Each 1% void can reduce the compressive

strength of concrete by 5%.

Over- vibration & under- vibration are harmful and should be avoided.

Fresh concrete should be thoroughly compacted near the construction joints.

CURING OF CONCRETE

Exposed surfaces of concrete shall be kept

continuously damp or wet condition by ponding or by covering with wet burlap,hessian etc.

For Concrete with blended cement or mineral

admixtures(flyash or ggbs or silica fume),

the curing period should be increased.

A white synthetic fiber mat with a white polyethylene backing that allows proper water content during the concrete curing process is being laid. They are lightweight and reusable.

CURING COMPOUNDS

Curing compounds may be used in case of scarcity of water or for high-

rise structures e.g bridge piers,RCC columns,chimneys and concrete roads. These compounds( wax-based or resin- based) are spray-applied on exposed concrete surfaces,as soon as possible after the concrete has set and when there is no water scene is visible on the surface.

SOME OF INDIGENOUS CURING COMPOUNDS

1 EMCORIL2 CONCURE(W B)3 ROFFCURE W B WHITE4 FREECURE5 CUREWELL –W B6 CHEMISTIK7 ANTISOL Coverage: 4-5 m2/Kg

CONCRETE COVER

Concrete cover should be adequate in concrete structures.

Inadequate cover to reinforcements

will result in corrosion of reinforcements.

NOMINAL COVER TO REINFORCEMENTSNOMINAL COVER TO REINFORCEMENTS

(IS 456)(IS 456)

Exposure Minimum nominal concrete cover (mm)

Mild 20

Moderate 30

Severe 45

Very Severe 50

Extreme 75

ENVIRONMENT EXPOSURE CONDITIONS

Mild Concrete surfaces protected against weather or aggressive conditions except those situated in coastal area

Moderate Concrete surfaces sheltered from severe rain or freezing whilst wet, sheltered from saturated salt air in coastal area. Concrete exposed to condensation and rain. Concrete continuously under water. Concrete in contact or buried under non-aggressive soil/ground water

ENVIRONMENT EXPOSURE CONDITIONS

Severe Concrete surfaces exposed to severe rain, alternate wetting and drying or occasional freezing whilst wet or severe condensation. Concrete completely immersed in sea water, and concrete exposed to coastal environments

ENVIRONMENT EXPOSURE CONDITIONS

Very Severe Concrete surfaces exposed to sea water spray, corrosive fumes or severe freezing conditions whilst wet. Concrete in contact with or buried under aggressive subsoil/ground water

Extreme Surface of members in tidal zone. Members in direct contact with liquid/solid aggressive chemicals

ENVIRONMENT EXPOSURE CONDITIONS

Abrasive Concrete surfaces exposed to abrasive action e.g. machinery, metal tyres, etc. for this, specialist literature to be referred, for durability requirement

VACUUM-DEWATERED CONCRETE

(Generally for slabs & floors)• Slump required: 75-100 mm.• Vacuum is applied through porous mats. (filter mat & suction mat)• Applied vacuum is about 0.08MPa.• About 20% of mixing water gets removed.• Process takes about 15 to 20 minutes.• Flyash or any other pozzolana should not be incorporated in the concrete mix.• Usual floating,trowelling,brooming&curing are requred.• Placed concrete bonds well with the old concrete(if any).