Inspection, Quality, Inspection, Quality, Variation, Statistical Control Variation, Statistical Control

and Acceptance Criteriaand Acceptance Criteria

Dr. J.SUDHAKUMARDr. J.SUDHAKUMAR

Assistant Professor Assistant Professor

Department of Civil Engg. Department of Civil Engg.

NIT, CALICUTNIT, CALICUT

Inspection, Quality, Variation, Statistical Control and Inspection, Quality, Variation, Statistical Control and Acceptance CriteriaAcceptance Criteria

INSPECTION AND QUALITY CHECK INSPECTION AND QUALITY CHECK

Need and scope of InspectionNeed and scope of Inspection

To ensure that work is done in To ensure that work is done in accordance with the plans, accordance with the plans, specifications and good practice, specifications and good practice, and to prevent mistakes.and to prevent mistakes.

The other requirements for the The other requirements for the same purpose includesame purpose include

Intelligent designIntelligent designAdequate specificationsAdequate specificationsReliable constructionReliable constructionCompetent inspectionCompetent inspection

The following items are covered by The following items are covered by the inspection of concrete the inspection of concrete construction at various stages:construction at various stages:

Sampling, Identification, Examination, Sampling, Identification, Examination, and any field testing of materialsand any field testing of materials

Control of concrete proportioning and Control of concrete proportioning and the measurement of materialsthe measurement of materials

Examination of the foundation, forms Examination of the foundation, forms and other work preparatory to and other work preparatory to concretingconcreting

Continuous inspection of the Continuous inspection of the batching, mixing, conveying, batching, mixing, conveying, placing, compacting, finishing placing, compacting, finishing and curing of concreteand curing of concrete

Testing for consistency of Testing for consistency of concrete, and preparation of concrete, and preparation of any concrete specimens any concrete specimens required for laboratory testingrequired for laboratory testing

General observation of General observation of contractor’s plant and contractor’s plant and equipment, weather, working equipment, weather, working conditions and other items conditions and other items affecting the concreteaffecting the concrete

Preparation of records and Preparation of records and reportsreports

Choice of an InspectorChoice of an InspectorAn ideal inspector should have An ideal inspector should have

both technical and practical know-both technical and practical know-how of the subject. He should how of the subject. He should essentially understand the essentially understand the following: following:

Bulking of fine aggregate (sand)Bulking of fine aggregate (sand) Well proportioned mix or notWell proportioned mix or not Whether the mix has desired slumpWhether the mix has desired slump

Whether the forms are sufficiently Whether the forms are sufficiently tight and bracedtight and braced

Whether the concrete is properly Whether the concrete is properly compacted or notcompacted or not

Whether the forms are removed Whether the forms are removed early or notearly or not

Authority of the InspectorAuthority of the InspectorAn authority should be given to the An authority should be given to the

inspector to :inspector to :Prohibit concreting until all Prohibit concreting until all

preliminary conditions (such preliminary conditions (such as completion of forms) have as completion of forms) have been fulfilled and inspection been fulfilled and inspection report for concreting has been report for concreting has been providedprovided

Stop the use of materials and Stop the use of materials and equipment, which do not equipment, which do not comply with the specificationscomply with the specifications

Stop any work which is not Stop any work which is not being done in conformity with being done in conformity with the plans and specificationsthe plans and specifications

Require the removal or repair Require the removal or repair of faulty construction or of of faulty construction or of construction performed construction performed without inspection and not without inspection and not accessible to being inspected accessible to being inspected laterlater

Normally, the inspector is Normally, the inspector is authorised to take direct action in authorised to take direct action in the first three cases abovethe first three cases above

He should report the matter He should report the matter immediately to his superiorimmediately to his superior

He should stop the work only as a He should stop the work only as a last resort, when it is clear that last resort, when it is clear that unsatisfactory concrete will result unsatisfactory concrete will result from the continuing operationsfrom the continuing operations

Quality check on concreteQuality check on concreteBefore concrete is placed, the Before concrete is placed, the

specification requirements in all specification requirements in all aspects must be fulfilledaspects must be fulfilled

Forms should be of proper size Forms should be of proper size and strength and in their correct and strength and in their correct locationlocation

Cement, aggregates, water and any Cement, aggregates, water and any other ingredients should be other ingredients should be inspectedinspected

Batching of materials, time of Batching of materials, time of mixing, possibility of segregation, mixing, possibility of segregation, proper curing etc., as this will proper curing etc., as this will influence the properties of influence the properties of hardened concretehardened concrete

Preparation of test specimensPreparation of test specimensAt least 3 specimens for each 200 At least 3 specimens for each 200

mm3 3 of concreteof concreteEach sample should be from Each sample should be from

different points of the structuredifferent points of the structure

Sampling should not be from the Sampling should not be from the conveying deviceconveying device

Taken at irregular times and Taken at irregular times and without prolonged preparationswithout prolonged preparations

Sample should be placed in a Sample should be placed in a water-tight non-absorbent water-tight non-absorbent containercontainer

Remixed fast enough to make it Remixed fast enough to make it uniform, and then moulded into uniform, and then moulded into specimensspecimens

For compression test, 150 mm For compression test, 150 mm cube moulds are usedcube moulds are used

Moulds are filled in 3 layersMoulds are filled in 3 layersEach layer is compacted with 25 Each layer is compacted with 25

strokes of a 16 mm diameter and strokes of a 16 mm diameter and 600 mm long, round bullet pointed 600 mm long, round bullet pointed steel rodsteel rod

After the top surface has been After the top surface has been levelled, the specimen is covered levelled, the specimen is covered to prevent evaporationto prevent evaporation

Flexure specimens are 150 mm Flexure specimens are 150 mm x 150 mm in section. Moulds x 150 mm in section. Moulds are placed with their long axis are placed with their long axis horizontal and are filled in 2 horizontal and are filled in 2 layers, each layer being rodded layers, each layer being rodded 50 times.50 times.

Quality check on Personnel and Quality check on Personnel and EquipmentEquipment

Should have a well trained team, Should have a well trained team, conversant with different quality conversant with different quality control procedure of inspection, control procedure of inspection, testing and data analysistesting and data analysis

An adequately equipped field An adequately equipped field laboratory for carrying out laboratory for carrying out routine control testsroutine control tests

Table 1 : Table 1 :

Daily testing programme Daily testing programme

and composition of teamand composition of team ( refer notes )( refer notes )

Table 2 : Table 2 :

Degree of quality control Degree of quality control

expected under different site expected under different site

conditionsconditions

( refer notes )( refer notes )

Measures of Variability of Concrete Mix Measures of Variability of Concrete Mix

DesignDesign

Factors contributing to VariabilityFactors contributing to Variability

It is found that strength of concrete It is found that strength of concrete varies from batch to batchvaries from batch to batch

The following are the sources of The following are the sources of variabilityvariability

Variation in the quality of Variation in the quality of constituent materials usedconstituent materials used

Variation in the mix proportions Variation in the mix proportions due to batching processesdue to batching processes

Variations in the quality of Variations in the quality of batching and mixing equipment batching and mixing equipment availableavailable

Quality of supervision and Quality of supervision and workmanshipworkmanship

Variation due to sampling and Variation due to sampling and testing of concrete specimenstesting of concrete specimens

These variations are inevitable These variations are inevitable during production of concreteduring production of concrete

The purpose of quality control The purpose of quality control using statistical means is to using statistical means is to produce concrete of uniform produce concrete of uniform qualityquality

If a large number of cube strength If a large number of cube strength test results are plotted on a test results are plotted on a histogram, the results are found to histogram, the results are found to follow a bell-shaped curve termed follow a bell-shaped curve termed as “Normal Distribution Curve”as “Normal Distribution Curve”

The arithmetic mean of a number The arithmetic mean of a number of test results gives no indication of test results gives no indication of the extent of variation of of the extent of variation of strengthstrength

However, this can be ascertained However, this can be ascertained by relating the individual strength by relating the individual strength to the mean strength and to the mean strength and determining the variation from the determining the variation from the mean, with the help of the mean, with the help of the characteristics of the N.D.curvecharacteristics of the N.D.curve

Standard DeviationStandard Deviation

The root mean square deviation of the The root mean square deviation of the whole consignment is termed as the whole consignment is termed as the ‘standard Deviation”. It can be defined ‘standard Deviation”. It can be defined numerically as:numerically as:

S = S = (x – (x – --xx--))22/(n-1)/(n-1)

WhereWhere

S = S.D. of the test resultsS = S.D. of the test resultsx = any value in the test resultsx = any value in the test results__x = arithmetic mean of the resultsx = arithmetic mean of the results

n = number of test results n = number of test results

Coefficient of VariationCoefficient of Variation

An alternate method of expressing An alternate method of expressing the variation of results about the the variation of results about the mean is by coefficient of variationmean is by coefficient of variation

This is a non-dimensional measure This is a non-dimensional measure of variationof variation

This is obtained by dividing the This is obtained by dividing the

standard deviation by the average standard deviation by the average value, and is expressed asvalue, and is expressed as

V = 100 S / V = 100 S / --XX--

wherewhere V = coefficient of variationV = coefficient of variation

S = S.D. in strengthS = S.D. in strength

--XX-- = Mean value in strength = Mean value in strength

When the C.V. is constant, S.D. When the C.V. is constant, S.D. increases with the increase in increases with the increase in strength of concrete strength of concrete

STATISTICAL CONCEPTS OF STATISTICAL CONCEPTS OF MIX DESIGNMIX DESIGN

Characteristic strengthCharacteristic strength

This means that value This means that value of the strength of concrete below of the strength of concrete below which, not more than 5 percent of which, not more than 5 percent of the test results are expected to fallthe test results are expected to fall

Target mean strength Target mean strength

fft t = f= fckck + K.s + K.s

wherewhere

fftt = target mean strength = target mean strength

ffck ck = characteristic strength = characteristic strength

K = a statistical constant, depending on K = a statistical constant, depending on

the definition of fthe definition of fckck and is derived and is derived

from the mathematics of Normalfrom the mathematics of Normal DistributionDistribution s = standard deviations = standard deviation

The value of K is equal to 1.65 The value of K is equal to 1.65 where not more than 5% of test where not more than 5% of test results are expected to fall below results are expected to fall below the characteristic strength the characteristic strength

fft t = f= fckck + 1.65 s + 1.65 s

Acceptance CriteriaAcceptance Criteria

(IS 456 : 2000)(IS 456 : 2000)

1.1. Compressive strengthCompressive strength Both the following conditions Both the following conditions

must be met :must be met :

a) The mean strength of any four a) The mean strength of any four consecutive test results compiles consecutive test results compiles with the appropriate limits in with the appropriate limits in Table 3.Table 3.

Table 3Table 3

For M15 gradeFor M15 grade

Mean of 4 consecutive results in Mean of 4 consecutive results in N/N/mmmm2 2 must be greater than or must be greater than or equal toequal to

ffckck ++ 0.825 x SD0.825 x SD or or

ffck ck + 3+ 3 N/mm N/mm22 , whichever is greater , whichever is greater

Table 3Table 3

For M20 or above gradeFor M20 or above grade

Mean of the group of 4 consecutive Mean of the group of 4 consecutive results in N/results in N/mmmm2 2 must be greater must be greater than or equal tothan or equal to

ffckck ++ 0.825 x SD0.825 x SD or or

ffck ck + 4+ 4 N/mm N/mm22 , whichever is greater , whichever is greater

Acceptance CriteriaAcceptance Criteria

b) Any individual test result b) Any individual test result complies with the appropriate complies with the appropriate limits in Table 3.limits in Table 3.

Table 3Table 3

For M15 gradeFor M15 grade

Individual test results in Individual test results in N/mmN/mm2 2

must be greater than or equal to must be greater than or equal to

( ( ffck ck –– 3 ) N/mm 3 ) N/mm22

Table 3Table 3

For M20 or above gradeFor M20 or above grade

Individual test results in Individual test results in N/mmN/mm2 2

must be greater than or equal to must be greater than or equal to

( ( ffck ck –– 4 ) N/mm 4 ) N/mm22

Acceptance CriteriaAcceptance Criteria

1.1. Flexural strength Flexural strength

Both the following conditions Both the following conditions must be met :must be met :

a)a) The mean strength of any four The mean strength of any four consecutive test results exceeds consecutive test results exceeds the specified characteristic the specified characteristic compressive strength by at least compressive strength by at least 0.3 N/0.3 N/mmmm22

b)b) The strength determined from The strength determined from any test result is not less than any test result is not less than the specified characteristic the specified characteristic strength less 0.3 N/strength less 0.3 N/mmmm22

THANK THANK YOUTHANK THANK YOU