a 6 concrete mix

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“BACK TO BASICS”

3A6 Concrete Technology

Dr. Roger P. WestNovember 2006



Part A:Basic Concepts and Site Practice

1. Introduction2. Sampling Concrete Materials

3. Workability and WorkabilityMeasurement4. Strength Development and StrengthMeasurement5. Sampling, Slump Testing and CubeMaking



1. Introduction:

Testing to ensure: – Concrete has been

specified, made and

transported correctly. – Quality satisfactory for

purpose intended.



2. Sampling Concrete Materials

Sampling: IS EN 12350-1.Provide certificate.

Good equipment.Take care / make representative.Take from mixer or as close todischarge as possible, or both.1. Sample in middle section of load not ends (slump alternative).2. At irregular times not evident to mixer operator.3. Note appearance, stony, creamy, sandy etc..



Sampling



3. Workability and Workability Testing

Objective is to produce a fully compacted concretewithout a loss of homogeneity or workabilityIncludes mixing, transporting, discharging, placing,

compacting and finishing

Problems:Improper constituents (e.g. additional water)Loss of workability prior to discharge (e.g.segregation / slump loss)Lack of compactionFinishing problems (e.g. excessive bleeding)



Workability

Strongly associated with the slump testFactors such as the fluidity, stability, pumpability,compactability and finishability all affect the workability

These properties are affected by:Design of mixAdjustment to the mix constituentsEnvironmental Conditions:

Ambient and concrete temperature

Relative humidity and the air speedDegree of agitation and friability of aggregratesElapsed time since mixing

EN206-1 uses concept of consistence



Plastic testing: Slump

Slump test: IS EN 12350-2.



4. Strength Development and StrengthMeasurement

Aggregates “glued” together by cement paste toform concreteCement hydration is a chemical reaction which

requires waterStrength gain reflects degree of hydrationStrength gain depends on – Type of cement –

Temperature history –

temperature and time – Curing – Admixtures



Factors Affecting Compressive Strength at 28days

Aggregate contentCement type and fineness

Water/cement ratioDegree of compactionExtent of curingTemperature

Between 65 and 80% of 28 day strength at 7 days



Strength Measurement

100mm or 150mm cubes at 7 and 28 days(note ratio 1:1 and square in plan)

300mm x 150mm cylinders at 7 and 28 days(note ratio 2:1 and circular in plan)Other tests – direct tension, bending and

coresNon-destructive testing



Cube Making:

Cube making: IS EN 12390-2Prime objectives –

to achieve full compaction – avoid loss of moisture – keep at proper temperature when in curing

tankUse proper tools.Advantage of cube shape is ease of makingaccurate sides.

Effect of cube shape.



The Slump Test



Cube Making



Part B:Specifications and Non-Compliance

6. Cube Curing and Cube Testing7. Specification and Compliance – Slump

Classes and New Concrete Grades8. Cube Reports and Cube Failures



6. Cube Curing and Cube Testing

Curing: IS EN 12390-3De-mould when stability of cube allows.

Prevent loss of moisture before placingin curing tank.Loss in strength due to initial drying out

is unrecoverable.No provision for in-situ cubes. BS1881gives method for temperature matched

curing.



Cube curing



Cube testing:

Cube test: IS EN 12380-3Specification compliance.

Desirable properties enhanced by increasingstrength.Effect of load rate, dry cubes.Effects of different machines.

General variations.Validity of uniaxial compression.



7. Specification and Compliance

Consistence ClassesNew Concrete Grades



Consistence Classes

Quantitative tests include the slump test, Vebe, degree of compaction and flow table values according to ISEN12350, Parts 2, 3, 4 and 5 respectively

Table 3 from ISEN206-1: Table 11 ISEN 206-1:Slump classes Tolerances for target values of consistence

Class Slump in mm Target Value(mm) < 40 50 – 90 >100Tolerance(mm) ± 10 ± 20 ± 30

S1 10 – 40S2 50 - 90

S3 100 - 150S4 160 - 210S5 > 220



Identity Testing

Extract from Table B-1, EN206 – 1: Identity criteria for slumpFor samples taken in accordancewith I.S. EN 12350-1

For spot samples taken from initialdischarge

Specified slump class Not less thanmm

Not more thanmm

Not less thanmm

Not more thanmm

S1 0 60 0 70S2 40 110 30 120S3 90 170 80 180S4 150 230 140 240S5 210 No requirement 200 No requirement

Specified target slump,mm

Not more than the following from the specified target valuemm

< 40 -20 +30 -30 +4050 to 90 -30 +40 -40 +50

> 100 -40 +50 -50 +60



Meeting Concrete Specification - Compliance

The delivery docket doesn’t have to state the precise mixproportions of the concrete if a product data sheet isacceptedThe docket must declare that it conforms to the

specification in ISEN206-1. Other information such astime of batching may be relevant, in the case of non-compliance (if the concrete exceeds the consistence classtolerances)

The addition of water and admixtures is forbiddenIn special circumstances, the producer can takeresponsibility for adding water providing that:

… „ the limiting values in the specification are not exceeded‟ .



Sampling for Assessing Conformity: Test Plan

Conformity assessed on site, in accordance with Table 13

Production Minimum rate of samplingSubsequent to first 50 m 3 of production a First 50 m 3 of

production Concrete withproduction controlcertification

Concrete withoutproduction controlcertification

Initial (until at least 35 testresults are obtained)

3 samples 1/200 m 3 or2/production week

1/150 m 3 or1/production day

Continuousb

(when at least35 test results are available)

1/400 m3

or1/production week

a Sampling shall be distributed throughout the production and should not be more than1 sample within each 25 m 3.

b Where the standard deviation of the last 15 test results exceeds 1,37 , the samplingrate shall be increased to that required for initial production for the next 35 tests results.



New Concrete Grades

Previously had 5 classes of exposure (mild,moderate, severe, very severe, extreme) in IS326(or BS8110), with a reasonable choice of gradesbetween 20 and 50 concrete.Now in ISEN206, or Eurocode 2, have 18exposure classes and only 5 grades in this range(cube strengths 20, 30, 35, 37, 45MPa)Specify cylinder/cube strengths as , for example,C30/37.ISEN206 NA Table X

Exposure classes



p

Norisk of

corros-ion

orattac

k

Carbonation-inducedcorrosion

Chloride-induced corrosion Freeze/thaw attack Aggressive chemical environments

Sea water Chloride otherthan sea water

X 0 XC1

XC2

XC3

XC4

XS1

XS2

XS3

XD1

XD2

XD3

XF1

XF2

XF3

XF4

XA 1 XA 2 XA 3

Maximumw/c

ratio

--- 0.65 0.60 0.55 0.55 0.55 0.50 0.45 0.55 0.50 0.45 0.60 0.55 0.55 0.45 0.55 0.50 0.45

Minimum

strength

class

C12/15

C25/ 30

C28/ 35

C30/ 37

C30/ 37

C30/ 37

C35/ 45

C40/ 50

C30/ 37

C35/ 45

C40/ 50

C28/ 35

C30/ 37

C30/ 37

C40/ 50

C30/37 C35/45 C40/50

Minimum

cementcontent(kg/m 3

)

--- 280 300 320 320 320 360 400 320 360 400 300 320 320 400 320(1)

280(2)

360(1),(3)

320(2)

400(1)(3)

360(2)

Minim

umair

content

If less thanC40/50 use5.5% (10 agg.)4.5% (14 agg.)3.5% (20 agg.)3.0% (40 agg.)

(1) CEM I(2) Sulfate resisting cement(3) Use sulfate resisting cement

if SO 42 > 1400 mg/l



Criteria for cube failures

A strength (the characteristic 28-day strength) isspecified based on design – the concrete GradeIn compression test, two tested cubes at 28 days =one result – Provided difference between individual results

is within 15% of averageRunning average of four cube results (for Grades< 50):

– average of any 4 consecutive results must begreater than characteristic + 3MPa (or N/mm 2)Individual cube result: – every individual result must be greater than the

characteristic -3MPa



Concrete Cube Test Result Variability

Variability – 28 day cube results have amean strength and a standard deviation

For an expected 5% defective level, thetarget mean strength is the specifiedcharacteristic strength plus 1.64 times thestandard deviation



Example

Grade 35 specifiedOver 100 cube results available from siteConsider individual results and running group of 4 averageConsider percentage 7 vs 28 day resultsInspect histogram and calculate mean and standarddeviationEnsure actual mean is greater than target meanstrength

Cube 7 28 28 28 day % diff Ratio Runn- Comment



CubeRef.

7day A

28day B

28day C

28 dayAvge.

% diff. Of 28d

Ratio7/28 %

Runn-ing Avge

Comment

21 35.0 45.0 48.0 46.5 6.5 75 45.1 OK

22 32.0 43.0 42.5 42.8 1.1 75 44.7 OK

23 31.5 39.5 32.5 36.0 19.4 88 OMIT >15%

24 28.0 39.0 40.0 39.5 2.5 71 43.1 OK

25 32.0 37.5 42.5 39.8 12.7 80 42.2 OK

26 35.0 42.0 41.0 41.5 2.4 84 40.9 OK

27 23.0 28.5 31.0 29.8 8.4 77 37.7 Ind & Gp FAIL

28 20.5 25.5 25.5 25.5 0.0 78 34.2 Ind & Gp FAIL

29 17.5 33.0 31.5 32.3 4.6 54 32.3 Gp FAIL

30 25.5 34.5 30.5 32.5 10.7 78 30.0 Gp FAIL

31 37.8 44.5 - OMIT 1no. 28d

32 35.5 41.5 45.5 43.5 9.2 82 33.5 Gp FAIL

33 38.0 47.0 42.0 44.5 11.2 85 38.2 OK

34 37.5 44.5 41.5 43.0 7.0 87 40.9 OK

35 32.5 36.5 39.0 37.8 6.6 86 42.2 OK



1 1

5

9

18

20

26

16

12

4

0

5

10

15

20

25

30

1 2 3 4 5 6 7 8 9 10

Cube Result Range (MPa)

F r e q u e n c y

Series1

Target Mean Strength = Characteristic + 1.64 Standard Deviation

or

TMS of 35 + 1.64 x 4.65 = 42.6MPa > Actual Mean => PROBLEM !

Characteristic =35MPa

Actual Mean = 40.2MPa

Standard Deviation = 4.65MPa

Actual Mean Compared to Target MeanCompressive Strength



Failure modes - Normal



Failure modes - Abnormal



Consequences of failure

In-situ testing,methods, validity,representative ofwhat?Cost of delays, lossin reputation.

a 6 concrete mix

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