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8/3/2019 A 6 Concrete Mix
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“BACK TO BASICS”
3A6 Concrete Technology
Dr. Roger P. WestNovember 2006
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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
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1. Introduction:
Testing to ensure: – Concrete has been
specified, made and
transported correctly. – Quality satisfactory for
purpose intended.
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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..
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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)
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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
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Plastic testing: Slump
Slump test: IS EN 12350-2.
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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
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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
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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
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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.
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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
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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.
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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.
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7. Specification and Compliance
Consistence ClassesNew Concrete Grades
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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
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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
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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‟ .
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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.
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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
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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
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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
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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
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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
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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
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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
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Failure modes - Normal
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Failure modes - Abnormal