1 09.06.2015/BMo/gbo Plastic state.ppt Holcim Group Support PECP06 2005 Learning Objectives Relevance of fresh concrete properties Tests on freshly

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18.04.23/BMo/gboPlastic state.ppt

Holcim Group Support PECP06 2005

Learning Objectives

Relevance of fresh concrete properties

Tests on freshly mixed concrete

Describe how fresh concrete properties are influenced by concrete constituents

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Why are we interested in the properties of Why are we interested in the properties of fresh concrete? fresh concrete?

Influence on the final quality of hardened concrete

Helps to detect variations in material and process

Uniform fresh concrete = Uniform hardened

Last chance to identify unsatisfactory quality

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TimeTime

DistanceDistance

5050

4040

3030

2020

1010

00

5050

4040

3030

2020

1010

00

TemperatureTemperature

º C º C

Job site


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Compaction ratio


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Tests on Freshly Mixed Concrete

Procedures used for testing freshly mixed concrete are standardized Workability & consistency Bleeding and settlement Setting time Air content Temperature Density

Used not only in the laboratory but also in the field

Designed to eliminate random variations that may occur in the test results and lead to unnecessary disputes on the quality of concrete

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Workability & Consistency

The ease of placing, consolidating and finishing freshly mixed concrete and the degree to which it resists segregation is called “workability”“workability”

Properties related to workability include: Consistency Segregation/cohesiveness Mobility Pumpability Bleeding Finishability

Degree of workability required is controlled by: Placement method Type of consolidation Type of concrete

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Factors influencing concrete workability are: Method and duration of transport Type and content of cement Aggregate characteristics (grading, shape…) Entrained air Water content Temperature (concrete & ambient) Admixtures

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Measurement of Consistency

Although it is a different characteristic from workability, in practice the two terms are often confused and merged into one - the “slump”“slump” of concrete

Slump ASTM - 143

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Workability Terminology Very stiff

Stiff

Plastic

Soft (wet)

Flowing

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Flow table - DIN 1048


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Influence of Water on Workability

Only very minor adjustments to workability should be made by the addition of water alone Reduce strength and durability Potential for drying shrinkage cracking

Therefore, adjustments to workability made by the addition of water should always be accompanied by an addition of cement to maintain a fixed W/C

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Influence of Water on Workability

Relation between water requirement of paste and concrete

0.53

0.54

0.55

0.56

0.57

0.58

23 24 25 26 27 28 29

Water requirement (%)

w/c

rat

io c

oncr

ete,

7.5

cm

slu

mp

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Influence of aggregates on Workability

Grading Affects workability, because the water demand necessary

to wet all the solids in the mix will depend on the surface area of the aggregates

The larger the particle size the greater the workability for a given cement content and W/C

Particle shape Rounded or roughly cubically shaped aggregates will

produce more workable concrete than that produced using flaky or elongated particles

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Sand

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Influence of temperature on Workability

ASTM C 1064

Glass or digital readouts thermometers are available

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Time Vs Slump

0

5

10

15

20

25

-20 10 40 70 100

Time(min)

Slu

mp

(mm

)

21 °C

32 °C

Influence of temperature on Workability

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Cohesive No Cohesive

Segregation


Cohesiveness of concrete Is a measure of its ability to resist the segregation of its

constituents during handling, placing and compaction

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Cohesiveness

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Cohesiveness of concrete

Factors affecting the cohesiveness of concrete: Water

- The higher the water content the greater is the risk of segregation and bleeding

- High water content retards the stiffening of concrete allowing sedimentation of heavier particles

Cold weather can also retard setting and promote bleeding Dry mix can be friable and also prone to segregation Grading

- Mixes that are deficient in fine particles tend to segregate more readily during handling and bleed after finishing (entrained air can help)

- Excessive fines make concrete “sticky” and very cohesive

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Bleeding and settlement

Bleeding is the development of a layer of water at the top or surface of freshly placed concrete

Bleeding is normal and should not diminish the quality of properly placed, finished and cured concrete

Some bleeding is helpful to control plastic cracking

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Excessive bleeding?

Cracks

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Measurement of Bleeding

Can be determined by the test method described in ASTM C 232 – rarely used in the field

Typical values range from 0.1 to 2.5 % of mix water Or 0.01 to 0.08 mL/cm2

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Setting time Can be determined by the test method described in

ASTM C 403 by means of penetration resistance measurements

Made on mortar sieved from the concrete mixture Initial and final time of setting corresponds to a

penetration resistance equal to 500 psi (3.4 MPa) and 4000 psi (27.6 MPa)

Typical values range Initial set: 2 to 6 hours Final set: 4 to 12 hours

Factors affecting setting time of concrete: W/C ratio Cement type and content Temperature Admixtures

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Measurement Setting time

0

500

1000

1500

2000

2500

3000

3500

4000

4500

5000

180 210 240 270 300 330 360 390 420 450

Elapsed time (min)

Pe

ne

tra

tio

n r

es

ista

nc

e (

ps

i) Final set

Initial set

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Setting time

Methods Vicat ASTM C 403

Limestone cement

Paste – w/c ~0.27 Concrete – w/c ~ 0.6

MSC Competitor MSC Competitor

Setting time

Initial 110 min + 30 min 280 min - 50 min

Final 140 min + 30 min 400 min - 40 min

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Air content

ASTM C231: pressure method Applied pressure compresses the air

within the concrete including in aggregates pores

Not suitable for lightweight aggregate concrete

ASTM C173: volumetric method Removal of air from a known volume of

concrete by agitating the concrete in an excess of water

Suitable for lightweight aggregate concrete

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Density

ASTM C138 Determine the volumetric

quantity of concrete produced per batch

Can also give indications of air content provided the relative densities of the ingredients are known

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1 09.06.2015/BMo/gbo Plastic state.ppt Holcim Group Support PECP06 2005 Learning Objectives Relevance of fresh concrete properties Tests on freshly