fresh concrete

Fresh Concrete

• Two sets of criteria to consider when making concrete

– Short-term requirements – consistence (workability)

– Long-term requirements – strength, volume stability,

durability

• Fresh concrete must be capable of satisfying the

following requirements

– Easily mixed and transported

– Uniform throughout a given batch and between batches

– Have flow properties to fill the forms completely

– Easily compacted without applying excessive energy

– No segregation during placing and consolidation

– Easily and properly finished

of 60

Fresh Concrete Definition (EN 206: 2013)

Fresh concrete

Concrete which is fully mixed and still in a condition that is capable of

being compacted by the chosen method

Consistence (Workability)

―that property of the plastic concrete mixture which determines the

ease with which if can be placed and the degree to which it

resists segregation (Powers, 1932)

―that properties of concrete which determines the amount of useful

internal work necessary to produce full compaction (Granville,

1947)

―that property of freshly mixed concrete or mortar which determines

the ease and homogeneity with which it can be mixed, placed,

consolidated, and finished‖ (ACI 116R-90)

―property determining the effort required to manipulate a freshly mixed

quantity of concrete with minimum loss of homogeneity‖ (ASTM

C 125-93)

Note: ease flow and resisting segregation (homogeneity) of 60

Fresh Concrete Consistence (Workability) includes:

Consistency: property of a material by which it resists

permanent change of shape

Compactability: ease with which concrete can be

compacted and air void removed

Mobility: ease with which concrete can flow into forms,

around steel bars and be remoulded

Stability: ability for concrete to remain a stable,

coherent, homogeneous mass during handling and

vibration without segregation

Flowability, Pumpability, Finishability, Harshness

Quantitative fundamental for concrete (Bingham model):

Yield value: stress below which no flow occurs, o

Plastic viscosity: excess of shear stress above yield

stress divided by rate of shear, = ( - o)/’ of 60

Fresh Concrete Components of fresh concrete

Well distributed system of coarse aggregate particles

A system of fine aggregate particles filling inter-particle spaces between coarse particles

Cement particles (including mineral additions, if added) filling the spaces between aggregate particles

Water voids (including chemical admixtures, if added) forming interconnected capillaries

Air bubbles (entrained and/or entrapped)

This complex system (solids, liquids and gas) changes from their initial spacial distribution with time resulting in ―bleeding‖, ―settlement‖ and ―segregation‖

After hardening, the resultant distribution of components retains the final stage of fresh concrete modified by cement hydration of 60

Basic Principle of Rheology

• Rheology

– dealing with deformation and flow of materials under stress

• Newton’s law of viscous flow

– Derived by considering the shearing of adjacent layers of liquid

– Valid for dilute suspension of solid in liquid with no inter-particle forces

– Single-point test (Mindess et al 2003)

of 60

Basic Principle of Rheology

• Fresh concrete has a shear strength which must be

exceeded before flow can occur

• Bingham model

where 0 = yield stress

= plastic viscosity

– Two- point test to determine 0 and

– Single - point tests of workability

current in use do not adequately

quantify the flow behavior of fresh concrete

0

(Mindess et al 2003)

of 60

Factors Affecting Consistence (Workability)

• Consistence (workability) generally implies ease with

which a concrete can be handled, starting from the

mixer to its final fully compacted state with segregation

• Intrinsic Factors

water content, composition and properties of other

constituent materials (cement content, cement type,

maximum size aggregate and grading of both coarse

and fine aggregates, shape and texture of coarse

aggregates, percentage of fine aggregate), entrained

air and chemical admixtures (if added)

External Factors

temperature, relative humidity, wind velocity and time

since mixing (loss of consistence), agitation while

being transported (ready-mixed concrete). of 60


• Water content, mix proportions, aggregate properties,

time, temperature, characteristics of cement, &

admixtures

• Water content

– For a given maximum size of coarse aggregate and

aggregate grading, the workability is a direct function of

water content

• concrete with very high workability tends to segregate and

bleed

• concrete with too low workability may be difficult to place

and compact

– Finer particles require more water, but minimum quantity

of fine material is essential to achieve ―plasticity‖

Note: for SCC, fines made up of inert powder + cement of 60

Factors Affecting Workability

• Influence of aggregate

– Amount of aggregate

• For a constant w/c, aggregate/cement will workability

– Relative proportions of fine and coarse aggregate

• For finer aggregate grading, more cement is needed

• If fine aggregate is not sufficient harsh concrete

• Excess fine aggregate more permeable concrete

– Shape and surface texture

• Nearly spherical particles will increase workability

• Smooth particles tend to increase workability

• Flakey and elongated particles need more paste

– Porosity

• Free water content – contribute to workability

• Total water content – including free water and water

absorbed by aggregate (below SSD) of 60

Factors Affecting Workability

• Temperature

– Ambient temperature ,

workability

• Cement

– Less important than aggregate

– Increased fineness will reduce workability at given w/c

– In normal concrete, at a given water content

• too low cement content produce harsh mixtures

poor finishability

• too high cement content or a very fine cement show

good cohesiveness, but tends to be sticky

(Concrete Manual, US Bureau

of Reclamation 1975)

of 60

Factors Affecting Workability • Admixtures

– Mineral admixtures

• Improve the cohesiveness (If they are used as cement

replacement, may have little effect on flowability)

• Fly ash

– Spherical shape acting as ball bearings

– Reduce water requirement for given slump

– Increase slump for given water content and w/cm

• Silica fume

– High specific surface

– Increase water requirement

– Superplasticizers are often used in combination with SF

• Slag

– Effect on workability is not significant

– Air-entraining and water-reducing admixtures (equal w/c)

• Improve workability of 60

p

(Wallevik 1990) Note: SP – change in o ; entrained air – change in

Water – change in both o and of 60

Effect of vibration on concrete flow curve

T = g + hN

where

N – rotational speed, corresponds to shear rate ’

T - measured torque at N, corresponds to shear stress ,

g - intercept, corresponds to yield stress o

h - gradient of the relationship, corresponds to viccosity

Principle of the

coaxial cylinders

viscometer

(Tattersall, 1991)

vibrated

concrete

unvibrated

concrete

T

N

of 60


• Time

• Loss of workability

– Slump loss is a normal phenomenon in all concrete

– Slump loss occurs when the free water from a concrete mixture

is removed by

• hydration reaction

• adsorption on the surface of hydration products

• evaporation

– The slump loss is approximately linear with time

• Greatest in the first 0.5 – 1 hr after mixing

• Thereafter, the rate of slump loss is determined mainly by

elapsed time, temperature, cement composition, admixtures

of 60


• Loss of workability (cont’d)

– Significance

• ―hang-up‖ of concrete within the drum of truck mixer

• difficulty in pumping and placing concrete

• extra labour needed in placement and finishing

• loss of strength, durability, and other properties when

retempering water is excessive or is not mixed properly

– How to overcome the slump loss

• starting with higher initial slump

• add extra admixtures

at job sites

of 60

Segregation and Bleeding

• Segregation - separation of the components of fresh

concrete so that they are no longer uniformly

distributed

– separation of coarse aggregate from concrete

• Concrete too wet

• Concrete too dry

– separation of water from concrete - bleeding

• Bleeding

– Upward movement of water after concrete has been placed and

compacted but before it has set

Segregation

of 60


• Significance

– Segregation: It is impossible to achieve full compaction after a

concrete has segregated. Affect strength, durability.

– Bleeding: The upper portion of concrete is weaker than the

concrete in the lower portion

• under reinforcing bars

• under coarse aggregate

(Mindess et al 2003) of 60


• Cause

– Excessive amount of large particles of coarse aggregate with

either too high or too low density

– Insufficient fine particles

– Mixes that are either too wet or too dry

– Over vibration

• Control

– Segregation of coarse aggregate

• Pay attention to aggregate grading, reducing max aggregate

size, use more sand or a finer sand

• Use mineral admixtures, air entraining admixture

– Bleeding

• Use mineral admixtures

• Use air - entraining admixture

• Reduce water content while maintaining workability of 60

Fresh Concrete

• Standard test methods for consistence:

Degree of

consistence

Test method

Very low Vebe time (s)

Low Vebe time (s), Degree of compaction (ratio) (replacing

compacting factor)

Medium Degree of compaction (ratio), Slump (mm)

High Slump (mm), Flow diameter (mm)

Very high Flow diameter (mm), Slump flow diameter (mm)

EN 12350-2, Testing of fresh concrete – Part 2: Slump test

EN 12350-3, Testing of fresh concrete _ Part 3: Vebe test

EN 12350-4, Testing of fresh concrete – Part 4: Degree of compactability

EN 12350-5, Testing of fresh concrete – Part 5: Flow table test

EN 12350-8, Testing of fresh concrete – Part 8: Slump flow test for SCC

Note: Additional tests methods for other requirements of SCC of 60

Specifying CONCRETE – Consistence Classes

Consistence classes in SS EN 206-1: 2009 Table 3 – Slump classes

Class Slump in mm

S1

S2

S3

S4

S51)

10 to 40

50 to 90

100 to 150

160 to 210

220

Table 4 – Vebe classes

Class Vebe Time in seconds

V01)

V1

V2

V3

V41)

31

30 to 21

20 to 11

10 to 6

5 to 3

Table 5 – Compaction classes

Class Degree of compaction

C01)

C1

C2

C3

C41)

1.46

1.45 to 1.26

1.25 to 1.11

1.10 to 1.04

< 1.04

Table 6 – Flow classes

Class Flow diameter in mm

F11)

F2

F3

F4

F5

F61)

340

350 to 410

420 to 480

490 to 550

560 to 620

630 Note: Not the same as compacting factor of 60


Consistence classes (Not yet included in BS EN 206-1: 2000)

Slump flow classes have been added to SS EN 206-1 Annex ZZA

(informative) Singapore guidelines – General (to be updated when

CEN has finalized the standards for self-compacting concrete)

Table ZZA 1 – Slump flow diameter classes

Class Slump in mm

SF11)

SF2

SF3

SF41)

540

550 to 650

660 to 750

760

1) Due to the lack of sensitivity of the test method beyond certain values

of consistence, these values are not recommended

Note: In special cases, consistence may also be specified by target

value

Slump flow test – Based on ISO 1920-2 Testing of concrete – Part 2:

Properties of fresh concrete, (4.7 Slump flow test)

Note:

Slump flow diameter classes for

SCC in EN 206-9: 2010 and now in

EN 206-1: 2013 which are not the

same values as shown In SS EN

206-1: 2009 (to be updated)

of 60


Consistence classes in BS EN 206: 2013 Table 3 – Slump classes

Class Slump in mm

S1

S2

S3

S4

S5a

10 to 40

50 to 90

100 to 150

160 to 210

220

Table 4 – Compaction classes

Class Degree of compactability

C0a

C1

C2

C3

C4b

1.46

1.45 to 1.26

1.25 to 1.11

1.10 to 1.04

< 1.04

Table 5 – Flow classes

Class Flow diameter in mm

F1a

F2

F3

F4

F5

F6a

340

350 to 410

420 to 480

490 to 550

560 to 620

630

a See Note 1 to 5.4.1

Note: For further information see

Annex L, line 10

Annex L (informative)

10 Recommended to use

Slump ≥ 10 mm and ≤ 210 mm

Degree of compactability ≥ 1,04 and

≤ 1,46

Flow diameter > 340 mm and ≤ 620 mm b C4 applies only to ligntweight concrete

of 60

Gently tap concrete on the side to provide additional information on workability

harsh, low on fines

plastic, cohesive

True Shear Collapse

EN ASTM

Tap

Fresh Concrete Testing – Slump

of 60

Fresh Concrete Testing – Slump EN 12350-2: 1999

Fill mould in 3 layers, each approximately 1/3 of height of the mould

when compacted, compact with 25 strokes of tamping rod uniformly

distributed over cross section

Report true slump to nearest 10 mm

Precision data for slump measurements

Range

(mm)

50 to 80

Single determination

Repeatability conditions Reproducibility conditions

Sr (mm) r (mm) Sr (mm) r (mm)

5,8 16 9,0 25

Duplicate determinations

4,1 11 8,0 22

ASTM C 143-12

Fill the mold in 3 layers, each approximately 1/3 of the volume of the

mold, rod each layer 25 times uniformly over the cross section

with the rounded end of the rod

Report slump to nearest 5 mm of 60

Fresh Concrete Testing – Flow Diameter

Fill mould in 2 equal layers, raise

mould vertically, raise table top

till it reaches upper stop and

allow table top to fall freely to

lower stop

Repeat cycle for total 15 drops

Measure maximum spread in

two directions, d1 and d2 (to

nearest 10 mm), parallel to

edges of the table of 60

Fresh Concrete Testing – Flow Diameter

Flow value of fresh concrete by measuring spread of

concrete on a flat plate which is subjected to jolting

Flow value F = (d1 + d2)/2

where

d1 and d2 are maximum dimension of concrete parallel

to edge of table edges

Precision data for flow measurement

Range

(mm)

Repeatability conditions Reproducibility conditions

Sr (mm) r (mm) Sr (mm) r (mm)

555 24,6 69 32,5 91

of 60

Fresh Concrete Testing – Degree of Compactability

Fresh concrete placed in a container, filled to the top

and struck off level, then compacted by vibration

and distance from concrete surface to upper edge of

container, ―s‖ measured to nearest mm at middle of

each side of the container

Container, made of metal, internal dimensions shall be:

base: (200±2) mm x (200±2) mm

height: 400 mm ± 2 mm

Degree of compactability, c (to two decimal places)

c = h1/(h1 – s)

where

h1 is the internal height of container (mm)

s is the mean value, (to nearest mm) of the 4 distances

from surface of compacted concrete to upper edges

of the container of 60

Fresh Concrete Testing – Degree of Compactability

200 mm x 200 mm Cross Section

Height, h1

400 mm

4 values:

sx1, sx2,

sy1, sy2,

X X

sx1 sx2

sy1

sy2

s = (sx1 + sx2 + sy1 + sy2)/4

Degree of compactability

c = h1/(h1 – s)

Y

Y

of 60

Consistence Classes for SCC – EN 206: 2013

(self-compacting /self-consolidating concrete)

Definition

Self-compacting concrete (SCC)

Concrete that is able to flow and compact under its own weight, fill the

formwork with its reinforcement, ducts, boxouts etc., whilst

maintaining homogeneity

Slump-flow (EN 12350-8)

Mean diameter of the spread of fresh concrete from a standardized

slump cone

Record time taken to nearest 0,1s for concrete to first touch 500 mm

circle (report t500 to nearest 0,5s), when specified t500 indicates

relative viscosity of concrete (see Table 7 for classes)

ASTM C1611-09 Slump Flow of Self-Consolidating Concrete

Filling Procedure A (Upright Mold):

with the larger opening facing down (as in conventional slump test)

Filling Procedure B (Inverted Mold):

with the smaller opening facing down (not in EN 12350-8) of 60

SCC Testing – Slump-Flow

Table 6 – EN 206: 2013

Class Slump-flow a tested in accordance with EN12350-8 (mm)

SF1 550 to 650

SF2 660 to 750

SF3 760 to 850

A The classification is not applicable to concrete with Dmax exceeding 40 mm

Slump-flow, SF = (d1 + d2)/ 2

where

SF is slump-flow, (mm)

d1 is largest diameter of flow spread, (mm)

d2 is flow spread at 90O to d1 (mm)

d1 and d2 (to nearest 10 mm)

Repeat with another sample if difference between d1 and d2 > 50 mm

If two consecutive tests show the difference between d1 and d2 > 50

mm, concrete lacks flowability for slump-flow test to be

suitable

Record time taken to nearest 0,1s for concrete to first touch 500 mm

circle (report t500 to nearest 0,5s) of 60

Consistence Classes for SCC

Class t500 a tested in accordance with EN 12350-8 (s)

VS1 < 2,0

VS2 ≥ 2,0

a The classification is not applicable to concrete with Dmax exceeding 40 mm

Table 7– Viscosity classes – t500

Definition

Viscosity of concrete

Resistance to flow of fresh concrete once flow has started

Class tv a tested in accordance with EN 12350-9 (s)

VF1 < 9

VF2 9,0 to 25,0

a The classification is not applicable to concrete with Dmax exceeding 22,4 mm

Table 8 – Viscosity classes – tv (V-funnel)

The classes in Table s 7 and 8 are similar but not exactly the same

May also be specified by a target value with tolerances given in Table 23 of

BS EN 206: 2013 of 60

SCC Testing – Viscosity

Time taken for volume of concrete to flow out until it is possible to

see vertically through the funnel into the container below for the

first time : V-funnel flow time (to nearest 0,5 s)

Volume of concrete in

fully filled funnel :

About 12 litres

Measure time to 0,1 s

of 60

Repeatability and Reproducibility

Slump-flow, SF (mm) < 600 600 – 750 > 750

Repeatability, r (mm) n/a 42 22

Reproducibility, R (mm) n/a 43 28

Repeatability and reproducibility for typical values of slump-flow

Repeatability and reproducibility for typical values of t500 times

t500 times (s) < 3,5 3,5 – 6.0 > 6,0

Repeatability, r (s) 0,66 1,18 n/a

Reproducibility, R (s) 0,88 1,18 n/a

Repeatability and reproducibility for typical values of V-funnel flow times

V-funnel flow time, tv (s) 3,0 5,0 8,0 12,0 >15,0

Repeatability, r (s) 0,4 1,1 2,1 3,4 4,4

Reproducibility, R (s) 0,6 1,6 3,1 5,1 6,6 of 60

Consistence Classes for SCC

Class L-box ratio tested in accordance with EN 12350-10

PL1 ≥ 0,80 with 2 rebars

PL2 ≥ 0,80 with 3 rebars

Table 9 – Passing ability classes – L-box

Definition

Passing ability

Ability of fresh concrete to flow through tight openings such as

spaces between steel reinforcing bars without segregation or

blocking

Class J-ring step (mm) a tested in accordance with EN 12350-12 (mm)

PJ1 ≤ 10 with 12 rebars

PJ2 ≤ 10 with 16 rebars


Table 10 – Passing ability classes – J-ring

The classes in Tables 9 and 10 are similar but not exactly the same

May also be specified by a minimum value when determined by L-box-test or

by a maximum value when determined by J-ring test of 60

SCC Testing – Passing Ability (L-box) Test

Passing ability ratio, (PL to nearest 0,01, H1 and H2 to nearest 1 mm):

PL = H2/H1

where

PL is passing ability ratio measured by L-box test

H1 is the mean depth of concrete in vertical section of the box (mm)

H2 is the mean depth of concrete at end of horizontal section of the box (mm)

Note: Gap of (41 1) or (59 1 ) mm

using 12 mm diameter bars

of 60

Repeatability and Reproducibility

Passing ability – PL ≥ 0,8 < 0,8

Repeatability, r 0,11 0,13

Reproducibility, R 0,12 0,16

Repeatability and reproducibility for typical values of passing ability ratio

L-box test is used to assess passing ability of SCC to flow through

tight openings including spaces between reinforcing bars and other

obstructions with segregation or block.

There are two variations: ―two bar test‖ and ―three bar test‖

―Three bar test‖ simulates more congested reinforcement

2 nos. (12 ± 0,2) mm bars, gap = (59 ± 1) mm

3 nos. ((12 ± 0,2) mm bars, gap = (41 ± 1) mm

Check concrete for signs of segregation before and after filling the

L-box

Report in qualitative way:

e.g. no indication of segregation,

strong indication of segregation

of 60

SCC Testing – Passing Ability (J-ring) Test

Record time taken to nearest 0,1 s for

concrete to reach the 500 mm circle at any

point, (t500J)

Measure largest diameter of flow spread ,

record as d1 to nearest 10 mm

Measure diameter of flow spread at right

angles to d1 to nearest 10 mm, record as d2

Measure height at central position, ho and

at 4 positions, hx1, hx2, hy1, and hy2 to

nearest 1mm

16 bars

Diameter = 18 mm

Gap = 41 ± 1 mm

12 bars

Diameter = 18 mm

Gap = 59 ± 1 mm

of 60

SCC Testing – Passing Ability (J-ring) Test

Passing ability PJ

PJ = ¼(hx1 + hx2 + hy1 + hy2 ) – h0 (to nearest 1 mm)

where

PJ is passing ability measured by blocking step (mm)

h are measurement heights (mm)

Flow spread SFJ (No specific requirement in EN 206 for SCC)

SFJ = (d1 + d2)/ 2 (to nearest 10 mm)

where

SFJ is flow spread (mm)

d1 is largest diameter of flow spread (mm)

D2 is flow spread at 90O to d1 (mm)

Flow time t500J (No specific requirement in EN 206 for SCC)

J-ring flow time t500J is period between cone leaving base plate and

when SCC first touches circle of diameter 500 mm (to nearest 0,5 s)

of 60

Repeatability and Reproducibility Repeatability and reproducibility for typical values of narrow gap J-ring

passing ability PJ, measured by blocking step

J-ring passing ability PJ,

measured by blocking step (mm) ≤ 20 > 20

Repeatability, r (mm) 4,6 7,8

Reproducibility, R (mm) 4,6 7,8

Repeatability and reproducibility for typical values of narrow gap J-ring

flow spread SFJ,

J-ring flow spread SFJ (mm) < 600 600 – 750 > 750

Repeatability, r (mm) 59 46 25

Reproducibility, R (mm) 67 46 31

Repeatability and reproducibility for typical values of narrow gap J-ring

flow time t500J

J-ring flow time t500J (s) ≤ 3,5 3,5 – 6 > 6

Repeatability, r (s) 0,70 1,23 4,34

Reproducibility, R (s) 0,90 1,23 4,34 of 60

Consistence Classes for SCC - Segregation

Class Segregated portion a tested in accordance with EN 12350-11 (%)

SR1 ≤ 20

SR2 ≤ 15


Table 11 – Sieve segregation resistance classes

Definition

Segregation resistance

Ability of fresh concrete to remain homogeneous in composition

when in its fresh state

Repeatability and reproducibility for typical values of segregated portion

Segregated portion SR (%) ≤ 20 > 20

Repeatability, r (%) 3,7 10,9

Reproducibility, R (%) 3,7 10,9

of 60

SCC Testing – Sieve Segregation Test

Segregated portion SR (to nearest 1 %)

SR = (mps – mp) x 100/ mc

where

SR is segregated portion (%)

mps is mass of sieve receiver plus

passed material (g)

mp is mass of sieve receiver (g)

mc is initial mass of concrete placed

onto the sieve (g)

Place (10 ± 0,5) litre of concrete in sample container, cover to prevent

evaporation

Allow to stand for (15 ± 0,5) min and record any bleed water observed

Pour from (500 ± 50) mm above the sieve (4,8 ± 0,2) kg of concrete

(including any bleed water) onto centre of sieve in one operation

Record actual mass, mc (g) on the sieve

Allow to stand for (120 ± 5) s, remove sieve vertically without agitation

Record mass of receiver, including material that has passed through sieve,

mps (g) of 60

SCC Testing - ASTM

ASTM C1611-09b, Slump flow of self-consolidating concrete

Procedure A (upright mold) – similar to EN 12350-8

Procedure B (inverted mold) – with smaller opening facing down

(may be needed for J-ring test when foot pieces interfere with ring)

T50 corresponds to t500

Stability (nonmandatory) indicated by Visual Stability Index Values

Table X1.1 Visual Stability Index Values

VSI Value Criteria

0 = Highly

Stable

No evidence of segregation or bleeding

1 = Stable No evidence of segregation and slightly bleeding observed as a

sheen on the concrete mass

2 = Unstable A slight mortar halo ≤ 10 mm and/or aggregate pile in the centre of

the concrete mass

3 = Highly

Unstable

Clearly segregating by evidence of a large mortar halo > 10 mm

and/or a large aggregate pile in the centre of the concrete mass

of 60

Self – Compacting Concrete: Visual Segregation Index

of 60

SCC Testing - ASTM

ASTM C1621-09b, Passing ability of self-consolidating concrete by J-ring

300 mm diameter ring, 16 bars of 16 mm diameter, gap = 42.9 mm

Blocking Assessment based on difference between slump flow and

J-ring flow (both to nearest 10 mm [1/2 in])

Slump flow = (d1 + d2)/2 and J-ring flow = (j1 + j2)/2

d1 or j1 = largest diameter of spread

d2 or j2 = spread at angle approximately perpendicular to d1 (or j1)

Difference between slump flow and J-ring Flow Blocking assessment

0 to 25 mm [0 to 1 in] No visible blocking

> 25 to 50 mm [> 1 to 2 in] Minimal to noticeable blocking

> 50 mm [> 2 in] Noticeable blocking

Table 1 Blocking Assessment

Note: EN 12350-12 records SFj - hence possible to consider Blocking Assessment

Difference between slump flow and J-ring flow may also be considered as

percentage of slump flow (same difference lower % for higher slump flow) of 60

SCC Testing - ASTM

Two test methods for static segregation:

ASTM C 1610-10, Static segregation of self-consolidating concrete

using column technique

A column of fresh concrete in 600 mm high mold allow to stand for 15±1

min.

Top and bottom sections of 165 mm removed for washing over 4.75 mm

sieve for coarse aggregate, dry and weigh to nearest 50 g

Difference between mass of coarse aggregate in top and bottom

sections to calculate % static segregation

ASTM C 1712-09, Rapid assessment of static segregation resistance of

self-consolidating concrete using penetration test

A special penetration apparatus to penetrate into the fresh concrete

over 30±2 s for penetration depth, Pd

Penetration depth, Pd Degree of static segregation resistance

Pd ≤ 10 mm Resistant

10 mm < Pd < 25 mm Moderately resistant

Pd ≥ 25 mm Not resistant of 60

Specifying CONCRETE – Consistence classes

Clause 4.2.1 Consistence classes (Tables for other types of consistence – in classes similar to slump)

(for details see Table 4, Table 5, and Table 6 of EN 206-1)

Table 4 – Vebe classes # (Vebe test conforming to EN 12350-3)

Table 5 – Compaction classes (not the same as compacting factor) (degree of compactibility conforming to EN 12350-4)

Table 6 – Flow classes ( flow diameter conforming to EN 12350-5)

1) Note to 5.4.1 Due to the lack of sensitivity of the test methods beyond certain values of consistence, it is recommended to use the indicated tests for:

Slump ≥ 10 mm and ≤ 210 mm

Vebe time 30 sec and > 5 sec #

Degree of compactability 1.04 and < 1.46

Flow diameter > 340 mm and 620 mm

In special cases, consistence may also be specified by target value Table 11 – Tolerances for target values of consistence

(for details see Table 11 of SS EN 206-1)

[Above information is now in EN 206: 2013 Annex L (informative)] # Vebe test – deleted in EN 206: 2013

of 60

Specifying CONCRETE – Consistence classes

Table 11 – Tolerance for target values of consistence (SS EN 206-1: 2009)

[Slump flow diameter from Annex ZZA (informative)]

Slump

Target value in mm ≤ 40 50 to 90 ≥ 100

Tolerance in mm ± 10 ± 10 ± 10

Vebe time

Target value in sec ≥ 11 10 to 6 ≤ 5

Tolerance in sec ± 3 ± 2 ± 1


Target value ≥ 1.26 1.25 to 1.11 ≤ 1.10

Tolerance ± 0.10 ± 0.08 ± 0.05

Flow diameter

Target value in mm All values

Tolerance in mm ± 30

Slump flow diameter


Tolerance in mm ± 30 of 60

Specifying CONCRETE – Consistence and Viscosity

Table 23 – Conformity criteria for target values a of consistence and viscosity

(BS EN 206: 2013, higher tolerance provided)

Slump

Target value in mm ≤ 40 50 to 90 ≥ 100

Tolerance in mm ± 10 ± 20 ± 30


Target value ≥ 1.26 1.25 to 1.11 ≤ 1.10

Tolerance ± 0.13 ± 0.11 ± 0.08

Flow diameter



a These values apply except where alternative values are given in

Annex D or in provision valid in place of use

Note: Annex D (normative) Additional requirements for specification and

conformity of concrete for special geotechnical wokrs of 60

Specifying CONCRETE – Consistence and Viscosity

Table 23 – Conformity criteria for target values a of consistence and viscosity

(BS EN 206: 2013, SCC) - continued

Slump flow diameter

Flow diameter



t500

Target value in s All values

Tolerance in s ± 1

tv

Target value in s < 9 ≥ 9

Tolerance in s ± 3 ± 5

a These values apply except where alternative values are given in

Annex D or in provision valid in place of use

of 60

y = 138500x-1.3

R2 = 0.81

0

200

400

600

800

1000

1200

1400

1600

1800

0 50 100 150 200 250 300Slump (mm)

Yie

ld s

tres

s (P

a)

>60 to 80>40 to 60>20 to 40_Power (_)

p (Pa.s)

Relation between Slump and Rheological Parameters

Yield stress to , Slump

• No clear correlation between plastic viscosity p and slump for non-air-entrained concrete

• For air-entrained concrete, air content , plastic viscosity , slump

(Chia 2006)

of 60

Setting of Concrete

• Defined as the onset of solidification in fresh concrete

• Transitional period between states of fluidity and rigidity

• Initial and final setting times of concrete are arbitrarily defined

by a test method such as ASTM C 403 (penetration resistance

method)

• Do not mark a specific change in the physical-chemical

characteristics of the cement paste or concrete; they are functional

points

• initial set: fresh concrete can no longer be properly handled

and placed

• final set: hardening begins

– Used

• to help regulate time of mixing and transportation

• to help plan the scheduling of finishing operations

• to determine the effectiveness of set-controlling admixtures

of 60

Setting and Hardening

• Setting

– When sufficient

contact has

formed between

hydration

products, paste

lose its fluidity

• Hardening

– Continued cement

hydration leads to

strength

development

(Mindess &Young 1981) & (Soroka 1993)

ASTM

C409

27.6 MPa

3.5 MPa

SS 320 (BS 5075-1)

Stiffening time at value of 0.5 MPa:

End of good workability

At value of 3.5 MPa:

Limit for avoidance of cold joint

(too stiff for vibrating previously

placed concrete to intermix with

newly placed concrete)

0.5 MPa

of 60

Time of Setting — ASTM C 403 or SS 320 (BS 5075)

Needle size:

ASTM C 403: various diameters

SS 320 (BS 5075) single size

diameter for area of 30 mm2

(6.175 mm) of 60

Effect of Hydration on Setting Time

• Role of C3S

– Setting is controlled primarily by the hydration of C3S

– Setting occurs when the induction period is terminated and

rapid hydration of C3S occurs in Stage 3

• Initial set – beginning of Stage 3, beginning of rapid

temperature rise

• Final set – midpoint of Stage 3,

• Role of C3A & gypsum

– In OPC, C3A plays a minor role in setting, except in cases of

abnormal set

• w/c (w/c , setting time )

• Temperature

• Admixtures

of 60

Abnormal Setting & Stiffening

• Sulphate related

– Delicate balance between C3A and

sulphate in solution in the first 15

min. If the balance is not right,

problems

– Form of calcium sulphate In cement

• Gypsum CaSO4.2H2O

• Hemi-hydrate CaSO4.1/2 H2O

• Anhydrate CaSO4

– Hemi-hydrate dissolves faster than

gypsum

– Anhydrate dissolves slowly

Rate of reaction: Hemihydrate > Gypsum > Anhydrate

of 60

Abnormal Setting & Stiffening

• Flash set

– Insufficient sulfate in solution

– C3A reacts quickly with water to form

CAH

– Flash set: immediate and permanent

hardening of mix

• False set

– Too much sulfate in solution

– Gypsum crystals precipitate

– Causing temporary stiffening

– If mixing continues, the gypsum will

re-dissolve and the stiffening will

disappear

(CTL Group) of 60

Abnormal Setting Behavior

• Water reducing admixtures related

– Some chemical admixtures (e.g. ASTM Type A or B) may interfere with cement hydration

• Accelerate C3A reaction

• Retard C3S reaction

– Interfere with the balance of aluminate and sulfate

• If the C3A is accelerated, flash setting

– Delay the addition of the WRAs

• Supplementary cementing materials related

– An SCM containing high C3A (typically Class C fly ash) can compromise the aluminate - sulfate balance

– Flash setting

– Desirable to use blended cements commercially produced instead of mixing cement and fly ash at ready mix concrete plants

of 60

Abnormal Setting Behavior

• Temperature related

– High temperatures generally increase solubility (except

calcium) and accelerate the rate of cement hydration

– Affect aluminate – sulfate balance

– Consumption of gypsum in cement paste system occurs

more quickly when the curing temperature is higher

– In warm weather, more sulfate is needed to control rapid

C3A reactions

of 60

Tests of Fresh Concrete - Application • As quality control measure and help to ensure proper mix

proportions

– Workability

– Setting times

– Air content

– Unit weight

Air content

(≤ 2% without entrained air) Unit weight

[Useful in verifying volume of concrete

(when compacted) in a truck] of 60

Quality Control of Concrete

• Control

– Mix proportion

– Compressive strength

– Durability (if specified)

• Importance of w/c ratio and

cement content

– No easy test method is available to

determine w/c and cement content

with sufficient accuracy

– Determine w/c ratio

• Concrete thin section under

optical microscope

• Light intensity passed through the

thin section w/c

• Accuracy 0.05

Petrography on concrete and interpretation

– by specialist petrographers

(Jacobsen & Brown 2005) of 60

fresh concrete

Documents