Onshore Wind Turbine Foundations: An Assessment of Freeze-Thaw Behaviour and the Development of Industry for New Construction

ETP Conference Edinburgh

10th October 2017

Background • Climate change statistics show that although winters and becoming milder

and wetter in the UK, sub-zero temperatures are still common and concrete is still be subjected to freeze/thaw cycles.

• Sustainability agendas published by the EU are pushing the use of non Portland cements in concrete construction to reduce the carbon footprint.

• Admixtures which are commonplace are required to be established on CEM I concretes/mortars (BS EN 480-11) which may not reflect performance in other concretes.

• Freeze/thaw attack can be a combination of both salt scaling effects and internal mechanisms (cracking).

Background What is freeze-thaw attack?

Air voids are created in the concrete by entrapped air

Drop in temperature causes water to freeze and expand

applying pressure to the pore walls and cracks to appear

These air voids become saturated with water through infiltration

Continual infiltration with further freezing and thawing enables the cracks to expand and eventually material to spall off

Background

Project Aims • Establish the range of materials for and suppliers of the test concretes for the

investigation. These will include concretes containing fly ash, GGBS, and limestone, all with F/T resisting aggregates. The effects of concrete curing/carbonation will also be taken as test variables.

• Review literature and collect information covering the use of the CEN/TS 12390-9 F/T scaling method and behaviour of various concrete constituent materials evaluated using this, with particular emphasis on the UK-relevant climate and regional variability. Examine field data with respect to the CEN/TS 12390-9 method, where available.

• Using an automatic image analysis system and following the BS EN 480-11 (2005) measurement method, quantify the air void characteristics of the test concretes.

Project Aims

• Carry out F/T scaling tests following the CEN/TS 12390-9 (3.0% NaCl) method to determine the performance of the test concretes.

• Analyse the data from the study to examine various issues with regard to estimating F/T damage (from fresh air content/air void characteristics), rates of deterioration within and between concretes, and comparisons between laboratory and field behaviour.

• Identify suitable test conditions/performance criteria for modifying the CEN/TS 12390-9

method, e.g. fixed number of F/T cycles, or vary temperature profile to achieve a particular mass loss, as appropriate.

Laboratory Study Exposure Class

Min Streng

th Class

Max w/c ratio

Min Air Content (%) and Min Cement or Combination Content (kg/m³) for max

aggregate size

Aggregate Requireme

nts

Cements and Combinations

32 or 40mm

20mm 14mm

10mm

XF3

C25/30 0.60 4.0 260

4.5 280

5.5 300

6.5 320

Freeze thaw

resisting aggregates

XF3 = MS25

XF4 = MS18

CEM I, CEM I-SR0, CEM I-SR3 IIA IIB-S, IIB-V IIB-V+SR IIIA1), IIIA+SR1) IIIB1), IIIB+SR1)

C40/50 Or

LC40/44

0.45 -

320 -

340 -

360 -

340

XF4

C28/35 0.55 4.0 280

4.5 300

5.5 320

6.5 340

C40/50 Or

LC40/44

0.45 -

320 -

340 -

360 -

340

Mix Code

Design Strength

Constituent Materials, kg/m3

w/c ratio

Admixtures, kg/m3

CEM I Water Aggregates

SP AE 0/4mm 5/10mm 10/20mm

CEM I Series 1 Non air entrained

M1 20 255 190 780 375 750 0.75 1.7 -

M2 30 300 190 760 375 750 0.63 1.7 -

M3 40 355 190 740 375 750 0.54 1.7 -

M4 50 415 190 720 375 750 0.46 1.7 -

M5 60 475 190 700 375 750 0.4 2.0 -

CEM I Series 2 Air entraind

M6 20 300 190 765 375 750 0.63 1.7 2.0

M7 30 365 190 740 375 750 0.52 1.7 2.0

M8 40 420 190 715 375 750 0.45 1.7 2.0

M9 50 480 190 690 375 750 0.4 1.83 2.0

Slump cone

Air content meter

Laboratory Study Air void analysis

Movement of the camera for linear traverse method Air void

analysis equipment setup

Slices blackened (a) Before (b) After

(a) (b)

Methods for analysing air void characteristics

Laboratory Study Air void analysis

Mix Code Hardened Air Content, %

Specific Surface,

mm-1

Spacing Factor, mm

Void Frequency,

mm-1

Average Chord

Length, mm

CEM I Series 1 Non-air Entrained M1 2.46 59.03 0.069 0.363 0.068 M2 1.36 62.43 0.098 0.213 0.064 M3 2.03 42.33 0.135 0.215 0.095 M4 1.06 67.33 0.117 0.178 0.059 M5 1.25 40.18 0.194 0.126 0.1

CEM I Series 2 Air Entrained M6 4.3 77.00 0.07 0.084 0.052 M7 4.4 41.17 0.132 0.098 0.101 M8 4.6 66.38 0.079 0.075 0.06 M9 4.5 56.26 0.096 0.082 0.072

M1

M2

M3

M4

M5

M6 M7

M8 M9

0

1

2

3

4

5

6

0 1 2 3 4 5 6

Har

dene

d Ai

r Co

nten

t, %

Fresh Air Content, %

Computational calculation of spacing factor

Fresh air content plotted against hardened air content

Air void characteristics determined by air void analysis

Laboratory Study Freeze-Thaw Testing

-50

-40

-30

-20

-10

0

10

20

30

40

50

0 5 10 15 20

Test

Cha

mbe

r Te

mpe

ratu

re,

°C

Time, hr

CEN Profile

Upper Limit

Lower Limit

Test Chamber Upper Temperature Limit

Test Chamber Lower Temperature Limit

Laboratory Study Freeze-Thaw Testing

20 MPa

30 MPa

40 MPa 50 MPa

Non-air entrained concrete

Air entrained concrete

20-30 MPa

40-50 MPa

Modifying the Test Method

Factors to be varied:

• Temperature profile

• Number of cycles used

• Salt concentration

• Carbonated concrete

Modifying the Test Method

Mix Code Week 1 Week 2 Week 3 Week 4 Week 5

mm

CEM I 2.0 3.7 4.7 6.3 7.3

CEM I A 3.1 3.9 4.4 5.5 6.1

CEM II-B 6.2 8.1 9.5 11.0 14.5

CEM II-B A 5.7 7.5 8.3 11.0 12.4

CEM III 4.6 6.4 8.2 10.4 10.6

CEM III A 4.2 4.0 5.2 7.1 8.7

CEM II-L 5.5 7.0 7.8 10.7 12.2

CEM II-L A 3.9 5.5 6.5 7.9 8.2

CEM III

CEM III A

CEM I

CEM I CEM I A CEM III CEM III A

0

0.5

1

1.5

2

2.5

3

3.5

4

0 10 20 30 40 50 60

Cum

ulat

ive

Mas

s of

Sca

led

Mat

eria

l Sn

, kg

/m2

Cycles

CEM ICEM I ACEM IIICEM III ALimit

CEM I A

Future Work • Continue with air void analysis and compile the results.

• Determine how much influence the microstructure of the concrete has on the

durability aspects.

• Complete carbonation testing to determine the influence carbonation has on freeze-thaw performance.

• Complete modifications to the CEN test to determine the validity of varying the parameters to better suit UK climate.

• Write the thesis

Thank you for listening

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