introduction to nitcal as sustainable corrosion...

Introduction to NitCalas Sustainable

Corrosion Inhibitor

Mehrdad TorabzadeganYara Technology Centre, Porsgrunn, Norway

• NitCal is a Calcium Nitrate based concrete admixture. It is a chloride free, environment friendly admixture.

• Calcium Nitrate can be used:• Stand alone product

• Setting accelerator• Corrosion inhibitor

• Joint formulation with other chemical admixtures to have synergies with:

• Super plasticizers• Blended cements• Air entrainers

• Very good performance• ready mix concrete• precast concrete• Wide range of environment casting temperature.

22/12/2015Yara Technology Centre, Porsgrunn, Norway 2

What is NitCal?

NO

CaO

O

NO O

O

• Concrete is a porous medium in which the pores are partially filled with water.• Durability of the concrete directly linked to the ease of chemical penetration into the concrete.• Chloride ion can migrate to the concrete by absorption and the diffuse further into the

concrete through pore water.• Concentration gradient is the main drive to migrate from surface to subsurface layer.• When concrete permanently exposed to diffusion is the means of transport. However, even

without drying the level of chloride ion in the pore water might be above the chloride source itself.


Introduction to chloride ingress

• Study to evaluate commercially available corrosion inhibitors

• Calcium Nitrite and Calcium Nitrate (in different dosages) have been tested as corrosion inhibitors for reinforcement steel in concrete with different contaminations

• Corrosion potential measurement with electrodes

• Calcium Nitrate at dosage of 4% has increased compressive strength compare to other inhibitor.

• Calcium Nitrite and Calcium Nitrate perform similarly, and improve the situation especially for brackish water exposure or in case of contaminated aggregates


Findings:King Fahd University, KSA (2003)

010 020 030 040 050 060 070 080 0

corro

sion

pot

entia

l [-m

V]

(SCE

)

Chloride

Chloride & Sulfate

Seawater

Brackish water

Unwashed aggregate

ASTM C 8 76limit

low probability

high probability

010 020 030 040 050 060 070 080 0

corro

sion

pot

entia

l [-m

V]

(SCE

)

Chloride

Chloride & Sulfate

Seawater

Brackish water

Unwashed aggregate

ASTM C 8 76limit

low probability

high probability

Medium/Ion concentrations Sea Water Brackish water

Chloride 24408 ppm 893 ppm

Sulfate 4211 ppm 630 ppm

Sodium 14400 ppm 459 ppm

pH 7,6 7,78

• Study to evaluate commercially available corrosion inhibitors for silica fume modified concrete

• Among others Calcium Nitrite and Calcium Nitrate have been tested as corrosion inhibitors for reinforcement steel in concrete with different chloride contaminations

• Calcium Nitrite and Calcium Nitrate perform similarly, and the corrosion current in case of Nitrate was lower compared to Nitrite


Findings:Saudi Aramco & King Fahd University, Saudi Arabia

Ca(NO3)2 Ca(NO2)2

reference

CI-1: Calcium NitrateCI-2: Calcium NitriteCl-3: Migratory corrosion inhibitorCI-4: Organic inhibitor

Refrence rebar with 2% chloride

Rebar incorporating CN with 2% chloride

Rebar incorporating MCI with 2% chlorideRebar incorporating CNI with 2% chloride


Findings: SINTEF long term effect of NitCalWall elements exposed to sea water for 12 years

Element 2 added nitrate

Element 1 added nitrite

Element 3 Reference

• The compressive strength of the concrete with nitrite was higher than concrete with nitrate and higher than the reference without admixture

• the compressive strength of both concrete with nitrite and reference concrete seemed to have a significant drop in strength from 1 year to 12 years, while the strength of concrete with nitrate was rather constant in the same period.

• The binder near the surface was substantially• cracked in the concrete with nitrite, and the sulphate

ingress was higher than for the two other concretes.

40

50

60

70

80

90

100

1 12

Com

pres

sive

str

engt

h (M

Pa)

Year

Compressive strength of specimen

Nitrite

Nitrate

Ref

Back Scattered Electron (BSE) images near the surface of the different mixes


Findings:Fate of Nitrate ions in cement matrix

• Cement hydration products:• Portlandite Ca(OH)• Calcium Silica Hydrate (C-S-H)• Aluminium bearing phases:

• Aluminate Ferrite mono-substituent phase (AFm). Shorthand for a family of hydrated calcium aluminate phases. Ithas a crystalline layer structure and is derived from that of portlandite, Ca(OH) , but with one third of the Caions replaced by a trivalent ion, nominally Al or Fe .

• Aluminate Ferrite tri-substituent phase (AFt) or ettringite. Product of C3A and gypsum and it has a trigonal needle shaped crystalline.

Trace 1: No Ca or Ca Trace 2: 0.01 moles Ca Trace 3: 0.01 moles Ca

Trace 1

Trace 2

Trace 3

Trace 1

Trace 2

Trace 3

CaCO3 containing cement

CaCO3 free cement

• Before adding nitrate XRD graph of cement types I/II shows carbonate and hemi-carbonate AFm in addition to un hydrated C3S.

• After adding Nitrate, carbonate and hemi-carbonate mostly are replaced by nitrate.


Findings:Fate of Nitrate ions in cement matrix

• Before adding nitrate XRD graph of cement types II/V shows sulphate bonding to AFm in addition to situation in Cement type I/II.

• After adding Nitrate, , or OH ions are expelled from the AFm phase at the expense of the nitrate-AFm (NO3-AFm) formation.

Sulphite to aluminate ratio (SO3/Al2O3) in cement type I/II is 0,5 while in cement type II/V is 0,83.

• Both crystals look similar• Significant wrapped and leaf like edges.


Influence of nitrate and nitrite on AFm phaseCharacterization - Scanning Electron Microscopy (SEM)

Nitrate AFm

Nitrite AFm

Solid Chemistry:Nitrate activated at the presence of Chloride• Nitrate is bound to AFm-

phases during cement hydration

• Due to the different binding powers (= Gibbs Energies for the solid system) Chloride can replace Nitrate/Nitrite in the matrix

• Thus bound Nitrate is released and available for hydroxide formation at the presence of chloride; chloride gets bound !

Balonis et al. (2010)



Aqueous Chemistry:The formation of Ferric Hydroxide layers

Does not happen in concrete(no self passivation)

Does happen!

Does happen!

NO2- mechanism: Rosenberg and Gaidis (1979) , Sagoe-Crentsil et al (1991/1992)NO3- mechanism: Justnes (2005)

• Standard specification for admixtures to inhibit chloride-induced corrosion of reinforced steel in concrete.

• The specification covers the material for use as chloride-corrosion-inhibiting admixtures for concrete.

• Terminology:• Chloride ion content: The acid-soluble chloride-ion content

measured at the depth of reinforcement.• Critical chloride-ion content: The mean chloride ion content in the

unreinforced control beams at .• is time to the mean integrated macro-cell current of the control

beams reaches 50 C.• is time to the mean integrated macro-cell current of the control

beams reaches 150 C.• Completion of testing

• when following conditions reached:• Mean integrated macro-cell current in control beam≥ 150 C.• Mean chloride ion content ≥ Critical ion content.


Introduction to ASTM Standard C1582/C1582M-11Scope

• shall be conform to the requirements prescribed in Table 1.

• The performance property of chloride-corrosion inhibiting shall consist of time of setting and compressive strength at 3, 7, and 28 days.

• Remaining compressive and flexural strength of 80% of the reference sample.

• At any age compare to the age before the reduction should not be more than 10%.

• Initial and final setting time should not be altered more than 3.5 hours.

• The chloride-corrosion inhibitor shall comply with ASTM C494/C494M specification as admixture.

• Aggregate origin


Requirements according to ASTM C1582/C1582MGeneral Requirements

• ASTM Test Method G109 or G180• Corrosion potential requirement (according to

Table 2)• Corrosion current measurement• Corroded area measurement • Chloride ion content

• Scope: G109 method covers a procedure for determining the effect of chemical admixtures on the corrosion of the concrete (chapter 1 ASTM G109)


Requirements according to ASTM C1582/C1582MCorrosion-Inhibiting Performance

• Composition requirements by ASTM G109:• CEM I 42,5R (EN 197/1)• W/C ≤ 0,5• Air entrainer 6±1%

• Ponding cycle:• 15 days dry• 15 days of ponding (3% NaCl solution)


Test Setup - Concrete beam

• Measure the voltage across the100 Ω resistor

• Measure the corrosion potential of bars against a ref electrode placed in salt containing dam.

Plastic tube + tape Plastic tube +tape

203

20 mm

Stainless steel screw

• According to ASTM requirements:• Time of setting, allowable deviation from control• Initial: not more than 3:30 earlier or later• Final: not more than 3:30 earlier or later


Test Results according to test method G109 setting time

Setting time (hh:mm)

Dosage 0% CN Dosage 4% CN ∆T CriteriaInitial End Initial End Initial End ∆T < +/- Initial End

CEM I 52.5 R 04:30 06:15 02:10 03:05 02:20 03:10 03:30 fulfilled fulfilledCEM IV/A 42.5R 06:00 07:25 03:50 04:50 02:10 02:35 03:30 fulfilled fulfilledCEM II/A-LL 42.5R 04:30 05:55 02:30 03:35 02:00 02:20 03:30 fulfilled fulfilled

Setting time (hh:mm) 0% CN 4% CN ∆T ∆T < +/- Criteria

CEM I 52.5 R white 03:00 01:00 02:00 03:30 fulfilled

CEM II/A-V 42.5 04:30 02:00 02:30 03:30 fulfilled

CEM III/B 52.5 04:00 00:30 03:30 03:30 fulfilled

Results from various reports by SINTEF, Norway

Results from ENCO report, Italy

• According to ASTM requirements:• Compressive strength and flexural strength minimum remain 80% of control


Test Results according to test method G109Compressive and flexural strength

1 day strength Dosage 0% CN Dosage 4% CN remain

_c [MPa] _f [MPa] _c [MPa] _f [MPa] _c _f

CEM I 52.5 R 34,50 5,70 36,00 5,60 104 % 98 %

CEM II/A-V 42.5 17,20 3,70 14,30 3,10 83 % 84 %

CEM III/B 52.5 14,50 3,00 12,20 2,70 84 % 90 %

Results from various reports by SINTEF, Norway, over the last decades

40%

60%

80%

100%

120%

140%

0

20

40

60

80

100

0.1 1 10 100 1000

rem

aini

ng s

tren

gth

com

pres

sive

str

engt

h (M

Pa)

time of experiment (days)

Compressive strength(CEM I 52.5 R-LA)

Dosage 0% CN s_c [MPa] Dosage 2% CN s_c [MPa]remain (%) s_c req. Remain (%)

• Corrosion Current starts at 10 μA (G109). • Control reached 10 μA in average after 97 days. • 3% CN treated samples reached current at 150 days and 4% CN samples not within 180 days.


Completion of testing (corrosion current)start and end – first check point

0

10

20

30

40

50

60

70

0 30 60 90 120 150 180

corr

osio

n cu

rent

(μA

)

duration of test (days)

Corrosion Current

Control (avr.) 3% CN (avr.)4% CN (avr.) G109untreated A untreated Buntreated C 3% CN A3% CN B 3% CN C4% CN A 4% CN B4% CN C

Results from ENCO (2014)

• Mean integrated macro-cell current in control beam≥ 150 C. That happened in day 156th , interpolated from the measurement at 150 days and 180 days

• Concrete beams with 3% and 4% of NitCal reached about same time to macro-cell charge of 50 C.


Completion of testingStart and end – second check point

0

25

50

75

100

125

150

175

200

225

250

0 30 60 90 120 150 180

Cha

rges

(C)

Days

Period of testing

3% NitCal

4% NitCal

Control mix


• Mean chloride ion content ≥ Critical ion content• Critical chloride ion content is the concentration that the corrosion is possible. Based on below

table 0.4% of cement weight is determined. (Browne 1982)


Completion of testingStart and end – third check point

Control (avr.) 3% CN (avr.) 4% CN (avr.)% 0.45 0.42 0.45

0.20

0.25

0.30

0.35

0.40

0.45

0.50

chlo

ride

cont

ent (

%)

Chloride content


Adopted from (Browne 1982)

• Corroded area of the treated samples shall not exceed 1/3 of the corroded area of the reference samples (C1582)

• After 180 days the corroded area was in average about 1/3 of the reference samples. (3% and 4% CN dosage)


Corroded areaCorrosion inhibition performance

0.32 0.39 0.33

0.0

1.0

2.0

3.0

4.0

A B C

avr(A

,B,C

) A B C

avr(A

,B,C

) A B C

avr(A

,B,C

)

ASTM

C15

82

untreated 3% CN 4% CN Req

abso

lute

are

a in

(cm

2)

rela

tive

area

(%)

Corroded area (180d)

absolute relative


• Extracted bars from concrete test beams confirm less corroded area for beam with 3% NitCal to the sample with 4%.


Corroded areaCorrosion inhibition performance

3% NitCal

4% NitCal

Reference 0% NitCal


• Chemically: • Calcium Nitrate Ca(NO3)2 contains one

Oxygen atom more than Calcium Nitrite Ca(NO2)2 therefore more available to form passive ferric hydroxide layers.

• Health and Safety:• Nitrate is no hazardous material (e.g.

utilized as fertilizer and energy source for micro-organisms), whereas Nitrite is poisonous (biocide and conservation agent)

• Economy:• Depending on market and logistics, Nitrate

is significantly cheaper than Nitrite


Why choose Nitrate and not Nitrite

NO

CaO

O

NO O

O

• With reference to literatures:• NitCal meets the general requirements of ASTM C1582 regarding

setting time and compressive strength. • Setting time is usually altered less than 3,5 hours.• Compressive strength is usually > 80% of the reference at all times.

• With reference to tests elaborated at ENCO:• NitCal, added as 3% and 4% bwoc. with minor deviation matches

the corrosion inhibitor requirements of ASTM C1582 (when tested in accordance with test method ASTM G109).

• The corrosion current stays within the documented tests below 10 µA.

• The integrated charges stay below 50 C (for 150 days).• The corroded surface is about 1/3 of the reference (180 days).

• Except lower corrosion current at 150 and 180 days, no significant improvement was found in the performance of calcium nitrate when the percentage was increased from 3% to 4%.


Summary

• Yara disclaims all responsibility and liability for any expenses, losses, damages and costs incurred as a result of relying on or using the information contained in this document. Yara reserves the right to adjust and revise this document at any time.

• Any forward-looking statement made by Yara in this document is based only on information currently available to Yara and speaks only as of the date on which it is made. Yara undertakes no obligation to publicly update any forward-looking statement.

• No rights, including, but not limited to, intellectual property rights, in respect of this document are granted to any recipient unless specifically stated.

• ©Yara International ASA. All rights reserved.

22/12/2015Yara Technology Centre, Porsgrunn, Norway

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