An Introduction to Improved Cold Weather Concreting

Concrete and Calcium Nitrate

An Introduction to Improved Cold Weather Concreting

Dr.-Ing. Wolfram Franke Yara Industrial

Application Development Yara Technology Center

[email protected]

5/09/2014 Page 2W.Franke

I. Calcium nitrate as a setting accelerator

II. Calcium nitrate and cold weather concreting

III. HESQ: Product and Application development for high quality concrete production

Topics

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5/09/2014 Page 3W.Franke 5/09/2014 Page 3

I. Calcium nitrate as a setting accelerator


General demand for non-corrosive accelerator

– Setting Accelerators are required to improve performance and productivity

– Chloride-based accelerators cause severe corrosion damage

Yara* performs systematic research on possible industrial applications for calcium nitrate

– In 1992 Norsk Hydro approached SINTEF, Trondheim/Norway, to start in-depth research of possible concreting applications

* formerly Norsk Hydro

Why Calcium Nitrate?


What brought the breakthrough ?

A unique project involving CN was the construction of the “Troll” oil/gas platform in the North Sea (construction 1991-1994)

Slip formation led to the need for a plasticizer - Productivity went down: – A non-corrosive accelerator was needed

Troll: the largest movable structure on Earth


Calcium Nitrate (CN) as a molecule

– Setting: Calcium speeds up the early hydration stage– Strength enhancement and Corrosion inhibition: Calcium reduces porosity– Corrosion Inhibition: Nitrate oxidizes dissolved rebar iron and forms a

protective layer around rebar, comparable to the effect of Nitrite

CN benefits over comparable alternatives

– CN does not corrode reinforcement, unlike Calcium Chloride– CN does not provoke alkali aggregate reactions, unlike Sodium Nitrate or

Sodium Nitrite – CN is environmental friendly, unlike Calcium Nitrite

What does Calcium Nitrate do ?


CN is a setting accelerator– Start of setting is shifted forward

in time– The reactions intensity within

setting is not affected (no hardening accelerator)

Efficiency depends strongly on type of cement

– CEM I 52.5, CEM II-V, CEM II-L benefit over full temperature range

– CEM I 42.5 benefits on low temperatures only

Calcium Nitrate as a setting accelerator

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0 3 6 9 12 15 18 2 1 24

tem

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t ime of experiment in h

Temperature development(cement paste, w/ c = 0 .4 5, 2 0 deg C)

CEM II A-V 42.5 R

CEM II A-V 42.5 R + 1CN

CEM I 52.5 N "white"

CEM I 52.5 N "white" + 1CN


II. Calcium nitrate and cold weather concreting


Purpose of an “antifreeze” agent are:

– Prevent temperature decrease below 5 °C within setting period

– Prevent freezing of water needed for hydration until a certain concrete strength is reached

– Prevent freezing the first day

Calcium Nitrate– Reduces setting time, produces

heat earlier and thereby provides the necessary temperatures for hydration

– does not reduce the freezing point of the mixing water

How does cold weather concreting work ?

2 hours earlier

7 hours earlier

Justnes and Nygaard (1993)


Best practice in compliance with ACI_306R-88

0 deg C5 deg C

T

Concrete

M ouldInsulation

Cover film

Frostfree ground or ”permafrost”

T

Concrete

M ould

Temporarily frozen ground

RightWrong Cover film

0 deg C5 deg C


Antifreeze:Keys are water control and set acceleration The concrete hydration of surface close areas is

crucial as the reinforcement is often placed here For the concrete hydration the availability of water is

essential. The two ways to prevent its freezing are– Keep water warm (for instance by hydration heat, as a

result of a set accelerator like NitCal) – dynamic solution at light frost

– Increase salt concentration of water to prevent freezing –static solution for deep frost

The way to increase salt concentration is the reduction of water, as the amount of salt added by admixtures is limited

The combined use of NitCal and a strong water reducing agent is recommended to obtain w/c ratio as low as 0,3 and thus minimize excess water.

When doing so, only minor ice formation is expected, and concrete can hydrate at even -15°C

Attention: – In this manner produced concrete develops compressive

strength very slowly– Final compressive strength might be reduced– Use of insulation is mandatory to support hydration– Use of hardening accelerator like Thiocyanate/Rhodanide

or Aluminum Nitrate is recommended for concreting jobs below -10°C


III.HESQ: Product and Application development for high quality concrete production


CN as water-free molecule is difficult to obtain and handle

– Strong oxidizer with challenging REACH classification

– Not available on the market

CN needs are provided as specialized products with improved handling and storage properties

– Liquids: • CN solutions with different

concentrations– Solids:

• Calcium-Ammonium-Nitrate (free flowing granule)

• Calcium-Potassium-Nitrate(free flowing granule)

• CN tetra hydrate(wet powder)

How to get Calcium Nitrate ?

0 % 20 % 4 0 % 60 % 8 0 % 10 0 %

CN 45% old

CN 45% new

CN 50 % old

CN 50 % new

NitCal

N itCal/K

CN Tetrahydrate

Composition of CN products

Ca(NO3)2 NH4NO3 or KNO3Crystal Water Free Water

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Market support Coordination of external R&D Customer communication Workshops and technical meetings on NitCal Concept development Screening tests, pre-testing (ISO certified production)

Certified testing Expertise Market Support

Special projects on Lignosulphonate and NitCal

Durability testing

Corrosion Inhibition, Models, Simulation

Market Support, Research and Development to ensure high quality concrete production

University of CaliforniaUCLA


The recommended CN dosages depend strongly on – Cement type used, the “antifreeze” feature in particular demands prior testing– Purpose of dosage

CN dosages refer to CN active contents – important when blends, hydrates and solutions are used!

Which dosages are recommended ?

0 1 2 3 4 5

Setting Accelerator(reduce setting time up to 50%)

Counteraction of Plasticiser(reduce setting time by 4h at +20°C)

Antifreeze(reduce setting time by up to 3h at +5°C)

Strength enhancement(additional 10% of compressive strength)

Corrosion Inhibitor(increasing duration to corrosion start by 20%)

dosage as % of cement weightcharacteristic up to(Given recommendations need to be proven in pre-tests with the local cement)


Thank you for your attention!

Yara Porsgrunn Plant


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• ©Yara International ASA. All rights reserved.

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Engineering

An Introduction to Improved Cold Weather Concreting