A brief history of supersulfated cement Beside the well-known Portland cement, another type of cement celebrated its 100th anniversary last year. In 1908, H. Kühl patented the so-called “gipsschlackenzement” and in so doing founded a new class of cement. It was discovered that the latent hydraulic properties of blastfurnace slags solidified in a glassy state cannot only be activated by basic matters like calcium hydroxide, but also by sulfuric matters such as gypsum. “Gipsschlackenzement” was therefore related to the two main components: granulated blastfurnace slag and gypsum. Later, the cement was called “sulfathüttenzement” or “supersulfated cement”, and this was approved in Germany in 19371 and later standardised2. Several other countries, such as the UK, developed their own standards3. Supersulfated cement was subsequently used in the 1940s to the 1960s, mainly in the UK but also in France, Italy, the Benelux countries and Germany. The major advantages of supersulfated cement were soon discovered and realised:

The production of a cement exclusively in a grinding process and therefore the possibility to avoid an energy intensive burning process.

The cement’s exceptional low heat of hydration.

The excellent resistance against chemical attacks by sulfatic and acidic elements.

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The UTilisaTion of GGBfs for AdvAnced sUpersUlfaTed CemenTsGünter Woltron, WopfinGer BuildinG

Materials Group, austria, descriBes

the technical, econoMic and

ecoloGical profile of the neW ceMent

slaGstar® 42.5 n c3a-free. additionally

WolfGanG Wetzer & cleMens plöchl,

enerGy chanGes projektentWicklunG

GMBh, austria, shed soMe liGht on cdMs

as a financinG instruMent for the

transfer of innovative technoloGies.

[Reprinted from Sep 09] worldcement.com

The literature gives a variety of reasons for the disappearance of supersulfated cement from the market later on. One important reason was the change in the composition of granulated blastfurnace slags as a result of using different raw materials. Granulated blastfurnace slags are therefore often less reactive nowadays than in former times and in many regions they can no longer be used for producing supersulfated cement using the old formulations.

The reinvention of supersulfated cementThe Wopfinger Building Materials Group, a privately owned Austrian company, is currently the only well-established producer of supersulfated cement on an industrial scale. The brand name of the product is Slagstar® 42.5 N C3A-free.

The first pilot applications with Slagstar® 42.5 N C3A- free were realised approximately ten years ago and it has been successfully implemented in the market for nearly a decade. The European Technical Approval (ETA) was granted in 20054

and therefore opened the international market access for the innovative cement. Based on recent developments, CEN Technical Committee TC 51 decided to designate a separate European standard for supersulfated cement. The draft of the standard EN 157435 is already available.

Over 100 Slagstar® projects have been successfully realised since the European Technical Approval was issued. Applications cover the whole range of structural concrete engineering.

Slagstar® was developed in order to overcome the historical problems of blastfurnace slags, characterised by a low reactivity. In addition to the standard components of supersulfated cements, minor amounts of special additives are used. This, combined with specific production know-how, enables the composition to be adopted to almost any blastfurnace slag available on the market, meaning high quality cement can be produced from almost any blastfurnace slag source available. The advanced cement is patented in over 50 countries and Slagstar® licenses are currently about to be granted worldwide.

Although the well-known properties of supersulfated cement are valid for Slagstar®, around 20 years of continuous research and development led to a technological lead, especially in:

Producing high quality and uniform supersulfated cement of improved strength development.

The ability to utilise granulated blastfurnace slag of low reactivity.

The deepened understanding of how the hydration mechanism is used to react on changes in raw material quality. This know-how is used to adopt the formulation and production parameters in order to keep the product quality stable.

Concrete and application technology.

This development of Slagstar® was driven from two more-or-less independent specific features of supersulfated cement.

The specific technological profile and the special product properties.

The specific ecological profile of the product.

The technological profile – property/application matrix of supersulfated cementsThe remarkable product properties of supersulfated cements have already been published internationally in recent years6 - 11. Its areas of application allow broad access to the market of

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Sewage treatment plant made of concrete incorporating Slagstar® 42.5 N C3A-free. Concrete for urban water supply and treatment is a typical application area for supersulfated cement.

The high resistance to chemical attack is a clear advantage of Slagstar® concrete. Corresponding applications can therefore be found in industrial areas or structures exposed to specific chemical attacks (sulfate, acids, salts).

A biogas tank made of prefabricated Slagstar® high performance concrete for severe aggressive conditions. Engineered and supplied by MABA Fertigteilindustrie GmbH, a Kirchdorfer Industriegruppe company.

worldcement.com [Reprinted from Sep 09]

precast and ready-mix concrete, especially in the high-quality and top-price segment. Supersulfated cement provides solutions to the increasing market demands for high quality concrete that cannot be covered by other cement types to this extent. The following product properties of concrete made with Slagstar® may be highlighted:

Excellent sulfate resistance.l

Increased resistance to acid attack.

Low permeability.

Low chlorine penetration.

Low heat of hydration.

Excellent water retention.

High stability under load.

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Table 1. Property/application - matrix of supersulfated cement

Quality requirement

Concrete in aggressive environment

Concrete exposed to seawater

Concrete for massive foundations

Concrete for special foundation engineering

Exposed concrete

Concrete with optimised leaching behaviour

Concrete avoiding alkali aggregate reaction

Concrete with decreased environmental impact

Application examples

Sewage treatment plants

Sewage pipes

Bio-gas plants

Agricultural buildings

Civil engineering in coastal areas

Massive bottom slabs

White tanks

Concrete piles

Subterraneous curtains

Civil engineering general

Concrete tiles with reduced efflorescence

Special underground engineering

Tunnel drainage systems

Civil engineering general

Civil engineering general

Relevant properties

Excellent sulfate resistance

Increased resistance to acid attack

Low permeability

Low chlorine penetration

Low heat of hydration

Excellent water retention

High stability under load

Low tendency towards bleeding

Low tendency towards efflorescence

Bright concrete colour

Low leaching behaviour

High resistance towards alkali aggregate reaction

Low environmental impact (low CO2 cement)

[Reprinted from Sep 09] worldcement.com

Low tendency towards bleeding.

Bright concrete colour.

Low tendency towards efflorescence.

Reduced leaching behaviour.

High resistance towards alkali aggregate reaction.

Decreased environmental impact (low CO2 cement).

An overview of some concrete applications that favour the utilisation of supersulfated cement is given in Table 1.

The ecological profile of supersulfated cement - the low CO2 cementThe CO2 topic has increasingly turned the spotlight onto cements with a reduced carbon footprint. As Slagstar® is a cement that can be produced without an energy intensive burning process, it is one of the most eco-efficient exponents of the ongoing initiatives to develop low CO2-cements.

The introduction of innovative, sustainable products like Slagstar®, is an essential contribution to environmentally-friendly building materials. The global cement industry caused around 5%12 of global annual anthropogenic CO2 emissions, by producing 2.77 billion tpa13 of cement (status in 2007).

By utilising GGBFS and gypsum as its main components, Slagstar® is characterised by a low consumption of natural resources. As a consequence, its production causes up to 90% less CO2 emissions compared with traditionally produced cement types. The minimisation of greenhouse gas emissions characterises the sustainable effect of the product, which can contribute significantly to the protection of the atmosphere.

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The high stability under load together with the low heat of hydration make Slagstar® concrete the perfect choice for special foundation engineering. Concrete piles or massive bottom slabs are a wide area of application. This image shows pillar foundations in road engineering.

Possible process flow for a mid-size project under the flexible Kyoto Clean Development Mechanism (CDM); CDM offers an interesting co-financing instrument for introducing environmentally-friendly production technologies. © Energy Changes/Wopfinger

worldcement.com [Reprinted from Sep 09]

Technology transfer - emission reductions as a financing instrument The international carbon markets, such as the flexible Kyoto Clean Development Mechanism (CDM)14, may act as an instrument to effectively disseminate and pre-finance this innovative and climate-friendly product, Slagstar®, and associated technology.

CDMs allow Annex I countries, or private entities from those countries, to obtain carbon credits called Certified Emission Reductions (CERs), by investing in projects that reduce emissions and are undertaken in emerging or developing countries that have signed the Kyoto protocol (“Non-Annex I countries”, e.g. China, India, etc.). A single CER unit is equivalent to one reduced tonne of CO2 emissions and has a current market value of E12.15

The production of Slagstar® represents such a project activity, which reduces greenhouse gas emissions and (when implemented in a Non-Annex I country) qualifies as a CDM project. The reduced tonnes of CO2, compared to traditional cement production, and the resulting income stream from the sale of CERs offers an interesting and essential co-financing instrument for project investors in the construction materials industry who want to launch less emissions-intensive technologies and innovative building products into existing or new markets.

The comeback of supersulfated cementAfter a long absence from the market, supersulfated cement is about to re-enter its position in civil engineering. This development is, on the one hand, driven by some inherent technical material properties (sulfate resistance, seawater resistance, acid resistance, low permeability, low heat development, etc.) and on the other by the ability to produce this type of cement with minimal environmental impact in terms

of consumption of natural resources, energy consumption and emissions. The process is facilitated by the initiatives to develop cements with a low carbon footprint. It can be expected that supersulfated cement will increasingly fill a market area that is currently dominated by other cement types in the coming years. Slagstar® is currently the only representative of this cement class with a decade of successful market appearance.

ReferencesReichsarbeitsblatt Nr. 2/38; Teil I, S. 11, 1937.

DIN 4210, Sulfathüttenzement, 1959.

British Standard BS 4248 Supersulfated cement, British Standards Institution.

European Technical Approval, ETA 05/0015, 2005.

prEN 15743, Supersulfated Cement – Composition, specifications and conformity criteria, 2008.

NOVAK, D., and NOVAK, R., ‘Practical experience with a new type of supersulfated cement’, Cement International No. 6/2004, pp. 116 - 125.

NOVAK, D, and NOVAK, R, ‘An environmentally friendly concrete binder based on supersulfated cement’, Ciments betons platres chaux, No. 871, 2005, pp. 54 - 62.

NOVAK, R, ‘Slagstar for greener concrete’, GCL Global Cement and Lime magazine; October 2004, pp. 18 - 22.

NOVAK, R, ‘Reducing CO2 emissions’, WORLD CEMENT; Vol. 34 No. 9, September 2003, pp. 27 - 30.

NOVAK, D., and NOVAK, R., ‘Superstar!’, WORLD CEMENT, June 2005, pp. 45 – 51.

NOVAK, R., SCHNEIDER, W., and LANG, E., ‘New knowledge regarding the supersulphated cement Slagstar’; ZKG International, No. 12-1 2005, pp. 70 - 78.

Vereinigung der Österreichischen Zementindustrie - www.zement.at/page.asp?c=116.

CEMBUREAU - Activity Report 2007 - www.cembureau.be/default.asp?p=Key_02.asp.

http://cdm.unfccc.int/index.html.

Pointcarbon 14 June 2009 - www.pointcarbon.com.

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[Reprinted from Sep 09] worldcement.com