International RILEM Conference on Material Science – MATSCI, Aachen 2010 – Vol. III, AdIPoC 45

RESEARCH FOR DURABLE CONCRETE WITH FLY ASH

T. Eck, VGB PowerTech e.V., Essen, Germany

ABSTRACT: In Germany, hard coal fly ash has been used as a concrete addition for more than forty years. Based on extensive research work on laboratory and real scale on the possible uses and benefits the use of fly ash in concrete is well proven and regulated by national and European standards and regulations. Every year more than 3.5 million tonnes of fly ash are used as concrete addition. This is based on the positive effects of fly ash on the properties of fresh and hardened concrete. However, due to new test procedures and requirements there is still a need for research.

Over the last years several research projects concerning the use of fly ash in concrete were funded by VGB Research. At present, the research work focuses the durability of fly ash concrete, the sustainability as well as application research. This paper deals with recent results from research work regarding the durability of fly ash concrete.

1 INTRODUCTION

VGB Research Foundation is coordinating and funding research projects in the field of power plant construction and operation of fossil-fired power plants and renewables as well as on environmental technology. One main issue is the research work on the properties and use of coal combustion products (CCPs). VGB Research Foundation offers a neutral platform for the cooperation on joint research by the members of VGB PowerTech e.V. VGB PowerTech e.V., abbreviated VGB, is - as the European technical association for power and heat generation - a voluntary association of companies for which power and heat generation - i. e. power plant operation as well as the appropriate technique - is an important basis of their business. VGB experts and committees formulate the need for research or examine external research proposals and supervise the handling of the projects and the transfer of the results. The VGB Research Foundation is a member of the German Association of Industrial Joint Research Institutions (AiF).

Over the last years several projects regarding the use of CCPs in different applications and especially the use of fly ash in concrete were organized and funded by VGB Research. This research work was first done to demonstrate the possible use of fly ash in concrete, which was proven in pilot projects. The results and the experiences gained within the research work have been taken into consideration in the revision of guidelines and standards. The main subjects of the last years have been the durability (frost attack with and without de-icing salt, alkali-silica-reaction, sulphate attack), the limits of binder composition and the combined use of different concrete additions as well as research on road concretes with fly ash or special concretes with high amounts of fly ash like self-compacting concretes. At the moment the focus of the research work is on the durability aspects of fly ash concrete.

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2 PRODUCTION OF FLY ASH FOR CONCRETE

Fly ash is produced during the combustion of fine ground coal in coal-fired power plants. Depending on the type of power station, firing conditions and temperature fly ash can be produced according to DIN EN 450-1 [DIN08]. Fly ash from fluidized bed combustion, from grate firing and from power plants, which burn oil or waste is not suitable as concrete addition.

After grinding the pulverised coal is incinerated in the furnace of the power plant boiler. A minor part of the coal ash falls on the ground of the furnace wherefrom it is removed as bottom ash. The major part, approximately 90% of the fine ash content is carried along with the flue gases via the DENOX catalyst up to the electrostatic precipitator where more than 99.9% of the ash is separated from the flue gas. Depending on its quality fly ash separated in the electrostatic precipitator is pneumatically fed into a silo for certified fly ash or into a silo for mixed ash. The material flow is controlled according to regular tests as defined in DIN EN 450-2 “Fly ash for concrete - conformity evaluation” [DIN05]. The tests consist of quality control measures of the power plant as well as those by third party control. Fly ash from silo for mixed ash is not used for concrete production, but for e.g. filling purposes in road constructions.

In 2007 approximately 25 million tonnes of CCPs were produced in Germany including 4.15 million tonnes of hard coal fly ash [VGB07]. About 99% of these hard coal fly ashes were used for construction materials. The major part was used as an addition for ready mixed concrete and concrete products, for mining mortars and dry building materials as well as for road construction.

3 R&D ACTIVITIES - OVERVIEW

In Germany, the use of fly ash as concrete addition is well developed and established. This is the result of research work which was first done to demonstrate the possible use and which was proven in pilot projects. Over the last years several projects were organized and funded by VGB Research Foundation (see Table 3.1). More information on these projects is given on the website of VGB Research Foundation [VGB10].

The aim of these projects was and still is the proof of the technical suitability and the environmental compatibility of fly ash for different applications. The research projects aim to establish and safeguard already existing fields of utilisation and to explore new ones. At present, the research work is focused on the durability of fly ash concrete (i.e. frost and frost-thaw resistance, alkali-silica-reaction (ASR) and sulphate resistance), sustainability as well as application research. In the next chapter the main effects of fly ash in concrete are described and some results of R&D projects with focus on the durability aspects are presented.

International RILEM Conference on Material Science – MATSCI, Aachen 2010 – Vol. III, AdIPoC 47

Table 3.1. VGB Research Projects on the use of fly ash since 1999

P 199 Thaumasit Formation in Concretes 1999-2001 P 203 Frost Resistance of Concrete with Fly Ash 1999-2004 P 206 Combined Use of Silica Fume and Fly Ash in Concrete 2000-2001 P 209 Use of Fly Ash in Self Compacting Concrete (SCC) 2000-2001 P 210 Use of Fly Ash in Air Entrained Concrete 2000-2003 P 215 Frost Resistance of SCC with Fly Ash 2001-2005 P 225 Fly Ash in Tunnel Concretes 2002-2003 P 226 Avoidance of Alkali-Silica-Reaction in Concrete by Use of Fly Ash 2002 P 234 Water Demand of Hard Coal Fly Ashes and Cements 2002-2003 P 240 Concrete with High Amounts of Fines and with Fly Ash 2003 P 244 Bond of Alkalis in Binders Containing Fly Ash 2003-2004 P 245 Prevention of Alkali-Silica-Reaction with Fly Ash in Concrete 2003-2005 P 249 Prevention of Alkali-Silica-Reaction in SCC with Fly Ash 2003-2007 P 254 Literature Study: Sulphate Resistance of Fly Ash Concrete 2004 P 256 Fly Ash from Co-combustion in Concrete 2004-2006 P 257 Fly Ash Concrete on the Basis of Equal Efficiency 2004-2007 P 264 Chromate Content in Cement and Fly Ash 2004-2005 P 267 Water Permeability of Paved Areas 2005-2007 P 270 Durability of the Surface Texture of Road Concrete with Fly Ash 2005-2007 P 272 Effect of Fly Ash Regarding Avoidance of Alkali-Silica-Reaction 2005-2007 P 275 Prevention of Alkali-Silica-Reaction by Fly Ashes 2006-2009 P 284 Fly Ash Concrete with High Amount of Fines 2006-2008 P 287 Sulphate Resistance of Fly Ash Concrete 2006-2008 P 298 Fly Ash Opulent Ultra High-Strength Concretes 2007 P 300 Avoidance of Alkali Reactions by Fly Ash 2007-2010 P 309 Combined Use of Fly Ash and Blast Furnace Slag 2008-2010 P 310 Air-entrained Concretes with Plasticising Concrete Admixtures 2008-2010 P 315 Composition Limits of Fly Ash Concretes 2008-2009 P 323 External Alkali Attack 2008-2011 P 329 Alkali-Silica-Reaction Performance Test for Fly Ash Concrete 2009-2011 P 330 Frost Resistance of Fly Ash Concrete (XF2) 2009-2010

4 EFFECTS OF FLY ASH IN CONCRETE AND RESULTS OF R&D PROJECTS

Hard coal fly ash works in three ways on concrete and improves both the fresh and hardened concrete properties. It has a rheological and a filling effect, besides it contributes to the strength of concrete by pozzolanic reaction and increases the durability of the concrete. The use of fly ash in concrete affects all relevant concrete properties such as workability, strength development, development of heat of hydration and durability. The effect depends on the concrete mixture, on other concrete components, on concreting and subsequent curing of the concrete.

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4.1 Fresh Concrete Properties - Workability

4.1.1 Rheology In concrete with usual composition a clear liquefying effect of the concrete can be observed when a part of the cement is exchanged with fly ash and the water content is kept on the same level. This liquefying effect of the fly ash can be used to lower the water content of the concrete. It is often described as “roller bearing effect”. This is connected to the idea that the ball shaped fly ash particles with smooth surface ease the sliding of the cement and sand particles and by doing so, result in an easier formability or an improved rheology. The results from comparative experiments have shown that an improved grain size distribution decreases the water demand and improves the plasticity due to the filling of the voids between the cement grains. This effect of fly ash on the rheology can be utilised in practice to reduce the water content in concrete. For structural concrete the amount of water saved is usually between 5 and 15 l/m3, but there are also fly ash/cement combinations where no savings in water have been found [SYB93, WIE96].

A second effect of fly ash on the rheology is the improvement of the workability of the concrete for a given consistency. This improves the pumpability and confinement capacity of the concrete, eases compaction and reduces to a minimum the time for concreting. The cavity-filling effect has also a positive impact on the compressive strength of mortars and concretes at an early age. The filler effect is of purely physical nature and depends on the refinement of the used material. The finer the filler is, the better its cavity-filling effect is [LEW93].

4.1.2 Heat of Hydration For many concrete structures, especially for mass concretes, reliability with regard to the formation of cracks due to hydration temperature is of much greater importance than rapid strength development. Since fly ash does not react during the critical time of initial hardening and therefore does not produce any heat of hydration, it can be specifically used for the production of concretes with low heat of hydration. This can be particularly advantageous if the age at which the strength of the concrete has to be established is, for example, 56 or 90 days.

Reducing the tendency to crack by controlled addition of fly ash has proved itself in numerous applications such as large foundations, white tanks, container structures, swimming baths and silos. Thus, in producing the tunnel linings for the new stretches of the German Federal Railway, fly ash was used as a concrete engineering solution for preventing the formation of cracks due to temperature. By using fly ash, a pumpable concrete could easily be produced with good workability and which easily achieved the required demoulding strength of 3 N/mm2 after 12 hours but without exceeding this to an undesirable extent [SCH96].

4.2 Hardened Concrete Properties – Strength and Pore Size Distribution

4.2.1 Pozzolanic reaction/strength development As described before the cavity-filling effect and the pozzolanic reaction with a reduction of the heat of hydration at early ages influence the compressive strength and its time development. The pozzolanic reaction is characterised by a slower reaction process compared to the hydration of Portland cement. The fly ash and the calcium hydroxide, which is produced during cement hydration, react to strength forming calcium-aluminate-hydrates and

International RILEM Conference on Material Science – MATSCI, Aachen 2010 – Vol. III, AdIPoC 49

calcium-silicate-hydrates. The long persisting reactivity of the fly ash causes a clearly higher compressive strength than comparable mortars with cement or cement with quartz powder do.

The contribution of the pozzolanic reaction of fly ash to strength is not noticeable until the concrete is 28 days old and will develop afterwards. Therefore, by simply substitution of cement with fly ash, the strength of the concrete with fly ash develops more slowly and is consequently more responsive to curing. If the strength development of a fly ash concrete has to match that of a cement concrete, the lack of strength in the young concrete must be compensated. It is possible to do this by reducing the water/binder factor in comparison to the water/cement ratio of the cement concrete.

4.2.2 Pore size distribution The pozzolanic reaction is also associated with a change in the pore size distribution in the hardened cement-paste. Although the total pore volume in the hardened cement paste matrix remains unchanged or only changes to a small extent, the amount of pores with smaller diameter is increased and that with greater diameter reduced respectively. Because of this change in pore size distribution the resistance of the concrete to penetration of aggressive media is improved. Hardened cement paste with fly ash practically has no capillary pores with diameter greater than 0.1 µm. It is within these pores that aggressive media are able to migrate. Where these pores are absent, resistance to the penetration of aggressive substances is correspondingly high.

4.3 Hardened Concrete Properties – Durability

Besides strength, durability is another performance characteristic of concrete, which can be affected by various forms of physical and chemical attacks. The essential keywords are the carbonation, the resistance to an attack by sulphates and penetration by chlorides and the resistance to an attack from frost and de-icing salt or the alkali-silica-reaction.

4.3.1 Carbonation A large part of the damage to concrete in the past and present is due to carbonation where there is insufficient cover. In the past, it had frequently been maintained that the rate of carbonation was increased by fly ash. Since then, the results from extensive investigations based on years of measurements both inside and outside Germany have shown that, for the same compressive strength, the carbonation behaviour of concretes containing fly ash does not significantly differ from concrete without fly ash [BER88].

A statistical analysis showed that the depth of carbonation and the compressive strength, which is regarded as the parameter with the greatest influence, is mainly affected by the type of cement and only to a small extent by the addition of fly ash (see Fig. 4.1). In general, it is possible to say that concrete produced with fly ash in accordance with DIN EN 206-1 and DIN 1045-2 [DIN01, DIN08a] shows carbonation depths in the same range as concrete with cements only, also under unfavourable storage conditions [HAE95, WIE91].

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Fig. 4.1. Carbonation depth after 10 years storage versus compressive strength at 28 days [WIE91]

4.3.2 Chloride Penetration The higher impermeability of mortars and concretes containing fly ash also acts against attacks from other chemicals. Comparative experiments have shown that chloride ions take significantly longer to penetrate mortars and concretes with fly ash than concretes with Portland cement and without fly ash. Fig. 4.2 shows the results of the chloride diffusion of mortars without and with different levels of fly ash addition.

The high resistance to the penetration of chloride ions and acid is essentially due to the change in pore structure of the hardened binder caused by the pozzolanic reaction of the fly ash. The changes in the ion diffusion caused by fly ash also have a highly beneficial effect on the electrolytic resistance of the concrete. High electrolytic resistance prevents the steel from corrosion. Fly ash concretes should therefore be recommended where there is exposure to chlorides [HAE95, WIE05].

Fig. 4.2. Chloride diffusion coefficient versus age; mortar with and without fly ash [WIE05]

4.3.3 Freeze-Thaw-Resistance The exposure of concrete with frost or frost and de-icing salt, sometimes in combination with an ASR, can be another big problem of concrete structures. There are different exposure classes according to the various forms of frost attack (XF1 to XF4). The exposure classes XF1 and XF2 describe a frost attack without and with de-icing salt at moderate water saturation

International RILEM Conference on Material Science – MATSCI, Aachen 2010 – Vol. III, AdIPoC 51

and the classes XF3 and XF4 classify a frost attack at high water saturation. Before 2008 fly ash was not allowed to be taken into account for concrete exposed to freeze-thaw attack with de-icing salt (XF2 and XF4). According to the current standards DIN EN 206-1 and DIN 1045-2 [DIN01, DIN08a], it now can be taken into account for the calculation of the water cement ratio as well as for the minimum cement content for all frost and de-icing salt exposure classes (XF1 to XF4).

The extension of the accounting of fly ash for the exposure classes XF2 and XF4 in the revision of DIN 1045-2 is a consequence of the results of research work over the last years. Some results are shown in Fig. 4.3. It can be concluded, that fly ash concrete with and without additional air pores has the same resistance to frost and de-icing salt than concrete without fly ash [VGB04]. Since air entraining agents (AEA) are sensitive to concrete components, the effectiveness of the AEA should be tested along with all concrete components. A change in one concrete component forces the need of new tests on effectiveness, as for all concretes.

Fig. 4.3. Scaling versus Freeze-Thaw-Cycles; concrete with and without fly ash [BRA05]

Another project [VGB03] dealt with the rules for accounting of fly ash for the exposition class XF2 for tunnel concretes, because in practice fly ash concretes are used in the entrance area of the tunnel inner shells. The investigations showed that the test methods for high water saturation are not suitable for concretes exposed to XF2. An alternative method, using the critical degree of water saturation with the Fagerlund test procedure was used to show indirectly in comparison to a reference concrete the adequate resistance of fly ash concretes against the exposition XF2 [BRA05a]. This method can be used as alternative test procedure in concretes for tunnels according the additional technical contract details for engineering concrete (ZTV-ING) of the German road authority [ZTV07].

The problem which still has to be solved is the lack of evaluation criteria for the use of concrete according the exposure class XF2. Test methods are only available for the evaluation of concrete under extreme conditions that means high water saturation without and with de-icing agents (XF3 and XF4). The resistance against the exposure at moderate water saturation is proofed with the stronger test method at higher water saturation. Due to the pozzolanic reaction of fly ash especially the fly ash concretes are misjudged by this test method. Comparative tests including the modified test method are under investigation at the moment.

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4.3.4 Alkali-Silica-Reaction Another reason for typical damages of concrete structures is the alkali-silica-reaction (ASR). It is affected by the different chemical composition of the pore solution where the dominating factor is the alkali concentration. Experiences with fly ash as concrete addition over many years have shown that fly ash can successfully be used to avoid damage to concrete by alkali-silica-reaction. The alkalis in the binder react with silicates in the alkali-sensitive aggregate and form a gel whose volume steadily increases leading to damage of the microstructure. The use of fly ash in the binder lowers the total alkali content of the concrete and additionally alkalis are incorporated in the reaction products of the fly ash.

The limitation of the alkali content of fly ash in DIN 1045-2 and the Alkali-Guideline of the German Committee for Structural Concrete (DAfStb) [DAF07] has been deleted in the current releases. This is caused by the results of recently finished research projects, e.g. the project “Use of Hard Coal Fly Ash in Concrete to Avoid a Damaging Alkali-Silica-Reaction” [VGB06]. Fly ash mortars and concretes with fly ash different in fineness and alkali content have been investigated regarding the avoidance of a damaging ASR.

Within ongoing research projects the effectiveness of fly ash to avoid a damage of concrete structures by alkali-silica-reaction is under investigation. On the basis of chemical tests of pore solutions the bond of the alkalis in the reaction products of fly ash was evaluated in one project [VGB07a]. The impact of storage temperature and additional calcium content of the fly ash reaction products on their binding characteristics of alkalis were investigated. In the pore solutions of all fly ash containing mixtures less alkali- and hydroxide ions were found than in the pore solutions of corresponding portland cement stones. The concentrations of alkali ions mostly are lower at 40°C than at lower or higher temperatures. At lower temperatures, the amount of fly ash reaction products is significantly lower. At higher temperatures there is only a minor increase in the amount of fly ash reaction products, while the Ca/Si-ratio keeps rising, which causes the decreasing binding capacity.

In Fig. 4.4 you can see the reduction of alkalis in the pore solution caused by the addition of three different fly ashes (F1 to F3). The results for concretes with greywacke (GW) as aggregate, 400 kg/m3 binder and a w/b ratio of 0.45 at a temperature of 40°C and an age of 90 days are shown. With the use of additions at first a thinning effect is observed (dotted line). For fly ash an additional reduction of the alkalis content was observed as these are incorporated in the reaction products of the fly ash. The effect is depending on the alkali content of the fly ash. The lower the alkali content of the fly ash and the higher the fineness, the higher the effect of additional binding of alkalis from the pore solution is.

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Fig. 4.4. (Na+ + K+)-concentration in the pore solution versus amount of concrete addition;

temperature 40°C; concrete age 90 days [HEI07]

With the revision of the Alkali-Guideline by the German Committee for Structural Concrete (DAfStb), a performance test has been introduced as an alternative test method for ASR which is being increasingly used in practice. This method uses a higher temperature of 60 °C, thus shortening the testing time. However, investigations show that the effect of fly ash is not adequately assessed with this method. This can lead to restrictions of the application of fly ash concrete if only this performance test is used as criterion. The present research project P 329 aims at the determination of robust assessment criteria for the effectiveness of concretes containing fly ash and alkali-sensitive aggregate.

4.3.5 Sulphate Resistance Due to the rheological and pozzolanic effects of fly ash, the pore structure of concretes is improved and the resistance to chemical attack is increased. For this reason, concrete with fly ash is frequently used for the construction of sewers, sewage-treatment plants and other structural components where chemical attack is expected. Fly ash is particularly effective against sulphate attack. There are various investigations on the effect of fly ash regarding the resistance against sulphate attack. In general the use of fly ash causes a more dense concrete structure, which leads to a lower penetration of sulphate ions from the sulphate containing ground water (see Fig. 4.5).

Fig. 4.5. Strain expansion versus age [SCH92]

54 ECK: Research for Durable Concrete with Fly Ash

Although a lot of details concerning the mechanism are well known the topic sulphate resistance is still one main area of investigation over the last few years. This is in some extend caused by the difference between the results of laboratory investigations and the practical experience. Over the last years, a thaumasite formation on a number of mortar samples was observed in laboratory tests regarding the sulphate resistance of concrete, especially with addition of limestone. It is well known that lab tests do not directly represent the conditions in practice - particularly the concrete composition and density, the strength development at the beginning of the sulphate attack as well as the thickness of concrete structure.

The evaluation of the sulphate resistance of a cement or cement fly ash combination is performed based on time-lapse examinations so far. The test procedures expose the samples to a much harder attack than normally occuring in practice, which leads to a controversial discussion regarding the evaluation of the received laboratory results. Unfavourable binders according to lab tests showed a good sulphate resistance in practice. For this reason, the sulphate resistance testing is under investigation regarding lower temperatures, the storage in sulphate solution of different concentration and sulphate containing grounds, as well as long term testing. A special research project organised by the German Committee for Structural Concrete deals with these unsolved questions.

5 SUMMARY

Fly ash has been successfully used as concrete addition for more than forty years in Germany. Fly ash for concrete must comply with the requirements of DIN EN 450 [DIN08, DIN05] or must have general approval for use in concrete. It has a positive effect on the properties of fresh and hardened concrete, improving the workability, influencing strength development due to the filler effect in the early stages and contributes to the strength due to the pozzolanic reaction at older concrete ages. The changes in pore structure of the hardened cement paste which are associated with the pozzolanic reaction result in a clear improvement of the durability, for example, in relation to its resistance to chloride and sulphate attack. Based on positive results from research work over the last years regarding alkali-silica-reaction and freeze-thaw and de-icing salt resistance normative regulations have been modified and the field of application of fly ash concrete has been expanded. However, due to new test procedures and mainly environmental requirements there is still a need for research.

REFERENCES

[BER88] vom Berg, W.: Karbonatisierung von Beton mit Flugasche. Tagungsband zur VGB-Konferenz „Forschung in der Kraftwerkstechnik 1988“, VGB TB 704, VGB Kraftwerks-technik GmbH,Essen 1988

[BRA05] Brameshuber, W.; Schießl, P.; Uebachs, S.; Brandes, C.; Eck, T.: Einfluss von Flugasche auf den Frost-Tausalzwiderstand von Beton, Abschlussbericht zum Verbundvorhaben IBAC/RWTH Aachen und cbm/TU München, Bericht Nr F 759/2 (VGB P 203), Aachen 2005

[BRA05a] Brameshuber, W., Pierkes, R., Tauscher F., Friebel, W.-D.: Anrechnung von Flugasche bei Betonen für Innenschalen von Straßentunneln, Beton, Heft 7/8, 2005

[DAF07] Deutscher Ausschuss für Stahlbeton; DAfStb: Richtlinie Vorbeugende Maßnahmen gegen schädigende Alkalireaktion im Beton (Alkali-Richtlinie), Februar 2007

[DIN01] DIN EN 206-1:2001-07, Beton - Teil 1: Festlegung, Eigenschaften, Herstellung und Konformität; Deutsche Fassung EN 206-1:2000

International RILEM Conference on Material Science – MATSCI, Aachen 2010 – Vol. III, AdIPoC 55

[DIN05] DIN EN 450-2:2005-05, Flugasche für Beton - Teil 2: Konformitätsbewertung [DIN08] DIN EN 450-1:2008-05, Flugasche für Beton - Teil 1: Definition, Anforderungen und

Konformitätskriterien; Deutsche Fassung EN 450-1:2005 + A1:2007 [DIN08a] DIN 1045-2:2008-08, Tragwerke aus Beton, Stahlbeton und Spannbeton - Teil 2: Beton -

Festlegung, Eigenschaften, Herstellung und Konformität; Deutsche Anwendungsregeln zu DIN EN 206-1

[HAE95] Härdtl, R.: Veränderung des Betongefüges durch die Wirkung von Steinkohlenflugasche und ihr Einfluss auf die Betoneigenschaften. Schriftenreihe des Deutschen Ausschusses für Stahlbeton, H. 448, Beuth Verlag GmbH, Berlin 1995

[HEI07] Heinz, D.; Schmidt, K.; Urbonas, L.: Vermeidung von schädigender AKR durch Steinkohlenflugasche. Beton- und Stahlbetonbau 102 (2007) H. 8, S. 511-520

[LEW93] Lewandowski, R.: Effect of different fly ash qualities and addition rates on the properties of concrete, Betonwerk und Fertigteiltechnik 43, 1993, H. 11, S. 576-580, H. 2, S. 105-110, H. 3, S. 152-158

[SCH92] Schießl, P.; Härdtl, R.: Einfluß von Steinkohlenflugasche (SFA) auf den Sulfatwiderstand von Betonen. Abschlußbericht zum Forschungsvorhaben F 262 vom 5.10.1992 (AIF-Nr. 7690)

[SCH96] Schießl, P.; Härdtl, R.: Betone für massige Bauteile, Beton (46), 1996, H. 11, S. 668-672 [SYB93] Sybertz, F.: Beurteilung der Wirksamkeit von Steinkohlenflugasche als Betonzusatzstoff.

Schriftenreihe des Deutschen Ausschusses für Stahlbeton, H.434. Beuth Verlag GmbH, Berlin 1993

[VGB03] VGB P 225: Fly Ash in Tunnel Concretes, Research report, IBAC, RWTH Aachen, VGB Forschungsstiftung, 2003

[VGB04] VGB P 203: Frost and de-icing salt resistance of fly ash conrete, Research report, IBAC, RWTH Aachen, VGB Forschungsstiftung, 2004

[VGB06] VGB P 245: Use of Hard Coal Fly Ash in Concrete to Avoid a Damaging Alkali-Silica-Reaction, Research report, Technical University Munich, VGB Research (AiF-Nr. 13605 N), 2006

[VGB07] VGB PowerTech e.V.: Production and Utilisation of Coal Combustion Products (CCPs) in Germany in 2007

[VGB07a] VGB P 272: Effect of Fly Ash Regarding Avoidance of Alkali-Silica-Reaction, Research report, Research Institute of the Cement Industry (FIZ), Düsseldorf, VGB Forschungsstiftung, 2007

[VGB10] https://www.vgb.org/en/research_environment.html [WIE91] Wierig, H.-J.; Scholz, E.: Carbonatisierung von Beton mit Steinkohlenflugasche. VGB-

Konferenz Flugasche in Beton – Fortschritte in der Betontechnologie, VGB-TB 702, Vortrag 6, VGB-Kraftwerkstechnik, Essen 1991

[WIE96] Wierig, H.-J.; Freimann, T.: Optimierung von Betonen mit Flugaschezusätzen im Hinblick auf die Verarbeitbarkeit des Frischbetons. VGB Technisch-wissenschaftliche Berichte TW 705, VGB Kraftwerkstechnik GmbH, Essen 1996

[WIE05] Wiens, U.: Zur Wirkung von Steinkohlenflugasche auf die chloridinduzierte Korrosion von Stahl in Beton. Schriftenreihe des Deutschen Ausschusses für Stahlbeton, H. 551, Beuth Verlag GmbH, Berlin 2005

[ZTV07] ZTV-ING, Zusätzliche Technische Vertragsbedingungen und Richtlinien für Ingenieurbauten. Verkehrsblattsammlung Nr. S 1056 - Vers. 12/07, Verkehrsblatt Verlag