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SUSTAINABLE PRECAST CONCRETE CONSTRUCTION USING THE NEXT GENERATION OF CONSTRUCTION CHEMICALS

Sunny Surlaker; Head Admixtures Division, MC-Bauchemie (India) Pvt. Ltd.; Mumbai, India

Introduction

Over the years pre-cast concrete construction has evolved as an alternative to in-situ concrete to speed up construction times, and achieve better quality in terms of finish and durability.

Precast Concrete Units offer this advantage by virtue of being factory finished. A production process ensures excellent finish, dimensional tolerances, required strength, adequate quality controls and consistency.

Figure 1 - Representative Graphic of Evolved PCE Structure

From the precast manufacturer’s perspective, the requirements above makes it imperative that units produced are of consistently high quality. For a manufacturer, targets on optical finish, sharp unbroken edges, compressive and flexural strengths and durability must be met. At the same time, the primary aim for every manufacturer is the achievement of high early strength to allow early stripping times / shorter cycle times to ensure financial viability.

Using a compaction aid / densifying additive reduces the amount of water that can be added, while improving compactability of the concrete by lubricating the mix as well as interface between the mix and the mould. This additive also makes the mix more robust by reducing sensitivity of the mix to added water, which allows the manufacturer to produce concrete goods with much more efficiency. In short adding a compacting aid expands the limit of water addition in the mix from a narrow point to a range of values. Lesser water means better green strengths of the concrete, better stability, better compaction and sharp edges in the concrete goods.

Table 1 - In use Mix Design at Precast Manufacturer in Poland 

Ingredients	Mix 1	Mix 2	Units of Measurement
Cement,OPC 42.5N	340	450	Kg / m3
Sand, 0 to 2mm	579	626	Kg / m3
Aggregate, 2 to 8mm	738	483	Kg / m3
Aggregate, 8 to 16mm	570	680	Kg / m3
Water	120	119	Kg / m3
New PCE	0.45	0.45	% by weight of Cement
w/c ratio	0.45	0.35
Initial Slump	21	25	cm

Advantages of Using Compaction Aids:

• Improvement of Compactness and Density of Concrete in Produced Good
• Complete Hydration of Cement Grains
• Increased Compressive Strength at Demoulding and 28 Days
• Increased Stability of Produced Goods
• Enhanced Surface Finish and Edges
• Decreasing adhesion of concrete to Moulds and Pressure Head
• No changes in water demand of the mix
• Decreased Efflorescence and Water Permeability
• Minimal Dosage at 0.2 to 1.0% by weight of cement
• Reduced Rejection Rate
• Better Quality - therefore higher returns on product
• Improving production efficiency, due to quicker demoulding

Areas of Application:

• Paver Blocks
• Manhole Covers
• Extruded Concrete Pipes
• Hollowcore Slabs and Walls
• Concrete Tiles and Roof Tiles
• Other Miscellaneous Concrete Goods

Curing Compounds for Precast Segments

Traditional Curing compounds are based on wax or hydrocarbon emulsions in water or solvents. The wax or the hydrocarbons are the film-forming element for this type of curing compound, while the water or solvents form the medium or vehicle for dispersion and evaporate when the curing compound is sprayed or applied. The advantages of these curing compounds include: Early Beginning, One Time application, no entry of water into the concrete, reduction of concrete temperature and no wetting and drying problem for the young concrete. Its limitations include: These curing compounds need complete degradation or manual /mechanical removal of the wax or resins (these act like bond breaking materials between concrete and subsequent layers of glue or coatings) before subsequent layers of treatment. If any part of the curing compounds remains within surface pores of the concrete, it may affect bonding of subsequent layers. Therefore the applications of these curing compounds can be limited to roads, open decks, external facades in buildings, etc.

New Generation curing compounds are based on a blend of various acrylic dispersions in an aqueous medium. These curing compounds can be universally used. Apart from the advantages offered by the group of curing compounds mentioned above, these curing compounds have the following additional advantages: healing of surface Micro-cracks in concrete, seals Concrete Safely, UV Stable, solar reflectivity and it has no need for removal and no hindrance in bonding of segments. Application for acrylic curing compounds can thus enhance precast segment casting process, reduce water used (increase sustainability), seal cracks, reduce rate of rejection in segments, can enhance bonding between elements and of course ensure optimal strength gain. Their usage should become mandatory in the precast production industry.

Non-Shrink Cementitious Grouts for Precast Construction

Grouts are a class of construction materials that consist of a dry mixture of cement, mineral aggregates and admixtures and additives. They are factory-made, dry-stored and protected from the weather. These materials are processed by Mixing water at the site and mixing to a flowable / pourable consistency.

Micro-Concrete’s have all the advantageous material properties of non-shrink grouts, and are additionally formulated to have a better flexural strength to allow its use in Repairing Structural Elements.

These materials find a plethora of uses to speed-up precast construction, apart from providing the reliability of materials, continuous supply, fast rate of strength development, ease of use and waterproof structures. Grouts and Micro-Concretes find a variety of application due to their high flowability, excellent rate of strength development, low shrinkage, their high density and waterproofness and good bonding to mineral substrates. These materials can be used in precast Construction for:

• Joints / Connections Between Precast Panels
• Column / Wall Foundations and Plinths
• Grouting Of Floor / Slab Joints and Connections
• Support for Anchor Bolts or Structural Steel Components
• To cast Micro-piles in-situ
• To Cast Precast Piles / Concrete Poles
• To Fill Narrow Trenches
• To Fill Junction Boxes for Pipes, Conduits and Wires
•  In repair strategies as jacketing for Columns and Beams
•  In Structural Repair of Bridge Decks and Bridge Superstructures

Concrete Cosmetics

Precast Concrete is cast under controlled conditions and is subjected to handling at early strengths. Due to this, the elements are often prone to surface damages such as blowholes, fine cracks, chipped edges, uneven surfaces and so on. These damages do not significantly hamper the durability of the element, but the visual damage often makes the elements unacceptable to the end users.

To address this concern, the concept of concrete cosmetics was introduced. Concrete cosmetics are very fine polymer modified cement mortars, that can be drawn into very thin layers and add durability to the applied surfaces. As the name suggests, these mortars are not intended as structural mortars, but are rather fairing coats that can be used to repair minor damages to the elements. Different applications of this material are shown in Figure 10.

The advantages as opposed to using conventional cement for such repairs are:

1. These mortars are non-shrink
2. These materials are modified with suitable polymers to improve adhesion and properties in flexure to ensure adequate bond to the substrate
3. These materials can be drawn into very thin layers without cracking
4. These materials are resistant to water and carbonation
5. They provide a smooth finish similar to fair faced concrete
6. Colors can be matched by mixing selected quantities of a white and grey mortars
7. Easy to mix and apply

Rapid development of mechanical properties

Figure 5 - Fibrous C-S-H Phases of OPC Hydration (left) and Foil like C-A-S-H Phases (right) of Metakaolin Hydration

Finally in terms of reactivity, calcined clays such as Metakaolin are much higher in Pozzolanic Activity as compared to flyash, slag and silica fume. We ascertained this by means of the “Chapelle Test” developed by Asbridge et al (ref. 3-4). Our results as per the test are given in Figure 6.

Figure 2 - Comparison of Slump flow between conventional and  PCE Technology

Calcined Clays improve concrete based on 4 main mechanisms, viz:

Figure 3a 3b - strength Development for the Mixes in Table 1

-Crystallization to impervious and highly stable C-S-H and C-A-S-H Phases to impart Water Resistance, Chemical Resistance, High Density and High Compressive Strength (Figure 5)

Figure 4 - The 4 Phase of reaction of Calcined Clays

-High Pozzolanic Reactivity and Consumption of Free Lime in Concrete - to Reduce Porosity, Enhance Chemical Resistance and Improve Compressive Strength (Figure 6)

Figure 5 shows the different between C-S-H phases in OPC hydration and C-A-S-H phases in the Metakaolin Hydration.

-Densification of Interfacial transition Zone Between Aggregate and Cementitious Paste - Imparts Strength, Chemical Resistance (Figure 7)

-Plate Structure - Imparting High Flexural Strength, Cracking Resistance and Of Course Better Pumpability and Aesthetics (Figure 4)

Using Calcined Clays to Improve Durability, Mechanical & Chemical Resistance of Precast Elements

Calcined clays, following optimal calcination, are able to react as a pozzolan in presence of Calcium Hydroxide in cementitious systems to form additional strength-building C-S-H or C-A-S-H phases. Figure 4 shows the 4-phases of reaction (example given for reaction of Metakaolin) viz.

1. Introduction of Metakaolin into the Matrix;
2. Dissolution of reactive calcined clay;
3. Beginning of the hydration;
4. Complete incorporation of the calcined clay into foil-like C-S-H, C-A-H (calcium aluminate-hydrate), C-A-S-H (calcium aluminosilicate-hydrate) andAF_m (monosulphate hydrate) phases (ref. 2).

For the precast manufacturer, a fusion of meeting the requirements above and securing cost benefits can only be achieved using Construction Chemicals. One of the basic reasons for evolution of Construction Chemicals was to remove the inherent disadvantage, associated with cement hydration. Though cement is the best construction material available it has inherent shrinkage and cracking mechanisms, which lowers the life cycle of construction / structures.

Figure 7 - Comparative SEM Images showing improvement in the ITZ for normalOPC and an OPC - Metakaolin blend

To remove these defects construction chemicals were designed and introduced. All in all durability can be achieved by improving the quality of concrete as well as protecting concrete from deterioration mechanism due to chemical, physical, thermal and environmental attacks.We look at durability as providing both sustainability and affordability (reduced maintenance and repair costs) over the life of the structure.

Figures 8a and 8b - Comparison of compressive & Flexural Strengths in UHPCs with Silica Fume & Metakaolin

Construction Chemicals have also evolved in terms of providing more specific solutions for the precast industry right from production of units to installation. This article reviews the underlying mechanisms of these additives and the latest applications / joint studies undertaken at MC-Bauchemie and other industry partners incorporating these materials in development of Precast Construction. These materials also help improve the life of the units themselves in addition to reducing maintenance of the structures assembled with them. This reinforces the mantra of “Sustainability Through Durability” for Precast Construction.

Solutions for Improvement of Concrete for Precast Units

Construction Chemicals today offer a wide variety of solutions for the Precast Industry ranging from the latest generation of PCE polymers for manipulation of green properties of concrete to mould-release agents and curing compounds to enhance the perfect surface finish and edges for the elements. There are also solutions available for improving green characteristics of dry / semidry concretes for use in concrete products like pavers, pipes, etc. Construction Chemicals also provide additives for enhancing the durability of the elements especially in aggressive or acidic media. The sections below highlight these latest developments.

Improved Green and Hardened Concrete Properties Using Latest PCE Technology

The use of PolyCarboxylate Ether (PCE) based admixtures for concrete is steadily gaining ground, due to the various advantages it provides. The hindrance on its widespread use in India has been on account of its higher initial cost. However, PCE Technology is rapidly evolving to the point where the molecular chemistry of the PCE can be adjusted to make it suitable for use in precast technology. One such evolved material (ref. 1) is discussed in this section.

The latest chemistry has been instrumental in designing a PCE molecule with a comb-type structure having a short backbone chain and short side chains in addition to a high acid content. Figure 1 shows the representative graphic of the structure of this PCE.

 

This unique structure allows the PCE to adsorb much faster onto the cement particles, provide a very fast plasticization effect on the mix and retain slump for upto one hour. Due to the molecular structure of the PCE molecule, it provides for a “stearic hindrance” effect, which allows for workability retention without hindering the hydration of the cement grain. This allows the concrete to gain strength rapidly once finishing works on the element are over.

Table 1 shows a Mix Design in production use. Figure 2shows the slump flow variation of this mix designwith respect to time. Figures 3aand 3bshow the development of early and final strength for the mix design using this PCE Technology. The unique molecular structure of the PCE also improves robustness of the mix (not greatly affected by minor variations in added mixing water) and shows excellent compatibility with a wide variety of OPCs or blended cements.

Economical advantages for the Precast Manufacturer

• Short mixing period
• Low dosage
• No loss in Workability for 60 minutes
• Robust performance and compatibility with different cements (greater manufacturing flexibility for precast manufacturer)
• A standard recipe can also be used for advanced precast parts

Double shift operation possible (8h hydration with 2h heat treatment)

In terms of Morphology, the primary difference between C-S-H formation in Ordinary Portland Cement and calcined clays is the formation of a more stable, foil like structure in case of calcined clays as opposed to the fibrous structure in case of OPC hydration (ref. 3). Figure 5 shows the difference between C-S-H phases in OPC hydration and C-A-S-H phases in the Metakaolin Hydration.

These mechanisms add to the durability of the concrete. The chemical resistance of concrete is improved due to the denser matrix and ITZ improvement of the calcined clays and reduction of Free Lime (Portlandite) in the cementitious matrix. Increased resistant to Alkali Silica Reaction is achieved through, reaction of the aluminosilicate with alkalis to form stable compounds. These same actions also account for better resistance to chloride penetration through concrete. Lastly, addition of calcined clays also improved the sulphate resistance of tested mixes. This reaction is based on the highly densified matrix structure, the dense ITZ and conversion reactions of the ettringite (ATf) phases in the cementitious matrix to more stable AFm (monosulphate hydrate) phases.

Due to the improvement in mechanical properties and durability that using calcined clays as concrete additives, the material opens up new avenues for production of various new forms of UHPCs. There is also a significant reduction of micro-crack formation, which makes it particularly suitable for the production of precast tunnel segments, concrete facades, ultra thin precast segments, filigree elements and precast element for heavy loading(ref. 6-8). Successful examples of UHPCs incorporating Metakaolin include acid resistant concrete for Budapest Central Wastewater Treatment Facility and acid resistant concrete for production of precast sewage pipes for Epiton GmbH and Co. KG (ref. 8).

Advantages of Calcined Clays in Precast Construction

• Provides Excellent Watertightness
• Reduces Chloride Ingress and Carbonation
• Increases Sulphate-resistant of Concrete
• Enhanced workability and finishing of concrete
• Reduced shrinkage, due to "particle packing" making concrete denser
• Improved color by lightening the color of concrete making it possible to tint concrete integrally
• Endless quantities
• Factory made Homogenous product
• Better workability
• Reduced dosage of superplasticizer
• Better pumpabilty

Additive Technology for Dry / Semidry Concrete for Pipes, pavers, etc.

Concrete Goods are defined as “small or large goods made of Plain Cement Concrete (PCC) or Reinforced Cement Concrete (RCC) and manufactured on a large scale”. These concrete goods include products such as paver blocks, concrete tiles, extruded pipes, manhole covers, and also hollowcore elements. These goods are characterized by their production methods, which includes casting dry / semi-dry concretes into moulds and forming them by application of pressure. This method is designed to provide early setting (due to the semi-dry concrete) and demoulding, and the pressure compaction / extrusion is designed to provide proper form and sharp edges to the goods.

However, this method of production has its limitations. Concrete used to make concrete products has different properties. Semi-dry concrete with lower water content is by nature difficult to compact. In addition products must be free of efflorescence. A particular challenge in the concrete products industry is the achievement of sufficient early strength to enable the rapid removal from forms. Only a perfectly matched combination of admixtures and casting techniques is able to produce the desired results.Basic requirements of concrete goods are:

• High green strength (instant formwork removal)
• Structural stability, no swelling or shrinkage
• Sharp edge formation, smooth side surface
• Compact / Dense Structure
• No bonding on tools, moulds or machinery in green state
• Free of Cracks and Efflorescence
• Resistance to Water / frost

To countermand these limitations and meet requirements, a series of additives were developed, which on one hand modify the rheology of the semi-dry mix by lubricating it and densifies the mix on the other hand to provide optimum compaction and hydrophobicity.

The general trend of adding water to a semi-dry mix for concrete goods is shown in Figure 9. The figure shows the effect of rising water content on the stability of the mix when compacted under pressure. As can be seen, the mix is very sensitive to the amount of water added. Add Less water (dry branch) and the concrete would not compact properly and add more water (wet branch) and the mix would collapse after demoulding.

Using a compaction aid / densifying additive reduces the amount of water that can be added, while improving compactability of the concrete by lubricating the mix as well as interface between the mix and the mould. This additive also makes the mix more robust by reducing sensitivity of the mix to added water, which allows the manufacturer to produce concrete goods with much more efficiency. In short adding a compacting aid expands the limit of water addition in the mix from a narrow point to a range of values. Lesser water means better green strengths of the concrete, better stability, better compaction and sharp edges in the concrete goods.

Advantages of Using Compaction Aids:

• Improvement of Compactness and Density of Concrete in Produced Good
• Complete Hydration of Cement Grains
• Increased Compressive Strength at Demoulding and 28 Days
• Increased Stability of Produced Goods
• Enhanced Surface Finish and Edges
• Decreasing adhesion of concrete to Moulds and Pressure Head
• No changes in water demand of the mix
• Decreased Efflorescence and Water Permeability
• Minimal Dosage at 0.2 to 1.0% by weight of cement
• Reduced Rejection Rate
• Better Quality - therefore higher returns on product
• Improving production efficiency, due to quicker demoulding

Areas of Application:

• Paver Blocks
• Manhole Covers
• Extruded Concrete Pipes
• Hollowcore Slabs and Walls
• Concrete Tiles and Roof Tiles
• Other Miscellaneous Concrete Goods

Curing Compounds for Precast Segments

Traditional Curing compounds are based on wax or hydrocarbon emulsions in water or solvents. The wax or the hydrocarbons are the film-forming element for this type of curing compound, while the water or solvents form the medium or vehicle for dispersion and evaporate when the curing compound is sprayed or applied. The advantages of these curing compounds include: Early Beginning, One Time application, no entry of water into the concrete, reduction of concrete temperature and no wetting and drying problem for the young concrete. Its limitations include: These curing compounds need complete degradation or manual /mechanical removal of the wax or resins (these act like bond breaking materials between concrete and subsequent layers of glue or coatings) before subsequent layers of treatment. If any part of the curing compounds remains within surface pores of the concrete, it may affect bonding of subsequent layers. Therefore the applications of these curing compounds can be limited to roads, open decks, external facades in buildings, etc.

New Generation curing compounds are based on a blend of various acrylic dispersions in an aqueous medium. These curing compounds can be universally used. Apart from the advantages offered by the group of curing compounds mentioned above, these curing compounds have the following additional advantages: healing of surface Micro-cracks in concrete, seals Concrete Safely, UV Stable, solar reflectivity and it has no need for removal and no hindrance in bonding of segments. Application for acrylic curing compounds can thus enhance precast segment casting process, reduce water used (increase sustainability), seal cracks, reduce rate of rejection in segments, can enhance bonding between elements and of course ensure optimal strength gain. Their usage should become mandatory in the precast production industry.

Non-Shrink Cementitious Grouts for Precast Construction

Grouts are a class of construction materials that consist of a dry mixture of cement, mineral aggregates and admixtures and additives. They are factory-made, dry-stored and protected from the weather. These materials are processed by Mixing water at the site and mixing to a flowable / pourable consistency.

Micro-Concrete’s have all the advantageous material properties of non-shrink grouts, and are additionally formulated to have a better flexural strength to allow its use in Repairing Structural Elements.

These materials find a plethora of uses to speed-up precast construction, apart from providing the reliability of materials, continuous supply, fast rate of strength development, ease of use and waterproof structures. Grouts and Micro-Concretes find a variety of application due to their high flowability, excellent rate of strength development, low shrinkage, their high density and waterproofness and good bonding to mineral substrates. These materials can be used in precast Construction for:

• Joints / Connections Between Precast Panels
• Column / Wall Foundations and Plinths
• Grouting Of Floor / Slab Joints and Connections
• Support for Anchor Bolts or Structural Steel Components
• To cast Micro-piles in-situ
• To Cast Precast Piles / Concrete Poles
• To Fill Narrow Trenches
• To Fill Junction Boxes for Pipes, Conduits and Wires
• In repair strategies as jacketing for Columns and Beams
• In Structural Repair of Bridge Decks and Bridge Superstructures

Concrete Cosmetics

Precast Concrete is cast under controlled conditions and is subjected to handling at early strengths. Due to this, the elements are often prone to surface damages such as blowholes, fine cracks, chipped edges, uneven surfaces and so on. These damages do not significantly hamper the durability of the element, but the visual damage often makes the elements unacceptable to the end users.

To address this concern, the concept of concrete cosmetics was introduced. Concrete cosmetics are very fine polymer modified cement mortars, that can be drawn into very thin layers and add durability to the applied surfaces. As the name suggests, these mortars are not intended as structural mortars, but are rather fairing coats that can be used to repair minor damages to the elements. Different applications of this material are shown in Figure 10.

The advantages as opposed to using conventional cement for such repairs are:

1. These mortars are non-shrink
2. These materials are modified with suitable polymers to improve adhesion and properties in flexure to ensure adequate bond to the substrate
3. These materials can be drawn into very thin layers without cracking
4. These materials are resistant to water and carbonation
5. They provide a smooth finish similar to fair faced concrete
6. Colors can be matched by mixing selected quantities of a white and grey mortars
7. Easy to mix and apply

Rapid development of mechanical properties

Areas of application for Concrete Cosmetics

• For porous or rough concrete the entire surface can be coated with Cosmetic repair mortar
• To repair pre-cast elements with shrinkage cracks
• To level off broken corner and edges on pre-cast elements
• To repair uneven surfaces in pre-cast concrete elements
• Finishing coat for concrete in isolated areas and whole surfaces as part of a concrete repair system
• Smoothening and restoring of concrete surfaces. Surface profile and character of fair-faced concrete can be retained.
• Closing of pores and blowholes (scratch coat)

Protection Technologies for Precast Construction

Despite Factory Production and Quality Control, Precast Concrete is as susceptible to carbonation as normal RCC. To prevent this from happening, we need to remedy the concrete cover both in terms of quality and quantity.

The application of protective coating is an attempt to increase the effective cover of concrete in terms of both quality and quantity. By virtue of their formulations, anti-carbonation protective coatings provide the protection quotient of meters of concrete cover in a very thin layer. Therefore the principle of equivalent cover is very valuable both in repair strategies and even to safeguard new structures that have a very long design life. Specialized protective coatings for precast concrete can be of many types:

1. Thick Coatings (1-2mm): Like Different Breathable waterproof cementitious polymer modified coatings to repair and enhance life of damaged precast units
2. Breathable, Elastic Elastomeric Crack bridging anti-carbonation coatings (200-300 micron thickness)
3. Breathable Hydrophobic impregnation coatings, based on silicone, silane-siloxane

The use of these protection technologies can help improve durability and sustainability of the precast elements themselves, apart from improving the optical finishes of the elements. Their use should thus become a part of specifications for precast elements.

Conclusion

This article explored the working mechanisms and applications of the latest construction chemical technologies in improvement of concrete for precast production. Of course, improved mix design techniques and placing techniques too play a very important role in the production of high quality, durable, precast elements. Construction chemicals do however, significantly broaden the range of possibilities of precast production to achieve different aims such as acid resistance (for pipes), improved durability, surface finish, faster cycle times in production and adding robustness to the concrete in terms of production.Using more durable precast elements for construction, would also mean lower life-cycle costs, reduced energy costs, reduced maintenance and of course benefits for the precast manufacturers as well. Correct usage of construction chemicals would be vital in all areas of precast construction to enhance benefits. Therefore, it is imperative that Construction Chemicals be a vital component of improving precast production to promote sustainable construction.

About the Authors

Brief Bio-data of Mr. Sunny Surlaker

Sunny Surlaker passed his B.E. in Civil Engineering from V.J.T.I Mumbai in 2005 and also holds a Masters in Civil Engineering from University of Michigan, Ann Arbor, USA. He is currently the Head of Admixture Division with MC-Bauchemie India Private Limited a joint venture with MC-Bauchemie, Germany manufacturing over 100 construction chemicals.

He has also worked extensively in Germany and Brazil with MC-Bauchemie. Before that he was a Material Specialist with the Global Multinational AMEC Earth and Environmental, in Phoenix, Arizona, USA. 

He was trained extensively in Germany and Brazil with extensive experience in concrete technology, admixture technology and innovative cementitious material design for grouts, screeds and high-build protective coatings. He is also an Expert in conducting laboratory trials, field trials, field training engineers and on-site admixture/additive improvements and fine-tuning. His experience further includes non-destructive testing of concrete, repair and retrofit materials, project management and training. In India he specializes in designing High Performing mixes for local material and placement conditions.

He is a member of many organizations such as American Concrete Institute (ACI), American Society of Civil Engineers, Institution of Engineers India, Indian Concrete Institute and Indian Society of Structural Engineers

References

1. Research Notes, MC-Bauchemie Mueller GmbH and Co. KG, Germany.
2. Prof. Dr.-Ing. Horst-Michael Ludwig, M.Sc. André Trümer, Bauhaus Universitaet, Weimar.
3. Jayant D. Bapat, (2013), Mineral Admixtures in Cement and Concrete, Chapters 5 and 6.
4. Asbridge, A.H., Walters, G.V., Jones, T.R., (1994), Ternary blended Concretes - OPC / GGBFS / Metakaolin, Concrete across Borders International Conference, Odense, Denmark.
5. EugenKleen, (2010), Technical Director, MC-Bauchemie Mueller GmbH and Co. KG, Germany, Laboratory Testing.
6. Technical data sheets and in-house testing of Centrilit NC, MC-Bauchemie Mueller GmbH and Co. KG, Germany.
7. Test Data from Dr. Huettl, TU-Berlin, Germany.
8. Technical Project References for Centrilit NC, MC-Bauchemie Mueller GmbH and Co. KG, Germany.