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Volume 47: Number 08

August 2016

ISSN 02636050

THIS MONTH’S COVER

MONTH

CONTENTS

WORLD CEMENT REGULARS

03 Comment

05 World News

12 Keynote: On the HorizonRick Bohan considers how cement based materials and additive manufacturing could be the next horizon in concrete technology.

98 Product News

104 Regional Report Infographic

REGIONAL REPORT

18 Air Filtration in ColombiaGiuliamaria Meriggi, Redecam, Italy.

BURNERS, KILNS, PREHEATERS, PRECALCINERS

24 An Essential StrategyJohn Kline and Charles Kline, Kline Consulting, USA.

32 New Multi-Fuel Kiln Burner Launched at RohoznikMads Nielsen and Carsten Damslund Jensen, FLSmidth A/S, Denmark.

37 Reducing CO2 Emissions Through Biomass

SubstitutionMichalis Akritopoulos and Tahir Abbas, Cinar Ltd, UK.

AIR POLLUTION CONTROL

43 A New Generation of AutomationNino Stölzel, Schenck Process, Germany.

CONTENTS

AUGUST

47 Seeing Clearly on Dust SuppressionBrigitte Pennington, Parker Conflow, UK.

51 Common Sense Dust Collector System Maintenance and TroubleshootingAndy Winston, BWF Envirotec, USA.

GENERAL INTEREST

56 Industrial Clinker Phases and their Microstructures Pinky Pandey & Ashwani Pahuja, National Council for Cement & Building Materials , and S. P. Pandey, Dalmia Cement, India.

65 Combining the AdvantagesEduardo Diez del Sel and Julio Escalona, Reyma Materiales Refractarios, S.A, Spain.

THERMAL IMAGING

69 How Accurate Thermal Measurement Can Reduce Maintenance CostsRichard Gagg, AMETEK Land Inc., USA.

FILTER MEDIA, ESPs, BAGHOUSES, GAS ANALYSIS

73 Capturing Fine DustM. Giavazzi, F. Di Natale, M. Esposito and A. Lancia,Boldrocchi and The University of Naples, Italy.

79 Updating Dedusting InstallationsEduardo Sauto, Gorco, Spain.

83 Particulate Control by Renewing Ageing ESPsThompson Tsai, Tina Anting and Harry T. Mangaoang, Tai & Chyun Associates Industries Inc., Taiwan.

MAINTENANCE AND REPAIR

87 Choosing a StrategyAlejandro Espejel, FLSmidth Operation & Maintenance A/S, Denmark.

93 Increasing ProductivityBruno Godoy and Michael Stalder, ABB, Switzerland, and Derya Derinyol, Bursa Cimento, Turkey.

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COMMENT

AUGUST

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SUBSCRIPTIONS

CONTACT DETAILSManaging Editor: James Little james.little@worldcement.com

Assistant Editor: Joseph Greenjoseph.green@worldcement.com

Contributing Editor: Paul Maxwell-Cook

Production: Charlotte Reynell charlotte.reynell@worldcement.com

Advertisement Director: Rod Hardy rod.hardy@worldcement.com

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Editorial Assistant: Rebecca Bowdenrebecca.bowden@worldcement.com

The World Cement team recently visited a UK plant that is rethinking the way we approach cement and cement additives, demonstrating that whilst the industry’s primary focus remains on emission reduction technology, new ideas and creative research remain present.

This summer, word has spread concerning the research conducted by scientist José Carlos Rubio into glow-in-the-dark cement. Dr Rubio, working out of the Michoacan University of Saint Nicholas of Hidalgo in Mexico, has created a light-emitting

cement that is designed to illuminate roads, pavements and bicycle lanes without using electricity. The energy-efficient material is capable of soaking up sunlight during daylight hours and begins to emit light as the sun sets.

In his paper on the product, Rubio explains the science behind his research, and the multiple possibilities and potential applications for light-emitting cement. He explains that, when water is added to common cement, crystal flakes are formed that block the absorption of solar energy. Rubio concentrated his research on modifying the micro-structure of the cement in order to eliminate the crystals.

The majority of fluorescent materials are constructed from plastic and have an average life span of three years because they decay under UV exposure; however, Rubio’s new cement is UV resistant and has an estimated lifespan of 100 years. On top of this, Rubio claims the material is ecologically sound as it is constructed from sand, dust or clay that becomes a gel, and gives off only water steam as a by-product.

This Mexican project has provided the inspiration for other countries to follow in Rubio’s footsteps. The researcher commented, “Due to this patent (the first one for this university), others have surfaced worldwide. In the UK, we received recognition from the Newton fund, given by the Royal Engineering Academy of London, which chooses global success cases in technology and entrepreneurship.”

Rubio’s invention has forced the cement industry to re-imagine how to use the material. The material could be used for exterior and interior applications. Rubio says that Doctors Without Borders have already shown an interest, opening up the possibility that the light-emitting cement could be utilised in areas where access to electricity is not guaranteed. A pilot plant is currently being built, with material expected to be produced before the end of the year, however, serious investment is required before the product can be commercialised.

One may be forgiven for assuming that not a great deal is changing within the world of cement. In today’s industry the focus is largely on reducing emissions and streamlining the production process. Nevertheless, Rubio’s research confirms that invention and innovation is still alive and kicking! We would love to hear your comments on this new product. Do you believe in the real-life application possibilities? Please contact us at joseph.green@worldcement.com or rebecca.bowden@worldcement.com with your thoughts.

I’d like to extend my warmest wishes to all our readers, authors and advertisers. Thank you for all your continued support, I hope you enjoy this issue.

JOSEPH GREEN, ASSISTANT EDITOR

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August 2016 / 5World Cement

IN BRIEF

WORLD NEWS

IN BRIEF

In April 2016 Claudius Peters Projects was awarded a contract from Biberci Insaat for the supply of two new cement multi cell silos for their Konya plant.

Biberci Insaat was established in 1967 and is located about 200 km south of Ankara, Turkey. The Biberci group focuses its business activities in infrastructure, construction, mining and fuel industries in Turkey.

The scope of supply consists of two dual cell silos type ME18/EC11. Each silo has an inner dia. of 18 m and an approximate total volume of 10 000 m³. The dual cell silos were designed with a total of three simultaneous discharges: two to feed the truck loading equipment and one to feed a packing line. Furthermore, each silo has been designed with two truck loading stations complete with mobile loaders with at a capacity of 200 tph.

Commissioning of the complete cement line is planned for mid 2017. Claudius Peters will be working close together with Partner Teknik whom is the Engineering company coordinating this project.

Turkey Silo order for Claudius Peters

LafargeHolcim has announced that it has entered into a letter agreement with Nirma Limited subject to approval by the Competition Commission of India (CCI) for the divestment of its interest in Lafarge India for an enterprise value of approximately US$1.4 billion. Lafarge India operates three cement plants and two grinding stations with a total capacity of around 11 million tpy. The company also markets aggregates and is one of India’s leading ready-mix concrete manufacturers. The proceeds from the divestment will be used to reduce debt further.

Eric Olsen, CEO, said: “This agreement is an important step in our CHF3.5 billion divestment program. With this deal, two thirds of the program has been secured and the remainder of the program is well on track. We are confident that we will meet our target by the end of this year. With the proposed buyer we have found the right partner who will be able to develop the business further in the interest of all our stakeholders.”

LafargeHolcim will continue to operate in India through its subsidiaries ACC Ltd. and Ambuja Cements Ltd. with a combined cement capacity of more than 60 million t and a distribution network that extends across the entire country.

The transaction with Nirma Limited as a purchaser will be submitted to the CCI for approval.

LafargeHolcim has a divestment target of CHF3.5 billion in 2016 and has already completed the sale of its business in South Korea and signed an agreement to divest its minority shareholding in Saudi Arabia. The Group has also expanded its joint-venture with SNI, its historical partner in Morocco, by merging Lafarge Ciments Maroc and Holcim Maroc to create LafargeHolcim Maroc.

India LafargeHolcim agrees deal for divestment of Lafarge India

2016 marks the 100th anniversary of the Stockertown Plant, Pennsylvania. The Stockertown plant is today one of five operating cement plants in the Lehigh Valley. On 4 June 2016, a Plant Open House was held, with over 250 workers, retirees, families, friends and community leaders attending the event. Tours of the plant and the recently created environmental reserve, ‘The Hercules Meadow’, were conducted. A custom magazine, ‘Stockertown Plant – A Hundred Years In The Making’ was developed to document the plant’s history.

Michael Hollermann and Johan P. Cnossen will be joining the management board of the Industrial Solutions business area of thyssenkrupp, effective 1 August 2016. Michael Hollermann has been CEO of the Regional Headquarters South America since 2012, and will be taking the position of Chief Human Resources Officer. Johan P. Cnossen will be the new Chief Operating Officer, having joined Industrial Solutions on 1 May as head of the transformation office for the implementation of ‘planets’. With the appointments, Jens Michael Wegmann, CEO, has now filled all board positions.

On 26 – 28 May, the paper sack industry held this year’s EUROSAC Congress in Marseille, France. It showcased its latest innovations and elected the winner of the EUROSAC Grand Prix Award 2016, which once again went to dy-pack for the Self-dy sack. The jury honoured the sack as an excellent product innovation which opens up great opportunities on the market. Additionally, activities were presented that have been launched in order to achieve the objectives of EUROSAC’s ambitious ten-year roadmap.

August 20166 \ World Cement

IN BRIEF

EVENTS

WORLD NEWS

On 10 July 2016, the ignition of the rotary kiln marked the successful start-up of the clinker production line of CILAS, 11 days ahead of the contract schedule.

The EPC contract was for a new 5000 tpd green line project and was originally awarded to CBMI on 28 April 2014, by Algeria (Ciment LAFARGE SOUAKRI) SPA CILAS. The scope of the work included limestone crushing to cement packaging and dispatch, along with engineering, supply, civil work, erection, training and commissioning.

Representatives of the Owner and the EPC Contractor CBMI pushed the ignition button together at the ceremony. The owner’s representative, Mr. Didier Michel from LafargeHolcim, expressed his great appreciation for the safety achievement and the beautiful works presented by CBMI. He also hoped that LafargeHolcim and CBMI will continue to cooperate and deepen their relationship in the future.

A representitive of CBMI, Mr. Wang Hui, expressed his great appreciation for the trust and support from the Lafarge team. He also recalled the construction progress across the whole project and expressed his gratitude on the behalf of the whole project team.

Algeria Success for LafargeHolcim CILAS project

On 2 June, the Vice President of Total Lubrifiants, Philippe Charleux, and of Lubrilog, Florian Rouby-Giraud, signed a distribution contract.

With this agreement, Total will have access to the full range of Lubrilog’s open gear lubricants, designed based on thirty years of experience in terms of gear set lubrication and inspection. Lubrilog will benefit from Total’s worldwide implementation through a network of more than 120 affiliates and back them up to conduct the open gear inspections. Cement customers will be able to address their requests for any kind of lubricant, from quarry to plant lubrication, including specialty products, to one unique supplier: TOTAL Lubrifiants.

France Specialty lubricants for the cement industry

Estanda has overseen the assembly of different components supplied to a cement grinding line in Africa.

The industrial cement plant belongs to a multinational cement group. Estanda has once again been entrusted with the implementation of various improvements to cement grinding line 1 (CM1).

Estanda had previously completed an upgrade of cement line 2 (CM2) for the same cement group.

The assembly and commissioning of the installation was focused on the following components:

l Inlet Feed chute system with new wear resistant components.

l Headwall liners inside the ball cement mill: customised designs and materials.

With these refurbishments, the cement company has improved the air ventilation and the filling level of the mill, achieving greater uniformity in the milling process.

Africa Estanda improves cement grinding line

5 – 7 September 2016 FICEMCartagena, Colombiawww.ficem.org

28 – 29 September 2016 59th International Colloquium on Refractories 2016 Aachen, Germanywww.ecref.eu

4 – 5 October 2016 11th Middle East CemenTradeDubai, UAEwww.cmtevents.com

5 – 6 October 2016 BULKEX16Harrogate, UKwww.mhea.co.uk

12 – 14 October 2016 ILA General Assembly Washington DC, USAwww.internationallime.org

16 – 18 November 2016 Arab International Cement Conference & ExhibitionAbu Dhabi, UAEhttp://www.aucbm.org/

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WORLD NEWS

The Cement Association of Canada has announced that it has become a member of the Carbon Pricing Leadership Coalition as a strategic partner and to join with other leading Canadian companies participating in a joint strategic statement issued by the Honourable Catherine McKenna, Minister of Environment and Climate Change.

The Carbon Pricing Leadership Coalition (CPLC) is a voluntary initiative that supports and encourages the successful implementation of carbon pricing around the world. It was initiated by the World Bank at the 2014 United Nations Climate Change Summit in New York City and officially launched in 2015 at COP21 in Paris.

“Well designed carbon pricing systems can drive innovation and prepare companies and communities to prosper in a competitive, low carbon and climate resilient economy,” said Michael McSweeney, President and CEO, Cement Association of Canada. “We have long advocated for carbon pricing in Canada and globally and are eager to continue our work with the federal and provincial governments to help them design and implement climate policies that support the goals of the Paris Agreement, protect and enhance the competitiveness of domestic industry and promote alignment on carbon pricing among our trading partners.”

Canada CAC joins Carbon Pricing Leadership Coalition

Bedeschi has been awarded a contract to manufacture a clinker and cement export terminal, with a loading capacity up to 1000 tph, by Sönmez Cimento.

The integrated cement plant will be based in the Adana Yumurtalik TAYSEP Free Zone (Turkey), in an advantageous area because of its closeness to land and sea transportation and raw material sources.The shiploader, slewing, luffing and travelling systems will be installed in this cement plant’s port terminal.

Turkey Bedeschi awarded cement and clinker export terminal contract

Worldwide Cemex obtains 'green' financing from IFC

Cemex, S.A.B. de C.V. has announced that the International Finance Corporation will grant Cemex a loan of approximately €106 million to support Cemex’s sustainable investment programs in emerging markets.

After a thorough assessment of Cemex’s environmental, governance and social practices, the IFC will grant Cemex funding for projects designed to enhance environmental performance that were completed in 2014 and 2015, as well as ongoing during 2016, which are part of the capital expenditure plan previously communicated by Cemex. Approximately 60% of the funds will be allocated for projects related to the reduction of Cemex’s greenhouse gas emissions, while the remainder of the funds will be allocated to cover improvements to Cemex’s overall air emission controls.

“IFC’s support underscores and validates Cemex’s sustainability efforts and vision,” said Fernando A. Gonzalez, CEO of Cemex. “We are very proud and encouraged by this relationship, and we continue to seek opportunities for further collaboration.”

The IFC is joining Cemex’s facilities agreement dated 29 September 2014, as amended and restated maturing in 2020. This transaction increases the currently outstanding commitments under the Credit Agreement by approximately €106 million and diversifies Cemex’s sources of funding.

On 28 June 2016, China Resources Cement (Fengkai) Limited, a subsidiary of China Resources Cement Holdings Limited, commenced operation of its sixth clinker production line. The line is at the cement production plant in Fengkai County, Guandong Province, and has a 5000 tpd clinker production capacity.

China Resources Cement Holdings Limited has completed the construction and commenced operation of all the planned production lines in Fengkai County, with production capacities of 9.3 million tpy of clinker and 8 million tpy of cement. The production lines aim to meet demand for cement in the Pearl River Delta area of Guangdong Province.

China New clinker line in Fengkai County

August 201610 \ World Cement

WORLD NEWS

HeidelbergCement AG has completed the acquisition of a 45% shareholding in Italcementi S.p.A. from Italmobiliare S.p.A. All conditions for the closing of the transaction have been fulfilled following the approval by the relevant competition authorities.

On 28 July 2015, HeidelbergCement and Italmobiliare entered into a share purchase agreement about the acquisition of a 45% shareholding in Italcementi. With the closing of the transaction, HeidelbergCement acquired 157.17 million ordinary shares, representing 45% of the share capital of Italcementi for a total consideration of €1.67 billion based on a price of €10.60 per Italcementi share. Thereof 82.82 million ordinary shares were acquired against cash. The remaining 74.35 million ordinary shares were acquired against the assignment of 10.5 million newly issued shares of HeidelbergCement. Thereby, Italmobiliare becomes the second largest industrial shareholder of HeidelbergCement with a stake of 5.3%.

In the share purchase agreement, Italmobiliare agreed to purchase certain non-core assets of Italcementi, including Italgen S.p.A., Bravosolution S.p.A., and certain non-core real estate. Italcementi has sold these assets to Italmobiliare on 30 June 2016 for total proceeds of €237 million. The proceeds from this disposal are part of the overall proceeds from divestments of at least €1 billion that HeidelbergCement targets as part of refinancing the acquisition. The divestment process for the assets in

Belgium and the USA as agreed with the antitrust authorities is progressing and significant interest has been attracted.

The acquisition of the 45% stake in Italcementi triggers the obligation to execute a mandatory tender offer to the remaining shareholders of Italcementi. The offering document will be filed with the Italian regulator, CONSOB, within 20 days after today’s closing, and will be published upon completion of CONSOB’s review period. The acceptance period will be agreed with Borsa Italiana. The acceptance period is expected to commence at the end of August. HeidelbergCement expects the entire transaction to be completed in the second half of 2016.

HeidelbergCement and Italcementi are a perfect fit. With the acquisition, HeidelbergCement becomes the number one producer of aggregates, the number two in cement and number three in ready-mixed concrete worldwide. HeidelbergCement enters new important markets, such as France and Italy in Europe, Egypt and Morocco in North Africa and Thailand in southeast Asia. In the USA, Canada, India and Kazakhstan, the takeover will further strengthen the existing market presence of HeidelbergCement. The enlarged Group has activities in around 60 countries with 63 000 employees working at more than 3000 production sites. HeidelbergCement operates 156 cement plants with an annual cement capacity of 197 million t, more than 1700 ready-mixed concrete production sites and over 600 aggregates quarries.

Europe HeidelbergCement completes Italcementi acquisition

On 23 May 2016, the Russian company Kazanskiy Zavod Sovremennoy Upakovki (KZSU) officially inaugurated its new production plant for AD*STAR block bottom sacks. Tatar President Rustam Minnikhanov personally attended the opening of the plant, which is situated in the Himgrad technology zone in Kazan, the capital city of the Republic of Tatarstan.

In the new plant, KZSU is producing AD*STAR block bottom sacks for the packaging of cement, gypsum, chemicals, fertilizer, animal feed and other dry bulk goods. The entire production equipment for the sacks, which are made of coated polypropylene (PP) tape fabric, was sourced from Austrian machinery supplier and technology leader Starlinger & Co. GmbH.

The investment includes extrusion, weaving, coating and printing lines, as well as 2 ad*starKON sack conversion lines and a recoSTAR universal recycling line for treating the production waste from Starlinger. The plant has a production capacity of 44 million AD*STAR sacks per year; the sacks will be supplied to Russian and foreign companies, among them JSC Chemical Plant Karpov, Asia Cement Ltd., Poliplast, Knauf Gypsum, Servolux (Belarus) or LLC Cement Plant Samadov (Tajikistan).

In the past few years, Starlinger has installed 10 AD*STAR production plants in other former Post-Soviet states; this is the first complete AD*STAR production plant that has been set up in Russia.

Russia Starlinger supplies production equipment for AD*STAR sacks

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ON THE HORIZON

ON THE HORIZON

RICK BOHAN CONSIDERS HOW

CEMENT BASED MATERIALS AND

ADDITIVE MANUFACTURING

COULD BE THE NEXT HORIZON

IN CONCRETE TECHNOLOGY.

Additive manufacturing or 3D printing is now an established technology with a rapidly expanding reach. Whether it becomes a disruptive and revolutionary technology or simply another evolution in technology is an open question. That question is particularly critical in terms of additive manufacturing and its potential impact with concrete or other cement based materials. Before that question can be answered, it’s important to define 3D printing.

Perhaps the easiest way to define 3D printing is by comparison. Most traditional manufacturing technologies either remove material through a subtractive process or add material through a casting process.

The subtractive process uses a block of material or a blank as its starting point. Successive layers of material are then removed through a series of processes. Additive manufacturing, in comparison,

12 \

KEYNOTEAUGUST

adds successive layers of material. The casting process requires pouring or placing material while it’s in a fluid or plastic state, allowing the material to solidify, and then removing the casting or form.

An example of subtractive manufacturing is the sculpting of marble while an example of casting would include a bronze sculpture. The term subtractive manufacturing did not appear in common usage until the term additive manufacturing was coined.

In the context of traditional manufacturing, it is quite common to use a variety of computerised numeric control (CNC) machinery such as mills, lathes, and drills, to remove larger amounts of material followed by grinders, welding arcs, and other devices to produce a finished surface or to separate individual pieces from a larger blank of material. The automation of this process can provide consistent, repeatable, and reproducible pieces. Unfortunately

/ 13

August 201614 \ World Cement

there are two significant disadvantages to these subtractive manufacturing processes.

The first disadvantage is the energy wasted in removing material. This waste is compounded by the energy required to clean the waste material (typically punchings or shavings) and reform it into usable size. The second disadvantage is that the processes involved in removing the material often distort the material because of the heat generated during the removal process. Both disadvantages can be reduced but not entirely eliminated.

The other form of traditional manufacturing is the casting or forming process. This approach pours or places liquid or plastic material into a mold. As the material solidifies the structure of the material transitions from the liquid or plastic state into a solid material. Metal casting is the foremost example of this manufacturing. Unfortunately there are disadvantages to this type of manufacturing as well.

Casting requires a precise mold and regardless of the mold material, molds can only be reused so often. In fact, an entire category of molds are expressly meant for single use only. Another disadvantage of casting is that as the material cools during its transition from a liquid to a solid, it shrinks. This solidification shrinkage can be several percentage points and must be taken into account. Likewise, if the cooling of the material is not precisely controlled, the final crystalline structure may not be suitable for its intended application. In some cases the structure might be flawed with inclusions or voids.

In some general ways, the placement of concrete is similar to metal casting. Both require some type

of mold but concrete practice refers to the mold as formwork. Both require the transition of the material from liquid to solid but the setting and hardening of concrete is a chemical process driven by formation of crystals rather than a thermal process. The similarity between concrete or metal casting is that some type of mold is required to support the material until the material has achieved sufficient strength and rigidity to support its own weight. There is also an additional similarity in the importance of temperature control for metals and concrete during their initial liquid and plastic states.

Additive manufacturing has significant advantages to traditional manufacturing processes. Chief among these is the virtual elimination of waste. Because material is added rather than subtracted, only the needed amount of material is actually used. The process of adding material by successive layers also helps avoid potential internal defects such as voids or inclusions. The final significant advantage is an increase in surface tolerances resulting directly from the incremental nature of adding successive layers in precise dimensional locations.

The vast majority of materials used in additive manufacturing include either metals or thermoplastics. These materials tend to lend themselves to additive manufacturing because they can liquefy and solidify fairly quickly and their strength gain upon solidification is very rapid. This nearly instantaneous ability to liquefy and solidify allows users to print incredibly sophisticated, intricate and complex shapes in just one operation.

Unfortunately all the attributes that make metals and plastics suitable for 3D printing become significant obstacles to the application of concrete in additive manufacturing. In its early ages, concrete is nearly fluid so that it fills virtually any imaginable shape. Yet concrete becomes plastic relatively quickly so that it can be finished with a variety of textures. Its ability to solidify within a matter of hours confirms its role as the superior building material.

And this is the crux of the matter. The concrete driveway placed at 8:00 in the morning isn’t able to withstand foot traffic until around lunch time and it isn’t strong enough to support a parked car until at least the next day. The advantages of working with concrete would seem to work against 3D printing.

The reason that’s the case is because cement hydration is essentially a two-step process (Figure 1). First, the cement dissolves within the mixing water and that dissolution releases ions into the mixing water. The mixing water now is a pore solution of ion enriched water. Some of the phase components of cement, particularly C3S and C3A along with gypsum are very soluble in that pore solution of ion enriched water. As those phase components dissolve quickly, the concentrations of their ionic species increase very rapidly, ultimately to a point of supersaturation. At that point, the pore solution

Figure 1. The dissolution precipitation process of cement hydration. (Thomas, Jeff and Jennings, Hamlin, The Science of Concrete, online monograph, http://www.iti.northwestern.edu/cement/index.html.Northwestern University, accessed 24 November 2015.)

August 2016 / 15World Cement

can no longer hold any more dissolved ions and that leads to precipitation, the second step of the cement hydration process. All the excess dissolved ions recombine into solid phases because it takes less energy for them to recombine than it does for them to remain supersaturated. This two-step dissolution precipitation reaction called hydration is a wonderful mechanism for traditional concrete but a significant barrier towards use of concrete in 3D printed applications.

As the cement particles continue to hydrate, the concrete sets in basically a chemical process of growing crystals. That process includes three phases (Figure 2). The first phase of concrete setting includes the point of initial mixing starting at the point when the material is fluid up until the point where the material is transitioning to the plastic state. It’s the point where you can still make handprints in the concrete. The next phase, the setting phase, includes the point where it is still possible to make indentations into the concrete although it requires increasingly larger amounts of force. The final phase of concrete setting is the point at which the concrete is a true solid and it behaves as a true solid. There are no clear dividing lines between each of these three phases. In fact, even solid concrete will continue to gain strength years, decades, and even centuries after it was initially placed, provided there are still unhydrated (unreacted) cement particles and a source of moisture.

This setting process of concrete is often observed using the heat evolution which corresponds to the chemical reactions taking place (Figure 3). The dormant phase noted reflects the time that dissolution continues to saturate the pore solution yet before the pore solution becomes supersaturated. This period of time is of significant benefit for traditional construction because it allows us to transport and place concrete before it starts to set up. Unfortunately it is not helpful if we want to use concrete for 3D printing.

The next area of interest is the transition from dissolution to precipitation. During this period the mixture of cement and water starts the transition from a supersaturated pore solution into the beginning and acceleration of precipitation of solids. This period of time is also an obstacle to 3D printing concrete because it takes some hours before the concrete is truly a solid material.

Ideally, if there were a means to eliminate the dormant period and get a much steeper slope to the transition period, concrete would transition from a liquid or plastic state to a solid state within a

matter of minutes as opposed to a matter of hours. This approach would provide a concrete able to support its own weight and the weight of successive layers of concrete almost immediately. That would provide a material capable of use in the 3D printing environment.

Since the setting of concrete is primarily dependent on the setting characteristics of the cement, changes in cement chemistry would seem to offer the potential to allow 3D printing of concrete. For example, the use of less sulfate (in the various forms of gypsum) is problematic because of the potential for flash set and the amount of heat generated. Heat generation entails expansion and as the material cools, contraction ensues. As concrete contracts, it tends to crack because concrete has far less tensile strength in comparison to compressive strength. Higher C3S or C3A levels in Portland cement do provide higher earlier strengths but here again they are accompanied by higher amounts of generated heat. Clearly changes in the chemistry of cement do not currently offer a means to develop a concrete material suitable for 3D printing.

The concrete admixture industry has extensive experience providing admixtures that make concrete more and more fluid. If effect these admixtures have fundamentally altered the basic rheology (the flow) of concrete. Changes in rheology and viscosity that proceed in the opposite direction by making concretes stiffer might be a direction towards 3D printed concrete. We now make concretes stiffer

Figure 2. Setting of concrete (Adapted from Young and others 1998). Portland Cement Association, 2011.

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either increasing the aggregate content of concrete. If there were a means to do this chemically or to restrict the amount of water used, then perhaps this approach would lead to the elusive 3D printed concrete. Unfortunately, changes in the rheology or thixotropy of concrete that allow concrete to set and harden extremely quickly are as yet undiscovered.

If the material challenges can be overcome, the concrete industry is well poised to provide the equipment necessary to 3D print concrete on a very large scale basis. The shotcrete industry, along with paving and pumping industry, have current off the shelf equipment and techniques suitable for large scale and rapid deposition of concrete. Additional improvements in automation are required to marry these technologies to the realities of 3D printing but those improvements are well within our grasp.

One required improvement is the placement of reinforcing steel. Concrete is weak in tension and this is why it is reinforced with steel. Continuous placement of 3D printed concrete would likely require some type of continuous deformed wire analogous to the technologies used in continuous wire welding.

However the material and the equipment problems are not the only issues precluding the use of 3D printed concrete. There is still the problem of placing concrete in an overhead application. This is the main problem for any material used in 3D printing. In the case of concrete, it may be possible

to extrude material beyond a vertical plane and, in effect, create a cantilever but actually ‘printing’ a floor from underneath is also the realm of fiction.

Although 3D printed concrete seems unrealistic, there continues to be steady progress towards this elusive goal. Some examples include a team from Loughborough University who claim that they can print a 2500 square foot home in just 24 hours or Behrokh Khoshnevis’ work on rapid prototyping (also known as contour crafting) for home construction at USC.

Yet even if the technical issues described were solved tomorrow, 3D printed concrete is still years away.

Architects and engineers are naturally risk adverse licensed professionals. They simply will not adopt a material for design and construction unless it meets building code requirements. There are no building code requirements for 3D printed concrete. And there are no building code requirements for 3D printed concrete because there are no standard specifications for 3D printed concrete. Without standard specifications for the sampling, testing, acceptance, materials, prescriptive or performance requirements of concrete used in 3D printing, there will not be a standard specification for 3D printed concrete or acceptance by building code authorities.

Although experience argues against the use of concrete in additive manufacturing, it is important to remember that experience also argued against the use of concrete as a construction material. Concrete’s history is one of discovery, innovation, incorporation, acceptance, and demand. There’s no reason to believe that we won’t see that same progress with 3D printed concrete. It may not be today but it just might be tomorrow.

ReferencesReferences can be found online, here: http://static.worldcement.com/media/documents/keynote-references.pdf

Figure 3. Heat evolution as a function of time for cement paste. Stage 1 is heat of wetting or initial hydrolysis (C3A and C3S hydration). Stage 2 is a dormant period related to initial set. Stage 3 is an accelerated reaction of the hydration products that determines rate of hardening and final set. Stage 4 decelerates formation of hydration products and determines the rate of early strength gain. Stage 5 is a slow, steady formation of hydration products establishing the rate of later strength gain. Portland Cement Association, 2011.

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