The 7th International VDZ Congress 2013, 'Process technology of cement manufacturing,' has successfully taken place in Duesseldorf, Germany, on 25 - 27 September, attracting around 600 delegates of whom around 250 were from outside Germany. The Congress - in English - takes place every four years and is regarded as one of the most prestigious cement technical conferences in the world.
The Congress was opened by Gerhard Hirth, president of the Verein Deutscher Zementwerke, the German cement plant association. He pointed out that cement is a high quality, high value material without which society would struggle to cope.
Howard Klee next spoke about the Cement Sustainability Initiative and stated that the initiative now has 24 member companies, covering 25% of global cement production, or 55% outside of China. Howard stated that the main objectives of the CSI include improving the cement industry's performance on climate impacts, employee safety, sustainability, water use and biodiversity. Co-processing and waste management are also now covered by the initiative. Four levers have been suggested to manage CO2 emissions from the cement industry, including the promotion of energy efficiency, alternative fuels use, clinker factor reduction and carbon capture and storage. On the safety side, incidents involving moving vehicles, falls from height, and being hit by moving machinery or objects are the main cases of injuries and fatalities in the cement industry, with continuing high fatality levels in the cement industry but even higher levels among contractors on cement plant sites. New action is being taken to address the cement industry's mercury emissions, with best available technology and best environmental approaches being developed. The CSI has also developed global guidelines for alternative fuels use, specifically excluding a variety of materials that local populations would object to, in order to help to retain the 'license to operate.' Action on biodiversity is ongoing in the global cement industry. Howard's organisation is encouraging concrete recycling, aiming towards 'zero landfill.' Howard Klee concluded, "The superior properties of concrete make it a superior construction and infrastructure material, but public perceptions differ from this standpoint."
Cecilia Tam of the International Energy Agency then gave an overview of the current development and future trends in energy markets. Cecilia suggested that there had been a resurgence of oil and gas production in a number of countries, notably in the US, that nuclear has gone into reverse due to events in Japan and that countries have increased their focus on energy efficiency. All-time high prices for oil have acted as a brake on the global economy. Gas prices are now around five times higher in Europe and eight times higher in Asia than in the US. Unsustainable fuel subsidies still abound, notably in the Middle East, putting a brake on energy efficiency efforts. Global energy demands are expected to rise by a third to 2035, underpinned by rising living standards in China, India and the Middle East. Cecilia suggested that the US will produce more unconventional oil and gas than conventional oil and gas within the next few years.
By 2035, around 90% of the Middle East's oil exports will go to Asia, while the US will become a net exporter of oil and gas. China, India and the EU are becoming more dependent on energy imports, whereas the US is moving the other way. Cecilia stated her belief that renewables will account for half of new global capacity. However, coal will still dominate electricity production in India and China, while at the same time reducing in importance in the US and the EU. Japan and the EU have the highest global electricity prices, with prices in the US being lower and China having the lowest prices, around 5c/kWh. Two thirds of the economic potential to improve energy efficiency will remain untapped in the period to 2035: power generation and buildings will lag behind industry and transport in realising efficiency improvements. Cecilia suggested that economically viable efficiency measures can halve energy demand growth to 2035, saving oil equal to the current production of Russia and Norway combined. However, the global energy supply is as carbon intensive today as it was in 1990: no overall progress has been made. Four levers have been proposed to reduce energy production carbon intensity: partial removal of fossil fuels subsidies, reduction of methane releases from upstream oil and gas, limiting the use of inefficient coal fired power stations and the implementation of energy efficiency policies.
Well-known cement industry analyst Dr Joe Harder from OneStone Consulting next gave a thought-provoking presentation, as always. Dr Harder stated that global cement product is set to grow from 3270Mt in 2010 by a CAGR of 2.9% to 4370Mt in 2020, and by a CAGR of 1% to 4780Mt in 2030. Growth in the BRIC countries will mostly depend on India since Chinese cement production is expected to start to decline some time within the next decade - and has possibly already started to decline. Indonesia and Iran are expected to continue to grow their cement industry capacities, alongside Mexico, Vietnam, Turkey, Egypt and Saudi Arabia. The 'Next 7' producers include Malaysia, Philippines, Thailand, Pakistan, Nigeria, Morocco and Algeria, growing their combined capacity from 120Mt in 2012 to closer to 300Mt in 2030. Joe pointed out that the market for grinding equipment is around a third of the total value of cement-related equipment. Around 200 new mills are ordered outside of China each year, equating to 45 - 60Mt of grinding capacity. Vertical Roller Mills now dominate orders, with around a 50% market share, followed by ball mills, high pressure grinding roller mills and by Horomills. A total of 1611 mills were ordered by Chinese cement producers from local suppliers in the period 2010-2012, around three times the total amount of grinding equipment ordered by the whole of the rest of the world during this time span. However, the Chinese market has now peaked and is declining rapidly. Clinker grinding makes up around 53% of the market, with 31% of orders for raw materials grinding, 13% for slag grinding and 4% for coal grinding. Raw material grinding and coal grinding will tend to decline, due to the trend towards lower clinker factors in cement. Joe Harder went on to speak about waste heat recovery (WHR) in the cement industry, pointing out that there are already 865 WHR systems operating in the global cement industry, with 98% of them conventional steam-based systems. 95% of the WHR units in operation are in China, with 739 units, followed by India (26 units) and Japan (24). The number of WHR units installed each year in China peaked in 2009 and has steadily decreased since then due to a decreasing number of new lines, a dwindling number of plants still available for retrofits and a reduction in CRM projects.
Andreas Schaab of Hochtief Construction AG spoke about modern cement requirements as seen from the construction industry. Mr Schaab said that concrete must be durable, have a long service life of more than 100 years and must be chemically stable. On the other hand, there is a strongly competitive construction market, with short construction periods and steadily decreasing levels of experience. Modern use of concrete requires high specifications, for example, in sprayed concrete the materials must be transported, mixed and emplaced at very high speed to very narrow tolerances: a high specification cement with constant properties must be supplied for the mix to work correctly. Mr Schaab pointed out a problem on one project that had occurred due to variations in cement composition (decreasing content of C3A and increasing C4AF content) and he suggested that it was due to a temperature change in the cement kiln due to the use of alternative kilns. The problem was rapidly fixed, although the means was not specified. In another case, the finger of blame for difficulties with shotcrete emplacement was pointed at a change of calcium sulphate composition and level of hydration, possibly due to a change in conditions in the clinker ball mill. Mr Schaab reiterated his point that not only must cement quality be high but that it must also be constant, with no significant changes over time.
Dr Martin Schneider of the VDZ rounded out the first day with a summary of the technological developments in the cement industry, in energy efficiency, grinding, emissions and in new cements. Dr Schneider pointed out that the overall energy demand of the German cement industry has hardly changed since 1990, but that alternative fuels have made up a progressively greater proportion of the energy mix over the years, with Germany placed among the most advanced alternative fuels-using countries in the world. He pointed out that the economic feasibility of WHR depends on specific situations such as the availability of excess heat, energy costs and overall efficiency. In grinding technology, the trend is towards larger installations, of perhaps 650t/hour for clinker and up to 850t/hour for raw meal. He pointed out that comminution of a single particle is far more energy efficient than bulk material comminution, at least in theory, possibly pointing towards more efficient future grinding technologies. Mercury is climbing up the legislative agenda worldwide and this is of great importance for the cement industry which currently accounts for 9% of global mercury emissions according to the UNEP Global Mercury Assessment, although this number is disputed by experts within the industry.
Abatement strategies and technologies are being developed and tested for the cement industry, including dust bleeding to release mercury cycles alongside careful temperature control, as well as input controls on alternative fuels and raw materials. The cement industry is under continued pressure to curtail its NOx emissions, through staged combustion, SNCR and SCR, to achieve a level of 200 - 450mg/m3 for preheater kilns. Optimisation of injection points of ammonia is being pursued to achieve high efficiency of SNCR. Martin Schneider mentioned post-combustion carbon capture and the Oxyfuel combustion process, but there remains widespread scepticism in the industry about the economic feasibility of the process, with costs amounting to above Euro50/t of CO2. He pointed out that CO2 could be reacted with hydrogen from electrolysis and converted into methane as an energy storage medium, allowing the storage of intermittent renewable energy in gas storage facilities. The oxygen generated from the electrolysis of water could then be used either in the cement process or in the Oxyfuel process. He also mentioned new cements, including belite calciumsulfoaluminate ternesite cement, belite-rich Portland cement and Celitement. Calcined clays could become more important as a constituent of cement, although reactive silica content must be kept below 25%. He concluded by stating that higher fineness will provide higher early strength, but that finer grinding will have other, perhaps unexpected and unwanted, side-effects.
Second day
Delegates were faced with a difficult choice on the second day, with two parallel sessions to choose from. Global Cement made a sampling of presentations from both sessions.
Sten Stoltze of FLSmidth presented his company's vision for how the cement industry will move ahead in cooperation with equipment suppliers. He noted a trend towards more stringent emissions regulations, higher energy efficiency, increasing amounts of clinker replacement materials and towards lower quality fuels and raw materials. "The alternative fuels of today will be the standard fuels of tomorrow," he said. Sten Stoltze suggested that alternative fuel usage will top-out at around 60% by 2030 in developed countries, meaning that utilisation rates will need to double or treble compared to today's rates. Sten mentioned the CataMax catalytic filter for the reduction of THC, NOx and other emissions, which has been developed from an experimental rig to the position of a new product for the cement industry. He echoed Dr Schneider's point that activated clays may make more of an impact in the future as an SCM, and said that FLS is ready to install a pilot demonstration plant in South America. It has been demonstrated that a significant proportion of the clinker component can be replaced by activated clays without deleterious effect on cement performance. He suggested that future technology developments will be in the form of collaborative efforts between the equipment supplier and the cement producer, an opinion proved by later presentations.
Fabio Wider of Holcim spoke about his company's experience with waste heat recovery at Untervaz. Kiln flue gas leaves the preheater at 360°C, while the cooler exhaust gas is 300°C. A two bundle heat exchanger was used at the project, with pressurized water as the heat carrier. Initially, the heat exchanger underperformed due to uneven gas flow: two 'winglets' had been installed at the inlet of the exchanger to try to ensure even gas flow, but the unit did not achieve its design values. The higher the flow velocity in the exchanger, the lower the heat exchange potential of the unit. Several design iterations and rebuilds were used to try to improve gas flow, and the problem was finally solved by installing partition plates in the dust bins at the bottom of the unit, similar to the designs previously used in electrostatic precipitators. However, passing the gas stream through the heat exchanger caused downstream problems in the plant's ESP, since the heat exchanger also preferentially collected the coarser fractions of dust in the gas stream. Dust arriving at the ESP thus tended to be finer, being less likely to accept a charge and making the particles harder to collect. Changes to the operation of the ESP were required to improve performance. "Even if waste heat is something non-classical in the cement industry, it almost always comes back to already well-known processes from the cement industry," he concluded.
Andreas Werner of the TU Vienna and co-author Helmut Leibinger of the Rohrdorfer Gruppe gave a comparison of the thermodynamics of different WHR systems. The single-pressure steam system has the advantage of simplicity and a non-toxic exchange medium, but the system is relatively inefficient. A dual-pressure steam system has higher efficiency but has greater complexity and higher investment cost. Organic heat exchange media can of course be used: for a given temperature of a heat source different organic fluids will give higher efficiencies, while also bringing higher complexity, toxicity and costs. Organic Rankine Cycle (ORC) systems are applicable for lower temperature sources: superheating is not necessary so that comparative costs can be kept down. The proprietary Kalina Cycle - offered by FLS - uses a mixture of ammonia and water, allowing the possibility of reducing the temperature difference between the heat source and the evaporated working fluid, and allowing its application to low grade heat sources. By varying the concentration of the NH3, a better adaptation to ambient temperatures can be achieved. Professor Werner pointed out that air from different parts of the cooler will be at different temperatures, ranging from 1100°C at the kiln end to perhaps 140°C at the end of the grate. If the air streams can somehow be kept separate, then different WHR solutions may be appropriate for the different qualities of heat sources. In the future, super-critical CO2-based systems will offer even higher efficiencies.
Gernot Kircher from Lafarge Zement and co-author Volker Hoenig of the VDZ next addressed the energy efficiency potentials and limitations of the cement industry. Gernot pointed out that the total amount of energy used to produce a kilo of cement in Europe, at around 3200kJ/kg of cement, has not changed in the last decade. CEM 1 has steadily lost market share in both the German and wider European cement markets, while blended cements have grown, with the clinker factor reducing from above 80% in 2000 to below 75% in 2012. Mr Kircher forecast that CEM1 will reduce its market share to below 15% by 2030, with CEM 2 cements coming to dominate, with a market share of around 30% by 2030. A clinker factor of 0.67 is forecast for 2030 in Europe if sufficient slag is available. Using the best available technology, replacing all kiln lines with the most modern and efficient types and using a maximum level of alternative fuels, Gernot Kircher calculated that the specific energy demand of the German cement industry could drop by up to 14% by 2030, suggesting that the industry is already being run in a fairly energy-efficient manner.
Mr Wang Wei of Sinoma gave a controversial presentation on Sinoma's investment return model, which claimed that Sinoma can dramatically decrease payback times on cement plant projects, mainly through reducing the initial cost and by reducing the length of the construction phase. Delegates were not universally in agreement with Mr Wang Wei's figures, but it cannot be denied that the low-cost Chinese equipment manufacturers have had a major impact on the business models of equipment manufacturers - and cement producers - in the rest of the world.
Frank Ruoss of ThyssenKrupp Resource Technologies (TKRT), the former Polysius, re-introduced his company, "a new company rich in tradition." The new company is an amalgamation of Polysius and ThyssenKrupp Fördertechnik, and now offers its services not only to the cement industry but also to the minerals and mining industries. The company group includes Maerz Ofenbau in lime and the German company FuelTrack, active in alternative fuels. Catalytic gas cleaning is offered by group company CemCat. Mr Ruoss pointed out the strong trend towards the award of turnkey projects in the cement industry, and suggested that the new TKRT company will be in a good position to be able to fulfil all future cement plant orders and service.
Rüdiger Matheis and co-authors from Dyckerhoff AG next spoke about high efficiency selective non-catalytic reduction, SNCR, for NOx reduction at the Göllheim cement plant in southern Germany. The plant site offered test conditions on two different kilns with both the best and worst preconditions for SNCR. The company stated a JV with STEAG Powitec, with Lechler as a subcontractor, in order to optimise its ammonia water (<25% NH3) injection, in order to preempt and to pass new emissions limits. Individually-controllable twin-fluid spray nozzles were used in the new project, with injection at up to ten points on different levels in the pyro-systems. The arrangement of nozzles meant that daily limits for NOx and ammonia slip were met on kiln 1, and with some difficulty on kiln 2. Optimisation of meal entrance and improvement in the position of the lances are the next steps towards reducing the level of ammonia use and slip. Rüdiger Matheis concluded that an emission limit of 200mg/m3 may be feasible for most of the time on most kilns, but that high levels of ammonia slip will have to be accepted.
Detlef Edelkott of Schwenk Zement reported on three years of experience with selective catalytic reduction of NOx in a high-dust gas stream using an Elex plant. The SCR process requires a temperature range of 260 - 400°C, so that the reactor can be placed directly in the preheater exhaust gas stream. It is important to keep the catalyst elements free from blockage and the catalyst elements should have a low rate of oxidation. Blowers are used to clean out the hexagonal channels in the catalyst modules. Exhaust air enters the top of the SCR catalyser module and is progressively cleaned as it descends. Early operation showed high pressure drop and the presence of blockages. Small but decisive changes to the geometry of the channels, and alterations to the operation of the blowers, meant that blockages could be avoided. It also became clear that the compressed-air cleaning system must be properly levelled and maintained. A high operating temperature of above 400°C was blamed for the relatively quick degradation of the catalyst elements, and a water-spray gas conditioning system has now been installed. A catalyst cost of around Euro0.3/t of clinker has been calculated, while operation of the SCR unit increases specific energy consumption by 5kW/t clinker. The presentation showed a really pioneering and persistent approach to the project.
Bernhardt Köck of Lafarge CTEC Vienna GmbH followed on by speaking about an attempt by the Mannersdorf plant to utilise SCR to achieve NOx emissions of lower than 200mg/m3, in expectation of future reduced emission limits. The 2500t/d plant is the largest in Austria and the plant has a very high dust load, due to the design of the pyro-system. A decision was made to semi-clean the dust before the SCR system, using a two-field ESP. Scheuch was the main contractor for the turnkey project. A gas conditioning tower is used before the vanadium pentoxide-based two-layer SCR. Such is the operational effectiveness of the new system that while the SCR is being used, the SNCR remains on standby. The NOx target was reached from the beginning of the project, alongside a reduction in VOC and almost complete oxidation of Hg. However, due to carbon fibres in the flue gas (originating from alternative fuels) and high dust resistivity, the ESP performance has not been as high as expected, leading to a dustier SCR unit and a higher than expected pressure drop. Urea consumption dropped from 750l/hour to 250l/hour and savings in urea costs compensate for power and catalyst costs of the SCR. The SCR must be preheated before operation to prevent poisoning of the catalyst and again, the operating temperature of any catalyst must be limited to a maximum of 350°C. Allowing the catalyst to drop below the dew point is strictly to be avoided and consequently the SCR must be purged with hot fresh air if the process is stopped. Elevated levels of thallium were progressively detected in the catalyst, leading to a slow reduction in catalyst efficiency and finite catalyst lifetimes. As with the previous presentation, the speaker mentioned that the dust blowing system must be optimised to allow continued operation, which in this case will be made easier with catalyst cells with wider openings in the near future.
Thomas Schmitz of ThyssenKrupp Resource Technologies gave delegates information on the Quadropol RD, the world's first vertical roller mill (VRM) with driven rollers. He pointed out that if the table is driven, the rollers are always running behind in speed, whereas with driven rollers, the rollers are faster than the table, drawing in material to be ground. A lower level of torque is required with driven rollers and standard gear unit sizes can be used, even with high capacity mills. Operation is still possible with one passive roller, albeit at lower capacity, while on mills with four or six rollers, operation is still possible with two opposing rollers lifted out. The overall design of the mill is largely unaffected by driving the rollers instead of the table, and the design concept means a very low level of vibration in the mill, with all grinding forces channelled directly into the concrete foundations. An increase in grinding efficiency has been recorded. The first mill has been installed at the Cruz Azul Lagunas plant in Mexico, with a throughout rate of 175t/hour at around 4500 Blaine and a specific power consumption of 28kWh/t, including main drives, mill, fan and separator. The mill has a table diameter of 5100mm, roller diameters of 2500mm and installed power of 3 x 1500kW. A second driven roller mill is currently being installed at Holcim's La Rochelle plant in France, while another mill will be installed at Cycna de Oriente's Palmar del Bravo plant in Mexico in the summer of 2015, with a table diameter of 6.4m and four rollers, each with an installed power of 1800kW.
Gerhard Philipp of Wopfinger Baustoffindustrie GmbH described his company's implementation of regenerative thermal oxidation (RTO) at the Wopfing cement plant, Austria, in cooperation with Austrian company CTC. The RTO unit has a volume flow of up to 218,000Nm3/h, with five heat exchanger beds consisting of 25,000 monolithic ceramic honeycomb catalysis blocks. The RTO is also equipped with 40 injection nozzles for SNCR. Odours, CO and VOCs were reduced, while the unit showed high availability, allowed more flexibility in the use of alternative fuels and raw materials and - most importantly - allowed a reduction in NOx emissions. The RTO must be operated at above 800°C and the unit has a pressure drop of 35mbar. Similar to the other gas cleaning methods previously described, the catalyst units can become plugged with dust, so that the unit is designed to allow high-dust gas streams to be sent into a bypass. Fouling of the ceramics can be caused by ammonium sulphate, in which case a bake-out cycle of above 400°C must be used to clean the catalysts. With the operation of an existing SNCR, the system can reach a NOx abatement level of over 90%, to below 200mg/m3. The system uses around 8kWh/t clinker, as well as natural gas and ammonia.
Finishing the day, Dan Crowley of Titan America gave an overview of mercury emission abatement measures currently being investigated in the US. New emissions permit levels for mercury from the EPA initially stipulated a level of no more than 12.5lbs per million short tons of clinker. After three years of negotiation, the level was raised to 55lbs of mercury per million tons of clinker, (or 21lbs for new plants) a level that half of the cement plants in America would currently fail. Stringent management of raw material mercury levels is the first and perhaps most important step. Removing a mercury-rich dust fraction to feed it into the clinker mill is also an option, but has its own problems, possibly including the handling of large tonnages of potentially toxic dust. The injection of activated carbon into the system can retain both elemental and oxidized mercury in the system and allows lower levels of reject dust to be handled. Other solutions may include scrubber systems, gas suspension absorbers or fixed bed gas remediation using sorbent polymer composites (involving costs of perhaps US$2/t of clinker). Dan Crowley said that the most important piece to solving the mercury puzzle is the installation of a continuous emissions monitoring system (CEMS) to generate good, continuous, reliable data for process knowledge and control.
On the evening of the second day of the conference, a glittering gala dinner and safety awards ceremony took place in the conference hotel, with technical discussions continuing very long into the night.
Third day
There were more tough choices between presentations on the third day of the conference, undoubtedly due to the high number of quality papers offered to the organizers.
Michel Delort of ATILH, France, spoke about low-clinker ternary (three-component) cements. In 2006, it was proposed to standardise a new type of cement, made from 30 - 64% Portland clinker, 30 - 50% blast furnace slag and 6 - 20% limestone. The cement would have low CO2, good workability and acceptable strength characteristics. Of 17 tested samples and compositions, 11 cements were classified as 32.5 or higher, but six cements with a clinker content of less than 50% failed to reach an adequate performance. No significant differences in shrinkage and creep characteristics were found between ternary cement-based concretes and CEM1 concretes. Chloride diffusion results were generally better than standard concretes. The results of freeze-thaw tests were variable and some high-scaling results are as yet unexplained. All samples performed better than CEM1 and CEM 2 in sulphate resistance tests. The low-clinker ternary cement is set to be included in new EN 197-1 standards as a new CEM2 type, or CEM6 where the clinker content is lower than 50%.
Jaroslaw Sawecki of Cemex Poland next spoke about the use of a new drum drier for alternative fuels. The Chelm cement plant uses 68% RDF, and over the last few years has noted a steady reduction in calorific value and an increase in water content, sometimes to over 30% in wet periods. Segregation of material from different suppliers, RDF homogenisation, regular testing and control of RDF material and the use of a dryer have all been used to try to increase the quality of the fuels. The dryer uses waste heat from the clinker cooler, and the dried fuel is not stored due to the fire hazard: the RDF from the dryer goes directly to the kiln and calciner feeders at once. The drum dryer has a capacity of 40t/hour, and is capable of evaporating around 8t/hour of water. The dryer typically reduces the water content of the fuel by around 10%, allowing a reduction in specific heat consumption in the pyro-process of around 10% as well. A fire extinguishing system is essential for protecting the dryer: sparks are often detected in the dryer and are immediately neutralised with a water spray.
Wolfgang Dienemann of HeidelbergCement and co-authors then spoke about belite calciumsulfoaluminate ternesite cement (BCT). A wide range of alternative binder concepts have been investigated and developed over the last few decades, including belite cements, magnesia-based cement and alkali-activated aluminosilicates, but so far no alternative binder has reached maturity to replace OPC-based cement in substantial volumes. Calciumsulfoaluminate belite cements are mainly produced in China at a rate of around 2Mt/year, with high early strength, but there are durability concerns. The main difference compared to normal OPC production is the use of higher levels of sulphate sources, for example from industrial by-products. The lower energy demand leads to a lower process temperature and a more grindable clinker. Many patents have been awarded for these cements, with the focus being on use in structural applications. The reactivity of belite largely depends on its crystallographic phase, with a higher temperature of reaction producing more reactive crystal forms. Ternesite is a reactive clinker phase, but only in the presence of an alumina source, potentially from the dissolution of other clinker phases. In BCT clinker testing, a wide range of alumina sources including slags and ashes have been utilised in order to reduce the use of more expensive alumina and bauxite. BCT clinker is formed at 1000 - 1250°C. The alite phase is absent in BCT cements, with ye'elimite instead dominating and providing early strength development. The strength development of BCT is comparable to OPC, depending on the aluminate/silicate ratio. The first industrial tests have been undertaken in a German cement plant, producing clinker for two days under relatively stable conditions. Many steps have yet to be undertaken before the final acceptance by customers: endurance and patience will be required all round, and the market arrival of a saleable product is at least five to seven years away.
Sui Tongbo of Sinoma International Engineering and co-authors from the China Building Materials Academy then spoke about belite-rich Portland cement and concrete. Mr Tongbo stated that high belite cement has a lower burning temperature compared to OPC, with energy saving of 10 - 20%, a reduction in CO2 emissions of over 10% and that it can be produced from low-grade limestone resources. Belite cements have better workability, with lower water demand and good compatibility with different types of chemical admixtures, with lower heat evolution, higher late stage strength (by 10MPa compared to comparable OPC and even higher when belite cement is blended with fly ash) and good durability. High-belite cement has been used in major engineering projects in China including the Three Gorges Dams, primarily for its low heat of hydration benefits which lead to cost savings in the cooling of mass concrete emplacement.
Hendrik Möller of Schwenk Zement gave details of his company's Celitement division and progress on its new pilot plant. Progress has not been as quick as originally planned, due to problems with the selection of activation grinding technology. The production of celitement involves a 'standard' raw material processing and raw meal production stage, an autoclave process at lower temperatures than in a conventional kiln and an activation grinding stage. It was found that some of the raw materials initially tested would not allow the required C/S ratio to be achieved in the autoclave. After extensive testing, the reactivity and role of many phases in typical raw materials are now known, and robust procedures for raw meal calculations are now in place. The autoclave can be run in either a wet mode, producing a slurry, or a dry mode using steam, which produces a dry powder. Yields of up to 90% of the desired calcium-hydro-silicate can now be produced with appropriate process control parameters. The mix of amorphous and crystalline C2SH phases can now be controlled, which is crucial for correct product performance. However, the activation grinding stage is vitally important: "it is not a trivial problem to correctly identify the amount, quantity and material characteristics of the desired calcium hydro silicate product," said Hendrik Möller. Activation grinding, 'tribochemistry,' is familiar in another guise to cement producers, in the grinding and partial dehydration of gypsum in the clinker mill. In the celitement activation grinding stage, there is a dewatering of the silicate particles, while at the same time there is the creation of fresh reaction surfaces. A vibrating tube mill was finally chosen as the activation grinding mill. Product optimisation has just started and as yet no samples have been supplied to third parties for testing. If all goes well, industrial production may commence in 2016 - 2017.
Christoph Müller of the VDZ gave the last presentation of the session and spoke about the durability requirements for concrete today and in the future. It is important to determine the elements that ensure concrete durability, including the exposure conditions, the composition and performance of the concrete, the emplacement requirements such as curing and the concrete coverage of any reinforcements. Durability can be measured from emplaced concrete in the field, can be measured in the laboratory and can also be forecast using compositional analysis and modelling. Christoph Müller reminded delegates that it is not just the cement that controls the durability of concrete and pointed out that concrete mixes change from country to country and from region to region, so that the same cement will give rise to different durabilities in different concretes. EN standards may be adapted in the future to give details about the carbonation and chloride resistance of cements and concretes, giving rise to the creation of a variety of new exposure classes. He finally pointed out some discrepancies between test results and long term practical experiences of durability and suggested that tests might need to be modified in the future, particularly with regards to new cementitious binders, for them to remain effective in future cement and concrete durability.
Until next time...
At the very end of the Congress, Dr Martin Schneider graciously thanked the speakers and all attendees, wished them a safe journey home and said that he and the rest of the VDZ organisation were already looking forward to welcoming delegates back to Düsseldorf for the next VDZ International Congress, in 2017.