Düsseldorf, Germany
Düsseldorf, Germany
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Rickert J.,VDZ
American Concrete Institute, ACI Special Publication | Year: 2012

In this research project several natural clays were examined in detail by X-Ray Fluorescence (XRF), Differential Thermal Analysis (DTA) and X-Ray Diffraction (XRD) to define optimal burning conditions to meet the requirements regarding the reactive silicon dioxide content of pozzolanic materials acc. to EN 197-1. The calcined samples were examined by means of Scanning Electron Microscopy (SEM), XRD and concerning their pozzolanic activity. Cements were made using the calcined clay with the highest reactivity as main constituents besides Portland cement clinker, respectively, and the cement performance according to EN 196 was examined. In summary, calcined clay may qualify as main constituent in cement. Its pozzolanic activity depends on the chemical and mineralogical composition of the starting material as well as the conditions of thermal treatment.

Schneider M.,VDZ | Romer M.,Holcim | Tschudin M.,Holcim | Bolio H.,Cemex
Cement and Concrete Research | Year: 2011

Cement will remain the key material to satisfy global housing and modern infrastructure needs. As a consequence, the cement industry worldwide is facing growing challenges in conserving material and energy resources, as well as reducing its CO2 emissions. According to the International Energy Agency, the main levers for cement producers are the increase in energy efficiency and the use of alternative materials, be it as fuel or raw materials. Accordingly, the use of alternative fuels has already increased significantly in recent years, but potential for further increases still exists. In cement, the reduction of the clinker factor remains a key priority: tremendous progress has already been made. Nevertheless, appropriate materials are limited in their regional availability. New materials might be able to play a role as cement constituents in the future. It remains to be seen to what extent they could substitute Portland cement clinker to a significant degree. © 2011 Elsevier Ltd. All rights reserved.

Schneider M.,VDZ
Cement and Concrete Research | Year: 2015

Over the years technology in the cement industry has been further developed with a growing focus on sustainable, cost- and energy-efficient production. While significant steps may not seem visible on a year to year basis, the medium-term view shows notable progress. The trend of increasing the capacity of cement kilns has slowed down in recent years - maximum clinker output still lies between 12,000 and 13,000 tpd. Burning and cooling technologies have progressed, especially with respect to burners specifically designed for the co-incineration of high levels of alternative fuels. Taking into account all process-integrated measures, thermal process efficiency reaches values above 80% of the theoretical maximum. The grinding of raw materials and cement has been in the focus of better energy utilisation, but product quality is also of the highest importance. In terms of sustainable production, NOx abatement and CO2 capture and its reuse remain in the focus of extensive research. © 2015 Elsevier Ltd. All rights reserved.

Over the years technology in the cement industry has been continuously further developed. Substantial energy savings were achieved in recent years and also product-related emissions like i.e. C02 have been significantly reduced The trend of increasing the capacity of cement kilns has decelerated in the past years - the maximum clinker output still lies between 12.000 to 13.000 t/d. No breakthrough technologies are currently in sight with respect to clinker burning. Fourth generation clinker coolers are available from several suppliers and can be seen as state-of-the-art Cooler efficiencies of about 75% can usually be achieved Some developments have been made in burner technology especially with respect to burners specifically designed for the co-incineration of high levels of alternative fuels. Grinding of raw materials and cement has been in the focus of better energy utilization; while vertical roller mills (VRMs) are mostly used for raw material grinding, different types of grinding systems are used for finished grindings. VRMs are well established, however, and roller-presses in conjunction with ball mills are also widely used. In any case, at a global level finish grinding with ball mills is still the main grinding system used. Ball mills are known as reliable and easy to operate for cement grinding. However, their energy efficiency is still a challenge for cement producers. This has an effect on the different grinding constellations as well as on the on-going optimization efforts. Any finish grinding constellation has to be seen against the background of existing quality require ments as well as clinker reactivity and availability of other main cement constituents. The substitution of alternative fuels for natural fuels and raw materials is under on-going positive development. Alternative fuels significantly substitute fossil fuels in many countries around the world. The cement industry has developed techniques and strategies to utilize even more heterogeneous waste materials. While many challenges remain, the cement industry will certainly proceed to develop its technology in the time to come. In doing this, it relies on good cooperation with the variou equipment suppliers.

The standardized format to be used to communicate the quantified environmental information is Environmental Product Declaration (EPD). The EN 15804 standard prepared by CEN/TC 350 specifies rules for the preparation of EPDs. This format aims to ensure that product manufacturers provide verifiable, consistent data whose determination relies on comparable rules for all construction products. In response to a resolution adopted by its executive board, the German Cement Works Association (VDZ) has prepared an Environmental Product Declaration for an average German cement. The composition of this cement is equivalent to the mean composition of the cements produced in Germany in 2010. ISO 14025 specifies that Environmental Product Declarations must be managed within an environmental declaration program. By applying so-called product category rules, the program operator must ensure that the EPDs published in its program are transparent and comparable.

Eickschen E.,VDZ
American Concrete Institute, ACI Special Publication | Year: 2012

From some job sites it was reported that the air void content of the hardened concrete was higher than that of the fresh concrete. Investigations with commercial air-entrainers based on synthetic and natural active agents showed that a substantial increase in air content can occur only if the fresh concrete is supplied with air-entrainer that is insufficient activated. The air void content may increase if mixing energy is subsequently applied during placement or transport. The air void formation was studied as a function of the type and quantity of the admixture added and of the mixing time. Furthermore, the precipitation of admixtures in calcium hydroxide was investigated. A subsequent increase in air content is to be expected only with admixtures based on synthetic active agents due to their better solubility in the pore solution. The knowledge of the working mechanisms allows giving recommendations for practice to avoid an increase in the air content.

Herrmann J.,Verein Deutscher Zementwerke e. V. VDZ | Herrmann J.,Clausthal University of Technology | Rickert J.,VDZ
American Concrete Institute, ACI Special Publication | Year: 2012

The influence of slag or limestone as a cement main constituent on the performance of superplasticizers based on polycarboxylate ether (PCE) was investigated on cements made of identical clinker and sulfate components. Investigations were done by means of pore solution analyses, zeta potential measurements and consistence tests. Depending on the proportion of clinker in the cement the composition of the pore solution, the zeta potential of cement paste and the effective charge of PCE varied significantly. This led to a modified adsorption behavior and plasticizing effect of PCE. Consequently, the specific plasticizing effect of PCE can be diminished with decreasing proportion of clinker in cement.

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