Research Institute of the Cement Industry

Düsseldorf, Germany

Research Institute of the Cement Industry

Düsseldorf, Germany
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Junghanns M.T.A.,Research Institute of the Cement Industry | Muller C.,Research Institute of the Cement Industry
Cement International | Year: 2011

Efficient cements have always been produced in Germany from the regionally available raw materials to ensure reliable and cost-effective methods of construction with cement-based building materials. One of these methods of construction involves the production of cement-based floor screeds. The constantly rising demands for environmental protection mean that particular importance is now placed on the production and use of Portland composite cements (CEM II) and blastfurnace cements (CEM III). Laboratory investigations and practical experience confirm that Portland cement and cements with two or three main constituents that contain granulated blastfurnace slag, limestone or oil shale are basically suitable for producing cement-based floor screeds. The article provides an overview of the constructionally relevant properties of cement floor screeds made with CEM I, CEM II and CEM Ill/A cements. The evaluation is based on investigations that were carried out or commissioned by member companies of the VDZ (German Cement Works Association) from 1998 to 2008.


Eickschen E.,Research Institute of the Cement Industry
Cement International | Year: 2011

From some job sites of concrete pavement, 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 substances showed that a substantial increase in air content can occur only if the fresh concrete is supplied with air-entrainer that is inadequately activated. The air void content may increase if mixing energy is subsequently applied during placement or transport. However, it was not possible to make an accurate determination of the influence of the type of active substance on the extent of this increase, the reactivation potential. 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. The test results were combined in a model that explains the effects of mixing time, type and addition quantity of active substance on air void formation. A subsequent increase in air content is to be expected only with admixtures based on synthetic tensides 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.


Emberger B.,Research Institute of the Cement Industry | Hoenig V.,Research Institute of the Cement Industry
Cement International | Year: 2011

Since establishing rotary kiln firing systems for cement clinker production, a suitable and high-efficient heat transfer process from the rotary kiln flame to the kiln feed has to be achieved in clinker processing. Based on rotary kiln technology, burners were developed for the necessary heat transfer from the flame to the kiln feed. Today, plant operators are confronted with the need to substitute fossilbased fuels by co-firing alternative fuels in rotary kiln firing systems. A fast development in burner technology has been taking place concerning the firing of multiple fuels with different combustion characteristics simultaneously. Differing concepts of burner designs for such multi-fuel burners suit the requirements of the clinker burning process. Depending on the technical design, burner air consists of a single air stream or may be split into several air streams. The coal can be fed inside or outside of the flame-twist generating air stream into the flame. Coarse and lumpy fuels retrieved from industry, commerce or municipal residues are mixed thoroughly with combustion air by swirl air. The control of rotary kiln firing systems taking into account varying fuel properties and combustion characteristics is a challenging task. Burner suppliers therefore developed various designs for rotary kiln burners providing the operators with highly flexible firing systems for the simultaneous use of multiple fuels.


From some job sites of concrete pavement, 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 substances showed that a substantial increase in air content can occur only if the fresh concrete is supplied with air-entrainer that is inadequately activated. The air void content may increase if mixing energy is subsequently applied during placement or transport. However, it was not possible to make an accurate determination of the influence of the type of active substance on the extent of this increase, the reactivation potential. 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. The test results were combined in a model that explains the effects of mixing time, type and addition quantity of active substance on air void formation. A subsequent increase in air content is to be expected only with admixtures based on synthetic tensides 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.


Eickschen E.,Research Institute of the Cement Industry | Muller C.,Research Institute of the Cement Industry
Cement International | Year: 2013

There have been reports of problems that have arisen in practice during the production of air-entrained concrete when using plasticizers, especially those based on polycarboxylate ether (PCE). The total air content fluctuated and in individual cases the requirements for the air void parameters measured on the hardened concrete were not met in spite of the fact that the total air content of the fresh concrete complied with the requirements. The dependable adjustment of the micro air void structure, which prevents damage by freeze-thaw with or without de-icing salt is no longer possible. The extent to which interactions between air-entraining agent and plasticizer can affect the air void microstructure was investigated in a research project. The formation of air voids was tested in mortar and concrete with different combinations of admixtures and cements. The aim was to manufacture appropriate air-entrained concrete containing plasticizers by identifying "robust" admixture combinations that reduces the risk of unwanted air void formation. The interrelationships were incorporated in a model which makes it possible to give recommendations. The sequence of addition of air-entraining agent and plasticizer and the active agent of the air-entrainer have a decisive influence on the air void formation. Admixture combinations of air-entraining agent and plasticizer containing air-entraining agents based on natural active substances are considered more "robust" than variants with synthetic air entraining agents.


Pierkes R.,Research Institute of the Cement Industry | Rickert J.,Research Institute of the Cement Industry
Cement International | Year: 2013

Part 3 of the Alkali Guidelines "Preventive measures against harmful alkali reactions in concrete" issued by the German Committee for Structural Concrete provides for the testing of aggregates in mortars and concretes in which the grading curve of the particulate material to be tested has to be supplemented with an "inert" sand. So far there have been no systematic investigations into the suitability of the test sand to be used with respect to the influence of its natural alkali reactivity on the concrete tests. The influence of quartzitic sands on the test results was examined in a research project promoted by the AiF (Federation of Industrial Research Associations) with the aid of investigations carried out on test sands and the mortars and concretes produced from them using alkali-reactive and inert crushed aggregate. The aim was to discover the actual importance of any possible sources of error in the test methods currently used in order not only to assess the need for tests on the sand fraction but also to avoid false evaluations of aggregates or concrete compositions with respect to their harmful alkali-silica reactions. The results of the research project confirm that the influence of uncrushed quartzitic sand on a harmful alkali-silica reaction in concrete is comparatively slight. Separate testing of this constituent can be dispensed with if the coarse aggregate has been adequately characterized in accordance with the provisions of the Alkali Guidelines.


Eickschen E.,Research Institute of the Cement Industry | Muller Ch.,Research Institute of the Cement Industry
Cement International | Year: 2014

If, as a result of a short mixing time, excess air entraining agent is added during the production of air-entrained concrete in order to achieve the required air content then the fresh concrete will contain air-entraining agent that has not been activated. If there is a subsequent input of mixing energy the air content of the concrete can rise. The extent of this rise (the re-activation potential) is affected substantially by the active substance on which the air-entraining agent (AEA) is based. A sufficiently long mixing time always avoids any rise in air content. Accurate understanding of the way the air void formation depends on mixing time is therefore very important for dependable production of air-entrained concrete that meets the requirements. The functioning of an air-entraining agent can be characterized in laboratory trials during extended initial testing. However, the air void formation is also affected by the mixer type, quantity of mixture, filling level and mixing intensity. The extent to which laboratory results can be applied to practical construction conditions has not yet been clarified. The air void formation in fresh and hardened concrete in relation to the mixing time was therefore determined in the laboratory and in a readymixed concrete plant in a research project. Comparison of the test series shows that the re-activation potential under practical conditions can be determined in laboratory trials.


Pierkes R.,Research Institute of the Cement Industry | Schulze S.E.,Research Institute of the Cement Industry | Rickert J.,Research Institute of the Cement Industry
RILEM Bookseries | Year: 2015

Cements consisting of different types of Portland cement clinker and calcined clays were produced by mixing in laboratory scale. The clinkers differed regarding their contents of Al2O3 and alkalis as well as their phase composition. The used kaolinitic, illitic and chloritic clays show low ceramic qualities and represent typical clays of cement plant quarries. The produced cements contained 20 and 40 mass % of the calcined clays, respectively. On selective cements the influence of the sulphate dosage was investigated by measuring the compressive strength development according to EN 196-1 and characterising the hydration products by means of X-Ray Diffraction analyses (XRD) and thermal analysis (DSC). These investigations were planned using DOE (design of experiments). It could be shown that there is some potential for increasing the performance of the pozzolanic cement by a chemical-mineralogical adjustment of the calcined clay, the clinker and the sulphate agent. © RILEM 2015.


Borchers I.,Research Institute of the Cement Industry | Muller Ch.,Research Institute of the Cement Industry
Cement International | Year: 2014

Damage caused by an alkali-silica reaction (ASR) in concrete structures can be avoided by using concrete composition with a low alkali reactivity. The German Cement Works Association (VDZ) has developed criteria for ASR performance tests in order to make a practical evaluation of the alkali reactivity of concrete composition for elements of the WF (moist) and WA (moist + external supply of alkalis) moisture classes. Investigations were carried out to find the conditions under which the 60°C concrete test with and without external supply of alkalis reproduces the requirements concerning measures in the Alkali Guidelines for the WF and WA moisture classes.


Rickert J.,Research Institute of the Cement Industry
Cement International | Year: 2012

The influence of four PCE-based superplasticizers (synthesized selectively in the laboratory) on the shear resistance, especially at the saturation point, of cement pastes was investigated at the FIZ (Research Institute of the Cement Industry) using two commercially available cements. The intention was to clarify whether, and possibly from which parameters of the molecular structure of the PCE (polycarboxylate ether), it is possible to deduce a general mode of operation in conjunction with different cements. Rheological investigations of the shear resistance, especially at the saturation point, were compared with zeta potential measurements. The influence of two limestones and two granulated blastfurnace slags on the zeta potential and the shear resistance of laboratory cements produced with them, as well as on the adsorption of a commercially available PCE, was also examined. For the cements investigated the PCEs with high charge densities were relatively independent of the lengths of the side and main chains with respect to reaching the saturation point most effectively. The duration of the plasticizing action on the saturation point did not always correlate with the lengths of the side chains. The shear resistance fell with increasing quantity of active substance and the zeta potential was displaced in the direction of the isoelectric point (0 mV) due to the displacement of the shear plane caused by adsorption of the PCE. There was a correlation between the quantity of active substance adsorbed, the zeta potential and the shear resistance. The saturation point was determined both with the aid of Theological measurements of the shear resistance and by determining the zeta potential. The limestones and granulated blastfurnace slags investigated were able to adsorb sulfate ions from the pore solution, resulting in a negative zeta potential. Competitive adsorption between sulfate ions and plasticizer molecules is therefore also to be expected with these components. Increasing the proportion of granulated blastfurnace slag led to a significant drop in the shear resistance of the cement pastes and displacement of the zeta potential in the direction of the isoelectric point. The limestones used affected the shear resistance and the zeta potential of the cement paste to different extents and more significantly than the granulated blastfurnace slags investigated.

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