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The use of recycled crushed sands contributes to closing the material cycles in the building materials industries that process non-metallic minerals. The potential that arises from the processing of mineral demolition waste for the production of resource-conserving concretes was investigated in the "R-Beton" joint research project. Investigations by VDZ gGmbH showed that the production and use of clinker-efficient cements that contain finely ground crushed sand as a main cement constituent can represent an alternative recycling route. Crushed sand from railway sleepers, railway ballast, crushed concrete, bricks, tiles and masonry was used in the project. In Germany, the recycling of crushed sand in this way involves proof of usability in accordance with building regulations law. In addition to the environmental compatibility of the crushed sands and the technical performance of the cements containing crushed sand as specified in DIN EN 197-1 it is also necessary to comply with the approval-relevant durability for the concretes to be produced with these cements (so-called R-cements) and fulfil building inspectorate requirements. The investigations in the project have shown, for example, that concretes made with R-cements containing 10 or 30 mass % crushed masonry with a high clay brick content can pass all the durability tests safely, in contrast to cements made with crushed sand of different origin. When the results obtained in the project are considered as a whole it can be stated that R-cements made with up to 30 mass % crushed sand could, at least, be used for internal component concretes but external components in building construction also appear to be possible. The investigations carried out on crushed sands with respect to their effects on soil and water have shown that the environmental analysis requirements for solids and eluates as specified in DIN 4226-101 can be fulfilled. [ABSTRACT FROM AUTHOR]

With reference to the General Circular on Road Construction No. 04/2013 on alkali reactivity, many traffic areas in the municipal sector are assigned to moisture class WS on account of being allocated to load classes Bk1.8 to Bk100. The suitability of aggregates or concrete mixes for moisture class WS can be verified by subjecting the concrete to WS aggregate testing or an ASR performance test. A lack of appropriate verification in many regions means that ready-mixed concrete can often not be supplied. The WS classification was selected for motorways (high dynamic loads and external alkali supply). On account of the lower speeds involved, the dynamic traffic load is however not as high in municipal areas. An additional aspect is that de-icing agents are often not used in urban areas, so that there is less likelihood of alkali supply and a lower risk of deleterious ASR here than in the case of motorways. Moisture class WA or a comparable classification may therefore be sufficient. Drill cores from the municipal road construction sector and laboratory concretes were therefore tested with the methods developed for moisture classes WS and WA in a research project. The test results were taken as a basis for drawing up criteria for alkali reactivity assessment and for the practical assignment of concrete moisture classes in the municipal road construction sector, [ABSTRACT FROM AUTHOR]

There is as yet no recommendation for an extended initial test with the combined use of air-entraining agent and superplasticizer. Practical testing in advance based on realistic construction conditions could provide an early indication of adverse developments. A research project therefore examined whether the connections between mixing time, active agent and the amount of air-entraining agent added and the potential for later activation found for air-entrained concretes without superplasticizer (stiff consistency) apply to air-entrained concretes with superplasticizer as well. Amongst other things, this involved investigating the influence of the sequence in which the air-entraining agent and superplasticizer are added. The studies yielded fundamental findings relating to the operating mechanisms of air entrainment with the combined use of air-entraining agents and superplasticizers for production in the laboratory and in practice, as well as during transport. The tests revealed that commonly employed procedures for air-entrained concrete without superplasticizer can also be used for air-entrained concretes with superplasticizer and that they can be applied to practical conditions. [ABSTRACT FROM AUTHOR]

In Qatar it is permissible to use granulated blastfurnace slag meal, fly ash and microsilica as additions in concrete beside Portland cement. Granulated blastfurnace slag meal accounts for the largest proportion of concrete additions used in Qatar. However, it is not always available in the required quantity because, like the other concrete constituents (with the exception of Portland cement and water), it has to be imported. The aim of these investigations was to check the fundamental suitability of a locally available fly ash in concrete under realistic conditions when compared with a granulated blastfurnace slag that is also regionally available. Test mix formulations were designed on the basis of selected reference concretes and of the QCS 2010 series of standards valid in Qatar, the analyses of the constituent materials and the requirements for the fresh and hardened concrete properties. All the mix formulations were produced and tested in Qatar by a concrete test laboratory. It was found that the use of the available fly ash at lower water/ binder ratios and slightly lower superplasticizer contents led to workability properties that were comparable with the properties of the reference concretes. This confirmed that, regardless of the temperature, fly ash can have a positive effect on the workability properties. As expected, the early strengths of concretes containing fly ash are lower. This is also normally associated with lower evolution of heat. The results of the durability investigations that were carried out showed that concretes containing fly ash can be placed in the same respective durability classes defined in QCS 2010 as the reference concretes containing granulated blastfurnace slag meal. [ABSTRACT FROM AUTHOR]

Associated with the trend towards softer concretes it is now often found that significant changes in the fresh concrete properties occur unexpectedly and unpredictably in longterm construction projects in spite of using the same concrete composition. In a joint research project between the Research Institute of the Cement Industry and the Chair of Building Materials Technology in the Institute for Structural Civil Engineering at Ruhr-University Bochum criteria were worked out for designing concrete mix formulations. The intention is that these criteria should be fulfilled to prevent the occurrence of undesirable fresh concrete behaviour and so that the inadvertent influence on the fresh concrete properties caused by material- and production-induced fluctuations in the concrete constituents is as small as possible. [ABSTRACT FROM AUTHOR]

The initial position for the research project was the increase in general technical approvals for cements that according to DIN 1045-2 are not approved in principle in Germany for all exposure classes. Various durability tests that are described in, for example [1], have to be carried out as part of the approval procedure. However, the corresponding test procedures are time-consuming and cost intensive. In a joint research project VDZ gGmbH and Clausthal Technical University have therefore identified some characteristic values based on degree of hydration that allow conclusions to be drawn about durability criteria. This could support and possibly accelerate the procedure for assessing cements that require general technical approval. Before the actual durability testing, which is not to be replaced but only amplified by the results of this research project, it is possible to test whether a cement is suitable to pass such a test. The concrete mix formulations are precisely defined in the approval test plans so the characteristic values developed in this research project are not aimed at concretes with arbitrary compositions but at cements with arbitrary compositions in defined concrete mix formulations. It has been possible to show that in most cases the concrete or mortar compressive strengths of the cements investigated in this research project provided only weak guide values or none at all for the results of the durability investigations. On the basis of the degree of hydration of the hardened cement paste and the porosity of standard mortars it was possible to identify characteristic values that seem suitable for carrying out an assessment with respect to the particular acceptance criteria of the durability tests. No tests on hardened concrete are needed for determining the characteristic values. The durability of concretes with compositions that conform to the approval test plans can be estimated with the aid of the properties of the hardened cement paste and mortar. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]