ce/papers最新文献

Schüttungen aus groben Porenbeton-Granulaten lassen sich durch eine mineralische Schaummörtelmatrix zusammenfügen und bilden so den „Schaumstein aus groben Porenbetongranulaten“, dessen Eigenschaften dem Primärprodukt Porenbeton stark ähneln. Porenbetonbruch kann so vor der Deponierung verschont bleiben und bietet stattdessen die Möglichkeit zur Herstellung eines ressourceneffizienten, klimaschützenden Recyclingbaustoffes mit beachtlichem Wertschöpfungspotenzial. Im Zuge der Weiterentwicklung des Schaumsteines ist es gelungen den Nachweis dafür zu führen, dass das Recycling-Produkt „Schaumstein” mit derselben verfahrenstechnischen Vorgehensweise abermals recycelt werden kann zum „RC-Schaumstein“ wobei dessen Baustoffeigenschaften auf selbem Niveau bleiben.

In zahlreichen Forschungsvorhaben gibt es aktuell Bestrebungen die bisherigen Bauweisen ökologischer zu gestalten. Da Beton der meistverwendete Baustoff in unserer gebauten Umwelt ist, gilt ihm und seinen Bestandteilen besonderer Beachtung. So ist der Einfluss von RC-Gesteinskörnungen in hochfesten Betonen noch nicht ausreichend erforscht und der Einsatz in Spannbeton bisher nicht zulässig. Aus diesem Grund wird der Einfluss von RC-Gesteinskörnung auf das Kriechverhalten unter Druckbelastung sowie das Schwinden untersucht. Der Beitrag zeigt erste Ergebnisse des Einflusses von drei unterschiedlichen RC-Gesteinskörnungen im Vergleich untereinander und zur Referenzmischung mit Zuschlag aus Basalt. Neben der Auswirkung auf die Druckfestigkeit wird auch der Einfluss auf das Schwinden und das Druckkriechen dargestellt. Es zeigt sich, dass sich das Druckkriechen von Betonbruch und Bauschutt ähnlich zum Referenzbeton mit Zuschlag aus Basalt verhält. Der Zuschlag aus Ziegelsplitt hingegen zeigt ein erhöhtes Kriechverhalten.

In a recent research project under the lead of the Fraunhofer Institute for Building Physics IBP, gravel and sand within a mixture of paving stones were replaced with LD converter slag and blast furnace slag for 50 wt. % and 100 wt. % to produce resource-efficient concrete components. For this purpose, first, the dry processing of the slags including metal separation and crushing was carried out. In the next step, the particle size distributions of slags using sieve analysis were determined. Finally, the mix designs were set based on the optimum combination of different size fractions of slags. This combination was determined in a way to lead to an almost identical grading curve as that of the original formulation. Splitting tensile strengths of the obtained samples were measured after 14 days of curing under a humidity of 95%. Several paving stone specimens containing slags showed higher splitting tensile strengths than that of the reference sample. Similar results were observed for industrially produced paving stones which demonstrates the successful transfer of the laboratory mixes to the industrial plant.

A highly interesting approach to lower CO₂ emissions in cement and concrete industry is to reduce the cement clinker content while using supplementary cementitious materials (SCMs) such as calcined clays. Whereas for classical Portland cement clinker, comprehensive studies are already available on the microstructural development during hydration as well as on the resulting macromechanical properties such as compressive strength or long-term deformation behavior, such understanding is missing for calcined clays. In this paper, systematic micromechanical investigations using microindentation of hardened cement pastes with various amounts of calcined clay at ages up to 28 days are presented. The micromechanical results indicate a faster strength development as well as a lower overall porosity of the classical clinker system compared to mixtures containing calcined clay. Looking to creep, the indentation creep modulus is higher for pure OPC mixtures compared to calcined clay systems up to seven days, indicating less pronounced creep. Beyond this age, however, the differences in creep behaviour became less pronounced. The outcomes suggest that the reactivity of the calcined clay seems to be decisive when it comes to mechanical properties and creep behaviour rather than the rate of substitution.

The use of supplementary cementitious materials is currently the most favorable strategy for reducing CO₂ emissions in cements. Limestone Calcined Clay Cements, LC³, are a type of cement that allows the reduction of CO₂ emissions up to 40%. The proportions of the mixtures can vary, but the most investigated combination, LC³-50, contains about 50 wt% clinker, 30 wt% calcined kaolinitic clay, 15 wt% limestone and an optimised calcium sulphate content. However, the mechanical strengths of LC³ at early ages are not good enough and they should be improved. One way of doing this is by employing commercial strength-enhancing (accelerator) admixtures based on C-S-H nucleation seeding. For this work, LC³-50 cements were prepared with clays with varying kaolinite contents. Mortars and pastes were fabricated using a new PCE-based superplasticizer developed to avoid the loss of fluidity at early ages typical of LC³ binders. The selected accelerator for this study was Master X-Seed STE53. The results show that the loss of fluidity of LC³ mortars during the first hours could be solved by a recently developed PCE-based superplasticizer. The compressive strengths at 1 day for LC³ mortars strikingly improved by using the C-S-H seeding admixture and this behavior was maintained for up to 28 days.

An industrial by-product of the steel industry called basic oxygen furnace (BOF) slag has recently undergone extensive research for high-end applications outside of road load and landfill. In contrast to the Bogue methodology used with regular Portland cement, BOF slag lacks a quick and straightforward quantitative phase analysis procedure that would allow it to be employed as a high-end raw material. The main phases of BOF slag (C₂S, C₂(A,F), Ff, RO-Phase, and f-C) can be calculated using the method presented in this paper based on chemical composition.