No abstract

This study reports the development of a fiber-reinforced alkali-activated binder (FRAAB) with an emphasis on the performance and the durability of the fibers in the alkaline alkali-activated binder (AAB)-matrix. For the development of the matrix, the reactive components granulated slag and coal fly ash were used, which were alkali-activated with a mixture of sodium hydroxide (2-10 mol/L) and an aqueous sodium silicate solution (SiO2/Na2O molar ratio: 2.1) at ambient temperature. For the reinforcement of the matrix integral fibers of alkali-resistant glass (AR-glass), E-glass, basalt, and carbon with a fiber volume content of 0.5% were used. By the integration of these short fibers, the three-point bending tensile strength of the AAB increased strikingly from 4.6 MPa (no fibers) up to 5.7 MPa (carbon) after one day. As a result of the investigations of the alkali resistance, the ARglass and the carbon fibers showed the highest durability of all fibers in the FRAAB-matrix. In contrast to that, the weight loss of E-glass and basalt fibers was significant under the alkaline condition. According to these results, only the AR-glass and the carbon fibers reveal sufficient durability in the alkaline AAB-matrix.

This paper reports the development of an Alkali Activated Binder (AAB) with an emphasis on the performance and the durability of the AAB-matrix. For the development of the matrix, the reactive components granulated slag and coal fly ash were used, which were alkali activated with a mixture of sodium hydroxide (2-10 mol/l) and aqueous sodium silicate solution (SiO 2 /Na 2 O molar ratio: 2.1) at ambient temperature. A sodium hydroxide concentration of 5.5 mol/l revealed the best compromise between setting time and mechanical strengths of the AAB. With this sodium hydroxide concentration, the compressive and the 3-point bending tensile strengths of the hardened AAB were 53.4 and 5.5 MPa respectively after 14 days. As a result of the investigation of the acid resistance, the AAB-matrix showed a very high acid resistance in comparison to ordinary Portland cement concrete. In addition, the AAB had a high frost resistance, which had been validated by the capillary suction, internal damage and freeze thaw test with a relative dynamic E-Modulus of 93% and a total amount of scaled material of 30 g/m² after 28 freeze-thaw cycles (exposure class: XF3).

Die robotergestützte Betonextrusion ist ein neuartiges additives Fertigungsverfahren, bei dem Strategie, Werkstoff und Förderanlage gezielt aufeinander abgestimmt sein müssen. Insbesondere die reale Form des extrudierten Materialstrangs unterliegt entlang des Startpunkts über Hauptextrusionsphase bis zum Ausschaltvorgang durch lokale Über‐ und Unterextrusionen signifikanten Schwankungen, die den Qualitätsvorgaben meist nicht genügen. In dieser Arbeit wird ein Kalibrierverfahren für Extrusionsprozesse entwickelt, softwareseitig angepasst und erprobt sowie Auswirkungen der Vorschubgeschwindigkeit auf die Bauteilqualität untersucht. Hierzu wurden unterschiedliche Kalibrierverfahren aktueller additiver Fertigungsprozesse betrachtet und hinsichtlich ihrer Verwendbarkeit für die Extrusion von mineralischen Suspensionen ausgewertet. Darauf aufbauend erfolgte die theoretische Erarbeitung einer allgemeingültigen Vorgehensweise zur Kalibrierung und deren praktische Umsetzung. In den durchgeführten Funktionstests verringerte das Kalibrierverfahren die Prozessvorbereitung, erhöhte die Prozesssicherheit durch die stabilisierte Extrusion und verkürzte die Taktzeit. Diese Steigerung der Produktivität in der additiven Fertigung führt einmal zu positiven wirtschaftlichen Effekten und des Weiteren werden Anwendungen von hochfesten Leichtbaustrukturen im Bauwesen attraktiver. Zudem ermöglicht es die serienmäßige Umsetzung von freigeformten Modulbauweisen.

In the course of revitalizing the Poseidon Building in Frankfurt, an energetically optimized façade, made of an architectural concrete was developed. The development of a fiber-reinforced architectural concrete had to consider the necessary mechanical strength, design technology and surface quality. The fiber-reinforced architectural concrete has a compressive strength of 104.1 MPa and a 3-point bending tensile strength of 19.5 MPa. Beyond that, it was ensured that the fiber-reinforced high-performance concrete had a high durability, which has been shown by the capillary suction of de-icing solution and freeze thaw test with a weathering of abrasion of 113 g/m² after 28 freeze-thaw cycles and a mean water penetration depth of 11 mm.