Frost‐Tausalz‐Widerstand von Mörtel: Einfluss der Expositionsbedingungen im jungen Alter

Since the early days of concrete construction, the deterioration of concrete due to the combined action of frost, water and de‐icing salts had been observed. This salt frost attack is typically associated with surface scaling. The underlying mechanism for that damage was unresolved for many decades and many conflicting damage theories exist. In the past, that knowledge gap was primarily of academic interest, as a good salt frost scaling resistance of clinker rich concretes was easily achieved with air entrainment. However, as that approach increasingly reaches its limit for “low‐carbon concretes”, an in‐depth knowledge of the damage mechanisms can help to identify alternative measures to ensure good salt frost scaling resistance of such concretes. Based on a novel theory, which can explain important characteristics of salt frost attack and the generation of scaling damage, an additional cause for the unfavourable influence of clinker reduction on salt frost resistance were identified.

“…Consequently, the salt frost scaling resistance for simple systems can be predicted to some extent, as was recently shown Haynack et al [35] for OPC-based mortars without air entrainment.…”

Section: Capillary Porosity Vs Salt Frost Scaling Resistance With Por...mentioning

confidence: 64%

The peculiar behaviour of low‐carbon concretes under salt frost exposure

Müller,

Ludwig,

Ehrhardt

et al. 2023

“…According to Thiel et al [34] frost suction mainly causes water transport from the test surface into deeper layers of the concrete while in the surface region, only a small increase in saturation is possible before the damage starts. Haynack et al [35] showed by 1H-NMR measurements that the amount of scaling during the CDF test (with deicing salts) depends on the preconditioning of the specimens. According to [35], two different factors have to be considered: the saturation degree at the beginning of the freeze-thaw exposure and the hydration degree depending on the preconditioning.…”

Section: Introductionmentioning

confidence: 99%

“…Haynack et al [35] showed by 1H-NMR measurements that the amount of scaling during the CDF test (with deicing salts) depends on the preconditioning of the specimens. According to [35], two different factors have to be considered: the saturation degree at the beginning of the freeze-thaw exposure and the hydration degree depending on the preconditioning.…”

Section: Introductionmentioning

confidence: 99%

Spatially resolved analysis of the progression of freeze‐thaw damage in concrete

Kind,

Werneck,

Müller

et al. 2023

To assess the durability of concrete structures, it is necessary to understand not only how deterioration evolves over time but also how the damage progresses through the structure. To determine the evolution of the freeze‐thaw damage, different damage criteria were examined in a spatially resolved manner during the CIF test. By measuring the ultrasound pulse velocity (UPV) in different axes, depth‐dependent changes of the relative dynamic modulus of elasticity (RDME) were investigated. The RDME started to decrease in regions close to the surface, whereas the RDME in regions farther from the test surface decreased with higher speed. Changes in the water content during the CIF test were examined by nuclear magnetic resonance (NMR). The freeze‐thaw exposed specimens showed an increase in their water content that is assumed due to the micro‐ice‐lens pump as well as microstructural changes. These changes progressed from the surface into deeper layers of the specimens, following an increase of saturation also progressing into the concrete. To consider the frost damage evolution in service life design, the authors propose the use of depth‐dependent threshold values for freeze‐thaw exposed concrete structures.

Analyse des Frost‐Tausalz‐Widerstands zementgebundener Baustoffe mittels 3D‐Laserscanning

Haynack,

Timothy,

Kränkel

et al. 2023

Self Cite

KurzfassungEine Herausforderung performancebasierter Prüfverfahren zur Bewertung der Dauerhaftigkeit ist die Beschleunigung natürlicher Mechanismen. Dies ist notwendig, um innerhalb kurzer Zeit die Langzeit‐Leistungsfähigkeit ermitteln zu können. Die Bestimmung der Frost‐Tausalzbeständigkeit von Beton kann durch den CDF‐Test erfolgen, welcher für Betone mit ausreichendem Frost‐Tausalz‐Widerstand sehr gut funktioniert. Bei Proben mit einer unzureichenden bzw. unbekannten Performance können erhöhte Randabwitterungen auftreten, welche durch das Ablösen des seitlichen Abdichtbands entstehen. Der zunehmende Randeinfluss führt so zu einer Verfälschung der Ergebnisse und zu einer Unterschätzung der tatsächlichen Performance des Bauteils. In diesem Beitrag werden Mörtel‐ und Betonprobekörper mit unterschiedlichen Abwitterungsraten in Anlehnung an das CDF‐Verfahren untersucht. Zusätzlich wird die Oberflächenschädigung der Proben anhand einer neuartigen Messmethode mittels hochauflösendem 3D‐Laserscanning ausgewertet. Die Ergebnisse zeigen, dass die Randeffekte mit der Laserscan‐Methode umgangen und vergleichbare Ergebnisse zu den CDF‐Untersuchungen erzielt werden können. Somit können Betone ohne Randeinflüsse charakterisiert und eine präzise Prognose der Langzeitbeständigkeit getroffen werden.