Empirical approach for the residual flexural tensile strength of steel fiber-reinforced concrete based on notched three-point bending tests

When designing steel fiber-reinforced concrete, for example, according to Model Code 2010, the residual flexural strength values must be specified as fundamental properties. It is often difficult to establish the relationship between residual flexural strength values and the required dosage of steel fibers depending on the type of steel fibers and the concrete quality. For an estimation of the presumably necessary dosage of steel fibers, various empirical approaches exist for the approximate determination of the residual flexural strength values, which, however, are based on different tests and have been almost exclusively been derived on the basis of few or “own” test results of the respective institute. For this reason, the validity of the respective approximation approach is often limited. Using the bending beam database “Steel Fibre Reinforced Concrete”, selected approaches were systematically analyzed and an improved approach for determining the residual flexural strength values of steel fiber-reinforced concrete was developed

Zur Rheologie und den physikalischen Wechselwirkungen bei Zementsuspensionen

Die Eigenschaften frischer Betone werden maßgeblich durch die rheologischen Eigenschaften der darin enthaltenen Zementsuspensionen beeinflusst. Das Ziel der vorliegenden Arbeit bestand in der Untersuchung des Verformungsverhaltens frischer Zementsuspensionen unter Berücksichtigung der physikalischen Wechselwirkungen zwischen den einzelnen Zementpartikeln. Besonderes Augenmerk galt dabei dem elastischen Verformungsverhalten dieser Suspensionen

Zur Rheologie und den physikalischen Wechselwirkungen bei Zementsuspensionen

Gegenstand dieses Buches ist die Untersuchung des Fließverhaltens von Zementsuspensionen. Hierbei wird insbesondere auf die dem Fließverhalten zugrundeliegenden Mechanismen der Partikelwechselwirkung eingegangen. Auf dieser Grundlage wird ein Materialmodell vorgestellt, dass es gestattet, das rheologische Verhalten von Zementleimen unter Kenntnis ausgewählter Zementparameter vorherzusagen

On Ecclesiology, “The Holy Spirit and the Upbuilding of the Christian Community,” Karl Barth in Dialogue with the Thought of Joseph Ratzinger

ABSTRACT On Ecclesiology in “The Holy Spirit and the Upbuilding of the Christian Community” Karl Barth in Dialogue with the Thought of Joseph Ratzinger Michael Haist Jr. This thesis is a dialogue between Karl Barth and Joseph Ratzinger on the topic of ecclesiology. The thesis follows the format of section 67 of Barth's Church Dogmatics, which deals with principles of ecclesiology in the context of the Doctrine of Reconciliation. The question this thesis addresses is whether there is any continuity between the thought of the two figures on certain topics of ecclesiology that are covered by this section of CD. There are several issues on which they agree. On the final topic, Church law, Barth suggests that laws held by different communities can be true despite being potentially contradictory. This paper posits that Ratzinger is in agreement with Barth on this last point

Baustoffe und Betonbau : Lehren, Forschen, Prüfen, Anwenden - Festschrift zum 60. Geburtstag von Prof. Dr.-Ing. Harald S. Müller

Die vorliegende Festschrift "Baustoffe und Betonbau - Lehren, Forschen, Prüfen, Anwenden" ist Herrn Prof. Dr.-Ing. Harald S. Müller zum 60. Geburtstag gewidmet. Sie würdigt die Tätigkeit von Herrn Prof. Müller als Hochschullehrer und Forscher, seinen unermüdlichen Einsatz für die Materialprüfung und Normung von Baustoffen sowie sein umfangreiches und langjähriges Engagement in vielen für die Betonbauweise relevanten Gremien und Vereinigungen

Entwicklungskonzepte für robuste Ökobetone

Beton ist der weltweit meist verwendete Baustoff und eines der meist produzierten Güter überhaupt. Seine Produktion in solch großen Mengen erfolgt jedoch unter erheblichen Eingriffen in die natürliche Umwelt, die sowohl signifikante Beiträge zu den anthropogenen CO2-Emissionen wie auch regionale Verknappungen der mineralischen Betonausgangsstoffe beinhalten. Ökobetone müssen sowohl eine verbesserte CO2-Bilanz aufweisen wie auch gegenüber Schwankungen in der Qualität ihrer Ausgangsstoffe robust sein, das heißt die für sie bestimmten Frisch- und Festbetoneigenschaften mit hoher Sicherheiz erzielen. Die granulometrischen Eigenschaften der Ausgangsstoffe und die Zusammensetzung der Gesteinskörnungen spielen hierfür eine zentrale Rolle. Dieser Beitrag erläutert Ansätze zur Entwicklung rheologisch robuster Ökobetone.Concrete is the most used construction material and one of the most produced goods of all. Its production in such large quantities causes great environmental impacts, including significant contributions to anthropogenic CO2-emissions and a decrease in the regional availability of high quality constituent materials. Green concretes must demonstrate an improved CO2-balance over their lifecycle and yet also be robust against variations in the quality of their constituent materials, meaning the desired properties of the concretes must be achieved with a high level of certainty. The granulometric properties of the aggregates are central to this challenge. This paper explains development procedures for rheologically robust concrete mixtures

ConsInstancy: learning instance representations for semi-supervised panoptic segmentation of concrete aggregate particles

We present a semi-supervised method for panoptic segmentation based on ConsInstancy regularisation, a novel strategy for semi-supervised learning. It leverages completely unlabelled data by enforcing consistency between predicted instance representations and semantic segmentations during training in order to improve the segmentation performance. To this end, we also propose new types of instance representations that can be predicted by one simple forward path through a fully convolutional network (FCN), delivering a convenient and simple-to-train framework for panoptic segmentation. More specifically, we propose the prediction of a three-dimensional instance orientation map as intermediate representation and two complementary distance transform maps as final representation, providing unique instance representations for a panoptic segmentation. We test our method on two challenging data sets of both, hardened and fresh concrete, the latter being proposed by the authors in this paper demonstrating the effectiveness of our approach, outperforming the results achieved by state-of-the-art methods for semi-supervised segmentation. In particular, we are able to show that by leveraging completely unlabelled data in our semi-supervised approach the achieved overall accuracy (OA) is increased by up to 5% compared to an entirely supervised training using only labelled data. Furthermore, we exceed the OA achieved by state-of-the-art semi-supervised methods by up to 1.5%

Fatigue-Induced Damage in High-Strength Concrete Microstructure

A high-strength concrete subjected to compressive fatigue loading with two maximum stress levels was investigated and the behaviour was evaluated using the macroscopic damage indicators, strain and acoustic emission hits (AE-hits), combined with microstructural analyses utilising light microscopy and scanning electron microscopy (SEM). A clustering technique using Gaussian mixture modelling combined with a posterior probability of 0.80 was firstly applied to the AE-hits caused by compressive fatigue loading, leading to two clusters depending on the maximum stress level. Only a few cracks were visible in the microstructure using light microscopy and SEM, even in phase III of the strain development, which is shortly before failure. However, bluish impregnated areas in the mortar matrix of higher porosity or defects, changing due to the fatigue loading, were analysed. Indications were found that the fatigue damage process is continuously ongoing on a micro- or sub-microscale throughout the mortar matrix, which is difficult to observe on a mesoscale by imaging. Furthermore, the results indicate that two different damage mechanisms take place, which are pronounced depending on the maximum stress level. This might be due to diffuse and widespread compressive damage and localised tensile damage, as the findings documented in the literature suggest

Prüfverfahren zur Bewertung der Mischungsstabilität von Beton unter Rütteleinwirkung

Die Mischungsstabilität von Beton stellt eine wichtige Frischbetoneigenschaft dar, um insbesondere unter herausfordernden Betonierbedingungen eine zielsichere Herstellung von Betonbauteilen sicher-zustellen. Jedoch existiert aktuell kein geeignetes Prüfverfahren, um die Mischungsstabilität im Rahmen des Bauprozesses quantitativ zu erfassen und zu bewerten. Der vorliegende Beitrag zeigt, dass der aus dem Bereich der Selbstverdichtenden Betonen bekannte „Auswaschversuch“ so modifiziert werden kann, dass er auch für übliche Rüttelbetone geeignet ist. Entscheidend hierfür ist die Berücksichtigung und genaue Definition der eingebrachten Rüttel-einwirkung, um eine Reproduzierbarkeit und Vergleichbarkeit der Prüfergebnisse sicher zu stellen. Erste Vergleichsuntersuchungen zeigen, dass mit Hilfe der Prüfergebnisse bei vergleichbarer Rütteleinwirkung auch eine Prognose der Sedimentation im Bauteil möglich ist.The stability of concrete represents an important feature of fresh concrete in order to ensure a targeted production of concrete components, especially under challenging processing conditions. However, there exists currently no suitable test method to test and evaluate the mixing stability of fresh concrete during the construction process. The present article shows that the "washout-test", known from the field of self-compacting concrete, can be transferred to conventional concrete. Decisive for this is the consideration and exact quantification of the vibrations introduced during the test and ensuring a reproducibility and comparability of the test results. Initial comparative investigations between construction components and results of the test method show that with comparable vibration a forecast from test results to sedimentation in the component is also possible