Natural Stone Waste Powders Applied to SCC Mix Design

In order to comply with current trends concerning sustainability, saving of primary materials and energy\ud savings, this paper addresses Eco-concrete. The major focus thereby is on the increased efficiency of cement\ud use. Applying a new mix design method for concrete, cement contents can be decreased and partially be substituted\ud by other fine powders, preferentially by waste powders which have no mass application so far. This\ud paper is giving examples of successfully introduced waste powders and characterizes the concretes produced\ud with these powders. These innovative, low cement concrete types obtain medium strength and exhibit furthermore\ud self-compacting abilities. This paper additionally highlights possibilities for the direct use of natural\ud stone sludges or filter cakes. A new grading based design method, developed in the authors’ research\ud group, enables the efficient use of all materials available. The method is applicable to self-compacting concretes,\ud earth-moist concretes and conventionally vibrated concretes

Self-cleaning surfaces as an innovative potential for sustainable concrete

Concrete technology is subject of continuous development and improvement. One of the very recent contributions to durability and sustainability of concrete is the self-cleaning ability. This effect is achieved by applying photocatalytic materials to the concrete mix. This paper describes the effect of self-cleaning and air purification. Since about 10 years concrete paving stones, provided with this function, are available. With the development of a test setup and using nitric oxide (NO) as model pollutant an approach was found to quantitatively assess the air-purifying ability of those paving stones. This seems to be of interest since a real comparative analysis of air purifying concrete products is not available and the establishment of a measurement standard for concrete products is still in a draft-state. A brief technical description of this test setup will be presented to the reader. Using this innovative setup, the influences on the degradation efficiency are studied and a basic reaction model is derived

Durability of ultra-high performance concrete – Experiences from a real-scale application

Ultra-High Strength Concrete or better Ultra-High Performance Concrete (UHPC) is finding increasingly more applications in real construction projects. However, mostly the focus is on the outstanding mechanical properties of this special concrete. But strength is just one side of this multifunctional material. Apart from that, it also comes along with distinguished durability properties which make it attractive to be used in construction projects despite a very high cost price. This paper refers to a real-scale application of UHPC used for the production of two bridge decks. The UHPC was produced in a ready-mixed concrete plant and delivered by concrete mixing trucks to a pre-cast plant. During the production, samples were made and later analysed regarding theirmechanical properties and durability performance. This research is focusing on the latter and shows by means of porosity measurements, freeze-thaw resistance tests, carbonation tests and chloride diffusion and migration tests, that UHPC is a very dense and durable material that will allow for much longer service life periods and low maintenance and repair costs compared to structures made from conventional concrete

Water-powder mixtures at the onset of flowing

The knowledge of water demands of the manifold concrete ingredients is of vital interest for the design of concrete mixes. Physical properties like workability or strength and durability in hardened state are controlled by the total water content. Water demand is defined as the volumetric ratio of water to solid material at a certain state, which is defined by the selected test method. Given that powders provide the b far highest percentage of specific surface area in a concrete mixture, their water demand is of special interest. In literature diverse methods for the determination of powders’ water demands can be found. However, it appears that the spread-flow test, sometimes referred to as mini-slump flow test, has achieved general acceptance in concrete technology. In this research the spread-flow test has been analyzed in more detail. In this way new measures are derived which contribute to a deeper understanding of wet granular mixtures at the onset of flowing. The deformation coefficient which will be derived by the spread-flow test was confirmed to correlate with the product of Blaine surface and intrinsic density of the individual powders when the mixture is flowing only under its own weight. Similarly, correlations with equal accuracy have been found with a computed specific surface based on measured particle size distributions instead of the Blaine surface. Using flow experiments it was possible to derive an overall factor for assessing the non-spherical shape of the powder particles. A good correlation of this computation algorithm was derived compared to the standard Blaine method. Finally, a constant water layer thickness around the powder particles was derived for all powders at the onset of flowing. This implies the possibility to predict flow behavior of mortar and concrete mixtures only based on the knowledge of their granular characteristics

Structural ultra-lightweight concrete – from laboratory research to field trials

This article presents the laboratory development and subsequent field trials of a novel structural ultra-lightweight concrete. The concrete is developed aiming at the application in monolithic buildings (i.e. no insulation layer required), which would facilitate the construction and recycling processes, as well as provide new opportunities to architects and structural engineers. The development of the ultra-lightweight concrete presented in this study includes the optimization of its composition (ultra-lightweight aggregates, binders, admixtures) and is targeted on the concrete properties such as the compressive strength, density and thermal conductivity. In order to reduce the risk of an excessive overheating of concrete during its early hydration process caused by its self-insulating properties, the binder composition and amount was further investigated and optimized. Finally, a material of an ultra-low density (< 800 kg/m3), ultra-low thermal conductivity (as low as 0.14 W/(m·K)) and a compressive strength of 10 MPa was developed. Subsequently, several batches of 2 m3 of concrete were produced in a ready-mix concrete plant and a L-shaped test-wall was cast. The temperature development as well as hardened concrete properties were monitored. The field tests show that, although there still are some issues to overcome (e.g. workability), the developed material has a very good potential to enter the concrete market and find new applications

Cavity-enhanced optical detection of carbon nanotube Brownian motion

Optical cavities with small mode volume are well-suited to detect the vibration of sub-wavelength sized objects. Here we employ a fiber-based, high-finesse optical microcavity to detect the Brownian motion of a freely suspended carbon nanotube at room temperature under vacuum. The optical detection resolves deflections of the oscillating tube down to 50pm/Hz^1/2. A full vibrational spectrum of the carbon nanotube is obtained and confirmed by characterization of the same device in a scanning electron microscope. Our work successfully extends the principles of high-sensitivity optomechanical detection to molecular scale nanomechanical systems.Comment: 14 pages, 11 figure

Photocatalysis applied to concrete products - part 2 : influencing factors and product performance

The second part of this three-part article series addresses the influence of physicochemical parameters on the degradation performance of concrete products containing photocatalytic active TiO2. The influence of process conditions like irradiance, relative humidity, pollutant concentration and flow rate on the degradation mechanism is investigated. Furthermore, a short overview on photo catalytic powders (especially TiO2) and their influence on the degradation of NO are presented. In addition the application of TiO2 coatings and their microstructural analysis is explained

Photocatalysis applied to concrete products - part 2 : influencing factors and product performance

The second part of this three-part article series addresses the influence of physicochemical parameters on the degradation performance of concrete products containing photocatalytic active TiO2. The influence of process conditions like irradiance, relative humidity, pollutant concentration and flow rate on the degradation mechanism is investigated. Furthermore, a short overview on photo catalytic powders (especially TiO2) and their influence on the degradation of NO are presented. In addition the application of TiO2 coatings and their microstructural analysis is explained

On the origin of the extremely different solubilities of polyethers in water

The solubilities of polyethers are surprisingly counter-intuitive. The best-known example is the difference between polyethylene glycol ([–CH2–CH2–O–]n) which is infinitely soluble, and polyoxymethylene ([–CH2–O–]n) which is completely insoluble in water, exactly the opposite of what one expects from the C/O ratios of these molecules. Similar anomalies exist for oligomeric and cyclic polyethers. To solve this apparent mystery, we use femtosecond vibrational and GHz dielectric spectroscopy with complementary ab initio calculations and molecular dynamics simulations. We find that the dynamics of water molecules solvating polyethers is fundamentally different depending on their C/O composition. The ab initio calculations and simulations show that this is not because of steric effects (as is commonly believed), but because the partial charge on the O atoms depends on the number of C atoms by which they are separated. Our results thus show that inductive effects can have a major impact on aqueous solubilities