Dietmar Stephan

Evaluation of the Effects of Crushed and Expanded Waste Glass Aggregates on the Material Properties of Lightweight Concrete Using Image-Based Approaches

Recently, the recycling of waste glass has become a worldwide issue in the reduction of waste and energy consumption. Waste glass can be utilized in construction materials, and understanding its effects on material properties is crucial in developing advanced materials. In this study, recycled crushed and expanded glasses are used as lightweight aggregates for concrete, and their relation to the material characteristics and properties is investigated using several approaches. Lightweight concrete specimens containing only crushed and expanded waste glass as fine aggregates are produced, and their pore and structural characteristics are examined using image-based methods, such as scanning electron microscopy (SEM), X-ray computed tomography (CT), and automated image analysis (RapidAir). The thermal properties of the materials are measured using both Hot Disk and ISOMET devices to enhance measurement accuracy. Mechanical properties are also evaluated, and the correlation between material characteristics and properties is evaluated. As a control group, a concrete specimen with natural fine sand is prepared, and its characteristics are compared with those of the specimens containing crushed and expanded waste glass aggregates. The obtained results support the usability of crushed and expanded waste glass aggregates as alternative lightweight aggregates.

Preparation and Application of Nanoscaled C-S-H as an Accelerator for Cement Hydration

In the present work an easy mechanochemical approach was used to prepare the C-S-H seeds out of simple commercial available materials. The preparation method was optimized with regard to achieve the highest acceleration by using statistical analysis of a factorial design of experiments setup (DoE). Isothermal heat flow calorimetry was used to quantify the efficiency of the seeds to accelerate the hydration of ordinary Portland cement (OPC). The setting and hardening behavior of cement pastes containing the seeds was studied by ultrasonic testing and Vicat needle penetration tests. The compressive strength after 12 h could be tripled by the addition of just 0.5 wt% in respect to the cement mass and a significant advance of strength remains for the following 3 days of hydration.

Relationships between the chemistry and the physical properties of bitumen

The aim of this research was to find relationships between the chemistry of bitumen and its material properties. To reach this objective, 11 bitumen samples in different ageing states and four aggregates were investigated by chemical, rheological and adhesion-related methods. Regarding the rheological properties, the asphaltenes as well as the resins, aromatics and saturates (SARA fractions) demonstrate a strong influence on stiffness, viscosity, deformation behaviour and temperature sensitivity of bitumen. The ageing behaviour depends mostly on the asphaltenes. Furthermore, the adhesion properties of bitumen depend on the aggregate using in the asphalt mixture. Regarding the aggregates, the adhesion properties are affected by the content of silicon dioxide and the surface charge. The results of this research show some significant influences of the chemical properties on the physical, rheological, ageing and adhesions behaviour of the binder whereby the asphaltenes and the other SARA fractions play a decisive role.

Reactivation of a Retarded Suspension of Ground Granulated Blast-Furnace Slag

An effective retarded suspension of ground granulated blast-furnace slag (GGBFS) needs a strong activator to reactivate the hydration. In this research study, sodium hydroxide (NaOH) as an alkali activator in two different concentrations (30 and 50 wt.%) was used to overcome the retardation and give the hardened GGBFS the reasonable strength. The study was carried out with a mixture of GGBFS, a solution of 1.0 wt.% d-gluconic acid (C6H12O7) as a retarder in the mixing water and a methyl cellulose as a stabilizer. The reactivation was executed after seven different periods (up to 28 days) after the system was retarded. The following investigations were performed: slump test, measurement of ultrasonic (US) velocity, compressive strength and gross density, thermogravimetry (TG) and scanning electron microscopy (SEM). The analyses of the hardened samples were carried out seven, 28 and 90 days after the reactivation. The result of the study is an effective reactivation of a retarded suspension. In this case, the activator with 50 wt.% NaOH shows a very high performance. The setting time of the reactivated binders is much longer compared to the reference, but, in the longer term, the compressive strength and the progress of the hydration exceed the performance of the reference.

The Influence of Nanomaterials on the Thermal Resistance of Cement-Based Composites—A Review

Exposure to elevated temperatures has detrimental effects on the properties of cementitious composites, leading to irreversible changes, up to total failure. Various methods have been used to suppress the deterioration of concrete under elevated temperature conditions. Recently, nanomaterials have been introduced as admixtures, which decrease the thermal degradation of cement-based composites after exposure to high temperatures. This paper presents a comprehensive review of recent developments related to the effects of nanoparticles on the thermal resistance of cementitious composites. The review provides an updated report on the effects of temperature on the properties of cement-based composites, as well as a detailed analysis of the available literature regarding the inclusion of nanomaterials and their effects on the thermal degradation of cementitious composites. The data from the studies reviewed indicate that the inclusion of nanoparticles in composites protects from strength loss, as well as contributing to a decrease in disruptive cracking, after thermal exposure. From all the nanomaterials presented, nanosilica has been studied the most extensively. However, there are other nanomaterials, such as carbon nanotubes, graphene oxide, nanoclays, nanoalumina or nano-iron oxides, that can be used to produce heat-resistant cementitious composites. Based on the data available, it can be concluded that the effects of nanomaterials have not been fully explored and that further investigations are required, so as to successfully utilize them in the production of heat-resistant cementitious composites.

Hydration kinetics of Portland cement in the presence of vinyl acetate ethylene latex stabilized with polyvinyl alcohol

Three vinyl acetate ethylene (VAE) latices and incorporated polyvinyl alcohol (PVOH) were investigated. Two of the VAE latices were stabilized by PVOH, while the third was stabilized with an anionic surfactant. The influence of VAE and PVOH on cement hydration was studied by means of isothermal heat flow calorimetry, ICP-OES and in situ XRD measurement. All of the latices prolonged the induction period with an increase in the polymer/cement ratio, whereas the latex stabilized by PVOH hardly influenced the hydration of the silicate phase. Instead, a strong secondary exothermic peak was observed. Based on the in situ XRD analysis, the peak was attributed to the rapid formation of ettringite. Furthermore, the concentration of SO42− in the pore solution was found to have reduced in the presence of polymers in the first hours of the hydration.

Multiphase CFD-Simulation of Transport Phenomena in Sewer Systems

This paper presents different computational fluid dynamics applications using the multiphase solver interFoam which is implemented in the open source software OpenFOAM. The solver uses the volume of fluid approach. When modelling tracer transport in the proximity of the interface between two phases, the problem of non-physical tracer spreading across the interface has to be overcome. In this paper, two ways are presented to model such systems successfully. First, tracer transport around concrete probes in the headspace of a sewer pilot plant is considered. In this case a two-phase (water-air) system is assumed by describing an idealized water surface as a boundary condition and a passive tracer is applied. Second, flow in a complex sewer stretch containing a hydraulic jump is simulated and a tracer is applied in the water phase. A multiphase transport approach based on the Henry coefficient is used in this case and plausible results are obtained.

Studying the Hydration of a Retarded Suspension of Ground Granulated Blast-Furnace Slag after Reactivation

This article presents a combined use of a retarder (d-gluconic acid) and an alkaline activator (sodium hydroxide) in a binder system based on ground granulated blast-furnace slag. The properties of the retarder are extending the dormant hydration period and suppressing the generation of strength-giving phases. Different retarder concentrations between 0.25 and 1.00 wt.% regulate the intensity and the period of the retardation and also the characteristics of the strength development. The activator concentration of 30 and 50 wt.% regulates the overcoming of the dormant period and thereby the solution of the slag and hence the formation of the hydration products. The research objective is to produce a mineral binder system based on two separate liquid components. The highest concentration of retarder and activator generates the highest compressive strength and mass of hydration products—after 90 days of hydration a compressive strength of more than 50 N/mm2. The main phases are calcium silicate hydrate and hydrotalcite. Generally, the combination of retarder and activator shows a high potential in the performance increase of the hydration process.

Bitumen as required – the dream of a designed binder

The objective of this work is to bring rheological and chemical properties of the bitumen together. As rheological investigation methods, the determination of the softening point (Ring and Ball method) as well as the determination of the complex shear modulus |G*| and the phase angle δ with the Dynamic Shear Rheometer were carried out. As chemical analyses, the separation of asphaltenes to determine the asphaltene content, the further separation of the maltene phase using column chromatography to determine the content of the saturates, aromatics and resins and the gel permeation chromatography to determine the molecular weight were carried out. The relationships between the rheological and chemical parameters were investigated by multiple regression analyses. It shows inter alia that the viscosity and the stiffness of the bitumen are dependent on both the asphaltenes and the maltene fractions. In contrast, the deformation behaviour of the bitumen is mainly determined by the asphaltene content. Furthermore, the contents and molecular weights of the SARA fractions provide information about the sensitivity of ageing and the bitumen behaviour after ageing. The findings can be of benefit for the selection of an appropriate binder for road construction and for the recycling of bitumen.