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Effect of Polycarboxylate Superplasticizer in Ordinary Portland Cement and Sulfate Resistant Cement
(2023)
Polycarboxylate superplasticizers (PCE) are the most widely used admixtures in today’s cementitious construction materials. The molecular structure has a decisive influence on the effectiveness of PCE, which also can be tailored to serve in a different cementitious system.
The current study investigates the influence of the backbone charge density of PCE on the rheology, hydration kinetics, and adsorption behavior of ordinary Portland cement (OPC) and sulfate-resistant cement (SRC). The results indicate that regardless of the PCE type, OPC requires a higher amount of PCE to be adsorbed to induce changing of rheological parameters and hydration kinetics. Regardless of the cement type, the PCE with a higher charge density exhibits higher adsorption behavior, corresponding to lower viscosity measurement.
Compared to OPC, SRC is more sensitive to the introduction of both PCEs and has a lower saturation dosage, indicating that SRC generally provides better workability properties regardless of the PCE.
There is no consensus on which hydration stoppage method is optimal to preserve the microstructure and mineral composition of samples, especially considering the specific aspects of different testing methods, such as TGA, MIP, or XRD. This paper presents a quantitative comparison between the most popular hydration stoppage strategies and parameters such as the sample piece size, the soaking time in a solvent, and the type, as examined on cement paste hydrated for 7 days. It was found that the carbonation appears either for samples smaller than 2.36 mm and bigger than 4.75 mm or samples soaked in a solvent for longer than 1 h. Fast solvent replacement leads to ettringite diminution and total pore volume increase. Among others, solvent replacement with subsequent gentle heating under a vacuum was found to be the most efficient, whereas it was experimentally demonstrated that isopropyl alcohol stops hydration faster than ethanol and acetone.
FAIR (findable, accessible, interoperable and reusable) data usage is one of the main principals that many of the research and funding organizations include in their strategic plans, which means that following the main principals of FAIR data is required in many research projects. The definition of data being FAIR is very general. When implementing that for a specific application or project or even setting a standardized procedure within a working group, a company or a research community, many challenges arise. In this contribution, an overview about our experience with different methods and tools is outlined.
We begin with a motivation on potential use cases for the application of FAIR data with increasing complexity starting from a reproducible research paper over collaborative projects with multiple participants such as Round-Robin tests up to data-based models within standardization codes, applications in machine learning or parameter estimation of physics-based simulation models.
In a second part, different options for structuring the data (including metadata schema) are discussed. The first one is the openBIS system, which is an open-source lab notebook and PostgreSQL based data management system. A second option is a semantic representation using RDF based on ontologies for the domain of interest.
In a third section, requirements for workflow tools to automate data processing are discussed and their integration into reproducible data analysis is presented with an outlook on required information to be stored as metadata in the database.
Finally, the presented procedures are exemplarily demonstrated for the calibration of a temperature dependent constitutive model for additively manufactured mortar. A metadata schema for a rheological measurement setup is derived and implemented in an openBIS database. After a short review of a potential numerical model predicting the structural build-up behavior, the automatic workflow to use the stored data for model parameter estimation is demonstrated.
Materials that support natural biodiversity on their surfaces can compensate for human activities that have a negative impact on nature and thus contribute to a carbon-neutral and nature-positive world. Specifically designing bioreceptive materials which favor the growth of biofilms on their surface is an approach complementing conventional, macroscopic green façades. But what exactly characterizes a bioreceptive substrate and how do biofilm and substrate interact? How and why does a spontaneous colonization and the formation of biofilms take place? What are biofilms and how can they be established in a laboratory setting? How can this existing knowledge be transferred to the artificial stone concrete so that this material can be tuned to increase (or decrease) its bioreceptivity?
This review paper aims at summarizing the existing state of knowledge on bioreceptive concrete and pointing out inconsistencies and contradictions which can only be removed by more interdisciplinary research in the field.
Quenching and partitioning (Q&P) steels are characterized by an excellent combination of strength and ductility, opening up great potentials for advanced lightweight components. The Q&P treatment results in microstructures with a martensitic matrix being responsible for increased strength whereas interstitially enriched metastable retained austenite (RA) contributes to excellent ductility. Herein, a comprehensive experimental characterization of microstructure evolution and austenite stability is carried out on a 42CrSi steel being subjected to different Q&P treatments. The microstructure of both conditions is characterized by scanning electron microscopy as well as X‐ray diffraction (XRD) phase analysis. Besides macroscopic standard tensile tests, RA evolution under tensile loading is investigated by in situ XRD using synchrotron and laboratory methods. As a result of different quenching temperatures, the two conditions considered are characterized by different RA contents and morphologies, resulting in different strain hardening behaviors as well as strength and ductility values under tensile loading. In situ synchrotron measurements show differences in the transformation kinetics being rationalized by the different morphologies of the RA. Eventually, the evolution of the phase specific stresses can be explained by the well‐known Masing model.
In this work, a methodology based on Fourier transform infrared (FTIR)spectroscopy and multivariate evaluation is presented to estimate the aging sensitivity of bitumen based on the unaged samples and thus without the need for time- and material-consuming aging simulations. For this purpose, factor analysis and linear discriminant analysis are used to develop a statistical model based on the FTIR spectra of unaged bitumen samples, which can be used fast and simple in everyday laboratory work and allows to assign the bitumen to a low, moderate, or strong aging sensitivity. The evaluation of the aging sensitivity is based on the complex shear modulus|G* | and the phase angle δ from the measurement with a dynamic shear rheometer(DSR), whose aging-related changes were captured as the slope in the Black diagram. A relevant influence on the classification concerning the aging sensitivity has the oxygen-containing compounds(sulfoxide, hydroxyl and partly carbonyl compounds), whereby lower contents and thus less preaged bitumen tend to have a stronger aging sensitivity. However, in addition to the oxygen-containing compounds, the structure of the aliphatic and aromatic compounds and, in particular, the interaction of the different structures are decisive for the aging sensitivity
The site of Schöningen (Germany), dated to ca. 300,000 years ago, yielded the earliest large-scale record of humanly-made wooden tools. These include wooden spears and shorter double-pointed sticks, discovered in association with herbivores that were hunted and butchered along a lakeshore. Wooden tools have not been systematically analysed to the same standard as other Palaeolithic technologies, such as lithic or bone tools. Our multianalytical study includes micro-CT scanning, 3-dimensional microscopy, and Fourier transform infrared spectroscopy, supporting a systematic technological and taphonomic analysis, thus setting a new standard for wooden tool analysis. In illustrating the biography of one of Schöningen’s double-pointed sticks, we demonstrate new human behaviours for this time period, including sophisticated woodworking techniques. The hominins selected a spruce branch which they then debarked and shaped into an aerodynamic and ergonomic tool. They likely seasoned the wood to avoid cracking and warping. After a long period of use, it was probably lost while hunting, and was then rapidly buried in mud. Taphonomic alterations include damage from trampling, fungal attack, root damage and compression. Through our detailed analysis we show that Middle Pleistocene humans had a rich awareness of raw material properties, and possessed sophisticated woodworking skills. Alongside new detailed morphometrics of the object, an ethnographic review supports a primary function as a throwing stick for hunting, indicating potential hunting strategies and social contexts including for communal hunts involving children. The Schöningen throwing sticks may have been used to strategically disadvantage larger ungulates, potentially from distances of up to 30 metres. They also demonstrate that the hominins were technologically capable of capturing smaller fast prey and avian fauna, a behaviour evidenced at contemporaneous Middle Pleistocene archaeological sites.
Inelastic incoherent neutron time-of-flight scattering was employed to investigate the low-frequency vibrational density of states (VDOSs) for a series of glassy Janus-poly(tricyclononenes), which consist of a rigid main chain and flexible alkyl side chains. Here, the length of the flexible side chains was systematically varied from propyl to octyl. Such materials have potential applications as active separation layers in gas separation membranes as a green future technology, especially for the separation of higher hydrocarbons. From the morphological point of view, the Janus polynorbornenes undergo a nanophase separation into alkyl side chain-rich nanodomains surrounded by a rigid polynorbornene matrix. Here, the influence of the nanophase-separated structure on the low-frequency VDOS is investigated from a fundamental point of view. The low-frequency VDOSs of these Janus polynorbornene show excess contributions to the Debye type VDOS known as the Boson peak (BP) for all side chain lengths. Due to the high incoherent scattering cross-section of hydrogen, most of the scattering comes from the alkyl side chain-rich domains.
Compared to conventional glass-forming materials, in the considered Janus polynorbornenes, the BP has a much lower intensity and its frequency position is shifted to higher values. These experimental results are discussed in terms of the nanophase-separated structure where the alkyl chain-rich domains were constrained by the surrounding matrix dominated by the rigid backbone. With increasing alkyl chain length, the size of the alkyl chain-rich domains increases. The frequency position of the BP shifts linearly to lower frequencies with the size of these nanodomains estimated from X-ray measurements. The obtained results support the sound wave interpretation to the BP
The addition of nanoparticles as reinforcing fillers in elastomers yields nanocomposites with unique property profiles, which opens the door for various new application fields. Major factors influencing the performance of nanocomposites are studied by varying the type and shape of nanoparticles and their dispersion in the natural rubber matrix. The industrial applicability of these nanocomposites is put into focus using two types of graphene and a nanoscale carbon black, all commercially available, and scalable processing techniques in the form of a highly filled masterbatch production via latex premixing by simple stirring or ultrasonically assisted dispersing with surfactant followed by conventional two-roll milling and hot pressing. Different processing and measurement methods reveal the potential for possible improvements: rheology, curing behavior, static and dynamic mechanical properties, swelling, and fire behavior. The aspect ratio of the nanoparticles and their interaction with the surrounding matrix prove to be crucial for the development of superior nanocomposites. An enhanced dispersing method enables the utilization of the improvement potential at low filler loadings (3 parts per hundred of rubber [phr]) and yields multifunctional rubber nanocomposites: two-dimensional layered particles (graphene) result in anisotropic material behavior with strong reinforcement in the in-plane direction (157% increase in the Young's modulus). The peak heat release rate in the cone calorimeter is reduced by 55% by incorporating 3 phr of few-layer graphene via an optimized dispersing process.
This study investigated the effect of incorporating three types of nanosilica (NS), two powders, and one colloidal suspension on the hydration, strength, and microstructure of calcium sulfoaluminate (CSA) cement pastes prepared with and without a superplasticizer (SP). X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy (SEM), and compressive strength tests were performed after 2, 5, and 28 days of hydration. The results showed that both NS powders delayed cement hydration at an early age, which was attributed to particle agglomeration (confirmed by dynamic light scattering). Whereas well-dispersed colloidal NS did not significantly affect the hydration of CSA at the investigated ages. SP incorporation improved the dispersion of CSA cement particles, resulting in a 10% increase in the degree of hydration of ye’elimite at 28 days for the system without NS. Conversely, when the SP was incorporated in NS-containing mixtures, it hindered cement hydration of the systems with powdered NS, but did not significantly affect the cement hydration of the system containing colloidal NS. The SEM images suggested that the SP changed the ettringite morphology, thereby negatively affecting the mechanical strength of the CSA pastes.