The influence of shrinkage-cracking on the drying behaviour of White Portland cement using Single-Point Imaging (SPI)

Adsorption Affinity of Linear and Aromatic Organic Anions Competing for Cationic Cement Surfaces

Competitive adsorption of chemical admixtures onto cement is of critical importance in delivering bulk performance requirements of cement slurries employed in constructing high-performing structures, like oil wells. This challenge is complex to investigate, because of the many variables that include the heterogeneity, high pH, and ionic strength of cement fluids; the multiple crystalline phases present in unhydrated and set cement; and the high number of admixtures required to meet performance criteria in commercial operations. The purpose of this study is to relate chemical structures to relative adsorption behavior of admixtures onto cement when present together and classify such interactions as beneficial (synergistic) or detrimental (antagonistic). Adsorption characteristics of single admixtures were examined by total organic carbon analysis, FT infrared spectroscopy, scanning electron microscopy, calorimetry, and UV/vis spectrophotometry. Results show that the adsorption of single chemical admixtures follows the order of monomeric hydroxycarboxylate molecule > sulfonated linear polymer > sulfonated aromatic polymer > carboxylated/sulfonated linear polymer > carboxylated branched polyether polymers. The observed adsorption behavior of polymers correlates extremely well with the order for cement hydration retardation, with carboxylated polymers being the most powerful retarders. Results correlate closely with the proposed mechanism that sulfonated polymers adsorb onto aluminate phases, presumably the tricalcium aluminate phase; and the carboxylate polymers onto silicate phases, particularly the predominant tricalcium oxysilicate phase. The hydroxycarboxylic monomeric molecule was the strongest retarder of all and has the highest adsorption level, presumably on tricalcium oxysilicate. The competitive adsorption behavior in binary mixtures was studied by monitoring the displacement of a signaling polymer by a second admixture. Results indicate that, for similar functional groups, shorter polymers are competitively more strongly adsorbed than longer chain molecules and that the shorter chain polymers were not desorbed significantly by longer chain polymer molecules. Rheological measurements correlated admixture adsorption behavior to the observed slurry fluidity.

Pressure measurement as a tool to identify moisture transport mechanisms in convective drying of non-shrinking material

The drying process is one of the most important stages in the production of building materials. The choice of the drying method affects the chemical and physical properties of the final product. The aim of this research is to measure and analyze the dynamic changes of internal pressure in non-shrinking, porous material during convective drying. In this work the problem will be discussed with special attention to the behavior of rewetted plaster. A commercial gypsum of company PIOTROWICE II (Alpol brand), typically used in construction and decorative plastering was applied. Gypsum was mixed with water in recommended proportion of 0.6 water/gypsum and drying experiments were performed at 50°C. The changes in sample overall mass as well as pressure and material temperature on the midpoint of sample axis were monitored. On the basis of the obtained experimental data of axial pressure, it is possible to perform a more detailed analysis of mass and heat transfer mechanisms than based on the drying kinetics alone. The pressure trends in the sample allow one to determine the moment of transition from the first to the second drying period, without the need to determine the kinetics of drying. The element of novelty consists of using a direct internal pressure measurement to provide information on the variation of the actual drying rate and mass transfer mechanisms.

Low-field permanent magnets for industrial process and quality control

In this review we focus on the technology associated with low-field NMR. We present the current state-of-the-art in low-field NMR hardware and experiments, considering general magnet designs, rf performance, data processing and interpretation. We provide guidance on obtaining the optimum results from these instruments, along with an introduction for those new to low-field NMR. The applications of lowfield NMR are now many and diverse. Furthermore, niche applications have spawned unique magnet designs to accommodate the extremes of operating environment or sample geometry. Trying to capture all the applications, methods, and hardware encompassed by low-field NMR would be a daunting task and likely of little interest to researchers or industrialists working in specific subject areas. Instead we discuss only a few applications to highlight uses of the hardware and experiments in an industrial environment. For details on more particular methods and applications, we provide citations to specialized review articles.

Optimal k-space sampling for single point imaging of transient systems

A novel approach for sampling k-space in a pure phase encoding imaging sequence is presented using the Single Point Imaging (SPI) technique. The sequence is optimised with respect to the achievable Signal-to-Noise ratio (SNR) for a given time interval via selective sparse k-space sampling, dictated by prior knowledge of the overall object of interest's shape. This allows dynamic processes featuring short T(2)( *) NMR signal to be more readily followed, in our case the absorption of moisture by a cereal-based wafer material. Further improvements in image quality are also shown via the use of complete sampling of k-space at the start or end of the series of imaging experiments; followed by subsequent use of this data for un-sampled k-space points as opposed to zero filling.

Multipoint mapping for imaging of semi-solid materials

Multipoint k-space mapping is a hybrid between constant-time (single-point mapping) and spin-warp imaging, involving sampling of a k-line segment of r points per TR cycle. In this work the method was implemented for NMR imaging of semi-solid materials on a 400 MHz micro-imaging system and two different k-space sampling strategies were investigated to minimize the adverse effects from relaxation-induced k-space signal modulation. Signal attenuation from T(2) decay results in artifacts whose nature depends on the k-space sampling strategy. The artifacts can be minimized by increasing the readout gradient amplitude, by PSF deconvolution or by oversampling in readout direction. Finally, implementation of a T(2) selective RF excitation demonstrates the feasibility of obtaining short-T(2) contrast even in the presence of tissues with long-T(2). The method's potential is illustrated with 3D proton images of short-T(2) materials such as synthetic polymers and bone.

Imaging of heterogeneous materials with a turbo spin echo single-point imaging technique

A magnetic resonance imaging method is presented for imaging of heterogeneous broad linewidth materials. This method allows for distortionless relaxation weighted imaging by obtaining multiple phase encoded k-space data points with each RF excitation pulse train. The use of this method, turbo spin echo single-point imaging-(turboSPI), leads to decreased imaging times compared to traditional constant-time imaging techniques, as well as the ability to introduce spin-spin relaxation contrast through the use of longer effective echo times. Imaging times in turboSPI are further decreased through the use of low flip angle steady-state excitation. Two-dimensional images of paramagnetic doped agarose phantoms were obtained, demonstrating the contrast and resolution characteristics of the sequence, and a method for both amplitude and phase deconvolution was demonstrated for use in high-resolution turboSPI imaging. Three-dimensional images of a partially water-saturated porous volcanic aggregate (T(2L) approximately 200 ms, Deltanu(1/2) approximately 2500 Hz) contained in a hardened white Portland cement matrix (T(2L) approximately 0.5 ms, Deltanu(1/2) approximately 2500 Hz) and a water-saturated quartz sand (T(2) approximately 300 ms, T(2)(*) approximately 800 microseconds) are shown.