Thomas A. Bier

Using exploratory factor analysis to examine consecutive in-situ X-ray diffraction measurements

A method is presented to examine consecutive in-situ X-ray diffraction (XRD) diffractograms using exploratory factor analysis. Systematic changes in the diffractograms are described numerically by score values that could be used to correlate diffraction data with other non-stationary sample properties. Phase and structure evolution in a reacting material can be studied by in-situ XRD. The consecutively collected data can be considered a time series of datasets. Time series are non-stationary data. Such non-stationary data are often hard to examine fully by conventional evaluation methods including applications of the Rietveld method. Here a method is presented to avoid shortcomings of conventional evaluation methods. The new method helps to identify and describe significant systematic changes in in-situ XRD datasets by numerical values. These systematic changes can represent structural changes as well as changes in phase composition. The method can be used to describe the development of the complex processes of compositional and structural changes. The method is demonstrated using the example of a hydrating Portland cement mortar. This hydration process involves at least 11 phases including non-crystalline phases. In the presented example factor analysis of in-situ XRD data results in three variables (factors) describing the observed changes numerically.

Mechanisms of Degradation in Rheological Properties Due to Pumping and Mixing

Excessive mixing and/or pumping can result in a degradation of rheological properties specifically for self-compacting concrete (SCC) or grouts. Consequently, adverse effects on the concrete performance and structural defects are experienced. In order to identify the dominant factors that influence the rheological properties in the process chain, our study focused on rheological behavior of cement-based grouts after mixing and pumping by examining the results from field and laboratory trials that measured the effects of several pumping parameters on grout characteristics, by describing the effects of compressive stress, shear stress, and sedimentation on grout properties at a laboratory scale, and by analyzing the results using rheographs. The underlying physico-chemical mechanisms were studied using amount of plasticizer adsorbed and specific surface area development during initial hydration. Our observations revealed that mixing and shear stress during pumping, respectively, do exhibit the most pronounced influence on the rheological properties of grouts. Pressurization and sedimentation (while grouts settle) induce only little changes. The degradation of rheological properties is explained by an increase of the specific surface area available for adsorption of plasticizer. This increase seems to be due not only to dispersion of the particles but also to an accelerated creation of pre-hydrates.