Ana Paula Kirchheim

Bio: Ana Paula Kirchheim is an academic researcher from Universidade Federal do Rio Grande do Sul. The author has contributed to research in topics: Cement & Portland cement. The author has an hindex of 18, co-authored 49 publications receiving 954 citations. Previous affiliations of Ana Paula Kirchheim include University of California, Berkeley.

Early age hydration of calcium sulfoaluminate (synthetic ye'elimite, ) in the presence of gypsum and varying amounts of calcium hydroxide

Abstract: Suspensions of synthetic ye'elimite ( C 4 A 3 S ¯ ) in a saturated gypsum ( C S ¯ H 2 ) and calcium hydroxide (CH) solution were examined in-situ in a wet cell by soft X-ray transmission microscopy and ex-situ by scanning electron microscopy. The most voluminous hydration product observed was ettringite. Ettringite commonly displayed acicular, filiform, reticulated, and stellate crystal habits. Additionally, pastes with C 4 A 3 S ¯ , 15% C S ¯ H 2 , and varying amounts of CH were prepared and examined with X-ray diffraction (XRD) and isothermal calorimetry. The XRD experiments showed that increasing CH content caused more solid solution (SO 4 2 − /OH − ) AFm phases to form at early ages ( 1 d). Calorimetry indicated that the increased production of solid solution AFm was accompanied with an increase in the initial (

Evaluation of the potential improvement in the environmental footprint of geopolymers using waste-derived activators

Abstract: Geopolymers produced from an aluminosilicate precursor and an alkaline activating solution have emerged as low carbon alternative binders which can substitute for Portland cement (PC) in many applications. The presence of soluble silicate in the activating solution of a geopolymer is known to yield a denser and more compact material with higher mechanical strength compared to hydroxide-activated geopolymers. However, these silicate solutions are the most expensive component of geopolymer cements, as well as the highest contributors to their environmental impacts in most life cycle categories. Geopolymers are widely accepted as a more environmental friendly material due to their claimed lower CO2 emissions due to their synthesis from industrial by-products or wastes, as well the low energy demand during their production. However, the use of alkali-silicate activators can significantly increase other environmental impacts, leading to controversies regarding whether geopolymers can really be considered as a more sustainable material. Thus, this study evaluates the life cycle impacts of a geopolymer produced from a kaolin sludge residue from the Brazilian mining industry. Alkaline solutions derived from sodium hydroxide solutions and two different soluble silica sources were used as activators: a commercial sodium silicate (waterglass), and chemically modified rice husk ash (RHA). The processes which contribute the most to the life cycle impacts of geopolymers are thermal curing, waterglass production, and sodium hydroxide production. The use of RHA-derived sodium silicate may reduce environmental impacts by more than 60% in 6 of the 9 categories assessed, indicating that this is a favourable alternative where RHA is locally available. Although the binders evaluated here have differences in mechanical properties, those using RHA-derived activators exhibit impacts lower than PC for 4 of the 8 categories evaluated, and a reduction of more than 70% in global warming potential. RHA-based activators are identified as a promising alternative for impact reduction in geopolymer production, and more detailed assessments of the performance and reactivity of these activators should be conducted.

Management and valorisation of wastes through use in producing alkali‐activated cement materials

Abstract: There is growing global interest in maximising the re-use and recycling of waste, to minimise the environmental impacts associated with waste treatment and disposal. Use of high-volume wastes in the production of blended or novel cements (including alkali-activated cements) is well known as a key pathway by which these wastes can be re-used. This paper presents a critical overview of the urban, agricultural, mining and industrial wastes that have been identified as potential precursors for the production of alkali-activated cement materials, or that can be effectively stabilised/solidified via alkali activation, to assure their safe disposal. The central aim of this review is to elucidate the potential advantages and pitfalls associated with the application of alkali-activation technology to a wide variety of wastes that have been claimed to be suitable for the production of construction materials. A brief overview of the generation and characteristics of each waste is reported, accompanied by identification of opportunities for the use of alkali-activation technology for their valorisation and/or management. © 2016 Society of Chemical Industry

Characterizing the nano and micro structure of concrete to improve its durability

Abstract: New and advanced methodologies have been developed to characterize the nano and microstructure of cement paste and concrete exposed to aggressive environments. High resolution full-field soft X-ray imaging in the water window is providing new insight on the nano scale of the cement hydration process, which leads to a nano-optimization of cement-based systems. Hard X-ray microtomography images of ice inside cement paste and cracking caused by the alkali?silica reaction (ASR) enables three-dimensional structural identification. The potential of neutron diffraction to determine reactive aggregates by measuring their residual strains and preferred orientation is studied. Results of experiments using these tools are shown on this paper.

Metakaolin-based geopolymers: Relation between formulation, physicochemical properties and efflorescence formation

Abstract: The efflorescence formation in metakaolin-based geopolymers is assessed in this study to provide a better understanding of the effect of the synthesis parameters. Efflorescence formation depends on the physical and chemical properties of geopolymers as well as the environmental exposure conditions. In this study a set of fifteen geopolymers were synthesized using different formulation. An accelerated test of efflorescence development is presented, where the grade of degradation was evaluated by visual observation and correlated to leaching potential, physical properties and microstructural features. The use of soluble silicate in the activator provides a denser and a less permeable matrix. This makes the extraction of free alkalis to the surface more difficult, reducing the extent of alkali leaching and therefore efflorescence. The use of K+ is also effective to reduce visible efflorescence. The efflorescence formation is predicted by the properties of the gel formed which are dependent on the mix proportioning.

American Society for Testing and Materials

Abstract: The American Society for Testing and Materials (ASTM) is an independent organization devoted to the development of standards.

Changes in portlandite morphology with solvent composition: Atomistic simulations and experiment

Abstract: Experimental work has been done to determine changes in the particle shape of portlandite grown in the presence of different ions. To quantify the experimentally observed changes in morphology a new analysis tool was developed, allowing the calculation of the relative surface energies of the crystal facets. The observed morphology in the presence of chlorides and nitrates was facetted particles of a similar shape, the addition of sulfates leads to hexagonal platelet morphology and the addition of silicates leads to the formation of large irregular aggregates. In addition to the experimental work, the surfaces of portlandite were studied with atomistic simulation techniques. The empirical force field used has first been validated. The equilibrium morphology of portlandite in vacuum and in water was then calculated. The results indicate that the presence of water stabilizes the [20.3] surface and changes the morphology. This is consistent with the experimental observation of [20.3] surfaces.

Alkali-activated materials

Abstract: This paper, which forms part of the UNEP White Papers series on Eco-Efficient Cements, provides a brief discussion of the class of cementing materials known as ‘alkali-activated binders’, which are identified to have potential for utilization as a key component of a sustainable future global construction materials industry. These cements are not expected to offer a like-for-like replacement of Portland cement across its full range of applications, for reasons related to supply chain limitations, practical challenges in some modes of application, and the need for careful control of formulation and curing. However, when produced using locally-available raw materials, with well-formulated mix designs (including in particular consideration of the environmental footprint of the alkaline activator) and production under adequate levels of quality control, alkali-activated binders are potentially an important and cost-effective component of the future toolkit of sustainable construction materials.

Nanoscale X-ray imaging

Abstract: Recent years have seen significant progress in the field of soft- and hard-X-ray microscopy, both technically, through developments in source, optics and imaging methodologies, and also scientifically, through a wide range of applications While an ever-growing community is pursuing the extensive applications of today's available X-ray tools, other groups are investigating improvements in techniques, including new optics, higher spatial resolutions, brighter compact sources and shorter-duration X-ray pulses This Review covers recent work in the development of direct image-forming X-ray microscopy techniques and the relevant applications, including three-dimensional biological tomography, dynamical processes in magnetic nanostructures, chemical speciation studies, industrial applications related to solar cells and batteries, and studies of archaeological materials and historical works of art

The strengths and weaknesses of NMR spectroscopy and mass spectrometry with particular focus on metabolomics research.

Abstract: Mass spectrometry (MS) and nuclear magnetic resonance (NMR) have evolved as the most common techniques in metabolomics studies, and each brings its own advantages and limitations. Unlike MS spectrometry, NMR spectroscopy is quantitative and does not require extra steps for sample preparation, such as separation or derivatization. Although the sensitivity of NMR spectroscopy has increased enormously and improvements continue to emerge steadily, this remains a weak point for NMR compared with MS. MS-based metabolomics provides an excellent approach that can offer a combined sensitivity and selectivity platform for metabolomics research. Moreover, different MS approaches such as different ionization techniques and mass analyzer technology can be used in order to increase the number of metabolites that can be detected. In this chapter, the advantages, limitations, strengths, and weaknesses of NMR and MS as tools applicable to metabolomics research are highlighted.