External sulphate attack (ESA) on cementitious building materials
Enormous cost may arise when concrete constructions are subjected to chemical attack. Various degradation processes such as the Thaumasite Form of Sulphate Attack (TSA) have repeatedly been discussed in the literature. However, it is still a matter of debate how thaumasite and ettringite is formed in concrete even at low sulphate concentration of the interacting solution.
A multiproxy approach provided excellent tools to reconstruct complex dissolution and precipitation behaviours for neo- and trans-formation in water-cement-aggregate systems.
For instance, (i) isotopic signatures indicate the sources of CO32- in calcite as well as CO32- and SO42- in thaumasite (e.g. atmospheric CO2, CO32- and SO42- from groundwater) and
(ii) chemical and isotopic compositions of the interstitial solutions of concrete provide evidence that evaporation is a driving force for TSA.
Contact: Dietmar Klammer
Advances in concrete materials for sewer systems affected by microbial induced concrete corrosion
The efficient, safe and cost-effective collection and transport of sewage is a key criterion maintaining expected sanitary standards of modern society. Microbial induced concrete corrosion (MICC) is accounted for ~40 % of the degradation of concrete based subsurface wastewater infrastructure globally. The current state of the art does not provide a sustainable construction material, which meets the long-term requirements in such aggressive and corrosive sewer environments. Within this project, we aim to close the existing gap between materials science (different binder types) and microbiological interactions for application of new innovative construction materials, with increased performance and functionality.
Key objectives are:
O1) to characterize role of physiochemical characteristics of conventional cement-based materials on biofilm adhesion, composition and growth and subsequent comparison to objective O2.
O2) to characterize microbiological growth on innovative concrete materials; influence of physical material properties on microbial growth, biofilm characterization and structure, microbial community composition, evaluation of antimicrobial additives.
O3) to establish multi-functionalities for the novel tailored concretes (acid resistance, antimicrobial effects, and versatility: encouraging wide application range in concrete structures as well as sprayable repair mortars).
Zeolites – Synthesis and Applications
Zeolites contain pores of molecular size (5 – 12 Å) and are used as molecular sieves, ion exchangers and catalysts. Zeolites occur in sedimentary and low-grade metamorphic rocks, but can also be synthesized under hydrothermal conditions. The goal of this project is to investigate processes of zeolite formation under hydrothermal conditions (80 - 150 °C) using precursors like fly ash, perlite and biogenic silica (e.g. diatoms).
Hydrothermal synthesis combined with SEM and XRD studies indicate that amorphous precursor of zeolites precipitates from solution. Assemblage of merlinoite and minor quantities of chabazite and zeolite L was synthesized. Ion exchange experiments demonstrate that the amorphous precursor can reduce the concentration of dissolved heavy metals like Cu, Pb and Zn more efficiently than the subsequently formed zeolite. This is due to its higher specific surface area than crystalline precursor.
Contact: Dietmar Klammer
Soil remediation using Fe0-doped bentonite slurries
Trichloroethylene (TCE) has been used as a solvent agent in industrial areas worldwide, especially from the 1920s to 1970s, which resulted in locally severe pollution of subsoils and groundwater with this cancerogenic and non-biodegradable substance. In the course of the HaloCrete project (initiated by the Austrian Institute of Technology and Keller Grundbau Ges.mbH) an experimental set-up was developed in which reductive de-chlorination of TCE was induced by the addition of nanoscale zero-valent iron (Fe0) particles mixed with bentonite slurries.
Gas chromatography and advanced electron microscopic, spectroscopic, and X-ray diffraction methods are used to ascertain (i) reaction rate constants for TCE degradation and
(ii) the physicochemical interaction mechanisms between Fe0 particles and bentonite; processes that affect a variety of biogeochemical processes involved in soil environments.
Contact: Andre Baldermann
Sprayed concrete hydration
The rapid setting and strength evolution during the first hours after spraying are the two main requisites for shotcrete. These properties are directly related to the microstructure development: formation of hydrated phases and pore structure. Detailed understanding of the early hydration reactions in shotcrete is crucial for the optimization of mixing and processing. However, the need of spraying equipment, together with the high speed of the reactions make laboratory analysis of these materials challenging.
Within the frame of the ‘Advanced and sustainable sprayed concrete’ (ASSpC) project, new mixing approaches are being developed with the final aim of reducing the impact of shotcrete on the environment. Mechanical performance and durability properties are being optimized for these new approaches. In parallel, the hydration reactions occurring in these systems are being studied (e.g. by isothermal calorimetry, shear modulus measurement, XRD and SEM) to gain deeper knowledge on their hydration and setting behavior and to optimize processing.
Durability aspects of shotcrete
Sprayed concrete, or “shotcrete”, is known to suffer from several chemical and mechanical degradation effects, including sulphate and chloride attack and calcium leaching. These attacks weaken the concrete and steel reinforcement or lead to unwanted calcium carbonate sinter formation. Using shotcrete with a higher durability against these hazards increases the service life of tunnels and underground buildings.
A technical objective of the ASSpC (Advanced Sustainable Sprayed Concrete) project is the development of durable and sustainable sprayed concrete to be used for construction and repair tasks. Increasing the sustainability of shotcrete ensures the economical use of resources in the context of a sustainable human development. To decrease the environmental impact of cement used in shotcrete production, substituting cement with supplementary cementitious materials and filler materials is getting more and more common. However, these additions alter the physical and chemical properties of the resulting shotcrete and therefore necessitate advanced research in the field of concrete durability.