High-resolution Luminescent Analysis of Construction Materials
The pH value and the chloride concentration of concrete-based construction materials are key parameters for the assessment of their stability and long-term performances. Major types of chemical degradation mechanisms such as carbonation, chloride induced steel corrosion, as well as leaching and acid attack, usually directly correlate with their changes. Accordingly, a precise characterization of these critical parameters is a central factor for assessment of the state of repair of concrete constructions and the development of sustainable materials. The aim of this project is to explore luminescent analytical methods as an advanced (imaging) technique for the measurements of pH and chloride on concrete-based materials. This will enable better concrete diagnostics to improve the understanding of ongoing corrosion processes and allow a more accurate assessment of the state of repair of concrete constructions. The main objectives can be summarized as follows:
Nanotechnology-based thermochromic materials for adaptive building envelopes
Thermochromic (TC) materials are smart materials characterized by a change in optical response with temperature. Their adaptive optical response to solar radiation has proven to be useful when implemented in building envelopes for improvement of energy efficiency and mitigation of environmental impact of urban areas, such as heat island effect.
Nanotechnology-based TC (nanoTC) materials offer the unique possibility of tailoring their optical properties. However, their implementation into building materials represents a clear research and technology challenge. Within the ‘Linka20220’ project nano-TC materials will be characterized at lab scale and proofs of concept will then be carried out.
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.
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.
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).
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