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The corrosion‐related damages on concrete infrastructure account globally for several billion US dollars annually. Up to 38 % of these costs could be saved by the application of optimized materials and/or more efficient monitoring technologies. In this contribution a novel sensor technology is presented, based on luminescent pH sensitive dyes, to quantitatively determine the pH distribution in cement‐based construction materials. Different sensor platforms were explored resulting in high‐resolution imaging techniques, as well as in miniaturized sensor probes for field application and in situ monitoring. To this point, pH sensors were successfully applied for cementitious materials to (i) quantitatively characterize the carbonation state in the lab, (ii) gain further understanding on phase assemblages and internal pH evolution related to carbonation, (iii) reveal that the actual pH at the inflection point of phenolphthalein may strongly vary depending on physicochemical material properties, (iv) monitor the pH evolution during the early hydration of different cementitious materials, and (v) measure carbonation depths using miniaturized sensor probes adopted for field applications. [ABSTRACT FROM AUTHOR]

Microbial induced acid corrosion is accounted for ~40 % of the degradation of subsurface wastewater infrastructure globally. While fundamental process understanding has increased significantly within the last decades, to date no sustainable building material exists, which meets the long-term requirements in such aggressive and corrosive environments. This work describes a novel model based on field studies, conducted in various Austrian sewer networks, intertwining biological, mineralogical and hydro-chemical factors. Additionally, an extensive field testing campaign over the duration of 18 months, conducted on different geopolymer concretes (GPC), particularly designed for the latter environments will be presented. Innovative GPCs were tested regarding their microstructural behavior, microbial accessibility and hydro-chemical alterations over time and compared to commercially produced cement based products, including OPC and CAC concretes. Additionally, the system specific environmental parameters, such as relevant gas concentrations (H2S, CO2, CH4), relative humidity and temperature were constantly monitored.

Major types of chemical concrete degradation such as carbonation, leaching and acid attacks are strongly associated with decreasing internal or external pH. Thus a precise determination of the latter is crucial for the assessment regarding the degree of corrosion and corresponding development of prevention strategies. Conventional pH measure methods for concrete, such as phenolphthalein indicator, pore solution extractions and flat surface electrodes have proven to contain significant limitations and inadequacies. This contribution presents the application of sensor foils based on luminescent pH sensitive dyes entrapped in a polymeric hydrogel matrix, to quantify and image the distribution of surface pH of concrete based construction materials. An imaging technique called time-domain dual lifetime referencing (t-DLR) was used, which suppresses artifacts from scattering of the background and other light inhomogeneities. Using this methodology high-resolution pH profiles of concrete samples exposed to carbonation and biogenic acid corrosion were recorded.

Limitations in the understanding of chemical key controls on concrete damaging mechanisms exacerbate predictions on the long-term performance and durability of cementitious materials. Therefore, the scope of the project “ASSpC Advanced and Sustainable Sprayed Concrete” is to obtain a better mechanistic understanding of the processes underlying deleterious chemical attacks. The herein presented alternative test, loosely following the regulations of the German Building Authority (DIBt) testing procedure (the so-called SVA test) for sulphate resistance, investigates the resistance of concrete mixes with high levels of limestone substitution (35%, 50% and 65%) against sulphate attack in a 10 g L-1 Na2SO4 solution at ambient temperature. Powdered samples were used in favour of prisms or drill cores to accelerate alteration reactions and to eliminate variations in microstructure or porosity. Based on throughout chemical and mineralogical characterisation of the experimental solutions and solid materials, we identified and traced several mineral reactions taking place in a chronological order: (1) dissolution of portlandite and Ca-leaching from C-S-H started immediately at the beginning of the experiments and provided the physicochemical conditions favourable for (2) the precipitation of massive calcite and ettringite during the advanced stage of chemical attack. Ongoing changes in the aqueous composition indicate that C-S-H dissolves incongruently and may be transformed into Si-bearing hydrogarnet. The amount of precipitated ettringite is apparently controlled by the availability of calcium, sulphate and aluminium and the precipitation rate correlates with the superplasticiser demand of the concrete mixes and with the pH of the solution during the nucleation and crystal growth stages, respectively. Our test allows distinguishing between competing reaction paths and kinetics and is capable to provide new insights into concrete damaging mechanisms in sulphate-loaded aqueous environments.