Microbially induced concrete deterioration can be observed in wastewater transport and treatment infrastructures. The attack on the concrete usually occurs due to the production of H2S and thus the subsequent biogenic formation of sulphuric acid. Calcium aluminate-based materials have demonstrated a better resistance to the biogenic acid attack compared to Portland cement-based materials and thus can be used as coatings to protect the supported concrete of the wastewater treatment plant. Early age deformations and movements of the protected substrate can cause cracks in the structure which might propagate into the coating. The presence of cracks might act as a pathway for aggressive agents to reach the supported concrete and thus alter the protective role of the coating. However, the precipitation of newly-formed phases inside the crack can possibly slow down or stop their penetration. To investigate the coupling of biodeterioration and cracking, cracked and uncracked coated specimens were exposed during 3 months to the BAC test which simulates the aggressive exposure conditions observed in sewer networks and can be developed for different types of cementitious materials and mineral coatings. The composite specimens were cracked with different width ranges using the three-point bending test; one between 150 and 200 μm and the other between 400 and 500 μm. The quantities of calcium and aluminum leached from the exposed surfaces of different specimens showed no influence of the crack on this durability indicator for both width ranges. The SEM-EDS observations demonstrated the presence of a newly-formed phase in the crack opening, close to the exposed surface of the coated specimens, which could possibly prevent more deterioration being a physical barrier to the penetration of aggressive agents.

This study investigates alkali-silica reaction (ASR) in alkali-activated slag (AAS) concretes with reactive and non-reactive aggregates, and the mitigating effect of aluminum additions. Non-reactive aggregates caused minimal expansion, whereas reactive siliceous limestone and flint exceeded the 0.02% limit due to ASR gel formation confirmed by SEM-EDS. Flint induced greater expansion than siliceous limestone in AAS, consistent with higher silica dissolution. Compared to ordinary Portland cement (CEM I), AAS showed lower expansions with siliceous limestone, likely due to higher pore-solution aluminum concentrations reducing silica dissolution. In contrast, AAS with flint aggregate displayed significantly greater expansions than CEM I, possibly due to the absence of a pessimum effect observed in CEM I.,Aluminum addition using a slow-dissolving Al(OH)₃ source effectively reduced expansions and enhanced early compressive strength by limiting silica dissolution without hindering slag hydration. Its ASR-mitigating mechanism was further assessed through batch dissolution and mixed-flow reactor tests. In particular, 18 mmol aluminum in NaOH solution at pH 13 reduced the silica dissolution rate by a factor of 2.4. These findings highlight aluminum’s dual role in controlling ASR expansions and improving mechanical properties in AAS concrete.

The durability of wastewater treatment plants has been a major concern for decades due to their significant economic and health importance. Structures built with concrete are subject to severe deterioration linked to aggressive chemical and biological exposure conditions. Portland cement concrete is particularly vulnerable to such attacks leading to major damages in the structures. One of the strategies to protect this concrete from the effects of biodeterioration is applying a thin coating based on calcium aluminate cement. These materials were proved to have a superior resistance to biodeterioration compared to ordinary Portland cement. However, the cracks initiated in the protected structure that might reach the coating raise questions on its ability to fulfill its protective role. This paper aims to study the effect of the crack on the durability of the coating using a biological laboratory test, the BAC test, which simulates the real conditions encountered in a sewer system. The calcium leached from the specimens exposed to the biogenic sulfuric acid attack was monitored in two campaigns of the BAC test. Each campaign was performed on reference OPC-based uncoated specimens and coated specimens with the CAC-based coating: uncracked and cracked with two ranges of crack width between 150 and 200 µm and between 400 and 500 µm. The leaching results demonstrate that the protective function was not altered by the effect of the cracks when comparing the reference uncoated specimen to the coated ones. The SEM-EDS observations show the existence of a newly-formed phase in the few hundreds of micrometers from the exposed surface of the coated specimens. This phase was composed mainly of calcium, sulfur and aluminum and was probably a mix of AH3 and ettringite. The formation of this phase near and inside the crack opening could possibly act as a physical barrier that prevents further deterioration.

This study evaluates the structural behavior of two low-carbon self-compacting concretes in comparison to an Ordinary Portland Cement (OPC) concrete, used as a reference: a binary binder S70 (OPC substituted by 70

This paper discusses the performance of calcium sulpho-aluminate (CSA) cement and a Sulphate-Resisting Portland Cement (SRPC) with a fly ash (FA) additive (i.e., a SRPC + FA binder system) in a ‘live’ sewer environment; it deepens the understanding of their deterioration mechanisms by using a laboratory test for simulated sewer conditions. It also studies the role of an iron-based additive (‘Hard-Cem®’, HC) in improving the performance of SRPC + FA concrete under a biogenic acid attack. The performance of 0.4 w/b concrete specimens of the three binders (CSA, SRPC + FA, and SRPC + FA + HC) with calcite aggregates in sewer exposure was assessed by visual observation, measurements of mass and thickness changes, and microstructural analysis for approximately 25 months. The laboratory test, i.e., the Biogenic Acid Concrete (BAC) test, was used to study the deterioration mechanisms of these binders in terms of leaching solution pH and standardised cumulative leached calcium and aluminium. The results indicate that CSA concrete had improved performance in the sewer environment, showing no mass loss and only about one-third of thickness lost in the SRPC + FA concrete over a 25-month exposure period in the sewer environment. The BAC test results complemented the field observations. The iron-based additive in sewer concrete slightly reduced mass loss, likely due to its better resistance to abrasion and erosion, but not due to any chemical influence, since it does not participate in hydration or dissolution reactions. The findings imply that CSA cement may represent a suitable alternative binder for concrete sewer construction. They also suggest that a surface hardener has limited benefits, except when it is under abrasive conditions. Further investigation is required, especially since CSA contains high amounts of sulphate, the effect of which is not well understood.

The carbonation-induced corrosion of steel reinforcement embedded in sodium carbonate alkali-activated slag (AAS) and a CEM III/B reference binder were investigated. The primary objective of this study was to evaluate the influence of both natural and accelerated carbonation (1% CO2) on reinforcement corrosion. Reinforced cylindrical mortars specimens with a low cover (8.5 mm) were cast and subjected to exposure under natural and accelerated carbonation conditions. The initial weights of the rebar were recorded with high precision prior to casting. Throughout one year of exposure, the corrosion potential and linear polarization resistance of the rebars were systematically monitored. Upon completion of the exposure period, the specimens were split to enable visual inspection of corrosion and to determine corrosion-induced mass loss. The applicability of the Stern-Geary equation to carbonated AAS systems was confirmed by comparing the corrosion current densities estimated from this equation (using a B-value of 26 mV) with the values calculated from the actual mass loss of the reinforcement, as determined by Faraday's law. Although accelerated carbonation at 1% CO2 induces differences in pH stabilization and carbonation product formation compared to natural carbonation, it was found to be representative method for quantifying reinforcement corrosion in AAS systems. Overall, AAS exhibited superior resistance to steel reinforcement corrosion compared to CEM III/B reference binder, which was attributed to the more stable and higher pH environment maintained within the AAS matrix.

GGBS composition and the choice of the activation systems have a large impact on the reactivity of GGBS-based binders. Here, the reactivity of 16 artificially-modified GGBSs was investigated in blended cements, alkali-activated binders and supersulfated cements, using isothermal calorimetry for hydration times between 24 h and 120 h. Lower glass network polymerization by addition of CaO or MgO increased the reactivity at all ages and in all activation systems. Increased Al2O3 content mainly resulted in higher early reactivity. This effect was more pronounced in blended and supersulfated cements. TiO2 addition decreased GGBS reactivity in all activation systems but the negative effect was reduced at high Al2O3 contents, especially at later ages in supersulfated cements. In alkali-activation, the hydration was delayed by several hours for some compositions. In summary, the results suggest that it is possible to increase the reactivity of GGBS by choosing an activation system optimized for a given GGBS composition.

This study aims to understand the effect of the natural and accelerated carbonation on the alkali-activated slag (AAS) activated by sodium carbonate. Carbonation increased AAS paste total porosity but reduced slag containing materials (CEM III) porosity. The pH after carbonation was higher in AAS than in CEM III, which was explained by the buffering effect of the alkalis and the carbonation of the hydrotalcite. A higher CO2 percentage promoted the precipitation of nahcolite (NaHCO3) rather than natron (Na2CO3) in AAS, which caused a decrease in the pH after carbonation in accelerated conditions. The decrease in the pH in accelerated conditions could also be due to a more advanced carbonation than in natural conditions.

Calcium aluminate-based materials have shown high resistance to the chemical and biological attack in sewer systems and thus are used to protect Portland cement-based structures and increase their durability. In this direction, a protective calcium aluminate-based coating, designed to be sprayed in a thin layer onto newly built wastewater infrastructures, was developed by Imerys Aluminates. The question arises of the ability of the coating to maintain its protective function when a crack is initiated in the concrete support and possibly propagates into the coating. Several phenomena may develop and condition the behavior of the cracked aluminous coating, including the self-healing of the cementitious material and the penetration of micro-organisms to reach the substrate. To study this coupling of cracking and biodeterioration in the lab, a method for the generation of representative cracks was developed. The three-point bending test was performed on these coated mortars to initiate cracks with a specific opening width, to be maintained after unloading. Then, to understand the mechanisms of biodeterioration, cracked and uncracked specimens were exposed to the BAC test which reproduces biodeterioration conditions observed in sewer environments. The biodeterioration process was monitored in terms of analyses of the composition of the leached solutions to quantify the calcium and aluminum leaching. The superior resistance of the coated substrates was significantly proven. The presence of a crack in the coated substrates has no influence on the leaching species for the specific duration of the test.

The study aims to understand the performance and durability of a sodium carbonate alkali-activated slag (AAS) based on a performance-approach. Equivalent performances were obtained between the AAS and CEM III/C-based concretes having a water/binder ratio of 0.4 regarding compressive strength, porosity, resistance to nitric acid, and sodium sulfate. AAS exhibited higher resistivity and better resistance to chloride, assessed by a chloride migration test. The AAS showed similar carbonation resistance to CEM III/C and CEM III/B concretes with w/b ratios of 0.47 and 0.53, respectively. A discussion of durability tests for their application to this type of binder is conducted.

Many concrete structures in aqueous environments suffer leaching, affecting their microstructure and durability. The resulting chemical and mineralogical degradation are difficult to predict over the long term and for environments of varying chemical composition, especially for severely degraded cement matrices. This is mainly because of the lack of chemical and thermodynamic data on the degraded phases formed during these attacks. In this context, this study aims to evaluate the chemical changes of leached ordinary Portland cement (OPC) paste by combining experimental (batch experiments) and modelling (thermodynamic equilibria calculations) approaches. The ground OPC paste was gradually added to an acetic acid solution. pH and chemical compositions of the solution were monitored throughout the experiment. The solid fraction was characterised over time, with particular attention paid to the phase obtained during the first additions. The latter was found to be an amorphous aluminosilicate gel (Al/Si = 0.3), with major contributions from Si Q4 and AlIV (obtained by 29Si and 27Al NMR analyses respectively). Existing databases (MINTEQ 3.0, Thermoddem, Cemdata) were first used in the thermodynamic simulation of the experiment using PhreeqC, which showed discrepancy with the experiment in the early stages of the attack. They were then improved by the addition of the Si-Al gel identified experimentally. The incorporation of the new phase enabled to better fit the experimental data. The calculated equilibrium constant of the gel at 20 degrees C (log Kgel = 0.37) was consistent with the equilibrium constants of similar Si-Al phases already explored in the literature.

The Al2O3-SiC-C or ASC castables are used in the main runners of blast furnaces. Most of the papers published to date focus on laboratory corrosion tests because access to the post-mortem samples of ASC castables is difficult. However, investigation of post-mortem samples is crucial in reducing the wear of ASC castables. The main runner is divided into the turbulence, middle, and non-turbulence zones. The microstructures of post-mortem samples located in working linings of different zones were investigated by SEM/EDS technique. The thermodynamic simulations were carried out in different systems, such as slag/refractory and iron/refractory, using the FactSage software. The SEM/EDS results showed the formation of phases with low melting points, such as gehlenite and anorthite, together with spinel solid solutions in the matrix and calcium dialuminate near the alumina aggregates. The thermodynamic simulations showed that slag and iron tend to react with alumina and silicon carbide, respectively.

This paper studies the behavior of four different calcined clay-based geopolymers under sulfuric acid attack and gives insights into their degradation mechanisms. Pastes were cast using metakaolin and meta-illite and were activated by two different alkaline solutions. Mineralogical and microscopic characterizations were performed on pastes before and after attack. Results indicated that all pastes were affected by low leaching of alkali cations, and thus by a linkage disequilibrium of the geopolymer network. Meta-illite based geopolymers, which had not been addressed in the literature until now, hold promise for improving the durability of materials in aggressive environments.

Anaerobic digestion, a renewable energy source, is the degradation of organic waste into biogas, mainly composed of CH4 and CO2. The sector is expanding rapidly due to its multiple environmental and economic benefits. This process is implemented industrially in concrete structures that are in direct contact with the biowaste being digested and the gas produced. Both phases can damage concrete through (i) the presence of volatile fatty acids, dissolved CO2, ammonium, and microbial biofilm in the liquid phase, and (ii) high concentrations of CO2 and various concentrations of H2S in the gas phase. In order to develop more sustainable concrete biogas units, long-term, in-situ experiments were carried out in a semi-industrial scale digester to provide new insights into the performance levels and deterioration mechanisms of various low-CO2 binders, including alkali-activated metakaolin (geopolymer), alkali-activated slag (AAS), and supersulfated cements (SSC), in comparison to calcium aluminate cement (CAC) and Portland cement based matrices. In the running conditions explored, carbonation of the cementitious matrices was predominant over other deterioration phenomena in both the digester liquid and the gas phases. Alkali-activated metakaolin and calcium aluminate cement performed better with few degradations observed. Supersulfated cements and alkali-activated slag showed an intermediate behaviour with good performance in the acidic liquid phase but low performance in the CO2-rich gas phase.

The results of phase 1 of an interlaboratory test, coordinated by the RILEM TC 267-TRM “Tests for Reactivity of Supplementary Cementitious Materials” showed that the R3 (rapid, relevant, reliable) test method, by measurement of heat release or bound water, provided the most reliable and relevant determination of the chemical reactivity of supplementary cementitious materials (SCMs), compared to other test methods. The phase 2 work, described in this paper aimed to improve the robustness of the test procedure and to develop precision statements for the consolidated test procedure. The effect of the pre-mixing and mixing conditions, and the impact of the mix design on the test method robustness were assessed and fixed for optimal conditions to carry out the R3 heat release test. The effect of the drying step was evaluated to define the R3 bound water test procedure in more detail. Finally, the robustness of the consolidated final test methods was determined by an interlaboratory study to define the precision statements.

RILEM TC 267 TRM– “Tests for Reactivity of Supplementary Cementitious Materials” recommends the Rapid Reliable Relevant (R 3 ) test as a method for determining the chemical reactivity of supplementary cementitious materials (SCMs) in Portland cement blends. In this paper, the R 3 test was applied to 52 materials from a wide range of conventional and alternative SCMs with the aim to validate such test. An excellent correlation was found between the cumulative heat release and the bound water determined following the R 3 test method. Comparison of the R 3 test results to mortar compressive strength development showed that all conventional SCMs (e.g. blast furnace slag and fly ashes) followed the same trend, with the notable exception of very reactive calcined kaolinitic clays. It is discussed, through an in-depth statistical regression analysis of the R 3 reactivity test results and the 28 days relative compressive strengths, how reactivity threshold values for classification of the chemical reactivity of SCMs could be proposed based on the R 3 test results.

During their service life, geopolymers may be in contact with Portland cementitious materials. As their porosity is open and connected, resaturation by the cementitious pore solution is possible, and may lead to the material destabilization with durability issues. This paper investigates the evolution of a sodium geopolymer after immersion tests in a neutral and basic environment (deionized water, and CEM V pore solution) for 18 months. A chemical equilibrium takes place between the immersion solution and the geopolymer pore solution, leading to a decrease in alkalinity which may destabilize the geopolymer. A leaching of aluminum ions indicates a degradation of the geopolymer by a slow dissolution process. Apart from that, no major change in mineralogy or porosity was evidenced. However, in contact with a CEM V pore solution, part of charge-compensating cations (Na+) were substituted by potassium ions (K+), which should not impact negatively the geopolymer paste.

In situ X-ray Micro-Tomography (XMT) analyses with a pixel size of 0.325 mu m were conducted on slag-based blended cements containing 75% of Ground-Granulated Blast-Furnace Slags (GGBS) and 25% of Ordinary Portland Cement (OPC), with or without CaCl2 acceleration. Results show the identification of the main cementitious phases and the need to perform data repeatability tests in order to allow their quantification. Investigation of the early hydration during the first 31 h of hydration by image subtraction showed (i) the dissolution of OPC/GGBS, (ii) the precipitation of hydrates including C-S-H, (iii) the accelerating effect of CaCl2, and (iv) phase-identification based on their specific grey level.

Various durability tests require a drying step to remove free water without altering the chemistry or microstructure of the materials. However, little is known about the effects of drying on alkali-activated materials (AAMs). This study focusses on the drying stage to assess the behaviour of four alkali-activated binders compared with conventional binders: a metakaolin-based geopolymer, ground granulated blast-furnace slag (GGBS) activated by sodium silicate or by sodium carbonate, and a mixture of metakaolin-GGBS activated by sodium silicate. After a 28-day autogenous cure, mortar and paste samples were dried at temperatures ranging between 20 degrees C and 125 degrees C. Micro-structural damage was observed in metakaolin-based AAMs dried at temperatures above 40 degrees C, but occurred only between 40 and 60 degrees C for GGBS-based AAMs. SEM observations and MIP porosimetry coupled with mineralogical analyses, allowed AAMs drying mechanisms to be better understood, and recommendations to be made for the preconditioning of these materials.