The study explores the mechanical performance and microstructure of alkali-activated pastes based on soda-lime silica glass activated with sodium carbonate (Na2CO3). The effects of glass powder fineness and Na2CO3 content (5, 10, 15, and 25 wt%) on compressive strength were evaluated using paste formulations prepared at a water-to-solid ratio of 0.30. Finer glass particle size enhanced mechanical strength, particularly after one day of curing. Using 5% and 10% Na2CO3 yielded the highest strengths at later stages (28-360 days). Based on XRD, TGA-DTA, and SEM-EDX analyses, a reaction mechanism for glass activation by Na2CO3 is proposed, involving Na2CO3 dissolution, Ca2+ leaching from the glass, and gaylussite formation. The reaction products responsible for strength are silicon- and sodium-rich N-(C)-S-H compounds, explaining compressive strengths of up to 92 MPa for sc+5 and 98 MPa for sc+10 at 180 days.

Recycled glass powder (GP) is a Si-rich, low-carbon supplementary cementitious material (SCM) that can reduce cement demand and carbon emissions. It may also improve the corrosion resistance of cement owing to its intrinsic acid stability and its ability to tailor hydrate chemistry. However, the durability of GP–cement binders under sulfuric acid attack relevant to sewer systems remains insufficiently understood, particularly the coupling between surface corrosion-layer evolution and internal acid-induced degradation. Here, Portland cement binders with 0–50% GP replacement were exposed to sulfuric acid (pH 1.0–1.9) for 75 d. Degradation performance and mechanisms were elucidated by integrating dimensional changes, degradation/infiltration depths, ionic leaching–infiltration, phase assemblage, and microstructural evolution. GP incorporation markedly reduced the apparent expansion by up to 38.4%, primarily attributed to a 31.3%–64.9% reduction in portlandite and the formation of C–(N)–S–H phases with lower Ca/Si ratios in the original binders, which limited leachable Ca2 +. Consequently, the corrosion layers exhibited improved structural integrity, with 10.9%–25.7% less gypsum formation and more continuous silica gel networks. However, the reduction in leachable OH– by 13.8%–51.7% due to the cement dilution and the pozzolanic reaction of GP facilitated deeper acid infiltration and greater Al3+ leaching. Overall, a dual effect of GP–cement binders was found: enhanced surface stability but slightly accelerated internal degradation. A 25% GP replacement provided a better balance, achieving superior sulfuric-acid resistance. These findings provide guidance for designing lower-carbon cementitious materials using upcycled Si-rich waste streams for aggressive service environments.

Since 2024, most electricity production on Réunion Island has been achieved through combustion of biomass, using either imported wood pellets or locally produced bagasse. Their combustion generates two types of ash, depending on the biomass source: Wood Biomass Fly Ash (WBFA) and SugarCane Bagasse Ash (SCBA). Their chemical compositions differ significantly, leading to different potential applications. The composition of SCBA is similar to that of Coal Fly Ash (CFA), with low variability between batches. Therefore, SCBA could be used as an alternative to CFA, as a Supplementary Cementitious Material (SCM) or in composite cements. SCBA also meets most of the requirements of the NF EN 450-1 standard. However, grinding of SCBA appears necessary to achieve mechanical performance required by the standard. In contrast, WBFA exhibits variable chemical composition, mainly due to differences in pellet origin prior to combustion. Nevertheless, WBFA contains significant levels of chloride ions and sulfate, which may act as activators for materials such as GGBS or metakaolin (MK). Although the high unburned carbon content of WBFA increases water demand, their incorporation into GGBS-based binders (SSC or CEM III) or metakaolin-based systems shows promising potential, particularly for improving early strength.

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.

This study demonstrates the synthesis of nanosilica aerogels (NSAs) from waste glass using a CO2-based extraction process. The process was optimized by varying key reaction parameters, including extraction temperature, reaction duration, NaOH concentration, and waste glass fineness. The resulting silicate precursors, which demonstrated high CO2 capture efficiency, were used to prepare NSA particles. The synthesized NSA exhibited an extremely high surface area and porosity; thus, these can be used as a value-added, lightweight, and reactive supplementary cementitious material for producing thermally insulating concrete. The incorporation of NSA accelerated hydration, with nucleation and pozzolanic effects contributing to 21% and 3%, respectively, to the hydration process. The initial hydration acceleration was attributed to the extremely high surface area of NSA, which facilitated the precipitation of hydration products on its surface. At later stages of hydration, the pozzolanic reaction of NSA promoted the formation of calcium silicate hydrate (C-S-H) in the cement matrix. This reaction increased the chain length of the C-S-H gel, resulting in a more robust and interconnected gel network. The densification effect mitigated potential mechanical property losses caused by the porous nature of NSA. Additionally, the porous structure of NSA significantly reduced the matrix density, leading to lower thermal conductivity and improved insulation performance. This study presents a new approach for valorizing recycled glass, promoting CO2 sequestration, and producing high-value aerogels for use as additives in the development of lightweight insulating concrete.

This study reported an ecofriendly inorganic zinc composite coating for protecting marine steel based on alkali-activated technology, which coupled synergistically with the passivated effect of alkali-activated slag (AAS) and the cathodic protection of zinc dust. The coating was directly coated on carbon steel and exposed to simulated seawater to explore its protective properties. The effects of chemical compositions of AAS on the corrosion protection of steel and the chemical durability of the coating were investigated. Results showed that the zinc-based AAS coating had a passivated ability for steel with chemical bonding with steel by forming a C-A-S-H/C-S-H gel-like layer. Furthermore, the AAS coating guaranteed excellent barrier protection owing to its superior durability, and no obvious steel rust deposits were found after long-term exposure to the chloride solution. The concentration of NaOH influenced the protective properties of the passivated film due to the reducing effect of OH groups. The addition of nanosilica in the AAS formed a compacted coating structure, which was beneficial for the long-term passivation process of steel/zinc and improved the cathodic protection efficiency of zinc dust. The loss of alkaline species of the pore solution and degradation of the AAS structure were the main failure mechanisms of the coating during the chloride solution immersion. The optimal coating exhibited 3.8 MPa bonding strength, a cathodic protection period beyond 2800 h (2 times more than organic coating), and negligible degradation of the AAS coating binder. The AAS-based coating exhibited longer corrosion protection and advantages in durability and sustainability. This study provides new insight into designing sustainable anticorrosion coating for protecting steel in harsh marine environments.

This study aims to evaluate the influence of high-volume (50-100 %) and low-volume (5-25 %) replacement of natural sand (NS) by crushed glass sand (CGS) on the fresh, mechanical, and durability properties of fly ash-ground granulated blast furnace slag (GGBS) blended alkali-activated mortar (AAMs). Setting time and flow table tests were conducted to evaluate the fresh properties; compressive and direct tensile strength tests were conducted to evaluate the mechanical properties of different AAMs. The impacts of CGS on the drying shrinkage and the alkali-silica reaction (ASR) were also assessed. Microstructural and molecular bond analyses were conducted to explain the results of the mechanical and durability studies. The flow of fresh AAMs exhibited significant decline (>22 %) for 50 % CGS replacement. The 28-day and 56-day compressive strength of wrapped-cured AAMs decreased by 20 % or more for CGS replacement above 50 %. In ambient-cured AAMs, the detrimental effects of moisture loss and poor interface bonding at high CGS replacement levels led to lower compressive strength at 56 days, compared to 28 days. The direct tensile strength decreased significantly (35 % to 78 %) when CGS replacement was 25 % or higher due to the lack of adherence between the paste and the aggregate. Shrinkage of AAMs reduced with increasing CGS proportion due to lower water absorption and higher angularity of CGS. Although the short-term ASR expansion was low, long-term ASR expansion exceeded allowable limits for high CGS replacement levels. This study suggests that CGS replacement levels can be recommended as a maximum of 50 %.

The major barriers to the widespread adoption of alkali-activated materials by the construction industry include concerns about durability and their exclusion from current standards. The chemical reactions characterizing alkali-activated binder systems differ drastically from the conventional hydration process of Portland cement. Thus, the mechanisms by which concrete achieves potential durability are different between the two types of binders. RILEM Technical Committee (TC) 283-CAM (Chloride transport in Alkali-activated Materials) aimed to address key questions related to chloride transport in alkali-activated binders and concretes, with a view toward drafting recommendations for the appropriate selection and application of testing methods, and this document represents a key output of that TC. The standard ASTM C1202 Rapid Chloride Permeability Test (RCPT) method fails to measure the charge passed through most alkali-activated concretes due to samples overheating when applying the specified 60 V potential difference. A modified RCPT using a 10 V potential difference was used in the interlaboratory testing campaign of TC 283-CAM. The 10 V-RCPT method described in this Recommendation allowed the successful completion of tests for all alkali-activated concretes considered. Various precursors were investigated including fly ash, GGBS, calcined clay and ferronickel slag. 10 V-RCPT results are validated against ASTM C1556 bulk diffusion test results. Performance-based specifications are proposed.

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

Concrete suffers significant performance degradation when exposed to high temperatures. This study explored the beneficial role of waste glass powder (WGP) in mitigating thermal damage and ultra-high performance concrete (UHPC) after elevated temperature exposure. The mechanism was elucidated through the chemical and microstructure changes, the composition of hydrates after exposure to elevated temperatures, and the subsequent re-curing. The presence of WGP significantly enhanced the residual mechanical properties of UHPC due to more wollastonite generation. The WGP also facilitated the recovery of mechanical properties and surface morphology during the post-fire self-healing process. The microstructural results confirmed that the WGP promoted the formation of the wollastonite phase in the thermal-damaged UHPC by reacting with the dehydrated products. Thermodynamic simulations indicated that the incorporation of WGP in UHPC resulted in an increase of liquid phase and its early appearance at high temperatures led to the transformation of gamma-C2S into more stable wollastonite phases. Meanwhile, the activation of unreacted WGP by limewater further generated secondary hydration products to reduce matrix porosity. These hydrates mainly consisted of C-(N)-S-H gels with a low calcium-to-silicon ratio (Ca/Si) and high sodium-to-silicon ratio (Na/Si) ratio, which could effectively fill the micropores and microcracks in UHPC. As a result, the densified microstructure induced by these regenerated C(N)-S-H gels largely contributed to the recovery of the thermally damaged UHPC. The outcome of this study provides a decarbonization solution to address damages of UHPC exposed to fire conditions.

Thermochemical energy storage (TCES) is a method of storing energy by using reversible chemical reactions to absorb and release heat. TCES materials generally possess the highest volumetric energy density and negligible heat losses during cyclic charging/discharging when compared with sensible and latent heat storage materials. The controllable charging/discharging processes in the TCES materials make them suitable for long-term or seasonal thermal energy storage, which can help improve the resilience of the existing energy system and built environment. In recent years, there has been a growing number of studies on the use of cementitious materials as low-cost and low-carbon thermochemical energy storage materials, including ettringite, calcium aluminate cements, and geopolymers. In this study, the state-of-the-art development using cementitious materials for thermo-chemical energy/heat storage applications is reviewed and systematically compared in terms of their compositions, energy storage operating conditions, and energy storage performance. Technical recommendations are proposed for standardised characterisation and testing protocols of these cementitious (composite) materials used for thermochemical heat storage. The current research challenges and future research needs in this field are also discussed.

The aim of this paper is to investigate the effect of natural and accelerated (1

Ultra-high performance concrete (UHPC) would suffer from severe degradation under elevated temperatures, resulting in the structural failure and huge maintenance cost. This study explored the beneficial effect of recycling waste glass powder (WGP) in mitigating thermal damage to UHPC after elevated temperature exposure. The influence of WGP on the macroscopic performance evolution of UHPC after exposure to 400-800 degrees C was revealed through compressive strength tests and surface morphology analysis. The hydration products, pore structure, and microstructure were characterized using Thermogravimetric Analysis (TGA), micro-CT scanning, and Scanning Electron Microscopy (SEM). Finally, numerical simulations were employed to elucidate the advantages of WGP for elevated temperature resistance from the perspectives of temperature field, stress distribution, and displacement. Experimental results indicated that the inclusion of WGP showed little influence on mechanical strength of UHPC, the low heat conductive coefficient of glass material reduced the thermal stress and improved the thermal stability of UHPC. Microstructural characterization verified the significant decomposition of hydration products and coarsening of pore structure in the reference UHPC in comparison with WGP blended UHPC. The surface morphology of thermally damaged UHPC was characterized by fractal dimension to non-destructively reflect the structural state. Moreover, numerical simulation demonstrated that the inclusion of WGP retarded the temperature transmission and changed the internal stress field with little displacement, resulting in a large improvement of thermal damage resistance in UHPC containing WGP with significant environmental benefits.

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.

Supplementary Cementing Materials (SCM) have been used for decades to replace fractions of pure Portland cement in concrete applications. These powdered materials can be from natural or industrial origins, and are usually considered as latent hydraulic or pozzolanic as they can react to improve the mechanical properties and durability of the concrete. Well-known SCMs such as ground granulated blast furnace slag (GGBS), coal fly ash (CFA), silica fumes (SF), metakaolin (MK) and natural pozzolans have been extensively used in industrial applications and numerous studies are reported in the scientific literature. This paper describes their use over time, why they are used and how they work. Finally, it discusses the future of SCMs by giving several examples of SCMs that could be developed in the next years, as well as the methodology to normalize them for secure use in low-CO2 cement and concrete.

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.

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.

Cementitious material with a high ettringite content can be considered effective in a long-term (seasonal) thermochemical energy storage (TCES) system, resolving the issue of intermittency between production and availability of renewable energy. However, to evaluate the behavior of the storage material, an experimental study of energy storage in a thermochemical reactor containing the proposed material was required. A new and innovative large-scale energy storage prototype based on ettringite material has been developed and tested. This prototype regulates the temperature, humidity, flow rate, and pressure of the flow circulating through a 50 L CSA (calcium sulfoaluminate) sample monolith. This CSA cement formed an ettringitic phase (3CaOA & sdot;Al(2)O(3)A & sdot;3CaSO(4) A & sdot;32H(2)O) to store thermochemical energy at about 60 C-degrees. After the storage cycle (high temperature, low relative humidity), the material was cooled down to room temperature and kept there until energy was needed. The stored energy was released on demand by the hydration of cement from a cold, humid nitrogen flow. About 50 MJ/m(3) was discharged from the 50 L monolith during the hydration cycle. The prototype showed the monolith's ability to store and release energy: the first discharge phase experimental test showed an energy release of about 10 % of the theoretical value (43 MJ/m(3)) for a temperature increase of 6 K. Complementary investigations have to be performed to understand the impact of the monolith cracks on the energy performances.

This paper presents an experimental approach to the study of the compressive strength, isothermal calorimetry and life cycle assessment (LCA) of alkali-activated pastes based on soda–lime–silica glass, established to investigate the effect of the nature and proportion of the activator. Four different activators are compared: Portland cement, sodium silicate, sodium carbonate (at four percentages by weight: 5, 10, 15 and 25 wt% relative to glass) and sodium hydroxide (3.5 wt%). Portland cement and sodium carbonate were added in dry form (powder), while sodium hydroxide (pellets) and silicate were used in solution. At room temperature, glass exhibited slow reaction kinetics, with mechanical performance increasing significantly beyond 28 days of curing. The nature of the activator had a direct impact on the mechanical performance of the activated glass. Cement-activated pastes and those containing 25 wt% of sodium carbonate developed strength at an early age (0–7 days). The other activators showed lower strength development before 28 days of reaction. While a higher activator content improved short-term performance, it also increased the environmental impact, primarily due to the activator. The LCA, conducted on 11 indicators, revealed that the environmental impact was largely driven by the type and amount of activator used. A performance impact indicator (PII) related to global warming was introduced to compare pastes with different performance values. At an early age (0–28 days), the PII was lower when the activator level was high but decreased over time as the strength improved. In terms of long-term performance (360 days), hydroxide and sodium carbonate (10 wt%) achieved compressive strengths of 91 and 74 MPa, respectively. These systems offered a balance between high performance and a reduced environmental impact, making them of interest for sustainable applications.

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.