Increased use of supplementary cementitious materials (SCMs) is limited by variability in their compositions and reactivities, since these factors significantly affect concrete properties and durability. Traditional durability testing is time-consuming, making it infeasible to apply widely to emerging SCMs. This paper develops and applies a computational method to screen many blended cements containing coal fly ash and granulated blast furnace slag to identify those that have higher potential to produce high freeze-thaw resistance and low CO2 emissions concrete, varying SCM chemical composition, reactivity, and replacement levels. This is achieved using the Panoramix algorithm, which integrates thermodynamic modelling, random sampling, grid search algorithm, a freeze-thaw prediction model, and life cycle assessment (LCA) to probabilistically explore the design space, thereby rigorously accounting for uncertainties in raw material properties. A novel SCM reactivity database is developed and used here, enabling application of Panoramix to blended cement concretes. The modelling results show that at constant air content (4%), increasing the replacement levels of coal fly ash and granulated blast furnace slag decrease the mean value of the freeze-thaw resistance indicator but increase its variance, due to their broader chemical composition ranges than Portland clinker. At constant air void system quality and content, higher values of the freeze-thaw resistance indicator are calculated at increased SCM reactivity levels, and reduced climate change impacts are calculated at increased SCM substitution levels. The results indicate that a balance between higher freeze-thaw resistance and lower CO2 emissions can be approached using high reactivity SCMs and low clinker-to-cement ratios. The methodology used here facilitates multi-objective concrete selection considering environmental impacts and durability performance.
Amorphous precipitated silica (APS) derived from olivine has potential to be used as a pozzolanic supplementary cementitious material, but high specific surface area reduces mix workability, accelerates sulphate depletion and decreases early age strength. This study investigates the feasibility of blending Portland cement with APS, limestone and gypsum to address these issues. Quaternary binders containing 5 - 20 wt.% limestone and 2 wt.% gypsum were prepared at CEM I: APS mass ratio of 8:2. Results show that limestone improves workability and early hydration reactions, while gypsum stabilises sulphate availability and promotes strength development. Mortars with a binder system containing 10 wt.% limestone with 2 wt.% gypsum show comparable workability and strength to control mortars. The research demonstrates that olivine-derived APS can be combined with limestone and gypsum to form a viable low-carbon cement with reduced clinker content.
Ladle furnace (LF) slag, a by-product of the steelmaking industry, is rich in calcium and silicate phases, compatible with those present in Portland cement (PC); however, its potential suitability as a supplementary cementitious material is largely unknown. In this study, blended Portland mixes containing LF slag in different quantities were produced and evaluated. The partial replacement of PC by LF slag did not impact the workability of the mixes at the replacement levels evaluated. At higher replacement levels, prolonged setting times were identified, consistent with the low hydraulic and limited pozzolanic reactivity of this material. The compressive strength determined in mortars revealed that increasing LF slag content in the mix led to reductions in strength. Changes in the pore-size distribution of the assessed mixes were also detected, particularly in coarser capillary pores, which are responsible for higher mass transport and provide potential routes for ingress of liquids and gases into these binders. These findings provide insight into the limitations and potential strategies for enhancing the performance of LF slag as a partial PC replacement.
The analysis of cementitious pore solutions provides valuable insights into the chemical properties of the cement clinker phases during cement hydration. Accordingly, the pore solution chemistry of Portland cement has been extensively studied. However, the first pore solution samples are usually obtained after a few minutes of hydration time. Therefore, pore solution data often lacks data points in the first seconds and minutes of hydration. During this initial stage, ettringite forms as the first nanostructured hydrate phase, creating new surfaces and decreasing the water-to-solid ratio, thereby influencing the rheology of fresh cementitious materials. A method to sample the pore solution during this stage with a large sampling frequency has been missing. This study demonstrates the application of dynamic crossflow filtration for obtaining early cementitious pore solutions at a high time resolution and to investigate their chemical composition under varying conditions. We systematically vary the water-to-cement ratio, temperature, and cement chemistry, and analyze the temporal evolution of ion concentrations using ICP-OES. The earliest pore solution sampling is feasible at 15 s after the start of hydration for high water-to-cement ratios. The results show that increasing the water-to-cement ratio reduces ion concentrations, particularly affecting calcium sulfate nucleation, while lower temperatures slow down cement dissolution and hydration product formation. Additionally, our findings confirm that the filter pore size (200 nm vs. 400 nm) does not impact determined ion concentrations, validating the exclusion of nanoparticles from the filtrate. The new method of ultrafast pore solution sampling at very early times of hydration is expected to be particularly helpful for hydration studies of the aluminate phase of Portland cement.
Evidence indicates that injected CO2 is mineralized over time by mafic and ultramafic minerals in basaltic formations. Accelerated carbonation of basaltic fines derived from quarry residues and similar materials is a promising approach to reducing CO2 emissions in the concrete industry. This study explores CO2 mineralization in basaltic fines and magnesium-rich olivine powders. Raw, mechanochemically (MCA), and thermally activated (TA) samples were carbonated under mild conditions. Aside from olivine, where TA did not enhance reactivity because its melting point exceeded the activation temperature, both MCA and TA increased the reactivity of the other samples significanty, turning them into reactive SCMs. All samples captured less than 1% CO2, except for the mechanochemically activated olivine, which achieved approximately 5.2% CO2 uptake.
Triisopropanolamine (TIPA) is an organic ethanolamine commonly used to neutralize the clinker surface charges during grinding and foster the cement hydration kinetics and formation of hydrated products. This paper assesses the efficiency of incorporating TIPA to control the loss in strength in concrete mixtures containing used engine oils (UEOs). An oil-based defoamer was systematically used in this work to control air entrainment in freshly mixed concrete. Regardless of the cement content and water-to-cement ratio, the use of TIPA proved efficient to compensate the negative influence of UEOs on the concrete mechanical strengths and durability properties. Hence, for example, the incorporation of 0.7% UEO required about 0.08% TIPA to restore the concrete properties, while the use of 0.9% UEO required about 0.12% TIPA. Such data can be of interest to concrete practitioners and municipalities for circular economy and appropriate valorization of UEOs in the construction industry.
Free-CaO represents a reactive component that is not fully incorporated into the clinker matrix, and it can also form or equilibrate with Ca-bearing clinker phases. Conventional wet-chemical methods often lack the selectivity required to distinguish free-CaO from other calcium-bearing phases (Ca(OH)2, C3S, (3-C2S, C3A, C4AF). In this study, ethylene glycol is evaluated as an extractant for calcium phases in Portland cement clinker (PCC). Wet extraction experiments confirmed high CaO recovery regardless of concentration, whereas Ca(OH)2 showed lower and content-dependent recovery. When applied to PCC with different particle sizes, ethylene glycol treatment revealed particle-size-dependent dissolution trends: coarse and fine particles showed preferential extraction of Ca-Si phases, whereas fine particles exhibited noticeable changes primarily in calcium-aluminate domains, indicating that C3A may be particularly susceptible to interaction with ethylene glycol. This investigation supports the use of ethylene glycol as an optimal extraction solvent for assessing reactive calcium in cementitious materials and the effects of mineral phases must still be carefully through combined analysis of wetchemical and XRD patterns.
There are increasing concerns on both sustainability of natural resources and the management of industrial residues. This study investigates the potential for recycling calcite rich residue from a vanadium recovery process, as a raw material in Portland cement. This type of residue has limited information as feedstock material in cement production. The produced clinkers were characterized by several techniques including X-Ray diffraction with Rietveld refinement, X-Ray fluorescence, isothermal calorimetry, and scanning electron microscopy. The results showed that up to 11 wt.% of the new residue can be incorporated in the clinker raw mix, accounting for a 9 wt.% limestone substitution in the reference clinker, without a significant change in cement composition and properties. Both clinkers were mainly made of alite, belite, aluminate and ferrite/brownmillerite, alite being the major phase at 46%, followed by belite at 17%, in the stream-based clinker. Thermal and microstructural analyses of 28-day hydrated cements showed the presence of approximately 20% portlandite, along with a substantial amount of C-S-H gel and remnants of unreacted belite. The leaching of V and Cr in the prepared mortar based on residue was negligible, considering the recommended safe limit by the World Health Organization for wastewater and soil, indicating the potential safe recycling of the side stream in clinker for reduced limestone consumption and sustainability of the cement industry.
This study illustrates the strength development models for recycled aggregate concrete (RAC) exposed to different curing regimes. Additionally, the present study examines the curing sensitivity, and the minimum curing period required to develop specified strength and durability for RAC composed of high-quality recycled concrete aggregate (RCA). RAC is observed to be lower curing sensitive than natural aggregate concrete (NAC). RAC with ordinary Portland cement (OPC) and RAC with Portland pozzolana cement (PPC) are approximately equal in curing sensitivity. RAC durability is significantly impacted by water curing on the first day. First-day water curing reduces RAC (OPC) and RAC (PPC) sorptivity by 42.85 % and 45.54 %, respectively. Moisture loss, especially within three days of casting, affects RAC strength over time. Contrary to the stipulated minimum curing period (7 days-10 days) for NAC to achieve 70 % of the specified compressive strength, RAC (OPC) and RAC (PPC) require a minimum curing period of only 2.32 days and 1.62 days, respectively, to achieve 80 % of the specified compressive strength. Following curing, RAC develops structural integrity and internal compactness in one to three days. In terms of internal compactness and uniformity, RACs cured for more than three days have no significant impact. It is possible to consider the initial curing of RAC for 7 days as the maximum curing period since it can develop 100 % of its compressive strength within 90 days to 100 days. RAC (OPC) cured for more than two days, and RAC (PPC) cured for more than one day may meet the requirements of chloride-ion penetration <1000 Coulombs and electrical resistivity of >208 Ohm-m.
The Damage Rating Index (DRI) method is increasingly used to assess the damage degree of concrete affected by alkali-silica reaction, although it has been criticized for its time-consuming character. This paper presents an optimized approach on how the method can be performed to provide a reliable estimate of the DRI number. A thorough sampling and statistical analysis was performed at the scale of 1 cm2 squares on 56 cores extracted from various structures, with a wide range of concrete mixtures and deterioration levels. The inherent variability between cores extracted in a "restricted" area of +/- 1 m2 was also investigated in seven locations. The average 90% confidence prediction DRI number range between cores extracted in a "restricted" area reached 263, but such variability was location dependent. The best sampling approach for DRI determination over the whole core is to divide the specimen in the form of lines, which are test units composed of squares that are oriented parallel to one another in the direction of the core's longitudinal axis. It was found that there is no minimum examination surface area for DRI determination, because there is usually internal damage variations within the investigated components and the inherent precision level is influenced by the damage degree. A representative number of lines should be targeted instead. An empirical model was developed to predict conservative estimates of the required number of lines to achieve a margin of error of +/- 150, 200, 250 and 300, based on the core's length and DRI number.
Although eco-efficient mixtures proportioned through a coupled particle packing models (PPMs)-mobility parameters (MP) approach demonstrated suitable performance in the fresh and short-term hardened state, further studies are still required to assess their durability and long-term aspects. This work evaluates the performance of four eco-efficient mixtures proportioned with varying cement contents i.e., (325, 250, 200, and 150 kg/m3) against one of the leading causes of premature deterioration of concrete infrastructure worldwide: alkali-silica reaction (ASR). Specimens from the above mixtures along with a control mixture containing 420 kg/m3 were manufactured incorporating two distinct types of highly reactive aggregates (Springhill coarse aggregate and Texas sand) and stored in conditions enabling ASR-induced development (38 degrees C and 100% R.H.); the specimens were monitored over time and microscopic analysis was performed to better understand ASR-induced deterioration in these low-alkali mixtures. The results show that besides being sustainable and displaying suitable performance in the fresh and hardened states, eco-efficient low alkali mixtures proportioned with PPM-MP present reduced ASR-expansion.
The long-term stability of wellbore sealants is crucial for the success of oil and gas operations. This study evaluates the performance of a low-calcium, granite-based two-part geopolymer (GP) system under hydrogen sulfide (H2S)-rich brine exposure. GP samples were immersed in H2S-saturated seawater at 100 °C and 11 bar for up to 12 months. Their mechanical, mineralogical, and microstructural integrity was assessed using unconfined compressive strength (UCS) testing, computed tomography (CT) scanning, X-ray diffraction (XRD), scanning electron microscopy with energy-dispersive spectroscopy (SEM-EDS), and Fourier-transform infrared spectroscopy (FTIR). Results showed a progressive increase in UCS and Young’s modulus during exposure, coinciding with changes in mass, density, and microstructural features. CT scanning revealed surface-localized density reduction and preserved interior structure, highlighting spatial zonation rather than temporal densification. XRD analysis indicated increased relative crystallinity in H2S-exposed samples compared to the initial cured state, while SEM-EDS revealed elemental redistribution and an increase in bulk sulfur content with exposure time, although no crystalline sulfur-bearing phases were detected within the resolution of XRD. The chemical form and binding state of sulfur could not be resolved with the applied techniques. Overall, the results indicate that the low-calcium, granite-based GP can retain mechanical integrity under prolonged H2S-rich brine exposure, with degradation largely confined to surface regions, suggesting its potential as an alternative wellbore sealant in sour environments while recognizing that further studies with chemically equivalent controls are required to fully resolve underlying mechanisms.
The long-term integrity of wellbore sealants is critical for successful CO2 storage in geological reservoirs. This paper addresses the durability of a one-part, granite-based geopolymer (GP) sealant batch-exposed to CO2 and H2O, with or without H2S or H2SO4 for up to 16 weeks. Microstructural and mineralogical changes were then characterized using a wide range of analytical techniques. Results show that exposure led to an increase in the material’s crystalline content. Vaterite was the dominant early carbonate in all cases. This then transformed primarily into aragonite in samples exposed to clean CO2, while calcite was more prominent in samples exposed to CO2 with H2S or H2SO4. The matrix's crystallinity was further enhanced through consecutive reactions of aluminosilicate gels. Even though exposure resulted in elevated sulfur contents, no sulfur-bearing minerals were detected. Despite these alterations, the GP maintained its integrity during exposure to chemically aggressive conditions, demonstrating its durability as a sealant.
Carbonation lowers the pH, leading to decalcification, shrinkage, and densification of the pore structure. Recalcification, the process of reintroducing calcium ions into decalcified cementitious materials, is a promising approach for restoring carbonated cement pastes. However, its impact on carbonated cementitious materials remains unelucidated. This study demonstrates, for the first time, how recalcification not only restores the Ca/Si ratio of calcium–(aluminum)-silicate-hydrate (C–(A)-S-H) to levels comparable with intact gel but also fundamentally alters its nanostructure. Using solid-state ²⁹Si NMR, we show that recalcification turned silica gel into cross-linked Q3(1Al) sites, introducing small capillary pores and reducing the surface area. The extent of microstructural changes depended on the initial degree of carbonation. Importantly, 29Si NMR suggested that recalcification is a diffusion-controlled process, similar to calcium leaching and carbonation. These findings highlight the potential of recalcification to restore the binding phase and improve the durability of carbonated cement pastes, with implications for the development of targeted repair techniques in the construction industry.
Amorphous precipitated silica (APS) produced by acid leaching of olivine has been characterised and assessed for use as a supplementary cementitious material (SCM). The APS was thermally treated between 400 and 1000°C to modify its pore structure, surface area, composition and reactivity. Pastes and mortars containing APS were cast with CEM I replacement levels from 0 to 30 wt.% and water-to-binder ratio of 0.5. TGA-MS, Q-XRD, FTIR and R3 tests show that APS has moderate to high pozzolanic reactivity. Mortars with 10 wt.% as-produced APS showed 30% increase in 28-day compressive strength compared to the control (50 MPa). Mortars with 20 wt.% replacement had comparable strengths to the control. Thermal treatment moderately reduced APS specific surface area and water demand, and improved mix workability, with mortars retaining comparable strengths to samples containing as-produced APS. The research demonstrates that silica derived from olivine has potential to be used as an SCM.
X-ray computed tomography (XCT) provides unique opportunities to investigate steel corrosion in reinforced concrete, the primary degradation mechanism compromising infrastructure durability and safety. Its non-destructive nature, combined with high-resolution three-dimensional imaging and time-lapse capabilities, allows for detailed insights into corrosion processes without altering the specimen. However, applying XCT to reinforced concrete remains challenging due to recurring methodological issues, such as selecting appropriate tube voltage and current, defining pre-filtering combinations, mitigating imaging artefacts, and balancing image resolution with sufficient X-ray transmission. These challenges are particularly pronounced when imaging systems with components of widely differing X-ray attenuation, such as steel, concrete, air, and water.This paper proposes a systematic guideline for designing XCT acquisitions tailored to the study of corrosion in reinforced concrete specimens, integrating theoretical considerations with practical examples. The guideline is supported by dedicated charts and design criteria, which guide researchers in selecting acquisition parameters, specimen configurations, and imaging strategies to achieve high-quality and reproducible results. This approach is built upon a critical review of previous studies, highlighting past limitations and identifying future research opportunities for the application of XCT to study corrosion in steel-concrete systems.By providing a coherent framework for experimental design, this paper allows researchers to fully exploit the potential of XCT for studying in-situ steel corrosion and to advance understanding of reinforced concrete degradation, thereby addressing an important challenge in engineering.
Cement is a critical construction material globally and particularly in Ethiopia, where its production is energy-intensive, costly, and a major source of greenhouse gas emissions. This study explores the partial replacement of Portland cement with volcanic ash and crushed laterite powder in cement mortar as a sustainable and cost-effective alternative. Preliminary mix designs were prepared with varying proportions of volcanic ash and laterite powder to determine optimal combinations which is equal percentage of volcanic ash and laterite powder as selected based the compressive strength result. Subsequent experimental mixes replaced cement with equal proportion of volcanic ash and laterite soil at 0%, 5%, 10%, 15%, 20%, 25%, and 30% by weight, following ASTM C109 standards. The study assessed characterization, mechanical (compressive strength and ultrasonic pulse velocity), durability (sulfate resistance, porosity, and water absorption), and microstructural properties using Fourier transform infrared (FT-IR), thermogravimetric analysis (TGA), and differential thermal analysis (DTA) analyses. Characterization results showed that volcanic ash and crushed laterite are finer than cement and are predominantly pozzolanic. Bernauer-Emmett-Teller (BET) analysis confirmed their fine particle sizes, contributing to the dense packing of the mortar. At 10% of replacement of cement by equal amount of volcanic ash and laterite soil, the highest compressive strength was recorded 33.1 MPa at 28 days and 46.2 MPa at 56 days. Water absorption decreased with increasing the replacement percentage up to 15%, indicating improved durability. Microstructural analysis revealed a denser morphology due to secondary C-S-H formation and filler effects. Overall, volcanic ash and laterite powder improved both mechanical and durability properties of mortar up to 15% replacement, with optimal performance at 10%. This shows the potential of those pozzolanic as a viable partial cement substitute, promoting sustainable construction practices in Ethiopia.
Numerous characterization techniques have been used to assess ASR-induced development (i.e., the formation of ASR products and cracks during expansion). Amongst those, scanning electron microscopy (SEM), coupled with energy dispersive X-ray spectroscopy (EDS), is a well-recognized technique enabling assessing the presence, morphology, and composition of ASR products. However, the correlation between ASR products' amounts and physicochemical features with induced damage (i.e., crack formation and impact on the mechanical performance of the affected concrete) via SEM is purely qualitative. Preliminary results showed that resonant ultrasound spectroscopy (RUS) could be a suitable technique to evaluate ASR-induced damage because it allows assessing the corresponding changes in the linear viscoelastic properties. Nonetheless, a systematic study fully demonstrating its potential to appraise ASR-induced expansion and deterioration, especially from ASR originating both from natural and from recycled aggregates, is still lacking in literature. This work aims to quantitatively appraise ASR-induced products and associated deterioration by the coupling of SEM-EDS and RUS, particularly a version thereof called SIngle MOde RUS (SIMORUS). Concrete mixtures incorporating highly reactive natural and recycled fine and coarse aggregates were cast and stored in conditions accelerating ASR development. At 4, 11, 16, 24 and 36 weeks, the samples were characterized by the abovementioned techniques. Quantifications of ASR-induced damage proxy parameters (i.e., Young’s, E, and shear, G, moduli), and the respective quality (Q-)factor, were performed over time. The results reported here suggest that SIMORUS is a promising technique to describe the impact of the ASR-induced development on the linear viscoelastic properties of an affected concrete. However, as shown, such an impact depends on the reactive aggregate type used in the mixture.
In technical mortars and refractory concrete, the reactivity of calcium aluminate cement (CAC) is typically controlled by retarders and accelerators. This study examines the retarding impact of five strong acids (HCl, HNO3, HClO4, H2SO4, and H3PO4) on CAC hydration (1) in dilute suspensions at a water-to-solid (w/s) ratio of 100, and (2) in pastes at a w/s of 0.3. Doing so, we identified several factors that affect the dissolution and hydration of CAC. In dilute suspensions, in-situ monitoring of the pH and conductivity reveals that the acids delay the initial dissolution of monocalcium aluminate (CA). The inhibition time depends exponentially on the proton concentration, and linearly on the available CA surface area, which is partially explained by the preferential formation of Al(OH)3 suggested by thermodynamic modeling. Notably, the acids’ efficiency varies at equimolar proton dosages. For H3PO4, we explain the outstanding inhibition efficiency by the joint formation of hydroxylapatite and Al(OH)3. For the other acids, the dissolution inhibition power follows an anion-specific sequence sulfate > chloride > nitrate > perchlorate, which aligns with the Hofmeister series and suggests a stabilization of calcium ion solvation by the anion. Isothermal calorimetry experiments performed on pastes show that the retardation order of these acids (H3PO4 > HClO4 > HNO3 > H2SO4 > HCl) differs from that observed at w/s of 100. Phosphoric acid still displays exceptional retardation properties suggesting a unique mechanism of action most likely related to early hydroxylapatite and Al(OH)3 formation. For the other acids, Al(OH)3 and anion-containing AFm phases formation may explain the differences in retardation maximum.
Clarifying the dissolution behaviour and mechanism of fly ash in acid activators is essential to understand the properties of fly ash-based silico-aluminophosphate geopolymer. This paper investigated the in-situ dissolution behaviour of fly ash (FA) in aluminium dihydrogen phosphate (MAP), phosphoric acid (PA), citric acid (CA), oxalic acid (OA), and tartaric acid (TA) using optical microscopy and electron probe microscopic analysis (EPMA). The phase and elemental changes before and after dissolution were further investigated using quantitative X-ray Diffraction (QXRD) and 2D-Fourier transform infrared (FTIR) spectrometry. In addition, the changes in dissolved elements were elucidated from a liquid phase perspective. The results showed that the capacity of each acid to dissolve FA was CA>MAP>PA>TA>OA. Ca-containing phases in FA were preferentially dissolved in all acids. The main contributor to FA dissolution in acid was the amorphous phase, and the SiOSi bond in quartz was more sensitive than other chemical bonds to acid. When FA was dissolved in OA and TA, new crystalline phases—calcium oxalate and calcium citrate—formed on the FA surface, inhibiting further dissolution.
