Cement Chemistry Research Articles

Influence of the basalt fibre and fly ash on the structural properties of sustainable high-strength concrete

Abstract The present article describes the experimental research carried out to investigate the properties of concrete containing basalt fibre reinforcement and concrete containing basalt fibres and fly ash additives. Each test was done as per Indian standards (IS-516). The experiments sought to establish both fresh and hardened concrete properties. In respect of new concrete, slump, setting time, bleeding, temperature, and density were estimated to check its quality. Compressive, flexural and split tensile strength are the three main parameters for assessing those qualities in a solidified state. It was determined that the utilization of fly ash with 20%, 30% or 40% proportions of cement involved resulted in a stronger concrete mixture. To these samples, different contents of basalt fibres 0.25%, 0.5%, and 0.75% by volume were added respectively. Standard samples were cast, cured and tested accordingly. Thus, the studies show that it is possible to mix concrete with basalt fibres without any segregation or balling effect on it or even sticking together during the mixing processes. Modestly increased splitting tensile and bending strengths have been obtained due to the introduction of basalt fibres on this composite material using which improved workability can be achieved more rapidly than conventional hydration reactions based solely upon Portland Cement chemistry, moreover, thermal stability has also been considerably enhanced, besides that even basic physical-chemical properties should be very much similar to those of ordinary Portland cement. Based materials thus ensuring better compatibility during processing from raw constituents towards final composites up-to-date with known technological aspects related specifically towards production practices carried out in developing countries like India. Such situations usually result primarily due to poor engineering control exercised over construction activities. Resulting problems areas namely joint locations limited access space between steel reinforcement bars inside walls. So often appearing weak points in overall design yield inadequate structural performance compared to intended specifications. Another reason why sustainable building methods cannot be fully adopted has been found that they lack proper skilled manpower despite having all necessary resources that are easily renewable. By compared with traditional ones made up of non-renewable sources such as fossil fuels. However, fly ash used in place of concrete only makes it harder without improving workability and strength at the optimum percentage.

Utilization of incense stick ash as a supplementary cementitious material: Effects on strength, cement chemistry, and sustainability

Incense stick ash (ISA), a by-product generated from the combustion of biomass during religious rituals, presents challenges regarding its high-volume disposal despite some emerging technologies offering avenues for its reuse. This study aims to investigate the feasibility of utilizing ISA as a supplementary cementitious material and its impact on fresh and hardened properties, hydration kinetics, microstructure, and environmental and economic aspects of Portland cement (PC) pastes. Results reveal that incorporating 5–20 % ISA increases the cumulative heat release per gram of PC. Specifically, replacing 5 % of PC with ISA enhances the 28-day compressive strength, with an increase of 19.78 % compared to plain cement paste. However, further elevation in ISA substitution leads to a decline in compressive strength. The utilization of 5 % ISA refines the pore structure of samples and elevates the content of calcium silicate hydrate (C-S-H), particularly the proportion of high-density C-S-H. Additionally, carbonates present in ISA react with AFm to form monocarbon calcium aluminate, which stabilizes AFt and enhances the microstructural compactness of cement paste. Compared to plain cement paste, the paste with 5 % ISA exhibits lower coefficients for the cost of pastes per cubic meter, CO2 emission of pastes per cubic meter, and non-renewable energy consumption, underscoring the effective utilization of ISA and its role in promoting sustainability. This study will facilitate the application of ISA in cement-based materials and provide technical guidance for subsequent research.

Multi-step nucleation of C-S-H: DFT simulation on silicate oligomerization and Si(Qn) evolution dynamics

Understanding the nucleation processes of calcium-silicate-hydrate (C-S-H) is fundamental to advancing the performance of cement. This study employs Density Functional Theory (DFT) to reveal the initial stages of C-S-H formation by focusing on silicate oligomerization. It examines the progression from monomer silicate species to the precursor formation, containing a range of silicate tetrahedra. Through DFT simulations, free energy changes and barriers of oligomerization reactions up to pentamers are obtained, unveiling an anionic condensation mechanism that establishes the kinetic and thermodynamic profile of this transformation. Observations reveal a dynamic evolution of Si species, with Si(Q3) indicating a transient presence, suggesting an intricate pathway towards the well-established silicate chain structure of C-S-H. This study provides detailed computational insight into the energy barriers, reaction pathways, and the thermodynamics of C-S-H formation, contributing substantial knowledge to the field of cement chemistry and its multi-step nucleation theory.

Molecular dynamics simulation of hydrocalumite as adsorbent for anionic radionuclides

Hydrocalumite, is a hydration product of aluminum-rich cements, and is known in cement chemistry as an AFm phase. Structurally, it belongs to the family of layered double hydroxides, or “anionic clays”, where positively charged crystal layers require the presence of negatively charged ions in the interlayer space. Therefore, AFm phases can serve as potential adsorbents for anionic radionuclides (e.g., 35Cl−, 125I−, 129I−, 131I−) from aqueous solutions. Here we use classical molecular dynamic simulations to analyze the structure and properties of AFm phases containing Cl− and I−. The classical ClayFF force field is used to quantitatively study the structure, energetics and mobility of anions and H2O molecules in the interlayers of these phases and at their interfaces with CsCl and CsI aqueous solutions. In this study we report that the basal (001) surfaces of AFm phases can strongly adsorb hydrated Cl− and I− anions due to the donated hydrogen bonds from the interfacial hydroxyls, but primarily due to their strong attraction to the structural Ca cations exposed at the surface. However, our simulations show that the adsorption of I− is weaker than that of Cl−, leading to the higher surface mobility of I− due to its stronger chaotropic effect. The interlayer diffusional mobility of the Cl− and I− anions in the AFm phases is also investigated by using the Eyring-Vineyard approach and is shown to be significantly lower than in larger nanopores. Hence, the most likely transport of such anionic radionuclides takes place through the nano- and micro-pores of hardened cement.

Geopolymer Implemented in Primary Casing Cementing

_ This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper OTC 32218, “First Global Implementation of Geopolymer in Primary Casing Cementing,” by Mark Meade, SPE, Yeukayi Nenjerama, SPE, and Chris Parton, SPE, SLB, et al. The paper has not been peer reviewed. Copyright 2023 Offshore Technology Conference. _ Portland cements are integral components in the oilfield well-construction process; however, the confluence of various business drivers have created the need to find sustainable alternative materials. The complete paper presents the evaluation of geopolymer cementing for use in oil and gas wells, specifically the primary cementing of liner strings in the Permian Basin. Geopolymer cementing offers a unique opportunity for the oilfield industry to decrease CO2 emissions related to well construction and reduce dependence on the constrained supply of Portland cements. Introduction Manufacturing Portland cement emits approximately 1 ton of CO2 for every ton of cement produced. Additionally, the manufacturing of Portland cement is a complex process requiring specialized equipment. Thus, during spikes in demand of Portland cement, the supply of cement cannot be rapidly increased to meet demand. Geopolymers are slurries that set to become a hard, durable solid that can withstand stresses and strains and are resistant to corrosion. Moreover, geopolymers can be made from a broad range of aluminosilicate raw materials sourced from waste products from other industries, mined materials, and biowaste. The low manufacturing and processing requirements reduce the carbon footprint of geopolymers to a fraction of that of manufacturing Portland cement. Whereas Portland cement chemistry is driven by hydration of calcium aluminates and calcium silicates, geopolymer chemistry is based on the polymerization of aluminosilicates initiated by activators. The creation of geopolymers starts with dissolution of the aluminosilicate raw material into monomers by an increase in the pH of the fluid from the activator. Then, the activator provides a site for covalently bonded chains to form, and these chains undergo polycondensation to form the set 3D network of polymers. Implementation of this new material with such a different chemistry into the complex oilfield-construction process presents challenges that must be overcome. Challenges Existing geopolymer formulations typically are characterized as either two-step or one-step geopolymers. In two-step geopolymers, the activators are added into the mix fluid, whereas, in one-step geopolymers, the activators are dry blended with the aluminosilicate source. Implementation of two-step geopolymers would come with operational and logistical constraints impairing their scalability, along with increased service quality and health, safety, and environmental (HSE) risks. On the other hand, common existing one-step geopolymers are formulated with activator types that dissolve rapidly and disperse in the slurry. Therefore, development of novel chemistries for one-step geopolymers are required to introduce geopolymers into oilfield well construction. Such applications expose geopolymers to temperatures and pressures significantly above ambient for extended periods of time during slurry placement within the wellbore. To ensure quality assurance of job placement, hydraulic simulators should be reliable predictors of the top of the placement, and geopolymers set within the wellbore must be detectable using established sonic logging tools.

Whole-life carbon emissions of concrete mixtures considering maximum CO2 sequestration via carbonation

A comparison of cradle-to-gate embodied carbon emissions and carbon dioxide (CO2) sequestration potential due to carbonation of portland cement (PC), portland limestone cement (PLC), and limestone calcined clay cement (LC3) concrete mixtures is presented in this work. First, the cradle-to-gate embodied carbon emissions of the concrete mixtures were calculated using life cycle assessment (LCA). Then, the CO2 sequestration potential of each mixture was computed using a theoretical model for CO2 sequestration that was derived using principles of cement chemistry to account for the carbonation of both calcium hydroxide (CH) and calcium silicate hydrate (C-S-H). The results indicate that a theoretical maximum of 33 % of the cradle-to-gate embodied carbon emissions of the concrete mixtures analyzed herein can be realistically sequestered via carbonation. Data also substantiate that concrete mixtures with higher cradle-to-gate embodied carbon emissions sequester the most CO2. However, concrete mixtures with lower cradle-to-gate embodied carbon emissions, namely PLC and Type I, II, III, IV, and V mixtures with high-SCM replacements, typically yield the lowest whole-life carbon emissions. The results indicate that concrete mixtures with high SCM replacement should be prioritized—regardless of which cement is used to produce the concrete—from a whole-life carbon emissions perspective.

Classical and new insights into the methodology for characterizing the hydration of calcium aluminate cements

Calcium aluminate cements [CACs] are typically used for cast-in-place structural work and high temperature applications due to their unique properties. The CaAl2O4 [CA] and Sm-doped CaAl2O4 [CA:Sm] cement clinkers obtained by the solid-state reaction were investigated using X-ray powder diffraction [XRD], scanning electron microscopy [SEM] and energy dispersive X-ray spectroscopy [EDS] and luminescence spectroscopy. The XRD result shows that the powders are pure CaAl2O4. As a next step, hydration behavior of as-synthesized cements was investigated by both classical methods including isothermal calorimetry and XRD, and the state-of-the-art techniques including time resolved electrochemical impedance spectroscopy [TR-EIS] and luminescence spectroscopy. The TR-EIS investigations were obtained by the Impedance Camera over the range of 100 Hz to 1 MHz frequencies. The evolution of obtained EIS and luminescence spectra easily manifested the beginning of the new solid formation and the hydration kinetics. The dynamics of hydration processes were also successfully traced by the changes of the luminescence intensity from the Sm3+ ions. This technique seems to be complementary, and consistent with other methods implemented in the cement chemistry, especially to investigate e.g. hydration of ordinary Portland cements [OPCs] and other binders.

Processing of earth-based materials: current situation and challenges ahead

With the overall aim of supporting the development of new construction techniques and materials that are more economical and less carbon intensive, RILEM has decided to launch three new technical committees on earth construction in 2022. One of these committees will focus on the manufacturing processes used in earth construction (TC PEM). The aim of this committee is to bring together experts from several disciplines (materials science, earth construction, rheology, geotechnics, cement chemistry, etc.) to advance earth construction techniques by sharing and promoting good practice. The processing of earth is today based on solid empirical knowledge which fails to convince structural design engineers. As a result, earth construction is still limited to small buildings. To upscale the use of earthen material in construction, it is required to provide a solid scientific background that can be used for the writing of standards and recommendations to guarantee minimal performances in service. Areas of work include improving understanding of the mechanical behaviour of the material in the fresh state, developing characterization methods, monitoring the material during curing, and studying new construction techniques, particularly digital ones. The work of the technical committee PEM “Processing of earth-based materials” is expected to gather the scientific knowledge that can be further used for the writing of construction and design codes for earthen materials.

Effect of sulfidic mine tailings used as mineral admixtures on the hydration of common and alternative cements

In this work, we investigate the use of pyrite-rich tailings from an operational mine as mineral admixture in different cement matrices [Portland cement, calcium aluminate cement (CAC), and calcium sulfoaluminate cement (CSA)]. Hydration and microstructure changes were studied on cement pastes produced with a 30 wt% replacement of cement with tailings, up to 200 days. Based on our results, the effect of the tailings on the hydration of Portland cement is limited to a physical effect, and no sulfide-induced degradation is observed. In the CAC and CSA pastes, minor mineral phases present in the tailings chemically react, leading to changes in the mineral phase composition of CAC and CSA hydrated pastes. In addition, in all cement pastes studied, and more effectively in the CSA pastes, most of the metal(loid)s contained in the tailings were safely immobilized. Cement chemistry notation: C: CaO; A: Al2O3; F: Fe2O3; S: SiO2; S̅: SO3; c: CO2; H: H2O.

XVI International Congress on Cement Chemistry – “Further Decarbonization and Circular Production and the Use of Cement and Concrete”

One of the authors is a participant in the XVI International Congress on Cement Chemistry (ICCC 2023), which was held in Bangkok (Thailand) on September 18–22, 2023 under the motto “Further decarbonization and recycling production and application of cement and concrete.” Statistical data, thematic areas of the congress are presented and some reports are presented, the content of which may be of most interest to Russian specialists.

A liquid-solid-chemical coupled mass transport model for concrete considering phase assemblages and microstructure evolution

Concrete is a highly alkaline porous medium that is prone to chemical reactions with acidic environments. The ion transport coupled with chemical reactions between concrete and solutions in acidic environments (acid rain, acid groundwater, acid industrial water, etc.) is a major challenge to the durability design of such infrastructure. Here, a liquid–solid-chemical coupled mass transport model of concrete considering phase assemblages and microstructure evolution was developed to tackle this problem. The highly nonlinear evolution of phase assemblages was solved via chemical thermodynamics. Further analysis was conducted on the spatiotemporal relationship of microstructure evolution caused by reaction kinetics, and the dynamic porosity and ion adsorption capacity were taken into account in the mass transfer equations. Furthermore, the nonlinear non-homogeneous partial differential equations were solved via finite difference method. Finally, the proposed model was validated based on four different types of cement-based concrete. The results indicated that considering the chemical reaction between highly alkaline concrete and acidic environments was crucial for the transport of chloride ions. The migration depth varied up to twice under the influence of acidic solutions. This study builds a bridge between mass transfer and cement chemistry knowledge, and is expected to improve the accuracy of life prediction for reinforced concrete structures.

On the Prediction of the Mechanical Properties of Limestone Calcined Clay Cement: A Random Forest Approach Tailored to Cement Chemistry

Limestone calcined clay cement (LC3) is a sustainable alternative to ordinary Portland cement, capable of reducing the binder’s carbon footprint by 40% while satisfying all key performance metrics. The inherent compositional heterogeneity in select components of LC3, combined with their convoluted chemical interactions, poses challenges to conventional analytical models when predicting mechanical properties. Although some studies have employed machine learning (ML) to predict the mechanical properties of LC3, many have overlooked the pivotal role of feature selection. Proper feature selection not only refines and simplifies the structure of ML models but also enhances these models’ prediction performance and interpretability. This research harnesses the power of the random forest (RF) model to predict the compressive strength of LC3. Three feature reduction methods—Pearson correlation, SHapley Additive exPlanations, and variable importance—are employed to analyze the influence of LC3 components and mixture design on compressive strength. Practical guidelines for utilizing these methods on cementitious materials are elucidated. Through the rigorous screening of insignificant variables from the database, the RF model conserves computational resources while also producing high-fidelity predictions. Additionally, a feature enhancement method is utilized, consolidating numerous input variables into a singular feature while feeding the RF model with richer information, resulting in a substantial improvement in prediction accuracy. Overall, this study provides a novel pathway to apply ML to LC3, emphasizing the need to tailor ML models to cement chemistry rather than employing them generically.

Recent advances in carbonatable binders

Carbonatable binder is relatively a new member of the cement family. This paper aims to review the progress in carbonatable binders given the increasing attention paid to this topic since the last International Congress on the Chemistry of Cement in 2019. Unlike hydraulic binders such as OPC and CSA clinkers, carbonatable binders react with CO2 in the presence of moisture to produce calcium carbonate as the major binding phase. This holds great potential in the utilization of emitted CO2 from anthropogenic sources. This paper will start with the introduction of definition and classification of carbonatable binders, followed by the presentation of phase composition, reactivity, microstructure and reaction mechanism. Lastly, a few cases on the recent production and application of carbonatable binders are introduced in the building industry.

From physics to chemistry of fresh blended cements

Tomorrow's mineral binders are called on to integrate a growing proportion of mineral powders other than Portland clinker. This impacts most properties of industrial interest including fresh state properties, the focus of this paper.We discuss the physical, physico-chemical and chemical changes that such an evolution in mix design is expected to induce.-Volume-driven effects (physics) control solid fraction, packing properties and strongly relate to particle shape, particle polydispersity and early hydrates morphology.-Surface-driven effects (physical chemistry) drive interparticle forces and admixtures adsorption, profoundly impacting the rheology by modifying the degree of dispersion.-Early hydration kinetics (chemistry) leads to hydrate nucleation and growth, which impact the above by modifying the specific surface area, admixture consumption and cohesion forces.We discuss the above features, their independence and their interplay and extrapolate the critical research questions and needs associated to a full understanding of the fresh properties of blended cements.

Molecular modelling of cementitious materials: current progress and benefits

Developing new sustainable concrete technology has become an urgent need, requiring faster and deeper insights into the fundamental mechanisms driving the cement hydration reactions. Molecular simulations have the potential to provide such understanding since the hydration reaction and the cement chemistry are particularly dominated by mechanisms at the atomic scale. In this letter, we review the application of two major approaches namely classical (including reactive) molecular dynamics simulations and density function theory calculations of cementitious materials. We give an overview of molecular simulations involving the major mineral and hydrate phases.

Solidification/Stabilization Technology for Radioactive Wastes Using Cement: An Appraisal.

Across the world, any activity associated with the nuclear fuel cycle such as nuclear facility operation and decommissioning that produces radioactive materials generates ultramodern civilian radioactive waste, which is quite hazardous to human health and the ecosystem. Therefore, the development of effectual and commanding management is the need of the hour to make certain the sustainability of the nuclear industries. During the management process of waste, its immobilization is one of the key activities conducted with a view to producing a durable waste form which can perform with sustainability for longer time frames. The cementation of radioactive waste is a widespread move towards its encapsulation, solidification, and finally disposal. Conventionally, Portland cement (PC) is expansively employed as an encapsulant material for storage, transportation and, more significantly, as a radiation safeguard to vigorous several radioactive waste streams. Cement solidification/stabilization (S/S) is the most widely employed treatment technique for radioactive wastes due to its superb structural strength and shielding effects. On the other hand, the eye-catching pros of cement such as the higher mechanical strength of the resulting solidified waste form, trouble-free operation and cost-effectiveness have attracted researchers to employ it most commonly for the immobilization of radionuclides. In the interest to boost the solidified waste performances, such as their mechanical properties, durability, and reduction in the leaching of radionuclides, vast attempts have been made in the past to enhance the cementation technology. Additionally, special types of cement were developed based on Portland cement to solidify these perilous radioactive wastes. The present paper reviews not only the solidification/stabilization technology of radioactive wastes using cement but also addresses the challenges that stand in the path of the design of durable cementitious waste forms for these problematical functioning wastes. In addition, the manuscript presents a review of modern cement technologies for the S/S of radioactive waste, taking into consideration the engineering attributes and chemistry of pure cement, cement incorporated with SCM, calcium sulpho-aluminate-based cement, magnesium-based cement, along with their applications in the S/S of hazardous radioactive wastes.

Hydration of blended ladle slag and calcium aluminate cement

Partial replacement and co-hydration of calcium aluminate cement (CAC) with ladle slag was investigated in this study as a pathway in valorizing the slag and reducing the economic cost of CAC. The impact of this replacement on the physical and microstructural properties were analysed using different techniques such as mechanical strength test, freeze-thaw, sulfate attack, XRD, SEM etc. Thermodynamic modelling was used to predict the phase assemblages of the blended cement using the hydration kinetics of the system. Experimental results showed the reference CAC mortar and the substituted mortar exhibited comparable strength gain at 7 and 28 days, and durability as measured by sulfate attack, abrasion, and freeze-thaw resistance. A low water-to-binder ratio (0.35) lessened the effect of conversion on the hydrates, as XRD showed metastable CAH10 and C2AH7.5 as the hydrates at 7, 28 and 60 days. This however can convert later to the thermodynamically stable phase C3AH6. Thermodynamic modelling suggests these two metastable phases as major binding phases, while Si-hydrogarnet and FeOOH appeared a minor trace in the binder.*Cement chemistry notation used, where C = CaO, A = Al2O3 and H = H2O

Concrete change: the innovative chemistry of sustainable cement

Concrete change: the innovative chemistry of sustainable cement

An Insight into the Chemistry of Cement—A Review

Even if cement is a well-consolidated material, the chemistry of cement (and the chemistry inside cement) remains very complex and still non-obvious. What is sure is that the hydration mechanism plays a pivotal role in the development of cements with specific final chemical compositions, mechanical properties, and porosities. This document provides a survey of the chemistry behind such inorganic material. The text has been organized into five parts describing: (i) the manufacture process of Portland cement, (ii) the chemical composition and hydration reactions involving a Portland cement, (iii) the mechanisms of setting, (iv) the classification of the different types of porosities available in a cement, with particular attention given to the role of water in driving the formation of pores, and (v) the recent findings on the use of recycled waste materials in cementitious matrices, with a particular focus on the sustainable development of cementitious formulations. From this study, the influence of water on the main relevant chemical transformations occurring in cement clearly emerged, with the formation of specific intermediates/products that might affect the final chemical composition of cements. Within the text, a clear distinction between setting and hardening has been provided. The physical/structural role of water in influencing the porosities in cements has been analyzed, making a correlation between types of bound water and porosities. Lastly, some considerations on the recent trends in the sustainable reuse of waste materials to form “green” cementitious composites has been discussed and future considerations proposed.

Influence of Chloride Transport Modes and Hydrated Cement Chemistry on Chloride Profile and Binding Mechanisms in Concrete

Influence of Chloride Transport Modes and Hydrated Cement Chemistry on Chloride Profile and Binding Mechanisms in Concrete