Portland Cement-based Materials Research Articles

Stability of two-phase flow with interfacial flux in porous media: CO2 mineralization

The primary objective of carbon capture, utilization, and storage (CCUS) applications in various natural and engineered porous materials is to achieve a stable and planar CO2 displacement front, thereby suppressing viscous fingering. A stable front can ensure uniform and exhaustive CO2 mineralization throughout a reactive medium (i.e., mineral carbonation). Drawing inspiration from experimental observations of CO2 flooding into cores of portland cement-based materials, we examine the stability of such systems. Under these conditions, the injected CO2 continuously dissolves into the resident water phase, which becomes chemically disequilibrated with the solid minerals and leads to mineral carbonation on the wetted surfaces. Focusing on the early injection time allows us to reduce the complex multiphysical problem to a simple two-phase flow scenario of immiscible displacement with a CO2 interfacial flux sink. The formulated equations are investigated using numerical simulations and linear stability analysis, which results in a closed-form criterion, and provide fundamental insights into system stability. Overall, the results show that several effects combine to stabilize the system, including the sink effect, which acts to eliminate instability; the reduction in flow velocity along the flow path, which limits flow focusing; and the relative increase in stabilizing capillary forces. Therefore, if the system is stable at early stages, it will likely remain stable later on. Finally, this research demonstrates the use of theory to simplify complex problems and shows that even when flow is inherently coupled, the state of systems can often be determined from fluid stability alone.

A randomized controlled clinical trial of the performance of three bioactive endodontic cements in primary molar teeth diagnosed with reversible pulpitis: 1-year follow-up study

ObjectivesThe objective of this clinical trial was to evaluate and compare the clinical and radiographic successes of three bioactive endodontic cements (BEC) including novel portland cement-based material releasing fluoride, resin-modified silicate glass cement, and pure tricalcium silicate-based cement—in the treatment of primary molars diagnosed with reversible pulpitis via indirect pulp capping. MethodsEighty-six (86) participants with previously untreated first and second primary molars were included in this study. The teeth were randomly allocated into three groups: pure tricalcium silicate-based cement, resin-modified silicate glass cement, and novel portland cement-based material releasing fluoride. Cavities were capped with the assigned cement after caries excavation using standard protocols. The teeth that underwent treatment were restored using glass ionomer cement and composite resin. Clinical and radiographic evaluations were performed at 1, 6, and 12 months. The data were analyzed using Pearson chi-square, Kruskal–Wallis H and Z test (P = 0.05). ResultsThe success rate was 88 % (n = 25) in the pure tricalcium silicate-based cement group, 88.5 % (n = 26) in the resin-modified silicate glass cement group, and 100 % (n = 25) in the novel portland cement-based material releasing fluoride group. The differences at the 1st, 6th, and 12th month follow-up visits were not statistically significant among the groups (P > 0.05). No difference was found between the integrity of the resin composite restorations overlying pure tricalcium silicate-based cement, resin-modified silicate glass cement, and novel portland cement-based material releasing fluoride according to the USPHS criteria. ConclusionsNovel portland cement-based material releasing fluoride can be considered an alternative for preserving the tooth, as it showed a high success rate in treating primary molars diagnosed with reversible pulpitis via indirect pulp capping. Clinical significanceNovel Portland cement-based material releasing fluoride could be beneficial in the treatment of primary molars diagnosed with reversible pulpitis via indirect pulp capping.

New elucidating into the microstructural evolution mechanisms and micromechanical properties of C4AF and gypsum synergistic hydration

Increasing the C4AF content significantly enhances the sulfate and impact resistance of Portland cement-based materials. However, the research on the microstructural evolution mechanisms and micromechanical properties of the binary synergistic hydration products of C4AF and gypsum is not yet sufficiently deep. This study employed thermodynamic simulations, phase structure characterization, and nanoindentation techniques to investigate the microstructure evolution of gypsum-assisted C4AF hydration. Results indicated that the final hydration product of C4AF, C3(A,F)H6, formed through the stacking of lamellar OH-AFm phases. The addition of gypsum altered the formation pathway of C3(A,F)H6, causing it to precipitate directly from an amorphous iron-aluminum gel, which resulted in smaller particles with higher crystallinity. Gypsum also filled pores in the hydration products, thereby positively influenced their micromechanical properties.

The role of ettringite seeds in enhancing the ultra-early age strength of Portland cement containing aluminum sulfate accelerator

The ultra-early age strength of shotcrete with Portland cement-based materials in various supporting constructions is crucial for safety and engineering efficiency. However, concerns exist about the low strength and uncertain mechanism when using aluminum sulfate, the main component of most-used alkali-free accelerators. This study addresses these concerns by introducing ettringite seeds into the Portland cement system with aluminum sulfate. Significant improvement in ultra-early age compressive strength of mortar, i.e., 242 % at 6 h and 201 % at 8 h, was achieved by mere 1 % seed addition. Analyses of hydration heat, composition and microstructure demonstrate that the ettringite seeds mainly affect the mechanical performance by forming a more prolonged and coarser ettringite skeleton, rather than directly accelerating cement hydration. Such an enhanced skeleton was proved to establish stronger interactions between particles in the Monte Carlo simulations. Additionally, the synergistic effect of the ettringite skeleton and C–S–H gel on ultra-early age strength was also explored. These proposed strengthening mechanisms were verified by the C3S and equivalent CaCO3 systems.

Research on the effect of tuff powder on the properties of moderate-heat portland cement-based materials and the methods for evaluating pozzolanic activity

Tuff powder (TP) has attracted significant attention due to its abundant resources, low carbon emissions, and potential enhancements in concrete property. This study investigates the effect of TP on the mechanical properties, hydration behavior, pore structure, microstructure morphology, economic and environmental analysis of moderate-heat portland cement (MHPC), comparing it with MHPC-based materials containing fly ash (FA). The synergistic morphological effect and micro-aggregate filling action of FA and TP result in higher early strength in the fly ash-tuff powder (FT) group mortar. The CH content and chemically bounded water content of TP paste are higher, showing a better early hydration promotion effect. The pore structure of the composite cement mortar is changed due to the addition of the admixture. Furthermore, the multi-factor response strength and strength activity index (SAI) model were developed based on response surface methodology (RSM), linking to TP specific surface area, dosage, and specimen curing age. This provides a reference for more accurate and comprehensive prediction of cement mortar property, quantification of effects, optimization of mix proportions, and evaluation methods for the activity of pozzolanic materials.

Rotational rheometry test of Portland cement-based materials – A systematic literature review

This study systematically reviews 62 papers on the use of rotational rheometry to assess the fresh state behavior of Portland cement-based materials. The research highlights the wide variation in test methods and aims to provide a comprehensive overview. Findings reveal that 50.0% of studies employed vane geometry, despite its limitations in providing transformation equations. Regarding dynamic shearing tests, 67.0% followed a consensus using a pre-shearing step and a step-wise routine with stabilization times ≥ 10 s. While the Bingham model is commonly used, the study emphasizes the importance of considering shear-thinning behavior in cementitious materials. Models like Herschel-Bulkley and modified Bingham may be more appropriate. This review offers insights into testing conditions for rotational rheometry of cementitious materials, serving as a foundation for future research in the field.

New insights into the immobilisation of Ce(IV) in Portland cement: Properties, hydration, microstructure and occurrence status of Ce

The immobilisation mechanism of Pu(IV) by Portland cement-based material is not well understood. This study aims to reveal the immobilisation mechanism and occurrence status of Ce(IV) (chemical analogue of Pu(IV)) in Portland cement paste. The addition of Ce(NO3)4 first slightly retarded then accelerated the early-age hydration of Portland cement, thereby resulting in an increase of compressive strength by 29 %. The main contributor to immobilisation of Ce is Portland cement rather than zeolite. The hydration products were not altered by Ce(NO3)4 addition, whereas the hydration degree and mean chain length of C-(Al/Ce)-S-H increased. Over 99.99 % of Ce was immobilised by synthesised C-S-H. A analysis of the synthesised C-S-H confirmed the formation of C-Ce-S-H, where Ce tetrahedra took the bridging site of silicate chain of C-Ce-S-H. Nano-crystalline CeO2 grains were identified, which intermixed with C-Ce-S-H. Approximately 90 % of Ce were immobilised by C-Ce-S-H, and the rest exist as nano-crystalline CeO2 grains.

Microsurgical Management of Nonsurgical Endodontically Treated Fiasco in Natural Permanent Upper Molar Tooth – A Clinical Case Report

Abstract The maxillary first permanent molar presents wide anatomical alterations for root number and their respective canal system. The medial root (mesiobuccal) specifically has been invariably associated to treatment failures when nonsurgical endodontic procedures have been solely carried out. In endodontic treatments, the decision to retreat the failed endodontic treatment with a surgical procedure depends on multiple factors. Evidence about the enduring prognosis of conventional retreatment (nonsurgical) comparative to invasive surgery (root end) remains questionable which requires additional scrutiny. The present case report presents a case of a patient (female, age 53 years) who presented with agony in relation to the maxillary first molar (left-sided) abutment of a four-unit fixed partial denture. Routine endodontic treatment was performed for the affected tooth which showed evidence of failure at 6-month follow-up intervals. Surgical intervention as part of the desired treatment was undertaken with the sealing of the canals done by Portland cement-based repair material. A pursual (6 months) after apicoectomy showed a complete rebuilding of the lateral apical region with freshly laid bone and a complete symptom-free patient. This clinical case report is directed to highlight the prospect of nonconservative clinical procedures once a noninvasive approach produces less anticipated results.

Masonry structures retrofitting by geopolymer plaster reinforced with natural fibers

Geopolymers describe a class of aluminosilicate materials obtained by alkaline activation of an aluminosilicate precursor at low temperatures and, nowadays, represents a very strong competitor to Portland cement-based materials in the field of constructions. To improve the mechanical characteristics of geopolymers, the adoption of fibers (natural or not) has been proposed and this is the topic of a very large literature. From the other hand, nowadays the problem of environmental sustainability is very important and the geopolymers possess many features making them as the cutting-edge material of the future. Further, the adoption of natural fibers makes geopolymers even more interesting from the environmental sustainability point of view. In many cases of practical application strengthening of existing masonry structures represents a very important topic involving the field of structural engineering as well as that of restoration. In both fields it is important to adopt sustainable materials showing the required mechanical characteristics. Aim of the paper is to verify the use of geopolymer plaster reinforced by natural fibers as strengthening tool for masonry structures. The aim will be firstly reached by suitably modelling the mechanical behaviour of samples of geopolymer plaster realized in laboratory starting from experimental results and secondly modelling the behaviour of a masonry panel reinforced with such plaster by means of a suitable FEM model in Abaqus.

Accelerated aging resistance, abrasion resistance and other properties of alkali-activated slag mortars containing limestone powder

The Earth's crust is widely recognized for its abundance of limestone (LS). Limestone powder (LSP) has a wide range of potential properties that make it suitable for various applications and fields. It has found extensive usage in Portland cement-based materials. Recently, the incorporation of LSP into geopolymers is becoming more of a concern than before and has become a hot topic. In this article, high range of LSP (2.5–50 wt%) was introduced into alkali-activated slag (AAS) mortars activated with NaOH and sodium silicate solution as a substitution of slag. For the first time, the effect of LSP on the accelerated aging resistance and abrasion resistance of AAS mortars was examined. In addition, the typical traditional routine properties such as flowability, setting time, mechanical strength, water absorption, and total porosity were studied. Sophisticated equipment was utilized to observe the changes in crystalline phases, hydration products, and microstructures of selected samples. The results showed higher flowability and longer setting time with including LSP. As the amount of LSP increased as the flowability and setting time increased. The introduction of 2.5–25% LSP positively affected the mechanical strength, aging resistance, abrasion resistance and transport properties. In contrast, the introduction of 35% did not show an essential change, whilst the introduction of 50% LSP negatively affected the mentioned properties.

Effect of tuff powder on the performance of low heat Portland cement-based materials

Low heat Portland cement (LHPC), a low-carbon cement variant, finds extensive application in expansive water conservancy ventures. To amplify energy efficiency and curtail CO2 emissions, supplementary cementitious materials (SCMs) are frequently harnessed as cement substitutes. This research delves into the impact of tuff powder (TP) on LHPC mortar traits via an array of evaluations encompassing rheological scrutiny, compressive strength assessment, isothermal calorimetry, X-ray diffraction (XRD), thermogravimetric analysis (TG), mercury injection porosimetry (MIP), and scanning electron microscopy (SEM). Notably, the research divulges that TP incorporation heightens yield stress and plastic viscosity within LHPC paste, concurrently expediting the hydration process and mitigating the maximum heat rate. Over a 90d span, TP efficiently increase of binding water content due to the pozzolanic reaction of TP and Ca(OH)2. Compared with FA, the addition TP can significantly enhance the 7d compressive strength of LHPC up to 39%. Augmented TP content engenders a more intricate and fine-pored structure in LHPC paste, bolstering cement paste density. Importantly, TP incorporation contributes to diminished energy consumption, lowered CO2 emissions, and amplified sustainability. In order to optimize material properties, the content of TP must be strictly controlled in the range of 20%-40%.

Effect of Graphite Addition on Thermal Behaviour of Metakaolin-Geopolymer Coating for Fire Protection of Steel

Geopolymers are inorganic binders that resulted from the alkali activation of aluminosilicate powder. Usually, geopolymers possess better high-temperature resistance than Portland cement-based materials. This makes them a promising candidate for high-temperature applications as well as for fire protection coating. The geopolymers pastes have been the focus as an intumescent coating. This study emphasizes the geopolymer pastes from metakaolin and silica fume precursors with the additive of graphite powder and intumescent compounds. The coupons test was made of carbon steel plate 50mm x 50mm x 4mm. Since steel loses a major of its mechanical properties at 500°C, then the time-temperature curve for the coated-steel plates was created from fire testing, compared to the naked steel. Moreover, the visual appearance and the SEM structure were recorded. It is found that the addition of graphite to geopolymer improves the fire resistance of geopolymer but does not affect the intumescent behaviour. is found that the geopolymer paste graphite addition did not result in better fire resistance.

MOC Composites for Construction: Improvement in Water Resistance by Addition of Nanodopants and Polyphenol.

The topic of modification of magnesium oxychloride cement (MOC) using specific functional additives is very much pronounced in the research of alternative building materials. This study deals with the co-doping of MOC by 1D and 2D carbon nanomaterials in order to improve its mechanical properties while using tannic acid (TA) as a surfactant. Furthermore, the effect of TA on MOC also improves its water resistance. As a filler, three size fractions of standard quartz sand are used. The proposed types of MOC-based composites show promising results considering their mechanical, macro- and microstructural, chemical, and hygric properties. The use of 1D and 2D nanoadditives and their mixture enables the improvement in the flexural strength and particularly the softening coefficient, which is the durability parameter characterizing the resistance of the prepared materials to water. After immersion in water for 24 h, the compressive strength of all tested specimens of modified composites was higher than that of the reference composite. Quantitatively, the developed co-doped composites show mechanical parameters comparable to or even better than those of commonly used Portland cement-based materials while maintaining high environmental efficiency. This indicates their potential use as an environmentally friendly alternative to Portland cement-based products.

Effect of carbonation curing on the physical, mechanical, and microstructural properties of metakaolin-based geopolymer concrete

Carbonation curing can absorb CO2 and fix it as a carbonate mineral in cementitious materials. Carbonation curing in Portland cement-based materials has been widely discussed in the literature, unlike carbonation curing in geopolymers. Therefore, the objective of this article was to evaluate the effect of carbonation curing on the physical, mechanical, and microstructural properties of metakaolin-based geopolymer concrete. Changes in pH value, carbonation depth, CO2 absorption, compressive strength, and microstructure formation were determined before and after carbonation curing. The results showed that the carbonation depth of Portland cement concrete is similar to the carbonation depth of geopolymer concrete. Furthermore, compressive strength after post-conditioning was not affected by carbonation curing, remaining statistically equal to reference concrete. Also, the formation of carbonates (Na2CO3 and CaCO3) refined the pore structure and increased closed pores, reducing the void ratio and the water absorption (permeability properties). A hybrid system containing N-A-S-(H) gel and carbonate crystals was identified.

The role of hydrotalcite in the chloride binding of hydrated C3A pastes containing dolomite

To better understand the limitations of the hydrotalcite formation and the capacity of hydrotalcite to bind chloride in dolomite-containing Portland cement-based materials, the reaction of dolomite in C3A pastes and the corresponding chloride binding behavior were investigated in this study. The phase assemblages, the chloride binding capacity, and the pH value were determined. The results indicate that hydrotalcite can only form in a limited range of (active magnesium)/(available aluminum) ratios. The dissolution of dolomite, which provides the magnesium activity, rather than the dedolomitization reaction, appears to be what drives the dolomite reaction with C3A and is primarily dependent on dolomite content. The hydrotalcite formation is not affected by Ca(OH)2. Hydrotalcite seems to possess a greater capacity to bind chloride than monocarboaluminate in hydrated C3A pastes, especially at high chloride concentrations. Chemical chloride binding contributes approximately 10% to the total chloride binding capacity of hydrotalcite. The remaining dolomite reduces chloride binding by increasing carbonate ion activity, and Ca(OH)2 reacts with dolomite to decrease carbonate ion activity and thereby promote chloride binding.

Geopolymer Antimicrobial and Hydrophobic Modifications: A Review

The article summarizes the state of the art in increasing antimicrobial activity and hydrophobic properties of geopolymer materials. Geopolymers are inorganic polymers formed by polycondensation of aluminosilicate precursors in an alkaline environment and are considered a viable alternative to ordinary Portland cement-based materials, due to their improved mechanical properties, resistance to chemicals, resistance to high temperature, and lower carbon footprint. Like concrete, they are susceptible to microbially induced deterioration (corrosion), especially in a humid environment, primarily due to surface colonization by sulphur-oxidizing bacteria. This paper reviews various methods for hydrophobic or antimicrobial protection by the method of critical analysis of the literature and the results are discussed, along with potential applications of geopolymers with improved antimicrobial properties. Metal nanoparticles, despite their risks, along with PDMS and epoxy coatings, are the most investigated and effective materials for geopolymer protection. Additionally, future prospects, risks, and challenges for geopolymer research and protection against degradation are presented and discussed.

A Review: Progress in Molecular Dynamics Simulation of Portland Cement (Geopolymer)—Based Composites and the Interface between These Matrices and Reinforced Material

Molecular dynamics (MD) is an important method for studying the molecular and atomic scale of cement (geopolymer)-based composites which provides an effective method for the optimal design of cementitious materials. In this paper, the research progress of MD simulation in Portland cement and geopolymer-based materials is discussed in detail, including molecular structure models of calcium silicate hydrate, calcium aluminosilicate hydrate, sodium aluminum silicate hydrate gel, and auxiliary experimental techniques. The basic mechanical properties of calcium silicate hydrate, calcium aluminosilicate hydrate and sodium aluminum silicate hydrate in Portland cement-based materials (CBM) and geopolymer-based materials are reviewed. In addition, the dynamic simulation of the interface between CBM and reinforcement materials such as rebar, synthetic fibers, plant fibers and nanoparticles is also discussed. Through the macroscopic experimental results of cement (geopolymer)-based materials and the performance analysis of an MD microscopic model, MD helps to better explain the macroscopic properties of materials, and can quickly and conveniently analyze the mechanical properties, transport properties and interface properties of composite materials, so as to improve the fine design of cement (geopolymer)-based materials. Existing structural models and force fields are affected by environment and time, and MD simulation shows great differences in application range and characterization ability. It is necessary to further study and reveal the internal mechanism for improving concrete performance through a large number of experiments and MD simulation, and lay a theoretical foundation for preparing the next generation of (super) high-performance concrete.

Advancements in the synthesis and processing of alkali-activated materials: Activator and precursors

Alkali-activated materials (AAMs) have gained attention in recent years as a sustainable alternative to traditional portland cement-based materials. This is due to their lower carbon footprint and ability to utilize waste materials as raw materials. However, the high embodied carbon and limited local supply of the conventional activators and precursors hinder large-scale deployment and acceptance as a sustainable alternative to portland cement-based materials. Nonetheless, the synthesis and processing of AAMs have been actively researched in recent years, leading to various advancements in the field. This review paper aims to provide an overview of the current state-of-the-art materials utilized in synthesizing AAMs and identify the areas for future research. Hence, it summarizes advancements in synthesizing AAMs regarding alternative activators and precursors and discusses the impact of these advancements on the properties of AAMs, such as strength, durability, and sustainability. Furthermore, this review addresses current challenges associated with the synthesis of AAMs.

Sequestration and utilization of carbon dioxide to improve engineering properties of cement-based construction materials with recycled brick powder: a pathway for cleaner construction

The research explores the possibility of utilizing carbon dioxide to modify the properties of recycled brick powder (RBP) and enhance the engineering performances of RBP-mortar. The RBP, crushed to the size range of 0.075 to 4 mm, is carbonated by exposing to 5% CO2 for 4 h and characterized for phase composition, porosity and micro-structure. The non-carbonated RBP (RBP) and pre-carbonated RBP (Carb-RBP) are applied to replace 25% and 75% of manufactured sand (M-sand) in cement mortars maintained at similar flow level (110 – 113%), which are then cured under three conditions - (i) ambient condition (N), (ii) 4 h of steam curing followed by moist and dry curing (STC), and (iii) accelerated CO2 curing (5% CO2 of 99% purity) for 4 h followed by moist curing and dry curing (CC). Physico-chemical characterizations suggest that Carb-RBP has higher micro-pore volume and surface area contributed by pores in the size range of 1 nm to 3 nm than RBP. After carbonation, the reactivity of RBP in alkaline environment is increased due to CO2-induced breakdown of calcium and alumino-silicate minerals into calcium carbonate and silica gel. Due to addition of 25% and 75% RBP and Carb-RBP, hydration kinetics is accelerated by 4 – 4.50 h compared to control due to nucleation of hydration products on the surfaces of RBP. Faster precipitation of hydration products, more micro-pore sites in RBP and higher porosity due to increased water demand enhance the carbon sequestration in RBP-mortars and Carb-RBP mortars by 30–82% compared to control (0% RBP). Use of Carb-RBP to replace 25% of M-sand offer similar compressive strength as control and 19 – 21% higher strength than mortars with RBP (non-carbonated). CO2 curing also reduces the total shrinkage of mortars with recycled brick powder by 12 – 17% compared to ambient curing and steam curing due to densification by calcium carbonate crystals. The findings from this research strongly suggests a significant reduction in embodied carbon of Portland cement-based construction materials by utilizing a combined approach of carbon sequestration and replacement of fine aggregates by recycled brick powder.

Improving the physicomechanical performance of geopolymer mortars using human hair as fibers: new horizons for sustainable applications

Blast furnace slag-based geopolymer mortars strengthened with human hair fibers were synthesized in the present study. The mixture of NaOH and Na2SiO3 was used as activating solution. Zero percent, 0.25%, 0.5%, 0.75%, 1%, and 1.25% hair fibers were added by weight of slag. Several analytical approaches, including compressive strength, flexural strength, P-wave velocity, bulk density, porosity, water absorption, infrared spectroscopy, X-ray diffraction, and scanning electron microscopy, were used to assess the physicomechanical and microstructural characteristics of the geopolymer mortars. Overall, the results found revealed that the incorporation of human hair fibers into the slag-based geopolymer matrix brought about a noticeable improvement in the mechanical characteristics of the geopolymer mortars. Similarly, based on FTIR analysis, the geopolymer mortar is characterized by the presence of three principal bonds, namely, the stretching of Al-O, a shift of the absorption band of the Si-O-Si (Al), and the stretching of the O-C-O. Likewise, the mineralogical analysis shows that quartz and calcite are two crystalline phases dominant in the geopolymer matrix. In addition, SEM-EDS analysis shows a dense and continuous morphology devoid of microcracks with a few pores existing on the matrix surface with perfect integration of the hair fiber in the geopolymer matrix. According to these relevant properties, the synthesized geopolymers have potential applications as a suitable substitute for many Portland cement-based materials whose manufacture is energy-consuming and polluting.