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Abstract Natural-based materials represent green choices for biomedical applications. In this study, resin pulp capping restoration enclosing strengthening silica and bioactive portlandite nanofillers were prepared from industrial wastes. Silica nanoparticles were isolated from rice husk by heat treatment, followed by dissolution/precipitation treatment. Portlandite nanoparticles were prepared by calcination of carbonated lime waste followed by ultrasonic treatment. Both were characterized using x-ray diffraction, energy dispersive x-ray, and transmission electron microscopy. For preparing pulp capping restoration, silica (after silanization) and/or portlandite nanoparticles were mixed with 40/60 weight ratio of bisphenol A-glycidyl methacrylate and triethylene glycol dimethacrylate. Groups A, B, and C enclosing 50 wt.% silica, 25 wt.% silica + 25 wt.% portlandite, and 50 wt.% portlandite, respectively, were prepared. All groups underwent microhardness, compressive strength, calcium release, pH, and apatite forming ability inspection in comparison to mineral trioxide aggregate (MTA) positive control. In comparison to MTA, all experimental groups showed significantly higher compressive strength, group B showed comparable microhardness, and group C showed significantly higher calcium release. Groups B and C showed prominent hydroxyapatite formation. Thus, the preparation of economic, silica-fortified, bioactive pulp capping material from under-utilized agricultural residues (rice husk) and zero-value industrial waste (carbonated lime from sugar industry) could be achieved.

Natural-based materials represent green choices for biomedical applications. In this study, resin pulp capping restoration enclosing strengthening silica and bioactive portlandite nanofillers were prepared from industrial wastes. Silica nanoparticles were isolated from rice husk by heat treatment, followed by dissolution/precipitation treatment. Portlandite nanoparticles were prepared by calcination of carbonated lime waste followed by ultrasonic treatment. Both were characterized using x-ray diffraction, energy dispersive x-ray, and transmission electron microscopy. For preparing pulp capping restoration, silica (after silanization) and/or portlandite nanoparticles were mixed with 40/60 weight ratio of bisphenol A-glycidyl methacrylate and triethylene glycol dimethacrylate. Groups A, B, and C enclosing 50 wt.% silica, 25 wt.% silica + 25 wt.% portlandite, and 50 wt.% portlandite, respectively, were prepared. All groups underwent microhardness, compressive strength, calcium release, pH, and apatite forming ability inspection in comparison to mineral trioxide aggregate (MTA) positive control. In comparison to MTA, all experimental groups showed significantly higher compressive strength, group B showed comparable microhardness, and group C showed significantly higher calcium release. Groups B and C showed prominent hydroxyapatite formation. Thus, the preparation of economic, silica-fortified, bioactive pulp capping material from under-utilized agricultural residues (rice husk) and zero-value industrial waste (carbonated lime from sugar industry) could be achieved. [ABSTRACT FROM AUTHOR]

In order to address the issues of energy depletion, more resources are being searched for in the deep sea. Therefore, research into how the deep-sea environment affects cement-based materials for underwater infrastructure is required. This paper examines the impact of ocean depth (0, 500, 1000, and 1500 m) on the ion interaction processes in concrete nanopores using molecular dynamics simulations. At the portlandite interface, the local structural and kinetic characteristics of ions and water molecules are examined. The findings show that the portlandite surface hydrophilicity is unaffected by increasing depth. The density profile and coordination number of ions alter as depth increases, and the diffusion speed noticeably decreases. The main cause of the ions' reduced diffusion velocity is expected to be the low temperature. This work offers a thorough understanding of the cement hydration products' microstructure in deep sea, which may help explain why cement-based underwater infrastructure deteriorates over time. [ABSTRACT FROM AUTHOR]

The present study evaluates the impact of calcium compounds on the reaction kinetics of alkali-activated construction demolition waste. Two materials, concrete and brick demolition waste, were milled to powders and supplemented with either carbonated cement stone or freshly ground cement stone. The mixed solids were further subjected to alkaline activation using a sodium silicate solution. X-ray diffraction, isothermal conduction calorimetry, thermogravimetric analysis, scanning electron microscopy and compressive strength tests were employed to understand the interaction of the reactants. The results indicate that cubes prepared from freshly ground cement stone exhibited higher compressive strength of around 18 MPa than those from carbonated cement stone with a maximum of 7 MPa. This superior strength was approved by subsequent analysis methods. A more significant reaction was observed in the material containing freshly ground cement stone, resulting in increased strength within the system. The presence of portlandite in freshly ground cement stone facilitated the initial formation of calcium silicate hydrate phases.

This research investigated the influence of using chemically treated glass microparticles as a partial replacement for cement in Portland cement pastes and mortars. The microparticles were obtained by grinding glass waste into three different particle size fractions (< 75 µm, < 45 µm, and < 25 µm), treated with calcium hydroxide (CH), and characterized using SEM/EDS and a laser particle size analyzer. Samples prepared with the incorporation of glass were characterized using XRD, TGA/DTG, and SEM/EDS. The pretreatment with calcium hydroxide induced the formation of C-S-H with different morphologies on the surface of the particles, in addition to causing changes in particle size distribution due to the formation of agglomerates. The pastes prepared with treated particles had lower amounts of CH and higher levels of hydrated silicates. However, when indirectly measuring the pozzolanicity of treated particles through the compressive strength of mortars, no significant differences were observed in the strengths of mortars made with treated and untreated particles.

The pozzolanic performance of crushed brick powder (CBP), obtained by grinding under-burnt waste bricks from a continuous brick kiln, is studied. Two size fractions of CBP considered for cement replacement are CBP1 (passes through 150 μm but is retained on 75 μm) and CBP2 (passes through 75 μm). Compressive strength tests on mortar with CBP reveal that strength does not exceed that of the control; however, 10–15% cement replacement by CBP is the optimum. The presence of hydrate phases by X-ray diffraction and quantification of portlandite in the paste samples as studied by thermogravimetric analysis up to 90 days confirms the action of pozzolanicity. Furthermore, to determine the feasibility of CBP1 and CBP2 fractions in concrete, the strength and carbonation of M25 grade concrete were studied by replacing 45% cement with a combined proportion of CBP1 (20%) and CBP2 (25%). This reduced the concrete grade from M25 to M20 and increased the accelerated carbonation depth. Nevertheless, the projected natural carbonation coefficient with accelerated carbonation data is determined as low. The CBP used is cost-effective, requiring little mechanical processing and no chemical activation; thus it can satisfactorily be used for low-cost housing construction and lower-grade structural and non-structural uses. [ABSTRACT FROM AUTHOR]

Cementitious materials can be treated with organosilicon compounds (silanes) to achieve a water‐repellent effect. However, the influence of silanes on cement hydration is still not fully understood. For this reason, we studied the hydration of the main Portland cement phase (C3S ‐ tricalcium silicate) and the interaction with iBTES (isobutyltriethoxysilane), iOTES (isooctyltriethxysilane) and nOTES (n‐octyltriethoxysilane) by isothermal calorimetry and in‐situ X‐ray diffraction (XRD). The results show that C3S hydration is initially retarded and subsequently accelerated by iBTES and iOTES. In addition to the hydration process, the crystal growth of the portlandites (calcium hydroxide) is also affected by the silanes. The XRD results indicate that the portlandites grow significantly more plate‐like. In this context, the influence of the silanes on the portlandite crystallization was therefore also recorded in a special experimental setup. From the scanning electron microscope images it can be shown that all portlandite crystals grown in the presence of silanes have a platelike morphology. This is due to the fact that the hexagonal surfaces of the portlandite are covered by silanes and thus the growth direction of the crystals is affected. The modified portlandite crystals indicate that silanes also influence the microstructure of the cement paste and therefore its chemical and mechanical properties. [ABSTRACT FROM AUTHOR]

It is important to accurately control the setting of concrete and mortars. Functional admixtures such as hydroxy carboxylic acids can modify the hydration mechanism by influencing the dissolution of clinker phases and the crystallization of hydrate phases. While the crystallization of phases like CaCO3 under the influence of various additives has been studied intensively, there is substantially less understanding with regard to the main products of cement hydration, i.e., C‐S‐H, portlandite, ettringite, etc. In this work a potentiometry based setup was used to study the influence of succinic, tartaric, and citric acid on the nucleation and growth of portlandite and C‐S‐H. We found that the investigated molecules not only lead to a significant delay in nucleation by stabilization of prenucleation clusters, but also show a strong influence on the process of crystal growth. Further the effect of these molecules on the hydration reaction of tricalcium silicate was examined using ex‐situ calorimetry. We found a decent retarding effect on this reaction, even when there was almost no observable effect on the nucleation process in the previous experiments. [ABSTRACT FROM AUTHOR]

The advanced technologies of modern civilization produce radioactive wastes that require careful disposal if they cannot be recycled. These materials can originate from a variety of activities, such as scientific research, medicine, or nuclear power generation and, as such, can result in numerous waste forms. In this paper, the corrosion behavior of several less‐common metals is studied, specifically: aluminum, copper, lead, magnesium, zinc, and zirconium, all under simulated cementitious environments. The data reported rely on the production of hydrogen as a corrosion end‐product to calculate the uniform corrosion rate as a function of time. At 50°C, in either young cement water (pH 13.5) or saturated portlandite (pH 12.5) and after approximately 2 years of exposure, magnesium was found to corrode at ∼10 µm/year; aluminum at 1 µm/year (portlandite only); zinc at ∼100 nm/year; lead at <1 nm/year and both copper and zirconium at less than 0.1 nm/year. [ABSTRACT FROM AUTHOR]

The carbonation of recycled concrete aggregates (RCA) has emerged as a possible significant carbon sink to mitigate the increase of CO2 concentration in atmosphere and global warming. A reliable determination of bound CO2 content is thus needed to optimize carbonation processes but there is no real consensus on the existing quantification methods, mainly based on thermal decomposition of calcium carbonate. With the aim of developing a relevant quantification method of bound CO2 during the carbonation of RCA, an experimental study based on the combination of two main techniques – thermogravimetric analysis (TGA) and high-temperature oven – was performed at different scales: paste, mortar, and concrete. XRD analyses allowed highlighting the overlaps between the decomposition of portlandite and calcium carbonate polymorphs during linearly increasing temperatures. Oven and TGA with isothermal steps were found to provide consistent and complementary data on RCA composition and their bound CO2 content from initially dried specimens.

The paper considers different aspects of natural and forced carbonization of binding agents and cement systems. It is shown that depending on the composition of binding agents, curing conditions, and transient factors, carbonization of hydrated cement can not only lead to corrosion and irreversible degradation, but also serve as a powerful productive endeavor for strengthening of concrete structures, self-healing of cracks in concrete, shrinkage reduction, and carbonization corrosion of constructional materials. Based on theoretical analysis of experimental data and the literature, a working hypothesis is developed concerning the observed processes of the structure formation based on the interaction of carbon dioxide and its derivatives with calcium aluminates and aluminate ferrites with the formation of hydrated calcium carboaluminates of various composition. Portlandite fixation is crucial for concrete structures capable of resisting to both carbon dioxide and sulfate corrosion and, sometimes, in introducing chemical additives, can lead to the structure strengthening. [ABSTRACT FROM AUTHOR]

The nitrite admixtures in cement and concrete are used as corrosion inhibitors for steel reinforcement and also as anti-freezing agents. The characterization of the protective properties should account for the decrease in the concentration of free NO2− ions in the pores of cement concretes due to their adsorption. Here we applied the classical molecular dynamics computer simulation approach to quantitatively study the molecular scale mechanisms of nitrite adsorption from NaNO2 aqueous solution on a portlandite surface. We used a new parameterization to model the hydrated NO2− ions in combination with the recently upgraded ClayFF force field (ClayFF-MOH) for the structure of portlandite. The new NO2− parameterization makes it possible to reproduce the properties of hydrated NO2− ions in good agreement with experimental data. In addition, the ClayFF-MOH model improves the description of the portlandite structure by explicitly taking into account the bending of Ca-O-H angles in the crystal and on its surface. The simulations showed that despite the formation of a well-structured water layer on the portlandite (001) crystal surface, NO2− ions can be strongly adsorbed. The nitrite adsorption is primarily due to the formation of hydrogen bonds between the structural hydroxyls on the portlandite surface and both the nitrogen and oxygen atoms of the NO2− ions. Due to that, the ions do not form surface adsorption complexes with a single well-defined structure but can assume various local coordinations. However, in all cases, the adsorbed ions did not show significant surface diffusional mobility. Moreover, we demonstrated that the nitrite ions can be adsorbed both near the previously-adsorbed hydrated Na+ ions as surface ion pairs, but also separately from the cations. [ABSTRACT FROM AUTHOR]

Portlandite (Ca(OH)2) preparation from phosphogypsum waste (PGW) was evaluated in numerous works; however, the use of this compound is not applied yet in the brine water salinity reduction. In this work, the purity of Ca(OH)2 prepared from PGW and soda aqueous solution was tested for different NaOH/PG molar ratios (MR) close to the stochiometric value (1.5 < MR < 3). The obtained Ca(OH)2 at the optimal conditions was used for both the CO2 capture and brine water (BW) salinity reduction, resulting in high-quality calcium carbonate synthesizing. The XRD results show that a MR higher than the stochiometric value (MR > 2) is most efficient to obtain high-quality portlandite (P2.5 and P3). An estimation of the carbon capture efficiency of the prepared portlandite was made. Based on the results of this work, using 4 g of P2.5 allows to capture 2.4 L of CO2 and treat 0.4 L of BW. Overall, our work confirms the technical viability of the proposed route to synergize CO2 capture, BW and PGW recycling. From an economic and ecological standpoint, our investigated routes were eco-friendly and cost-effective. [ABSTRACT FROM AUTHOR]

The use of high percentages of substitution of Portland cement by pozzolans can provoke the total consumption of portlandite. The present research proposes the study of ternary systems of Portland cement (PC), fly ash (FA), and hydrated lime (CH). After 180 days of curing, the mortar with 50% substitution of PC by FA obtained 65.9 MPa versus the mortars with an addition of 20% of CH and control mortar (100 PC) that obtained 69.9 MPa and 76.7 MPa respectively: this behavior is very positive value considering that tested FA containing mortars had a 50% of Portland cement. Regarding the effect of the amount of extra hydrated lime on durability issues, the evolution against carbonation of PC-FA and PC-CH-FA mortars was studied: the reduction of carbonation velocity was around a 37% for the mortar with CH respect the PC-FA mortar.

The oxygen-isotope fractionations between brucite and water, portlandite and water, and brucite and portlandite have been calculated over the temperature range of 0 to 450 °C using quantum-chemical methods and several basis sets and functionals. The calculations also employ embedded clusters that are chosen using the Pauling-bond-strength-conserving termination method that maintains a neutral cluster with fractional charges assigned to terminal atoms. These calculations improve upon the previous semiempirical methods for predicting mineral-mineral fractionations. These semiempirical methods fail to accurately predict the relative enrichment and depletion of oxygen isotopes for the brucite-portlandite pair. The quantum calculations presented here also fail to predict at the absolute values for enrichment of oxygen isotopes between minerals and water, and a simple correction must be employed to achieve agreement with experiments if water is in the reaction. No such correction is needed to predict fractionation between minerals. The trends derived from the calculations are robust to changes in basis sets and functionals.

In this experimental study, nine different lightweight aggregate concrete (LWAC) specimens - in which natural lightweight scoria aggregate was used as coarse aggregate - were prepared for investigating the size of portlandite crystals in their interfacial transition zone (ITZ). Scanning Electron Microscope (SEM) was used to determine the size of portlandite crystals in ITZ of LWAC specimens. The size of portlandite crystals in ITZ of these LWAC specimens was determined quantitatively in order to identify its relation with ratios of ingredients and properties of LWAC that were investigated. It was determined that the size of portlandite crystals in ITZ of nine LWAC specimens is in the range of (0.91-2.047) µm. The size of portlandite crystals in ITZ is found to be increased when the water/cement (W/C) and coarse aggregate/total aggregate (Ac/A) ratios of LWAC get increased. On the other hand, the compressive strength and the oven-dry density of LWAC are found to be decreased when the size of portlandite crystals in ITZ gets increased. The best way to make portlandite beneficial from mechanical, physical and durability points of view is to transform it into so-called secondary hydration products by making it react with materials that have proper chemical properties for this transformation. In this case, the small portlandite crystals dissolve entirely, and the large portlandite crystals become smaller. Lightweight scoria aggregate used in this study is thought to have chemical properties to assist such a transformation in ITZ. [ABSTRACT FROM AUTHOR]

In this study, nano-structural and nano-constraints behavior of two silica aggregate mortars are investigated. The first silica aggregate (A) is almost pure silica and the second one (B) contains silica, calcite and dolomite phases. The relationship between the durability and nano-structural changes is evidenced using Transmission Electron Microscope, X-ray diffraction (XRD) and TGA/DTA. The nano-structural results show that the macroscopic properties of mortars greatly depend on physico-chemical properties of aggregates. Higher the water absorption, higher the consumption of the Portlandite; the consumption of Portlandite, after 28 days of curing, is more in Bm sample than in Am sample. A relationship between the Portlandite content and the water absorption is evidenced. The relationship between reactivity and nano-constraints deduced from XRD modeling is highlighted.

The structural damages caused to some layered hydrated minerals by 2.5 MeV electron irradiation using the SIRIUS platform were studied by powder X-Ray diffraction and, in some cases, by 1H MAS-NMR spectroscopy. It is clearly demonstrated that the radiation damages are distinguishable from the heating effects. It is shown that: i) in all cases electron irradiation leads to distortions of the unit cell and very limited volume expansion, compared to heating; ii) radiation damages increase with increasing the structural complexity of the mineral; iii) portlandite Ca(OH) 2 and brucite Mg(OH) 2 remain crystalline up to high doses (a few GGy), with appearance of stacking fault disorder especially in brucite; iv) brushite CaHPO 4.2H 2 O and gypsum CaSO 4.2H 2 O undergo a phase transformation of type amorphization for brushite involving the strongest intralayer H bond between the acidic proton and the phosphate tetrahedral, and decomposition for gypsum involving interlayer H bonds between water molecules. Investigation of electron irradiation effects at low flux and high dose on structural damage of some layered hydrated minerals (portlandite and brucite, gypsum and brushite). [Display omitted] • X-Ray diffraction study of lamellar hydrated minerals following electron irradiation. • For all compounds, radiation damages cannot be assimilated to heating effects. • Very limited unit cell thermal expansion under irradiation compared to heating. • Gypsum transforms into less hydrated crystalline phases while brushite amorphizes. • Amorphization occurs via the strong intralayer H-bonds linking PO 4 units of brushite. [ABSTRACT FROM AUTHOR]

This study aims to achieve an in-depth understanding of the manufacturing process of natural hydraulic lime (NHL) by assessing the influence of raw materials' chemical- mineralogical composition and the effect of the slaking process. NHLs with variable hydraulicity were manufactured using 56 raw materials from carbonate outcrops in Andalusia (Spain). This study shows that siliceous limestones with microcrystalline quartz generate hydraulic phases after calcination. However, when the amount of this reactive silica exceeds 18% by weight, CaO is not formed, and only calcium silicates appear. It was also found that slaking of NHL leads to partial hydration of the most reactive calcium silicates, reducing the expected reactivity of the lime. Instead, exposure of NHL quicklimes to environmental relative humidity promotes the formation of disordered portlandite and reduces the partial hydration of hydraulic phases. Our findings demonstrate that standard slaking can be replaced by alternative methods for the studied binders. • Natural hydraulic limes were manufactured from local raw materials. • Cementation index is suitable to select raw materials with different hydraulicity. • Microcrystalline quartz is a reactive source of silica. • Temperatures around 950 °C inhibit the formation of Fe-bearing hydraulic phases. • Passive slaking under air exposure of the quicklime favours the crystallization of disordered portlandite. [ABSTRACT FROM AUTHOR]

Introduction. Construction of large-scale offshore structures in the coastal area of Vietnam requires new compositions of binders for hydraulic concretes, advanced concrete mixing technologies, and concrete transportation to depositing sites.Materials and methods. The binder, containing sulfate resistant Portland cement and finely dispersed mineral additives, including low calcium fly ash of TPP “Vung Ang” and silica fume SF-90 (SF-90), was added to the mortar mix, and the same about SR 5000F superplasticizer and quartz river sand. Powder particle shape and size were measured using laser granulometry; X-ray diffraction was employed to identify the mineral composition of sulfate-resistant cement; the effect of multi-component organo-mineral additives on the phase composition of the cement stone was studied using methods of thermogravimetric analysis; the absolute volume method was employed to analyze the composition of the mortar.Results. The co-authors have analyzed the application of new compositions of multi-component organic-mineral additives whose content, if taken as a percentage of the cement weight, reaches 1.1-1.45 % of SF 5000F superplasticizer, 10-15 % of SF-90, and 30 % of fly ash. New additives accelerate compressive and tensile strength development by 1.4-1.9 times, and that’s been confirmed by bending early-age and 28-day cement-sand mortar specimens, that have sulfate-resistant cement, and their benchmarking against control specimens. It’s been identified that SF-90 and fly ash, if added to the mix, reduce the Portlandite content in the cement stone by 1.27-3.29 % at the age of 28 days in comparison with the benchmark composition due to their high pozzolanic activity.Conclusions. Testing results enable co-authors to recommend the application of multi-component organo-mineral additives to increase the resistance of cement-sand compositions to sulfate corrosion due to the denser structure and lower porosity of the cement stone, caused by the lower value of the water/binder ratio and the packing of pore spaces with active mineral fillers. Therefore, new additives are recommended for use in the production of corrosion resistant concretes suitable for construction of offshore hydraulic structures in Vietnam.

In this study, Mactra veneriformis shells (MVS), a seafood by-product with high Ca content, was assessed as an adsorbent for fluoride removal from contaminated water. MVS was calcined at various temperatures (100–900 °C), and MVS calcined at 800 and 900 °C (MVS-800 and MVS-900) had the highest adsorption capacity. The high fluoride adsorption of MVS-800 and MVS-900 originated from the conversion of CaCO 3 present in the raw MVS to CaO and Ca(OH) 2 by calcination at high temperatures. The kinetic and equilibrium adsorption of fluoride by MVS-800 were accurately described by the pseudo-second-order and Langmuir models, respectively. The maximum fluoride adsorption capacity was 244.61 mg/g, which is comparable to that of other adsorbents reported in the literature. The enthalpy and entropy of adsorption were 7.42 kJ/mol and 56.48 J/mol‧K, respectively, and the Gibbs free energy was negative at all reaction temperatures. The interactive effects of pH, reaction time, dosage, and temperature and the optimal values for fluoride removal by MVS-800 were explored using response surface methodology (RSM) and artificial neural networks (ANN). The RSM results demonstrated that reaction time, dosage, and temperature significantly influenced fluoride removal; however, pH was an insignificant term. The accuracy of the ANN model (R2 = 0.9932) for predicting fluoride removal was higher than that of RSM (R2 = 0.9347). The optimal fluoride removal at a dosage of 3.3 g/L under optimized conditions (pH 5; reaction time 9 h; temperature 35 °C) was predicted to be 98.5% by the ANN model. [Display omitted] [ABSTRACT FROM AUTHOR]

The landfill disposal of waste newspapers has triggered an environmental concern that must be addressed. The ink from the waste newspaper is toxic and could be leached out of the waste newspapers by rainwater at landfill sites, causing water contamination. This contributed to the degradation of aquatic ecosystems. In another environmental problem, cement manufacturing resulted in a large emission of carbon dioxide into the air. Considering all these issues, it is necessary to investigate waste newspaper ash as a supplementary cementing material in concrete cylinders for cleaner production. The waste newspaper ash was produced by incineration in an electric furnace at 800 °C for 1 h before it was cooled down and sieved. Based on the ACI 211.1–91 standard, two sets of concrete cylinders were cast, namely control and waste newspaper ash treated concrete cylinders; each having a size of 150 mm diameter × 300 mm height. They were cured in water for 3 to 90 days before being tested for their mechanical and chemical properties. The mix design of 7.5% waste newspaper ash as partial cement replacement in the treated concrete cylinders was found to be the optimal one. The optimally treated concrete cylinder was tested to have an average 28-day compressive strength of 33.28 MPa, which is 2.15 MPa lower than the control ones. At 90-day curing age, however, its average compressive strength value was traced to be 44.06 MPa, which is 3.17 MPa higher than the control ones. Investigation of the surface morphology and X-ray diffraction patterns of the treated concrete cylinder samples revealed that there was a progressive pore refinement and a continuous decrease in portlandite when the curing age was prolonged from 28 to 90 days. Inspection of a failed 90-day optimally treated concrete cylinder revealed that it had higher stiffness and fewer extreme macrocracks compared to that cured in 28 days. These positive outcomes pointed out that the pozzolanic reaction in the optimally treated concrete cylinders was pronounced at 90-day curing age and added to their strength improvement in the long term.

This paper studied the adsorption of carboxyl-containing monomers on portlandite (CH) surface based on density functional theory (DFT) method, attempting to explain the retardation of cement slurry due to nucleation. The geometric structure, bond length, adsorption energy, charge transfer, difference charge density and partial density of states (PDOS) were calculated. The results indicated that all four carboxyl-containing monomers (acrylic acid, citraconic acid, itaconic acid, and maleic acid) had strong adsorption energies on CH (001) surface. The adsorption energies of citraconic acid, itaconic acid, and maleic acid on CH (001) had little difference, which were nearly twice that of acrylic acid on CH (001). In addition, the charge density difference and PDOS results proved the strong adsorption. The charge density of the area between O atom of the carboxyl group and Ca atom on CH (001) surface increased. The overlapping of peaks and the hybridization occurred between Ca 3d and O 2p orbits. The study of this paper deepens the understanding of the retarding mechanism on oil well cement. [ABSTRACT FROM AUTHOR]

Pore solution expression (PSE) is the most commonly used method to obtain the aqueous phase in cementitious material. However, the high pressure applied on the sample during PSE can affect the composition of the solid phase. An experimental study on the chemical and mineral composition of cement paste before and after PSE was conducted. The results indicate that a small part of the alkali contained in the samples was excluded during PSE, depending mainly on the alkali concentration in the pore solution. Due to the expulsion of interlayer water in calcium silicate hydrate under high pressure, PSE reduced the bound water content (measured by thermogravimetric analysis (TGA)). The portlandite content determined by TGA was not affected by PSE, but it led to an overestimation of portlandite by means of quantitative X-ray diffraction, because of the enhanced preferred orientation of the (001) plane under the applied high pressure. In addition, the size of the portlandite crystals decreased to some extent due to the creep caused by pressure. The content of the hemicarbonate phase was found to decrease slightly after PSE, which may be due to increased solubility under high pressure. [ABSTRACT FROM AUTHOR]

3D-printing could offer substantial benefits to the construction industry including the fabrication of customized/bespoke components, eliminating formwork, and reducing material waste. Despite these advantages, control of the pumpability, extrudability, and buildability of 3D-printed concrete (3DPC) remains challenging. This study demonstrates how the use of fly ash (FA) enables enhanced thermal stiffening, and rapid alkali-activation in the presence of portlandite (Ca(OH) 2 , CH). In general, blends of CH and FA exhibit less structural build-up at low temperatures, but upon reaching a trigger temperature of 75 °C, these blends achieve rapid stiffening, at rates of ∼800 Pa/s. The rapid stiffening arises from the flocculation of CH particles, and the onset of the pozzolanic/alkali-activation reactions between CH and FA, resulting in the formation of C-A-S-H and N-A-S-H during stiffening. Careful selection of the FA-CH blend ratio, which displays an optimum at ∼20 mass % CH, enables the composition of cement-free formulations for 3D-printing applications. The outcomes have important implications on alternate feedstock pathways to compose carbon-efficient formulations for construction. [ABSTRACT FROM AUTHOR]

A clinker-free cement (CFC) based on portlandite, calcined clay, slag, limestone powder, anhydrite, and C-S-H seeding is reported. The aim was to develop a low-carbon clinker-free cementitious binder using supplementary cementitious materials (SCMs), portlandite, a sulfate source, and accelerators. The impacts of ordinary Portland cement (OPC), portlandite, calcined clay and anhydrite on the strength of the C-S-H-seeded CFC were investigated. Strength, flow, setting and expansion of the mortar were investigated. Hydration kinetics were studied using calorimetry and XRD Rietveld analysis. Results showed that the seeded CFC exhibited similar strength and flow to OPC but produced significantly less heat. The factors contributing to the enhanced strength and improved flow behavior of the CFC were examined. Expansion behavior of CFC and its relationship with anhydrite content and ettringite formation was analyzed. Additionally, the microstructure of the hardened paste was characterized using SEM and mercury intrusion porosimetry (MIP) to evaluate the impact of C-S-H seeding. The combination of a low-carbon binder mix design and C-S-H seeding effectively reduced the CO 2 footprint of cementitious binders, with the seeded-CFC achieving >50 % reduction in CO 2 emissions per MPa compared to OPC. The proposed CFC binder approach was further validated using other types of SCMs. [Display omitted] • A clinker-free cement (CFC) based on portlandite, SCM and C-S-H seeding. • C-S-H seeding accelerates SCM reaction, leading to strength gain and meeting 32.5 grade cement. • CFC advantages: similar mortar flow to OPC, low heat release, and reduced CO 2 footprint. • CFC exhibits enhanced early strength with C-S-H seeding; late strength correlates with seeding dose. • CFC shows better mortar flow than LC3 cement, limited expansion, and dense structure. [ABSTRACT FROM AUTHOR]

Several experimental studies have been conducted on the thermoelectric properties of cementitious materials, but a detailed inspection of the intrinsic properties of their main ingredients is still missing. This work focuses on the thermoelectric properties of portlandite and tobermorite, two mineral components found in Ordinary Portland Cement pastes. To this end, atomistic simulations were carried out to predict the thermoelectric properties of cement-based materials. The methodology is based on the density functional theory approach together with GW-quasiparticle and Boltzmann transport equation methods. As expected, the undoped minerals have low thermal conductivity. However, both the Seebeck coefficient and the electrical conductivity can be dramatically increased by appropriate carrier doping. In fact, an enhanced figure of merit of Z = 0.6 at 650 K and 0.79 at 600 K is observed for portlandite and tobermorite. Therefore, our results confirm that there are still much promising prospects for enhancing the characteristics of concrete materials for energy harvesting. • Proposed the calculation of thermal conductivity of cement composite with slack model. • Significantly improved the ZT of portlandite and tobermorite-11 by carrier doping. • Doping one atom of silicon with aluminum achieves ZT = 0.5 at 600 K. [ABSTRACT FROM AUTHOR]

To investigate the effect of leaching on chloride ingress profiles in concrete and mortar, we exposed concrete and mortar specimens for 90 and 180 days to two different exposure solutions: 3% NaCl, and 3% NaCl with KOH added to limit leaching. The solutions were replaced weekly. After exposure, we determined total chloride profiles to investigate the chloride ingress, and portlandite profiles to assess the extent of leaching. The results showed that leaching during exposure greatly affects the chloride ingress profiles in mortar and concrete. We found that leaching leads to considerably higher maximum total chloride content and deeper chloride penetration into the concrete than in the specimens where leaching was limited. We recommend therefore that leaching should be taken into account in standard laboratory testing and that more mechanistic service life models should be used to take into account the impact of leaching. [ABSTRACT FROM AUTHOR]

Cement paste hydration is a complex physical-chemical process. The aim of this paper is to use three approaches to determine the degree of hydration: portlandite quantification, scanning electron microscopy and bound water quantification. In order to investigate the physical-chemical and mechanical properties, as well as the hydrates generated. Portland cement was synthesized and characterized in the laboratory. At all hydration durations, the portlandite quantification method and SEM-BSE image analysis show similar results. The method of SEM images analysis requires time to gather and process images, but is unaffected by the type of hydrates produced. The bound water quantification method gives a lower degree of hydration than two other methods at all hydration times. To test the reliability of these procedures, the compressive strength was calculated based on the degree of hydration. The results indicate that the portlandite quantification method and SEM-BSE image analysis are more accurate than the bound water quantification approach in terms of reproducing the experimental results.

Comparison of the content of Ca(OH)2 in hardened cement matrices, which contains the additive SiO2 nanoparticles and in matrice without additives was performed by the method of thermogravimetric analysis. Alite portland cement «SsangYong» and «Denki» were used. Hydrothermal sol of «Geosil» was introduced as an additive of nanoparticles of SiO2. The amount of introduced nano-SiO2 was from 1.15 to 1.74 wt.% in respect to cement consumption. Water-cement ratio was provided at the level of W/C = 0.39–0.26. The compensating amount of polycarboxylate SVC-5Neu was 0.2–0.77 wt. %. The Ca(OH)2 content was calculated from the mass loss of the cement matrice sample in the temperature range 460–510о C. It was determined that the sol «Geosil» additive reacts quickly with Ca(OH)2 (CH) in cement matrice, significantly (up to 40%) reducing its content. By the period of 24 h sol «Geosil» binds 750 [mg CaO /g SiO2 ] and continues to bind CH up to 100–700 days, to the value δCaO = 1300 [mg CaO /g SiO2 ]. The pozzolan binding reaction Ca(OH)2 with the formation of calcium hydrosilicates may be one of the mechanisms for increasing the strength of concrete when introducing SiO2 nanoparticles.

Portlandite (Ca(OH)2; also known as calcium hydroxide or hydrated lime), an archetypal alkaline solid, interacts with carbon dioxide (CO2) via a classic acid–base "carbonation" reaction to produce a salt (calcium carbonate: CaCO3) that functions as a low‐carbon cementation agent, and water. Herein, we revisit the effects of reaction temperature, relative humidity (RH), and CO2 concentration on the carbonation of portlandite in the form of finely divided particulates and compacted monoliths. Special focus is paid to uncover the influences of the moisture state (i.e., the presence of adsorbed and/or liquid water), moisture content and the surface area‐to‐volume ratio (sa/v, mm−1) of reactants on the extent of carbonation. In general, increasing RH more significantly impacts the rate and thermodynamics of carbonation reactions, leading to high(er) conversion regardless of prior exposure history. This mitigated the effects (if any) of allegedly denser, less porous carbonate surface layers formed at lower RH. In monolithic compacts, microstructural (i.e., mass‐transfer) constraints particularly hindered the progress of carbonation due to pore blocking by liquid water in compacts with limited surface area to volume ratios. These mechanistic insights into portlandite's carbonation inform processing routes for the production of cementation agents that seek to utilize CO2 borne in dilute (≤30 mol%) post‐combustion flue gas streams. [ABSTRACT FROM AUTHOR]

Despite the awareness of the alkali–silica reaction (ASR) since 1940, the need for an efficient and reliable method of evaluating the potential reactivity of aggregates for use in concrete still exists. Current standards to assess the ASR susceptibility of aggregates have limitations due to inherent problems with accelerated testing conditions. This paper introduces a novel chemical reactivity index (RI) to evaluate the alkali–silica reactivity of coarse aggregates or concrete mixtures by exposing samples to a simulated pore solution with composition mimicking that expected in the concrete. Based on the mix design to be evaluated, aggregate samples are exposed to an alkaline solution of appropriate concentration and fixed amounts of CaO. The newly proposed alkali–silica RI is calculated based on the concentrations of silicon, aluminum, and calcium in solution after 21 days of exposure at 55°C. This RI, sensitive to alkali concentration and aggregate mineralogy, exhibited strong agreement with physical expansion. [ABSTRACT FROM AUTHOR]

The objective of this work is the quantification of hydration in cement. To monitor this quantity of hydrated cement "hydration degrees" we adopted the method of thermogravimetric analysis (TGA) which allowed us to determine the degree of hydration a(t), bound water (WB) and non-evaporable water. This study is completed by the analysis of diffractometers (DRX). Cements containing different percentages of slag. The evolution of the kinetics was studied during 3, 7 and 28 days. According to the results obtained, the hydration rate is inversely proportional to the addition content in the cement. The degree of hydration is directly related to the formation of hydrates and portlandite, more non-evaporable water retained in the hydrates corresponds to a high degree of hydration. This technique is coupled with the carbonation and strength of ordinary mortar. The experimental data obtained have been correlated and interpreted with regard to the evolution of strength and carbonation as a function of the degree of hydration, bound water and non-evaporable water of the cement hydrates. The Bhatty method is verified for the calculation of the degree of hydration and can be successfully applied for composite cements. [ABSTRACT FROM AUTHOR]

Due to the yearly enormous amounts of produced phosphogypsum waste and the continuous increase of CO2 emissions in the atmosphere, it is necessary to find attractive approaches to solve these two environmental problems. The present work proposes an efficient method, which allows both the valorization of the Moroccan phosphogypsum waste (MPG) by synthesizing marketable products and the reduction of the emission of greenhouse gases especially the carbon dioxide (CO2). We have examined the effect of the following operational parameters: Molar Ratio KOH/MPG (2 ≤ MR ≤ 3), CO2 injection flow rate (5 ≤ V CO 2 ≤ 20) mL min−1, Portlandite concentration (10 ≤ CPort ≤ 25) g L−1 and the temperature (18 ≤ T ≤ 37) °C on the precipitation of calcium carbonate (CC) from the Portlandite (P) prepared by dissolving Moroccan phosphogypsum (MPG) in a KOH solution. The simultaneous change in electrical conductivity and pH of saturated solutions has also been studied. This technique can be particularly useful when we are interested in controlling the chemical reaction process. In all cases, we have observed a general similarity between the corresponding X-ray diffraction patterns of calcium carbonate (CC) precipitated from pure Gypsum (G) and from Moroccan phosphogypsum (MPG). This study can pave the way towards using Moroccan phosphogypsum, originated from phosphate chemical plants producing phosphoric acid, as a substituent for natural gypsum. This leads to effective waste management and environmental sustainability. K2SO4 and CaCO3 produced were highly recommended in the field of the agriculture, chemical and construction industries. [ABSTRACT FROM AUTHOR]

Cement-based materials (CBMs), such as paste, mortar and concrete, are highly alkaline with an initial high pH of approximately 12.0 to 13.8. CBMs have a high pH due to the existing oxide mineral portlandite and alkali metal contents in Portland cement. The high pH of concrete provides excellent protection and reinforces the steel bars against corrosion. The pH of concrete does not remain constant due to ageing and other defect-causing factors, such as chloride ingress, alkali leaching, carbonation, corrosion, acid attack, moisture and biodegradation process. Reducing the concrete pH has negative impact on the strength, durability and service life of concrete buildings. However, the high pH of concrete may also cause concrete structure deterioration, such as alkali silica reaction, porosity and moisture related damages in concrete structures. The pH of CBMs can be influenced by high temperatures. For instance, the extremely high volume (85%–100%) of slag-blended cement pastes shows considerable pH reduction from 12.80 to 11.34 at 800 °C. As many concrete structure deterioration are related to concrete pH, using an accurate and reliable method to measure pH and analyse the durability of reinforced concrete structure based on pH values is extremely important. This study is a comprehensive review of the pH of CBM in terms of measurement, limitations and varying values for different CBM types. [ABSTRACT FROM AUTHOR]

The influence of the capacity of supplementary cementitious materials (SCMs) to consume portlandite on the carbonation resistance of mortar was investigated. Seven different mineral additives (two types of slag, two types of fly ash, two calcined clays and limestone) were used and their reactivity was measured using isothermal calorimetry, strength index measurements, Chapelle's test and thermogravimetric analysis. Mortar samples were cast by substituting 30% cement by mass with SCMs and their carbonation performance was investigated. The carbonation resistance of cement was found to have no specific correlation with the compressive strength of the mortar cast using it. Different reactivity test methods showed a reasonable correlation between the reactivity of the non-hydraulic SCM and the carbonation resistance of the cement containing that SCM. The performance of different cement binders under carbonation was found to be influenced by the alkaline content and compressive strength collectively. [ABSTRACT FROM AUTHOR]

Distributions of calcareous calthemite deposits have been widely documented, but depositional processes and the architecture of their internal fabrics are not well understood. These concrete degradation products from a case study area in western Canada have external morphologies comparable to calcite speleothems formed in natural limestone caves, but the internal microstructural architecture and mineralogy are markedly different. The mineralogy consists of mostly calcite with secondary halite and minor percentages of trona and portlandite. A novel morphogenetic model explains depositional processes resulting in calcareous crusts that follow fractures of an overlying concrete surface, and how sufficient structural integrity provided by the internal architecture supports attachment areas of tubular soda straws. Interiors of these multi-cm crusts consist of curvilinear calcite laminae arrayed as sub-parallel walls, compartmentalizing water–gas interfaces along variously interconnected conduits and basin-form chambers. Overall porosities of 40–60% or more are prevalent, in contrast to < 1% associated with externally similar drapery-form crusts deposited within natural limestone caves. Several calcite fabrics new to calthemite deposits are described, including dendritic shrubs that coalesce into concentric growth rings along central canals of soda straws. [ABSTRACT FROM AUTHOR]

This study evaluates the effect of ten organic additives belonging to the classes of carbohydrates and sulfonates on the microstructure of portlandite crystals during CaO hydration. Calcium hydroxide modified with selected additives was prepared and characterised in terms of crystal size and habit, platelets abundance, crystallinity, specific surface area, particle size distribution, calcium concentration and organics in solution, using XRD, SEM, N 2 absorption/BET, laser diffraction, ICP-OES and HPLC-MS. The results suggest that the microstructure of portlandite is altered by the presence of carbohydrates and sulfonates, mostly showing higher platelets abundance, smaller crystallite size, and higher specific surface area. The presence of hydroxyl-rich carbohydrates induced more marked effects compared to sulfonates. These results show that it is possible to tailor the properties of lime to specific applications. Consequently, this study can impact the conservation and the construction industry by enabling the development of novel binders for modern construction with optimal properties, and more broadly fields such as the synthesis of precipitated calcium carbonate and the design of CO 2 sorbents, all of which will have the added value of reducing the global anthropogenic CO 2 emissions. [ABSTRACT FROM AUTHOR]

Energy storage provides a greener path of efficient energy utilization. Recent trends of research suggest concrete as a potential thermal energy storage (TES) material. Its cheap commercial availability makes it one of the most deserving candidates. Cement paste is the key glue of concrete, hence performance of its major components in thermal conduction seeks thorough scientific study. Portlandite or calcium hydroxide is the second major component of cement paste, microscopically visible at a scale length of <10−4 m. Molecular dynamics (MD) simulation has been utilized to investigate the thermal transport mechanism of portlandite at an atomistic scale. The thermal conductivity of this component has been computed using three major force fields which are compared with the experimental outcome using modulated differential scanning calorimetry (MDSC). It has been observed that the simulation outcomes are in order with the experimental value but the results are sensitive to the choice of force fields. Excitation of molecules during thermal transport is predominantly governed by lower-frequency molecular vibration indicating the existence of Boson Peaks. This manuscript presents the full thermal conductivity tensor of portlandite along with the possible mechanism associated with thermal transport. [ABSTRACT FROM AUTHOR]