Unreacted Particles Research Articles

Effect of sodium gluconate addition on setting, hardening, and microstructure behaviour of hybrid alkaline mortar

In this investigation, the influence of adding 2%, 4%, 7%, and 10% sodium gluconate (SG) on the setting time of hybrid alkaline paste, and hardened and microstructure properties of hybrid alkaline mortar mixes were examined, and the results were compared with a control mix that made without addition of sodium gluconate. The hybrid alkaline paste and mortar mixes were prepared using a fixed proportion of OPC/fly ash (25%/75%), NaOH solution molarity of 9M, and sodium silicate to hydroxide ratio of 1.5. The results of this investigation found that the quick setting and abrupt loss of flowability of the control mix were improved by adding sodium gluconate, however, more promising results were observed at 7% and 10% sodium gluconate. The delay in polymerization due to lower availability of calcium ions, and adsorption of carboxyl and hydroxyl groups associated with sodium gluconate on the unreacted particles of binding materials and earlier formed products assisted in prolonging the time required for hardening. Further, the compressive strength declined at a higher dosage of sodium gluconate, however, the mortar mixes made with 2% and 4% sodium gluconate exhibited higher compressive strength than the control mix. The peak intensity of albite, nepheline, and C–S–H gel decreased at higher dosages of sodium gluconate, which was supported by a weaker microstructure characterized by more pores, micro-cracks, and partially reacted fly ash particles. Furthermore, the lower bridging oxygen content and greater Si–O–Na/ Si–O–T ratio at higher dosage of sodium gluconate confirms the delayed polymerization process.

Detection of Organic Explosive Residues from Outdoor Detonations using Confocal Raman Microscopy

The detection of post-blast residues in the aftermath of an explosion involving organic explosives with spectroscopic techniques is challenging as, typically, no microscopically visible unreacted particles remain after the explosion. However, some low-order explosions may leave visible particles behind, as well as the presence of significant amounts of unreacted material. In this study, four authentic open-air detonations using two simulated improvised explosive devices (IEDs) containing a mixture of military explosives (TNT and RDX), and two IEDs containing smokeless powder were conducted. The various materials they contained, including plastic, wood, and metal, were swabbed and extracted with acetone to create post-blast liquid extracts. The extracts were then dried and examined using confocal Raman microscopy, alongside a 50 ppm reference mixture of smokeless powder constituents, which was created to evaluate the effects of Raman scattering within the full smokeless powder mixture. Smokeless powder constituents, such as ethyl centralite, diphenylamine, nitroglycerin, and dibutyl phthalate, were successfully identified by comparison to the reference mixture on most substrates, with the exception of the paint stick (wood) substrate. TNT/RDX was also able to be identified in the extracts, with RDX crystals being observed in some dried extracts after solvent evaporation. However, the detection of TNT/RDX in the second detonation was unsuccessful, possibly due to an explosive chain reaction that was highly efficient. No trends were seen in substrate affinity for TNT/RDX. The challenges and benefits with the developed methodology for the detection of organic explosive residues from a variety of substrates are discussed in detail.

Synchronous vacuum hot pressing ultra-high performance geopolymer: Ultrafast polymerization and early strength development

To overcome the application bottleneck of geopolymer in high-end industries, this study aims to develop ultra-high performance geopolymer products. By employing Synchronous Vacuum Hot Pressing, we have significantly enhanced the rate of polymerization and mechanical properties of Geopolymer based on Metakaolin-Fly Ash. The influence of Si/Al ratio, alkali equivalent, and molding time on the geopolymerization process, mechanical properties, and microstructure of geopolymers was investigated, while elucidating the underlying mechanisms. The compressive strength of SVHP-MFG reaches 90.92 MPa when the Si/Al ratio is 2, alkali equivalent is 8 %, and molding time is 30 min, owing to increased production of aluminosilicate gels and matrix structure densification. The ongoing reaction of unreacted particles and the subsequent transformation from "alumina-rich gel" to "silica-rich gel" in later stages further enhance the mechanical properties of the material. Additionally, the mean pore diameter of Synchronous vacuum hot pressing of metakaolin-fly ash geopolymer measures below 13.24 nm, thereby significantly enhancing the pore structure of the geopolymer. The synchronous vacuum hot pressing metakaolin fly ash-based geopolymers synthesized in this study represents a novel category of ultra-high performance ceramic-like geopolymers, exhibiting exceptional early strength and early stability. The research aims to promote the application of geopolymer in high-end industry and provide technical and theoretical support for the development of ultra-high performance geopolymer based products.

Electrochemistry Beyond Solutions: Modeling Particle Self-Crowding of Nanoparticle Suspensions.

Nanoparticle suspensions hold promise to transform functionality of next-generation electrochemical systems including batteries, capacitors, wastewater treatment, and sensors, challenging the limits of existing electrochemical models. Classical solution-based electrochemistry assumes that charge is transported and transferred by point-like carriers. Herein, we examine the electrochemistry of a model aqueous suspension of nondissolvable electroactive nanoparticles over a wide concentration range using a rotating disk electrode. Past a concentration and rotation rate threshold, the electrochemistry deviates from solution theory with a maximum attainable current due to particle "self-crowding" where reacted particles on the electrode surface reduce the area accessible for charge transfer by unreacted particles. The observed response is rationalized with an analytical model considering the physical adsorption/desorption kinetics and interfacial transport of nondissolvable finite-size charge carriers. Experimental validation shows the model to be applicable across a range of electrode sizes and thus suitable for engineering electrochemical systems employing nondissolvable nanoparticle suspensions.

New geopolymer preparation methods and its application by recycle of double-waste: ground granulated blast furnace slag and fly ash

ABSTRACT This article mainly studies new geopolymer preparation methods by recycle of double waste:ground granulated blast furnace slag (GGBFS) and fly ash as geopolymer precursor, through different mass ratio of GGBFS and fly ash, to prepare geopolymers by alkali activation, the samples is cured at ambient temperature and the mechanical test is carried out together with the analysis of XRD, SEM and EDS to research the mechanism of strengthening and geopolymerisation. After analysis we find that the sample prepared by 30% mass ratio of GGBFS have good initial strength and short setting time, as well as best mechanical performance, which is attributed to moderate Ca2+ introduction accelerates the speed of geopolymerisation and the reactants of N-A-S-H gel, C-A-S-H gel and hydrated C-S-H help to bridge the gaps between the different hydrated phases, unreacted particles and matrix, result in a homogeneous and compacted geopolymeric sample. When GGBFS mass ratio above 50%, the mechanical of samples is deteriorated due to too much hydrated calcium containing compounds are formed and covered on the unreacted GGBFS particles surface to block further geopolymerisation. The acid attack test and water resistance test are carried out to analysis the durability between 30% GGBFS introduced geopolymer and ordinary Portland cement (OPC). In additional, a field application in case of 30% GGBFS introduced geopolymer grouting repair material indicated desirable construction based on visual observation and ground-penetration radar scanning.

Selective extraction of molybdenum from an industrial powdery tungsten-molybdenum mixture scraps through ultrasonic-assisted electrochemical dissolution mechanism

Extraction and recovery of W and Mo from waste scraps hold significant importance for sustainable resource utilization and environmental protection. Ultrasonic-assisted leaching was demonstrated to be a clean and efficient method for metal dissolution and separation, and the research emphasis of this work was focused on ultrasonic electrochemical behaviors. The HNO3 leaching behaviors of W and Mo under conventional and ultrasonic-assisted processes from powdery W-Mo mixture scraps generated in the powder metallurgy process were investigated. It’s demonstrated that Mo and W can be selectively separated by the regulation of lixiviant concentration and temperature, in which the Mo is converted into the soluble ions (MoO22+) while the W particle is kept in original metallic state and covered with insoluble WO3·H2O. Experiment results indicated that 96.38 % Mo and 8.03 % W were rapidly leached in 2 mol/L HNO3 within ultrasonic-assisted leaching for 10 min at 25 °C, showing a favorable pre-separation effect. Phase transformation and microstructure evolution of the leaching residues under conventional and ultrasonic-assisted leaching processes were analyzed. It’s suggested that Mo can precipitate in the form of molybdenum oxide hydrates, covering the unreacted particle surfaces and further hindering the Mo leaching, especially at higher temperature. This unfavorable situation can be relieved by the introduction of ultrasonic cavitation effect. Importantly, the electrochemical dissolution behaviors of pure W, pure Mo, and W-Mo alloy sheets in HNO3 solution were compared employing the potentiodynamic polarization and electrochemical impedance spectroscopy testing to reveal the ultrasonic intensifying mechanism in this study. Eventually, the ultrasonic electrochemical intensifying mechanism can be referential for the efficient dissolution of metal-based scraps for resource recycling.

Enhancing geopolymer binder reactivity and performance via mechanochemical activation: A comprehensive study of rheological, mechanical, and microstructural properties

In this study, mechanochemical activation was utilized to formulate an eco- and user-friendly geopolymeric binder. This method offers an alternative approach to address challenges inherent in conventional two-part geopolymers. The process involves milling solid-state raw materials with diverse compositions, followed by the addition of water solely to initiate the geopolymerization reaction. Comparative analyses were conducted using conventionally activated geopolymer (CAG) paste and ordinary Portland cement (OPC) paste. The study also investigates the effects of ground granulated blast furnace slag/fly ash (GGBFS/FA) ratios (50:50, 75:25, and 100:0) and sodium silicate/sodium hydroxide (SS/SH) ratios (0.5, 1.5, and 2.5) on the rheological, fresh, mechanical, and microstructure characteristics of mechanochemically activated geopolymer (MAG) paste. The experimental findings indicate that mechanochemical activation reduced rheological characteristics and setting time, accompanied by an 11% increase in strength compared to the conventional activation method. Additionally, increased GGBFS content positively influenced rheological characteristics and mechanical properties, whereas higher SS/SH ratios adversely impacted these aspects. Setting time was significantly reduced with higher GGBFS content but increased with higher SS/SH ratios. Microstructural analysis revealed the presence of additional unreactive particles in both conventionally activated geopolymer and MAG paste containing 50% GGBFS.

Preparation of geopolymers from thermally activated lithium slag as sole precursor: Mechanical properties and microstructure

Lithium slag (LS) is a waste residue generated during lithium extraction, posing significant environmental challenge due to its extensive accumulation. This study proposes a method of utilizing thermally activated LS as the sole precursor for geopolymer synthesis. The thermal activation mechanism of LS was investigated using XRD, FTIR, ICP, and SEM techniques, while exploring the optimal composition for LS geopolymers(LSG). The research revealed that heating at 700 °C increased the amorphous content of LS from 15.9 % to 48.1 %, altering the chemical structure of its aluminosilicates and enhancing its leaching capacity in alkaline environments, thereby boosting its reactivity. The activator modulus and alkali equivalent were found to significantly influence the strength and microstructure of LSG. As the modulus increased from 1.0 to 1.4, geopolymer strength initially rose before declining, whereas strength progressively increased with alkali equivalent from 0.10 to 0.16. The geopolymer synthesized with a modulus of 1.2 and alkali equivalent of 0.16 exhibited the highest compressive strength of 53.1 MPa after 28 days. Test results indicated that the internal structure of LSG primarily comprised unreacted particles, N(C)-A-S-H gel, and microcracks. The increased alkali equivalent facilitated the dissolution of Si4+ and Al3+ within LS, intensifying geopolymerization to produce more N(C)-A-S-H gel, thereby densifying the structure and significantly enhancing compressive strength. This study elucidates the mechanism by which high-temperature calcination enhances LS reactivity, as well as the impact of activator on compressive strength and microstructural properties of LSG, offering new insights into the engineering applications of LS in high-performance cementitious materials.

Potassium citrate-activated pure BOF slag-based mortars utilizing carbonated and autoclaved BOF slag aggregates

This study proposes novel basic oxygen furnace (BOF) slag mortars formulated with tri-potassium citrate (TPC) activated BOF slag as binder and treated BOF slag (carbonated (CB) and autoclaved (AB)) as aggregates, aiming to maximize the utilization of BOF slag in the construction industry. Untreated BOF slag (UB) and natural sand (NS) were employed as reference aggregates. The effects of carbonation and autoclaving were investigated, focusing on the interfacial transition zone (ITZ) properties through SEM-BSE greyscale thresholding and constituent segmentation analysis. Results indicate that both treatments reduce the free CaO, promote CaCO3 formation, and modify the aggregate surface. The 28 d compressive strength of pure BOF slag-based mortars with UB, CB, and AB aggregates are 25.8, 29.4, and 34.8 MPa (average at varying TPC dosages), significantly higher than that with NS (19.6 MPa). Pure BOF slag-based mortars also show narrower ITZ thicknesses and the absence of bond cracks. Mortars with CB and AB aggregates exhibit fewer unreacted particles and more hydration products within the integral binder region compared to those with UB. Overall, pure BOF slag-based mortars present a more robust aggregate/binder interface that is further enhanced by the aggregate treatments. Leaching values of all mortars are well below the Dutch legal limits. The findings suggest promising application prospects for pure BOF slag-based mortars in substituting cement mortars and valorizing BOF slag.

Effect of Public Fillers on Cement-Stabilized Recycled Mixes of Road Performance: Mechanical Properties, Microstructure, and Durability.

In order to address the challenges of resource utilization posed by construction waste, the substitution of natural aggregate (NA) with public fill (PF) contents was investigated for load reclamation and road grassroots applications. A comprehensive assessment of road performance for the recycled mixture was conducted, focusing on parameters such as unconfined compressive strength, splitting strength, compressive resilience modulus, dry shrinkage, and frost resistance. Additionally, the impact of incorporating PF at various types and replacement ratios on the microstructure of cement-stabilized aggregate (CSA) was analyzed. The results indicated that the unconfined compressive strength of cement-stabilized recycled mixture with varying PF contents meets the base strength requirements for heavy, medium, and light traffic pavement on secondary and sub-secondary roads in China. Notably, the unconfined compressive strength and resilience modulus follow a similar pattern, reaching their peak at a 25% PF content. Microscopic examination reveals that an appropriate PF content leads to the predominant formation of C(N)-A-S-H, hydrotalcite, Ca(OH)2, and CaCO3 as paste reaction products. As the replacement of public fill increases from 0% to 25%, there is a gradual stacking of gel products, which enhances the compactness of the microstructure by cementing together unreacted particles. Consequently, this process reduces dry shrinkage strain and effectively mitigates the formation of reflection cracks. Applying large quantities of public fill to road construction can effectively deal with various waste accumulation problems and produce a novel road material with significant social, economic, and environmental benefits.

Kinetics of Estonian Phosphate Rock Dissolution in Hydrochloric Acid

The kinetics of the dissolution of Estonian phosphate rock and the governing reaction mechanisms in hydrochloric acid in technological processes were investigated. The influences of particle size and acid concentrations of 0.5–1.5 M on the reaction rate and the pH variation during the process were studied at a dosage of 2.1 moles of HCl per mole of calcium for 60 min. The results indicated that the solubility of phosphorus reached 94%–100% for the fine samples and 82%–99% for the coarse samples. The time required to achieve an apparent steady-state pH reduced with the increasing acid concentrations and decreasing particle sizes. It was determined that the CaF2 precipitation in solutions starting at 1 M was faster at higher concentrations. The SEM surface analysis of the insoluble particles proved the existence of etch pit formation. The XPS and EDX analyses affirmed that the dissolution was incongruent. The surface composition of the unreacted particles gave a stoichiometry of CaF1.8, showing the formation of CaF2 on the surface. The dissolution kinetics were analyzed using the shrinking core model and showed a combination of chemical reaction, diffusion or interfacial transfer, and diffusion, sequentially for coarse particles or simultaneously for fine fractions.

Large-scale application of coal gasification slag in nonburnt bricks: Hydration characteristics and mechanism analysis

Coal gasification slag (CGS) is a typical solid waste from the coal gasification process. Reusing CGS into building materials is a key means of realizing its large-scale utilization. This study aims to utilize CGS at a large dosage for the preparation of nonburnt bricks. The CGS, red mud, fly ash and desulfurization ash were utilized to synergistically prepare nonburnt bricks. The mechanical, durability and environmental performance of nonburnt bricks were analysed. Moreover, XRD, thermogravimetric analysis, FTIR, MIP and SEM were conducted to analyse the hydration products and microscopic morphology. The results revealed that when the CGS dosage reached 60%, the best performance of prepared nonburnt bricks was achieved. The unconfined compressive strength was 8.3 MPa at 3 d, 18.2 MPa at 7 d and 24.0 MPa at 28 d. Undergoing 25 cycles of freeze-thaw, the mass loss ratio was 0.9% and strength loss ratio was 10.67%. The alkaline solid wastes (red mud) have a promoting effect on the dissolution of active components in CGS, and the calcium content in blast furnace slag and desulfurization ash, as well as the sulfate in desulfurization ash, can enhance the formation of hydration products. The microstructures displayed the formed clustered C-S-H gels and reticulated C(N)-A-S-H gels tightly wrapped unreacted particles and filled the interstitial spaces of the materials, causing to an elevation in the compactness and a decline in the number of harmful pores. In addition, heavy metals (Cr, As, Cd and Pb) in CGS were well solidified. This study provides a rationale for the harmless and resourceful utilization of CGS.

Behaviour of alkali-activated fly ash-slag paste at elevated temperatures: An experimental study

As an environmentally friendly material, alkali-activated fly ash-slag (AAFS) is considered as a promising alternative cement because of its excellent mechanical properties and thermal stability. Nevertheless, high temperature induced damage in AAFS can potentially bring serious risks for its practical applications. This paper presents a systematic experimental study on behaviour of AAFS paste subjected to elevated temperatures up to 800 °C in terms of microstructure as well as thermal and mechanical properties. Microstructural evolution was characterised by means of Rietveld-based quantitative X-ray diffraction (QXRD), backscattered scanning electron microscope (BSEM) and X-ray microcomputed tomography (XCT), while thermal and mechanical properties were evaluated from thermogravimetric analysis (TGA), thermal deformation and compressive and flexural strengths. Results indicate that the compressive strength of AAFS paste rises by 77.5 % at 200 °C, followed by a mitigation from 200 to 600 °C and a regain at 800 °C. Different phases in AAFS paste including unreacted particles, reaction products and pores took up 30 %, 67.7 % and 2.31 % at ambient temperature, and 4.95 %, 84.8 % and 10.3 % after exposure to 800 °C, respectively, suggesting the recrystallisation with the formation of nepheline and gehlenite. In addition, the relationships between microstructural characteristics including three-dimensional (3D) pore structure features and thermal and mechanical properties of AAFS paste at elevated temperatures were explored and discussed in depth to gain insights into the underlying degradation mechanisms including pore pressure build-up, thermal gradient and phase transformation.

A grain-scale modeling on the surface burning and agglomeration of the metalized solid propellants

This study delves into the dynamic behavior of reactive grains within metalized propellants during surface deflagration. Our grain-scale simulations account for both fast and slow deflagration processes involving two distinct metal fuels, namely zirconium and magnesium, with potassium perchlorate (KClO4) as the common oxidizer. Our primary goal is to develop a model and numerical technique capable of replicating the surface reactions observed in experiments. To achieve this, we utilize the compressible Navier–Stokes equations, incorporating the Arrhenius rate law and Johnson-Cook stress model. We pay particular attention to the melt layer, where surface burning occurs in an open atmosphere, and we develop a mechanism to describe the interaction between reactive grains and exhaust gases. We differentiate between two limiting scenarios: convective burning, where unreacted particles experience high-speed compression waves leading to reduced thermal diffusion within the cold reactant, and diffusive burning, characterized by insufficient pressure from particles undergoing both reaction and deformation to erode the burning surface. This results in pronounced agglomeration and the formation of gaseous metal oxides above the melt layer. The results shed light on critical factors influencing surface combustion, including the thermal softening of reactive particles, the time required for particle agglomerations, and tangential forces at multi-element interfaces within the grain-scale simulation domain.

Immobilization of fluorinion in phosphorus tailings-blast furnace slag based geopolymers activated by waste alkalis

Calcium carbide reduce-mirabilite was used as an alkaline activator to prepare geopolymer materials based on phosphorus tailings (PT) and blast furnace slag (BFS) for immobilization of anion fluorine (F). The influence of free F on mechanical properties, microstructure, and microtopography of geopolymers was discussed. The immobilization effect and mechanism of geopolymers on free F were studied. The results show that free F will cause more pores in the geopolymer, increase the proportion of unreacted particles and N-A-S-H gel, and reduce the proportion of C-(A)-S-H gel, resulting in a slight decline in mechanical properties. The leaching test shows the F leaching concentration gradually decreases while immobilization rate gradually increases with increasing BFS proportion. The immobilization mechanism of free F is reflected in that Ca2+ in geopolymer reacts with free F to form insoluble precipitates CaF2 and Ca5(PO4)3F, and the further immobilization of free F by the physical encapsulation of gel in geopolymer.

Exploring the Impact of Surface Functionalization on the Reaction, Magnetophoretic, and Collective Transport Behavior of Nanoscale Zerovalent Iron.

This study provides a systematic analysis of the transport and magnetophoretic behavior of nanoscale zerovalent iron (nZVI) particles, both bare and surface functionalized by poly(ethylene glycol) (PEG) and carboxymethyl cellulose (CMC), after undergoing a chemical reaction. Here, a simple and well-investigated chemical reaction of methyl orange (MO) degradation by nZVI was used as a model reaction system, and the sand column transport and low-gradient magnetophoretic profiles of the nanoparticles were measured before and after the reaction. The results were compared over time and analyzed in the context of extended Derjaguin-Landau-Verwey-Overbeek (DLVO) theory to understand the particle interactions involved. The colloidal stability of both bare and functionalized nZVI particles was enhanced after the reaction due to the consumption of metallic Fe content, resulting in a significant drop in their magnetic properties. As a result, they exhibited improved mobility across the sand column and a slower magnetophoretic collection rate compared to the unreacted particles. Here, the colloidal filtration theory (CFT) was employed to analyze the transport behavior of nZVI particles across the packed sand column. It has been observed that the surface properties of the reacted functionalized particles changed, possibly due to the entrapment of degraded products within the polymer adlayer. Moreover, quartz crystal microbalance with dissipation (QCM-D) measurements were performed to reveal the viscoelastic contribution of the adlayer formed by both bare and functionalized nZVI particles after the reaction on influencing their transport behavior across the sand column. Finally, we proposed the implementation of a high-gradient magnetic trap (HGMT) to reduce the transport distance of the colloidally stable CMC-nZVI, both before and after the reaction. This study sheds light on the behavioral changes of iron nanoparticles after the reaction and highlights environmental concerns regarding the presence of reacted nanoparticles.

Lightweight, robust hierarchically porous ceramics from cost-effective powders for dye removal

A facile and cost-effective approach for hierarchically porous ceramics has been proposed firstly, using coal fly ash as the main powder while secondary aluminum dross (SAD) as curing and foaming agents. Benefited from the hydrolysis of AlN and Al in SAD, gas and lamellar aluminum hydroxide sol attached to the surface of unreacted particles were produced, meanwhile pH value and viscosity increased, realizing foaming and coagulation casting simultaneously to fabricate porous green body. The increase of SAD amount could contribute to more intensive formation of flaky aluminum hydroxide sol, enhancing mechanical strength of green body, which has high compressive strength of 1.03 MPa at a bulk density of 0.68 g/cm3. Porous mullite-based ceramics could be sintered at a relatively low temperature of 1200–1250 °C owing to alkali metal oxide and amorphous SiO2 in the solid wastes, which also help to form micropores on the pore wall due to partially sintering. Porous mullite-based ceramics possess hierarchical pores, bulk density of 1.00 g/cm3, open porosity of 66.15%, specific surface area of 2.24 m2/g and compressive strength of 9.14 MPa. Their removal rate of malachite green solution reaches 99.1% at a concentration of 100 mg/L and an adsorbent dosage of 100 g/L.

Phosphorus removal by porous aggregate from aerated concrete waste residues：Simulating porous structure, performance optimisation, adsorption mechanisms

In order to reveal the action mechanism of porous structure of aerated concrete waste residues as aggregate on its working performance and phosphorus removal performance, the porous aggregate is prepared by adjusting the of hydrogen peroxide (H2O2) content to simulate the pore structure of aerated concrete. The results show that with the increase of H2O2 content, the porosity and pore diameter of porous aggregate increases, which causes that the loose bulk density, cylinder compressive strength and softening coefficient decrease and the water absorption through time increases. The correlation coefficients between the four performances and total porosity exceeds 0.95. With the increase of H2O2 content, the pH value decreases and TP removal rate increases. The better fitting of the pseudo-second-order model and Elovich model confirms the key existence of chemical adsorption. In the fitting curve of Intraparticle diffusion model the second stage of rapid absorption becomes the main control step due to calcium and aluminum ions from capillary pores and gel pores and the hydration of unreacted particles. The Ca/Si and Al/Si decreases by 57.7% and 46.6% in EDS maps after phosphorus removal, and CaO/SiO2 and Al2O3/SiO2 in XRF results decrease. The hydration of unreacted C4A3Š and dissolution of Ca2+ and Al3+ during phosphorus removal promote the chemical absorption of porous aggregate. P/Si increases by 631.9% and P2O5/SiO2 increases from 0.01 to 0.11. The fluffy substances appears on the smooth inner wall of the porous aggregate in SEM morphology is phosphate mineral.

Low clinker systems - Towards a rational use of SCMs for optimal performance

Progress in understanding the use of SCMs in blended Portland cement and related effects is reviewed. An optimized use of cement components will avoid wasting unreacted particles that do not contribute to the mechanical and durability performances. The reactivity of cement components increases with fineness and by controlled production processes. Clinker may become a minor component in the cementitious mix due to the optimized particle packing of blended cements. An optimized mineralogy of the clinker coupled to the addition of activators can help to further reduce its use in composite cements while maintaining concrete performance. Other cement constituents introduce different filler and chemical effects to the overall reaction and contributes differently to the performance. Filler and chemical effects influence the hydrates assemblage and in particular C-S-H formation, morphology, and chemical composition. The cement and concrete properties at different ages are tightly linked to these properties. Future approaches could be more technical than simply grinding and blending, allowing a better use of each cement component to achieve a lower CO2 intensity.

Impact of solution pH (5–9) and dissolution products on in vitro behaviour of the bioactive glass S53P4

The impact of dissolution products on the reaction behaviour of bioactive glasses was explored. Bioactive glass S53P4 particles were immersed in solutions with initial pH of 5–9. After 24 and 72 h, the solution extracts were used for testing unreacted particles. The pH, ion concentrations, and glass surfaces were analysed as functions of immersion time. More Ca, Na, and P dissolved at lower pH (5) than at higher pH (7.4 or 9). The dissolution changed from an incongruent to an apparent congruent with increasing pH. Dissolution products in extracts changed the reaction layer structure on glass particles and led to lower ion release at pH 7.4 and 9. Dissolution increased almost linearly with time in acidic solutions. Silica-rich layer and calcium phosphate were identified on the particles after immersion in all solutions except at pH 9. Local ion concentration variations affected dissolution, leading to nonuniform ion release rates.