Crystalline Hydrates Research Articles

INFRARED SPECTROSCOPIC ANALYSIS OF COMPLEX OXIDE CATALYST 50%Cu3(PO4)2•50%Ni3(PO4)2

It is established that the frequencies and intensities of the absorption bands of the infrared spectra of the obtained air-dried sample 50%Cu3(PO4)2∙50%Ni3(PO4)2 and calcined at the optimum heat treatment temperature of 600оС are characterized by significant absorption in the valence (3460-3020 cm-1) and strain (2360-1400 сm-1) vibrations of hydroxyl OH-groups of water molecules. Valence vibrations of phosphate ion are most manifested in dehydration products in the form of clear bands in the absorption frequency range 1110-410 сm-1. For the investigated sample, three absorption bands were observed in the region: 3188,72 сm-1, 1621,84 сm-1 та 1434,78 сm-1. They confirm the existence of two types of crystalline hydrate water molecules, which are characterized by different hydrogen bonding energies. In the process of heat treatment of the synthesized sample in the temperature range of 120-700оС , the process of dehydration occurs. In this case, the intensity of the absorption bands in the region of valence and strain vibrations of water molecules gradually decreases in the obtained IR spectra. The phenomenon of complication of the spectrum of orthophosphate ion by additional absorption bands is obviously associated with the distortion of the tetrahedron structure in real crystals and the reduction of its symmetry. It can be a consequence of both low symmetry of the environment and perturbation of the orthophosphate anion РО43– by water molecules when intermolecular hydrogen bonds occur. It may also be due to possible additional coordination of orthophosphate anion with metal cations Сu2+ and Ni2+. Calcination of the sample at the final heat treatment temperature of 700оС leads to an anhydrous orthophosphate system. This will lead to a decrease in the value of surface acidity and catalytic inertness of the sample.
 Keywords: catalysts; heterogeneous catalysis; phosphates; complex oxides; oxidation; n-alkanes; hydrocarbons; ethane; ethylene; IR spectroscopy.

New Bench-Scale Method To Elucidate Active Pharmaceutical Ingredient Drying Mechanisms

Drying of an active pharmaceutical ingredient, in the form of a crystalline hydrate, was investigated using a small-scale flow cell methodology. A new laboratory tool was developed and demonstrated using a simple segregated column technique to quickly distinguish different drying mechanisms using a minimal number of experiments. For the case studied here, increasing vacuum levels improved the removal of solvents while use of nitrogen flow through the solids facilitated water removal. Additional results are presented from experiments conducted to assess the impact of the crystallization solvent system and washing on drying behavior and cake properties. A system was identified which avoided issues associated with poor cake handling and improved overall drying performance. This article provides details on the new experimental method used that helped lead to the rapid development of an improved drying process and presents results demonstrated through the pilot plant scale.

THE THERMAL CONDUCTIVITY OF MOLTEN MIXTURES OF СeCl<sub>3</sub>–MCl (M = Li, Na, K, Cs) SYSTEMS

The paper presents experimental data on the thermal conductivity of molten salt mixtures СeCl3–MCl, where M = Li, Na, K, Cs. The concentration of cerium trichloride varies from 0.25 to 0.75 mole percent in 0.25 increments. The initial salts of alkali metal chlorides were certified by DSC. The obtained values of melting temperatures are in good agreement with the literature data. Anhydrous cerium trichloride was obtained from cerium(IV) oxide in 2 stages: preparation of cerium crystalline hydrate and removal of water of crystallization. The measurements were carried out by the stationary method of coaxial cylinders in a nickel device in the temperature range individually selected for each composition. The relative measurement error does not exceed 5%. In this work, the convective and radiative contributions to heat transfer were estimated. The value of the product of Prandtl and Grashof numbers is less than 1000, which confirms the absence of convection. The calculated radiative contribution to heat transfer does not exceed 2.4%. The thermal conductivity of all investigated melts increases with increasing temperature. The concentration dependences of molten mixtures of cerium and alkali metal chlorides were obtained. The thermal conductivity decreases upon passing from Li to Cs, which is due to an increase in the radius of the alkali metal cation and, as a consequence, an increase in the interionic distance.

МАТЕМАТИЧЕСКИЕ МОДЕЛИ ЗАВИСИМОСТИ СТРУКТУРНЫХ И ДЕФОРМАЦИОННО-ПРОЧНОСТНЫХ СВОЙСТВ ГИПСОДРЕВЕСНОГО КОМПОЗИТА ОТ КОМПОНЕНТНОГО СОСТАВА

The production of cement-wood composites (CWC) is difficult due to the presence of extractable substances in the wood filler, which have a negative effect on the hydration of cement, the shape and size of the resulting crystalline hydrates, and the setting time, which leads to a decrease in the strength characteristics of the CWC. Gypsum-wood composites (GWC), in contrast to CWC, are less sensitive to the effects of extractable substances, but they are characterized by low strength and deformability. In order to improve the structural and deformation-strength properties of the GWC, the article presents a mathematical modeling of the effect of the component composition on the average density, open porosity, compressive strength and modulus of elasticity of a gypsum-wood composite for the installation of partitions and enclosing structures in buildings for various purposes. Mathematical models of the dependence of GWC properties on the amount of building gypsum, urea-formaldehyde resin and wood filler from freshly cut hardwood are presented. According to Student's and Fisher's criteria, an assessment was made of the statistical significance and adequacy of the obtained mathematical models, which make it possible to determine the rational values of recipe factors in the manufacture and operation of GWC with an average density of 1250-1370 kg/m3, an open porosity of 25-36%, and a compressive strength of 25-30 MPa, modulus of elasticity 1210-1780 MPa.

ПОЛУЧЕНИЕ НАНОКОМПОЗИТОВ СЕРЕБРА ТЕРМОЛИЗОМ МЕТАЛЛСОДЕРЖАЩИХ МОНОМЕРОВ

A number of new metal-containing monomers have been obtained by direct interaction of unsaturated mono- and dicarboxylic acids with silver nitrate. The study of their thermal properties showed that thermolysis proceeds in two or three (for crystalline hydrates) stages. The end products of thermolysis are silver nanocomposites containing metallic silver nanoparticles stabilized by a carbon matrix. Silver particles are located relatively evenly in the object, the amplitude during scanning in a given direction allows us to state that the particles have a shape close to spherical, while some of the large particles, about 30 nm, are aggregates of smaller particles formed during thermolysis.

Influence of MgAl-LDHs/TiO2 composites on the mechanical and photocatalytic properties of cement pastes and recycled aggregates

To study the effects of MgAl-LDHs/TiO2 on the properties of cement paste and recycled aggregates, MgAl-LDO (MgAl-LDHs calcined products) and TiO2 were mixed during the reconstruction of MgAl-LDHs laminates based on the memory effects of layered double hydroxides (LDHs), and then MgAl-LDHs/TiO2 was synthesized. The performance changes were characterized with hydration heat tests, the microscopic morphologies of the hydration products, and the physical and mechanical properties of the cement paste. The effect of the MgAl-LDHs/TiO2 on the multi-interfacial transition zone (ITZ, the interface between the old paste and new paste) of the recycled aggregates was characterised with the micromorphology, meso-mechanical properties, and element diffusion behaviour. The photocatalytic activity of MgAl-LDHs/TiO2 loaded on recycled aggregate was evaluated with the degradation of methylene blue under sunlight. The results showed that the addition of MgAl-LDHs/TiO2 promoted the initial hydration of ordinary Portland cement (OPC) and induced and promoted the growth and formation of crystalline cement hydration products. The initial setting time and final setting time were shortened, and the compressive strength of the hardened paste was improved when MgAl-LDHs/TiO2 was added to the cement paste. The MgAl-LDHs/TiO2 compacted the recycled aggregates and improved the structural properties of the ITZ. The MgAl-LDHs/TiO2 altered diffusion within the ITZ. The total efficiency for the degradation of methylene blue by the 5–10 mm MgAl-LDHs/TiO2 loaded on recycled aggregate reached 82.2% after 80 min under simulated sunlight.

Synthesis of Hydrophobic Nanosized Silicon Dioxide with a Spherical Particle Shape and Its Application in Fire-Extinguishing Powder Compositions Based on Struvite.

Textural and morphological features of hydrophobic silicon dioxide, obtained by the hydrolysis of tetraethoxysilane in an ammonia medium followed by modification of a spherical SiO2 particles surface with a hydrophobic polymethylhydrosiloxane, were studied in this work. The size of silicon dioxide particles was controlled during preparation based on the Stöber process by variation of the amount of water (mol) in relation to other components. The ratio of components, synthesis time and amount of the hydrophobizing agent were determined to obtain superhydrophobic monodisperse silicon dioxide with a spherical particle size of 50-400 nm and a contact angle of more than 150°. In the case of the struvite example, it was demonstrated that the application of spherical- shaped hydrophobic silicon dioxide particles in powder compounds significantly improves the flowability of crystalline hydrates. The functional additive based on the developed silicon dioxide particles makes it possible to implement the use of crystalline hydrates in fire-extinguishing powders, preventing agglomeration and caking processes. The high fire-extinguishing efficiency of the powder composition based on struvite and the developed functional additive has been proven by using thermal analysis methods (TGA/DSC).

An approach for predicting the true density of powders based on in-die compression data

Helium pycnometry, a commonly used technique for measuring the true density of powders, is sensitive to the release of volatiles during measurement. This can lead to over-estimated true density, and as such, an accurate method for determining the true density of powders containing volatile components is needed. Here, a method based on in-die compression data obtained with a compaction simulator was assessed. Specifically, the stress transmission coefficient (STC), measured using an instrumented die, was used to predict the in-die Heckel mean yield pressure (Py). A true density was derived by repeatedly performing a Heckel analysis using iteratively estimated true density values until the predicted Py value from the measured STC value is obtained from in-die density - pressure data. This novel method was validated using a set of water-free powders. Using crystalline hydrates, we further showed that the calculated true densities were closer to values calculated from crystal structure than those from helium pycnometry. Hence, this method may be used for determining the true density of powders from their STC values.

Man-Made Raw Materials for the Production of Composite Silicate Materials Using Energy-Saving Technology

This paper presents the development of composite silicate mass compositions based on man-made waste for the production of autoclave hardening products, as well as the results of physico-chemical studies of hydration products of silicate materials. The possibility, expediency and efficiency of using multi-tonnage technogenic waste of Kazakhstan in the industry of composite building materials is shown. Based on the results of the conducted research, the composition of a composite silicate mass based on burnt carbonate-barium tailings (8–12%), electrothermophosphoric slags (82–90%) or sand and dust from cement kiln electrofilters (2–5%) for the production of autoclave hardening products was developed. It was found that the cementing substance in composite silicate materials is represented by CSH(B) calcium silicate hydrates, tobermorite and serpentine. The simultaneous presence of fibrous and crystalline calcium and magnesium silicate hydrates in hydration products leads to the creation of composite products with a maximum strength of 41–49 MPa.

An initial study on the effect of nano-zirconium on the behavious of alkali-activated slag cement subjected to seawater attack

In this article, for the first time, the possibility of adding nano-zirconium (NZ) into alkali-activated slag (AAS) cement as a modifier agent against seawater attack was studied. Different ratios of 1 %, 3 % and 5 % from NZ were added into the neat AAS cement. The effect of these additions on workability and compressive strength was measured. After initial curing, some specimens were exposed to seawater attack for 3, 6 and 12 M, whilst the others were cured in the air and tap water for the same periods for comparison purposes. The variation in the crystalline phases, hydration products and microstructures caused by the inclusion of different ratios of NZ were monitored by using X-ray diffraction (XRD), thermogravimetric analysis and its differential (TGA/DTG) and scanning electronic microscopy (SEM). The results showed a negative effect of NZ on workability. The incorporation of 1 % and 3 % NZ showed a positive effect on compressive strength before and after exposure to different media, whilst the incorporation of 5 % showed a negative effect. The optimum ratio of NZ was 1 %. This ratio can produce a denser and more compact microstructure, which can act as a barrier against ions and chloride diffusion from seawater to the specimens as well as migration of alkalis from the specimens to seawater.

Mechanical Strength and Microstructure of Ultrahigh-Performance Concrete under Long-Term Autoclaving

Solar thermal energy is a technology that collects radiant energy from the sun to generate heat or electricity. Thermal energy storage is required to compensate for the solar thermal energy variations across time scales, and a popular strategy is storing thermal energy in hot water tanks. Due to superior strength and durability, ultrahigh-performance concrete (UHPC) is exploited to construct such water tanks for applications at 200°C. Therefore, the mechanical strength and microstructure of UHPC after long-term temperature-pressure load (autoclaving) is studied. The compressive strength of UHPC can stay robust due to the accelerated formation of hydrates, while the flexural strength is vulnerable to long-term autoclaving due to the transformation of amorphous calcium silicate hydrate (C-S-H) to more ordered phases. The main hydrates in autoclaved samples are poorly crystallized C-S-H, hydroxylellestadite, and hydrogarnet. The porosity of autoclaved samples is not strictly related to the mechanical strength, and the influence of hydrate assemblage outweighs that of porosity on mechanical strength after long-term autoclaving. The partial replacement of cement by limestone powder can decrease crystalline hydrates and increase poorly crystallized C-S-H, which densifies the microstructure and enhances the mechanical strength. However, excessive poorly crystallized C-S-H aggravates the thermal mismatch between the matrix and quartz aggregates after autoclaved samples cool to room temperature, leading to interstice in matrix-quartz interfaces and, thus, reduced mechanical strength. Therefore, an appropriate addition of limestone powder is required to induce the hydrate assemblage with appropriate poorly crystallized C-S-H, ensuring durable UHPC structures under autoclaving.

Homogeneous nucleation of crystalline methane hydrate in molecular dynamics transition paths sampled under realistic conditions.

Methane hydrates are important from a scientific and industrial perspective, and form by nucleation and growth from a supersaturated aqueous solution of methane. Molecular simulation is able to shed light on the process of homogeneous nucleation of hydrates, using straightforward molecular dynamics or rare event enhanced sampling techniques with atomistic and coarse grained force fields. In our previous work [Arjun, T. A. Berendsen, and P. G. Bolhuis, Proc. Natl. Acad. Sci. U. S. A. 116, 19305 (2019)], we performed transition path sampling (TPS) simulations using all atom force fields under moderate driving forces at high pressure, which enabled unbiased atomistic insight into the formation of methane hydrates. The supersaturation in these simulations was influenced by the Laplace pressure induced by the spherical gas reservoir. Here, we investigate the effect of removing this influence. Focusing on the supercooled, supersaturated regime to keep the system size tractable, our TPS simulations indicate that nuclei form amorphous structures below roughly 260K and crystalline sI structures above 260K. For these temperatures, the average transition path lengths are significantly longer than in our previous study, pushing the boundaries of what can be achieved with TPS. The temperature to observe a critical nucleus of certain size was roughly 20K lower compared to a spherical reservoir due to the lower concentration of methane in the solution, yielding a reduced driving force. We analyze the TPS results using a model based on classical nucleation theory. The corresponding free energy barriers are estimated and found to be consistent with previous predictions, thus adding to the overall picture of the hydrate formation process.

ПОЛУЧЕНИЕ СМЕШАННЫХ КОМПОЗИЦИОННЫХ ЦЕМЕНТОВ НА ОСНОВЕ ФЕРРИТНОГО КЛИНКЕРА

The possibility of using ferritic clinker as a component of binders with special performance properties is considered. Such types of cements can solve the problems of providing the construction industry with high-strength, resistant to external aggressive effects and relatively cheap binders. However, the mechanism of hardening and curing of cement stone obtained by using ferritic clinkers is complicated and depends on a number of parameters.
 It was found that the greatest thermal effect (more than 70%) during the hydration of the resulting ferritic clinker with the introduction of various additives (lime and gypsum stone) is achieved up to 4 hours from the moment the binder compositions are mixed by means of a calorimetric analysis carried out during the hydration of the developed special binder compositions. That corresponds to the course of the induction period of hydration of the used Portland cement, at the time of the occurrence of primary contacts between crystalline hydrates and sufficient mobility of the cement mass. In this time interval, the strength of the cement stone is not high enough and the produced iron-containing hydration products are able to fill the space of the cement matrix, making it more dense and less defective. 
 The formation of iron-containing crystalline hydrates from ferritic clinker can proceed in several stages: hydrolysis of dicalcium ferrite at the initial stage of the reaction and further interaction of its products with portlandite in the period from 7 to 14 days from the moment of mixing the binder compositions. The main crystalline hydrates formed from ferritic clinker are iron-bearing ettringite and hydrogarnet.
 The study of the physical and mechanical characteristics of cement stone showed that the optimal content of ferritic clinker in the composition of the binder compositions is 5%. With a given quantity, the strength of the cement stone in compression and bending exceeds that of the control sample by 11.5%. The input of 15 and 30% ferritic clinkers into the composition of special binders reduces the strength characteristics by 15-20%.

Influence of innovative technologies on the physical and mechanical properties of building materials in the construction industry

A multifunctional additive based on a gel-like dispersion of taunitic carbon nanomaterial (CNM) is considered. The influence of its quantitative composition on the physical and mechanical properties of fine-grained concrete is studied. The results of a study of the frost resistance of fine-grained concrete enriched with a gel-like dispersion of CNM "Taunit" are presented.The main hypotheses describing the formation of the porous structure of concrete under the action of alternate freezing and thawing are considered, and the influence features of the structure of nanomodified concrete on its frost resistance and density. Nano-modified fine-grained concrete was tested by scanning microscopy, which shows that the process of forming changes in its structure occurs not only as a result of reinforcement, but also as a result of growth crystalline hydrates, the centers of which are particles of CNM "Taunit".

Tetrapyridineplatinum(II) Carboxylates: Synthesis and Crystal Structure

A series of mono- and bimetallic cation-anionic complexes based on the [PtPy4]2+ cation with different single-charge anions of carboxylic acids (RCOO–) is synthesized and structurally characterized. A synthetic approach to the preparation of tetrapyridineplatinum complexes [PtPy4]2+ soluble in polar solvents from available reagents is developed. The reaction of tetrapyridineplatinum dichloride [PtPy4](Cl)2 with silver acetate or trifluoroacetate affords compounds [PtPy4](OOCMe)2·6H2O (I) and [PtPy4](OOCCF3)2· 2H2O (II) in the form of crystalline hydrates (CIF files CCDC nos. 2161100 and 2161101, respectively) in high yields. Other carboxylates can be prepared by the treatment of compound I with an excess of a stronger acid, for example, trifluoroacetic acid, with the formation of the corresponding complex trifluoroacetate [PtPy4](OOCCF3)2·4CF3COOH (IIa) (CIF file CCDC no. 2161102). Another method consists of the displacement of acetic acid with an excess of a lowly volatile acid, for example, pivalic acid, when [PtPy4](Piv)2· 5HPiv (III) is formed from the acid melt, and solvatomorph [PtPy4](Piv)2·4HPiv·3C6H12 (IIIa) (CIF files CCDC nos. 2161103 and 2161104, respectively) is formed in a cyclohexane medium. Heteroanionic heterometallic complex [PtPy4](OOCFc)(OOCMe) (IV) (CIF file CCDC no. 2161105) is shown to be formed by the reaction of complex I with ferrocenecarboxylic acid under mild conditions.

Sintering Property and Hydration Resistance of CaO-Y2O3 Composite Materials

A preparation method of CaO-Y2O3 composite materials and its sintering property and hydration resistance were investigated in this paper. The CaO-Y2O3 core-shell structure powders were obtained by precipitation, after calcination, pressing and sintering the CaO-Y2O3 composite materials were prepared. The obtained powders and composite materials were characterized by crystalline phase formation, thermodynamic property, density, hydration resistance and microstructural analysis. The results showed that the prepared CaO-Y2O3 core-shell structure powders had good coating property, the sintering property and hydration resistance of composite materials were excellent. As the molar ratio Ca to Y was 1:1, the relative bulk density was 95.68%, the apparent porosity was 1.28%, and the hydration weight gain rate of the sample after 21 days in the atmospheric environment was 0.45%.

ANALYSIS OF THE MICROSTRUCTURE OF CONCRETE FRACTURES IN STRUCTURES THAT WORK ON COMPRESSION AND ITS IMPACT ON STRENGTH

Comparative microanalysis and elemental analysis of the structure of chips of concrete composites of different strength from compressive structures were used. Analysis of the microstructure of concrete chips was performed using a scanning electron microscope from Oxford SU 70 using a CCD detector. Elemental analysis of objects was performed using energy-dispersive X-wave spectroscopy (EDC analysis). The method of energy-dispersive X-wave spectroscopy is used. The character of opening of cracks of concrete samples in the course of their destruction is analyzed. From the data of X-ray and spectral analysis it follows that in a series of samples of strength of 120 MPa in the process of hydration of clinker minerals during hardening of concrete a number of chemically active substances is formed. These are primarily potassium oxide hydrate, calcium silicate hydrate (HSC) and structural gel models such as Janite and Tobermorite. Modification of the concrete composite with a complex of MK and MTK create conditions for the conversion of unstable and soluble calcium hydroxide into a strong crystalline hydrate of calcium silicate. The structure of concrete compacted in this form gives a significant increase in strength. The influence of ultrafine modifiers on the microstructure of cement stone formed during the operation of the structure and the strength of concrete are determined. The results of the scanning electron microscopy analysis show that the phase sizes differ slightly, but are not larger than ≈20 μm. Characteristic destruction of the sample with a strength of 120 MPa occurred in the main cracks, which develop due to the greater number of phases in contrast to the nature of the destruction of the sample with a strength of 50 MPa, which broke mainly on one structure. The complex of modifiers based on microsilica and metakaolin in the concrete mixture creates conditions for the conversion of unstable and soluble calcium hydroxide into a strong crystalline hydrate of calcium silicate. When using cement with a low content of C3S less than ≈50% significantly complicates the production of high-strength concretes, in particular when using silica and metakaolin, because the effectiveness of these additives implies the presence of excess portlandite Ca (OH)2 in the curing system, while systems with low C3S content is characterized by a reduced content of Ca (OH)2.

Liquid crystalline phase behavior and hydration of hydroxypropyl cellulose in water: A liquid and solid NMR investigation

AbstractHydroxypropyl cellulose (HPC) is a functional material with numerous applications as a drug solubilizer, thickener, and stabilizer. Herein, the mobile and rigid regions of HPC are investigated using liquid‐ and solid‐state NMR, respectively, in the high‐viscosity regime of concentrated aqueous samples, below and above the formation of an ordered chiral liquid‐crystalline (LC) mesophase. Liquid NMR 13C relaxation and hydration studies reveal that hydroxypropyl pendant chains remain more fluid than the pyranose sugar rings at concentrations below the formation of the LC phase. The inner part of the pendant chains close to the cellulose backbone exhibits a higher water structuration and a lower water renewal than the outer part and the pyranoses, which likely compensates for their higher hydrophobicity. When the LC phase is formed, the sample viscosity increases and the differences in flexibility and hydration of the pendant chains are reduced with respect to the pyranoses, while the whole system is rigidified. The system is not completely rigid even at concentrations above the formation of LC, as the interaction of water with the pyranoses considerably enhances their fluidity. In contrast, the pendant chains are much less affected.

EXERGY ANALYSIS OF AN OPEN-MODE ADSORPTIVE HEAT STORAGE UNIT BASED ON COMPOSITE ADSORBENT ‘SILICA GEL – CRYSTALLINE HYDRATE’

Exergy analysis of an open-mode adsorptive heat storage unit has been performed when a composite ‘silica gel – crystalline hydrate’ used as an adsorbent. The crucial factors affecting the exergy efficiency factor are stated to be temperature and initial humidity of airflow supplied to the inlet of adsorbent layer, temperature of external air and methods of air flow humidification. Procedure of calculation of the operating characteristics of an open-mode adsorptive heat storage device was further developed. The suggested procedure involves determination of adsorption, specific adsorption heat and final airflow temperature, useful heat, heat inputs for operating heat storage device and its efficiency factor, then exergy recovered, exergy supplied and exergy efficiency are calculated. Exergy efficiency depends on characteristics of flow of humid air fanned into the adsorbent layer such as temperature and initial absolute humidity which strongly affect the adsorption and final airflow temperatures. Increase of initial temperature of the humid air leads to decreasing of the exergy efficiency. Maximal values of exergy efficiency are determined at the absolute humidity and temperatures of initial airflow within the ranges of 0.03 – 0.04 kg/m3 and 20 – 30ºC, respectively. These characteristics are corresponded to the maximal airflow temperatures after passing through the adsorbent layer which meet to the Sanitary Regulations. Dependence of exergy efficiency vs. external air temperature and initial airflow temperature is shown. The exergy efficiencies of the open-mode adsorptive heat storage unit with steam and ultrasonic humidification were compared. Ultrasonic humidification is shown to allow increasing the exergy efficiency by 7 % against steam humidification. The obtained results can be used when energy-efficient heat and ventilation systems for residential premises developed.

Research on the Mechanical Properties and Microstructure of Modified Silt Sediment Geopolymer Materials.

The treatment of silted sediment in the river is a global problem. The accumulation of waste sediment will lead to an adverse impact on the environment. In this paper, the silted sediment was reused to produce geopolymer composite materials via alkali-activated gelling modification. The effects of the modifiers of sodium silicate solution, quicklime, and Na2SO4 admixture, and the dosage of the slag, fly ash, and silica fume admixture, and curing conditions and age, on the compressive strength and microstructure of the geopolymer-modified sediment materials were studied. The crystalline phase and hydration products of the modified sediment geopolymer composites were analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS), respectively. A compressive strength test was conducted to evaluate the mechanical properties of the composites. The results showed that the type and dosage of modifier, amount of mineral admixture additive, cure conditions, and cure age had significant effects on the mechanical properties of the composites. The effect of the addition of mineral admixture on the compressive strength of the modified sediment specimens was more noticeable than that of the modifier. The compressive strength of the geopolymer-modified specimens was greatly increased by the addition of mineral dopants. When 10 wt.% silica fume is added, the compressive strength reaches a maximum value of 33.25 MPa at 60 days. The SEM-EDS results show that the C-S-H gels and C-A-S-H gels were the main hydration products. The results indicate that river siltation sediment is an excellent raw material for geopolymer-modified materials. It is feasible to produce reliable and sustainable hydraulic engineering materials by using river sediment geopolymer-modified materials.