Chitin extraction from crab shells and synthesis of chitin @metakaolin composite for efficient amputation of Cr (VI) ions.

The present research study combines chitin from shrimp waste with the oxide-rich metakaolin. Metakaolin is a blend of mixed oxides rich in silica and alumina with good adsorbent properties. The chitin@metakaolin (CHt@M.K.) composite was synthesized and characterized using FTIR, SEM, TGA, XRD and XPS techniques. Cr(VI) removal studies were compared for chitin and CHt@M.K. through adsorption. It was found that the adsorption capacity of CHt@M.K. is 278.88 mg/g, almost double that of chitin, at pH 5.0 in just 120 min of adsorption. Isotherm models like Langmuir, Freundlich, Temkin and Dubinin-Radushkevich were investigated to comprehend the adsorption process. It was revealed that Langmuir adsorption isotherm is most suitable to elucidate Cr(VI) adsorption on CHt@M.K. The adsorption kinetics indicate that pseudo first order was followed, indicating that the physisorption was the process that limited the sorption process rate. The positive enthalpy change (20.23 kJ/mol) and positive entropy change (0.083 kJ/mol K) showed that the adsorption process was endothermic and more random at the solid-liquid interface. The negative free energy change over entire temperature range was an indicator of spontaneity of the process. Apart from all these, the non-covalent interactions between Cr(VI) and composite were explained by quantum calculations based models.

Effect of PFDS on the immobilization of Cs+ by metakaolin-based geopolymers in complex environments.

Metakaolin-based geopolymers are very promising materials for improving the safety of low and intermediate level radioactive waste disposal, with respect to ordinary Portland cement, due to their excellent immobilization performance for Cs+ and superior chemical stability. However, their application is limited by the fact that the leaching behavior of Cs+ is susceptible to the presence of other ions in the environment. Here, we propose a way to modify a geopolymer using perfluorodecyltriethoxysilane (PDFS), successfully reducing the leaching rate of Cs+ in the presence of multiple competitive cations due to blocking the diffusion of water. The leachability index of the modified samples in deionized water and highly concentrated saline water reached 11.0 and 8.0, respectively. The reaction mechanism between PDFS and geopolymers was systematically investigated by characterizing the microstructure and chemical bonding of the material. This work provides a facile and successful approach to improve the immobilization of Cs ions by geopolymers in real complex environments, and it could be extended to further improve the reliability of geopolymers used in a range of applications.

A study on the role of surface functional groups of metakaolin in the removal of methylene blue: Characterization, kinetics, modeling and RSM optimization.

In this study, thermally activated kaolinite clay is explored as a suitable material for dye removal applications, which gave rise to highly reactive silica species in a broad range of aluminosilicate clusters. Multinuclear NMR studies described it as a short-range network in which Al sites in IV, V, and VI are coordinated, and Si is present mainly as Si(Q4(1Al)). Critical parameters for methylene blue (MB) were determined by the Placket Burman Design (PBD) as initial dye concentration, contact time, adsorbent dosage, pH and size. The % of MB removal studied after optimizing the parameters by central composite design (CCD), based on Response Surface Methodology, was found to be 90%. The adsorption kinetics and thermodynamics were systematically studied and reported by fitting them into different models. The maximum removal of the dye reached 97.8 mg/g according to the Freundlich isotherm, accomplished through chemisorption, following a pseudo-second-order reaction and the process is thermodynamically spontaneous and endothermic. The line spectrum of X-ray photoelectron spectroscopy (XPS) shows the participation of Si, Al, O, Ca and Na of Metakaolin (AK) and nitrogen of MB in the adsorption process. The appropriate stabilization of the N atom of the chromophore on the Si and Al atom in AK resulting from the ionic interaction on the surface is established from an increase in the binding energy of Al and Si. A single bridging oxygen signal at 532.32eVcorresponding to AK after dye adsorption tends to form siloanol/aluminol, and their interaction is lowered to 531.58eV. Regeneration of adsorbent after thermal treatment without loss of efficiency proved.

Adsorption of dyestuff by nano copper oxide coated alkali metakaoline geopolymer in monolith and powder forms: Kinetics, isotherms and microstructural analysis.

To remove contaminants and pollutants from wastewater systems, adsorbents are widely used. Geopolymers offer a convenient alternative as adsorbents in the wastewater treatment system as they are low-cost, environmentally friendly, and safer. A new adsorbent material prepared by coating nano copper oxide on the surface of alkali-activated metakaolin showed a higher ability to remove methylene blue (MB) dye from wastewater, thus making them attractive in dye removal applications. First, nano copper oxide was prepared by sol gel method and metakaolin geopolymer was produced using sodium silicate solution having a Ms value of 1.1 (M). Afterwards, nano copper oxide (MC) was coated on the surface of the geopolymer. The ability of MB dye to bind to both pristine (Mp, MCp) and powder forms (Mpr, MCpr) of the geopolymer was evaluated. X-ray diffraction revealed that the halo found at 27.40°-31.077° (2θvalue) in both samples related to amorphous gel's composition and the major peaks of copper oxide in MCpr were sited at a 2θ value of 35.45° and 38.88°.The dye removal efficiency can be inferred from the increased adsorption capacity of 11.9 mg/g (Mp) and 14.4 mg/g (MCp) for the monolith form and 81.43 mg/g (Mpr) and 87.82 mg/g (MCpr) for the powder form. The adsorption of reused active sites was 73% for Mpr and 83% for MCpr up to the fifth cycle after regeneration by heat treatment at 400 °C. The models that best suited the adsorption data were pseudo-second-order and Freundlich isotherms, which indicated possible chemisorption with intra-particle diffusion. Furthermore, the binding energy is shifted to lower value in XPS spectra due to dye adsorption arising from electrostatic attraction. A higher electron density is formed due to interaction with an equal contribution of silanol Si-O-H and Si-O-Na/Cu(O1s). The adsorbents are effective over a wide pH range and their improved recycling capability increases their applications for a wide range of uses.

Effect of Yttrium on Ce/Ni-Metakaolin Catalysts for CO2 Methanation.

In recent years, major economies have implemented carbon reduction and carbon neutrality policies. Furthermore, with advancements in science and technology, carbon dioxide (CO2) is now considered a valuable raw material for producing carbon-based fuels through hydrogenation. Various concentrations of yttrium (referred to as Y hereafter) were introduced to assess their influence on the catalytic performance of CO2 methanation. At a temperature of 300 °C, the catalyst exhibited an impressive CO2 conversion rate of 78.4% and maintained remarkable stability throughout a rigorous 100 h stability assessment. The findings suggest that the inclusion of yttrium (Y) promotes the formation of oxygen vacancies and alkaline sites on the catalyst. This, in turn, enhances the reducibility of nickel species, improves the dispersion of nickel particles, and plays a pivotal role in enhancing thermal stability. Furthermore, it offers an innovative design approach for creating highly efficient composite CO2 methanation catalysts by controlling particle size and harnessing synergistic catalytic effects at the metal/support interface.

Use of a Piezoelectric Bender Element for the Determination of Initial and Final Setting Times of Metakaolin Geopolymer Pastes, with Applications to Laterite Soils.

This study proposes the use of a non-destructive testing technique, based on piezoelectric bender element tests, to determine the initial and final setting times of metakaolin geopolymer pastes. (1) Background: Metakaolin geopolymer is a new eco-friendly building material that develops strength rapidly and is high in compressive strength. (2) Methods: The initial and the final setting times were investigated via bender element and Vicat needle tests. Metakaolin powder was prepared by treating kaolin at 0, 200, 800, 1000, and 1200 °C. All metakaolin powder samples were then mixed with geopolymer solution at different mixing ratios of 0.8:1.0, 1.0:1.0, 1.2:1.0, and 1.5:1.0. The geopolymer solution was prepared by adding 10 normal concentrations of sodium hydroxide (10 N NaOH) to sodium silicate (Na2SiO3) at various solution ratios of 1.0:1.0, 1.0:1.2, 1.0:1.5, 1.0:2.0, 1.2:1.0, 1.5:1.0 and 2.0:1.0. (3) Results: The optimum temperature for treating metakaolin is established at 1000 °C, with a mixing ratio between the metakaolin powder and the geopolymer solution of 1.0:1.0, as well as a solution ratio between NaOH and Na2SiO3 of 2.0:1.0. (4) Conclusions: The use of piezoelectric bender elements to determine the initial and final setting times of metakaolin geopolymer pastes is a useful method by which to detect geopolymerization by shear wave velocity in a real-time manner. Moreover, the penetration of the Vicat apparatus can confirm the setting times at specific intervals. The relationships between the shear wave velocity and the Vicat penetration appear to be linear, with an initial setting time of 168 m/s and a final setting time of 187 m/s. Finally, the optimum metakaolin geopolymer pastes are applied to improve laterite soils, as measured by CBR tests.

Experimental Study on the Mechanical Properties and Microstructure of Metakaolin-Based Geopolymer Modified Clay.

Clay is found in some countries all over the world. It usually has low compressive strength and cannot be used as a bearing material for subgrade soil. In this paper, the influence of basicity on a metakaolin-based polymer binder to improve clay was studied. The effects of the molar concentration of the alkali activator, different concentration of the metakaolin-based geopolymer and curing time on unconfined compressive strength were studied. The alkali activator-to-ash ratio was maintained at 0.7. The percentage of metakaolin added to the soil relative to metakaolin and soil mixture was 6%, 8%, 10% and 12%. The sodium hydroxide concentrations are 2M, 4M, 6M and 8M. Unconfined compressive strength (UCS) was tested on days 3, 7, 14 and 28, respectively. Compared with original clay, the results show that the unconfined compressive strength increases with the increase in metakaolin content and molar concentration of NaOH. The maximum compressive strength of the sample with NaOH concentration of 8M and percentage of 12% was 4109 kN on the 28th day, which is about 112% higher than that of the original clay. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) results showed that the cementing compound covered the clay particles due to the reaction of the geopolymer with the clay, resulting in the formation of adhesive particles. The main purpose of this study is to verify the effectiveness and stability of metakaolin-based geopolymer binder polymerization under normal temperature and a strong alkali environment. The results can provide parameters for the application and promotion of metakaolin-based geopolymers in soil improvement engineering.

Effect of the Introduction of Reactive Fillers and Metakaolin in Waste Clay-Based Materials for Geopolymerization Processes.

In this study, the role of two reactive fillers, specifically a sand from a clay washing process as an alternative to waste glass powder and a commercial metakaolin (MK), into the geopolymerization process of waste clay-based materials was assessed. Three kinds of clayey wastes from mining operations-halloysitic, kaolinitic and smectitic clays-were tested as potential precursor of geopolymeric materials in view of a potential valorisation of these by-products. A mix-design based on the addition of low percentages (20%) of these fillers or MK to improve the mechanical and chemico-physical properties of geopolymeric formulations was evaluated. All the clays were thermally treated at a temperature of 650 °C, while the geopolymeric pastes were cured at room temperature. In particular, the chemical stability in water (pH and ionic conductivity of leachate water, weight loss), the variations in the microstructure (XRD, SEM), and in the mechanical performance (compressive strength) were analysed. The most reactive additive was MK, followed by sand and waste glass at very similar levels-1:1 or 2:1-depending upon the type of the clay but not strictly related to the clay type. The increase of geopolymeric gel densification due to the presence of MK and sand was replaced by a crack deflection mechanism in the case of the WG grains. The worst performance (chemical stability and mechanical properties) was found for the halloysitic clay, while kaolinitic and smectitic clays developed strengths slightly below 30 MPa.

Characterization of Modified Natural Minerals and Rocks for Possible Adsorption and Catalytic Use.

This study focused on natural materials such as clinoptilolite (CLI), metakaolin (MK), marlstone (MRL) and phonolite (PH). Clinoptilolite is one of the most known and common natural minerals (zeolites) with a unique porous structure, metakaolin is calcined kaolin clay, marlstone is a sedimentary rock and phonolite is an igneous rock composed of alkali feldspar and other minerals. These natural materials are mainly used in the building industry (additions for concrete mixtures, production of paving, gravels) or for water purification, but the modification of their chemical, textural and mechanical properties makes these materials potentially usable in other industries, especially in the chemical industry. The modification of these natural materials and rocks was carried out by leaching using 0.1 M HCl (D1 samples) and then using 3 M HCl (D2 samples). This treatment could be an effective tool to modify the structure and composition of these materials. Properties of modified materials were determined by N2 physisorption, Hg porosimetry, temperature programmed desorption of ammonia (NH3-TPD), X-ray fluorescence (XRF), X-ray powder diffraction (XRD), diffuse reflectance infrared Fourier transform (DRIFT) and CO2 adsorption using thermogravimetric analysis (TGA). The results of N2 physisorption measurements showed that that the largest increase of specific surface area was for clinoptilolite leached using 3M HCl. There was also a significant increase of the micropore volume in the D2 samples. The only exception was marlstone, where the volume of micropores was zero even in the leached sample. Clinoptilolite had the highest acidity and sorption capacity of CO2. TGA showed that the amount of CO2 adsorbed was not significantly related to the increase in specific surface area and the opening of micropores. Hg porosimetry showed that acid leaching using 0.1 M HCl and 3 M HCl resulted in a significant increase in the macropore volume in phonolite, and during leaching using 3M HCl there was an increase of the mesopore volume. From the better properties, cost-efficient and environmental points of view, the use of these materials could be an interesting solution for catalytic and sorption applications.

Simultaneous removal of Ni(II), As(III), and Sb(III) from spiked mine effluent with metakaolin and blast-furnace-slag geopolymers.

The mining industry is a major contributor of various toxic metals and metalloids to the aquatic environment. Efficient and economical water treatment methods are therefore of paramount importance. The application of natural or low-cost sorbents has attracted a great deal of interest due to the simplicity of its process and its potential effectiveness. Geopolymers represent an emerging group of sorbents. In this study, blast-furnace-slag and metakaolin geopolymers and their raw materials were tested for simultaneous removal of Ni(II), As(III) and Sb(III) from spiked mine effluent. Blast-furnace-slag geopolymer proved to be the most efficient of the studied materials: the experimental maximum sorption capacities for Ni, As and, Sb were 3.74 mg/g, 0.52 mg/g, and 0.34 mg/g, respectively. Although the capacities were relatively low due to the difficult water matrix, 90-100% removal of Ni, As, and Sb was achieved when the dose of sorbent was increased appropriately. Removal kinetics fitted well with the pseudo-second-order model. Our results indicate that geopolymer technology could offer a simple and effective way to turn blast-furnace slag to an effective sorbent with a specific utilization prospect in the mining industry.

Mechanical Properties and Reaction Kinetics of Alkali-Activated Metakaolin.

In this study, the influence of the physicochemical properties and proportioning conditions of metakaolin on the mechanical properties of the synthesized metakaolin geopolymers was comprehensively evaluated, and the issue of the reaction control mechanism for the formation of mechanical properties during the synthesis of geopolymers was addressed. The reaction mechanism was analyzed by SEM and FTIR, and the kinetic analysis of the geopolymerization process was carried out using isothermal calorimetry combined with the Jander model. The test results show that the physicochemical properties of the metakaolin and the proportioning conditions together affect the mechanical properties of the geopolymer, with the correlation between the active aluminum content of the metakaolin and the strength of the geopolymer reaching over 0.87. The early stages of the geopolymerization reaction are all controlled by nucleation-growth mechanisms (N < 1), and the variability in control mechanisms is mainly found in the later stages of the geopolymerization reaction. The low reactivity and slow exothermic hydration of metakaolin are more inclined to the nucleation-growth mechanism responsible for the hydration process due to the large amount of encapsulation.

The Influence of Diatomite Addition on the Properties of Geopolymers Based on Fly Ash and Metakaolin.

Geopolymer materials, considered to be an alternative to Portland cement-based concretes, can be produced from various types of waste aluminosilicate raw materials. This article presents the results of research related to the use of diatomite as an additive in geopolymers. The results of testing geopolymer composites with 1%, 3%, and 5% additions of diatomite with a grain size of 0-0.063 mm after and without thermal treatment were presented. This article presents the physical properties of the diatomite additive, the morphology of diatomite particles SEMs, thermal analysis, and compressive strength test results. In this research, diatomite was treated as a substitute for both fly ash and metakaolin (replaced in amounts of 1 and 3%) and as a substitute for sand introduced as a filler (in this case, 5% of diatomite was added). As a result of this research, it was found that the addition of diatomite instead of the main geopolymerization precursors in amounts of 1 and 3% had a negative impact on the strength properties of geopolymers, as the compressive strength was reduced by up to 28%. The introduction of crushed diatomite instead of sand in an amount of 5% contributed to an increase in strength of up to 24%.

Comparative Study of the Structural, Microstructural, and Mechanical Properties of Geopolymer Pastes Obtained from Ready-to-Use Metakaolin-Quicklime Powders and Classic Geopolymers.

This study compares the structural, microstructural, thermal, and mechanical properties of geopolymer pastes (GPs) created through traditional methods and those derived from ready-to-use powders for geopolymer (RUPG) materials. The metakaolin (MK) precursor was activated using a sodium silicate solution or CaO and MOH (where M is Na or K). Various ratios of precursor/activator and Na2SiO3 or CaO/MOH were tested to determine the optimal combination. For RUPG, the MK precursor was activated by replacing the sodium silicate solution with quicklime. Metakaolin, alkaline hydroxide, and quicklime powders were mixed at different CaO ratios (wt%) and subjected to extensive ball milling to produce RUPG. The RUPG was then hydrated, molded, and cured at 20 °C and 50% relative humidity until testing. Analytical methods were used to characterize the raw and synthesized materials. Classic geopolymers (CGPs) activated with quicklime burst after one hour of molding. The results indicated slight amorphization of GP compared to raw MK, as confirmed by X-ray diffraction analysis, showing N(K)-A-S-H in CGP and N(K)-A-S-H with calcium silicate hydrate (C-S-H/C-A-S-H) in RUPG. The compressive strength of MK-based geopolymers reached 31.45 MPa and 34.92 MPa for GP and CGP, respectively, after 28 days of curing.

Effect of Microwaves on the Rapid Curing of Metakaolin- and Aluminum Orthophosphate-Based Geopolymers.

This paper deals with the influence of microwaves on the hardening and curing of geopolymer binders synthesized from metakaolin or aluminum orthophosphate with sodium silicate solution as the activator. Pure geopolymer pastes as well as geopolymer mortars were considered. The variable parameters were the modulus of the sodium silicate solutions (molar ratio of SiO2 to Na2O: 1.5, 2.0 and 2.5) and the Si/Al ratio (3/1 and 2/1). Selected samples were cured in a microwave oven until hardening, so the curing time depended on the mixture. For comparison some samples were cured at ambient temperature. To investigate the influence of microwave radiation on the reaction kinetics, isothermal heat flow calorimetry, ultrasonic velocity measurements and rheological investigations into the variation of curing temperature were used. In addition, the mechanical properties of the cured samples were characterized. The results show that microwave curing only takes a few minutes, so it is the most time-saving method. Key factors influencing the geopolymer reaction under microwave radiation are the raw materials as well as the Si/Al ratio. Metakaolin-based geopolymer binders are more stable than those based on aluminum orthophosphate, especially regarding their salt efflorescence. Microwave radiation is an efficient method to accelerate the geopolymer reaction.

Up-scaling of fly ash-based geopolymer concrete to investigate the binary effect of locally available metakaolin with fly ash.

Owing to the increasing threat to environment due to the emission of greenhouse gases from cement industry globally, various promising solutions has been introduced in the past decades. The development of geoplymer concrete (GPC) is one of the contribution by the researches towards ecofriendly and sustainable construction. In this research, geopolymer concrete (GPC) is optimized by adding fixed amount of fly Ash (FA) and alkali activator to fine aggregate ratio as 0.5 with varying Molarity from 12 M to 16 M and Na2SiO3/NaOH ratio from 1.5 to 2.5. Physical and mechanical properties along with effect of heat and ambient curing conditions were investigated at various ages. The optimized mixture of fly ash based geopolymer concrete was then up scaled by blending with locally available Metakaolin (MK) with different dosages (i.e., 10%, 20%, 30%, 40%). The aim of the study is to identify the binary effect of FA and MK on overall performance of geopolymer concrete. Results showed that 30% FA-MK based GPC depicted 21%, 19% and 26% more compressive strength, split tensile strength and flexural strength respectively than Fly Ash based GPC alone at heat cured condition. This can be explained mainly due to two facts namely binary action of metakaolin that enhances compaction of GPC and pozzolanic activity of MK that expedite geopolymeric strength causing phases. The results were further verified by Modified Chapelle test and FTIR. Morphology of the developed GPC is also examined from SEM images. The work is an effort to utilize the fly ash produced by coal power plants to effectively address UN sustainable development goal related to sustainable cities and communities.

Research on mix design and mechanical performances of MK-GGBFS based geopolymer pastes using central composite design method.

In order to alleviate environmental problems and reduce CO2 emissions, geopolymers had drew attention as a kind of alkali-activated materials. Geopolymers are easier access to raw materials, green and environment friendly than traditional cement industry. Its special reaction mechanism and gel structure show excellent characteristics such as quick hardening, high strength, acid and alkali resistance. In this paper, geopolymer pastes were made with metakaolin (MK) and ground granulated blast furnace slag (GGBFS) as precursors. The effects of liquid-solid ratio (L/S) and modulus of sodium silicate (Ms) on the performances of MK-GGBFS based geopolymer paste (MSGP) were characterized by workability, strength and microstructural tests. The regression equations were obtained by central composite design method to optimize the mix design of MSGP. The goodness of fit of all the equations were more than 98%. Based on the results of experiments, the optimum mix design was found to have L/S of 0.75 and Ms of 1.55. The workability of MSGP was significantly improved while maintaining the strength under the optimum mix design. The initial setting time of MSGP decreased by 71.8%, while both of the fluidity and 28-d compressive strength increased by 15.3%, compared with ordinary Portland cement pastes. Therefore, geopolymers are promising alternative cementitious material, which can consume a large amount of MK and GGBFS and promote green and clean production.

Recycled Excavation Soils as Sustainable Supplementary Cementitious Materials: Kaolinite Content and Performance Implications.

In response to the environmental implications of the massive quantities of excavation soil generated by global urbanization and infrastructure development, recent research efforts have explored the repurposing of calcined excavation soils as sustainable supplementary cementitious materials (SCMs). As it is still at an early stage, current research lacks systematic analysis across diverse soil deposits regarding their reactivity and mechanical properties within cementitious binders, despite recognized geographical variability in kaolinite content. Through comprehensive experimentation with soils sourced from four major southern Chinese cities, this study presents a pioneering assessment of the compressive strength, pozzolanic reactivity (X-ray diffraction, Fourier-transform infrared spectroscopy, solid-state nuclear magnetic resonance), and microstructural development (mercury intrusion porosimetry, scanning electron microscopy) of mortars modified by various calcined excavation soils (up to 28 days curing). The experimental data suggest that soils with a kaolinite content above 53.39% produce mortars of equal or superior quality to plain cement mixes, primarily due to their refined pore structures, microstructural densification, and enhanced hydration reactions. The findings highlight kaolinite-specifically, aluminum content-as the principal indicator of excavation soil viability for SCM application, suggesting a promising avenue for sustainable construction practices.

Mechanical, Durability, and Microstructure Assessment of Wastepaper Fiber-Reinforced Concrete Containing Metakaolin.

This study evaluates the potential use of discarded plasterboard paper as fibers from buildings to reinforce concrete. Various concentrations of wastepaper fibers (0.5%, 1%, 1.5%, 2%, and 2.5% by weight of the binder) were investigated in this research. To mitigate the water absorption effect of the paper fibers, metakaolin was employed as a partial cement replacement. The results demonstrate that the inclusion of the wastepaper fiber enhances the mechanical and durability performance of the concrete. The optimal fiber proportion was identified as 1%, leading to a 29% increase in the compressive strength, a 38% increase in the splitting tensile strength, a 12% decrease in the water absorption, and a 23% decrease in the drying shrinkage with respect to the concrete containing 20% metakaolin. However, exceeding this optimal fiber content results in decreased mechanical and durability properties due to the fiber agglomeration and non-uniform fiber distribution within the concrete matrix. Based on the microstructural analysis, the improved performance of the concrete is ascribed to decreased porosity, more refined pore structure, and reduced propagation of microcracks within the concrete matrix in the presence of wastepaper fiber. According to the results, concrete containing 20% metakaolin and 1% wastepaper fiber exhibits durability and mechanical properties comparable to those of the traditional concrete. This finding highlights the significant promise of reducing dependency on conventional cement and incorporating suitable recycled materials, such as discarded plasterboard, and secondary by-products like metakaolin. Such a strategy encourages the preservation of resources, reduction in carbon dioxide emissions, and a decrease in the ecological footprint resulting from concrete production.

Preparation and Application of Nano-Calcined Excavation Soil as Substitute for Cement.

Rapid urbanization in many cities has produced massive amounts of problematic excavation soil. The direct disposal of untreated excavation soil often leads to significant land use and severe environmental concerns. A sustainable solution is to transform the soil waste into high-quality nano-calcined excavation soil (NCES) for application as a substitute for cement in construction. However, research in this area is very limited. This study presents a systematic investigation of the nano-sized calcined soil materials from preparation to application in cementitious material. The influence of milling parameters, including the rotational speed, milling duration, ball diameter, and milling strategy, was investigated to produce NCES with various specific surface areas. The effect of NCES substitution (15 wt% of Portland cement) in cementitious materials was then examined for mechanical performance, hydration dynamics, hydration products, and microstructure. A cement mix with very fine NCES (specific surface area of 108.76 m2/g) showed a 29.7% enhancement in mechanical strength and refined pore structure while a cement mix with un-grounded calcined soil showed a mechanical loss in comparison to the Control specimen. Delayed and reduced heat release at an early age was observed in a cement paste mixed with NCES. The underlying mechanism was investigated. The results of this work will contribute to the high-quality application of excavation soil waste.

Development and characterization of a composite material with geopolymer matrix obtained by incorporation of microparticles from plastic bottles.

The composite material with a geopolymer matrix of 7 M molarity, obtained by incorporating microparticles from plastic bottles is developed and characterized in the present paper. To do this, we made cylindrical specimens whose the diameters are the half of their heights and stored them at a temperature of (31±2°C). The compression test using a hydraulic press is carried out, as well as the thermal characterization test using a device respecting the experimental method of the asymmetric hot plane, which was used to determine the thermal conductivity, the volumetric heat capacity, the effusivity and the diffusivity. Then optical characterization tests on hardened samples were carried out, namely chemical analyses of the composition of the kaolin, and particle size characterization of the raw microscopic imaging of the specimens. The results found showed that as the amount of polyethylene terephthalate increases, the compressive strength decreases by 33.65 % for 10%polyethylene terephthalate and 67.77 % for 20 % polyethylene terephthalate. According to the thermal conductivity, it improves with the percentage of polyethylene terephthalate added as: at 10% it is 1.19Wm-1K-1 and at 20%, one has 0.595Wm-1K-1; similarly for effusivity where we obtained 1376.05 JK-1m-2s-1/2 and 560.81 JK-1m-2s-1/2 for 0 and 20% respectively. According to these results, the use of polyethylene terephthalate aggregates as a partial substitute of aluminosilicate raw material for the development of a composite can be a good alternative for recycling plastic bottle waste. The composite obtained could be used for the manufacture of ceiling lights and brick facings, and therefore would significantly reduce the amount of waste plastic produced every day in environment.