Alkali Activation Research Articles

A novel use of incineration bottom ash for H2 aeration in the production of artificial lightweight aggregates

Cold bonding is an energy-efficient method for producing artificial aggregate (AA). However, the relatively high density of AA restricts its use in lightweight concrete products. This study aims to fully upcycle aluminum (Al) content in municipal solid waste incineration bottom ash (IBA) for H2 aeration in the production of lightweight artificial aggregate through alkali activation. To achieve this, the glass particles (GP) in IBA were ground into powder and used as the precursor for NaOH, while the remaining IBA (RIBA), rich in Al, served as the foaming agent. The results showed that RIBA particles (<300 μm) can be used to produce lightweight AA with a loose bulk density ranging from 780 to 840 kg/m3, comparable to sintered fly ash aggregates, and a wide pore size distribution ranging from 0.02 mm to over 1 mm. The inclusion of finer RIBA particles (<75 μm) enhanced the homogeneity of the pore structure, resulting in aggregate strengths of 0.4–0.6 MPa. Moreover, increasing the GP content in IBA up to 40% further boosted the aggregate strength to 1.1 MPa by refining the pore structure and promoting more (C)-N-A-S-H gels with Q4 structures. To ensure sufficient geopolymerization reactions and achieve high strength in the AAs, the alkali concentration should be kept above 3 mol/L. The proposed strategy for lightweight AA production reduced the global warming potential by about 20% compared to the conventional sintered method, offering a more environmentally friendly approach.

Impact of Nano-SiO2 on the Compressive Strength of Geopolymer-Solidified Expansive Soil

Expansive soil is widely distributed and often needs to be improved for engineering and construction needs. Using blast furnace slag and fly ash as precursors and NaOH as an alkali activator, a geopolymer was prepared to solidify expansive soil, and the effect of nano-SiO2 on the compressive strength and water stability of the geopolymer-solidified expansive soil was further studied. The effects of alkali addition ratio, nano-SiO2 addition ratio, and curing agent addition ratio on the unconfined compressive strength and water stability of the cured soil were studied through unconfined compressive strength tests, and the curing mechanism was analyzed by electron microscopy scanning. The experimental results showed that the unconfined compressive strength and water stability of geopolymer-stabilized soil first increased and then decreased with an increase in alkali activator dosage. The optimal dosage of alkali activator was found to be 12.5%. Furthermore, it was found that adding nano-SiO2 can further enhance the strength and water stability of solidified soil. When the content of nano-SiO2 was 3%, the unconfined compressive strength was increased by 15%. With an increase in the content of nano-SiO2 doped polymer (GFNS), the unconfined compressive strength and water stability of the solidified soil showed a trend of first increasing and then decreasing, reaching a peak at a content of 20%. The cementitious materials, such as hydrated calcium silicate and hydrated calcium silicate aluminate, generated by the reaction between nano-SiO2 and geopolymer played a role in bonding and filling in the solidified soil. Under the joint action of the two, the structural arrangement between the solidified soil particles became more compact, which improved the strength of the solidified soil.

Utilizing raw phosphogypsum to prepare one-part geopolymer: Mechanical properties, optimization, and hydration mechanisms

The accumulation of phosphogypsum (PG) poses environmental risks. This study investigates the feasibility and performance of one-part geopolymers derived from a ternary system, where raw phosphogypsum (PG) partially replaces ground blast furnace slag (GBFS) in combination with fly ash (FA). The effects of raw PG on geopolymerization kinetics, mechanical properties, and efflorescence were examined. PG addition affected compressive strength, gel formation, and efflorescence. An optimal PG replacement rate of 10–20 % for GBFS was identified to balance the positive effect on ettringite formation and the negative impact on gel phase formation. Using a composite alkali activator, combining NaOH and Na2SiO3, promotes strength development and enhances the anti-efflorescence properties of one-part geopolymers synthesized with PG. One-part PG-incorporated geopolymers demonstrate excellent performance in the fixation of heavy metal contaminants in raw PG, offering a more convenient and safer alternative to conventional two-part synthesis methods.

Evaluating Alkali Activation in Magnesium Slag Carbonization and Its Mechanism

In recent years, magnesium slag has been used as a raw material for solid waste treatment using the carbonization method and has proven to be promising in reducing carbon emissions. In this study, the alkali activation reaction was introduced to promote the carbonization of magnesium slag. The resulting mechanical properties, microstructural attributes, and carbonization mechanism were studied by varying the sodium hydroxide content, temperature, and carbon dioxide concentration during the reaction process. The results showed that the amounts of calcium hydroxide, C-S-H, and calcium carbonate in the reaction products increased with the sodium hydroxide content, which enhanced the compressive strength of the composite. However, it does not influence the carbonization mechanism with the increasing reaction temperature, which only elevates the reaction rate. With the increase in the carbon dioxide concentration during alkali activation, the carbonization reaction is dominated by the amount of CO2 dissolved in the reaction medium, and the carbonization mechanism is changed. Thus, a significant decrease in the calcium hydroxide content and a sharp increase in the calcium carbonate content in the products occurred, which significantly improved the compressive strength of the resulting magnesium slag composite. Among them, the maximum compressive strength is 6.83 MPa.

Behavior of zero cement reinforced concrete slabs under monotonic and impact loads: Experimental and numerical investigations

Currently, there is a shift toward the use of low-carbon construction materials to reduce global carbon dioxide emissions. Zero-cement concrete (ZCC) synthesized from alkaline activated fly ash (FA) is a promising alternative for Portland cement in the construction industry to reduce global CO2 emissions, increase the consumption of waste materials, and save energy. A substantial amount of research on the impact load behavior of ordinary reinforced concrete (RC) structural components has been conducted. However, investigations on the behavior of zero cement concrete (ZCC) slabs under impact loads have not been reported. In this work, twenty simply supported two-way flat reinforced fly ash ZCC slabs (including two normal concrete (NC) slabs as reference samples) were tested under monotonic and impact loads. The test samples were categorized into eight groups on the basis of various parameters. Twelve RC slabs (1 NC and 11 ZCCs) were prepared for repeated impact tests, and eight slabs (1 NC and 7 ZCCs) were prepared for monotonic loading tests. Various parameters were investigated herein, including slab thickness, bar spacing, molarity concentration of alkali activators, hammer height, and hammer mass. Nonlinear finite element models were also developed and validated by using ABAQUS software for additional parametric study purposes. The results revealed that the behavior of ZCC slabs is approximately similar to that of NC slabs. The results also revealed that an increase in the ZCC slab thickness, reinforcement ratio, hammer height, and hammer mass has a noticeable effect on the dynamic response of the slab. However, increasing the molarity concentration of alkali activators has clearly a slight influence on the impact loadtime history. When the slab thickness was increased or the bar spacing was reduced, the static and impact energy absorption capacities were increased by 1.5 and 2.0 times, respectively. For impact load tests, the damage degree, penetration, and cracking pattern at failure were approximately typical for all test samples at the first hit except when the hammer mass and impact height were changed. For the samples subjected to monotonic loading, a flexural response was observed for almost all the slab samples at the first loading stage, and cracking started from the midpoint of the slab and propagated toward the slab edges; ultimately, punching shear failure was observed.

Unraveling the interactive effects of Na2O/Al2O3, SiO2/Al2O3 and calcium on the properties of geopolymers from circulating fluidized bed fly ashes

Circulating fluidized bed fly ash (CFB-FA), generated as solid waste from the thermal power plants with different contents of calcium. The reuse of CFB-FA for construction materials is the most promising method for the large-scale transformation of waste to resource. This paper examines the ratio effects of Na2O/Al2O3 and SiO2/Al2O3 on geopolymers from low-calcium fly ash (CFB-FA1) and high-calcium fly ash (CFB-FA2) by using a mixture of Na2SiO3 and NaOH as the alkali activator. The detailed mechanistic study with XRD, FTIR, SEM, and MAS NMR is also conducted for the roles of silicon, aluminum, and calcium in the reaction process and their mutual interaction mechanism, along with the regulating mechanism for the compressive strength and setting time of geopolymers. The results indicate that the increased ratios of Na2O/Al2O3 and SiO2/Al2O3 are favorable for the reactions and reduce the setting time of CFB-FA1 and CFB-FA2 based geopolymer. In CFB-FA1, the higher silicon and aluminum content is conducive to their dissolution by regulating the Na2O/Al2O3 ratio, forming N-A-S-H and resulting in the increased strength. A small amount of calcium mainly exists in the form of CaSO4, which completely participates in the reaction. In CFB-FA2, the silicon and aluminum contents are relatively low, while the calcium content is high. The compressive strength is achieved by regulating the SiO2/Al2O3 ratio to increase the dissolution of silicon and aluminum, allowing CaSO4 and CaO to react and form C-A-S-H and ettringite, with CaCO3 as unreactive. The low calcium is favorable for the long-term strength, but the high calcium acts oppositely, primarily attribute to the decomposition of ettringite, a critical component for maintaining the compressive strength of CFB-FA2 based geopolymers.

The strength, reaction mechanism, sustainable potential of full solid waste alkali-activated cementitious materials using red mud and carbide slag

Alkali-activated cementitious material (AACM) is a green building material which effectively utilizes industrial solid wastes, such as red mud (RM), ground granulated blast furnace slag (GGBS). However, there are problems with using conventional alkali activators (NaOH, Na2SiO3), including strong corrosivity and high cost. In order to solve this problem, this study prepares full solid waste cementitious materials (FSWCM) by activating RM and GGBS using carbide slag (CS) instead of traditional alkali activator. Based on the response surface method (RSM), the effects of RM content, CS content and water-binder ratio on the performance of FSWCM were studied. The microstructure changes of FSWCM with different RM contents were analyzed by XRD, TG, FTIR and SEM-EDS. The results showed that the optimized content of RM and CS was 40 % and 20 % respectively, and the 28-d compressive strength reached 14.11 MPa, which met the requirements of road base materials. The regression model established by RSM had high accuracy and could accurately predict the performance response values. The alkaline environment created by CS-RM facilitated the decomposition of active components in GGBS, resulting in the formation of a considerable amount of C-(A)-S-H gel via polycondensation. With the increase of age, Na+ dissolved in RM replaced Ca2+ in C-A-S-H to form N-A-S-H gel. The hydration products N-A-S-H, C-(A)-S-H and CaCO3 were intertwined to form a stable and dense three-dimensional network structure, which provided excellent mechanical properties. Sustainability analysis shows that FSWCM has significant advantages in cost control and environmental friendliness compared with AACM.

Synergic valorization of nickel-chrome plating sludge via alkali activation of steel slag and fly ash: performance analysis

Synergic valorization of nickel-chrome plating sludge via alkali activation of steel slag and fly ash: performance analysis

Optimizing Construction Spoil Reactivity for Cementitious Applications: Effects of Thermal Treatment and Alkaline Activation

Construction spoil (CS), a prevalent type of construction and demolition waste, is characterized by high production volumes and substantial stockpiles. It contaminates water, soil, and air, and it can also trigger natural disasters such as landslides and debris flows. With the advent of alkali activation technology, utilizing CS as a precursor for alkali-activated materials (AAMs) or supplementary cementitious materials (SCMs) presents a novel approach for managing this waste. Currently, the low reactivity of CS remains a significant constraint to its high-value-added resource utilization in the field of construction materials. Researchers have attempted various methods to enhance its reactivity, including grinding, calcination, and the addition of fluxing agents. However, there is no consensus on the optimal calcination temperature and alkali concentration, which significantly limits the large-scale application of CS. This study investigates the effects of the calcination temperature and alkali concentration on the mechanical properties of CS–cement mortar specimens and the ion dissolution performance of CS in alkali solutions. Mortar strength tests and ICP ion dissolution tests are conducted to quantitatively assess the reactivity of CS. The results indicate that, compared to uncalcined CS, the ion dissolution performance of calcined CS is significantly enhanced. The dissolution amounts of active aluminum, silicon, and calcium are increased by up to 420.06%, 195.81%, and 256.00%, respectively. The optimal calcination temperature for CS is determined to be 750 °C, and the most suitable alkali concentration is found to be 6 M. Furthermore, since the Al O bond is weaker and more easily broken than the Si O bond, the dissolution amount and release rate of active aluminum components in calcined CS are substantially higher than those of active silicon components. This finding indicates significant limitations in using CS solely as a precursor, emphasizing that an adequate supply of silicon and calcium sources is essential when preparing CS-dominated AAMs.

Optimal development and performance evaluation of electrolytic graphene oxide synergistic all-solid waste cementitious grouting material

The low-carbon and friendly alkali-activated cementitious (AACM) grouting material has a broad application potential in the field of grouting engineering due to its excellent workability and higher early strength and is expected to replace cement grouting material in the future. In this study, an AACM grouting material using electrolytic graphene oxide (EGO) synergistic ground granulated blast-furnace slag (GGBS)-fly ash (FA)-rice husk ash (RHA) solid waste was proposed. The optimal ratio was 0.025 % EGO, 8.13 % FA, 26.6 % RHA, and 65.27 % GGBS, which determined by the Analytic Hierarchy Process (AHP), Entropy Weight Method (EWP), and Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS) methods. A systematic evaluation of the mechanical properties and impermeability of the proposed AACM grouting material was conducted by macro experiments (compressive strength, flexural strength and permeability) and micro experiments (XRD, SEM-EDS, Fourier Transform Infrared Spectrometer (FTIR) and Thermogravimetry Analysis (TG)). The results show that the increment of compressive strength and flexural strength for AACM grouting material with 0.025 % EGO compared to the cement water-glass grouting material were 161.2 % and 2.9 %, respectively, at 7-day. While the permeability coefficient compared to AACM grouting material without EGO decreased by 43.9 %. The XRD results show that the EGO reduced the intensity of AACM grouting material diffraction peaks, and FTIR analysis reveals that EGO increased the visibility of O-C-O characteristic peaks. These confirmed that EGO could enhance the degree of alkali activation reaction. The TG results indicate that the addition of EGO promoted the formation of carbonates, which strengthen the mechanical properties of AACM grouting material. The SEM-EDS results demonstrate that EGO increased the Ca/Si ratio, promoted the formation of highly polymerized hydration products.

Enhanced self-cementation of arsenic-contaminated soil via activation of non-thermal plasma-irradiated ferromanganese: A mechanistic investigation

The self-cementation characteristics of arsenic (As)-contaminated soil were comprehensively investigated in this study. Different non-thermal plasma-irradiated binary (hydro)oxides of polyvalent ferromanganese (poly-Fe-Mn) were synthesized and exploratorily dispersed to soil samples to activate solidification and stabilization during the self-cemented process. The maximum compressive strength of 56.35 MPa and the lowest leaching toxicity of 0.004 mg/L were obtained in the proof test under optimal conditions (i.e., the mass ratio of the poly-Fe-Mn to the soil sample of 0.05; the mass ratio of the composite alkali activator (NaOH + CaO) to the soil sample of 0.25; the mass ratio of CaO to NaOH of 1.5; the mass ratio of the DI water to the binder of 0.515). The composite alkaline activator primarily contributed to the strength formation of the self-cemented matrix while the poly-Fe-Mn significantly influenced the reduction of the As-leaching toxicities. The poly-Fe-Mn maintained diffusion-controlled polycondensation and strengthened the nucleation process during self-cementation. The amount of water and the dosage of poly-Fe-Mn caused an interactive influence on the self-cemented solidification of contaminated soils. The solidified samples with poly-Fe-Mn exhibited better thermal decomposition than their counterparts, reflecting the enhancement of poly-Fe-Mn to the matrix. Some minerals including C-S-H, kaolinite, gehlenite, diopside sodian, augite, and albite were matched in the samples, directly demonstrating the geopolymerization-steered self-cementation of the As soil. The employment of poly-Fe-Mn not only reinforced the immobilization of As pollutants in the matrix but also induced the self-cementation of soils by intensifying the composite alkaline-activated geopolymerization kinetics.

Evaluation of the effect of curing conditions on compressive strength and microstructure of alkali-activated binders

Alkali-activated binders (AABs) are increasingly researched as sustainable alternatives to ordinary Portland cement (OPC), providing comparable strength. In recent years there has been a growing interest in studies focusing on the development of suitable composites and their fabrication methods. Composites' properties are significantly affected by temperature, humidity, formulations, and constituent types. Therefore, it is essential to understand these factors comprehensively to obtain the desired adequacy to use. This article aims to assess the impact of (i) temperature through ambient curing (25°C) and thermal curing (50°C for 24 hours), (ii) exposure to air (isolated or exposed to the air atmosphere), and (iii) susceptible to external humidity (air contacted or submerged) as curing conditions. The evaluation encompassed compressive strength tests at 1, 28, 63, and 91 days, along with microstructural evaluation through morphology analysis and incidence of voids. Digital image processing (DIP) through ImageJ software was employed. The AAB proposed consisted of fly ash (FA) and steel slag from the Basic Oxygen Furnace (BOF) process as precursors, with sodium hydroxide (NaOH) and sodium silicate (NaSi2O3) as alkali activators, applied in mortar production. Compressive strength results revealed that mortar subjected to thermal curing, isolated from air contact and external humidity, exhibited the highest strength outcome, with 46.05 MPa. Microstructural analysis indicated the formation of hydrated aluminosilicate gels and the presence of voids, including partially reacted particles and microcracks. The DIP analysis of the sectional area demonstrated that void incidence under 50 µm2 predominantly did not affect compressive strength.

Sustainable construction materials from alkali-activated waste fiberglass and waste refractory

In this work, waste fiberglass was up-cycled, alone, or mixed with used alumina-zirconia-silica (AZS) refractory from dismantled glass melting furnaces. Alkali activation was performed by suspending fiberglass and fiberglass/AZS powders in NaOH aqueous solution of various concentrations (8M, 6M, and 3M). The activation of waste fiberglass with 8M NaOH yields a gel with calcium and sodium-containing aluminosilicate hydrates. The addition of AZS refractory enabled the release of aluminates into the solution, which had beneficial effects on the mechanical properties. Low molarity activation yielded weaker materials which could be used as precursors for firing at moderate temperatures (800 °C and 1000 °C) to create cellular glass-ceramics, with a total porosity of up to 92 %. The firing of 8M activated samples resulted in glass ceramics with a 66–75 % porosity range and compressive strength of 10–23Mpa. The compressive strength-to-density ratio before and after firing was comparable to that of established commercial construction materials.

Preparation of solid alkali activator for geopolymer synthesis using vanadium-bearing shale tailing

The vanadium-bearing shale tailing (VST) with large reserves pollutes the environment and urgently needs to be utilized as a resource. Due to its main component being silica, VST has great potential as a raw material for geopolymer. Therefore, this study uses VST to prepare the solid alkali activator (SAA) by thermochemical methods. Analysis show that the temperature and NaOH dosage of thermochemical reaction significantly affect the alkaline activation effect of SAA. Temperature affects the silicate content and the amount of NaOH affects the soluble silicate content in SAA. When the reaction temperature is high (such as above 900 ℃) and the amount of sodium hydroxide is low (such as the mass ratio of sodium hydroxide to VST is 0.6), quartz almost transforms into silicates, but the silicates have a stable cyclic chemical structure and are difficult to dissolve during the geopolymerization reaction. When the reaction temperature is low (such as less than 700 ℃) and the amount of sodium hydroxide is high (such as the mass ratio of sodium hydroxide to VST is 0.9), quartz in VST is difficult to fully convert into silicates, there are unreacted quartz and sodium hydroxide in SAA, and SAA has poor alkaline activation performance. The optimal synthesis process conditions for SAA are as follows: synthesis temperature is 900 °C and the mass ratio of sodium hydroxide to VST is 0.95. The main silicate components of SAA are Na2SiO3 and Na15.6Ca3.8Si12O36. During the synthesis of one-part geopolymer (OPG), Na2SiO3 dissolution generates a strong alkaline reaction environment and provides active silicon-oxygen tetrahedron monomers or oligomers, Na15.6Ca3.8Si12O36 is bonded with geopolymer gel structure by stable cyclic silicate structure, which makes OPG have a compact integrated structure. When the mass ratio of SAA to MK is 1:1.3, the 7-day compressive strength of the prepared OPG is about 49 MPa, SAA has the potential as a substitute for commercial sodium silicate to prepare geopolymers.

Pengaruh Air Laut terhadap Kuat Tekan, Permeabilitas, dan Mikrostruktur Beton Geopolimer dengan Flyash dan Tanah Putih sebagai Pengganti Semen

The increasing infrastructure development of an area is sometimes located in an aggressive environment, one of which is in coastal areas so that direct contact with sea air cannot be avoided. This research aims to determine the effect of sea water on geopolymer concrete using fly ash and white soil as cement substitutes with testing parameters for compressive strength, permeability and microstructure. The test objects used were cylindrical in shape measuring 150x300 mm and 100x200 mm. The ratio of fly ash and white soil used was 85%:15% and the activator used was NaOH 8M and Na2SiO3 with a ratio of 1:2,5. The mixture proportion using a ratio of 1 fly ash: 1,497 sand: 2 split: 0,451 alkali activator with a mutual plan is 35 MPa. Tests were carried out after the concrete had gone through a curing process for 56 days, then the concrete was conditioned without soaking and with soaking for 28 days. Tests were carried out at concrete ages of 56 and 87 days. The test results show that geopolymer concrete with the influence of sea water has a higher compressive strength value and a smaller permeability coefficient compared to concrete without the influence of sea water. Microstructural testing of geopolymer concrete under the influence of sea air produces a matrix-shaped structure morphology that is denser with fewer pores compared to concrete without the influence of sea air.

Synthesis of composites from coal gasification slag by acid leaching and NaOH activation for efficient adsorption of methylene blue

This study successfully developed a carbon-silicon composite material (C-Si@GS) by acid leaching (HCl) and alkali activation (NaOH) treatments from solid waste CGS and applied to the adsorption of methylene blue (MB). The effects of material dosage, pH, contact time, initial concentration and co-existing ions on the removal of MB were investigated. The results revealed C-Si@GS had good adsorption performance at different pH and cations, suggesting that the material had stable properties. The adsorption of MB by C-Si@GS reached the equilibrium within 12 h, and the removal rate was up to 99 %. The maximum adsorption capacity of C-Si@GS was 456.8 mg/g calculated by Langmuir model (C0 (MB) = 120 mg/L, pH=7 ± 0.2, dosage = 0.6 g/L, and T=298 K). The adsorption process is consistent with Pseudo-secondary and Freundlich models, suggesting that both physical and chemical adsorption processes coexist. Adsorption mechanisms are mainly van der Waals forces, hydrogen bonding, electrostatic attraction and π-π bond interaction, as analyzed by XPS and FT-IR. The composites were regenerated using HCl as desorption agent and the removal rate was about 50 % after 3 cycles. The results illustrated that C-Si@GS can serve as an effective adsorbent for removing MB.

Shrinkage and Creep Properties of Low-Carbon Hybrid Cement.

Hybrid cements combine clinker with large amount of supplementary cementitious materials while utilizing hydration and alkali activation processes. This paper summarizes shrinkage and creep properties of industrially produced H-cement, containing only 20% of Portland clinker. In comparison with a reference cement CEM II/B-S 32.5 R, autogenous shrinkage is smaller after 7 days, and drying shrinkage is similar at similar times. A different capillary system of H-cement leads to faster water mass loss during drying. Basic and total creep of concrete remains in the standard deviation of B4 and EC2 creep models. The results demonstrate that shrinkage and creep properties of concrete made from H-cement have similar behavior as conventional structural concrete or high-volume fly ash concrete.

Research on Alkali-Activated Slag Stabilization of Dredged Silt Based on a Response Surface Method.

To improve the resource utilization of dredged silt and industrial waste, this study explores the efficacy of using ground granulated blast furnace slag (GGBS), active calcium oxide (CaO), and sodium silicate (Na2O·nSiO2) as alkali activators for silt stabilization. Through a combination of addition tests, response surface method experiments, and microscopic analyses, we identified key factors influencing the unconfined compressive strength (UCS) of stabilized silt, optimized material ratios, and elucidated stabilization mechanisms. The results revealed the following: (1) CaO exhibited the most pronounced stabilization effect, succeeded by Na2O·nSiO2, whereas GGBS alone displayed marginal efficacy. CaO-stabilized silt demonstrated rapid strength augmentation within the initial 7 d, while Na2O·nSiO2-stabilized silt demonstrated a more gradual strength enhancement over time, attributable to the delayed hydration of GGBS in non-alkaline conditions, with strength increments noticeably during later curing phases. (2) Response surface analysis demonstrated substantial interactions among GGBS-CaO and GGBS-Na2O·nSiO2, with the optimal dosages identified as 11.5% for GGBS, 4.1% for CaO, and 5.9% for Na2O·nSiO2. (3) X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses clarified that the hydration reactions within the GGBS-Na2O·nSiO2 composite cementitious system synergistically enhanced one another, with hydration products wrapping, filling, and binding the silt particles, thereby rendering the microstructure denser and more stable. Based on these experimental outcomes, we propose a microstructural mechanism model for the stabilization of dredged silt employing GGBS-CaO-Na2O·nSiO2.

Preparation and characterization of alkali-activated Pisha sandstone-slag composite cement

This study explores the development of a novel alkali-activated cementitious material (APKC) using Pisha sandstone and slag as the main raw materials, offering a sustainable alternative to traditional cement. The APKC's flowability and mechanical properties are comparable to those of ordinary Portland cement (OPC), but it is significantly more cost-effective, with lower carbon emissions and energy consumption. Specifically, at a water-to-binder (w/b) ratio of 0.3, with an optimal activator content of 17.5 % and a Pisha sandstone-to-slag ratio of 1:1, APKC achieves excellent performance: a flowability of 195 mm, and 28-day compressive and flexural strengths of 59.1 MPa and 9.96 MPa, respectively. Moreover, the production of one ton of APKC reduces costs to 64.01 %, carbon emissions to 22.76 %, and energy consumption to 28.56 % of those associated with one ton of OPC, highlighting its potential as a viable replacement in engineering applications. The primary hydration products of APKC include hydrotalcite, C,N-A-S-H gels, C-S-H gels, and natrolines. It is crucial to maintain the alkali activator content and Pisha sandstone-to-slag ratio within optimal ranges, as insufficient alkali dosage or an excessive Pisha sandstone-to-slag ratio can diminish the mechanical properties by reducing hydration product content. Conversely, too much alkali activator can lead to high-porosity hydration products due to the dissolution of Al in C,N-A-S-H gels.

Development of Fly Ash-Based Geopolymer Lightweight Aggregates

This research delves into the utilization of microwave hybrid heating as a curing technique for producing fine aggregates from fly ash. Various concentrations of alkali activator solutions were employed as binders to pelletize the fly ash (ranging from 0% to 10%). The resultant green fly ash-based geopolymer (FAG) aggregates were subjected to a 15-minute microwave kiln treatment. The microwave-sintered FAG fine aggregates, varying in sizes from 0.60 to 2.36 mm, were then utilized to fabricate 50 mm cubic cement mortar samples. Findings indicated that the density of FAG aggregates was approximately 36% lower than that of natural sand, while the water absorption capacity of FAG aggregates exhibited a fivefold increase compared to natural sand. Notably, cement mortar samples made with FAG aggregate of 4% alkali activator exhibited maximum compressive strengths of 31, 37, and 42 MPa at 7, 14, and 28 days of curing, respectively. These compressive strengths were only 12% lower than those of cement mortars made with natural sand across all curing periods. The use of microwave hybrid heating to transform fly ash into aggregates with sufficient strength appears viable, suggesting that these manufactured FAG aggregates could serve as substitutes for natural aggregates in concrete production