Positive Influence of Liquid Sodium Silicate on the Setting Time, Polymerization, and Strength Development Mechanism of MSWI Bottom Ash Alkali-Activated Mortars

Morphological and mechanical studies of Al2O3-Na2SiO3 as a skin barrier coated with TiO2 for carbon fiber reinforced composite materials

The utilization of adhesive compounds in bonding lightweight and high-performance composite structures, including carbon fiber reinforced polymer (CFRP) composites, has garnered significant attention from researchers. This study presents the novel application of Al2O3 coated with TiO2 as a thermal protective layer for CFRP substrate. Initially, the CFRP substrate underwent a protective treatment involving the application of Al2O3 as a middle coat, followed by a further protective layer consisting of TiO2 as a top coat. The deposition of TiO2 onto an Al2O3-based thermal barrier coating (TBC) was carried out utilizing the flame spray method. The use of a TiO2 coating as a top coat was employed to enhance protection and heat dispersion across the middle coat and substrate. In order to achieve sufficient adhesion between the CFRP substrate, an intermediate coat consisting of Al2O3 with a Na2SiO3 binder, the impact of varying nozzle distances on adhesion strength and pull-off test outcomes was investigated, with a nozzle distance of 180 mm yielding the highest adhesion strength. The thermal stability of a CFRP substrate was enhanced through the deposition of a layer of TiO2 on Al2O3. The surface and cross-sectional morphologies of the composite were analyzed using a Scanning Electron Microscope (SEM). It was observed that the presence of a TBC on the composite surface effectively reduced the amount of heat that was transferred to the composite material. In order to assess the effectiveness of TBC on CFRP substrates, a series of experiments involving thermal torch and conductivity tests were undertaken. The interaction between the top and middle coats of a composite material results in enhanced mechanical properties, hence improving its thermal insulation capabilities. The artificially produced TBC coatings have the potential to function as adhesive materials, ensuring the sustained high performance of CFRP substrates.

Improvement of Mechanical Properties and Condensation Behavior for Alkali-Activated Materials by Sodium Silicate

To further enhance the compressive strength of alkali-activated materials and reveal their condensation behavior, the reactivity of alkali-activated slag materials was enhanced through the addition of different kinds and proportions of sodium silicate. The mechanical properties of the specimens were observed regularly and the condensation behavior was further analyzed. The results showed that both solid and liquid sodium silicate could significantly improve the compressive strength. The maximum increase in compressive strength was 123.7%, while the initial and final setting times were significantly shortened to 9 min. When solid sodium silicate content increased from 5% to 15%, the compressive strength first increased to 34.6 MPa and then decreased to 28.6 MPa, indicating that 10% was the optimum solid sodium silicate content. The large amount of crystallized solid sodium silicate in the specimen led to the decrease in mechanical properties. When liquid sodium silicate content increased from 5% to 15%, the compressive strength first increased to 52.8 MPa and then tended to be stable, implying that 10% was the optimum content. This shows that its reinforcement effect has a maximum limit. The activation effect of liquid sodium silicate was better than that of solid.

Preparation and Properties of Municipal Solid Waste Incineration Alkali-Activated Lightweight Materials through Spontaneous Bubbles

A self-foaming alkali-activated lightweight material was prepared by the pretreatment of municipal solid waste incineration bottom ash (BA). The low weight could be achieved without adding a foaming agent by using the low-density and self-foaming expansion characteristics of BA in combination with a strong alkali. The effects of BA, liquid sodium silicate (LSS), and calcium hydroxide (CH) on dry and wet densities, as well as water absorption, are discussed. The results show that increasing the BA content can significantly improve the foaming effect and reduce the dry and wet densities of specimens. However, it also leads to a sudden decrease in compressive strength and a significant increase in water absorption. LSS and CH can significantly improve the ability to seal bubbles by accelerating condensation, and they further reduce dry and wet densities without significantly improving water absorption. It is most effective at BA, LSS, and CH contents of 60, 20, and 2%, respectively.

Influence of Different Parameters on the Performance of Alkali-Activated Slag/Fly Ash Composite System

In order to study the influence law of each parameter on the performance of the alkali-activated composite gelling system, the influence degree was sorted, and the most important parameter affecting each performance was found. The solution of liquid water glass and solid sodium hydroxide was used as the alkaline activator, and the mixing ratio was designed by the orthogonal test method. The effects of four parameters of fly ash content, water glass modulus, water glass solid content, and water–solid ratio on the working performance and mechanical properties of alkali-activated slag–fly ash composite cementation system were discussed. The gelling system was studied by microscopic experiments such as SEM and FTIR. The results show that the solid content of water glass has the greatest influence on the fluidity of the composite cementitious system, and the content of fly ash is the primary factor affecting the setting time of the material. The flexural and compressive strengths at the age of 7 d and 28 d were most affected by the content of fly ash, and the solid content of water glass had the greatest influence on the flexural and compressive strengths at the age of 2 d. From the perspective of microscopic morphology, in the high-strength samples, the fly ash particles and the remaining outer shell are embedded in the gel to form a dense whole. When the amount of silica in the composite gelling system is too high, it will cause the phenomenon of low macroscopic mechanical properties.

Effect of Temperature and Humidity on the Synthesis of Alkali-Activated Binders Based on Bottom Ash from Municipal Waste Incineration

Weathered bottom ash (WBA) from municipal solid waste incineration is a calcium aluminosilicate-rich material mainly used in construction and civil engineering as a secondary aggregate. However, its use is also being considered as a precursor in the manufacture of alkali-activated binders (AA-WBA). This preliminary research aimed to deepen understanding of the potential use of WBA (>8 mm fraction) as the sole precursor of alkali-activated binders. To gain better knowledge of this material, the physicochemical, mechanical, and environmental properties of AA-WBA binders were evaluated. In addition, the effect of curing temperature (25 °C, 45 °C, 65 °C, and 85 °C) and humidity conditions (oven and climate chamber) were assessed. The results of this study revealed that temperature and humidity conditions play a fundamental role during the early formation stages of AA-WBA binders. Maximum compactness and compressive strength (29.8 MPa) were obtained in the sample cured at 65 °C in the oven and room humidity. At higher temperatures (85 °C), a substantial decrease in mechanical strength (21.2 MPa) was observed due to a lower cohesion of the binder phases. Curing in the climate chamber led to an increase in humidity, and therefore a decrease in compressive strength. Finally, lower porosity and longer curing time substantially decreased the heavy metals and metalloid leaching concentration of AA-WBA binders.

Effect of Sodium Hydroxide, Liquid Sodium Silicate, Calcium Hydroxide, and Slag on the Mechanical Properties and Mineral Crystal Structure Evolution of Polymer Materials

To study the key factors that affect the mechanical properties of polymer materials and explore the relationship between mineral crystal formation and strength development, fly ash (FA) polymer samples were prepared using sodium hydroxide, slag, liquid sodium silicate, and hydrated lime as activators. A change in the compressive strength was observed, and X-ray diffraction measurements were carried out to confirm the change. The effects of different types and amounts of activators on the formation and transformation of mineral crystals in FA polymer samples as well as on the development of compressive strength were studied. Moreover, the relationship between the formation and transformation of mineral crystals and the development of compressive strength was established. The results show that the strongly alkaline excitation environment established by sodium hydroxide is the prerequisite for crystal formation and development of compressive strength. Under this strongly alkaline excitation environment, slag, hydrated lime, and liquid sodium silicate can increase the amounts of calcium and silicon, which promote the formation and development of hydrated calcium silicate and hydrated calcium silicoaluminate in polymers and significantly improve the compressive strength.

Experimental Study of the Mechanical and Microstructure Characteristics of Coal Gangue Road Stabilization Materials Based on Alkali Slag Cementation

To accelerate the resource utilization of coal gangue and meet the strategic requirements of carbon neutralization, alkali-activated, slag-cemented coal gangue is applied in the preparation of solid waste-based road stabilization materials. Here, the cementation characteristics and microstructure characteristics of alkali-activated, slag-cemented coal gangue road stabilization materials are studied using the alkali equivalent and coal gangue aggregate ratio as experimental variables. The results show that with the increase in alkali equivalent from 1% to 7%, the unconfined compressive strength of the alkali-activated coal gangue road stabilization material initially increases and then decreases, with 3% being the optimal group in terms of stabilization, the aggregate ratio of coal gangue increases from 70% to 85%, and the 7-day unconfined compressive strength of the stabilized material decreases approximately linearly from 8.16 to 1.68 MPa. At the same time, the porosity gradually increases but still meets the requirements of the specification. With the increase in hydration time, a large number of hydration products are formed in the alkali slag cementation system, and they are closely attached to the surface of and interweave with the coal gangue to fill the pores, resulting in the alkali slag slurry and coal gangue being brought closer together.