Search Results (6)

Fluidized solidified soil (FSS) has emerged as a promising material for marine pile scour remediation, yet its limited construction window and vulnerability to hydraulic erosion before sufficient curing constrain its broader application. This study systematically evaluates FSS formulations based on dredged sediment, cement partially replaced by silica fume (i.e., 0%, 4%, 8%, and 12%), and quicklime activation under three water–solid ratios (WSR, i.e., 0.525, 0.55, and 0.575). Experimental assessments included flowability tests, unconfined compressive strength, direct shear tests, and microstructural analysis via XRD and SEM. The results indicate that SF substitution significantly mitigates flowability loss during the 90–120 min interval, thereby extending the operational period. Moreover, the greatest enhancement in mechanical performance was achieved at an 8% SF replacement: at WSR = 0.55, the 3-day UCS increased by 22.78%, while the 7-day cohesion and internal friction angle rose by 13.97% and 2.59%, respectively. Microscopic analyses also confirmed that SF’s pozzolanic reaction generated additional C-S-H gel. However, the SF substitution exhibits a pronounced threshold effect, with levels above 8% introducing unreacted particles that disrupt the cementitious network. These results underscore the critical balance between flowability and early-age strength for stable marine pile scour repair, with WSR = 0.525 and 8% SF substitution identified as the optimal mix. Full article

Quicklime (CaO) is extensively used in metallurgy, chemical engineering, materials science, and greenhouse gas reduction due to its high reactivity, low energy consumption, and environmental benefits. It is considered as one of the most promising raw materials for nanomaterial synthesis and carbon dioxide capture. Previous studies have predominantly focused on the impact of limestone composition and calcination condition. Recent research, however, suggests that the structural characteristics of limestone also play a crucial role in determining the reactivity of quicklime. This study investigates the effect of limestone structure on quicklime reactivity and provides a mechanistic analysis. Three types of limestone with varying structures—clastic-structured, transitional-crystalline-structured, and crystalline-structured—were selected for experiments under different calcination times. The results indicate that quicklime produced from clastic-structured limestone exhibits the highest reactivity. The observed differences in quicklime reactivity can primarily be attributed to the following factors: (1) Clastic-structured limestone possesses larger pore volume and specific surface area, which enhance heat conduction and ensure the uniform decomposition of calcite across various regions. (2) The rock-forming calcite particles are fine and small, allowing for the simultaneous decomposition of the outer shell, middle, and core during heating. This prevents “overburning” of the shell or “underfiring” of the core, thereby improving the overall reactivity. Based on these findings, we propose that fine-grained, high-purity clastic-structured limestone is more favorable for producing high-activity quicklime. Full article

Quicklime is not only an important raw material for the steel and nano-calcium carbonate industries but also a key carrier for capturing carbon dioxide in the fight against global warming, and its reaction activity plays a vital role in these processes. Recent studies have found that quicklime produced from limestones with similar chemical compositions under the same production process has significantly different reaction activities, which indicates that something other than the chemical composition of limestone affects quicklime reaction activity. To explore the factors affecting quicklime reaction activity, this study analyzed the textures and calcite particle size of limestone collected from different areas of Guangxi, China, and measures the quicklime reaction activity with different calcination times. It has been found that: (1) limestone with a clastic texture is preferred to that with a crystalline texture (including transition type) in yielding quicklime with higher reaction activity; and (2) for limestone with a clastic texture, fine-grained limestone tends to produce the same or higher quicklime reaction activity with lower energy consumption. Full article

The by-products of the circulating fluidized-bed boiler combustion (CFBC) of coal exhibit self-hardening properties due to the calcium silicates generated by the reaction between SiO₂ and CaO, and the ettringite generated by the reaction of gypsum and quicklime with activated alumina. These reactions exhibit tendencies similar to that of the hydration of ordinary Portland cement (OPC). In this study, the self-hydration and carbonation reaction mechanisms of CFBC by-products were analyzed. These CFBC by-products comprise a number of compounds, including Fe₂O₃, free CaO, and CaSO₄, in large quantities. The hydration product calcium aluminate (and/or ferrite) of calcium aluminate ferrite and sulfate was confirmed through instrumental analysis. The CFBC by-products attain hardening properties because of the carbonation reaction between calcium aluminate ferrite and CO₂. This can be identified as a self-hardening process because it does not require a supply of special ions from the outside. Through this study, it was confirmed that CFBC by-products generate CaCO₃ through carbonation, thereby densifying the pores of the hardened body and contributing to the development of compressive strength. Full article

Adverse side-effects occurred in slurry foaming and thickening process when carbide slag was substituted for quicklime in HCS-AAC. Cement accelerators were introduced to modify the slurry foaming and coagulating process during pre-curing. Meanwhile, the affiliated effects on the physical-mechanical properties and hydration products were discussed to evaluate the applicability and influence of the cement accelerator. The hydration products were characterized by mineralogical (XRD) and thermal analysis (DSC-TG). The results indicated that substituting carbide slag for quicklime retarded slurry foaming and curing progress; meanwhile, the induced mechanical property declination had a negative effect on the generation of C–S–H (I) and tobermorite. Na₂SO₄ and Na₂O·2.0SiO₂ can effectively accelerate the slurry foaming rate, but the promoting effect on slurry thickening was inconspicuous. The compressive strength of HCS-AAC obviously declined with increasing cement coagulant content, which was mainly ascribed to the decrease in bulk density caused by the accelerating effect on the slurry foaming process. Dosing Na₂SO₄ under 0.4% has little effect on the generation of strength contributing to hydration products while the addition of Na₂O·2.0SiO₂ can accelerate the generation and crystallization of C–S–H, which contributed to the high activity gelatinous SiO₂ generated from the reaction between Na₂O·2.0SiO₂ and Ca(OH)₂. Full article

This study investigated the use of coal bottom ash (bottom ash) and CaO-CaCl₂-activated ground granulated blast furnace slag (GGBFS) binder in the manufacturing of artificial fine aggregates using cold-bonded pelletization. Mixture samples were prepared with varying added contents of bottom ash of varying added contents of bottom ash relative to the weight of the cementless binder (= GGBFS + quicklime (CaO) + calcium chloride (CaCl₂)). In the system, the added bottom ash was not simply an inert filler but was dissolved at an early stage. As the ionic concentrations of Ca and Si increased due to dissolved bottom ash, calcium silicate hydrate (C-S-H) formed both earlier and at higher levels, which increased the strength of the earlier stages. However, the added bottom ash did not affect the total quantities of main reaction products, C-S-H and hydrocalumite, in later phases (e.g., 28 days), but simply accelerated the binder reaction until it had occurred for 14 days. After considering both the mechanical strength and the pelletizing formability of all the mixtures, the proportion with 40 relative weight of bottom ash was selected for the manufacturing of pilot samples of aggregates. The produced fine aggregates had a water absorption rate of 9.83% and demonstrated a much smaller amount of heavy metal leaching than the raw bottom ash. Full article