Emulsion-based cold recycling can reduce the demand for virgin aggregate and high-temperature asphalt production, but mixtures with high reclaimed asphalt pavement (RAP) contents often have limited early strength and moisture resistance. This study evaluated a dense-graded cold-mix system containing 0%, 60%, and 70% RAP, combined with a 2 & times; 3 additive matrix comprising cement (0.5% and 1.0%) and Class C fly ash (0.5%, 1.0%, and 1.5%). The 70% RAP blend fell outside the adopted dense-graded envelope, whereas the 60% blend satisfied that envelope and was therefore selected, not claimed as a universal optimum for the additive stage. Hot-mix asphalt was included only as a benchmark. Marshall stability, indirect tensile strength, Marshall quotient, tensile strength ratio, retained Marshall stability, and retained Marshall quotient were measured under the reported laboratory curing and conditioning procedures. Among the tested cold mixtures, the 60% RAP formulation containing 1% cement and 1% fly ash produced the highest measured stability (13.1 kN), dry indirect tensile strength (1.11 MPa), and Marshall quotient (6.89), with retained-property indices of approximately 87%. These short-term results indicate that gradation control and low-dose cementitious additions can improve strength development and moisture retention in the studied emulsion-RAP system. The contribution of the work is an integrated, formulation-level comparison of RAP screening and a cement-fly ash dosage matrix; the findings remain specific to the materials, gradation envelope, curing regime, and screening tests used.
Spent coffee grounds (SCGs) and ammonium lignosulfonate (ALS) are promising renewable constituents for wood-fiber biocomposites, but the effect of their relative proportion within the binder phase remains insufficiently understood. This preliminary study evaluated wood-fiber panels produced at a constant dry-matter matrix-to-fiber ratio of 50:50 while varying the SCG:ALS ratio from 70:30 to 30:70. The panels were hot-pressed and characterized for their physical and mechanical properties, while the corresponding SCG-ALS matrix formulations were evaluated by simultaneous TGA-DSC analysis. Increasing the SCG fraction generally improved dimensional stability and mechanical performance, whereas formulations containing 50% or more ALS showed a marked deterioration in water resistance. The SCG-rich 70:30 formulation provided the highest bending performance, with MOE and MOR values of 2156.5 and 12.83 N & centerdot;mm-2, respectively. Thermal analysis revealed ratio-dependent changes in mass loss and in the principal heat-flow event, which occurred between approximately 113 and 136 degrees C, confirming that the SCG:ALS ratio altered the early thermal behavior of the binder system. Overall, the SCG:ALS ratio was identified as a key formulation parameter, with SCG-rich systems providing the most favorable balance between mechanical performance, dimensional stability, and internal cohesion.
This study investigates the influence of biomass fly ash (BFA) produced from high-temperature combustion of woody biomass fuels typical of Lithuanian energy plants on the mechanical performance, microstructure, and reactivity of alkali-activated binders based on diatomite and iron dust. Diatomite was used as a reactive silica source, while iron dust served as a matrix-modifying component enhancing binder density and strength. The role of BFA (10-30%) was evaluated in terms of compressive strength, softening factor, water resistance, and structural development using XRD and FTIR analyses. The results show that the formation of a compact geopolymer gel is the key factor controlling strength development. The highest compressive strength (53 MPa) was obtained at 10% BFA; however, it decreased to 33 MPa after thermal treatment at 200 degrees C, indicating limited structural stability. Increasing the BFA content to 20% and 30% improved the softening factor and water resistance but significantly reduced compressive strength to below 20 MPa and 10 MPa, respectively, demonstrating a trade-off between strength and durability. XRD analysis confirmed similar mineralogical compositions in all samples, dominated by largely unreacted quartz and magnetite, while minor amounts of andradite formed after thermal treatment. FTIR results revealed increased polymerisation with higher BFA content, reflected by the shift of the Si-O-T band (similar to 966-985 cm(-1) to similar to 988-995 cm(-1)), although the presence of Ca-rich and partially unreacted phases led to a less efficient geopolymeric network. Overall, the performance of the studied systems is governed by the balance between gel formation, phase composition, and microstructural integrity, with optimal properties achieved at moderate BFA content rather than at extreme compositions.
Carbon deoxidation is a clean steelmaking route, but rapid CO generation can increase gas holdup, raise the melt level, and cause splashing. However, a quantitative link between internal deoxidation kinetics and melt-level rise has not yet been established. Hot-state experiments at 1873 K in a 2 kg crucible under argon with 0.20-1.00 wt.% C were coupled with a dual-pathway kinetic model developed by decoupling free-surface mass transfer from internal CO generation through heterogeneous nucleation at active refractory pores and incorporating an effective reaction depth constrained by hydrostatic pressure. The model reproduced measured oxygen evolution and revealed three deoxidation stages. Internal gas generation initially dominated, contributing 96.6% of the overall rate. As carbon-oxygen supersaturation fell below a critical threshold, the nucleation zone receded upward and free-surface mass transfer became dominant. Within the investigated conditions, the internal apparent deoxidation rate constant during the rapid stage showed an empirical linear relationship with the measured maximum melt-level rise. The critical splash-prevention rate was 4.25 min-1 for the crucible and was estimated to be 2.43 min-1 for a selected 85 t ladle by combining this relationship with the average gas holdup relation and ladle geometry. The present results provide a kinetic basis for assessing splash risk during atmospheric carbon deoxidation.
In view of the differences in the specified substitution rates of construction and demolition waste (C&DW) recycled materials in road applications between China and other countries, this study focuses on a highway reconstruction and expansion project in Guangdong Province, China, and systematically analyzes the influence of the recycled aggregate substitution rate on the road performance of subgrade filler and cement-stabilized recycled aggregate (CSRA). Based on the current domestic JTG series specifications, combined with a literature review and comparative analysis, the effects of particle size, maximum dry density (MDD), optimum moisture content (OMC), and California bearing ratio (CBR) on the compactness, stability, and strength of subgrade fillers under different substitution rates were systematically evaluated. Furthermore, the study investigates the variation in the performance of CSRA, including crushing value, 7-day unconfined compressive strength, 90-day splitting tensile strength, compressive rebound modulus, and scouring resistance. The results indicate that (1) when recycled materials are used for roadbed filling, they can meet the specified compactness and CBR value requirements at a 100% substitution rate. The key is to control the impurity content and maximum particle size during the crushing process. (2) When recycled materials are used in a pavement structure layer, their performance is significantly affected by the material source and substitution rate. CSRA produced from demolished old pavements and bridges exhibits better performance. It is recommended that the substitution rate should not exceed 80% for subbase layers and 50% for base layers. This research provides recommended substitution rates and material-selection guidelines for the scientific utilization of C&DW recycled materials for specific engineering applications. The study has practical significance for improving C&DW resource utilization, reducing engineering costs, and lowering carbon emissions.
