Durability evaluation of cement-stabilized semi-rigid base courses incorporating recycled aggregates from steel slag, coal gangue, and construction waste

Steel slag (SS), coal gangue (CG), and construction waste (CW) were investigated as partial replacements in cement-stabilized aggregate mixtures for highway semi-rigid bases, with incorporation rates ranging from 0% to 80%. Performance assessments included unconfined compressive strength, flexural strength, drying shrinkage, and freeze-thaw resistance, followed by optimal material selection using a comprehensive fuzzy algorithm. Results indicated that SS synergistically enhanced overall performance. Active components within SS induced micro-expansion, reducing drying shrinkage by 29.5%–40.0%. Furthermore, continued hydration increased 360-day compressive strength by 16.0%–36.2%, flexural strength by 42.1%–52.9%, and the freeze-thaw strength ratio by 17.3%. Conversely, CW content exceeding 60% increased drying shrinkage by 10.8% due to fine aggregate hydration, yielding only marginal compressive strength gains (4.4%–7.3%) at 360 days. High CG levels (>40%) caused significant degradation in mechanical and durability properties due to layer structure disintegration; compressive strength decreased by 30.9%–46.9%, flexural strength fell by 40%, and freeze-thaw resistance declined by over 10%. Drying shrinkage for all mixtures conformed to the EXPASSOC model (R2 > 0.99), exhibiting a three-stage pattern where 85% of shrinkage occurred within 60 days, followed by stabilization after 100 days. A derived cracking resistance index confirmed that SS dosages of >40% provided optimal anti-cracking performance. Fuzzy comprehensive algorithm analysis identified SS (40%–80% incorporation) as the optimal material choice. Consequently, CG requires strict limitation to ≤40%, whereas CW is permissible at ≤ 40% (excluding fine aggregates). These findings provide theoretical support for the classified resource utilization of multi-source solid wastes in highway base courses.