Self-compacting concrete (SCC) is widely used in reinforced concrete structures, yet its residual structural behaviour after fire exposure remains insufficiently understood, particularly under the combined effects of mixture composition, heating rate, and boundary restraint. This study experimentally investigated reinforced SCC beams incorporating fine-to-coarse aggregate (F/C) ratios of 0.90 (SCC-L), 1.00 (SCC-R), and 1.10 (SCC-H). A total of 90 beams were tested at ambient temperature and after exposure to 300 and 500 °C using heating rates of 20 and 30 °C/min under simply supported and restrained-end conditions. Residual ultrasonic pulse velocity (UPV) measurements and four-point flexural tests were conducted. The ambient simply supported reference beams had ultimate loads of 11.2, 11.8, and 10.7 kN and first crack loads of 4.95, 5.20, and 4.50 kN for SCC-L, SCC-R, and SCC-H, respectively. Exposure temperature was the dominant factor governing deterioration, while higher heating rates accelerated thermal damage. At 500 °C and 30 °C/min, simply supported beams retained 66.95–78.50% of their ambient ultimate loads, whereas first crack loads decreased to 36.54–60.00% of their corresponding ambient- temperature values. SCC-H consistently exhibited the highest retention of residual mechanical and structural properties. End restraint increased the residual ultimate load by up to 21.52% and first crack load by up to 89.47% relative to simply supported beams with the same mixture, exposure temperature, and heating rate. The developed empirical model showed a good fit to the experimental ultimate flexural loads (R2 = 0.9637) within the investigated parameter ranges. The results demonstrate that mixture composition and boundary restraint significantly influence post-fire performance, while UPV provides a reliable indicator of residual structural condition.
Rapid construction development increases the demand for raw materials and makes variations in their quality, including mixing-water quality, increasingly relevant to cementitious-material performance. This creates a need for assessment tools capable of integrating several material properties under variable raw-material conditions. Fuzzy Logic can support such assessment by combining mechanical and physical responses into a single comparative index. This study evaluated the effects of gypsum and sodium sulfate on CEM III mortars with and without 10% fly ash. Compressive strength, flexural strength, and mass water absorption were measured after 28 days and integrated using a Mamdani Fuzzy Logic model into a Fuzzy Performance Index (FPI). The sulfate-free mortar containing fly ash showed mean compressive and flexural strength values 3.73% and 1.47% higher than the reference mortar. Gypsum produced the strongest adverse changes, with the higher dosage reducing compressive strength by 26.87% and increasing water absorption to 11.67%. The response to Na2SO4 was non-monotonic and depended on binder composition. Sensitivity analysis showed stable separation of the mixtures into performance groups, with Spearman coefficients of 0.9286–1.000, although closely ranked mixtures could exchange positions. The results support the use of Fuzzy Logic as a local screening tool for integrating conflicting material responses within the investigated experimental domain.
Recycled refractory brick aggregate (RRBA) offers a potential means of reducing natural-sand consumption while improving the post-heating performance of concrete. However, comparisons among previous studies are frequently affected by differences in aggregate grading. In this study, a grading-controlled design was therefore adopted by blending two RRBA fractions to closely match the particle-size distribution of natural sand. Nine concretes with 0–60% fine-aggregate replacement were characterised at 28 days. All mixtures exceeded the target mean compressive strength of 50 MPa, while mean flexural strengths showed limited variation without a systematic trend with RRBA content. Separate specimens were heated at an age of 90 days to 100, 150, 200, 400, 600 and 800 °C. Mass loss and macroscopic damage were assessed after heating and cooling, while compressive strength, water-accessible porosity and saturated electrical resistivity were determined following 28 days of moist reconditioning. Thermal deterioration was generally less pronounced at 100–200 °C and intensified from 400 °C onwards. At 600 °C, the reference concrete retained only 25.4% of its unheated compressive strength, compared with 62.2% for RRBA-10. At 800 °C, the reference exhibited negligible compressive strength, whereas RRBA-15 achieved the highest observed mean post-thermal compressive strength, at 24.38 MPa (41.8% of its unheated strength). At 600 °C, RRBA-05 limited the relative porosity increase to approximately 10%, compared with 54.9% for the reference. Electrical resistivity losses for RRBA-05 to RRBA-15 ranged from 42.2% to 45.8%, compared with 75.8% for the reference mixture. A weighted geometric index combining compressive-strength, porosity and resistivity conservation identified 5–10% RRBA as a favourable interval at 600 °C, with RRBA-05 and RRBA-10 also occupying the first two positions under all eight alternative weighting schemes examined. The favourable replacement level therefore depended on exposure temperature and the performance criterion considered.
Crumb rubber (CR) modification offers a sustainable approach to improving asphalt performance while promoting the beneficial reuse of end-of-life tyres. This study evaluates the structural performance of CR-modified hot mix asphalt (HMA) under service conditions through an integrated mechanistic and machine-learning framework. Laboratory-measured resilient moduli for conventional and 15% CR-modified HMA at 20, 40, and 60 °C were incorporated into a three-layer Odemark–Shell analysis considering 11 asphalt-layer thicknesses and three representative seasonal temperature periods established from an 11-year (2015–2025) climatic record for Karbala, Iraq. Pavement performance was assessed for a 20-year design period under 6 × 106 equivalent single axle loads (ESALs), with fatigue and rutting damage accumulated using Miner’s rule. Eight machine-learning algorithms were additionally evaluated as fast surrogate models for predicting the critical pavement responses. Incorporating CR increased the resilient modulus by 8.5–9.2%, resulting in reductions of 9.7–10.4% in horizontal tensile strain and 1.2–2.8% in vertical compressive strain over the investigated temperature range. The continuous interpolation of the fatigue-damage criterion indicated required asphalt thicknesses of approximately 27.3 cm for conventional HMA and 25.8 cm for CR-modified HMA, corresponding to a reduction of approximately 1.5 cm (5–6%). At the common 27.5 cm design thickness, CR modification reduced the governing fatigue damage index from 0.954 to 0.723, representing a 24.2% reduction in accumulated fatigue damage and increasing the estimated service life from approximately 21.0 to 27.7 years. Gradient Boosting achieved surrogate-model fidelity, with R2 values of 0.993 and 0.9998 for the critical strain responses, while asphalt-layer thickness emerged as the dominant performance variable, consistent with the known analytical structure of the governing equations. The use of CR could additionally divert approximately 10.9 tonnes of scrap tyre rubber from the landfill per lane-kilometre. The findings demonstrate that the CR modification can reduce the continuously estimated required asphalt thickness and extend the theoretical pavement service life under the adopted assumptions, although the thickness reduction is not resolved when standard 2.5 cm construction increments are considered. Additionally, CR modification provides measurable sustainability benefits through the reuse of scrap-tyre rubber.
This study investigates expanded perlite production waste (EPPW), an under-valorized industrial by-product, as the main pozzolanic component of lime mortars at high replacement levels, aiming to reduce conventional binder demand. To this end, mortars were prepared with 50%, 67%, and 75% EPPW by binder mass and subjected to air, water, and accelerated heat curing. Their physical, hygric, and mechanical properties were assessed, including porosity, capillary water absorption, water vapor diffusion resistance, ultrasonic pulse velocity, flexural and compressive strength tests, supported by XRD and DTG analyses. EPPW exhibited pozzolanic activity, and the highest compressive strength, about 10 MPa, was obtained at 67% replacement after 7 days of heat curing and 90 days of water curing. Under the same curing conditions, the 50% replacement level provided the lowest water and vapor transport, whereas 75% EPPW increased transport properties. As EPPW requires only grinding, grinding emissions were estimated at no more than about 3% of those avoided by the lime it replaces. The results indicate that EPPW can be upcycled into pozzolanic lime mortars potentially suitable for non-load-bearing applications such as rendering, plastering, and historic building conservation, although hygric performance, compatibility, and long-term durability require further investigation.
