Abstract Bacterial concrete has been proposed as a potential approach to address sustainability challenges in concrete, primarily through its self-healing capabilities that may extend service life and reduce long-term maintenance needs. This study investigated the influence of different precursors and bacteria on the performance of self-healing concrete. Two different minerals (calcium lactate and sodium lactate at 75 mM / L ) were used as precursors with and without Bacillus pseudofirmus bacterial spores (at 10 8 cells / mL ) to prepare concrete specimens containing impregnated coarse lightweight aggregate. This approach quantifies the effects of precursor type and bacterial incorporation on healing efficiency and strength recovery, establishing clear links between chemical composition and performance outcomes. The compressive strength, crack healing efficiency, flexural strength, and strength recovery were evaluated for each mix type. The NaLac + Bac mix exhibited the highest self-healing efficiency (79% bottom faces, 69% side faces) and flexural strength recovery (18%) after 28 days without compromising compressive strength. MANOVA and violin plots showed significant differences between mix types with and without bacteria. The results indicated that a combination of sodium lactate and bacteria had the highest self-healing efficiency and flexural strength recovery. Scanning Electron Microscopy (SEM) revealed the morphology of calcite crystal healing products, whereas Energy Dispersive X-ray Spectroscopy (EDS) analysis confirmed the role of bacteria in promoting the formation of calcium-rich healing products, with Ca content increasing from 25% to 57% in the bacteria-containing mixes. Additionally, principal component analysis (PCA) correlated EDS elemental data with crack area reduction, confirming that calcium enrichment in bacteria-containing mixes corresponds to improved healing performance.
Abstract This study investigated the strength development of alkali-activated cements (AACs) synthesized from lime kiln dust (LKD) as a novel high-calcium precursor. The experimental program evaluated soft- and hard-burn LKDs, alone and blended with high-calcium fly ash (HCFA), under ambient and heat-curing conditions (50°C–70°C). X-ray fluorescence (XRF) and X-ray diffraction (XRD) analyses characterized the chemical composition and phase assemblages influencing strength evolution. Under ambient curing, soft-burn LKD exhibited higher reactivity and compressive strength ( ≈ 6 – 7 MPa at 28 days) than hard-burn LKD ( ≈ 0.2 – 0.6 MPa ). Optimum activation occurred at 8 M NaOH for soft-burn and 10 M for hard-burn LKD. Incorporating HCFA markedly enhanced performance, with a 30 ∶ 70 LKD-to-HCFA blend achieving ≈ 20 – 25 MPa , providing an effective balance between strength and sustainability. At 60°C—the optimal curing temperature—soft-burn and hard-burn LKD AACs attained 9–12 and 2.5–3 MPa, respectively, confirming the critical role of temperature in accelerating polymerization. The findings demonstrate that LKD-based AACs, particularly when combined with HCFA, offer a promising low-carbon binder for precast and accelerated construction applications.
Abstract Despite its potential as a geomaterial, fly ash (FA) has limitations in geotechnical applications because of its low strength, high deformability, and poor durability, necessitating sustainable improvement strategies. This study investigated the strength and durability enhancement of FA stabilized with two biopolymers, xanthan gum (XG) and guar gum (GG), at varying dosages, curing periods, curing methods, and mixing techniques. Unconfined compressive strength (UCS) tests were performed to evaluate the strength development in XG- and GG-treated FA (XFA and GFA), along with their durability, assessed by wetting and drying (WD) strength. Test results indicate that both biopolymers significantly improved the strength and durability of FA, with GFA consistently outperforming XFA. At the optimal dosages of 0.75% XG and 0.50% GG, the UCS of XFA and GFA increased by 1,029% and 1,282%, respectively, with GFA exhibiting 105% higher strength than XFA. The strength gain was more prominent during early curing (7 days), with GFA and XFA achieving improvements of 619% and 378%, respectively. Wet mixing with air curing enhanced the UCS by up to 97% (XFA) and 76% (GFA) compared to moist curing. Dry mixing further enhanced the UCS, especially under moist curing conditions, where XFA and GFA exhibited 65% and 57% higher UCS than their wet-mixed counterparts. After 12 WD cycles, GFA retained 58% of its UCS, outperforming XFA, which retained 50.7%, indicating better long-term durability. Furthermore, microstructural analyses revealed enhanced particle binding, bridging, and distinct bonding mechanisms in the XFA and GFA.
Abstract To address the issues of low strength, uneven particle distribution, and weak interfacial bonding in ultralight expanded polystyrene (EPS) concrete, this study proposes a powder precoating process. This process involves precoating the surface of EPS particles with a layer of powder material. The differences in the effects of this process and the ordinary process on the properties of ultralight EPS concrete were systematically compared. The results showed that the precoating process increases the compressive strength by 21.4%–25.6% for ultralight EPS concrete with a low density grade of 200 – 400 kg / m 3 , and the flexural strength is increased by up to 40.6% for the concrete with a density grade of 600 kg / m 3 . Additionally, it can effectively alleviate the phenomenon of reduced concrete strength caused by the incorporation of fly ash. The uniformity index of ultralight EPS concrete prepared by the precoating process reached 0.78, whereas that of the ordinary process was 0.59. Cross-section observations confirmed that the EPS particles are more evenly distributed, the number of pores is reduced, and the delamination phenomenon is basically eliminated. The slope of the thermal conductivity of the precoating process with increasing density decreases from 1.64 × 10 − 6 (of the ordinary process) to 1.57 × 10 − 6 , indicating that the precoating process provides better thermal insulation performance at the same density. Microscopic analysis revealed that the precoating process improves compactness by optimizing the structure of the interfacial transition zone, promoting the formation of calcium silicate hydrate (C─S─H), and reducing the residual calcium hydroxide ( Ca ( OH ) 2 ), without introducing new chemical bonds. This process provides technical support for the application of ultralight EPS concrete in energy-efficient buildings.
Abstract This study investigated the fracture resistance and self-healing ability of conductive multilayer asphalt roads integrated into inductive power transfer (IPT) infrastructure for wireless charging of electric vehicles. The study also focused on minimizing the thermal gradient caused by uneven magnetic field distribution during the induction heating process to eliminate varying healing effects within the multilayer inductive healing layers (ML-IHLs) made of very thin asphalt concrete and binder layers. To do so, waste steel fibers (WSFs) was added in varying proportions, specifically incorporated into very thin asphalt and binder layers. The fracture resistance and self-healing ability of both the very thin asphalt concrete and binder layer were assessed using the fracture-healing-fracture approach based on semicircular bending (SCB) tests. Additionally, to evaluate the effect of WSF content on the mechanical performance of very thin asphalt concrete, Marshall stability and indirect tensile stiffness modulus (ITSM) tests were conducted. The fuzzy analytic hierarchy process (AHP)-based weighted aggregated sum product assessment (WASPAS) method was used to determine the optimum asphalt design by considering the mechanical performance and self-healing ability of asphalt mixtures. The results show that WSFs enhance the deformation capacity of very thin asphalt concrete and enables effective self-healing when applied before microcracks deepen.
