Self-healing concrete is an advanced, sustainable technique that has the potential to reduce maintenance costs by automatically repairing cracks. Some Bacillus species produce a urease enzyme to precipitate calcite during biomineralization, which can act as a binding filling material. This study investigated the effects of bacteria type, content and concentration, and nutrient content on the properties of self-healing concrete, especially at the age of 90 days. Bacillus Sphaericus and Bacillus Megaterium were introduced into the concrete at two concentrations, 2 × 10⁸ and 2 × 10⁹ (CFU/ml), and different percentages of bacteria were selected using calcium lactate as a nutrient material. Tests were performed for compressive strength, SEM, EDS, water permeability, rapid chloride permeability, and TGA/DTG. The results show significant development in compressive strength and microstructure characterization of concrete, especially with Bacillus Megaterium using a 2.5% bacterial proportion with a concentration of 2 × 10⁹ CFU/ml and 1% of calcium lactate.

The creation of cracks, which are the most common cause of structural failure, has a significant impact on the structure's strength and durability. As a result, effective repair and maintenance are vital and unavoidable for treating any of these issues. Self-healing mortar holds promising benefits for reducing the cost of repair as cracks are autonomously repaired without any human intervention. This study investigated the effect of bacteria type, bacteria content, bacteria concentration, and nutrient type on the properties of the self-healing mortar. Three types of bacteria, Bacillus sphaericus, Bacillus Megaterium, and Bacillus subtilis encapsulated in calcium alginate beads, were introduced into the mortar. Two concentrations of bacteria, 2× 108 and 2× 109 Colony Forming Units per milliliter, and different percentages of bacteria of cement weight were selected for the study. In addition, calcium lactate and calcium acetate were used at 0.5% of cement weight as nutrition for bacteria. Tests were performed for compressive strength, bending strength, SEM, EDX, and TGA/DTG. The results show a significant development in the mechanical behaviour of mortar, especially with Bacillus Megaterium using a 2.5% bacterial proportion with a concentration 2× 109 CFU/ml. This can be related to the filling of voids and cracks in microbial mortar by calcite, which was confirmed by SEM and EDX.

Concrete cracks and sulfate degradation severely compromise structural durability, highlighting the need for sustainable solutions to enhance longevity and minimize environmental impact. This study assesses the efficacy of bacterial self-healing technology utilizing Bacillus megaterium (BM) and Bacillus sphaericus (BS) in enhancing the resistance of concrete to sulfate attacks and improving its mechanical properties. Bacterial suspensions (1% and 2.5% of cement weight) were mixed with concrete containing silica fume or fly ash (10% of cement weight) and cured in freshwater or sulfate solutions (2%, 5%, and 10% concentrations). Specimens were tested for compressive strength, flexural strength, and microstructure using a Scanning Electron Microscope (SEM), Energy-Dispersive X-ray Spectroscopy (EDS), and X-ray diffraction (XRD) at various ages. The results indicate that a 2.5% bacterial content yielded the best performance, with BM surpassing BS, enhancing compressive strength by up to 41.3% and flexural strength by 52.3% in freshwater-cured samples. Although sulfate exposure initially improved early-age strength by 1.97% at 7 days, it led to an 8.5% loss at 120 days. Bacterial inclusion mitigated sulfate damage through microbially induced calcium carbonate precipitation (MICP), sealing cracks, and bolstering durability. Cracked specimens treated with BM recovered up to 93.1% of their original compressive strength, promoting sustainable, sulfate-resistant, self-healing concrete for more resilient infrastructure.

Concrete completely submerged in sulfate solutions has been used as the primary study subject for the durability of concrete subjected to sulfates. On the other hand, empirical data from the field indicates that concrete exposed to sulfates may exhibit physical attack-induced surface scaling above. This study aims to study the two different types of local bacteria, (BS) and (BM), with content of 0%, 0.25%, 1%, 2.50%, and 5.00% by cement weight used in this work under curing in sulfate to examine the efficiency of bacterial self-healing of cracks for sustainable concrete in aggressive sulfate attack environments. The results show that in both curing in freshwater, FW, and sulfate, SUL, the optimum bacteria ratio was 2.5% BM, and the compressive strength improved by 43.34% for FW and 47.65% for sulfate. On the other hand, the results proved that the crack-filling and crack-repairing methods may be considered quicker than conventional methods. Moreover, a detailed conclusion about the preparation and processing of bacteria to provide the most significant content of locally accessible bacteria in Egypt, mainly when using chemical and mineral additives.

The combined use of ceramic waste powder (CWP) as a supplementary cementitious material and magnetized water (MW) as mixing water represents a promising strategy for producing sustainable concrete with reduced cement consumption while maintaining mechanical performance and durability. However, the synergistic effects of burnt ceramic waste powder (BCWP) and unburnt ceramic waste powder (UBCWP) combined with MW, particularly under aggressive environmental conditions, remain insufficiently investigated. This study evaluates the influence of BCWP and UBCWP, used as partial replacements for ordinary Portland cement (OPC) at replacement levels of 10%, 20%, and 30% by weight, together with conventional tap water (TW) and MW produced using a dual-field magnetic device (0.9 T and 1.5 T). A total of fourteen concrete mixtures were investigated through compressive strength tests at 7, 28, and 120 days; indirect tensile and flexural strength tests at 28 and 120 days; sulfate resistance after 120 days of MgSO₄ immersion; residual strength after thermal exposure at 200 °C; and microstructural characterization using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD). The results indicate that increasing the CWP replacement level progressively reduced the mechanical properties of concrete; however, MW consistently mitigated these reductions by promoting cement hydration and producing a denser cementitious matrix. The mixture containing 20% BCWP with MW achieved a 120-day compressive strength comparable to that of the TW control, demonstrating that cement consumption can be reduced without compromising structural performance. Furthermore, MW mixtures exhibited significantly improved durability, with compressive strength losses of only 16–28% after sulfate attack compared with up to 42% for TW mixtures, and 1–13% after thermal exposure compared with up to 53% for TW mixtures. SEM and XRD analyses confirmed the development of denser microstructures with enhanced C–S–H gel formation in MW–CWP concretes. Overall, the findings demonstrate that the synergistic combination of ceramic waste powder and magnetized water provides an effective strategy for producing sustainable concrete with enhanced long-term mechanical performance, improved durability under aggressive environmental conditions, and reduced environmental impact.

Reinforced concrete structures have a critical durability challenge due to crack formation, facilitating moisture penetration, steel corrosion, and progressive structural deterioration. To address these challenges, this work systematically investigates the synergistic effects of pozzolanic materials in cement mortar and encapsulated healing agents on the autonomous repair capability of sustainable concrete notched beams under flexural loading. In this work, an experimental program consisting of three types of cement mortar with dimensions of 50 × 50 × 220 mm, it was performed using advanced material systems involving pozzolanic additives (silica fume (SF), marble powder (MP) and an encapsulated system incorporating expansive minerals (MgO, CaO, and bentonite) in macro-capsules with a thickness of 0.45 mm, a length of 50 mm, and inner diameters of 6.15 mm and 11.4 mm for the inner and outer capsules, within optimized mortar matrices. Healing efficiency was evaluated via crack area efficiency and load recovery coefficient measurements. Also, advanced microstructure characterization techniques (SEM–EDS, XRD, FT-IR) provided multiscale analysis of healing products and matrix-capsule interfaces to assess healing efficiency. The results showed that SF had superior pozzolanic and healing performance, achieving 87.5% crack sealing and 20% load recovery through increased pozzolanic activity and CSH production. Furthermore, microstructural analyses (SEM/XRD/FT-IR) validated its activity in matrix densification, CH reduction, and interfacial refinement. However, MP mostly acts as an inert filler, revealing the vital performance of SF for self-healing mortar systems. These findings contribute to developing autonomous self-healing technology, providing concrete with an extended service life for sustainable construction applications.