Mohamed Heikal

Micro-crack formation is a major factor limiting the durability of concrete structures. This study investigates a sustainable self-healing approach based on microbially induced calcium carbonate precipitation (MICP). Fifty bacterial isolates were obtained from alkaline soils in Wadi El-Natrun, Egypt, and screened for their ability to precipitate calcium carbonate. Isolate code W39 exhibited the highest activity, producing 0.453 g/100 mL of CaCO₃. Molecular identification by 16 S rRNA sequencing confirmed the strain as Bacillus albus (Accession number: PQ288981). Optimal precipitation occurred at pH 8, with 25 mM CaCl₂ and 20 g/L urea, after seven days of incubation at 30 °C. Instrumental analyses, including scanning electron microscopy (SEM) coupled with an energy-dispersive X-ray (EDX) analyzer, high-resolution transmission electron microscopy (TEM), Fourier-transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), and the N₂ desorption/adsorption isotherm (BET) method, verified that the biogenic CaCO₃ consisted of nanoscale, high-purity calcite. The self-healing potential was evaluated by embedding viable Bacillus albus cells in cement mortar at optical densities (OD₆₀₀) of 0.5, 1.0, and 1.5, and curing in urea-enriched media with varying CaCl₂ concentrations (25–100 mM). Bacterial incorporation significantly enhanced mechanical performance over a 90-day curing period. The optimal dosage depended on Ca²⁺ availability: OD₆₀₀ 1.5 provided the greatest improvement at 25 mM CaCl₂, whereas OD₆₀₀ 0.5 was more effective at 50–100 mM. Microstructural analyses, comprising x-ray diffraction (XRD), differential thermal/thermogravimetric analysis (DTG/TGA), and scanning electron microscopy (SEM), confirmed the formation of additional C–S–H and calcite, resulting in reduced porosity and a denser matrix. The bio-mortar also demonstrated increased durability, including resistance to exposure to MgSO₄ and MgCl₂, as well as thermal stability up to 1000 °C. These findings demonstrate that the indigenous Bacillus albus strain is a promising agent for durable, self-healing bio-concrete. Overall, these results show that microbial incorporation improves the pore system, encourages the formation of more hydrates and CaCO ₃ , and creates a more resilient mortar that can withstand extreme thermal exposure.

This research aimed to assess the efficacy of synthetic zirconia nanomaterials (NZr) in improving the physico-mechanical, textural, fire resistance, and photocatalytic properties of Ordinary Portland Cement composite pastes. Zirconia nanoparticles (NZr-NPs) were synthesized via a precipitation method, with an average crystallite size between 7 to 15 nm and a surface area of 88.01 m ² /g. Six composite formulations were prepared, denoted as NZr0, NZr1, NZr2, NZr3, NZr4, and NZr5, with varying NZr doses. The physicochemical characteristics were investigated over hydration periods up to 3 months. After 28 days of hydration, specimens were dried and fired at temperatures ranging from 200 to 1000°C to assess their thermal resistance. The addition of 0.25% NZr was identified as the optimal dosage, enhancing the fire resistance of the composites. However, increasing the NZr content to 0.50–1.00% led to a reduction in compressive strength (CS), although it remained higher than that of the unmodified paste. The composite incorporating 1.5% NZr demonstrated superior photocatalytic degradation performance, exhibiting the highest dye degradation percentages after 300 min of UV irradiation at 3, 7, 28, and 90 days, measuring 83%, 86%, 89%, and 97%, respectively. These results highlight the enhanced photocatalytic degradation capabilities of the composite containing Zr-NPs. These findings identify several promising avenues for future research, particularly the optimization of zirconia dosage and its integration into cementitious systems to improve durability, environmental performance, and cost-effectiveness in sustainable construction applications.

Microbial-induced calcium carbonate precipitation (MICP) has garnered significant attention for its construction and geotechnical engineering applications. In this study, 24 bacterial isolates were obtained from various edges of Wadi El-Natron Lake, Egypt, and subsequently assessed for their capacity for calcium carbonate (CaCO₃) precipitation. Among these isolates, strain D16 exhibited the highest CaCO₃ precipitation, yielding 0.404 g/100 mL, alongside robust bacterial growth and a final pH of 9.09. Morphological and biochemical characterization revealed that the isolate was rod-shaped, Gram-positive, Catalase-positive, Urease-positive, and Spore-forming. The optimal growth conditions for the isolate included a pH of 8, with ideal Ca²⁺ and urea concentrations of 25 mM and 20 g/L, respectively, at an incubation temperature of 30 °C over seven days. Molecular identification confirmed the isolate as Bacillus tropicus strain D16, which has been recorded in GenBank under the accession number PQ817131. The precipitated CaCO₃ was quantified and characterized using scanning electron microscopy (SEM) equipped with energy-dispersive X-ray (EDX) analysis, Fourier-transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), and the N₂ desorption/adsorption isotherm (BET) method. The effect of calcium carbonate nanoparticles (CaCO₃-NPs, denoted as NC) on the properties of cement paste was investigated. Four composite pastes were prepared with varying dosages of CaCO₃-NPs: NC0.0, NC0.5, NC1.0, and NC1.5. These pastes were subjected to a series of tests, including compressive strength, bulk density, total porosity, and chemically combined water content, over a hydration period of up to 90 days. The results demonstrated that the addition of NC enhanced the compressive strength of the cement paste up to an optimal dosage content of 0.5%, beyond which the strength decreased due to nanoparticle agglomeration. These findings were further corroborated by X-ray Diffraction (XRD), Differential Thermal Thermogravimetric Analysis (DTG/TGA), and Scanning Electron Microscopy (SEM), which provided microstructural and phase composition insights. Overall, the results indicate that the inclusion of an optimal dosage of CaCO₃-NPs can significantly improve the performance of cement composite pastes.

The utilization of two kinds of iron slag in the production of pozzolanic cement is introduced. A series was created with a fixed percentage of OPC (30%) and varying amounts of imported granulated blast-furnace slag (IGBFS) and air-cooled slag (ACS) at which imported IGBFS was substituted by ACS with the mass ratios of 10, 20, and 30%. Physico-mechanical properties and hydration parameters of the hardened pastes were examined at different time intervals. Furthermore, the aggressive attack of seawater on chosen specimens was studied for up to one year of immersion. The hardened composite cement pastes were tested in terms of weight loss, compressive strength, bulk density, total porosity, and free lime at different thermally treated temperatures starting at 105 °C and ending at 800 °C for 2 h of a socking period to investigate its thermal characteristics. XRD, IR, and DTA/TGA techniques were used to examine some chosen samples. The results revealed that the incorporation of ACS reduces the water consistency and prolongs setting times. Compressive strengths are higher in samples containing 10% ACS than those specimens containing 20–30 wt% and without ACS. A 7% reduction in the compressive strength was achieved by A1 (30%OPC and 70% IGBFS), which is the lowest one over 1 year of exposure to seawater. The incorporation of ACS at the expense of IGBFS tends to lower the strength but tends to enhance the bulk density.

This research investigates the long-term resilience of an environmentally friendly cement blend comprising Egyptian Ordinary Portland Cement OPC and Ground-Granulated Blast Furnace Slag GGBFS when exposed to a corrosive seawater environment. This scientific investigation explores the effects of exposure to seawater on various properties of cement pastes, encompassing parameters such as free lime content (FLC), chemically combined water content (CWC), bulk density (BD), total porosity (ϕ), total sulfate content, total chloride content, and compressive strength (CS). By contrast, Differential Thermal Analysis (DTA), FT-IR spectroscopy, and X-ray diffraction (XRD) analysis can be utilized to investigate the influence of exposure to seawater on the hydration products of GGBFS cement pastes over a period of up to one year. This analytical approach offers valuable insights into the alterations that occur in hydration products and their resilience when subjected to seawater conditions. The results obtained from this investigation reveal that all cement pastes incorporating GGBFS exhibit heightened resistance to deterioration in seawater, with slag cement containing 60 wt. % GGBFS and achieving a notable compressive strength of 85.7 Mpa after one year of immersion in seawater. These findings underscore the capacity of these cement blends to effectively withstand challenges in durability in marine environments.