الفهرس 
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Abstract
Concrete is commonly used in construction, but they are susceptible to various types of deterioration due to environmental factors, such as moisture, temperature changes, and chemical attacks. Researchers have explored the use of microbial-induced calcite precipitation (MICP) to improve the durability and mechanical properties of concrete. MICP involves the use of bacteria to promote the precipitation of calcium carbonate in the pores and cracks of cement mortar, which improves its mechanical properties and reduces its permeability. In this study, the effectiveness of MICP in enhancing cement mortar’s physical and mechanical properties is evaluated using various bacterial mixes and nutrients. The study aims to evaluate the ability of bacterial mixes to restore the compressive and flexural strength of cement mortar and to assess the influence of bacterial addition on the water absorption rate, capillary permeability coefficient, and acid resistance of cement mortar. Furthermore, the study employs advanced techniques, such as SEM and DTA, to examine the influence of bacteria and nutrient addition on the microstructure and composition of cement mortar. To accomplish the above objectives, the present study had been divided into three major phases: In phase І: a preliminary study had been conducted to investigate the effect of three types of bacteria: (Bacillus pasteurii (PaM1), Bacillus sphaericus (SpM1), and Bacillus subtilis (SuM1), the bacteria were added to cement mortar at a concentration of 0.5% by weight of cement and with 0.25% calcium lactate as a nutrient. Physical, mechanical, and durability performance were conducted for cement mortar specimens. Moreover, the performance of ferrocement laminates with dimensions 150× 300× 30 mm, setting times, flow%, rate of water absorption, coefficient of permeability, compressive strength, flexural strength at different ages (7, 28, 56 and 90 days) were studied. In phase ІІ: The influence of increasing calcium lactate concentration enhancing cement mortar’s physical and mechanical properties. Two types of bacteria: Bacillus pasteurii (PaM2) and Bacillus sphaericus (SpM2) were added to cement mortar at a concentration of 0.5% by weight of cement with 1.5% Calcium lactate by weight of cement. In phase (ІІІ): restoration of compressive strength and flexural strength against preloading (up to 50% of maximum capacities at different ages), and residual compressive strength after exposure to 1.5% sulphuric acid were the main responses taken into consideration. The results indicated that all different types of bacteria affect the performance of cement mortar, the setting developed faster due to high formation of initial CaCo3 hydration. A reduction of about (30%-70%) and (49.8%-86.5%) in rate of water absorption and permeability coefficient, respectively were recorded in compared to mortar specimens without bacteria. Whilst the improvement in compressive and flexural strengths of about (28% and 13%) at early ages and (9% and 49%) at later ages, respectively. The test results of the restoration of compressive and flexural strengths proved that MICP by utilizing bacteria can improve the durability performance of the mortar specimens by achieving to (90.6% and 75.5%) of their original compressive and flexural strengths at early ages (7-28 days) and (92% and 76.8%) at later ages (28-56 days), respectively. On the other hand, the ferrocement laminates with bacteria restored up to 107.4% of its original loads at 90 days. SEM analysis confirmed that mortar samples have a denser structure with fewer voids, attributed to the MICP process. DTA indicated that bacterial specimens had an increased amount and degree of crystallinity of calcium carbonate compared to the control, leading to improved mechanical properties in bio concrete. Furthermore, the performance of ferrocement laminates incorporating bacteria at different ages exhibited significant improvement, with respect to maximum load capacity and toughness.