الفهرس 
CHAPTER (1) “INTRODUCTION”Only 14 pages are availabe for public view
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Abstract
Microbial or bacterial concrete is product of MICP (Microbial Induced Calcite Precipitation), produced by ureolytic bacteria. Such bacteria are abundant in nature. It could be cultivated at fast rate and low cost. Calcium Carbonate precipitated during the process of MICP might help building materials and structures by improving compressive strength, impermeability, and ultimately their durability.
The goal of this study is to illustrate the effect of microbial induced calcite precipitation to improve the physical and mechanical properties of cement mortar. Two species of bacteria Bacillus pasteurii and Bacillus sphaericus, were used in this study with two ratios (0.25% and 0.5%) of cement weight. Calcium Lactate was added as nutrition of bacteria by (0.125% and 0.25%) of cement weight, respectively. In this study, two types of curing were used. The first was under tap water and the other was under a solution of 20 g/l urea and 25mM CaCl2 to ensure that there is no effect of curing solution on cement mortar. Bacterial samples except reinforced were cured by a solution of 20 g/l urea and 25mM CaCl2. Control samples were cured by tap water. The cell concentration of BS (Bacillus sphaericus) and BP (Bacillus pasteurii) of all bacterial mortar mixes were counted. Setting time test of cement pastes was performed to measure the effect of bacteria on fresh mortar properties. The bacterial mixtures were compared to control mix to study the influence of adding bacteria on physical and mechanical properties. Rate of Water Absorption test, capillary permeability coefficient, dry density, volume of permeable voids, percentage of absorption and compressive strength test were performed at the age of 7, 28, 90 and 120 days. Flexural Strength test was performed at the age of 28, 90 and 120 days. In addition to the mechanical and physical, advanced techniques were employed to evaluate the influence of bacteria addition, e.g. SEM (Scanning Electron Microscope) and DTA (Differential Thermal Analysis). The cell concentration of BS (Bacillus sphaericus) and BP (Bacillus pasteurii) of all bacterial mortar mixes were counted. Also, the restoration of bacterial mixes were tested.
The bacteria and its nutrition acts as retarded accelerator of cement pastes for initial setting time for all bacterial mortar compared to control mortar, while acts as accelerator of cement pastes for final setting time for bacterial mortar except B. Pasteurii 0.25% compared to control mortar. Initial and final setting for all mortar were within limit according to the Egyptian code for design and construction of concrete structures E.C.P.203- 2007.
Rate of water Absorption, Volume of permeable voids and Percentage of absorption decreased with time for all bacterial samples at the age of 120 days. Compressive strength of B. Sphaericus 0.25% at 120 days age improved by 112% compared to the control specimens compressive strength. Flexural strength value of B. Pasteurii 0.25% at the age of 120 days improved by 104% compared to flexural strength of control mortar. At the age of 28 days, the max flexural strength of laminates value of B. Pasteurii 0.25% was 166.67% of flexural strength of control mortar.
Bacterial Samples restored more compressive strength than that of control samples. At the age of 120 days, the restored compressive strength value of B. Pasteurii 0.5% was 103.8 compared to 86.9% restoration of control. That ensures the self-healing had occurred.
SEM (Scanning Electron Microscopy) proved that the bacterial mortars had less voids and were denser than that of control mortars. MICP (Microbial Induced Calcite Precipitation) is responsible for filling up the pores in mortar and hence decreased the rate of water absorption and the capillary permeability coefficient, while increased the compressive strength and the flexural strength for bacterial mortar. DTA (Differential Thermal Analysis) indicated that both the amount and degree of crystallinity of calcium carbonate is increased in case of bacterial mortar specimens compared to the control mortar.