Experimental Studies on Mechanical Properties of Bacterial Concrete with Fly Ash
Concrete, a strong, durable material composed of cement, aggregate and water, is the most used building material in the world. Concrete has an ultimate load bearing capacity under compression but the material is weak in tension. That is why steel bars are embedded in the concrete for the structures to carry tensile loads. The steel reinforced bars take the load when the concrete cracks in tension. On other hand the concrete protects the steel reinforced bars from the environment and prevents corrosion. However, the cracks in the concrete form a major problem which affects the durability of the structures. Here the ingress of water and chloride ions takes place and deterioration of the structure starts with the corrosion of the steel. To increase the strength and durability of the structure either the cracks that are formed should be repaired conventionally using epoxy injection or latex treatment or by providing extra reinforcement in the structure during the design phase to ensure that the crack width stays within a permissible limit. This extra reinforcement is only needed for durability reasons (to keep the crack width small) and not for structural capacity. Especially with current steel prices on rise providing extra steel is not economically viable. Main reason to prevent cracks or limit crack width is to enhance the durability of the structure. If in some way a reliable method could be developed that repairs cracks in concrete automatically (self healing) this would increase and ensure durability of the structure enormously. On the other hand it would also save a lot of money, time and energy. Investigations have shown that the bacteria Bacillus pasturii can be used for improving the resistance of concrete to alkali or sulphate attack, drying shrinkage etc. which will increase the strength and durability of concrete. However, not much investigation is reported in India for producing bacterial concrete using Bacillus subtilis. Keeping this in view, the present experimental investigations are taken up to study the strength characteristics in ordinary grade concrete and standard grade of concrete with and without addition of bacteria Bacillus subtilis JC3. The utilization of fly ash in concrete as partial replacement of cement is gaining immense importance, mainly on account of the improvements in the long term durability of concrete combined with ecological benefits. Technological improvements in thermal power plant operations and fly ash collection systems have resulted in improving the consistency of fly ash. To study the effect of partial replacement of cement by fly ash, studies have been conducted on concrete mixes by replacing cement content by 10% 20% and 30% with fly ash. In this investigation the effect of fly ash on compressive strength, split tensile strength and flexural strength are studied. INTRODUCTION Concrete is a construction material that is used worldwide because of its first rate properties. However, the drawback of this material is that it easily cracks due to its low tensile strength. Cracks can occur during any stage of a life of a concrete structure. They can be due to concrete material itself as in the case of volume instabilities or due to external factors such as external loading, harsh environmental exposure, poor construction procedures or design error. There cracks have many negative effects on mechanical performance and durability of concrete structures. The development of concretes which can automatically regain this loss of performance is very desirable. Along these lines, self healing of cracked concrete is often studied phenomenon. Experimental investigation and practical experiences have demonstrated that crack in cementitious materials have the ability to seal themselves rapid crack healing is necessary since it is easier for substances to ingress into concrete through cracks than through the concrete. It is known that it is costly to inspect, monitor and repair cracks, monitor and repair cracks. Moreover, some repair methods currently used are not so sustainable. The chemical and physical process of self healing of cracks in concrete has been previously investigated by other researchers. The effects of self healing by crack width, water pressure, pH of healing water, temperature, water chloride concentration and concrete composition have been discussed by many researchers. For autogeneous healing to occur, the following reasons have been cited. Further hydration of un reacted cement, expansion of concrete in the cracks flanks (swelling) crystallization (calcium carbonate) closing of cracks by solid matters in the water (impurities) and closing of cracks by spilling of loose concrete particles resulting from cracking. Among these reasons, most researchers has indicated that the crystallization of calcium carbonate within the cracks was the mechanism self healing of mature concrete. Therefore, it would be desirable if concrete cracks could be healed autonomously by releasing healing agents inside the matrix when cracks appear International Journal of Applied Engineering Research ISSN 0973 4562 Volume 13, Number 15 (2018) pp. 11857 11870 (c) Research India Publications. http:/www.ripublication.com 11858 In 1885, an American engineer named William LeBaron Jenny became the creator of the modern skyscraper when he realized that an office building could be constructed using totally different materials. He chose structural steel and incorporated it into a revolutionary system that was to make possible the soaring office towers that mow symbolize the modern metropolis. Two technological developments, the elevator and modern metal frame construction, removed the prevailing limitations on the height of the buildings, and the race for tallness was on. In 1913, the Woolworth building was the first to reach 60stories, soaring up 732 ft (242 m) in lower Manhattan. This Gothic cathedral style building is still in vigorous use after 70 years of service and the installation of conditioning and automatic elevators. The demand for tall buildings increased because large corporations recognized the advertising and publicity advantages of connecting their names with imposing highrise office buildings even though their operations required a relatively small percentage of floor space. The collapse of the financial market during the depression put an end to speculative high rises, and only in the late 1940s in the wake of world war2 did a new era of high rise building set in addition to the stimulus of new resources provided by technology was the spur of necessity, with the population doubling in almost every generation and production growing at an even faster pace, developers could scarcely keep up with the demand for space. SELECTION OF REPAIRS PROCEDURES Based on the careful evaluation of the extent and cause of cracking procedures can be selected to accomplish one or more of the following objective: Restore or increase strength Restore or increase stiffness Improve functional performance Provide water tightness Improve appearance of the concrete surface Improve durability and Prevent development of corrosive environment at reinforcement. Self healing bacterial concrete Self healing bacterial concrete refers to a new generation of concrete in which selective concentration by microbiologically induced CaCo3 precipitation has been introduced for remediation of micro cracks. Self healing concrete could solve the problem of concrete structure deteriorating well before the end of their service life. The bacterial remediation technique can be used for repairing structures of historical importance to preserve the aesthetic value, and conventional technique, such as epoxy injection cannot be used to remediate cracks in those structures. Its prospective application include remediation of surface cracks and fissures in various structural formations, in base and sub base stabilization and surface soil consolidation. Incorporating living matter into structural concrete material to enhance its strength and durability performance is a great innovation. This can be done in two ways. The first way will see bacteria in water with nutrients are used as mixing water for concrete preparation. The second way will see the bacteria and food nutrients dissolved into a liquid that is sprayed onto the surface of the concrete from where it can seep into the crack. Most of the works done on this subject have clearly indicated that bio mineralization of some specific bacteria with urease activity is mainly responsible for the enhancement of mechanical properties of modified cement sand mortar and depend on type of mineral precipitating bacteria, cell concentration of the bacteria, age and environmental conditions (moisture, temperature e. Bio mineralization Natural processes, such as weathering, faults, land subsidence, earthquakes and human activities create fractures and fissures in concrete structures and historical monuments. These fractures and fissures are detrimental since they can reduce the service life of the structure. In case of monuments and buildings of historic importance, these cracks tend to disfigure and destroy the structure. Use of synthetic agents such as epoxies for remediating these structures will reduce the aesthetic appearance of the structure. Therefore a novel technique for remediating damaged structural formation has been developed by employing a selective microbial plugging process, in which microbial metabolic activities promote calcium carbonate (calcite) precipitation is shown in figure 2.1. The technique is called microbiologically induced crack remediation (MECR) This technique comes under a broader category of science called bio mineralization. It is a process by which living organisms from inorganic solids, bacterial deposition of a layer of calcite on the surface of the specimens resulted in a decrease in capillary water intake and permeability towards it. Th