Comparative study on Steel fibre reinforced Cum control concrete under flexural and deflection
Fibre reinforced concrete, a composition of concrete and fibres is being prominently used for various important applications. The hook tain steel fibres assist in controlling the propagation of micro-cracks present in the matrix, first by improving the overall cracking resistance the matrix and later by bridging across even smaller cracks formed after the application of load on to the member thereby preventing there widening into major cracks. In the present paper, the effect of steel fibre reinforcement with different percentage of fibre 0, 1%, 2% and 3% by volume for M-40 grade of concrete with aspect ratio 50, 60 and 67 are studied. The beam is tested for flexural strength. The percentage increase through utilization of steel fibers is reported. A relationship between aspect ratio vs. flexural strength represented graphically.
Mechanical properties of fibre-reinforced high strength concrete
The increased use of high strength concrete in structural applications dictates the need to enhance its brittle behaviour under compressive and tensile loads. An experimental programme has been conducted to investigate the effects of introducing polypropylene fibres into higher strength concrete applications. Different fibre volume fractions were used in the study. Three types of concrete grades were cast. Uni-axial compressive and splitting cylinder tests were conducted. Longitudinal, transverse and volumetric strains were monitored and reported at different stress levels during testing. Material properties including peak compressive stresses for both cylinders and cubes, splitting cylinder tensile strengths, elastic moduli and Poisson's ratios were determined.The study revealed that polypropylene fibres significantly enhanced the tensile properties of higher strength concretes, increased the ductility under compressive loads, reduced transverse deformations however reduced the peak attainable strength under compressive loads. A model for calculating the tensile strength of concrete as a function of both the concrete grade and the fibre volume fraction has been developed. The model shows excellent agreement with the experimental results.
A quantitative measure of nitrifying bacterial growth.
Nitrifying bacteria convert ammonia (NH3) to nitrate (NO3-) in a nitrification reaction. Methods to quantitatively separate the growth rate of these important bacterial populations from that of the dominant heterotrophic bacteria are important to our understanding of the nitrification process. The changing concentration of ammonia is often used as an indirect measure of nitrification but ammonification processes generate ammonia and confound this approach while heterotrophs remove nitrate via denitrification. Molecular probe methods can tell us what proportion of the microbial community is nitrifying bacteria but not their growth rate. The technique proposed here was able to quantify the growth rate of the nitrifying bacterial populations amidst complex ecological processes. The method incubates [methyl-3H] thymidine with water samples in the presence and absence of an inhibitor of nitrification-thiourea. The radioactively labeled DNA in the growing bacteria was extracted. The rate of incorporation of the label into the dividing bacterial DNA was used to determine bacterial growth rate. Total bacterial community growth rates in full-scale and pilot-scale fixed-film nitrifying reactors and an activated sludge reactor were 2.1 x 10(8), 4.1 x 10(8) and 0.4 x 10(8)cell ml(-1)d(-1), respectively; the growth rate of autotrophic-nitrifying bacteria was 0.7 x 10(8), 2.6 x 10(8) and 0.01 x 10(8)cell ml(-1)d(-1), respectively. Autotrophic-nitrifying bacteria contributed 30% and 60% of the total bacterial community growth rate in the nitrifying reactors whereas only 2% was observed in the activated sludge reactor that was not designed to nitrify. The rates of ammonia loss from the nitrifying reactors corresponded to the rate of growth of the nitrifying bacteria. This method has the potential to more often identify factors that enhance or limit nitrifying processes in both engineered and natural aquatic environments.