Within the availability of large number of experimental data
Within the availability of large number of experimental data, it is easy to develop the relation between the mechanical strength and corrosive resistance of the RHA added cement concrete. The developed correlation is given in the following Eq. (4.8). This equation can be used to predict any of the property mentioned above with order of high accuracy. The detailed statistical analysis of the models are described in the next section.
Statistical validation of experimental results T-test analysis was carried out for assessing statistical significance of the obtained experimental data. This test may be used to identify a parameter which has significant effect on concrete strength and corrosive resistance. Critical value of t was found from T table using degrees of freedom. Confidence level of each parameter was arrived by comparing absolute T statistical value and T critical value. Table 2 shows that T statistical value and the corresponding confidence level of each parameter. From Table 2, size (R)-PFI 2 hydrochloride ratio, pozzolanicity, specific surface area, curing time and the thermal diffusivity are the key parameters in producing high strength and corrosive resistance cement concrete excluding RHA loading, SiO2, FM and insignificant variation in its physical properties.
Conclusions and recommendations The compressive strength of RHA replacement in cement concrete is in the order of alkali attack>water curing>acid attack. For the case of without RHA, the compressive strength water curing>alkali attack>acid attack was observed. Hence, RHA replacement in cement concrete showed better durability on corrosive environment than normal concrete. From the above summary, it can be concluded that the replacement of fine size of RHA in concrete mix proves to be a promising method for improving the mechanical strength and durability towards corrosive environment. Therefore, the RHA replacement facilitates a possible alternate solution for reducing the environmental pollution like CO2 emission during cement manufacturing process and agricultural solid waste disposal. Additionally, the total cost involved in cement manufacture may be lowered due to RHA replacement which solves the resource depletion as well.
Acknowledgement The authors earnestly acknowledge the financial support from the SSN Trust, Chennai, Tamilnadu, India.
Introduction The low electrical conductivity, low thermal expansion coefficient and density of SiO2 when compared to SiC and B4C, makes it an appealing prospective reinforcement for metal matrix composites , , , . Owing to its unique natural structure – while having silica as a major constituent –, rice husk ash (RHA) has the potential to be a value-added recycling material for use as silica monoliths, reinforcement and functionality phase in metal and ceramic matrix composites , , , . Nonetheless, as an oxide material, the wettability of RHA by molten aluminum alloys is poor , , . One alternative for overcoming the wettability issue is by engineering coatings on RHA with materials that improve wetting, protect the reinforcement from attack by liquid aluminum or enhance the matrix/reinforcement interface strength. It has been reported that low contact angles are observed in aluminum alloys in contact with silicon nitride (Si3N4), making it a promising material for coating RHA , . In addition, Si3N4 has a low impurity incorporation, low self-diffusion coefficient, good thermal conductivity and good resistance to high temperature. For these reasons, recently Si3N4 has caught the attention of several technological and industrial fields, including microelectronics and optoelectronics , . The production of silicon nitride powders with different purity, morphology and sintering activity lies essentially in four synthesis routes: (a) the direct reaction of elemental silicon with nitrogen gives place generally to coarse products which have to be milled prior to further processing ; (b) carbothermal reduction, which utilizes fine mixture of SiO2 and carbon powders in nitrogen atmosphere at 1500 °C ; the diimide-process, which uses liquid or gas-phase precursors ; (d) CVD techniques, which use volatile silicon compounds such as SiCl4, SiH4 or related molecular compounds by reaction with ammonia , . Silicon nitride films with a large number of hydrogen radicals incorporated in its structure are produced when using silane by CVD (SiH4) . The -SiH radicals may act as charge traps in the silicon nitride ,  and produce a great instability in the electric characteristics of the devices.