Water Permeability in Fly Ash-Based Geopolymer Concrete

This research investigated the water permeability coefficient of fly ash-based geopolymer concrete. The effect of sodium hydroxide （Na（OH）） concentrations and Si/AI ratios on water permeability and compressive strength of geopolymer concretes were studied. The geopolymer concrete were prepared from Mae Moh fly ash with sodium silicate （Na2SiO3） and sodium hydroxide （Na（OH）） solutions. In the first group, concentration of Na（OH） was varied at 8, 10, 12, and 14 molar and the Si/AI ratio was kept constant at 1.98. In the second group, a concentration of Na（OH） was kept constant at 14 molar and the Si/AI ratio was varied at 2.2, 2.4, 2.6, and 2.8. The hardened concretes were air-cured in laboratory. The compressive strength and water permeability were tested at the age of 28 and 60 days. The results showed that compressive strengths of geopolymer concrete significantly increased with the increase of a concentration of Na（OH） and Si/AI ratio. The water permeability coefficients increase with the decrease of compressive strength. In addition, the high reduction of water permeability coefficients with time was found in geopolymer concrete with lower Na（OH） concentration than that higher Na（OH） concentration.

The Influences of Electric Fields on Soot Formation and Flame Structure of Diffusion Flames

The influences of DC and AC electric fields,at frequencies up to 1.48 MHz and the maximum strength of about 6 kV/cm,on soot formation and flame structure were investigated using a counterflow type acetylene diffusion flame.The distributions of flame luminosity,soot volume fraction,flame temperature and OH concentration in flame were measured by non-invasive detection methods. Under the influence of electric fields,the changes in distribution of the soot volume fraction were confirmed. Electric fields of high frequency and high intensity reduced the soot volume fraction,whereas other electric fields increased it.The maximum values of flame temperature and OH concentration decreased. In the relationship between the maximum value of the soot volume fraction and the maximum temperature,the maximum soot volume fraction showed both increase and decrease with maximum temperatures depending on the frequencies and intensities of the electric fields,and both of them occurred at temperatures lower than 1900 K.The production of the incipient particles seemed to be the dominant process controlling the soot volume fraction due to the electric fields.The luminosity of a sooting diffusion flame was found to depend on the volume fraction and temperature of the soot particles in the flame.As for the behavior of the flame in the electric fields,the ionic wind effect was not found to be dominant in the present work,and the result of the previous simulation based on the ionic wind theory was not consistent with the present experimental results.