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Call number: LD2668 .T4 1959 C45

Call number: LD2668 .T4 1961 S27

The term "impervious" is commonly used in urban settings to describe the permeability of buildings, roads, and parking lots. When estimating recharge to an aquifer underlying an urbanized area, impervious cover becomes a prime consideration. It is commonly assumed that an increase in impervious cover leads to a decrease in precipitation recharge. However, even a cursory glance at most roads, sidewalks, or parking lots reveals that, far from being impervious, there are abundant fractures that may provide avenues of infiltration. For this study, method was developed to determine the secondary permeability of pavements using a double ring infiltrometer to measure the infiltration rate of water into fractured pavements. Linear extrapolation is employed to determine the infiltration rate as the water depth approaches zero, which is used as a proxy for hydraulic conductivity by assuming that the gradient is unity. Data were collected on concrete and asphalt pavements located in Austin, Texas, at each point a fracture or expansion joint intersected along 30-meter scanlines. By dividing the sum of the discharges for each fracture by the area represented by the scanline we are able to determine the equivalent-porous-media hydraulic conductivity. The equivalent hydraulic conductivities for discrete fractures were found to range at least three orders of magnitude, from >10⁻² to 10⁻⁵ cm/sec; scanline hydraulic conductivities range two orders of magnitude from >10⁻⁴ to 10⁻⁶ cm/sec; permeability along the scanlines tends to be dominated by one or two highly conductive fractures; and the hydraulic conductivity of the entire paved surface is 5.9·10⁻⁵ cm/s. Both apertures and point hydraulic conductivities were found to have logarithmic distributions but cross plots demonstrated no correlation, which indicated that a combination of the fill material and sub grade, not the fractures and expansion joints themselves, limit infiltration. By multiplying the paved surface hydraulic conductivity by the time the surface can be expected to be saturated, we find that 170 mm or 21 percent of mean annual rainfall is available as potential recharge. When coupled with an enhanced subsurface permeability structure resulting from the installation of utilities and the reduction of evapotranspiration from the reduction of vegetation, the net effect of roads and parking lots could be an increase in precipitation recharge. / text

A thesis submitted to the Faculty of Engineering, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Doctor of Philosophy. Johannesburg, 1994. / This thesis presents the details and results of an investigation into the effects of early age curing on the durability of concrete The two main objectives of the investigation were: to develop simple test methods, applied at relatively early ages, for measuring the effects of early-age moist curing on the advance of hydration in the cover zone of concrete; to quantify the effect of early age curing on the durability performance of concretes of various strength grades and made with different binder types. [Abbreviated Abstract. Open document to view full version]

Two underground concrete manure reservoirs of 70 m$ sp3$ were tested for their infiltration rate to water as well as to 1% and 3% total solid dairy manure. Positive and negative infiltration were measured for the water test while only negative infiltration was measured with the manure. / Positive infiltration is met when the water table into the soil is above the liquid level into the reservoir. In that case, the water is moving from the outside to the inside of the reservoir. An opposite situation is met when the infiltration is negative. / From the results, the infiltration rate varied from 0.00 to 6.684 $ times$ 10$ sp{-7}$ m/s. The minimum value was recorded at the reservoir 55 with 1% of total solid manure and the maximum value was recorded with same reservoir with positive pressure to water.

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