Journal of Cold Regions Engineering

A sludge‐freezing bed is a new unit operation for dewatering sludges produced by water and wastewater treatment plants in cold regions. Sludge is applied to the bed in layers, where it is allowed to freeze naturally during the winter. Freezing causes the solid and liquid fractions to separate during ice crystal formation. After the sludge thaws in the spring the water is drained away, leaving the solids that can be handled with conventional earth‐moving equipment. This paper presents the development of a mathematical model for predicting the total depth of sludge that can be frozen in the bed. An analysis of this model indicates that the time needed to cool the sludge to the freezing point is insignificant compared to the time needed to freeze it. Data from a pilot‐scale freezing bed and other freezing experiments were used to evaluate the model. The average wind velocity at the site was found to be a primary factor in determining the freezing depth. An example of how to use the model for design is also presented.

Laboratory experiments on the local bond behavior of high‐strength concrete were carried out under monotonic, repeated cyclic and reversed cyclic loading conditions in the temperature range of $-10°C$ and $-70°C$ ($+14°F$ and $-94°F$). The values of maximum bond stress and the relationship between maximum bond stress and concrete compressive strength at low temperature are quite different from those at normal temperature $[+20°C(+68°F\left)\right]\text{,}$ especially under reversed cyclic loading. The experimental results are also compared with those for normal strength concrete observed and reported in an earlier study. Under monotonic loading conditions the ratio of maximum bond stress at low temperature to the maximum bond stress at normal temperature is different between high strength and normal strength concrete. Under reversed cyclic loading the average value of the bond factors (maximum bond stress divided by the concrete compressive strength) of both loading directions is smaller than those under monotonic or repeated cyclic loading conditions.

High‐strength concrete has been used extensively in high‐rise buildings and long‐span bridges. However, very little is known regarding its mechanical properties at low temperature. This paper presents the results of an experimental study on the mechanical properties of high‐strength concrete in the temperature range between $+20°C$ and $-70°C$ ($+68°F$ and $-94°F$) without considering the effect of freezing cycles. Test results show that the values of compressive and splitting tensile strength, modulus of elasticity and Poisson's ratio increase as the temperature decreases. The ratio of bond strength at low temperature and the bond strength at normal temperature are generally larger under reversed cyclic loading than under monotonic or repeated cyclic loading. The rate of increase in compressive and splitting tensile strength, Young's modulus, local bond strength and Poisson's ratio for high‐strength concrete at corresponding different low temperatures ($-10°C\text{,}$ $-30°-C\text{,}$ $-50°C$ and $-70°C\text{,}$ i.e., $+14°F\text{,}$ $-22°F\text{,}$ $-58°F$ and $-94°F$) is generally lower than that for normal strength concrete.