Characterization of lime sludge for engineering applications

Abstract

Chemical composition and engineering properties of 20 samples of lime sludge, produced from the lime calcining process, were determined in order to evaluate its potential applications as an engineering construction material. The results indicate that lime sludge is composed mainly of calcium (51.48%), silica (8.30%), and aluminum (3.24%). Iron, magnesium, and sulfur each make up less than 3% by weight, while zinc, chromium, selenium, lead, cadmium, barium, and silver collectively make up less than 0.01% of the total composition. The loss on ignition (LOI) is 34.4% by weight of the total composition. Engineering tests show that lime sludge can be considered as a uniformly-graded, nonplastic silt (ML) with an average liquid limit of 48, average natural water content of 90%, average maximum dry density of 64 pcf (1.03 Mg/m 3), average optimum water content of 50%, and an average friction angle of 27 degrees. The average permeability and unconfined compressive strength of samples compacted to at least 90% of maximum dry density are 2 × 10 −5 cm/sec and 38 psi (0.26 MPa), respectively. Because of its high natural water content, low density, and poor strength characteristics, lime sludge in its natural state is considered unsuitable for engineering construction. However, when lime sludge was mixed with varying percentages of a silty soil, it was found that the density of the admixtures increased and the permeability decreased with an increase in soil content. This suggests that lime sludge-soil admixtures may have potential for such engineering applications as daily landfill cover, hydraulic barriers, and structural fill material.