Long-term stability of superplasticized monoliths of a solidified electroplating sludge

Abstract

In this work, physicochemical durability of superplasticized monoliths, solidified from an electroplating sludge, were investigated. Two categories of superplasticizer, namely modified lignosulphonates and sulphonated naphthalene formaldehyde condensates, were employed in this study. Each was used as an auxiliary binding agent or as a modifier to ordinary portland cement, which was the major binder for solidification. The solidified mo- noliths were then subjected to various physical and chemical tests. Tests carried out included measurements of the unconfined compressive strength (UCS), the leaching toxicity by the TCLP method, the physical durability test (i.e., freezing and thawing test and wetting and drying test), and the chemical durability test (i.e., multiple TCLP test). It was found that superplasticized, solidified monoliths outperformed the corresponding control monoliths (without addition of any superplasticizer) in terms of various physical and chemical properties. Generally, the performance of both superplasticizers was found to be comparable in this study. Experimental results indicated that the physical durability test only resulted in less than one percent of corrected, cumulative weight loss for solidified monoliths modified by any type of superplasticizer. However, results of UCS measurements have shown that these very solidified specimens have been deteriorated to some degree after physical weathering tests. As for the resistance of solidified monoliths against the leaching of contaminants due to repetitive precipitation of a synthetic acid rain, the multiple TCLP test results have shown that the employment of either superplasticizer will be satisfactory.