Properties of high strength aggregates from clay-amended industrial sludge

This study examines the use of industrial sludge and marine clay wastes as substitutes for regular coarse granite aggregate in concrete. The raw materials were dried, pulverized and mixed at various proportions, molded with water into desired shapes, and sintered at elevated temperatures to produce the aggregates in pelletized or crushed forms. The pelletized aggregates displayed a higher particle density compared to the crushed counterparts. Both types of aggregates displayed lower densities relative to that of granite. The pelletized aggregate exhibited moderate aggregate strength of 18.1 to 30.4% aggregate impact value (AIV), while the crushed aggregate exhibited lower strength of 23.1 to 42.9% AIV The AIV values are comparable to that of granite. A complete replacement of regular granite aggregates in concrete was accomplished by substituting the coarse aggregates with the same volume of sintered sludge-clay aggregate. The pelletized and crushed aggregate made from 100% sludge provided moderate 28-day concrete compressive strengths of 38.5 and 39.0 N/mm(2), respectively, which was comparable to that of the control granite specimens with a strength of 38.0 N/mm(2). The results indicated that complete replacement of conventional granite aggregates by sintered aggregates of suitable sludge-clay proportions could produce concrete of structural grade.