Solidified waste water treated sludge as partial replacement of cement in concete composites

Abstract

In this research, tests of mortar and porous concrete made with solidified waste water treatment sludge (SWWTS) used in two forms as a partial replacement of cement were carried out. SWWTS mainly consisted out of CaCO3 and Ca(OH)2, having no pozzolanic properties. For this reason, it was used both, as produced, and modified by adding Al2O3 and Mg3Si4O10(OH)2 in certain percentages. One mortar type and two types of porous concrete were tested. For each of the three products two mixtures were prepared: the reference mixture and the mixture made with 30% replacement of cement, while the other components remained the same. Based on the given comparative analysis, conclusions were drawn regarding the structure of porous concrete slabs, which refer to individual analyzed properties, but also to the possibility of applying energy-efficient materials. The obtained results point to the conclusion that the use of SWWTS reduces the values of almost all tested properties of porous concrete (flexural and compressive strength, pull-off strength, abrasion resistance), but also that the modification of SWWTS led to a smaller difference in the results of the samples made with 30% of cement replacement and the reference samples. Although, the use of SWWTS led to the reduction of mechancal properties of concretes, the most important benefit is development of possible way for reuse of this waste material and avoid its disposal in the landfills.