Possibilities for Application of Modified Solidified Water Treatment Sludge as Supplementary Cementitious Material

Abstract

The increased number of water treatment plants induces intensified production of water treatment sludge (WTS) that needs to be stabilized and reused. One of the possible stabilization processes is solidification, which involves the reaction of wastes with additives based on calcium-oxide and calcium-hydroxide. The final product of these reactions (solidified water treatment sludge - SWTS) is an inert material that can be used as a filler, but not as a supplementary cementitious mate-rial (SCM) - due to its insufficient pozzolanic activity. The paper presents the possibilities of application of modified SWTS (MSWTS) as a SCM when mixed with aluminium-oxide and magnesium-silicate. In order to achieve this, mortar mixtures were prepared with partial replacement of cement by using MSWTS in amounts of 10%, 20% and 30%. Flexural and compressive strength tests, togeth-er with ultrasonic pulse velocity, as well as with capillary water absorption and freeze-thaw resistance were performed. The obtained results point to the conclu-sion that the increase in the percentage content of MSWTS consequently led to a decrease in the mechanical properties of the tested samples, which limits the pos-sible cement percentage replacement in plasters. The decrease in flexural strength ranged between 3% and 8% and in compressive strength between 8% and 19%.