Properties of alkali-activated controlled low-strength material produced with waste water treatment sludge, fly ash, and slag

Controlled low-strength material (CLSM) is a self-compacting, flowable, and low-strength construction material that is used widely in variety construction applications. The present study evaluates the properties of CLSM that was prepared using a mixture of class-F fly ash (FA) and ground granulated blast-furnace slag (GGBFS) with the addition of three different ratios (0%, 10%, and 20% as calculated by combined FA and GGBFS weight) of waste water treatment sludge (WTS). A sodium hydroxide (NaOH) solution was used to activate these powder materials in the mixture in order to produce the alkali-activated CLSM. The effects of adding WTS on the properties of both fresh and hardened CLSM are evaluated using workability, setting time, drop ball time, unit weight, compressive strength, and toxicity characteristic leaching procedure (TCLP) tests. Moreover, a scanning electron microscope (SEM) coupled with an energy dispersive spectrometer (EDS) and X-ray diffraction (XRD) is used to examine the microstructural properties of the CLSM. Results show that adding WTS to the CLSM samples reduces workability and increases fresh unit weight and compressive strength. Additionally, initial setting time and drop ball time are both associated positively with level of WTS content. Moreover, the liquid-to-solid (L/S) ratio and the alkali equivalent (AE) are shown to affect the properties of the CLSM significantly. The TCLP assessed leaching concentrations of heavy metals are all significantly below the regulatory thresholds that are currently allowed by the Environmental Protection Administration (EPA) in Taiwan. Finally, the properties of the CLSM sample with an L/S ratio of 0.9, WTS of 10%, and AE of 9% are found to conform well to the requirements of the Public Works Department, Taipei Government in terms of design principles and provisions.