Evaluation of the Stability of Waste-Based Geopolymeric Artificial Aggregates for Wastewater Treatment Processes under Different Curing Conditions

Waste geopolymeric artificial aggregates (WGA) with different atomic ratios of mining waste mud/Na2SiO (4 to 5) and Na2SiO/NaOH (1.25 to 5) were produced using curing temperatures of 20ºC and 130ºC and its structural stability and pH variation after immersion in water was observed during 3 months. Results showed that WGA with mud/Na2SiO and Na2SiO/NaOH of 5 and 4, respectively, cured at 20ºC presented good stability in water and pH decreased from 10 to 7 in 24 days. Compressive strength was determined in additional samples cured at 20ºC and 80ºC in dry conditions, for 13 curing ages and 15 water immersion periods (up to 14 weeks). Results of this second stage showed that increasing temperature to 80ºC accelerated compressive strength gain but only during the first 3 weeks (up to 15.4 MPa). After 24 h in water compressive strength decreased to half of the initial values determined in dry conditions in all samples and, therefore, the increase of temperature did not bring benefits to WGA strength in water. Regardless the curing temperature and the dry curing age comprehensive strength stabilizes between 1 MPa and 2 MPa after 4 weeks immersion in water, which are values that makes WGA suitable to be used as bed material for wastewater treatment processes.