Investigation of the Effect of Using Different Fly Ash on the Mechanical Properties in Cemented Paste Backfill

Abstract

In the cemented paste backfill (CPB) method, which can also be used for fortification purposes in mines, different additive materials with pozzolanic properties can be employed as substitutes instead of cement that is the main binder. One of the most popular pozzolanic materials that can be employed instead of cement is fly ash, which is thermal power plant tailings. But the compositions of fly ash and tailings used in high amounts in the CPB method, as well as the chemical structures that these materials form by interacting with the cement binder, affect the mechanical properties of the material depending on time. In this study, fly ash with 4 different chemical compositions (TFA, SFA, YFA, and CFA) was used as a cement substitute in CPB. By substituting fly ash with different chemical compositions in different proportions, CPB samples were created and their strength was elucidated according to 28, 56, and 90-day curing times. The results of the study revealed that TFA with the highest CaO/SiO2 and SO3 ratios remained stable at the strength values of 6 MPa (total 9% binder) and 10 MPa (total 11% binder) in the long term. However, CFA with the lowest CaO/SiO2, SO3, and the highest SiO2+Al2O3+Fe2O3 ratios resulted in the greatest strength increase at a 20% substitution rate (11% of the total binder). Nevertheless, it was found that the SFA, which is in Class F, increased its strength in the early period based on the CaO rate.