Laboratory Investigation of the Use of Rock Flour Residue for the Construction of Landfill Liner

1. The use of marble rock flour residue was investigated in the laboratory for the potential use as a landfill liner material. The clayey soil, sand, and cement were used as the additives. The rock flour and the additive material were mixed, compacted, and tested for diffusion and the hydraulic conductivity. The obtained diffusion coefficients were compared with the recommended diffusion coefficient for a compacted clayey liner. The comparison showed that the mixed material containing 65% rock flour and 35% clayey soil is acceptable with regard to diffusive transport mechanism compared to other mixed materials. The hydraulic conductivity was determined by the flexible wall triaxial hydraulic conductivity apparatus and the value of 1.210-10 m/s was obtained for this mixed material. This amount of hydraulic conductivity is in the range of values recommended for the compacted clayey liners and therefore this material is acceptable in terms of advective transport. The results showed that the diffusion coefficient and the hydraulic conductivity of the compacted mixed material containing 65% marble rock flour and 35% clayey soil are in the range of the recommended values for the compacted clayey liners.2. Methodology2.1. The marbel rock flour, clayey soil, sand, and cement were used as the materials for this study. These materials were mixed in different percentages to obtain three types of mixed material. The type 1 mix included 67% rock flour, 27% sand, and 5% clayey soil. The type 2 mix included 65% rock flour and 35% clayey soil. The type 3 mix included 90% rock flour and 10% cement. The 100% pure rock flour was also tested. The material were compacted in a polyethylene tube and were tested for chloride ion diffusion coefficient. The mixed material type 2 was tested for the hydraulic conductivity.2.2. Theoretical modeling: The program POLLUTE [1] was used for the prediction of the chloride diffusion coefficient in the tested material based on the observed chloride concentrations data. The following diffusion coefficients were obtained: 5.310-10 m2/s for pure rock flour, 810-10 m2/s for type 1 mix, 5.510-10 m2/s for type 2 mix, and 710-10 m2/s for type 3 mix. 3. Results and discussion3.1. Diffusion: The comparison of the results for chloride diffusion coefficients showed that the mix material type 2 has the lowest diffusion coefficient. This material has 30% clayey soil which gives the mixture enough absorption capacity as a liner material [2]. Thus, type 2 mix material is found to be suitable as a liner material in the landfill applications compared to two other mixed material. Fig. 1 shows the observed and predicted concentration profiles for type 2 mix material.3.2. Hydraulic conductivity: The type 2 mix material was tested for the hydraulic conductivity using the flexible wall hydraulic conductivity apparatus. The hydraulic conductivity value of 1.210-10 m/s was obtained for this material.4. The type 2 mix which included 65% rock flour and 35% clayey soil materials resulted in a reasonable low diffusion coefficient of 5.510-10 m2/s which is in the range of the reported diffusion coefficients for the compacted landfill liner material. The resulted hydraulic conductivity of 1.210-10 m/s for this mix material is also acceptable and is in the range of the standard value for the compacted landfill liner material. Thus, the type 2 mix is recommended as an alternative liner material for solid waste landfill liner applications.