Permeability and Leaching Properties of Recycled Concrete Aggregate as an Emerging Material in Civil Engineering

In this article, a study of the threshold gradient and leaching properties for recycled material, namely, recycled concrete aggregate (RCA), was conducted. The RCA in this study is a material that comes from recycling concrete debris. A series of tests in permeameter apparatus in a constant head manner were conducted. The test method has been improved to eliminate common mistakes, which occur when the constant head method is used. During the following study, aggregates with gradations equal to 0–8, 0–16, and 0.05–16 mm were tested. The tests were conducted on gradients ranging from 0.2 to 0.83. This range of tested gradients led to the evaluation of the flux velocity and indicated non-Darcian flow. For engineering applications, the threshold gradients for three RCA blends were calculated using a statistical analysis. The average coefficient of permeability, kavg, for linear flow was equal to 1.02 × 10−4–1.89 × 10−4 m/s. In this paper, suffosion analysis was also conducted for the three blends in order to eliminate the possibility of particle movement. Moreover, for RCA blend 0–16 mm, leaching properties was examined. It was found that the concentration of chlorides, sulphates, and heavy metals in the water solution does not exceed the permissible standards. This paper ends with conclusions and proposals concerning the threshold gradients obtained from the statistical analysis, suffosion analysis, and flux velocity.

Variation of the Hydraulic Conductivity of Clayey Soils in Exposure to Organic Permeants

Clayey soils are the most common material used in waterproofing and play an essential role in waste and contamination control. Permeability is a key parameter in such problems and its determination is needed in ensuring the satisfactory performance of the soil. Research has shown that a permeant fluid with a low dielectric constant can shrink the double layer around the clay particles which will, in turn, increase the permeability of the soil. In this paper, the permeability of two types of clay with different plasticity, exposed to the flow of water and methanol as polar and miscible solvents and gasoline and car oil as non-polar and immiscible solvents is investigated. In addition, the effect of soil properties such as plasticity and compaction water content on permeability of the samples is examined. To this end, soil samples are prepared and compacted at various water contents. Then, permeability tests are conducted according to the modified constant head method and the effects of parameters such as the fluid dielectric constant, water content of the samples and soil plasticity are examined. The results demonstrate that the lower dielectric constant of the organic fluid decreases the thickness of the double layer, providing more space for the flow of the permeant and as a result, the permeability of the clay increases. The reduction of the permeant dielectric constant from 80.4 to 2.28 led to a remarkable increase in soil permeability.

Effects of petroleum hydrocarbon concentration and bulk density on the hydraulic properties of lean oil sand overburden

In the Alberta oil sands, sand containing less than 8% petroleum hydrocarbon (PHC) is referred to as lean oil sand (LOS) and is used as subsoil in reclamation. The objective of this study was to determine how bulk density and PHC concentration affect the hydraulic properties of LOS. The LOS was packed in soil cores at varying bulk densities and PHC concentrations, representing the range in these parameters that occur in the reclamation setting. The cores were placed on a tension table and pressure plates to measure water retention. The constant head method was used to measure the saturated hydraulic conductivity (Ks) of the LOS. Results show that increasing PHC concentration reduced the water retention of LOS due to the presence of PHCs in soil micropores. PHC concentration also had a significant effect on the van Genuchten curve fitting parameters for the water retention curve, although the shape of the curves remained similar regardless of PHC content. Furthermore, there is a significant reduction in Ks at the high bulk density and high PHC concentrations (3.25%–7.48%), compared with low PHC concentrations (0%–1.63%). Due to the reduced Ks with increased PHCs and bulk density, LOS used as the base material in reclamation will reduce percolation and increase water storage in the reclamation soil cover.

Water Permeability of Pervious Concrete Is Dependent on the Applied Pressure and Testing Methods

Falling head method (FHM) and constant head method (CHM) are, respectively, used to test the water permeability of permeable concrete, using different water heads on the testing samples. The results indicate the apparent permeability of pervious concrete decreasing with the applied water head. The results also demonstrate the permeability measured from the FHM is lower than that from the CHM. The fundamental difference between the CHM and FHM is examined from the theory of fluid flowing through porous media. The testing results suggest that the water permeability of permeable concrete should be reported with the applied pressure and the associated testing method.