Effect of long-term acid attack on impermeability and microstructure of compacted cement-bound soils.

ABSTRACT

Compacted cement-bound soils (CCS) are widely used as leakage barriers around solid waste landfills and contaminated sites. However, a study of its long-term reliability in an acidic environment is relatively scarce. A 3-year-long experimental study on the changes in permeability coefficient and microstructure of CCS under acid attack was conducted, from which the following conclusions can be drawn the permeability coefficient of CCS under weak acid (pH = 5.00) attack decreased progressively with time, from 4.90 × 10-8 cm/s at the beginning to 6.70 × 10-10 cm/s after 3 years. Under strongly acidic environments with pH values of 2.65 and 3.65, the permeability coefficients of CCS initially decreased and then increased with time, reaching 6.70 × 10-5 and 9.37 × 10-8 cm/s, respectively. The degradation effect of a weak acid (pH = 5.00) on the hydration products of cement was mild as a large amount of hydration products (e.g. C-S-H shaped in short fibrous) remained in the pores of CCS after 3 years of immersion. However, strong acid caused an obvious degradation effect on the hydration products, which almost disappeared after 3 years of immersion. Based on the study data, a unified mathematical model was developed to correlate the permeability coefficient of CCS, immersion time and acidic solution pH value. Furthermore, a quantitative expression function between the service life of CCS and solution pH value was established.