Magnesium Chloride Deicer Chemical Effects on Pervious Concrete

摘要

Pervious concrete pavement systems can provide a transportation surface and stormwater management, in addition to other benefits. In cold climates, pavement systems may be subjected to deicers that may cause deterioration in the pervious concrete layer. Chemical impacts of magnesium chloride on pervious concrete were investigated. Magnesium chloride deicer treatments, with tap water and sodium chloride as controls, were applied weekly to laboratory specimens for a period of 4 months. Specimens were made with basalt aggregate and ordinary Portland cement (OPC) or a combination of OPC and 25% fly ash. Specimen ages ranged from 8 years to a few months and were tested in an ambient or cold (4 degrees C) laboratory. The specimen mass change, influent and effluent volumes, masses, and calcium ion concentrations were recorded weekly. Magnesium ions may exchange with calcium ions in the hydrated cement paste based on complexation stability constants with hydroxides, possibly impacting strength and durability. Specimens treated with magnesium chloride experienced a greater calcium concentration increase from influent to effluent than the controls. OPC specimens tended to leach similar to 20-30% more calcium than the fly ash specimens which supports the ion exchange hypothesis. Older OPC specimens had lower calcium effluent concentrations than the newer specimens, implying more resistance to chemical attack since the additional carbonate species in the older specimens are less favorable to magnesium complexation than the hydroxide species. Chemical interactions presented show that the cement-paste matrix is being chemically altered by the magnesium chloride deicer.