Neutron Radiography Measurement of Salt Solution Absorption in Mortar
Catherine Lucero, Robert Spragg, Dale P. Bentz, Daniel S. Hussey, David L. Jacobson, Jason Weiss
A portion of the concrete pavements in the US have recently been observed to have premature joint deterioration. While this damage has been attributed to a wide variety of potential factors, it is hypothesized that one component of this damage can be attributed to a reaction that occurs when salt-laden water is absorbed in the concrete and reacts with the matrix. This study examines the absorption of CaCl2 solution in mortar. Due to its high spatial and temporal resolution, neutron imaging was used in this investigation to measure fluid movement. Neutrons interact with the nuclei of atoms and are therefore sensitive to light atoms such as hydrogen. This makes neutron imaging ideal for measuring changes in fluid content of a porous media. The change in the moisture content was determined along the length of the specimen during absorption. Mortar specimens were prepared with water to cement ratios, (w/c), of 0.36, 0.42 and 0.50 by mass. The mortar specimens were conditioned to 50 % relative humidity before being exposed to chloride solutions with concentrations ranging from 0 % to 29.8 % by mass. The depth of fluid penetration was monitored continuously for approximately 12 h as the fluid penetrated and subsequently at 24 h, 48 h, and 96 h. At low concentrations of CaCl2 (10 % by mass) the sorptivity (mm/s1/2) decreased by 38 %, 20 %, and 26 % in mortars with a w/c of 0.36, 0.42 and 0.50, respectively. At high CaCl2 concentrations (29.8 % by mass), the sorptivity decreased by 83 %, 87 %, and 87 % in the same mortars. It is known that changes in the surface tension and viscosity will reduce the rate of absorption. The decrease in absorption at low concentrations can be attributed to these changes in fluid properties. Additionally, a reaction can occur between CaCl2 and cement paste creating products (Friedels salt, Kuzels salt, or calcium oxychloride) that block the pores and reduce absorption at higher concentrations.