Using Isothermal Calorimetry to Assess the Water Absorbed by Fine LWA during Mixing

Abstract

Fine lightweight aggregate (LWA) is being increasingly used for the manufacture of internally cured concrete. Internally cured concrete can be viewed as a concrete that contains fluid (water) in the pores of the LWA (or other porous inclusions) that can be released to the paste after setting. Most research performed on internally cured concrete assumes the LWA has been prewetted for some time before mixing (generally lab studies use 24-h soaking, whereas this value varies in practice). The research described in this paper investigated the potential for using aggregate that begins the mixing process from a different moisture state (i.e., not 24-h prewetting). Specifically, this paper considers oven-dry aggregate as a worst-case scenario to determine how much water would be absorbed by the LWA during the mixing and placement processes. To determine the amount of water absorbed by the LWA, isothermal calorimetry was used. Two different mixing scenarios were investigated, showing that 56–71% of the 24-h water absorption could be achieved using the worst-case scenario of oven-dry aggregates. Although the use of oven-dry aggregate would be extremely rare for a field application (except for possible application to bagged products), this approach could be extended to include fine LWA with other initial moisture conditions.