DETERMINATION OF REQUIRED INSULATION FOR PREVENTING EARLY-AGE CRACKING IN MASS CONCRETE FOOTINGS

摘要

One of the methods for controlling heat of hydration of mass concrete structures is to insulate the poured concrete. Currently, no method can provide adequate insulation to prevent early-age cracking for mass concrete footings. This study developed a method for determining the required insulation for rectangular footings. The study included isothermal calorimetry testing of cementitious materials, field monitoring of temperature in footings, and finite element modeling. A fully insulated bridge pier footing constructed in the field in Florida was monitored for temperature development and for assessing the efficiency of insulation used. A parametric study consisting of 63 finite element analyses was conducted on 3 different footing shapes consisting of cubic shape, length:width:depth ratio of 4:4:1, and length:width:depth ratio of 4:2:1, to determine required insulation for footings with volume-to-surface area ratio ranging from 1.1 ft to 13.1 ft. From the obtained results, it was found that the Styrofoam insulation used for the specific monitored footing might be excessive, thus the actual insulation thickness of 2 inches should be reduced to 1 inch in order to reduce the construction cost. In general, with a volume15to-surface area ratio of less than 4.0 ft, under the same insulation condition, and using the same concrete mix, larger footings require a greater thickness of insulation. However, with a volume17to-surface area ratio of 4.0 ft or greater, larger footings only require a similar thickness of insulation to prevent cracking. The developed method for determining the required insulation for footings presented in this paper would be practice-ready for implementing in the field.TRB