Title: Planning and Execution of a Mass Concrete Placement Utilizing Insulation Regimen
Author(s): Ufuk Dilek
Publication: Symposium Paper
Appears on pages(s): 1.1-1.12
Keywords: mass concrete, adiabatic heat rise, thermal control plan, fly ash, thermal cracking, heat or hydration
This paper summarizes the planning and execution stages of a critical mass concrete placement performed during summer months. The subject structure was a critical
component of a large heavy industrial facility, consisting of large load bearing elevated flexural members. The planning and execution of this critical mass placement consisted
of multiple tasks.
A laboratory study was performed for the purpose of making improvements to the mixture proportions existing and currently in use, admixture dosages and investigating
placement temperature options. Adiabatic and semi adiabatic temperature rise was also measured during the laboratory study along with set times. Final proportions and
admixture dosages were selected as a result of the laboratory phase. Primary outcome was increase in fly ash percentage from the existing mix design to control heat of hydration.
Based on the findings of the measured adiabatic temperature rise, a thermal control plan was developed adapting the new approach to structural mass concrete placements. A thermal protection/insulation regimen was developed using the mix parameters, expected ambient temperatures following placement, member dimensions and
formwork/blanket insulation properties. The pre-placement modifications to the mixture proportions and the delivery temperature requirements protected the concrete
against high internal temperatures and potential of Delayed Ettringite Formation (DEF), while the insulation regimen protected the concrete against rapid cooling and occurrence of thermal gradients between core and perimeter.
As part of the thermal control plan analysis, target placement temperatures were recommended to control maximum temperatures to prevent occurrence of DEF, in light
of the heat rise of the modified mix. The placement temperature was accomplished by starting the placement at night and the use of ice to draw the temperature down. Upon
completion of finishing, a curing compound was applied in lieu of water curing and the placement was insulated.
The thermal control plan simulation predicted a gradual reduction in the temperature of the placement, within limits of maximum internal temperatures and temperature gradients. The actual placement was monitored for core and perimeter temperatures using maturity probes. Monitoring enabled the team to react to abrupt changes in temperature if any was to occur. The placement was completed successfully with
internal temperatures and gradients controlled within the desired ranges.