The 35 °F (20°C) maximum temperature gradient specification has been a “cut-and-paste” specification on mass concrete projects for decades. This specification often causes tremendous challenges for the contractor, and adds unnecessary costs and delays to projects. In most cases the flat 35 °F (20°C) requirement is an overly-restrictive requirement after a short period of time.
ACI 207.2R discusses methods of calculating temperature gradients and tensile stresses that cause thermal cracking in mass concrete. These techniques can be used to calculate safe temperature gradients based on concrete mix design, placement conditions, and concrete properties. One result from this analysis is performance-based temperature difference limit based on actual jobsite and concrete mix-design parameters. This calculated limit is much more pertinent and attainable than a flat 35 °F (20°C) specification.
Using intelliRock, the placement's temperature and strength can be monitored in real-time. This allows the in-place strength to be considered when determining what temperature gradient is currently safe.