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.
As concrete maturity technology gains popularity, users are continuing to leverage its benefits. Today's application trend offers substantial cost saving opportunities on mass concrete pours. And if you could shave 10%, or even 20%, off of your concrete material cost before bidding, wouldn't that offer you a substantial competitive advantage?
Temperature management is a key risk-management task on mass concrete pours. Usually, maximum temperatures need to be kept below ~160F to avoid DEF issues and thermal gradients must be kept below some threshold value, such as 35F, to minimize the thermal cracking. These requirements are often viewed as challenges, BUT the root cause of these thermal control "problems" can also be viewed as a tremendous opportunity. Since cement hydration generates heat, and that heat gets trapped in mass pours (which is what causes the temperature rise), it takes a lot less cement to get the job done. And less cement means lower temperatures and substantial reductions in material cost! Even if cement content is reduced in the mix-design, the trapped heat will continue to drive the hydration reactions and strength gain. So this really creates a win-win opportunity to both reduce concrete temperatures and material costs at the same time.
To "tune" your mix design, use intelliRock concrete maturity sensors in your pre-pour test blocks. By instrumenting blocks made with multiple mix designs, and simultaneously calibrating the maturity values using cylinder breaks, intelliRock maturity sensors can determine the anticipated temperature rises AND strength gain profiles. Once you have real data defining the temperatures and strengths for each mix design, you can make some cost-saving decisions by using lower-cost mix designs!
For more information see the blog post below. And remember that these opportunities are compounded by the retained heat in mass concrete placements!
http://www.engius.com/blog/post/Using-intelliRock-to-Lower-Material-Costs.aspx
"With the performance-based mass concrete in hand, and intelliRock loggers in the concrete, Walsh uses the new wireless data transmission system to overcome the data collection challenges."
"About the Author: Eric Hayes is an assistant project manager for Walsh Construction, currently on-site managing the construction of the twin Allegheny River Bridges. For more information about Walsh Construction, visit www.walshgroup.com."
Read the case study from Modern Contractor magazine here!
Over the years intelliRock has been used on jobsites with extremely harsh conditions for electrical instrumentation. For these applications we developed “armored” cables to protect the download wires from being damaged as the concrete was being placed. These tough cables, suitably dubbed “yellow wire loggers”, were so reliable we started using the tougher wire on all loggers with cable lengths over 4 ft. Today 4ft red-black cables are still available on loggers as a cost-effective solution on small concrete placements. However, on large placements we highly recommend that 8ft or longer cables be used to maximize durability and reliability even if the placement isn’t considered a “mass concrete” pour.
intelliRock loggers are currently available with the following cable lengths: 4ft, 8ft*, 15ft*, 30ft*, 50ft*, and 100ft* (* denotes loggers with tough “yellow wire” cables) . Cables longer than 100ft are available by special order.
Special loggers are available for users needing to monitor mass concrete temperatures over "years." These loggers were originally developed to monitor long-term temperatures on the Tom Sauk Reservoir rebuild where engineers wanted a way to conveniently monitor mass concrete temperatures as long as possible. The "MEGA" loggers are physically larger than standard intelliRock loggers because they contain larger batteries. Although only guaranteed for three years, the larger battery theoretically gives the loggers enough power to log for 5 to 10 years.
If you have a mass concrete monitoring project where you could employ MEGA loggers, give us a call and we can discuss needs and capabilities!