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

Clayco, Inc. and concrete sub Concrete Strategies, Inc. recently completed a 2 story parking garage for online brokerage firm Scottrade in St. Louis, Missouri. Information from intelliRock concrete maturity sensors was used to time critical workflow activities such as post tensioning.

Left: Scottrade Building HQ and garage site in St. Louis, MO.
Right: Post tension cables which were stressed in two stages, 1600 PSI and 3000 PSI

Concrete Strategies VP, Barclay Gebel explains “For crack controlling reasons we stressed the PT cables in two stages. The first stage was when the concrete achieved 1600 psi and the second stage was 3000 psi. We use intelliRock to determine when to do the stressing.”

Project engineer Curt Costello continues, ”We were able to determine when different crews would come in to start stripping forms and preparing the PT cables for stressing. Once the strengths were met, we were able to stress the cables without losing much time. This was because we were able to anticipate concrete strengths based on information from intelliRock.”

The graph above is an example of the information available to Concrete Strategies in real-time at the jobsite. intelliRock sensors evaluated the concrete’s maturity every 60 seconds. The maturity reading could be correlated to a concrete strength using a calibration curve for the mix design. This gave Concrete Strategies up-to-the-minute concrete strength values.

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Clayco, Inc. is one of the nation's largest, privately owned real estate, architecture and engineering, design/build and construction firms. Read more about Clayco at www.claycorp.com.

Concrete Strategies is a leading edge, full service, design/build and general contracting firm specializing in all forms of concrete and structural steel construction. The firm operates nationally and has an unparalleled track record in architectural site cast concrete, structural concrete, flatwork and all types of self-perform construction related to commercial projects. For more information see their website at www.concretestrategies.com

If you’re ever wondering what a maturity calibration curve (graph shows strength vs maturity in °C-Hrs) could tell you about the time needed to reach a target strength, there is a simple calculation can give you enough information to at least see what’s feasible.

Maturity, using the Nurse-Saul method, is given in units of °C-Hours.   The calculation is simply “Time x Temperature” with the units of time being hours, and units of temperature in °C.  Assuming the common datum temperature of 0 °C, the math gets that simple:  Maturity = Time x Temperature.  Just be sure you get the units right.

Let’s assume you need 4,000 PSI and your calibration curve says the maturity needed for 4,000 PSI is 3,500 °C-Hrs.  How long is that?  A convenient first approximation is to see how long 3,500 °C-Hrs is at a comfortable 23 °C (73 °F) temperature.  Maturity/Temperature  = time, 3500 °C-hrs/23 °C = 152 hours, which is a little over 6 days.  If your goal is 4,000 PSI in 7 days and it’s warm outside, then you’re probably fine with that mix design.  If you need the 4,000 PSI in 3 days, then what do you need to do to get there?  You need higher temperatures!  How high?  Temp = Maturity/Time,  Temp = 3,500 °C-Hrs/(3 days* 24hrs/day) = 49 °C (104 °F).  Is it reasonable for the concrete to have an average curing temperature of at least 49 °C?   Mass concrete in Florida during July – you’re just fine.  A thin elevated deck during January in Chicago – you’ll either have to supply supplementary heat or use a “hotter” mix.

This simple calculation is especially insightful when considering leaner, lower cost mix designs.  Take the example where you need to achieve 3,000 PSI in 2 days and your maturity data says you are achieving 5,000 PSI in 2 days using your expensive high-early mix.  Would a standard lower-cost mix design still get you there?  Grab the calibration curve for the leaner mix, see what maturity is necessary, divide maturity by 48 hours and see what average curing temperature you need (remember, that’s the temperature of the concrete, not the ambient temperature).  Compare the calculated temperature to the temperatures profile you’re currently getting with the high-early mix. Considering that the leaner mix will run somewhat cooler, is it likely that the average 48 hour concrete temperature will be at or above what the maturity calculation said?  This simple calculation can at least tell you yes, no or maybe.  For a 60 second effort, that’s a lot of insight.