Concrete Mix – Not As Simple As It Appears!

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I don’t know about you, but every time I drive through a tunnel, especially one that goes beneath a large body of water, I’m grateful for the expertise of the engineers, concrete experts, and contractors who developed and placed this tunnel for me to get from one place to another. ECS is extremely fortunate to have one of these experts on our team, Construction Materials Testing Department Manager Bill Denison.

Mike Galli, P.E., Branch Manager of ECS Chesapeake, Mr. Denison, and his team, along with our client CSI Tunnel Systems, Hudson, NH and CBBT consulting inspectors, have been performing Pre-Production Testing of trial concrete mix designs for the CBBT Precast Tunnel Segmental Liners, which are scheduled to start production in late May 2018.

The specialty concrete designed by Mr. Denison will be used on the new ‘bored’ tunnel being constructed for the Chesapeake Bay Bridge Tunnel Thimble Shoals Crossing in Virginia. The nature of this project requires that the concrete be designed for a 150-year-service life cycle. One of the features of this very special concrete design includes having 2 1/4 inch steel fibers embedded in the mix for reinforcement. The concrete is also designed to handle various conditions or constraints for a bored tunnel liner system.

Mr. Denison’s support staff for the pre-production testing includes ECS employees Michael Simmons, Heather Rassio, Dave Matheny, Sam Smith, and Christine Francis. The ECS Chesapeake team also had CSI Tunnel Systems lead Quality managers from Seattle, WA and Boston, MA, along with Dragados Consultants from Parsons. Our pre-production testing started soon after CSI Tunnel systems managers arrived. Additional shout out to our office administrative staff, Chelsea Jacox and Cathie Sale, for welcoming our client, CSI Tunnel Systems, along with Dragados consultants Parsons, Sika Admixtures National BD from Raleigh N.C., and technical advisors from Northern VA.

Phase I of this process involved Mr. Denison designing three concrete mixtures that meet the project specifications per CSI Parameters and Dragados Parameters. The trial mixes were then batched in the lab, then molded the sample specimens that were required for testing.

And just to show that all this is not as simple as it might appear, this project required several specialized tests, including:

  • Raw materials testing (chemical and physical properties)
  • Compressive strength testing (ASTM C39)
  • Rapid chloride permeability (VTM 112)
  • Drying shrinkage(ASTM C157)
  • Water soluble chloride ions (ASTM C1218)
  • Split tensile strength of cylindrical specimens (ASTM C496)
  • Flexural strength testing of beams (ASTM C1609)
  • ASTM C666 Freeze-thaw determination with beams, ASR Mitigation (ASTM C1567)
  • NTBuild 492 for Chloride migration coefficient from non-steady state migration experiments

…just to name a few.

ECS will also be performing periodic independent testing during production, Uniformity and Washout testing, along with Rapid Chloride Permeabilities. This is just the first piece of our involvement with this nearly $800-million-dollar privately-funded project.