A local ready-mix producer supplied the concrete, and the CNT...

A local ready-mix producer supplied the concrete, and the CNT additive was dosed at their plant after the trucks were filled with concrete using their dry-batch operation. After batching, trucks were spun ~70 revolutions before adding the CNT additive. After the addition and in route to the jobsite, trucks were spun another ~45 revolutions to incorporate the product thoroughly into the mix. Upon arrival to the jobsite, GDOT added calcium chloride flake (CaCl2) to the trucks at a rate of ≈ 1.8%, by weight of cement. The truck was spun an additional ~30 revolutions to incorporate the accelerator well before placement on the job site.
All trucks were within specification for fresh properties and the concrete was placed without issue. Testing was contracted by a 3rd party to verify compressive strength (ASTM C39) conformance at 24 and 72-hours, and included 7, 28, and 56-days of age. Although it was not required by the specification or by GDOT Engineers, the resistance to abrasion was measured in the lab at 56-days using ASTM C779, proc. C, which plots the depth of abrasive wear versus time. Test results from the lab are graphed below in figure 4.
View attachment 5318794
Lab testing confirmed the ability of CNT additive’s to significantly improve the compressive strength by as
much as 30% over the reference (at all ages). At 24 and 72-hours, the strength easily exceeded the
requirements of the section 504 specification. At 56-days, abrasion resistance was improved by more than
40% over the reference. At the end of the 20-minute test, it should be noted that the test samples with the
CNT additive were abraded to a depth measured on the reference samples after only the first 2 minutes of
the test. These results demonstrate the CNT additive’s ability to significantly extend the service life of
concrete as it pertains to surface deterioration from vehicle tire abrasion. Although lab testing showed well,
the true evaluation was occurring on the ground over time, requiring 4 seasons (12-months) in-service before
an assessment would be made by GDOT engineers. In February 2016, after approximately four months inservice,
a visit to the jobsite revealed significant abrasion and cracking to the slab without the reference slab,
as well as ravelling of the joints around the perimeter. However, the test slab containing the CNT additive
was in excellent shape with no cracking or ravelling anywhere. The vehicle tire path was only slightly
abraded and discoloured, and the broom finish was still intact on the surface.

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