The GDoT evaluation was considered a comprehensive, controlled,...

The GDoT evaluation was considered a comprehensive, controlled, non-political evaluation by the Australian Concrete Pavements Association. This is an extract from EDE's technical paper which won an award for contributions to concrete technology advancement.

"GEORGIA DEPARTMENT OF TRANSPORT – I-20 TRIAL #1 EVALUATION

In the past, it was common for the concrete repair work on Georgia’s interstate to crack and abrade from
heavy in-service conditions only a few months after placement. In August 2015, the Georgia DOT agreed to
a trial evaluation of a CNT additive on Interstate Highway-20 in Augusta, GA. This project was chosen due
to its placement occurring in an area known to have aggressive in-service conditions and high volume of
traffic from passenger and commercial vehicles. The CNT additive was under evaluation for its ability to
extend the performance of the newly repaired sections of interstate. It was anticipated that the CNT additive
would improve the strength and resistance to abrasion and cracking. Abrasion resistant concrete is critical in
roadway construction, necessary to maintain friction enough for safe stopping distances, especially in winter
weather conditions. Concrete that has a surface which has been abraded smooth can extend the braking
distance for passenger vehicles traveling at a high rate of speed.

Beneath the interstate concrete, figure 3 shows

the level clay in the sub-base combined with the elevated water table from the nearby Savannah River created additional challenges with preparation of the sub-base. The project included a full-depth slab replacement on requiring approximately 32 cubic yards of
concrete. For the comparison, the section was split up into two 16-yard slabs supplied by four 8-yard trucks, spaced 45-minutes apart.

It was decided to place the 16-yard slab with the CNT additive on day 1, and the reference slab was placed the second day. Slabs were located adjacent to one another, end to end in the right (southbound) lane of I-20 West. Their location was chosen to provide identical in-service conditions for both the reference and the sections with the CNT additive.

Upon examination of the jobsite, the existing concrete to be removed was cracked to full depth in several
places. In some cases where the concrete was cracked to full-depth, water would shoot upward when large
semi-trucks drove over top. The concrete was abraded to the point that the paste was flush with the surface
of the coarse aggregate. In the beginning, 16.6 L/m3 was a common dosage selected for the most extreme of
project conditions using the CNT additive. After observing the condition of the existing concrete to be replaced,
a dosage equal to 16.6 litres per cubic meter of concrete (L/m3) was recommended for the CNT additive. The
Georgia DOT Engineers had no objections and the mix design was set for the project.

The maintenance project conformed to two specifications within the Georgia DOTs construction handbook;
sections 452 and 504. The section 452 specification provides the requirements for preparation of full-depth
concrete slab replacement, and the section 504 specification provides the requirements for the 24-hour
Accelerated Strength concrete mix used in a full-depth slab replacement.
Since the slab is unreinforced, the specification allows calcium chloride to be used as an accelerator at ≤4%
by weight of cement. This is done to ensure the interstate is reopened to traffic within several hours of
placement.

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