This investigation concerns observed differences between the strengths of molded cylinder and beam specimens and the strength of concrete in situ. The specific project is a section of I 64 in Rowan County [I 64-6(15)130]. The paving was done between August 19 and September 27, 1968. Cylinder specimens molded on the project were tested after they had cured 28 days. Beam specimens were tested before they had cured 14 days. Those test results were "normal". However, cores taken to measure thickness of the pavement were subsequently tested for strength; and the pavement cores, even though older when tested, yielded strengths which were considerably below 28-day cylinder strengths.

Having already explored all reasonable courses of investigation and inquiry, the matter was referred to Research.

The findings reported herein indicate that the concrete was manufactured or hatched In nearly the proper proportions but was not well consolidated in situ. Excess voidages arising from excess entrained and entrapped air suffice to explain the lower strength of the concrete in the pavement.

Report Date


Report Number

No. 285

Digital Object Identifier