Evaluation of Concrete Strength and Permeability

Research Project Statement:

Questions have arisen in practice about how concrete systems (pavements and bridge decks) gain strength over time, and the relationship between in-field concrete conditions and those derived from cylinder tests.

This study involves the evaluation of the strength gain and permeability, over time, of a series of concrete mixtures containing different cementitious materials, including an optimized aggregate gradation, three blends of cementitious materials (100% portland, 35% slag, and 15% C-Ash/25% Slag), and three casting seasons, spring, summer and fall. Three sets of cylinders (lab-cured, field-cured, and cored from 10-in. concrete slabs) will be tested at 28, 56, 90, 180, 360, and 720 days for strength and permeability properties. Cores will be taken from concrete slabs that aqiure cast on an aggregate sub-base in a field station at the Adams Campus. The slabs will be 10-in. thick and 60 ft 2 to allow 54 cores (4 in. x 8 in. cylinders) to be sampled with 12 inches center-to center between the cores. Permeability will be tested using the KDOT Boil Test and ASTM C1202 Rapid Chloride Permeability Test (RCPT). All RCPT tests will be performed at KDOT Materials Laboratory, Boil and Strength tests will be conducted at KU.

KU will perform an additional series of permeability tests to compare the results obtained with the Boil test and RCPT with those obtained in the AASHTO T 259 ponding test. Three specimens for each mixture will be cast in the laboratory with air contents of 5 to 6%, 7 to 8%, and 9 and 10%. The RCPT specimens will be evaluated by the KDOT materials laboratory. The three measures of permeability will be compared at 28 days, 56 days, and 90 days.

For the optimized aggregate gradation mixes, the total cementitious material content will be 520 lb/yd 3, with supplementary cementitious material replacements by mass. The optimized aggregate gradation will be selected using the Shilstone Method and “haystack” gradation as designed using the KU Mix optimization program. Three aggregates will be used: limestone coarse aggregate, pea gravel intermediate aggregate, and Kansas River sand.

Curing will follow the guidelines specified by KDOT for concrete pavement materials. Cold-weather concreting protection measures will be taken as necessary. Temperature sensor will be embedded in the slabs and in two field cured cylinders from each mixture to develop maturity curves.