Carbonate Aggregate in Concrete

Project Details
STATUS

Completed

START DATE

08/09/12

END DATE

05/31/15

RESEARCH CENTERS InTrans, CP Tech Center, CTRE
SPONSORS

Minnesota Department of Transportation

Researchers
Principal Investigator
Kejin Wang

PCC Engineer, CP Tech Center

Co-Principal Investigator
Fatih Bektaş

About the research

The current Minnesota Department of Transportation (MnDOT) specification for coarse aggregate to be used in concrete pavements is based on either a maximum absorption of 1.75% (for Class B aggregate) or a maximum carbonate content of 30% by weight (for Class C aggregate). There is a concern that these specified limitations may reject potentially acceptable aggregates. This study was designed to evaluate the available methods for effectively characterizing the freeze-thaw (F-T) durability of aggregates.

In this study, aggregates from 15 different sources in Minnesota were investigated. The experimental program included measuring the carbonate content, absorption, desorption, specific gravity, Iowa pore indices (i.e., primary pore index [PPI] and secondary pore index [SPI]), and pore size distribution of the carbonate and non-carbonate fractions.

The results indicate that carbonate aggregates generally have higher absorption, lower specific gravity, and higher PPI and SPI than non-carbonate aggregates. Although there is no direct correlation between absorption, carbonate content, and SPI, a combination of high specific gravity (>2.60) and low absorption (<1.75%) often indicates a low SPI value. Carbonate aggregates generally have a much finer pore structure than non-carbonate aggregates, and the characteristics of their pore size distributions are clearly different. PPI correlates well with pores in the size range of 0.1–100 mm, and SPI correlates well with pores in the size range of 0.01–1 mm.

Further research is necessary to identify the critical pore size range that has the most significant effect on aggregate F-T durability and to determine the critical SPI value below which an aggregate will be truly F-T durable.

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