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INTERGROUND LIMESTONE/CEMENT BLENDS WILL WORK IN LOUISIANA

Interground limestone/cement blends are appropriate for all uses in the Pelican State, say Tyson D. Rupnow, Ph.D, P.E., and Patrick J. Icenogle, P.E., Louisiana Transportation Research Center, Baton Rouge, in their paper, Louisiana’s Laboratory Experience with Type IL Portland Cement.

Portland cement concrete (PCC) is the world’s most versatile and most used construction material, note Rupnow and Icenogle, but it occupies a substantial carbon emissions “footprint.” A new method of reducing the carbon footprint and increasing the sustainability of PCC, however, has emerged that incorporates a much larger portion of interground limestone (Type IL cement) into the finished cement.

ASTM and AASHTO have now changed specification language of C595 and M240, respectively, to allow up to 10 percent use of interground limestone, the authors report. The incorporation of the increased limestone content significantly reduces the carbon dioxide (CO2) footprint of the resultant PCC while extending the life of cement quarries. The blend also permits cement companies to make powder “go farther,” producing more cementitious material without having to expand production facilities—thus sidestepping associated capital expenditures and environmental permitting.

“The use of these cements is widespread in Europe and much of the research work can be found in state-of-the-art reports,” observe Rupnow and Icenogle, adding other research finds portland/limestone cement and ordinary portland cement has similar mechanical performance, with restrained ring shrinkage behavior of the blend being similar as well.

Several states have conducted field trials or currently allow the use of PLC, including Utah, Oklahoma and Iowa. “Work is also ongoing at the University of Toronto and University of New Brunswick, looking at low temperature sulfate attack, potential interaction with deicers, and early age shrinkage cracking potential,” Rupnow and Icenogle report. “Work by Holcim has also shown the potential for further synergistic action of ternary cementitious systems that contain Type IL cement.”

Recently the Louisiana Department of Transportation and Development has implemented the use of ternary mixtures for both structural and paving concrete applications at the rate of 70 and 50 percent replacement of cement, respectively, they write, but a concern arose with the introduction of Type IL cement as to whether the new specifications would need revision.

Evaluation saw the researchers characterize the fresh and hardened concrete properties of binary and ternary combinations incorporating Type IL cement. Three binary and three ternary mixtures were prepared and tested for both fresh and hardened characteristics. Concrete samples were produced in laboratory conditions with a w/cm ratio of 0.45. Fresh concrete properties measured included: slump, unit weight, air content, and set time. Hardened concrete properties measured included: compressive strength, flexural strength, surface resistivity, freeze-thaw durability, and shrinkage.

“The results of this study showed that the use of Type IL portland cement in Louisiana should be allowed for all applications, including ternary mixtures up to 70 percent replacement,” Rupnow and Icenogle affirm. “Compressive and flexural strength results were comparable. Type IL mixtures exhibited less shrinkage when compared to the control mixtures with Type I cement. Surface resistivity results were comparable and indicated that the surface resistivity meter use will be applicable for mixtures containing Type IL cement.”