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South Dakota Department of Transportation
Project Synopsis
SD2002-02


Title: Optimized Aggregate Gradation for Structural Concrete
Project Researcher: V Ramakrishnan, SDSM&T
Project Manager: Daris Ormesher
Research Period: 1/23/2002 - 6/30/2006
Status:
Cost: $80,000.00

Problem Statement: New bridge decks increasingly show early transverse cracking which is undesirable because it allows the ingress of water and chlorides that further damage structure. Although several causes may contribute to cracking, one probable cause is the Department's use of concrete mixes based on high cement content and a gap graded (coarse and fine) aggregate. With the current aggregate gradation, the concrete mix must contain a high proportion of cement-water paste and high cement content, which contribute to shrinkage cracking. Current literature indicates the use of a more well-graded aggregate should permit lower cement paste content which should result in reduced shrinkage cracking. SDDOT currently uses a gap graded aggregate gradation with a 1 top size for structural concrete.

SDDOT needs to develop a well graded aggregate gradation to minimize transverse cracks in bridge decks and still provide a structural concrete that maintains strength and durability.



Findings:

Research Objectives:
1  To produce a new set of Class A45 Concrete mix designs using SDDOT aggregate sources-that minimize drying shrinkage by optimizing the coarse aggregate amount and gradation, and minimize cement and water content, while maintaining or improving strengt

Research Tasks:
1  Review and summarize literature relevant to mix designs using a well graded aggregate to minimize drying shrinkage in structural concrete and identify laboratory test procedures to determine concrete’s tendency for shrinkage cracking.
2  Meet with the Technical Panel to review the research scope and work plan.
3  Determine the extent of cracking in bridge decks by quantifying amount, average width and type of cracking present on steel girder and pre-stressed girder bridges. A survey of six steel girder and six pre-stressed girder bridges should be done. Three
4  Determine gradations for starting points of mix designs using limestone, quartzite, and granite coarse aggregates. The objective is to maximize the coarse aggregate amount and size - up to 1.5.
5  Develop a well-graded aggregate gradation to minimize cement past content.
6  Obtain panel approval of the proposed gradation before conducting mix designs.
7  Develop mix designs using limestone, quartzite, and granite coarse aggregates. Each coarse aggregate will be tested with a coarse, medium and fine sand. Each coarse and fine aggregate combination will be tested with no fly ash and a Class F fly ash.
8  Conduct performance tests on hardened concrete for laboratory mix combinations and on the collected field samples for the structural concrete. Performance tests should include, but not be limited to, permeability, freeze thaw, durability, drying shri
9  Provide mix design results for inclusion by Construction Change Order in bridges being constructed during the 2002 construction season by May 1, 2002.
10  Conduct performance tests on hardened concrete for field mix combinations and on the collected field samples for the structural concrete. Performance tests should include, but not be limited to, permeability, freeze thaw, durability, drying shrinkage
11  Conduct petrographic analysis of selected cores to evaluate the mix design characteristics and the relationship between the aggregate-paste ratio as it relates to the strength and durability of the concrete.
12  Survey bridge(s) constructed using the new gradation during the 2002 construction season within 6 months after construction to determine amount, average crack width, and type of cracks on continuous concrete slab, steel girder, and pre-stressed girde
13  Recommend Class A45 Concrete mix designs, including aggregate gradation, for optimized structural concrete based on results from this study.
14  Submit a final report summarizing relevant literature, research methodology, test results, findings, conclusions, and recommendations.
15  Make an executive presentation to the SDDOT Research Review Board summarizing the findings and conclusions.

Documents Available:
SD2002_02_Final_Report.pdf

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