INSIDE THE DOT
South Dakota Department of Transportation
Using Admixtures with Dacotah Cement
Dan Johnston, SDDOT
1/1/1900 - 1/1/1900
SDDOT often gets requests from contractors and concrete suppliers to use high-range water-reducers (HRWR) and set retarding admixtures in concrete mixes. When these admixtures have been tried in the past, experience has shown that an unexpected and untimely loss of workability can result. These results have been experienced with retarders in the laboratory and in the field. As a result of these experiences the department has been reluctant to approve the use of these admixtures. A reliable set retarder would be desirable during hot weather, long hauls, or when it would be advantageous to delay the time of initial set (i.e. long bridge deck pours). It would also be desirable to be able to use a reliable HRWR when a high slump low water/cement ratio or high early strength is desired, such as for fast track concrete, drilled shafts, pier walls, box culverts, or for any concrete to be placed in forms with tight rebar spacing. If the factors responsible for the unreliable performance of these admixtures could be determined, then guidelines could be established for their use to produce quality concrete that consistently has the desired properties.
1 Determine the behavior of HRWR and set retarders with typical SDDOT concrete mix designs.
2 Attempt to duplicate loss of workability problems and identify causative factors.
3 Develop written guidelines for design and field personnel to ensure reliable use of HRWR and set retarders. These guidelines could include mixing instructions, concrete testing, and cautions against improper use, etc.
1 Review relevant literature and SDDOT's past experience with HRWR and set retarders.
2 Laboratory tests: Using different brands of cement (although primarily Dakotah) and different brands of admixtures, test typical SDDOT concrete mixes and note if any mixing problems were encountered. The dosage of the admixture should be varied according to manufacturer's recommendations. Each brand of cement should have samples manufactured at different times. The concrete mixes should be tested over a range of 75 to 90 degrees Fahrenheit.
3 Identify factors responsible for premature stiffening and poor workability and necessary for reliable use of acceptable admixtures.
4 Field tests: Demonstrate the satisfactory use of the proposed admixtures, using field tests on either actual projects or test pours. All field tests need the consent of the Department.
5 Write a manual, for design and field use, outlining the proper use, minimum mixing time, testing, continuous agitation, etc. of the proposed admixtures.
6 Submit a final report describing the research methodology, findings, conclusions, and recommendations.
7 Present findings and conclusions to SDDOT Research Review Board upon completion of the project.
Copyright © 2013 State of South Dakota. All Rights Reserved.