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South Dakota Department of Transportation
Project Synopsis
SD1997-09


Title: Field Performance of Concrete Admixtures
Project Researcher: Dan Johnston, SDDOT
Project Manager: Jon Becker
Research Period: 5/1/1998 - 9/30/1998
Status:
Cost: $40,000.00

Problem Statement: Admixtures can improve the quality of concrete by improving workability and set times. The use of set retarders can be beneficial for long hauls (40 or more miles) and large pours. However, when cement and set retarders are incompatible, the concrete can become sticky and prematurely stiff, similar to false set. High-range water reducers are desirable for pours that are crowded with steel reinforcing or have formwork with small openings. However, the problems with incompatibility are much more severe for high-range water reducers than set retarders. The results of incompatibility between high-range water reducers and cement are premature stiffening and rapid slump loss. These two commonly reported problems are frequently associated with unacceptably low compressive strength. Study SD92-07, Evaluation of the Performance of Set Retarders and High-Range Water Reducers in Typical SDDOT Concrete Mixes identified an incompatibility observed with set retarders and high-range water reducers (HRWR) when added to cements that have low tricalcium aluminate (C3A) and tricalcium silicate (C3S) contents. Because cements with high C3A contents are susceptible to sulfate attack and South Dakota has relatively high sulfate soils, cements with higher C3S contents are more desirable.

Study SD92-07 included lab tests which determined that the primary determinant of whether a compatibility problem might arise is governed by the rate of hydration of the cement. This is directly related to the amount of C3A and C3S in the cement. Field tests were intended in SD92-07 but not performed. Study SD92-07 recommended that The Office of Research should initiate a study to conduct field testing that would use the most recently developed set retarders and high-range water reducers as well as the new Type I-II Dacotah Cement that will have 57% C3S. Dacotah Cement increased the content of C3S to 57% in June 1996. Field tests will be performed with the new cement in this study.

The researcher was not able to provide written guidelines since the attempts to use admixtures in the field were hampered by time and logistical constraints. However, based on laboratory testing the researcher made a recommendation suggesting a delayed admixture addition to allow sufficient hydration of the cement. This study will provide the written guidelines originally anticipated from SD92-07.

Even though SDDOT allows the use of admixtures on paving projects, many contractors and even DOT personnel are not aware of it. Those that are aware might not use admixtures simply because they have no experience with admixtures and fear that concrete might have low strength because of them.



Findings: 1. The regional questionnaire revealed that although a common cement source is shared by the six states surrounding South Dakota, no common problems exist in terms of cement/admixture compatibility. A variety of problems were reported, but these were not necessarily compatibility problems. 2. Analysis of the thirty-three concrete mixture proportions showed that no incompatibility exists between Dacotah portland cements (Type I/II and V) and the high-range water-reducing admixture (Daracem 100) and the retarder (Daratard 17) from W.R. Grace Products, Inc, when the manufacturers recommended mixing procedures are followed. 3. The mortar flow table test combination of Type V Dacotah portland cement and HRWRA (Daracem 100) exhibit an optimum time of addition of the HRWRA to be at four minutes after water and cement contact. The retarder (Daratard 17) showed no effect on the flow table test results. 4. Concrete mortar flow table results as illustrated in Figures 5.0 and 6.0 show an improved performance with delayed addition of the HRWRA (Daracem 100) and retarder (Daratard 17) admixtures. Improved flow with delayed addition, is illustrated on the vertical axis. 5. The field demonstration project displayed incompatibility between the admixtures (Daracem 100 and Daratard 17) and Dacotah cement; however, both admixtures were used at the maximum recommended dosage rate. The HRWRA (Daracem 100) concrete exhibited rapid slump loss and poor finishability with a tendency to tear and be sticky. The retarder (Daratard 17) concrete, without delayed addition, showed significant incompatibility in the form of very poor workability; with 2.5 minute delayed addition showed very good workability. The intent of the field demonstration was to verify the performance of the admixtures using maximum dosages, not to produce a user-friendly concrete. 6. As shown in Figure 13, during the field demonstration project the concrete mixture proportion using maximum dosage of HRWRA possessed a low w/c which resulted in a high early strength gain. The retarder concrete mixture exhibited a slow initial strength gain but surpassed the control mixture by the fifth day of monitoring compressive strengths. 7. As illustrated in Figure 14, the time of set test conducted during the field demonstration, on the concrete mixture proportion having a maximum dosage, exhibited a 34 hour initial set with a 2.5 minute delay prior to adding the retarder. Note: The ambient temperature was approximately 42° F and given warmer conditions the time of set would be significantly less. 8. Broad guidelines can only suggest in advance which admixture could or should be used. Written guidelines to trouble-shoot any problem encountered with concrete are not possible due to the multitude of components and conditions which can affect concrete. Experience with a particular mixture is the best avenue to success. 9. Workability or other problems can occur any time, due to many things other than incompatibility.
Title: Field Performance of Concrete Admixtures
Project Researcher: Dan Johnston, DOT
Project Manager: Jon Becker
Research Period: 5/1/1998 - 9/30/1998
Status:
Cost: $40,000.00

Problem Statement: Admixtures can improve the quality of concrete by improving workability and set times. The use of set retarders can be beneficial for long hauls (40 or more miles) and large pours. However, when cement and set retarders are incompatible, the concrete can become sticky and prematurely stiff, similar to false set. High-range water reducers are desirable for pours that are crowded with steel reinforcing or have formwork with small openings. However, the problems with incompatibility are much more severe for high-range water reducers than set retarders. The results of incompatibility between high-range water reducers and cement are premature stiffening and rapid slump loss. These two commonly reported problems are frequently associated with unacceptably low compressive strength. Study SD92-07, Evaluation of the Performance of Set Retarders and High-Range Water Reducers in Typical SDDOT Concrete Mixes identified an incompatibility observed with set retarders and high-range water reducers (HRWR) when added to cements that have low tricalcium aluminate (C3A) and tricalcium silicate (C3S) contents. Because cements with high C3A contents are susceptible to sulfate attack and South Dakota has relatively high sulfate soils, cements with higher C3S contents are more desirable.

Study SD92-07 included lab tests which determined that the primary determinant of whether a compatibility problem might arise is governed by the rate of hydration of the cement. This is directly related to the amount of C3A and C3S in the cement. Field tests were intended in SD92-07 but not performed. Study SD92-07 recommended that The Office of Research should initiate a study to conduct field testing that would use the most recently developed set retarders and high-range water reducers as well as the new Type I-II Dacotah Cement that will have 57% C3S. Dacotah Cement increased the content of C3S to 57% in June 1996. Field tests will be performed with the new cement in this study.

The researcher was not able to provide written guidelines since the attempts to use admixtures in the field were hampered by time and logistical constraints. However, based on laboratory testing the researcher made a recommendation suggesting a delayed admixture addition to allow sufficient hydration of the cement. This study will provide the written guidelines originally anticipated from SD92-07.

Even though SDDOT allows the use of admixtures on paving projects, many contractors and even DOT personnel are not aware of it. Those that are aware might not use admixtures simply because they have no experience with admixtures and fear that concrete might have low strength because of them.



Findings: 1. The regional questionnaire revealed that although a common cement source is shared by the six states surrounding South Dakota, no common problems exist in terms of cement/admixture compatibility. A variety of problems were reported, but these were not necessarily compatibility problems. 2. Analysis of the thirty-three concrete mixture proportions showed that no incompatibility exists between Dacotah portland cements (Type I/II and V) and the high-range water-reducing admixture (Daracem 100) and the retarder (Daratard 17) from W.R. Grace Products, Inc, when the manufacturers recommended mixing procedures are followed. 3. The mortar flow table test combination of Type V Dacotah portland cement and HRWRA (Daracem 100) exhibit an optimum time of addition of the HRWRA to be at four minutes after water and cement contact. The retarder (Daratard 17) showed no effect on the flow table test results. 4. Concrete mortar flow table results as illustrated in Figures 5.0 and 6.0 show an improved performance with delayed addition of the HRWRA (Daracem 100) and retarder (Daratard 17) admixtures. Improved flow with delayed addition, is illustrated on the vertical axis. 5. The field demonstration project displayed incompatibility between the admixtures (Daracem 100 and Daratard 17) and Dacotah cement; however, both admixtures were used at the maximum recommended dosage rate. The HRWRA (Daracem 100) concrete exhibited rapid slump loss and poor finishability with a tendency to tear and be sticky. The retarder (Daratard 17) concrete, without delayed addition, showed significant incompatibility in the form of very poor workability; with 2.5 minute delayed addition showed very good workability. The intent of the field demonstration was to verify the performance of the admixtures using maximum dosages, not to produce a user-friendly concrete. 6. As shown in Figure 13, during the field demonstration project the concrete mixture proportion using maximum dosage of HRWRA possessed a low w/c which resulted in a high early strength gain. The retarder concrete mixture exhibited a slow initial strength gain but surpassed the control mixture by the fifth day of monitoring compressive strengths. 7. As illustrated in Figure 14, the time of set test conducted during the field demonstration, on the concrete mixture proportion having a maximum dosage, exhibited a 34 hour initial set with a 2.5 minute delay prior to adding the retarder. Note: The ambient temperature was approximately 42° F and given warmer conditions the time of set would be significantly less. 8. Broad guidelines can only suggest in advance which admixture could or should be used. Written guidelines to trouble-shoot any problem encountered with concrete are not possible due to the multitude of components and conditions which can affect concrete. Experience with a particular mixture is the best avenue to success. 9. Workability or other problems can occur any time, due to many things other than incompatibility.

Research Objectives:
1  To verify compatibility between Dacotah Cement with higher C3S content and commonly available admixtures, including new air entraining agents as they become available.
2  To develop written guidelines for routine use of admixtures, including water reducers, high range water reducers, set retarders and set accelerators.
3  To familiarize DOT field personnel and contractors in South Dakota with the use of admixtures and their applications.

Research Tasks:
1  Meet with the technical panel to review project scope and discuss work plan.
2  Perform literature search including literature from vendors of admixture products, technical literature and interviews with surrounding states regarding their guidelines for use of admixtures. Nebraska, Minnesota and Iowa have been working with admix
3  Develop work plan including tests to be performed such as penetration, flow, air, slump, etc. Include acceptable criteria for successful tests, and summarize information from literature search and state interviews.
4  Perform lab tests using new Dacotah cement with higher C3S content with admixtures in present DOT mixes.
5  Meet with the panel to evaluate the work plan, review lab tests and literature, and select study sites.
6  Review and sample non-DOT construction projects if possible.
7  Perform pilot testing using full scale concrete ready-mix plant to test the compatability between the new cement and the admixtures.
8  Perform field tests on DOT construction projects.
9  Contact organizers of the National Quality Initiative (NQI) and of other SDDOT field meetings. The purpose would be to invite contractors and field people to the NQI and SDDOT field meetings where the use of admixtures can be discussed.
10  Write guidelines for the routine use of admixtures and recommend specification changes if necessary.
11  Prepare final report including methodology, findings, conclusions and recommendations.
12  Make an executive presentation to the Research Review Board at the conclusion of the project.

Documents Available:
SD1997_09_final_report.pdf

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