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.
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
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.