EVALUATION OF CURING COMPOUND APPLICATION TIME ON THE SURFACE DURABILITY OF CONCRETE
Helgeson, Samuel Robert
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The Wisconsin Department of Transportation WISDOT) has sponsored investigations on the causes of freeze-thaw scaling damage on Portland Cement Concrete (PCC) roadways within the state that are coated with membrane forming curing compounds (MFCCs). Several studies have identified excess bleed water at the time of curing compound application as a potential cause of reduced scaling resistance of concrete pavements. Increasing the delay between concrete finishing steps and MFC application should serve to lessen scaling damage. However, there is currently no literature that sought to quantify a possible linkage between MFCC application time and the scaling resistance. The primary goal of this research was to evaluate the influence of MFCC application time on the freeze-thaw scaling damage resistance of roadway concrete made with materials native to Wisconsin. A factorial experiment was designed to probe the effect of MFCC application time on scaling damage as measured by ASTM C672. Three emulsion-based curing compounds, Linseed Oil, Wax, and Poly-alpha-methyl-styrene (PAMS) were evaluated at three application times on concrete specimens prepared with one of two sources of coarse aggregate and one of three cementitious materials. An Acrylic solvent-based sealing compound was evaluated at two application times with respect to concrete scaling resistance. Untreated specimens from each mix type were cured in a wet room and tested as controls. A secondary goal of this project was to evaluate a new method for determining the presence of bleed water on a concrete surface by constructing a device to detect changes in the relative humidity of the air above the concrete surface over time to more reliably determine the cessation of the bleeding than current methods. To achieve this goal, a device was built and its operational capability was tested during the study. ii Concrete mixes were designed and specimens were prepared according to WISDOT procedures to provide a good representation of the pavements within Wisconsin. Freeze-thaw scaling damage testing was performed on all specimens and data was recorded following the appropriate testing standard. Properties such as fresh concrete slump, air content, 28-day compressive strength, and curing compound application rates were measured and recorded to ensure compliance with WISDOT standards. Results in this study indicate that the influence of MFCC application time on the scaling resistance of concrete is dependent upon the compound chosen. The Linseed Oil and Acrylic formulations displayed significantly increased scaling resistance with an increase in application time. The Wax and PAMS formulations did not display significant increases in scaling resistance with an increase in application time. Results from the untreated wet room cured specimens indicate that curing compounds do not promote scaling resistance levels that compare favorably to the humidity control method wet room curing. Scaling resistance was also found to be dependent upon composition of the concrete, especially with respect to the coarse aggregate and cementitious material choice. Elevated levels of ambient relative humidity at the time of specimen manufacture appeared to decrease the scaling resistance, regardless of application time. The device was found not to be reliable for monitoring the presence of bleed water in its current design. Analysis of the data collected by the device showed that future modifications could be made improve its operational capability.