Abstract:
The stability of a suspension grout is determined by using either a column bleed test (low-pressure applications and higher w/c rations) or the API filter press (high-pressure grouting and lower w/c ratios). In a column bleed test, the amount of bleed, the amount of clear water that appears at the top of a grout column after a waiting time of two hours, determines whether a grout is “ unstable” or “ stable” , based on a limiting bleed percentage. The test is very simple to run and doesn’ t require any specialized equipment, which makes it widely available for field implementation, both for grout mix design and batch-to-batch quality control. However, the method doesn’ t account for how the bleed changes over time and, more importantly, how the concentration of the suspension vary along the height of the column. This paper presents a new, more comprehensive method of analyzing changes in grout concentration along the height of a bleed column over time using image analysis techniques. The image analysis tests allow for the collection of significantly more data with little to no added effort. Microfine cement grouts with different w/c ratios and superplasticizer percentages were tested in this study. The image analysis results were able to capture the change in grout concentration long the height of the column and track its progression over time. The concentration distribution for different grout mixes varied from having uniform suspension concentration throughout the height to having higher/lower concentrations at the bottom/top, respectively, with a gradually changing concentration in between. Manual pipette tests were used to verify the image analysis results. The measured changed in grout concentration along the column height indicate that the use of the clear water bleed as a measure for grout stability can be misleading, particularly in the presence of superplasticizers/dispersing agents. Keywords: Internal stability, microfine cement, bleed column test, Image analysis