Fact Sheet: Isolation and Quarantine, May 1, 2009

To contain the spread of a contagious illness, public health authorities rely on many strategies. Two of these strategies are isolation and quarantine. Both are common practices in public health, and both aim to control exposure to infected or potentially infected persons. Both may be undertaken voluntarily or required by public health authorities. The two strategies differ in that isolation applies to persons who are known to have an illness, and quarantine applies to those who have been exposed to a person who is ill but who may or may not become ill.

Vibration Study for Consolidation of Portland Cement Concrete, MLR-95-4, 1999

The Iowa Department of Transportation has noticed an increase in the occurrence of excessively vibrated portland cement concrete (PCC) pavements. The overconsolidation of PCC pavements can be observed in several sections of PCC highways across the state of Iowa. Also, excessive vibration is believed to be a factor in the premature deterioration of several pavements in Iowa. To address the problem of excessive vibration, a research project was conducted to document the vibratory practices of PCC slipform paving in Iowa and determine the effect of vibration on the air content of pavement. The primary factors studied were paver speed, vibrator frequency, and air content relative to the location of the vibrator. The study concluded that the Iowa Department of Transportation specification of 5000 and 8000 vibrations per minute (vpm) for slipform pavers is effective for normal paver speeds observed on the three test paving projects. Excessive vibration was clearly identified on one project where a vibrator frequency was found to be 12,000 vpm. When the paver speed was reduced to half the normal speed, hard air contents indicated that excessive vibration was beginning to occur in the localized area immediately surrounding the vibrator at a frequency of 8000 vpm. Analysis of variance testing indicated many variables and interactions to be significant at a 95% confidence level; however, the variables and interactions that were found to be significant varied from project to project. This affirms the complexity of the process for consolidating PCC.

Vibration Study for Consolidation of Portland Cement Concrete, Preprint, MLR-95-4, 1997

The Iowa Department of Transportation has discovered an increase in the occurrence of excessively vibrated portland cement concrete (PCC) pavements. The overconsolidation of PCC pavements has been observed in several projects across the state. Overconsolidation is also believed to be a factor in acceleration of premature deterioration of at least two pavement projects in Iowa. To address the problem, a research project in 1995 documented the vibratory practices of PCC slipform paving in Iowa in order to determine the effect of vibration on consolidation and air content of pavement. Paver speed, vibrator frequency, and air content relative to the location of the vibrator were studied. The study concluded that the Iowa Department of Transportation specification of 5,000 to 8,000 vibrations per minute (vpm) for slipform pavers is effective for normal paver speeds on the three projects that were examined. Excessive vibration was clearly identified on one project where a vibrator frequency of 12,000 vpm was discovered. When the paver speed was reduced to half the normal speed, hard air contents indicate that excessive vibration was beginning to occur in the localized area immediately surrounding the vibrator at a frequency of 8,000 vpm. The study also indicates that the radius of influence of the vibrators is smaller than has been claimed.