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Florissant Monitoring

Preliminary temperature data collected from P47.

Exterior ambient temperature (red)
embedded temp. ~8” (green).

At the location highlighted (by the red vertical line), a temperature range of 30 deg F (11 deg C) is present at 2:30PM 02/09/2018. This suggests a significant thermal lag of the stone between the interior and exterior surface during the winter.
Environmental Monitoring

Theoretical freeze-thaw nomogram compiled from ambient temperature data collected at FLFO stump p47 between 9/20/2017 and 6/5/2018.
Two identical on-site weather monitoring systems have been installed at FLFO since 2017, each capable of collecting data related to wind speed and direction, ambient temperature and relative humidity, solar radiation, and liquid precipitation. The premise for the installation of these systems is to collect relevant data needed to characterize the stumps’ micro-climatic behavior at FLFO and provide the unique information necessary to make informed treatment and conservation decisions for the petrified stumps. The environmental data collected is intended to supplement and not replace local and regional weather data necessary for macro-scale analysis of climate-related phenomena.
The research objectives for the ongoing environmental monitoring system are:

  1.  Establish baseline environmental conditions to which the petrified stumps are exposed seasonally.
  2. Identify a hierarchy of vulnerability related exposure end environmental conditions.
  3. Correlate active deterioration with these environmental factors.
  4. Evaluate the impact of the shelters on the environmental performance and deterioration mechanisms of the petrified stumps.

Embedded Monitoring
An embedded monitoring system was designed and installed to validate preliminary hypotheses seeking to explain the deterioration mechanisms of the petrified stumps at FLFO. Characterizing the hygrothermal performance of the stone is critical. 
Four type-k thermocouples were embedded into P47 at varying depths and orientations to collect temperature data. This data aims to quantify the contributing effects of thermal variables such as solar radiation gains as well as the thermal response of the stone to these factors. Additionally, soil moisture sensors were installed in the soil atop the stumps and at grade adjacent to the stump.
Lastly, as part of ongoing CAC research that is exploring applications for low-cost, passive embedded moisture monitoring, a single passive RFID moisture tag was installed in P47. Given the nature of this technology, and leveraging its low-cost, passive, and sacrificial nature, the installation of the tag was integrated with the pilot epoxy consolidation campaign applied to this stump. The tag was laminated in plastic to improve durability, and it was installed behind a loose piece of petrified wood on P47. This installation will evaluate the methodology in situ as well as the performance of the applied treatments without visually intrusive cabling.

Time-Lapse Photography
In parallel to the embedded monitoring efforts, a time-lapse photography system was installed adjacent to P47 to capture macro-climatic factors, such as snow deposition patterns and moisture uptake and wetting, as well as to detect changes to the fabric of the stump itself. The system has exceeded expectation, and the preliminary imagery collected clearly demonstrates the catalog of environmental impacts on exposed (unsheltered) stumps such as P47. Even under relatively warmer conditions, where the ambient diurnal temperature is well above freezing, such as in later October, snow can linger in shaded areas of the stump depression and within recesses of the stump itself in excess of 24 hours (Table 1). This condition has significant implications for differential moisture deposition in addition to the perpetual sources such as rising damp, falling damp, and lateral moisture ingress.

Diurnal min-max
Diurnal minimum and maximum ambient external temperatures present at FLFO, compared over a season between September 2018 and August 2019.

Preliminary analysis of embedded temperature data collected over the course of 269 days, between 9/20/2017 and 6/5/2018 from P47 reveals a variety of notable observations relevant to the conditions and performance of the petrified stumps. First, and most immediately apparent, is the thermal range to which the stump is subjected to at various depths (Figure 1). A maximum ambient temperature swing, with a range of 30.52 deg F (11 deg C) was observed on October 17, 2017. Secondly, the data collected was used to calculate the number of theoretical freeze-thaw days unsheltered stumps were subjected to. A Freeze-thaw day is a 24-hour period during which the conditions for at least one freeze-thaw event were present in the ambient environment. Theoretical freeze-thaw events are a function of mean daily temperature and mean diurnal temperature range (Figure 2) (Wexler, 1982). Unsheltered stumps were exposed to theoretical freeze-thaw conditions for approximately 80% (214 days) of the observational period. Once enough comparable data has been collected for the sheltered stump, P31, a freeze-thaw comparison should be calculated to evaluate the actual environmental performance of the shelters.
Compared to theoretical conditions, it is possible to ground-truth these observations using recorded diurnal ambient temperature minimums and maximums rather than calculated means (Figure 3). That is, where sufficient moisture is present, freeze-thaw cycling does occur on days during which the minimum recorded temperature falls below 0 deg C (32 deg F) and the maximum recorded temperature is above 0 deg C. At FLFO, preliminary data suggests 360 individual freeze-thaw cycles occurred during the observation period.
snowfall progression
Table 1 Progression of a snowfall event on October 30, 2017. (left) 10/30 8am. (center) 10/31 10am. (right) 10/31 12pm.
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