Skip to main content

Lund University Publications

LUND UNIVERSITY LIBRARIES

Evaluation of an Embedded Wireless Relative Humidity Probe for Monitoring Concrete Drying

Åhs, Magnus LU orcid (2024) In TVBM
Abstract
In this study, wireless embedded relative humidity, RH, probes, developed by Electrotech Kalix AB, were evaluated in a laboratory setting. These RH-probes are designed to monitor the drying of concrete at construction sites in a Swedish climate. Two concrete slabs, each with a thickness of 100 mm, were fabricated, using two different concrete mixes, with water-to-cement (w/c) ratios of 0.6 and 0.4. Drying was monitored for approximately six months using these wireless RH-probes embedded in the concrete. This extended testing period is important, as the drying of a concrete slab is slow and may take longer than 6 months to reach the required RH-level.

The performance of the RH-probes during temperature fluctuations was also... (More)
In this study, wireless embedded relative humidity, RH, probes, developed by Electrotech Kalix AB, were evaluated in a laboratory setting. These RH-probes are designed to monitor the drying of concrete at construction sites in a Swedish climate. Two concrete slabs, each with a thickness of 100 mm, were fabricated, using two different concrete mixes, with water-to-cement (w/c) ratios of 0.6 and 0.4. Drying was monitored for approximately six months using these wireless RH-probes embedded in the concrete. This extended testing period is important, as the drying of a concrete slab is slow and may take longer than 6 months to reach the required RH-level.

The performance of the RH-probes during temperature fluctuations was also studied. Given that such fluctuations commonly occur at construction sites, this parameter is crucial to include in the study. Consequently, the ambient setpoint temperature varied during the test period, although it was initially constant at +20°C. After 14 days of drying at constant ambient conditions, two five- day periods were employed, separated by a five-day period at +20°C. During the first period, the ambient temperature varied daily between +20°C and +6°C, “Summer case”, and during the second period, it varied between -5°C and +5°C, ”Winter case”. Such temperature variations are plausible in a Swedish climate. Lower temperatures also occur. At temperatures below +5°C, special winter measures are usually adopted to protect newly cast concrete slabs.

The RH was successfully measured using wireless embedded RH-probes in two separate concrete specimens over a 6-month period. Calibration of RH-probes was made before embedding and after 71 and 182 days of embedment in the concrete. The data indicate that the sensors demonstrated exhibit a high degree of accuracy, with the average deviation between the generated RH and the recorded RH readings being less than 1% RH. Calibration results showed that linear regression could be applied within the tested RH range, allowing for pre-installation calibration of the RH-probes. The calibration procedure confirmed that the RH-probe exhibited a response time suitable for tracking expected RH changes. The stability (or drift) of the RH-probes over the 6-month period was minimal, with an average deviation of less than 1% RH. The temperature sensor was calibrated at 20°C, with an achieved uncertainty of ±0.04 °C. Additionally, RH was measured using Vaisala HMP110 RH-probes installed in boreholes, as well as on concrete samples extracted from the specimens at the end of the test period.

The w/c 0.4 concrete exhibited a substantial self-desiccation, and a faster drying compared with the w/c 0.6 concrete. The temperature increase of the w/c 0.4 concrete during hydration was larger, reaching around 38°C, compared with the w/c 0.6 concrete which showed a maximum temperature of 32°C. Data transmission was set at 10-minute intervals and was found to be reliable, with only a few short-duration exceptions. At this transmission rate, the RH-probes were able to transmit data continuously for six months.
(Less)
Please use this url to cite or link to this publication:
author
organization
publishing date
type
Book/Report
publication status
published
subject
in
TVBM
issue
3191
pages
76 pages
publisher
Division of Building Materials, LTH, Lund University
language
English
LU publication?
yes
id
98e16060-8b65-45c0-9f4b-12bda6d7b024
date added to LUP
2024-11-26 16:47:13
date last changed
2025-04-04 14:28:51
@techreport{98e16060-8b65-45c0-9f4b-12bda6d7b024,
  abstract     = {{In this study, wireless embedded relative humidity, RH, probes, developed by Electrotech Kalix AB, were evaluated in a laboratory setting. These RH-probes are designed to monitor the drying of concrete at construction sites in a Swedish climate. Two concrete slabs, each with a thickness of 100 mm, were fabricated, using two different concrete mixes, with water-to-cement (w/c) ratios of 0.6 and 0.4. Drying was monitored for approximately six months using these wireless RH-probes embedded in the concrete. This extended testing period is important, as the drying of a concrete slab is slow and may take longer than 6 months to reach the required RH-level.<br/><br/>The performance of the RH-probes during temperature fluctuations was also studied. Given that such fluctuations commonly occur at construction sites, this parameter is crucial to include in the study. Consequently, the ambient setpoint temperature varied during the test period, although it was initially constant at +20°C. After 14 days of drying at constant ambient conditions, two five- day periods were employed, separated by a five-day period at +20°C. During the first period, the ambient temperature varied daily between +20°C and +6°C, “Summer case”, and during the second period, it varied between -5°C and +5°C, ”Winter case”. Such temperature variations are plausible in a Swedish climate. Lower temperatures also occur. At temperatures below +5°C, special winter measures are usually adopted to protect newly cast concrete slabs.<br/><br/>The RH was successfully measured using wireless embedded RH-probes in two separate concrete specimens over a 6-month period. Calibration of RH-probes was made before embedding and after 71 and 182 days of embedment in the concrete. The data indicate that the sensors demonstrated exhibit a high degree of accuracy, with the average deviation between the generated RH and the recorded RH readings being less than 1% RH. Calibration results showed that linear regression could be applied within the tested RH range, allowing for pre-installation calibration of the RH-probes. The calibration procedure confirmed that the RH-probe exhibited a response time suitable for tracking expected RH changes. The stability (or drift) of the RH-probes over the 6-month period was minimal, with an average deviation of less than 1% RH. The temperature sensor was calibrated at 20°C, with an achieved uncertainty of ±0.04 °C. Additionally, RH was measured using Vaisala HMP110 RH-probes installed in boreholes, as well as on concrete samples extracted from the specimens at the end of the test period.<br/><br/>The w/c 0.4 concrete exhibited a substantial self-desiccation, and a faster drying compared with the w/c 0.6 concrete. The temperature increase of the w/c 0.4 concrete during hydration was larger, reaching around 38°C, compared with the w/c 0.6 concrete which showed a maximum temperature of 32°C. Data transmission was set at 10-minute intervals and was found to be reliable, with only a few short-duration exceptions. At this transmission rate, the RH-probes were able to transmit data continuously for six months. <br/>}},
  author       = {{Åhs, Magnus}},
  institution  = {{Division of Building Materials, LTH, Lund University}},
  language     = {{eng}},
  month        = {{11}},
  number       = {{3191}},
  series       = {{TVBM}},
  title        = {{Evaluation of an Embedded Wireless Relative Humidity Probe for Monitoring Concrete Drying}},
  url          = {{https://lup.lub.lu.se/search/files/200750141/Evaluation_of_an_Embedded_Wireless_Relative_Humidity_Probe_for_Monitoring_Concrete_Drying_TVBM-3191_final_draft.pdf}},
  year         = {{2024}},
}