Saffron Walden Library has temporarily closed after RAAC was potentially identified in a recent survey.
According to Essex Library Service, the closure is expected to last one week while further surveys are conducted and additional mitigations are added.
The Essex Record Office branch and the Gibson Library will also be unavailable.
A spokesperson for Essex County Council said: "The closure is expected to last one week while further surveys are conducted, and additional mitigations added.
"Reviews are currently taking place of all our properties, including our libraries, and we will act accordingly if any mitigation is required.
"Updates on Saffron Walden Library will be posted on the Library Service social media channels and signs will be placed at the front of the building."
RAAC (reinforced autoclaved aerated concrete) is a form of lightweight concrete used to form panels or planks.
It has recently caused concern in the UK due to structural issues, having been used in a number of public buildings such as schools and hospitals.
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