Difference between revisions of "Reinforced autoclaved aerated concrete"

Latest revision as of 08:14, 12 September 2023

RAAC ceiling Panels
Department of Education (UK) report: RAAC Guide

RAAC wsll panels
Department of Education (UK) report: RAAC Guide

RAAC fragment
Department of Education (UK) report: RAAC Guide

Description

A lightweight, inexpensive, ‘bubbly’ form of concrete masonry blocks and pre-cast panels commonly used in construction between the 1950s and mid-1990s. Autoclaved Aerated Concrete (AAC) is made with fine aggregates, cement, and an expansion agent that produces concrete containing 80 percent air. The mixture is poured into molds with a steel reinforcement (RAAC) network, left to rise, then "baked' with high heat, steam and pressure to complete the chemical curing process. The initial result was a lightweight material with excellent sound and thermal insulation, and like all cement-based materials, was strong and fire resistant. However, with age, RAAC has been found to have poor load-bearing ability and weak bonding with its embedded metal reinforcement.

RAAC pre-cast panels were predominantly used in in roofs (commonly flat roofs, sometimes pitched) and occasionally in floors and walls. The panels are light-grey or white in appearance, with a smooth, paintable surface. The inside of the planks will appear bubbly, often described as looking like an Aero bar. Unlike traditional concrete, there will not be visible stones (coarse aggregate) in the panels. The panels have distinctive V-shaped grooves at at the connection points (every 600 mm). A bituminous or latex coating was sometimes added as a water barrier.

Synonyms and Related Terms

RAAC; Reinforced AAC

Risks

Cracking and spalling
Load-bearing failure
Corrosion of metal reinforcements
Movement and deflections of panels

Forms and Sizes

Typically 600 mm wide panels

Resources and Citations

Conservation Distlist: RAAC concrete thread Accessed August 2023
Department of Education (UK): RAAC: Government Identification guide
Structural-Safety: Failure of RAAC
Wikipedia: Reinforced Autoclaved Aerated Concrete Accessed August 2023

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 [[File:RAAC concrete fragment.jpg|thumb|RAAC fragment<br>Department of Education (UK) report: [https://community.culturalheritage.org/HigherLogic/System/DownloadDocumentFile.ashx?DocumentFileKey=790694ad-3963-4926-86ea-f4821752715f RAAC Guide]]]
 ==Description==
-A lightweight, ‘bubbly’ form of concrete masonry blocks and pre-cast panels commonly used in construction between the 1950s and mid-1990s. Autoclaved Aerated Concrete (AAC) was made using a fine aggregate mixed with chemicals to create gas bubbles then cast with a metal reinforcement (RAAC) network and cured with high heat. The result was a relatively weak concrete that had poor load-bearing ability and weak bonding with its embedded metal reinforcement. RAAC pre-cast panels were predominantly used in roofs (commonly flat roofs, sometimes pitched) and occasionally in floors and walls. The panels are light-grey or white in appearance, with a smooth, paintable surface. The inside of the planks will appear bubbly, often described as looking like an Aero bar. Unlike traditional concrete, there will not be visible stones (coarse aggregate) in the panels. The panels have distinctive V-shaped grooves at at the connection points (every 600 mm).  A bituminous or latex coating was sometimes added as a water barrier.
+A lightweight, inexpensive, ‘bubbly’ form of concrete masonry blocks and pre-cast panels commonly used in construction between the 1950s and mid-1990s. Autoclaved Aerated Concrete (AAC) is made with fine aggregates, cement, and an expansion agent that produces concrete containing 80 percent air. The mixture is poured into molds with a steel reinforcement (RAAC) network, left to rise, then "baked' with high heat, steam and pressure to complete the chemical curing process. The initial result was a lightweight material with excellent sound and thermal insulation, and like all cement-based materials, was strong and fire resistant.  However, with age, RAAC has been found to have poor load-bearing ability and weak bonding with its embedded metal reinforcement.
+RAAC pre-cast panels were predominantly used in in roofs (commonly flat roofs, sometimes pitched) and occasionally in floors and walls. The panels are light-grey or white in appearance, with a smooth, paintable surface. The inside of the planks will appear bubbly, often described as looking like an Aero bar. Unlike traditional concrete, there will not be visible stones (coarse aggregate) in the panels. The panels have distinctive V-shaped grooves at at the connection points (every 600 mm).  A bituminous or latex coating was sometimes added as a water barrier.
 == Synonyms and Related Terms ==