Content deleted Content added
→Common failure modes of steel reinforced concrete: included thumbnail picture. |
m Disambiguating links to Concrete cancer (link changed to Alkali–silica reaction) using DisamAssist. |
||
Line 237:
This a reaction of [[amorphous]] [[silica]] ([[chalcedony]], [[chert]], [[siliceous]] [[limestone]]) sometimes present in the [[Construction aggregate|aggregate]]s with the [[hydroxyl]] ions (OH<sup>−</sup>) from the cement pore solution. Poorly crystallized silica (SiO<sub>2</sub>) dissolves and dissociates at high pH (12.5 - 13.5) in alkaline water. The soluble dissociated [[silicic acid]] reacts in the porewater with the [[calcium hydroxide]] ([[portlandite]]) present in the [[cement]] paste to form an expansive [[calcium silicate hydrate]] (CSH). The [[alkali–silica reaction]] (ASR) causes localised swelling responsible for [[tensile stress]] and [[Fracture|cracking]]. The conditions required for alkali silica reaction are threefold:
(1) aggregate containing an alkali-reactive constituent (amorphous silica), (2) sufficient availability of hydroxyl ions (OH<sup>−</sup>), and (3) sufficient moisture, above 75% [[relative humidity]] (RH) within the concrete.<ref>{{cite web |url=https://www.bbc.co.uk/dna/h2g2/A4014172 |title=Concrete Cancer |website=h2g2 |publisher=BBC |date=March 15, 2012 |orig-year=2005 |access-date=2009-10-14 |archive-date=2009-02-23 |archive-url=https://web.archive.org/web/20090223173400/http://www.bbc.co.uk/dna/h2g2/A4014172 |url-status=live }}</ref><ref>{{cite web |url=http://www.cementindustry.co.uk/main.asp?page=272 |title=Special Section: South West Alkali Incident |website=the cement industry |publisher=British Cement Association |date=4 January 2006 |access-date=2006-11-26 |url-status=dead |archive-url=https://web.archive.org/web/20061029112122/http://www.cementindustry.co.uk/main.asp?page=272 |archive-date=October 29, 2006 }}</ref> This phenomenon is sometimes popularly referred to as "[[Alkali–silica reaction|concrete cancer]]". This reaction occurs independently of the presence of rebars; massive concrete structures such as [[dam]]s can be affected.
===Conversion of high alumina cement===
| |||