THE CARBONATION OF RECYCLED CONCRETE AGGREGATE AFFECTED BY ALKALI-SILICA REACTION

Author(s): M. Thomas, S. Monkman
Paper category: Proceedings
Book title: CO2STO2019 - International Workshop CO2 Storage in Concrete
Editor(s): Assia Djerbi, Othman Omikrine-Metalssi, Teddy Fen-Chong
ISBN:
e-ISBN: 978-2-35158-232-9
Publisher: RILEM Publications SARL
Publication year: 2019
Pages: 138-145
Total Pages: 08
Language : English

Abstract: Recycled concrete aggregate (RCA) produced by crushing concrete from structures affected
by alkali-silica reaction (ASR) can induce expansion and damage in new concrete produced
using the RCA even when preventive measures are implemented to control ASR. The damage
can be prevented by carbonating the RCA prior to its use in new concrete. Laboratory data are
presented from a study using RCA produced from crushing mortar containing a highly-reactive
(Jobe) sand and a high-alkali cement. The mortar was crushed to produce coarse aggregate
in the size range from 5 to 20 mm. A portion of the RCA was carbonated prior to use. Concrete
samples were then produced with the carbonated RCA (RJC-CO2) and non-carbonated RCA
(RJC). The binder used in the concrete was a blend of 80% low-alkali cement plus 20% fly
ash. This blended cement has been shown to be effective in preventing ASR expansion when
used with the Jobe aggregate. Concrete prisms containing untreated RJC expanded
significantly (0.163% in 2 years) when stored over water in sealed containers at 38°C whereas
concrete produced with RJC-CO2 did not (<0.040% at 2 years). The mechanism is discussed.
In the case of the untreated RJC there is a sufficient concentration of alkali hydroxides within
the mortar portion of the RJC to fuel ASR with the remaining reactive silica in the sand particles.
However, in the carbonated RJC-CO2 the concentration of alkali hydroxides is significantly
reduced by the carbonation process and this prevents ASR expansion despite the abundance
of reactive silica present in the recycled aggregate particles.

Online publication : 2019
Publication type : full_text
Public price (Euros) : 0.00