Effect of alkali on the hydration of blast furnace slag in the presence of calcium hydroxide

Title: Effect of alkali on the hydration of blast furnace slag in the presence of calcium hydroxide
Author(s): J. J. Biernacki, R. Dirrix, K. Meenakshisundaram, W. Hansen
Paper category : conference
Book title: International RILEM Symposium on Concrete Science and Engineering: A Tribute to Arnon Bentur
Editor(s): J. Weiss, K. Kovler, J. Marchand, and S. Mindess
Print-ISBN: None
e-ISBN: 2912143926
Publisher: RILEM Publications SARL
Publication year: 2004
Nb references: 11
Language: English

Abstract: Model systems containing blast furnace slag (BFS) and calcium hydroxide (CH) were used to gain insights into the hydration of BFS and the interaction between BFS and CH. The effect of alkali, sodium hydroxide (NaOH) and water glass (sodium silicate), on hydration rate and product stoichiometry was studied. Samples were hydrated at 30, 40 and 50 oC for between 1 and 32 d. The effect of alkali was studied by comparing samples hydrated with pure water, .1, 1 and 2 M sodium hydroxide and 3 wt% waterglass (3 wt% Na2O equivalents on a total solids basis). Thermal analysis was used to determine the extent of conversion of the CH and quantitative energy dispersive spectroscopy (EDS) was used to determine the chemical composition of various phases. The presence of NaOH was found to retard (slow) early age hydration rates. A number of possible mechanisms are considered and explored including suppression of Ca+2 concentration due to the common ion effect, modification of the Ca/Si ratio in the hydration product and changes in the water content of the hydrate gel. Evidence in support of all three mechanisms was found although some appear to be time dependent. At early ages the Ca/Si ratio appears to vary with solution molarity, while at later ages it does not. TGA/DTG analysis suggest that the gel phase may evolve differently in the presence of strong alkali concentrations as evident by the thermal stability of the apparent gel. Gel formed in strong alkali solution also appears to imbibe more water.

Online publication: 2004-03-25
Classification: Microstructure
Publication type : full_text
Public price (Euros): 0.00
doi: 10.1617/2912143926.008