Counteracting retardation of plasticizers by calcium nitrate

Title: Counteracting retardation of plasticizers by calcium nitrate
Author(s): H. Justnes, K. De Weerdt
Paper category : conference
Book title: 2nd International RILEM Symposium on Advances in Concrete through Science and Engineering
Editor(s): J. Marchand, B. Bissonnette, R. Gagné, M. Jolin and F. Paradis
Print-ISBN: 2-35158-003-6
e-ISBN: 2351580028
Publisher: RILEM Publications SARL
Publication year: 2006
Nb references: 4
Language: English

Abstract: Plasticizers are used to increase flow for cementitious materials at equal water-to-cement ratio, but will also to a variable extent retard cement setting as a side effect. The objective was to find an accelerator that at least partially would counteract this retardation without negatively affecting the rheology too much.
Calcium and sodium lignosulphonate (CLS and NLS), as well as polyether grafted polyacrylate (PA), were added in different dosages to plasticize two different Portland cement pastes. The setting accelerator calcium nitrate (CN) was used to counteract retardation. Rheological parameters recorded were flow resistance taken as the integral of part of the flow curve (at low shear rates relevant for pouring concrete) and static gel strength after 10 s and 10 min (difference being gelling rate). The hydration heat rate as function of time was recorded in an isothermal calorimeter at 20?C and used to evaluate plasticizer retardation.
The CLS and NLS retarded the cement setting more than the PA, but CN addition was able to substantially counteract the retardation. On the other hand, increasing dosages of CN lead to some increased flow resistance and static gel strength. However, flow resistance of pastes with plasticizer/accelerator combinations was still less than paste without plasticizers.
The most interesting combinations of NLS and PA with and without CN were also tested in mortar. Mortar strength was recorded at 5 and 20?C at 2 and 1 day, respectively, as well as at 28 days. Strength data indicated that even PA induces a substantial retardation at 5?C and that CN was able to counteract some of that (2 days compressive strength more than doubled).

Online publication: 2006-08-02
Classification: 3.2 Theme 2: From Fresh to Hardened Concrete
Publication type : full_text
Public price (Euros): 0.00
doi: 10.1617/2351580028.066