Title: Counteracting Retardation of Cement Setting By Other Admixtures with Calcium Nitrate
Author(s): H. Justnes and B. G. Petersen
Publication: Symposium Paper
Appears on pages(s): 39-50
Keywords: admixtures; calcium nitrates; retardation
High dosages of lignosulphonates for super-plasticizing are prohibited by the simultaneous setting retardation. However, the set retardation of lignosulphonates can be counteracted by calcium nitrate without destroying the rheology. Thus, such combinations can be cost-effective alternatives to super-plasticizers. The effect of different calcium nitrate dosages on 5 different lignosulphonates is documented by Fann viscosity, flow resistance and setting time on two different cement pastes. It has also been shown that calcium nitrate is capable of counteracting the effect of strong setting retarders like citric acid etc. Another application can thus be over-retardation of concrete for long transport from the concrete ready mix plant, followed by activation by adding calcium nitrate to the revolving drum of the concrete truck when arriving at, or being close to, the construction site.