Title: Early-Age Shrinkage Of Cement Paste Containing Humic Substances as that from River Dredging Sediments in France
Author(s): Hamza Beddaa, Amor Ben Fraj, Francis Lavergne and Jean Michel Torrenti
Publication: Symposium Paper
Appears on pages(s): 23-39
Keywords: autogenous shrinkage, chemical shrinkage, dredging sediments, humic substances
Dredged river sediments can be considered as a promising alternative for conventional aggregates in concrete. However, the effect of sediments’ properties and particularly their organic matter (OM) content on those of the concrete have to be assessed. Indeed, the organic weight fraction of organic matter in sandy sediments dredged in the Seine watershed is highly variable as it varies from 0 wt% to 10 wt% of the dry matter. This research aims at assessing the effects of humic substances (HS) on the early age behavior of a cement paste. HS are organic compounds resulting from the chemical, physical and microbiological transformation of animals and plants residues and which are also the most representative component of sediments organic matter. A soluble HS, potassium humate, is added as partial substitution of cement; 0.2 wt%, 0.5 wt% and 1 wt%. The results indicate that HS causes a delay of both chemical and autogenous shrinkages by retarding the hydration process. In addition, the chemical shrinkage amplitude is not significantly affected by the presence of HS in the mixture, while the autogenous shrinkage is decreased especially for the high w/b (water/binder; binder=cement+HS) ratios, due to bleeding. Furthermore, for high rates (2% and 3%), this bleeding could generate a delay of setting between the top and the bottom of the sample causing cracks due to a restrained shrinkage in the upper part of the sample.