Chloride Ion Diffusion Resistance of Bulk Hydrophobic Concrete: Comparison of w/c and Dosages
2023
Utgenannt, Peter
Post-cast application of hydrophobic agents onto hardened concrete is successful at reducing external ion diffusion into cement paste, this work examines pre-cast application of hydrophobic admixtures in fresh concrete. Concretes, with water to cement ratios (w/c) 0.45 and 0.50 (CEM I; low C(3)A), were mixed. Adding alkyltrialkoxysilane or triacylglycerol admixtures ranging from 1 to 3 wt%(cem) in these concretes were evaluated. Increasing the dosage of hydrophobic admixtures decreased the compressive strength. The usage of these admixtures did not hinder the further development of the microstructure as all concretes gained strength after one year, but not in the same percentage increase as the reference concrete.Chloride ion diffusion, after exposure to 3 wt% NaCl solution at 20 degrees C for 91 days, in concretes with 1 wt%(cem) admixture showed slight reductions in diffusion rate (8-17%) compared to the reference. At 3 wt%(cem), triacylglycerol admixtures showed better hindering effects of inward chloride diffusion, this was especially evident in w/c = 0.45. Equivalent addition of alkyltrialkoxysilane-based admixtures increased the diffusion of chloride ions transferred into the cement matrix.
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