Alkaline hydrogels as ion‐conducting coupling material for electrochemical chloride extraction

Abstract

One method to rehabilitate chloride-contaminated reinforced concrete structures is electrochemical chloride extraction, by which chloride ions are extracted from the pore system of the concrete using an externally applied voltage. Although many factors influence the efficacy of electrochemical chloride extraction, a number of these, such as the concrete cover and the chloride profile, are predefined by the structure. One factor with major influence that can be improved is the coupling material. In this contribution, we present a suitable coupling material in the form of a highly alkaline hydrogel, with which the applied voltage can be reduced from 40-50 to 1 V under laboratory conditions. The reduction is due to the high conductivity of the gel and its excellent electrolytic contact with concrete. In a field test on chloride-infested car-park columns, more than 95% of the chloride could be extracted with 2-3 cycles, each comprising of 21 days of extraction and 7 days of rest. During the entire treatement, the gel did not require any attending to, such as replacing evaporated moisture.

Multivalent Allylammonium-Based Cross-Linkers for the Synthesis of Homogeneous, Highly Swelling Diallyldimethylammonium Chloride Hydrogels

“…1 H-and 13 C-NMR spectra of copolymer gels containing TAAB (1a) swollen in D 2 O were not decisive, as these vinyl signals partially overlap with the broad signals of the DADMA + backbone, and the cross-linker concentrations are generally rather small (Figures S17 and S18 in the Supporting Information). Double-bond signals found in the 13 C-NMR spectra could be addressed to the unreacted DADMAC monomer. However, the TAAB homopolymer clearly showed double-bond signals in the 1 H-NMR spectrum (Figure S19 in the Supporting Information), which are not identical with the TAAB monomer.…”

“…From that, the real part Z real can be calculated (Figure 6). 13 C-NMR spectra could be addressed to the unreacted DADMAC monomer. However, the TAAB homopolymer clearly showed double-bond signals in the 1 H-NMR spectrum (Figure S19 in the Supporting Information), which are not identical with the TAAB monomer.…”

“…1 H-NMR and 13 C-NMR spectra were recorded on a Mercury 400 spectrometer (Varian, Palo Alto, CA, USA). Chemical shifts were calculated using the HDO signal at 4.64 ppm or the CDCL 3 signal at 7.26 ppm as a reference.…”

“…This protects the reinforcement from further corrosion. A similar hydrogel was recently used as coupling material for electrochemical chloride extraction [ 13 ], an excellent method to counteract chloride-induced steel corrosion. However, the use of BIS as cross-linker in these allyl-based systems can be precarious.…”

Hydrolytic Stability of Crosslinked, Highly Alkaline Diallyldimethylammonium Hydroxide Hydrogels

“…Hydrogels that are particularly suitable for the construction industry can be obtained by using cationic networks with hydroxide as a counterion; these have recently been realized based on diallyldimethylammonium hydroxide (DADMAOH) as a monomer and N , N ′-methylenebisacrylamide (BIS) as a crosslinker. Such highly alkaline polymer networks were not only shown to be valuable materials in the rehabilitation of steel-reinforced concrete by exchanging carbonate ions in aged concrete with hydroxide ions, thereby restoring the high pH value necessary for preventing steel corrosion [ 8 ], but also as a coupling material for electrochemical chloride extraction [ 9 ]. A similar hydrogel was recently used to seal water-bearing cracks, while at the same time restoring the protective passive-layer on the exposed parts of steel rebars [ 10 ].…”