New Publication:Innovative Hydrogel Solutions for Sustainable Concrete Re-Alkalisation
A recent publication in Soft Matter (Issue 40, 2018) introduces a novel highly alkaline hydrogel designed to restore the alkaline buffer capacity in carbonated cementitious materials. This property is essential for preventing steel corrosion in reinforced concrete.
The hydrogel is based on a copolymer of diallyldimethylammonium hydroxide (DADMAOH) and methacrylamide. The addition of methacrylamide as a co-neutral monomer allows for extensive tunability of the gel’s rheological properties. The viscosity increases a thousandfold—from 0.35 Pa s to over 350 Pa s—when 10 mol% methacrylamide is used, showcasing the material’s adaptability.
- Ion Exchange: Experiments demonstrated efficient diffusion of hydroxide ions from the hydrogel into carbonated material, accompanied by the release of carbonate ions.
- Re-Alkalisation: The gel’s effectiveness was confirmed through the phenolphthalein test (DIN EN 14630:2007-01) and IR spectroscopy.
- Universal Applicability: The gel can be applied both for modern infrastructure maintenance and the preservation of historical monuments.
Jung, A.; Weichold, O.
Preparation and characterisation of highly alkaline hydrogels for the re-alkalisation of carbonated cementitious materials
Soft Matter 2018, 14 (40), 8105–8111. https://doi.org/10.1039/c8sm01158c.
New publication
Corrosion current drives corrosion sensor
New corrosion sensor for reinforced concrete requires no external power source. Steel corrosion causes enormous economic damage every year, which could be reduced by installing suitable monitoring devices. These should be simple, reliable and durable and should not require any maintenance or servicing. The present electrochromic device is designed to use the macrocell current of an active, chloride-induced corrosion element as an energy source to trigger a colour change. In this way, the system remains inactive until corrosion occurs. The device consists of diheptyl viologen in a liquid polymer electrolyte of LiClO4 and poly(ethylene glycol). The addition of viologen lowers the resistance but does not cause any further changes in the electrochemical properties of the polymer electrolyte. The impedance spectra indicate that ion transport rather than capacitive effects dominate the electrochemical properties. Experiments with direct current in the μA range show electrochromic switching times of several minutes, which is sufficient for the intended monitoring application.
T. Juraschek, O. Weichold
Development of an electrochromic device triggered by the macrocell current in chloride‐induced corrosion of steel‐reinforced concrete
J. Phys. Org. Chem. 2017, e3739. https://doi.org/10.1002/poc.3739
New Publication:Water-Repellent Layers Unveiled: Nondestructive Analysis with NMR
The recent study by Prof. Dr. Oliver Weichold and Udo Antons explores the use of single-sided nuclear magnetic resonance (NMR) as a nondestructive method to analyze hydrophobing agents on concrete. This technique examines the ingress behavior of 𝑛-octyltriethoxysilane and 𝑖-butyltriethoxysilane and the properties of the resulting water-repellent layers.
Remarkably, the study discovered that targeted blending and cross-linking of PEO- and PPO-based polyesters can create synergistic effects. A 1:1 blend of short-chain PPO and long-chain PEO exhibited a resistivity five times lower than pure PEO and three times lower than pure PPO. These effects are attributed to enhanced chain mobility and intrachain hopping mechanisms, which are amplified by the cross-linking process.
Beyond improved ion conductivity, these networks offer rubber-like elasticity and high water tolerance, making them suitable for diverse applications, particularly under mechanical stress, in atmospheric conditions, or even in aqueous environments where standard ion-conducting systems often fail.
Weichold, O.; Antons, U.C.
Assessing the Performance of Hydrophobing Agents on Concrete Using Nondestructive Single-Sided Nuclear Magnetic Resonance
Journal Of Infrastructure Systems 2017, 23 (4). https://doi.org/10.1061/(ASCE)IS.1943-555X.0000366
New Publication:Silane-Based Water Repellents
Together with co-author J. P. Lecomte, Prof. Dr. Oliver Weichold contributed the chapter Silane-based Water Repellents for Inorganic Construction Materials in the book Silicone Dispersions (2016).
This chapter explores the use of silane-based water repellents specifically designed to protect inorganic construction materials such as concrete and cement. Moisture and its resulting damages pose significant challenges to the durability of structures. Silanes and siloxanes, as organic compounds, counteract this issue by penetrating deeply into porous materials and creating hydrophobic properties.
The authors demonstrate how these technologies help mitigate damage from freeze-thaw cycles, chemical attacks, or reinforcement steel corrosion without compromising the breathability of the materials. In light of global challenges such as limited raw material availability and increasing sustainability requirements, extending the service life of structures is of paramount importance.
Weichold, O.; Lecomte, J.P.
Silane-Based Water Repellents for Inorganic Construction Materials
CRC Press: Boca Raton, FL, USA, 2016;Volume 10 10.1201/9781315371177-11
New publication
Structure formation in oligomers
How can the thermal stability and crystallinity of oligomers be controlled? Four members of a homologous series of chlorinated poly(vinyl ester) oligomers from poly(vinyl acetate) to poly(vinyl stearate) with degrees of polymerisation of 10 and 20 were prepared by telomerisation with carbon tetrachloride. All oligomers are thermally degraded in two main steps, whereby HCl and side chains are lost before the backbone is degraded. The polymers with short side chains, up to poly(vinyl octanoate), are amorphous and show internal plastification, while those with long side chains are semi-crystalline due to side chain crystallisation. The glass transition and melting temperatures as well as the initial decomposition temperature are more strongly influenced by the side chain length than by the degree of polymerisation. Thermal stability is improved when both the size and the number of side chains increase, but only long side chains lead to a significant increase in decomposition resistance.
D. Heinze, T. Mang, C. Popescu, O. Weichold
Effect of side chain length and degree of polymerization on thedecomposition and crystallization behaviour of chlorinated poly(vinylester) oligomers
Thermochimica Acta 2016, 637, 143-153. http://dx.doi.org/10.1016/j.tca.2016.05.015
Cold as Ice – gently dry
With Coolsafe Pro freeze drying, we can gently dry sensitive materials using an established process. The frozen water sublimates directly into the vapour phase. The process enables efficient, resource-saving drying, which increases the quality and shelf life of the materials. We use it to dry lignified starting materials, reaction products from aqueous syntheses or gels.
Tg, Tm, OMG – Understanding polymers
With every change in a system (e.g. phase transformation, chemical reactions), heat is either absorbed or released. This can be analysed quantitatively using differential scanning calorimetry. We can use a DSC 204 F1 Phoenix from Netzsch to measure cooling and heating processes from approx. -50 to 600 °C. The cooling and heating rates can be set from 0.1 to 100 K•min−1 .
New publication
Poly(vinyl acetate) plasticises itself
No additional plasticiser required. Poly(vinyl acetate), PVAc, with a degree of polymerisation Xn≈10 was produced by free radical chain transfer polymerisation with carbon tetrachloride and used as an oligomeric plasticiser for commercial PVAc. After H/Cl exchange at the chain ends, the product exhibits high thermal stability and excellent melt compounding properties. Blends of oligomeric and commercial PVAc show simple glass transition temperatures, which decrease with higher oligomer content, and exhibit small negative deviations from Fox’s linear additivity rule. This suggests that plasticisation and miscibility are mainly due to entropic effects. Injection moulded thick specimens show ductile behaviour at oligomer contents >10 wt%, while sheets with a thickness of 0.2-0.5 mm appear flexible already at 7.5 wt%. The oxygen permeability coefficients are an order of magnitude lower than those of low-density polyethylene. Due to the sum of their properties, the plasticised sheets represent a promising alternative for the production of barrier materials.
D. Heinze, T. Mang, K. Peter, M. Möller, O. Weichold
Synthesis of Low Molecular Weight Poly(vinyl acetate) and Its Application as Plasticizer
J. Appl. Polym. Sci. 2014, 40226. https://doi.org/10.1002/APP.40226
