Measurement and Modeling of the Ability of Crack Fillers to Prevent Chloride Ingress into Mortar.
A common repair procedures applied to damaged concrete is to fill cracks with an organic polymer. This operation is performed to increase the service life of the concrete by removing a preferential pathway for the ingress of water, chlorides, and other deleterious species. To effectively fulfill its mission of preventing chloride ingress, the polymer must not only fully fill the macro-crack, but must also intrude the damage zone surrounding the crack perimeter. Here, the performance of two commonly employed crack fillers, one epoxy, and one methacrylate, are investigated using a combined experimental and computer modeling approach. Neutron tomography and microbeam X-ray fluorescence spectrometry (μXRF) measurements are employed on pre-cracked and chloride-exposed specimens to quantify the crack filling and chloride ingress limiting abilities, respectively, of the two polymers. A two-dimensional model of chloride transport is derived from a mass balance and solved by the finite element method. Crack images provided by μXRF are used to generate the input microstructure for the simulations. When chloride binding and a time-dependent mortar diffusivity are both included in the computer model, good agreement with the experimental results is obtained. Both crack fillers significantly reduce chloride ingress during the 21 d period of the present experiments; however, the epoxy itself contains approximately 4 % by mass chlorine. Leaching studies were performed assess the epoxy as a source of deleterious ions for initiating corrosion of the steel reinforcement in concrete structures.
Nanofibrous Patches for Repairing Cracked Surfaces
Crack repairing aims at reducing crack propagation to maintain the mechanical properties and extend the lifetime of materials. Self‐healing materials require the presence of fillers containing healing agents or a material's matrix with an intrinsic healing ability. A “patch‐and‐heal” strategy is proposed here to repair small cracks on existing materials. First, nanofibrous patches encapsulating photoinitiators or catalysts are fabricated by electrospinning. Then, small cracks are covered with flexible nanofibrous patches containing a photoinitiator or a photocatalyst. After dropping monomers on the patches, a polymer film and a foam are formed rapidly after UV‐irradiation or a thermal treatment, respectively. The “patch‐and‐heal” strategy is therefore a promising concept for repairing small cracks in a rapid and convenient manner.
Reducing Drying Shrinkage of Bridge-Deck Concrete
A number of Alabama Department of Transportation (ALDOT) engineers concur that concrete shrinkage is a primary cause of bridge-deck cracking, which is the main cause of premature deck deterioration and reduced durability in Alabama. Because shrinkage-compensating concrete (SCC) substantially reduces shrinkage and thus shrinkage cracking, the ALDOT engineers decided to examine SCC as a candidate material for bridge decks. These engineers also wanted to test new shrinkage-reducing admixtures (SRA) that reduce early drying shrinkage cracking of bridge decks. This article describes a research project conducted for ALDOT that tested the behavior and properties of fresh and hardened SCC and concrete employing SRA. The aim was to improve the durability of bridge decks in Alabama by reducing instances of early bridge-deck cracking. The research was limited to lab tests on fresh and hardened concrete for 4 mixtures.