Search

Impressed current cathodic protection (ICCP) is an effective corrosion protection and prevention technique for reinforced concrete structures served in chloride-contaminated environment. The acidification damage in the external anode mortar caused by the anodic reactions significantly influences the efficiency of ICCP for reinforced concrete. Therefore, improving the acidification resistance of the external anode mortar is of great importance for the successful application of ICCP treatment. In this study, a novel type of lightweight functional aggregates was proposed to mitigate the acidification damage in the external anode mortar. The influence of the prepared lightweight functional aggregates both on the electrochemical performance of the primary anode and morphology, mineral compositions and microstructure of the secondary mortar were investigated. The results indicated that the lightweight aggregates efficiently mitigated the damage of MMO coating on the primary anode surface, thus maintaining the high stability and catalytic activity of the primary anode. Severe acidification damage happened in the mortar matrix within a distance of 300 μm from the primary anode; beyond this region, the acidification damage was mainly propagated along the interfacial transition zone around the aggregates. Because the lightweight functional aggregates maintained the high alkalinity in the secondary mortar, the acidification damage both in the vicinity of the primary anode and ITZ around aggregates was significantly halted. Therefore, the prepared lightweight functional aggregates can be potentially used for preparing the high performance external anode mortar, further improving the stability and efficiency of ICCP treatment and durability of reinforced concrete structures.

Non-uniform stresses, strains and microcracking of the concretes with three coarse aggregate sizes (5–10 mm, 10–16 mm, 16–20 mm) dried under 40% relative humidity (RH) for 60 days were quantified using digital image correlation and lattice fracture modelling. The influencing mechanism of coarse aggregate size on the drying-induced microcracking of concrete was clarified: (1) As the coarse aggregate size decreases, propagation paths of microcracking are increased, which increase the number of small microcracks and release the drying shrinkage force from mortar phase. (2) Tensile stress shells surrounding the coarse aggregates become thinner, thereby decreasing the area of large microcracks. As the coarse aggregate size decreased from 16-20 mm to 5–10 mm, the average thickness of tensile stress shells decreased from 2.13 mm to 1.09 mm at the beginning of drying, and the area of the microcracks >5 μm in width decreased from 796.6 mm2/m2 to 340.2 mm2/m2 at 60 days since drying., Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public., Materials and Environment

In this study, a new concept on self healing of cracks that the ingressive ions in the crack is chemically bound to improve the self-healing efficiency was proposed for cracked cementitious materials in a marine environment. Thermodynamic modeling was performed to determine the appropriate masses and ratio of Ca2+ and Al3+ provided by chemical agents for a good efficiency of self-healing and chemical binding of Cl-, SO4 2-, and Mg2+ ions from sea water. It was found that when CaO-NaAlO2 and CaO-metakaolin are used as self-healing agents, Friedel’s salt, kuzel’s salt, ettringite and hydrotalcite can be formed and, thus, Cl-, SO4 2- and Mg2+ from sea water are chemically bound. Moreover, the volume of phase assemblages becomes larger, which facilitates the self-healing of cracks. For a ratio of 0.3 between the mass of self-healing agent to the mass of sea water, the removal efficiency of Clions for CaO-NaAlO2 agent with a Ca/Al of 5 reaches the maximum value, i.e. 87%, while for CaO-metakaolin agent the removal efficiency of Cl- ions reaches the maximum when the Ca/Al is 3. The chemical binding of Mg2+ and SO4 2- ions is hardly influenced by Ca/Al when it is larger than 2 and the removal efficiency approximates 100%.

New self-healing agents that can chemically bind seawater ions invading cracked cementitious materials were proposed. The potential of self-healing and binding of seawater ions were investigated by thermodynamic modeling. It was found that CaO-NaAlO2 and CaO-metakaolin agents can have Cl−, SO42− and Mg2+ chemically bound by reacting with sea water to form Friedel's salt, Kuzel's salt, ettringite and hydrotalcite. The removal of Cl− from seawater firstly increased and then decreased with the increase of Ca/Al molar ratio in both agents, while the removal of Mg2+ and SO42− were hardly influenced and approximated 100%. Because NaAlO2 dissolves and releases Al(OH)4− rapidly, precipitates binding Cl−, SO42− and Mg2+ were formed fast. In comparison, the reaction of metakaolin binding aggressive ions occurred after 3 days. Because of the faster reaction and the capacity to make [Cl−]/[OH−] lower in the solution, CaO-NaAlO2 would be more efficient for self-healing and mitigating reinforcement corrossion than CaO-metakaolin., Accepted Author Manuscript, Materials and Environment

Concrete generally deforms and cracks in a non-uniform manner under drying-induced stress. This study used the lattice fracture model to simulate the drying-induced non-uniform deformations, stresses, and micro-crack propagation in concrete. Experiments were designed to validate the lattice fracture model, wherein the drying-induced non-uniform deformations and micro-crack patterns in concrete were measured using a digital image correlation technique and a fluorescent epoxy impregnation method, respectively. It was found that the simulated non-uniform deformations and micro-crack patterns were close to the experimental observations. The interaction mechanism between drying-induced non-uniform stresses and micro-cracks was analysed based on the validated lattice fracture model. The micro-cracks were found to cause stress concentration both in coarse aggregate and the mortar that covered coarse aggregate, which could lead to high micro-cracking risk as drying continues., Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public., Materials and Environment

To assess the effect of relative humidity (RH) on drying-induced damage in concrete, the non-uniform strains and microcracks in concrete under different RH conditions were obtained using the digital image correlation (DIC) technique and lattice fracture model. The simulated non-uniform displacements were consistent with those captured using DIC. A new damage index was proposed by considering all the subsets with equivalent strain larger than the threshold tensile strength. The calculated damage index showed good correlation with the microcracks' total area and indicated that RH equal or lower than 55% could cause relatively high cracking risk. This work provides an attractive method for quantifying drying-induced damage in concrete using the DIC technique., Materials and Environment