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.@en

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.

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A structure-based modelling framework was established to simulate the three-dimensional autogenous shrinkage of cement paste. A cement hydration model, HYMOSTRUC3D-E, was used to obtain the microstructures and ionic concentrations of the cement paste. A lattice fracture model based on the effective stress and effective modulus was used to consider the elastic and creep parts of autogenous shrinkage. For Portland cement pastes with water-to-cement ratios of 0.3 and 0.4 (where the time zero of autogenous shrinkage was set as the time of the drop in internal relative humidity), the simulated linear elastic autogenous shrinkage was respectively −188 and −79 μm/m at 160 h. The obtained linear total autogenous shrinkage including elastic and creep deformations was respectively −501 and −236 μm/m at 160 h. These values of the elastic autogenous shrinkage and total autogenous shrinkage are close to the predications of poromechanical models and experimental data obtained using a corrugated tube.@en

This study is undertaken to explore the relationship between the reaction products and the drying shrinkage of alkali-activated slag (AAS) with the varying hydroxide dosage. AAS pastes were firstly produced with either Al(OH)3 or Mg(OH)2 to investigate the effects of hydroxide on the composition of reaction products and the drying shrinkage of AAS. Secondly, the main reaction products formed in AAS pastes, viz. C4AH13, M4AH10, C-S-H, C-A-S-H and C-M-S-H, were synthesized individually. Synthetic products were then taken to cast the respective paste sample to examine the performance against the drying exposure. The results show that adding Mg(OH)2 indeed improved the shrinkage resistance of AAS. This is primarily connected to the increased crystalline phases, namely the hydrotalcite-like phases and the unreacted Mg(OH)2. Whereas adding Al(OH)3 did not relieve the drying shrinkage of AAS as the interlayer spacing of C-A-S-H was enlarged, which in turn allowed for more shrinkage. Further, the investigation of individual synthetic products illustrates that their drying shrinkage scales satisfied the following order: C4AH13 < M4AH10 < C-M-S-H < C-S-H < C-A-S-H. Moreover, the shrinkage scale of C-S-H was found to evolve as the Ca/Si ratio decreased.@en

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.

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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.@en