Xinxin Li

Crack-induced durability deterioration remains a critical challenge for concrete structures. Cementitious capillary crystalline waterproofing materials (CCCW) enable moisture-driven crystallization, while alginate/epoxy microcapsules provide stress-induced bonding. However, it remains unclear whether combining the two agents produces a complementary repair effect or only an additive one under different humidity conditions. This study investigates the self-healing properties of concrete containing CCCW and alginate/epoxy microcapsules. The results indicate that the healing performance of microcapsules depends little on moisture dependence and shows stable repair performance, while CCCW performs well in humid environments but is inhibited under dry conditions. At a fixed total dosage of 3%, the optimal hybrid system containing 2% microcapsule and 1% CCCW achieves higher recovery rates than any single-admixture group under all three curing conditions. This improvement is consistent with potentially complementary contributions from microcapsules and CCCW, although the detailed chemical nature and temporal evolution of the observed deposits require further investigation. This study provides a reference for the design and application of multi-component self-healing concrete in complex service environments.

The use of flawed excavated-mass aggregates produced from crushing and screening hydraulic engineering waste in concrete projects can reduce natural resource extraction, increase waste utilization rates, and minimize environmental pollution. However, the direct application of flawed excavated-mass aggregates is limited due to their high crushing index and water absorption rate. Therefore, this paper measures the multi-dimensional physical and mechanical properties of defective aggregates. A strengthening slurry is prepared by comprehensively modifying the crystallization strength and penetration path of sodium silicate solution using various chemical reagents. The strengthening mechanism of the slurry on flawed excavated-mass aggregates is analyzed using SEM and MIP tests. Concrete tests are designed to investigate the workability and mechanical properties of flawed excavated-mass aggregate concrete. The pore structure of the ITZ (Interfacial Transition Zone) in defective aggregate concrete is analyzed through BSE (Backscattered Electron) imaging to elucidate the strengthening mechanism of secondary crystallization reactions on the ITZ. The research findings can provide technical support for repairing aggregates with defects.

Concrete structures are vulnerable to sulfate attacks during their service life, as sulfate ions react with cement hydration products to form expansive phases, generating internal stresses that cause mechanical degradation. In this study, a cementitious capillary crystalline waterproofing material (CCCW) was incorporated into concrete to mitigate sulfate ingress and enhance sulfate resistance. The evolution of compressive strength, ultrasonic pulse velocity, dynamic elastic modulus, and the microstructure of concrete was investigated in sulfate-exposed concretes with varying CCCW dosages and strength grades; the sulfate ion concentration profiles were also analyzed. The results indicate that the enhancement effect of CCCW on sulfate resistance declines progressively with increasing concrete strength. The formation of calcium silicate hydrate and calcium carbonate fills the pores of concrete, hindering the intrusion of sulfate solution. Moreover, the self-healing effect of concrete further inhibits the diffusion of sulfate ions through cracks, improving the sulfate resistance of concrete. These findings provide critical insights and practical guidance for improving concrete resistance to sulfate-induced deterioration.

The rate sensitivity of concrete material is closely related to the inertia and viscous effects. However, the effect of inertia on the dynamic strength of concrete remains unclear. In this paper, digital image correlation technology was applied to study the strain variation of dry and saturated concrete with different loading rates. The test results indicated that the strain gradually decreased with the distance from the load end, and the strain gradient around the load region increased with the strain rate, especially for saturated concrete. Then, a single degree of freedom model was established to evaluate the dynamic compressive strength of elastic concrete. The calculated results indicated that the influence of inertia on the dynamic increase factor (DIF) was negligible for concrete within a low strain rate. When the strain rate is larger than 10⁰/s, the inertial effect on the strength of concrete should be considered. After that, a quasi-static concrete damaged plasticity (CDP) model was employed to simulate the influence of inertia on the stress distribution and axial reaction force at the loaded end of concrete under different rates of compressive loading and verified with experimental results. The results obtained in this study indicated that the dynamic nominal strength of concrete obtained from the tests could not be directly used for structural analysis which may overestimate the effect of inertia on the dynamic response of the structure.