International Concrete Abstracts Portal

This study employs machine learning (ML) to predict ultrasonic pulse velocity (UPV) based on the mix composition and curing conditions of concrete. A dataset was compiled using 1495 experimental tests. Extreme Gradient Boosting (XGBoost) and Support Vector Regression (SVR) were applied to predict UPV in both direct and surface transmissions. The Monte Carlo approach was used to assess model performance under input fluctuations. Feature importance analyses, including the Shapley Additive Explanation (SHAP), were conducted to evaluate the influence of input variables on wave propagation velocity in concrete. Based on the results, XGBoost outperformed SVR in predicting both direct and surface UPV. The accuracy of the XGBoost model was reflected in average R² values of 0.8724 and 0.9088 for direct and surface UPV, respectively. For the SVR algorithm, R² values were 0.8362 and 0.8465 for direct and surface UPV, respectively. In contrast, linear regression exhibited poor performance, with average R² values of 0.6856 and 0.6801 for direct and surface UPV. Among the input features, curing pressure had the greatest impact on UPV, followed by cement content. Water content and concrete age also demonstrated high importance. In contrast, sulfite in fine aggregates and the type of coarse aggregates were the least influential variables. Overall, the findings indicate that ML approaches can reliably predict UPV in healthy concrete, offering a useful step toward more precise health monitoring through the detection of UPV deviations caused by potential damage.

Corrosion of prestressing steel can threaten the durability of prestressed concrete. To ensure the durability of unbonded post-tensioning (PT) systems, it is crucial to investigate the effects of construction defects such as grease leakage and high-density polyethylene (HDPE) sheath damage. This study quantified the thickness of grease coating (PT-coating) and HDPE sheath damage as experimental variables. An accelerated corrosion test was conducted in two environments: 1) chloride ions only (Cl-) and 2) both chloride ions and dissolved oxygen (Cl- + DO). The corrosion current density and weight loss of prestressing strands and the suspended concentration density of corrosion cell solution were measured to quantify the corrosion performance. Increasing the grease coating thickness over 0.3 mm (0.012 in.) did not significantly enhance corrosion resistance. Realistic levels of HDPE sheath damage had no significant detrimental effects on durability; however, excessive HDPE sheath area loss must be avoided for long-term durability. It was examined to quantify the interrelationship between three data: electrochemical measurement, weight loss, and suspended concentration density as quantitative corrosion data. The findings of this study can serve as a basis for developing durability-related provisions, as well as controlling the construction defects of unbonded PT systems in field applications.

Prolonged neutron irradiation can damage concrete biological shields, particularly when nuclear power plants extend reactor lifespans. Retrofitting biological shields with thin and highly efficient neutron shields may limit neutron damage. Portland cement mortars amended with boron carbide and polyethylene powders were assessed for neutron attenuation. Shielding performance was compared to concrete with a similar design and coarse aggregate as a biological shield at an operational nuclear plant. Boron carbide enhanced the shielding performance of specimens under the full energy spectrum of the neutron source. Boron carbide and polyethylene synergistically enhanced neutron attenuation under a purely high-energy neutron flux. Engineered thin composite mortars needed 90% less thickness to achieve similar or better shielding efficiency as the concrete in a typical biological shield under the test conditions. Isothermal calorimetry, compressive strength, and thermal expansion results indicate that mixture design parameters of thin shields can be adjusted to achieve adequate structural properties without diminishing constructability or structural performance.

A capsule phase change material (CPCM) was synthesized using n-tetradecane as the core, expanded graphite as the shell, and ethyl cellulose as the coating material through a controlled assembly process. The results demonstrate that the infiltration of n-tetradecane significantly enhances the density of the expanded graphite, while the ethyl cellulose coating effectively prevents the desorption and leakage of the liquid phase change material during phase transitions. As a result, the CPCM exhibits a compact structure, chemical stability, and excellent thermal stability. The incorporation of this CPCM into cement-based materials endows the material with an autonomous heat-release capability at temperatures below 5°C. When the CPCM content reaches 20%, the thermal conductivity of the cementitious matrix increases by 24.66%. Moreover, the CPCM significantly improves the freeze-thaw resistance of the cement-based materials, reducing the compressive strength loss by 96% and the flexural strength loss by 65% after freeze-thaw cycles. This CPCM fundamentally enhances the frost resistance of cement-based materials, addressing the issue of freeze-thaw damage in concrete structures in cold regions.

While many studies have evaluated the corrosion performance of hot-dip galvanized reinforcement (ASTM A767), few have evaluated that of the newer continuously galvanized reinforcement (ASTM A1094). This study compared the corrosion resistance of A767 and A1094 reinforcement, along with uncoated reinforcement, using the Southern Exposure (SE) and cracked beam (CB) tests. The galvanized reinforcement was tested both with and without damage to the coating, as well as after bending the bars. Both A767 and A1094 reinforcement exhibited better corrosion resistance than uncoated reinforcement, but corrosion rates on both types of galvanized reinforcement increased when the bars were bent. ASTM A767 and A1094 reinforcement exhibited similar corrosion resistance and can be used interchangeably.