Internal curing cement-based materials utilizing superabsorbent polymer (SAP) demonstrates a significant mitigation of shrinkage effects. And the water ab- and desorption behavior of SAP provides critical insights for optimizing the mix proportion design in internal curing applications of cement-based materials. Herein, the ab- and desorption curves of SAP with different parameters in real cement pastes were quantitated through X-ray radiography. The influence laws and mechanisms of SAP size, SAP dosage and water-to-cement ratio (w/c) on the curves in cement pastes were clarified. The experimental results demonstrate that both the maximum water absorption capacity and desorption rate of SAP exhibit a positive correlation with w/c at early age, owing to more free water content and lower Na⁺/K⁺ concentrations for higher w/c. However, at later age, the desorption rate of SAP becomes inversely proportional to w/c owing to the humidity. Besides, the water retention capacity of SAP at later age shows a direct proportionality to SAP dosage. And a quite unexpected finding is the reabsorption behavior of SAP in high w/c (over 0.42) after 7 hours of cement hydration. The mechanism behind the reabsorption phenomenon is the deduction of calcium ions concentration in cement-based environments, which make SAP exhibit calcium ion leaching behavior.

The performance of self-compacting concrete (SCC) could be predicted through the paste rheological threshold theory based on certain assumptions. As the basic assumption, the excess mortar model regards all the coarse aggregate particles ignored the particle size distribution. That neglects the arrangement changes caused by actual factors such as shape and particle size distribution. This paper focused on modification of the excess mortar model considering the influence of the coarse aggregate packing characteristics. To study the effects caused by packing state of coarse aggregate particle system on the excess mortar system, the size ratio s_G and void content coefficient β were proposed for a better description of the packing status of coarse aggregate particles. Thus, the calculation methods for correcting the excess mortar volume and the related excess mortar film thickness were proposed, and a modified excess mortar model was established. According to the modified model, the calculation formulas for the paste rheological threshold were modified. The validation of the proposed model was conducted by paste and SCC performance tests. As visualization results of the paste threshold theory, the self-compacting zones could reveal the prediction accuracies of the calculated thresholds, by which the prediction accuracy comparison could be done. The results show that through the modification, the relative accuracy index Δε ≥ 0, and the modification index Δ|ε′ − 1| < 0, indicating that the modification increased the prediction accuracies. Both the overlap area and relative position of the self-compacting paste and concrete zones achieved by the original and new methods could be evaluated. Finally, the variation trends of paste thresholds under the effect of coarse aggregate were analyzed. The modified excess mortar model can achieve a more accurate prediction of SCC performance through simple paste performance test.

Underground ecological silos offer significant advantages, including low temperature and sealing capabilities, environmental sustainability, and conservation of energy and land. However, their widespread adoption is impeded by challenges such as the necessity for high-standard waterproofing and moisture-proofing, extended construction periods due to wet operations, and substantial costs associated with foundation pit support. The prefabricated steel plate-concrete composite underground silo emerges as a novel solution, boasting a shorter construction period and superior waterproofing and moisture-proofing performance. Despite these benefits, the method for calculating the internal forces on the silo wall under earth pressure has not been thoroughly explored. This study aims to address the gap in understanding circumferential stress in prefabricated steel plate-concrete underground silos. Using experimental testing and numerical simulations, we developed modified equations for calculating circumferential stresses in concrete, internal steel plates, and circumferential steel bars. Our findings reveal that circumferential stress initially increases and then decreases along the wall's height, with peak compressive stress occurring one-third from the bottom. The finite element model's accuracy is confirmed by a deviation of less than 10% between numerical results and experimental values. These insights provides a robust theoretical basis for designing prefabricated steel plate-concrete underground silos.

Early strength concrete is widely used in rapid repair and special working conditions. And it is of great significance to study its early dynamic mechanical properties for normal use and safety evaluation. The Ф100 mm SHPB test system is used to study the dynamic mechanical properties of early strength concrete at ages of 4 h, 12 h, 1 d, 3 d, 7 d and 28 d, and the Dynamic Increase Factor (DIF) model of early strength concrete at different ages is established. In addition, based on Ottosen constitutive model, the dynamic constitutive model of early strength concrete considering strain rate and age is established. The results show that the mechanical indexes of early strength concrete have strain rate strengthening effect and age strengthening effect. The dynamic compressive strength and specific energy absorption of early strength concrete increase with the increase of strain rate or age. With the increase of age, the strain rate sensitivity of mechanical indexes of early strength concrete increases. After comparing the calculation formulae of DIF given by CEB, Tedesco, etc., the DIF model of early strength concrete at different ages is proposed. The dynamic constitutive model curves show good agreement with the test curves, which can accurately describe the stress-strain relationship of early strength concrete before failure at different ages.

The high degree of agglomeration of layered double hydroxides (LDH) nanosheets poses a significant challenge to the application of LDH as chloride absorbents in cementitious materials. To address this issue, this study attempts to grow LDH on the surface of sepiolite using an in-situ synthesis via co-precipitation. The effect of the as-synthesized sepiolite@MgAl-LDH core-shell materials (SEP@LDH) on the chloride transport resistance of cement mortar is evaluated via rapid chloride migration (RCM) and chloride natural diffusion tests. Additionally, the microstructural characteristics of the as-synthesized sepiolite@MgAl-LDH core-shell materials and cement mortar were analyzed. The findings demonstrate that, compared to pure LDH and sepiolite, the as-synthesized SEP@LDH exhibits a markedly larger specific surface area. Additionally, the SEP@LDH substantially improves the chloride retention capacity of the cement relative to pure LDH. Furthermore, the incorporation of SEP@LDH markedly improves the chloride migration resistance of the cement paste. This enhancement can be ascribed to the improved chloride retention capacity of the highly dispersed LDH and the enhanced pore refinement in the cement mortar resulting from the addition of SEP@LDH.

Three self-compacting concrete (SCC) mixtures using different cements from the Xizang Autonomous Region were tested for macro-performance before freeze-thaw cycles (FTCs) via rheological, compressive, and splitting tensile strength tests. After FTCs, mass loss rate, relative dynamic elastic modulus (RDEM), and compressive strength were assessed, with scanning electron microscope and mercury intrusion porosimetry used for microstructural analysis. Damage and service life prediction models based on the Weibull distribution were established using mass loss rate and RDEM as failure indicators. Concurrently, a comprehensive evaluation model was developed, integrating compressive strength, freeze-thaw resistance, and material cost. Results show that cement with large negative zeta potential gives SCC better flowability. Lower total porosity correlates with higher compressive strength before FTCs. After 250 FTCs, compressive strength loss and porosity increase are proportional. Within 200 FTCs, lower porosity reduces mass loss and raises RDEM. After 250 FTCs, fewer harmful and highly harmful pores lead to lower mass loss and better RDEM. Damage models were employed to predict SCC the service life of SCC, followed by comprehensive evaluations of the mixtures. These analyses provide valuable guidance for selecting suitable cement brands for construction projects in the Xizang Autonomous Region.

This study investigates the potential of volcanic glass powder (VGP) as the primary precursor in alkali-activated materials (AAMs), using a blend of 70% VGP and 30% ground granulated blast-furnace slag. The influence of curing conditions before and after demolding on strength and durability was evaluated. Sealed curing at 80 °C for 24 hours enhanced C-A-S-H gel stability, improved early strength, and reduced drying shrinkage, but resulted in decreased long-term strength and sulfuric acid resistance. Conversely, sealed ambient curing promoted the development of a denser microstructure and higher long-term strength, albeit with increased drying shrinkage. The findings underscore the pivotal role of curing in optimizing the performance of VGP-based AAMs.

This study aims to actively control the radio wave propagation environment through the physical properties of concrete itself rather than through communication devices, and investigates the radio wave transparency of various types of concrete and their influencing factors to identify the conditions that improve transparency. First, the theoretical equations for electromagnetic wave propagation in concrete and the forms of water present in concrete are reviewed, and the influence of water on radio wave transparency is discussed. Based on these considerations, radio wave transmission tests were conducted on plate specimens with controlled internal moisture conditions. The results revealed that reducing evaporable water by lowering the water-to-powder ratio alone had little effect on improving radio wave transparency. In contrast, a significant improvement in radio wave transparency was achieved by simultaneously reducing evaporable and non-evaporable water using geopolymer instead of hardened cement paste, in combination with a low water-to-powder ratio. This paper is the English translation from the authors’ previous work [Sakamoto, R., Chijiwa, N., Saito, K., Nakayama, K., & Kang, C. (2025). Study on radio wave transparency improvement of concrete focusing on internal water content. Japanese Journal of JSCE, 81(3), 24-00070. (in Japanese)].