Ultra High Performance Concrete (UHPC) is a fiber-reinforced concrete with high compressive strength and durability; however, its tensile strength and tensile toughness remain insufficient. In this study, three-dimensional dog-bone specimens were used to investigate UHPC with different fiber types. Uniaxial tensile tests examined ultimate tensile strength, ultimate tensile strain and energy dissipation, clarifying the influence of hybrid fiber configurations on tensile behavior. Increasing fiber volume fraction generally enhanced UHPC tensile performance. Within the steelfiber hybrids, at the same total fiber volume, mixtures combining short straight (S) and short hooked (H) fibers outperformed those with short straight (S) and long straight (LS) fibers in both tensile and compressive strength. The S1H1.5 mixture achieved a tensile strength of 12.34 MPa and a tensile strain of 0.462%, with an energy absorption capacity of 52.9 kJ/m3 before softening. In PE/steel hybrids, tensile strength decreased but tensile strain increased with higher PE content. The PL1.5S0.5 mixture showed the highest tensile strain (1.390%), with a tensile strength of 4.86 MPa and a pre-softening energy absorption capacity of 35.1 kJ/m3. Based on these findings, a reusable hybrid-fiber design and evaluation framework was also proposed.

Although a variety of self-healing admixtures have been developed to improve the crack-healing capability of cementitious materials, achieving effective self-healing in wide cracks under flowing water conditions remains a significant challenge. In this study, the contents of organic chelating agents and crystallization promoters in a polycrystalline self-healing admixture (PSA) were systematically adjusted, and the formulation ratio was optimized to identify a PSA with minimal adverse effects on mortar properties. In the mortar self-healing experiments, the effect of PSA on the self-healing of impermeability in the mortar matrix was first investigated. Subsequently, the spatiotemporal evolution of preformed wide cracks in mortar was monitored using optical microscopy, and a water permeability test was conducted to evaluate the erosion resistance of the self-healing products formed within the cracks under flowing-water conditions. The experimental results showed that PSA enhanced the self-healing of impermeability pressure, with the second impermeability pressure ratio reaching 108.5%. In addition, abundant crystalline products were formed within the cracks of mortar specimens containing the PSA. Under static water curing conditions, cracks with nominal widths of 0.4 and 0.5 mm were visually closed. After 112 d, the self-healing ratio of 0.4 mm and 0.5 mm cracks under flowing water conditions reached 61.4% and 42.1%, respectively.

This study develops recycled aggregate-based sandwich permeable bricks, which adopt a three-layer functional design consisting of high-strength permeable surface layer, ceramsite core layer and recycled aggregate base layer. Through structural design, performance experiments, and Life Cycle Assessment (LCA), the sponge effect enhancement mechanism and carbon emission reduction potential of the bricks were systematically explored. The results show that while ensuring engineering performance with a 28-day flexural strength of 3.12 MPa, compared with traditional permeable bricks, the recycled aggregate-based sandwich permeable brick exhibits significant performance improvements, which demonstrates a balanced integration of infiltration, storage, retention, and drainage functions and mechanical stability. LCA quantification indicates that with the functional unit defined as 1 m2 of permeable brick over a 20-year service life, the total carbon emission reduction reaches 10.13 kgCO2. A sensitivity analysis varying the ceramsite factor by +/- 20% yields a net reduction ranging from 1.97 to 18.29 kgCO2, confirming a positive carbon reduction potential. Functional emission reduction driven by the sponge effect is the primary contributor, and the carbon emissions from ceramsite core layer production are effectively compensated by the functional emission reduction. Scenario analysis based on Hangzhou's road network planning, under low, medium, and high replacement rates, the total carbon emission reductions over 20 years are 0.16, 0.75, and 1.92 million tons respectively, with the annual average emission reduction accounting for 0.01%-0.13% of Hangzhou's total carbon emissions in 2022. This study realizes the high-value utilization of solid wastes such as recycled aggregates, provides a technical path for material innovation and large-scale application in the low-carbonization of municipal pavement engineering, and supports the coordinated development of Sponge Cities and low-carbon cities.

Hybrid MTMS-silica aerogels incorporating calcium silicate hydrate (C-S-H), the primary hydration product in cementitious systems, were synthesized via sol-gel processing followed by freeze-drying. The influence of C-S-H loading on pore structure, density, wettability, and thermal transport was investigated. The lowest thermal conductivity (0.068 W/m·K) and tap density (0.30 g/cm3) were obtained at 10% C-S-H loading (wM-CSH10), while the thermal conductivity increases to approximately 0.075-0.082 W/m·K at higher C-S-H content. All samples exhibit mesoporous structures with pore diameters in the range of 10-21 nm. Increasing C-S-H content progressively densified the network, reduced mesopore volume, and enhanced high-temperature mass retention up to 540 °C. FTIR analysis confirmed Si-O-Ca interfacial interactions, while nitrogen adsorption demonstrated persistent mesoporosity across all compositions. Thermal conductivity showed a positive correlation with density, indicating that bulk densification governs heat transport in the hybrid system. Beyond structural modification, the incorporation of C-S-H introduces chemical and microstructural features relevant to cement-based materials, suggesting potential compatibility with cementitious matrices. The results highlight the compositional trade-off between insulation efficiency and structural stability and demonstrate the potential of C-S-H-modified MTMS-silica aerogels for future integration into cement-based composites. These findings provide fundamental insight into their possible use in thermal insulation applications, such as building envelope systems (walls, façades, and roofs used for thermal insulation).

In order to facilitate the recycling of sewage sludge ash (SSA), and to reveal the effects of SSA and super absorbent polymers (SAP) on the volumetric deformation of the high performance cement-based materials, the separate and coupled effects of SSA and SAP on the volumetric deformation of the cement pastes with a low water/binder ratio (0.25) under different environmental conditions (sealed, drying, and water immersion environments) were studied. The results showed that the addition of SSA or SAP reduced the autogenous and drying shrinkage, and increased the water immersion expansion strain of the cement pastes. The addition of SSA and SAP together further reduced the autogenous and drying shrinkage, and increased the water immersion expansion. The synergistic effect of SSA and SAP on the volumetric deformation of the cement pastes was observed under a sealed environment. It was less significant under a water immersion environment. Under drying environment, the reduction in shrinkage caused by the combined addition of SSA and SAP was lower than the sum of the reduced shrinkages caused by SSA and SAP alone. These findings provided a new potential approach for the recycling and utilization of SSA.

Nano-engineered cementitious materials (NECMs) integrated with superior mechanical performances, enhanced durability and multifunctionality, are represented as the next-generation infrastructure materials. Nevertheless, a considerable gap remains between laboratory-scale investigation and industrial-scale implementation of NECMs. This review aims to provide a comprehensive understanding of NECMs performances with the objective of elucidating their potential for practical application. Firstly, the production and dispersion of nanomaterials are systematically reviewed, which primarily govern the cost and industrial feasibility of NECMs. Afterwards, the progress of the research on the hydration kinetics, microstructure, mechanical performance, durability and functionalities of NECMs is analyzed and summarized. In addition, representative case studies of NECMs in structural, industrial and large-scale applications are presented to illustrate the potential prospects for the development of NECMs. Through the comprehensive evaluation of NECMs, this review aims to offer valuable insights to guide both academic research and practical implementation, promoting the sustainable and large-scale application of NECMs in modern construction.

In the synthesis process of superabsorbent polymer (SAP), calcium sulfate dihydrate (C$H2) dispersion in water or colloidal silica sol (CSS) was used for the modification of SAP. The effects of modification on water absorption of SAP in water or saturated calcium hydroxide (CH) solution and the impacts and mechanism of the modified SAP on the performance of UHPC were investigated. The results showed that the modification results in a significant decrease in water absorption in both tap water and saturated CH solution for the SAP with water-based dispersion, but an increase in saturated CH solution though a decrease in tap water for that with the CSS-based dispersion. The SEM observation showed that a large amount of long ettringite crystals formed around the voids left by the SAP modified with the water-based dispersion. However, few ettringite crystals but more hydration products were observed to fill in the voids and a C-S-H gel shell-structure was also found in the voids left by the SAP modified with the CSS-based dispersion. Because of these, it was interestingly found that the crack resistance was further improved and a significant improvement in both flexural and compressive strength was observed, though the internal curing effect was weakened because some internal curing water carried by the SAP was consumed during the formation of the ettringite crystals and the C-S-H gels in the voids.

Superabsorbent polymers (SAP) are widely utilized as internal curing (IC) agents to effectively mitigate the autogenous shrinkage of ultra-high-performance concrete (UHPC). However, the macropores left behind by SAP can pose significant risks to the mechanical properties of UHPC. To address this challenge, this study developed double-emulsion microcapsules with an alkali-sensitive shell, designed to simultaneously achieve reduced shrinkage and enhanced mechanical strength in UHPC. The effects of these microcapsules on hydration, mechanical properties, shrinkage, and the micro-and nano-scale structure of UHPC were systematically investigated. The results revealed that the incorporation of microcapsules substantially reduced autogenous shrinkage while promoting hydration without compromising compressive strength. Specifically, at an optimal microcapsule content of 1.0 %, the autogenous shrinkage rate decreased by 49.5 % compared to UHPC without microcapsules, while the compressive strength remained unaffected. Additionally, the IC process was significantly improved, as evidenced by enhancements in the interfacial transition zone (ITZ) and the mitigation of microcrack development, validated through nanoindentation and X-ray microcomputed tomography (X-ray mu CT) analyses. A quantitative method evaluating the fragmentation degree of internal cracks in UHPC is proposed to systematically characterize the impact of microcapsules on IC efficiency, providing theoretical insights into leveraging microcapsule technology to achieve UHPC with low shrinkage and high strength.

The rheological properties of concrete paste significantly influence its tensile creep behavior. In this study, the tensile creep behavior of high-volume fly ash concrete (HVFAC) employing the same cementitious pastes was experimentally investigated, and the rheological properties of the paste containing a high volume of fly ash using the nanoindentation (NI) technique was investigated in order to explore the influence of the paste’s rheological properties (such as micro-mechanical properties and microscopic creep) on the early-age tensile creep of HVFAC. The results demonstrated that the micro-strain of paste containing a high volume of fly ash (HVFA) showed a larger value than that without fly ash. As the test age extends, a decreasing trend in microscopic creep was observed which could be attributed to the growth of the content of HD C–S–H (high density C–S–H) gel. Moreover, within the same age period, the experimental data revealed that the incorporation of fly ash resulted in the reduction of the values of the creep modulus C and characteristic time τ. The effects of fly ash dosages and loading age on the creep properties of concrete was consistent with the micro-creep properties of the cementitious paste. The tensile specific creep values derived from the ZC (“ZC” are initials for the word ‘‘self-developed” in Chinese) model based on nanoindentation data closely match those obtained from experiments.

To improve wood utilization in the field of construction engineering, a fiber reinforced recycled composite wood was successfully prepared using waste wood, polypropylene and polyester fiber in this work. The polypropylene was utilized as a hot melt adhesive and the fiber was employed as a lashing bundle, which both enhance the mechanical property of the composite wood. The flexure performance of the composite wood was tested and its constitutive model was established for analyzing its stress–strain characteristics. The results show that the waste wood combined with polypropylene and fiber can be recycled as a serviceable composite, and its flexural strength and flexural stiffness were elevated by approximately 54

Ultra-high toughness cementitious composites (UHTCC) are suitable for hydraulic structures due to their enhanced ductility and effective crack control capacity. This research investigated the dynamic tensile behavior of two different types of UHTCC: one featuring a normal strength matrix reinforced with polyvinyl alcohol (PVA) fibers, and another combining a high-strength matrix with polyethylene (PE) fibers. The findings revealed that water saturation effect on the dynamic tensile behavior of two types of UHTCC were opposite. After saturation, normal UHTCC made with PVA fibers exhibited increases in tensile strain capacity, while UHTCC made with PE fibers and high-strength matrix exhibited reduction in deformation by 56%. Under dynamic tensile loading, moisture content notably affected the strain rate sensitivity of tensile properties in normal UHTCC with PVA fibers, demonstrating significant variations in DIF (Dynamic Increase Factor) for strength, deformation, and energy dissipation. However, these influences were minimal in composites made with a high-strength matrix and PE fibers. The mechanism for such phenomenon were discussed based on the result of matrix fracture test and fiber pull out test.

Starch is often used as a viscosity modifying agent (VMA) in self-compacting concrete (SCC) and highly flowable concrete. In this paper, starches possessing different degrees of hydroxypropyl substitution (DS) were used to study the shear rheological properties and hydration kinetics of cement paste in the presence of and without polycarboxylate superplasticizer (PCE). The starch with the highest DS increases the yield stress and the plastic viscosity stronger than others. Regardless of the dosage and DS of starch the structural build-up is not affected specifically by the starch during the induction period. During the acceleration period starches reduce the structural build-up, but with the highest DS this effect was less prominent than for the other modifications. In the presence of PCE the addition of starch notably increases the yield stress, whereas the influence on the plastic viscosity is limited. Yet, the combined application of PCE and starch allows to control rheological properties and maintain the structural build-up rate.

The sulfate-rich sewage sludge ash (SRSSA) could be recycling used as expansive agents in selfleveling cement mortars, and superabsorbent polymers (SAP) can effectively reduce the shrinkage of cement-based materials. Therefore, SRSSA and SAP were used as admixtures to prepare self-leveling cement mortars. The influences of SRSSA and SAP on the fluidity, strength, drying shrinkage, crack resistance and microstructure of self-leveling cement mortars were studied. The initial fluidity and 20-min fluidity of self-leveling cement mortars were slightly reduced when SRSSA and SAP were added. The flexural strength and compressive strength of selfleveling cement mortars improved when the SRSSA content was lower than 6 % of binders, and the strengths were reduced when SRSSA were added by 8 % and 10 %. The addition of SAP further reduced the strengths of self-leveling cement mortar. The drying shrinkage of self-leveling cement mortars decreased when SRSSA was added as expansive agents, and the added SAP further reduced the drying shrinkage. The addition of SRSSA postponed the initial cracking time and improved the crack resistance of self-leveling cement mortars. When SAP was added together, the crack resistance of self-leveling cement mortars became better. The formation of ettringite in self-leveling cement mortars was promoted by the presence of SRSSA and SAP, and the addition of SAP with SRSSA also reduced the porosity tested with mercury intrusion porosimeter. Generally, SRSSA can be used as expansive agents in self-leveling cement mortars, which is a new method to recycle use SRSSA in cement-based materials.

Despite significant advances in understanding the material properties of High Strength-High Ductility Concrete (HSHDC), there remains a critical gap in studies examining the influence of reinforcement configurations on the impact resistance of HSHDC components in practical applications. This study explores the influence of reinforcement ratios on the impact resistance of HSHDC beams through multiple drop-weight impact tests. Key parameters including impact force, reaction force, deflection, energy dissipation, crack propagation, and failure mechanisms, were analyzed. The results reveal that, with the same reinforcement ratio, utilization of HSHDC can significantly reduce mid-span, peak deflections and spall compared to traditional reinforced concrete (RC), while enhancing cumulative energy dissipation by 12.9%. Increasing the ratio to 1.67% transitioned the failure mode to adequately reinforced, resulting in a 155% increase in cumulative energy dissipation compared to the 0.74% group. Higher longitudinal reinforcement ratios promote more uniform deflection distribution and slower increases in post-impact residual deflection, exhibiting a "pseudo-stabilization" phenomenon similar to that observed in metallic structures. Additionally, HSHDC's superior shear resistance leads to ductile shear failure behavior. These findings highlight the potential of HSHDC to enhance structural performance while allowing for reduced stirrup usage, offering significant economic and practical benefits for construction applications.

In this paper, low-cost dihydrate gypsum (CaSO4.2H2O) was used as calcium source together with sodium metasilicate solution to prepare calcium silicate hydrate (C-S-H) gels through a mechanochemical activation strategy by using planetary and vibrational ball-milling. The influences of the prepared C-S-H gels on hydrating and hardening properties of super-retarded cement-based materials with sucrose were investigated. The results showed that CaSO4.2H2O reacted with sodium metasilicate solution under mechanochemical effect during both planetary and vibrational ball-milling, although CaSO4.2H2O was just slightly dissolved in water. It was also interestingly found that the C-S-H gels can continuously form while resting for a certain time after ball-milling. Under the mechanochemical activation, the prepared C-S-H gels had complete characteristic diffusion peaks and were composed of layered, flocculent and fibrous structures. While incorporating the prepared C-S-H gels into the super-retarded cement paste with sucrose, the cement hydration was greatly accelerated and the compressive strength of the hardened cement-based materials was also effectively improved at early age as expected. Through X-ray diffraction (XRD) analysis, it was found that C-S-H gels can effectively promote the growth of CH crystals along the (001) and (101) crystal planes. The scanning electron microscopy (SEM) results supported that the C-SH gels inhibited the refinement of ettringite (AFt) crystals in super-retarded HCP with sucrose, which was more obvious at 28 d.

The leading cause of concrete cracking is the generation of internal stress generated by the volume change under restrained conditions, which exceed the ultimate value of strength. In particular, the restrained stress generated by temperature change is significant, particularly for large-volume concrete. This study proposed a new restrained method to separate the thermal stress, autogenous shrinkage stress, and drying shrinkage stress from total restrained stress. Unlike traditional restrained methods, Invar steel’s characteristic low coefficient of linear expansion was used to generate the thermal stress in this method. To investigate the feasibility of this method, two ordinary cement concrete with 0.30 and 0.40 water-to-binder (w/b) ratios and a ultra high performance concrete (UHPC) with 0.21 w/b ratio were tested. The total stress obtained by the accumulation of the three separated stresses were compared with the experimental total stress. The discrepancy between the direct value and the accumulated value of total stress was within 20 %, indicating that the restrained stress separation method proposed in this study produced viable results. Overall, the new restrained method proposed in this study enabled to test and separate the concrete restrained stresses easily and accurately, which was meaningful for evaluating the risk of concrete cracking in practical engineering.

Recycled coarse-aggregate (RCA) derived from waste concrete can be re-used for concrete preparation, which is now limited due to its drawbacks such as micro-cracks, high-porosity, and reduced concrete strengths. To remedy these deficiencies, carbon-sequestration was employed to enhance RCA and the conditions were optimized, including the temperature (20 °C-40 °C), pressure (0.1 MPa-0.3 MPa), time (5 h-24 h) and initial water content (25%-75%). There parameters were optimized based on the orthogonal test with scheme L9(34), which was evaluated based on RCA carbon-sequestration amount as well as its properties. With the optimized parameters, RCA was enhanced as CRCA. Both RCA and CRCA were utilized to fully replace natural coarse-aggregate (NCA) in concrete and concrete basic performances were investigated systematically, including strengths, shrinkage and medium transport properties. The results show that the effects of carbon-sequestration time and initial water-content of aggregate on the carbon-sequestration efficiency of RCA are the most significant. The optimized parameters were 30 °C temperature, 0.3 MPa pressure, 24 h time and 25% initial water content with the maximum amount of carbon-sequestration at 8.42%. The carbon-sequestration reduced the width of the recycled aggregate interfacial transition zone (ITZ) in concrete, increased the microhardness of ITZ and mortar, and decreased the porosity of CRCA. The CRCA elevated the compressive strength, splitting tensile strength and flexural strength of the concrete (28d) by 13.5%, 8.5% and 7.4%, respectively. The drying shrinkage at 28d of RCA-concrete was decreased by 12.0% when RCA was replaced with CRCA, however with the CRCA value still 16.2% higher than that of NCA-concrete. Moreover, CRCA can decrease the medium transport coefficients of water, chloride, and gas in concrete when compared with the RCA-concrete while they are still greater than those of NCA-concrete.

The rheological properties of concrete paste significantly influence its tensile creep behavior. The micromechanical properties, microscopic creep, and other rheological characteristics of high-volume fly ash cementitious pastes (60% and 30%) were investigated using nanoindentation techniques in this study. Concurrently, the time-dependent tensile creep behavior of high-volume fly ash concrete (HVFAC) employing the same cementitious pastes was investigated through experimental studies, culminating in the formulation of a predictive ZC model expression that incorporates the paste's rheological properties. The results showed that the paste rheological property plays a decisive role during the tensile creep development of HVFAC at early ages. And the fly ash enhances the evolution of microscopic creep within cementitious pastes at consistent test ages. Moreover, when fly ash substitutes an equivalent mass of the original material, the convergence rate of microscopic creep accelerates as the test age progresses. The influence of fly ash and loading age on the development of HVFAC creep is consistent with the influence law of cementitious paste’s micro creep without aggregate. Base on the correlation analysis on the parameters of Et,28d/(EV+EH), Et,28d/χφ, φ and relative compressive strengthfc(t0)/fc,28d, the parameters of C, τ and test ages, it showed that these parameters are in good agreement with the function y = A+Bx. The tensile creep prediction expression of ZC model considering the rheological properties of cement paste can reflect the structure of the model unit cell.

The digital image method of monitoring structural displacement is receiving more attention today, especially in non-contact structure health monitoring. Some obvious advantages of this method, such as economy and convenience, were shown while it was used to monitor the deformation of the bridge structure during the service period. The image processing technology was used to extract structural deformation feature information from surveillance video images containing structural displacement in order to realize a new non-contact online monitoring method in this paper. The influence of different imaging distances and angles on the conversion coefficient (η) that converts the pixel coordinates to the actual displacement was first studied experimentally. Then, the measuring and tracking of bridge structural displacement based on surveillance video images was investigated by laboratory-scale experiments under idealized conditions. The results showed that the video imaging accuracy can be affected by changes in the relative position of the imaging device and measured structure, which is embodied in the change in η (actual size of individual pixel) on the structured image. The increase in distance between the measured structure and the monitoring equipment will have a significant effect on the change in the η value. The value of η varies linearly with the change in shooting distance. The value of η will be affected by the changes in shooting angle. The millimeter-level online monitoring of the structure displacement can be realized using images based on surveillance video images. The feasibility of measuring and tracking structural displacement based on surveillance video images was confirmed by a laboratory-scale experiment.