Construction and Building Materials最新文献

Selective Paste Intrusion (SPI) is an additive manufacturing (AM) process in which thin layers of aggregates are selectively bonded by cement paste only where the structure is to be produced. In this way, concrete elements with complex geometries and structures can be created. Reinforcement is required to increase the flexural strength of the concrete elements and, thus, enable their applicability in practice. Integrating the reinforcement is a difficult task, particularly in the case of SPI, due to the layerwise printing method. Especially with respect to possible complex structures, the production of the reinforcement needs to be adapted to SPI, thereby offering a high degree of freedom. One concept for reinforcement integration is combining the two additive manufacturing processes, SPI and Wire and Arc Additive Manufacturing (WAAM). However, since the two processes serve different fields of application, their compatibility is not necessarily given. Ongoing investigations show that the temperatures caused by WAAM adversely affect both the cement paste rheology required for sufficient paste penetration into the particle bed and the overall concrete strength. This paper provides an overview of ongoing research focusing on different cooling strategies and their effects on the compressive strength of SPI-printed concrete parts.

Carbonation curing is currently one of the most effective methods for reducing carbon and absorbing carbon dioxide in cement-based materials. This study evaluated the macroscopic, microscopic, and thermal properties of red sandstone and limestone with different dosages under different curing methods. The results show that the carbonation rate is higher when 20 % red sandstone is added, and the carbon fixation amount is the highest. The inclusion of red sandstone provides more nucleation sites for the formation of carbonation product silica gel. At 600°C, the strength reduction of the carbonation samples is lower than that of the sealed samples, and the carbonation products are more resistant to high temperatures. Furthermore, the relationship between the microscopic, macroscopic, and thermal properties of red sandstone and limestone under different curing methods is explored. This study provides a new approach to the utilization of red sandstone resources.

Ultra-High Performance Concrete Filled Stainless Steel Tubular (UHPCFSST) column is a novel type of composite columns appealing to be adopted in corrosive and marine environment. To explore the axial performance of UHPCFSST columns, this paper initiates an experimental program containing 14 UHPCFSST columns subjected to either monotonic or cyclical axial compressive loading. The test variables in this program mainly include the column dimension, tube thickness and the loading schemes. Based on the test results, the damage evolution process, ultimate failure mode, load-deformation response and the typical mechanical performance indexes inclusive of loading-carrying capacity, stiffness degradation, as well as ductility coefficient are thoroughly examined. After that, theoretical analysis is carried out to explore the interaction behavior between UHPC and stainless-steel tube and hence judge the degree of confinement effect. To assess the applicability of the code equations stipulated in current international design guidelines and the empirical formulas proposed by other researchers, a small-scale dataset containing 41 UHPCFSST columns was compiled to make comparison of axial capacity between test results and analytical predictions. In view of the limited accuracy or the burdensome calculation process, a new formula considering actual loading carrying mechanism was proposed to calculate the axial capacity of UHPCFSST columns, which exhibits enhanced accuracy and efficiency than the current formulas.

Antioxidants can effectively mitigate or delay the oxidative aging degradation of asphalt binder, thereby improving pavement durability. While research has largely concentrated on the application of antioxidants to asphalt binders from a single source, limited studies have explored their effects on binders derived from different crude oil sources. Moreover, the relationship between the chemical and rheological properties of antioxidant-modified asphalt binders remains insufficiently understood. In this study, three antioxidants - zinc diethyldithiocarbamate (ZDC), Irganox 1010 and kraft lignin - were utilized and blended with base binders sourced from three distinct regions globally. Fourier transform infrared spectroscopy (FTIR) was utilized to analyze the impact of these antioxidants on the chemical composition of aged binders. Additionally, dynamic shear rheometer (DSR) and bending beam rheometer (BBR) tests were conducted to assess the high- and low-temperature performance of the antioxidant-modified binders, identifying the most effective antioxidant. The linear amplitude sweep (LAS) test further evaluated the performance of ZDC across binders from different crude oil sources. The results revealed three key findings: first, chemical functional group changes due to antioxidants are not always reflected in rheological performance; second, ZDC demonstrated superior performance across different base binders, as evidenced by improved aging indices, high-temperature rutting resistance, and enhanced fatigue and low-temperature cracking resistance; and third, asphalt binders from different crude oil sources exhibit varying sensitivities to antioxidant type and dosage. This study underscores the necessity of determining optimal antioxidant dosages for different asphalt binders, as the relationship between antioxidant dosage and effectiveness is not straightforward.

Many studies have shown that direct tensile tests are fraught with numerous challenges. The Double Punch Test (DPT) is considered a more reliable alternative for evaluating tensile properties among the indirect tensile methods. While DPT is efficient and reliable, its size effect should not be overlooked. Previous studies on DPT size effects have primarily focused on specimen size, with little discussion on the impact of punch size variations. Additionally, with the evolution of construction materials, the applicability of the generalized DPT formula to new materials, such as Ultra-High-Performance Concrete (UHPC), with its exceptional strength, toughness, durability, and crack resistance, needs to be evaluated. This study conducts experimental research on UHPC, focusing on the relationship between specimen and punch sizes and their impact on tensile strength measurements. By designing experiments with 12 different specimen sizes and punch ratios, we explore the differences between actual experimental results and simplified formula calculations. Bažant's theoretical methods are also applied to analyze the size effects of specimen and punch dimensions on DPT. The results indicate that, with appropriate specimen size and punch ratio, DPT can provide tensile strength measurements closer to those of Direct Tensile Tests (DTT). It was also found that tensile strength, strain, and toughness decrease with increasing specimen size. When the ratio of UHPC specimen to punch size (d/D) is 1/3, the results align well with the predictions of the simplified formula. This indicates that the optimal punch ratio is not fixed for different specimen sizes. These findings offer valuable references for designing related experiments and improving quality control and structural performance in various engineering fields.

Steel-fiber reinforced polymer (FRP) composite bars (SFCBs) present a promising solution to corrosion issues associated with conventional reinforcement in marine environments, offering a viable alternative. While the performance of SFCBs under marine environments or fatigue loading is well understood, their behavior under combined conditions remains unreported. This study conducted tension-tension fatigue tests on seawater-immersed SFCBs to assess the effects of fatigue loading (at a stress level of 0.36), various aging temperatures (23°C, 40°C, and 60°C), and durations (30, 180, and 360 days) on their residual properties. Microscopic analysis was used to investigate the degradation mechanisms due to environmental aging. The results indicate that environmental aging deteriorates the GFRP matrix in the outer layer of SFCBs, with fatigue loading further causing matrix cracking and reducing the quasi-static tensile strength. The residual tensile strength of SFCBs decreases with increasing aging times or temperatures, while aging shows no significant effect on their fatigue life. Additionally, a model predicting the residual tensile strength of SFCBs based on damage accumulation was proposed. According to the model, tensile strength initially rapidly decreases with aging time and eventually stabilizes. These findings offer practical insights for the application of SFCBs in concrete structures.

The degree of blending (DOB), which is controlled by the diffusion between virgin and aged/rejuvenated asphalt binder, has a major impact on the performance of the asphalt mixture incorporated with reclaimed asphalt pavement (RAP). Despite numerous studies investigating the DOB through experimental methods, the blending efficiency of warm mix asphalt (WMA) and synchronous rejuvenated SBS-modified asphalt (SBSMA) is still unexplored. In this study, a dynamic shear rheometer (DSR) testing approach was developed to quantify the blending efficiency of WMA modified SBSMA and synchronous rejuvenated SBSMA. The novelty of this approach lies in the innovative use of a DSR asphalt double-layer structure to determine the DOB in combination with a developed theoretical calculation framework. The individual and synergistic effects of WMA additive and rejuvenator type on the DOB of WMA modified SBSMA-Synchronous rejuvenated SBSMA were investigated, while the influence of blending temperature, blending time, and dosage of aged/rejuvenated SBSMA on the blending efficiency were systemically evaluated. Results indicated that the SBS repairing agent in the synchronous rejuvenator can dramatically increase the DOB, while the presence of WMA additive can further increase the DOB by improving the fluidity of the virgin SBSMA. Furthermore, increasing the blending temperature/blending time and decreasing the dosage of aged/rejuvenated SBSMA were also conducive to enhancing the DOB. In addition, a blending chart of the WMA modified SBSMA-Synchronous rejuvenated SBSMA was developed to facilitate the accurate prediction of the DOB at any given blending temperature and blending time.

This research demonstrates the synthesis of GGBS-based ready-mix (one-part) geopolymer (RMG) utilizing MBS as partial replacement to GGBS (10, 20 and 30 % by-mass) in addition to solid-alkaline reagents (NaOH-flakes and Na₂SiO₃ powder) using thermal and mechanical treatments, resulting in the formation of “ready-to-use” geopolymer product, “just-add-water” alike cement. The RMG was characterized by analyzing mineral phases, functional-groups identification followed by surface-morphology and elemental analysis at multiple stages, and engineering properties such as setting-time, flowability, compressive strength and ultrasonic-pulse-velocity were evaluated under ambient curing condition. The results show that GGBS-MBS-based RMG has dense morphology, affirming the development of C-S-H and C(N)-A-S-H gels due to its amorphous nature with some crystalline-phases (SiO₂) which are in-linked to Si-O-Si and Al-O-Si bonds. The dry-mix of GGBS with powdered-Na₂SiO₃ and 4 m molality NaOH (Na₂SiO₃/NaOH=1), pre-heated at 105±5°C for 6 h, followed by 6 h ball-milling with 20 % MBS replacement, achieved the highest 28-day compressive strength of 72.8 MPa, 10 % higher than the referenced mix and had satisfactory UPV results. The RMG not only solves handling problems caused due to concentrated aqueous-alkaline reagents used in two-part geopolymer synthesis but also provides sustainability by utilizing industrial and agricultural waste/by-products, hence reducing Portland cement demand, carbon footprint and waste-disposal issues.

The enhancement of mechanical properties of concrete meso-components and the interaction caused by non-uniform deformation as well as phase change can cause significant changes in the macro-mechanical performances of concrete at low temperatures. Based on the action mechanism of the above low-temperature effect, this paper established a thermal-mechanical sequential coupled simulation method with explicit modelling of pore ice at the mesoscale level to quantitatively investigate the direct tensile failures and the corresponding size effect of concrete with four structural sizes (D75, D150, D225 and D300) and three moisture contents (2.0 %, 4.0 % and 6.0 %) at different temperatures (20, −30, −60 and −90°C), in term of failure mode, deformation curve, peak strength and residual strength. The numerical results show that the direct tensile peak strength performs an obvious low-temperature enhancement effect due to the more damaged aggregates and more areas being in a state of multi-axial stress caused by low-temperature non-uniform stress field. However, with the decreasing temperature, the residual strength shows a decrease trend and the trend slows down with the increasing moisture content. Besides, as the temperature drops from 20°C to −90°C, both the size effects on direct tensile peak strength and residual strength are strengthened (with the increase approaches nearly 200 % for peak strength while 33 % for residual strength). Finally, a modified size effect theoretical model was developed considering the quantitative coupling effects of low temperature and moisture content. The present research results can provide a reference for the performance evaluation and safe design of large-sized concrete exposed to low-temperature environments.

Hydrated magnesium silicate (M-S-H) samples with good fluidity of 270 mm were prepared. The mechanical properties of the M-S-H samples cured in CO₂ conditions were examined. Moreover, the M-S-H samples under 70 % RH wet curing and standard curing conditions were prepared as comparison samples. As a result, the mechanical properties of the M-S-H samples under CO₂ curing conditions significantly improved. Compared to the M-S-H samples under 70 % RH wet curing and standard curing conditions, the 28-day compressive strength of the samples under CO₂ curing conditions was increased by 116.83 % and 74.25 %, respectively. Additionally, the microstructure of the M-S-H samples under the three curing conditions was investigated using XRD, SEM-EDS, TG/DSC, FTIR, and pore structure analysis. The results revealed that brucite reacted with CO₂ to form nesquehornite under CO₂ curing conditions. Furthermore, the volume stability of M-S-H was greatly affected by humidity, exhibiting expansion under standard curing and strong shrinkage under 70 % RH wet curing, while CO₂ curing can attenuate the shrinkage of the M-S-H samples.