Construction and Building Materials最新文献

When exposed to chloride-rich environments, reinforced concrete (RC) structures have serious concerns about rebar corrosion. In this study, a strengthening method was developed for RC columns with corrosion damage. Five full-scale RC columns with the same dimensions and rebar arrangements were experimented under reversed cyclic loading, where an axial stress equal to 1 MPa was applied to the specimens. Out of the five test specimens, two specimens underwent an average of 10 % rebar corrosion (Group 1), another two specimens underwent an average of 15 % rebar corrosion (Group 2), and one specimen acted as the sound specimen. One specimen from each group was retrofitted with 50 mm thick ultra-high-performance concrete (UHPC) layers. The experimental outcomes showed that reinforcement corrosion reduced ductility and maximum load-carrying capacity (MLC) significantly. The ductility and MLC of the specimen with 15 % rebar corrosion was decreased by 17 % and 9.2 %, respectively, compared to the sound specimen. However, the 15 % corroded specimen strengthened with UHPC layers displayed superior structural performance, for example, the MLC was increased by 24 % compared to the sound specimen. The performance of the strengthening scheme was evaluated using important performance indices, i.e., MLC, ductility, stiffness degradation, energy absorption, curvature distribution, etc. A simplified numerical model was developed and verified with experimental results. Experimental and numerical results revealed that the proposed approach can be very effective in strengthening corrosion-damaged RC columns.

The accelerator significantly influences the setting and hardening performance of shotcrete, in order to develop novel setting components, this study investigates the underlying mechanisms through which polyaluminum sulfate (PAS) facilitates the setting of cement paste. QXRD, Isothermal calorimetry, Zeta potential and Rheological test were employed to analyze the effects of PAS addition on the setting and hardening behavior, hydration kinetics, and rheological properties of cement paste. When the dosage of PAS is 10 %, the initial and final setting times are reduced by 54.39 % and 38.57 % respectively, meanwhile the compressive strength after 6 hours increases by 659.09 %. The influence of PAS on cement setting acceleration and rheological properties were analyzed using the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory and the Water Film Thickness (WFT) theory. PAS leads to an acceleration in particle aggregation rate and an increase in shear stress and plastic viscosity of the cement paste. Furthermore, the accelerated hydration effect of PAS promotes the formation of additional hydration products, strengthens the interparticle connectivity, and facilitates the formation of a rigid network. This study highlights a novel pathway for understanding the rapid setting mechanism of aluminum-based accelerators.

High Pozzolan concrete has an extended setting time and inhibits early-age compressive strength development, which can cause construction delays and limit its application in the concrete industry. The main aim of this study is to evaluate the effectiveness of graphene nanoplatelets (GNPs) in enhancing the mechanical properties of mortar containing high levels of natural Pozzolan. In the beginning, a relatively simple ultrasonication treatment process produced an almost uniform dispersion of GNPs in the mixing water to avoid agglomeration which limits the efficiency of GNPs. Tests on engineering properties indicated that the compressive strength of mortar containing 40 and 60 % natural Pozzolan as a partial replacement of cement was enhanced with the addition of the optimum content of graphene nanoplatelets which was found to be 0.03 % and 0.01 % by weight of binder at 40 % and 60 % cement replacement levels, respectively. The compressive strength was enhanced by 29.6 %, 27.4 %, and 27.5 % at 40 % cement replacement level, and by 86.3 %, 23.7 %, and 25.8 % at 60 % cement replacement level at 7, 28, and 56 days of curing, respectively. SEM investigations indicated that the addition of GNPs densified the structure thus enhancing the performance of mortar.

To establish a curing regime that facilitates the rapid enhancement and stable progression of early-age strength and tensile ductility in engineered cementitious composites with full desert sand (DSECC), aligning with production efficiency, this study examines the effects of different curing regimes (standard curing, natural curing, 20℃ water curing, and 90℃ water bath curing) on DSECC 's the mechanical properties and microstructure. The findings indicate that 90℃ water bath curing is beneficial to enhance the mechanical properties of DSECC, and its early 7 days strength and tensile deformation capacity (up to 7.05 %) can reach or exceed the standard curing 28 days level. In the uniaxial tensile test, samples cured in 20℃ water exhibit increased crack widths and reduced crack numbers, resulting in a sharp decline in the ultimate tensile strain from 4.96 % at 14 days to 1.57 % at 28 days. Natural curing leads to regression in strength at 28 days. The microstructure analysis revealed that 90℃ water bath curing fostered the development of high-density C-S-H gel and the dissolution of desert sand, while preserving the integrity of the fibers, enhancing the fiber-matrix interface transition zone (ITZ). The pore characteristic parameters under 90℃ water bath curing are superior, which has a notable refinement of the DSECC matrix's pore size. 20℃ Water curing can make up for the defects caused by desert sand and improve the compactness of matrix-aggregate ITZ. Natural curing yields the lowest degree of matrix hydration, with porosity reaching as high as 41.90 %, and pores smaller than 50 nm accounting for only 8.97 %.

Tunnel lining defects, such as discontinuous reinforcing steel, concrete dehollowing, and incomplete pouring, can substantially undermine structural durability and stability. Addressing limitations such as strong subjectivity and low accuracy in traditional quality assessment methods, we introduce the YOLO-LD tunnel lining quality detection algorithm. This model is an adaptation of the original YOLOv7 algorithm, where the original feature pyramid network is substituted by an asymptotic feature pyramid network, and a convolutional block attention module is added subsequently to backbone extraction. Electromagnetic wave propagation is simulated using gprMax3.0, while the tunnel lining structure is imaged through ground-penetrating radar employing the finite-difference time-domain method. These simulations yield a comprehensive radar image dataset for tunnel lining quality evaluation. A performance comparison of YOLO-LD with four other established algorithms reveals its superiority in detecting the three aforementioned defects, yielding an mF1 score of 91.07 % and a mAP score of 94.13 %. The model demonstrates robust performance in comprehensive defect detection and generalization.

Epoxy based grouting materials should concern with low viscosity, high strength, rapid curing, and low shrinkage. A polyurethane/epoxy grouting material was prepared. Through formula design, its initial viscosity was reduced to below 200 mPa·s. The morphology observation confirmed its porous and IPN structure. Compared with pure EP, its tensile strength, compressive strength, and impact strength were increased by 87 %, 20 %, and 50 %, respectively, as well as the volume shrinkage was significantly reduced. The inherent strength of PU/epoxy resin grouting materials was significantly higher than that of concrete, even in humid environments, their bond strength was 3.26 MPa. The theoretical grout flow rate and diffusion radius at different stages of the grouting process were also determined, which achieved an excellent on-site grouting effect.

This study investigates the impacts of environmental humidity on moisture absorption and mechanical properties of polymer-based waterproofing membranes. Membranes of polymer-CaCO₃, polymer-white cement composites and pure polymer were used for measurements after treated in different relative humidities (RHs). Results indicate that the humidity treatment greatly changes the mechanical properties of the membranes and increasing RH from 0 % to 100 % leads to reduction of tensile strength by 60–80 %, which is believed to originate from the plasticizing effect of the absorbed moisture. LF NMR (Low field NMR) enables quantification of moisture distribution in the polymer-filler composites and three types of water, i.e. the water stored inside polymer matrix (O/O water), the water located in interfacial regions between polymer phase and fillers (I/O water), and the free water in air voids are detected with increasing T₂ values. The absorbed moisture majorly accumulates in the O/O interfacial region during the humidity treatments with RH of 0∼80 %, which is because of the larger O/O interfacial area compared with the I/O interface. A large amount of free water appears only at RH of 100 %. A core-shell structure of the polymer domains with dry core and moisturized shell, is interestingly found during the moisture absorption process of the membranes, based on the LF NMR measurements using MSE sequence. It is surprisingly found that the drop of tensile strength of the membranes upon moisture absorption is majorly related to the growing shell thickness of the polymer domains whereas the moisture accumulated in the I/O interfacial region plays a minor role.

The utilization of industrial wastes as feedstock for binders in soil stabilization is a promising approach toward environmental consequences; however, the optimization of chemical compositions and gradation are commonly disregarded especially for binders derived from multiple industrial wastes. This study presents a novel framework for designing multiple industrial waste blends (MIWB) consisting of ground blast furnace slag (GB), fly ash (FA), silica fume (SF), and calcium carbide residue (CR) and assesses its feasibility and performance in soil stabilization. The concept of three chemical moduli (TCM) and the strength activity index (SAI) are applied to control chemical composition, and Dinger–Funk particle size distribution is adopted to attain optimal gradation. A case study exemplifies sediment stabilization utilizing MIWB designed, and sodium hydroxide (NH), sodium metasilicate nonahydrate (NS), sodium sulfate (SS), and aluminum sulfate (AS) are used as chemical additives, the mechanical and microstructural studies by Atterberg limits, compaction, unconfined compressive strength, one-dimensional consolidation, cyclic wetting-drying, X-ray diffraction, scanning electron microscopy and nuclear magnetic resonance tests are comprehensively examined. The outcomes demonstrate that: (ⅰ) MIWB is more efficient than ordinary Portland cement (OPC) in enhancing the compressibility and durability of stabilized sediment, and the optimal mix design of the composite binder was 14.25, 47.5, 9.5, 23.75, and 5 wt% of GB, FA, SF, CR, and AS respectively. (ⅱ) The sulfate additives can dramatically improve the strength development of designed MIWB stabilized sediment than that of alkaline additives, (ⅲ) The C-S-H, C-A-S-H, and AFt crystals are identified as the primary reaction products, arising from pozzolanic reactions between active phases present in the industrial waste. (ⅳ)The pore volume of stabilized samples is reduced due to the excellent filling and cementation effects, contributing to higher mechanical properties. In particular, MIWB has been applied and proven effective in engineering practice.

The surface properties of fibers significantly influence fiber-reinforced asphalt mastic (FRAM) performance. However, the impact of composite-modified basalt fiber (BF) on basalt fiber-reinforced asphalt mastic (BFRAM) remains unclear. This study examines the effects of acid-base/KH550 modified BFs on BFRAM performance, providing an experimental basis for further optimization. Tests included SEM and fiber leakage for BFs and separation, physical properties, DSR, and DMA for BFRAMs. The research indicates that (1) Composite modification enhances the fiber’s surface roughness, activity, oil-holding properties, and compatibility with SBS-modified asphalt. (2) Due to differences in acid-base etching, acid etching combined with KH550 promotes a more uniform and extensive coupling reaction with the BFs. In contrast, alkali etching with KH550 facilitates a deeper, localized reaction. (3) Composite modification of the BFs significantly improves the high-temperature rheological properties of the BFRAMs, with acid-base etching making the grafting reaction between the fiber and coupling agent more pronounced. At a test temperature of 82°C, the rutting factor of BFRAMs containing composite-modified (acid-etched + KH550) BFs is 2.7 times that of asphalt mastic without BFs. (4) The glass transition temperature of BFRAMs modified by acid etching and KH550 is 4.9°C lower than that of the original asphalt mastic, proving that composite-modified BFs enhance the low-temperature elastic deformation capacity of the BFRAMs.

Significant unloading failure zones in artificial freezing shaft sinking projects in western China are primarily caused by stress release. To investigate the deformation and failure mechanisms of frozen weakly cemented sandstone (FWCS), three groups of triaxial unloading tests were conducted under different initial principal stresses (σ₃ = 3, 6, and 10 MPa) with an unloading rate of 0.05 MPa/s. Scanning electron microscopy (SEM) was employed to examine the micro-fracture characteristics of the failure surfaces. The results revealed that, compared to traditional triaxial and room-temperature triaxial compression tests, the strength and plastic deformation characteristics of FWCS are significantly weakened under unloading conditions. However, lateral deformation, particularly volumetric strain, increased markedly, exhibiting pronounced dilatancy characteristics, especially along stress path III (i.e., post-peak axial stress loading with confining pressure unloading). Unloading leads to a reduction in cohesion and an increase in the internal friction angle of FWCS, with the most significant changes observed along stress path IV (i.e., pre-peak constant axial displacement loading with confining pressure unloading). Macroscopic and microscopic analyses indicate that the failure mechanism of FWCS under complex unloading stress paths is driven by the rapid accumulation of energy caused by unloading, which results in the development and propagation of axial and circumferential cracks, widespread particle breakage, and the formation of inter-granular and trans-granular fractures, as well as shear scratches at the micro level, ultimately manifesting macroscopically as shear-tensile composite failure.