This study investigated the influence mechanism of sulphoaluminate cement (SAC) on the hydration behavior and pore structure characteristics of magnesium potassium phosphate cement (MKPC). Hydration products were characterized using scanning electron microscopy-energy dispersive spectroscopy, X-ray diffraction, and Fourier transform infrared spectroscopy. The pore structure was examined using a combination of mercury intrusion porosimetry and computed tomography, and macroscopic properties were evaluated by water stability tests. The results showed that SAC incorporation enhanced the water stability of the MKPC paste. Compared to that of the control group without SAC (MKPSC0), the water resistance coefficients of MKPSC10, MKPSC20, MKPSC30, and MKPSC40 increased by 15.23 %, 32.79 %, 31.43 %, and 24.36 % respectively, indicating an optimal SAC content of approximately 20 %. Microscopic analysis revealed that increasing SAC content promoted the formation of ettringite, calcium sulfate, and gel-like hydroxyapatite, which became the dominant hydration products. In addition, the amount of K-struvite decreased due to the reduced availability of MgO and KH2PO4. Both ettringite and hydroxyapatite exhibited excellent water resistance, contributing to the improved durability of the MKPC system. Furthermore, SAC-derived hydration products effectively filled internal pores, facilitating the transformation of harmful pores into harmless ones and reducing overall pore size and connectivity. However, excessive SAC addition led to increased voids between hydration products, an increase in the most probable pore size into the harmful range, and higher pore connectivity, which diminished the pore-blocking effect and weakened the water stability improvement effect. Overall, this study provides a theoretical basis for optimizing SAC content to improve the performance and durability of MKPC systems.

This study aimed to analyze the properties of the interfacial transition zone (ITZ) in fly ash geopolymer concrete (FAGC) containing various concentrations of calcium aluminate cement (CAC) (5%, 10%, 15%, and 20%). The micro-mechanisms of the ITZ were investigated using nanoindentation, scanning electron microscopy–energy dispersive spectroscopy, and backscattered electron imaging. The macro-properties, such as the interfacial bonding strength and the interfacial fracture energy, were also evaluated. The results indicated a trend of decreasing ITZ width with increasing CAC content from the nanoindentation test. The minimum ITZ width was observed in the FAGCC20 sample at 10 μm, representing a 71.43% reduction compared with the 35 μm width of the FAGCC0 sample. The formation of greater amounts of polymerization products, i.e., N-A-S-H and C-A-S-H gels, filled the pores and weakened the cracks, which notably improved the porous state of the ITZ. The changes in the microstructure of the ITZ directly affected the macroscopic performance of the FAGC. The FAGC samples with CAC showed higher interfacial bonding strengths and fracture energies than the FAGCC0 sample. Consequently, the FAGCC20 sample exhibited the highest interfacial bonding strength and fracture energy of 2.37 MPa and 31.1 N/m, respectively.

Guano are an important factor affecting the cleanliness of photovoltaic modules on floating solar power plants at sea. It can lead to a decrease in photoelectric conversion efficiency, power loss, and even the occurrence of “hot spots”, thereby causing damage to the components. Therefore, the segmentation and detection of guano are crucial for visual automation in the cleaning and inspection processes. However, the composition, density, and thickness of guano naturally vary, leading to inconsistent levels of transparency and color. The uneven intensity of guano images greatly reduces the accuracy of segmentation and detection. Addressing this issue, this study proposes a segmentation algorithm based on combining different color channels to segment guano on the surface of photovoltaic modules. The mean shift method is used for adaptive segmentation to facilitate the detection of guano. Furthermore, the segmentation results obtained by this method are introduced into the input space to improve the traditional Mask RCNN. In addition, this study successfully produced a dataset of guano on the surface of photovoltaic modules using on-site data collection and with the help of a platform built in-house in the laboratory. The experimental results on the self-constructed dataset demonstrate that the enhanced Mask R-CNN model has shown an approximate increase of 5.9% and 6.0% in mAP values for object recognition and segmentation compared to the traditional Mask R-CNN model. This indicates the effectiveness of the methodology proposed in this study.

Rebar corrosion induced by chloride erosion and concrete deterioration caused by sulfate attack are two critical factors that affect bond properties between rebar and concrete in marine environment. However, current studies about above two influencing factors on bond properties either consider rebar corrosion or sulfate attack. The bond properties between rebar and concrete considering the coupled effects of rebar corrosion and concrete deterioration caused by sulfate attack are required to further explored. In this paper, through the accelerate corrosion test, pull-out test and microscopic analysis (including scanning electron microscopy and X-ray diffraction measurements), the bond properties considering rebar corrosion and concrete deterioration caused by sulfate attack were investigated. A total of 88 RC specimens were designed to study the influences of rebar corrosion level, sulfate attack degree, sulfate ions associated cation types (sodium and magnesium ions) and concrete materials types (ordinary concrete and concrete incorporating fly ash and silica fume) on bond properties. The bond strength, bond-slip curve and failure mode were measured, and the effects of cracking width on bond properties were considered. Results show that the rebar corrosion level corresponding to the peak bond strength decreases with the increase of sulfate concentration. The bond strength decreases and the slip increases with the rise of sulfate concentration. Sodium sulfate attack causes the splitting failure, and severer magnesium sulfate attack leads to the transition from splitting failure to pull-out failure. The rebar corrosion level causing the concrete to crack decreases with the increase of sodium sulfate concentration. The higher the magnesium sulfate concentration, the less prone to produce rust-expansion cracks, but the worse cementing properties of RC bonding interface. Magnesium sulfate attack results in the severer attenuation of bond strength than sodium sulfate attack. The bond properties can be significantly improved by incorporating 20% fly ash and 5% silica fume. A prediction model of bond strength variation coefficient considering rebar corrosion level, sulfate ions concentration, sulfate ions associated cation types, and concrete materials types was established and verified.

Cementitious materials exposed to sulfate environments often suffer from the combined effects of external sulfate attack and dry wet cycling. In order to predict the long-term performance of cement-based materials in sulfur rich environments, this paper aims to establish a numerical model that can reasonably characterize the degradation process of cementitious materials in sulfate environments. Using this model, we can address durability problems common to cementitious materials in real sulphate environments, such as determining the degree of corrosion, predicting the durability life of materials, and calculating the time to failure. The model consists of three parts: transportation, chemical reactions, and material damage. We establish the degradation model for cement-based materials in sulfate environments by considering ion diffusion, water convection, chemical reactions, accumulation of corrosion products, and the development of material strengthening/degradation. Compared with existing sulfate corrosion models, this model not only considers ettringite, but also takes into account the volume changes of gypsum formation, calcium leaching, and salt crystallization precipitation, which can more reasonably simulate the sulfate corrosion process in real environments. The model can reasonably simulate the distribution pattern of ion concentration, hydration products and corrosion products in the cementitious material, and on this basis calculate the porosity of the cementitious material. In order to make the simulation results more applicable to experimental and non-destructive testing results, the model uses easily obtainable relative dynamic elastic modulus to evaluate the degree of material strengthening/degradation and predict the durability life of the material.

以中国东部沿海某防波堤为依托工程,其建成后多次受到风暴潮破坏,修复后仍出现继续破坏的情况,为全面评估现状,开展了智能巡检工作.防波堤水上可见工程利用无人机航拍技术,水下隐蔽工程利用无人艇搭载多波束声呐测量水深,测量获得的点云数据融合处理后建立防波堤三维可视模型,并提取现状断面与设计对比研判防波堤破坏程度与破坏原因.该防波堤水下坡面多处受损,坡面形态与设计断面存在一定差异,水下扭工字块断肢、扭王字块滑落现象较多,结合分析得出超出设计标准的自然灾害是造成该防波堤频繁破坏的主要原因.

The incorporation of supplementary cementitious materials (SCMs) in concrete can improve the properties of concrete partially immersed in salt solution. However, the current partial immersion environment only considers the capillary action above the still water level, does not consider the capillary action above the fluctuating water level in dry-wet cycling environment. In this paper, a series of indoor exposure experiments were carried out to investigate the effects of incorporating polynary SCMs including fly ash (FA), ground granulated blast furnace slag (GGBFS) and silica fume (SF) on the sulfate resistance and chloride impermeability of concrete considering the capillary action above the fluctuating water level in dry-wet cycling environment. A total of 15 groups of concrete with different mix proportions (total 150 concrete specimens) were designed to study the effects of different replacement levels of polynary SCMs on concrete properties. The effects of incorporating polynary SCMs on the chloride impermeability of concrete above and in the fluctuating water level zone were investigated. The scanning electron microscope (SEM), x-ray diffraction (XRD) and mercury intrusion porosimetry (MIP) tests were used to analyze the microstructure of concrete. The results indicate that when concrete is incorporated with polynary SCMs and subjected to capillary action above the fluctuating water level, the compressive strength and chloride impermeability first increase and then decrease with the increase of FA content; the compressive strength and chloride impermeability decrease with the increase of GGBFS content; the compressive strength first increase and then decrease with the increase of SF content, and the chloride impermeability increase with that. The transport process of chloride in concrete above the fluctuating water level zone includes the longitudinal transport under capillary action and the transverse transport under concentration gradient action. The combined effects of both cause the higher chloride concentration in concrete above the fluctuating water level zone. Comprehensively considering the influence of different mix proportions on the sulfate resistance and chloride impermeability of concrete, it is determined that 20% FA + 5% SF is the optimal replacement level with the excellent performance considering the capillary action above the fluctuating water level in dry-wet cycling environment.

Microbially induced calcium carbonate precipitation (MICP) has recently become an intelligent and environmentally friendly method for repairing cracks in concrete. To improve on this ability of microbial materials concrete repair, we applied random mutagenesis and optimization of mineralization conditions to improve the quantity and crystal form of microbially precipitated calcium carbonate. Sporosarcina pasteurii ATCC 11859 was used as the starting strain to obtain the mutant with high urease activity by atmospheric and room temperature plasma (ARTP) mutagenesis. Next, we investigated the optimal biomineralization conditions and precipitation crystal form using Plackett-Burman experimental design and response surface methodology (RSM). Biomineralization with 0.73 mol/l calcium chloride, 45 g/l urea, reaction temperature of 45°C, and reaction time of 22 h, significantly increased the amount of precipitated calcium carbonate, which was deposited in the form of calcite crystals. Finally, the repair of concrete using the optimized biomineralization process was evaluated. A comparison of water absorption and adhesion of concrete specimens before and after repairs showed that concrete cracks and surface defects could be efficiently repaired. This study provides a new method to engineer biocementing material for concrete repair.

Newly proposed pile wall frame structures (PWFSs), notably with small-spaced row piles, have great potential for cofferdams of artificial islands applied for oil recovery in shallow seas. Studies have been called to analyze the bearing performance of small-spaced row piles subjected to lateral loads. A numerical investigation of laterally loaded row piles with small pile spacing was conducted to achieve a fitted algebraic expression of the P-Y curve. Significantly different from the hyperbolic P-Y curves of a single pile reported in other studies, the P-Y curve of small-spaced row piles is similar to an elastic–perfectly plastic curve, which simply depends on the ultimate lateral bearing capacity of piles (Pu) and initial slope of curves (Ki). Parametric studies have revealed that Pu and Ki values are affected by pile spacing, depth, untrained shear strength of soil, and relative soil–pile rigidity. Algebraic expression of the P-Y curve could be employed for the subgrade reaction method and be effectively used in predicting the behavior of small-spaced row piles, such as PWFSs.

以大连某填海造地工程为例,研究了局部软弱夹层对挡泥坝边坡稳定性的影响规律.通过现场地勘判定软弱夹层位置,采用数值分析方法建立挡泥坝模型,基于极限平衡理论讨论了局部软弱夹层对软基上挡泥坝稳定性的影响.分别采用瑞典圆弧法、简化毕肖普法、摩根斯坦-普瑞斯法,对比分析边坡坡比对挡泥坝稳定性安全系数及最危险滑弧位置的影响.分析结果显示,最危险滑弧会经过软弱夹层,使得挡泥坝稳定性显著降低,边坡坡比会对滑弧深度产生影响,不同的边坡稳定性计算方法得到的安全系数具有良好的一致性.研究表明,清淤不彻底会显著影响挡泥坝的边坡稳定性,对坝后吹填作业产生严重隐患,应该给予足够重视.

Pile wall frame structures (PWFSs) are double-wall sheet-pile structures with an integrally precast framework of reinforced concrete to connect double rows of closely placed piles. An engineering test on a cofferdam of PWFSs was conducted in Binzhou, where lateral displacement along pile shaft was carefully monitored during the hydraulic filling process. A 3D finite element model (FEM) of the test was established to study the stability failure mechanism of PWFSs. Then, a design method for PWFSs was proposed through a structural stability analysis based on the limit equilibrium method, with special consideration of the cutting pile force influenced by row spacing. According to FE results, lateral pile displacements drawn from the FEM correspond well with field observations, and earth pressures applied on closely spaced piles are in line with Rankine's theory. Results of the theoretical analysis indicate that the control slip surface lies on the bottom of a soil layer with a poorer shear strength index. The effects of framework width, pile spacing, pile length and diameter on structural stability are also evaluated. The feasibility of PWFSs has been verified by an engineering test, and the simplified design method established here is reasonable and effective for structural stability prediction.

通过现场试验探究了真空预压技术在低渗透性软粘土中的处理加固效果,设计了6组试验组次共4组对照试验,分析了膜下处理方式、排水板深度、排水板类型和排水板间距对真空预压处理效果的影响.对于该工程中的超低渗透性软粘土,试验结果表明:排水板间距为0.8 m的分布型式优于间距为1.0 m的分布型式;采用长短板相结合的分布方式较单一长度的排水板处理方式,可有效提高真空预压的处理效果;采用较大的滤膜等效孔径可有效提高排水板真空度的传递效率,从而加强真空预压效果;传统铺设砂垫层的膜下处理方式虽然效果最佳,但考虑到施工成本和时间成本的因素,可采用三维排水网+直排式处理的方式进行替代.

针对深水软土地基,研究开发箱筒型基础结构,介绍箱筒型基础结构的应用情况.针对箱筒型基础结构可气浮的特点,提出一套气浮运输和定位、抽负压下沉安装的施工方法.该方法不需要大型起吊运输船舶,设备简单,下沉速度快,偏斜度容易控制,综合费用低.箱筒型基础结构对软土地基的适应性强、稳定好、施工便捷、投资省,具有良好的经济效益和社会效益.

The frame-fixed soldier pile structure (FSPS) is a new cofferdam structure of artificial island, with a notable feature of closely-spaced row-piles. Microstructure of soft soil has a significant effect on macroscopic physical quantities. The relationship between microstructure deformation characteristics of soft clay and shear strength index of soil was established by scanning electron microscope (SEM) test. Based on the subgrade reaction approach, a plane pole system finite element model (PPSFEM) was established to study displacement and internal force distribution along pile of FSPS under lateral load. The "load migrating" process was considered in the model that partial lateral load would transfer from rear pile to front pile via interior soil as interior soil reached the ultimate state. Study on how these factors affect the distribution of horizontal displacement and internal forces along pile has been performed through PPSFEM, including constraint form between frame structure and pile, m-values of subsoil and backfilling materials. The shear strength index of soil is significant affected by the microstructure. Parameter analysis indicates that the frame structure improves internal force distribution of pile foundation, that the feature of separated piles decreases the horizontal soil resistance of front pile, and that the articulated constraint form between pile and underpart of framework benefits to reduce the maximum bending moment of pile.

Multi-footing system composed of multiple separate footings is a common type of offshore foundation. Based on failure envelope theory, the failure mode of multi-footing system on sand is analyzed in this study. Additionally, the corresponding analytical method of the bearing capacity is established and its feasibility is verified. The comparison of the calculated load safety factors between the single footing and multi-footing system is conducted in different loading paths. The analytical method of foundation bearing capacity is also conducted based on the combination of the failure envelope theory and partial factor method. From the analysis of failure mode, head sea side footings with four-legged platform firstly reach the failure envelope as result of increasing horizontal load, and their failure modes further become sliding. However, the sliding of head sea side footings would not occur due to the constraints among other footings. Since the head sea side footings bear less horizontal and vertical loads with increasing the horizontal load, the back wave side footings have to undertake larger load. At last, back wave side footings also reach the failure envelope, which results in the failure of the multi-footing system. It is shown that load paths have critical influence on load safety factors, and thus they should be specified when calculating load safety factors. Since the size and shape of failure envelope depend on a variety of factors, the calculation of bearing capacity needs to consider the failure envelope under particular conditions during design of foundations.