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A novel procedure has emerged in recent years within oilfields - namely, the utilization of a hybrid fracturing method employing pre-CO2 injection along with sand-carry slick water. In this paper, based on the real logging data of shale oil reservoirs in the second member of Cangdong Sag, Huanghua Depression, combined with the GOHFER, a coupled 3-D hydraulic fracture propagation model is proposed. This research delves into an examination of how engineering factors exert their influence on the process of fracture propagation. The quantitative analysis is conducted encompassing critical fracture parameters such as half-length, height, and width, and self-defined fracture seepage area and fracture front fractal dimension. The research findings indicate that as injection displacement increases, the fracture shape undergoes a transformation from being "long, low, and wide" to becoming "short, high, and narrow". [ABSTRACT FROM AUTHOR]

The cement manufacturing industry, a resource- and energy-intensive sector, took up more than 15% of total greenhouse gas emissions in China, thus finding a clean technology option for sustainable development is essential. CO 2 curing has emerged as a promising novel method for large-scale carbon sequestration and mechanical properties improvement of cement-based composites. Currently, a body of related works is mainly investigated in the laboratory, and understandings of the behaviors of CO 2 -cured cement-based composites are still less than complete, including, 1) the CO 2 storage potential has plenty of room for improvement due to the influence mechanism of variables factors remains unclear; 2) previous evaluations were mostly based on the subsets of individual result rather than an integrated dataset; 3) whether CO 2 curing is suitable for the manufacturing process of reinforced concrete. Therefore, this paper presents a comprehensive overview covering a wide range of parameters as well as fabrication, mechanical (compressive strength), and environmental (CO 2 uptake value) performances on the basis of a correct understanding of the differences between active and passive carbonation reactions. Notably, the influences of critical factors, including those less understood, e.g., types of curing setup (flow-able, enclosed, and others), components of binder, and aggregate/binder ratio, are also analyzed and the corresponding mechanisms discussed to achieve satisfied curing efficiency. Besides, corrosion-related challenges are also be pointed out to convince the widespread acceptance of this technology. Finally, based on this paper, limitations of existing research are identified and future scope on CO 2 curing regime is proposed. • 170 studies related to CO 2 /carbonation-cured cement-based composites are analyzed. • The differences between active/passive-carbonation together with reaction mechanisms are expounded. • Fabrication and influence factors on engineering and environmental properties are systematically reviewed. • CO 2 -cured cement-based composites exhibit excellent resistance to aggressive conditions. • The challenges and opportunities in the CO 2 curing method are innovatively discussed. [ABSTRACT FROM AUTHOR]

The disposal of waste coal gangue (WCG) is still a serious problem for areas that rely on the coal mine industry, especially in the northern part of China. This paper investigated the improving behavior and corresponding mechanism by waste coal gangue on the dispersivity, water stability and mechanical properties of dispersive soil. Dispersive soil samples with different contents of natural waste coal gangue, varying from 1% to 10%, were prepared and cured for 0, 1, 3, 7, 14 and 28 days. Dispersivity and water stability of soil samples were evaluated by pinhole test, cube sample crumb test and remoulded sphere sample crumb test. Electric conductivity and pH of soil samples were monitored during 28 days of curing. Unconfined compression test and splitting test were performed to determine the compressive and tensile strength of soil samples. Microstructural and mineral analysis methods such as SEM, EDS and XRD were conducted to determine the microstructural and mineral changes during curing time. Experiments show that waste coal gangue could restrain the dispersivity and enhance the water stability of dispersive soil, subsequently changing dispersive soil into nondispersive soil. Increases of 591% and 192% are observed when WCG content increases from 1% to 10% and curing time increases from 0 to 28 days for compressive and tensile strength, respectively. Increasing in waste coal gangue content and curing time would better promote the positive effect of waste coal gangue, on both the dispersivity modification and strength improvement of dispersive soil. Microstructural and mineral analyses show that newly generated products among soil particles increase the friction and cohesion between soil particles. Results indicate that reusing of waste coal gangue as an admixture in dispersive soil is a feasible way, which would solve the disposal of waste coal gangue and optimize the poor properties of dispersive soil at the same time. Enhancing water stability of dispersivity soil would ensure the safety and normal operation of soil structures. • Modification experiment of dispersive soil by waste coal gangue is studied. • Waste coal gangue is capable of changing dispersive soil into nondispersive soil. • Water stability of dispersive soil is enhanced by waste coal gangue. • Mechanical property of dispersive soil is improved by waste coal gangue. [ABSTRACT FROM AUTHOR]

• The EBW test of different weld penetration and scale FW with W/Cu sheets was realized. • When the weld penetration is small, the surface focus welding is the best. Otherwise, the lower focus welding is the best. • Reduced scale FW welding with weld width less than 4 mm and good surface forming is realized. Water- cooled ceramic breeder (WCCB) blanket is one of the candidate blanket for China Fusion Engineering Test Reactor (CFETR) independently developed by China Institute of plasma physics. The first wall (FW) is a component of WCCB, which directly faces the plasma. FW contains flow channels and has complex shape structure, therefore, it is difficult to complete the full-scale manufacturing by one kind of welding process. Hence, in the development process, the components of FW are first connected by hot isostatic pressing (HIP), and then connected by electron beam welding (EBW), so as to form the full-scaled FW connection. In this paper, the EBW process of FW was studied. The results showed that when the electron beam current was 50 mA and the focus was on the surface, the welded joint with 20 mm penetration and good shape can be formed. After the one time welding and the twice welding (overlapping first welding) of the weld, the tensile test fracture occurred in the base metal. The impact energy of the one time welding was 13 MPa, 18 MPa, and 21 MPa, respectively, and the impact energy of the twice welding was 19 MPa, 20 MPa, and 51 MPa, respectively. The microstructure of the joint was composed of δ-ferrite and lath martensite. When the weld penetration was increased to 50 mm, the lower the focus is, the smaller the porosity at the bottom of the weld is. Similarly, when the lower focus was used, the porosity at the bottom of the weld disappeared basically; The EBW test on the scaled FW with W/Cu sheets showed that when the we took the test pieces with the W-Cu sheet spacing is 4 mm, the welded joint with good surface shape and no internal defects can be formed without scanning deflection electron beam welding, and ultrasonic testing showed that EBW does not affect on the HIP interface. This provides a favorable basis for the future test of equal ratio FW test piece and the welding of actual FW. [ABSTRACT FROM AUTHOR]

Polymer-modified concrete and fiber concrete are two excellent paving materials that improve the performance of some concrete, but the performance of single application material is still limited. In this paper, polymer-modified concrete with strong deformation and fiber concrete with obvious crack resistance and reinforcement effect were compounded by using the idea of composite material design so as to obtain a high-performance pavement material. The basic mechanical properties of high-content hybrid fiber–polymer-modified concrete, such as workability, compression, flexural resistance, and environmental durability (such as sulfate resistance) were studied by using the test regulations of cement concrete in China. The main results were as follows. (1) The hybrid fiber–polymer concrete displayed reliable working performance, high stiffness, and a modulus of elasticity as high as 35.93 GPa. (2) The hybrid fiber–polymer concrete had a compressive strength of 52.82 MPa, which was 31.2% higher than that of the plain C40 concrete (40.25 MPa); the strength of bending of the hybrid concrete was 11.51 MPa, 191.4% higher than that of the plain concrete (3.95 MPa). (3) The corrosion resistance value of the hybrid fiber–polymer concrete was 81.31%, indicating its adjustability to sulfate attack environments. (4) According to cross-sectional scanning electron microscope (SEM) images, the hybrid fiber–polymer concrete was seemingly more integrated with a dense layer of cementing substance on its surface along with fewer microholes and microcracks as when compared to the ordinary concrete. The research showed that hybrid fiber–polymer concrete had superior strength and environmental erosion resistance and was a pavement material with superior mechanical properties. [ABSTRACT FROM AUTHOR]

Abstract: Fracture data available for one of the rock masses (limestone) in the dam site of Yujian River Reservoir were used to build and validate a stochastic 3-D fracture network model, and to perform a REV and equivalent continuum study in 3-D. A number of relations are developed in the paper between the rock mass mechanical parameters and fracture tensor components in 3-D. Based on the mechanical parameter values obtained in every 45° direction in 3-D, the principal parameter values, principal directions and tensors are developed for rock mass mechanical parameters to represent the REV block size properties. An incrementally linear elastic, orthotropic constitutive model is suggested to represent the equivalent continuum pre-failure mechanical behavior of the jointed rock mass by incorporating the effect of joint geometry network by the fracture tensor components. [Copyright &y& Elsevier]

• 52 tensile coupons of high-performance bolt material are tested. • Effects of test strain-rate on the elevated temperatures are clarified. • Elevated-temperature behaviour of the steel is elucidated at microstructure level. • Prediction equations are proposed for elevated-temperature performance. • Constitutive model of full-range stress-strain relation is developed. Mechanical properties of steel at elevated temperatures are critical to the fire-resistant analysis and the fire safety design of steel structures. Thus, one solution for improving the fire resistance is use of high-performance (HP) steel, such as fire-resistant (FR) steel. However, practical use of the FR steel in steel structures implies requirements of sufficient fire resistance for the high-strength (HS) bolts as well, so that the loading capacities of bolted connections commonly used in steel structures can be guaranteed in case of fire. In this paper, material properties of grade 10.9 HP bolts recently developed in China, possessing both fire resistance and corrosion resistance, are tested at various elevated temperatures. Their stress-strain curves, modulus of elasticity, yield strength, ultimate tensile strength (UTS), and elongation percentage after fracture are obtained. These results are compared with that of conventional HS bolts and with reduction factors given in national standards. Constitutive models and prediction equations of the HP bolts at elevated temperatures are proposed. Besides, the relationship between degradation in macro mechanical properties and change in microstructure is clarified. The research outcomes may provide essential bases for the fire response analysis of steel structures applying the FR steel and the HP bolts. [ABSTRACT FROM AUTHOR]

The abundant reserve of shale gas in Sichuan Basin has become a significant natural gas component in China. To achieve efficient development of shale gas, it is necessary to analyze the stress state, pore pressure, and reservoir mechanical properties such that an accurate geomechanical model can be established. In this paper, Six wells of Neijiang-Dazu and North Rongchang (NDNR) Block were thoroughly investigated to establish the geomechanical model for the study area. The well log analysis was performed to derive the in-situ stresses and pore pressure while the stress polygon was applied to constrain the value of the maximum horizontal principal stress. Image and caliper data, mini-frac test and laboratory rock mechanics test results were used to calibrate the geomechanical model. The model was further validated by comparing the model prediction against the actual wellbore failure observed in the field. It was found that it is associated with the strike-slip (SS) stress regime; the orientation of SHmax was inferred to be 106–130° N. The pore pressure appears to be approximately hydrostatic from the surface to 1000 m true vertical depth (TVD), but then becomes over-pressured from the Xujiahe formation. The geomechanical model can provide guidance for the subsequent drilling and completion in this area and be used to effectively avoid complex drilling events such as collapse, kick, and lost circulation (mud losses) along the entire well. Also, the in-situ stress and pore pressure database can be used to analyze wellbore stability issues as well as help design hydraulic fracturing operations. [ABSTRACT FROM AUTHOR]

Membrane structures deteriorate with time. This results in reduction of their resistance, and consequently, of their reliability. Material aging is one of the main causes of structure deterioration. This paper investigates statistical characteristics of naturally aged polyvinylidene fluoride PVDF-coated fabrics' mechanical properties and calculates reliability indexes on the basis of Central Point Method and Rackwitz-Fiessler Method. Five groups of experimental fabrics were taken from different existing engineering structures or indoor warehouse in China, which have been naturally aged for more than 10 years. First, series of tearing tests, uniaxial and biaxial tensile tests were carried out to study the mechanical properties. Then, the uncertainties of material properties, material's dimension, computational model and load effects were discussed and the reliability indexes were studied by two methods according to the ultimate limit state. Finally, reliability indexes of aged PVDF-coated fabrics were compared with that of unaged coated fabrics. Results show that the impact of natural ageing on the properties of PVDF-coated fabric can not be ignored in reliability analysis and membrane structures design. These data offer a further understanding of aged PVDF-coated fabrics' mechanical properties and provide references for the durability analysis of tensioned membrane structures. • Five groups of naturally aged PVDF-coated fabris were taken from engineering structures or indoor warehouse in China. • Series of tests were carried out to study their mechanical properties. • Uncertainties of material properties, material's dimension, computational model and load effects were studied. • Reliability indexes were calculated by two methods. • Reliability indexes of aged coated fabrics were compared with those of unaged fabrics. [ABSTRACT FROM AUTHOR]