Failure mechanism on sulfate attack and dissolved corrosion of diseased tunnel lining structure

To study the corrosion failure mechanism of tunnel lining structure subjected to sulfate attack and dissolved corrosion, site investigation was carried out on a diseased tunnel in Chongqing. The corrosion products were analyzed by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy. The results showed that the tunnel lining structure had been exposed to groundwater containing substantial concentrations of salts (SO42-, HCO3-, et al.) for many years, resulted that the concrete strength was lower than its design value. The formation of thaumasite made concrete lose its strength completely. Concrete structure would be destroyed when crystallization pressure exceeded the tensile strength of concrete. The tunnel also appeared dissolved corrosion which made the cement stone density and concrete strength reduce

Basalt-polypropylene fiber reinforced concrete for durable and sustainable pipe production. Part 1: experimental program

This is the peer reviewed version of the following article: [ Deng, Z, Liu, X, Chen, P, et al. Basalt-polypropylene fiber reinforced concrete for durable and sustainable pipe production. Part 1: Experimental program. Structural Concrete. 2022; 23: 311– 327. https://doi.org/10.1002/suco.202000759], which has been published in final form at https://onlinelibrary.wiley.com/doi/abs/10.1002/suco.202000759. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving.An experimental program consisting in producing and testing reinforced concrete pipes (RCPs) under the three-edge bearing tests considering different types of reinforcement was carried out. Four types of RCPs were produced, these reinforced with: (1) polypropylene macrofibers; (2) basalt microfibers; (3) combination of both (hybrid reinforcement); and (4) plain concrete. The analysis of the crack patterns and both service and ultimate mechanical responses allowed concluding that the use of fibers do not lead to an effective increase of the first cracking load; however, both types of fibers allowed a better crack width control respect to the standard RCP. In this regard, basalt microfiber reinforced concrete led to a better response caused by concentrated loads (jacketing) whilst polypropylene macrofibers increased the concrete pipe performance in terms of bearing capacity and flexural crack control. The hybrid fiber reinforced concrete was found to be the most suitable alternative for increasing the load bearing capacity and the crack width control for service loads. These incipient experimental results permit to conclude that this type of hybrid basalt-polypropylene fiber reinforced concretes are an interesting alternative to traditional steel-cage RCPs.This work is supported by the National Key Research and Development Program of China (2018YFC1504802), Natural Science Foundation Project of Chongqing, Chongqing Science and Technology Commission (cstc2018jscxmszdX0071), Postgraduate Research Innovation Project of Chongqing (CYS19005, CYS18026). In addition, Prof. Albert de la Fuente also wants to express his gratitude to the Spanish Ministry of Science and Innovation for the financial support received under the scope of the project CREEF (PID2019-108978RB-C32).Peer ReviewedPostprint (author's final draft

Study on Tensile Damage Constitutive Model for Multiscale Polypropylene Fiber Concrete

Polypropylene fibers perform well in roughness enhancement and corrosion resistance. They can dissipate energy when cracks occur in concrete. Furthermore, they can improve the concrete tensile properties by synergistic work with it. To study the tensile properties of the multiscale polypropylene concrete, uniaxial tensile strength of 18 fiber reinforced and 3 plain concrete specimens was experimentally tested using the paste steel method. The test results indicate that both the strength and the peak strain can be substantially improved. Based on the results, a tensile damage constitutive model was proposed and implemented into FLAC3D for numerical experimentation. The numerical results are consistent with the experimental observations in general and some discrepancies are discussed

An experimental study of bending resistance of multi-size PFRC beams

To study the effects of macro- and micro-fiber on the concrete beams, bending resistance tests were conducted on the polypropylene fiber-reinforced concrete beams. Stepwise loaded tests were carried out to obtain the load–deflection curves for different test pieces, cracking load values of the first inclined crack, recording and depicting crack development, changes in mid-span deflection of the test pieces, load–strain relationships of concrete, etc. The crack patterns and failure modes were observed. The research findings have shown that the ultimate load of the concrete beams doped with multi-size polypropylene fiber is 58.31 and 34.08% higher than that of ordinary concrete beams and concrete beams with single macro-fiber, respectively. Notably, the ultimate anti-bending bearing capacity of the beams significantly improves following the addition of macro-fiber. Polypropylene fiber can offset the defects caused by macro-fiber, remarkably suppress the development of cracks, and control the deformation of beams due to the effects of micro-fiber of different dimensions

A Study of Impact Response and Its Numerical Study of Hybrid Polypropylene Fiber-Reinforced Concrete with Different Sizes

Compressive properties of hybrid polypropylene fiber-reinforced concrete (HPFRC) with different sizes of polypropylene fibers (PPFs) under the impact load (101∼102/s) were tested by using a 74 mm diameter various cross-section split-Hopkinson pressure bar (SHPB), in which the fiber content of fine PPFs was 0.9 kg/m3 and that of coarse PPFs was 6.0 kg/m3. The effect of strain rate and PPF hybridization on the impact characteristics of HPFRC was analyzed. It is found that dynamic compressive properties, including dynamic compressive strength, dynamic compressive strength increase factor (DCF), ultimate strain, and impact toughness, increased with the increase of strain rate. Meanwhile, both fine PPFs and coarse PPFs can enhance the impact strength of concrete, and an appropriate hybridization of two sizes of PPFs in concrete was more effective than the concrete reinforced with one size of PPF. Moreover, a modified constitutive model for HPFRC was proposed based on the Holmquist–Johnson–Cook (HJC) constitutive model. Then, the numerical study of SHPB tests for HPFRC was conducted based on the modified model, which showed that the modified HJC constitutive model could well describe the dynamic stress-strain relationship of HPFRC

Flexural performance of a new hybrid basalt-polypropylene fiber-reinforced concrete oriented to concrete pipelines

The bending performance of a basalt-polypropylene fiber-reinforced concrete (HBPFRC) was characterized by testing 24,400 × 100 × 100 mm3 prismatic specimens in a four-point bending test JSCE-SF4 configuration. The type and content of both fibers were varied in order to guarantee different target levels of post-cracking flexural performance. The results evidenced that mono-micro basalt fiber reinforced concrete (BFRC) allows the increase of the flexural strength (pre-cracking stage), while macro polypropylene fiber reinforced concrete (PPFRC) can effectively improve both bearing capacity and ductility of the composite for a wide crack width range. Compared with the plain concrete specimens, flexural toughness and equivalent flexural strength of macro PPFRC and the hybrid fiber-reinforced concrete (HFRC) increased by 3.7–7.1 times and 10–42.5%, respectively. From both technical and economic points of view, the optimal mass ratio of basalt fiber (BF) to polypropylene fiber (PPF) resulted in being 1:2, with a total content of 6 kg/m3. This HFRC is seen as a suitable material to be used in sewerage pipes where cracking control (crack formation and crack width control) is of paramount importance to guarantee the durability and functionality of the pipeline as well as the ductility of the system in case of local failures.This research project was funded by the Spanish Ministry of Science and Innovation for the financial support received under the scope of the project CREEF (PID2019-108978RB-C32), the National Key Research and Development Program of China (Grant No. 2018YFC1504802), Natural Science Foundation Project of Chongqing (Grant No. cstc2018jscx-mszdX0071) and National Natural Science Foundation of China (Grant No. 41772319).Peer ReviewedPostprint (published version

Post-quantum adaptor signatures and payment channel networks

Adaptor signatures, also known as scriptless scripts, have recently become an important tool in addressing the scalability and interoperability issues of blockchain applications such as cryptocurrencies. An adaptor signature extends a digital signature in a way that a complete signature reveals a secret based on a cryptographic condition. It brings about various advantages such as (i) low on-chain cost, (ii) improved fungibility of transactions, and (iii) advanced functionality beyond the limitation of the blockchain’s scripting language. In this work, we introduce the first post-quantum adaptor signature, named $${\mathsf {LAS}}$$. Our construction relies on the standard lattice assumptions, namely Module-SIS and Module-LWE. There are certain challenges specific to the lattice setting, arising mainly from the so-called knowledge gap in lattice-based proof systems, that makes the realization of an adaptor signature and its applications difficult. We show how to overcome these technical difficulties without introducing additional on-chain costs. Our evaluation demonstrates that $${\mathsf {LAS}}$$ is essentially as efficient as an ordinary lattice-based signature in terms of both communication and computation. We further show how to achieve post-quantum atomic swaps and payment channel networks using $${\mathsf {LAS}}$$.</p

Analysis and application of friction calculation model for long-distance rock pipe jacking engineering

For long-distance rock pipe jacking, the coupled actions of mud float and sediment generate pipe-rock interactions, which are challenging from the analysis point of view and the general methods available for calculating the friction resistance of pipe-soil can lead to unrepresentative results. These friction forces must be quantified properly, as the magnitude of those determines the technical and economical construction requirements. In this regard, a novel approach that combines experimental and numerical stages is proposed in this research paper for dealing with the assessment of these friction forces. The results derived from the proposed approach were compared and validated with others obtained from a practical case, with satisfactory outcomes. The approach proposed herein is found to be a valuable guide for assessing the magnitude of the frictional forces that occur during the pipe jacketing and for identifying the parameters that govern the magnitude of these forces. Eventually, design and construction optimization and productivity-oriented measures can be derived from the application of the method.This study is supported by the National Key Research and Development Program of China (Grant No. 2018YFC1504802), Natural Science Foundation Project of Chongqing (Grant No. cstc2018jscx-mszdX0071). Prof. Albert de la Fuente also wants to express his gratitude to the Spanish Ministry of Science and Innovation for the financial support received under the scope of the project CREEF (PID2019-108978RB-C32).Peer ReviewedPostprint (author's final draft

Numerical study of the mechanical process of long-distance replacement of the definitive lining in severely damaged highway tunnels

Mountain road tunnels are prone to water leakage and lining corrosion under the complex geological conditions and corrosive environments, which will reduce the strength of the lining structure until it loses its load-bearing capacity; eventually, the definitive lining will need to be replaced. In this paper, a highway tunnel in a mountainous area in Southwest China is taken as an example. Field investigation found that the tunnel was seriously corroded by sulfate, the strength of the definitive lining decreased, and large-scale cracks and spalling appeared on the surface, so the operator decided to replace the definitive lining by the method of interval replacement. Based on the data obtained from drilling and coring, a numerical model of long-distance replacement of the definitive lining of the damaged tunnel is established. First, the back analysis of the calculation parameters is carried out, and the modified calculation results are compared with the field monitoring results for verification. Then, the deformation trend of the tunnel and the development of the plastic zone during the process of long-distance replacement of the definitive lining are studied. Finally, the construction scheme is optimized. Numerical analysis results show that the replacement of the definitive lining of the tunnel mainly leads to the settlement of the arch crown and the uplift of the inverted arch. The deformation of the tunnel shows two rapid growth stages and two stable stages during the replacement process; after replacement, the deformation of the arch crown and the inverted arch is divided into two buffer zones and one stable zone. In the progress of the replacement of the definitive lining, the plastic zone does not change. Regarding the reinforcement measures, with the increase in the grouting range, the grouting efficiency decreases, and the effect of the temporary steel arch on controlling the overall deformation is not obvious. The length of the replacement of the single section should be determined according to the geological conditions of the replacement section and the monitoring data during construction. The research results can provide a reference for similar projects for the replacement of the definitive lining