Concrete Application Research Articles

Packet-optical transport network for future radio infrastructure

The advent of 6G is expected to transform connectivity by necessitating robust and scalable transport networks, capable of managing the escalating demands for enhanced bandwidth, negligible latency, and heightened network automation. The progression towards centralized radio access networks and the cloudification of network functions introduce additional requirements to the transport network. Addressing these demands, the integration of packet and optical systems combines packet flexibility with the high bandwidth and low latency of optical systems, aiming for a balance between performance, efficiency, and functionality. This process considers cost and the reuse of existing infrastructure towards a seamless transition to 6G. The concept of a Mini-ROADM, a cost-effective, energy-efficient optical switch created using silicon photonics, is presented and demonstrated in a ring network application. The role of a transport-aware end-to-end orchestrator in coordinating resources across radio, transport, and cloud domains to ensure a diverse range of quality-of-service levels is also discussed. A system demonstrator that highlights the integration of packet and optical layers and the concrete application of these concepts in a network environment is presented.

Effect of eco-friendly pervious concrete pavement with travertine waste and sand on the heavy metal removal and runoff reduction performance

To address the negative environmental and economic impact of the large amounts of solid waste generated during travertine mining and to reduce the dependence on natural aggregates and cement for pervious concrete pavement applications, travertine waste, as aggregate and powder, was used for the travertine powder pervious concrete (TPPC) to improve the utilization of solid waste and decrease CO2 emissions. The experimental results showed that using 25% travertine aggregate and 5% powder results in a compressive strength reduction of only 9.8% to 25.92 MPa but a significant improvement in water permeability of 57.1% from 3.89 to 6.11 mm/s. To improve the performance of TPPC, further research was done on the effect of sand addition rate (SAR) on TPPC's density, compressive strength, porosity, water permeability, freeze-thaw resistance and heavy metal removal capacity to obtain an optimal incorporation ratio. As SAR rises, the compressive strength of TPPC with sand (STPC) initially increases and then decreases, while permeability behaves inversely. At 3% SAR, the compressive strength reached a maximum of 26.51 MPa, primarily due to the sand added to fill in some of the pores and stabilize the gradation. After 25 cycles, the strength loss rate of STPC varies from 11.39 to 17.93% and the freeze-thaw resistance is most excellent when SAR is 3%. The removal rate of heavy metals using the immersion method was found to be significantly higher (83.4–100%) compared to the rapid method (11.7–28.1%). Therefore, the 3% SAR was recommended for the mixture design of STPC. A laboratory-scale version of the pavement was constructed to assess the efficacy of STPC pavement (STPCP) in reducing runoff and removing heavy metals. The results showed that STPCP could remove more than 94% of runoff with varying intensities after 1 h. The STPCP exhibited removal rates ranging from 42.0 to 99.4% for Cd2+ and 79.5–95.4% for Cu2+. STPCP also attained a removal rate above 98% for Pb2+ after 30 min, demonstrating its environmental friendliness.

Effect of recycled concrete aggregates on the punching strength of slab-column connections without shear reinforcement

This paper presents the results of tests on six reinforced concrete slab-column connections. The slabs were octagonal, centrally supported on square columns, and concentrically loaded at their borders. The tests investigated the effects of replacing natural coarse aggregates with recycled concrete aggregates. The experimental results were also compared to resistance estimates from ACI 318 (2019) and Eurocode 2 (2004) and results from a database with tests on slabs without recycled concrete aggregates. The results show that using RCA reduces the concrete's modulus of elasticity and tensile strength but has little effect on its compressive strength. Furthermore, using RCA has little impact on the flexural response and punching resistance of the slabs. The findings suggest that RCA has potential for use in concrete applications, but further tests are required to draw definitive conclusions.

Compressive stress-strain relationship of steam free reactive powder concrete at ultra-low temperatures

To explore the applicability of reactive powder concrete (RPC) as a material for LNG storage tanks, the mechanical properties of RPC at ultra-low temperatures were investigate in this paper. Forty-two axial compressive strength tests were conducted on RPC prisms at 20 °C ∼ −165 °C. The influence of temperature and steel fiber on the compressive stress-strain relationship of RPC at ultra-low temperatures was evaluated. The results showed that the axial compressive strength of RPC increases at low temperatures, with a compressive strength increase of over 70 % at −165 °C compared to room temperature. The increase in compressive strength of RPC at ultra-low temperatures is significantly greater than that of ordinary concrete. A relation for predicting the axial compressive strength development of RPC at ultra-low temperatures was also proposed. Steel fibers can increase the toughness of RPC at ultra-low temperatures to a certain extent, and effectively improve the failure mode of RPC, allowing the damaged RPC to maintain its integrity. This work provides a basis for RPC applicability as LNG storage tanks.

A Review on the Recycling Waste Materials for Green Concrete

This has increased the generation of solid waste, creating environmental and economic problems on an international scale. The construction industry, one of the major environmental degrading and resource-consuming industries, plays a major role. This study examines how waste material is used in green concrete as a sustainable solution to minimize environmental burdens and save natural resources. Utilizing waste material such as silica fume, fly ash, recycled aggregates, and ground-granulated slag from blast furnaces (GGBFS), recycled plastic, and biopolymers, green concrete minimizes carbon emissions as well as reduces the need for virgin materials. In this paper, it is discussed how the application of such waste products in green concrete minimizes the carbon footprint and saves natural resources, whereas on the other hand, it also saves material and construction costs. Life cycle assessment studies and sustainability analysis give a valuable comparison in overall sustainability between green concrete and conventional concrete. Challenges and future directions in this field elucidate the uniformity of waste material quality, regulatory support, and public acceptance. The scope of further research lies in the development of material characterization, long-term durability studies, and technological advancement, which promise to deliver desired performance and applications of green concrete.

“Advancements in Lightweight Concrete: A Comprehensive Review”

Abstract: Lightweight concrete (LWC) has garnered considerable attention in recent years due to its advantageous properties such as reduced density, improved thermal insulation, and enhanced sustainability. This review paper provides a comprehensive overview of the advancements, properties, production methods, applications, and future prospects of lightweight concrete. It covers various types of lightweight aggregates, admixtures, and innovative techniques employed in the production of lightweight concrete. Furthermore, it discusses the mechanical, thermal, and durability properties of LWC and compares them with conventional concrete. The review also explores the wide range of applications of lightweight concrete in construction projects and its contribution to sustainable development goals. Finally, it identifies current challenges and future research directions in the field of lightweight concrete.

A Multiphase and Multicomponent Model and Numerical Simulation Technology for CO2 Flooding and Storage

In recent years, CO2 flooding has become an important technical measure for oil and gas field enterprises to further improve oil and gas recovery and achieve the goal of “dual carbon”. It is also one of the concrete application forms of CCUS. Numerical simulation based on CO2-EOR plays an indispensable role in the study of the mechanism of CO2 flooding and buried percolation, allowing for technical indicators to be selected and EOR/EGR prediction to be improved for reservoir engineers. This paper discusses the numerical simulation techniques related to CO2 flooding and storage, including mathematical models and solving algorithms. A multiphase and multicomponent mathematical model is developed to describe the flow mechanism of hydrocarbon components–CO2–water underground and to simulate the phase diagram of the components. The two-phase P-T flash calculation with SSI (+DEM) and the Newton method is adopted to obtain the gas–liquid phase equilibrium parameters. The extreme value judgment of the TPD function is used to form the phase stability test and miscibility identification model. A tailor-made multistage preconditioner is built to solve the linear equation of the strong-coupled, multiphase, multicomponent reservoir simulation, which includes the variables of pressure, saturation, and composition. The multistage preconditioner improves the computational efficiency significantly. A numerical simulation of CO2 injection in a carbonate reservoir in the Middle East shows that it is effective for researching the recovery factor and storage quantity of CO2 flooding based on the above numerical simulation techniques.

Influence of combined substitution of slag and fly ash in improving the pore structure and corrosion resistance of foam concrete mixtures used for reinforced concrete applications

Foam concretes (FCs) have been used for several light-weight applications demanding low strength; however, their use for reinforced concrete (RC) applications is limited since high macrovoid amounts result in weaker matrices. The high w/c and overlapping of macrovoids have been identified as critical factors constituting a permeable microstructure in FC systems. Since corrosion performance is a critical aspect in the design of RC members and that the durability parameters of concrete, such as its porosity, pore size distribution, and permeability, also play a vital role in restricting the diffusion of chloride ions, particularly in the cover region of members, it is imperative to determine these properties and thoroughly understand the material behaviour or characteristics. In the current study, five FC mixtures (GF0 to GF4) were produced using ground granulated blast furnace slag (GGBS) and fly ash (FA) as a replacements for cement and sand, respectively, at different dosages, considering both economic and environmental aspects. The principal objective of the study is to determine the pore and permeability related properties of produced FCs, assess their corrosion performance, and ascertain their suitability for RC applications by comparing their performance with that of conventional M25-grade concrete. Also, the influence of the combined effect of GGBS and FA addition and the individual effect of FA addition were assessed. The research findings showed that FCs had a higher water absorption capacity and porosity compared to M25 concrete. In addition, the inclusion of GGBS and FA resulted in a decrease in water absorption by 8%–19% and a decrease in porosity by 23%–36% compared to the control FC mixture. The Mercury Intrusion Porosimetry (MIP) results indicated a substantial enhancement in gel pores, threshold, and critical pore diameter, while the size of the larger capillary pore decreased by 90%–95% when GGBS and FA were added compared to the control FC mixture. The scanning electron microscopy (SEM) analysis and binary images from the image analysis revealed the presence of uniformly distributed and distinct macrovoids formed by foam. These macrovoids were predominantly found within the size range of 7.1μm – 100 µm. The addition of GGBS and FA particles to FC mixes resulted in a significant improvement in the chloride ion permeation (CIP) class, reducing it from 'High' to 'Very Low' compared to M25 concrete. The Accelerated Corrosion Test (ACT) results obtained from FCs demonstrated a significant increase in cracking time ranging from 30% to 323%, as well as a notable decrease in mass loss ranging from 56% to 85% when compared to M25 concrete. The Fourier transform infrared (FTIR) and energy dispersive spectroscopy (EDS) analysis results revealed the presence of corrosion products, including feroxyhyte, akageneite, and Friedel's salt crystal, in both FCs and M25 concrete, indicating the occurrence of corrosion by the chloride ions present in the NaCl solution outside the specimen. Overall, the porosity, CIP, and corrosion resistance of FC with GGBS and FA are superior to those of the M25 concrete, making it suitable for use in RC applications.

Climate Litigation

The last decade has seen an increase in the number, specificity and importance of laws codifying national and international responses to climate change. As these laws have recognised new rights and created new obligations, they have led to the initiation of lawsuits challenging either their effectiveness or their concrete application. The aim of these disputes is to force legislators and policy makers to take a more ambitious and thorough approach to climate change. In addition, litigation has continued to fill the gaps left by legislative and regulatory inaction. As a result, the courts are increasingly adjudicating disputes over actions – or inaction – in relation to climate change mitigation and adaptation efforts.

Electromagnetic wave absorption value of iron-rich steel slag for application in foam concrete

In this study, iron-rich steel slag (IRSS) and carbon fiber (CF) were incorporated into foam concrete to maximize the economic benefits of composites and multifunctional integration while improving the overall performance of foam concrete. The study found that the optimal IRSS content for maximizing foam concrete’s compressive strength was 15 %, which increased by 18.59 % compared to the control. Additionally, S15 specimens showed a 37.87 % increase in electrical conductivity compared to the control. In addition, the average value of the fundamental part of the dielectric constant of the S15 specimen was 7.409, the average value of the imaginary part was 3.057, and the angular tangent of the electrical loss (tanδε) value and the reflection loss were both improved, which indicated that the S15 specimen material had a better ability to absorb electromagnetic waves and had an excellent performance of electromagnetic loss.

Structural Lightweight Concrete Containing Basalt Stone Powder

In spite of the demonstrated efficacy of basalt stone powder as a cost-effective and readily available additive in enhancing the mechanical properties and durability of ordinary-weight concrete, its application in Structural Lightweight Concrete (SLWC) remains unexplored. This study introduced a mixing design for SLWC incorporating Light Expanded Clay Aggregates (LECAs) and basalt stone powder with a subsequent evaluation of its strength and durability characteristics. The experimental procedure involved creating various samples, considering differing proportions of cement, water, basalt stone powder, sand, LECA, superplasticizer, and aerating agent. The compressive strength and density of the 28-day-cured concrete specimens were determined. An optimal SLWC with a compressive strength of 42 MPa and a density of 1715 kg/m3 was identified. The flexural and tensile strength of the optimal SLWC exceeded those of ordinary-weight concrete by 6% and 3%, respectively. Further evaluation revealed that the optimal SLWC exhibited 1.46% water absorption and an electrical resistivity of 139.8 Ohm.m. Notably, the high porosity of LECA contributed to the low durability of SLWC. To address this, cost-effective external coatings of emulsion and fiberglass were applied to enhance the durability of the SLWC. Four coating scenarios, including one-layer bitumen, two-layer bitumen, three-layer bitumen, and three-layer bitumen with fiberglass, were investigated. The measurements of electrical resistance and compressive strength revealed that the use of three layers of emulsion bitumen and fiberglass improved the durability of the concrete by over 90% when the SLWC was exposed to severe chloride attack. Consequently, the durability of the SLWC with an external coating surpassed that of ordinary-weight concrete.

Reconstructing higher-order interactions in coupled dynamical systems

Higher-order interactions play a key role for the operation and function of a complex system. However, how to identify them is still an open problem. Here, we propose a method to fully reconstruct the structural connectivity of a system of coupled dynamical units, identifying both pairwise and higher-order interactions from the system time evolution. Our method works for any dynamics, and allows the reconstruction of both hypergraphs and simplicial complexes, either undirected or directed, unweighted or weighted. With two concrete applications, we show how the method can help understanding the complexity of bacterial systems, or the microscopic mechanisms of interaction underlying coupled chaotic oscillators.

3D printing of cementitious composites with seashell particles: Mechanical and microstructural analysis

Seashells are abundantly available as waste products from the seafood industry and from coastal areas. Accordingly, processed shells can be used to partially replace aggregates in traditional concrete. This paper investigates the effects of different proportions of seashell particles on the mechanical and microstructural properties of 3D-printed cementitious composites. The seashells were crushed and milled to be transformed into seashell particles, replacing the river sand at 15 wt% and 30 wt%. It was found that when the seashell particle content increased to 15 wt% and 30 wt%, the mechanical strengths all decreased significantly, which could be attributed to the increasing volumetric proportion of voids and the lower elastic modulus of seashell particles compared to river sand. However, when the seashell particle proportion further rose from 15 wt% to 30 wt%, the mechanical strengths did not continue decreasing substantially. Instead, the compressive and indirect tensile strengths nearly levelled off with minor fluctuations. Based on the microstructural analysis results, it was inferred that the fine seashell powders as part of the seashell particles, which were comprised of aragonite-based calcium carbonate, participated in the cement hydration process that could help with microstructure densification of the cement matrix. This positive effect brought by the fine seashell powders was thought to prevent the further weakening of mechanical properties. Overall, this study aims to understand the role of seashell particles on the mechanical performance of 3D-printed cementitious composites from the perspectives of microstructural characteristics, further promoting the utilisation of waste seashells in 3D concrete printing applications.

Feasibility of using 2304 duplex stainless steel in seawater-mixed concrete pore solutions: A preliminary passivation consideration

Due to the growing shortage of fresh water resources worldwide, it is necessary to explore the feasibility of using seawater to produce concrete. However, the passivation and pitting corrosion resistance of reinforcing steel will inevitably be impaired by the chlorides contained in seawater. Therefore, it is particularly important to develop a corrosion-resistant steel that could be employed in seawater-mixed concrete. One option being considered is using duplex stainless steel (DSS). To evaluate the feasibility of application in seawater-mixed concrete, the passive films of 2304 DSS were both generated by cyclic voltammetry and naturally formed in alkaline solutions with and without admixed chlorides, which was further compared with those of the conventional low-carbon steel (HRB400E steel). Unlike 2304 DSS, HRB400E steel failed to be passivated with admixed chlorides. Furthermore, the passive film of 2304 DSS was investigated by EIS, AFM and XPS measurements. Although the passivation ability was slightly reduced by admixed chlorides, and the morphology and composition of passive film were also modified, the high pitting corrosion resistance of 2304 DSS guaranteed its application in seawater-mixed concrete.

Non-Parametric Estimation of the Renewal Function for Multidimensional Random Fields

This paper addresses the almost sure convergence and the asymptotic normality of an estimator of the multidimensional renewal function based on random fields. The estimator is based on a sequence of non-negative independent and identically distributed (i.i.d.) multidimensional random fields and is expressed as infinite sums of k-folds convolutions of the empirical distribution function. It is an extension of the work from the case of the two-dimensional random fields to the case of the d-dimensional random fields where d>2. This is established by the definition of a “strict order relation”. Concrete applications are given.

Influence of the multiple element ions contained in seawater and sea sand on the freeze-thaw resistance of cementitious materials

Preparation of concrete with seawater and sea sand can increase the pore solution salinity due to the introduced multiple ions, which can affect the freeze-thaw resistance of concrete by changing the crystallization pressure and freezing temperature. This study aims to investigate the influence of these multiple element ions in seawater and sea sand on the freeze-thaw damage characteristics of cementitious materials. The seawater sea-sand mortar (SSM) samples and reference specimens (Freshwater and river sand-FRM) were first prepared with same mix design. The accelerated freeze-thaw tests were then conducted in an environment chamber under the temperature range of [-20 °C, 7 °C]. The surface spalling, mass loss, and mechanical performance (Compressive strength, stiffness and fracture resistance) evolution during freeze-thaw cycles were characterized to examine the freeze-thaw resistance. The influence mechanism is analyzed through characterization of pore solution and structure, and Discrete Element Method (DEM) simulation. It is indicated that the introduced multi-element ions from seawater and sea sand accelerate the freeze-thaw deterioration of cementitious materials. After 150 freeze-thaw cycles, the mass loss rates of SSM and FRM samples reach above 10 % and 8 %, respectively. And the corresponding reduction rates for dynamic modulus are 51 % and 36 % for the SSM and FRM specimens. The deterioration in compressive strength is slightly higher than the loss of fracture resistance. The mechanism analysis indicated that deteriorated freeze-thaw resistance due to the introduced multi-element ions from seawater and sea sand mainly originated from the degradation of pore structure and the increase in freezing pressure. This study can serve as a solid base for the durability design and application of seawater sea-sand concrete in cold regions.

Effect of stone powder and practical evaluation on mechanical property of manufactured sand concrete

ABSTRACT Manufactured sand concrete (MSC) is a specific type of concrete successfully employed in many projects and structures made of reinforced concrete, and improving concrete structures. The important characteristic of mechanical sand is that the fine aggregate contains stone powder composed of particles which could pass 75 urn BS sieve. The influence of different stone powder contents on the properties of hardened concrete was studied through experiments. In addition, the experimental relations for estimating the mechanical parameters of MSC compared with CC is presented in this paper. Specimens made of MSC were prepared, on which the axial compression test, cube compression test, splitting test, flexural test and elastic modulus test were conducted. The experimental relations were obtained between the compressive strength, tensile strength and elastic modulus for MSC, and their validity were then investigated. Stone powder can fill the pores in the MSC, improve the overall grading of mechanism sand concrete, improve its working performance, and help to improve the mechanical strength of MSC. The optimum value of stone powder content is accepted as 7.5–10%. The conclusions obtained can provide a basis for the research and promotion application of mechanism sand concrete. The results indicated that the obtained relations could be used to estimate the mechanical properties of MSC with accuracy.

On spectral inclusion sets and computing the spectra and pseudospectra of bounded linear operators

In this paper, we derive novel families of inclusion sets for the spectra and pseudospectra of large classes of bounded linear operators, and establish convergence of particular sequences of these inclusion sets to the spectrum or pseudospectrum, as appropriate. Our results apply, in particular, to bounded linear operators on a separable Hilbert space that, with respect to some orthonormal basis, have a representation as a bi-infinite matrix that is banded or band-dominated. More generally, our results apply in cases where the matrix entries themselves are bounded linear operators on some Banach space. In the scalar matrix entry case, we show that our methods, given the input information we assume, lead to a sequence of approximations to the spectrum, each element of which can be computed in finitely many arithmetic operations, so that, with our assumed inputs, the problem of determining the spectrum of a band-dominated operator has solvability complexity index one in the sense of Ben-Artzi et al. (2020). As a concrete and substantial application, we apply our methods to the determination of the spectra of non-self-adjoint bi-infinite tridiagonal matrices that are pseudoergodic in the sense of Davies [Commun. Math. Phys. 216 (2001), 687–704].

Research and Development of New Polylactic Acid (PLA) Fiber Concrete Materials and Performance Research

Polylactic acid (PLA) fiber concrete has broad application prospects in the field of building materials. This article summarizes the current research status of fiber-reinforced concrete and its importance in improving the mechanical properties of cement-based materials. In view of the modification of the physical properties of PLA fiber, experimental research is conducted to improve its mechanical properties, solve the problem of natural degradation, and explore the application of anti-corrosion materials. In terms of concrete preparation technology, experiments were carried out to study uneven fiber distribution and compatibility with cement slurry to determine the optimal proportion and processing technology. Mechanical property tests and theoretical studies have shown that fiber type and length have a significant impact on the performance of concrete, and it is necessary to further explore the mechanical properties of the transition zone between the fiber and the concrete matrix. Aiming at the durability, fire resistance and other issues of PLA fiber concrete, relevant experimental research plans were proposed. Finally, the mechanical properties of ultra-high toughness PLA fiber concrete were optimized by improving the mix design, optimizing fiber type and dosage, and surface treatment technology. These research results provide an important reference for the wide application of ultra-high toughness PLA fiber concrete in building structures.

An Experimental Study on Compressive Properties of Composite Fiber Geopolymer Concrete

Background: The production process of Portland cement (OPC) consumes energy and releases carbon dioxide, which affects the environment. It has been found that geopolymer cementing material is a better substitute for it. The strength effect of fiber on geopolymer materials is the basis of the application of fiber geopolymer concrete in structural beams, slabs, and other components. Methods: Geopolymer concrete was prepared with fly ash, slag, and water glass as the main raw materials, and the effects of fiber type, quality, and blending method on the compressive properties and elastic modulus of geopolymer concrete were compared to explore the working mechanism of fiber-reinforced geopolymer concrete. Results: Through experimental research, the results showed that in 0.2% flocculent lignin fibers, when the mass ratio of carbon fibers was increased, the strength of the geopolymer concrete decreased. Due to the increased mass ratio of wavy steel fibers, comprising 0.2% flocculent lignin fibers, the strength enhancement effect was not apparent. Moreover, with regard to enhancing the modulus of elasticity of geopolymer concrete, blending fibers exerted the most significant effect. The fiber was added to geopolymer concrete to form a three-dimensional supporting frame system. When cracks occurred under the action of force, the development of cracks was limited due to the fibers, and the bonding slip delayed the propagation of cracks. The composite fiber could make full use of the advantages of each material and improve the strength of geopolymer concrete. Conclusion: The compressive properties of geopolymer concrete could be enhanced by blending single-fiber or mix-fibers, and the effect of mix-fibers was more optimal than that of others. The above research results provide a theoretical reference for the design of geopolymer concrete and a theoretical basis for the application of fiber geopolymer concrete in structural beams, slabs, and other components.