Protection Of Concrete Structures Research Articles

Impact Behaviour of Steel-Fibre-Reinforced Alkali-Activated Slag Concrete Exposed to Elevated Temperatures.

Concrete protective structures are mainly meant to withstand impact loads. However, fire events weaken concrete and reduce its impact resistance. This study investigated the impact behaviour of steel-fibre-reinforced alkali-activated slag (AAS) concrete before and after exposure to elevated temperatures (i.e., 200 °C, 400 °C, and 600 °C). Hydration products' stability under elevated temperatures, their effects on the fibre-matrix bond, and, consequently, AAS's static and dynamic responses were investigated. The results reveal that adopting the performance-based design concept to achieve a balance between AAS mixtures' performance under ambient and elevated temperatures is a crucial designing aspect. Advancing hydration products' formation will increase the fibre-matrix bond at ambient temperature while negatively affecting it at elevated temperatures. High amounts of formed and, eventually, decomposed hydration products at elevated temperatures reduced the residual strength due to lowering the fibre-matrix bond and developing internal micro-cracks. Steel fibre's role in reinforcing the hydrostatic core formed during impact loads and delaying crack initiation was emphasized. These findings highlight the need to integrate material and structure design to achieve optimum performance and that low-grade materials can be desired based on the targeted performance. A set of empirical equations for the correlation between steel fibre content in the AAS mixture and corresponding impact performance before and after fire exposure was provided and verified.

Evaluation of automatic versus material test-based calibrations of concrete models for ballistic impact simulations

Concrete is used for protective structures all over the world. Accurate response estimates to a given threat is vital for designing such structures. Concrete models often require numerous input parameters for which sufficient experimental data can be challenging to obtain. Some models are accompanied by parameter generators which use the unconfined compression strength to extrapolate the remainder of the parameters based on experimental databases. This study investigates simulation of ballistic impact on high-strength concrete with 75 MPa nominal unconfined cylindrical compressive strength. The first objective is to investigate the accuracy parameter generators to produce input data for commonly used concrete material models. The second objective is to establish and evaluate a simplified parameter calibration procedure based on standard material experiments and data from the literature. The results employing parameter generators varied notably between the models while still giving decent ballpark estimates. The parameters obtained from inverse modelling of standardized material tests improved the results significantly. The findings of this study recommend caution when using automatic parameter generators. Although a detailed calibration of these concrete models is complicated, a simplified calibration gives reasonable predictions, making this the advisable approach for designing concrete protective structures.

Blast responses of BFRP-bar reinforced AAC panels

Basalt fiber reinforced plastic (BFRP) bars can replace steel bars in concrete protective structures because of their advantages of corrosion resistance and high load-bearing capacity. In this paper, the BFRP-bar reinforced autoclaved aerated concrete (AAC) panels (BFRP-AACPs) were designed and prepared. Based on close-in explosion experiments, the dynamic responses and failure modes of the BFRP-AACPs were revealed. Through the quasi-static three-point bending experiment, the residual load capacity of each BFRP-AACP was evaluated, which can quantitatively reveal the damage degree of the BFRP-AACP after explosion. Calculated by the equivalent static load method, the critical scaled distance of the designed panel is 2.08 m/kg1/3, which provides a design basis for the application of the BFRP-AACP.

Sustainable and Bio-Based Coatings as Actual or Potential Treatments to Protect and Preserve Concrete

The durability of reinforced concrete strongly depends on the environment in which it is located; in any case, the concrete and the reinforcing bars it contains are constantly subject to slow deterioration processes. The protection of concrete structures is, therefore, essential to increase their service life, reducing the costs for their repair and maintenance. The commercial widely used coatings are mainly based on petroleum derivatives (i.e., resins, solvents): increased sensitivity and attention to human health and the protection of the environment pressed research to find alternatives to synthetic products, identifying safer materials with a low environmental impact to employ as protective coatings. In this review, new sustainable products already used or potentially suitable to act as protective treatments for concrete were analyzed and presented. These are natural (bio-based) or waste materials, in which the use of synthetic resins and hazardous solvents, for humans and the environment, are minimized, exploiting waste materials or by-products of other processes, if possible. The main properties and characteristics of these new products are illustrated, highlighting the potential advantages over commercial products also in terms of performance.

Abrasion resistance enhancement of concrete using surface treatment methods

Abrasion is a phenomenon in which the reduction of volume and mass of the material surface is caused by friction, scratching and percussion, thus, it is promising to modify the surface characteristics for abrasion resistance enhancement. In this study, polyurea waterproof adhesive (PUA), polyurethane waterproof coating (PUR), iron sheet (IS), and rubber (RB) are applied for surface treatments to improve the abrasion resistance of concrete, and their effects on the mechanical strength, nano-scratch, drop-weight impact and resistance to debris flow abrasion are investigated. The results show that all surface treatment methods improve the flexural strength of concrete, while PUA, PUR and IS surface treatments reduce the compressive strength due to the size effect of concrete. The high-hardness surface treatments (PUA and IS) significantly reduce the abrasion rate due to their excellent resistance to impact and scratches, exhibiting a low roughness after abrasion. Abrasion rate of concretes PUA and IS at 48 h are 0.04 g/h and 0.03 g/h, respectively, which decrease by 75% and 81%, compared to the untreated concrete. The aggregates cutting, micro-cracks, scratches and indentation formation are abrasion failure mechanisms of surface-treated concrete caused by debris flow. PUA and IS surface treatment methods with a suitable thickness are recommended to enhance the resistance to debris flow abrasion of concrete protective structures.

Probabilistic demand models and performance-based fragility estimates for concrete protective structures subjected to missile impact

The manifold missile attacks upon structures and deficiency of codal provisions motivated the current study to develop probabilistic demand models for protective structures subjected to hard missile impact. These energy-based models are estimated using a defined performance-based design framework (PBD) with three performance levels associated with four damage states, i.e. from minor damage to total collapse. The evaluation of unknown model parameters is constructed using the Bayesian approach. The current and upcoming range of structural variables is chosen for numerical experimental design. LS-DYNA, a finite element (FE) numerical method, is used to generate necessary probabilistic data of Reinforced Concrete (RC) & Prestressed Concrete (PC) panels subject to a hard missile. Novel formulations for local damages of a target, such as perforation limit of RC panel & Ballistic limit of the missile for RC & PC panels, are estimated. The developed demand models are used to assess the fragility estimation of either panel under chosen performance levels for a containment structure located in Tarapur, Palghar, India. An accurate fragility plot and comparative study shows the consistency of probabilistic models with test results. These models consider aleatory and epistemic uncertainties in modeling, material & geometrical properties, strain rate & inertia effect, and complex interaction involved in an impact scenario.

Modelling the response regimes of elastomer-coated concrete slabs subjected to blast pressure loading

Elastomer coatings have been found to offer protection to structural components when subjected to dynamic load cases, such as impact and blast. One such application of interest is the protection of concrete structures. Elastomer coatings have the potential to provide a cost effective and practical protective solution. The dynamic response of quasi-brittle concrete structures to blast loading is complex, with a range of dynamic response regimes. It remains to be identified in which regimes of response an elastomer coating can offer a protective benefit. Numerical and analytical modelling of thin, one-way reinforced concrete slabs subjected to varying intensities of simulated blast loading is carried out, in order to ascertain the protective effect of an elastomeric coating. Three configurations are considered: uncoated, coated with elastomer on the blast-receiving face and coated with elastomer on the non-blast-receiving face. It is found that the slab is relatively insensitive to the elastomer coating during response regimes where concrete damage is minimal. At higher load intensities, where the slab exhibits severe damage, the numerical results indicate a substantial reduction in slab deflections may be achieved by coating on the non-blast-receiving face. At the highest loading intensities, a shift in failure mechanism is observed to one dominated by transverse shear at the supports. An analytical model quantitatively predicts a substantial coating benefit in protecting against this failure mechanism.

Researching on penetration process of steel warheads in concrete protectives by using ansys autodyn

The analysis of penetration of warheads in concrete protective structures is an important part of the study of weapon effects on protective structures. This type of complicated analysis requires that the design loading in the form of a warhead is determined. The characteristic and performance of the protective structure have to be known. To resolve it, there are several ways to find it such as experimental equation or using finite element (FE) analyses. However, it requires the combination of several factors, e.g. development of suitable material models for concrete, enhancement of numerical methodology and affordable high capacity computer systems. Furthermore, warhead penetration has primarily been of interest for the armed forces and military industry, with a large part of the conducted research being classified during considerable time. Hence, the paper is focused on simulating the progress of penetration of a steel warhead into the protective plate.

Performance-based probabilistic capacity models for reinforced concrete and prestressed concrete protective structures subjected to missile impact

A performance-based design (PBD) framework for nuclear containment structure (NCS) subject to missile impact is developed. These are, in turn, used to estimate probabilistic energy-based capacity models centred on three performance levels associated with four damage states of NCS. The present study considers multi-level PBD as opposed to single-level conventional collapse based design. Bayesian inference is used to evaluate the unknown model parameters based on available numerical data. The data of reinforced concrete (RC) and prestressed concrete (PC) panels subjected to hard missile impact is obtained from finite element (FE) numerical modelling (LS-DYNA). Formulations for local damages such as penetration depth, perforation limit and residual velocity of the missile are also developed. The established models account for the multi-modal response of the structure, the transition of failure modes and their interaction, inherent aleatoric and epistemic uncertainties associated with the modelling, configuration and material properties. A comparative study is performed with these predicted models and experimentation achieves the desired prediction level. These probabilistic models can be used for designing the NCS when subject to ballistic missiles. The work can also be extended to scenarios like ship collisions, vehicles falling on slabs due to tornadoes by following the developed framework. Not alone NCS the obtained results accommodate other protective structures like bunkers, storage tanks, residential slabs, and many similar configurations considered in the study.

Protection of Concrete Structures: Performance Analysis of Different Commercial Products and Systems

The increasing demand for reconstructions of concrete structures and the wide availability on the market of surface protective products and systems could lead to misunderstandings in the decision of the most effective solution. Surface protectors have become increasingly widespread in recent years in concrete restoration interventions thanks to their properties: they are able to protect the substrate from aggressive agents and consequently extend the useful life of the structures. The aim of this article is first of all to present the surface protective treatments available on the market, outlining their strengths and weaknesses. Subsequently, a characterization of seven different commercial coatings for reinforced-concrete structures is provided, taking into account chemical nature, fields of use and effectiveness, both in terms of physic and elastic performance and resistance to aggressive agents that undermine the durability of the treated concrete elements.

Modeling the reinforced concrete shell with a protective structure

The results of the mathematical modeling and experimental studies for the stress-strain state of the annular section of the reinforced concrete shell with the protective structure are presented. Computer simulation has been formulated as a stationary temperature problem. The distribution of deformations and stresses is shown using the equations of the elastic theory. A comparison of theoretical dependences on the results of experimental studies of physical models is given. Conclusions are drawn about the possibility of using them in the calculations of reinforced concrete protective structures.

Олигометилфенилсилоксаны и метилфенилсилоксановые смолы: получение, применение и композиции

A review is given on the class of organosilicon compounds of oligomethylphenylsiloxanes and methylphenylsiloxane resins. The review includes the main chemical methods for producing oligomethylphenylsiloxanes and methylphenylsiloxane resins, the main reactions, occurring with the participation of oligomethylphenylsiloxanes, areas of application of oligomethylphenylsiloxanes. The review provides compositions of oligomethylphenylsiloxanes. The review consists of 50 literature sources. To obtain oligomethylphenylsiloxanes, several production methods are used. Basically, this is a method of hydrolytic co-condensation of the corresponding organochlorosilanes with subsequent catalytic rearrangement of the hydrolysis products, a heterofunctional condensation reaction, or exchange decomposition. High-polymer organosilicon compounds are obtained as a result of synthesis from alkyl and aryl-substituted esters of orthosilicic acid or from alkyl and arylsilane chlorides, which upon hydrolysis form hydroxy derivatives (silanols), condensing into resins when heated. At present, new fields of application of oligomethylphenylsiloxanes have appeared. This is the creation of radiation-resistant materials, heat-resistant paints, protection of concrete structures, heat-resistant fiberglass.

Research progress of anti-penetration yaw technology for concrete protective structures

Concrete protective structure is an important part of national defense engineering. It is of great significance to study its development status and penetration mechanism. This article summarizes the recent research status of concrete protection yaw technology, and summarizes the existing yaw technology by distinguishing materials and structural asymmetry. The anti-penetration and yaw mechanism of the protective structure is summarized: The first is to analyze the effects of warhead shape and material, the incident state of the projectile, the configuration of the reinforcement and the aggregate parameters on the resistance to the penetration and yaw. The second is angle of attack effect and contact theory; the third is to analyze the role of numerical simulation in the research of yaw technology; and put forward suggestions for future research work.

Effect of marine environment on the behaviour of concrete structures reinforced by composite materials

This study deals with experimental investigations of beam performances in a marine environment. Two kinds of concrete beams, unreinforced and reinforced with carbon plates and carbon rods, are being tested. The first one is stored in a laboratory, the other is exposed to a marine environment located in the north of France. After 12 months, all beams are tested via a four-point bending test in a laboratory. Results obtained have shown that beams stored in marine environment have a better behaviour than those stored in laboratory. It should be noted that no damage has occurred on these beams. However, we observe a significant increase of load of about 32% to 48% causing the first crack observed on the beams stored in marine environment compared to those stored in the laboratory. This means that beams in situ offer increased stiffness and a slight gain of failure loads. This may be due to the development of living organisms (in a marine environment) which acted as additional adhesive and sealing, providing a protection of concrete structures against damage.

Improving the Cement Systems Corrosion Resistance Based on Clogging Theory

One of the most important elements of the primary protection of concrete structures against chemical aggression is the correct choice of the type of cement. Specialists have done a lot of work to clarify the comparative stability of various types of cement systems in aggressive media containing various aggressive components [1-3]. Resistant cements for certain types of corrosion are known, but there is no complete concept of their choice. This causes difficulties in choosing the type of cement for specific types of corrosion in organic media, for complex types of corrosion, when the application of empirical approaches is unsuitable. This work is devoted to this issue.

Experimental study and numerical simulation of explosion resistance of GFRP reinforced concrete beams

Glass fiber reinforced polymer (GFRP) bars have the advantages of corrosion resistance and high tensile bearing capacity. It can be used as longitudinal reinforcement of concrete protective structures instead of steel reinforcement. In order to clarify the anti-explosion performance of GFRP reinforced concrete beam (GRCBs), the explosion experiment, static bending experiment and numerical simulation analysis of GFRP reinforced concrete beam and reinforced concrete beam (SRCBs) are carried out. The results show that, in the four-point bending static experiment, the bearing capacity of GRCBs designed with the same equivalent stiffness is 5.5 times that of SRCBs under the working condition of 3kg-0.65m explosion loading. With the action of near explosion (proportional detonation distance is less than 0.5159 m kg–3), because the GFRP bars are in the elastic stage, the failure forms are mainly crack, flake and collapse of concrete. According to numerical simulation, the increase of the stiffness of FRP bars can reduce the mid-span displacement of GRCBs. The ratio of the maximum mid-span displacement reduction rate to EA ratio is 0.1, which can reduce the crack and damage of GRCBs and enhance the anti-explosion performance of GRCBs. When the proportional detonation distance is less than 0.4095 m kg–3, C50 and above concrete used in GFRP reinforced concrete beams can effectively reduce concrete collapse and spall. The results show that GRCBs have higher blast resistance than SRCBs.

Loading branch of the barotropic equation of state for cementitious composites under extremely high pressures

The behavior of cementitious materials under severe loadings is of major importance for the security and protection of concrete structures. One of the key mechanical properties of materials subjected to extremely high loading is the relationship between the hydrostatic pressure and the volumetric strain, which is often referred to as the equation of state. In porous materials such as cement paste and mortar, this relationship is substantially inelastic due to the closure and collapse of capillary pores. The paper presents an enhanced theoretical model of the loading branch of the barotropic equation of state for cement paste, mortar, and concrete that utilizes non-linear bulk behavior of cement paste matrix and aggregates. A multi-scale approach is applied to simulate the bulk behavior of cement paste. At the micro-level, the model assumes that the Portland cement paste matrix has the same properties in any concrete or mortar, and the difference in bulk behavior is caused by the difference in pore structure and aggregates. In the presented model, we applied a four-stage equation of state comprising of a trilinear elastic-plastic behavior prior to the closure of the pores followed by a nonlinear Hugoniot-type behavior stage after the closure of the pores at high pressures. At the macro-scale level, the equation of state of the paste is obtained by averaging the micro-domains solutions. The equation of state for the aggregate material is described by the three-stage equation of state with bi-linear elastic-plastic behavior followed by nonlinear Hugoniot-type compaction for the high pressures range. The Hirsch phase mix rule is applied to obtain the equation of state of the composite concrete material. The proposed model allows prediction of the bulk behavior of cementitious composites based on its composition and properties of its components for a wide range of pressures up to extremely high pressures.

Blast responses of concrete beams reinforced with steel-GFRP composite bars

Steel-GFRP (glass fiber reinforced polymer) composite bars (SGCBs) have advantages in corrosion-resistance and high load-bearing capacity endowed by GFRP, as well as ductility inherited from steel bars. They can be used as reinforcements in concrete protective structures. Two types of composite-bar reinforced concrete beams (CRCBs) were designed and casted. Explosion experiments reveal that cracking and spalling are the main damage patterns of the CRCBs. Composite bars reduce the plastic deformation and the residual deflection compared with the steel-bar reinforced concrete beams (SRCBs). Anti-blast ability is evaluated by quasi-static four-point-bending experiment on exploded beams. Intact CRCBs have three typical deformation stages, including elastic, elastoplastic and post-plastic deformations, and fail when the mid-span flexural crack almost runs through the beam. GFRP bars make the CRCB have much greater load capacity than the SRCB. Exploded beams have similar deformation and failure styles with the unexploded beam and even have greater load capacity than the unexploded SRCB. Having both high load capacity and excellent ductility, the SGCBs have advantages over steel bars in protective structures in some cases.

Blast responses of concrete beams reinforced with GFRP bars: Experimental research and equivalent static analysis

The glass fiber reinforced polymer (GRFP) bars have advantages in corrosion resistance and high load bearing capacity. They can be used as reinforcements in concrete protective structures to replace the steel bars. In this paper, the GRFP bar reinforced concrete beams (GRCBs) were designed, casted and tested. As a reference, the steel bar reinforced concrete beams (SRCBs) having the same flexural rigidity with the GRCBs were also designed, casted and tested. Under close-in explosions, the GRCBs have smaller displacement than the SRCBs, because the GFRP bars are still in elastic state while the steel bars enter into plastic deformation. Cracks, spalling and cratering are the main damage modes of the concrete beams. Through the quasi-static four-point-bending experiments, the residual load capacity of each beam has been evaluated, which quantitatively reveals the damage degree of the exploded concrete beams. In current research the explosion produces negligible damage to the GRCBs, while the load capacity the SRCBs reduces at a level of 28% at the most. The research proves that the GRCB has greater blast-resistance.

Protection of concrete structures under sulfate environments by using calcifying bacteria

Abstract Application of microbial induced calcium carbonate precipitation (MICP) via biomineralization process has been considered as a novel method in improving durability properties of concrete. This bio-based treatment had been extensively targeted to improve the overall performance of concrete at lab scale experiments. Durability of microbial treated concrete under aggressive environments is still unexplored. In the current study, the durability properties of microbial treated concrete structures were studied after exposure to chemical and physical sulfate salt solutions (5% Na2SO4 and 5% MgSO4). It has been observed that sulfate attack damaged the untreated concrete specimens causing ultimate failure due to expansion under both exposure regimes. Thick salt efflorescence and severe surface scaling was observed in untreated mortar during physical sulfate attack. However, specimens treated with bacteria (Bacillus sp. CT5) significantly improved the resistance towards sulfate ingress. The experimental results indicate the extensive reduced expansion rate, salt efflorescence and surface scaling in bacterial treated concrete in sulfate exposure. The present study results indicates the potential of this technology in the overall improved resistance of microbial concrete against sulfate environment.