Innovative Approaches to Concrete Durability in Harsh Environments

1. Introduction

Concrete is the predominant construction material, widely used for the construction of various infrastructures.

The wide use of concrete makes human life highly dependent on the performance of this material (Almutairi et al.2021). Over the past few decades, concrete has faced several durability issues, leading to early distress of infrastructure. Assessment of in-service structures revealed that many structural degradations can be related to durability issues (Zvirko, 2021). This leads to an urgent need to consider the enhanced durability of concrete structures to ensure their long-term performance and the sustainability of the planet. The concept and process of providing resistance against deterioration to the structure under prescribed conditions are called durability. The durability of materials can be assessed through the cost of protecting, restoring, maintaining, and rehabilitating infrastructure against corrosion.

Currently, many options are available to improve the durability of concrete, and the most challenging part is to choose the right approach for the local environmental conditions. Durability can be realized by using traditional as well as innovative and advanced materials and techniques. The need for innovative approaches to enhance durability is discussed after providing comprehensive knowledge of the principles of concrete durability and the effects of harsh environmental conditions on concrete degradation. This special issue aims to contribute insights into the use of innovative approaches to improve concrete durability in aggressive environments. There is considerable interest in this topic. However, limited information is available about the innovative approaches and developments happening to achieve desirable durabilities. This open access special issue will provide unrestricted access for both direct and interactive development.

2. Importance of Concrete Durability in Harsh Environments

In regions of the world that suffer from moisture problems, thermal fluctuations, and chemical environments, and are home to industries or practices susceptible to off-gassing of sulfate, acid, or salt chemicals, the durability of concrete infrastructure can be quickly compromised.

Extreme severity conditions lead to the rapid dissolution of the cement paste via externally aggressive environmental factors, leading to greatly accelerated internal leaching of paste ingredients and to the formation and propagation of cracking. Long-term loss of serviceability of structures at an increasing rate may affect society via its economy, environmental, and safety implications.

The concrete industry has many times over used the promise of improved concrete durability as a feature of the construction material to justify large capital investments involving infrastructure renovation and sometimes new construction. Impacts on infrastructure related to the use of high durability concrete include increased service lives for the civil works due to reduced rates of corrosion, weathering, or breakage of the material, extending to reduction of the environmental footprint of associated construction costs and reduced costs in terms of monetary capital and embodied energy by limiting the requirement for future maintenance activities. Durability-enhancing technologies do not cost excessively more than their conventional alternatives for most materials; yet their use may offer immeasurable benefits in economic terms. Thus, society, within reason, is happy to pay more for a longer-lasting product. There is also a general public feeling that lower or essentially zero maintenance in a given day and age is the domain of physical structures.

3. Challenges Faced in Maintaining Concrete Durability

Concrete durability is challenged in different regions due to specific environmental and exposure conditions. Material degradation by external chemical and physical actions occurs principally in two forms: by thermal variations or freeze-thaw cycles and by chemical attack. In both cases, material degradation is due to volume changes that develop as a result of the transport of aggressive agents through pores, microcracks, and micro- and meso-pores. Property changes provoked thereby can be ameliorative or cumulative, reversible or irreversible, and take place at the surface, within the material, or along its interface over time, affecting the intrinsic mechanical performance of materials. Further, poor construction practices and inadequate maintenance have significant effects on the durability of concrete. Long-term performance of concrete is not only determined by the concrete mix quality but also by surrounding environmental conditions, maintenance regimes, and service life assessment methodologies.

In industrialized areas, environmental factors like aggressive pollutants, direct application of de-icing salt, and wetting-drying climatic conditions all cause severe degradation of concrete, aggregate, and reinforcement (Yi et al., 2020), even within 5 to 10 years of service life of the bridge structures. In fact, failures of bridges and other transportation structures have increased in recent years; therefore, it is crucial to investigate the issues affecting and limiting their service life. Developing and maintaining infrastructure requires a long-term approach that considers not only original expectations for construction but also those related to service life. Many components and structures are designed for a serviceable lifetime of 75 years, although they are seldom maintained or replaced before significant issues associated with structural performance and durability are evident. Of increasing concern are the implications of significant economic impacts should any such structure fail, as is currently being faced following bridge collapses. The immediate cost is extreme, and sums of billions need to be allocated to address issues of public safety resulting from such failures, not to mention long-term costs in terms of lost services and increased material usage.

4. Traditional Approaches to Enhancing Concrete Durability

Innovative Approaches to Concrete Durability in Harsh Environments

Concrete has been modified in various ways to ameliorate its response in harsh exposure conditions. Traditional methods included optimization of the proportioning of mixes using chemical admixtures to improve durability, but typically admixtures are used instead to enhance workability, frost resistance, impermeability, antifreeze properties, thermal resistance, and aesthetics. These chemical admixtures activate the achievement of different mechanisms by which damage is inhibited, which can be simultaneously enhanced by the care of the paste quality. Other strategies in this framework included optimization of the mix design to achieve a balance between performance capacities, most importantly, between compressive strength and durability, and/or to exploit admixtures available to enhance these properties. The most promising is the use of very dense and very low porous concretes while they are achieved by adopting low water/cement ratios, water-reducing chemical admixtures, high fineness and low porosity binders, and aggregates like basalts.

Adherence to manufacturing and application best practices could only lead to reliable concrete in terms of durability, but traditional approaches as they are now understood and carried out could provide benefits for a significant effect. Increasingly, exposure conditions are requiring innovative solutions. However, total neglect for the traditional 'good reasons' for better resistance to deterioration should be avoided even when research and technology offer innovative ways to reach results.

4.1. Use of Chemical Admixtures

Chemical admixtures are a traditional tool for making concrete more durable in a variety of environments (Coppola et al.2022). Admixtures alter concrete’s properties to enhance its resistance to one or more deteriorating mechanisms.

For example, chemical admixtures can be employed to make concrete more resistant to freeze-thaw cycles, seawater, carbonation, deicing chemicals, and sulfate attack. These mixtures are primarily added to fresh concrete; however, they may also be sprayed or injected into the surface of a structure. Chemical admixtures are designed to modify concrete’s resistance to a particular deteriorating process; however, in practice, admixtures can have multiple benefits. Water-reducing chemicals work as accelerators, while air-entraining agents act as retarders, using which the required mix-design proportions and proportioning agents have to be adjusted properly for the overall durability and workability.

Water-reducing admixtures are used to reduce the required amount of water in a mixture and to increase the workability of hard-to-pour concrete. Therefore, they are added to reduce the size of the mastic; if they do not work properly, water content must be added again. The most important characteristic of these additives is their potential ability to reduce the concrete’s initial compression, reduce setting time, and increase 28-day compressive strength. Air-entraining agents are usually used to improve the deicing resistance of concrete in cold environments. When constructing with concrete, a small amount of tempered air reduces excessive pressure due to freezing temperatures, thereby increasing resistance to attendant spalling. The properties of concrete are improved by the use of various additives; these pozzolans are also used as replacement materials in concrete manufacturing. These types of chemical methods are suitable for modifying the concrete properties to enhance durability.

4.2. Proper Mix Design

One of the most crucial steps to concrete durability is mix design that is suitable for the intended use and the environmental exposures the concrete will likely experience. This discipline generally involves material selection and proportion decisions taken to optimize certain parameters such as strength, economics, fresh concrete workability, and service life. In order to control different performance characteristics and to set the mix proportions, a number of methods have been suggested by various researchers and engineers after considering different factors such as water/cement ratio, cement content, and aggregate quality. A comprehensive review of important considerations for durable concrete mix design, along with some critical issues related to the field implementation of sustainable concrete mix designs, has been outlined to produce an effective guide for precast concrete mix designs. Four important factors show a significant effect on the strength and durability of concrete: aggregate type, cement content, water/cement ratio, and curing conditions. Concrete mix will have a long life if these factors blend well.

Though mix design seems to be a vague concept, it is necessary for well-designed concrete in harsh environments. A durable mix can save the service life of a concrete structure. However, a mix suitable for one location may not be suitable for another due to several reasons. Firstly, the available materials in one location may not be available in another. Secondly, the job conditions where concrete will be fabricated vary. Different factors affect these circumstances. The strength of the concrete largely depends on the blend of these constituent materials. Additionally, durability is one of the vital properties of concrete related to the performance of hardened concrete. A good understanding of the interaction of the constituents aids in successful mix designing for a desired purpose.

5. Innovative Technologies for Improving Concrete Durability

The development of new technologies, such as durable, improved concrete materials, has shown promise. Self-compacting concrete, nano-additives, micro-encapsulated phase change materials, surface coatings, etc., have been used to provoke autogenous healing. As these technologies have advanced to enable concrete to overcome various limitations, research aimed at promoting the development of all kinds of new technologies remains ongoing. New and more comprehensive ideas for evaluating durability, as well as new performance requirements, are also being created, while efforts related to the redefinition of sustainability in construction are increasingly reflecting "the kind of future mankind wants."

One of the innovative defensive techniques in concrete is to supplement substantial materials with rejuvenating compounds to make them self-healing. Consequently, a self-healing concrete system can autonomously fill in the cracks formed inside concrete. The repair system can be incorporated into concrete materials through a broad range of potential technologies. In general, self-healing concrete is advanced due to the utilization of concepts of inactive repair, which means the depot of some repair agents inside concrete beforehand and remit them through specified triggering agents into the cracks. A fulfilling self-healing concrete can autonomously “detect” the occurrence of a crack and “deliver” repairing factors. Nanotechnology applications can also repair the degradation pores and enhance the dense matrix in concrete. With respect to the above-described development, this paper presents innovative technologies, taking into account various technologies that show great promise to improve durability. After reinforcing recent advancements in technologies, their real-world practical applications are presented in the next section.

5.1. Self-healing Concrete

Durability

Self-healing concrete is among the innovative solutions that forward-looking engineers and scientists are proposing to further extend the service life of concrete infrastructure in harsh environments. Self-healing concrete is a type of concrete that can autonomously repair cracks. In other words, the concrete is designed in such a manner that the healing agents are stored in the concrete material. When a crack is initiated in concrete due to any reason, the stored healing agent is then released from the voids inside the concrete and placed along these cracks where any further ingress of the aggressive environment can be healed.

In general, four different methodologies can be adopted to incorporate the healing agents inside the concrete: (1) incorporating a capsule that contains a liquid healing agent in a fresh concrete mix; (2) incorporating solid healing agents in a concrete mix; (3) incorporating granular or molten healing agents inside the concrete; and (4) integrating living organisms or spores of bacteria that can produce the healing agent in situ. After incorporating the healing agent in the concrete, various mechanisms can be adopted to initiate the release of the healing agent. Self-healing concrete, if implemented at a large scale in harsh environments, can prolong the service life of the structure and reduce the need for maintenance and repair. Furthermore, it can also provide a solution to save a significant amount of money by improving structural integrity and limiting failure consequences in harsh environments. As a trade-off, several challenges are related to its implementation and scaling up, such as health, safety, and long-term stability considerations. Some recent studies revealed the application and performance of self-healing concrete in civil engineering applications.

5.2. Nanotechnology Applications

Nanoscale Systems and Materials

5.2. Nanotechnology Applications Due to the increasing developments in fabrication techniques in the micro- and nanoscales, nanoscale materials, including calcium silicate hydrate, metakaolin, and amorphous SiO2, have started to be used to enhance concrete properties (Monteiro et al., 2022). These nanoscale components, because of their highly active surface with high specific area, can significantly refine the structure of concrete at nano/microscales and then act to optimize its performance, such as strength, durability, and permeability resistance. Nanotechnology consists of nanoparticles or nanofibers different from the traditional additives, which usually come in micrometric scale. Different types of nanoparticles are available, such as silica nanoparticles, magnetite nanoparticles, and titania nanoparticles, among others, that could improve concrete performance. Furthermore, nanosilica and nanoclay can be used in the modified concrete with coir fibers. Precisely, new high-performance concretes are being developed to replace traditional concretes with higher ductility, functionality, and strength.

The use of nanoparticles instead of micrometric particles involves a significant absorption of silica. The fine particles achieve a good dispersion in a lower quantity of water and show a high reactivity for the cement interblending available. Consequently, the percolation phase is avoided, and a significant interface is developed between the nanoparticles and the matrix. Many studies are trying to stabilize the new system while developing the use of nanotechnology for commercial use in the building industries. Some researchers have studied the effect of using nanosilica or silica fume by partially replacing aggregate in fly ash concrete. There were indeed significant changes in fresh and hardened properties. However, the researchers found little impact when using nanosilica as a partial substitute for the binder. This was expected, as nanosilica added in a very low percentage could not significantly modify the properties. In another study, researchers modified the sulfate-resistant cement with small percentages of nanoparticles and nanofibers. Many studies at the international level are in progress for the development and commercial uses of nanotechnology. The introduction of nanoparticles in Portland cement-based concrete has shown a significant improvement in the physical and mechanical properties. The properties that have gained worldwide attention for modification by the use of nanotechnology in materials are compressive strength, workability, cohesiveness, durability, splitting tensile strength, porosity, microstructure, chloride penetration, mass transport, early strengths, and long-term properties. Some researchers have studied the effect of nanotechnology aspects to improve some specific materials, such as metakaolin, fly ash, graphite, and steel fibers. The potential applications of nanotechnology in various materials are shown.

6. Case Studies of Successful Implementation

There have been a number of successful case studies in practical applications of new innovative technologies, making it possible to build durable structures. This section offers a review of projects in which innovative reinforcement, concrete technology, or surface protection were applied. The case studies have demonstrated the tangible benefits of implementing new durability-improvement techniques that have resulted from the application of the theoretical tools presented in the first section.

6.1. Offshore Concrete Platforms in the North Sea The oil and gas platforms in the offshore North Sea environment are designed to withstand the harsh conditions characterized by extreme weather, rough seas, and the possibility of heavy impact and explosion loads. The reinforced concrete structures on the caisson are exposed to severe seawater exposure with cyclic wetting and drying and are penetrated by chlorides through multiple mechanisms, such as capillary suction. The method based on the diffusion of single ions was used to calculate the depth of cover required. A total depth of cover of 80 mm was calculated, and this was achieved on site on the semi-submersible by building a reinforced concrete roof on top of the high-performance concrete deck. The actual reduction of chloride diffusion was measured, showing a 50% reduction and confirming the theoretical assumptions.

6.2. Microwave Enhanced Concrete Strength The fiber was used to minimize curling and reduce the strain concentration in the concrete due to the volume changes. High expansion cements are usually used in the production of ultra-high performance concrete. To minimize the effect of the expansive materials, fillers have been used to reduce the volume and cost. The concrete mixture design was produced under two conditions, plus seven series incorporating the filler. To reduce the heat of hydration of ultra-high performance concrete, an ultrafine powder was used. Ultra-high performance concrete has proven to improve the behavior of concrete structures in seismic loading and impact conditions and increase concrete durability in exposed marine environments. Several studies have been conducted to investigate the practical uses, particularly in Europe and Asia, where ultra-high performance concrete can be applied in different types of structures such as offshore oil storage tank construction.

6.1. Offshore Oil Platforms

Offshore oil platforms are subject to extremely aggressive environments, developed specifically to withstand the detrimental effects of these conditions. These environments present unique and difficult durability challenges for the massive concrete structures utilized in such platforms. Reinforced concrete members serving in saltwater exposure may become subjected to rapid or slow rates of deterioration due to corrosion of the embedded reinforcing steel. Structural members, support connections, and risers exposed to extreme atmospheric conditions, including high winds, subzero temperatures, and freezing sea spray, as well as loads from associated seismic and marine events, must meet strict performance criteria for long-term utility. This section covers specific concrete durability solutions adopted for successful offshore applications: two concrete gravity-based structures in the North Sea. Detailed case studies are presented summarizing research and construction, key findings, resulting concrete properties, important lessons learned, and the studies that influenced the strategies. The first study describes the development of an ECC-polymer concrete overlay used on the legs of offshore drilling platforms. The second case discusses a successful engineering collaboration program to develop specialized HPC formulations tailored to mitigate internal and external sulfate attack on grouting for the world's largest offshore oil platforms, both located in the North Sea. Outcomes of these case studies on platform concrete construction include longer average intervals between needed repairs, further increasing asset and end-of-life viability for these structures. The last part of this section covers critical performance safety considerations for possible solutions to express temporary shear connectors used for transporting gravity-based offshore platforms. Initial testing confirmed the viability of a hybrid proposal complying with safety and regulatory guidance.

6.2. Highway Infrastructure in Cold Climates

Highway infrastructure in cold regions can be significantly affected by freeze-thaw cycles and de-icing chemicals, particularly by extreme winters and early and late thaws (Meng et al.2022). These specific issues are of the biggest concern from the durability standpoint. The relatively low temperature can also alter the performance of concrete in both fresh and hardened states. Conversely, some problems such as curling and cracking of concrete due to the temperature differential are common to concrete anywhere. A group of stakeholders developed a second edition of a comprehensive technical guide to assist with the design and construction of jointed concrete pavements in cold climates. With this, several case studies were included that detailed cold-weather concreting and concrete durability in freezing and thawing environments. Relevant, short anecdote-like poems are presented to shed light on specific components of the guide. This one examines: Innovative Approaches to Concrete Durability in Harsh Environments. The section begins by stating:

Studies of deterioration mechanisms and durability procedures related to concrete used in highway infrastructure are of paramount importance in determining the safe and effective operation of such essential systems. While the development of new technologies to mitigate distress and improve system resilience is an ongoing priority, communication strategies and practices designed to inform knowledgeable application of new materials and methods are also critical to durable infrastructure. Five case studies on the effective application of innovative technologies used to extend the service life of highway infrastructure are briefly presented in this special section. In the case studies, new protection measures such as advanced mix designs, protective coatings, and layers adapted to specific needed properties were carefully applied to ensure success. Techniques such as in-situ freeze-thaw tests and climate chambers were proven to be valuable tools for the design and validation of such innovative solutions.

For performance concrete pavements located in cold regions, collaboration among state highway agencies, research agencies, and contractors has resulted in several new and innovative approaches for the enhancement of concrete pavement preservation in chloride-impaired structures. Experiments and accelerated concrete testing of these unique mix designs have demonstrated that locally available cementitious materials can be used to increase corrosion resistance properties while simultaneously increasing the mechanical strength of the concrete. The aging infrastructure of concrete pavements and bridge decks requires long-lasting systems that do not require repair and rehabilitation for our economy. The Department of Transportation has recognized that durable infrastructure benefits the economy and will spend more up front to ensure that the estimated amount of rebar and cubic yards of structural concrete in our bridges surpass the design life of 75 years. In this collaborative environment, several approaches have been pursued for durable infrastructure, optimized for a variety of purposes, such as the desirability of minimal or no impacts to traffic during construction, and others that provide options to try new and still experimental approaches. This paper particularly summarizes two technologies utilized currently to lessen the intended or unintended ingress of chlorides into the concrete superstructure and substructure of our highway infrastructure. Grooving and hydrodemolishing new bridge decks for a permeable surface and applying clear anti-graffiti coatings are intriguing and cutting-edge approaches to a resilient infrastructure.

7. Future Directions and Emerging Trends

Concrete has been extensively employed throughout the world due to its strength, durability, resilience, and relative economic cost, as well as cost-effective design in infrastructure.

However, increasing pollution and deteriorating environmental conditions necessitate a more detailed investigation of concrete durability under several harsh environmental phenomena. In anticipated future research, advanced techniques will be used to further customize concrete for various aggressive conditions (Abdal et al.2023). Research will aim to refine various problems, such as the design of concrete to ensure a long-term service life based on multi-axial stress-strain considerations, in response to harmful activity. The studies will focus on altering concrete microstructures at the nanoscale, including optimizing hydration mechanisms and aggregate-cementitious material interactions, using artificial intelligence to make decisions, i.e., to deform and invent concrete solutions. Environmentally responsible construction will be the main concern of anticipated research directions. One key area of future research planned by a predicted 40% of international concrete experts is the development of materials and technologies that are more environmentally sustainable. These collaboration opportunities will greatly benefit scientific peer reviewers, policymakers, and key stakeholders. Furthermore, the use of digital technology has already integrated concrete durability properties. However, a multidisciplinary approach is critical to ensuring that the findings are utilized for modeling, designing, specifying, constructing, maintaining, and managing the built environment. Benchmark tests and protocols are needed to ensure that the developed digital tools benefit industry and society. Concerning future emerging trends and predicted materials, one crosscutting future research priority is smart self-healing nano-engineered materials. Objective 5 contains seven strategies for addressing durability challenges in structural materials, including concrete. Not all of the predicted concrete smart technology trends are passive; that is, existing materials undergo degradation and self-healing or can be applied to a concrete surface.

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