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Abstract Concrete durability is greatly influenced by the transport rate of aggressive chemicals. Moisture diffusion plays a key role in the long-term performance of cementitious materials, as it facilitates the entry of aggressive chemicals into concrete. The pore size distribution plays a critical role in determining moisture diffusivity. However, the characteristics of the concrete pore structure have not been included comprehensively in the material models so far. In this paper, a theoretical model was developed to obtain the pore size volume fractions for each diffusion mechanism including Molecular, Knudsen and Surface diffusions. An effective moisture diffusivity in concrete was then obtained using the weighted average based on the diffusion mechanisms and pore size volume fractions. The model’s validity was demonstrated by comparing model predictions with available experimental data. The findings of this study provide valuable insights into the behavior of the concrete pore structure and its impact on moisture diffusivity.

Abstract Chloride-induced steel corrosion is known to be a very common kind of deterioration of reinforced concrete. It is beneficial to bind free chloride ions to reduce the corrosion probability of the reinforcement embedded in the concrete. The binding capacity of the concrete varies according to its cementitious system. This paper investigates the chloride binding capacity of different kinds of supplementary cementitious materials (SCMs): Ground granulated blast furnace slag (GGBFS), Fly ash, and Metakaolin as a partial replacement of Ordinary Portland Cement (OPC). Different properties of concrete after chloride binding are assessed by carrying out the following tests: half-cell potential, accelerated corrosion test, compressive strength, rapid chloride penetration test, sorptivity test, measuring pH value of concrete, and XRD. The results showed that utilizing the SCMs in concrete can enhance the chloride binding capacity, especially those materials that have high quantities of aluminate and calcium in their chemical composition like GGBFS. Based on testing results, it’s recommended that the limit of the chloride content in the different codes should be revised regarding the binding capacity according to the type and quantity of the cementitious materials used.

If it is desired to experimentally verify the regularity in the effects of air-voids on the properties of concrete, methods of altering voids must be relied on. Consequently, this research explored a method that reduced the curing air pressure after mixing concrete so as to modify air-void characteristics. In addition, in order to avoid introducing variables besides air-voids, a limit was placed on the duration of low-pressure maintenance, which was restoring the air pressure to atmospheric pressure after the formation of the concrete's air pressure transient resistant strength. The results showed that if the reduction in air pressure was insufficient, the differential pressure between the inside and outside of the original bubbles was not enough to cause them to break through energy barriers resulting in expansion. Only bubble regeneration due to the decrease in gas solubility was observed. When the differential pressure exceeded the energy barriers, bubble expansion could be achieved. In addition, it was possible to achieve the air pressure transient resistant strength in short time, which was achieved in only 7 h for the concrete used in this paper. Water loss calculation, X-ray diffraction, thermogravimetry-derivate thermogravimetry, scanning electron microscope, and mercury intrusion porosimetry were used to evaluate the hydration of the concrete confirming that the low-air pressure curing of 7 h had almost no effect on hydration. The method proposed can provide an effective means of specimen preparation for scientific research involving the effects of air-voids on the properties of concrete.

Research on the combined substitution of supplementary cementitious materials (SCMs) has already demonstrated that it might be one of the few viable options to produce low-carbon concrete at scale. This paper presents an experimental investigation on the performance and durability of rice husk ash (RHA) and calcined clay (CC) in ternary blended concrete exposed to chloride attacks under wet/dry cycles. Portland cement (PC) was replaced by RHA and CC up to 50% by weight to produce low-carbon concrete. Samples were subjected to wet/dry cycles in 3.5% NaCl water, with mineralogical composition and microstructure development before and after exposure analysed by TGA-DSC, MIP, XRD, and SEM. The durability of the concrete against wet/dry cycles was investigated in terms of compressive strength, water absorption, open porosity, density, thermal conductivity, and electrical resistivity. The results showed that concrete mixes with CC and RHA up to 60% exhibited an increase of 33% in compressive strength, followed by minimal changes in water absorption. While a decrease in electrical resistivity was measured in all samples with RHA and CC, increasing the CC content to 50% resulted in improved resistance to chloride penetration. Increasing the CC content resulted in a more refined microstructure, with an overall decrease in porosity of up to 32% compared to the control series. While RHA alone did not contribute to significant improvements after wet/dry cycles, the combined substitution of RHA and CC at SCM replacement levels of 60% showed an overall improvement in hardened properties and durability. This investigation provides valuable insights into the long-term performance and strength of innovative low-carbon concrete.

The use of concrete is widespread, but it poses challenges due to its high consumption of Earth's raw resources and difficulties in recycling and reclamation. Today, the pressing climate issues, including global warming and the emergence of a complex climate, continue to test cement-based polymers in the civil engineering industry. As a result, there is a growing demand for higher performance, renewable resources, and reduced carbon dioxide production, leading to a shift in the traditional industrial revolution. Composite nano concrete has emerged as an effective solution to address the challenges related to concrete mechanics and durability, aligning with the principles of sustainable development goals. The research focuses on utilizing composite nano-modified concrete to enhance the life cycle of structures. This nano-modified concrete incorporates Nano-SiO₂ (NS) and Nano-CaCO3 (NC) particles to create a new composite nano-concrete structure called NSC concrete. The research paper explores different dosages of composite nano concrete, specifically 2.5 %, 3.0 %, and 3.5 %, denoted as NSC25, NSC30, and NSC35, respectively. It examines the performance of the composite nano concrete under various temperature conditions, including 25 °C, 200 °C, 400 °C, and 600 °C, to simulate real-world scenarios and evaluate its value-based applications. The article analyzes multiple aspects, including mechanical properties, durability, visual appearance, and economic benefits of composite nano concrete. It also assesses NSC concrete's temperature dissipation capacity and insulation level and investigates the interfacial transition zone influenced by nanoparticles and temperature. The results indicate that the new composite nano concrete retains substantial enhancements in mechanical properties, with a maximum increase of 1.22 % in splitting strength and up to 45.69 % improvement in flexural strength at a temperature of 600 °C. Additionally, it demonstrates commendable durability and economic efficiency

Determining the binding capacity of concrete to chloride ions has always been the focus of the durability study of reinforced concrete structures. In many cases, concrete interior is in the electric field environment, such as railway track affected by stray current, component under electrical chloride removal (ECR), and concrete in corrosion electric field. However, the influence of electric field intensity on the chloride binding ability of concrete has not been determined clearly and quantitatively. In this paper, an experimental study is conducted to investigate the evolution of chloride binding capacity under various electrical current densities. The results indicate that the binding capacity of concrete is degraded by the electrical field, and the amount of physical adsorption for chloride is far less than the that of chemical binding. Based on experimental data, the modified Langmuir isotherm is given, and the evolution of key coefficients is measured quantitatively. The research findings are of great significance to the accurate evaluation of subsequent transmission of chloride ions after the initiation of steel corrosion and corrosion protection effect by ECR technique.

Routing is of great significance for durability monitoring of concrete structures in wireless sensor networks. However, current solutions cannot satisfy the requirement of comprehensive network performance, including reliable communication, low data delay, and high energy efficiency. In this paper, we study the multi-objective data transmission problem and propose a hybrid routing strategy named HRRS based on packet retransmission and packet reproduction. The goal is to achieve the tradeoff of low energy consumption, low delay and high reliability. This strategy combines the reproduction mechanism and retransmission mechanism to ensure high reliable communication, and reduces the number of reproduction paths to reduce the number of packet copies in the network, and accordingly reduce the energy consumption of the network. Meanwhile, the average transmission delay of the network is guaranteed by the reproduction mechanism. Furthermore, the data load, network reliability and delay of the nodes are analyzed, and the multi-objective constraint model is established. Simulations are implemented to evaluate the HRRS scheme that proposed in this paper greatly improves the reliability of transmission while ensuring the average transmission delay of the network, and is superior to the PR scheme in energy efficiency performance. The energy cost of HRRS is reduced by 10%-20% compared to the PR.

The deterioration of concrete microstructures in freeze–thaw (F–T) cycles is the primary reason for the reduction in the service life of concrete. This paper reviews recent progress in the theory of damage mechanisms and damage models of concrete in F–T cycles. It is a detailed review of the salt-freeze coupling condition, microstructure testing, and models for the evolution of concrete properties that are subjected to F–T damage. Summarized in this paper are the deterioration theory of water phase transition; the mechanism of chloride-F–T and sulfate-F–T damage; the microstructure testing of hydration products, pore structure, microcracks, and interfacial transition zones (ITZ). Furthermore, F–T damage models for the macrostructure are presented. Finally, the issues that are existing in the research and outlook of concrete F–T damage are highlighted and discussed. This paper is helpful in understanding the evolution of F–T damage, and also provides a comprehensive insight into possible future challenges for the sustainable design and specifications of concrete in cold environments.

Today, there are several methods for predicting the durability of reinforced concrete structures. In most cases, one of the dominant destruction processes is taken into account – either carbonization or chloride penetration. Experimental results and field observations show that this is an unrealistic approach. Therefore, it is necessary to develop a method for determining the durability of concrete under combined impacts, i. e. with the penetration of chlorides into it and mechanical load. The paper describes in detail an experimental method for studying the effect of mechanical load on the penetration of chlorides into the pore space of cement-based materials. A test method is presented that makes it possible to determine realistic diffusion coefficients of chloride ions in concrete under compressive or tensile stress. As a result of the experiments carried out, it has been determined that the combination of mechanical loads and environmental influences can be much more significant than just environmental influence without the influence of mechanical loading. In fact, the service life of reinforced concrete structures depends on many possible combinations of mechanical loads and environmental influences, including freeze-thaw cycles. Thus, cracks formed during freeze-thaw cycling should be taken into account in tests of combined environmental and mechanical stress in order to better understand and systematically describe the effect of such exposure on the durability of concrete. For reliable prediction of the service life of reinforced concrete structures, it is also necessary to take into account the influence of the applied cyclic stress.

Natural and artificial pozzolans are widely used in building materials and play an increasingly important role in minimizing costs and mitigating environmental effects in the manufacturing of building materials. These pozzolans can be obtained as by-products from various industries, generally they are wastes without any application or added value. However, when implemented in cement mixtures, their effectiveness is somewhat questionable. Therefore, it is necessary to determine the properties, characteristics, and behavior of these materials. This study aims to summarize the main pozzolans used in building materials. Volcanic pozzolans, pozzolans of sedimentary origin, fly ash, blast furnace slag, silica fume, metakaolin, ceramic wastes, demolition, and construction wastes, rice husk ash, bagasse ash, biomass ash, and paper sludge were considered. The chief characteristics studied were particle size, specific area chemical composition, and mineralogical composition. In addition, the impact on mechanical properties and durability in cement mixtures using pozzolans was analyzed. It was observed that the mechanical properties of cement mixtures change by increasing pozzolan replacement. The maximum percentage of replacement depends on the characteristics of the pozzolan. In the case of durability, pozzolans decrease absorption and permeability by reducing the porosity of the binder. This decreases acid diffusion and autogenous shrinkage, thus improving concrete durability. Finally, future studies are suggested to consider the implementation of artificial intelligence techniques and machine learning algorithms to improve the properties of the concrete mixtures.

Basalt fiber-reinforced concrete (BFRC) is relatively a new type of fiber-reinforced concrete, which has demonstrated good mechanical performance. Several types of fibers such as steel, glass, and carbon fibers, are used to improve the performance of plain concrete. However, basalt fibers (BF) are being considered superior to these because of their comparable mechanical strength, higher durability than glass fibers, lesser cost than carbon fibers, sustainability due to abundant raw material, and environment-friendly production process. Hence, the number of studies on BFRC are increasing over the years. This review paper covers the properties of BF and BFRC. The effects of BF length and dosage are discussed in detail in term of fresh, hardened, and durability properties of BFRC, followed by highlighting some areas for future research. It is concluded that BF can potentially replace the other conventional fibers which are being used in the industry.

The causes of cracks in concrete are varied, and regardless of their origin, these cracks invariably have a detrimental impact on the durability of concrete structures and escalate their maintenance costs. This paper presents a comprehensive review of current knowledge regarding the methods of self-healing in concrete, ranging from autogenic and improved autogenic self-healing to the autonomous self-healing of concrete. Particular emphasis is placed on the methods of autonomous concrete self-healing: the bacterial healing method, the crystalline hydrophilic additives healing method, and the capsule-based self-healing method. The hypothesis is that applying these self-healing methods could potentially prevent damages or cracks in concrete caused by freeze–thaw cycles, thereby extending the lifespan of concrete structures. The mechanism of action and current achievements in the field are provided for each method.

In recent years, different research works have been conducted to evaluate the addition of nanometer materials to concrete materials. In this paper, the influence of Nanosilica on compressive strength, abrasive strength, durability, and improvements in the micro-structure of concrete are discussed. The results showed that the compressive strength of concrete samples with Nanosilica and silica fume were higher than the compressive strength of other samples without nanometer materials in all ages, as well as increasing the dosage percentage of Nanosilica led to higher levels of compressive strength. In the mix designs with an equal dosage percentage, samples containing Nanosilica have shown a higher level of strength in comparison to samples containing silica fume. The application of Nanosilica in self-compacting concrete resulted in higher level of compressive strength, flexural strength, abrasive strength, elasticity module, ultrasonic waves permeability velocity (UPV), and lower water absorption compared to samples without Nanoparticles. Despite the evidences which show the improvement in mechanical characteristics of concretes with Nanosilica-particles, further developments for the applicability of Nanoparticles for improving the characteristics of concrete require the right knowledge and higher control over the effective mechanisms of Nanoparticles on concrete’s structure.

The paper presents an overview of current knowledge and progress in service life design and modelling of concrete structures, taking an international view but also giving local examples from South Africa. It raises the question of why service life modelling is needed, and indicates that modern demands for longevity, durability, and sustainability of concrete structures cannot be fulfilled without service life modelling. It addresses the current approaches to durability design and specification and concludes that a move to performance-based approaches is imperative if progress is to be made. Examples from international experience are cited to illustrate progress that has been made. Lastly, the paper discusses ways of moving forward, recognizing that the philosophical bases are already firmly in place in the form of general code formulations, but these need to be converted into useful approaches.

Abstract The performance of accelerated test methods to determine the chloride diffusion coefficient in concrete is an important tool in the evaluation of the durability-related properties of the material and in the service life prediction of structures. In this way, this paper presents an experimental assessment of three standardized test methods for determining chloride diffusion coefficient. The migration-based tests presented by NT Build 492 and UNE 83987 and the diffusion-based test presented by ASTM C1556 were carried out. Six concrete mixes were produced: three with different water/binder ratios (0.45, 0.55, and 0.65) and three with replacement of cement by silica fume in the levels of 5, 10, and 20%. The results indicate that the method standardized by NT Build 492 has the best correlation with the diffusion test, in addition to being the one that requires the shortest execution time and has the lowest coefficient of variation of the results.

Concrete is a multiphase composite material composed of coarse aggregate, cement mortar, and interface transition zone (ITZ). It is of great significance to study the effect of ITZ and coarse aggregate on chloride microscopic diffusion behavior for predicting the service life of reinforced concrete (RC) structures. By introducing the random distribution function, a random coarse aggregate model considering the randomness of the thickness of the ITZ was established. Furthermore, a two-dimensional (2D) chloride ion diffusion mesoscopic model was developed by specifying different diffusion properties for different phase materials of concrete. Moreover, the effects of coarse aggregate rate, ITZ thickness, and ITZ diffusion property on chloride ion diffusion behavior were investigated in this paper. The research showed that the aggregate has hindrance and agglomeration action on chloride ion diffusion. Although the volume content of the ITZ was very small, less than 0.2% of the total volume of concrete, the effect of the ITZ on the chloride diffusion in concrete cannot be ignored. More importantly, the mechanism of promoting chloride diffusion in the ITZ was revealed through the chloride diffusion trajectory. The research revealed the transmission mechanism of chloride ions in the meso-structure of concrete and provides theoretical support for the design of RC structures in coastal areas.

Concrete production consumes enormous amounts of fossil fuels, raw materials, and is energy intensive. Therefore, scientific research is being conducted worldwide regarding the possibility of using by-products in the production of concrete. The objective is not only to identify substitutes for cement clinker, but also to identify materials that can be used as aggregate in mortar and concrete productions. Among the potential alternative materials that can be used in cement composite production is rock dust of different geological origin. However, some adversarial effects may be encountered when using rock dust regarding the properties and durability of mortars and concrete. Therefore, comprehensive research is needed to evaluate the adequacy of rock dust use in cementitious composite production. This paper presents a comprehensive review of the scientific findings from past studies concerning the use of various geological origins of rock dust in the production of mortars and concrete. The influence of rock dust as a replacement of fine aggregates on cementitious composites was analyzed and evaluated. In this assessment and review, fresh concrete and mortar properties, i.e., workability, segregation, and bleeding, mechanical properties, and the durability of hardened concrete and mortar were considered.

Service life modeling of reinforced concrete structures in a chloride environment is mainly performed without considering the loading effects. Different loading effects can produce different service life results. This study presents a theoretical framework for the modeling of the service life of reinforced concrete structures in a chloride environment using loading factors, showing that, depending on the loading nature (either compression or tension), different diffusion results could be obtained. This paper also highlights various approaches to service life modeling, such as the deterministic, probabilistic, and semi-probabilistic, which consider different ways to estimate the service life of reinforced concrete structures in chloride environments. The importance of various distributions for the input parameters in the chloride ingress modeling was examined. The proposed framework includes a procedure to estimate the probability of concrete failure in chloride environments.

The macroscopic mechanical properties and frost resistance durability of concrete are closely related to the changes in the internal pore structure. In this study, the two-dimensional and three-dimensional ICT (Industrial Computerized Tomography) pore characteristics of C30 concrete specimens before and after freezing and thawing in clean water, 5 wt.% NaCl, 5 wt.% CaCl2, and 5 wt.% CH3COOK solution environments are obtained through concrete frost resistance durability test and ICT scanning technology. The effects of pore structure changes on concrete frost resistance, durability, and compressive strength mechanical properties after freezing and thawing cycles in different salt solution environments are analyzed. This paper provides new means and ideas for the study of concrete pores. The results show that with the increase in the freezing and thawing times, the concrete porosity, two-dimensional pore area, three-dimensional pore volume, and pore number generally increase in any solution environment, resulting in the loss of concrete compressive strength, mortar spalling, and the decrease in the relative dynamic elastic modulus. Among them, the CH3COOK solution has the least influence on the concrete pore changes; the NaCl solution has the greatest influence on the change in the concrete internal porosity. The damage of CaCl2 solution to concrete is second only to the NaCl solution, followed by clean water. The increase in the concrete internal porosity from high to low is NaCl, CaCl2, clean water, and CH3COOK. The change in the pore volume of 0.1 to 1 mm3 after the freeze–thaw cycle is the main factor for reducing concrete strength. The test results have certain guiding value for the selection of deicing salt in engineering.

The paper focuses on investigating the effect of impregnation of recycled concrete aggregate on the mechanical and durability properties of concrete using this aggregate. Cement paste, limewater and diluted water glass were used to impregnate the aggregate. Both a single impregnation and a double impregnation using two different solutions were carried out. A total of four groups of concrete series, with two values of w/c ratio (0.45 and 0.60), were made. Concrete made using the impregnated aggregate was tested and the results were compared with those of concrete made using untreated recycled aggregate of the same kind. The results indicate that impregnation of aggregate improves the mechanical properties of concrete in many cases but reduces its resistance to cyclic freezing and thawing. Furthermore, in the case of impregnation with two solutions, the order in which the impregnants are applied influences the effect obtained. Using the results received, the impregnation methods were ranked in order from best to worst. The best impregnation method proved to be with cement paste, followed by diluted water glass, while the worst results were obtained with limewater, followed by diluted water glass.

Coating materials are considered one of the most antique materials of human civilization; they have been used for decoration and the protection of surfaces for millennia. Concrete structures—due to their permanent exposure to different types of environments and contaminants—require the use of coatings that contribute to its preservation by reducing the corrosion of its components (steel and aggregates). This article intends to introduce the principal causes of concrete deterioration and the coating materials used to protect concrete structures, including a summary of the coating types, their advantages and disadvantages, and the latest developments and applications. Furthermore, this paper also assesses brief information about the potential challenges in the production of eco-friendly coating materials.

The technological process of concrete production consists of several parts, including concrete mix design, concrete mix production, transportation of fresh concrete mix to a construction site, placement in concrete framework, and curing. Proper execution of these steps provides good quality concrete. Some factors can disturb the technological process, mainly temperature and excessive precipitation. Changing daily temperature and rainfall during fabrication, transportation, and placement can shape not only the properties of the concrete mix but also the compressive strength of hardened concrete. In this paper, we tried to answer the question of how temperature and precipitation affect concrete production. The scope of this study was to determine the change of compressive strength of the hardened concrete in a specific period for selected concrete mix recipes, taking into account changing daily temperature and precipitation magnitude. The investigated concrete mixes concrete compressive strength beyond that of the concrete grade, termed “concrete superstrength”. This concrete post limiting behaviour of concrete is also discussed.

The paper presents the composition and properties of low-emission ternary cements: Portland multicomponent cement CEM II/C-M and multicomponent cement CEM VI. In the ternary cements, Portland clinker was replaced at the levels of 40% and 55% with a mixture of the main components such as limestone (LL), granulated blast furnace slag (S) and siliceous fly ash (V). Portland multicomponent cements CEM II/C-M and CEM VI are low-emission binders with CO2 emissions ranging from 340 (CEM VI) kg to 453 (CEM II/C-M) kg per Mg of cement. The results obtained indicate the possibility of a wider use of ground limestone (LL) in cement composition. This is important in the case of limited market availability of fly ash and granulated blast furnace slag. The tests conducted on concrete have shown that the necessary condition for obtaining a high strength class and durability of concrete from CEM II/C-M and CEM VI ternary cements is low water–cement ratio. Durability characteristics of concrete (carbonation susceptibility, chloride ion permeation, frost resistance) made of CEM II/C-M and CEM VI cements were determined after 90 days of hardening. This period of curing reflects the performance properties of the concrete in a more effective way.

This paper discussed the effects of modified metakaolin (MK) with nano-silica (NS) on the mechanical properties and durability of concrete. In the first phase, trial mixes of concrete were prepared for achieving the desired value of the 28 days compressive strength, and the charge passed in rapid chloride permeability test (RCPT). In the second phase, statistical analysis was performed on the experimental results using the response surface method (RSM). The RSM was applied for optimizing the mix proportions for the required performance by exploiting the relationship between the mix characteristics and the corresponding test results. A blend of 10% MK + 1% NS as part of cement replacement exhibited the highest mechanical properties and durability characteristics of concrete; concrete mix showed that the 28-days compressive strength (CS) was 103 MPa, which was 15% greater than the CS of the control mix without MK or NS. The same mix showed more than 40% higher flexural and split-tensile strength than the control mix; also it resulted in a reduction of 73% in the rapid chloride permeability value. ANOVA technique was used for optimizing the nano-silica and metakaolin content for achieving maximum compressive strength and minimum RCPT value. Statistical analysis using ANOVA technique showed that the maximum compressive strength and lowest RCPT value could be achieved with a blend of 10% MK and 1.55% NS.

Cracks in concrete structures present a threat to their durability. Therefore, numerous research studies have been devoted to reducing concrete cracking. In recent years, a new approach has been proposed for controlling temperature related cracking—utilization of phase change materials (PCMs) in concrete. Through their ability to capture heat, PCMs can offset temperature changes and reduce gradients in concrete structures. Nevertheless, they can also influence concrete properties. This paper presents a comprehensive overview of the literature devoted to using PCMs to control temperature related cracking in concrete. First, types of PCMs and ways of incorporation in concrete are discussed. Then, possible uses of PCMs in concrete technology are discussed. Further, the influences of PCMs on concrete properties (fresh, hardened, durability) are discussed in detail. This is followed by a discussion of modelling techniques for PCM-concrete composites and their performance. Finally, a summary and the possible research directions for future work are given. This overview aims to assure the researchers and asset owners of the potential of this maturing technology and bring it one step closer to practical application.

The paper provides an overview of different methods that can be used for concrete maturity determination, outlining Romanian Concrete Code Specification (NE 012-99) in relation to using an effective and rational method in evaluating in-situ concrete strength at different ages.

Great durability problems are being found in concrete structures related to the penetrability of aggressive agents through the concrete (ie. chloride penetration, sulphate attack, carbonation, freezing and thawing, and so on). Air permeability coefficient is used as an effective tool to estimate the potential durability of concrete structures due to its direct relation with the microstructure and the moisture content. This paper discusses the effect of the aggregate grading and water/cement ratio on the air permeability coefficient. An aggregate grading with more sand than coarse aggregates has resulted more beneficial from the point of view of concrete air permeability. This fact can be attributed to a denser skeleton formed by the finer aggregates. With fine aggregates, the higher water/cement ratio, the lower air permeability. However, the contrary was found with coarse aggregates. Overall, a temperature increase from 20 °C to 60 °C during preconditioning led to a Dair increase of 40–80%.

There are numerous mechanisms that can lead to deterioration of portland-cement concrete in service. The best known are corrosion of reinforcement, freezing-thawing expansion, alkali-silica reaction, acid attack, and sulfate-related problems, including delayed ettringite formation. Additionally, concrete can deteriorate as a consequence of improper processing, including curing. Often, several of the above mechanisms of deterioration are jointly responsible for the observed damage. This paper briefly reviews the light-optical and electronoptical microscopic methods available to study some of the causes of concrete deterioration, and briefly describes selected case studies. Specifically, microstructural features resulting from physical (e.g., freezing-thawing) and chemical (e.g., alkali-silica reaction, delayed ettringite formation) deterioration of concrete are highlighted. Corrosion of reinforcement is not discussed.