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Structural health management constitutes an essential factor in ensuring the durability of concrete structures. Cracks in concrete, reinforcement corrosion, alkali–silica reaction and efflorescence attacks are common concrete defects that can be identified visually. However, the detection and classification of these defects in concrete bridges and other high-rise concrete structures is a difficult and expensive process using manual approaches. In this research, a deep learning application is applied to detect and classify concrete defects. Concrete images from the public repository were used to create the explored database. The database was divided into training and validation subsets. The visual geometry group (Vgg19), neural search architecture (nasnetlarge) and residual inception block (vinceptionresnetv2) algorithms were used to analyse the images. The results of the overall performance show that the Vgg19 algorithm recorded higher accuracy in the detection and classification of concrete defects when compared to the nasnetlarge and inceptionresnetv2 algorithms. The efficiency of the proposed approach was evaluated using a new dataset containing images of concrete defects. The outcome of this research shows clearly that deep learning models could enhance the efficiency of concrete structural health monitoring in a multi-classification scenario. [ABSTRACT FROM AUTHOR]

As economies and industrialisation have grown, the foundry industry has produced a significant amount of ceramic mould casting waste (CMCW). To promote resource utilisation, this study investigates recycling CMCW as a partial replacement for lightweight aggregates in lightweight concrete. The durability of lightweight concrete mixes with varying CMCW content was studied using surface electrical tests, ultrasonic pulse velocity measurements, non-steady-state accelerated chloride penetration tests and carbonation resistance experiments. The results indicate that a lightweight concrete containing 80% CMCW exhibited greater density and uniformity, greater resistance to chloride ion penetration and better resistance to carbonation. These findings suggest that CMCW can be an effective and sustainable replacement for lightweight aggregate in lightweight concrete, improving durability and environmental performance. This research contributes to the development of sustainable construction materials and provides insights for the use of CMCW in the foundry industry. [ABSTRACT FROM AUTHOR]

Chloride binding capacity is an important factor affecting the durability of concrete, which is directly related with the hydrates of paste. Therefore, this research investigated the chloride binding capacity of calcium silicate hydrates (C-S-H) and Friedel's salt (Fs) to demonstrate the impact of three common mineral admixtures on the binding behavior of pastes. The results show that the binding capacity of pastes can be enhanced when the dosage of fly ash (FA), slag (SL), and silica fume (SF) does not exceed 30%, 45%, and 5%, respectively. The reinforcement effect of SL is the most significant; with 30% dosage, for example, the chloride binding capacity can be increased by 32.0%. Moreover, the single incorporation of FA/SL/SF increases the overall content of C-S-H and decreases the chlorides adsorbed in unit mass C-S-H in general, leading to the result that the binding capacity of paste does not develop positively with the content of C-S-H or Fs. It is thus necessary to take the content and chloride binding performance of phases into consideration when explaining the chloride binding capacity of pastes. Furthermore, Fs fixed chlorides per unit mass paste decline with the increase of FA/SF, while SL dosage has limited impact; further, C-S-H adsorbed chloride per unit mass paste first grows and then reduces for the three series pastes. Moreover, when the NaCl solution concentration is 3.0 mol/L , the chloride content combined by C-S-H is significantly higher than that by Fs in all pastes, with the proportion of the former above 75% in total bound chloride. [ABSTRACT FROM AUTHOR]

This work examined the performance of self-heating concrete under laboratory thermal conditions and outdoor real-time conditions during the fall and winter seasons. Snow-melting and freeze–thaw performance of low-temperature phase change materials (PCM) incorporated self-heating concrete slabs in various scales were evaluated. PCM exhibited high enthalpy of fusion (ΔHf≈170–180 J/g), long-term thermal stability, and desirable supercooling. The experimental program included (1) optimization of concrete mix designs for maximum PCM incorporation, (2) characterization of thermal properties of PCM-mortar specimens using longitudinal guarded comparative calorimetry (LGCC), and (3) large-scale PCM concrete slabs in outdoor conditions to evaluate the real-time thermal performance against freeze–thaw events and snow-melting efficiency. Two different approaches were used to incorporate PCM in concrete: (1) submersion of liquid PCM in porous lightweight aggregates (PCM-LWA); and (2) microencapsulated PCM (MPCM). Both PCM-LWA and MPCM concrete not only exhibited promising snow-melting capabilities but also lowered the number of freeze–thaw cycles during cold seasons. PCM-LWA concrete performed better in decreasing the number of freeze–thaw (F-T) cycles due to the undercooling phenomenon created by the LWA pore network confinement pressure, allowing gradual latent heat release; the undercooling phenomenon in PCM-LWA results in phase transformation in a wider low-temperature range (i.e., 3.94°C to −13.04°C). Therefore, the PCM-LWA concrete was effective in melting snow within a wider range of low temperatures. MPCM concrete was found to provide a rapid melting capability during a snowfall event due to its "one-shot" heat release phenomenon. Both LWA-PCM and MPCM concrete slabs demonstrated promising heat response and snow-melting capability. Snowfall and freeze–thaw cycles occur frequently during winter seasons in North American regions with cold climate, resulting in snow accumulation on concrete roads and flatworks as well as concrete freeze–thaw damage. In this paper, a "self-heating" concrete was developed via incorporation of low-temperature phase change material (PCM), and its promising snow removal and freeze–thaw improvements were validated. The self-heating concrete can be used to construct pavements, driveways, bridge decks, and any other types of flatworks. When the ambient temperature falls to ∼0°C , PCM will release desirable amounts of heat energy (ΔHf=170–180 J per g of PCM added) by changing its phase from liquid to solid. As a result, the accumulated snow and ice melts at a gradual pace. In addition, heat release from the incorporated PCM lowers the number of freeze–thaw cycles, improving freeze–thaw performance of concrete made elements in cold regions, which in turn improves concrete durability and service life by minimizing the susceptibility to freeze–thaw scaling and spalling. [ABSTRACT FROM AUTHOR]

This review focuses on recent advances in concrete durability using graphene oxide (GO) as a nanomaterial additive, with a goal to fill the gap between concrete technology, chemical interactions, and concrete durability, whilst providing insights for the adaptation of GO as an additive in concrete construction. An overview of concrete durability applications, key durability failure mechanisms of concrete, transportation mechanisms, chemical reactions involved in compromising durability, and the chemical alterations within a concrete system are discussed to understand how they impact the overall durability of concrete. The existing literature on the durability and chemical resistance of GO-reinforced concrete and mortar was reviewed and summarized. The impacts of nano-additives on the durability of concrete and its mechanisms are thoroughly discussed, particularly focusing on GO as the primary nanomaterial and its impact on durability. Finally, research gaps, future recommendations, and challenges related to the durability of mass-scale GO applications are presented. [ABSTRACT FROM AUTHOR]

The ductility and exhibition of the multiple, fine, self-controlled cracking of strain-hardening cementitious composites (SHCCs) under tension has made them attractive for enhancing the durability of civil infrastructure. These fine cracks are key to preventing the ingress of water and harmful chemicals into the structure and thereby achieving steel reinforcement. However, several studies have suggested that the short-term fine cracks shown in the laboratory may end up exceeding the acceptable crack widths that are specified in design codes when SHCC members are subjected to sustained constant loads. In real structures, however, the load is also shared by the steel reinforcement in the member, so the SHCC within may not be under a constant load; therefore, the crack widening will not be as severe. This study focuses on the creep behaviour of SHCCs when they are applied as an external layer on reinforced concrete to enhance durability. A novel approach to simulate various stress–strain regimes in such systems is developed by using a fixture to share a sustained moment exclusively between a reinforcement member and SHCC. The developed load-sharing system allows stresses within the reinforcement and SHCC to be monitored against time during the imposed loading, while ensuring access to the SHCC layer for instrumentation and monitoring of strain/cracking. The time-dependent widening of cracks in the SHCC layer is found to be much less significant than that under constant loading, so resistance to water/chemical penetration can still be ensured in the long term. The obtained information on the variation in stress, strain, and crack opening with time will be useful for the development of a general model for the creep behaviour of SHCC members. [ABSTRACT FROM AUTHOR]

Compaction quality significantly influences the strength and durability of concrete in structures. Under-compacting can retain entrapped air, reducing strength, while over-compacting can lead to segregation, creating local variances in strength distribution and modulus of elasticity in the concrete structure. This study examines the widely adopted concept that compaction is optimal when bubbles cease to emerge on the concrete surface. We recorded the surface activity of six comparable concrete specimens during the compaction process using a 4K video camera. Four specimens were compacted using a table vibrator and two with a poker vibrator. From the video frames, we isolated the bubbles for analysis, employing digital image processing techniques to distinguish newly risen bubbles per frame. It was found that the bubbles continuously rose to the surface in all specimens throughout the compaction process, suggesting a need for extended compaction, with some specimens showing a slow in the rate of the bubbles' emergence. However, upon examining the segregation levels, it was discovered that all the specimens were segregated, some severely, despite the continued bubble emergence. These findings undermine the reliability of using bubble emergence as a principle to stop compaction and support the need for developing online measurement tools for evaluating compaction quality. [ABSTRACT FROM AUTHOR]

Supplementary cementitious materials (SCMs) are eco-friendly cementitious materials that can partially replace ordinary Portland cement (OPC). The occurrence of early-age cracking in OPC-SCM blended cement is a significant factor impacting the mechanical properties and durability of the concrete. This article presents a comprehensive review of the existing research on cracking in OPC-SCM concrete mix at early ages. To assess the effects of SCMs on the early-age cracking of concrete, the properties of blended cement-based concrete, in terms of its viscoelastic behavior, evolution of mechanical performance, and factors that affect the risk of cracking in concrete at early ages, are reviewed. The use of SCMs in OPC-SCM concrete mix can be an effective method for mitigating early-age cracking while improving the properties and durability of concrete structures. Previous research showed that the shrinkage and creep of OPC-SCM concrete mix are lower than those of conventional concrete. Moreover, the lower cement content of OPC-SCM concrete mix resulted in a better resistance to thermal cracking. Proper selection, proportioning, and implementation of SCMs in concrete can help to optimize the performance and reduce the environmental impact of OPC-SCM concrete mix. [ABSTRACT FROM AUTHOR]

An alkali–silica reaction (ASR) is a chemical process that leads to the formation of an expansive gel, potentially causing durability issues in concrete structures. This article investigates the properties and behaviour of ASR products in mortar with the addition of low-purity calcined clay as an additional material. This study includes an evaluation of the expansion and microstructural characteristics of the mortar, as well as an analysis of the formation and behaviour of ASR products with different contents of calcined clay. Expansion tests of the mortar beam specimens were conducted according to ASTM C1567, and a detailed microscopic analysis of the reaction products was performed. Additionally, their mechanical properties were determined using nanoindentation. This study reveals that with an increasing calcined clay content, the amount of the crystalline form of the ASR gel decreases, while the nanohardness increases. The Young's modulus of the amorphous ASR products ranged from 5 to 12 GPa, while the nanohardness ranged from 0.41 to 0.67 GPa. The obtained results contribute to a better understanding of how the incorporation of low-purity calcined clay influences the ASR in mortar, providing valuable insights into developing sustainable and durable building materials for the construction industry. [ABSTRACT FROM AUTHOR]

The reaction of alkalis with aggregate containing reactive forms of silica (ASR) plays a significant role in shaping the durability of concrete, as the strongly hygroscopic reaction products generated lead to internal stress, causing its expansion and cracking. This study presents an extended analysis of corrosive processes occurring in mortars with reactive natural aggregate from Poland, using computed tomography and scanning microscopy methods. Numerous cracks in the grains and the surrounding cementitious matrix were observed, indicating a high degree of advancement of corrosive processes. Over time, the proportion of pores with reduced sphericity increased, indicating ongoing degradation of the mortars. The usefulness of computed tomography in studying the progress of ASR was demonstrated. Scanning microscopy confirmed that the cause of mortar degradation is the formed ASR gel with a typical composition, located within the volume of reactive grains, cracks propagating into the cementitious matrix, and accumulated in air voids. [ABSTRACT FROM AUTHOR]

A new, sustainable polypropylene terephthalate (PPT) coating was synthesized from recycled polyethylene terephthalate (PET) and applied onto a hydraulic concrete substrate to improve its durability. For the first step, PET bottle wastes were ground and depolymerized by glycolysis using propylene glycol (PG) in a vessel-type reactor (20–180 °C) to synthesize bis(2-hydroxypropyl)-terephthalate (BHPT), which was applied as a coating to one to three layers of hydraulic concrete substrate using the brushing technique and polymerized (150 °C for 15 h) to obtain PPT. PET, BHPT, and PPT were characterized by FT-IR, PET, and PPT using TGA, and the PPT coatings by SEM (thickness), ASTM-D3359-17 (adhesion), and water contact angle (wettability). The durability of hydraulic concrete coated with PPT was studied using resist chloride ion penetration (ASTM-C1202-17), carbonation depth at 28 days (RILEM-CPC-18), and the absorption water ratio (ASTM-C1585-20). The results demonstrated that the BHPT and PPT were synthetized (FT-IR), and PPT had a similar thermal behavior to PET (TGA); the PPT coatings had good adhesion to the substrate, with thicknesses of micrometric units. PPT coatings presented hydrophilic hydrophilic behavior like PET coatings, and the durability of hydraulic concrete coated with PPT (2–3 layers) improved (migration of chloride ions decreased, carbonation depth was negligible, and the absorption water ratio decreased). [ABSTRACT FROM AUTHOR]

As an environmentally friendly natural polymer, citric acid-modified chitosan (CAMC) can effectively regulate the hydration and exothermic processes of cement-based materials. However, the influence of CAMC on the macroscopic properties of concrete and the optimal dosage are still unclear. This work systematically investigates the effects of CAMC on the mixing performance, mechanical properties, shrinkage performance, and durability of concrete. The results indicated that CAMC has a thickening effect and prolongs the setting time of concrete. CAMC has a negative impact on the early strength of concrete, but it is beneficial for the development of the subsequent strength of concrete. With the increase in CAMC content, the self-shrinkage rate of concrete samples decreased from 86.82 to 14.52 με. However, the CAMC-0.6% sample eventually expanded, with an expansion value of 78.49 με. Moreover, the long-term drying shrinkage rate was decreased from 551.46 to 401.94 με. Furthermore, low-dose CAMC can significantly reduce the diffusion coefficient of chloride ions, improve the impermeability and density of concrete, and thereby enhance the freeze–thaw cycle resistance of concrete. [ABSTRACT FROM AUTHOR]

There are four critical factors that affect air voids (VA) of asphalt concrete over time: traffic loads and repetitions, environmental regimes, compaction, and asphalt mix composition. Because of the high as-construct VA content of the material, it is expected that voids will reduce over time, causing rutting during initial traffic periods. Eventually, the material will undergo shear flow when it reaches its most dense state with optimum aggregate interlock or refusal VA content. Furthermore, to accurately model the performance of an asphalt mixture, the VA must be predicted over time. This study aims to implement two ensemble learning methods namely Cubist and gradient boosting regression tree (GBRT) hybridized with equilibrium optimizer algorithm (EOA) to predict the VA percentage of asphalt concrete during the service life of flexible pavements. For this purpose, 324 data records of VA were collected from the literature. The variables selected as inputs were original as-constructed air voids, VAorig (%); mean annual air temperature, MAAT (°F); original viscosity at 77°F (25°C) , ηorig,77 (Mega-Poises); and time (months). GBRT-EOA and Cubist-EOA were found to be superior to other classical single ML approaches [for instance, artificial neural network (ANN), support vector machine (SVM), and Gaussian process regression (GPR) and M5Tree] and existing nonlinear regression models. In the training phase, the GBRT-EOA had R2 , root mean square error (RMSE), mean absolute error (MAE), and mean of absolute percent error (MAPE) values of 99.8%, 0.136%, 0.093%, and 1.324%, respectively, while these values changed to 95.1%, 0.701%, 0.53%, and 7.825% in the testing phase. Also, only less than 5% of the records were predicted using this model with more than 20% deviation from the observed values. As determined by the sensitivity analysis, time (months) is the most significant of the four input variables, while MAAT (°F) is the least one. A parametric study showed that regardless of the MAAT, the ηorig,77 of 1.0 Mega-Poises, and the VAorig above 6% can be ideal for improving the pavement service life in terms of the VA of the asphalt concrete layer during service life. [ABSTRACT FROM AUTHOR]

Organic corrosion inhibitors (OCI) have been widely accepted as a reliable method for enhancing the durability of marine reinforced concrete structures. However, the effect of OCI on steel corrosion is not clear in the case of cracks appearing in the concrete cover. In this paper, steel corrosion behaviors in cracked concrete with different crack widths, intact concrete containing OCI, and cracked concrete containing the OCI exposed to the marine tidal zone were investigated through open-circuit potential tests and EIS measurements. The obtained results illustrate that the corrosion rate of steel in cracked concrete is reduced with the decrease of crack width having an initial width of less than less than or equal to 200 μm in the marine tidal zone. Based on the Rf and Rct values, it is found that the alcohol amine-based OCIs can improve the corrosion resistance of steel in intact concrete and concrete with microcracks (with a width of less than 100 μm) exposed to the marine tidal zone. The carboxylic acid-based OCIs aggravate the steel corrosion due to the hydrophobicity provided by carboxylic acids for seawater transport through cracks. The ester-based OCIs also increase the steel corrosion rate as it accelerates concrete carbonation. [ABSTRACT FROM AUTHOR]

The use of seawater and sea sand as replacements for fresh water and river sand in the preparation of seawater and sea sand concrete can effectively address issues such as high transportation costs, extended construction periods, and resource wastage. Nevertheless, in northern coastal areas, the problem of concrete durability in the complex and changing marine environment is more prominent. Research on the durability of seawater sea sand concrete is beneficial to the widening of its application range. To investigate the impact of glass fiber (GF) and polyvinyl alcohol fiber (PVA) with different blending methods on the seawater freeze–thaw resistance of seawater sea sand concrete (SSC), corresponding specimens were prepared, and seawater freeze–thaw cycling tests were conducted. By adopting the slow-freezing method and combining macro-structure and micro-morphology, the damage mechanism and the deterioration law of fiber-reinforced SSC under seawater freezing and thawing were investigated. The results indicate that, macroscopically, the incorporation of GF and PVA can effectively mitigate the damage to the matrix and reduce the effects of external erosive substances on the rate of strength loss, the rate of mass loss, and the relative dynamic elastic modulus. After 75 cycles, the SSC with a total volume doping of 0.3% and a blending ratio of 1:1 showed a 41.23% and 27.55% reduction in mass loss and strength loss, respectively, and a 29.9% improvement in relative dynamic elastic modulus compared with the basic group. Microscopic analysis reveals that the combined effect of freezing and expansion forces, the expansive substances generated by seawater intrusion into the interior of the matrix, and salt crystallization all weaken the bond between aggregate and mortar, leading to accelerated deterioration of the concrete. The incorporation of fibers enables the matrix to become denser and improves its crack-resistant properties, resulting in a better durability than that of the basic group. The damage prediction model established by the NSGM(1,N) model of gray system theory exhibits high accuracy and is suitable for long-term prediction, accurately predicting the damage of seawater sea sand concrete under seawater freeze–thaw coupling. [ABSTRACT FROM AUTHOR]

Current regulatory documents and the scientific literature lack a theoretical framework and practical guidance for calculating centrifugally compacted reinforced concrete structures, taking into account the variatropy of their structure and the material's characteristics across the section. A problem related to this research lies in the need to form a systematized, theoretical, and practical knowledge base about variatropic concretes, the importance of which has been proven by various scientists without, to date, the creation of a unified scientific methodological base. The importance of this study is linked to the need for the world's construction projects and processes to transition to the most economically, materially, and resource-efficient types of building structures, which, of course, include structures made of variable-type concrete. This study's objective is to fill these scientific and engineering gaps. The purpose of this study was to systematize the existing knowledge base about the technology, structure formation, and properties of variatropic concrete, using an analytical review of previously conducted studies by ourselves and others, both in Russia and abroad. A theoretical justification for the formation of the structure of variatropic materials is presented. An analysis of the basic physical and mechanical properties of variatropic concretes is carried out and the features of their microstructures are considered. The main structures created using centrifugation technology are considered. Variatropic concrete has an increased amount of mechanical characteristics compared to traditional concrete, on average by up to 45%. The durability of variatropic concrete is improved, on average, by up to 30% compared to conventional concrete. [ABSTRACT FROM AUTHOR]

Ultra-high performance concrete (UHPC) with excellent durability has broad application prospects in improving the durability of reinforced concrete (RC) structures. To clarify the influence of freeze–thaw cycles on the axial compression performance of UHPC-RC composite columns, axial compression tests were carried out on composite columns with different cycles (0, 100, 200, 300 cycles) and stirrup spacing (35, 70, 105 mm). The results showed that the UHPC shell did not fall off when the composite column was destroyed, even in the freeze–thaw environment. Under the action of freeze–thaw cycles, the peak load N u , t and initial elastic modulus E of the composite column decreased, but the ductility coefficient μ increased. Increasing the stirrup spacing could significantly improve the ductility of the composite column. After 100 freeze–thaw cycles, the ductility coefficient μ of the 35 mm stirrup spacing specimen was 112.6% higher than that of the 105 mm specimen. A prediction model for the bearing capacity of UHPC-RC composite columns under freeze–thaw cycles was established, and the predicted results were in good agreement with the experimental results. This study lays a theoretical and experimental foundation for the application and design of UHPC-RC composite columns in the freeze–thaw environment. [ABSTRACT FROM AUTHOR]

Microbial attacks rapidly degrade concrete structures in wastewater facilities, leading to brief service lifespans. Hence, producing concrete resistant to chemical and sulfuric acid corrosion is more cost-effective. In the present study, a total of six concrete mixtures incorporating 7.5% silica fumes (SF) and 10% natural zeolite (ZE) were immersed in 0.5% and 1% sulfuric acid solutions with a maximum pH threshold of 2 and 1, respectively, for 70 weeks. The specimens were regularly monitored for surface deterioration, mass change and crushing load change. To better understand the relationship between the pore structure of concrete mixtures and resistance to sulfuric acid, various durability tests such as rapid chloride penetration, water absorption, electrical resistivity and chloride diffusion coefficient were performed. Based on the results obtained, converting calcium hydroxide into calcium silicate hydrate gel through pozzolanic reactions and then refining the porosity of concrete with silica fumes (SF) and natural zeolite (ZE) was effective in enhancing the resistance of concrete to attack by sulfuric acid of relatively low concentration. As a result, using silica fumes (SF) and natural zeolite (ZE) is a lower-cost method for reducing corrosion rates to extend the service life of facilities, particularly in lower concentrations. [ABSTRACT FROM AUTHOR]

Sulfuric acid corrosion is a non-negligible problem affecting the durability of concrete materials. To explore the mechanism of sulfuric acid corrosion on the fracture performance and microstructure of concrete, three-point bending test was utilized to analyze the evolutionary characteristics of the crack mouth opening displacement and the fracture toughness of concrete corroded by sulfuric acid. Scanning electron microscope and energy-dispersive spectrometer were utilized to analyze the characteristics of microscopic morphology and corrosion products of concrete corroded by sulfuric acid. The result shows that the fracture evolution of concrete can be divided into four stages: nonlinear development stage, linear development stage, deceleration expansion stage, and accelerated expansion stage. In purified water environment, the peak fracture load and fracture toughness of concrete is positively related to corrosion time. In sulfuric acid corrosion environment, the peak fracture load and fracture toughness of concrete are negatively related to corrosion time and concentrations of sulfuric acid solution. Microscopic experiments show that the interior of concrete is less affected by sulfuric acid corrosion, and the structure is relatively dense compared with the surface. The expansion crystal ettringite formed at the fracture surface of the concrete specimen during sulfuric acid corrosion was the main reason for the durability reduction of concrete. [ABSTRACT FROM AUTHOR]

The coal gangue coarse-aggregate content in ordinary concrete should not be too large. In order to further improve the utilization rate of coal gangue coarse aggregate, this study used the principle of "strong wrapped weak" to prepare high-performance concrete. This study considered four factors, namely, water–binder (W/B) ratios, non-spontaneous combustion coal gangue (NCCG) coarse-aggregate contents, fly ash–slag mass ratios, and silica fume coating to prepare high-performance concrete. The workability, mechanical, and durability properties were studied, and the changes in the interfacial transition zone (ITZ) of concrete before and after sulfate attack and freeze–thaw cycles were analyzed based on the SEM test. The life prediction of NCCG coarse-aggregate high-performance concrete was carried out based on the grey system GM(1,1) prediction model. The results show that the NCCG coarse-aggregate contents have the greatest effect on compressive strength, sulfate resistance, and frost resistance. The W/B ratio has the greatest effect on the anti-carbonization properties. Fly ash–slag mixing can obtain better durability. Considering the effect on the design service life of high-performance concrete, NCCG coarse aggregate is used to prepare high-performance concrete in North China, and the recommended content is 60%; in the Northwest and Northeast regions, the recommended content is 45%. This study provides a basis for the preparation of high-performance concrete with NCCG coarse aggregate. [ABSTRACT FROM AUTHOR]

One of the most significant damages of reinforced concrete is caused by chloride attacks. Solutions including the use of coatings or special concrete with low permeability have been proposed to promote concrete durability in previous research. Geopolymer mixes is a viable alternative in this context. Notwithstanding the advantages of geopolymer, problems with quick setting, shrinkage, increased cost, etc., may make its use problematic. Using permanent formworks (PFs) will therefore be a solution in this respect. PFs can be used both during the construction and during the repair of the structures. In this study, the considerations of fabricating PFs as well as their on-site implementation are examined. Compressive strength, impact resistance during transportation and installation, chloride ions penetration depth, and capillary absorption (from the seams and bulk) are among the experiments which are carried out to assess the performance of PFs. The significant increase in the service life of structures under chloride attack, the elimination of a part of the molding process in the construction of new structures, and the minimization of the low quality of execution are among the advantages of using PFs. The results reveal that the performance of PFs under harsh environmental conditions is appropriate. Although the use of polyurethane mastic in the seams has favorable results, reducing the number of seams decreases the probability of PFs damage. Although the implementing cost of PFs is slightly higher than conventional concrete (~ 37%), the life cycle cost assessment of the structure shows economic savings if PFs are applied. [ABSTRACT FROM AUTHOR]

The advantages of using geopolymer materials instead of cement in concrete are not limited to high durability properties. geopolymer concrete was introduced to mitigate the environmental damages caused by CO2 emissions and the great level of fossil fuels consumption during cement manufacturing. In the present investigation, a number of experimental studies were conducted on slag-based geopolymer concrete. Accordingly, nano-silica particles were used to improve the geopolymer concrete structure's matrix. In the current study, slag-based geopolymer concrete was used with 0–2% polyolefin fibres and 0–8% nano-silica. They were subjected to water absorption and permeability tests to assess their durability. The addition of nano-silica enhanced the whole properties of the slag-based geopolymer concrete. By using the nano-silica, the concrete paste microstructure became denser and more homogeneous, and the pores decreased. The compressive strength and tensile strength of the concrete increased by up to 22% and 14% respectively. On the other hand, in terms of durability, the nano-silica lowered the water absorption and permeability coefficients by up to 24% and 44%, respectively, by filling the pores of the concrete. In the weight loss test, geopolymer concrete achieved superior results (up to 16%) compared to ordinary concrete. [ABSTRACT FROM AUTHOR]

As a pozzolan, waste glass powder (WGP) can improve the mechanical properties and durability of concrete, especially at a later age. However, the modification mechanisms should be fully understood and discussed. One of the effective approaches is to investigate the improvement in interfacial transition zones (ITZs) between aggregate and mortar matrix. In this paper, soda-lime WGP was used as a supplementary cementitious material and replaced 20% by weight cement in the sample with modeled aggregate. The phases and chemical composition within the ITZs and the adjacent mortar matrix were investigated by backscattered electron (BSE) imaging combined with image analysis. Advanced nanomechanical techniques were simultaneously applied, and the results obtained from nanoindentation and nanoscratch were compared. The results show that WGP can significantly reduce the width of ITZs and increase the content of calcium-silicate-hydrate (C-S-H) and Si/Ca ratio in both ITZs and matrix. The high heterogeneity of ITZ with WGP made it susceptible to errors caused by unreacted WGP during the measurement of C-S-H nano- and micromechanical properties. For the control group without WGP, the test results of nanoindentation and nanoscratch showed a high degree of consistency. However, for the samples with 20% by weight WGP, there are some differences in the test results between nanoindentation and nanoscratch. Nanoscratch was able to acquire abundant data in a short testing time and proved more suitable for the tests of homogeneous materials. On the other hand, for the sample with 20% by weight WGP, nanoindentation was found to more likely to reflect the real micromechanical properties of ITZs based on abundant indentation tests. [ABSTRACT FROM AUTHOR]

Reducing cement usage and replacing it with solid waste in high volume is one of the most important ways for the sustainable development of the cement industry. In the present work, sustainable foamed concrete with a high content of phosphogypsum (PG) was prepared through the combination activation and synergistic strengthening of waterglass, ground blast furnace slag (GBFS), and cement. The fluidity, mechanical properties, volume stability, and durability of this sustainable foamed concrete were studied and its reaction mechanisms were also investigated using hydration calorimetry, X-ray diffraction (XRD), and scanning electron microscopy (SEM) techniques. The results show that the early age cohesive strength for this foamed concrete is mainly derived from ettringite formation, which is a product of the pozzolanic reaction of GBFS in the presence of sulfate ions. Cement in this sustainable foamed concrete is presented as an alkali activator. Too small addition of cement would weaken its activation effect and reduce the hydration product formation, which delays the strength development of the foam concrete. High cement content would provide sufficient Ca2+ ions, which can also retard the GBFS hydration. The unreacted PG particles are covered by ettringite and other hydration products during the reaction process to prevent its dissolution in a moist environment and help improve the water resistance and durability of foamed concrete. The sustainable foamed concrete prepared with 15% of cement and more than 50% of PG has 7 and 28 days compressive strengths of 2.86 and 3.36 MPa, respectively. In addition, it has a water-softening coefficient of 0.81 and a volume microexpansion feature in a moist environment, which is suitable for subgrade or underground filling. [ABSTRACT FROM AUTHOR]

The nucleation and growth of calcium–silicate–hydrate (C–S–H) is of fundamental importance for the strength development and durability of the concrete. However, the nucleation process of C–S–H is still not fully understood. The present work investigates how C–S–H nucleates by analyzing the aqueous phase of hydrating tricalcium silicate (C3S) by applying inductively coupled plasma-optical emission spectroscopy as well as analytical ultracentrifugation. The results show that the C–S–H formation follows non-classical nucleation pathways associated with the formation of prenucleation clusters (PNCs) of two types. Those PNCs are detected with high accuracy and reproducibility and are two species of the 10 in total, from which the ions (with associated water molecules) are the majority of the species. The evaluation of the density and molar mass of the species shows that the PNCs are much larger than ions, but the nucleation of C–S–H starts with the formation of liquid precursor C–S–H (droplets) with low density and high water content. The growth of these C–S–H droplets is associated with a release of water molecules and a reduction in size. The study gives experimental data on the size, density, molecular mass, and shape and outlines possible aggregation processes of the detected species. [ABSTRACT FROM AUTHOR]

Calcium sulfoaluminate belite (CSAB) cement has gained prominence as a viable environmentally friendly substitute for conventional portland cement (PC). The current study investigates the relative performance of expansive and nonexpansive CSAB cement-based concretes, and PC-based concretes when subjected to chloride-rich conditions. Multiple testing methodologies, including surface resistivity measurements, chloride migration, rapid chloride penetration, long-term bulk diffusion, and water sorptivity, were employed to assess the durability of these concrete systems. Surface resistivity measurements indicated that CSAB systems exhibited significantly higher resistivity when compared with PC-based counterparts. Increased resistivity in CSAB systems was influenced by the conductivity of the pore solution, emphasizing that the formation factor provides a more accurate representation of the pore structure within the system. The expansive and nonexpansive CSAB cement–based concrete outperformed PC-based concrete in migration-based tests and rapid chloride penetration test (RCPT). In contrast, the CSAB and PC systems demonstrated similar performance in the long-term bulk diffusion-based test. Although CSAB systems exhibit finer pore structures than PC-based counterparts, their performance in chloride-rich environments is affected by their reduced binding capacity. The study emphasizes that the conclusions drawn from accelerated tests and resistivity measurements of CSAB cement–based concrete must be cautiously interpreted because these results may not indicate real-world performance. [ABSTRACT FROM AUTHOR]

Sewer concrete structures are vulnerable to acidic corrosion due to the biological oxidation of sulfide in the wastewater to sulfuric acid. The use of photosynthetic bacteria in the coating layer on the sewer concrete is proposed to be an effective approach to prevent such corrosion. Here we report two strains, PN6 and PN7, isolated from a drainage system in Hanoi that were identified as Rhodopseudomonas palustris PN6 and Rhodobacter capsulatus PN7 based on a comparative analysis of the 16S rDNA and pufM gene sequences. Both strains performed versatile metabolic paths, including anoxygenic and microaerophilic phototrophy and aerobic chemotrophy, allowing them to adapt to the fluctuating sewer conditions. Furthermore, they exhibited notable capability of oxidizing sulfide and producing glycocalyx, and therefore were able to prevent concrete corrosion by scavenging sulfide and reducing the production of sulfuric acid, at the same time sealing the tiny cracks on the concrete surface and preventing further attack of the corrosive agents. Two strains grew well at an alkali pH of 9 and formed biofilm extensively, and therefore can be incorporated into porous material vermiculite, allowing them to survive in the coating mortar. The protective effect of coating mortar containing strains PN6 or PN7 singly or in a combination of both incorporated in vermiculite was demonstrated in a laboratory model simulating the sewer environment with an acidic vapor atmosphere. Without bacteria in the coating mortar, the concrete surface suffered severe corrosion with spots of 0.01–0.2 mm in width and up to 4.5 mm in length clustering in rafts of 10–70 mm2 , whereas the concrete surface coated by bacteria-containing mortar was intact to corrosion. The study proposed the possibility of applying purple nonsulfur bacteria (PNSB) to protect sewer concrete, and also prolong the service life of these important structures. Practical Applications: Sewer concrete systems are daily attacked by acidic corrosion established via the biological oxidation of sulfide to sulfuric acid. The repair is generally costly and has difficulties in implementation. The use of PNSB with the capabilities of scavenging H2S and producing exopolysaccharide (EPS) for the development of a coating layer would be a feasible approach to constrain the corrosion process. Suitable strains of PNSB such as the two strains Rhodopseudomonas palustris PN6 and Rhodobacter capsulatus PN7 reported in this study are supposed to be incorporated in a porous material like vermiculite before being added to the coating mortar to better stabilize and adapt to the harsh conditions of the coating layer. These types of PNSB can survive in the coating layer and multiply by utilizing organic carbon and sulfide from wastewater with the production of sulfur (instead of sulfuric acid) and glycocalyx that can instantly seal the tiny corrosion spots and prevent further corrosion attacks. This approach is supposed to be a prevention solution to increase the service durability of sewer concrete systems and reduce the need for repair implementation. [ABSTRACT FROM AUTHOR]

The moisture content within the concrete pore network significantly influences the mechanical, thermal, and durability characteristics of concrete structures. This paper introduces a novel fully embedded wireless temperature and relative humidity sensor connected to an automatic acquisition system designed for continuous concrete monitoring. Relative humidity measurements from this new sensor are compared with those obtained by a commercial system based on the borehole method at different depths (2.5 and 4.0 cm) and exposure conditions (oven drying and humid chamber). The results allow for proving that both systems provide consistent internal relative humidity measurements aligned with the exposure conditions and highlight the capability of fully embedded wireless sensors as a practical and reliable alternative to the conventional borehole method. Additionally, the continuous monitoring of the wireless cast-in sensor exhibits reliability during unintended temperature fluctuations, emphasizing the effectiveness of permanently installed sensors in promptly detecting unintended curing variations in real time. The continuous real-time information provided combined with the practicality of these sensors might assist construction managers to improve the quality control of the concrete curing process and shrinkage behavior, and ensure the integrity of concrete surface finishing. [ABSTRACT FROM AUTHOR]

Ground Granulated Blast-Furnace Slag (GGBS) and silica fume (SF) are frequently utilized in gel materials to produce environmentally sustainable concrete. The blend of the two components contributes to an enhancement in the pore structure, which, in turn, increases the mechanical strength of the material and the compactness of the pore structure and decreases the permeability, thereby improving the durability of the concrete. In this study, the pore structures of GGBS and SF blends are assessed using Nuclear Magnetic Resonance (NMR) and Mercury Intrusion Porosimetry (MIP) tests. These methodologies provide a comprehensive evaluation of the effect of GGBS and SF on the pore structure of cementitious materials. Results showed that the addition of SF and GGBS reduces the amount of micro-capillary pores (10 < d < 100 nm) and the total pore volume. The results indicate that the transport properties are related to the pore structure. The incorporation of SF reduced the permeability of the concrete by an order of magnitude. The pore distribution and pore composition had a significant effect on the gas permeability. The difference in porosity obtained using the MIP and NMR tests was large due to differences in testing techniques. [ABSTRACT FROM AUTHOR]

Efficient and accurate prediction of chloride concentration distribution in concrete is extremely important for evaluating the durability of reinforced concrete (RC) structures in the coastal region. A peridynamic (PD) framework for chloride diffusion–reaction is proposed to explore the mechanisms of the long-term chloride ingress in concrete. Specifically, the improved intermediately homogenized peridynamic (IH-PD) method is substituted for the solid modeling method of the interface transition zone (ITZ), with the consideration of the mesoscopic characteristics of concrete and great computational efficiency. In addition, considering the effect of concrete mesostructure, an effective chloride diffusion coefficient is constructed based on the Mori–Tanaka method, in which the proportion of various bonds is determined by the statistics. To verify the reliability of the proposed model, the numerical results are compared with the third-party experiments data. From the results, the randomness of concrete mesostructure leads to the randomness of chloride concentration at the same ingress depth, following the normal distribution. Moreover, the chloride diffusion performance which reflects the speed of chloride diffusion is significantly improved with the increase in the water-cement ratio. Noteworthily, the ITZ thickness can be appropriately increased without affecting the reliability of the results. [ABSTRACT FROM AUTHOR]

Chloride ion corrosion has been considered to be one of the main reasons for durability deterioration of reinforced concrete structures in marine or chlorine-containing deicing salt environments. This paper studies the relationship between the amount of fly ash and the durability of concrete, especially the resistance to chloride ion erosion. The heat trend map of total chloride ion factor correlation displayed that the ranking of factor correlations was as follows: sampling depth > cement dosage > fly ash dosage. In order to verify the effect of fly ash dosage on chloride ion resistance, three different machine learning algorithms (RF, GBR, DT) are employed to predict the total chloride content of fly ash proportioned concrete with varying admixture ratios, which are evaluated based on R2, MSE, RMSE, and MAE. The results predicted by the RF model show that the threshold of fly ash admixture in chlorinated salt environments is 30–40%. Replacing part of cement with fly ash in the mixture of concrete below this threshold of fly ash, it could change the phase structure and pore structure, which could improve the permeability of fly ash concrete and reduce the content of free chloride ions in the system. Machine learning modeling using sample data can accurately predict concrete properties, which effectively reduce engineering tests. The development of machine learning models is essential for the decarbonization and intelligence of engineering. [ABSTRACT FROM AUTHOR]

The durability of concrete is critical for the service life of concrete structures, and it is influenced by various factors. This paper investigates the impact of the relative humidity (RH) of the curing environment on the durability of five different concrete types. The aim is to determine a suitable approach for designing concrete that is well-suited for use in the salt lake region of Inner Mongolia. The concrete types comprise ordinary Portland cement (OPC), high-strength expansive concrete (HSEC), high-strength expansive concrete incorporating silica fume, fly ash, and blast furnace slag (HSEC-SFB), steel fiber-reinforced high-strength expansive concrete (SFRHSEC), and high elastic modulus polyethylene fiber-reinforced high-strength expansive concrete (HFRHSEC). All these concrete types underwent a 180-day curing process at three distinct relative humidities (RH = 30%, 50%, and 95%) before being subjected to freeze–thaw cycles in the Inner Mongolia salt lake brine. The curing environment with a 95% RH is referred to as the standard condition. The experimental results reveal that the durability of OPC and HSEC decreases significantly with increasing relative humidity. In comparison with the control sample cured in 95% RH, the maximum freeze–thaw cycles for concrete cured in lower RHs are only 31% to 76% for OPC and 66% to 77% for HSEC. However, the sensitivity of the durability of HSEC-SFB, SFRHSEC, and HFRHSEC to variations in RH in the curing environment diminishes. In comparison with the corresponding reference value, the maximum freeze–thaw cycles for samples cured in dry conditions increase by 14% to 17% for HSEC-SFB and 21% for SFRHSEC. Specifically, the service life of HFRHSEC cured in a low RH is 25% to 46% higher than the reference value. The durability of HSEC-SFB, SFRHSEC, and HFRHSEC has been proven to be appropriate for structures located in the salt lake region of Inner Mongolia. [ABSTRACT FROM AUTHOR]

The widespread use of carpets in residential and commercial buildings and their relatively short life span result in large volumes of carpet being landfilled. A potential solution to this problem is the use of post-consumer carpet fibers in concrete. To this end, this paper systematically identifies the common fiber types in a typical post-consumer carpet fiber bale and evaluates their durability under exposure to varying levels of alkalinity. The tensile strengths and toughness of the fibers belonging to the nylon and polyethylene terephthalate (PET) families (the dominant fibers in most post-consumer carpets) are reduced by up to 50% following exposure to extreme alkalinity, the reasons for which are determined using spectroscopic and microscopic evaluations. The chloride ion transport resistance of concretes (~40 MPa strength) containing 2.5% carpet fibers by volume (~25 kg of fibers per cubic meter of concrete) is comparable to that of the control mixture, while mortar mixtures containing the same volume fraction of carpet fibers demonstrate negligible enhancement in expansion and loss of strength when exposed to 1 N NaOH. This study shows that moderate-strength concretes (~40 MPa) for conventional building and infrastructure applications can be proportioned using the chosen volume of carpet fibers without an appreciable loss of performance. Consideration of low volume fractions of carpet fibers in low-to-moderate-strength concretes thus provides a sustainable avenue for the use of these otherwise landfilled materials in construction applications. [ABSTRACT FROM AUTHOR]

Concrete technologists use different types of additives such as fly ash, slag, natural pozzolans and nanomaterials toenhance concrete performance and durability. However, a detailed explanation of the early-age hydration process and microstructural modification of concrete in the presence of nanomaterials remains to be presented and extensive research is required for strategic modification of cementitious systems. This study focused on the precise monitoring of early-age hydration with the incorporation of nanoalumina (nAl) in tricalcium silicate (C3S) and Portland cement paste and mortar. The dosage of nAl was varied from 1 to 5% (by weight) in C3S and from 0.1 to 1.0% in Portland cement, with a water/cement ratio of 0.4. The hydration studies showed that the nAl increased the cross-linkage in calcium silicate hydrate gel through substitution of aluminium by silicon, which was responsible for the enhancement of the modulus of elasticity (by 40%) with 1.0% nAl) after 7 days of hydration. In summary, the incorporation of nAl modified the concrete microstructure in the initial days of hydration, leading to higher concrete performance and longer service lives of concrete structures. [ABSTRACT FROM AUTHOR]

Despite alkali–silica reaction (ASR) being a major durability problem in concrete, structural features and properties of ASR gels remain poorly understood. Inspired by the success of coarse-grained (CG) simulations in unveiling key features of calcium-silicate-hydrate (C-S-H) gels, we deploy these simulations to model ASR gels. Our goals are (1) to test the suitability of these simulations to capture ASR gels structural features and mechanical properties; and (2) to quantify any alkali-dependency in the response. Effective interactions obtained at the molecular scale for Na-ASR and K-ASR (sodium-ASR and potassium-ASR) products are adopted. Simulation results are consistent with the available data on the structure, elastic, and viscous behavior of ASR gels. The ASR gel mesotexture development and mechanical properties are ion-specific, with Na-ASR showing a more rigid/less viscous behavior overall. Our results demonstrate the suitability of CG simulations to investigate ASR. [ABSTRACT FROM AUTHOR]

The durability of bridges plays a vital role in their regular operation and transportation, particularly as service life increases. The ability of a bridge to reach its expected service life is closely linked to its durability. In cold regions, the deterioration of bridge concrete durability due to freeze-thaw damage is a common cause of failure, posing a threat to structural safety. In this study, a highway bridge over a sluice that was built 63 years ago was selected for coring and freeze-thaw testing. Two nondestructive testing methods were employed: three-dimensional optical scanning and X-ray computed tomography (X-CT). The former was used to observe and analyze the external surface of the concrete, while the latter was used to analyze its internal structure. The surface morphology was characterized using height, spatial, hybrid parameters, and fractal dimension, and the Abbott–Firestone curve reflected the profile characteristics of the material surface. Moreover, the internal components of concrete were identified and reconstructed in three dimensions based on threshold segmentation, and the changes in internal porosity, pore fractal dimension, and pore size distribution were calculated. Finally, the evolution of bandwidth in the color heat map was analyzed, combining the gray level cooccurrence matrix (GLCM) to reflect the growth of cracks and defects with freeze-thaw cycles. [ABSTRACT FROM AUTHOR]

This study presents a method for identifying sustainable concrete that incorporates toughened waste glass aggregate (TWG). The study takes into account the physical and chemical properties of TWG as quality parameters. Initially, TWG was mechanically treated to produce cubical-shaped aggregates ranging from 6 to 10 mm. Based on their performance, TWG aggregates were selected for an experimental study to validate the methodology. Several tests were conducted to establish the workability, mechanical strength, durability, and microstructural properties of TWG concrete, aiming to examine its feasibility. The results indicated that TWG concrete exhibits favorable fresh and hardened properties, and durability characteristics that are comparable to those of conventional concrete. The compressive strength of TWG concrete at 28 days was 17.95% lower than that of conventional concrete. In parallel, the split tensile strength and flexural strength values of TWG concrete are lower than those of conventional concrete. Additionally, TWG concrete demonstrates lower water absorption and better resistance to rapid chloride ion penetration (RCPT) than conventional concrete. The obtained experimental results were supported by morphological studies, reinforcing the findings of the study. These findings indicated that TWG aggregates possess the necessary quality to be utilized as a construction material, thus presenting the potential for future use in the construction field. [ABSTRACT FROM AUTHOR]

In the northern region of China, freeze–thaw cycles and chloride ion (Cl−) penetration are the primary factors affecting the durability of marine concrete. To investigate the influence of nanoparticles on the Cl− penetration resistance of marine concrete under the action of freeze–thaw cycles, nano-SiO2 and nano-Fe3O4 were added to plain concrete in different amounts. The Cl− penetration resistance of concrete under the action of freeze–thaw cycles was measured in a 5% NaCl solution. The relative dynamic modulus, mass loss rate, and Cl− content at different depths in concrete were measured to evaluate the salt-scaling resistance. The test results show that under salt freeze–thaw cycles, the relative dynamic modulus, bound Cl− content, and Cl− binding capacity of concrete with nanoparticles were higher than those of plain concrete. However, the mass loss, total Cl− content, and free Cl− content in concrete with nanoparticles were lower than those of plain concrete. With increasing nanoparticle content, the relative dynamic modulus, bound Cl− content, and Cl− binding capacity of the concrete first increased and subsequently decreased. However, the mass loss rate, total Cl− content, and free Cl− content first decreased and subsequently increased. The optimum amount of nano-SiO2 and nano-Fe3O4 in the concrete was 2%. The improvement effect of nano-SiO2 on the salt-scaling resistance of concrete was superior to that of concrete with the same amount of nano-Fe3O4. The addition of nanoparticles can accelerate the formation of hydrated products, enhance the chemical binding capacity and physical adsorption capacity of hydrated products to Cl−, and reduce the free Cl− content in concrete. This can improve the Cl− penetration resistance of marine concrete under the action of freeze–thaw cycles. This study provides a reference for the durable design of marine concrete in the northern region. [ABSTRACT FROM AUTHOR]

Chloride transport within concrete is critical for the durability of reinforced concrete structures; however, its diffusion under the coupling action of temperature and humidity has not been fully comprehended. Therefore, in this work, the coupling effects of temperature, relative humidity, and mineral admixtures on chloride transport in concrete were investigated through experimental and numerical simulation work. The results show that the chloride diffusion coefficient decreases with the decreased temperature and growth of relative humidity; however, the chloride concentration on the concrete surface is increased with the growth of temperature and relative humidity. Moreover, compounding about 15% fly ash (FA) and 30% granulated ground blast furnace slag (GGBS) to replace the cement is the most beneficial for improving the antichloride capacity of concrete, considering also the strength. In addition, the numerical simulation considering the coupled effect of temperature and relative humidity of chloride transport in concrete has good agreement with that of experimental results. [ABSTRACT FROM AUTHOR]

The paper concerns destructive and non-destructive (NDT) evaluation of the effect of the addition of superabsorbent polymer (SAP) used as a carrier of mixing water and a means of internal curing on the durability of concrete. The research concerns testing of five concretes—an ordinary reference concrete and four concretes differing in the content of mixing water introduced into the concrete mix in the form of pre-saturated SAP particles (25%, two variants of 50% and 75% of the total mixing water in the form of SAP hydrogel). The research consisted of 4 stages of tests. The subsequent stages involved the analysis of the effect of using SAP as a carrier of mixing water on the particular characteristics of concrete mix and hardened concrete, i.e., consistency and density of concrete mix (1st stage), carbonation tested using two indicators—phenolphthalein and thymol phenolphthalein (2nd stage), and finally: the homogeneity of the concretes' structure by means of ultrasonic method (determination of ultrasonic pulse velocity) 28 days after production (3rd stage) and 3 years after production (4th stage). The ultrasonic pulse (or wave) velocity was then correlated with the content of water applied in the form of SAP hydrogel. The statistical analysis of results showed that the method of introducing the mixing water into the concrete mix in the form of pre-absorbed superabsorbent polymer, although it changed the concrete mix consistency, did not significantly affect the concrete ability to resist carbonation. Meanwhile, after 3 years, the densification of the microstructure of concrete with SAP has been observed. [ABSTRACT FROM AUTHOR]

The present paper highlight upon research work is that curing is one of most important aspect of construction. The life of concrete and its serviceability depends heavily on curing. The method of curing applied on concrete will affect its final strength and durability. Owing to this fact this paper contains the research done on concrete under various curing methods. The standard method of curing concrete is done by water and results wastage of a lot of water. With the increase in the deficiency of availability of water, curing becomes a problem. Hence this research aims at providing better methods of curing which will not only improve the strength and durability of concrete but will also save water. The various methods that have been researched upon are plastic covered curing, addition of sodium silicate to curing water, and addition of curing compounds to curing water. The tests are carried on concrete with desirable strengths of M15 and M20. In this research the fine aggregate used in making of M15 and M20 concrete consists of a mixture of sand and crusher dust. Two mixes of ratio 50:50 and 60:40, sand to crusher dust have been taken and the effects of curing on these mixes are considered. Plastic curing is done by covering the concrete with plastic soon after demolding. Hence minimum water is required. The curing done by sodium silicate is done by adding 2% by weight of sodium silicate to curing water. Concrete is submerged in water containing sodium silicate. Once the concrete is cured, this water mix can be reused to cure freshly cast concrete, thereby saving more water. Curing by curing compounds is done in a similar way as that of curing with sodium silicate, only that instead of sodium silicate, curing compounds are used. The effect of these three methods on concrete is studied and discussions are made. [ABSTRACT FROM AUTHOR]

One fascinating concept for enhancing the durability and lifespan of concrete buildings involves the use of self-healing concrete. This study focuses on the effect of crystalline admixtures and coatings on various properties of self-healing concrete and provides a comparison with traditional concrete. Four different concrete mixtures were prepared to assess their effectiveness in bridging crack openings, their flexural and compressive strengths, and water absorption. Various testing methods, including destructive, semi-destructive, and non-destructive tests, were used in this research. The capacity of the mixes to repair themselves was assessed on the destroyed and semi-destroyed test specimens using crack-healing and microstructure testing. Additionally, all mixtures were also subjected to the slump cone test and air content test in order to investigate the characteristics of the concrete in its fresh state. The findings demonstrate that crystalline coating and admixture combinations have significant potential for healing concrete. The compressive and bending strengths of self-healing concrete mixtures were shown to be slightly higher compared to traditional concrete when the additive dose was increased. Self-healing concrete mixtures also exhibited much lower water absorption, a tightly packed and improved microstructure, and signs of healed gaps, all of which indicate greater durability. [ABSTRACT FROM AUTHOR]

The article presents research results regarding the possibility of modifying pre-stressed concrete railway sleepers to improve their durability. The cracks that appear in these elements are one of the reasons for shortening the period of safe use. They do not have a significant impact on the load-bearing capacity of these elements, but on their durability. The resulting scratches become an easy way for the external environment to migrate inside the element, including the reinforcement area. Despite efforts to eliminate the possibility of cracking, this phenomenon still occurs in railway sleepers. In order to reduce the negative effects of cracking the cement matrix, a technology for modifying a prefabricated concrete element with resin-filled tubes towards its autonomous self-healing was developed and tested. The tests were divided into three stages, including laboratory tests carried out on cement mortar beams, semi-technical tests carried out on reinforced concrete beams, and industrial tests carried out on pre-stressed concrete and prefabricated railway sleepers. All research conducted on a laboratory and semi-technical scale, preceding the target stage, was intended to ultimately enable the development of tube application technology on an industrial scale while verifying the effectiveness of self-healing at the laboratory level. The use of self-healing cementitious materials potentially reduces the negative effects of cracking railway sleepers, as shown by observations conducted during the research. [ABSTRACT FROM AUTHOR]