Abstract

Terahertz (THz) and sub-terahertz (sub-THz) waves are unexplored waves between the infrared and microwave ranges. This range features unique characteristics of both light resolution and electromagnetic wave transmission. Sub-THz waves are part of attractive new diagnostic methods for inner objects because they are safer than normal non-destructive inspection methods involving high energy, such as X-rays. In this study, a novel non-contact and non-destructive inspection method for reinforced concrete (RC) structures using sub-THz reflection imaging is proposed to inspect the deterioration of inaccessible damaged RC structures. The results of this study confirmed that the proposed sub-THz imaging method can detect cracks and voids in concrete, as well as in metals inside or behind the concrete, based on differences in reflectance. In addition, the camera-based measurement system makes real-time on-site field measurements possible.

Introduction

In recent years, the deterioration of reinforced concrete (RC) structures has become an issue all over the world. Especially in Japan and other developed countries, large number of social infrastructures built during periods of rapid economic growth are aging significantly ( Alexander and Beushausen, 2019 ). The importance of appropriate maintenance management, including investigation and diagnosis, has been highlighted. In addition, from the perspective of a decarbonized society, it is desirable to avoid demolishing buildings and extend the service life of RC structures through necessary and affordable repairs. Thus, these considerations highlight a growing need for non-contact, non-destructive inspection methods to diagnose infrastructure deterioration without compromising performance. Furthermore, if remote inspection is possible, it is expected to improve measurement efficiency and expand the applicable areas. Therefore, a new inspection method that is not only non-destructive but also non-contact is required.

Several non-destructive and micro-destructive testing methods have been proposed for RC structures. For example, for internal defects that cannot be detected by visual inspection, some of the most widely used methods include percussion inspection ( Kazemi et al., 2019 ), ultrasonic flaw detection ( Lawson et al., 2011 ; Choi et al., 2016 ) and ground penetrating radar (GPR) ( Hugenschmidt and Mastrangelo, 2006 ; Chang et al., 2009 ; Laurens et al., 2005 ; Liu et al., 2020 ; Wiwatrojanagul et al., 2017 ). Table 1 shows a comparison between these methods. During percussion inspection, the concrete surface is knocked, which makes it possible to infer the state of internal deterioration based on the difference in the echo sound. In the case of ultrasonic waves, also a type of elastic wave, it is possible to measure the location of cracks and rebars inside concrete due to differences in acoustic impedance inside the material. Using GPR makes it possible to probe embedded rebars and voids inside concrete owing to its high penetration depth. However, these methods require contact with an object to be measured, which causes measurement problems at elevated or generally inaccessible places, thus highlighting the need for developing a method that can inspect the interior of concrete without contact.

Conclusion

In this study, we conducted measurements using a sub-THz camera to simulate embedded rebar and defects on the surface and inside concrete, assuming that a non-destructive inspection method using sub-THz waves will be applied to reinforced concrete structures. We then conducted actual measurements on real structures. The findings are as follows:

1) An aluminum tape placed on the back of the specimen to simulate the embedded rebar was detected up to 20 mm thickness of the specimen.

2) Field measurements at 10 GHz indicated the possibility of exploring rebars with a cover thickness of approximately 30 mm.

3) In the measurement of specimens with slits simulating cracks, detection was possible for slit widths greater than 1 mm.

4) Even when the slit was hidden by placing a 5-mm-thick mortar, detecting a slit up to 2.5 mm was possible.

5) The reflectance and transmittance varied sensitively with frequency. This fact indicates the potential for more detailed measurement with the selected appropriate frequencies. Further studies are needed to establish their relationship.

6) Camera-based measurement enables areal measurement and real-time monitoring.

7) Downsizing and weight reduction of the measurement system improved its transportability, confirming the possibility of measuring real structures.

Abstract

Composite slabs, consisting of a precast plank and a cast-in-situ concrete topping, are the most commonly used horizontal structural components in prefabricated buildings. In order to solve the problem that the precast plank of composite slab is easy to crack and a lot of vertical supports are needed in its construction, this study proposes a new type of composite slab with a joint. The precast plank of this novel composite slab is fully prefabricated in the midspan area, and concrete is poured on-site only at the surrounding joints. In this paper, the bending performance of three composite slabs with a joint in different shapes of concrete topping and one cast-in-situ slab was investigated. The test results showed that the novel composite slabs with a joint in T-shape and trapezoidal concrete topping had similar properties as the cast-in-situ slab, including bearing capacity and cracking load, which can meet practical requirement. The use of bent-up steel bars and roughening of the interface between the precast plank and topping concrete can ensure effective transmission of internal forces at joint. The bearing capacity of the composite slabs with a joint in T-shape and trapezoidal concrete topping was evaluated using the formula in GB50010–2010, and the experimental values were 1.06 and 1.1 times the theoretical values, respectively, which provides a foundation for the design of two types of composite slabs with a joint. Meanwhile, based on the FEA software ABAQUS, numerical simulation was conducted on the composite slab with a joint in T-shaped concrete topping. The numerical finding exhibit close agreement with experimental results in terms of load-midspan deflection curve and the crack distribution.

Introduction

Precast concrete (PC) structures can be seen in buildings throughout the world due to its advantage of better construction quality, lower labor costs, and shorter construction times [1]. Composite slab, as one of the most commonly used elements in floor systems of PC residential buildings, is formed by bottom precast planks and a cast-in-situ concrete topping. In order to improve the flexural stiffness of the bottom precast plank and increase the bonding performance between the precast plank and the cast-in-situ concrete topping, lattice girders are usually installed in the precast plank. However, due to the limitation of the thickness of the composite slab with lattice girders used in China, the height of the lattice girder is usually small [2]. As a result, the improvement in stiffness of the precast plank by the lattice girder is limited, which requires the erection of vertical supports during the construction process, increasing the construction cost and prolonging the construction period [3]. Therefore, it is very necessary to propose a composite slab that can achieve unsupported construction.

Some improvement measures have been proposed to reduce the use of vertical supports in the construction process of composite slabs. Wu et al. [4] set a detachable truss rib on the bottom of the precast plank to replace the vertical support, realizing the construction without vertical support and improving the crack resistance of the slab. The truss rib that was placed at the bottom of the precast plank can be reused, but it is inconvenient to remove it. Moreover, based on the concept of a steel-concrete composite structure, measures such as concrete ribs and steel ribs were set on top of the precast plank can effectively improve its bending performance [5], [6], [7]. In addition to the above measures, good results have also been achieved by using grout steel tube, special materials, or components. Hou et al. [8] proposed a new type of composite slab with grouted-round-steel tube truss and conducted bending tests on it. The test results indicate that this type of composite slab has good ductility and can meet construction requirements. Ou et al. [9] investigated the flexural performance of composite slabs made of crumb rubber concrete or conventional concrete. They discovered that the bearing capacity and end-slippage of composite slabs made of crumb rubber were equivalent or even better than those made of the conventional concrete. Erfan et al. [10] conducted numerical simulations on concrete beams strength with FRP materials and found that using CFPR sheets to reinforce concrete beams can effectively improve their bearing capacity and prevent crack propagation. Maedeh et al. [11] conducted bending tests on concrete beams with steel reinforcement and a hydrid usage of GFRP reinforcement with varying fiber ratios, respectively. They concluded that concrete beams using 1.5% polypropylene fibers and GFRP rebars can reach the same bending strength as concrete beams using steel bars. Wang et al. [12] proposed a novel bamboo-concrete composite beam with precast lightweight concrete slab. Shear test results indicated that this new type composite slab had a similar shear strength but a higher stiffness that the cast-in-situ bamboo-lightweight concrete composite slab. However, the composite slabs mentioned above have a large amount of concrete poured on site and a low assembly rate.

Conclusions

In this study, the flexural behaviors of composite slabs and three different forms of cast in-situ slabs with a joint were compared, and the specimen SS-1 was taken as an example to conduct finite element analysis. the conclusions are as follow:

The failure mode of cast-in-place slabs and composite slabs with a joint in shape of T-shaped and rectangular concrete topping is that the crack width reaches the standard limit, while the failure mode of trapezoidal composite slabs is that the midspan deflection reaches the limit. Overall, all four slabs are ductile failure.

The ultimate bearing capacity of composite slabs with a joint in the shape of T-shaped and trapezoidal concrete topping are equivalent to or even higher than that of cast-in-situ slabs, and 12.9% and 19.7% higher than that of composite slab with a joint in shape of rectangular concrete topping.

According to the calculation formula for the bearing capacity of cast-in-situ slabs provided by GB50010–2010, the measured bearing capacity of composite slabs was evaluated. The ratio of actual measured values to theoretical values of CS, SS-1, SS-2, and SS-3 was 1.09, 1.09, 1.16, and 0.97 respectively. The reasonable agreement indicating a good potential for the code in the design of the composite slabs with a joint in shape of T-shaped and trapezoidal concrete topping.

Abstract

Concrete’s weak tensile strength renders it susceptible to cracking under prolonged loads, leading to reduced load-bearing capacity and reinforcing bar corrosion. This study investigates the effectiveness of microbial-based self-healing in high-strength concrete, focusing on two bacterial strains: Sporosarcina koreensis and Bacillus. Results demonstrate significant enhancements in micro- and macro-physical properties of high-strength bacterial concrete with Bacillus flexus and S. koreensis, surpassing the control. Bacillus flexus-infused concrete exhibits a remarkable 21.8% increase in compressive strength at 7 days and 11.7% at 56 days. Similarly, S. koreensis-treated concrete shows 12.2% and 7.4% increases at 7 and 56 days, respectively. Enhanced crack healing occurs due to calcite precipitation, confirmed by X-ray diffraction and scanning electron microscopy. Both bacterial strains achieve crack closure within 42 days, with widths of 259.7 µm and 288.7 µm, respectively. Moreover, bacterial concrete from these strains excels in durability against water, acid, and salt exposure, surpassing control concrete. These findings emphasize microbial-based self-healing’s potential in high-strength concrete, providing a practical strategy to enhance structural resilience and extend concrete infrastructure lifespan.

Introduction

High-strength concrete (HSC) has gained widespread recognition for its enhanced mechanical properties, making it suitable for demanding structural applications (Krishnapriya et al., 2015). However, like conventional concrete, HSC is susceptible to cracking under various stress conditions, which can compromise its durability and load-bearing capacity (Iheanyichukwu et al., 2018). The resulting cracks not only diminish load-bearing capacity but also trigger environmental and economic issues, including carbon emissions during repair (Rosewitz et al., 2021). Additional weakness of concrete structure is the presence of voids and fissures in its body matrix. The circumstance of such voids in the matrix of concrete plays substantial role in determining its mechanical properties and durability (Feng et al., 2021; Khaliq & Ehsan, 2016).

The concept of self-healing concrete, facilitated by microbial activity, has emerged as a promising avenue to address these challenges, aiming to autonomously fill and repair such voids and cracks via bio-mineralization. In this process, bacteria induce the conversion of calcium particles within the cement composite into calcium carbonate, calcite. Precipitation and deposition of calcite due to microbial activity of bacteria seals such voids and fissures in the concrete body matrix. This in turn advances the mechanical properties and durability of concrete as well as healing rate of crack formed due variously initiated stress (Rohini & Padmapriya, 2021; Singh & Gupta, 2020). These bacteria must exhibit robust urease activity, withstand high pH levels, and endure mechanical stress within the concrete matrix (Rohini & Padmapriya, 2021; Rosewitz et al., 2021).

Conclusions

This study investigated the impact of microbes on high-strength concrete properties, utilizing B. flexus and S. koreensis. The research encompassed their effect on mechanical strengths (compressive, flexural), ultrasonic pulse velocity, acid and salt resistance, and microbial healing. Key findings are presented as follows:

High-strength bacterial concrete, employing B. flexus and S. koreensis, exhibited improved macro-physical properties compared to conventional concrete. B. flexus concrete showed 21.8% and 11.7% higher compressive strength at 7 and 56 days, while S. koreensis concrete exhibited 12.2% and 7.4% increases. Flexural strength for B. flexus concrete was 6.0% and 9.0% higher at 14 and 28 days, and for S. koreensis concrete, it increased by 5.2% and 6.4%.

Microbial-induced calcite deposition significantly enhanced the healing capacity of cracked bacterial concrete. Within 42 days, B. flexus and S. koreensis concrete restored cracked sections by 259.7 µm and 288.7 µm crack widths, respectively.

Bacterial concrete exhibited greater strength restoration following 55% stress-level crack initiation. While normal concrete regained only 64.0% of its 28-day compressive strength, B. flexus and S. koreensis concrete achieved 96.1% and 94.1% restoration, respectively.

Enhanced durability against acid and salt attacks was observed in bacterial concrete, with reduced weight and strength loss compared to conventional concrete. B. flexus and S. koreensis concrete experienced lower strength losses (4.8% and 5.3% for sulfuric acid, 1.8% and 2.1% for magnesium sulfate) than conventional concrete.

Abstract

This study aims to the practical detection of sub-meter scale voids located inside reinforced concrete structures with different diameters and depths using different frequency antennas of 800, 1000, 1200, and 1600 MHz. The experiment was performed on two concrete blocks with medium-sized voids between 70 and 100 mm diameter, and small-sized voids between 10 and 25 mm diameter. A GPR survey was conducted by dividing each block into two grids of profiles with 50- and 100-mm profile spacing. Then, GPR data was collected along both the horizontal and vertical directions of each block with multi-frequency antennas. The gathered data was processed in 2D and 3D to detect the exact location, dimension, and brightness of these voids. The results showed that GPR has the potential to be quite effective in automating the identification and location of embedded voids within concrete blocks. The accuracy with which the system was able to identify void locations depended mainly on the frequency of the antenna used and the diameter of the void, while the depth of penetration was inversely proportional to the frequency of the used antenna, with estimated depths ranging from 25 cm (using a 1600 MHz antenna) to 1.5 m (using 800 MHz antenna). Moreover, a GPR survey was conducted to evaluate two sites inside residential buildings before and after the rehabilitation process. The radar scan exhibited a notable proficiency in identifying the positions of rebar sites, whether they were situated at a single level or two levels, inside certain areas of construction. The study revealed the ability of GPR to identify the depth of the reinforcing steel within the cement material, particularly in areas where the soil has experienced subsidence.

Introduction

Ground-penetrating radar (GPR) is a well-established characterization and analysis tool in non-destructive test applications ( Brian et al., 2018 ). GPR is now a widely accepted field of scanning technology for surveying and imaging subsurface conditions (Annan, 1992, Tzanis, 2017 , Yang et al., 2020 ). GPR is an effective non-destructive testing method that is characterized by its rapidity, continuity, high detection accuracy, and ability to overcome the shortcomings of the core sampling and impact echo methods. The unique advantage of GPR causes concern for many scholars. Recently, GPR has been used in a wide range of civil engineering and geotechnical applications ( Li et al., 2003 , Rao et al., 2007 , Wu and Chang, 2007 , Rister and Graves, 2008 , Alhasanat et al., 2013 , Tian et al., 2018 ), and in reinforced concrete tests applications, due to its capabilities, benefits and fast performance in the non-destructive exploration of all defects that may be found inside the cement layers.

GPR can also be used to conduct a real-time concrete inspection survey using radar to locate rebar, pipes, tension bars, dowels, and plastic and fiber-optic conduits ( Bungey and Millard, 1993 , Muldoon et al., 2007 , Bala et al., 2015 ). There are few studies on concrete inspection surveys to detect voids/cavities within and under concrete slabs ( Watanabe et al., 2004 , Pollock et al., 2008 , Roger et al., 2011 , Abdul Razak et al., 2015 , Nobes, 2017 ). Radar surveys can be conducted on airport runways, tunnels, abutments, dams, pavements, and garages ( Millard et al., 2002 , Loizos and Plati, 2007 , Evans, 2009 , Lee, 2011 ). Asphalt roads and bridges can also be scanned ( Parry and Davis, 1983 , Maser and Scullion, 1992 , Hugenschmidt and Mastrangelo, 2006 , Loken, 2007 , Hoegh et al., 2015 ). The concrete slabs can be inspected for issues including relative thickness, deterioration, and structural problems ( Roddis et al., 1992 , Loizos and Plati, 2007 )

Results

These two blocks have been surveyed along the same lines to detect the internal voids by different GPR devices such as CX11 (with antenna of 1200 and 1600 MHz), Conquest (with antenna of 1000 MHz), Ramac (with an antenna of 800 MHz), and HandyScan with antenna of 1500 MHz) and the results are then compared.

4.1. Medium-scale void-size (70 mm and 100 mm)

For block No.1, using an 800 MHz antenna, the location of both voids could be detected at a depth of 280 mm for the first void and 200 mm for the second one ( Fig. 3 a). When a 1000 MHz antenna was used the accuracy level of the data increased in the second step for both 2D and 3D, due to the good coverage of the survey concerning the 28-grid lines with a spacing of 50 mm. The first void was represented more accurately in the second step ( Fig. 3 b & 3c) while the level of accuracy decreased significantly concerning 14-grid radar profiles for the same void ( Fig. 3 d & 3e). When a 1200 MHz antenna was used, the depth of penetration increased up to 500 mm ( Fig. 3 f). The degree of brightness decreased in the upper part of block No.1, however, due to the decrease in the frequency range compared to what is considered to be the optimum value in the case of deeper targets. When a 1600 MHz antenna was used, it was noticed that the buried voids could be detected to a depth of 450 mm ( Fig. 3 g). The accuracy level of data decreased with the increasing depth (e.g., see void No.2 which was represented with low accuracy at a depth of 280 mm, and compared with void No.1 at a depth of 200 mm).

Abstract

Durability property is a critical performance indicator of concrete in different environments and locations. However, durability also plays a key role in the sustainability and climate resiliency of concrete structures which is mostly ignored in the context of ways to improve the sustainability of concrete materials and structures. Hence, this paper aims to bring focus to this area by presenting an overview of the critical role of concrete properties especially durability on the sustainability and climate resiliency of concrete structures. This paper first presents a general overview of concrete materials followed by the connection of concrete to sustainability and climate resiliency. Discussions from this paper indicate that to improve concrete sustainability, there is a need to use materials with lower environmental impacts upfront in addition to producing concrete with improved durability to ensure long-term performance. In other words, merely reducing the upfront embodied carbon of materials is not sufficient to achieve sustainable concrete if the impact of such alternative low-carbon materials used to replace the traditional materials in concrete is not considered. On the other hand, the climate resiliency of concrete structures is mostly dependent on improved durability which would sustain their adaptation over time to the impacts of the changing climate conditions. Overall, to achieve sustainability and climate resilience of concrete structures; lower environmental impact, higher durability performance and resilience to applicable climatic conditions must be achieved.

Introduction

Concrete being the most used construction material in the world can be associated with its outstanding performance coupled with its lower cost and availability of raw materials locally in various parts of the world. Concrete has been used extensively to build various infrastructures ranging from transportation systems, health, residential and commercial buildings, water systems, etc. However, the high production and use of concrete have been found to yield negative environmental impacts on the environment due to its contribution to greenhouse gas (GHG) emissions and consumption of natural resources [1] , [2] .

In contrast to other construction materials, such as steel and glass; concrete has a lower unit embodied carbon as depicted in Fig. 1 which shows the carbon emissions per kilogram of each material. However, the production and use of concrete in large quantities have resulted in the concrete industry being a major contributor to the world’s human-induced GHG emissions. A critical part of concrete responsible for the high GHG emission is the production of portland cement (PC) which is the primary binder in concrete and other cementitious materials. Out of all cementitious materials (i.e. concrete, mortar, grout, etc.), concrete consumes PC the most with an estimated amount of 70% while the other 30% is used for other cementitious materials such as mortar, grout, etc.

Conclusion

This paper presents an overview of various properties, specifically the durability of concrete and how it influences concrete sustainability and climate resiliency. Discussions in this paper show that the durability of concrete is very critical to both concrete sustainability and climate resiliency and a holistic approach needs to be employed. Improving the durability of concrete would result in the reduction or elimination of raw material and energy use for rehabilitation and reconstruction resulting in lower environmental impact thereby enhancing sustainability. Similarly, enhanced durability of concrete would ensure that concrete structures can adapt to the changing climate changes thereby improving its climate resiliency.

Thus, to improve the sustainability and climate resiliency of concrete infrastructures; core attention must be placed on the embodied carbon of the materials and the durability performance rather than the former only. Finally, initiatives to improve concrete sustainability and climate resiliency should be specific geographical zone-based rather than a global approach as the availability of raw materials and climate conditions varies with location.

Abstract

     Concrete is one of the most widely used materials in various civil engineering applications. Its global production rate is increasing to meet demand. Mechanical properties of concrete are among important parameters in designing and evaluating its performance. Over the past few decades, machine learning has been used to model real-world problems. Machine learning, as a branch of artificial intelligence, is gaining popularity in many scientific fields such as robotics, statistics, bioinformatics, computer science, and construction materials. Machine learning has many advantages over statistical and experimental models, such as optimal accuracy, high-performance speed, responsiveness in complex environments, and economic cost-effectiveness. Recently, more researchers are looking into deep learning, which is a group of machine learning algorithms, as a powerful method in matters of diagnosis and classification. Hence, this paper provides a review of successful ML and DL model applications to predict concrete mechanical properties. Several modeling algorithms were reviewed highlighting their applications, performance, current knowledge gaps, and suggestions for future research. This paper will assist construction material engineers and researchers in selecting suitable and accurate techniques that fit their applications.

Introduction

     Concrete is the most widely used building material worldwide. With population growth and urbanization, the demand for concrete is expected to reach 18 billion by 2050 [[1], [2], [3]]. In order to improve the design of concrete structures, it is necessary to gain a better understanding of concrete performance, relying on accurate evaluation of its mechanical properties. Among the various properties of concrete, compressive strength has been considered a direct indicator of performance. It is directly related to the safety and performance of the structure throughout its life cycle [1,4,5].

     Concrete is a complex system of combinations of different components (coarse and fine aggregates, water, cement, and additional mixtures) that are randomly distributed throughout the concrete matrix [[6], [7], [8], [9]]. This heterogeneous feature makes it difficult to accurately predict certain mechanical properties, especially compressive strength [[10], [11], [12]]. The most direct way to evaluate the compressive strength of concrete is through physical tests performed on specimens cured to the desired age [13,14]. Such a method for evaluating the compressive strength needs time while being affected by other factors related to specimen fabrications and test operators. Moreover, the test tends to damage the specimens. Empirical regression methods were therefore proposed to predict compressive strength [[15], [16], [17]], but the disadvantage of this method is the non-linear relationship between the concrete mixture and the concrete’s compressive strength. This prevents an accurate regression expression. Numerical simulation is another method that can predict the behavior of concrete. However, a good prediction of concrete behavior is not easy to achieve due to the non-linearity and randomness [[18], [19], [20]].

Conclusions and recommendations

     The present study investigated the performance of different ML/DL models to predict the mechanical properties of concrete. Among the wide range of ML/DL models, support vector machines, decision trees, evolutionary algorithms, and artificial neural networks were examined due to the popularity of these models as well as their frequent use in the field of civil engineering. Therefore, the performance of these models in various studies to evaluate the compressive strength, tensile strength, shear strength, flexural strength, and elastic modulus was evaluated. A comparison of experimental models with ML/DL methods shows that ML/DL models with better updating capability and the ability to analyze large datasets perform better. On the other hand, statistical models are not good for predicting complex structures due to their high cost and time-consuming nature. According to ML/DL methods, selecting the appropriate model for predicting the target strength of concrete should be made by considering different criteria. A review of various studies shows that the relationship between concrete components and mechanical strength is influential in choosing the forecasting model. Therefore, models that can respond in nonlinear space should be used if the relationship is nonlinear. In these cases, SVM and ANN models can be used for their acceptable performance in a non-linear environment with fewer errors. To achieve more accurate results, optimization of these models with metaheuristic algorithms can also be used. But if we need the transparency of the model and the explicit mathematical formula between input and output, we can use decision tree models and evolutionary algorithms. On the other hand, the use of ensemble models to optimize these models, although it results in higher accuracy, increases computation time and model complexity. The combined SVM and ANN models, although they increase the computation time, have accurate results in the face of extensive data. Therefore, based on the study, the best option for predicting the strength of concrete in terms of model accuracy and model implementation is the combined use of SVM and ANN combined models.

Abstract

     This paper presents a rapid machine learning-based damage detection framework for identifying the damage extent of concrete shear wall buildings. For this purpose, a parametric study was carried out to determine the most efficient machine learning algorithm in classifying the damage states of the building. According to this parametric study, the K-Nearest Neighbor (KNN) learner was selected as the reference prediction model because of the higher accuracy achieved by this algorithm. Bayesian Optimization (BO) algorithm was used to tune the hyperparameters affecting the accuracy of the model. The most efficient attributes were selected from the set of damage indicators through the BO algorithm to train the model. Three different benchmark buildings, including 7-,9-, and 13-story concrete shear wall buildings, were used to evaluate the robustness of the proposed framework. A suite of 111 pair motions, originally developed for the SAC project, were employed to create a generalized dataset. These motions were uniformly scaled from 0.05 g to 1.5 g to expand the intensity range of the events. All the acceleration signals were polluted to 10% noise using white Gaussian signals to simulate the field condition. Results reveal the efficiency of the proposed framework in identifying the extent of damage in concrete shear wall elements of the building. In addition, a parametric study was conducted to illustrate the reliability of two commonly used features, called Cumulative Absolute Velocity (CAV) and the energy ratio between the acceleration response and the input excitation, in determining the damage states of the shear walls under seismic motions.

Introduction

     Assessment of structural safety is essential for post-earthquake restoration. Generally, to evaluate the post-earthquake vitality of the exposed structures, a complete visual inspection is required [1]. Coordination and implementation of the manual visual inspection needs several dedicated teams and monetary resources. In this regard, considerable efforts have been carried out to automate the visual inspection process, e.g., image-based visual inspection [2]. However, such an engineering visual inspection is only able to detect the visible defects that occurred in the structures [3]. This means that some serious invisible damages may be left latent during the visual inspection. The process of identifying and tracking the structural damage is known as the Structural Health Monitoring (SHM) [4,5]. In SHM, damage detection is related to the methods developed for identifying the probable existence, severity, and location of the structural damage. Model-based and data-driven methods are two of the most commonly used strategies proposed for damage detection. Model-based methods generally involve a system identification algorithm paired with a finite element analysis to update the structural model [6]. The performance of the model-based approaches directly depends on the accuracy of the information about the physical properties of the under-study structure. In addition, updating the finite element model based on the physical properties of the structure is computationally expensive for large-scale structures, and rapid condition monitoring could be challenging in this condition [7,8]. On the other hand, data-driven methods apply statistical learning algorithms to the vibration data captured from the structure. This method uses learning algorithms to construct a classification or regression learner for predicting structural damage [9, 10]. Tsou and Shen [11] proposed the use of Neural Networks (NNs) for predicting the severity and location of the structural damage. They used the variations in the modal properties of the structure as the damage feature to identify the damage. Worden et al.

Conclusion

     This paper presented a rapid algorithm for identifying the severity of local damage in the concrete shear wall buildings. A total number of 1884 nonlinear response history analyses were conducted for each building using the SAC motions. A suite of damage indicators was extracted from the acceleration signals to construct the prediction models. A parametric study was carried out to determine the most efficient learner for classifying the damage states of the buildings. The KNN classifier was selected to construct the predictive models because of its maximum accuracy compared to the other algorithms. The Bayesian optimization algorithm implemented to tune the hyperparameters of the classification learners. The main conclusions derived from the study are as below:

Abstract

The Alcántara Bridge is one of the most important Roman bridges in the world and has been a Spanish National Monument since 1924. Since its construction, almost two thousand years ago, it has suffered numerous damages due to the passage of time and human action, which has led to different interventions. The most important was that carried out by Millán (1856–1860), for the reconstruction of the arch demolished in 1810. During a visit to the bridge, areas with reinforced concrete were observed. Given the areas where it appears, the geometry of the reinforcement and its configuration, is possible to think that it is a very old intervention, which could date from the same period as that carried out by Millán. If so, it would be the first application of reinforced concrete in Spain and one of the first in the world. The aim of this study is to date the intervention and validate the initial hypothesis. To this end, based on a 3D survey of the rehabilitated areas using a drone, a comparative analysis has been carried out with the plans of Millán’s project, as well as sheets and photographs from different periods to establish the date of the interventions. Research was also carried out in the archives of the Real Academia de Bellas Artes de San Fernando to gather information on the interventions on the bridge throughout the 19th century. Finally, the geometry and layout of the reinforcement is analysed in relation to the knowledge of reinforced concrete from its first patents worldwide to its widespread application in Spain. These analyses allow us to conclude that the date of the reinforced concrete repairs on the bridge is undoubtedly 1857, which would be the first application in Spain and the first in Europe on bridges.

Introduction

Reinforced concrete is the most widely used material in the construction of bridges and buildings during the last 150 years. This new material emerged as the result of the combination of concrete and steel bars strategically placed inside the section of the structural element, which allows it to acquire the advantages of both compressive and tensile strength respectively [1].

On the other hand, concrete is the result of combining a binder, fine aggregate and coarse aggregate. The most common binders used in the manufacture of concrete have been aerated lime and hydraulic lime, giving rise to common and hydraulic concretes, respectively [2].

The first scientific studies of hydraulic binders were carried out by Smeathon for the construction of Eddystone’s Third Lighthouse (1756–1759) in search of a material that would harden under water [3]. But it was Vicat, at the beginning of the 19th century, who deepened his knowledge of the hydraulicity of limes, laying the foundations of hydraulic cement [4], the basis of concrete, and therefore of reinforced concrete.

Throughout the first half of the 19th century, natural cement was developed in Europe, which began to be manufactured in Spain in 1835 [4]. Artificial cement, also known as Portland cement, began to be manufactured in France and Great Britain in the second quarter of the 19th century, but its manufacture in Spain did not begin until 1898, more than half a century late [5].

Conclusions

The Alcántara Bridge is one of the most important Roman bridges in the world due to its size and state of conservation. Since its construction almost two thousand years ago, it has suffered damage because of the passage of time and human action, and therefore, it has required restoration work. During an inspection of the bridge, areas with reinforced concrete were observed, which, due of its typology, suggested that it was a very old intervention. In order to date this intervention, a comparative analysis was carried out between the current situation, the survey plans that Millán made for the repair of the collapsed arch, the sheets from different periods and photographs from different dates. In addition, research has been carried out in the archives of the Real Academia de Bellas Artes de San Fernando on other possible restoration works on the bridge in the 19th century.

Following this research, it can be concluded that the areas of the bridge with reinforced concrete were built during the restoration work carried out by the engineer Millán (1856–1860). Specifically, the application of reinforced concrete was carried out during the year 1857.

Abstract

Strategic reuse of demounted concrete elements in new buildings may be one of the solutions that will support the transition to circular construction. To ensure wider application of concrete reuse, RISE developed a methodology for the assessment of the structural condition of existing buildings, and the selection of elements suitable for reuse, including guidelines for their disassembly, storage, and installation. However, one of the main obstacles for wide application of concrete reuse is the uncertainty concerning the remaining service-life of concrete elements and evaluation of quality over the future service-life in a new building. This paper describes a methodology for material and structural assessments which combine non-destructive, on-site testing with traditional laboratory tests of samples extracted from the structures. The results are intended to support the decision-making process on reuse and give a technical basis for the design of new buildings. Great consideration is put on various deterioration mechanisms for concrete and steel corrosion affecting structural condition of housing and office buildings. To assess the impact of degradation processes, theoretical models are considered, while the remaining service life is estimated by means of a simplified approach that provides the basis for evaluation of likelihood and severity of consequences entailed by material degradation on the structural performance. The proposed approach was validated on the results from three pilot projects, where real buildings in Stockholm and Uppsala, Sweden, were reused or prepared for reuse to different extent. The analysed buildings had different functions (housing, office, parking) and structures (prefabricated elements and in-situ casted concrete), being representative for Swedish building stock. One of the buildings has been already dissembled and the prefabricated, where prestressed hollow-core slabs have been successfully reused for a new office building construction. Based on these experiences, a simple classification system for quality of concrete elements for reuse was proposed with three main parameters, namely calculation of remaining service-life, extent of cracking and the target exposure class. The proposed system is not complete and must be further validated for various types of elements and structures by wider group of market actors.

Introduction

When a structural element is dismantled from a building, it loses its legal status as a building part and becomes waste. The social and economic perception of waste has evolved in the last decades and its potential as a resource for reuse, recycling, or energy production (depending on its material properties, ease to reuse or recycle, financial, and environmental value) has gained considerable attention. Reuse is the second step in the waste pyramid after prolongation of the service-life due to preservation of the embodied value and, as such, it has minimal impact on the environment. To accelerate the transition from linear to circular economy, it is mandatory to ensure the quality of the concrete elements for reuse in terms of mechanical performance, as well as fire-safety, acoustic or thermal properties, and longevity required by building standards. The most logical approach to achieve that is to apply existing standards and regulations for new structures. Mechanical properties or other functional requirements can be assessed with the same experimental methods used for new materials or structures. However, this approach is not applicable for durability, which is normally ensured by design than evaluated by testing on building and element levels. Moreover, most of current regulations and standards are formally restricted to production of new materials and elements, and do not apply to the assessment of existing ones. Therefore, current building norms and standards have to be updated to meet the challenges posed by circular economy.

Conclusions and future work

Durability and assessment of remaining service-life are main technical hinders in reuse of structural concrete elements due to the standards defining it by design approaches rather than performance-based regulations. The updates of Eurocode 2 may bring new opportunities in these terms.

The performed literature review of degradation models for concrete and steel corrosion indicated that cracking and relative humidity have major influence for the degradation and consequences for service-life and should be handled with special attention.

Prefabricated concrete elements from the 70′ and 80′ in Sweden have usually higher quality and resistance against carbonation than in-situ casted elements, thus being more attractive candidates for reuse in new buildings. Additionally, prestressed elements tend to be uncracked, which increases their durability and makes disassembly much easier.

Abstract

     As a key component in composite beams, the studs are prone to fatigue failure under reciprocating load. Fatigue problem is more prominent especially under circumstances of concrete cracking, stud corrosion or with initial damage. Therefore, static and fatigue tests are carried out to study the fatigue properties of push-out specimens with initial defects, including stud damage and concrete cracking. The test results show that the damage of stud has a great influence on fatigue life, while the crack of concrete has a little influence on fatigue life. The damage of stud has a greater influence on fatigue performances compared to static properties. In addition, based on the dissipative energy theory and experimental phenomenon, the roles of stud and concrete in the process of stud fatigue failure and their interaction are summarized. The dissipative energy mainly includes the shear plastic strain energy of the stud, the plastic strain energy of concrete under compression after the stud, and the heat energy generated by the friction between the stud and concrete.

Introduction

     Steel-concrete composite beams have become popular in recent years for use in bridge engineering [1,2]. Under the complicated environment and load, there may be some damage to the composite beam. There might be some damage, such as corrosion, fractures of weld leg and longitudinal or transverse cracks in the concrete deck. The static and fatigue behavior of stud connection is sophisticated and affects the design resistance and stiffness of composite beams [3,4]. The damage of the stud and concrete may have a great influence on the shear fatigue performance of the interface.

      Welding defects significantly lower the shear capacity of studs, as is widely known. There are many types of welding defects that might appear, such as inadequate penetration, absence of fusion, and gas inclusion [5]. To determine how the damage location and degree affected the static behavior and shear capacity of stud shear connections, six specimens with identical geometrical dimensions were investigated by Qi et al [6]. The test findings showed that, in comparison to the shear capacity of normal specimen, a loss of up to 36.6 % and 62.9 % of the shank area might cause a falling shear capacity of 7.9 % and 57.2 %, respectively. The push-out test was simulated using mathematics, and the results of the test were used to validate the study. It was shown that even though the area of the stud had significantly decreased, the shear capacity was not affected by the severity of the damage when the damaged part was placed 0.5d (where d is the shank diameter) from the stud root, based on the numerical model.

Conclusions

     Static and fatigue tests were carried out on studs in steel–concrete composite study the effects of initial damage in stud and concrete on fatigue performance. The following conclusions are drawn:

     1.  Compared with nondestructive specimens, the fatigue life of transverse crack and longitudinal crack specimens were reduced by 22 % and 4.9 %, respectively, which is determined by the stress characteristics of the stud. Transverse crack makes the stud easily in a state of bending and shear composite, while longitudinal crack does not

     2.  Compared with the preset cracks of concrete, the damage of stud and weld collar had more influence on fatigue performance, in which the loss of stud section of 62.9 % leaded to only about 10 % of fatigue life. The initial damage of stud accelerates the damage accumulation in the stable fatigue development stage, while the concrete cracking leads to the increase of residual slip in the early stage.

     3. The existing calculation methods of residual slip are not completely applicable to the test results of different stresses, and most of the calculation results are too small, which requires some modification of their coefficients.

Highlights

Abstract

Keywords

1. Introduction

2. Research significance and objectives

3. Experimental program

3.1. Concrete specimens

3.2. Test setup and instrumentation

3.3. Concrete properties and test parameters

4. Results and discussion

4.1. Concrete deformations: Strains and deflections

4.2. Recovery strains

4.3. Deflection recovery

4.4. Analysis of uncracked and cracked concrete beams

5. Conclusions

CRediT authorship contribution statement

Declaration of Competing Interest

Acknowledgments

References

Abstract

The purpose of this research is to analyse the long-term deformations of reinforced concrete beams made of recycled coarse aggregates (RCA), using four different replacement ratios, 0%, 20%, 50% and 100%. For said purpose, three different loading stages were carried out: firstly, loading and sustained load for 1300 days, secondly, unloading and recovery where the deformations were registered over a one year period, and lastly, testing the concrete beams up to failure in order to analyse the effect of recycled aggregates on pre-cracked concrete members. The results led to the analysis of deformations under sustained load, as well as those produced after removing the load and the performance of pre-cracked members, while identifying the effect of recycled coarse aggregates on concrete performance in terms of plastic deformation, recoverability and concrete stiffness, and also on structural design.

1. Introduction

In recent years, the use of construction and demolition waste as aggregates for structural concrete has been widely studied. Numerous authors have contributed to the increasing knowledge in this field, analysing the structural performance of recycled concrete and its properties, such as mechanical strength, modulus of elasticity, creep and shrinkage or durability [1], [2], [3]. As a result, several expressions and methods have been assessed for the design of structural concrete using recycled aggregates [4], [5], [6], [7], [8], [9], [10], [11], [12]. Most authors deal with the short and long-term behaviour of concrete while considering only the influence of creep and shrinkage [13], [14], [15] and very few include the ageing effect of concrete, its different cracking behaviour or its ability to recover from deformations after a load is varied or removed [16].

As common concrete structures are usually submitted to load variations during their service life, it is important to consider the effect of creep over time, including not only loading periods but also unloading the stages and the recoverability of concrete. As mentioned by Rossi et al. [17] understanding the behaviour of concrete structures is greatly simplified by the numerical modelling of their mechanical behaviour. However, progress needs to be made to predict the long-term behaviour of concrete with sufficient accuracy. In order to determine the deformational mechanism, it is also important to analyse the effect of cracking and residual strain i.e. the irreversible part of strain. Many factors influence deformation and the ability of concrete to recover after unloading. Once the hysteretic recovery has finished, the residual deformation can be defined as plastic deformation. Additionally, it can be assumed that concrete deformations under loading are mainly due to creep, especially for long periods of loading and therefore, the ability of deformations to recover after unloading is closely linked to creep recovery.

Abstract

     Bioenergy with carbon capture and storage (BECCS) is a carbon dioxide removal (CDR) solution necessary to achieve net-zero-carbon-emissions goals. While the BECCS potential from large industrial emitters has been quantified, the BECCS potential of small emitters, such as biogas facilities, has not been investigated. Moreover, most BECCS solutions rely on the expected availability of large geological storage capacity for future CDR implementation, although the deployment of CO2 transport and storage supply chains is still a barrier for geological carbon storage ambitions. An alternative opportunity for permanent sequestration of CO2 is concrete, in which captured CO2 can be permanently fixed through carbon dioxide mineralization technologies. We describe and discuss this solution by quantifying the potential of a European bioenergy with carbon capture, utilization, and storage (BECCUS) supply chain, which relies on biogenic CO2 from biogas facilities as a CO2 source, and on carbon dioxide mineralization in concrete as a permanent CO2 sink. This solution is available today, can be adopted seamlessly, and does not need economies of scale for its deployment. We find that European biogas facilities produce 24 Mtons of biogenic CO2 per year, of which 4 Mtons of CO2 per year are emitted from facilities already upgrading biogas into bio-methane.

Introduction

     Reaching net-zero greenhouse gas (GHG) emissions by 2050 requires a rapid decarbonization of European economies (European Commission, 2018), as well as the deployment of carbon dioxide removal (CDR) solutions to offset unavoidable emissions (European Commission, 2021). About 10% (500 Mton CO2eq per year) of current European GHG emissions are estimated to be hard-to-decarbonize and will likely need some degree of CDR (European Commission, 2021). Many net-zero-GHG emissions (hereafter simply net-zero) scenarios rely on CDR using bioenergy with carbon capture and storage (BECCS) (Scott and Geden, 2018; Rogelj et al., 2019). BECCS consists in deploying biomass to produce bioenergy, capturing, and transporting the resulting CO2, and permanently storing it in underground geological formations (Bui et al., 2018; Fuss et al., 2018). Because sustainable biomass is a limited resource (Rosa et al., 2021b), there is a growing consensus that the societal value of using biomass for CDR (i.e., BECCS) will exceed the value of using biomass for bio-energy production only (Sandalow et al., 2021a; Fajardy et al., 2021).

Conclusions

     A portfolio of solutions will be required to mitigate climate change. We introduce biogas-concrete BECCUS supply chains that permanently store biogenic CO2 in recycled concrete aggregates through carbon dioxide mineralization technologies. Biogas-concrete BECCUS supply chains combine carbon utilization with permanent sequestration and have the potential to permanently remove CO2 from the atmosphere while generating a marketable product, namely concrete, thus implementing a circular economy model. BECCUS supply chains represent a CDR solution available for small enterprises, such as biogas facilities, to mitigate their carbon emissions without the need of economies of scale and complex supply chains to transport and store CO2. We find that biogas-concrete BECCUS supply chains can permanently store 8 Mtons of CO2 per year in recycled concrete aggregates in Europe. On the one hand, this is a relatively small fraction of the CO2 that will likely need to be removed in Europe to reach net-zero GHG emissions (500 Mtons of CO2eq per year); in other words, the limited CO2 storage potential in recycled concrete aggregates is the bottleneck of BECCUS supply chains. On the other hand, short CO2 source-sink transportation distances represent a promising and efficient CDR opportunity for small emitters. This suggests that BECCUS supply chains should be deployed whenever possible and will have to be complemented with geological CO2 storage (or BECCS) to achieve European ambitious climate targets.

Abstract

     This paper studies the fresh and mechanical properties of high-strength concrete (HSC) by incorporating recycled concrete aggregates (RCA) of varying sizes and concentrations. The recycled aggregate concrete (RAC) was prepared by partially replacing RCA with natural coarse aggregate (NCA) at 0%, 15%, 30%, and 45%, with aggregate sizes ranging from 5 to 12 and 12–20-mm. Fresh concrete properties, such as slump, Kelly ball, compacting factor, K-slump, and fresh density, were tested to determine the influence of RCA size and concentration. In addition, the mechanical properties were studied through the execution of compressive, split-tensile, and stress-strain tests. The test results revealed that increasing the RCA concentration declines the fresh and hardened properties of HSC. In the fresh concrete experimentation, the 12–20 mm aggregate size RAC mixes exhibited greater workability than the 5–12 mm aggregate mixes. On the contrary, 5–12 mm aggregate mixes RAC had higher compressive and split-tensile strength and a higher modulus of elasticity than 12–20 mm aggregate mixes concrete. When it comes to sustainability, the study found that the smaller size range of RAC produces inferior embodied CO2 (eCO2) and provides a cost-effective and sustainable solution for the construction industry.

Introduction

     Over the last decades, the construction community has faced several challenges, including a scarcity of natural resources and excessive energy consumption that directly impacts environmental pollution. These challenges include using natural resources and energy, the generation of greenhouse gases (CO2), and the growth of building and demolition waste (Datta et al., 2022, Vo et al., 2021). Recycling the demolition waste is the most promising option for reducing the building industry’s adverse environmental effects in the construction sector. This attention is increasingly growing since it was projected that the world has to reckon with the problems of disposing of 3 billion tons of demolished concrete waste annually until 2012 (Akhtar et al., 2018). In recent years, Zhang et al. (2020) reported that the global accumulative carbonation of concrete waste might produce roughly 3.0 Bt CO2 between 2018 and 2035. As a result, using recycled concrete aggregate (RCA) made from waste concrete in engineering construction can help protect the environment while increasing the residual value of waste concrete. In addition, these RCAs have gained widespread acceptance from the construction research community as alternative building structure materials in recent decades.

Conclusions

     In this paper, the size and concentration effect of RCA on the production of HSC has been studied. Eight concrete mixes with different RCA concentration levels with an interval of 15% were considered. The obtained experimental results of the rheological and mechanical properties are concluded as follows:

• All the mixes had a satisfactory slump result greater than 150 mm, which led to the high workability of concrete. Concrete mixtures of the 12–20 mm aggregate size range have a larger slump, compacting factor, ball penetration, and K-slump value than the 5–12 mm size range concrete. In addition, the high density and workability of mixes decrease with an increasing concentration of RCA replacement level.

• The decrease in the split-tensile strength of RAC with the increase of the RCA concentration is relatively smaller than compressive strength and MOE. The 5–12 mm coarse aggregate size enhances the strength and MOE of the mixes compared to the 12–20 mm aggregate size. In terms of sustainability assessment, the cost and eCO2 emission decrease with RCA incorporation, leading to a low-cost and environment-friendly concrete production with better strength.