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

The strain hardening fiber reinforced concrete—generally known as the Engineered Cementitious Composite (ECC)—has rapidly gained the attention of researchers in recent years. However, most of the research on ECC is limited to material and member level, leaving a gap in the understanding of its behavior at the structural scale. Therefore, this study investigates the global seismic response of ECC structures and compares their performance with conventional reinforced concrete (RC) structures. For this purpose, a case study long span building structure (an aircraft hangar having a span length of 40 m) is selected. Under the design-level gravity and lateral loads, its members are separately designed using the conventional RC and ECC. It is observed that for ECC members, the requirement of longitudinal steel is reduced by 30% when compared with the conventional RC members. Similarly, owing to an improved tensile behavior, the ECC members also exhibited a higher shear capacity than RC members, resulting in a significant reduction in the requirement of transverse reinforcement. The detailed inelastic finite element models for both design cases (RC and ECC) were subjected to the pushover analysis and nonlinear response history analysis (NLRHA) to assess their seismic performance. It is observed that (in terms of local and global seismic demands, structural damage, and ductile behavior) the performance of the ECC structure is significantly improved when compared to the conventional RC structure. The comparative cost analysis showed a reduction of 11.9% in the overall material cost of the ECC structure as compared to RC. These results show that ECC can be effectively used at the full structural level as an economic solution to ensure the ductile response and superior seismic performance.

Introduction

The structural design of long-span concrete structures is extremely challenging for designers. This is mostly owing to high moment demands, which cause undesired high tensile stresses [1] and most of the construction materials except steel are weak in tension. Despite the complexity involved in their design, they are very popular commercially. Their popularity derives from their necessity in numerous special applications such as industrial sheds, aircraft hangars, halls, auditoriums, etc. Additionally, long-span structures may assist in cutting off the cost of intermediate supports, resulting in a more economical design. In the early 10th century, these high demands were resisted by the use of arches and domes, which reduced the flexural stresses and produced axial compressive stresses [2]. Later in the 1940 s, reinforced concrete (RC) was proposed for medium to long-span structures incorporating an excessive amount of steel reinforcement [3]. Furthermore, the advancements in construction materials helped structural engineers to design cost effective infrastructures. In this way, pre-stressed concrete was introduced for long-span structures, eliminating high reinforcement and cross-sectional requirements. However, prestressed concrete possesses a shortcoming related to its ductility [4], [5]. This limitation becomes a critical concern when the structure lies in a seismically active region, as seismic design codes recommend the structure and its elements to be ductile in high seismic zones [6]. Therefore, RC with an excessive amount of steel reinforcement becomes a compulsion in seismic regions to ensure adequate confinement for ductility [4], [5]. However, RC makes the design uneconomical due to high reinforcement requirements. So, there is a need for an innovative material that can provide ductility without any compromise on cost, to ensure resilient and cost effective infrastructures.

Several innovative solutions have been proposed to improve the seismic performance of structures by providing ductile elements and links [7], [8]. One of these is to introduce fibers in the cementitious matrix to make the composite ductile. These composites are termed as fiber reinforced concrete (FRC) [9], [10], [11], [12]. A special class of high performance FRC that exhibits strain-hardening behavior in uniaxial tension is classified as Engineered Cementitious Composite (ECC) [13], [14], [15] [16], [17], [18]. ECC can be a potential candidate to reduce cross sections and reinforcement requirements due to its enhanced tensile capacity as compared to conventional concrete[19]. Additionally, ECC is lightweight and highly ductile which may also help to improve the seismic performance of the structure [20], [21], [22], [23], [24], [25], [26]. However, its material processing and design is not as simple as that of conventional concrete [27], as it requires a micro-mechanical model to obtain a mix that will ensure strain hardening response. To study its structural behavior, its material properties are incorporated by the integrated structures and materials design (ISMD) approach proposed by Li [28]. ISMD specifies that material design should be carried out first to obtain the necessary constitutive model for structural analysis and design.

Conclusions and recommendations

This research was able to conduct a comprehensive seismic assessment of the long-span ECC structure. For the very first time, both linear and nonlinear FEA models of ECC on the structural scale were developed considering a material level constitutive model. A complete structural design and nonlinear analyses of ECC structures and their comparison with RC structures were performed, and the following conclusions were made:

• Due to the lower unit weight of ECC, the design actions for structural members were approximately reduced by 25% because of the reduction in dead and seismic loads.

• Due to the better tensile capacity of ECC, the cross sectional sizes of the structural members were reduced by 25%, making ECC a good alternative to RC in the case of long-span structures. This observation indicates the potential of ECC for long-span structural applications.

• The structural design performed using JSCE guidelines showed an over 30% reduction of longitudinal steel in flexural members and about 15% reduction in longitudinal steel in compression members. Alongside, theoretically, the shear reinforcement requirement throughout the structure was eliminated, due to additional shear capacity provided by the fibers.

• The nonlinear analyses clearly showed better seismic performance (in terms of local and global seismic demands, structural damage, and ductile behavior) of ECC due to its increased capacity and lower inertial forces being developed within the structure.

Abstract

It is imperative for residents to have access to safe facilities after an earthquake. This ensures the safety and well-being of individuals while minimizing the risks posed by aftershocks. This research has used multi-criteria decision-making (MCDM) and network-based analysis to select and allocate emergency shelters (ESs). Several ESs are initially chosen as potential candidates. A weighting process is then used to evaluate various criteria, including proximity to the fault, fire stations, hospitals, main roads, the area of the ESs, and the population’s vulnerability. The centers are evaluated and ranked using the CRiteria Importance Through Intercriteria Correlation (CRITIC) and Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS) methods. The Maximized Weighted Capacitated Coverage with a Radius (MWCCR) problem is used to address location and allocation issues for varying ESs using option rankings. The findings showed that increasing the number of centers does not always lead to a higher level of service delivery, assuming a consistent service delivery radius. The distribution of the centers is more crucial. Additionally, line density analysis is used to evaluate traffic conditions in the study area, assisting in finding areas with heavy traffic flow. When the radius of access for ESs is assumed to be small, the main roads bear less additional traffic, and with the increase of the radius, the amount of traffic on the main roads gradually increases. This is valuable information for emergency services following an earthquake.

Introduction

Earthquakes, as natural disasters, can cause extensive damage. Due to their potential to cause widespread damage to critical urban infrastructure, they are a significant challenge for large cities. Therefore, organizing crisis planning, including implementing policies that govern urban decisions, is very important to respond effectively to earthquakes [1], [2]. After an earthquake, one of the priorities is to quickly and safely evacuate citizens to protect them from potential hazards such as earthquakes, fires, and the spread of infectious diseases [3]. Emergency shelters (ESs) are safe places with necessary services for evacuating citizens during earthquakes [4]. Therefore, it is crucial to construct secure and appropriately located emergency evacuation facilities to mitigate risks following an earthquake. These facilities should have sufficient resources to support affected citizens [5]. Researchers face challenges in selecting the appropriate location for emergency evacuation due to multiple criteria. The city officials should allocate a budget to adapt the facilities and create a wide range of services in these centers. Therefore, it is crucial to determine the optimal location and quantity of ESs to minimize costs. Selecting these centers’ locations involves a location–allocation problem with two components. A positioning component determines the placement of ESs and outlines how these centers serve the population in the allocation section [6], [7]. Therefore, to determine appropriate locations for ESs, a solution must be selected to address the location allocation problem.

Various approaches have been used in studies on location allocation for ES planning. Some approaches have focused on allocating ESs to citizens in a single-objective manner, considering only one criterion, such as time or distance. Many studies commonly use single-objective techniques such as p-median, p-center, and maximum coverage. Multi-objective and hierarchical models have been used in some studies. Additionally, geographic information systems (GIS) methods, such as the Voronoi diagram, can be used [8], [9].

Conclusion

ESs are essential for promoting peace and ensuring the safety of individuals during earthquakes and potential aftershocks. These centers’ locating and coverage areas should be optimized to prioritize citizen safety and maximize accessibility. This study aimed to identify and allocate ESs in a part of Tehran’s 12th district. Potential ESs were initially selected based on specific criteria, including their proximity to fault lines, fire stations, hospitals, main roads, ES areas, and population vulnerability. The criteria were weighted, and the centers were ranked using the CRITIC and TOPSIS methods.

According to the results obtained using the CRITIC method, the criteria of distance from the hospital and fire department had the highest weight (0.19). In contrast, the area criteria had the lowest weight (0.12). The TOPSIS method has been used to rank the ESs by assigning weights to the criteria. The ranked centers were utilized to address the issue of location and allocation. In the location problem, priority was given to centers with higher ratings. The location and allocation issues have been resolved for different numbers of ESs. Based on the results, the service delivery radius is assumed to remain constant. Simply increasing the number of centers does not guarantee better service delivery. The distribution is crucial. When the coverage radius was set to 500 m, increasing the number of ESs decreased the occupancy percentage of the centers. This indicates that the centers were not fully utilized because they were more than 500 meters away from the residents. If the coverage radius is small, the distribution of centers becomes more significant. This requires considering multiple centers in different locations. In cases where the radius was set at 1000 and 1500 m, there was an increase in the percentage of service delivery and occupancy of ESs. The service coverage percentage within a 1500-meter radius was only about 60%, well below the desired value of 80%. It is possible to expand the distance to increase this case’s coverage. It is important to note that as the distance from centers increases, quick and easy access becomes more complex, which is crucial during times of crisis.

Abstract

To achieve sustainability in bridge design, it is critical to ensure both economic viability and low environmental impact. While stainless steel has great mechanical properties and life cycle performance, the material is expensive, which has limited its use in bridges. This research aims at exploring the benefits of using stainless steel corrugated web girders as an alternative to carbon steel flat web girders in composite road bridges. This concept is expected to lower the investment cost, which enables a broader utilization of the good properties offered by stainless steel. A genetic algorithm optimization routine has been developed to produce bridge designs with minimum weight, investment cost, life cycle cost (LCC), or life cycle impact. Multiple parametric studies are conducted using a simply supported reference bridge. The optimal design solutions are compared for two main design alternatives: conventional S355 flat web girders and duplex (EN 1.4162) corrugated web girders. The parametric studies consider the effects of different design parameters, including the span length, available girder depth, average daily traffic (ADT) with the corresponding indicated number of heavy vehicles in the slow lane , and the paint maintenance schedule, on the optimal solutions. Furthermore, a sensitivity analysis is carried out to analyse the impact of inflation and discount rates on the obtained results. The results show that the concept of stainless steel corrugated web girders offers significant potential LCC and environmental impact saving for the examined span lengths, particularly in the case of deeper girders, high ADTs, and more intensive maintenance activities. Also, despite the influence of inflation and discount rates on LCC results, the studied concept consistently demonstrated favorable results.

Introduction

Nowadays, sustainability is a priority in the design, construction, and maintenance of civil engineering structures [1]. The United Nations established the 2030 Agenda for Sustainable Development in 2015, along with 17 Sustainable Development Goals (SDGs) [2]. The SDGs address urgent and crucial concerns that humans are currently confronted with, such as climate change and resource depletion [2]. The Communication “Next Steps for a Sustainable European Future” makes it clear that the European Union (EU) prioritizes the transition to a sustainable society [3]. One of the biggest obstacles for the EU in achieving its aim of reducing climate change is mitigating the environmental impacts of buildings and construction. The construction and building sector in the EU accounts for around 40% of total energy final consumption, 35% of greenhouse gas emissions (GHG), and more than 50% of all extracted materials [4]. Furthermore, the construction industry generates a large amount of waste, accounting for one-third of the EU’s yearly waste creation [5].

The bridge industry has shown growing interest in sustainable development, particularly in light of its huge potential impacts on the economy and environment [6]. Composite bridges are well-known bridge types, usually designed with steel girders having flat webs (Fig. 1a) and connected to a concrete deck using shear studs. The shear studs allow composite action and enable the best possible utilization of the two materials [7]. The steel girders are typically made of conventional carbon steel, which is prone to corrosion and necessitates frequent maintenance in the form of inspection, repainting, and replacement throughout its service life. In addition to the costs of these activities, the impact on the environment and the disruption of traffic during the maintenance work are considerable [8].

To mitigate the problems associated with maintenance activities, stainless steel is a good solution. Corrosion resistance is the main justification for using stainless steel [9]. The high durability and corrosion resistance of stainless steel can be utilized to minimize the need for maintenance during the bridge’s design life, leading to a lower life cycle cost. The term “stainless steel” refers to a group of alloys with at least 10.5% chromium that, when exposed to water and oxygen, forms a protective layer against corrosion. Duplex stainless steels are the most commonly used type in bridge applications because of their excellent strength and corrosion resistance [1]. Duplex stainless steel is composed of austenite and ferrite. Ferrite increases strength, whereas austenite is ideal for structural applications because of its ductility, toughness, and excellent corrosion resistance [10]. Not only that but also duplex stainless steel has a comparable or higher strength-to-weight ratio compared to carbon steel. In addition, stainless steel’s improved fire resistance makes it useful for civil engineering applications [11].

Results and discussion

The design of all bridges in the parametric study was governed by either ULS or FLS criteria, specifically related to welded vertical stiffeners (detail C for flat web and detail D for corrugated web, Fig. 4). SLS criteria only governed in cases with limited height (ID14 and ID16). The following sections will present the results of the parametric study, focusing on the examined parameters.

6.1. Optimization objective
As mentioned in Section 5, as the first step in the parametric studies, the influence of the optimization objective on the design solution is studied. This is done on the reference case study bridge made of flat-web S355 girders, ID 1–4, and corrugated-web duplex girders, ID 5–8. The results are presented in Fig. 5.

Abstract

In the emergency repair process of seismic-damaged structures, it is necessary to determine the optimal repair strategy according to damage assessment results, available repair resources and repair time. In this study, the applicable conditions of various member-level and structure-level damage indexes or models are compared. Then, considering the actual conditions of limited available repair resources and repair time in the emergency repair process, the determination method of the optimal imperfect repair strategy is established. On this basis, the determination method of the optimal repair sequence is proposed by taking seismic resilience as the evaluation index. Finally, a seismic fragility analysis method that considers uniform collapse risk and residual service life of structures is introduced, which can be used to analyze the seismic performance of seismic-damaged structures and to compare the repair effectiveness of different repair strategies. Taken a 5-story reinforced concrete structure as an example for analysis. The analysis results show the optimal imperfect repair strategy and the optimal repair sequence determined by the proposed methods can effectively improve the seismic performance of seismic-damaged structures. The fragility analysis results further confirm that the repair based on the optimal imperfect repair strategy can effectively reduce the collapse risk of seismic-damaged structures.

Introduction

A strong earthquake can cause serious damage to engineering structures. The damage or collapse of engineering structures and secondary disasters caused by structural damage or collapse are the main causes of casualties and economic losses [1,2]. After a main shock, it is of great theoretical significance and engineering value to repair seismic-damaged structures according to feasible damage assessment methods and the ideas of seismic performance rapid improvement, so as to reduce the damage degree and collapse risk of seismic-damaged structures under aftershocks, and to reduce casualties and economic losses.

The whole process of performance restoration of seismic-damaged structures includes three important parts: damage assessment, structure repair and retrofit, and seismic performance analysis. In the research on damage assessment, the damage of members can be assessed by damage indexes or models such as maximum drift ratio [3,4], residual drift ratio [5], crack characteristics [[6], [7], [8]], and Park-Ang model [9], and the overall damage of an integral structure system can be comprehensively assessed by deformation-related [10,11] or energy-related [12,13] damage indexes or models. Liu et al. [14] proposed a rapid damage assessment method for reinforced concrete members based on the fractal dimension of cracks, considering the correlation between the fractal characteristics of cracks and the damage state. The reliability of this method was demonstrated through experiments. Tazarv et al. [15] established the relationship between the damage state and deformation of beam and column members, and the computer vision technology was used to quickly detect cracks and failure modes of members, thereby achieving rapid identification of damage state. Makhloof et al. [16] reviewed existing damage assessment methods and emphasized the overall damage assessment methods based on deformation, frequency or modal parameter.

Conclusions

The repair strategy formulated through the damage assessment results of seismic-damaged structures can effectively improve the seismic performance. In this study, the application scope and application condition of different damage indexes or models are compared, the methods for determining the optimal imperfect repair strategy and the optimal repair sequence for seismic-damaged structures under the condition of limited available repair resources is proposed, and a seismic fragility analysis method considering the uniform risk and the residual service life of structures is introduced. Taking a 5-story RC frame structure with a residual service life of 40 years as an example for analysis, the main conclusions obtained from this study are as follows:

Abstract

To evaluate influence of external environment and material composition on skid-resistance durability of high viscosity modified asphalt (HVMA) mixture, the accelerated abrasion test was selected to simulate decay of skid resistance for asphalt mixture by setting different test conditions. The influence of aggregate gradation, asphalt type, ambient humidity and overload on skid-resistance durability of asphalt mixture was discussed, and the significant effect of selected factors on skid-resistance durability of asphalt mixture was revealed. The results show that the skid-resistance durability of SMA-13 (Stone Mastic Asphalt) mixture is better than OGFC-13(Open Graded Friction Course) and PA-13 (Porous Asphalt) mixture under different conditions, and attenuation rate of different indexes of SMA-13 mixture is 1.6–2.2% and 0.8–2.1% lower than compared with OGFC-13 and PA-13 mixture. The attenuation rate of texture depth for asphalt mixture is closely related to aggregate gradation and asphalt, but the attenuation rate of british pendulum number for asphalt mixture with the same mineral aggregate is only significantly affected by the asphalt. The skid resistance of SMA-13 and PA-13 mixture is improved slightly by addition of high viscosity modified asphalt. The attenuation rate of texture depth of SMA-13 and PA-13 mixture with HVMA is reduced about 0.6–3.0% and 2.2–4.2% than SBS modified asphalt, but the attenuation rate of british pendulum number of above mixtures is increased about 1.2–1.6% and 0.3–1.7%. The skid-resistance durability of asphalt mixture with TPS (TAFPACK-Super) and SINOTPS high viscosity agent is better than HVA (High viscosity additive). The skid-resistance durability of asphalt mixture based on texture depth is improved under wet condition. However, the skid-resistance durability of asphalt mixture for british pendulum number gets worse due to water intrusion. The skid-resistance durability of asphalt mixture is rapidly decreased under overload condition. The influence of overload and SBS modified asphalt on skid-resistance durability of asphalt mixture is higher than ambient humidity and HVMA. This paper will provide foundation for high viscosity modified asphalt applied in asphalt pavement.

Introduction

The surface layer of asphalt pavement is directly contact with tire, and automobile stability during running is affected by skid resistance of asphalt pavement. The skid resistance of asphalt pavement is inevitably degraded under the synthetic effect of vehicle load, natural environment and asphalt aging, so the traffic accident is occurred frequently [1]. The skid resistance of asphalt pavement remains at a high level, and it is conducive to reduce traffic accident rate. Now, the skid resistance of asphalt mixture is required to evaluate in the quality acceptance of asphalt pavement. But the skid resistance of asphalt pavement in the early stage is inconsistent with skid-resistance durability. The skid-resistance durability of different asphalt mixture needs a long term to test. Zhu et al. [2] has evaluated the long-term skid resistance of SAS-16, GAC-16 and AC-16 mixture with SBS modified asphalt, and found that the long-term skid resistance of asphalt mixture is affected by the oil-stone ratio (asphalt-aggregate ratio), gradation type and coarse aggregate type. Besides the initial and final values as well as the attenuation trend of texture depth for AC-16, SAS-16 and GAC-16 mixture is different, which is related to that the 4.75 mm sieve passage rate of AC-16 is higher than SAS-16 and GAC-16. Huang et al. [3] has studied that frictional coefficient of AC-13I, SAC-13 and SMA-16 mixture with different coarse aggregate is little difference at the initial stage, but the BPN of AC-13I, SAC-13 and SMA-16 mixture is 15.5, 25 and 27 after repeated loading of 70 × 104 circles, which is related to surface feature and polish value of coarse aggregate. Tan et al. [4] has found that skid-resistance durability of SMA-10 mixture is lower than UTAC-10 mixture, but the initial BPN of SMA-10 mixture is better. The aggregate gradation of above mixture is fundamentally the same, but the optimum asphalt content of UTAC-10 mixture is relatively low. So it is necessary to study the skid-resistance durability and influencing factors of asphalt mixture. Besides, the skid-resistance durability of asphalt mixture is closely related to mechanical property of aggregate, volume ratio of mixture, nominal maximum aggregate size[5], [6], [7]. But the influence of external conditions on skid-resistance durability of asphalt mixture has been paid little attention.

Conclusions

The skid resistance of OGFC and PA mixture is better than SMA mixture, but SMA mixture has the good skid-resistance durability. The attenuation rate of different indexes for SMA-13 mixture is 1.6–2.2% and 0.8–2.1% lower than compared with OGFC-13 and PA-13 mixture. The mixture and asphalt type have significant influence on the attenuation rate of texture depth for asphalt mixture, but the attenuation rate of british pendulum number for asphalt mixture with the same mineral aggregate is only significantly affected by the asphalt type.

The skid resistance of SMA-13 and PA-13 mixture is improved by the addition of high viscosity modified asphalt, and skid-resistance durability of SMA-13 mixture with different asphalt is better than PA-13 mixture. The evaluation index of skid-resistance durability of asphalt mixture is affected by the asphalt.

The skid-resistance durability of asphalt mixture with SINOTPS additive is better. The attenuation rate of texture depth for asphalt mixture with SINOTPS additive modified asphalt is lower than TPS additive and HVA. The attenuation rate of british pendulum number for asphalt mixture with SINOTPS additive is in the middle of selected high viscosity modified asphalt.

Abstract

The primary objective of this research is to examine the effects of green knowledge management (GKM) on green technological innovation (GTI) and sustainable performance in construction firms. The study also investigates the role of artificial intelligence (AI) as a moderator of the relationship between GKM and green human capital (GHC). A survey questionnaire was used to obtain data from 309 construction firms in Pakistan, and the AMOS-24 and SPSS PROCESS macro software packages were used to test the hypotheses. The findings revealed that GKM had significant positive impacts on GTI and long-term performance. Aspects of GIC (e.g., green structural capital, green relational capital, and green human capital) were found to be significant mediators of GKM and GTI interactions and correlations between GKM and sustainable performance. Furthermore, the study showed that AI significantly influenced the relationship between GKM and GHC. The study’s findings have important theoretical and practical implications for organizations and governments. The study theoretically contributes to the knowledge-based view of the firm by providing empirical evidence of the role of various GIC characteristics as mediators in the interactions between GKM, GTI, and sustainable performance. In practice, the findings suggest that firms can improve GTI and sustainable performance by investing in GKM and GIC.

Introduction

Nineteenth-century industrialism successfully lifted millions of people from poverty. However, this economic success caused environmental and resource degradation (Dahlquist, 2021). This raises the following question: Is damage to the environment necessary for economic stability? Despite the abundance of natural resources, their vulnerability to climate change jeopardizes emerging economies’ economic progress. For decades, governments have been eager to set rules and standards to ensure the environmentally friendly production of goods and services (Khan, 2022; Mehmood et al., 2022; Sana, 2020). The United Nations (UN) established its Sustainable Development Goals (SDGs) to safeguard and enhance social and environmental conditions (Ham et al., 2021). In response, firms have started to recognize the importance of environmental preservation, and have been inspired to modernize their operations and management frameworks. Previous studies have shown the importance of business capabilities to the development of innovations that uncover new uses for existing goods, expertise, and resources (Hui & Khan, 2022; Khan & Khan, 2021). As innovation frequently necessitates the acquisition and application of new knowledge (Berraies & Zine El Abidine, 2019), knowledge assets are an essential resource for firms.

The capacity of an organization to gain and keep knowledge determines its failure or success (Argote et al., 2000). Firms use knowledge to boost customer satisfaction and gain a competitive edge (Dabbous & Tarhini, 2019). Knowledge management (KM) has grown in popularity in the corporate world over the last few years (Caputo et al., 2019; Kianto, 2011). It is regarded as an essential element in strategizing, developing new goods and services, and managing operations (Donate & de Pablo, 2015). An efficient KM system can boost a firm’s effectiveness (Brachos et al., 2007). Moreover, given ecological challenges, vibrant firms have broadened the scope of KM and begun to integrate environmental issues into business knowledge (Sahoo et al., 2022).

Discussion

By applying a KBV framework, this study tested the relationships between GKM, GTI, and sustainable performance through GIC. This study also tested the moderating effects of AI on the relationships between GKM and the three GIC components. To the best of our knowledge, this study is among the first to test these relationships in the construction industry, which is famous for its destructive impacts on the environment (Kinnunen et al., 2022). The findings add to the literature on KM, innovation, sustainability, and AI by using an experimental approach to produce insights with theoretical and practical implications and to identify new areas for future research. The findings are described below.

This investigation of GKM’s effects on GTI and sustainable performance yielded noteworthy findings. The empirical evidence is consistent with studies that found organizational resources to be positively associated with green innovation (Su et al., 2020; Wang et al., 2022). Sahoo et al. (2022) found a similar connection between GKM and green innovation and green performance. This important conclusion suggests that Pakistani construction firms can improve their GTI and sustainable performance by applying GKM. The findings demonstrate that GKM has a positive influence on GIC. The results corroborate previous research showing a similar positive association (Martín-Rubio, 2021; Sahoo et al., 2022), and are consistent with the idea that firms can improve their GIC if they have resources and GKM competencies.

Abstract

This research is about how farmers adapt to water scarcity. Using experimental economics methods, field experiments were carried out in a region exposed to severe water scarcity in Colombia. Willingness of water users to cooperate in conforming to extraction caps, as a means of adapting to water availability declination was calculated. Two information treatment groups were implemented in order to assess water allocation decisions when: (i) the amount of water was reduced and (ii) time before aquifer exhaustion was announced. Extant literature on cooperation in common-pool resources (CPR) has focused on demonstrating to what extent resource users depart from egoistic attitudes. Alternatively, the sustainability of water resources requires more research to further understand cooperative behavior. Since the literature on water scarcity is classified in three orders, namely physical, institutional, and socio-political, behavioral dimensions are suggested as a subdivision of the social order. This, in turn, may help to operationalize strategies aimed at improving adaptation to all orders of scarcity. The quantitative results suggest that farmers are inclined to follow the cap. The main difference between the quantity and time treatments differs in that in the time treatments farmers allocate much more water to be consumed in the future, whereas in the former, they prefer to allocate more water to be consumed in the present. Adaptation options provide favorable inputs for implementing the Sustainable Development Goals, especially SDG 6, which is related to water use efficiency. Target 6.4 establishes that, by 2030, water efficiency and extraction sustainability should be accomplished. Thus, water policy interventions might benefit from this contribution. However, since success in water conservation programs might be difficult to achieve due to complexity in human-decision making, more research is needed to deepen our understanding of cooperation drivers in aquifer conservation.

Introduction

Despite the abundance and precision of current information on aquifers status ( van der Gun, 2022 ), this type of data – commonly managed by governmental institutions – rarely flows to the communities that depend upon them ( Margat & van der Gun, 2013 ). In effect, underground water availability data is currently assessed through satellite and underground monitoring of aquifer levels, but farmers´ communities do not have access to this information in a format they can readily use. Climate change is entering the aquifer overexploitation game as a new player ( Damania et al., 2017 ), since droughts are becoming more frequent than in the past ( UNWATER, 2023; Yuan et al., 2023 ); therefore, public environmental and water entities promote water conservation during droughts. Public entities usually stimulate the reduction of water extraction volumes by instructing users to consume less or save the resource. This information, however, lacks the necessary context and specificity, two features that play an important role in water extraction curbing adapted to ensuing water scarcity.

Although water scarcity has an important political dimension ( Metha, 2007 ), from the perspective of its physical and social dimensions, it can be observed how climate change is motivating farmers towards strategies to face the challenge. In spite of the complexity of hydrogeological information, farmers certainly want to know more about the status of the aquifers they are exploiting. They need information not only about the effects of their extraction decisions, but also about the way to moderate these decisions as an adaptation to scarcity according to aquifers’ statuses.

Conclusions

This article was designed for presenting the results on how farmers adapt to water scarcity. Framed field experiments were run to collect quantitative data on the decisions made by farmers when they were exposed to reductions in water availability. Time and water quantity treatment groups were prepared to test their effects on water allocation as limited by suggested extraction caps. Quantitative and qualitative analysis of data and information were carried out. Behavioral regularities and social institutions were drawn from the quantitative data and graphics and the narratives expressed by the players after the experiments.

The setting for the understanding of adaptation strategies was demarcated by the limits imposed by nature. For this reason, water availability as a physical limiting factor for water extraction was used as an instrument to connect allocation, decision-making and intertemporal consequences for adaptation. Thus, limited availability under time and quantity limits pushed the farmers (players) to decide whether to cooperate or not in water conservation. Thus, the individuals who cooperated better were adapting to water scarcity. More precisely, the farmers informed on time before aquifer exhaustion, revealed greater awareness about the possibilities of cooperation. Contrarily, in the control group situation, farmers allocated much more water to all uses and the cap volume was reached in most of the rounds. While in the time and quantity treatment groups, the aggregated water volumes declined through the time (rounds), in the control group this amount averaged 1800 m3 (close to the cap). It can be said that the communication amongst farmers on how to manage remaining stocks, and, similarly the hydrogeological information play a key role in incentivizing the cooperative behavior under extraction caps contexts. Since the stability of cooperation was part of the research aims, providing quantitative information to farmers on extraction decisions and the remaining time of aquifer availability is suggested as a key factor to more effectively address the adaptation to water scarcity.

Abstract

Significant population growth with rapid economic development have led to water scarcity problems around the world. Currently, most of the simple water scarcity assessment methods only refer to per capita water use, failing to take into account actual water availability and actual human domestic water use. Therefore, we have developed a simple and practical method to assess water scarcity, incorporating total water resources, water use efficiency, and the proportion of domestic water. In this approach, a new water scarcity index is employed to describe different levels of water scarcity using various thresholds based on the basic daily human water use per person. This may help to visualize the extent of water scarcity in a region while focusing on human interests. To illustrate this approach, we take China–the world’s largest developing country–as an example, analysing its nationwide water scarcity in 2021 while validating it with the results of other scholars on China’s water scarcity. The results show that our water scarcity assessment index is very accurate, revealing that in 2021, the disparity in water resources between the northern and southern regions of China remains substantial, with severe water scarcity still widely concentrated in northern China.

Introduction

Continuous water supply plays a vital role in daily life and social development ( Ethaib et al., 2022 ). However, increasing water consumption is due to the significant population growth and rapid economic development, resulting in extremely high water resource pressures, which cause water scarcity in numerous places around the world ( Liu et al., 2017 ). For instance, in regions such as Greater London with high population density, intense irrigation present in areas like the High Plains of the United States, and nations like India that exhibit both traits, there is a prevalent issue of water scarcity ( Mekonnen and Hoekstra, 2016 ). Nevertheless, in addition to direct water supply shortages caused by the forces of nature, human factors, as well as socio-political factors, are often overlooked, leading to the masking of the causes of scarcity. This complexity of water scarcity is labelled by Mehta as ‘real’ scarcity (related to socially and ecologically relevant physical phenomena like grass cover, fodder, distance to water for disadvantaged groups, cycles of natural resource abundance and scarcity, agro-meteorological hydrology, etc.) and ‘manufactured’ scarcity (constructing water scarcity as a perpetual and pervasive natural phenomenon, the industry of disaster relief and drought relief, and perverse benefits) ( Mehta, 2003 ). Moreover, there are also sudden and uncontrolled factors affecting water resources, such as the outbreak of the COVID-19 pandemic crisis, which has put many additional pressures on water resources, including the increase in local agricultural irrigation brought about by the localised production of food, and the parallel alteration of the virtual water trade caused by the changes that have taken place in the food trade ( Al-Saidi and Hussein, 2021 ).

Results

3.1. Statistical analysis of the results

A comparison of the water scarcity index calculated using Eq. (1) for each region of China, with a threshold of 0.2 (no stress), is shown in Fig. 2 . The results show that most regions in China are still suffering from water problems, including some economically developed cities with heavy water problems, such as Beijing (0.01), Tianjin (0.008), and Shanghai (0.02). In contrast, Qinghai (1.43) and Xizang (10.56) have abundant water resources, which are significantly higher than in other regions.

3.2. Spatial analysis of the results

In this study, ArcGIS Pro software was used to raster water resource data from various provinces in China in order to comprehensively and visually assess water scarcity across the country. As can be seen in Fig. 3 , the water scarcity index shows obvious spatial distribution differences, mainly between the northern and southern regions of China. Overall, the water scarcity index shows absolute scarcity in the north and no stress in the south. Specifically, a wide range of areas in northern China, including Inner Mongolia, Liaoning, and Shaanxi, exhibit water scarcity and some pressure on water resources. It is worth noting that some areas in the north also show absolute water scarcity, especially in Beijing, Tianjin, Hebei and Shanxi, indicating that the available water resources in these regions do not meet the minimum basic human needs of the region.

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

Two destructive earthquakes (Mw: 7.7 and Mw: 7.6) occurred in Kahramanmaraş, Türkiye, on February 6, 2023. The epicenters of these two earthquakes were very close to each other (approximately 90 km apart), and both took place on the same day. The first earthquake occured at 04:17 local time with a magnitude of 7.7 and a depth of 8.6 km, while the second earthquake occurred at 13:24 local time with a magnitude of 7.6 and a depth of 7.0 km. These two earthquakes caused extensive damage, particularly in 11 provinces, with Adıyaman being one of the hardest-hit areas. Most buildings in Adıyaman were severely affected or collapsed as a result of the earthquakes. Reports indicate that over 35,000 buildings collapsed in the aftermath. Furthermore, between February 6, 2023, and May 6, 2023, more than 30,000 aftershocks, ranging in magnitude from 0.2 to 6.6, were recorded. In this study, earthquake damages in reinforced concrete buildings in Adıyaman province were evaluated. The causes of damages in reinforced concrete buildings were evaluated in terms of material quality, design of building and reinforcement details. Field observations are also provided, along with accompanying pictures. The earthquake regulations in Türkiye, established in 1975, 1998, 2007, and 2018, which apply to a significant portion of the country’s buildings, are discussed. An evaluation was conducted to assess whether the damaged buildings complied with the earthquake regulations in Türkiye. Field observations revealed that the earthquake regulations, particularly in relation to reinforcement details, were overlooked. In addition, designers should avoid design mistakes such as to make discontinuous of frames, to place most of vertical element strong axis in one direction, insufficient support condition of stairs and adjacent building effects.

Introduction

Türkiye has active earthquake fault zones, including the North Anatolian Fault, East Anatolian Fault, and West Anatolian Fault zones, which have the potential to cause destructive earthquakes. Türkiye has often been exposed to destructive earthquakes in the past. After these earthquakes, many studies about structural failures have been conducted and documented in the literature [1], [2], [3], [4], [5], [6], [7], [8], [9], [10], [11], [12]. On 6 February 2023, two destructive earthquakes occurred in Kahramanmaraş provinces in Türkiye (Mw: 7.7 and Mw: 7.6). The first earthquake was occurred in Pazarcık (distinct of Kahramanmaraş) at 04:17 local time with a magnitude of Mw:7.7. The second earthquake was occurred in Elbistan (distinct of Kahramanmaraş) at 13:24 local time with a magnitude of Mw:7.6. These two earthquakes were occurred in same day (approximately nine hour apart) and there is approximately 90 km distance between epicenters of these earthquakes [13]. The pair of earthquakes resulted in significant structural damage, particularly impacting 11 provinces, including Kahramanmaraş, Hatay, Gaziantep, Malatya, Diyarbakır, Kilis, Şanlıurfa, Adıyaman, Osmaniye, Adana, and Elazığ, where many buildings either sustained severe damage or collapsed entirely.

According to official announcements from the Disaster and Emergency Management Authority (DEMA) on 2 June 2023, it was reported that over 35,000 buildings had collapsed after the earthquakes. Furthermore, during the period from February 6, 2023, to May 6, 2023, more than 30,000 earthquakes with magnitudes ranging from 0.2 to 6.6 were documented [13]. The Kahramanmaraş earthquakes had a profound impact on Türkiye, causing severe damage not only during the initial earthquakes but also due to subsequent aftershocks.

Conclusions

Two destructive earthquakes occurred in Pazarcık (Mw: 7.7) and Elbistan (Mw: 7.6), Kahramanmaras¸, Türkiye. These earthquakes severely affected 11 provinces (Kahramanmaras¸, Hatay, Gaziantep, Malatya, Diyarbakır, Kilis, S¸ anlıurfa, Adıyaman, Osmaniye, Adana,Elazıg). Adıyaman is one of the provinces most affected by the earthquakes. Due to these two earthquakes occurring on the same day ˘ (nearly 9 h apart), damaged buildings were only examined after the second earthquake. This study focuses on examining the damaged reinforced concrete buildings in Adıyaman. Structural damages and the reasons for these damages are examined in comparison with Türkiye Earthquake Codes.

Abstract

Concrete structures are widely used in modern constructions including energy storage system such as all concrete liquefied natural gas (ACLNG) storage tanks. In ACLNG tanks, concrete structure is exposed to cryogenic temperatures and freeze-thaw (FT) cycles. Cryogenic temperatures and FT cycles are recognized to influence the mechanical characteristics of concrete. To ensure safety of the critical energy infrastructure, it is crucial to explore the concrete structural response under the combined cryogenic FT cycles and accidental impact loading. This study aims to numerically examine the damage caused by impact loading on reinforced concrete panels after exposure to cryogenic FT cycles. A plasticity based continuous surface cap model was adopted to simulate concrete. The material modulus, uniaxial and triaxial strength surface as well as damage parameters were updated to incorporate the effect of cryogenic FT cycles. A numerical model was established to forecast the impact resistance of the reinforced concrete panels after various cryogenic FT cycles. Through the numerical simulation, it was evident that FT cycles exerted detrimental effects on the impact resistance of reinforced concrete panels. With an escalation in the number of FT cycles, there was a pronounced increase in the size of the crater formed on the top surface, accompanied by a corresponding rise in the penetration depth of the panel. The results of this research offer insights into the impact resistance of reinforced concrete structures following cryogenic FT cycles. Such insights are vital for the design and maintenance of critical structures like liquefied natural gas (LNG) storage tanks and other cryogenic facilities.

Introduction

Reinforced concrete structures play a vital role in various engineering applications, providing strength, durability, and resilience. However, when subjected to extreme environmental conditions, like cryogenic freeze-thaw (FT) cycles, the structural safety of concrete elements can be remarkably affected. Moreover, of specific concern is the accidental impact resistance of reinforced concrete structures while enduring the challenges posed by cryogenic FT cycles. The demand for efficient and reliable energy storage systems, particularly All Concrete LNG (ACLNG) storage tank, has been rapidly increasing in recent years [1], [2]. Liquid natural gas storage tanks commonly maintain a storage temperature of approximately − 165 °C, therefore, concrete is under ultra-low temperature condition. These storage tanks are subjected to both cryogenic temperatures, FT cycles and potential impact loading scenarios, rendering it crucial to assess their structural response and safety under such conditions.

Numerous researchers have investigated the concrete’s mechanical properties at low and super-low temperatures to facilitate the scientific, rational, and cost-effective design of structures while ensuring their performance and safety in extreme cold environments [3], [4], [5], [6], [7]. Van de Veen [8] had a comprehensive review on the properties of concrete such as the compressive strength, tensile strength, modulus of elasticity at low and cryogenic temperature and after FT cycles. It revealed that the mechanical properties of concrete could be affected by the type of aggregate, cooling condition, water to cement ratio (w/c) and moisture content (MC). It is commonly reported that the strength of concrete was improved at low or super-low temperatures [1], [8], [9], [10]. This improvement can be attributed to several factors. Firstly, as water within the concrete freezes at lower temperatures, it crystallizes into a solid reticulated pattern that imparts prestress to the concrete. This prestressing phenomenon contributes to an enhancement in the compressive strength due to the existence of multiaxial stress [6]. Moreover, the complete filling of capillary pores with ice helps eliminate stress concentrations within the concrete and inhibits the formation of microcracks at low temperatures. For a more comprehensive understanding of the reinforcement impacts of low temperatures on concrete, researchers have employed micro-scale models to explore the formation of ice within concrete pores and subsequent cracks [11], [12].

Conclusions

The impact resistance of reinforced NSC panels after FT cycles was investigated using a refined finite element model. The CSCM model was adopted and modified to incorporate various parameters such as shear modulus (G), bulk modulus (K), uniaxial and triaxial compression surface, as well as damage parameters. The subsequent conclusions can be drawn:
• After FT cycles, the elastic modulus, splitting tensile, and compressive strength as well as fracture energy of concrete decrease. As the number of FT cycles increases, the performance of concrete also continuously decreases.

• The modified CSCM model effectively captures the impact behaviour of reinforced concrete panels after FT cycles, considering various mechanical parameters.

• The predictive capability of the numerical model was validated through experimental verification, demonstrating its reliability in assessing the impact resistance of reinforced concrete structures.

• FT cycles were observed to adversely affect the impact resistance of the concrete structures. As the number of FT cycles increased, there was an observable escalation in the dimensions of craters formed on the surface as well as an increase in the penetration depth of the panels. These trends collectively suggested a decline in the impact resistance of the panels with the progression of FT cycles.

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.