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

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

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.

Abstract

Recycling of abandoned waste bottom ash has been a key issue in Republic of Korea in terms of environmental protection as well as economic concern. In this work, a method for recycling of abandoned bottom ash has been discussed based on the results from laboratory and industrial-scale experiments. Abandoned bottom ash was magnetically separated and properties of magnetically separated bottom ash samples as well as properties of mortar and masonry cement brick made of bottom ash were investigated. According to the experimental results, bulk and skeletal densities were ranked in the order of strongly magnetic > weakly magnetic > as-received > non-magnetic (from heavier to lighter) bottom ash. From laboratory-scale experiments, compressive strengths of mortars made of bottom ash samples (measured by ASTM C 109) were lower than that of mortar made of standard sand. Among bottom ash samples, mortar made of non-magnetic bottom ash (after removal of unburnt carbon) showed higher compressive strength with lower thermal conductivity (measured by ASTM C 1113) and weight than others. Masonry cement brick made of magnetic bottom ash showed lower weight and thermal conductivity than those made of standard sand, while meeting the KS strength guideline as a masonry cement brick. The results suggest the applicability of bottom ash as lightweight aggregate for production of masonry cement brick. However, considering the lower strength obtained from masonry cement brick made of as-received bottom ash (without removal of unburnt carbon), unburnt carbon content should be removed prior to its utilization as lightweight aggregate.

Introduction

Consumption of fossil fuels for operation of coal fired power plant has been consistently increasing all over the world (International Energy Agency, 2009; Korre et al., 2010; Leblond, 2006; Shafiee & Topal, 2008). Although reduction in CO2 emission is very critical issue in this industry (Hussain et al., 2022), recycling of waste by-products is as important issue as the reduction of CO2 emission in terms of environmental protection (Abbas et al., 2020; Bui et al., 2019; Lee et al., 2020; Meek et al., 2021; Oakes et al., 2019) considering the amount of waste that has been generated so far. Approximately 730 million tons of bottom ash (Abbas et al., 2020) and 600 million tons of fly ash (Çiçek & Çinçin, 2015; Nyale et al., 2013) are annually produced in the world. Although fly ash has been successfully utilized as a supplementary cementitious material due to its beneficial properties such as reduction in the heat of hydration (Atiş, 2002a, 2002b; Langan et al., 2002; Matos et al., 2020; Nocuń-Wczelik, 2001; Schindler & Folliard, 2005), improvement in workability (Atiş, 2002b; Leung et al., 2016; Nocuń-Wczelik, 2001; Uysal et al., 2012; Yao et al., 2015), and long-term strength and durability (Pala et al., 2007; Siddique, 2003; Tikalsky et al., 1988), most of the bottom ash has not been recycled and abandoned in the waste storage site.

The utilization of bottom ash as a supplementary cementitious material has been limited. The chemical compositions of bottom ash are similar to that of fly ash. However, the particle size is larger and the structure is more crystalline than fly ash. For this reason, the pozzolanic activity of bottom ash is very weak. The work of (Cheriaf et al., 1999) showed that bottom ash did not react with calcium hydroxide at early ages. The pozzolanic activity was very slow until 28 days, and became accelerated after 90 days. Jurič et al. (Jurič et al., 2006) recommended to replace up to 15 wt% of cement by bottom ash to use it as a supplementary cementitious material. Kula et al. (Kula et al., 2002) showed that bottom ash can be used as a supplementary cementitious material depending on its particle size distribution. Jaturapitakkul et al. (Jaturapitakkul & Cheerarot, 2003) observed a glassy aluminosilicate phase (diffused halo maxima) at 20–27° 2θ (Cheriaf et al., 1999; Chindaprasirt et al., 2009) that can be a source of pozzolanic reaction, but reported that the pozzolanic activity of bottom ash can be increased by grinding the particle size lower than 45 μm. According to the literature, pozzolanic activity of bottom ash was so slow or weak that it cannot be effectively utilized as a supplementary cementitious material without additional mechanical or chemical treatment (Filipponi et al., 2003; Liu et al., 2018; Mangi et al., 2018).

Conclusion

In this work, magnetic separation was applied on bottom ash that was stored in the pond site of Hadong coal fired power plant. Properties of magnetically separated bottom ash were analyzed, mortar specimens as well as masonry cement brick samples were prepared, and compressive strength, water absorption, and thermal conductivity were measured. According to the results obtained from this work, following conclusions can be drawn.

1) Magnetic separation with 1000 and 3000 gauss magnet was effective for separating bottom ash samples that contains higher amount of magnetite. As a result, bulk and skeletal density of strongly magnetic bottom ash were higher than those of as-received bottom ash. Non-magnetic bottom ash showed the lowest bulk and skeletal density.

2) Pozzolanic activity of bottom ash was ranged 53 ~ 62% of fly ash that was stored at the same pond site. Considering the particle agglomeration observed from the fly ash, it is possible to evaluate the pozzolanic activity of bottom ash either as non-pozzolanic or as very weakly pozzolanic.

3) From laboratory scale experiments, non-magnetic bottom ash showed the better performance than strongly magnetic bottom ash in terms of compressive strength and thermal conductivity. Since large amount of unburnt carbon stayed together with non-magnetic bottom ash, removal of unburnt carbon is a key factor for successful utilization of non-magnetic bottom ash.

4) Masonry cement brick made of magnetic bottom ash showed 40% reduction in unit weight, 20% reduction in thermal conductivity. Utilization of non-magnetic bottom ash for masonry cement brick production after removal of unburnt carbon can also be a successful application, considering the results from laboratory-scale experiments (density and thermal conductivity was lower for non-magnetic bottom ash).

Abstract

This study evaluated the potential of sugarcane bagasse fly ash, collected from boiler exhaust stacks via a bypass pipe, as a renewable supplementary cementitious material. The bagasse fly ash was ground into three different particle sizes (D50 of 10, 20, and 30 μm) and characterized in terms of morphology, porosity, specific surface area, and pozzolanic activity. The influence of the ashes on paste hydration was investigated using isothermal calorimetry. Mortars were then tested with 20% cement replacement by fly ash, analyzing packing density, compressive strength evolution, and durability against sulfuric acid. Results indicated the suitability of the fly ash as a supplementary cementitious material, with low contamination and greater pozzolanic activity at smaller particle sizes. This enhanced initial hydration and long-term strength, with finer ashes showing superior mechanical properties when compared to the reference mortar (an 8% increase). Mortars with fly ash exhibited higher packing density and reduced mass loss under sulfuric acid attack, but increased water absorption and capillarity, alongside decreased compressive strength compared to the reference. Briefly, the findings highlighted that the potential of bagasse fly ash as a promising low cost and eco-beneficial material for sustainable construction practices.

Introduction

It is imperative to act now to reduce global environmental impacts by combating CO2 emissions and preserving our planet for future generations. The cement industry plays a pivotal role in the necessary reduction of global emissions, requiring innovation and more sustainable practices to build a greener and healthier future for our planet. On the other hand, industrial waste discharged into the soil poses a significant environmental threat and can lead to soil contamination, compromising agricultural land quality, groundwater, and overall ecosystem health ( Mohan et al., 2023 ). Sales and Lima (2010) emphasized the negative impact of improper disposal and the use of these residues as fertilizers, especially in powder form, due to their low soil enrichment potential.

In this scenario, sugarcane bagasse ash (SCBA), an abundant residue generated globally every year, is of paramount importance, particularly in the cement industry, with its silica-rich composition making it an attractive and valuable resource. Thus, SCBA is a promising pozzolanic material, recognized in several studies conducted in recent decades ( Ahmad et al., 2021 ; Minnu et al., 2021 ). It is mainly generated via the conventional methods used in the sugar and ethanol agroindustry, which involve storing sugarcane bagasse outdoors for subsequent calcination in boilers.

Conclusions

The following conclusions were drawn from the study on producing finely ground bagasse fly ash and its application in pastes and mortars. The chemical composition of the bagasse fly ash was suitable for use as a supplementary cementitious material, largely because of the presence of 24% amorphous silica and low loss on ignition (2.8%). Moreover, the ashes showed increased pozzolanic activity with a decline in particle size, resulting in accelerated hydration in the initial hours and greater long-term compressive strength of the mortars. A good correlation was observed between packing density and ash particle size, with finer ash resulting in higher mortar packing density. Thus, finer ash exhibited the best mechanical performance, although adequate ash can be produced with D50 of 20 μm. In terms of durability, the acid-attacked M-REF specimens experienced greater mass loss during sulfuric acid attack. However, given the different degradation mechanism of the attacked mortars containing SBFA samples, water absorption increased and compressive strength declined when compared with their nonattacked counterparts and the attacked reference specimens.

In summary, while the use of ultrafine bagasse fly ash in cementitious materials offers several advantages, such as enhanced mechanical performance, accelerated hydration, and environmental benefits, there are also limitations related to durability and mechanical performance with coarser particles. Overall, proper consideration of these factors is necessary for effective large-scale use of sugarcane bagasse fly ash in cementitious applications. Further research should focus on (i) understanding the long-term performance of cementitious materials containing bagasse fly ash; (ii) performing life-cycle assessments to evaluate the environmental impact of using bagasse fly ash as a supplementary cementitious material compared to conventional materials; (iii) investigating the economic feasibility of incorporating bagasse fly ash into cementitious materials, including cost-benefit analyses and assessing the potential for commercial-scale production. By addressing these research directions, further advances can be made in harnessing the potential of bagasse fly ash as a sustainable and effective supplementary cementitious material, contributing to the development of eco-friendly construction practices.

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.