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 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

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.

Abstract

Keywords

1. Introduction

2. Related work

3. Application research of Internet of Things in solar photovoltaic power station monitoring and management system

4. Development of integrated computer-aided design system for solar photovoltaic buildings

5. Conclusion

Declaration of Competing Interest

References

Abstract

At the same time of economic development, the increasing scarcity of energy has had a great impact on people’s development. People’s production and life demand for electricity is also increasing rapidly, and solar power technology has received more and more attention. As a new energy source, solar energy has the advantages of environmental protection and sustainability, and it has no regional restrictions, can be used on-site, and designed to scale. Solar power generation is an important way to use solar energy. As the main component of the grid-connected power generation system, solar grid-connected inverters complete the tracking problem of the maximum power point in the photovoltaic array and transmit electrical energy to the grid through a set of control algorithms. The electrical energy is transmitted to the grid through the inverter, consistent with solar energy. In order to solve the problems of low integration, low energy efficiency, low reliability, high power consumption and lack of effective monitoring measures for solar energy devices. This article starts with the design of the solar cell integrated system, and through detailed analysis of the solar production system and building integrated planning, establishes the shadow radiant energy model of the solar cell system building electrical and solar cell system based on the Internet of Things, and designs an object-based Networked comprehensive auxiliary platform.

1. Introduction

Today’s society is an information society centered on the Internet. Digitization, informationization and world economics are the hallmarks of the current era. With the continuous rapid development of information technology, the process of world economics has been continuously strengthened. The use of computer technology, communication data and the Internet to complete e-logistics and Internet commerce has been widely used in society. The continuous improvement of information technology and information storage is just the prelude to the transformation of the IT industry. The cost of information dissemination is getting less and less, and it is bound to usher in the era of the Internet of Things dominating. As a post-IP product, the Internet of Things is developing rapidly and will become popular in the future. This is a major plan to realize the intelligentization of the world.

Highlights

Abstract

Keywords

1. Introduction

2. Research significance and objectives

3. Experimental program

3.1. Concrete specimens

3.2. Test setup and instrumentation

3.3. Concrete properties and test parameters

4. Results and discussion

4.1. Concrete deformations: Strains and deflections

4.2. Recovery strains

4.3. Deflection recovery

4.4. Analysis of uncracked and cracked concrete beams

5. Conclusions

CRediT authorship contribution statement

Declaration of Competing Interest

Acknowledgments

References

Abstract

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

1. Introduction

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

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

Abstract

Introduction and background

Materials and methods

Methods

Results

Service life extensions

Conclusions

Acknowledgements

Funding

References

Abstract

     With increasing economic pressures worldwide, the amount of money spent on pavement preservation needs to become more effectively utilised. Historically, the Long-Term Pavement Performance (LTPP) study has led to data-driven performance expectations for treatments. Pavement management systems (PMS) allowed many to form analytical methods to evaluate pavement performance, from trend fitting to benefit analysis. Taking these methods and applying them to the Iowa Department of Transportation’s (DOT) pavement management information system (PMIS) database can determine preservation utility as well as provide expectations of pavement treatments. Thirteen slurry seal projects across the wet/freeze climate of Iowa, U.S.A., were analysed to determine the service life extensions and yearly benefit for their pavement condition, rutting, riding, and cracking indices. This study aims to provide a framework for future analysis of more preservation treatments and other PMS databases. Understanding local performance of various preservation methods leads to better pavement management and economically sound decisions.

Introduction and background

     With increasing economic pressures worldwide, the amount of money spent on pavement preservation needs to become more effective and appropriately utilised. To properly allocate spending on pavement preservation, two general approaches utilising a pavement management system (PMS) can be used. The first approach involves prioritising various roads within a network, typically based on the roadway type (arterial, collector, residential, etc), current pavement condition, annual average daily traffic (AADT), and other factors important to the involved agency. However, the second approach involves the understanding of preservation performance based on actual treatments applied with local means and materials. Analysing past performance data and identifying trends provides the ability to better quantify the effectiveness of preservation treatments.

     The objective of this study is to evaluate the performance of slurry sealing on Iowa roadways, a wet/freeze climate, to better understand their effectiveness as a pavement preservation treatment. Four pavement performance indices are evaluated and compared using reflected, logistic, sigmoidal (RLS) curves.

Results

     All projects were analysed, and a best fit function was fitted to the data using an RLS function to develop a pavement performance curve, the index benefit throughout each relative year, and the service life extensions for PCI and the rutting, riding, and cracking indices was evaluated for the thirteen slurry seal projects. Each ‘Do Nothing’ and ‘Observed Performance’ trends for all four indices of all thirteen projects were measured and life extensions were evaluated. Statistical data from such small sample sets only provide limited results; however, observed trends over multiple projects help to develop performance expected trends as performance of more treatments becomes available.