Showing papers in "Journal of building engineering in 2022"

Structural health monitoring of civil engineering structures by using the internet of things: A review

Abstract: Structural health monitoring (SHM) and damage assessment of civil engineering infrastructure are complex tasks. Structural health and strength of structures are influenced by various factors, such as the material production stage, transportation, placement, workmanship, formwork removal, and concrete curing. Technological advancements and the widespread availability of Wi-Fi networks has resulted in SHM shifting from traditional wire-based methods to Internet of Things (IoT)-based real-time wireless sensors. Comprehensive structural health assessment can be performed through the efficient use of real-time test data on structures obtained from various types of IoT sensors, which monitor several health parameters of structures, available on cloud-based data storage systems. The sensor data may be subsequently used for various applications, such as forecasting masonry construction deterioration, predicting the early-stage compressive strength of concrete, forecasting the optimum time for the removal of formwork, vibration and curing quality control, crack detection in buildings, pothole detection on roads, determination of the construction quality, corrosion diagnosis, identification of various damage typologies and seismic vulnerability assessment. This review paper summarizes the applications of the wireless IoT technology in the monitoring of civil engineering infrastructure. In addition, several case studies on real structures and laboratory investigations for monitoring the structural health of civil engineering constructions are discussed.

Recycled aggregates from construction and demolition waste towards an application on structural concrete: A review

Abstract: The construction sector, in addition to being very important for the economy of several countries, also has a significant impact on the environment as it causes a huge natural resources depletion and generates an enormous amount of waste. Therefore, the use of recycled aggregate from construction and demolition waste, instead of conventional aggregates, has a double environmental advantage: it decreases the consumption of natural resources and reduces the land needed for waste disposal. Thus, in the last decades, many researches have been conducted to analyse the feasibility of recycled aggregate in several civil engineering works, which can help in a long way the economic and environmental sustainability of countries. This article presents a literature review on the production and utilization of recycled aggregate in concrete. Because of its higher water absorption and lower density, the use of recycled aggregate can cause a slight reduction in workability and compressive strength of concrete. Thus, authors have evaluated methods to remove the adhered mortar or to seal the pores of recycled aggregates, enhancing the material quality. Some articles also show the feasibility of using recycled aggregate concrete in structural elements, either through reduced-scale elements at a laboratory or full-scale elements in real projects. Summarily, this review may help to alleviate the concerns of consumers and further promote the use of recycled aggregate on a larger scale in civil engineering. The literature survey was conducted on an extensive database; however, a greater emphasis was placed on articles published after the year 2000.

Vision-based concrete crack detection using a hybrid framework considering noise effect

Abstract: Diagnosing surface cracks of concrete structures has been a critical aspect of assessing structural integrity. Existing diagnosis technologies are time-consuming, subjective, and heavily dependent on the experiences of inspectors, which leads to low detection accuracy. This paper aims to resolve these challenges by proposing a vision-based automated method for surface condition identification of concrete structures, consisting of state-of-the-art pre-trained convolutional neural networks (CNNs), transfer learning, and decision-level image fusion. For this purpose, a total of 41,780 image patches of various concrete surfaces are generated for the development and validation of the proposed method. Each pre-trained CNN is employed to establish the predictive model for the initial diagnosis of surface conditions via transfer learning. Since different CNNs may generate conflicting results due to differences in network architectures, a modified Dempster-Shafer (D-S) algorithm is designed to conduct decision-level image fusion to improve the crack detection accuracy. The superiority of the proposed method is validated via the comparison with single CNN models. The robustness of the proposed method is also verified using the images polluted with various types and intensities of noise, with satisfactory outcomes. Finally, this hybridised approach is applied to the analysis of images of concrete structures captured in the field, through an exhaust search-based scanning window. The results show that it is capable of accurately identifying the crack profile with wrong predictions of limited areas, demonstrating its potential in practical applications.

Building energy consumption prediction for residential buildings using deep learning and other machine learning techniques

Abstract: The high proportion of energy consumed in buildings has engendered the manifestation of many environmental problems which deploy adverse impacts on the existence of mankind. The prediction of building energy use is essentially proclaimed to be a method for energy conservation and improved decision-making towards decreasing energy usage. Also, the construction of energy efficient buildings will aid the reduction of total energy consumed in newly constructed buildings. Machine Learning (ML) method is recognised as the best suited approach for producing desired outcomes in prediction task. Hence, in several studies, ML has been applied in the field of energy consumption of operational building. However, there are not many studies investigating the suitability of ML methods for forecasting the potential building energy consumption at the early design phase to reduce the construction of more energy inefficient buildings. To address this gap, this paper presents the utilization of several machine learning techniques namely Artificial Neural Network (ANN), Gradient Boosting (GB), Deep Neural Network (DNN), Random Forest (RF), Stacking, K Nearest Neighbour (KNN), Support Vector Machine (SVM), Decision tree (DT) and Linear Regression (LR) for predicting annual building energy consumption using a large dataset of residential buildings. This study also examines the effect of the building clusters on the model performance. The novelty of this paper is to develop a model that enables designers input key features of a building design and forecast the annual average energy consumption at the early stages of development. This result reveals DNN as the most efficient predictive model for energy use at the early design phase and this presents a motivation for building designers to utilize it before construction to make informed decision, manage and optimize design.

Building energy consumption prediction for residential buildings using deep learning and other machine learning techniques

Abstract: The high proportion of energy consumed in buildings has engendered the manifestation of many environmental problems which deploy adverse impacts on the existence of mankind. The prediction of building energy use is essentially proclaimed to be a method for energy conservation and improved decision-making towards decreasing energy usage. Also, the construction of energy efficient buildings will aid the reduction of total energy consumed in newly constructed buildings. Machine Learning (ML) method is recognised as the best suited approach for producing desired outcomes in prediction task. Hence, in several studies, ML has been applied in the field of energy consumption of operational building. However, there are not many studies investigating the suitability of ML methods for forecasting the potential building energy consumption at the early design phase to reduce the construction of more energy inefficient buildings. To address this gap, this paper presents the utilization of several machine learning techniques namely Artificial Neural Network (ANN), Gradient Boosting (GB), Deep Neural Network (DNN), Random Forest (RF), Stacking, K Nearest Neighbour (KNN), Support Vector Machine (SVM), Decision tree (DT) and Linear Regression (LR) for predicting annual building energy consumption using a large dataset of residential buildings. This study also examines the effect of the building clusters on the model performance. The novelty of this paper is to develop a model that enables designers input key features of a building design and forecast the annual average energy consumption at the early stages of development. This result reveals DNN as the most efficient predictive model for energy use at the early design phase and this presents a motivation for building designers to utilize it before construction to make informed decision, manage and optimize design.

Seismic retrofitting of existing frame buildings through externally attached sub-structures: State of the art review and future perspectives

Abstract: Earthquakes cause serious damage to buildings and result in heavy losses to society, therefore, it is necessary to enhance the seismic capacity of existing buildings via structural retrofitting. The traditional retrofitting approaches are based on the component-level, but their improvement effect for the overall structure is not obvious. The ultimate goal of seismic retrofitting is to improve the overall seismic performance of the whole structure, thus a variety of external sub-structure retrofitting methods have been developed at home and abroad since the 1970s. The external sub-structure is connected with the existing structure as a whole on the structural-system-level, and it is of great significance for lifeline projects or non-interrupted buildings. At this stage, the external sub-structure retrofitting technology has received wide attention in the seismic community and is still developing in bloom. This paper gives a state of the art review of the advances and research interests of the external sub-structure retrofitting technology. First, the general concepts of the external sub-structure retrofitting technology are given, including (1) retrofitting principle and (2) retrofitting superiority. Then, the typical types of the external sub-structure retrofitting technology are summarized, including (1) external frame sub-structures, (2) external frame-brace sub-structures, (3) external wall sub-structures and (4) other external sub-structures. Finally, some critical issues of the external sub-structure retrofitting technology are extracted, including (1) interfacial shear transferring mechanism, (2) joint property and connection performance, (3) combination with precast-assembly technology, (4) combination with prestress technology, (5) numerical approach and assessment indicators, (6) optimization strategy and design procedure, (7) environment interaction and maintenance cost, and (8) application in practical engineering. The future perspectives of the external sub-structure retrofitting technology are also pointed out, and the contents can provide some reference for the subsequent research as well as the developing trend in the future. • State of the art review and future perspectives of the well-known external sub-structure retrofitting technology. • Give the general concepts and summarize the typical types of the external sub-structure retrofitting technology. • Extract eight critical and technical issues of the external sub-structure retrofitting technology worthy of attention. • Point out the further developing trends and potential technical improvements of the external sub-structure retrofitting technology.

The role of nanomaterials in geopolymer concrete composites: A state-of-the-art review

Abstract: Geopolymers are novel cementitious materials that have the potential to replace conventional Portland cement composites completely. The production of geopolymer composites has a lower carbon footprint and uses less energy than the production of Portland cement. Recently efforts have been made to incorporate different types of nanoparticles (NPs) in geopolymer composites to enhance the properties of the composite with improved performances. Nanotechnology is one of the most active research areas with novel science and valuable applications that have gradually gained attention, especially during the last two decades. Many studies have been undertaken to date in order to understand better the impacts of NPs addition on the fresh, physical, mechanical, durability, and microstructure properties of geopolymer composites. In the current comprehensive review paper, the effects of different NP types on the most essential fresh, mechanical, durability, and microstructure characteristics of geopolymer paste, mortar, and concrete composites were reviewed, analyzed, and discussed in detail. In this regard, more than 280 published papers were used to create an extensive database that includes the main features of geopolymer composites modified with different NPs. In addition, the main mechanisms behind the influence of different NP types on the properties of geopolymer composites were examined. Past progress, recent drifts, current obstacles, and the benefits and drawbacks of these geopolymer composites enhanced with NPs were also highlighted. Based on the findings of this study, the addition of NPs has a promising future for developing high-performance geopolymer composites that the construction industry can efficiently implement due to significant improvements in strength, durability, microstructure by providing additional C–S–H, N-A-S-H, and C-A-S-H gels as well as filling nano-pores in the geopolymer matrix.

Hydration, reinforcing mechanism, and macro performance of multi-layer graphene-modified cement composites

Abstract: Multi-layer graphene (MLG) has excellent mechanical properties and a unique stacked structure. In this paper, sulphoaluminate cement replaced ordinary portland cement to prepare low-carbon ecological ultra-high-performance-concrete (UHPC); the effects of MLG on the hydration, microstructure, and mechanical properties of UHPC were investigated, revealing the hydration mechanism and reinforcing mechanism of MLG on UHPC. Results show that adding MLG can significantly enhance the macro performance of UHPC. When the MLG content is 0.08%, UHPC has better macro performance. Compared with the M0 group, the flexural strength and compressive strength of the M3 group increased by 31.6%, 35.3%, 43.3%, 50.9%, and 9.5%, 13.5%, 22.2%, 21.7% after curing for 1 d, 7 d, 28 d, and 56 d, respectively. We quantitatively characterized the content of hydration product changes in UHPC. Various characterization analyses showed that the adsorption effect and nucleation effect of MLG promoted the hydrolysis and ions exchange of Ca2+ and Al3+, which provided sites for the growth of hydration products and accelerated the hydration process of cement, forming more hydration products, including AFt (ettringite) and AH3 (gibbsite). AFt, AH3, and MLG are closely connected, filling the pores and reducing the porosity of the matrix, optimizing the pore structure, and the medium and large pores transformed into micro-nano pores. Revealing the multi-level reinforcing mechanism, namely hydration products (AFt, AH3) and MLG filling the pores; MLG prevented the extension of micro-cracks and changed micro-cracks development path through filling effect, deflection effect, pulling out, and bridging effect.

Properties of geopolymer sourced from construction and demolition waste: A review

Abstract: Geopolymers have been recognised as a viable replacement to ordinary Portland cement (OPC), providing a cleaner solution since it can significantly reduce greenhouse gas emissions as well as accomplishing effective waste recycling. Construction and demolition waste (CDW) has been recently identified as raw materials for geopolymers due to its availability and high contents of silica and alumina. This paper aimed at reviewing the current state-of-the-art on the geopolymer paste, mortar, and concrete production and their properties, with special attention paid to geopolymers incorporating CDWs. The review covers brief assessment of using CDWs in concrete, the mix design of geopolymer mixtures in addition to identification of the main factors influencing the performance of geopolymer containing CDW. The most recent data related to the mechanical and durability properties of CDW-based geopolymers are presented, while the cost and environmental impacts of using recycled materials in producing geopolymer concretes are also discussed. Geopolymer concretes have a vast range of possible applications, however, there are still several barriers facing commercialisation of geopolymers in construction industry. The review indicated that it is possible to produce geopolymer concretes from CDW-based materials with properties comparable to OPC-based ones; however, the selection of proper material composition should be carefully considered, especially under normal curing conditions. • Use of construction and demolition wastes (CDWs) in geopolymer materials were assessed. • Factors affecting CDW-based geopolymers were discussed. • Mechanical and durability properties of CDW-based geopolymer materials were evaluated. • Use of CDWs and other wastes in geopolymers were discussed cost- and environmental impact-wise. • Challenges to large-scale adoption of geopolymers were highlighted for future research.

Effect of different burning degrees of sugarcane leaf ash on the properties of ultrahigh-strength concrete

Abstract: The global expansion of agricultural production increases agricultural waste ash (AWA). Accordingly, AWA should be disposed to preserve the environment. This study focuses on using AWA as a partial substitute for cement to produce ultrahigh-strength concrete (UHSC). This research investigated the effect of using sugarcane leaf ash (SLA) as a pozzolanic material on the properties of UHSC. The cement replacement rates by SLA were 10%, 20% and 30% by weight. SLA was heat-treated at 400, 500, 600, 700 and 800 °C for 2 h to improve its physical and chemical properties. The effects of the heat-treated SLA on UHSC mechanical properties such as, compressive strength, split tensile strength, flexural strength and modulus of elasticity, were studied. The effects of heat-treated SLA on UHSC durability such as, water permeability, chloride penetration and sorptivity of UHSC were also investigated. In addition to, microstructure analysis of several UHSC mixtures was presented. Results showed the efficiency of SLA as a partial substitute of the 20% of cement weight with mechanical properties and durability higher than the mechanical properties and durability of the reference mixture. Compared with the reference mixture, the heat-treated SLA used as a partial substitute generally improved all properties. The UHSC containing SLA heat-treated at 700 °C and a 20% substitution rate achieved the best results of 162.5, 17.78, 24.05 and 55,820 MPa for compressive strength, tensile strength, bending strength and modulus of elasticity at test age of 28 days.

Fiber-reinforced alkali-activated concrete: A review

Abstract: Alkali-activated materials (AAMs) received broad recognition from numerous researchers worldwide and may have potential applications in modern construction. The combined use of AAM and steel fibers are superior to typical binder systems because the matrix and fibers exhibit superior bond strength. The results obtained by various authors have shown that good dispersion of the fibers ensures good interaction between the fibers and the AAM matrix. The tensile strength of FR-AAC is superior to that of Ordinary Portland cement (OPC)-based materials, with the addition of silica fume (SF) being particularly remarkable. However, the tensile strength of fiber-reinforced alkali-activated concrete (FR-AAC) decreases with increasing fiber length. The bond strength increases with the increasing grade of concrete, the roughness of interface, and the solution's strength activated by alkalis. Regardless of fiber type, AAC's modulus of elasticity is linearly correlated with compressive strength. Fibers can affect the modulus of concrete due to the stiffness of the fiber and the porosity of the composite. Poisson's ratio for AAC corresponded to the ASTM C469-14 standard (about 0.22) and decreased to about 0.15–0.21 with silica fume addition. There are limited resources for the experimental Poisson's ratio and it is only estimated using the predictive equations available. Therefore, it is necessary to conduct additional experimental studies to estimate Poisson's ratios for FR-AAC composites. Retention of 59% and 44% in flexural strength during exposure at 800 °C and 1050 °C was observed in the FR-AAC stainless steel composite, and the chopped alumina fibers achieved higher yield strength at these temperatures. For FA-based AAC mortars with 1% SF with a hooked end, activated with a solution of NaOH and sodium silicate, an increase in the number of bends increased the bond strength, load pull-out and maximum pull-out strength. Autogenous shrinkage and drying shrinkage increase with higher silicate content, while shrinkage decreases with higher NaOH concentration. Relatively little research has been completed on FR-AAC in terms of durability or different environmental conditions. In addition, trends of development research toward the broad understanding regarding the application possibilities of FR-AAC as appropriate concrete materials for developing robust and green concrete composites for modern construction were extensively reviewed.

Fiber-reinforced alkali-activated concrete: A review

Abstract: Alkali-activated materials (AAMs) received broad recognition from numerous researchers worldwide and may have potential applications in modern construction. The combined use of AAM and steel fibers are superior to typical binder systems because the matrix and fibers exhibit superior bond strength. The results obtained by various authors have shown that good dispersion of the fibers ensures good interaction between the fibers and the AAM matrix. The tensile strength of FR-AAC is superior to that of Ordinary Portland cement (OPC)-based materials, with the addition of silica fume (SF) being particularly remarkable. However, the tensile strength of fiber-reinforced alkali-activated concrete (FR-AAC) decreases with increasing fiber length. The bond strength increases with the increasing grade of concrete, the roughness of interface, and the solution's strength activated by alkalis. Regardless of fiber type, AAC's modulus of elasticity is linearly correlated with compressive strength. Fibers can affect the modulus of concrete due to the stiffness of the fiber and the porosity of the composite. Poisson's ratio for AAC corresponded to the ASTM C469-14 standard (about 0.22) and decreased to about 0.15–0.21 with silica fume addition. There are limited resources for the experimental Poisson's ratio and it is only estimated using the predictive equations available. Therefore, it is necessary to conduct additional experimental studies to estimate Poisson's ratios for FR-AAC composites. Retention of 59% and 44% in flexural strength during exposure at 800 °C and 1050 °C was observed in the FR-AAC stainless steel composite, and the chopped alumina fibers achieved higher yield strength at these temperatures. For FA-based AAC mortars with 1% SF with a hooked end, activated with a solution of NaOH and sodium silicate, an increase in the number of bends increased the bond strength, load pull-out and maximum pull-out strength. Autogenous shrinkage and drying shrinkage increase with higher silicate content, while shrinkage decreases with higher NaOH concentration. Relatively little research has been completed on FR-AAC in terms of durability or different environmental conditions. In addition, trends of development research toward the broad understanding regarding the application possibilities of FR-AAC as appropriate concrete materials for developing robust and green concrete composites for modern construction were extensively reviewed. • Alkali-activated concrete has the potential use to replace the ordinary Portland cement. • Alkali-activated concrete offers rapid and high strength development. • Fiber-reinforced alkali-activated concrete has attracted the interest of many researchers worldwide. • Addition of natural fiber as reinforcement is a relatively novel advancement in concrete composites. • Research on the durability of microfiber-reinforced AAC mortars for rehabilitation is required.

Microstructure of ultra-high-performance concrete (UHPC) – A review study

Abstract: A comprehensive study of the microstructural properties of ultra-high performance concrete (UHPC) provides essential information about the underlying causes of its mechanical properties. The present article reviews studies that used X-ray diffraction (XRD), scanning electron microscope (SEM), mercury intrusion measurement (MIP), energy-dispersive X-ray spectroscopy (EDS), and thermal analysis to investigate the microstructure of UHPC containing silica sand and different cementitious materials as partial replacement of cement, including silica fume, zeolite, ground-granulated blast furnace slags, lithium slag, metakaolin, limestone powder, and rice husk ash. Moreover, the importance of microstructural analyses for expressing the cause of optimal percentages of different cement replacements, determining the best type of pozzolan, the appropriate sand in UHPC, and the appropriate curing method to create the best mechanical properties were highlighted. The results proved the rather small transition zone in the UHPC indicating a strong bond between the cement paste and the aggregates, and a very dense internal structure.

A review on shrinkage-reducing methods and mechanisms of alkali-activated/geopolymer systems: Effects of chemical additives

Abstract: Alkali-activated binders or geopolymers are identified as an ideal substitute for ordinary Portland cement (OPC) binders because of their outstanding mechanical characteristics and durability. However, the high-magnitude shrinkage for alkali-activated composites induces uneven deformation across the material and further triggers the formation of harmful cracks, which creates ways for various aggressive substances to permeate the composites, severely reducing the load capacity and threatening the durability of concrete structures. Recently, relevant researchers have reported adding chemical additives is an effective way in alleviating the shrinkage for alkali-activated or geopolymer systems. However, to date, only limited information summarizing and classifying these chemical additives and their shrinkage-reducing mechanisms is available. Therefore, this paper presents a well-documented literature review on the shrinkage characteristics for alkali-activated or geopolymer composites, and systematically summarizes chemical additive types and their shrinkage-reducing mechanisms. The frequently-used chemical additives in alkali-activated or geopolymer systems can be divided into four types: expansive agents (EAs), shrinkage-reducing admixtures (SRAs), superabsorbent polymers (SAPs), and nano-particles (NPs). Then, the influences of these chemical additives on the mechanical behavior and shrinkage for geopolymer or alkali-activated systems were compared and discussed. It was found that the inclusion of SAPs achieved the best shrinkage-mitigating effect, followed by SRAs, EAs, and NPs, respectively. There were about 30%, 45%, and 55% declines in the shrinkage of alkali-activated or geopolymer systems when 3% NPs, EAs, and SRAs were added. Whereas, a reduction of about 70% can be observed by incorporating only 0.3% SAPs. Additionally, it is concluded that the shrinkage reduction mechanisms achieved by the application of these chemical additives are primarily ascribed to densifying the pore structures, reducing the total porosity as well as the proportion of mesopores, coarsening the pore structures, and promoting the generation of crystalline phases (i.e., calcium hydroxide, AFt, and AFm).

Effect of aggregate and fibre types on ultra-high-performance concrete designed for radiation shielding

Abstract: This research examines the properties of ultra-high-performance (UHPC) and heavyweight radiation shielding concrete (UHPHSC). Several types of heavy-weight fine aggregates (sand, magnetite, hematite ilmenite and barite) were used to achieve these properties. In addition, the different types of fibres (steel fibre, lead fibre and basalt fibre) with a volume fraction of 2% were used. The fresh properties of workability and density, and hardened properties of compressive strength, splitting tensile strength, flexural strength, and water permeability were studied. Radiation attenuation was measured at two different gamma-ray energies at 137Cs0.662 and 60Co 1.173 (MeV) sources. Linear attenuation coefficient, half-value layer and tenth-value layer were evaluated. UHPHSCs were exposed to different temperatures at 22 °C, 250 °C, 500 °C and 750 °C to study their effect on the compressive strength and the mechanical shielding properties of gamma rays. The highest density of concrete, 3850 kg/m3, was achieved using magnetite aggregate and steel fibre. Although the highest compressive strength of 180.6 MPa was achieved using Ilmenite aggregate and steel fibre, the best radiation protection properties were achieved using lead fibre and magnetite aggregates.

A systematic review of bacteria-based self-healing concrete: Biomineralization, mechanical, and durability properties

Abstract: Cracking is one of the major deteriorating causes of concrete, which allows the entrance of chemicals and can lead to the loss of physico-mechanical and durability properties of concrete structures. To protect, repair, and rehabilitate concrete structures, the application of different surface coating agents and sealants, binding agents, as well as adhesives has been commonly practiced. Although such techniques have mostly been applicable, due to their inherent mechanism difference, major challenges such as delamination and lack of cost effectiveness have resulted in searching for alternative methods of crack sealing or self-healing. One of the novel self-healing mechanisms is using bacterial induced calcite precipitation in concrete mixtures to heal concrete cracks. In this technique, bacterial mineralization (biomineralization) is performed through decomposing urea and calcium to produce calcium carbonate (CaCO 3 ), which can fill cracks. To review the mechanisms ruling this precipitation, this article aims to present an in-depth analysis of biomineralization, CaCO 3 precipitation, physico-mechanical, durability and microstructural properties of bacterial concrete. To do this, over 70 research articles have been reviewed and their data including the types and dosage of bacteria, mixture proportions, as well as the result of mechanical and durability tests are gathered, provided and analyzed. Based on this review, it is found that the biomineralization is mostly dependent on factors such as the applying method and consistent preservation of the living bacteria. In addition, the environmental impact of bacterial concrete is found to be directly linked with the urea content in the concrete mixture. • A review of bacteria-based calcium carbonate precipitation for self-healing of concrete is presented. • In bacterial concrete , alkaliphiles bacteria is mostly used due to their high resistance to alkalinity. • Bacterial concrete has an enhanced mechano-durability properties due to high compaction and reduced defects. • The environmental impact of bio-concrete is directly linked with the amount of urea used.

Effect of fillers on the behaviour of low carbon footprint concrete at and after exposure to elevated temperatures

Abstract: Low carbon footprint concrete (LCFC), which is produced by using fillers, such as ground granulated blast furnace slag (GGBFS), fly ash (FA) and silica fume (SF), etc. to replace partial cement, has become increasingly popular due to its low-cost, sustainable and superior mechanical performance. This paper establishes a systematic and scientific experimental study to investigate the effect of GGBFS, FA and SF on the behaviour of LCFC at and after exposure to elevated temperatures. The heating temperature – time curve, mass loss, surface change, spalling behaviour, failure mode and residual compressive strength of ten groups of concrete mixes with different filler types and replacement volumetric ratios were studied at and after exposure to 400, 600, 800 and 1000 °C. Test results showed that the heat-insulation capacity of LCFC was enhanced. Besides, explosive spalling was observed only for concrete containing SF with replacement ratio ≥10% at elevated temperatures ≥600 °C. The larger the ratio, the higher was the probability of spalling. To avoid this undesirable failure mode, concrete's wet packing density ≤0.8280 was recommended. Moreover, the residual compressive strength (index) improved for concrete containing OPC only, GGBFS and FA (≤25% replacement ratio) after exposure to 400 °C due to rehydration effect. After exposure to elevated temperatures ≥600 °C, the residual strength reduced significantly. For concrete containing GGBFS and FA, the residual strength (index) was larger than that of OPC concrete. Lastly, it was found that the prediction of EC2 was conservative by comparing the measured residual strength of concrete with and without fillers with that predicted by the code.

A comprehensive review on effects of mineral admixtures and fibers on engineering properties of ultra-high-performance concrete

Abstract: The unparalleled attributes of ultra-high-performance concrete (UHPC) reported over the last three decades sum up the development of this material in two phases: UHPC and ultra-high-performance fiber-reinforced concrete (UHP-FRC)/ultra-high-performance hybrid fiber-reinforced concrete (UHP-HFRC). The integration of scientific knowledge pertaining to material interactions and technical observations of developed UHPC has laid the foundation for further research and development. Microstructural research has revealed the contribution of finer sizes mineral admixtures along with lower water/binder ratios in the range of 0.16–0.24 to the development of high-density calcium silicate hydrate with a very low possibility of ettringite formation and alkali silica reactions in UHPC matrix. The addition of fibers is challenging when seeking to maintain the rheology of UHPC; therefore, technically sound concrete experts are required for the field applications. The challenges preventing the widespread use of UHPC are the higher initial cost, the requirement of special skilled labor for execution, and the lack of open discussions about various UHPC standards available worldwide to reach an agreement on minimum strength achievements and test standards. The hurdles hindering the use of UHPC in recent emerging 3D printing technology are also discussed in the present study. The vast literature compilation also reveals that less research has concentrated on UHP-HFRC as compared to UHPC and UHP-FRC. Therefore, a comprehensive review regarding the effects of mineral admixtures and fibers on the microstructural characteristics , fresh properties, and mechanical properties overall to address the upcoming challenges preventing the widespread use of UHPC and UHP-FRC/UHP-HFRC is essential.

Thermal comfort in hospital buildings – A literature review

Abstract: Hospital buildings are required to secure a variety of indoor environments according to the diverse requirements of patients and staff. Among these requirements, thermal comfort is an important design criterion for indoor environmental quality that affects patients' healing processes and the wellbeing of medical staff. The patients’ thermal comfort is given priority due to their medical conditions and impaired immune systems. Thermal comfort and related contexts have been well-covered in many research articles; however, the number of review articles is limited. This article aims to conduct a holistic and critical review of existing studies offering insights on future research trends (180 articles were analyzed). The key research themes are identified using scientometric analysis. Focus is on influencing factors, field-surveys, improving measures and energy saving related to thermal comfort. The primary outcome concludes that ventilation systems play a key role in maintaining acceptable, thermally-comfortable conditions for patients and medical staff. It is also found that acceptable thermal comfort is highly case-dependent and varies substantially based on the health condition of the patient as well as the type and level of staff activities. The measures currently mentioned to minimize energy consumption are also discussed. Some interesting issues, including the inaccuracy arising from the use of predicted mean vote (PMV) and the impact of gender, age, and related factors on thermal comfort, have been noted. This review provides insights into the design and assessment of hospital thermal environments.

A review on indoor green plants employed to improve indoor environment

Abstract: With the urban development, indoor air quality (IAQ) is of growing public health concern due to that fact people spend 80%–90% of their time indoors, which has prompted the use of plants to reduce the air pollution through the phytoremediation from interior spaces, especially in the enclosed rooms with air-conditioning and heating. Indoor plants have been proved to improve the indoor environment, relieve anxiety, and reduce CO2 concentration. However, the comprehensive review has not been published to summarize the development status and potential deficiencies of indoor green plants after 2018. The 50 published articles related to indoor green plants were selected by the primary retrieval system and the later manual screening. This review mainly focused on the effects of green plants on the indoor thermal environment and indoor pollutants including volatile organic compounds (VOCs), and CO2 concentration, while the application efficiency of green plants was described on learning or productivity efficiency, patients' post-operative recovery and emotion comprehensively.

Effects of recycled fine aggregates on properties of concrete containing natural or recycled coarse aggregates: A comparative study

Abstract: Most of the past studies related to recycled concrete aggregates (RCA) dealt with only coarse RCA (CRCA), while there were many hesitations regarding incorporation of fine RCA (FRCA) into concrete. Therefore, the present study analyses the compatibility of FRCA with coarse natural aggregates (CNA) and CRCA based on their combined influence on concrete. In this study, the original concrete (produced on-site and tested in the laboratory) was broken down to 50–70 mm with a hand hammer, followed by more size reduction using a jaw crusher (maximum size∼25 mm). Further, they were graded into CRCA and FRCA as per IS 383. FRCA was used directly in concrete, but CRCA was ground further in an abrasion machine. 30%, 60% and 100% FRCA (as a replacement of fine natural aggregates (FNA) by volume) were utilised either with 100% CNA or 100% CRCA to study their effect on fresh properties (workability and density), mechanical properties (compressive, flexural and split tensile strength) and durability properties (water permeability and carbonation) of concrete. The properties of recycled concrete were mostly inferior to conventional concrete at each curing age (except for 90 days compressive strength of concrete incorporated with 30% FRCA). However, the performance gap between conventional and recycled concrete was reduced with an increase in curing age. The recycled concrete containing three different combinations of FRCA and CRCA (0% and 100%, 30% and 0%, 30% and 100%) satisfied IS 10262's target compressive strength criteria for M30 grade concrete. The density of RCA affected the concrete properties more than its water absorption. Also, the water permeability of recycled concrete (followed by its carbonation depth and compressive strength) was most influenced by incorporation of RCA. Conclusively, it was found that FRCA is more compatible with CNA at 30% FNA replacement and with CRCA at 60% and 100% FNA replacement.

Enhanced early hydration and mechanical properties of cement-based materials with recycled concrete powder modified by nano-silica

Abstract: In recent years, an ever-increasing amount researchers dedicated themselves to exploring the possibility of introducing recycled concrete powder (RCP) into concrete as a substitute for cement. To optimize the effect of RCP on cement-based materials, this paper uses nano-silica (NS) to learn the hydration and mechanical properties of cement-based materials with RCP. The results indicated that after adding NS into RCP-cement pastes, the setting time of cement pastes was significantly reduced, while the samples' early hydration rate and hydration heat increased. Besides, the mechanical strength of the mortar decreased as RCP replaced part of the cement, while 2% NS can compensate for the mechanical strength loss of mortar caused by RCP as supplementary cementing materials. The X-ray computer tomography (X-ray CT) and mercury intrusion porosimetry (MIP) results showed that RCP increased mortar's pore volume fraction and porosity. In contrast, NS in RCP blended mortar significantly decreased the number of pores with a pore volume between 0.01 and 0.03 mm3 and increased the proportion of harmless pores (From 28.6% to 31.4%). Hence, NS reduced the pore volume fraction and porosity of mortar. The results of X-ray CT and MIP showed that NS could refine the pore size in RCP blended mortar. X-ray diffraction (XRD) and scanning electron microscope (SEM) further revealed that the existence of NS can eliminate the adverse effects brought by RCP.

Buildings with less HVAC power demand by incorporating PCM into envelopes taking into account ASHRAE climate classification

Abstract: In this study, focusing on comfort time, the effect of phase change material (PCM) presence in ten climatic zones with an average temperature of 13.1–26.9 °C, cooling degree-days of 2500–6700 and heating degree-days of 400–2800 were discussed. Numerical results were deduced by developing energy equations for the whole building along with momentum and continuity equations for PCM. The results showed that for all regions adding PCM significantly increases comfort time. If the PCM is installed closer to the indoor, its comfort time is longer than other locations. To select a suitable PCM, five materials with a melting temperature in the range of 18–24 °C were selected and it was observed that a suitable PCM has a slight dependence on the comfort temperature range. By defining the comfort range 18–27 °C, it was found that for a simple building (without PCM), the comfort time percent varied in the range of 26–40%. With the addition of PCM, it was observed that the comfort time percent varied in the range of 54–82%. In other words, in the presence of a suitable PCM without energy consumption, the internal temperature can be set in the range of 18–27 °C up to 82% in a year. In this scenario, PCM-22 was suitable for six regions (out of ten regions). For scenarios of 20–25 °C, it was found that PCM-23 was suitable for eight regions. If PCM-23 was added to conventional buildings, without energy consumption at least in 54% of a year, the temperature can be set in the range of 20–25 °C.

Efficient estimating compressive strength of ultra-high performance concrete using XGBoost model

Abstract: An ensemble technique using XGBoost model is employed to predict the compressive strength of ultra-high performance concrete (UHPC). A 931 UHPC mixture collection with 17 input variables is employed, in which 230 were from laboratory experiments and the rest from scientific literature. The best results are obtained by tuning the hyper-parameters using Pareto multi-objective optimisation to find the optimum values of R 2 for both train and test dataset . The obtained solution with R 2 = 0.8922, RMSE = 7.860 MPa, MAE = 5.930 MPa show better performance with those from previous study. Partial dependence plots are illustrated to investigate the effects of some important input variables on the compressive strength of UHPC. Graphical User Interface (GUI) is written in Python and provided freely for users to support the design and interpretation the results of UHPC. This model could be benefit in the development of new dosages of UHPC by reducing the time and cost of the experimental campaign, which allows the preselection of components with better response in the model. • XGBoost model is used to predict compressive strength predictions of Ultra-High Performance Concrete. • Partial dependence plots are illustrated to reveal the inherited disadvantages of black-box model. • GUI is provided freely for users to support the design and interpretation the results. • The comparison with previous study shows higher prediction accuracy.

Self-centring hybrid-steel-frames employing energy dissipation sequences: Insights and inelastic seismic demand model

Abstract: This paper explored the seismic behaviour of self-centring hybrid-steel-frame (SC-HSF) employing energy dissipation sequences and the corresponding inelastic seismic demand model. The SC-HSF employing energy dissipation sequences was composed of the self-centring main frame (SCMF) and energy dissipation bays (EDBs). Two prototype structures were designed and developed using modelling techniques validated by experimental data. Nonlinear cyclic pushover analyses and nonlinear dynamic analyses were conducted to examine the seismic behaviour of the prototype structures. The seismic response of prototype structures including peak interstorey drifts and post-earthquake residual interstorey drifts were examined in detail. After verifying the promise of the SC-HSF structures, the energy factor for quantifying the inelastic seismic demand was developed by nonlinear spectral analyses based on the equivalent single-degree-of-freedom (SDOF) systems assigned with the structural hysteretic model. The effects of the structural hysteretic parameters on the mean and probabilistic features of the energy factors were discussed in detail. In addition, the lognormal distribution was selected to develop a probabilistic spectral seismic demand model based on a comparative study, and the prediction equations were developed to simulate the probabilistic features of the energy factors. Finally, the probabilistic spectral seismic demand model was used for evaluating the behaviour of the prototype structures, and the sufficiency of the model was justified.

Impact of sulfate activation of rice husk ash on the performance of high strength steel fiber reinforced recycled aggregate concrete

Abstract: One of the sustainable substitutes for traditional concrete is to incorporate recycled concrete aggregates (RCA) as a substitute for natural aggregates and rice husk ash (RHA) as a partial substitute for Portland cement. Worldwide request for high-strength concrete (HSC) is raising quickly. HSC is very brittle, as it needs some type of reinforcement. Lately, hooked steel fibers (HSF) are gaining momentum in the concrete industry due to their high tensile strength. The problem with RHA-RCA concrete is its low early strength due to which researchers have suggested utilizing chemical activators (sodium sulfate) to enhance the early age strength of RHA concrete. In the present research, compression, and split tensile strength were assessed. For durability properties, water absorption, chloride penetration, sorptivity, and acid resistance test was conducted. It was noted that recycled aggregate concrete with chemically activated RHA had considerably improved strength than samples with no sodium sulfate, particularly in early age strength. The mix (R35-45RHA–SF–A) showed increased compression and split tensile strength among all mixes at 90 days. At 70% recycled aggregate, activated concrete with 45% RHA and 2% HSF displayed enhanced strength to the reference mix. The positive impact of the activator was likewise observed in the durability characteristics of samples with recycled aggregates. X-ray diffraction (XRD) analysis confirmed the development of strength of RHA concrete at later ages. Chemically activation of RHA could be a beneficial answer to address the problem of low strength and durability of RHA modified high strength fiber reinforced recycled aggregate concrete.

A systematic review of waste materials in cement-based composites for construction applications

Abstract: There is a remarkable impact of the construction industry on the environment, contributing considerably to CO2 emissions, natural resource dwindling, and energy demand. The construction sector is now trending toward using alternative building materials in place of natural resources and cement, therefore decreasing environmental impact and increasing sustainability. The research carried out for sustainable development based on waste material utilization in cement-based composites has been reviewed in this study. Two approaches have been adopted in this review, i.e., a scientometric analysis and a comprehensive manual review. Scientometric analysis was performed to provide the statistical overview of the present research over the last two decades. The scope of the study was narrowed to the utilization of waste materials, including recycled aggregates from construction and demolition waste, waste glass, rice husk ash , and natural fibers in cementitious composites for construction sustainability. Moreover, their various aspects were described in detail, including the influence on mechanical and microstructural characteristics of materials, sustainability aspect, limitations, and possible improvement techniques. It was concluded that utilizing these waste materials in cementitious materials may lead towards eco-friendly construction; however, their impact on the performance of the resulting material is inconsistent. Their use in lower proportions is favorable, while a higher proportion has detrimental effects on material properties. This study also identified gaps in the present research, and future studies are suggested.

Using machine learning techniques for predicting autogenous shrinkage of concrete incorporating superabsorbent polymers and supplementary cementitious materials

Abstract: Superabsorbent polymers (SAP) are a very effective means of decreasing high-performance and ultra-high performance concrete autogenous shrinkage. However, their efficiency can hardly be predictable because of various parameters: SAP properties, supplementary cementitious materials (SCM) nature, and cement replacement ratios. This study provides a machine learning approach for predicting shrinkage/expansion in cementitious materials incorporating SAP and SCM. A dedicated database is built, and four machine learning models are compared. Extreme Gradient Boosting (XGBoost) model exhibited the highest accuracy. SHapley Additive exPlanations (SHAP) allowed the identification of the most influential inputs, and partial dependence plots provided quantitative information about their relative influence.

Prediction of failure modes, strength, and deformation capacity of RC shear walls through machine learning

Abstract: Shear walls are typically the major lateral load-carrying components in high-rise buildings owing to their high lateral strength and stiffness. This study introduces a technique for predicting the seismic performance of reinforced concrete (RC) walls using machine learning (ML) methods. Based on various ML algorithms , predictive models were developed using a database containing experimental data of 429 RC walls collected from the literature. The performance of each predictive model was discussed in detail. The results indicated that the XGBoost and GB algorithms accurately predicted the failure modes of RC walls with an accuracy of 97%. The gradient boosting and random forest algorithms performed best in predicting the lateral strength and ultimate drift ratio of RC walls, with a mean predicted-to-tested strength ratio of 1.01 and a predicted-to-tested ultimate drift ratio of 1.08. The flexure-to-shear strength ratio and shear-to-span ratio of RC walls had a greater influence on the failure modes of RC walls, with a relative importance factor of 54.1% for these two characteristics. Boundary longitudinal reinforcement, shear-to-span ratio, and distributed reinforcement had an obvious influence on the lateral strength of RC walls with summation of relative important factors of over 80%. The greatest influence on the ultimate drift ratio of RC walls is shear-to-span ratio, with a relative importance factor of 34.1%. The comparisons indicate that the model developed in this study can predict the shear strength and flexural strength of RC walls more accurate and efficient than the existing design formulas. Furthermore, a brief boundary that could separate flexure-shear failure from other failure modes is provided based on the ML models. Finally, a graphical user interface (GUI) platform is created to facilitate the practical design of RC walls. • The performance of ML algorithms in predicting the seismic behavior of RC wall is studied. • ML model developed in this study predict the strength of RC wall more accurate and efficient. • A brief boundary that separate flexure-shear failure from other failure modes is provided.