Concrete System Research Articles

Investigation on the behaviour of concrete composite slab system with different levels of interface shear design

Investigation on the behaviour of concrete composite slab system with different levels of interface shear design

A Review of Waterborne Polymer–Cementitious Composite Repair Materials for Application in Saline Soil Environments: Properties and Progress

The properties of a large number of concrete infrastructures in China are deteriorating year by year, raising the need for repairing and strengthening these infrastructures. By introducing waterborne polymers into a cement concrete system, brittle cracks and easy bonding performance defects of concrete can be compensated for to form a long-life, semi rigid, waterborne polymer-modified cementitious repair material with a promising development prospect. This paper investigates the modification effect of polymer emulsions on ordinary cement mortar. Our research mainly focused on the physical and mechanical properties, durability, microstructure and application status of waterborne polymer-modified cementitious composites. Literature studies show that with the increase in waterborne polymer content (0 wt%~20 wt%), the performance of cement mortar significantly improves, which in turn expands its application range. Compared with ordinary cement mortar, the introduction of waterborne polymers blocks some of the pores in the cement to a certain extent, thus improving its permeability, freeze–thaw resistance and durability. Finally, this paper describes the application of waterborne polymer–cementitious composites in western saline soil environments, as well as discusses the prospects of their development.

Durability and pore structure of metakaolin-based 3D printed geopolymer concrete

An alternative to Portland cement concrete is metakaolin (MK)-based digitally fabricated geopolymer concrete. However, global adoption is sparse due to the prolonged setting time of a two-part geopolymer concrete (GPC) system and the uncertain long-term durability properties. The durability and pore structure of the MK-based 3DPGPC (M1) and slag-modified MK-based 3DPGPC (M2) are examined and juxtaposed with mould-cast specimens. Firstly, the fresh properties, rheological behaviour, compressive and flexural strength of 3DPGPC and cast specimens were characterised. Thereafter, the durability and pore structure are investigated by examining the drying shrinkage, water absorption, capillary and gel porosity, and oxygen permeability index (OPI) and X-ray computed tomography (X-CT) analysis. A 5% slag inclusion reduced workability and final setting time from 17 hours in M1 to 4 hours in M2. Also, slag inclusion increased the initial static and dynamic yield stresses by 0.1 and 2%, respectively, resulting in an increase in buildability from 27 of 42 layers. At the 28-day curing age, the average compressive strength of M2–3DPGPC is 11 and 21% higher than M1–3DPGPC in D1 and D3 specimens, while the flexural strength is 33 and 28% higher, respectively. Drying shrinkage and water absorption are mitigated with slag inclusion, and the OPI compares with OPC concrete. Specimens cored along the printing direction (D3) are less permeable compared to disc specimens’ core in the perpendicular to the printing direction (D1). The M1 and M2–3DPGPC specimens contain lower average CT scan macro pores of 2.98 and 1.81% in comparison to the mould-cast specimens having 4.48 and 4.07%. The porosity is position-dependent in 3DPGPC due to the presence of more voids at the interlayer region. 3DPGPC specimens depicted a more compact pore structure in the range of 0.1–1.7 mm, whereas pores in mould-cast are in the range of 0.1–2.5 mm. The durability index tests indicate that 3DPGPC is a potentially durable material.

Prediction of fracture failure and fracture parameters for dam gallery concrete specimens of arbitrary size and age via boundary effect model and fracture extreme theory

Cracking-associated problems may occur in the construction and operation periods of dam galleries, necessitating attention to the fracture characteristics of gallery concrete. The fracture parameters of concrete exhibit size effects and also change with age. A correct evaluation of the cracking risk or crack stability of gallery structures at any given time requires a comprehensive understanding of both the size effect and time-variant characteristics of the gallery concrete fracture parameters. In the present study, 75 wedge-splitting specimens, with effective heights ranging from 200 mm to 600 mm, were cast using gallery concrete produced by the concrete mixing system at the Baihetan Dam construction site. Subsequently, fracture tests were conducted on these specimens at curing ages spanning from 7 days to 90 days. According to the test results, the fracture parameters of concrete with a specific size exhibited an increasing trend with age within 90 days, while the fracture parameters of concrete at specific ages show a significant size effect, tending to stabilize as the effective depth of specimens gradually increases. The boundary effect model was utilized for analyzing the fracture test results of concrete specimens at different ages, yielding the size-independent double-K fracture parameters and scale parameters for concrete at each age, along with their time-varying patterns. Subsequently, equations for predicting the failure loads of concrete specimens of any age and size were established. Based on the prediction results of failure loads, the double-K fracture parameters of concrete specimens of any age and size were solved by the fracture extreme theory. The predicted failure loads and fracture parameters were in good agreement with the experimental results. The findings of this study can be applied to the full lifecycle crack risk analysis or crack stability assessment of Baihetan Dam gallery structures.

Experimental and numerical study on behavior of channel-shaped GFRP perforated rib shear connectors

Effective shear connections at the interface of Pultruded Fiber Reinforced Polymer (FRP) - concrete hybrid system play a pivotal role in maintaining the structural integrity of composite structures. In this vein, this study presents a comprehensive investigation-encompassing experimental, analytical, and numerical approaches-into the shear behavior of a novel, channel-shaped Glass Fiber Reinforced Polymer (GFRP) perforated rib shear connector (GPRSC), designed for hybrid GFRP-concrete systems. Ten full-scale push-out specimens were tested to investigate the effect of the inclusion and diameter of the perforating rebar, the diameter and the spacing of the perforated hole, and concrete strength on the shear behavior of the channel-shaped GPRSC. The push-out tests highlighted two distinct failure modes: (i) shear failure of concrete dowel, and (ii) debonding failure of interface. To supplement these findings, numerical models were established that incorporate 2D Hashin's theory to account for laminate damage of GFRP. This allowed for an in-depth examination of the load transfer and failure mechanisms of the channel-shaped GPRSC. Finally, calculation formulae for shear resistance and load-slip relationship were proposed. A comparative evaluation between experimental results and values predicted by these formulae yielded a reasonably strong correlation. This research constitutes a significant advancement in the field of hybrid GFRP-concrete systems.

Crack Detection and Analysis of Concrete Structures Based on Neural Network and Clustering.

Concrete is extensively used in the construction of infrastructure such as houses and bridges. However, the appearance of cracks in concrete structures over time can diminish their sealing and load-bearing capability, potentially leading to structural failures and disasters. The timely detection of cracks allows for repairs without the need to replace the entire structure, resulting in cost savings. Currently, manual inspection remains the predominant method for identifying concrete cracks. However, in today's increasingly complex construction environments, subjective errors may arise due to human vision and perception. The purpose of this work is to investigate and design an autonomous convolutional neural network-based concrete detection system that can identify cracks automatically and use that information to calculate the crack proportion. The experiment's findings show that the trained model can classify concrete cracks with an accuracy of 99.9%. Moreover, the clustering technique applied to crack images enables the clear identification of the percentage of cracks, which facilitates the development of concrete damage level detection over time.

Geotechnical and Structural Damages Caused by the 2023 Kahramanmaraş Earthquakes in Gölbaşı (Adıyaman)

On 6 February 2023, two independent earthquake pairs on the East Anatolian Fault Zone, with epicenters in Pazarcık (Mw = 7.7) and Elbistan (Mw = 7.6) districts of Kahramanmaraş province, caused great destruction. Adıyaman and Gölbaşı districts of this city are among the settlements most affected by the earthquake. Especially in the district where geotechnical damages are most observed, the destructive effects of earthquakes have been clearly observed in buildings with different structural systems. In this study, information is given about the earthquakes that hit the region and the fault zone where the earthquakes occur. Geotechnical and structural damages occurring in the villages and center of the district were evaluated within the scope of earthquakes and structural engineering. It can be stated that damages observed in the district center are generally caused by soil–structure interaction problems. The fact that masonry structures, which are widely used in rural areas, do not benefit from any engineering services has an impact on the level of damage. The main reason for the damages occurring in the reinforced concrete structures in the district is the reinforced concrete system that is not designed properly or not built in accordance with the design. This case study demonstrated the importance of earthquake–soil–structure interactions in line with earthquake-resistant building design principles.

Experimental Study of Two-way Half Slab Precast Concrete using Rextangular Rigid Connection

A half-slab precast concrete (HSPC) system with precast bottom layers and in-situ cast top layers has been widely applied in various constructions. It generally behaves as a one-way slab due to the absence of positive-flexural reinforcements in the perpendicular direction to the precast component. However, in some cases, the HSPC was also applied in a two-way slab system. Consequently, a particular design and treatment in the connection between precast members was required, so that the bending moment in two orthogonal directions could be accommodated. In the present study, an innovative rectangular rigid connection (RRC) in a two-way HSPC system was investigated through an experimental test. It was found that the RRC-HSPC presented only a 9.13% reduction of the load at the crack, a 16.44% reduction of the ultimate load, and a 6.06% increase of the deflection at the crack when compared to the monolithic one.

Connecting Actionable Feedback with Course Concepts Using an Auto-Feedback Framework - A Case Study in a Database Course

Effective feedback is crucial in engineering education to ensure students are progressing and staying on track. However, providing such feedback can be complex and time-consuming, leading to delays for students. To address this issue, this paper introduces an auto-feedback framework that aims to connect actionable feedback with course concepts in a personalized and efficient manner. We implemented a concrete feedback system using the framework in a database course. We found that students generally could improve their solutions within a few submissions, and the feedback helped students achieve better learning outcomes.

A Finite Element Modeling Approach for Analyzing the Cyclic Behavior of RC Frames

Numerous approaches and inputs for nonlinear finite element analysis used for modeling reinforced concrete systems under cyclic loads have been outlined. Practitioners usually take into account a number of significant factors when modeling, for example deciding upon the constitutive relations, the connection among concrete and steel reinforcement, and the mesh sensitivities, in order to accurately simulate the nonlinear response of reinforced concrete under cyclic loads. Therefore, it is essential to thoroughly assess popular modeling approaches and develop a reliable modeling approach with reliability, stability, and consistency. A modeling technique and practical guidelines for nonlinear finite element analysis of reinforced concrete frames subjected to cyclic loading are described in this study, taking into account the influence of parameters such as dilation angle, stiffness recovery, friction coefficient, and mesh sizes. The hysteretic force–displacement behavior and load-carrying capacity of reinforced concrete frames subjected to cyclic loading have been compared using numerical and experimental curves. Discrete fracture paths are specified in the model’s geometry to achieve an accurate depiction of the stress distribution and an adequate fit of the hysteretic behavior. The proposed modeling approach provides a precise representation of the stress distribution and hysteretic behavior while keeping computational costs reasonable.

The introduction and development of reinforced concrete structures in modern Suzhou（1919–1933）: a case study of the Cline Hall at Soochow University

ABSTRACT The introduction of reinforced concrete structures to China occurred in the late 19th century via Shanghai and other cities. While Shanghai has been extensively researched in terms of its reinforced concrete structures, Suzhou, located near Shanghai and one of the early adopters of reinforced concrete construction, has received less attention. This study aims to investigate the impact of reinforced concrete structures in early modern Suzhou, focusing on Cline Hall as a case study, which stands one of Suzhou’s earliest buildings with a reinforced concrete structure. Drawing on the close relationship between Suzhou and Shanghai in terms of architectural design, construction technology and materials. The study examines the opportunities for the introduction, the types and layouts of reinforced concrete structure systems, and the forms of materials in modern Suzhou (1919–1933). Additionally, material testing was conducted to provide a preliminary assessment of the aggregate ratios and durability of the reinforced concrete. This paper offers a foundation and recommendations for the conservation of Cline Hall, as well as other modern reinforced concrete buildings in Suzhou. By shedding light on the lesser-explored aspect of reinforced concrete heritage in modern Suzhou, this paper contributes to the broader understanding of architectural history and conservation practices.

Air void system and freezing-thawing resistance of concrete composite with the incorporation of thermo-expansive polymeric microspheres

Air-entraining agent (AEA) was first used in concrete in 1930’s to improve freezing – thawing resistance of concrete. After about 90 years of experience, many debates have been raised regarding the benefit of durability improvement using AEA in concrete. Under this circumstance, polymeric microspheres show promising ability to replace the AEA with the purpose of entraining air in concrete. In this study, thermo-expansive polymeric microspheres were added to concrete. As a comparison, concrete specimens with the addition of AEA were also prepared. The air contents of freshly mixed concrete and hardened concrete were characterized. In addition, compressive strength development was measured. Moreover, the microstructure and air-void system of concrete was characterized by multiple methods. Finally, the dynamic modulus of elasticity and scaling of concrete beams after the cyclic freezing–thawing attack were evaluated. It was found that compared with the addition of AEA, adding polymeric microspheres entrained comparable air content in concrete. The void size distribution of polymeric microspheres mixed concrete is finer than that of AEA mixed concrete, which provides comparable freezing–thawing resistance of concrete in the viewpoint of dynamic modulus. However, due to the potential “internal curing” and nucleation effects with the presence of microspheres, the strength of microsphere-mixed concrete is slightly higher than that of plain concrete, and freezing–thawing caused surface scaling of concrete mixed with microspheres is much less severe than that incorporated with AEA.

Effect of colloidal nano silica on the freeze-thaw resistance and air void system of portland cement concrete

The present study investigates the impact of colloidal nano silica (CNS) on the freeze-thaw durability of concrete, with a particular focus on understanding the fundamental mechanism via a systematic analysis of the air void system. Experimental results suggest that the incorporation of CNS increases the total air content of the sample while reducing the average void size. This phenomenon can be attributed to the remarkable capacity of CNS to stabilize air bubbles within the concrete matrix, by a heightened viscosity and lower surface tension of the fresh concrete mixture. The increase in air void chambers facilitates the release of internal stress during freezing expansion, thereby enhancing the freeze-thaw resistance of the concrete. Additionally, the inclusion of CNS results in the formation of a denser cement matrix that improves the water impermeability of the concrete and prevents the ingress of water and other potentially corrosive substances.

Evaluation of vibration properties of an 18-story mass timber–concrete hybrid building by on-site vibration tests

Timber–concrete hybrid structural systems are a practical option to provide tall mass timber buildings with a lateral load-resisting system. This paper discusses the dynamic behavior of an 18-story timber–concrete hybrid building based on the vibration properties evaluated by on-site vibration tests. First, microtremor measurements and human-powered excitation tests were carried out and the obtained vibration data were analyzed using a stochastic subspace identification method to derive natural frequencies, damping ratios, and mode shapes. Then, a finite-element (FE) model was developed based on detailed structural design information, and its eigenvalues and eigenvectors were compared with the test results. The vibration test results showed various mode shapes, including in-plane deformation of the floor diaphragm composed of cross-laminated timber (CLT) panels. The damping ratios in all the modes were scattered between 1 and 3%, and no frequency dependency was observed. The modal properties of the FE model agreed well with the test results by considering the additional stiffness of non-structural components. In order to simulate the in-plane deformation of the CLT floor diaphragm, detailed modeling of the connection between each CLT floor panel and the connection between CLT floor panels and concrete cores is recommended. The findings provide practitioners with an insight into dynamic properties and FE modeling methods of tall timber–concrete hybrid buildings.

Cost-Benefit Analysis of Earthen Ponds against Concrete Tanks Production System in Fish Farming in Abuja FCT, Nigeria

This study comparatively analysed the costs and benefits of fish production for earthen ponds and concrete tanks system in Abuja (FCT), Nigeria. A reconnaissance survey of the six area councils of the area was carried out to locate the fishers. The study further employed multistage sampling technique to select the study respondents. In all, 80 fishers were chosen. Data for the study were collected from primary sources using a well-structured questionnaire with open-ended and close-ended questions. The data was analysed using descriptive statistics (tables, percentages, frequency and mean). The cost-benefit analysis was determined using simple budgetary techniques such as Gross Margin, Net Farm Income, Benefit Cost Ratio and Profitability Ratio. Multiple regression analysis was employed to analyse the factors that contribute to the technical, allocative and economic efficiencies of the two production systems in the study area. The result showed that the Gross Margin Index (GMI) for earthen ponds is 3,099,978.98 and 2,960,635.08 for concrete ponds with Cost Benefit Ratio of 2.4 and 2.2, respectively. Feed cost in earthen ponds represents 77% of the TVC, while it represents 67% in the concrete tank production system. Though the concrete tank production system uses more feed than the earthen pond production system. The revenue generated from fish sales is greatly influenced by the location and method of sale. The study concludes that earthen pond system was slightly more economic than the concrete tank production system. The study, therefore, recommends that fishers should come together to form a cohesive and strong association which will be able to negotiate with wholesalers and other middlemen for price bargaining.

Numerical Simulation of Soil–Structure Interaction of RC Frame

An Attempt has been made to study the effect of soil media on the response of RC frame structure. Therefore, the present work focuses on the implementation of a two dimensional finite element model of reinforced concrete frame and pile foundation system which explicitly incorporates the soil response. The superstructure members have been represented by means of three-node isoperimetric beam elements with three degrees of freedom per node. The soil mass is idealized by the eight-node isoperimetric quadrilateral element at the near field and five nodes isoperimetric infinite element to simulate the far-field behavior of the soil media. The applicability of this model was demonstrated by analyzing a multi-story building. The results have shown that the influence of the soil behavior on the overall response of the structure.

Evaluation of the Seismic Performance of a Dual Reinforced Concrete System with Different Levels of Torsional Irregularity

En el presente estudio, se analiza el desempeño sísmico de un sistema dual de hormigón armado (pórticos y muros especiales) con diferentes niveles de irregularidad torsional. Se plantean tres arquetipos, cada uno con un nivel de irregularidad torsional distinto (IT 1.0, IT 1.2 e IT 1.4) con la finalidad de evaluar el efecto de la irregularidad torsional en el desempeño sísmico. Los elementos estructurales de los arquetipos cumplen con el diseño sismorresistente. Además, se tomó en cuenta los factores de sobre-resistencia y amplificación dinámica para determinar el corte de diseño en los muros estructurales. Se realizaron análisis estático y dinámicos no lineales para cuantificar las respuestas globales y locales de cada uno de los modelos. Los modelos analíticos de muros estructurales son calibrados en función de los datos obtenidos en ensayos experimentales existentes, de esta manera se valida los elementos tipo fibra (infrmFB) usados y los parámetros de los modelos constitutivos de los materiales. Se realizan análisis dinámicos incrementales (IDA) para cada uno de los arquetipos con los once registros sísmicos seleccionados de la base del PEER. Las curvas IDA son desarrolladas con dos parámetros de demanda ingenieril: derivas de piso y deformaciones unitarias. Finalmente, se elaboran las curvas de fragilidad para los niveles de desempeño de ocupación inmediata, seguridad de vida y prevención de colapso, y se determinan los coeficientes de margen con la finalidad de cuantificar las probabilidades de alcanzar los niveles de desempeño mencionados.

Microcapsule Triggering Mechanics in Cementitious Materials: A Modelling and Machine Learning Approach.

Self-healing cementitious materials containing microcapsules filled with healing agents can autonomously seal cracks and restore structural integrity. However, optimising the microcapsule mechanical properties to survive concrete mixing whilst still rupturing at the cracked interface to release the healing agent remains challenging. This study develops an integrated numerical modelling and machine learning approach for tailoring acrylate-based microcapsules for triggering within cementitious matrices. Microfluidics is first utilised to produce microcapsules with systematically varied shell thickness, strength, and cement compatibility. The capsules are characterised and simulated using a continuum damage mechanics model that is able to simulate cracking. A parametric study investigates the key microcapsule and interfacial properties governing shell rupture versus matrix failure. The simulation results are used to train an artificial neural network to rapidly predict the triggering behaviour based on capsule properties. The machine learning model produces design curves relating the microcapsule strength, toughness, and interfacial bond to its propensity for fracture. By combining advanced simulations and data science, the framework connects tailored microcapsule properties to their intended performance in complex cementitious environments for more robust self-healing concrete systems.

Ballast-Supported Foundation Designs for Low-Cost Open-Source Solar Photovoltaic Racking

Although solar photovoltaic (PV) system costs have declined, capital cost remains a barrier to widespread adoption. Do-it-yourself (DIY) system designs can significantly reduce labor costs, but if they are not attached to a building structure, they require ground penetrating footings. This is not technically and economically feasible at all sites. To overcome these challenges, this study details systems designed to (1) eliminate drilling holes and pouring concrete, (2) propose solutions for both fixed and variable tilt systems, (3) remain cost effective, and (4) allow for modifications to best fit the user’s needs. The ballast-supported foundations are analyzed for eight systems by proposing two separate ballast designs: one for a single line of post systems, and one for a double line of post systems, both built on a 4-kW basis. The results of the analysis found that both designs are slightly more expensive than typical in-ground concrete systems by 25% (assuming rocks are purchased at a landscaping company), but the overall DIY system’s costs remain economically advantageous. Sensitivity analyses are conducted to show how modifications to the dimensions influence the weight of the system and thus change the economic value of the design, so users can trade dimensional freedom for cost savings, and vice versa. Overall, all wood-based PV racking system designs provide users with cost-effective and easy DIY alternatives to conventional metal racking, and the novel ballast systems presented provide more versatility for PV systems installations.

Comparative life cycle assessment of light frame timber and reinforced concrete masonry structural systems for single-family houses in Luxembourg

The building sector's significant greenhouse gas emissions and energy consumption present added challenges to meeting European climate commitments amidst rapid population growth. In Luxembourg, single-family houses dominate the residential buildings, noticeably contributing to construction waste and CO2 emissions. This study compares the environmental impacts of a three-story reinforced concrete masonry single-family house and an identical timber building in Luxembourg, emphasizing greenhouse gas emissions and embodied energy. A cradle-to-grave life cycle assessment was conducted using Building Information Modelling (BIM) models to analyze the global warming potential and primary energy requirements. Environmental product declarations from the producers and the ÖKOBAUDAT German database were used to determine the environmental impacts of the materials. The results show that the timber building outperforms the concrete building with a 43.5% lower global warming potential, while the concrete building demonstrates a 15.6% reduction in primary energy demand. This aligns with the average outcomes of seven similar studies discussed in this paper, at 33.2% and 4.7%, respectively. Moreover, the timber building is 78.6% lighter than the concrete one. When evaluating benefits and loads beyond the system boundary, the timber building provides 3.6 and 4 times greater advantages in terms of global warming potential and primary energy, respectively, compared to the reinforced concrete masonry building. Additionally, the study explores the impact of reusing the floors in the timber building. The cradle-to-grave LCA reveals that reusing the timber slabs improves the building's global warming potential and primary energy by 2.4% and 1.2%, respectively. However, when considering the benefits and loads beyond the system boundary, floor system reuse exhibits a 38.9% surge in global warming advantages while reducing primary energy benefits by 28.1%. The findings advocate for a policy promoting timber construction and reuse in Luxembourg, aiming to achieve the net-zero emission target by 2050.