Advances In Concrete Technology Research Articles

Predictive modeling of compressive strength in silica fume‐modified self‐compacted concrete: A soft computing approach

AbstractSelf‐compacting concrete (SCC) is a specialized type of concrete that features excellent fresh properties, enabling it to flow uniformly and compact under its weight without vibration. SCC has been one of the most significant advancements in concrete technology over the past two decades. In efforts to reduce the environmental impact of cement production, a major source of CO2 emissions, silica fume (SF) is often used as a partial replacement for cement. SF‐modified SCC has become a common choice in construction. This study explores the effectiveness of soft computing models in predicting the compressive strength (CS) of SCC modified with varying amounts of silica fume. To achieve this, a comprehensive database was compiled from previous experimental studies, containing 240 data points related to CS. The compressive strength values in the database range from 21.1 to 106.6 MPa. The database includes seven independent variables: cement content (359.0–600.0 kg/m3), water‐to‐binder ratio (0.22–0.51), silica fume content (0.0–150.0 kg/m3), fine aggregate content (680.0–1166.0 kg/m3), coarse aggregate content (595.0–1000.0 kg/m3), superplasticizer content (1.5–15.0 kg/m3), and curing time (1–180 days). Four predictive models were developed based on this database: linear regression (LR), multi‐linear regression (MLR), full‐quadratic (FQ), and M5P‐tree models. The data were split, with two‐thirds used for training (160 data points) and one‐third for testing (80 data points). The performance of each model was evaluated using various statistical metrics, including the coefficient of determination (R2), root mean square error (RMSE), mean absolute error (MAE), objective value (OBJ), scatter index (SI), and a‐20 index. The results revealed that the M5P‐tree model was the most accurate and reliable in predicting the compressive strength of SF‐based SCC across a wide range of strength values. Additionally, sensitivity analysis indicated that curing time had the most significant impact on the mixture's properties.

Low-carbon cementitious composite incorporated with biochar and recycled fines suitable for 3D printing applications: hydration, shrinkage and early-age performance

In recent years, the construction industry has witnessed significant advancements in concrete technology, particularly with the integration of 3D printing in cement-based materials. While this innovation offers promising opportunities for the sector, the high binder and fine particle content of 3D printing mixes presents a substantial environmental challenge due to their considerable carbon footprint. To mitigate this impact, strategies often involve substituting portions of the binder or aggregate with waste materials. This article presents a comparative analysis of two promising approaches to reducing the carbon footprint of 3D printing concrete mixes by partially replacing cement with biochar and recycled fines. The study examines the effects of these materials on the rheological properties and early-age hydration processes of the 3D printing mix. A reference mix (REF) was established, followed by the development of eight additional mixes, with four incorporating biochar and four incorporating recycled fines, each replacing 1.25%, 2.5%, 5%, and 10% of the cement volume. The findings indicate that recycled fines have a neutral effect on the spread flow diameter of the mixture but increase initial deformations in printed elements. Conversely, biochar, due to its water absorption capacity, reduces fluidity, enhancing buildability by enabling faster printing with minimal initial deformation. Additionally, replacing up to 2.5 vol.% of cement with either material accelerates the normalized heat flow, contributing to a quicker gain in mechanical properties. However, biochar increases shrinkage deformations within the first 12 hours, while recycled fines mitigate them. Importantly, replacing up to 10 vol.% of cement with these materials does not significantly compromise early compressive strength.

Enhancing M30 Grade Concrete: A Comparative Study of Hooked vs. Crimped Steel Fibers in Fly Ash Mixes

The realm of concrete offers vast opportunities for inventive applications, design, and construction methodologies, given its adaptability and cost-effectiveness. Its versatility in meeting diverse requirements has established it as a highly competitive building material. To address escalating structural demands and harsh environmental factors, new cementitious materials and concrete composites are continually being developed, followed by the need for enhanced durability and performance, as well as pressure to utilize industrial waste materials. The research explores the impact of incorporating fly ash and steel fiber into M30-grade concrete, alongside cement, coarse, and fine aggregate, through experimental methods, with the primary aim of determining optimal ingredient proportions for achieving desired strength. The study evaluates compressive strength variations with fly ash ranging from [10%] to [30%] while hooked and crimped steel fibers [ranging from 0% to 1.5%] in concrete, alongside cement, fine and coarse aggregate. Environmental considerations and the imperative to utilize industrial waste have significantly contributed to advancements in concrete technology and sustainability. Through meticulous analysis of results, meaningful inferences are made in relation to the strength attributes of fly ash fiber-reinforced concrete. Two sets of experiments were conducted, one altering fly ash content while maintaining fixed steel fiber content, and the other varying steel fiber content while keeping other parameters constant. The study aims to provide practical insights for engineers seeking cost-effective and sustainable building construction methods, adhering to specified norms (IS Code: 456-2000).

ML driven optimization of mechanical properties in hybrid fiber-reinforced tertiary blended high-performance concrete

This study focuses on optimizing the mechanical properties of hybrid fiber-reinforced tertiary blended high-performance concrete (HFRTHPC) by integrating CSF and polypropylene fibers (PPF) into a mix of silica fume (SF), metakaolin (MK), and fly ash (FA). These mineral admixtures replace Ordinary Portland Cement (OPC) at varying levels of 0%, 15%, 22.5%, and 30%. A comprehensive analysis was conducted on 80 different concrete mixes, each with W/B ratios ranging from 0.275 to 0.375, and a total fiber content of 1.25% (0.5%-1% CSF and 0.25% PPF). The results showed a significant increase in compressive strength, with a maximum improvement of 30.24% after 28 days of curing. The optimal mix was identified as containing 5% SF, 5% MK, 5% FA, 1% CSF, and 0.25% PPF at a W/B ratio of 0.275. Additionally, regression equations were developed to predict the mechanical properties. The study also utilized three machine learning techniques—AdaBoost Regressor, Random Forest, and Extreme Gradient Boost Regressor—to model compressive, split tensile, and flexural strengths. Among these, the Extreme Gradient Boost Regressor exhibited superior predictive accuracy and generalization capabilities. This research offers valuable insights for optimizing sustainable concrete compositions and provides a foundation for future advancements in concrete technology.

Life-cycle analysis of cement mortars with ladle furnace steel slag

The utilization of ladle slag holds potential for innovative advancements in concrete technology, contributing to the progression of environmentally sustainable and durable construction materials. This research explores the environmental impact of mortars incorporating treated ladle furnace steel slag at cement replacement ratios of 10%, 20%, and 30%. The ladle furnace steel slag was integrated into cement mortars of varying cement types. Life Cycle Assessment (LCA) was conducted using SimaPro software, version 9.3, employing ReCiPe and IPCC 2013 methodologies. The environmental impacts were assessed within the cradle-to-gate system boundaries, considering the grinding process of ladle furnace steel slag. The outcomes were expressed in terms of mid-point indicators. Across all cement types, a discernible reduction in the values of key environmental indicators was observed for the steel slag substitution samples compared to reference samples without cement substitution. Notably, the climate change indicator (GWP – global warming potential) exhibited a reduction of up to 54 g CO2eq per 1 kg of mortar. Grinding the slag to a higher fineness did not result in a significant escalation in the values of the monitored environmental indicators.

A New Insight into the Design Compressive Strength of Ultra-High Performance Concrete

Compressive strength is one of the most critical mechanical properties of various types of concrete and is the main input variable for structural concrete design. Recently, with the advances in concrete technology, applications of fiber-reinforced concrete (FRC), including ultra-high performance concrete (UHPC), have grown rapidly. These new types of concrete are well known to exhibit superior mechanical characteristics such as compressive strength, fracture toughness, and durability compared to conventional concrete and thus are popularly used in urgent repair jobs where compressive strength is an important parameter to determine the required curing time until open to the public. Considering the importance of compressive strength in practice, this study aims to evaluate the effect of age and maturity on the compressive strength characteristics of three different types of concrete, namely UHPC with micro and macro steel fibers, FRC, and plain concrete, and to propose a new design strength criterion for UHPC. To this end, 180 concrete cube specimens were tested at 12 different ages between 3 and 126 days. The results indicated that irrespective of the type and presence of fibers, UHPC gained more than 90% of their ultimate compressive strength after only 21 days, while FRC and plain concrete specimens required a longer time (i.e., 28 days) to achieve 90% of their ultimate strength. Therefore, UHPC may adopt a 21-day compressive strength as a design input instead of a 28-day compressive strength commonly required for structural concrete specified by many codes of practice. Moreover, the obtained experimental results were compared with existing compressive strength predictive models in the codes of practice.

Experimental Study on Strength Properties of Triple Blended Self-Compacting Concrete

Self-compacting concrete (SCC) is a flowing concrete mixture that can self-consolidate under its own weight, and it is one of the most significant advancements in concrete technology in the recent decade. SCC's very fluid character makes it ideal for use in challenging situations and in sections with crowded reinforcing. SCC, which was initially created in the late 1980s, has since expanded around the world, with an ever-growing variety of applications. Because of its unique features, SCC has the potential to significantly improve the quality of concrete buildings while also opening up new areas for concrete use. The addition of treated and untreated industrial byproducts, raw materials, and home wastes to SCC is becoming increasingly popular as a way to make it more durable and cost effective. This not only allows waste materials to be reused, but it also results in a eco-friendly environment. The Strength Characteristics of Self-Compacting Concrete were determined by an experimental investigation (SCC). The goal of this research is to see how Fly Ash (FA), Ground Granulated Blast Furnace Slag (GGBS), and Silica Fume (SF) can be used as cement substitutes and what influence they have on the fresh and hardened qualities of concrete. The investigation involves the notion of using a triple blend of Fly ash, GGBS, and Silica Fume to produce better concrete. This triple blend takes use of the favorable properties of Pozzolanic materials.

Durability evaluation and environmental implications of blended cement with colloidal nano-silica for use in recycled fine aggregate concrete: Experimental and theoretical study

The incorporation of waste materials in concrete is currently a practical solution to solve certain environmental concerns. Because of the property degradation of the produced concrete owing to the addition of waste materials, using pozzolans in the concrete mix can help improve the mechanical performance of recycled concrete. Therefore, in this research, the mechanical specifications of recycled concrete were evaluated at different volume fractions of recycled fine aggregates (RFA) replacing natural fine aggregates (NFA). In addition, the impact of adding colloidal nano-silica particles on the performance of conventional and recycled concretes was investigated. Various parameters comprising compressive strength, pulse velocity, splitting tensile strength, flexural strength, elastic modulus, and water absorption were carefully examined. The attained experimental results reveal that the mechanical and physical characteristics of concrete degrade with increasing the volume fraction of RFA replacing NFA. Also, increasing the weight percentage of nano-silica replacing cement up to 6% in conventional concrete and that containing RFA improves the mechanical and physical properties, the optimum percentage of which was determined as 4.5%. Furthermore, relationships were recommended for predicting the compressive, splitting tensile, and flexural strengths as well as the elastic modulus of concrete mixes by including the RFA and nano-silica replacement levels, which are in acceptable accordance with the experiments in the present study and those available in the technical literature. Finally, to investigate the environmental effects of recycled concrete with different RFA substitution levels and colloidal nano-silica incorporation, the problem-based CML 2000 and the damage-based IMPACT2002 + methods were applied using SimaPro9 software. Thus, environmental parameters such as acidification, global warming potential (GWP), eutrophication, natural resources, ecosystem quality, and human health were inspected. Subsequently, the GWP results were compared and presented using the CML 2000 and the Intergovernmental Panel on Climate Change (IPCC) approaches. To verify the estimates, all the attained results were examined against those captured from the Building for Environmental and Economic Sustainability (BEES) method. Findings show that despite the implementation of different unit measurements in different methods, the environmental effects in the CML 2000 and BEES methodologies are almost the same, suggesting that nano-silica is a raw material with the greatest environmental impact. Additionally, based on the life cycle comparison results of manufacturing one cubic meter of concrete with different mix designs using the damage evaluation approach, IMPACT 2002+, concrete with the RF0NS6 mix design triggered the highest damage extent in natural resource, climate change, ecosystem, and human health categories, respectively. This study fills a significant research gap from an environmental perspective by comprehensively investigating the durability and mechanical specifications of concrete containing RFA and nano-silica pozzolan. The findings presented in this research provide valuable insights into the realm of sustainable construction practices, paving the way for novel advancements in concrete technology.

Development of sustainable ultra-high-performance concrete containing ground granulated blast furnace slag and glass powder: Mix design investigation

Ultra-high performance concrete (UHPC) is one of the most important advances in concrete technology. Since UHPCs possess outstanding mechanical properties and durability, they require less material consumption and post-maintenance conventional concrete. This helps reduce the detrimental impacts of concrete structures on the natural environment. However, the high price and high carbon intensity of UHPCs are main hurdles for their wide adoption. Recently, studies have revealed that waste glass at a certain fineness exhibits pozzolanic behaviour. This paper investigates the effect of replacing cementitious components in UHPCs with “medium-size” glass powder (GP) on the workability, mechanical properties, sustainability, and cost efficiency of the UHPCs. While principal binders (cement and silica fume (SF)) were replaced by “medium-size” GP in Series I, ground granulated blast furnace slag (GGBFS) and coarse GP were simultaneously used to substitute for SF in Series II. Regardless of curing regimes, slag GP-UHPC mixtures always exhibited better workability and greater compressive/flexural resistance, indicating the great synthetic effect of GP and GGBFS substitution. In addition, results showed that up to 30% of GP replacement, most specimens yielded reasonable mechanical properties, high cost efficiency, and low carbon indexes compared to the reference mixture. Specifically, while workability reduced with the increase of GP portions in the GP-UHPCs, it rose with larger replacement percentages of SF in the slag GP-UHPCs. For both series, 20% replacement of GP was the optimal ratio, resulting in cost-saving and carbon-efficient mix designs with comparable compressive/flexural capacity.

Assessing the performance of concrete made with recycled latex gloves and silicone catheter using ultrasonic pulse velocity

Significant advances in concrete technology in modern times have prompted the search for environmentally friendly materials that could improve the properties of concrete. The inclusion of recyclable materials to conventional concrete can help in conserving key resources and produce environmentally friendly concrete. The incorporation of latex gloves and silicone catheter waste in concrete is one of the most important approaches to minimize the environmental problems associated with their disposal. In this study, an experiment was conducted to evaluate the effects of using latex gloves and silicone catheter waste as a substitute for coarse aggregates in concrete mixes. Concrete which was made with latex gloves and silicone catheter waste were subjected to UPV evaluations, i.e., ultrasonic pulse velocity tests at 28 curing days. Compressive strength and workability tests were also performed for reference and compared to the replacement sample. The inclusion of latex gloves and silicone catheter waste in proportions of 2.5%, 5%, 7.5 and 10% decreased the UPV values of the concrete. The results showed that the UPV values of the concrete decreased significantly from excellent to very good to poor for all specimens as the proportion of silicone catheters and latex gloves increased. The results showed that the addition of different proportions of latex gloves and silicone catheters decreased the compressive strength of the concrete by 86% and 59%, respectively, when the proportion of latex gloves and silicone catheters in the concrete mix was replaced by 10%. In addition, the fresh concrete property of concrete containing latex gloves and silicone catheters was decreased by 22% and 53%, respectively, when the proportion of latex gloves and silicone catheters was replaced by 10%. This study helps to raise environmental awareness by improving understanding of the waste generated and the importance of reusing waste as a substitute in concrete mixes.

To Study the Properties of Concrete Mix on Partial Replacement of Coarse Aggregate with Burnt Bricks

These days, materials such as over-burned bricks blast are employed as an alternative to coarse aggregates. This paper investigates the physical features of concrete formed with burned bricks blast. Natural rock is by far the most common coarse aggregate used in concrete, however not all types of rock appropriate for concrete production are available everywhere. Due to a paucity of aggregate from natural sources in India's north-eastern states, brick aggregate concrete is commonly utilised for ordinary concrete. Due to advancements in concrete technology and to meet the requirements for durability, As a result of the need to utilise standard concrete, which only uses stone aggregate, construction costs have increased as materials are carried from other states. Making good quality concrete with the finest sand (grading zone – IV as per Indian code IS:383-1970) is difficult enough, but the natural coarse aggregate is scarce locally. Burnt brick aggregate has a high-water absorption rate (12 to 20% by mass), which makes it difficult to utilise in practical work. As a result, an attempt has been made to provide a viable solution for real-world use. To test various strength characteristics, an experimental investigation was done. In our project, waste material was employed as a coarse aggregate while simultaneously keeping the strength of the concrete. The effects of a percentage replacement of stone aggregates with burn brick aggregates on the compressive strength of concrete are presented in this study. Concrete cubes of M25 grade samples containing various percentages of brick aggregate, such as 0%, 10%, 20%, and 30%, are made 7-, 14-, and 28-days tests were performed.

Machine learning-based models for predicting the shear strength of synthetic fiber reinforced concrete beams without stirrups

Stirrups can be added to reinforced concrete (RC) beams made of plain concrete to increase the shear strength providing better performance against embrittlement. If the need for shear stress is less than the strength of RC beams, reinforced with the minimum number of stirrups, then this choice might not be the most cost-effective. Synthetic Fiber Reinforced Concrete (SyFRC) in Reinforced Concrete (RC) structures is limited due to the lack of predicting models for this emerging material in current literature. However, recent advances in concrete technology have revealed more significant benefits of SyFRC, including high deformation capacity and less corrosive concrete. This study predicts shear strength of SyFRC beams without stirrups using the ACI 318-19 equation in addition to Machine Learning (ML) methods such as LightGBM, XGBoost, and Gene Expression (GEP). A database of 102 tested SyFRC specimens were compiled, processed, and evaluated. With R2 values of 98.91% and 97.22%, respectively, the LightGBM and XGBoost outperformed the other examined algorithms by having the least predictions discrepancy and highest accuracy values. As the ACI 318-19 equation does not account for the fibers volume ratio and shear span-to-depth ratio effects on the shear strength contribution, it projected shear strength with the lowest degree of accuracy, with R2 = 75.5%. The feature importance analysis revealed that these two factors, in addition to the effective beam depth, beam width, longitudinal steel reinforcement ratio, and concrete compressive strength should not be negligible in shear strength prediction. For forecasting the shear strength, a closed-form GEP-based model was suggested. The proposed GEP model has a little lower prediction accuracy with R2 = 88.4%. The performance of the four examined models was evaluated from various perspectives. The analysis shows that, apart from the ACI equation, all considered models effectively predict the effects of shear span-to-depth ratio. This is critical for investigating deep and slender beams, and size effect, which are critical for beams with high effective depths. The current study's findings should give practitioners a solid platform for making precise and straightforward assessments of shear strength.

Influence of Tie Configuration on Seismic Behaviour of Ultra High Performance Concrete Columns

Ultra-High-Performance Concrete (UHPC) is one of the latest advances in concrete technology as it overcomes the shortcomings of conventional concrete such as low strength to weight ratio, high permeability, low tensile strength, low ductility, and volume instability. Confinement is capable of increasing capacity of the concrete structure to sustain large deformation without a substantial strength loss. The present study discusses the influence of tie configuration, percentage of longitudinal reinforcement and tie spacing in improving the confinement and behaviour of UHPC columns. In order to determine the behaviour of UHPC column, half scaled specimens of original short column with four different tie configurations were used. The configurations considered for the study included a double legged ties (A), welded ties with bars running centrally across the length and width (B), ties with inclined bars connecting two adjacent mid-points (C) and ties with bars connecting two adjacent sides at one-third distances (D). For the same tie configuration, the transverse reinforcement ratios are varied by changing the diameter of the ties. The specimens were tested under quasi static reverse cyclic loading under a constant axial load. The test results were represented and compared in terms of load-deflection envelope, ductility and cracking patterns. Tie configuration C exhibited better performance in stiffness and ductility, when compared with other configurations. For same parameters, “B” and “D” configuration displayed better behaviour than “A” configuration. This variation in performance was due to increase in transverse reinforcement percentage and the consequent effectiveness of core confinement. Transverse reinforcement percentage of “B” and “C” configurations is less than “D” configuration. The enhancements of properties of “B” and “C” configurations are better than “D” configuration. It was due to the effective core confinement of “B” and “C” configuration. For the same tie configuration, ultimate load, initial stiffness and relative ductility increases with increase in transverse reinforcement percentage. UHPC columns with “C” type tie configuration can effectively use in moderate and high seismic areas and its performance can be improved by increasing the transverse reinforcement ratio.

Health monitoring of cracked concrete structure by impedance approach

Cracks/damages in concrete structures are the core concern for reduction of service life of infrastructures. Therefore, the effective technique is required for the prevention of cracks growth to improve the durability of structures. The cracks growth can be minimised by the incorporation of bacteria in the cementitious materials. The development of calcium carbonate heals the cracks automatically without any kind of human effort. The health of structures can be monitored and the presence of damages/cracks can be determined using various structural health monitoring techniques. In this paper, the research is focused on the monitoring of concrete cubes to explore the effect of bacteria. Two types of cube specimens were considered such as control concrete and bacterial concrete cubes, respectively. The six cubes of control concrete and six cubes of bacterial concrete of dimension 150 × 150 × 150 mm were cast. The compressive load of 300 kN was applied on control concrete cubes and bacterial concrete cubes to induce the incipient cracks/damages. After inducing the damages in the cubes, these cubes were tested after 7 days and 28 days curing. It was observed that the compressive strength of bacterial concrete was increased with respect to the control concrete by 19 % and 23 % at 7 and 28 days, respectively. The Electro-Mechanical Impedance (EMI) technique was used for monitoring the development of strength in both the cubes continuously. Piezo-ceramic lead Zirconate Titanate (PZT) patches were used to extract the signature. Admittance signatures were determined to access the health of cube specimens. Any deviation in signature from the healthy state that is baseline signature designates the change in compressive strength of concrete cubes. The increased strength was quantified in terms of signature change. The proposed investigation is applicable for monitoring of bacterial concrete structures. The research paper will be resulted new research directions and develop sustainable advancements in concrete technology.

The Future and Prospects of Periwinkle Composites in Reinforced Concretes: A Review

The choice of building materials and the rising cost of construction materials have continued to plaque the building and construction industry without an immediate solution. Industrialists and scholars are investigating several naturally occurring materials for concrete composite reinforcements. The article chronologically reviewed the growth and development of periwinkle shell powder (PSP) and periwinkle ash powder (PSA) as composite materials in concretes. Findings showed that 28 days of curing age are required for lightweight concretes reinforced with PSP or PAP at 10-30% optimum. Produced lightweight concretes were susceptible to acidic medium and induce lower compressive strength which eventually leads to concrete/structure disintegrate and collapse. Research challenges and funding hamper the application of PSP/PAP in the concrete formulation and are unable to drive innovations and economic benefits as a composite. Advances in concrete technology showed that PSP/PSA mollusk shells achieve pillar strength grade and weight/load bearing status for the improvement of PSP/PSA blended concretes. Also, the composite potential showed that the functionalization of PSP/PSA, sustainability, and nano modification of cementitious materials and concretes are promising. Future studies are required to develop periwinkle reinforced concrete silos, sewers, and smart concrete materials with improved mechanical, thermal, and aesthetic properties.

Concrete compressive strain behavior and magnitudes under uniaxial fatigue loading

Recent advances in concrete technology and construction have promoted an increasing utilization of concrete in fatigue-critical structures, such as wind turbine towers. While research into concrete fatigue is not a new topic and has been going on for several decades, a large majority of this research has primarily been focused on the determination of concrete fatigue capacity. However, understanding and advancing concrete fatigue behavior (e.g., fatigue stress vs. strain response) has received limited attention, even though this is also crucial, especially considering the inherently nonlinear behavior of concrete. To address this knowledge gap and further advance our understanding of concrete fatigue behavior, an experimental investigation consisting of uniaxial compressive fatigue testing of concrete cylinder specimens until failure was undertaken, and axial strains were recorded throughout the duration of fatigue loading. The behavior and evolution of concrete axial strains, including the rate of accumulation of strains, through the fatigue loading process were extensively analyzed and are reported. Additionally, the influence of key parameters, such as peak stress levels and number of cycles to failure, on peak strain evolution were investigated and are described. Magnitudes of peak axial strain at the end of the stable strain accumulation phase, as well as at failure, are also reported, and recommendations are made for estimating strain magnitudes at these critical junctures when conducting fatigue analysis and design. The results will help advance the understanding of concrete axial strain behavior under compressive fatigue loading. The results also provide guidelines for estimating the magnitudes of concrete strains under fatigue loads, which in turn will be beneficial to designers, as it allows them to also consider structural performance during the analysis and design of fatigue critical concrete structures.

A review of tests on slab-column connections with advanced concrete materials

Advances in concrete technology during the last decades have resulted in the development of materials with enhanced mechanical properties, such as High Strength Concrete (HSC), Fibre Reinforced Concrete (FRC) and Ultra-High Performance Fibre Reinforced Concrete (UHPFRC). The application of these materials in flat slabs, which are a popular structural solution in Reinforced Concrete (RC) buildings worldwide, has the potential of significantly reducing raw material consumption by enabling the design of slenderer and therefore lighter structures. However, flat slabs are susceptible to punching shear failure, which is a complex phenomenon that remains challenging, even though significant efforts have been made to experimentally study it. For advanced concrete materials (HSC, FRC and UHPFRC), the challenge is further accentuated by the continuous and rapid development of these materials. With the purpose of identifying and highlighting gaps in the published literature, a review of tests with HSC, FRC and UHPFRC slab-column connections in non-seismic and seismic loading applications is presented in this paper. It is shown that future research directions in this field include, among others, testing thicker slabs, HSC slabs with higher concrete compressive strength, HSC combined with FRC and several more cases related to seismic loading conditions.

Numerical simulation of ultra-high-performance fiber-reinforced concrete frame structure under fire action

The research activity in progress and the advancements in concrete technology are leading to an increased use of ultra-high-performance fiber-reinforced concrete (UHPFRC) in structural engineering. UHPFRC is characterized by steel fibers, cement, silica fume, fine sand, superplasticizer, and very low water–cement ratio. UHPFRC is defined as a new material, with unique properties (high ductility, low permeability, very high strength capacity in compression, higher toughness) in comparison with conventional concrete (Buttignol et al, Revista IBRACON de Estruturas e Materiais 10(4):957–971, 2017). This makes it possible to make slender constructions because a smaller cross section can transfer the same force as a larger cross section. However, in case of fire safety design a disadvantageous behavior of UHPC compared to normal-strength concrete is well known and documented. The high packing density of the cement matrix is the main reason for explosive spalling behavior when exposed to fire. In this paper, the numerical simulation using finite-element method has been used to evaluate the behavior of UHPFRC frame structure under fire action. According to results, the three-dimensional finite-element model can be used for calculating the mechanical localized of UHPFRC concrete frame structures subjected to nominal fire curves. The results of numerical analysis under fire action are also compared to the other materials for more understanding the fire resistance between UHPFRC material (with PP fiber, without PP fiber) and high-strength concrete.

Pulse velocity–strength and elasticity relationship of high volume fly ash induced self-compacting concrete

ABSTRACTSelf-compacting concrete (SCC) represents one of the most outstanding advances in concrete technology during the last decade. The amount of SCC used for the structural purpose has strongly increased worldwide, and consequently, there is a need to assess the applicability of non-destructive testing techniques to survey SCC’s transient in situ mechanical properties. Information of the elastic behaviour of SCC is alluring if the behaviour of concrete structures is to be translated legitimately. Ultrasonic Pulse Velocity (UPV) method is a standout among the most prominent non-destructive techniques utilized in the appraisal of concrete properties. This paper deals with the investigation of the velocity–strength and elasticity relationship of high volume fly ash (HVFA) induced SCC. The relationship between UPV, static and dynamic Young’s modulus is analyzed. A new general simplified expression that allows estimation of compressive strength from UPV has been defined and is based on the ratio of dynamic modulus of elasticity to the static modulus of elasticity. The mathematical model has been validated by comparing predicted versus measured compressive strength.

Mineralogical and microstructural response of hydrated cement blends to leaching

Recent advances in concrete technology have enabled the manufacturing of hydrated cements blended with high levels of supplementary cementitious materials (SCMs). These composites can exhibit mechanical and physical properties similar to ordinary Portland-based cements; yet their equivalent performance in “corrosive” environments has to be proven. In this paper, we describe mineralogical, microstructural and geochemical alteration patterns of hydrated cement pastes, despite adequate curing, containing 10 wt-% up to 70 wt-% replacement of Portland cement by SCMs, due to combined leaching and carbonation attack for 182 days. Such knowledge is highly relevant for assessing degradation features of steel-reinforced concrete in tunnels.The dissolution of portlandite, katoite and tobermorite as well as recrystallization of C-S-H caused the development of a leached layer around the specimen‘s surface. Calcite, vaterite and hydrotalcite precipitated within the altered zone, but no passivation effect due to clogging of pore space by these deposits was observed. The thickness of the altered layer, the amounts of portlandite dissolved and CaCO3 phases neo-formed, the decrease in the Ca/Si molar ratio of C-S-H and the increase in total porosity were highest in pure cement paste. All hydrated cements blended with different types and levels of SCMs (including metakaolin, silica fume, limestone, granulated slag, and their combinations) have behaved better than the pure cement paste, which demonstrates the equivalent performance of these blended mixes in weakly aggressive environments.