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Calcined clays (CCs) as supplementary cementitious materials (SCMs) can be a promising option to reduce clinker content and CO2 emissions in eco-friendly concretes. Although CCs as components of composite cements in combination with Ordinary Portland Cement (OPC) and limestone powder (LSP) have attracted industry interest, their use as concrete additives is limited. This study investigates the effects of the addition of CCs on the fresh and hardened properties of industry-standard ready-mixed concretes. Four concrete mix designs, each with three superplasticizer dosages, were tested, resulting in 12 variations. The CCs used, which are typical of 2:1 bentonite clays with low metakaolin content, reflect the clays available in Germany. The results showed that CCs significantly influenced the workability, which could be controlled with a high superplasticizer dosage. Increased CC contents reduced bleeding tendencies, which was beneficial for certain structural applications. Early age strength decreased with CCs, but the 28-day strength exceeded that of pure OPC concretes up to 30 wt% CCs. Resistance to CO2-induced carbonation decreased with higher levels of CCs but was comparable up to 15 wt%. Freeze–thaw damage decreased, and chloride migration resistance improved due to a denser microstructure. The global warming potential (GWP) of the concretes tested is in line with that reported in the literature for concretes made from highly blended cements, suggesting that CCs can improve the sustainability of concrete production. [ABSTRACT FROM AUTHOR]

To optimally preserve and manage our civil structures, we need to have accurate information about their (1) geometry and dimensions, (2) boundary conditions, (3) material properties, and (4) structural conditions. The objective of this article is to show how imaging and image fusion using non-destructive testing (NDT) measurements can support structural engineers in performing accurate structural evaluations. The proposed methodology involves imaging using synthetic aperture focusing technique (SAFT)-based image reconstruction from ground penetrating radar (GPR) as well as ultrasonic echo array (UEA) measurements taken on multiple surfaces of a structural member. The created images can be combined using image fusion to produce a digital cross-section of the member. The feasibility of this approach is demonstrated using a case study of a prestressed concrete bridge that required a bridge load rating (BLR) but where no as-built plans were available. Imaging and image fusion enabled the creation of a detailed cross-section, allowing for confirmation of the number and location of prestressing strands and the location and size of internal voids. This information allowed the structural engineer of record (SER) to perform a traditional bridge load rating (BLR), ultimately avoiding load restrictions being imposed on the bridge. The proposed methodology not only provides useful information for structural evaluations, but also represents a basis upon which the digitalization of our infrastructure can be achieved. [ABSTRACT FROM AUTHOR]

In the case of concrete built into a structure, the static secant modulus of elasticity (Ec,s) is often estimated based on its dynamic value (Ed) measured by the ultrasonic pulse velocity method instead of direct tests carried out on drilled cores. Meanwhile, the prevailing equations applied to estimate Ec,s often overlook the impact of concrete moisture. This study aimed to elucidate the moisture impact across two normal-weight structural concretes differing in compressive strength (51.6 and 71.4 MPa). The impact of moisture content was notably more evident only for the weaker concrete, according to dynamic modulus measurements. In other cases, contrary to the literature reports and expectations, this effect turned out to be insignificant. These observations may be explained by two factors: the relatively dense and homogeneous structure of tested concretes and reduced sensitivity of Ec,s measurements to concrete moisture condition compared to Ed measurements obtained using the ultrasonic method. Additionally, established formulas to estimate Ec,s were verified. The obtained modulus results tested under different moisture conditions of normal-weight concretes were also compared with those of lightweight aggregate concretes of identical volume compositions previously obtained in a separate study. [ABSTRACT FROM AUTHOR]

Abstract The replacement of natural aggregate in concrete with artificial and/or recycled one has recently gained attention as meaningful strategy to reduce the environmental impact of structural concrete and promote circular economy principles. This study investigated the possibility to use Reclaimed Asphalt Pavement (RAP), in the “as received conditions”, as a partial or complete substitution of natural aggregate for structural concrete. RAP aggregate was firstly characterized in terms of grain size distribution, density, assessment of fines, chloride content, moisture content and water absorption. Subsequently, a total of twenty-four concrete mixes were designed, considering two cement types, two w/c ratios and several aggregate substitution percentages. For each mix, properties at the fresh and hardened state were investigated, such as workability, density and total open porosity, compressive strength, dynamic modulus of elasticity, and electrical resistivity. Results showed that RAP has a good potential to be used in reinforced concrete, provided that different water absorption and moisture content are considered in the mix design. RAP concrete was characterized by a lower density and increased total open porosity; however, an accurate tailoring of the concrete recipe could compensate the strength loss for several applications. Other properties, such as electrical resistivity and the relationship between dynamic modulus of elasticity and compressive strength did not result significantly altered by the presence of RAP.

Abstract Concrete, the construction industry’s most utilized construction material, has transformed the environment and the modern built-up lifestyle. Although concrete is a first-rate supplier to the carbon footprint, it is imperative for buildings to display sustainable characteristics. Scholars have explored techniques to lessen the carbon footprint and the way to put into effect strategic waste control plans in which waste is reused. This study explores the dual benefits wherein concrete ingredients are replaced through abandoned waste which reduces the unwanted waste materials that have a substantial carbon footprint and thus results in the recycling of waste as part of a sustainable economic system. In this study, timber ash is utilized as a partial substitute for sand and cement, crumb rubber and waste glass as a partial substitute for sand, recycled concrete, and waste glass as a substitute for gravel. Characteristics studies were done to check the influence of each waste replacement on the modulus of elasticity of concrete. More than sixty-five combinations of waste have been examined to attain the modulus of elasticity of concrete. A total of about 200 concrete cylinders were cast to provide at least three cylinders for each generated data point. Three different ASTM standards were utilized to determine the modulus of elasticity of each mix. Four mixes comprising of the combination of two waste materials and two mixes comprising of the combination of three waste materials replacing natural materials were determined to exhibit an equal or superior modulus of elasticity of the control mix of 25 GPa.

Concrete, the construction industry's most utilized construction material, has transformed the environment and the modern built-up lifestyle. Although concrete is a first-rate supplier to the carbon footprint, it is imperative for buildings to display sustainable characteristics. Scholars have explored techniques to lessen the carbon footprint and the way to put into effect strategic waste control plans in which waste is reused. This study explores the dual benefits wherein concrete ingredients are replaced through abandoned waste which reduces the unwanted waste materials that have a substantial carbon footprint and thus results in the recycling of waste as part of a sustainable economic system. In this study, timber ash is utilized as a partial substitute for sand and cement, crumb rubber and waste glass as a partial substitute for sand, recycled concrete, and waste glass as a substitute for gravel. Characteristics studies were done to check the influence of each waste replacement on the modulus of elasticity of concrete. More than sixty-five combinations of waste have been examined to attain the modulus of elasticity of concrete. A total of about 200 concrete cylinders were cast to provide at least three cylinders for each generated data point. Three different ASTM standards were utilized to determine the modulus of elasticity of each mix. Four mixes comprising of the combination of two waste materials and two mixes comprising of the combination of three waste materials replacing natural materials were determined to exhibit an equal or superior modulus of elasticity of the control mix of 25 GPa. [ABSTRACT FROM AUTHOR]

The partial replacement of conventional natural coarse aggregate (NCA) with artificial light weight aggregate (LWA) manufactured from local clay and solid waste to develop a lightweight aggregate concrete (LWAC) for the structural use was studied in this paper. Red clay and Savar clay were used individually with solid wastes like rice husk ash (RHA) and waste glass to produce LWA. The suitability of raw materials and LWA was evaluated by investigating various properties. The mechanical, thermal and durability properties of manufactured LWAC were explored. The results of physical, chemical, thermal and geotechnical properties revealed that Red clay is better than Savar clay for the preparation of LWA. All the physical and mechanical properties of LWA prepared from Red clay are suitable for the preparation of LWAC compared to Savar clay. The test results demonstrated that the concrete manufactured by replacing 30 % of NCA with LWA produced a concrete of lightweight properties. The compressive strength of LWAC for 7 and 28 days was observed as 28 and 48 MPa, respectively. The results of modulus of elasticity, splitting tensile strength, flexural deformation, and creep test of LWAC revealed that these mechanical properties meet the requirements for the structural concrete. The RCP test proves that chlorine permeability of LWAC is comparable with NCA. It was observed that the superior performance of LWAC can be achieved only when the optimized mix designed is followed strictly. The suitability of the replacement of natural aggregate by LWA may be helpful for Bangladesh due to the scarcity of natural coarse aggregate and reusability of solid waste materials.

Robotic clay formwork three-dimensional printing combined with incremental concrete casting controls concrete's hydrostatic pressure and enables the production of building-scale structures. Clay formwork is self-demolding and less carbon intensive than concrete and polymer, often used in formwork additive manufacturing. This research investigates the recycling and reuse of clay to re-print formworks and tailors a self-compacting concrete formula with 60% reduced cement content and 90% larger maximum aggregate size. The study then explores integrating steel fibers and longitudinal rebars into the fabrication process to provide shear and bending reinforcement. When comparing the load-bearing behaviour of the fabricated beams against those cast traditionally using wooden formworks, the fabricated beams demonstrated 20% lower load-bearing capacity, with peak load mid-span deflections staying in a similar range. While more investigation is required to address formwork deformations using mixed steel fibers and recycled clay, this research paves the way for more sustainable concrete construction practices.

Some materials, such as reinforced and prestressed concrete, involve non-linear constitutive relationships in elasticity problems defined on them. In particular, the shear strength of a reinforced concrete beam may be calculated by considering a diagonal struts field in the context of the so-called “Compression Field Theories” (CFTs). This work presents an efficient Machine Learning method alternative to numerical methods for obtaining the full shear response of reinforced and prestressed concrete beams based on CFT regarding stresses, strains, and crack angles. For that, a regression task is developed using state-of-the-art Machine Learning (ML) models. A ML model per output variable is trained with the existing Newton-Raphson solutions database. The solvability region of the embedded steel constitutive model is also considered, demonstrating the comprehensive character of the proposed method. The model is validated on two real beam responses, where the results obtained demonstrate that this alternative method based on ML algorithms effectively addresses the problem of prediction of the shear response in reinforced and prestressed concrete beams. The proposed ML approximation performs reasonably well without requiring any initial approximations. Moreover, the ML regressor here developed shows a low dependence on the concrete tension stiffening area surrounding the steel reinforcement, which significantly improves the performance of this methodology in a higher number of design cases. Thus, in the practical context of structural engineering, this last approach establishes an efficient alternative procedure for obtaining numerical solutions of mechanical models based on the CFTs framework.

Calcined clays (CCs) as supplementary cementitious materials (SCMs) can be a promising option to reduce clinker content and CO2 emissions in eco-friendly concretes. Although CCs as components of composite cements in combination with Ordinary Portland Cement (OPC) and limestone powder (LSP) have attracted industry interest, their use as concrete additives is limited. This study investigates the effects of the addition of CCs on the fresh and hardened properties of industry-standard ready-mixed concretes. Four concrete mix designs, each with three superplasticizer dosages, were tested, resulting in 12 variations. The CCs used, which are typical of 2:1 bentonite clays with low metakaolin content, reflect the clays available in Germany. The results showed that CCs significantly influenced the workability, which could be controlled with a high superplasticizer dosage. Increased CC contents reduced bleeding tendencies, which was beneficial for certain structural applications. Early age strength decreased with CCs, but the 28-day strength exceeded that of pure OPC concretes up to 30 wt% CCs. Resistance to CO2-induced carbonation decreased with higher levels of CCs but was comparable up to 15 wt%. Freeze–thaw damage decreased, and chloride migration resistance improved due to a denser microstructure. The global warming potential (GWP) of the concretes tested is in line with that reported in the literature for concretes made from highly blended cements, suggesting that CCs can improve the sustainability of concrete production.

This study aims to promote the application of recycled aggregate concrete using low‐quality recycled aggregate, which can be easily obtained in Vietnam, mixed with normal aggregate. This is achieved by examining the performance evaluation of concrete using the relative quality index method and mix proportion design. If low‐quality recycled aggregate and normal aggregate can be combined in concrete in a suitable replacement ratio, as has been done in Japan, the proposed method can be used for structural concrete applications in Vietnam. [ABSTRACT FROM AUTHOR]

Rebar‐to‐concrete bond is a fundamental aspect of the behavior of reinforced concrete structures. The characterization of the interface response is challenging due to the complexity of the physical phenomena and the large number of factors involved. Locally, the response is characterized by the bond–slip relationship, which is typically obtained experimentally from pull‐out tests with short bonded lengths. The behavior of longer anchorages in structural members differs significantly from short tests as the bond stress distribution is not uniform. In this context, this paper presents the results of a comprehensive research aiming to establish a better relationship between the local bond–slip response from short pull‐out tests and the response of medium‐length anchorages. The results of an experimental program are presented, including the effect of some parameters commonly found in structural applications, such as casting conditions, clear cover, rib geometry, and rib orientation. A local bond–slip relationship for well‐confined conditions is proposed on the basis of the tests performed by the authors and on the examination of a database on short pull‐out tests from the literature. Based on this relationship and some mechanical considerations, the local bond–slip relationship for unconfined conditions can satisfactorily be formulated based on crack‐width measurements from the concrete surface. This can be useful for the assessment of existing structures and can be seen as a step forward in the development of a consistent mechanical model for bond. [ABSTRACT FROM AUTHOR]

An issue related to using concrete for building structures is to ensure their stability and durability during operation within wide limits. Therefore, the object of research was the change in the properties of concrete in case of fire and its protection when applied with a reactive coating capable of forming a foam coke layer under the influence of high temperature on the coating. It has been proven that in the process of thermal action on the fire-resistant coating, the process of heat insulation of concrete involves the formation of soot-like products on the surface of the material. Thus, under the influence of the flame of the burner, a temperature arose on the surface of the sample, which led to the swelling of the coating by more than 18 mm. The measured temperature on the surface of the concrete sample under the layer of foam coke was no more than 140 °C, which indicates the formation of a fire barrier. In this regard, modeling of the process of heat transfer through the formed layer of foam coke in the process of its protection with a reactive coating was carried out and dependence was established, which makes it possible to estimate the coefficients of temperature conductivity and thermal conductivity during high-temperature action. According to the experimental data and the established dependences, the coefficient of temperature conductivity and heat conductivity of foam coke was calculated, which is 9.17·10–7 m²/s and 0.17 W/(m·K). The assessment of the maximum possible penetration of fire through the layer of foam coke was carried out. A temperature was formed on the surface of the sample, which significantly exceeded the temperature of the destruction of concrete, and on the surface of concrete under the coating it did not reach 250 °C. So, there are reasons to assert the possibility of targeted regulation of concrete fire protection processes by using reactive coatings capable of forming a protective layer on the surface of the material that inhibits the rate of heat transfer [ABSTRACT FROM AUTHOR]

In the case of concrete built into a structure, the static secant modulus of elasticity (Ec,s) is often estimated based on its dynamic value (Ed) measured by the ultrasonic pulse velocity method instead of direct tests carried out on drilled cores. Meanwhile, the prevailing equations applied to estimate Ec,s often overlook the impact of concrete moisture. This study aimed to elucidate the moisture impact across two normal-weight structural concretes differing in compressive strength (51.6 and 71.4 MPa). The impact of moisture content was notably more evident only for the weaker concrete, according to dynamic modulus measurements. In other cases, contrary to the literature reports and expectations, this effect turned out to be insignificant. These observations may be explained by two factors: the relatively dense and homogeneous structure of tested concretes and reduced sensitivity of Ec,s measurements to concrete moisture condition compared to Ed measurements obtained using the ultrasonic method. Additionally, established formulas to estimate Ec,s were verified. The obtained modulus results tested under different moisture conditions of normal-weight concretes were also compared with those of lightweight aggregate concretes of identical volume compositions previously obtained in a separate study.

Abstract This study aims to promote the application of recycled aggregate concrete using low‐quality recycled aggregate, which can be easily obtained in Vietnam, mixed with normal aggregate. This is achieved by examining the performance evaluation of concrete using the relative quality index method and mix proportion design. If low‐quality recycled aggregate and normal aggregate can be combined in concrete in a suitable replacement ratio, as has been done in Japan, the proposed method can be used for structural concrete applications in Vietnam.

Free‐form reinforced concrete, prestressed concrete and composite components: Calculation of cross‐section values A resource‐efficient use of concrete as a construction material can be achieved by adapting the individual shape of a component under consideration to the stresses that occur and by arranging composite construction materials (e. g. reinforcing steel, prestressing steel or structural steel) in suitable areas of the component. Due to the advancing digitalisation in the construction industry, for example in the context of Building Information Modeling, computer‐aided 3D modelling methods are increasingly being used in the planning of structures. These allow engineers to design components in free form. In reinforced concrete, prestressed concrete and composite construction, the design of such components is currently still associated with great effort. In the context of the development of a practical method for the calculation of free‐form concrete components, this paper presents a CAD‐integrated method for the calculation of cross‐section values. Cross‐section values are required as an essential calculation basis when real, three‐dimensional structural components are treated using simplified calculation theories, such as the beam theory. In this paper, the mathematical and numerical fundamentals of a method for the calculation of cross‐section values of free‐form concrete, reinforced concrete, prestressed concrete and compound components are presented. The calculation method is based on flat geometric regions described by Non‐uniform rational B‐Spline tensor product surfaces, which can be extracted from solid models, for example. [ABSTRACT FROM AUTHOR]

Concrete is one of the building industry's most used construction materials. Reducing natural resources, enormous production costs, and environmental issues in cement production have encouraged researchers to partially explore suitable options to substitute Portland cement and the built environment. This article provides a thorough review of the research on the prudent utilization of sugarcane bagasse ash (SCBA) as a Portland cement replacement in the production of concrete. The methods used to produce SCBA, the effect of calcining temperature on bagasse ash, its physical and chemical characteristics and the strength development phenomenon are discussed. The impact of SCBA on the properties of concrete under the fresh state is also discussed. The physical and durability properties of concrete manufactured with SCBA are reviewed in-depth to understand its impending use for commercial applications. Finally, SCBA-related issues and challenges are described. A few of the outcomes are: (i) An organized incineration method is required for producing good quality SCBA, (ii) the optimum replacement level of cement by SCBA for mechanical and durability properties are 20%, (iii) improved durability due to an impervious microstructure of SCBA-concrete to harmful agents that cause degradation. Even though there is some disagreement among researchers, the majority continue to agree that using SCBA in cementitious composites is advantageous. However, researchers do not consider its usage in reinforced concrete elements such as slabs and beams; thus, further research is recommended. Finally, the formulation of codal recommendations on technical and environmental factors calls for additional research. [ABSTRACT FROM AUTHOR]

The Eggshell fabrication process combines the 3D printing of formwork with the simultaneous casting of a fast-hardening concrete. One limiting factor to reaching mass-market adoption is a suitable reinforcing strategy. In this study, a reinforcement strategy combining steel reinforcing bars with steel fibres is explored. A series of eight beams were produced using the Eggshell process or conventionally cast. The longitudinal reinforcement was provided by two reinforcing bars, and two types of fibres, either mixed with the concrete or placed and aligned between the cast concrete layers, were used as shear reinforcement. The results showed that combining conventional longitudinal reinforcement and fibres as shear reinforcement is a suitable strategy. These findings were applied to fabricate an optimised beam with a volume reduction of almost 50%. The structural performance of this beam was similar to the beam with a rectangular cross-section with the same reinforcement strategy showing the potential of Eggshell in combination with an innovative reinforcement strategy to produce material-efficient structural concrete elements.

Considering that the production of concrete is a resource and energy intensive process, the utilisation of recycled aggregates is one of the approaches that can be adopted to circumvent the issue of high extraction of natural aggregates (NA). In addition, construction and demolition (C&D) wastes are dumped in landfills, resulting in social, environmental and economic difficulties. The present study focuses on the use of recycled concrete aggregates (RCA) from C&D waste as coarse aggregates for concreting applications. A low-cost and simplified treatment method was used for valorise waste generated from demolition of concrete structures. Crushed RCA were placed in a drum type concrete mixer and rotated with water at a speed of 10 rpm for 30 min. Results showed that the remaining adhered mortar adversely affects aggregate properties, with a reduction in density and increases in porosity, aggregate impact value, Los Angeles abrasion value and water content compared with those of NA. The complete substitution of coarse aggregates with RCA reduced slump, density, dry and wet compressive strength by 47%, 1.8%, 28% and 27%, respectively, but enhanced water absorption by up to 5.6%. Results showed that proposed technique provides feasible and cost-effective way for valorisation. The manufacture of quality RCAs is essential and the removal level of adhered mortar will determine RCA quality, and consequently, the quality of concrete. To meet standard requirements for structural concrete, RCA can be used to replace NA by implementing proper control of the proposed valorisation technique, subsequently conserving natural resource for sustainable future. [ABSTRACT FROM AUTHOR]

The findings from the investigation conducted, to compare the structural performance of concrete containing treated (TOPEFB) and untreated Empty Oil Palm Fruit Bunch (OPEFB) fibres are presented in this paper. For the TOPEFB fibres, the dried fibres were treated with 0.2% NAOH solution following the procedures of ap-propriate authority. The structural parameters investigated were consistencies, setting times, densities, com-pressive and tensile strengths of concrete incorporating TOPEFB and OPEFB fibres in the mix. The addition of fibres was limited to 1.20% by weight of cement in the concrete. The interval of addition was 0.2%. The results showed that (i) the setting times of mortars containing TOPEFB fibres were higher than that of mortars with OPEFB fibres, (ii) concrete specimens containing TOPEFB fibres are more workable that concrete specimens with OPEFB fibres, (iii) densities of concrete specimens containing OPEFB fibres were in the range for normal concrete applications while the densities for specimens with TOPEFB developed densities that fell in the heavy weight concrete classification, (iv) concrete specimens containing TOPEFB fibres developed higher compressive strengths than specimens with OPEFB fibres and (v) tensile strengths of concrete specimens containing TOPEFB fibres were higher than specimens with OPEFB fibres by at least 59.04%. The overall conclusion from the findings of this study is that concrete specimens containing TOPEFB fibres have superior structural properties than specimens with OPEFB fibres. [ABSTRACT FROM AUTHOR]

Abstract. White Portland cement (WPC) in Indonesia is generally used for architectural work. WPC is still rarely used in structural concrete because the price is relatively higher than grey cement. This research reviewed the compressive strength of concrete using WPC and compared it with concrete using grey cement. Compressive strength testing of concrete using WPC and grey cement was carried out at ages: 3, 7, 14, 21, and 28 days. From the research, the compressive strength of concrete using WPC was 13.81 MPa (60%) at 3 days, 16.68 MPa (72%) at 7 days, 19.45 MPa (84%) at 14 days, 22.34 MPa (97%) at 21 days, and 23.11 MPa (100%) at 28 days. The compressive strength of concrete using grey cement was 13.03 MPa (63%) at 3 days, 15.11 MPa (74%) at 7 days, 17.22 MPa (84%) at 14 days, 18.78 MPa (91%) at 21 days, and 20.54 MPa (100%) at 28 days. The compressive strength of concrete using WPC is higher than grey cement at all ages. The rate of compressive strength of concrete using WPC is almost the same as grey cement at all ages.

The findings from the investigation conducted, to compare the structural performance of concrete containing treated (TOPEFB) and untreated Empty Oil Palm Fruit Bunch (OPEFB) fibres are presented in this paper. For the TOPEFB fibres, the dried fibres were treated with 0.2% NAOH solution following the procedures of appropriate authority. The structural parameters investigated were consistencies, setting times, densities, compressive and tensile strengths of concrete incorporating TOPEFB and OPEFB fibres in the mix. The addition of fibres was limited to 1.20% by weight of cement in the concrete. The interval of addition was 0.2%. The results showed that (i) the setting times of mortars containing TOPEFB fibres were higher than that of mortars with OPEFB fibres, (ii) concrete specimens containing TOPEFB fibres are more workable that concrete specimens with OPEFB fibres, (iii) densities of concrete specimens containing OPEFB fibres were in the range for normal concrete applications while the densities for specimens with TOPEFB developed densities that fell in the heavy weight concrete classification, (iv) concrete specimens containing TOPEFB fibres developed higher compressive strengths than specimens with OPEFB fibres and (v) tensile strengths of concrete specimens containing TOPEFB fibres were higher than specimens with OPEFB fibres by at least 59.04%. The overall conclusion from the findings of this study is that concrete specimens containing TOPEFB fibres have superior structural properties than specimens with OPEFB fibres

The use of old building design codes and improper execution of recent seismic design practices resulted in substandard and vulnerable reinforced concrete building stock, the majority of which is built with weak beam-column joint connections (i.e. joint panels having no transverse reinforcement and built in low strength concrete). In order to understand the seismic response and damage behavior of recent special moment resisting frame (SMRF) structures with the defect of weak beam-column joints, shake table tests were performed on two 1:3 reduced scale two storey and one bay RC frame models. Reference code design and weak beam-column joint frame models were subjected to unidirectional dynamic excitation of increasing intensities using the natural record of 1994 Northridge Earthquake. The input scaled excitation were applied from 5 % to 130 % of the maximum input peak ground acceleration record, to force the test models from elastic to inelastic stage and then to fully plastic incipient collapse stage. The weak beam-column frame experienced flexural cracking of the columns, longitudinal bar-slip in beam members, cover concrete spalling and severe damageability of the joint panels under multiple dynamic excitations. The deficient frame was able to resist only 40 % of the maximum acceleration record as compared to the code design frame, which was able to resist up to130 %. Based on the experimental observations, a drift-based damage scale was developed for different performance limits states that can be employed for the global performance assessment of deficient weak beam-column joint RC frames.

Using biomass waste as supplementary cementing material (SCM) in concrete has attracted researchers' attention for efficient waste utilization and reducing cement demand. Sugarcane bagasse ash (SCBA) is one such example of biomass waste. It is an agricultural waste obtained when sugarcane bagasse from the sugar industry is used for power generation and disposed of in open-air dumping sites. Its waste disposal causes the generation of particulate matter, degrading air quality. In this study, the effect of processed SCBA as SCM in concrete has been investigated. The processing of the SCBA involved the removal of fibrous and carbon-containing particles by sieving followed by grinding. The SCBA was ground for 45 min until the surface area was comparable to that of cement and was then used for further characterization and incorporation into concrete. The 45 min grinding time resulted in 2.92 times higher pozzolanic reactivity of the SCBA. The SCBA was incorporated by replacing cement in different weight fractions (10%, 20%, 30%, 40%) in concrete. Test results showed that the concrete workability increased with SCBA incorporation, whereas the resulting concrete density was reduced. The results of the mechanical properties, including compressive sstrength and hardened density, were enhanced upon the cement replacement by SCBA. Concrete containing 30% SCBA can be used for structural applications as its 28 days compressive strength was 21 MPa, which complies with ACI 318-16 specifications. Concrete resistance against scaling and leaching due to adverse effects of sulfuric and hydrochloric acid considerably increased with SCBA addition and was due to microstructure densification by secondary hydrates formation as lower portlandite content was detected by thermogravimetric analysis. Hence, SCBA processing increases its reactivity, as reflected by the improved mechanical properties and greater durability of SCBA-incorporated concrete. [ABSTRACT FROM AUTHOR]

To promote the in-situ and structural application of waste concrete in cold regions, the sustainable application potential of waste concrete in a freeze-thaw (F-T) environment was comprehensively evaluated from three aspects of performance, environmental load, and economic benefit. The recycled aggregate concrete (RAC) was produced by recycled coarse aggregate (RCA), which was obtained from the crushing of natural aggregate concrete (NAC) after every F-T 150 cycles until F-T failure. The effects of F-T damage of parent concrete on the physical properties of RCA and mechanical and frost resistance of RAC under 35% flexural stress were studied. Besides, the sustainability of NAC and RAC was compared and analyzed by emergy theory. The results suggested that the physical properties of RCA deteriorated gradually with the accumulation of F-T damage to parent concrete. The RCA obtained from parent concrete that suffered F-T damage could be used as coarse aggregate for structural concrete when F-T damage is smaller than 0.367. The F-T damage of parent concrete had an adverse effect on the mechanical properties and frost resistance of RAC. The frost resistance of RAC obtained from parent concrete with larger F-T damage was worse. The RAC prepared from parent concrete without F-T failure can serve 50 years in cold regions, while that with F-T failure can only serve 30 years. The F-T damage microelements were dispersed in the adhesive mortar of RCA and transferred to RAC, resulting in the reduction of the mechanical properties and frost resistance of RAC. Emergy analysis showed that the reuse of waste concrete after F-T failure required higher economic input, higher environment load, lower output efficiency, and sustainability. The performance, environmental load and economic benefit of RAC prepared by using waste concrete after F-T failure were inferior to that of waste concrete without F-T failure. Waste concrete after F-T failure is not recommended to be used as coarse aggregate for structural concrete. [ABSTRACT FROM AUTHOR]

The Eggshell fabrication process combines the 3D printing of formwork with the simultaneous casting of a fast-hardening concrete. One limiting factor to reaching mass-market adoption is a suitable reinforcing strategy. In this study, a reinforcement strategy combining steel reinforcing bars with steel fibres is explored. A series of eight beams were produced using the Eggshell process or conventionally cast. The longitudinal reinforcement was provided by two reinforcing bars, and two types of fibres, either mixed with the concrete or placed and aligned between the cast concrete layers, were used as shear reinforcement. The results showed that combining conventional longitudinal reinforcement and fibres as shear reinforcement is a suitable strategy. These findings were applied to fabricate an optimised beam with a volume reduction of almost 50%. The structural performance of this beam was similar to the beam with a rectangular cross-section with the same reinforcement strategy showing the potential of Eggshell in combination with an innovative reinforcement strategy to produce material-efficient structural concrete elements. [ABSTRACT FROM AUTHOR]

This paper reviews the technical aspects related to the long-term field exposure practice in marine environments, based on the return of experiences of major marine exposure sites in world-wide scope. The long-term exposure practice helps both the research on durability mechanisms of structural concretes under real environments and the calibration of durability models to support the life-cycle management of concrete structures. The presentation of the field exposure data can be categorized into the information relevant to exposure sites, the data related to the exposed materials and specimens, the information of environmental actions, and the data related to the performance of materials. A standardized presentation of these data can help the efficiency of data sharing and exploitation. The exploitation of exposure data employs various models to represent the chloride ingress and the induced corrosion risk of the embedded steel bars. There are needs for models addressing the strong environment-material interactions, and simple yet reliable durability indicators for engineering use. The design and operation of exposure stations need the careful choice of exposure sites and specimens, the appropriate scheme for monitoring and inspection of exposed specimens, the systematic recording and management of exposure data, and the regular maintenance of exposure facilities. The support of exposure data for life-cycle management is demonstrated through the durability planning of a real project case. The good practice of long-term field exposure is summarized in the end. [ABSTRACT FROM AUTHOR]

To perform the assessment of reinforced concrete infrastructures in service, a multi-scale simulation has been developed and improved with an integrated hygro-thermal-chemo-electrical-mechanistic approach. Various durability issues are successfully evaluated in terms of fatigue behaviours with damage induced by moisture motion through pores and cracks, temperature-related deterioration such as frost/fire damage, degradation by chemical reaction like alkali-silica reaction, and the macro-cell corrosion coupled with multi-ion equilibrium which is electro-chemical phenomenon. Moreover, the long-term performance evaluation influenced by the drying shrinkage is also successfully conducted. Furthermore, the multi-scale integrated approach is coupled with AI technique and data assimilation techniques. The crack locations and their widths are converted to space-averaged strains, which are built inside the cyber storage for the futural performance prediction. The hazard map of crack patterns on the surface of concrete deck is inversely derived from the artificial neural network, which is built according to the big dataset of the past maintenance records. Through both methods, the importance of using both-eye diagnosis is realized and proposed for lifetime assessment of structural concrete. [ABSTRACT FROM AUTHOR]

Shrinkage in hydraulic materials is a complex time-dependent process. For standard concretes, one of the most significant parts of shrinkage is drying shrinkage. In fact, to predict deformations of concrete due to shrinkage, various predictive models have been developed; most of them use many numbers of factors that can affect shrinkage such as concrete strength, concrete age at loading, curing conditions type, ambient conditions, type of cement and aggregates, water to cement ratio, concrete mix, member shape and size, loading duration and type. A such number of parameters increases the complexity of using these models lead to some prediction imperfections; thence a new simplified model is needed. The main target of the current paper is to formulate a novel and simplified model with a minimum of factors that affect drying shrinkage behaviour as like as relative humidity and volume to area ratio of the concrete element (V/S). To achieve this goal, we had developed a prediction model based on probability density function and a small number of parameters that influence shrinkage like relative humidity and volume to surface ratio of the element. A huge database has been used to calibrate our model's parameters using the most recent studies and researches to validate the model. [ABSTRACT FROM AUTHOR]

Recycled materials from construction and demolition waste, such as recycled concrete aggregate, recycled brick aggregate, or recycled asphalt coming from the milling of road/motorway surfaces, are the key for a sustainable production of concrete. This paper reviews in particular the use of recycled asphalt pavement (RAP) aggregates in the production of concrete for structural uses. An overview is initially presented to describe the different areas of use of RAP, its definition and the limitations imposed by codes and standards. Relatively to the experimental data provided by the literature, a comparison with the Italian minimum requirements is also provided. Lastly, the influence of RAP on the characteristics of concrete such as compressive strength, flexural strength, Young's Modulus and a study of durability are presented to define the possible applications of RAP in structural concrete in relation to the current allowable percentage of substitution. [ABSTRACT FROM AUTHOR]

In this paper, the behavior of structural concrete linear bar members was studied using numerical model implemented in a computer program written in MATLAB. The numerical model is based on the modified version of the procedure developed by Oukaili. The model is based on real stress-strain diagrams of concrete and steel and their secant modulus of elasticity at different loading stages. The behavior presented by normal force-axial strain and bending moment-curvature relationships is studied by calculating the secant sectional stiffness of the member. Based on secant methods, this methodology can be easily implemented using an iterative procedure to solve non-linear equations. A comparison between numerical and experimental data, illustrated through the strain profiles, stress distribution, normal force-axial strain, and moment-curvature relationships, shows that the numerical model has good numerical accuracy and is capable of predicting the behavior of structural concrete members with different partially prestressing ratios at serviceability and ultimate loading stages.

Abstract Due to the population increase, to the improvement of life conditions, to the elevation of levels of consumption and the growing industrialization of developing countries, it is estimated that the production of concrete will present significant increase in the next decades. The process of producing cement is responsible for approximately 5 % of the emissions of CO2, an expressive environment pollutant. In this context, this work presents an evaluation of the influence of partial substitution of cement by ornamental rock waste (ORW) on the physical and mechanical properties of concrete. ORW from a local marble and granite processing company was used. The waste was mineralogically characterized through X-ray diffraction (XRD) essays, energy-dispersive X-ray (EDX) microanalysis, and physically characterized through laser granulometry and specific mass. For this, was adopted a concrete trace as reference, produced with CP V-ARI cement (similar to ASTM Type III), from IPT dosage. Waste was used in proportions of 5 %, 7.5 %, 10 % and 12.5 % of substitution of cement by mass. Results were treated with ANOVA and multiple comparison of means, indicating a possibility of substitution of until 10% of cement by ORW, creating a concrete with proper resistance to Brazilian regulations regarding the classification as structural.

On the basis of strut-and-tie models (STMs) in accordance with international concrete codes such as ACI 318-14, AASHTO LRFD, CSA A23.3, Eurocode2 and fibMC 2010, a safety-based evaluation of shear design methods for RC deep beams was performed and is reported in this paper. The variability in load actions and member resistances consisting of uncertainty in material characteristics, fabrication tolerances and modeling uncertainties were taken into account as random variables. Using Rackwitch-Fiessler’s procedure with typical ranges for normal and high strength concrete and an extensive range of live-to-dead load ratios, the reliability or safety indices used to measure the safety level were investigated. It was found that the deep beams made from normal strength concrete and designed using STMs following the international concrete codes considered here provided a satisfactory safety level. Finally, for each of the STMs for design of deep beams, probability-based reduction factors are suggested to fulfill the target reliability index by greater than 3.5.

In the construction industry, there is growing attention of using effective external strengthening techniques such as bonding of Carbon Fiber Reinforced Polymers (CFRP) composites onto the external deficient faces of the structural members due to their ease of installation, low invasiveness, high corrosion resistance, and high strength to weight ratio. As a result, the center of consideration of the majority of previously published studies was either only on the impact of fibers on the structural behavior of reinforced concrete elements or using CFRP composite as external strengthening for flexural or shear. The intent was to arrive at the vital CFRP strengthening technique that provides an effective increase in the flexural and shear strength while maintaining ductile failure mode. Therefore, this paper investigated the behavior of simply supported RC beams strengthened using CFRP and subjected to combined bending and torsion using Nonlinear Finite Element Analysis (NLFEA). Twenty-six models have been constructed and divided into six groups to scrutinize the effect of clear span to depth ratio; CFRP length; CFRP strip spacing; and CFRP depth. The results showed that the increase in the clear span to depth ratio as well as length of CFRP leads to a notable increase in the ductility and decreases the ultimate load. The models with zero spacing CFRP strips (Fully) showed a higher considerable effect than the models with strips wrapping. Furthermore, this enhancement was the highest for group six which contains the models with the highest CFRP depth.

The partial replacement of conventional natural coarse aggregate (NCA) with artificial light weight aggregate (LWA) manufactured from local clay and solid waste to develop a lightweight aggregate concrete (LWAC) for the structural use was studied in this paper. Red clay and Savar clay were used individually with solid wastes like rice husk ash (RHA) and waste glass to produce LWA. The suitability of raw materials and LWA was evaluated by investigating various properties. The mechanical, thermal and durability properties of manufactured LWAC were explored. The results of physical, chemical, thermal and geotechnical properties revealed that Red clay is better than Savar clay for the preparation of LWA. All the physical and mechanical properties of LWA prepared from Red clay are suitable for the preparation of LWAC compared to Savar clay. The test results demonstrated that the concrete manufactured by replacing 30 % of NCA with LWA produced a concrete of lightweight properties. The compressive strength of LWAC for 7 and 28 days was observed as 28 and 48 MPa, respectively. The results of modulus of elasticity, splitting tensile strength, flexural deformation, and creep test of LWAC revealed that these mechanical properties meet the requirements for the structural concrete. The RCP test proves that chlorine permeability of LWAC is comparable with NCA. It was observed that the superior performance of LWAC can be achieved only when the optimized mix designed is followed strictly. The suitability of the replacement of natural aggregate by LWA may be helpful for Bangladesh due to the scarcity of natural coarse aggregate and reusability of solid waste materials., Competing Interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (© 2024 The Authors.)