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Concretes made with different fine aggregates (natural river sand, artificial crushed sand, artificial gravel sand and a hybrid sand (50% river sand and 50% gravel sand by mass)) were experimentally investigated. The concretes were found to have little differences in compressive strength and elastic modulus (less than 6.4%). Compared with the concrete made with natural river sand, the concretes made with artificial sands demonstrated higher flexural strengths (3.5–11.1%) and splitting strengths (4.4–12.8%) at 28 days, but lower workability (21.4–35.7%), water permeation resistance (34.3–53.7%) and abrasion resistance (2.9–20.6%). The compressive, flexural and splitting tensile strengths of the concretes increased with time under water curing. Under sulfate attack, the compressive strengths of the concretes were enhanced at 56 days but reduced at 90 days. In comparison with water curing, the reductions in compressive strength due to sulfate attack were 2.6–7.7% at 56 days and 11.8–24.4% at 90 days. Weibull distribution analysis was conducted to explore the sensitivity of concrete strength to the type of fine aggregate. [ABSTRACT FROM AUTHOR]

The creation of lightweight aggregate self-compacting concrete (LWA-SCC) is a challenging endeavor with substantial consequences for the construction sector. However, the absence of firmly established design suggestions and recommendations as well as the limited availability of design approaches pose a noteworthy obstacle. To accomplish the anticipated mechanical properties while minimizing production costs as well as preserving natural resources, a thorough comprehension and understanding of the optimal combination of binders and coarse aggregate content is required. This study examines the impact of several supplementary cementitious materials (SCMs) such as silica fume (SF) and metakaolin (MK) on the fundamental mechanical characteristics of ecofriendly LWA-SCC mixes prepared with 100% sintered fly ash aggregate (SFAA) as a replacement of natural coarse aggregates (NCAs). A total of nine LWA-SCC mixes were prepared including one base SCC mix. The base SCC mix (C-SFAA100) encompasses 100% ordinary portland cement (OPC) as the sole binder, and 100% natural fine aggregates (NFAs) along with 100% SFAA. The remaining eight mixes were further parted into two Series. Series I and Series II comprise SF and MK as a replacement for OPC by 7.5%, 10%, 12.5%, and 15%, respectively. The fundamental mechanical characteristics such as compressive strength, split tensile strength, direct shear, and elastic modulus were measured after several intervals. In addition, microstructural analyses were also executed to appraise the overall efficacy of LWA-SCC combinations. The results such as the compressive strength of the SCC mixes CSF15-SFAA100 and CMK15-SFAA100 increased by 11.3% and 18.5%, respectively, after a curing time of 90 days compared to the base SCC mix C-SFAA100 confirmed that the incorporation of SCMs into LWA-SCC mixtures improves their mechanical characteristics. [ABSTRACT FROM AUTHOR]

Chloride attack severely impacts the performance of reinforced concrete. The total and free chloride ion concentration (CIC) of self-compacting concrete (SCC) prepared with three supplementary cementitious materials (SCM) – fly ash (FA), blast furnace slag (BS) and silica fume (SF) – were measured by accelerated salt immersion tests. The apparent chloride diffusion coefficient (CDC) at any exposure time and erosion depth were calculated using the Boltzmann–Matano method. The influence of the type and content of SCM, the water–binder ratio (W/B) and the type of salt solution on CIC and CDC were investigated. Both the introduction of SCM and the reduction of W/B effectively reduced the CIC. The SCM that most effectively reduced CIC was SF, followed by BS and then FA. Free CIC was reduced to a greater degree than total CIC in FA and BS concrete, but the opposite was true for SF concrete. The presence of calcium chloride in salt solution increased total CIC while reducing free CIC. Apparent free CDC dropped over exposure time and initially increased with erosion depth but eventually stabilised. A model of apparent free CDC considering time–depth dependency was created, which shows that time reduction factors of CDC is greater in SCC containing SCM than in control SCC. [ABSTRACT FROM AUTHOR]

AbstractThe concrete equivalent mortar (CEM) method, mainly used in the laboratory, offers a course that facilitates and accelerates experimental test programs with relatively small amounts of materials. To this end, two CEM mixes, with natural and recycled aggregates, at different superplasticizer (SP) concentrations, were tested. The key objective was to investigate how CEM flow property changed at 0, 30, and 60 min of resting time, emphasizing the material’s structuring and destructuring effects. This study describes the flow behaviour of CEMs applying specific tools. Also, a vane-geometry rheometer was used to obtain rheological flow curves. Whatever the SP content in the structuring state, the results indicated reduced flow properties over time. However, an SP content of 1.3% retard the structural build-up property that was not evident at 60 min-rest time. Spread diameters ranging between 300 and 400 mm are measured with the mini cone immediately after mixing. After 60 min of resting time, these diameters were reduced between 260 and 300 mm. Remixing after prolonged rest periods reduces the flow stress values, which decrease from 10 to 18 Pa to 6 to 14 Pa. After a structural build-up at a rest time, the structural break-down effect by remixing re-fluidifies the mixtures. The fluidity has recovered its initial state, reflecting a thixotropic property. [ABSTRACT FROM AUTHOR]

Improvement of hydrophysical properties and corrosion resistance of self-compacting concrete to the effects of alternate freezing–thawing and aggressive soils of Southern and Central Kazakhstan is of interest to a wide range of researchers from the side of practical application of the obtained results in construction practice. It is proposed to form a spatially reinforced fine crystalline structure of a cement matrix with the maximum dense packing by using a complex modifier (hyperplasticizer + polymer + microsilica + fibro fibers) in the composition of self-compacting concretes (SCCs). The introduction of the calculated amount of the above additives increases the operational reliability of the current SCC compositions, increasing the water resistance to W16, frost resistance to F = 500, increasing the compressive strength by 20%, and reducing the mass loss of samples during corrosion leaching to 50%. It has been experimentally established that the proposed addition of the complex modifier (hyperplasticizer + polymer + microsilica + fibro fibers) to the SCC composition allows obtaining self-compacting concrete of high quality with improved performance characteristics (compressive strength, water resistance, frost resistance, and corrosion resistance). Studies have shown that the complex modifier-modified SCC compositions have a high degree of resistance in aggressive environments and leaching corrosion. Based on the results of the conducted tests, it is possible to recommend the obtained SCC compositions for the production of building products working in the zone of alternating freezing–thawing and aggressive soils. [ABSTRACT FROM AUTHOR]

This paper explores the new potential strategy of using fine recycled aggregates (fRA) derived from waste 3D printed concrete (3DPC) as a substitute for cement in additive manufacturing. This study hypothesizes that fRA can optimize mixture design, reduce cement content, and contribute to sustainable construction practices. Experimental programs were conducted to evaluate the fresh and hardened properties, printability window, and buildability of 3DPC mixes containing fRA. Mixes with replacement rates of cement with fRA by 10 vol%, 20 vol%, 30 vol%, 40 vol%, and 50 vol% were produced. A comprehensive experimental protocol consisting of rheological studies (static and dynamic yield stress), dynamic elastic modulus determination (first 24 h of hydration), flexural and compressive strengths (2 d and 28 d), and an open porosity test was performed. The obtained results were verified by printing tests. In addition, an economic and environmental life cycle assessment (LCA) of the mixes was performed. The results indicate that up to 50 vol% cement replacement with fRA is feasible, albeit with some technical drawbacks. While fRA incorporation enhances sustainability by reducing CO2 emissions and material costs, it adversely affects the printability window, green strength, setting time, and mechanical properties, particularly in the initial curing stages. Therefore, with higher replacement rates (above 20 vol%), potential optimization efforts are needed to mitigate drawbacks such as reduced green strength and buildability. Notably, replacement rates of up to 20 vol% can be successfully used without compromising the overall material properties or altering the mixture design. The LCA analysis shows that reducing the cement content and increasing the fRA addition results in a significant reduction in mix cost (up to 24%) and a substantial decrease in equivalent CO2 emissions (up to 48%). In conclusion, this study underscores the potential of fRA as a sustainable alternative to cement in 3D printed concrete. [ABSTRACT FROM AUTHOR]

Chloride attack severely impacts the performance of reinforced concrete. The total and free chloride ion concentration (CIC) of self-compacting concrete (SCC) prepared with three supplementary cementitious materials (SCM) – fly ash (FA), blast furnace slag (BS) and silica fume (SF) – were measured by accelerated salt immersion tests. The apparent chloride diffusion coefficient (CDC) at any exposure time and erosion depth were calculated using the Boltzmann–Matano method. The influence of the type and content of SCM, the water–binder ratio (W/B) and the type of salt solution on CIC and CDC were investigated. Both the introduction of SCM and the reduction of W/B effectively reduced the CIC. The SCM that most effectively reduced CIC was SF, followed by BS and then FA. Free CIC was reduced to a greater degree than total CIC in FA and BS concrete, but the opposite was true for SF concrete. The presence of calcium chloride in salt solution increased total CIC while reducing free CIC. Apparent free CDC dropped over exposure time and initially increased with erosion depth but eventually stabilised. A model of apparent free CDC considering time–depth dependency was created, which shows that time reduction factors of CDC is greater in SCC containing SCM than in control SCC. [ABSTRACT FROM AUTHOR]

This study aimed to present the effect of mixture proportions (including coarse-to-fine aggregate ratio and water-to-binder ratio) and mixture compositions (including the addition of different supplementary cementing materials and fibers) on the impact resistance and mechanical properties of concrete cured in cold temperatures. The impact resistance was evaluated using drop-weight and flexural impact tests conducted on concrete samples cured in different curing conditions. The studied parameters included coarse-to-fine aggregate (C/F) ratio (0.7 and 1.2), water-to-binder (w/b) ratio (0.4 and 0.55), type of supplementary cementing materials (SCMs) [20% metakaolin (MK) and 10% silica fume (SLF)], and the addition of steel fibers (0.35%) (SFs). The studied mixtures were cured under different curing conditions, including moisture condition at 23°C, air condition at 23°C, +5°C curing condition, and −10°C curing condition. The positive effect of using SFs and SCMs (MK and SLF) on enhancing the impact resistance and splitting tensile strength (STS) was more pronounced in samples cured at normal curing temperatures compared to samples cured at low temperatures. The mechanical properties and impact resistance of mixtures developed with higher C/F and w/b ratios were more affected by the low-temperature curing condition compared to the control mixture (with lower C/F and w/b ratios). The results also showed that low-temperature curing had a more pronounced negative effect on the impact resistance and STS than the compressive strength. [ABSTRACT FROM AUTHOR]

Compared with traditional portland cementitious material, alkali-activated material (AAM) had the advantages of low carbon emission, energy saving, excellent durability, strength, and high temperature resistance. It has been proved that the addition of a fiber or nano-particle could improve the mechanical properties of AAM. The fresh and hardened properties of nano-CaCO3 (NCC) and polypropylene fiber (PPF) reinforced AAM were studied in this paper. The hybrid effects of PPF with various volume fractions (0%, 4%, and 8%), aspect ratios (0–464.52), and NCC with various content (0%, 1%, and 2%) on the slump spread, flow rate, flexural strength, compressive strength, and ultrasonic velocity of AAM were investigated. For flowability, the mixture with 0.4% 6 mm and 0.4% 12 mm PPF was the optimal, showing a positive hybrid effect. The hybrid use of PPF and NCC significantly improved the flexural strength, but the compressive strength was not significantly improved. The hybrid effect factors for compressive strength were lower than those for flexural strength. The positive hybrid effect of strength was most obvious when the nano-CaCO3 was 1%. The threshold for fiber factors was 200. Microstructure studies showed that the bridging effect of PPFs can limit the crack development and enhance the strength of AAM. Nano-CaCO3 promoted the denseness of AAM and bond between fiber and matrix. The hybrid of PPF in different lengths and NCC could decrease fiber consumption, reducing the cost and promoting the engineering application of fiber-reinforced AAMs. The effect of hybridization of calcium carbonate nano-particles with polypropylene fibers on the fresh and hardening properties of alkali-activated materials has practical applications in the construction industry. One of its main advantages is its excellent flowability, which allows the material to be self-consolidating. This property allows it to be used effectively in areas such as post-tensioned grouting, pipe concrete, and other grouting processes, where the material flows effortlessly and fills voids efficiently. In addition, the mixing effect of the CaCO3 -nano-particles and the polypropylene fibers enhances the stability and strength of the material, which further enhances the durability and structural stability of the concrete elements. Overall, this blend has excellent flow and self-consolidation properties, making it an important choice for applications such as postgrouting and reinforced concrete construction. [ABSTRACT FROM AUTHOR]

This paper presents a pilot study on the characterization of the physical and mechanical properties of a novel green concrete with two different substituted recycled plastic aggregates. A reference mix with an average compressive strength of around 60 MPa is considered. Recycled polyethylene terephthalate (PET) powder and recycled mixed plastic [polypropylene (PP) and polyethylene (PE)] granules were adopted to substitute fine and coarse aggregates. Two different substitution strategies were employed. In the first one, the PET powder is used to substitute the fine sand by volume. In the second one, the PET powder is used to substitute the fine sand while the recycled mixed plastic granules are used to substitute the coarse sand and fine coarse aggregates by volume (50% for PET powder and 50% for recycled mixed plastic granules). Four total replacement levels (5%, 10%, 20%, and 30%) by volume were considered. The fresh concrete properties (slump and density), compressive and flexural behavior, toughness, and permeability are investigated. Finally, a microscale characterization of the plastic-paste interface is provided. An interpretation of the test results of this study by comparing them with the findings of previous studies is provided, along with the provision of two predictive equations for the compressive and flexural strength reduction factors. Results show reduced flowability for PET cases due to particle shape, slight compressive strength reduction at low substitutions, improved flexural strength at low levels, decreased permeability, and microscale enhancements. The comprehensive evaluation indicates promising physical and mechanical performance of the novel green concrete. [ABSTRACT FROM AUTHOR]

A sustainable and green approach to concrete mix design is fundamental for the construction sector in terms of reducing carbon dioxide ( CO 2 ) emissions and conserving non-renewable natural resources. This article proposes a novel mix design method for sustainable high-strength self-compacting concrete (HSSCC) based on rheological and mechanical properties with the aim of reducing cement content in such mixes. HSSCC mixes were designed using ground granulated blast furnace slag (GGBS) and fly ash to replace up to 40% of the cement content and tested for target compressive strengths ranging between 70 and 100 MPa. The proposed design method was numerically programmed to provide straightforward and realistic guidance in the form of design charts and verified through the design and production of sixteen HSSCC mixes consisting of varying sand-to-aggregate ratios (S/A). All mixes satisfied the self-compacting concrete criteria in the fresh state and achieved the targeted viscosity and compressive strength values. The effects of S/A and paste-to-solid (P/S) ratios on the rheological properties were evaluated. The experimental results demonstrated that the proposed mix design method could produce HSSCC with excellent fresh and mechanical characteristics while being eco-efficient with respect to CO 2 emissions and cement consumption. [ABSTRACT FROM AUTHOR]

In this article, the potential of employing self-compacting geopolymer concrete in massive elements has been investigated. The main binder consisted of 85% ground granulated blast furnace slag and 15% fly ash. An alkaline solution of sodium hydroxide and sodium silicate was utilised. The effects of four parameters (binder content, water-to-binder [W/B] ratio, Na2O% and coarse-to-fine aggregate [C/F] ratio) on the fresh, mechanical and thermal properties of Massive Self-Compacting Geopolymer Concrete (MSCGC) mixes were evaluated. Taguchi's design of experiments was used to minimise the number of trial mixes. The heat of geopolymerisation of MSCGCs was monitored using a semi-adiabatic chamber and then applied to concrete samples using a temperature match curing system. The maximum compressive and splitting tensile strengths and modulus of elasticity were 62.7 MPa, 5.04 MPa and 33.26 GPa, respectively. Binder content was identified as the most significant parameter affecting the thermal and mechanical properties of the mixtures. The impact of the C/F ratio was greater than the W/B ratio on the thermal characteristics. The results of a numerical analysis reveal that although a higher binder content enhances the mechanical properties of the MSCGCs, it leads to an increased risk of cracking owing to greater heat production. [ABSTRACT FROM AUTHOR]

Composite constructions made of wood and concrete are being researched as revolutionary structural components that offer many benefits. The connection in timber-concrete-composite (TCC) is typically made via mechanical means. This study describes the TCC bonded by adhesives, particularly the mechanical behaviour of the joints between timber (GL24h) and self-compacting concrete (SCC) set by the dry or wet bonding process. For this purpose, double push-out shear tests on TCC joints bonded by epoxy resin of adhesives were performed. The role of several variables was considered for both fabrication processes. These parameters were: variation of moisture content (m.c.) of timber, adhesive type, adhesive thickness, sand addition, concrete surface treatment, and scale of bonding length. The results showed that glueing seems to be a feasible alternative instead of mechanical means for producing dry and wet TCC joints. Under dry conditions of timber elements, the shear strength can be considered highly satisfactory, with a mean value range of 6–8 MPa. The failure mode is primarily affected by concrete and timber failure. However, the findings of this study confirm the hypothesis that increasing the moisture content of timber before the gluing process significantly reduces the shear strength of adhesively bonded TCC joints by approximately 30% in certain instances. These results contribute to understanding the challenges and limitations of the bonding system, providing valuable insights for optimizing the design and manufacturing of timber-concrete composites. [ABSTRACT FROM AUTHOR]

Compaction quality significantly influences the strength and durability of concrete in structures. Under-compacting can retain entrapped air, reducing strength, while over-compacting can lead to segregation, creating local variances in strength distribution and modulus of elasticity in the concrete structure. This study examines the widely adopted concept that compaction is optimal when bubbles cease to emerge on the concrete surface. We recorded the surface activity of six comparable concrete specimens during the compaction process using a 4K video camera. Four specimens were compacted using a table vibrator and two with a poker vibrator. From the video frames, we isolated the bubbles for analysis, employing digital image processing techniques to distinguish newly risen bubbles per frame. It was found that the bubbles continuously rose to the surface in all specimens throughout the compaction process, suggesting a need for extended compaction, with some specimens showing a slow in the rate of the bubbles' emergence. However, upon examining the segregation levels, it was discovered that all the specimens were segregated, some severely, despite the continued bubble emergence. These findings undermine the reliability of using bubble emergence as a principle to stop compaction and support the need for developing online measurement tools for evaluating compaction quality. [ABSTRACT FROM AUTHOR]

This research study aims to understand the application of Artificial Neural Networks (ANNs) to forecast the Self-Compacting Recycled Coarse Aggregate Concrete (SCRCAC) compressive strength. From different literature, 602 available data sets from SCRCAC mix designs are collected, and the data are rearranged, reconstructed, trained and tested for the ANN model development. The models were established using seven input variables: the mass of cementitious content, water, natural coarse aggregate content, natural fine aggregate content, recycled coarse aggregate content, chemical admixture and mineral admixture used in the SCRCAC mix designs. Two normalization techniques are used for data normalization to visualize the data distribution. For each normalization technique, three transfer functions are used for modelling. In total, six different types of models were run in MATLAB and used to estimate the 28th day SCRCAC compressive strength. Normalization technique 2 performs better than 1 and TANSING is the best transfer function. The best k-fold cross-validation fold is k = 7. The coefficient of determination for predicted and actual compressive strength is 0.78 for training and 0.86 for testing. The impact of the number of neurons and layers on the model was performed. Inputs from standards are used to forecast the 28th day compressive strength. Apart from ANN, Machine Learning (ML) techniques like random forest, extra trees, extreme boosting and light gradient boosting techniques are adopted to predict the 28th day compressive strength of SCRCAC. Compared to ML, ANN prediction shows better results in terms of sensitive analysis. The study also extended to determine 28th day compressive strength from experimental work and compared it with 28th day compressive strength from ANN best model. Standard and ANN mix designs have similar fresh and hardened properties. The average compressive strength from ANN model and experimental results are 39.067 and 38.36 MPa, respectively with correlation coefficient is 1. It appears that ANN can validly predict the compressive strength of concrete. [ABSTRACT FROM AUTHOR]

Damage Assessment in concrete under fatigue loading – method for modeling energy transport through ultrasonic waves This paper assumes that the wave field of an ultrasonic pulse in the 200 to 800 kHz range in a conventional self‐compacting concrete specimen has both ballistic and diffuse components. Therefore, it is necessary to apply a generalized analytical model based on radiative transfer theory to realistically describe the energy transport of elastic waves in concrete. To solve this energy transport problem, both an analytical solution approach and a numerical model have been presented. The numerical model was created using the Monte Carlo method. The initial energy E0, the mean free path ls and the absorption length la were used to characterize the wave scattering in concrete. The evaluation of a fatigue loaded specimen show that the energy transport has both components over the test duration, with the ballistic component dominating for the undamaged sample and the diffuse component dominating for the severely damaged sample. The stiffness degradation during fatigue tests was described based on well‐known parameters such as the static and dynamic modulus of elasticity and the energy transport parameters E0, ls and la. [ABSTRACT FROM AUTHOR]

This experimental study investigated the performance of self-compacting concrete (SCC) mixes with magnesia (MgO) waste. In the series produced with a water/binder ratio of 0.40, cement was replaced by magnesia waste at 2%, 4% and 10% by weight in the SCC. Le Chatelier test, slump flow, compressive strength, flexural strength, depth of penetration of water under pressure, ultrasonic pulse velocity and water absorption by capillary testing was conducted to assess sample performance. X-ray diffraction, thermogravimetric analysis, mercury intrusion porosimetry, differential thermal analysis and scanning electron microscopy were used for the microstructural analysis and quantification of phases within each sample. The results indicated that concrete with magnesia waste contains magnesium silicate hydrate (M–S–H) and brucite ((Mg(OH)2) products. Brucite causes strength loss in concrete. Up to 90 days, specimens with magnesia showed increasing compressive and flexural strength. As the amount of magnesia waste increased, the porosity, depth of water penetration under pressure and water absorption by capillary increased. Incorporating more than 10% of magnesia waste in the SCC mixtures resulted in declining strength. The addition of magnesia waste enhanced the expansion of SCC. An optimum dosage (2%) of magnesia waste was the most advantageous to the strength of SCC. [ABSTRACT FROM AUTHOR]

The acoustic emission (AE) method is a nondestructive test method used when monitoring the damage propagation by detecting high-frequency elastic waves produced by the refraction process. Self-compacting concrete (SCC) is a special type of concrete that does not require vibration, has excellent fluidity, and is resistant to segregation. In this study, it is aimed to investigate the functioning of the AE technique, which is frequently used in normal concrete, in the behavior of SCC. For this purpose, simultaneous monitoring of SCCs under uniaxial compression load was performed with the AE method. In the concrete production, CEM I 42.5 R cement was used as binder, and fly ash (FA) and marble powder (MP) were used as mineral additives. The mineral additives used in the mixture were replaced with cement at a rate of 20%. In addition to the compressive strength of SCCs, crack analysis, AE amplitude, AE energy, ringing counts, and cumulative count results were investigated as a result of AE measurements. With the AE parameters obtained as a result of the simultaneous measurement, the behavior of SCCs under uniaxial load was successfully monitored. It has been observed that the behavior of SCC using different mineral additives changes according to the mineral additive type. Although the differences in compressive strengths are small, it has been demonstrated that the AE method can be followed successfully in different concrete types and different contents and the behavioral differences are revealed. [ABSTRACT FROM AUTHOR]

Solid waste generation and its sustainable disposal are big concerns in the present decade. Mine tailings and incinerated bottom ash are among the greatest solid waste contributors to the environment. To promote sustainable development, material reuse and recycling are important. In the present study, a feasibility study was conducted by utilizing such tailings and bottom ash for the production of controlled low-strength material (CLSM). The amount of cement was utilized less, and by controlling the design mix with a targeted flow, low-strength material was produced. Three different cement contents (60, 80, and 100 kg/m3) and 100% mine tailings or incinerated bottom ash were used as fine aggregate material. Fresh properties of different CLSM mixes, mechanical performance, and leaching behavior were conducted to confirm the final product. It was observed that both the mine tailings and bottom ashes are suitable as an aggregate material for CLSM mixes. The compressive strength values of different CLSM mixes at 28 days were observed between 0.13 and 1.88 MPa for various aggregate materials (mine tailings and bottom ash) and cement content. Moreover, there is an influence in the reactivity of cement hydration by the aggregate (tailings and ash), which was confirmed by the calorimetry study. The selected mine tailings and bottom ashes are not inert (like natural aggregate) within the CLSM mixes, and the chemical composition of the raw materials affects their fresh and hardened properties. The leaching test further shows that the final product could leach different heavy metals beyond the limit for inert materials, but within the nonhazardous limits by international standards. The present work deals with CLSM mixes with locally available industrial side streams; some important properties such as hardening time, penetration resistance, shrinkage, excavatability, and other durability properties (i.e., acid attack, freezing and thawing resistance) were not considered in the study and can be studied further. [ABSTRACT FROM AUTHOR]

Rheology of Self-Compacting Concrete (SCC) containing selected silica fume dosages (0% (control mix), 5%, 10% and 15%) in a binary binder has been investigated using the flow-curve test protocol implemented on a co-axial cylinder rheometer. At each silica fume dosage, coarse recycled concrete aggregate volumetric replacement levels were 0%, 50% and 100%. Calibration of selected flow models with the measured flow data showed that rheology transitioned from shear thickening to shear thinning as the silica fume dosage increased from 0% to 15%, other mix constituents remaining unchanged. Similar flow behaviour was noted in the SCCs made with the recycled concrete aggregates (SCRACs) across all replacement levels though for a given silica fume dosage, degree of shear thinning decreased with increasing contents of the coarse recycled aggregates. The experimental results have been used to propose a workability box containing bounds for acceptable rheology of the SCCs and the SCRACs. [ABSTRACT FROM AUTHOR]

A new type of small, dry-filled geotextile tubes is introduced, that, in a stacked formation, can be used as dike cores. Dikes made out of these tubes consist of great potential regarding more resilient flood protection. The geotextile protects the fill from erosion, enabling steeper slopes along with reduced material and less land consumption. The behavior and potential failure mechanisms of such dikes were investigated first by literature research and second by full-scale hydraulic model tests under systematic variation of tube number, number of textile layers, filling ratio, and fill material. The tubes were exposed to the loads of seepage and overflow. Most relevant failure mechanisms were seepage-induced sagging, lateral displacement, and overturning of the upper tube due to overflow. During seepage, the tube height was reduced by up to 22.8 % due to sagging. Overflow led to a lateral displacement of up to 13 cm and, at overflow heights of 23.1 cm and 26.8 cm, to overturning of the upper tube. The present results give new insights into the behavior of innovatively constructed geotextile tubes under hydraulic loads and serve as basis for the development of design rules. • Dry-filled geotextile tubes represent a promising way towards resilient river dikes • Tube behavior is investigated experimentally under parameter variation • Sagging and lateral deformation must be considered in design rules • The tubes withstand overflow heights of >20 cm • Compacting the tubes increases the stability [ABSTRACT FROM AUTHOR]

Modeling of concrete damage is an important branch of concrete structural analysis; however, the damage behavior of different types of concrete varies. In this study, mechanical property tests were conducted to modify the damage model for aeolian sand self-compacting concrete (ASSC). Damage behaviors and stress–strain curves of prismatic ASSC specimens were investigated using the XTDIC technique, which demonstrated the increasingly decreased peak strain and deteriorated ductility of concrete with the increase of replacement rate of aeolian sand (AS). On the basis of the experimental results, the model proposed by Mazars and colleagues was modified, where scaling factors were introduced. Numerical simulations with the modified model were performed on the ANSYS platform using the Usermat subroutine and its mesh dependency was verified. The results revealed that the modified model could better reflect the effect of AS addition on the concrete structure, and it was less sensitive to the mesh accuracy. [ABSTRACT FROM AUTHOR]

To aid in the creation of sustainable structures, scientists have utilized waste materials found in the environment to serve as alternatives for traditional resources in the construction sector. They have undertaken extensive investigations pertaining to this matter. In this particular study, tempered glass as waste glass coarse aggregate (WGCA) was substituted for natural coarse aggregate (NCA) at varying proportions of 15%, 30%, and 45% in the formulation of eco-friendly self-compacting concrete (SCC), combined with hooked-end steel fibers (SFs) at various volumes. The study assessed concrete's flowability, permeability, compressive strength, and fracture parameters at 28 and 56 days. A total of 240 edge-notched disc bending samples (ENDB) and 60 cubic samples (150 × 150 mm) were tested to assess fracture resilience and compressive strength, respectively. The results showed that increasing SF and WGCA content reduced slump flow diameter and blockage ratio, particularly at higher levels. The solidified characteristics of all specimens incorporating SF and WGCA displayed heightened attributes when contrasted with the reference sample. Among the entire array of specimens, WG15SF0.5 and WG30SF0.5 exhibited the most superior performance, demonstrating an average percentage elevation of 20.29 and 27.63 in both compressive strength and fracture toughness assessments across the different curing periods. SF had the most significant impact on post-cracking behavior by enhancing load-bearing capacity through a bridging fiber mechanism. Through a comparison of the influence of SFs and WGCA on the fracture toughness of pure mode III, it was observed that the inclusion of SF in samples with a 30% replacement of WGCA resulted in an average increase of approximately 15.48% and 11.1% in this mode at the ages of 28 and 56 days, respectively, compared to the control sample. [ABSTRACT FROM AUTHOR]

Additives such as nano-silica and fly ash are widely used in cement and concrete materials to improve the rheology of fresh cement and concrete and the performance of hardened materials and increase the sustainability of the cement and concrete industry by reducing the usage of Portland cement. Therefore, it is important to study the effect of these additives on the rheological behavior of fresh cement. In this paper, we study the pulsating Poiseuille flow of fresh cement in a horizontal pipe by considering two different additives and when they are combined (nano-silica, fly ash, combined nano-silica, and fly ash). To model the fresh cement suspension, we used a modified form of the power-law model to demonstrate the dependency of the cement viscosity on the shear rate and volume fraction of cement and the additive particles. The convection–diffusion equation was used to solve for the volume fraction. After solving the equations in the dimensionless forms, we conducted a parametric study to analyze the effects of nano-silica, fly ash, and combined nano-silica and fly ash additives on the velocity and volume fraction profiles of the cement suspension. According to the parametric study presented here, larger nano-silica content results in lower centerline velocity of the cement suspension and larger non-uniformity of the volume fraction. Compared to nano-silica, fly ash exhibits an opposite effect on the velocity. Larger fly ash content results in higher centerline velocity, while the effect of the fly ash on the volume fraction is not obvious. For cement suspension containing combined nano-silica and fly ash additives, nano-silica plays a dominant role in the flow behavior of the suspension. The findings of the study can help the design and operation of the pulsating flow of fresh cement mortars and concrete in the 3D printing industry. [ABSTRACT FROM AUTHOR]

The current work examines an experimental and numerical investigation into how steel fiber reinforced concrete (SFRC) slab failure behavior is influenced by fiber orientation by pouring concrete in slab elements. Double‐ended hooked steel fibers with an aspect ratio of 50 were used in varying percentages by volume. Fresh and hardened properties of SFRC were determined based on slump flow, V‐funnel, L‐box, J‐ring test, compression, and flexure tests. The effects of different pouring/casting locations (center and corner), fiber orientation, and fiber content (0, 0.5%, and 1.0%) on the crack pattern of the SFRC slab were observed. While casting, the concrete was allowed to flow through a 30° chute angle to enhance the flowability of concrete. The SFRC slabs without fiber reinforcement undergo brittle failure without forming any prior micro cracks. Slabs with fibers experience ductile failure and show significant post‐cracking strength. The concrete's pouring position only affects the failure crack's inclination for the given workability. In the case of the corner cast slab, the crack was propagated from one edge to the opposite edge of the slab in a straight line and split into two halves. This crack pattern suggested that the fiber distribution was concentrated in half of the slab part in which the pouring corner was located. Adding 0.5% and 1.0% fiber content increased the load‐carrying capacity of slabs by 1.31 and 2.15 times, respectively. In addition to fiber content, the pouring position of concrete also made a difference in the load‐carrying capacity of slabs. The concrete pouring in the slab from the center position with 0.5% and 1.0% fiber content has 17.2% and 40% more load‐carrying capacity compared to the concrete poured in the slab from the corner position with the same fiber content. The deflection and load‐carrying capacity obtained through finite element modeling (FEM) fit the experimental results well. [ABSTRACT FROM AUTHOR]

The influence of various supplementary cementitious materials (SCMs) and fibres on the fire resistance of composite systems that combine engineered cementitious composites (ECCs) in tension with self-compacting concrete (SCC) in compression was examined. The study was designed to determine the ideal ECC formulation for optimising mechanical properties and bonding performance at ambient and elevated temperatures. The SCC and ECC were hot-joined without vibration or surface preparation, using a fresh-to-fresh casting method. Modifications to the chemical composition of the ECCs included the addition of class F fly ash (FAF), class C fly ash (FAC) or slag, as well as polyvinyl alcohol (PVA) fibres or steel fibres. The samples were exposed to temperatures of 200°C, 400°C, 600°C and 800°C, followed by comprehensive testing to evaluate their flexural strength, tensile strength and interfacial properties. The results indicate that the incorporation of an ECC layer within the SCC system significantly improved mechanical strength and thermal stability, both at ambient temperatures and under high-temperature conditions. Notably, the addition of FAF (rather than FAC or slag) in the ECC layer offered superior thermal stability and ensured the retention of desirable residual mechanical properties. Moreover, steel fibre reinforcement greatly improved the SCC/ECC bonding, outperforming PVA reinforcement at elevated temperatures. [ABSTRACT FROM AUTHOR]

This experimental study presents the effect of steel fiber (SF) and recycled coarse aggregate (RCA) on the fresh and hardened properties of Self-compacting geopolymer concrete (SCGC). Sixteenth alkali-activated based metakaolin (MK) concrete mixtures with constant binder content of 500 kg/m³ incorporated 0, 0.5, 1.0, and 1.5% volume fraction of SF and 0, 10, 20, and 30% RCA as a partially replacement for natural coarse aggregate (NCA) with sodium hydroxide concentration of 12 Molarity at ambient conditions. Fresh state of SCGC were examined slump flow, T500 flow, V-funnel, and L-box test. At 28 and 90 days the compressive strength and splitting tensile strength were investigated, the flexural strength was evaluated at 90 days. The results highlighted that RCA (30%) and SF (1.5%) significantly constrain the fresh properties of SCGC mixes. Moreover, SCGC incorporated RCA can be produced with compressive strength as high as 31.91-41.13 at 28 and 90 days, respectively. However, 1% SF and 30% RCA in MK-based SCGC appear better performance than the control mixture and leads to an ecologically friendly concrete mix that has appropriate hardening properties and that would contribute to the longevity of the construction industry. [ABSTRACT FROM AUTHOR]

Waste recovery and environmental protection and the production of low-cost UHPFC are the most trends areas of current researchers. Ultrafine (silica fume) is the basic component of ultra-high-performance fiber concrete (UHPFC), which is very sophisticated and its manufacture is limited by the capacity of some industries. This work, which falls within this context, aims to recover waste (glass, ceramics, and granite) as recycled fillers partially substituted silica fumes in the composition of the UHPFC. The study consists of two parts, the first is to find a formulation based on local materials, the second is to replace the silica fumes by recycled fillers with the percentage of 10% and 20%. The tests carried out on the fresh state mixtures are density, workability and occluded air, and on hardened state are the compressive and flexural tensile strength, sclerometer, ultrasound regarding untreated concrete, and the performance in compressive and tensile strength concerning the concrete heat treated at 90°C, as well as durability parameters (water absorption and chlorides penetrations). The results show that recycled ceramic fillers and 20% of the recycled granite fillers present an acceptable compressive strength, the recycled fillers increase the flexural tensile strength of the UHPFC and the heat treatment improves the mechanical strength. Recycled fillers affect sustainability parameters. [ABSTRACT FROM AUTHOR]