Reduction In Compressive Strength Research Articles

Investigating the Pozzolanic Properties of Canarium schweinfurthii (‘Atili’) Seed Shell Ash as Partial Replacement for Cement in Concrete

Ethnomedicinal, insecticidal, biological and other non-engineering uses of Canarium seed have been identified but little or no engineering uses have been explored. This research investigates the effect of Canarium schweinfurthii Seed shell Ash (CSSA) on the mechanical properties of concrete. CSSA was obtained after calcination of Canarium schweinfurthii seed shell at 4000C, 7000C and 1000 0C. X-ray Florescence (XRF) analysis carried out revealed the best sample of CSSA to be used for this work, and found to be a Class C pozzolana, which contains 51.21% of (SiO2 + Al2O3 + Fe2O3). The compressive and flexural strengths were determined at 7, 14, 21 and 28 days. The workability of the concrete was found to have dropped with the increment in the percentage of CSSA in the concrete. The compressive strength and flexural strength of the concrete cubes declined with the increment in the percentage of CSSA in the concrete. The compressive strength of the CSSA concrete after each curing age for the control and all the different percentages of CSSA replacement all met the minimum requirement for the characteristic strength (20 N/mm2). From the result, the reduction in compressive strength of the concrete at 28 days is between 0% and 5%, with the optimal increment in the strength achieved at 10% CSSA. The flexural strength of the CSSA concrete reduces drastically with increment in the CSSA content across all the curing ages, having an optimal replacement at 5% CSSA replacement.

Structural Sustainable Recycled Aggregate Concrete Production Under Environmental Conditions

The use of recycled aggregates (RA) in the concrete industry has become increasingly popular due to the reduction in natural aggregate (NA) consumption and the ability to reuse demolition waste. This research focuses on analyzing the performance of recycled aggregate concrete (RAC) cured with sodium sulfate (Na2SO4). Five different mixtures were created, varying from 0% RA without supplementary cementitious material (SCM), to 0%, 15%, 30%, and 45% substitution of NA with RA and SCM. The slump test was performed on all fresh RAC mixtures, which showed a decrease in slump with an increase in RA content. Both 5% Na2SO4 solution curing at 91 days and standard curing at 7, 28, and 91 days resulted in a reduction in compressive strength and ultrasonic pulse velocity (UPV) as the proportion of RA increased. Compared to standard curing, the compressive strength of specimens cured with 5% Na2SO4 solution at 91 days showed a decrease of approximately 5-7%. The UPV of SCM-based mixes showed 14-28% improvement with respect to normal aggregate concrete (NAC) in normal water curing. Furthermore, the SCM-included specimens have produced less deterioration in Na2SO4 immersion as SCM particles resist the severity of the dominant sulfate environment.

An experimental and numerical study on the hybrid effect of basalt fiber and polypropylene fiber on the impact toughness of fiber reinforced concrete

As the civil aviation industry advances, higher requirements are put forward for the performance of airport cement pavement. The frequent takeoffs and landing of aircraft will cause continuous and large impact load on airport pavement, and combined with long-term natural factors, there will be various structural diseases. These diseases not only affect the service life of pavement, navigation safety. To enhance the impact resistance and durability of concrete, the incorporation of fiber has proven an effective approach, and basalt fibers (BF) and polypropylene fibers (PF) are selected as reinforcement materials in this study. Firstly, the effects of single BF and hybrid BF and PF on the mechanical properties of concrete were explored through compressive and flexural tests considering fiber volume contents (0.1%, 0.15, 0.2%) and lengths (6 mm, 9 mm, 12 mm). Then, the drop hammer impact test method, recommended by ACI committee 544, was refined to evaluate the impact resistance toughness of concrete. Finally, the numerical simulation of the impact test was established to explain the concrete impact damage mechanism. The results show that under less than 0.15% volume content, the single BF can effectively enhance the compressive strength, flexural strength, and impact resistance of concrete. Compared with the single BF, the combination of 12 mm BF and 6 mm PF yields favorable results, encompassing improved mechanical properties and impact resistance, thus exhibiting a positive hybrid effect. The increase in PF length (9 mm) leads to a reduction in compressive strength but an improvement in flexural strength and impact resistance. The simulation of the impact test is constructed and the accuracy is confirmed by comparing the impact times and failure patterns of the specimens. The tensile damage of plain concrete is much greater than the compressive damage, and the cracks will spread rapidly from the upper surface to the lower surface. Compared with plain concrete, the crack width of hybrid fiber reinforced concrete is larger, but the damage degree is more uniform. Fiber can absorb a large amount of impact energy, reduce the emergence of micro-cracks, and improve the impact toughness and toughness coefficient of concrete.

Axial compressive strength of concrete encased extended T-shaped steel composite columns with less reinforcement

A novel concrete encased extended T-shaped steel composite stub (ET-CES) column with less reinforcement for the prefabricated structure is proposed. Eight ET-CES columns, including one covered by concrete fireproof boards and two bare extended T-shaped steel stub columns, were tested under axial compression. Finite element analysis was also conducted. The effects of stirrup spacing, stirrup form, steel ratio, and concrete compressive strength on the axial compressive behaviour were studied. Furthermore, the failure modes, axial load-displacement curves, axial load-strain curves, and post-peak deformability of ET-CES columns were also investigated. The results demonstrated that the concrete cover with less reinforcement and a thin concrete encasement for the ET-CES column could still prevent steel skeleton instability under axial compression. Premature spalling of concrete cover might be prevented by installing fireproof boards, reducing stirrup spacing, and using closed stirrups. The steel ratio in ET-CES columns increasing from 8.1% to 10.4% had no effect on the maximum normalized resistance but could enhance the post-peak ductility and residual strength. The reduction of the concrete compressive strength of ET-CES columns from C50 to C30 could improve the maximum normalized resistance and residual strength. ET-CES columns had excellent post-peak deformability. Finally, an axial strength formula for ET-CES columns was proposed and validated.

Influence on Physical and Mechanical Properties of Concrete Using Crushed Hazelnut Shell

Concrete production requires a significant amount of natural resources, with aggregates comprising between 55% and 80% of the total volume. However, the over-exploitation of natural aggregates has led to the exploration of alternative materials for use in concrete production. In this study, crushed hazelnut shells were investigated as a partial replacement for fine aggregate, addressing the problem of natural resource depletion and offering a second use for this important agricultural waste product available in Chile. Hazelnut shells were incorporated in percentages of 2.5%, 5%, and 10% by weight of sand for water/cement ratios of 0.4 and 0.5. The compressive strength at 7 and 28 days and bending strength at 28 days were determined, alongside physical properties such as the workability, temperature, air content, fresh density, and hardened density of the concrete. Our findings showed that replacing 2.5% of the fine aggregate with hazelnut shells led to a higher compressive strength at 28 days, exceeding the strength of the standard specimens by 9.5%, whereas replacing 5% of the fine aggregate led to the highest bending strength, exceeding the strength of the standard specimens by 3.5%. Moreover, the 0.4 w/c ratio consistently led to better results for both compressive and bending strength, with fewer and lower reductions in mechanical strength compared to the standard mixture. Our results suggest that concrete mixes with hazelnut shells as a replacement for fine aggregate at a percentage of up to 2.5% can be used in construction systems with a compression strength lower than 17 MPa, and mixtures with up to 10% hazelnut shell replacement can be used in structures with tensile bending stress requirements lower than 6 MPa. Overall, the use of hazelnut shells as a partial replacement for fine aggregate in concrete production presents an environmentally friendly and cost-effective solution for the construction industry.

Inner superhydrophobic materials based on waste fly ash: Microstructural morphology of microetching effects

Superhydrophobic technology in construction can effectively improve the barrier ability of the substrate to harmful water-based erosion media, among which the coating scheme is the most practical choice at present, but it may easily fail due to mechanical damage. Therefore, the current research focus has shifted to the development of internal superhydrophobic materials (ISMs) that maintain stable hydrophobicity even under harsh conditions of use and do not rely on expensive fluor-based surface modifications. In this study, the topological structure of waste denitrification fly ash (FA) was constructed using an innovative method, by precisely controlling the etching medium concentration and the form of FA, a one-step process was developed to create ISM with excellent matrix strength and strong waterproof properties. In this study, the alkaline environment generated by FA hydration was used to induce the silica-hydrogen bond dehydrogenation of polymethylhydrosiloxane (PMHS) and the free ammonium ion deamination to toughen the film; PMHS and liquid phase are used to produce the oil-water phase, and the oil film adheres to the surface of the generated NASH and sodium silicate crystals; The porous inner surface of ISM is formed with hydrogen- and ammonia-induced rough structure; The synthesized ISM retains superhydrophobicity and less compressive strength reduction value, and its superhydrophobicity even at damaged or friction interfaces. The material preparation method provides a good foundation and innovative design concept for the seepage prevention and maintenance of concrete structures, the construction of aerated FA bricks, the preparation of foam insulation materials, and the batch utilization of waste FA.

Compressive response of GFRP and BFRP bars at different temperatures and quasi-static rates

The adoption of fiber-reinforced polymer (FRP) bars in concrete structures has increased due to their superior mechanical properties and durability. However, the compressive response of FRP bars at high temperatures remains unclear. This article presents an experimental study on the behavior of glass FRP (GFRP) and basalt FRP (BFRP) bars subjected to compressive loads at different elevated temperatures and deformation rates. The study considers four different temperature conditions: ambient temperature (25 °C), 50 °C, 100 °C, and 150 °C, and two different deformation rates: 0.5 mm/min and 1000 mm/min. Digital Image Correlation (DIC) was used to accurately measure strains at high temperatures by generating a suitable speckle pattern over the specimen surface for full-field deformation measurements. The study results revealed that the modulus of elasticity and compressive strength of both GFRP and BFRP bars degraded as the temperature increased from 25 °C to 150 °C. The compressive strength reduction was higher at 150 °C compared to 100 °C, and the reduction was more significant for BFRP bars than GFRP bars. The compressive strength of GFRP bars was comparable under both strain rates for all temperature conditions. However, the elastic modulus of the bars showed a slight variation between the different load rates, especially at an elevated temperature of 150 °C. For the BFRP bars, the study found that different strain rates at ambient temperature resulted in significant deviation in the compressive strength and modulus of elasticity results. At higher temperatures, the reduction in mechanical properties was more pronounced. In summary, the study provides valuable insights into the behavior of GFRP and BFRP bars under compressive loads at elevated temperatures, which is useful for designing and assessing the performance of FRP-reinforced structures under fire conditions.

Performance analysis of paraffin microcapsules and phase change concrete based on microporous cenospheres

Combining concrete and phase change materials has created a novel method for building energy conservation. However, introducing phase change materials into the concrete will cause various impacts on its performance. This study explores a novel approach to enhance thermal energy storage in building materials by incorporating phase change materials (PCMs) into concrete. Microporous cenospheres were extracted from fly ash through a three-step process and used to produce composite PCM microcapsules containing paraffin as the core material. The produced PCM microcapsules were characterized by scanning electron microscopy (SEM), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and phase change cycle analysis. Phase change concrete was then formulated by substituting 0–25 % sand with these microcapsules. Effects of the addition of the PCM microcapsule on both the mechanical and thermal properties of concrete were experimentally examined. While the incorporation of microcapsules significantly improved concrete's thermal properties, it also led to a reduction in compressive strength (up to 19.65 % at 28 days), though still meeting specifications. The introduction of microcapsules notably enhanced the temperature control capabilities of concrete. In spring, the model room made with the phase change concrete exhibited a 2.2 °C lower indoor peak temperature 2 h 40 min later than the one room with the ordinary concrete. During active heating in winter, the phase change concrete demonstrated significantly lower indoor temperature fluctuations, with a maximum reduction of 45.39 %. Furthermore, the study found that the particle size of microcapsules had varying effects on concrete performance, with larger particles improving thermal properties and smaller particles enhancing mechanical properties. Overall, this research highlights the potential of composite phase change microcapsules and phase change concrete based on microporous cenospheres for effective temperature control and energy conservation in building applications.

High-strength high-performance concrete incorporating different macro fiber types and contents: Engineering and durability performance

ABSTRACT Generating a synergistic response by combining the advantages of different fiber types in concrete is of current scholarly interest. This study investigated the effects of different hooked-end steel fiber (SF) volume fractions up to 1.6% and three macro fiber types including polypropylene (PP), SF, and typical hybrid fibers (HF: 50% SF + 50% PP) at a fixed dosage of 1.6% on properties of high-strength high-performance concrete (HSHPC). A novel densified mixture design algorithm was used to incorporate a high quantity of fly ash and rice husk ash as an eco-binder. Results showed the specimens with added macro SF exhibited improved mechanical strength, dynamic modulus of elasticity and rigidity, and lower drying shrinkage while the ones with added PP exhibited reductions in compressive strength and dynamic modulus. Interestingly, the incorporation of macro fibers, regardless of fiber type and content, reduced electrical resistivity, ultrasonic pulse velocity and increased the total charge passed in the chloride ion penetration test, resulting in likely underestimation of the reinforcement corrosion resistance, especially for SF specimens. The findings also confirm that HF demonstrating synergistic response may be effective and creative in improving most of the concrete characteristics, contributing to the efficient use of HSHPC in real-world structures.

Critical cold joint angle in concrete

This study aims to understand the effect of different cold joint angles on splitting tensile and compressive strength of concrete. A series of tests were conducted in the context of this study. Four different concrete grades (10, 20, 25, 30 MPa) were selected to demonstrate the very low grade, low grade, minimum grade and normal grades of concretes according to Turkish Earthquake Codes 2007 and 2018. In addition to the concrete grades, cold joint angle is also a parameter to be investigated. Zero angle was the control angle. Besides, 20, 45, 65 and 90 degrees were studied to understand the effect of cold joint angle on tensile and compressive strength of the concrete. It was found that compressive strength was not adversely affected from the cold joint angles of 0°, 20°, 45° and 90°. The difference is almost 10 %. However, 65° of cold joint angle seems to affect the compressive strength significantly since the reduction in compressive strength varied between 32.5 % and 48.4 %. Specimens having 65° cold joint angle was observed to fail by sliding over the cold joint plane. Splitting tensile tests showed that 90° cold joint angle was the most unfavorable situation. Introducing vertical cracks parallel to the loading direction before the test resulted in the lowest tensile strengths. Splitting tensile strength equation considering the cold joint angles was proposed.

Saturation Influence on Reduction of Compressive Strength for Carbonate Dimension Stone in Croatia

Dimension stone is a valuable mineral raw material whose importance is increasing worldwide. According to its mineralogical and petrographical composition, Croatian dimension stone belongs to the carbonates, primarily limestones. As saturation influences the reduction of compressive strength, in this study, the relationship between the uniaxial compressive strength in the dry and saturated states is shown, which has a coefficient of determination of 0.9605. Models were created to estimate the compressive strength based on the values of water absorption, total porosity, and real density of the material from 26 sites, all determined according to the European standards EN 1936:2006 and EN 13755:2008. Thirty varieties of dimension stones were tested, and 150 values were collected from different tests. A dependence between the uniaxial compressive strength in the saturated state was established, including the explanation in which cases the correlation can be used to estimate the uniaxial compressive strength of carbonate dimension stones with a remarkably high degree of confidence (0.994 and 0.9374). In addition, the limitations of geomechanical estimation of the uniaxial compressive strength of rock material and its unsuitability for estimating of dimension stones construction are described.

Investigating PCM encapsulated NaOH additive for set-on-demand in 3D concrete printing

This study investigates the print head activation of an encapsulated additive to attain on-demand setting in 3D concrete printing for buildability enhancement. Sodium hydroxide (NaOH) is considered as a set accelerating additive, and it is encapsulated using a phase change material (PCM). The encapsulated NaOH is added during the initial mixing stage and the mix is heated at the print head to release the NaOH, which subsequently reacts with cementitious materials to attain the on-demand setting of the printed layer. The dosage of NaOH was varied from 0 to 5 wt% of the cement to determine the optimum dosage for buildability enhancement. The results showed that the static yield strength of the printable concrete after the print head activation increased with the NaOH dosage, however, this has resulted in reducing the compressive strength of the mixes. The fresh and hardened properties of the mixes with encapsulated NaOH were compared with the mix with nano-clay to assess two buildability enhancement approaches (set-on-demand vs traditional). It was found that the buildability enhancement using nano-clay was limited by pumpability constraints, whereas the activation of encapsulated NaOH was limited by compressive strength reductions.

Long-term thaumasite sulfate attack on mortar containing coral sand filler and SCMs exposed to sodium sulfate solution

The use of coral sand filler and supplementary cementitious materials partially replacing Portland cement facilitates the utilization of coral debris waste in oceanic construction as well as CO2 emission. The effect on thaumasite sulfate attack by coral sand powder is compared with limestone powder since thaumasite sulfate attack has been studied extensively in limestone Portland cement. This work was conducted on the evaluation of resistance to sodium sulfate solution by measuring changes in visual appearance, compressive strength and length, as well as XRD, FTIR, SEM and MIP analyses. The results show that thaumasite sulfate attack would occur in mortars with coral sand powder and SCMs probably without noticeable expansion and a reduction in compressive strength of the specimens’ core. The mortar incorporating coral sand powder and silica fume leads to greater sulfate resistance than coral sand powder-Fly ash and Coral sand powder-Slag mortars, and the coral sand powder performs severer deterioration compared with the limestone powder by simultaneously used with fly ash or slag. More deteriorated crystal morphologies of portlandite and C-S-H were exhibited in Coral sand powder-SCMs mortars under sulfate attack at low temperatures. No obvious deterioration occurred in blended mortars under corrosion at 20 °C for up to 18 months in this work.

Experimental Study on The Effect of Size, Type, and Replacement Ratio of Recycled Aggregate on The Mechanical Properties of Reactive Powder Concrete

This paper presents an experimental investigation of the mechanical characteristics of Reactive Powder Concrete (RPC) and Recycled Aggregate Reactive Powder Concrete (RPC-RA), utilizing two types of recycled aggregate (RA), recycled concrete aggregate (RCA), and recycled concrete brick aggregate (RCBA) as alternative aggregates. A series of sixteen RPC and RPC-RA mixes were prepared and tested. A reference RPC mix without RA was tested to determine the maximum compressive strength of 128.17 MPa, the tensile strength of 15.56 MPa, and the flexural strength of 25.90 MPa. Then, the study examines twelve different mixes of RPC-RA, each with RCA with maximum particle sizes of 0.6, 1.18, 2.36, and 4.75 mm and replacement ratios of 20%, 40%, and 60%, to study the effects of varying replacement ratios of the RCA and various maximum particle sizes. Additionally, three mixes of RPC-RA are investigated using RCBA with a maximum particle size of 0.6 mm and replacement ratios of 20%, 40%, and 60%. The use of RA resulted in various percentages of reduction in compressive, splitting, and flexural strength, as shown in the results of the study.

Investigation of the dynamic compressive mechanical properties of concrete under the combined effects of freeze–thaw and salt erosion

The objective of this study is to investigate the dynamic compressive mechanical properties of concrete under the combined effects of freeze–thaw (F-T) and salt erosion. The Split Hopkinson Pressure Bar (SHPB) test system was employed to conduct dynamic compression tests on concrete specimens subjected to 0 ∼ 250 cycles of F-T in NaCl solutions with concentrations ranging from 0 % to 8 %. The influence of strain rate, F-T cycles, and chloride concentration on the dynamic properties of concrete were analyzed, and a constitutive model considering rate-dependency was developed to describe its compressive mechanical response. The research findings suggest that the dynamic compressive strength of concrete gradually increases with an increase in strain rate, indicating a strengthening effect due to higher strain rates. Additionally, the dynamic growth factor exhibits an exponential relationship with the logarithm of strain rate. Moreover, an increase in the number of F-T cycles results in a gradual reduction in the dynamic compressive strength of concrete and an accompanying increase in specimen fracture. Furthermore, the dynamic compressive strength of concrete exhibits a non-linear trend concerning chloride solution concentration: initially decreasing and subsequently increasing. The minimum compressive strength is observed at a concentration of 3.5 %, indicating the most severe damage to the concrete. However, it should be noted that a higher strain rate mitigates the influence of chloride solution concentration on specimen breakage. To comprehensively understand the mechanical behavior of concrete under combined F-T and salt erosion effects, we propose a dynamic constitutive model based on established mechanical and damage theories relevant to composite materials. The experimental results demonstrate that the proposed model effectively captures the mechanical response of concrete subjected to the combined influence of F-T and salt erosion.

Prediction of Progressive Frost Damage Development of Concrete Using Machine-Learning Algorithms

Understanding the deterioration mechanism of concrete structures in cold climates that are susceptible to frost damage from repeated freezing and thawing cycles is imperative for ensuring their durability and serviceability. This study analyzed the impact of freeze–thaw (FT) exposure on concrete structural behavior by developing three machine-learning approaches—artificial neural networks (ANN), random forests (RF), and support vector machines (SVM)—to quantify the progressive loss in compressive strength after repeated FT cycles. The results demonstrate that all of the proposed models can predict the deteriorated compressive strength of concrete and align closely with the experimental results. The ANN model demonstrated the highest prediction accuracy with an R2 of 0.924, exhibiting a higher prediction accuracy than RF and SVM models. Sensitivity analysis using Shapley additive explanations (SHAP) revealed that concrete with an initially high strength, along with a lower water–cement ratio and air entrainment, exhibited the least reduction in compressive strength after freezing–thawing cycles, underlining the positive impact of these factors on the FT durability of concrete. The proposed modeling approach accurately predicts the residual compressive strength after FT exposure, enabling the selection of optimal concrete materials and structural designs for cold climates.

Synergic effect of polyester fiber and nano silica on chemical resistance of geopolymer mortar.

The aim of this study is to evaluate the synergistic effect of polyester fiber-reinforced and nanoslica on the technical performance and durability of geopolymer mortar in terms of the chemical resistance. The study examined how the addition of polyester fiber and nanosilica affects the short-term severe durability of geopolymer mortar specimens made with fly ash (type F). The specimens were cured under ambient conditions. Different percentages (0.6%, 1.2%, and 1.8%) of polyester fiber were used, both with and without nanosilica. Additionally, a reference mixture containing only nanosilica was prepared.All mixtures had a liquid to binder ratio of 0.50, and the ratio of NaOH to Na2SiO3 solution was kept at 2.5:1 by weight. The produced mixes, after 28 days of ambient curing, were immersed for another 28 days in solutions containing 3.5%, 5%, and 5% of sodium chloride, magnesium sulphate and sulfuric acid, respectively. For comparison, control specimens which were not exposed to chemical attacks were tested at the same age of 56 days. Moreover, water absorption and sorptivity tests were conducted to explain the durability performance in a more detailed way. The test results express that the combination of both materials showed a synergistic effect and resulted in greater improvements in compressive and flexural strengths. Both materials can reduce the reduction in compressive strength caused by sulfuric acid exposure, but polyester fiber can increase mass loss. The presence of magnesium sulfate and sodium chloride can lead to a reduction in strength, but the addition of both polyester fiber and nanosilica can mitigate these effects. The addition of fibers creates a network of pores that can limit water absorption, and nanosilica can further enhance the microstructure and reduce water absorption. However, using polyester fiber beyond 1.2 percent can adversely affect the rate of water absorption.

Influence of Temperature on Shear Behavior of Lightweight Reinforced Concrete Beams Using Pozzolana Aggregate and Expanded Polystyrene Beads

The innovation inherent to employing expanded polystyrene (EPS) beads lies in its transformative impact on traditional concrete practices. Through the incorporation of EPS beads in concrete mixtures, a novel approach emerges that significantly alters the material’s characteristics, and opens up new avenues for construction and design. Studying the shear behavior of RC beams made with EPS beads is essential for advancing knowledge, improving design practices, ensuring structural integrity, and promoting the effective and responsible use of innovative materials in construction. This research experimentally investigated the effect of using EPS beads and pozzolana aggregate (PA) on the shear behavior of the RC beams. A total of 27 simply supported rectangular beams were cast, using three novel distinct mix designs, and were subjected to two-point load testing until failure. These three mixes were categorized as follows: a control mix, a mix with only EPS, and a mix with EPS, along with an additive. The ultimate failure load was experimentally recorded for all specimens, and the influence of the temperature (300 °C and 600 °C) on the RC beams made with EPS was examined. The findings revealed a reduction in the concrete compressive strength and density in the beams containing EPS and EPS with superplasticizers of (21.7%, 24.9%) and (11.3%, 16.2%), respectively. Additionally, EPS played a significant role in diminishing the ultimate shear capacity of the beams, compared to the control beams, by about 19.4%. However, the addition of a superplasticizer along with the EPS helped to maintain the beam capacity, to some extent. Conversely, the beams exposed to a temperature of 300 °C exhibited an almost similar capacity to that of the control beams without heating. Nevertheless, at 600 °C, the beams displayed a noticeable decrease in the ultimate load capacity, compared to the unheated control beams.

Behaviour of carbon or glass FRP-confined rubberised concrete under monotonic compression

This paper presents a comparative assessment of the compressive behaviour of rubberised concrete (RuC) confined with FRP jackets. In total, three RuC mixes were investigated with rubber content of 6%, 12% and 18% of the total aggregate volume, as well as a conventional concrete mix as a reference. A total of 100 cylindrical concrete specimens (Ø100 × 200 mm) subjected to monotonic axial compression were tested. Confinement scheme comprised 1 or 2 FRP layers of either carbon or glass uniaxial fabric. The mechanical properties, stress–strain behaviour, and confinement effectiveness ratios were assessed. The discussion includes a comparative assessment of the influence of rubber content, confinement and the type of fibre of the fabrics used on the aforementioned properties. The efficiency of analytical models in predicting the experimental results was also investigated. The results revealed a significant reduction of the compressive strength when crumb rubber was used as mineral aggregate replacement in concrete. FRP confinement of RuC was able to mitigate the reduction in compressive strength. Confinement of RuC with glass or carbon FRP jackets having similar axial rigidity resulted in similar stress–strain behaviour, which was mostly affected by the rubber content. Existing analytical models were able to predict the experimental results with moderate accuracy.

Understanding of EPS beads on mechanical properties and void morphology of a CO2-solidified foam concrete based on solid wastes

Two major issues of EPS doped concrete are apparent reduction in compressive strength associated with the presence of EPS-formed artificial defects and ultra-light weight related easy segregation in the mixes, even though the thermal conductivity of composites shows a satisfactory reduction. This paper presents a composite lightweight concrete by introducing EPS into a solid waste (carbide slag and quartz sand tailings) prepared industrial grade γ-C2S-based foam concrete (CFC) to partially replace foam-formed voids. Results show that the partially EPS-substituted CFC with reasonable EPS parameters (Especially 1 mm in diameter and 5 wt% in content) exhibits a notable improvement in compressive strength (24.3%) while accompanied by the reduction in sorptivity, drying shrinkage and thermal conductivity. This is attributed to the fact that the EPS can effectively improve the foam stability by delaying foam drainage velocity due to its hydrophobicity and discrete smooth surface during the pre-curing procedure, which results in a refinement of void morphology and distribution as well as the optimized interfacial transition zone (ITZ). Accompanied by the compact inner surface and optimized ITZ, leading to a lower drying shrinkage, thermal conductivity, and also a reduction in sorptivity due to the increasing of tortuous path for the capillary flow. Moreover, magnesium slag (MS) containing dicalcium silicate mineral phase is also used to prepare MS-based CFC to further reduce costs and achieve the resource utilization of solid waste and a large amount of CO2 storage, which contributes to the sustainable development of CFC.