Reduction In Flexural Strength Research Articles

Mechanical characteristics of structural concrete using building rubbles as recycled coarse aggregate

Abstract The aim of this research is to investigate whether construction rubbles may be utilized as coarse aggregates in concrete. Experimentally, the slump, unit weight, compressive, tensile, and flexural strength tests were applied on concrete samples with varying percentages of recycled coarse aggregate (RCA) and compared with reference concrete produced with natural coarse aggregate. This research conducted 96 concrete samples with RCA replacement percentages of 0, 35, 65, and 100%, respectively. The control mixture produced with natural aggregate showed better results than the mixtures containing recycled aggregate; thus, compressive, tensile, and flexural strengths reduced as the amount of the recycled aggregate increased. Using 100% RCA, the compressive, tensile, and flexural strength reduction reached up to 64, 29, and 38%, respectively.

A Novel Zwitterion Incorporated Nano-Crystalline Ceramic and Polymer for Bacterial Resistant Dental CAD-CAM Block

ObjectivesTo create bacteria-resistant dental CAD-CAM blocks with a biofilm-resistant effect by incorporating Nano-crystalline ceramic and polymer (NCP) with 2-methacryloyloxyethyl phosphorylcholine (MPC) and sulfobetaine methacrylate (SBMA) and at an equimolar ratio, referred to as MS. MethodsExperimental groups comprised NCP blocks containing zwitterions at 0.15wt% (MS015) and 0.45wt% (MS045). NCP blocks without MS served as control (CTRL). Flexural strength, surface hardness, water sorption and solubility, photometric properties, and cytotoxicity were assessed for all samples. Additionally, the resistance to single and multi-species bacterial adhesion was investigated. ResultsMS045 showed significant reduction in flexural strength (P < 0.01) compared to both CTRL and MS015. Both MS015 and MS045 showed significantly increased water sorption and significant reduction in water solubility compared to CTRL. Light transmission remained consistent across all MS content levels, but the irradiance value decreased by 12% in the MS045 group compared to the MS015 group. Notably, compared to the CTRL group, the MS015 group exhibited enhanced resistance to adhesion by Porphyromonas gingivalis and a multi-species salivary biofilm, with biofilm thickness and biomass reduced by 45% and 56%, respectively. ConclusionsNCP containing 0.15% MS can effectively reduce adhesion of multiple species of bacteria while maintaining physical and mechanical properties. Clinical SignificanceNCP integrating zwitterions is clinically advantageous in resisting bacterial adhesion at internal and external margins of milled indirect restoration.

Hygroscopicity in Epoxy Powder Composites

Epoxy powders offer a low-cost way of manufacturing thick-section composite parts, such as those found in wind and tidal turbines. Currently, their processing cycle includes a lengthy drying stage (≥15 h) to remove ambient moisture. This drying stage prevents void defect formation and, thereby, a reduction in mechanical properties; however, it constitutes up to 60% of the processing time. Little research has been published which studies the drying stage or its optimisation. In the present work, experimental and simulated analyses are used to investigate the effects of hygroscopicity in epoxy powder composites. Tests are performed to quantify the void content of dried and undried laminates and to measure its impact on transverse flexural strength. Dynamic vapour sorption analysis is used to study the sorption behaviour of the epoxy powder. It is shown that the epoxy powder is slightly hygroscopic (1.36 wt%) and exhibits sorption behaviour that is characteristic of glassy polymers. This results in up to 4.8% voids (by volume) if processed in an undried state, leading to a 43% reduction in transverse flexural strength. A modified linear driving force model is fitted to the desorption data and then implemented in existing process-simulation tools. The drying of a thick epoxy powder composite section is simulated to investigate the influence of powder sintering on the duration of the drying stage. Process simulations reveal that a standard drying cycle prematurely sinters the powder, which inhibits moisture release. By maintaining the powder state, simulations show that the drying cycle can be reduced to 5 h.

Additive Manufacturing of Fiber‐Reinforced Zirconia‐Toughened Alumina Ceramic Matrix Composites by Material Extrusion‐Based Technology

Material extrusion‐based additive manufacturing becomes interesting to fabricate oxide ceramic matrix composites. Herein, 0–30 vol% alumina fibers are added to zirconia‐toughened alumina powder mixture and extruded into filaments. Shrinkage and mechanical properties of filaments and 3D‐printed samples are investigated. Thermomechanical analysis is conducted on filaments with and without fiber content indicating lower shrinkage in the direction of fiber alignment during the sintering process. The flexural strength of the extruded filaments and printed bars is measured through a 4‐point bending test. Filaments containing 15 vol% fiber exhibit the highest flexural strength of 110 MPa, with additional fiber content leading to a reduction in flexural strength. Using Weibull calculation, it is observed that printed bars without fibers result in significantly lower bending strength in comparison to the filaments because of the presence of printing failures. Bars with 10 vol% fibers, printed with 0° infill orientation achieve the same mechanical properties as the filaments, even though in microcomputed tomography gaps between printed lines and voids between raster lines can be observed. These results demonstrate that fiber reinforcement of ceramics offers a great potential to avoid the reduction of mechanical properties by printing defects.

Feasibility study of the use of concrete blocks produced from plastic marine garbage for use in civil construction.

The pursuit of development in an economically sustainable and ecologically sound manner is a goal of modern society. It has been investing in products that minimize their environmental impact, particularly concerning the use of plastic. This material is highly detrimental to nature due to its toxicity and long decomposition period. The present study aims to analyze the feasibility of producing blocks made of concrete with different amounts of waste plastic taken from coastal and estuarine areas. After laboratory analysis, it was found that blocks containing 5% plastic exhibit good compressive strength and are lighter. Additionally, there was an increase in the acidity of the sample, a decrease in the density of the block, and reductions in both flexural and compressive strength. The prototype, composed of 5% plastic by mass, proves to be efficient for constructing single-story houses. It meets the minimum requirements for normative resistance, effectively encapsulating the plastic within the block and thereby reducing its environmental impact.

Flexural behavior of circular rubberized concrete-filled double-skin steel tubular beams: Experiments

The study aims to assess the impact of RuC on twelve concrete-filled double-skin steel tube (CFDST) specimens. The research explores key variables, including outer tube slenderness ratio, hollow ratio, and rubber replacement ratio. Rubber particles replace natural aggregates at replacement ratios (ρνr) of 0%, 15%, and 30% by mass. The experimental findings are comprehensively discussed, encompassing member flexural capacity, confinement effects, ductility, energy dissipation, and failure mechanisms. The findings reveal that replacing normal concrete (NC) with RuC leads to a reduction in beam flexural strength ranging from 5.0% to 18.1%, depending on ρνr and outer tube diameter. In contrast, RuC members exhibit an increase of up to 70% in ductility and 27.7% in energy dissipation compared to members with NC, depending on rubber content. Increasing the outer tube thickness proves to be an effective method for mitigating strength reduction due to rubber replacement. Specifically, elevating the outer tube thickness from 3.6 mm to 4.5 mm results in strength enhancements of 17.0%, 19.0%, and 23.7% for beams with NC, 15%RuC, and 30%RuC, respectively. Furthermore, the results are applied to assess existing design models and to suggest modifications that offer improved strength estimations for a broad spectrum of rubber replacement ratios.

Effects of temperature and pre-bending on the flexural properties of carbon fiber/epoxy composites

This study investigates the combined influence of temperature and pre-bending (PB) on the flexural properties of Carbon Fiber/Epoxy (CF/Epoxy) composites. The study demonstrated the influence of temperature on CF/Epoxy’s flexural characteristics, noting a marginal reduction in stiffness at higher temperatures ([Formula: see text]C) compared to room temperature ([Formula: see text]C). Notably, even under HT, the composite exhibited a commendable load-bearing capacity, with a 29% reduction in strength. Additionally, the investigation focused on the impact of PB on CF/Epoxy’s flexural properties. The PB resulted in very small reductions in flexural strength (10%). It was observed that when subjected to both PB and HT, the material exhibited a collective response, with temperature exerting a more dominant influence than PB. Significantly reduced the flexural properties, resulting in a substantial 35% decrease in strength, surpassing the individual effects of temperature or PB. The findings emphasize the significant impact of the combined influence of temperature and PB on CF/Epoxy, shedding light on the material’s behavior under varying environmental conditions.

Development of cellular construction material-based flax shives: Physico-mechanical and thermal characterisation

The reduction of energy consumption in construction, production of thermal insulation materials, and the solution of environmental problems by recycling by-product derived several industrial sectors are becoming greater problems. In this context, vegetable by-products are an excellent alternative product to substitute mineral aggregates because they are easily available and renewable low-cost raw materials, and have higher advantage for economy and environment concerns. The viability of using vegetable materials such as flax shives for developing a sustainable Lightweight Cellular Construction Material (LCCM) is investigated in this paper. The produced material containing different volumes of flax shives (0V (control specimen), 1V, and 2V) was lightened by creating a porous structure in the matrix through a chemical reaction between Aluminium powder and free lime from pre-formulated Tradical PF70 binder. A study conducted on hardened material properties has indicated a significant reduction in sample unit weight, thereby resulting in a level of compressive strength compatible with a load-bearing wall. The reduction in flexural strength was lower than that in compressive strength. This study has also highlighted the effect of the porous structure on the thermal conductivity that lead to provide a high degree of thermal insulation. These results show that the cellular material based on flax particle can be used as suitable insulated load-bearing walls.

Cracking resistance performance of epoxy asphalt mixture collected from in-service steel bridge deck pavement: Multiscale testing and evaluation

Epoxy asphalt (EA) mixture is commonly used in steel bridge deck paving due to its high strength and fatigue properties. However, cracking remains a problem on the steel bridge. The performance of damaged EA mixtures in the field after several years of service is unclear. Therefore, this study collected typical in-situ EA mixture and evaluated the attenuated performance of damaged materials at multiscale levels. The low- and intermediate-temperature cracking resistance and fatigue properties of field specimens from both the top and bottom layers were investigated by semi-circular bending (SCB) test. The micro-mechanics, microstructure, and element distribution of the interfacial transaction zone (ITZ) in damaged and fresh EA mixtures were characterized by the nano-indentation and energy dispersive spectrometer (EDS) tests. After 13 years of service at low and intermediate temperatures, the in-situ EA mixture exhibited a reduction in flexural tensile strength and fracture energy by approximately 31.4 % to 36.7 % and 54.9 % to 59.9 %, respectively. The top layer exhibited worse cracking resistance and fatigue properties than the bottom layer. The ITZ of the top layer showed more intense oxidation and significantly higher modulus than the bottom layer, contributing to the durability decay of the top layer EA mixture. The oxidative aging of the bottom layer was almost negligible compared to the new EA mixture, indicating that the degradation of the bottom layer was mainly caused by traffic or thermal loading from the steel bridge.

Enhancing concrete performance: Surface modification of recycled coarse aggregates for sustainable construction

In this study, the researchers introduce an innovative method to enhance the utilization of recycled coarse aggregates (RCA) derived from construction and demolition waste (C&D) in sustainable concrete production. The presence of old cements mortar on the surface of these aggregates poses a challenge to their mechanical properties. To tackle this issue, the researchers propose a unique approach that combines chemical treatment and abrasion techniques. Firstly, RCA is immersed in a 0.5 mol hydrochloric acid (HCl) solution, weakening the adhering mortar. Subsequently, abrasion treatment removes the weakened mortar from the RCA surface. The study explores the incorporation of these surface-modified RCAs at varying levels, from 0% to 100% in 25% increments. Various concrete properties, including workability, compressive strength, flexural strength, split tensile strength, and microstructural characteristics (XRD, SEM, and EDAX), along with modulus of elasticity, are assessed. Results indicate that the combination of these modification techniques significantly enhances RCA properties. At the 100% replacement level, surface-modified RCA results in a reduction of compressive, flexural, and split tensile strength by 08.31%, 10.61%, and 07.90%, respectively, in comparison to the reference concrete. Likewise, the modulus of elasticity decreases to 30.82, and porosity decreases to 27.82% at the same replacement level. However, SEM analysis illustrates improved bonding between RCA and cement matrix due to surface modifications, leading to reduced porosity and the formation of dense Interfacial Transition Zones (ITZs). Cost analysis reveals that recycled aggregate concrete (RAC) mixtures can be more economical than those utilizing natural aggregates (NA). In summary, this novel surface modification technique presents a promising avenue for optimizing RCA utilization in sustainable concrete production, promoting environmental conservation, and efficient waste management in the construction sector.

Investigation on the compositional and performance evolution of cement paste subjected to Xenon radiation

This study addresses the critical question of how Xenon radiation, simulating natural solar radiation, affects the compositional, structural, and mechanical properties of cement paste. This aim is to understand the micro-to macro-scale changes in cement paste subjected to such radiation, a key concern for the durability of construction materials in solar-intensive environments. Employing a comprehensive suite of analytical techniques, including XRD, TG, 29Si NMR, 1H NMR, CT, SEM, and Vickers hardness testing, we systematically analyze the changes in phase composition, bound water content, silicate chain length in C–S–H, microstructure, and micro-mechanical behavior before and after radiation exposure. Our research uncovers a substantial decomposition of ettringite and a discernible reduction in the bound water content within the cement paste post-radiation exposure. Crucially, we detected a significant elongation in the C–S–H chain length, with a peak increase observed at 6%. This elongation is coupled with an increase in pore coarseness and a proliferation of internal defects. These alterations collectively lead to a marked decrease in the material's mechanical strengths: we noted a reduction in flexural strength by up to 18% and in compressive strength by as much as 25% at the macroscopic level. This research thus provides essential insights into the design and development of high-durability cementitious materials for solar radiation-intensive environments, contributing to the advancement of sustainable and resilient infrastructure.

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.

Ultrahigh-temperature mechanical behavior and failure mechanisms of SiCf/SiC composites

SiCf/SiC composites are potential candidates in the aerospace fields for application as high-temperature structural components. Their mechanical properties and failure behaviors at ultra-high temperatures (above 1473 K) are important to obtain systematically. This work performed the in-plane compressive, bending, and interlaminar shear tests at 1573 K and 1773 K in an inert atmosphere. The results showed dramatically that the in-plane compressive and interlaminar shear strengths increased with the temperature increment from 1573 K to 1773 K. In contrast, a reduction in flexural strength was noticeable. To reveal the failure mechanisms, fracture surface microstructures of these SiCf/SiC samples were characterized. It was found that the fiber surfaces for the samples tested at 1773K were rougher than the samples tested at 1573K. It meant that, with the temperature increasing, the fiber-matrix interfaces enhanced, which resulted in increasing compressive and interlaminar strengths. For the bending tests, serious delamination occurred when the temperature increased to 1773K, which induced the flexural strength reduction. The numerical simulations of bending samples were developed to reveal the mechanism of strength degradation as the temperature elevated.

Hygrothermal aging effects on fiber-metal-laminates with engineered interfaces

This short work is to communicate the influence of hygrothermal aging on the mechanical performances of fiber-metal-laminates (FMLs) with various ingenious metal surface treatments, namely, nano-scale electrochemical sculpture (NES), the conventional surface polishing (PS) and NaTESi anodizing (NaTESi). The specimens with different edge conditions were prepared using milling or wire-electrode cutting and subjected to hygrothermal aging treatment in a climatic test chamber at 60 °C and 96% relative humidity. Interlaminar shear and flexural testing results showed that the wire-electrode cutting method produced edges with exposed fibers and spalling resin after hygrothermal aging, while the milling cutting method resulted in edges with a micro-porous and defective surface, but without exposing fibers or spalling resin. The degree of reduction in interlaminar shear strength (ILSS) and flexural strength varied depending on the surface treatments and machining methods used. After undergoing hygrothermal aging, the wire-electrode cutting method causes a greater decrease in ILSS compared to the milling cutting method. This reduction is particularly pronounced in specimens with weaker interfacial bonding strength, in which the ILSS of wire-electrode cut FMLs-PS decreased by 32.5%, while that of FMLs-NES decreased by 17.8%.

Effect of Fibres on Physico-Mechanical Properties of Bulk-Fill Resin Composites.

To measure the flexural strength (FS) of bulk-fill resin composites and assess their long-term water absorption and solubility properties with and without the inclusion of short glass fibres. One resin composite, everX Flow with fibres, and four commercially available bulk-fill composites without fibres, namely, PALFIQUE, Activa, SDR Plus, and Filtek Bulk Fill One, were tested. Six specimens (2 × 2 × 25 mm) were fabricated for each material and stored in water for 1 day and 30 days to measure the flexural strength using a three-point bending test. To evaluate water absorption and solubility, circular disks measuring 15 × 2 mm (n = 5) were immersed in water for 60 days, and their weights were recorded periodically. After 60 days, the specimens were dried for an additional 21 days to determine solubility. Flexural strength values ranged from 101.7 to 149.1 MPa. Significant distinctions were observed among the resin composites at the onset of the study (p < 0.05). The highest FS value was identified in everX Flow, while ACT exhibited the lowest (p < 0.05). However, the flexural strength values exhibited a significant decrease with increased storage time (p < 0.05), except for ACT, which demonstrated a noteworthy increase. Concerning water absorption and solubility, ACT displayed the highest absorption, while the range of solubility varied from -0.88 to 5.8 μg/mm3. ACT also had the highest solubility, whereas everX Flow exhibited negative solubility. The addition of short fibres, along with potential differences in matrix composition, enhanced the flexural strength of everX Flow. However, the substantial reduction in flexural strength observed in everX Flow and SDR following exposure to water corroborates the manufacturers' recommendation to apply a conventional resin composite cap on these materials.

Investigation of alkali-silica reaction on mortars with alternative binder systems: Alkali activated Slags and Celitement

This study investigates the resistance against alkali-silica reaction (ASR) of two alternative binder systems, alkali-activated slag (AAS) and Celitement (Celite). Experimental studies on expansion and mechanical strength are carried out. Coupled kinetic and equilibrium thermodynamic modeling is used to clarify the role of binder chemistry on ASR. It was observed that under accelerated conditions OPC based mortars were more susceptible to ASR compared to AAS and Celite-based mortars. Based on experimental and modeling results, a correlation is shown between the dissolution of silica and the degree of expansion, but no correlation was found between the predicted amount of ASR products and the measured degree of expansion. Finally, the expansion degree could only be correlated with the reduction in compressive and flexural tensile strength for ASR-exposed samples.

Effect of siliceous sand volume fraction on the properties of alkali-activated slag mortars

One of the critical factors affecting the performance of alkali-activated slag (AAS) is the nature and dose of alkali activator. The activator type can play a significant role during the transition from pastes to mortars or concretes. Therefore, three basic sodium activators (water glass, carbonate, and hydroxide) of the same molarity of 4M Na+ were used to prepare AAS-based mortars with different volume fractions of siliceous sand. These were compared by means of workability, mechanical strength, and long-term shrinkage under autogenous conditions. The results were compared to those obtained on pastes with similar workability. Increasing the content of the sand tended rather to decrease the mechanical properties, while greatly decreased autogenous shrinkage. Nevertheless, the most remarkable differences for different activators were observed when comparing the mortars with pastes. The transition from pastes to mortars resulted in the highest reduction in both compressive and flexural strength for sodium hydroxide. The flexural strength of the mortars with sodium water glass and sodium carbonate even increased considerably in presence of sand.

Comparison of compressive, flexural, and temperature-induced ductility behaviours of steel-PVA hybrid fibre reinforced OPC and geopolymer concretes after high temperatures exposure

This paper presents a comparison of the performances of geopolymer concrete (GPC) and ordinary Portland cement concrete (OPCC) with and without fibres after exposure to 200, 500, and 800 ˚C. The influences of elevated temperatures on the concretes were investigated by the cracking patterns, residual compressive strength, flexural toughness, failure modes, ductility, and thermogravimetric analysis. The results indicate that steel-PVA hybrid fibre is effective to improve the initial flexural strength, flexural toughness, and equivalent flexural strength ratio of GPC and OPCC. Exposure to temperatures at 500 ˚C and above caused distinct deterioration in mechanical properties of the concrete specimens. Additionally, temperature-induced ductility behaviour, which is quantitatively characterised by equivalent flexural strength ratio and normalized absorbed energy (NAE), is observed in concrete specimens after exposure to 500 and 800˚C. The temperature-induced ductility behaviour having an obvious characteristic of ultimate flexural strength reduction and ductility increase, which is influenced by decomposition of the components at elevated temperatures. The decomposition of calcium compound is the primary factor for the higher mass loss values for OPC than the geopolymer specimens.

Experimental Investigation on Flexural Behavior of U-Shaped Steel–Concrete Composite Beams with Bolt Connections under a Negative Bending Moment

Because U-shaped steel beams filled with concrete have the advantages of reduced construction period and superior structural performance, they have been widely used as structural elements. In this study, the flexural behavior of newly developed bolt-connected U-shaped steel and concrete composite beams under a negative bending moment was experimentally evaluated. The main test variables were bolt spacing in bottom steel plates and types of U-shaped steel sections. Test results showed that the flexural behavior of the composite beams is determined by the plate-buckling mode of bolt-connected bottom steel plates. Composite beams with a greater bolt spacing than that in the standard AISI S100-16 experienced early plate buckling of the bottom steel plates, resulting in reduction of flexural stiffness and maximum flexural strength. Thus, the buckling mode of bolt-connected bottom plates should be considered for bolt-connected U-shaped composite beams under a negative bending moment. The longitudinal lips of U-shaped steel sections can increase the flexural performance of composite beams due to anchorage performance of the steel sections with lips.

Thermal energy saving and physico-mechanical properties of foam concrete incorporating form-stabilized basalt powder/capric acid based composite phase change material

The incorporation of phase change materials (PCM) in construction materials for the purpose of thermal energy storage (TES) can prevent temperature fluctuations and enable the conservation of thermal energy in buildings. Accordingly, this study aims to create a novel, environmentally friendly foam concrete incorporating a composite PCM composed of capric acid saturated waste basalt powder. Basalt powder, a byproduct of the grinding or crushing of basalt volcanic rock, was selected as a carrier material due to its high porosity resulting from its lightweight and porous nature. This allowed for the creation of a leak-free composite PCM, which was then integrated with foam concrete made of CEM I 42.5R cement, water, quartz sand, and a foaming agent. Basalt-PCM was substituted into the mixture at 50% and 100% by weight of quartz aggregate. Comprehensive evaluations were conducted on the novel foam concretes with regard to their morphological, mechanical, physical, thermal, and TES properties. The results indicate that the incorporation of basalt-PCM causes a minor reduction in the dry unit weight of the mixtures and a reduction in compressive and flexural strength. However, the leak-proof basalt powder/capric acid composite displayed a phase transition behavior, melting at 28.5 °C with a latent heat of fusion (47.9 J/g), which retained 99.5% capacity after 500 melting-solidification cycles. The specimen with 100 wt% basalt-PCM exhibited a melting temperature and latent heat of 27.8 °C and 17.4 J/g, respectively. Additionally, the basalt powder/capric composite exhibited high thermal stability up to 156 °C, far above its normal operating temperature. The foam concretes incorporating the basalt-PCM demonstrated solar thermoregulation properties, maintaining a more stable and comfortable indoor temperature. These results suggest that the form-stable PCM-incorporating foam concretes developed in this study can be considered as environmentally friendly building materials for thermoregulation and energy conservation.