Compressive Toughness Research Articles

Evaluation of mechanical properties and abrasion resistance of PAN fiber-reinforced sulfoaluminate cement composites

The studies of polyacrylonitrile (PAN) fiber-reinforced composites primarily focused on Portland cement, and there are few researches related to its effect on the performance of sulfoaluminate cement (SAC). The role of PAN fibers on the mechanical properties and abrasion resistance of SAC-based mortars is studied in this work, and the improvement mechanism of PAN fibers is investigated using scanning electron microscopy (SEM) and X-ray computed tomography (CT). The results demonstrate that the use of PAN fibers significantly enhances the strengths, compressive toughness, and abrasion resistance of the mortars, especially the early performance. The PAN fibers with grooves helped form a strong bond with the matrix. Based on the CT scan results, the fibers effectively inhibit microcrack initiation and restrain crack propagation under loading because they play a positive role in pull-out, crack bridging, and deflection, which is confirmed by SEM observation. This study provides the theoretical support for application of PAN fiber-reinforced sulfoaluminate cement composites in rush repair and construction of pavements.

Effect of Basalt Fiber on Uniaxial Compression-Related Constitutive Relation and Compressive Toughness of Recycled Aggregate Concrete

The deformation performance of recycled aggregate concrete can be effectively improved when basalt fiber is reasonably added. In this paper, the effects of the basalt fiber volume fraction and the length-diameter ratio on the uniaxial compression-related failure characteristics, feature points of the complete stress-strain curve and the compressive toughness of recycled concrete under different replacement rates of recycled coarse aggregate were studied. The results showed that with the increase in the fiber volume fraction, the peak stress and peak strain of basalt fiber-reinforced recycled aggregate concrete first increased and then decreased. With the increase in the fiber length-diameter ratio, the peak stress and strain of the basalt fiber-reinforced recycled aggregate concrete first increased and then decreased, whereas the effect of the length-diameter ratio on peak stress and strain of the basalt fiber-reinforced recycled aggregate concrete was clearly smaller than that of the fiber volume fraction. Based on the test results, an optimized stress-strain curve model of concrete under uniaxial compression was proposed for the basalt fiber-reinforced recycled aggregate concrete. Furthermore, it was found that the fracture energy is more suitable for evaluating the compressive toughness of the basalt fiber-reinforced recycled aggregate concrete than the tensile-compression ratio.

Compressive behaviour and microstructures of concrete incorporating pretreated recycled powder/aggregates: The coupling effects of calcination and carbonization

The incorporation of recycled powder (RP), recycled fine aggregate (RFA), and recycled coarse aggregate (RCA) can adversely affect the performance of cement-based materials. In this study, RP, RFA, and RCA (with or without pretreatment) are used to replace cement, natural fine aggregate (NFA), and natural coarse aggregate (NCA), respectively, to prepare recycled concrete (RC). With an increase in the replacement ratio of recycled materials, the mechanical properties of recycled cement paste (RCP), recycled mortar (RM), and RC are found to gradually decrease. Pretreatment (calcination and carbonization) of recycled materials favours the improvement of their physical and chemical properties, in which the coupling pretreatment of calcination and carbonization is found to lead to the best improvement in material properties. Among the RCs containing 50% RCA, the RCA carbonized for 24 h after calcination at 400 °C favours the best performance improvement for RC, with the compressive strength, elastic modulus, and compressive toughness increased by 35.8%, 19.3%, and 39.9%, respectively. The coupling effect of pretreatment results in the bonding between the matrix and RCA becoming closer, accompanied by an effective improvement in the ITZ. However, a too high calcination temperature (>600 °C) will negatively affect the performance of RC, whereas carbonization for a prolonged period of time barely alters the performance of RC.These results indicate that the coupling pretreatment of recycled materials favours the properties of the as-obtained RC, and calcination at 400 °C with carbonization at 6 h is the optimal pretreatment for recycled materials in terms of economic value and mechanical properties.

Experimental study on compression failure characteristics of basalt fiber-reinforced lightweight aggregate concrete: Influences of strain rate and structural size

This paper presents systematic experimental investigations on the combined influences of loading strain rate and structural size on uniaxial-compression failure characteristics of LAC and basalt fiber-reinforced lightweight aggregate concrete (BFLAC), in terms of workability, failure morphology, deformation curve, failure strength, elastic modulus and energy absorption, with a special focus on the size-dependence of strain rate effect. Results indicate that the uniaxial-compression strength, elastic modulus, compression toughness as well as specific toughness are increased when the basalt fibers with 0.3% volume content is added in LAC, which can be ascribed to the synergistic effect of three working modes of basalt fibers in restricting the crack propagation and fracture failure. As the strain rate increases, specimens with larger size perform a stronger strain rate effect, resulting in that the influence of structural size on uniaxial-compression failures is weakened. The addition of basalt fibers can also weaken the size-dependence on uniaxial-compression strength, compression toughness and specific toughness, which contributes to the promotion and application of basalt fibers in LAC, especially for large-scale engineering structures. The dynamic increase factor (DIF) empirical formulas of LAC and BFLAC with various structural sizes have been obtained, which can provide a reasonable reference for structure safety design and numerical computation of LAC and BFLAC.

Compressive-Tensile Mechanics and Energy Consumptions of a Cementitious Composite with High Utilization of Steel Slag

In response to the National Development and Reform Commission's “Guiding Opinions on Comprehensive Utilization of Large Solid Wastes during the Fourteenth Five Year Plan”, further expand the use of steel slag as concrete admixture in construction projects and other fields, and gradually improve the comprehensive utilization ratio, a cementitious composite with high utilization of steel slag (CHS) was developed, which is with the cement replaced by high-content super-fine steel slag powder (SSP) (replacement ratio υ ≥ 30%) as the cementitious materials, steel slag sand (SS) as the only aggregate and environmentally basalt fiber (BF) for toughening. It improves the utilization percentage of steel slag (SSP and SS) and reduces the consumption of natural resources such as cement and natural sand. Use BF to achieve better strength and toughness. In order to better understand the performance of CHS and make it better used in the engineering field. Study the influence of each component on the strength and energy consumption of compression and splitting tension, and strive to find the optimal proportion and lay the theoretical foundation for its application. Through the tests, the effects of high replacement ratio υ (30%–50%), low binder-aggregate ratio γ (0.31–0.44), and BF content ρv (0%–2%) on the aspects of peak strength, force-deformation curve and energy consumption were analyzed. The results show that the standard curing fck and ft,s can reach 40 MPa and 5 MPa respectively. With the increase of υ, the maximum axial compressive strength fck and splitting tensile strength ft,s decreased insignificantly. The γ has an important influence on fck and ft,s. When it increases from 0.31 to 0.44, fck increases linearly by 63.1% to 40.4 MPa, while ft,s increases by 52.8% to 5.18 MPa. As ρv increases, fck and ft,s show a trend of first increasing and then decreasing. ρv exerts a significant impact on the descending segments of stress-strain response curves of the compression which expressed as bilinear and trilinear models with different ρv after normalization. The energy consumptions of peak, total, and residual (Epeak, Edisp, Eres) show a slight downward trend with the increase of υ, a significantly upward trend with the increase of γ. With the increase of γv, and Edisp increase first and then tend to be flat, while Eres always increases and the percentages of Eres/Edisp in the compressive test increase from 22.6% to 38.5%, reflecting the improvement of the compressive toughness of BF.

Characteristics of Charcoal Briquettes, Activated Charcoal, and Liquid Smoke from Palm Shells (Elais Guineensis Jacq)

This study contains three products made from palm shells, namely charcoal briquettes, activated charcoal, and liquid smoke. Aims to know and analyze the characteristics of the three products. Charcoal briquettes are made by printing palm shell charcoal powder and then testing for density, moisture content, compressive toughness, volatile matter, ash content, bound carbon content, and heating value. Activated charcoal uses shell charcoal powder which is activated by soaking for 5 hours in 5% hydrochloric acid (HCl) then tested for its adsorption on spills of used lubricant. Liquid smoke from oil palm shells is obtained by pyrolysis process and multilevel purification and then the yield, pH value, specific gravity, and color are measured. Palm shell charcoal briquettes had the following values: density 0.691 g/cm3, moisture content 4.935%, compressive strength 13.444 kg/cm2, volatile matter content 42.700%, ash content 3.000%, bonded carbon content 62.200% and heating value 6070.667 cal/ g. Palm shell activated charcoal has the ability to adsorb used lubricants up to 1.505 times stronger than activated charcoal with a bonded carbon content of 90.667%. Grade 3 palm shell liquid smoke produces a yield of 12.61%, a pH of 3.58, a specific gravity of 1.004, and a dark brown color. Grade 2 produces 8.91% yield, pH 3.24, specific gravity 1.004, and yellow color. Grade 1 produces 6.30% yield, pH 2.99, specific gravity 1.001, and pale yellow color

Influence of different fibers on compressive toughness and damage of early age cemented tailings backfill.

For improving the utilization rate of tailings and the safety of cemented tailings backfill (CTB) as earthwork materials, the influence of three types of fibers (e.g., glass, polyacrylonitrile and mixture fibers of both) on compressive toughness and damage of early age CTB was studied. An equation for quantitative analysis of compressive toughness of fiber-reinforced CTB was established. An uniaxial compression test was carried out to monitor the damage acoustic emission (AE) activities of CTB during the loading process. Then, the microstructure of CTB after uniaxial compression test was observed by scanning electron microscope (SEM). The results indicated that mixed fiber has the most comprehensive reinforcement effect on compressive toughness and peak load of CTB. Three fibers inhibited the crack development rate of CTB, glass fiber mainly absorbed axial strain energy of CTB before peak load, while polyacrylonitrile fiber mainly absorbed fracture energy generated during the crack development of CTB after peak load, mixed fiber combined their advantages. The AE activities of three fiber-reinforced CTB samples are much stronger than those of non-reinforced CTB samples in the loading process, and these are no "quiet period" of AE activities. Three fibers all improved the durability of CTB in the damage process, and the damage process of mixed fiber-reinforced CTB is the most stable and showed an approximate linear growth trend. Polyacrylonitrile fiber has a strong resistance to crack after the peak load of CTB because of its ellipsoid part on the surface. As a result, this study can provide a theoretical reference for construction units to use fiber-reinforced CTB for engineering applications and filling work.

Axial compressive behaviour of thin-walled composite columns comprise high-strength cold-formed steel and PE-ECC

A new form of thin-walled composite columns, made of high-strength cold-formed steel (CFS) open sections and thin layers of engineered cementitious composites (ECC), is presented in this paper. The axial behaviour of columns with slenderness ratios (le/r) ranging between 10.08 and 13.86 under concentric loads were experimentally investigated. Twelve column specimens were divided into four groups of bare CFS columns, plain ECC columns, composite columns with SupaCee sections, and composite columns with Lipped-Cee sections. A specific ECC mixture with three PE-fibre contents: 0.75%, 1.75%, and 2.25% by mix volume, was placed in the tested columns in two thin thicknesses of 16.0 mm and 26.0 mm. Additionally, a high-strength concrete (HSC) mixture was utilised in two test columns for comparison with ECC. The results revealed that the composite CFS/ECC columns exhibited enhanced axial compressive capacities up to 2.79 times that of the bare CFS columns. The ductility indices and compressive toughness of the composite CFS/ECC columns were improved to 1.56 and 3.85 times those of the bare CFS columns, respectively. Strength prediction equations were developed based on the experimental observations to estimate the axial compressive capacity of composite CFS/ECC columns susceptible to local buckling.

Influence of multi-scale fiber on residual compressive properties of a novel rubberized concrete subjected to elevated temperatures

Green and environment-friendly rubberized concrete has attracted extensive attention from scholars worldwide. However, the incorporation of crumb rubber can weaken the mechanical properties of concrete, particularly when it is subjected to elevated temperatures. To improve the residual compressive performance of rubberized concrete, a novel multi-scale fiber reinforced rubberized concrete (MSFRRC) is developed by adding calcium carbonate whiskers, polyvinyl alcohol (PVA) fibers, and steel fibers. In this study, 10%, 20%, and 30% of the sands are substituted by the same volume of crumb rubber with sizes between 0.4 mm and 0.8 mm. The impacts of the crumb rubber content and multi-scale fiber on the residual Young's modulus, axial compressive strength, peak strain, stress-strain curve, and compressive toughness of MSFRRC after being heated up to various temperature levels (25 °C, 200 °C, 400 °C, 600 °C, and 800 °C) are discussed. Also, the failure mode combined with the acoustic emission technology and the thermal effect on the microstructure of rubberized concrete specimens, are investigated. Results reveal that incorporating multi-scale fiber can effectively restrain the development of cracks and explosive spalling under high temperatures. Besides, it can cover the strength loss caused by crumb rubber and impose a positive effect on resisting thermal damage. The compressive strength of MSFRRC can be enhanced by about 5.4%–19% with the incorporation of different fibers. The results show that specimens without fibers suddenly fail once the peak stress is reached and exhibit brittle fracture. However, the brittleness can be improved by adding multi-scale fibers. It can be observed that, after exposure to 800 °C, the damage of MSFRRC can develop at the early loading stage and develop in the whole loading process, showing a relatively ductile fracture. Meanwhile, the pore structure can be refined by adding CaCO3 whiskers and the addition of multi-scale fibers can slightly increase the porosity and cannot restrain the heating-induced pore coarsening. Furthermore, the empirical formulas to predict the residual stress-strain relation of MSFRRC under uniaxial compression are proposed by considering crumb rubber, multi-scale fibers, and high temperature.

Physical and mechanical properties of coral aggregates in the South China Sea

Coral aggregate (CA) is a type of marine resource with rich storage capacity and complex physical characteristics, and it is increasingly recognized as an important island engineering material. For the regional variability of CA in the South China Sea, the physical and mechanical properties of different CAs were experimentally studied in this paper. Using the X-ray Computed Tomography technique, the pore characteristics of CA were quantitatively studied in term of the pore shape, size, sphericity, number, volume, etc. Additionally, the uniaxial compressive properties of cylinder CA samples were investigated in term of the failure patterns, stress-strain curves, elastic modulus, strength, and toughness. Results indicate that different CA samples contain a considerable amount of pores with different shapes that are closely related to the coral growth environment. It was found that content of the millimeter-sized pores with a diameter of 0.5∼1 mm is the highest, while the content of the centimeter-sized pores with a diameter greater than 1 cm is the lowest. The porosity of light and heavy CA was determined as 1.37%–22.55% and 3.72%–22.64%, respectively. Splitting failure is the main form of failure to CA under uniaxial compression loading. While the compressive toughness of CA could be effectively improved by the surface-filling method treatment using coral mortar. According to the present results and the existing data, a series of regression equations concerning the physical-mechanical properties of CA were established, which has significant values for the study and application of CA in the South China Sea.

Flexural performance of layered macro fiber reinforced concrete beams

Fiber-reinforced polymer (FRP) composites have been increasingly used in various sectors, which inevitably results in an increasing amount of FRP waste to be dealt with. A recent study conducted by the authors’ group explored a novel mechanical recycling method to process glass fiber-reinforced polymer (GFRP) waste into small slender elements (referred to as “macro fibers”) for reinforcing concrete, leading to so called “macro fibre reinforced concrete” (i.e., MFRC). The macro fibres recycled from waste FRP composites shows to effectively enhance the tensile performance of the resulting concrete (e.g., tensile strength, tensile toughness), while have a negligible effect on the compressive properties of MFRC. The concept of the layered beams has been therefore adopted with the bottom layer fabricated with MFRC and the top layer with plain concrete (PC) to improve the utilization and added values of the macro fibers from the structural level. A series of tests were conducted to justify the proposed technique. Test results indicate that an increase of 4.6%, 27.6%, and 44.3% in splitting tensile strength was observed for concrete with a macro fiber content of 1%, 1.5%, and 2%, respectively. Some of other mechanical properties of the resulting concrete (e.g., the compressive toughness, flexural strength and flexural toughness) were apparently enhanced as well by the incorporation of macro fibers. In addition, the flexural performance of concrete beams shows to be superior if the macro fibers mainly concentrated in the bottom layer (i.e., a layered beam), demonstrating a higher utilization and added values of macro fibers achieved by the application of layered beams.

Synergistic Effect of PVA Fiber and PTB Emulsion on Mechanical Properties of Cementitious Composites for Damage Repair in Operating Tunnels

Operating tunnels are often located in complex geological conditions and are prone to various types of damage. Even after structural repair, the repaired material may be vulnerable to secondary damage. It is difficult to effectively repair operating tunnel damage. Hence, developing high-performance repair materials for tunnel structures is critical. This study aimed to develop repair materials by studying the synergistic effects of fiber and polymers. The effect of polyvinyl alcohol (PVA) fiber and PTB (COMPAKTUNA.PRO) emulsion on the compressive strength (40 × 40 × 40 mm, GB/T 17671-2020), flexural strength (40 × 40 × 160 mm, GB/T 17671-2020), uniaxial tensile properties (330 × 60 × 13 mm, JC/T 2461-2018), bond strength (40 × 40 × 160 mm, JC/T 2537-2019), rapid chloride migration coefficient (ϕ100 × 50 mm, GB/T 50082-2009), porosity (40 × 40 × 40 mm, SY/T 6490-2014), and scanning electron microscopy (less than 1 cm3, GB/T 27788-2020) was analysed. The test was completed in the laboratory of our school, and the average value of three specimens per mix ratio was taken. The results indicate that both PVA fiber and PTB emulsion addition reduce the compressive strength but significantly increase the flexural strength, tensile strength, and ultimate tensile strain of cementitious composite. The compressive-to-flexural strength ratio decreases, and the uniaxial compression toughness index increases. The cementitious composites exhibit good integrity after damage. The influence of the PVA fiber is more potent than that of the PTB emulsion. The PTB emulsion increases the impermeability and bonding strength of the cementitious composite and can improve the disadvantages caused by adding the PVA fibers. The bridging effect of the PVA fiber and the membrane-forming effect of the PTB emulsion together influence the performance and cause a synergistic effect to achieve superposition and complementation of advantages. The optimal content of the PVA fiber and PTB emulsion under the synergistic effect can be obtained. The findings can provide a theoretical basis for the optimal design and practical application of restoration materials.

Experimental investigation on static compressive toughness of steel fiber rubber concrete

Abstract Recycled rubber particles can be produced by using waste tires. Adding recycled rubber particles to concrete can form rubber concrete (RC). RC can not only reduce the amount of natural sand and reduce the cost of concrete but also improve the static compressive toughness of concrete. Adding steel fiber into RC can improve the strength of concrete. In order to study the compressive toughness of steel fiber rubber concrete (SFRC), rubber particles washed with NaOH are added to steel fiber reinforced concrete. This can enhance the bonding performance between the recycled rubber particles and concrete. The volume ratio of recycled rubber is 5, 10, and 15%. Prismatic and cubic test blocks were prepared and their compressive tests were carried out. The results show that the stress interaction between the rubber particles and steel fiber in concrete significantly improves the compressive strength, elastic modulus, and stress–strain relationship of concrete. The compressive toughness and ductility of concrete are improved. When the content of rubber particles is 15–20%, the compressive toughness of SFRC is improved most obviously. Through experiments, the toughness index and specific toughness of rubber steel fiber reinforced concrete are calculated, which explores a new way and method for studying the compressive toughness of similar recycled material concrete.

Less Is More: Hollow-Truss Microlattice Metamaterials with Dual Sound Dissipation Mechanisms and Enhanced Broadband Sound Absorption.

Being a lightweight material with high design freedoms, there are increasing research interests in microlattice metamaterials as sound absorbers. However, thus far, microlattices are limited to one sound dissipation mechanism, and this inhibits their broadband absorption capabilities. Herein, as opposed to improving performances via the addition of features, a dissipation mechanism is subtractively introduced by hollowing out the struts of the microlattice. Then, a class of hollow-truss metamaterial (HTM) that is capable of harnessing dual concurrent dissipation mechanisms from its complex truss interconnectivity and its hollow interior is presented. Experimental sound absorption measurements reveal superior and/or customizable absorption properties in the HTMs as compared to their constitutive solid-trusses. An optimal HTM displays a high average broadband coefficient of 0.72 at a low thickness of 24mm. Numerically derived, a dissipation theorem based on the superimposed acoustic impedance of the critically coupled resistance and reactance of the outer-solid and inner-hollow phases, across different frequency bands, is proposed in the HTM. Complementary mechanical property studies also reveal improved compressive toughness in the HTMs. This work demonstrates the potential of hollow-trusses, where they gain the dissipation mechanism through the subtraction of the material and display excellent acoustic properties.

Compressive Toughness Loss Rate and Softening Characteristic Analysis of Pasture Fiber-Rubber Powder Concrete

To develop the utilization of pasture fibers and waste tire rubber powder, the effect of different blending levels of modified pasture fibers (2 kg/m3, 3 kg/m3, and 4 kg/m3) on the loss rate of compressive toughness and softening characteristics of rubber powder concrete was studied. In addition, RapidAir457 system imaging analysis and microscopic electron microscope photo analysis were carried out to analyze the distribution pattern of modified pasture fibers and rubber powder in concrete. The results show that the peak load of concrete is higher than other pasture fiber dosing test groups when 3 kg/m3 is incorporated in 20 mesh and 60 mesh rubber powder. With the increase of pasture fiber content, the compressive toughness loss of MC60 group and MC80 group increased first and then decreased. The softening curve analysis showed that MC-3 was more capable of absorbing damage energy in the strain range of 0.0005–0.0009 than the MC-2 group. According to the RapidAir457 system imaging analysis, the pasture fibers form a web-like organization inside the concrete when the pasture fiber is mixed at 3 kg/m3.

Insights into Stoichiometry Adjustments Governing the Performance of Flexible Foamed Polyurethane/Ground Tire Rubber Composites.

Polyurethanes (PU) are widely applied in the industry due to their tunable performance adjusted by changes in the isocyanate index—stoichiometric balance between isocyanate and hydroxyl groups. This balance is affected by the incorporation of modifiers of fillers into the PU matrix and is especially crucial for PU foams due to the additional role of isocyanates—foaming of the material. Despite the awareness of the issue underlined in research works, the contribution of additives into formulations is often omitted, adversely impacting foams’ performance. Herein, flexible foamed PU/ground tire rubber (GTR) composites containing 12 different types of modified GTR particles differing by hydroxyl value (LOH) (from 45.05 to 88.49 mg KOH/g) were prepared. The impact of GTR functionalities on the mechanical, thermomechanical, and thermal performance of composites prepared with and without considering the LOH of fillers was assessed. Formulation adjustments induced changes in tensile strength (92–218% of the initial value), elongation at break (78–100%), tensile toughness (100–185%), compressive strength (156–343%), and compressive toughness (166–310%) proportional to the shift of glass transition temperatures (3.4–12.3 °C) caused by the additional isocyanates’ reactions yielding structure stiffening. On the other hand, formulation adjustments reduced composites’ thermal degradation onset due to the inferior thermal stability of hard segments compared to soft segments. Generally, changes in the composites’ performance resulting from formulation adjustments were proportional to the hydroxyl values of GTR, justifying the applied approach.

Compressive Behavior and Durability Performance of High-Volume Fly-Ash Concrete with Plastic Waste and Graphene Nanoplatelets by Using Response-Surface Methodology

Plastic waste (PW) generation continuously increases every year due to the growing population and demand for plastic materials. This situation poses a challenge to many countries, including developed ones, on how to dispose of PW. Accordingly, PW was utilized in this study to replace coarse aggregates partially in high-volume fly-ash (HVFA) concrete. However, PW decreased the strength and durability of concrete. To address this issue, graphene nanoplatelets (GNPs) were added to mitigate the negative consequences of PW and HVFA on concrete’s properties. The objective of this study is to investigate the influences of PW and GNP contents on the durability and deformation of HVFA concrete. Response-surface methodology (RSM) was used to design and optimize a series of cement mixes to achieve the most desirable properties. Independent variables included PW content as partial replacement for coarse aggregates (0%, 15%, 30%, 45%, and 60% by volume), fly ash as partial substitute for cement (0%, 20%, 40%, 60%, and 80% by volume), and GNPs as additives (0%, 0.075%, 0.15%, 0.225%, and 0.3%). The considered responses were concrete unit weight, modulus of elasticity (MoE), and Cantabro abrasion loss at 300 revolutions. Results showed that PW and HVFA decreased concrete unit weight and MoE but increased Cantabro abrasion loss. By contrast, GNPs increased concrete unit weight and MoE but decreased Cantabro abrasion loss. PW and HVFA also increased the compressive toughness and porosity of concrete, while GNPs increased its stiffness but decreased its compressive toughness and porosity. The mathematical models developed to predict the unit weight, MoE, and abrasion resistance of concrete were significant, with errors of less than 6%. An optimized mix was achieved by partially replacing 12.44% of coarse aggregates with PW and 24.57% of cement with fly ash and adding 0.279% GNPs with a desirability of 100%.

Cement - Hollow Glass Microballoons Syntactic Foams: Preparation and Compressive Properties

The present study focuses on the preparation of cement-hollow glass microballoons (40–60 % v/v) syntactic foams for construction applications. Conventional rigid fillers like mortar and aggregates enhance the compressive properties but poses heavy load on the buildings and structures. The use of hollow glass microballoons (K46) with a density of 0.46 g cm−3, as filler in cement binder, offers higher compressive strength at comparable densities. Moreover, the compressive toughness and specific compressive toughness values at 40 percent loadings of K46 are found to enhance by ∼ 87 percent and ∼ 157 percent respectively when compared to neat cement. The use of hollow glass microballoons as a filler material is expected to open new possibilities for the construction industry.

Experimental investigation on flexural and compressive toughness of mortar and concrete with hybrid toughening materials

In this work, the effects of hybrid toughening materials on the flexural and compressive toughness of cement-based materials were studied experimentally. In specific, mortar and concrete specimens incorporating multiple toughening materials, including PVA fibers, rubber particles, and polymer latex powders, were designed and manufactured. The flexural load–deflection response and compressive load–displacement behavior of these prepared mortar and concrete specimens were tested, and then were analyzed with special attention to the influences of hybrid toughening materials on the flexural toughness index and compressive energy absorption index. In addition, the mechanism of toughness enhancement was discussed. The results show that, compared with the addition of PVA fibers only, the hybrid of multiple toughening materials could considerably improve the flexural toughness of mortar and concrete, while it had an insignificant effect on the compressive energy absorption index of mortar and concrete. After incorporating hybrid toughening materials, the toughening effects on the flexural toughness of concrete specimens were better than those of the corresponding mortar specimens. As detected from scanning electron microscopy images, the incorporation of hybrid toughening materials could promote the formation of network structures with a good capacity for crack resistance. This resulted in multiple ways for energy dissipation, and consequently enhanced the flexural toughness of cementitious materials.

Investigation on the mechanical characteristics of multiscale mono/hybrid steel fibre-reinforced dry UHPC

Dry ultra-high performance concrete (DUHPC) is a promising building material with better mechanical and durability properties, developed on the basis of retaining the advantages of traditional dry concrete, such as fast hardening speed, high early age strength and rapid demoulding. In the current study, the impacts of multiscale mono and hybrid steel fibre reinforcements on the static mechanical behaviour of DUHPC were further studied based on the benchmark mix ratio and optimal curing regime obtained from the previous study. The experiments carried out included the quasi-static uniaxial compression, four-point bending and split-tensile tests. The mono fibre reinforcement (0.5–2.0 vol. %) comprised of straight steel fibres with the same diameter but different lengths (6, 10 and 13 mm), while the hybrid fibre reinforcement was composed of different combinations of foregoing fibres at a fixed content (1.5 vol. %), which could be further divided into double and ternary hybridization. Test results revealed that compared to control samples without fibre reinforcement, the single addition of any steel fibres improved the static mechanical behaviour of DUHPC, particularly for flexural and split-tensile performance. In the case of fibre hybridization, the replacement of longer fibres with more addition of short (6 mm) ones evidently reduced the flexural toughness and energy absorption capacity of DUHPC upon cracking, whereas the mixtures with hybrid medium (10 mm) and long (13 mm) fibres as well as with hybrid short, medium and long fibres showed better compressive toughness and energy absorption capability. The proposed multivariate regression linear, nonlinear and most of the mixed models could well estimate the compressive, flexural and split-tensile strength values of mono steel fibre-reinforced DUHPC at a given range of fibre length, volume content and curing age. The updated best-fit models containing compressive strength as an additional independent variable performed better in predicting both the flexural and split-tensile properties.