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Carbon fibre, steel fibre and graphite were used as conductive fillers to prepare cementitious materials with excellent electrothermal properties. The electrically conductive cementitious materials with different volume dosages were analysed through compressive and flexural strength, electrochemical impedance spectroscopy and temperature rise tests. An equivalent circuit model was established to study the electrically conductive heat generation mechanism in the electrically conductive cementitious composites. The results indicate that the mechanical properties of cementitious composite materials with a ternary conductive phase are better than those of pristine cementitious materials because the fibrous filler improves their mechanical properties. However, the incorporation of graphite in the material reduces its strength. Introducing fibrous and point-like conductive phase materials into the cementitious material enhances the overall conductive pathway and considerably reduces the electrical resistance of the cementitious material, enhancing its conductive properties. The volume ratios of carbon fibre, steel fibre and graphite that achieve an optimal complex doping in the cementitious material were 0.35%, 0.6% and 6%, respectively. This was determined using the mutation point of each circuit element parameter as the percolation threshold. In addition, at a certain safety voltage, there is a uniform change between the internal and surface temperatures of the conductive cementitious material, and the heating effect in this materialis is considerably better than that in the pristine cementitious material. [ABSTRACT FROM AUTHOR]

This paper explores the computational modeling of transient heat conduction in thermal energy storage (TES) systems for buildings made of cementitious composites with microencapsulated phase change materials (PCMs). Addressing solid ↔ liquid phase transitions, the study examines numerical approaches and homogenization techniques to define effective thermal properties. Discussion spans both numerical and analytical homogenization models, followed by a comprehensive exploration of approaches to incorporate phase change effects into the numerical solution of transient heat conduction problems. Challenges such as enthalpy-temperature hysteresis and supercooling phenomena are addressed, proposing alternative formulations for stable solutions and improved convergence. The paper highlights the complexities of phase change phenomena and emphasizes the need for ongoing research to enhance modeling techniques for practical applications. [ABSTRACT FROM AUTHOR]

This study investigates crack growth and propagation in Engineered Cementitious Composite (ECC) beams reinforced with polyvinyl alcohol (PVA) fibers through numerical analysis. The research evaluates numerical findings alongside experimental data from a prior stage. Similar to the experimental phase, the numerical procedure models eight ECC beam specimens, comprising four with 2% and four with 1.5% PVA fibers, utilizing the extended finite element method (XFEM) in Abaqus software. Force-displacement and force-crack mouth opening displacement (CMOD) graphs are generated and compared with experimental results. The study demonstrates XFEM's high accuracy in numerically solving fracture problems and predicting structural behavior, as well as determining parameters assessing ECC behavior during crack growth. Findings reveal that ECC beams with 2% fibers exhibit lower loading capacity and higher displacement values, displaying greater CMOD and ductility compared to those with 1.5% fibers. Additionally, a slight impact on flexural capacity is observed with increasing PVA fiber percentages. [ABSTRACT FROM AUTHOR]

Poultry litter (PL) disposal is a major concern for poultry farms around the world, it is estimated that millions of metric tons of this waste are generated globally and as consumption rates increase so does the associated waste; the usual means of disposal include soil fertilization and livestock feeding, however, these disposal strategies are linked with hazardous environmental consequences: eutrophication, ammonia (NH3) emissions and leaching of heavy metals. New environmentally friendly processes have been developed in order to reduce the impact of poultry litter and provide new means of revalorization: proper management and selection, elemental recovery (P, K and N) and its use as biomass for energy generation. One of the most promising revalorization opportunities for this ash residue lies in the development of greener cementitious composites in the pursuit of net-zero energy projects by reducing the carbon footprint of the modified concrete by replacing cement or aggregates, given the typical chemical composition (> 40% CaO) of poultry litter ash (PLA). The present review deals with PLA potential to replace cement or fine aggregates in cementitious composites, how this substitution affects the transport properties of the resultant composite and the effects on strength development and future considerations to be further investigated. [ABSTRACT FROM AUTHOR]

This study systematically investigates modification methods for recycled aggregate, including acid modification, abrasion testing, and triple-mixing improvement. Recycled aggregate from a single source replaced 50% and 100% of natural aggregate in concrete mixes, which were compared to controls using natural aggregate and unmodified recycled aggregate. Simultaneously, recycled aggregate and recycled waste tire steel fibers were employed to enhance sustainability. Modification effects on properties were isolated by adjusting aggregate gradations and using superplasticizer to control water-binder ratios. Key quantitative findings include a 10% reduction in compressive strength with 50% recycled aggregate and a 15.7% reduction with 100%, due to lower density, increased porosity, and cracks. Modification methods improved strength by 4–9.5% for 50% recycled aggregate and 2–5% for 100% replacement. The triple-mixing method notably enhanced 50% recycled concrete, while acid modification was most effective for 100% recycled concrete. Unit weight decreased by 5% with 50% and 3.6% with 100% recycled aggregate. Workability reduction was observed with recycled fiber addition, while modified recycled aggregate mitigated this effect. Axial stiffness decreased by 21.76% with 100% recycled aggregate, with modification methods showing varied effects. Energy absorption decreased by 19.5% with 50% and 24.3% with 100% recycled aggregate, minimally impacted by modification. [ABSTRACT FROM AUTHOR]

One of the major challenges in the civil engineering sector is the durability of reinforced concrete structures against carbonation during the physico-chemical process of interaction of hydrated cementitious composites with carbon dioxide. This aggressive process causes carbon penetration into the reinforcement part, which affects the behavior of the structure during its lifetime due to corrosion risk. A countermeasure is using alternative cementitious materials to improve concrete texture and resist increased carbonation depth (CD). Considering that the CD test requires a long time and a skilled technician, this study strives to provide an alternative approach by moving from traditional laboratory-based methods towards artificial intelligence (AI) techniques for modeling the CD of sustainable concrete containing fly ash (CCFA). Despite the development of single AI models so far, it is undeniable that utilizing metaheuristic optimization techniques in the form of hybrid models can improve their performance. To this end, a new hybrid model from the integration of biogeography-based optimization (BBO) technique with artificial neural network (ANN) is developed for the first time to estimate the CD of CCFA. The error distribution results revealed that 59% of the ANN predictions had errors within the range of (− 1 mm, 1 mm], while the corresponding percentage for the ANN-BBO predictions was 70%, indicating an 11% reduction in the prediction errors by the proposed hybrid model. Furthermore, A10-index highlighted a performance improvement of 78% for the hybrid model, which met the closeness of the predicted values to the observed ones, so that the value of this index for models of ANN and ANN-BBO was 0.5019 and 0.8947, respectively. Analyzing the cross-validation confirmed the reliability and generalizability of the developed model. Also, the three most influential variables in estimating the CD were exposure time (27%), carbon dioxide concentration (22%), and water/binder (18%), respectively. Finally, the superiority of the ANN-BBO model was verified by comparing it with previous studies' models. [ABSTRACT FROM AUTHOR]

Concrete, the ubiquitous cementitious composite though immensely versatile, is crack-susceptible. Cracks let in deleterious substances causing durability issues. Superseding conventional crack-repair methods, the innovative application of microbially induced calcium carbonate precipitation (MICCP) stands prominent, being based on the natural phenomenon of carbonate precipitation. It is eco-friendly, self-activated, economical, and simplistic. Bacteria inside concrete get activated by contacting the environment upon the crack opening and filling the cracks with calcium carbonate—their metabolic waste. This work systematizes MICCP's intricacies and reviews state-of-the-art literature on practical technicalities in its materialization and testing. Explored are the latest advances in various aspects of MICCP, such as bacteria species, calcium sources, encapsulations, aggregates, and the techniques of bio-calcification and curing. Furthermore, methodologies for crack formation, crack observation, property analysis of healed test subject, and present techno-economic limitations are examined. The work serves as a succinct, implementation-ready, and latest review for MICCP's application, giving tailorable control over the enormous variations in this bio-mimetic technique. [ABSTRACT FROM AUTHOR]

The use of natural fibers in cementitious composites has been gaining prominence in engineering. The natural lignocellulosic fibers (NLFs) used in these composites have advantages such as reduced density, reduced fragmentation and concrete cracking, thus improving flexural performance and durability. Coconut-fiber is one of those natural fibers and its use presents technical, ecological, social and economic benefits, as it is improperly disposed of, representing a large waste of natural resources, in addition to causing environmental pollution.. Thus, composites reinforced with natural fibers are promising materials for the construction industry, as in addition to meeting the sustainability of buildings, there will also be a reduction in urban solid waste generated and gains for structures with the use of environmentally friendly materials that meet to active efforts and with greater durability. This work aims to evaluate the tensile behavior of green coconut-fibers subjected to different drying temperatures through chemical, thermal (TG/DSC), morphological, visual and mechanical analysis. Drying temperatures of 70 °C, 100 °C and 130 °C were analyzed and the results indicated that the drying temperature at 70 °C was satisfactory, providing fiber-reinforced composites with good tensile strength, combined with good ductility. [ABSTRACT FROM AUTHOR]

The mesoscale fiber–matrix interfacial transition zone (FM-ITZ) under induced curing pressure plays a key role in the effectiveness of fiber reinforcement and the engineering application of fiber-reinforced cementitious composites (FRCCs). This critical review establishes the link among induced curing pressure (i.e., external loading condition), multiphysics processes (i.e., internal governing mechanism), and interface behavior (i.e., material behavior) for FRCC materials through analysis of the state-of-the-art research findings on the FM-ITZ of FRCC materials. The following results are obtained. For the mechanical process, the induced curing pressure changes the stress state and enhances multicracking behavior, which can strengthen the FM-ITZ. For the hydraulic process, the strengthened seepage of the FM-ITZ under induced curing pressure weakens the effective stress and exaggerates the deficiency in water retention capacity between the bulk matrix and the FM-ITZ. For the thermal process, the induced curing pressure causes a steep temperature gradient in the FM-ITZ and thus influences the temperature evolution and thermally-induced microcracks in the FM-ITZ. For the chemical process, the induced curing pressure enhances hydration kinetics and results in the formation of additional hydration products in the FM-ITZ. Moreover, recommendations are proposed on the basis of findings from this review to facilitate the implementation of fiber reinforcement in cemented paste backfill technology. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

In this study, the particle size distribution (PSD) of class F and C fly ash (FA) was optimized using theory of the Fuller-Thompson. After defining the optimal size distribution, the distribution modulus (q) of 0.4 yields the best mechanical property results. The freeze–thaw up to 300 cycles on mechanical and permeability properties of 90-day cementitious composites incorporating optimized class F and C fly ash (5, 10, 15, 20, 25, and 30% by weight of cement) were investigated. Optimized FA has improved the mechanical and permeability properties of cementitious composites under freeze–thaw cycling by ensuring a better filler effect. The cementitious composite mortars with 20% optimized class C fly ash and class F fly ash replacement yielded high compactness and better mechanical properties than the control cementitious composite mortars without any fly ash replacement after 90 days. Finding the best particle size distribution of FA providing high compactness will save cement, reduce the carbon dioxide (CO2) emission that pollutes the environment in cement production, and contribute to the economy and environment. [ABSTRACT FROM AUTHOR]

In this work, the instant mechanical recovery and the thermal resistance of nanosilica(NS)-incorporated cement composites were investigated. The composites were exposed to various heating temperatures (200, 500, 800, and 1000 °C) and rehydration conditions (25 °C/65% RH or water rehydration), and weight, surface morphology, density, compressive strength, and X-ray diffraction were assessed. 29Si nuclear magnetic resonance was used to analyze the relationship between the mean chain length (MCL) of calcium silicate hydrates (C–S–H) and instant mechanical recovery. Increasing the NS content substantially increased the compressive strength after heating and strength recovery through rehydration at 25 °C/65% RH, particularly after exposure at 500 and 800 °C. The NS pozzolanic reaction afforded strength recovery and was linearly related to increasing MCL of C–S–H. The pozzolanic reaction produced a compact matrix; therefore, the strength recovered considerably following rehydration in water, even after heating to 800 °C, because of the combined effect of hydrate formation and the resistance of the matrix to thermal shock. [ABSTRACT FROM AUTHOR]

Acid mine drainage presents an important threat to cementitious structures. This study is aimed at investigating the effect of cellulose nanocrystals (CNCs) on the acid resistance of cementitious composites. CNCs were added to mortar mixtures as additives at cement volume ratios of 0.2vol%, 0.4vol%, 1.0vol%, and 1.5vol%. After 28 d of standard curing, the samples were immersed in a sulfuric acid with a pH value of 2 for 75 d. The unconfined compressive strength (UCS) test, the density, water absorption, void volume test, and thermogravimetric analysis were carried out to investigate the properties of CNC mixtures before sulfuric acid immersion. It was found that the addition of CNC reduced the volume of permeable voids and increased the hydration degree and mechanical strength of the samples. Changes in mass and length were monitored during immersion to evaluate the acid resistance of mixtures. The mixture with 0.4vol% CNC showed a reduced mass change and length change indicating its improved acid resistance. [ABSTRACT FROM AUTHOR]

This research aims to experimentally evaluate the behaviour of multi-layered fibrous cementitious composites with intermediate Glass Fibre Meshes (GFM) under repeated projectile load. The impact load was subjected through a convex edge projectile needle at a low velocity on cylindrical specimens of three-layered fibrous cementitious composites, which have two different steel fibre distributions. In series A mixtures, a constant steel fibre dosage of 2.5% by volume was used. On the other hand, the fibre dosage of the outer layers was 3.0%; while it was 1.5% in the middle layer of series B mixtures. The number of intermediate GFM was the variable that distinguishes the mixtures of each series. The resistance to projectile impacts was evaluated on the basis of penetration depth, near surface distortion, weight loss, damage ratio and failure pattern. The test results showed that due to the combined effect of steel fibre and GFM, significantly lower weight losses were recorded for series A and B specimens compared with reference specimens. However, the different fibre distributions (series B) led to lower penetration depths and weight losses with less surface distortion compared with the fixed fibre distribution (series A). The reduction in the destroyed front surface area of series A specimens compared with reference specimens ranged from 27.8 to 38.1%; while that of series B specimens ranged from 34.8 to 53.4%. In addition, a simplified analytical model was introduced to predict the ejected composite mass. The model predictions were found to be in good agreement with the experimental masses. [ABSTRACT FROM AUTHOR]

Self-sensing concrete materials, also known as smart concretes, are emerging as a promising technological development for the construction industry, where novel materials with the capability of providing information about the structural integrity while operating as a structural material are required. Despite progress in the field, there are issues related to the integration of these composites in full-scale structural members that need to be addressed before broad practical implementations. This article reports the manufacturing and multipurpose experimental characterization of a cement-based matrix (CBM) composite with carbon nanotube (CNT) inclusions and its integration inside a representative structural member. Methodologies based on current–voltage (I–V) curves, direct current (DC), and biphasic direct current (BDC) were used to study and characterize the electric resistance of the CNT/CBM composite. Their self-sensing behavior was studied using a compression test, while electric resistance measures were taken. To evaluate the damage detection capability, a CNT/CBM parallelepiped was embedded into a reinforced-concrete beam (RC beam) and tested under three-point bending. Principal finding includes the validation of the material's piezoresistivity behavior and its suitability to be used as strain sensor. Also, test results showed that manufactured composites exhibit an Ohmic response. The embedded CNT/CBM material exhibited a dominant linear proportionality between electrical resistance values, load magnitude, and strain changes into the RC beam. Finally, a change in the global stiffness (associated with a damage occurrence on the beam) was successfully self-sensed using the manufactured sensor by means of the variation in the electrical resistance. These results demonstrate the potential of CNT/CBM composites to be used in real-world structural health monitoring (SHM) applications for damage detection by identifying changes in stiffness of the monitored structural member. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Zhejiang University: Science A is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Journal of Zhejiang University: Science A is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The present work investigates the hydration heat of different cement composites by means of conduction calorimetry to optimize the composition of binder in the design of heavyweight concrete as biological shielding. For this purpose, Portland cement CEM I 42.5 R was replaced by a different portion of supplementary cementitious materials (blast furnace slag, metakaolin, silica fume/limestone) at 75%, 65%, 60%, 55%, and 50% levels to obtain low hydration heat lower than 250 j g−1. All ingredients were analyzed by energy dispersive X-ray fluorescence (EDXRF) and nuclear activation analysis (NAA) to assess the content of major elements and isotopes. A mixture of two high-density aggregates (barite and magnetite) was used to prepare three heavyweights concretes with compressive strength exceeding 45 MPa and bulk density ranging between 3400 and 3500 kg m−3. After a short period of volume expansion (up to 4 h), a slight shrinkage (max. 0.3°/°°) has been observed. Also, thermophysical properties (thermal conductivity, volumetric specific heat, thermal diffusivity) and other properties were determined. The results showed that aggregate content and not binder is the main factor influencing the engineering properties of heavyweight concretes. [ABSTRACT FROM AUTHOR]

Among the products used in the construction industry, cement composites with lignocellulosic reinforcement have been highlighted in the research. These materials have advantageous characteristics, such as being lighter and more economical. This work aimed at evaluating the effect of different lignocellulosic materials use on the physical, mechanical, and durability properties of fiber cement. The composites were produced in laboratory scale by extrusion. The formulation consisted of 5% lignocellulosic material, 30% agricultural limestone, 1% hydroxypropylmethylcellulose, and 1% polyether carboxylic additive and the remainder of the material was Portland cement (CPV-ARI) to complete the formulation. The samples were cured for 2 days in a saturated environment and for 5 days in thermal curing. Fiber cement properties such as bulk density, water absorption, apparent porosity, modulus of elasticity, modulus of rupture, and tenacity after curing and after 200 and 400 aging cycles were evaluated. Eucalyptus, coffee husk, banana pseudostem and coconut shell particles could be used for fiber cement production since they met the marketing standards after the aging process. [ABSTRACT FROM AUTHOR]

Rutile phase TiO 2 with the diameter of 50 nm and 500 nm were used to fabricate TiO 2 modified cementitious composites (RTMCC) in this paper. The mechanical property and microstructures of RTMCC were compared. Research results showed both types of TiO 2 can improve the flexural and compressive strengths of cementitious composites. The addition of 2.32 vol.% 50 nm and 500 nm TiO 2 increased the 28 days flexural strength/compressive strength by 27.7%/10.78% and 53.71%/18.58%, respectively. In addition, the fracture toughness of cementitious composites can be enhanced by the inclusion of TiO 2. The microstructure analysis demonstrated that the strengthening effect of TiO 2 to cementitious composites results from the nucleation effect, filling effect, pinning effect and self-curing effect. However, the reinforcing effect of 500 nm TiO 2 is superior to that of 50 nm TiO 2. Nuclear magnetic resonance and energy dispersive spectrum analyses suggested that 50 nm TiO 2 can make the decalcification of the C–S–H (i.e., calcium is removed from the interlayer) and cause defect sites in the silicate chains, which lead to the less-density C–S–H. In addition, zeta potential and scanning electron microscope analyses manifested that 50 nm TiO 2 is easier to reunite, therefore generating more defects in cementitious composites. [ABSTRACT FROM AUTHOR]

Urea formaldehyde/epoxy resin microcapsules were prepared by an in situ polymerization method and the effect of emulsifier on the syntheses process of the microcapsules was discussed. The surface morphology of the microcapsules was observed by optical microscopy and scanning electron microscopy (SEM). Chemical structure was characterized by Fourier transform infrared spectroscopy (FTIR). Thermal stability was obtained using simultaneous thermal analysis (STA). The microcapsules were composed of urea-formaldehyde resin shell and epoxy resin core. Emulsifier played an important role in the polymerization process when the core material was packed by pre-polymer, so the effects of different emulsifiers (OP-10, SDS and SDBS) were discussed respectively. Results showed that the particle size of the microcapsules was uniform when SDBS as an emulsifier. Microcapsules showed good thermal stability below 240 °C and the initial decomposition temperature of the microcapsules was 265 °C. The core materials released after microcapsules rupturing, which could be proven by the images of SEM. When implanted in cementitious composites, complete shape of microcapsules and good interface between microcapsules and cement specimen substrate could also be observed. [ABSTRACT FROM AUTHOR]

The use of porous materials as restrictor in aerostatic bearings provides many advantages over conventional restrictors, such as small variation of temperature, high damping, high operational speeds, limited wear and capacity to support radial, axial, and combined loads, being considered important features for precision machines and instruments. This work evaluates the load carrying capacity for different air gaps and pressures of thrust porous bearing made with cementitious composites. The cementitious composites consisted of Portland cement and monomodal silica particles (44 μm) were fabricated via uniaxial cold-pressing (10 MPa). The load capacity was determined for different air pressures, such as 3, 4, 5 and 6 bar. The air gap was measured using pneumatic transducers. A pneumatic instability was observed when the air pressure level increased from 3 to 6 bar. A similar loading capacity, for bearing gaps between 7 and 30 μm, was achieved in comparison to hot-pressed porous alumina found in the literature. In addition, the cementitious porous bearing provided a superior loading capacity for gaps higher than 10 μm when compared to graphite porous bearing found in the literature. The results revealed the cementitious composites are promising materials for porous restrictor in aerostatic thrust bearings. [ABSTRACT FROM AUTHOR]

Cementitious composites with 0–1.5 wt.% Nano-SiO 2 (NS), nano-TiO 2 (NT), carbon nanotubes (CNTs), carbon nanofibers (CNFs) and carbon microfibers (CFs) are fabricated and tested. The enhancing effects of different fillers on the compressive strength and electrical resistivity of composites are compared, and the underlying modification mechanisms of fillers to composites are investigated by analyzing the difference in the morphology of fillers and rheology of composites. The compressive strength of composites containing 0.1% NS, 0.5% NT, 0.1% CNTs and 0.5% CFs by weight of cement presents approximately 12.5%, 20.8%, 16.8% and 21.4% higher than that of control sample, respectively. It is revealed that CFs also have improving effect on the compressive strength of composites besides flexural strength. When the composites with nano-fillers cannot be processed to ideal state, the reinforcing effect of nano-fillers is no better but even worse than that of micro-fillers. Composites with CNTs, CNFs and CFs possess good electrical conductivity. Composites with CNFs and CFs have a percolation threshold of electrical resistivity below 0.5%, while the percolation threshold of electrical resistivity of composites with CNTs is about 1%. Although CNFs do not have significant effect on compressive strength of composites, they have the best improvement to electrical resistivity. [ABSTRACT FROM AUTHOR]

Fiber reinforced concrete (FRC) can be designed to exhibit pronounced ductility, energy absorption capacity, post-cracking strength depending on the fiber type and volume fraction. FRC have been classified into two categories, namely, strain softening and strain hardening cement composites (SSCC and SHCC). SSCC and SHCC are ultra-ductile class of materials developed for applications in the large material volume usage in the cost sensitive construction industry. Strain hardening behavior can be obtained by adding relatively low volume (typically <2%) of randomly distributed fibers and demonstrates a well formed distributed crack system. Mechanical properties under uniaxial tensile, flexural, and shear tests indicate superior performance such as tensile strength as high as 25 MPa, and strain capacity of 1-8%. Development of proper design and analysis tools are very essential to fully utilize these materials. Several approaches are presented in this paper for analysis, simulation, back-calculation, and design of strain softening and strain hardening cement composite systems, and are applicable to all classes of SSCC and SHCC such as steel fiber reinforced concrete, textile reinforced concrete, and ultra-high performance fiber reinforced concrete. [ABSTRACT FROM AUTHOR]

The application of fibre composites in the construction of protective structures for impact and blasts is an active area of research. Important mechanical properties like compressive strength, tensile strength, flexural toughness, acoustic impedance, mass density, ultrasonic pulse velocity, are required to determine the high velocity impact (HVI) resistance of the cementitious composite target panels. However, the above mechanical properties of steel fibre reinforced cementitious composites (SFRCC) for varying fibre volume fraction are difficult to find in existing literature. This paper presents results of an extensive experimental study, conducted to characterize the SFRCC for varied fiber volume fractions between 0 and 12 %. Hooked end steel fibres having an aspect ratio about 66 (fibre length 30 mm diameter 0.45 mm) are used in the preparation of control specimens. Important engineering properties like, compressive, tensile, and flexural strengths, toughness and acoustic impedances are determined through the laboratory tests. A total of 250 numbers standard cylinder, cube, prism and dog-bone specimens are prepared for the characterization of steel fibre reinforced cementitious composite. The significance of the present study in impact resistance applications is also demonstrated through the HVI tests on SFRCC panels. This study highlights various aspects related to judicious selection of materials in layered cementitious composite targets. [ABSTRACT FROM AUTHOR]

The fracture performance of a high-strength concrete reinforced with steel fibers was studied. Tests of notched beams subjected to fracture in the three-point bend configuration were conducted in accordance with RILEM recommendations TC 162-TDF. The R-curve concepts based on load-CMOD responses and the RILEM criteria were used for the performance evaluation of concrete beams reinforced with steel fiber mixtures and loaded up to fracture. Steel fibers of different types (regular and microfibers), in different proportions were employed as the reinforcement. The hybrid-fiber-reinforced concrete demonstrated a superior performance regarding their resistance and toughness properties as a result of interaction between the fibers. [ABSTRACT FROM AUTHOR]

The synthesis and characterization of a new class of cementitious composites filled with polymer emulsions were investigated, and their superior mechanical strength and durability properties compared to composites devoid of fillers were reported. Polymer emulsions were utilized to mechanically reinforce the composite and bridge the cement, fly ash, aggregate and fibers. The results reveal that the epoxy emulsion and poly (ethylene-co-vinyl acetate) emulsion markedly enhance the mechanical and durability properties of cemetitious composites. The fibers can be pulled out in the form of slip-hardening and the abrasion phenomenon can be observed clearly on the surface of the fibers. The hydration extent of cement is higher than that of the pristine composites. The polymer modified cementitious composites designed on micromechanics, have flexibility and plasticity which could be applied for a novel form of multifunctional materials with a range of pipeline coatings applications. [ABSTRACT FROM AUTHOR]

In this paper, a constitutive model for short fibre reinforced cementitious composites will be presented. This model is based on the St. Venant-Kirchhoff model, which is a special case of a hyperelastic material. This model is refined to include the fibre orientation distribution. Numerical FEM simulations with the developed constitutive model and fracture simulations using the discrete element method are presented. The outcomes of these numerical methods demonstrate how important it is to monitor and further to control the fibre orientation distribution during the manufacturing process. As the manufacturing process might involve casting, as, e.g., in the case of steel fibre reinforced concrete, an outlook on simulations of the manufacturing process in order to predict and to control the fibre orientation distribution is given. [ABSTRACT FROM AUTHOR]

The deformation and damage behaviors of strain hardening cementitious composites (SHCC) under the uniaxial stress state were investigated in this paper. Two ductile failure-based constitutive models were introduced to describe the uniaxial tension and compression properties of SHCC only using a few parameters. The computation method of model parameters was developed to ease the simulation procedures. Damage evolution of the SHCC was simulated by the formulation of continuum damage mechanics subsequently. The results show that the proposed models fit the stress-strain curves reasonably well, and the damage variables show different growth rules under uniaxial tension and compression. It is concluded that the proposed method can not only simply simulate the constitutive behavior of SHCC with the reasonable accuracy but also capture the characteristic of material degradation. [ABSTRACT FROM AUTHOR]

The recycling of mineral wastes is considered today an activity of utmost importance, contributing in the diversification of products, reduction of final costs, besides promoting alternative raw materials for some industrial sectors. This work focuses on the incorporation of steatite wastes in cementitious composites. A full design of experiment was carried out in order to investigate the effect of the experimental factors: fraction and particle size of steatite and compaction pressures (10 and 30 MPa) on the mechanical properties of the ceramic composites. The increase of the steatite fraction provided an increase of the bulk density and apparent porosity of the composites. Large particles of steatite provided an increase of the apparent porosity decreasing the mechanical strength. The increase of the pressing compaction decreased the apparent porosity, increasing the bulk density and the mechanical strength of the composites. [ABSTRACT FROM AUTHOR]

This paper investigates the physical properties of cement composites based on ordinary Portland cement (OPC) and silica particles as a potential material for porous aerostatic bearings for precision engineering applications. A full factorial design (2241) was carried out to study the effects of silica properties (size and geometry) and uniaxial pressure (10 and 30 MPa) on the composite properties, namely bulk density, apparent porosity and intrinsic permeability of the ceramic composites. Scatter graphs were plotted to identify the existence of significant correlations between parameters. The cementitious composite manufactured with small silica particles, non-spherical shape and low level of compaction pressure exhibited the most appropriate properties for the proposed application. In addition, mathematical models obtained from the response-correlation plots are potentially important tools for the development and design of new composites for porous bearing applications. [ABSTRACT FROM AUTHOR]

Utilizing pre-cast ECC panels as participating permanent formwork of concrete members, and the validity of using ECC to disperse the single crack in concrete into multiple ones in ECC were studied. In the process, totally two kinds of ECC with different tensile properties, 7 series of flat panels with different top surface figures and 3 U-shape panels with different inner surface forms were investigated. To evaluate the performance of the permanent formworks, small ECC-concrete composite beams were cast and tested mechanically. The 4-point bending test results show that the use of pre-cast ECC panels as permanent formwork can significantly improve the load capacity and toughness of a concrete member, effectively dispersing single widely opened crack in concrete into multiple ones in ECC. Most permanent formworks show perfect bond with the concrete cast on them, while the ones with partially debonded zone achieve the best mechanical performance. The U-shape permanent formworks show better performances than the flat ones, achieving much better improvements in both the load capacity and toughness, together with better crack width control. [ABSTRACT FROM AUTHOR]

Fracture behavior is one of the most important, yet still little understood properties of ultra-high performance cementitious composites (UHPCC), a new marine structural engineering material. Research on the fracture and direct tension behavior of UHPCC was carried out. The constitution law of UHPCC was divided into three phases: pre-partial debonding, partial debonding, and pullout phases. A direct tension constitution law was constructed based on the proposed fiber reinforcing parameter as a function of fiber volume fraction, fiber diameter and length, and fiber bonding strength. With the definition of linear crack shape, the energy release rate of UHPCC was derived and the R-curve equation was calculated from this. Loading tests of UHPCC using a three-point bending beam with an initial notch were carried out. The predictions from the proposed R-curve were in good agreement with the test results, indicating that the proposed R-curve accurately describes the fracture resistance of UHPCC. Introduction of a fiber reinforcement parameter bridges the fracture property R-curve and micro-composites’ mechanics parameters together. This has laid the foundation for further research into fracture properties based on micro-mechanics. The proposed tension constitution law and R-curve can be references for future UHPCC fracture evaluation. [ABSTRACT FROM AUTHOR]

Experiments were carried out to design polyvinyl alcohol (PVA) fiber reinforced cementitous composites (PVA-FRCCs) holding high ductility and energy consumption ability. Besides, the properties of each ingredients in composites, mixing method and technology for fresh mixture were described in detail. Then, the pseudo-strain-hardening (PSH) behavior was investigated in uniaxial tension test. As a result, the maximum ultimate tensile strain can reach 0.7 percent. On the other hand, the single edge notch (SEN) thin sheet specimens were employed to gain the normal tensile load via crack mouth opening displacement (CMOD) curves, which can show obvious PSH behavior. In addition, the curves can be divided into four zones whose fracture toughness calculation methods were discussed. The wedge splitting (WS) test method can be applied to discuss the fracture toughness. Moreover, fracture energy of SEN and WS specimens were both approximately evaluated. [ABSTRACT FROM AUTHOR]