Cement-based Matrix Research Articles

Effects of fiber–matrix interaction on multiple cracking performance of polymeric fiber reinforced cementitious composites

The effects of polymeric fiber addition on the multiple cracking performance of composites have been investigated. For this purpose, cement-based matrices incorporating fly ash and a latex emulsion have been designed. Prismatic samples have been prepared and subjected to four-point bending load. The load-midpoint deflection curves and crack patterns have been determined. Meanwhile, flexural strength and relative toughness values have been calculated. Finally, the number of visible cracks formed throughout the testing period has been analyzed.Test results showed that the toughening improvement mechanisms of PP and PVA fibers in a cement-based matrix are extremely different and matrix modifications significantly change the multiple cracking performance. The addition of a latex emulsion in a weak matrix decreased the multiple cracking tendency of PP fiber reinforced composites. However, the same modification attempt improved the multiple cracking capacity of weak matrix in case of PVA fiber reinforcement. The possible causes of this performance improvement have been discussed with the aid of microstructure investigations.

Mechanical, Electrical and Microstructural Properties of Cement-Based Materials in Conditions of Stray Current Flow

This investigation presents a comparative study on mechanical properties, electrical resistivity and microstructure of mortar under DC current, compared to mortar in rest (no current) conditions. Monitoring was performed from 24h after casting until 84 days of cement hydration. A current density level of 10 mA/m2 was chosen as a simulation regime. It was found that the DC current exerts microstructural changes in the bulk mortar matrix and thereby affects electrical properties and mechanical performance. Whereas the latter were slightly influenced, the former were modified to a more significant extent; the current flow was found to cause initial densification of the bulk matrix at earlier stages (until 14 days of age), whereas coarsening of the material was observed after 56 and until 84 days of cement hydration. Additionally, numerical simulation of the stray current distribution is performed, meant to serve as a basis for further elaborated modelling of the level of current density that could exert significant microstructural alterations in a bulk cement-based matrix.

Modelling of the interaction between chemical and mechanical behaviour of ion exchange resins incorporated into a cement-based matrix

In this paper, we present a predictive model, based on experimental data, to determine the macroscopic mechanical behavior of a material made up of ion exchange resins solidified into a CEM III cement paste. Some observations have shown that in some cases, a significant macroscopic expansion of this composite material may be expected, due to internal pressures generated in the resin. To build the model, we made the choice to break down the problem in two scale’s studies. The first deals with the mechanical behavior of the different heterogeneities of the composite, i.e. the resin and the cement paste. The second upscales the information from the heterogeneities to the Representative Elementary Volume (REV) of the composite. The heterogeneities effects are taken into account in the REV by applying a homogenization method derived from the Eshelby theory combined with an interaction coefficient drawn from the poroelasticity theory. At the first scale, from the second thermodynamic law, a formulation is developed to estimate the resin microscopic swelling. The model response is illustrated on a simple example showing the impact of the calculated internal pressure, on the macroscopic strain.

The effect of fibre chemical treatment on the steel fibre/cementitious matrix interface

This paper aims to study the interfacial bonding between steel fibres and cement-based matrix. The fibres were treated chemically using a zinc phosphate conversion to achieve enhanced bonding with the mortar matrix. In order to gain a better perspective on the effect of chemical treatment different fibre parameters were considered in this research, such as the fibres shape, length and diameter. In this respect, single-sided fibre pullout tests were conducted on treated as well as on as received (untreated) fibres of hooked-end, straight and undulated shape. The analysis of the experimental results revealed that the fibre shape is of great importance since it contributes to mechanical interlocking that prevail during the pullout of the fibres. Chemical treatment was also shown to play an important role on the fibre–matrix interface especially when mechanical interlocking is absent. Treated fibres exhibited a modified surface with a rough topology caused by precipitation of ZnPh crystals on the fibre. Optimum fibre configuration for maximum pullout performance can be chosen based on the fibre surface contact area, since the pullout load and pullout energy is directly related to this property.

Hybrid polyethylene/polypropylene blended fiber-reinforced cement composite

This article reports the results of a study related to the reinforcement of mortar-based composites with newly developed polyethylene/polypropylene blended fibers. The study showed the hybrid fibers to have a mechanical/reinforcing effect in the cement-based matrix. Mechanical strengths improvements, as high as 40 ± 2%, were obtained for composites with a fiber length of 24 mm and a fiber volume fraction of 2.9%. The mechanical enhancement was associated with a strong mechanical interlocking between the fibers/cement matrix interfaces promoted by the fibers’ surface ridges and fibrillation ability. Macro/microstructure and morphological observations showed a post-cracking ductility improvement of composites by the hybrid (bridge effect) fibers, also evidenced a multi-cracking mechanism.

The nature of limestone filler and self-consolidating feasibility—Relationships between physical, chemical and mineralogical properties of fillers and the flow at different states, from powder to cement-based suspension

This paper is a part of a large study aimed at identifying the physical and chemical properties of limestone fillers (LF) that govern their behaviour towards self-consolidating flow. Five LF were studied, complying with the standards and selected for their significant differences in properties on the basis of the supplier's database. Despite their specific manufacturing, a thorough characterization showed that the selected LFs had very different properties in terms of surface charges, morphology, wettability and size distribution. Then, relationships were sought between these properties and the flow of LF in powder form and suspended in water, or water + polycarboxylate type High Range Water Reducer Admixture (HRWRA), or water + HRWRA + cement (OPC or slag blended cement). The flow measurements concerned flowability, floodability and shear under consolidation in the dry state, and static yield stress and apparent viscosity in the suspension state. The main results show that the LFs act in the same way on the flow as long as cement is not incorporated into the suspension. From the dry state to the water + HRWRA suspensions, the flow is dependent on the fineness of the LF. The significant relationships between the surface charges, wettability and fineness of LFs show that impurities like clays are key factors in the flow of LF suspensions. When cement was incorporated into the suspension, the flow was dependent on the interactions existing among all the constituents. Then, with a view to self-consolidating applications, it becomes possible to identify how best to incorporate LF in a cement-based matrix through the measurement of the arrangement of cement and filler particles in suspension.

Investigation on polymeric fibers as reinforcement in cementitious composites: Flexural performance

The objective of this article is to evaluate the effect of some synthetic polymeric fibers on the flexural behavior of cement-based matrix. On this basis, polypropylene (PP), nylon 6,6 (N66), and polyacrylonitrile (PAN) fibers were selected and characterized by optical microscopy, tensile test, aging in chemical solution, surface free energy testing, and scanning electron microscopy. The flexural behavior of fiber-reinforced cementitious composites was determined using a three-point bending test. N66 and PAN fiber reinforced composites had higher toughness and maximum flexural strength, which were in line with the results of surface free energy of the fibers.

Fiber reinforced cement-based composite system for concrete confinement

This paper reports on a feasibility study to develop a reversible and potentially fire-resistant fiber reinforced cement-based matrix (FRC) composite system for concrete confinement applications. The first part of this study aimed at selecting a candidate FRC system from different fiber (including glass and basalt) and inorganic matrix combinations on the basis of: constructability, by verifying the workability and ease of installation on concrete cylinders; structural performance, by evaluating strength and deformability enhancement in confined concrete cylinders tested under uniaxial compression; and compatibility, by examining the quality of the concrete–FRC interface and the level of fiber impregnation using scanning electron microscope images. In the second part of this study, the selected FRC system was further assessed through compression tests of additional concrete cylinders confined using different FRC reinforcement ratios, where both axial and in-plane (radial) deformations were measured to assess confinement effectiveness. The feasibility of making the application reversible was investigated by introducing a bond breaker between the concrete substrate and the composite jacket in a series of confined cylinders. The prototype FRC system produced a substantial increase in strength and deformability with respect to unconfined cylinders. A superior deformability was attained without the use of a bond breaker. The predominant failure mode was loss of compatibility due to fiber–matrix separation, which points to the need of improving fiber impregnation to enable a more efficient use of the constituent materials. Semi-empirical linear and nonlinear models for compressive strength and deformation in FRC-confined concrete are also presented.

Flexural Strengthening of RC Beams with Cement-Based Composites

In this paper, the effectiveness of fiber-reinforced cementitious matrix (FRCM) materials for the strengthening of reinforced concrete (RC) beams is experimentally investigated. Bending tests on RC beams strengthened with different FRCM materials, made out of (1) carbon fiber nets; and (2) poliparafenilenbenzobisoxazole (PBO) fiber nets embedded in cement-based matrix, are performed. For case (2), different net shapes, cementitious matrices, and a number of net layers were considered. Depending on the type of fibers and matrix, different flexural debonding failure modes are identified. The fiber strain at debonding is evaluated by comparing the experimental results with those obtained with two different theoretical models. The results obtained in this study confirm the effectiveness of FRCM materials for the strengthening of RC structures and encourage further experimental and theoretical work on the topic. A better understanding of the debonding phenomenon is crucial for an optimal design of the strength...

The hornification of vegetable fibers to improve the durability of cement mortar composites

Abstract The use of vegetable fibers to reinforce a cement-based matrix has its weakest point in terms of durability. The alkalinity of the matrix and the volumetric instability of the fibers are the main causes of the loss of resistance of vegetable fiber-reinforced cement mortar composites. The aim of this study was to determine the effects of the previous hornification of the vegetable fibers on the mechanical performance and durability of softwood kraft pulp and cotton linters cement mortar composites. For this purpose, composites containing 4 wt.% of the hornificated fibers and the untreated ones were prepared with both fiber types. The mechanical performance of these composites was tested after 28 days of cure treatment and after aging with four wet–dry cycles. Results indicated that the previous treatment of fibers had beneficial effects on the mechanical performance and durability of the resulting cementitious composites.

Experimental investigations to study the effect of carbon nanotubes reinforced in cement-based matrix composite beams

The present paper investigates the behaviour of cement beams reinforced with multi-walled carbon nanotubes (MWCNTs). The addition of MWCNTs was varied at 0.25, 0.5, 0.65, 0.75, 0.85, and 1 per cent by weight of cement. Dispersion of MWCNTs was carried out using ultrasonic energy. Composite beams were tested under flexure in order to evaluate their mechanical properties such as flexural strength and load–deflection criteria. These results were then compared with those from plain cement control beams. The present work also investigated the optimum percentage of MWCNTs that gives the best results in terms of both enhanced properties and economy. Scanning electron microscopy was conducted to examine the bond between the MWCNTs and the cement matrix.

Modelling of ageing effects on crack-bridging behaviour of AR-glass multifilament yarns embedded in cement-based matrix

This article focus on modelling of ageing effects on crack-bridging behaviour of AR-glass multifilament yarns embedded in cement-based matrix. In the first step, age-dependent changes in the crack-bridging behaviour of AR-glass multifilament yarns were investigated at the meso and micro levels. Two cementitious matrices were considered where the binder contained Portland cement clinker and ground granulated blast furnace slag cement, respectively. Mechanical characteristics of the bond between matrix and multifilament yarns after accelerated ageing were measured by means of double-sided yarn pullout tests. In these tests the multifilament yarns bridged a single crack in the matrix arising in a notched area of the specimen. Losses in performance with increasing age differed widely depending on matrix material composition. The essential cause of such losses was discovered to be the microscopic densification of the fibre-to-matrix interface. This led to increased bond intensity and restricted slip-ability of the filaments. Subsequently, these micro-structural phenomena were related to the mesoscopic material behaviour by means of a phenomenological bond model. This cross-linkage model describes the crack-bridging effect of the entire multifilament yarn at the single filament level. According to the model, each filament possesses a specific deformation length depending on its position in the cross-section of the yarn. This deformation length depends on bond characteristics between single filament and cementitious matrix, which vary with age. Characteristic values of the model were computed from load-crack width curves obtained from the yarn pullout tests. The changes in the microstructure were represented by the characteristic values of the model.

Progressive Micromechanical Modeling for Pullout Energy of Hooked-end Steel Fiber in Cement-based Composites

A progressive micromechanical damage-plasticity formulation is proposed to analyze the single hooked-end steel fiber pullout energy from the surrounding cement-based matrix within the context of hooked-end steel fiber-reinforced cementitious composites (HSFRCC). As the hooked-end steel fiber has a unique fiber geometry, its fiber pullout energy from the cement-based matrix consists of the interfacial fiber-matrix debonding, the frictional sliding and pullout energy, and the elastoplastic deformation energy of the steel fiber hooked end. The aforementioned energy components are analytically derived first, and the superposition principle is subsequently employed to obtain the total energy dissipation during the fiber pullout process. Good agreement is obtained for comparisons between the experimental results of single hooked-end steel fiber pullout tests and the proposed analytical predictions. This satisfactory verification supports the validity and applicability of the proposed damage-plasticity energy prediction formulation, and suggests the applicability of this methodology to further investigation on micromechanical fracture energy prediction of HSFRCC during flexural macro-cracking.

Observation and quantification of water penetration into Strain Hardening Cement-based Composites (SHCC) with multiple cracks by means of neutron radiography

Durability of reinforced concrete structures has become a crucial issue with respect to economy, ecology and sustainability. One major reason for durability problems of concrete structures is the limited strain capacity of cement-based materials under imposed tensile stress. By adding PVA fibers, a new material named Strain Hardening Cement-based Composites (SHCC) with high strain capacity can be produced. Due to the formation of multiple micro-cracks, wide cracks can be avoided in SHCC under an imposed strain. The high strain capacity, however, is beneficial with respect to durability only if the multi-crack formation in SHCC does not lead to significantly increased water penetration. If water and aggressive chemical compounds such as chlorides and sulfates dissolved in water penetrate into the cement-based matrix and reach the steel reinforcement service-life of reinforced concrete structures will be reduced significantly. In this project, neutron radiography was applied to observe and quantify the process of water penetration into uncracked SHCC and after the multi-crack formation. In addition, water penetration into integral water repellent cracked and uncracked SHCC, which has been produced by adding a silane-based water repellent agent to the fresh SHCC mortar has been investigated. Results will be discussed with respect to durability.

Enhancement of Crack Distribution of UHP-SHCC under Axial Tension Using Steel Reinforcement

Ultra High Performance-Strain Hardening Cementitious Composites (UHP-SHCC) are a composite material comprising a cement-based matrix and short fibers with outstanding mechanical and protective performance. Surface protection repair using a thin layer of UHP-SHCC to extend the service life of concrete structures has been proposed, and surface protec-tion performance associated with both a durable matrix and multiple fine cracks is required. This paper presents an ex-ample of decreased cracking ability and decreased strain capacity in UHP-SHCC specimens of a practical size. Note that, the small size dumbbell-shaped UHP-SHCC specimen can exhibit a large number of cracks and higher strain capacity. Also, this paper assesses the usage of a small amount of steel reinforcement in order to enhance the crack distribution and strain capacity of practical size UHP-SHCC specimens in tension. Practical-size specimen dimensions (cross sectional size: 200 x 50mm), which are similar to the typical size used for surface protection repair applications (depth of 30 to 70 mm), were selected in this study. Different reinforcement ratios ranging from 0.3% to 1.2% were used to evaluate the effect of the reinforcement ratio on the specimens' strain capacity and crack distribution.

Structural Upgrade Using Basalt Fibers for Concrete Confinement

This paper aims to appraise the opportunities provided by a new class of composites based on using basalt fibers bonded with a cement-based matrix as an innovative strengthening material for confinement of reinforced concrete members. The effectiveness of the proposed technique is assessed by comparing different confinement schemes on concrete cylinders: (1) uniaxial glass-fiber-reinforced polymer (FRP) laminates; (2) alkali-resistant fiberglass grids bonded with a cement-based mortar; (3) bidirectional basalt laminates preimpregnated with epoxy resin or latex and then bonded with a cement-based mortar; and (4) a cement-based mortar jacket. The study showed that confinement based on basalt fibers bonded with a cement-based mortar could be a promising solution to overcome some limitations of epoxy-based FRP laminates.

Quantitative evaluation technique of Polyvinyl Alcohol (PVA) fiber dispersion in engineered cementitious composites

Abstract The fiber dispersion in fiber-reinforced cementitious composites is a crucial factor with respect to achieving desired mechanical performance. However, evaluation of the fiber dispersion in the composite Polyvinyl Alcohol-Engineered Cementitious Composite (PVA-ECC) is extremely challenging because of the low contrast of PVA fibers with the cement-based matrix. In the present work, a new evaluation technique is developed and demonstrated. Using a fluorescence technique on PVA-ECC, PVA fibers are observed as green dots in the cutting plane of the composite. After capturing the fluorescence image with a Charged Couple Device (CCD) camera through a microscope, the fiber dispersion is evaluated using image processing and statistical tools. In the image processing step, the fibers are more accurately detected by employing a series of processes based on categorization, watershed segmentation, and morphological reconstruction. Test results showed that the dispersion coefficient α f was calculated reasonably and the fiber-detection performance was enhanced.

PVA-ECC단면 이미지의 섬유 분류 및 검출 기법

초록·키워드 목차 오류제보하기 등록된 정보가 없습니다. ABSTRACT1. 서론2. 섬유 이미지의 섬유 검출 기법3. 검증 및 분석4. 결론참고문헌요약

Effects of fibre-reinforced cement composites' ductility on the seismic performance of short coupling beams

The current study examines the effects of the deformation behaviour of cementitious material ductility on the seismic performance of shear-dominant coupling beams. Matrix ductility and reinforcement layouts comprise the main testing variables. Three short coupling beams with two different reinforcement arrangements and matrices are constructed and tested. They are subjected to cyclic loading under a suitable experimental set-up. All specimens are characterised by a shear span–depth ratio of 1·0. The reinforcement layouts consist of a classical scheme and diagonal scheme without confining ties. The effects of cement-based matrix ductility on crack patterns, failure modes, hysteretic characteristics and the ultimate shear load of the coupling beams are examined. The combination of a ductile cement-based matrix and steel reinforcement is found to result in improved energy dissipation capacity, simplification of reinforcement details, and damage-tolerant inelastic deformation behaviour. Test results show that high-performance hybrid fibre-reinforced cement-based composite (HPHFRCC) coupling beams behave better than normal reinforced concrete (RC) control beams. These results are evidenced by the tensile deformation capacity, damage tolerance and tensile strength of HPHFRCC material.

Relationship between static bending and compressive behaviour of particle-reinforced cement composites

Innovative particle-reinforced materials made of alumina particles and cement-based matrix were designed, manufactured and tested to evaluate the potential use of ceramic aggregates in concretes. These particle-reinforced composites were tested in three-point bending and uniaxial compression conditions to determine the influence of the shape and size of the ceramic inclusions, and the addition of silica fume on the mechanical properties. A specific methodology combining post-mortem observations with a statistical analysis of tensile failure stresses (average strength and Weibull modulus) was conducted to deduce the origin of failure for each cement-based composite (porosity or ceramic particles/matrix decohesion). A remarkable correlation is observed between bending failure stress level and the average strength measured under uniaxial compression loading. As main conclusion, addition of alumina particles in a mortar appears to strengthen or to weaken the composite depending on whether silica fume is used in the cementitious matrix.