Cementitious Matrix Composites Research Articles

SnO wrap on SnS reinforced thermoelectric properties of CF/EG cement matrix composites

In this study, SnO wrap on SnS was prepared and incorporated into carbon fiber/expanded graphite (CF/EG) cementitious composites by the coating process. The effects of different SnO wrap on SnS coating ratios and contents on the microstructures of CF/EG cementitious composites were investigated and discussed, and the thermoelectric properties of SnO wrap on SnS CF/EG cementitious composites were systematically investigated in the temperature range of 35–70 °C. The results show that the coating ratio and content of SnO wrap on SnS have a significant effect on the thermoelectric properties of CF/EG cementitious composites. It is noteworthy that when the SnO wrap on SnS is 2:1, the thermoelectric properties of its cementitious composites are greatly improved. For example, when it is added at 1.0 wt%, the conductivity is 2.27 S/cm, the Seebeck coefficient is 41.90 µV/°C and the power factor is 0.38 µW·m−1K−2. The addition of SnO wrap on SnS to CF/EG cementitious materials generates a large number of interfaces, and the presence of high-density interfaces hinders the motion of carriers, which leads to the scattering of carriers at the interfaces and enhances the Seebeck effect in cementitious composites. Therefore, SnO wrap on SnS has great potential for thermoelectric applications.

Mechanical characteristics, microstructural evolution, and reinforcement mechanisms for a cement-matrix nanocomposite

The present paper is focused to understand the reinforcement mechanisms exerted by GO nanosheets to both strengthen and toughen cement-matrix composites since, despite intensive research, such mechanisms are still not completely clear. To such an aim, the mechanical characteristics (that is, mechanical strengths and fracture toughness) of a cement-matrix nanocomposite, with the 0.05 % of GO used as an additive, are experimentally investigated at different curing times. Since reinforcement mechanisms are closely related to cement hydration products, they are qualified and quantified by chemical, mineralogical and microstructural analyses performed at the above times of curing. The present investigation leads to the conclusion that the role of both CSH and AFt content is dominant in strengthen and toughen of cement matrix-nanocomposites with GO used as an additive.

Effect of ICCP on tensile performance of carbon fiber bundles in seawater sea-sand cementitious matrix

Impressed current cathodic protection (ICCP), carbon fabric reinforced cementitious matrix (CFRCM) composites, and piezoresistive effect have been widely studied in delaying steel bar corrosion, strengthening steel-reinforced concrete structures, and structural health monitoring, respectively. In this study, the effect mechanism of the ICCP procedure on the tensile performance degradation of CFRCM bundles with the two types of matrix (normal matrix (i.e., sand conforming to ISO standard) and seawater sea-sand matrix), as well as the tensile performance differences between them, were investigated through carbon fiber bundle tensile tests and CFRCM bundle tensile tests. The piezoresistive effects of CFRCM with the two types of matrix after the ICCP procedure and the effect of ICCP on the piezoresistive effect were analyzed. Prediction formulas for the tensile performance were established based on the different charge densities. Based on the dual functionality of carbon fiber strengthening and self-sensing, this study lays a foundation for the development of a triple-functional system of impressed current cathodic protection, structural strengthening, and structural health monitoring (ICCP-SS-SHM). The study indicates that seawater sea-sand positively influences the delay of CFRCM degradation through ICCP. This is advantageous in tackling the issue of scarce freshwater river sand resources.

Effect of ICCP on tensile performance and piezoresistive effect of CFRCM plates

Currently, extensive research has been conducted on carbon fabric−reinforced cementitious matrix (CFRCM) composites, impressed current cathodic protection (ICCP), and the piezoresistive effect in the field of strengthening of reinforced concrete (RC) structures, corrosion protection of steel reinforcement, and structural health monitoring, respectively. This study utilized two types of matrix materials: normal matrix (sand conforming to ISO standard) and seawater sea-sand matrix. The mechanism by which the ICCP procedure affects the degradation of tensile performance in CFRCM plates with these two types of matrix materials was investigated in the study. Additionally, the piezoresistive effects of CFRCM with the two types of matrix materials after the ICCP procedure were analyzed, and the impact of ICCP on the piezoresistive effect was also investigated. By observing the piezoresistive effect of each CFRCM segment, the sequence of crack propagation and an approximate crack location can be inferred. Finally, the tensile performance of CFRCM with charge density was investigated. Leveraging the dual functionality of carbon fiber reinforcement and sensing, this study lays the groundwork for the development of a triple-functional system encompassing impressed current cathodic protection, structural strengthening, and structural health monitoring (ICCP-SS-SHM). Seawater sea-sand has the potential to be used as an alternative to freshwater river sand, which is beneficial for addressing the shortage of freshwater river sand resources.

Fatigue and post-fatigue behavior of FRCM-concrete specimens under direct shear and bending conditions

The combined effect of cyclic loading and steel rebar corrosion can determine the premature deterioration of reinforced concrete (RC) structures subjected to dynamic and environmental actions. The use of fabric-reinforced cementitious matrix composites (FRCM) is a promising solution to extend the fatigue life of RC structures. Externally bonded FRCMs are applied to the tension side of structural members to reduce the rebar stress level, thus delaying fatigue crack nucleation and/or propagation. A key aspect for the design of FRCM strengthening of these structures is the matrix-fiber bond behavior under fatigue loading. In this paper, a critical review of currently available studies on the fatigue behavior of FRCM-strengthened RC beams is presented. Then, the results of 25 bond tests on PBO FRCM-concrete specimens are provided and discussed. These tests include both single-lap direct shear and modified beam tests performed in quasi-static and cyclic mode. The results obtained show that the cyclic load may induce progressive debonding at the matrix-fiber interface with rupture of fiber filaments. Modified beam tests are more affected by these phenomena than direct shear tests. The rupture of fiber filaments is confirmed by the results of post-fatigue tests that show capacities lower than those of corresponding quasi-static tests.

Restoration of two-span RC beams with severely corroded reinforcement using C-FRCM composites

The feasibility and viability of using carbon fabric-reinforced cementitious matrix (C-FRCM) composites for restoration of continuous reinforced concrete (RC) beams with severely corroded reinforcement were examined. Five large-scale dual-span RC beams were fabricated and tested. One beam was not corroded to serve as a control. Four beams were subjected to accelerated corrosion that corresponded to a tensile steel cross-sectional loss of 40% in either the sagging or the hogging region. Such a steel cross-sectional loss would cause a comparable reduction in the yield load of bare steel reinforcing bars. Two of the corroded beams were repaired with C-FRCM composites. An analytical model was formulated and utilized to design the number of C-FRCM layers required to fully restore the original load capacity. Experimental results verified the redistribution of moments between the sagging and hogging regions due to yielding of the tensile steel at critical sections. Both sagging and hogging sections contributed to the load-bearing capacity, and hence, the reduction in the load capacity caused by corrosion in one of the critical sections was smaller than the tension steel cross-sectional loss caused by corrosion. It was possible to predict the load capacity of the tested beams with reasonable accuracy considering the residual cross-sectional area of the corroded tension steel bars while keeping their yield strength and Young’s modulus unaltered in addition to implementing other conventional assumptions adopted by international codes and guidelines. As predicted analytically and verified experimentally, rehabilitation of corroded continuous beams with appropriate number of C-FRCM composite layers fully restored their original load capacity. Research findings would assist practitioners in conducting a proper analysis of continuous RC beams with corroded reinforcement before and after repair with C-FRCM composites.

Simplified Procedure to Determine the Cohesive Material Law of Fiber-Reinforced Cementitious Matrix (FRCM)-Substrate Joints.

Fiber-reinforced cementitious matrix (FRCM) composites have been largely used to strengthen existing concrete and masonry structures in the last decade. To design FRCM-strengthened members, the provisions of the Italian CNR-DT 215 (2018) or the American ACI 549.4R and 6R (2020) guidelines can be adopted. According to the former, the FRCM effective strain, i.e., the composite strain associated with the loss of composite action, can be obtained by combining the results of direct shear tests on FRCM-substrate joints and of tensile tests on the bare reinforcing textile. According to the latter, the effective strain can be obtained by testing FRCM coupons in tension, using the so-called clevis-grip test set-up. However, the complex bond behavior of the FRCM cannot be fully captured by considering only the effective strain. Thus, a cohesive approach has been used to describe the stress transfer between the composite and the substrate and cohesive material laws (CMLs) with different shapes have been proposed. The determination of the CML associated with a specific FRCM-substrate joint is fundamental to capture the behavior of the FRCM-strengthened member and should be determined based on the results of experimental bond tests. In this paper, a procedure previously proposed by the authors to calibrate the CML from the load response obtained by direct shear tests of FRCM-substrate joints is applied to different FRCM composites. Namely, carbon, AR glass, and PBO FRCMs are considered. The results obtained prove that the procedure allows to estimate the CML and to associate the idealized load response of a specific type of FRCM to the corresponding CML. The estimated CML can be used to determine the onset of debonding in FRCM-substrate joints, the crack number and spacing in FRCM coupons, and the locations where debonding occurs in FRCM-strengthened members.

FRCM Confinement of Masonry: Strain Model Assessment and New Proposals.

One of the main limitations to the use of fabric-reinforced cementitious matrix (FRCM) composites for the external confinement of masonry is the lack of accurate formulas for estimating the compressive strength and ultimate strain of confined members. With the aim of providing a contribution on the topic, the authors have been carrying out studies on the FRCM-confined masonry for some time and, in a recent study, they proposed some formulations for the prediction of compressive strength. In continuity to that work, an analytical study on the ultimate strain of FRCM-confined masonry is presented in this paper, and preliminary models were derived by considering a wide experimental database compiled from the technical literature. The accuracy of the found relationships was examined based on a comparison with the few formulas published in the literature or reported in international guidelines. To this purpose, it is worth highlighting that the current Italian Guidelines CNR-DT 215/2018 do not provide indications about the estimation of the ultimate strain of FRCM-confined masonry, and the study proposed here attempts to provide a contribution to the mentioned document.

Mechanical Properties of Cement Matrix Composites Reinforced with Polyoxymethylene Fibers of Different Lengths

Mechanical Properties of Cement Matrix Composites Reinforced with Polyoxymethylene Fibers of Different Lengths

Bond behavior between carbon fabric reinforced cementitious matrix (FRCM) composites with added short fibers and concrete substrates

Fabric reinforced cementitious matrix (FRCM) composites show an innovative solution for strengthening existing concrete structural elements to solve the drawbacks of organic resins in fiber-reinforced polymers (FRP) system. However, the brittle fracture of the cementitious matrix significantly reduces the efficiency of the fabric. Hence, the incorporation of short fibers into the matrix is proposed to increase the fabric efficiency. For externally bonded FRCM composites to structural element surfaces, it is a crucial issue to investigate the bond behavior at the fabric-matrix and matrix-substrate interfaces, where the effect of short fibers is non-negligible and requires further investigation. In this study, a single-lap direct shear test was used to investigate the bond behavior between carbon FRCM composites with added short fibers and concrete substrates. 36 specimens were tested and discussed by considering the effects of bond length, volume content of short fibers, type of short fibers, and bond width. The experimental results were discussed in terms of failure mode, load-slip curve, and characteristic parameters. Subsequently, the contribution of weft yarns was studied and accounted for in the developed bond-slip model, which additionally takes into account the effects of the volume content of the short fibers, the type of short fibers, and the bond width.

Influence of severe thermal preconditioning on the bond between carbon FRCM and masonry substrate: Effect of textile pre-impregnation

Fabric-reinforced cementitious matrix (FRCM) composites often include polymer-impregnated bundles to improve the exploitation of the textile mechanical properties. However, organic components may degrade when exposed to elevated temperature. In this paper, the bond behavior of a carbon FRCM applied to a masonry substrate and exposed to a thermal preconditioning up to 300 °C for 250 min is investigated. Tensile tests on the textile and flexural and compression tests on the mortar matrix, as well as single-lap direct shear tests of FRCM-masonry joints with bare and impregnated textiles, are performed. Results show that the polymeric impregnation improves the mechanical properties of the FRCM even after thermal preconditioning.

Study on the physicochemical properties of Chinese PVA fibers: Toward low-cost cement-based composites

Engineered Cementitious Composites (ECC) reinforced by Japanese Polyvinyl Alcohol (PVA) fiber showed excellent tensile ductility, which attracted much attention in the field of civil engineering in recent years, but the application was still limited by cost. There were quite a few kinds of low-priced PVA fibers in China, with a tremendous difference in physical and chemical properties. In this paper, a variety of typical PVA fibers produced in different regions in China were compared with the products imported from Japan to analyze the performance differences, especially the dispersion and enhancement effect in fiber reinforced cement matrix composites. Combining with the physical and chemical characteristics of each fiber, the relationship between the characteristics of fibers and the properties of composites was summarized. The experimental results illustrated the strength and interface characteristics of PVA fibers were the dominating influencing factors to the bending and tensile properties of PVA-ECC, while hardly affected the compressive strength. Insufficient intrinsic strength of fibers significantly decreased bending resistance and tensile strength. Excessive oil agent treated PVA fibers performed lower interfacial reaction with the cement matrix, meanwhile original PVA fiber with high hydrophilicity was not conducive to the dispersion and bridging function. The appropriate interface treatment approach could guarantee the fibers to achieve the sliding pull out bridge connection, and also meet the high slip strengthening effect, leading to the multi-seam cracking and strain hardening characteristics of ECC material. This work provided the preparation of low-cost cement-based composites, guiding the selection of fiber raw materials in ECC.

Shear capacity prediction for FRCM-strengthened RC beams using Hybrid ReLU-Activated BPNN model

This study presents a robust Hybrid ReLU-Activated Backpropagation Neural Network (BPNN) model for predicting shear strength (VFRCM) in RC beams reinforced with Fiber-Reinforced Cementitious Matrix (FRCM) composites. The model demonstrates exceptional accuracy, boasting a coefficient of determination (R2) of 0.924 and a mean root mean squared error (RMSE) of 10.611 kN on the test set. Leveraging k-fold cross-validation, the model's performance is rigorously assessed across ten data splits, emphasizing its reliable predictive capabilities. Hyperparameter optimization, guided by Particle Swarm Optimization (PSO), reveals an optimal value of α = 0.5757, minimizing the Mean Squared Error (MSE) to 74.53 for the dataset. Feature importance analysis underscores the significant role of critical parameters in shear strength prediction, with the longitudinal reinforcement ratio (ρl) emerging as the most influential feature, contributing 37.55 % to the model's predictive power. Additionally, the effective beam depth (d) is identified as the second most influential feature, providing approximately 16 % to the accurate prediction of VFRCM in RC beams strengthened with FRCM composites.

Analysis of probable consequences of cement composite frost destruction

The article presents an analysis of variations in the internal resistance of standard and fiberreinforced cement composites under non-stationary low-temperature and humidity effects. Various aspects of the response kinetics of prismatic samples in the monotonous compression mode are considered. The sample set included control samples and those subjected to cyclic freezing and thawing according to their standard frost resistance. Test samples (100 × 100 × 400 mm) were made of conventional (B series) and fiber-reinforced (FB, polypropylene fibers df = 0.8 mm, lf = 40 mm, µf = 1.5 vol%) concrete with a component ratio of cement: sand: crushed stone: water = 1:1.42:3.57:0.55. The accepted base of T-W cycles corresponded to the standard concrete grade in terms of frost resistance, established in control tests (F200). Static tests of composites were preceded by low-temperature exposures according to an accelerated method for assessing frost resistance with a temperature decrease down to minus 35℃ and thawing in a 5% NaCl solution. Samples were automatically loaded (Instron 5989 test complex) according to a special program with a constant deformation rate of 5·10-5 mm/s and continuous recording of deformations. Significant differences were observed in the strength kinetics, magnitude and structure of deformations, along with a high sensitivity and quantitative informativeness of the significant parameters of the strength kinetic concept for solid bodies. The expediency of a differentiated approach to the selection of calculation models and criteria for the temperature and humidity transformations of cement-matrix composites, which takes operational requirements into account, is substantiated.

IMPACT OF HEAT TREATMENT METHOD AND MILLET POD TYPE ON REAL DENSITY AND POZZOLANIC ACTIVITY INDEX BY ASH RESISTANCE

Artificial pozzolans derived from agricultural by-products are generally obtained by heat treatment. The thermal treatment method used and the type of waste influence the quality of the final product. The aim of this study was to measure the actual density and pozzolanic activity index of millet pod ash produced in three different ways. Ash A is produced by direct calcination of the husks from which the millet seeds are removed (without the stalk). Ash B is obtained by burning and then calcining the millet husks. Ash C is produced by direct calcination of the millet straw (husks + stalks). The actual density was determined in accordance with standard NF EN 1097-6. The pozzolanic activity index by resistance was measured on the basis of the recommendations of American standard ASTM-C618. For the ashes A, B and C produced, we respectively obtained true densities of 2.256 g/cm3 2.150 g/cm3 and 2.033 g/cm3. The pozzolanic activity indices per strength obtained were 0.42, 0.23 and 0.70 respectively. These results showed that the ash produced from direct calcination of raw millet waste (straw) had the best reactivity and the lowest density. It is therefore well suited to the production of low-density cementitious matrix composites.

Relationship between Alternated Current Impedance Spectrum and Microstructure of Graphene Enhanced Concrete

This study presented experimental research on the alternating current (AC) impedance spectrum of graphene-enhanced cement matrix composites with dosage amounts of 0.1%, 0.2%, 0.4%, 0.8%, 1.6%, and 3.2%, respectively. The electrical properties were compared and analyzed with the Nyquist diagram, Bode diagram, and phase angle diagram. The microscopic pore structure was studied using mercury intrusion porosimetry (MIP) to establish the relationship between the pore structure parameters, the equivalent circuit fitting parameters of the AC impedance spectrum, and the mechanical properties. This study found that the incorporated graphene decreases the arc diameter of the impedance spectrum and causes the slope of the straight lines of the low-frequency region to drop. For the Bode curves, within low frequencies (1 Hz and 10 Hz), the impedance gradually increases as the graphene dosage increases. However, when the frequency is between 100 KHz and 1000 KHz, the impedance drops with an increase in the amount of graphene. According to the MIP test results, the proper incorporations of graphene increase the proportion of pores below 0.1 μm, which leads to a denser micro-structure and higher strength.

Enhancing the thermoelectric characteristics of thermoelectric cement matrix composites by (Ca0.87Ag0.1La0.03)3Co4O9 binary metal oxide

In recent years, the expansion of urban buildings has caused buildings and road surfaces to absorb large amounts of heat energy during the summer, exacerbating the heat island effect. The application of thermoelectric cement matrix composites can convert the surface heat energy of roads and buildings into electrical energy. The performance enhancement for thermoelectric cementitious composites is shown by the addition of carbon materials and metal oxides, and great research progress has been made. The current research on metal oxides as functional fillers is mostly for monomeric metal oxides and less for binary metal oxides. In this study, (Ca0.87Ag0.1La0.03)3Co4O9 was produced by co-precipitation, and a strategy to enhance the thermoelectric characteristics of thermoelectric cement matrix composites was suggested. To reduce surface defects, this approach involved pretreating the (Ca0.87Ag0.1La0.03)3Co4O9 with hydrochloric acid. Using acid etching to transform the metal oxides' morphology from granular to layered, the interface was expanded, improving carrier scattering and, in turn, the Seebeck coefficient. The thermoelectric characteristics of cement substrates with low content, acid-treated (Ca0.87Ag0.1La0.03)3Co4O9, and a fixed mass fraction of expanded graphite were compared to a control group without acid treatment. The results showed that the method resulted in an increase of the Seebeck coefficient to −100.5 μV/°C and the introduction of nano-silver inclusions caused an increase of the conductivity to 13.5S/cm. The improvement of the Seebeck coefficient and electrical conductivity has increased the power factor to 13.8μWm−1K−2. This study proposes a method to improve the thermoelectric properties of cement matrix composites.

Shear stress analysis in the textile-to-matrix and TRC-to-masonry interfaces of Textile-Reinforced Cement (TRC) applied to masonry using distributed fibre optic sensors

Masonry has been used extensively in civil engineering for centuries. However, various factors can reduce its performance over time. To extend its life and increase its load-bearing capacity, it needs to be reinforced. Strengthening with composite materials, in particular with Textile-Reinforced Cementitious (TRC) matrix composites, has proven to be effective. However, the assessment of the load transfer between TRC and masonry, as well as between matrix and textile at the core of the TRC remains a significant scientific challenge for optimal reinforcement. In this context, this paper aims to contribute to the understanding of the load transfer mechanisms at these interfaces, particularly for shear behaviour.To this end, this study investigates the reinforcement of masonry using TRC. Six different configurations of TRC-to-masonry prisms were subjected to single-lap shear bond tests: two types of textile reinforcements, two types of matrices and two reinforcement ratios. These six configurations were instrumented by distributed fibre optic sensors in the core of the TRC. These sensors measured the mechanical strains of the matrix and textile in the core of TRC with millimetric spatial resolution. From these strains, the local shear stresses and bond behaviour of the textile-to-matrix and TRC-to-masonry interfaces were experimentally quantified, assessed and analysed. A decreasing parabolic trend of these shear stresses along the effective length was obtained before the appearance of cracks, while cracks considerably modify this trend.The contributions of the matrix and the textile to the interface shear stresses were assessed. Before cracking, the contribution of the matrix prevails, while after cracking, the contribution of the textile is predominant. The shear stresses over the TRC thickness were also quantified and analysed. The debonding at the textile-to-matrix interface was tracked and analysed before, during and after crack propagation in TRC. The results obtained confirm that this debonding evolution can be predicted by pull-out tests.

EVALUATION OF RETROFIT EFFECTIVENESS AND COST IMPLICATIONS OF MRF STRUCTURES USING DISTINCT FRCM COMPOSITE SYSTEMS

This paper summarizes the results of a numerical investigation to assess the effectiveness of retrofitting pre-seismic code concrete framing structural systems using two distinct fiber-reinforced cementitious matrix (FRCM) composites. While FRCM composites were focused in the literature at the member level, this study focuses on implementing this retrofit technique effectively at the structure level. Several static pushover analyses (SPAs) and inelastic dynamic simulations (IDSs) are carried out for FRCM-retrofitted RC frames representing the lateral force-resisting system of a moment-resisting frame (MRF) structure. Correlating the numerical simulation results and experimental results obtained from another study verified the selected fiber discretized section modeling technique for FRCM retrofitted MRFs and reflected the effectiveness of the adopted approach in prolonging local and global damage states. The verified modeling technique of the risk-mitigation measure is then employed to evaluate the performance of an upgraded RC building using three-dimensional fiber-based numerical models. Finally, a parametric study using SPAs and IDSs using multiple seismic scenarios is conducted to select the most effective FRCM retrofit material for the seismic performance enhancement of the benchmark structure. The study concludes that using the selected FRCM retrofit technique effectively mitigated the structural collapse damage state of the substandard building at the design and maximum considered seismic intensity levels by 28% and 32%, respectively.

The evaluation of the adhesion defects in FRCM reinforcements for masonry constructions by Sideband Peak Count based nonlinear acoustic technique

Fabric-reinforced cementitious matrix (FRCM) composites have emerged as reliable strengthening materials especially for historical masonry constructions. Their strengthening effectiveness strongly depends on the bond at the matrix-fibers interface and at the matrix-substrate interface; thus, the analysis of FRCM bond behavior is of crucial relevance. The strong diffusion of the FRCM composites for the reinforcement of masonry and concrete constructions requires suitable experimental techniques for assessing possible defects in the adhesion between FRCM and masonry, and between FRCM layers. To this aim, in this paper, an innovative nonlinear ultrasonic approach based on the sideband peak count technique is proposed. This approach is discussed and validated through acoustic (sonic and ultrasonic) tests performed on masonry tuff substrates reinforced with FRCM mortars embedding a basalt fibers grid and having known artificial defects at the adhesion between masonry and the reinforcement as well as in the fiber grid.