Tensile Strain Capacity Prediction of Engineered Cementitious Composites (ECC) Using Soft Computing Techniques

Plain concrete is strong in compression but brittle in tension,having a low tensile strain capacity that can significantly degrade the long-term performance of concrete structures,even when steel reinforcing is present.In order to address these challenges,short polymer fibers are randomly dispersed in a cement-based matrix to forma highly ductile engineered cementitious composite(ECC).Thismaterial exhibits high ductility under tensile forces,with its tensile strain being several hundred times greater than conventional concrete.Since concrete is inherently weak in tension,the tensile strain capacity(TSC)has become one of the most extensively researched properties.As a result,developing a model to predict the TSC of the ECC and to optimize the mixture proportions becomes challenging.Meanwhile,the effort required for laboratory trial batches to determine the TSC is reduced.To achieve the research objectives,five distinct models,artificial neural network(ANN),nonlinear model(NLR),linear relationship model(LR),multi-logistic model(MLR),and M5P-tree model(M5P),are investigated and employed to predict the TSCof ECCmixtures containing fly ash.Data from115 mixtures are gathered and analyzed to develop a new model.The input variables include mixture proportions,fiber length and diameter,and the time required for curing the various mixtures.The model’s effectiveness is evaluated and verified based on statistical parameters such as R2,mean absolute error(MAE),scatter index(SI),root mean squared error(RMSE),and objective function(OBJ)value.Consequently,the ANN model outperforms the others in predicting the TSC of the ECC,with RMSE,MAE,OBJ,SI,and R2 values of 0.42%,0.3%,0.33%,0.135%,and 0.98,respectively.

Multiphysics processes in the interfacial transition zone of fiber-reinforced cementitious composites under induced curing pressure and implications for mine backfill materials: A critical review

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 FMITZ. 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.

Evaluation of Self-Healing Efficiency of Microcapsule-Based Self-Healing Cementitious Composites Based on Acoustic Emission

Microcapsule self-healing technology is one of the effective methods to solve the durability problem of cementbased composites.The evaluation method of the self-healing efficiency of microcapsule self-healing cement-based composites is one of the difficulties that limits the self-healing technology.This paper attempts to characterize the self-healing efficiency of microcapsule self-healing cement-based composites by acoustic emission(AE)parameters,which provides a reference for the evaluation of microcapsule self-healing technology.Firstly,a kind of self-healing microcapsules were prepared,and the microcapsules were added into the cement-based composites to prepare the compression samples.Then,the specimen with certain pre damage was obtained by compression test.Secondly,the damaged samples were divided into two groups.One group was directly used for compression tests to obtain the damage failure process.The other group was put into water for healing for 30 days,and then compression tests were carried out to study the influence of self-healing on the compression failure process.During the experiments,the AE signals were collected and the AE characteristics were extracted for the evaluation of self-healing efficiency.The results show that the compression pre damage test can trigger the microcapsule,and the compression strength of the self-healing sample is improved.The failure mechanism of microcapsule selfhealing cement-based composites can be revealed by the AE parameters during compression,and the self-healing efficiency can be quantitatively characterized by AE hits.The research results of this paper provide experimental reference and technical support for the mechanical property test and healing efficiency evaluation of microcapsule self-healing cement-based composites.

Mechanics Behavior of Ultra High Toughness Cementitious Composites after Freezing and Thawing

Mechanical behaviors of UHTCC after freezing and thawing were investigated,and compared with those of steel fiber reinforced concrete（SFRC）,air-entrained concrete（AEC） and ordinary concrete（OC）.Four point bending tests had been applied after different freezing-thawing cycles（0,50,100,150,200 and 300 cycles,respectively）.The results showed that residual flexural strength of UHTCC after 300 freezing-thawing cycles was 10.62 MPa（70% of no freezing thawing ones）,while 1.58 MPa（17% of no freezing thawing ones） for SFRC.Flexural toughness of UHTCC decreased by 17%,while 70% for SFRC comparatively.It has been demonstrated experimentally that UHTCC without any air-entraining agent could resist freezing-thawing and retain its high toughness characteristic in cold environment.Consequently,UHTCC could be put into practice for new-built or retrofit of infrastructures in cold regions.

Impact Properties of Engineered Cementitious Composites with High Volume Fly Ash Using SHPB Test

The split Hopkinson pressure bar （SHPB） testing with diameter 40 mm was used to investigate the dynamic mechanical properties of engineered cementitious composites （ECCs） with different fly ash content. The basic properties including deformation, energy absorption capacity, strain-stress relationship and failure patterns were discussed. The ECCs showed strain-rate dependency and kept better plastic flow during impact process compared with reactive powder concrete （RPC） and concrete, but the critical compressive strength was lower than that of RPC and concrete. The bridging effect of PVA fiber and addition of fly ash can significantly improve the deformation and energy absorption capacities of ECCs. With the increase of fly ash content in ECCs, the static and dynamic compressive strength lowered and the dynamic increase factor enhanced. Therefore, to meet different engineering needs, the content of fly ash can be an important index to control the static and dynamic mechanical properties of ECCs.

Electromagnetic Shielding and Absorption Properties of Fiber Reinforced Cementitious Composites

In order to investigate the electromagnetic shielding effectiveness （SE） and absorbing properties of fiber reinforced concrete, steel fiber, carbon fiber and synthetic polyvinyl alcohol （PVA） fiber reinforced concrete were researched. The results show that with the increase of fiber Volume fraction, the SE and trend of frequency change of corresponding fiber reinforced concrete are enhanced. When the volume content of steel fiber is 3%, the SE of concrete is above 50 dB and its frequency is above 1.8 GHz. Moreover, in the range of 8-18 GHz, steel fiber, carbon fiber and PVA fiber all can improve the microwave absorption properties of concrete. The concrete with 0.5% carbon fiber can achieve the best absorbing property, the minimum reflectivity is about -7 dB; while steel fiber optimal volume fraction is 2%. The reflectivity curve of PVA fiber reinforced concrete fluctuates with the frequency, and the minimum value of the reflectivity is below -10 dB. The results show that fiber reinforced concrete could be used as EMI（electromagnetic interference） prevention buildings by attenuating and reflecting electromagnetic wave energy.

Damage evolution model of strain hardening cementitious composites under the uniaxial stress state

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.

Effects of Water/Binder Ratio on the Properties of Engineered Cementitious Composites

The effects of water/binder ratio （w/b） on the toughness behavior, compressive strength and flexural strength of engineered cementitious composites （ECC） were investigated. The w/b ratios of 0.25, 0.31, 0.33 and 0.37 were selected and the specimens were tested at the ages of 7 d and 28 d. The experimental results showed that there was a corresponding increase in first cracking strength, modulus of rupture, compressive strength and flexural strength with the decrease of w/b. Within the w/b range of 0.25-0.37, higher w/b was found to have improved effects on deflection, strain hardening index and toughness index of ECC. In the permission of meeting the requirement of compressive strength grade, selecting higher w/b in mix design will help to obtain robust ECC.

Methods of Modifying the Brittle Behavior of Cementitious Composites

We put forward effective methods of increasing the tensile strain of cementitious composites with 2% PVA fiber and high fly ash content. The test results show that curing condition has a significantly effect on the tensile performance. It is approved that the specimens incorporated appropriate volume fraction rubber powder and lightweight aggregate greatly increase the tensile strain of composites at medium-term age, but indefinitely at long-term age. To a certain extent, EVA can limitedly enhance the tensile performance of comentitious composites owing to the formation of polymer membrane and the hindered hydration of cement.

Properties and Microstructure of Polymer Emulsions Modifi ed Fibers Reinforced Cementitious Composites

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 fi llers 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 fi bers 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 fl exibility and plasticity which could be applied for a novel form of multifunctional materials with a range of pipeline coatings applications.

Shrinkage Reducing Measures for Engineering Cementitious Composites

Inhibition measurement of shrinkage of engineering cementitious composites （ECC） was investigated due to typical ECC with higher free drying shrinkage.The effects of expanded admixture （EA）,shrinkage reducing admixture （SRA）,coarse sand＋stone powder （CS＋SP） and superabsorbent polymer （SAP） on drying shrinkage and mechanical properties were studied.The experimental results show that ECC incorporating EA,SRA and coarse sand can retain around 60% of the typical ECC＇s free drying shrinkage.Superabsorbent polymerl（SAP） can delay the development of free drying shrinkage of ECC at different ages,and the effect of SAP is not distinct like the actions of EA,superabsorbent polymer（SRA） and coarse sand.Significantly,SAP may act as artificial flaw to form a more homogeneous defect system that increases the potential of saturated multiple cracking,hence the ductility of ECC will be improved greatly.

Tensile Behavior of Strain Hardening Cementitious Composites (SHCC) Containing Reactive Recycled Powder from Various C&D Waste

This work investigates the feasibility of utilizing reactive recycled powder(RP)from construction and demolition(C&D)waste as supplementary cementitious material(SCM)to achieve a ductile strain hardening cementitious composites(SHCC).The recycled mortar powder(RMP)from mortar waste,recycled concrete powder(RCP)from concrete waste and recycled brick powder(RBP)from clay brick waste were first prepared,and the micro-properties and tensile behavior of SHCC containing various types and replacement ratios of RPs were determined.The incorporated RP promotes pozzolanic and filler effects,while the hydration products in cementitious materials decrease with RP incorporation;therefore,the incorporated RP decreases the compressive strength of SHCC.Attributed to the reduction in the matrix strength,the incorporated RP increases the crack-bridging extent and ductility of SHCC;the irregular micro-structure and high reactivity of RP also help the strain-hardening performance of the prepared SHCC.In addition,the strainhardening performance of SHCC containing RMP and RBP is surperior to that of SHCC with RCP and is slightly lower than that of SHCC with fly ash(FA);for instance,the ultimate strain of SHCC containing 54%FA,RMP,RCP and RBP is 3.67%,3.61%,2.52%and 3.53%,respectively.In addition,the strain-hardening behavior of an SHCC doubled mix with FA and RMP or RBP has a similar ultimate strain and a higher ultimate stress than SHCC containing only FA.

High Temperature Flexural Deformation Properties of Engineered Cementitious Composites (ECC) with Hybrid Fiber Reinforcement

Engineered Cementitious Composites(ECC)is a class of high-performance fiber reinforced composites with ultra-ductility designed based on micromechanics,and it has been developed for increasing application in the construction industry during recent decades.The properties of ECC at room temperature have been tested and studied in depth,however,few studies focus on its performance after high temperature that is one of the worst conditions to ECC.To investigate the change tendency and mechanism for the high temperature flexural properties of hybrid fiber reinforced ECC and the feasibility of calcium carbonate whisker to reduce the cost of ECC materials,polyvinyl alcohol fiber(PVA)reinforced strain hardening cementitious composites(PVA-ECC),steel fiber+PVA fiber reinforced ECC(defined as HyFRECC-A)and steel fiber+PVA fiber+CaCO3 whisker reinforced ECC(defined as HyFRECC-B)subject to room temperature and 200℃,400℃,600℃,800℃elevated temperature exposure were experimentally compared.The results indicate that equally replacing PVA fibers by steel fibers degraded the flexural hardening ability of PVA-ECC at room temperature,while the addition of appropriate amount of CaCO3 whisker improved the flexural strength,toughness and flexural hardening behavior.The elevated temperature posed a significant effect on the flexural strength and toughness of the three types of ECCs.Flexural deflection hardening behavior of the three types of ECCs was eliminated after high temperature exposure.Flexural strength and toughness of PVA-ECC presented an exponential decay along with the increase of temperature.The addition of steel fiber slowed down the decay rate.Although the use of CaCO3 whisker increased the post-temperature flexural strength and toughness of HyFRECC-B,the decay rate was not further decreased.

Influence of Thickeners on Cement Paste Structure and Performance of Engineered Cementitious Composites

Hydroxypropyl methylcellulose （HPMC） and amphoteric polyacrylamide （ACPAM） were respectively used to prepare engineered cementitious composite （ECC） which exhibits strain-hardening behavior under uniaxial tension. The connections between cement paste structure and the performance of the composite in fresh and hardened state were investigated, aiming at achieving the desirable workability at a given solids concentration. The experimental results of viscosity and miCrostructure of cement pastes show that the intimate connections between flocculation groups lead to the growing increase in viscosity. The results of deformability and fiber dispersion demonstrate that fiber dispersion coefficient is a comprehensive index which can reflect the performance of deformability as well as uniformity. And the desirable fresh mixture can be achieved by optimizing the viscosity of cement paste. At last, the ductile strain-hardening performance of the ECC prepared with HPMC or ACPAM was investigated through uniaxial tensile test.

Effects of cellulose nanocrystals on the acid resistance of cementitious composites

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.

Study of the Superficial Modification of Sisal Fibres with Lignin, and Its Use As a Reinforcement Agent in Cementitious Composites

The objective of this work was to evaluate different superficial treatments of sisal fibres employing lignin,and their use as a reinforcement agent in cementitious composites.The treatments consisted of superficially impregnating sisal fibres(S)with organosolv lignin(LO),organosolv lignin and glutaraldehyde(LOG),Kraft lignin(LK)and Kraft lignin and glutaraldehyde(LKG).The fibre modifications were verified by FTIR-ATR and SEM analyzes,and the presence of lignin on the surface of the fibres was evidenced,confirming the effectiveness of the treatments.The mechanical,thermal(by TGA)and water absorption properties of the fibres before and after the modifications were also investigated.After treatment,the modified fibres presented an expressive reduction of the water absorption and did not show significant changes in the mechanical properties when compared with the natural unmodified sisal fibre(SNAT).It was verified an increase in the thermal stability of the treated fibres which can be attributed to the insertion of lignin on the fibres.To evaluate the performance of the fibres in the cementitious composites,cement plates(CP)were produced with different treated fibres(CP-SLOG,CP-SLO,CP-SLKG,CP-SLK)and fibres without treatment(CP-SNAT).The composites were evaluated concerning to the water absorption,porosity and mechanical properties.The fractured regions were also investigated by SEM.All composites prepared showed similar values of absorption and porosity indexes.From the mechanical properties,the composites prepared with modified fibres showed a significant increase in the modulus of rupture and modulus of elasticity compared with CP-SNAT,while toughness was similar to all samples.From the SEM images,it was observed that the modified fibres immersed in the cementitious plates showed no degradation,indicating that the impregnation of lignin acted as a protective agent of the fibres.Therefore,the treatments of the fibres with lignin led to a significant improvement in the properties of the composites generating a treatment with potential for industrial application.

Characteristics of Self-Healing Microcapsules for Cementitious Composites

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 ℃ and the initial decomposition temperature of the microcapsules was 265 ℃. 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.

Cementitious Composites Containing Multifunctional Sugarcane Fibres

This work investigates the reuse of natural(SCB)and minopropyltriethoxysilanemodifed(MSCB)sugarcane bagasse fbres in cementitious composites.ugarcane bagasse fbres are pre-used in the treatment of motor oil contaminated effluents.A full factorial design is used to identify the effects of fbre type(SCB and MSCB),fbre length(0.6 and 1.2 mm),fbre amount(1 and 2 wt%)and fbre condition(before and after oil filtration)on apparent density,water absorption,apparent porosity,ultra-pulse velocity,dynamic modulus,flexural strength and modulus.SCB fibres lead to increased apparent density compared to MSCB fibre reinforced composites.MSCB fibres contribute to reduce composite porosity,leading to higher mechanical properties.The smaller area of MSCB fibres promotes a larger amount of cementitious phase per unit volume,thus increasing the strength of the sample.Longer sugarcane fbres(1.2 mm)have a larger surface area,leading to a higher fibre concentration per unit volume,which increases water absorption.The amount of fibre has no significant effect on mechanical and physical responses.Composites made with 2 wt%0.6 mm long MSCB fibres achieve promising results for non-structural civil engineering applications.

Strengthening of the concrete face slabs of dams using sprayable strain-hardening fiber-reinforced cementitious composites

In this study,sprayable strain-hardening fiber-reinforced cementitious composites(FRCC)were applied to strengthen the concrete slabs in a concrete-face rockfill dam(CFRD)for the first time.Experimental,numerical,and analytical investigations were carried out to understand the flexural properties of FRCC-layered concrete slabs.It was found that the FRCC layer improved the flexural performance of concrete slabs significantly.The cracking and ultimate loads of a concrete slab with an 80 mm FRCC layer were 132%and 69%higher than those of the unstrengthened concrete slab,respectively.At the maximum crack width of 0.2 mm,the deflection of the 80-mm FRCC strengthened concrete slab was 144%higher than that of the unstrengthened concrete slab.In addition,a FE model and a simplified analytical method were developed for the design and analysis of FRCC-layered concrete slabs.Finally,the test result of FRCC leaching solution indicated that the quality of the water surrounding FRCC satisfied the standard for drinking water.The findings of this study indicate that the sprayable strain-hardening FRCC has a good potential for strengthening hydraulic structures such as CFRDs.

Transition from Multiple Macro-Cracking to Multiple Micro-Cracking in Cementitious Composites

This paper presents an experimental study of the possibility of transition from multiple macro-cracking to multiple micro-cracking in cementitious composites. Conventional polyvinyl alcohol fiber reinforced cementitious composites normally exhibit macroscopic strain-hardening and multiple cracking after the first cracks appear. However, the individual crack width at the saturated stage is normally 60 to 80 μm. In the current study, the effect of fine aggregate size on the cracking performance, especially the individual crack width in the strain-hardening stage was studied by bending tests. The results show that the individual crack widths can be reduced from 60-80 μm to 10-30 μm by modifying the particle size of the fine aggregates used in the composites.