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Hydration, microstructure and autogenous shrinkage behaviors of cement mortars by addition of superabsorbent

Beibei SUN, Hao WU, Weimin SONG, Zhe LI, Jia YU

《结构与土木工程前沿（英文）》 2020年第14卷第5期页码 1274-1284 doi: 10.1007/s11709-020-0656-x

摘要： Superabsorbent Polymer (SAP) has emerged as a topic of considerable interest in recent years. The present study systematically and quantitively investigated the effect of SAP on hydration, autogenous shrinkage, mechanical properties, and microstructure of cement mortars. Influences of SAP on hydration heat and autogenous shrinkage were studied by utilizing TAM AIR technology and a non-contact autogenous shrinkage test method. Scanning Electron Microscope (SEM) was employed to assess the microstructure evolution. Although SAP decreased the peak rate of hydration heat and retarded the hydration, it significantly increased the cumulative heat, indicating SAP helps promote the hydration. Hydration promotion caused by SAP mainly occurred in the deceleration period and attenuation period. SAP can significantly mitigate the autogenous shrinkage when the content ranged from 0 to 0.5%. Microstructure characteristics showed that pores and gaps were introduced when SAP was added. The microstructure difference caused by SAP contributed to the inferior mechanical behaviors of cement mortars treated by SAP.

关键词： Superabsorbent Polymer mechanical properties hydration heat autogenous shrinkage microstructure

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Numerical modelling of reinforced concrete flexural members strengthened using textile reinforced mortars

《结构与土木工程前沿（英文）》 2023年第17卷第4期页码 649-668 doi: 10.1007/s11709-023-0919-4

摘要： Externally bonded (EB) and near-surface mounted (NSM) bonding are two widely adopted and researched strengthening methods for reinforced-concrete structures. EB composite substrates are easy to reach and repair using appropriate surface treatments, whereas NSM techniques can be easily applied to the soffit and concrete member sides. The EB bonded fiber-reinforced polymer (FRP) technique has a significant drawback: combustibility, which calls for external protective agents, and textile reinforced mortar (TRM), a class of EB composites that is non-combustible and provides a similar functionality to any EB FRP-strengthened substrate. This study employs a finite element analysis technique to investigate the failing failure of carbon textile reinforced mortar (CTRM)-strengthened reinforced concrete beams. The principal objective of this numerical study was to develop a finite element model and validate a set of experimental data in existing literature. A set of seven beams was modelled and calibrated to obtain concrete damage plasticity (CDP) parameters. The predicted results, which were in the form of load versus deflection, load versus rebar strain, tensile damage, and compressive damage patterns, were in good agreement with the experimental data. Moreover, a parametric study was conducted to verify the applicability of the numerical model and study various influencing factors such as the concrete strength, internal reinforcement, textile roving spacing, and externally-applied load span. The ultimate load and deflection of the predicted finite element results had a coefficient of variation (COV) of 6.02% and 5.7%, respectively. A strain-based numerical comparison with known methods was then conducted to investigate the debonding mechanism. The developed finite element model can be applied and tailored further to explore similar TRM-strengthened beams undergoing debonding, and the preventive measures can be sought to avoid premature debonding.

关键词： fiber reinforced polymer textile reinforced mortar finite element analysis concrete damage plasticity calibration and validation parametric study

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Advanced cement based nanocomposites reinforced with MWCNTs and CNFs

Emmanuel E. GDOUTOS,Maria S. KONSTA-GDOUTOS,Panagiotis A. DANOGLIDIS,Surendra P. SHAH

《结构与土木工程前沿（英文）》 2016年第10卷第2期页码 142-149 doi: 10.1007/s11709-016-0342-1

摘要： Cementitious materials reinforced with well dispersed multiwall carbon nanotubes (MWCNTs) and carbon nanofibers (CNFs) at the nanoscale were fabricated and tested. The MWCNTs and CNFs were dispersed by the application of ultrasonic energy and the use of a superplasticizer. Mechanical and fracture properties including flexural strength, Young’s modulus, flexural and fracture toughness were measured and compared with similarly processed reference cement based mixes without the nano-reinforcement. The MWCNTs and CNFs reinforced mortars exhibited superior properties demonstrated by a significant improvement in flexural strength (106%), Young’s modulus (95%), flexural toughness (105%), effective crack length (30%) and fracture toughness (120%).

关键词： multi-walled carbon nanotubes carbon nanofibers mortars toughness Young’s modulus