Performance Of Multi-Scale Hybrid Fiber Reinforced Concrete Using Steel Fiber,Basalt Fiber And CaCO₃ Whisker

Concrete is a widely used construction material due to its abundant availability,ease of use in any form,high strength and better performance in ordinary condition.However,the brittle behavior of plain concrete(PC)is always a matter of concern that is reduce by mixing of fiber in concrete.The addition of fibers in concrete help in reducing the brittle behavior as well as offer the resistance against cracking in concrete.The cracking in concrete composite is important aspect to consider,as it is one of the main reason for damage.Fiber reinforced concrete(FRC)is used to control the cracking and addition of single length fiber has presented the better mechanical properties.The inclusion of one-length fibers is helpful to restrict the cracking at one scale,but the cracking in concrete is multi-level process from micro to macrostage.However,single length fiber is acceptable at particular scale,but the multi-scale performance by one length fiber cannot be achieved.Recently,hybrid fiber reinforced concrete(HFRC)is used as an alternative to FRC and PC.The hybridization of fibers are done in order to obtain the performance of each individual fiber at its own scale and size,and the combination of different fibers will result in complementary benefits together at multi-level.The performance of mixture of fiber together in HFRC will provide better mechanical characteristics than that of single length FRC.Therefore,the hybridization of multi-scale hybrid fibers in concrete is hypothesis in the study to attain the overall best mechanical performance at different scale.Three kind of fibers,i.e.calcium carbonate whisker,basalt fiber and steel fiber are selected to restrict the cracking at micro,meso and macro-level,respectively.The overall aim of this research program is to develop a better and sustainable construction material with utilization of mineral basalt fiber obtained from natural resources.The specific aim of this doctoral study is to investigate the in-depth properties of basalt fiber in hybrid concrete for its possible use as a construction material under the various surrounding conditions such as at room condition,under high temperature and aggressive environments.In this research,the use of basalt fiber in multi-scale hybrid fiber reinforced concrete is explored.The applicability of basalt fiber is assessed in hybrid fiber concrete in terms of its cracking behavior and analytical modelling.The multi-scale cracking phenomena is discover via microstructural investigation and suitability of analytical models are observed for hybrid fiber concrete prepared with basalt fiber.A new modified reinforcing index(MRIv)is proposed to calculate the effect of fiber aspect ratio and content on properties of concrete composite.After that,the mix proportion is optimized and then the various basalt fiber length and content are studied in hybrid fiber concrete for its optimal mechanical performance in term of compressive and fracture characteristics.The analytical models are also establish for compressive stress-strain curves of hybrid basalt fiber concrete and a range for ascending and descending branches are suggested.The cracking phases for fracture parameter is also display by using scanning electron microscopy analysis.Furthermore,the high temperature resistance of basalt fiber in hybrid concrete is examine and compared with that of concrete specimens at room temperature.In addition,a new analytical model is develop considering the parameter of temperature effect for hybrid fiber concrete having basalt fiber.Correspondingly,the microstructure study is done to evaluate the impact of high temperature on basalt fiber and the interaction of fiber with the matrix.Lastly,the durability of hybrid fiber concrete with basalt fiber is studied and a new fiber factor is develop under various aggressive environments to link the analytical models with mechanical attributes.The consequence of acidic and sulfate environmental conditions on characteristic of basalt fiber and matrix are studied by scanning electron microscopy examination.The properties of PC,single length FRC and HFRC without basalt fiber is consider as a reference in all the tasks.The main conclusions and achievements of this study are as follows:firstly,the incorporation of basalt fiber showed the great potential for its use in hybrid concrete by indicating better performance in term of resistance against cracking behavior and also showed good compatibility with analytical modelling.The results obtained from proposed modified reinforcing index presented better consistency with the experimental results and is helpful to predict the strength properties of HFRC.The best mix proportion is set up for optimization of basalt fiber length and content in hybrid fiber concrete for compressive and fracture parameters.The basalt fiber with different length and contents showed positive effect in HFRC and indicated substantial degree of enhancement up to 126%and 258%for compressive and fracture properties,respectively,as compared to that of PC.The proposed constitutive models equations of HFRC stress-strain curves indicated great suitability for predication of experimental behavior with R2?0.92.The basalt fibers in concrete interacted competently with hybrid fibers(whisker and steel fibers)and contributed effectively towards crack resistance process that eventually caused the improvement in compressive and fracture characteristics.The fiber pull out,fiber bridging,and proper bonding are the most efficient reinforcement mechanism offered at different levels by multi-scale hybrid fibers.The substantial improvement is indicated by addition of basalt fiber in hybrid fiber concrete for stress-strain response,peak stress,elastic modulus,peak strain,ultimate stain,toughness and specific toughness at room temperature and at 850?.Furthermore,the new proposed analytical model is useful to calculate the precise and accurate behavior of stress-strain curves form experimental results.It is revealed that the mineral basalt fiber demonstrated overall good appropriateness in the hybrid fiber concrete for all the compressive properties under high temperature.Test results under various aggressive environments revealed considerable enhancements in the water absorption,weight loss and strength of HFRC after the inclusion of basalt fibers and the basalt fibers presented overall suitability for durability enhancements.Moreover,a new proposed hybrid fiber factor(FFhybrid)demonstrated good fitness with the experimental data and fiber factor is beneficial to predict the mechanical properties of HFRC via analytical models.Conclusively,the addition of basalt fiber in hybrid fiber concrete presented the overall best mechanical performance in term of various aspects with less or higher degree of improvement as compared to that of PC,single length FRC and HFRC without basalt fiber.Thus,it is revealed that the basalt fiber in hybrid fiber reinforced concrete is favoring its utility for its use as structural material.