| Geopolymers are considered to have the most potential to replace traditional Portland cement cementing materials because of their excellent performance,green and low carbon,and the ability to realize the resource utilization of industrial waste.In recent years,geopolymers have received increasing attention from researchers.However,with the continuous progress of economy and society,the service environment of engineering materials is becoming more and more complicated,and higher requirements are put forward for the performance of geopolymers.Geopolymers have poor ductility and large shrinkage,which obviously cannot meet the requirements of modern engineering for engineering materials.Therefore,looking for effective admixtures to improve the inherent defects of geopolymers has become a key problem that needs to be solved urgently to realize the engineering application of geopolymers.Polypropylene(PP)fiber is a kind of synthetic fiber,which has the advantages of economy,high corrosion resistance,easy dispersion,high tensile strength and strong deformation ability.It is very suitable as a reinforcing fiber for brittle materials.In this study,the red mud-coal metakaolin base geopolymer(RCG)was prepared from industrial waste red mud and metakaolin obtained by calcining coal-based kaolin as raw materials,and polypropylene fiber was used as a reinforcing material.The influence of polypropylene fiber on the basic physical properties,mechanical properties and shrinkage characteristics of RCG are tested and analyzed.The main research contents and results are as follows:(1)The basic physical properties such as fluidity,density,water absorption,etc.of RCG with different content and length of polypropylene fibers have been tested.The results show that the RCG doped with fibers exhibit the properties of a decrease in the density of the geopolymer and an increase in water absorption,because the fibers are entangled with each other and aggregated into a cluster,in turn introduced the air in during the mixing of the geopolymer.The fiber also hinders the fluidity of the freshly mixed geopolymer slurry and reduces the workability of the geopolymer.(2)The compressive and flexural strengths of geopolymers with different fiber mix ratios were tested.It was found that the incorporation of polypropylene fibers had no positive effect on the compressive strength of geopolymers or even slightly weakened them,but it effectively improved the flexural strength of geopolymers.The optimal fiber length and content are 6mm and 0.4 vol.%,respectively.Under this fiber mix ratio,the 7 d and 28 d flexural strengthes of geopolymer are increased by 28.12%and 31.62%,respectively.Furthermore,the failure mode of the polymer blended with fibers changes from obvious brittleness to a certain degree of ductility during the compression process,and the residual strength appears.(3)Microscopic scanning electron microscopy and nuclear magnetic resonance tests show that the introduction of polypropylene fibers increases the porosity of the RCG,which explains why the compressive strength of the fiber-toughened geopolymer is lower than that of the geopolymer without fiber.The microscopic image of the fibertoughened geopolymer sample shows that the polypropylene fiber is tightly bonded to the geopolymer matrix and is suitable as a reinforcing material for the geopolymer.(4)The 56 d drying shrinkage of RCG containing different lengths and contents of polypropylene fibers under natural temperature and humidity conditions was tested.The results show that the drying shrinkage of the geopolymer first decreases and then increases with the increase of fiber content,and decreases monotonously with the increase of fiber length.Furthermore,the Eurocode 2 model was revised based on the measured data in this paper,and the parameters reflecting the influence of the fiber were introduced.A modified model suitable for predicting the shrinkage of fiber-toughened polymers was obtained. |
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