Compressive Strengthes And Microstructural Characteristics Of Fiber Reinforced Geopolymer

Geopolymer is a novel inorganic polymer, whose molecular chain consists of Si, O, Al connected by covalent bond is made with zeolite-like three-dimensional structure. Geopolymer also has the structure of organic polymer and characteristics of inorganism, such as high strength, good permeability resistance, acid-base resistance, able to withstand long-term effects of radiation and water instead of aging, especially the durability is unmatched by Portland cement. What's more, the energy consumption required for the synthesis of geopolymers and CO2 emissions are less than production of cement, indicating it is an environment-friendly material. So to immobilization of chemical waste, toxic heavy metals and nuclear wastes, it has great potential to replace the cement.In recent years, a lot of researches have highlighted the potential use of geopolymers as composite materials, repair materials and construction materials. However, aluminum silicate polymers have a character of quite low strength and toughness, which severely limit their extensive applications in high-tech materials field of a certain carrying capacity and reliability requirements. Possessing advantages of large Young's Modulus, little deformed under loads and high strength, fiber becomes a new strong candidate for enhancing strength and toughness of geopolymer.Based on the high flexural strength of geopolymer improved by fibers, the geopolymer reinforced by 0.1%,0.2%,0.3% and 0.4% fibers including cellulose fibers, polyester fibers, polyacrylonitrile(PAN) fibers and carbon fibers have been adequately prepared for the compressive strength testing, which can be applied to study the compressive and flexural effects on geopolymer materials varying fiber contents and types in this procedure. The experimental results show that: the best mass percentage of fibers is 0.2%, and the predominant strengthening and toughening mechanisms can be obviously attributed to fibers as the compressive and flexural strength of four kinds of fiber-geopolymers are much higher than the blank. Under the optimum ratio of fibers, the enhancement effects of polyester and PAN fibers are evidently superior to carbon and cellulose fibers. In these comparisons, the compressive strength of polyester fiber-geopolymers and PAN fiber-geopolymers get up to a high level in a early stage while the cellulose fiber-geopolymers own a strong endurance in the later stage;And the carbon fiber-geopolymers have great properties in strength and environmental steadiness.Subsequently XRD, FT-IR and TG-DTA techniques are employed to further characterize the microstructure of the fibers geopolymeric matrix and then deduce the most probable toughness mechanism. The microscopic analysis reveals that both the fiber-geopolymers and the blank geopolymeric matrix possess the amorphous to semi-crystalline structure of Si-O-Al framework. In addition, fibers diminish free water in the geopolymer and give an even tighter structure which increases the compressive strength.