Preparation And Performance Of Fly Ash-Slag Geopolymer

Geopolymer is a new type of green cementitious materials in recent years.Compared with Portland cement, geopolymer has many excellent properties, such as low energy consumption, environment friendly, rapid development of early strength,high temperature resistance, good durability, etc., so it has wide development prospects.In this paper, geopolymer based on fly ash and slag as a binary gel system, was prepared by alkali silicate activator. The compressive strength of the hardened geopolymer under the influence of the fly ash/slag ratio, modulus and solid content of alkali silicate activator, the CaO pattern and CaO content of fly ash, liquid-binder ratio were investigated; the microstructure and chemical composition of raw materials, the structures of alkali silicate activator, and the hardening mechanism of geopolymer were analyzed by XRD, SEM, FT-IR and NMR. At the same time, the durability(including high temperature resistance and carbonation resistance) of geopolymer and the performance of the fiber reinforced geopolymer were also studied.The results indicate that the compressive strength of the hardened geopolymer decreases gradually with the increase of the proportion of the fly ash to the total cementitious material ratio; with the increase of the modulus, the compressive strength of geopolymer increases at first and then decreases when the solid content of alkali silicate activator is 32%; when the modulus of activator is 1.2, the 28 d compressive strength of the products reach up to 102MPa; with the increase of the ratio of liquid to binder, the compressive strength of the geopolymers first increases and gradually decreases, when the ratio of liquid to binder is 0.48, the compressive strength of the geopolymers is the largest; the more amorphous CaO of fly ash, the highercompressive strength of fly ash-slag geopolymer, and the high content of crystal CaO in fly ash will result the late compressive strength decreasing of prepared geopolymer due to forming of the delated Ca(OH)2.The results of carbonation test on the fly ash-slag geopolymer indicate that the carbonation of geopolymer developed faster at early stage, with the increase of the age,the carbonation depth of geopolymer GFAN, GFAX and ordinary Portland cement all growth gradually. Compared with Portland cement, the carbonation resistance performance of geopolymer is poor.The results of high temperature resistance show that geopolymers compressive strength are higher than ordinary Portland cement under the room temperature, and the high temperature resistant performance of geoplymer is better than that of ordinary Portland cement under the high temperature. The compressive strength of geoplymer and ordinary Portland cement also decrease with the increasing of the treatment temperatures during 400℃~1000℃.When the temperature reached 1000℃, the compress strength of geopolymer still remains 50.1% of the original strength, and the geopolymer dose not appear the phenomenon such as crack and loose; On the contrary,the compressive strength of ordinary Portland cement is almost lost with the specimens surface serious destruction, loose and the cracks widened.Toughening effects of fibers on fly ash-slag geopolymer have been explored including carbon fiber(CF) and basalt fiber(BF). The results show that CF and BF can improve the mechanical strength of geopolymer, when mixed with 0.5% carbon fiber,the 7d flexural strength and 7d tensile strength for the specimen improved by 27.3%and 62.1% compared with the specimen without fiber.