Study On Properties Of Reactive Powder Concrete With Circulating Fluidized Bed Combustion Fly Ash

Reactive powder concrete?RPC? as one kind of ultra-high performance concrete has ultra-high strength, low brittleness, excellent durability, the main raw mixtures of RPC were cement, silica fume, slag,quartz powder, superplasticizer and other additives. Exerting higher pressure in the production process, adding a certain content fiber,high-temperature steam curing or high-temperature water curing were used to obtain higher strength and better durability performance for RPC,but these processes also causes greater drying shrinkage. Circulating Fluidized Bed Combustion?CFBC? fly ash is an industrial by-products containing high content of SO₃ and f-Ca O, AFt, Ca?OH?2 and other hydration products with expansion characteristics are formed with hydration of CFBC, which influences the performance of the matrix material, and therefore limits the application of CFBC used as building materials and other large-scale application.The main purpose of this paper is for reducing the dry shrinkage problem of RPC by using CFBC as expansion agent. Influence of original CFBC content, fineness, SO₃ content, water-cement ratio, basalt fiber content and length, curing methods and other properties of RPC were studied. Phase composition and microstructure of RPC were analyzed by means of XRD, SEM. The optimum CFBC content, fineness, SO₃ content,water-cement ratio, fiber content and so on were gotten by this study, the durability of RPC after 28 d standard curing conditions was also investigated.The results showd that when silica fume content is 15%, CFBC content is 10%, fineness?D50? is 15.88?m, SO₃ content is 10.72%, the compressive strength of RPC is higher than those of control groups and dry shrinkage of sample decreased 29.3%. Based on these results, higher strength RPC with 19.5% dry shrinkage decreased is obtained when the water-cement ratio is 0.17, fiber length is 6mm, content of fiber is 1.0%of cementitious materials and curing 2d at 90? steam.RPC with best raw mixtures ratio after curing under standard condition for 28 d was used to test its durability, such as its resistance to freezing-thawing cycles, anti-carbonation and sulphate attack. The results of anti-carbonation test show RPC has good anti-carbonation performance,the carbonation depth remain zero when carbonation for 28 d. The mass loss of RPC keep zero after freezing-thawing cycles to 350 times, this results also show RPC has good freezing-thawing resistance. The compressive strength of RPC loss only 21.2% and 21.1% when soaked in strong acid solution, alkali solution in a month. RPC also show better resistance to sulphate erosion when soaked in different concentrations of Na2SO4 solution for a month.The results of this study show that RPC with CFBC addition has better strength, less dry shrinkage and higher resistance to sulphate attack,anti-carbonation, freezing-thawing cycles and other properties, which will propose a new path for applying CFBC in RPC.