Research On Shrinkage And Cracking Of Fly Ash Concrete At 20 To 70 Degrees Celsius

Shrinkage and cracking are important factors to the durability of concrete. Thispaper mainly studied the effect of fly ash on the strength and linear expansioncoefficient of C50 concrete, and the effect of coupling impact of ash and differenttemperature on combine chemical content, drying shrinkage, since Autogenousshrinkage of concrete in the early age. A experimental was arranged for studing theconcrete crack discipline in constraint condition. At the same time, using Optical fiberBragg grating sensor in the constraint conditions to test the variant rule of concretevolume.Finally, combined with laboratory research results, monitored the mass concretestructure on the construction site construction of some actual key projects, and achievedgood results.Through the content of the research, we conclude that:Improve the fly ash willreduce the C50 concrete early strength and combine chemical content, when the masspercent of fly ash was 50, the strength of the 7d is only 59.2% of the benchmarkconcrete. When the fly ash content is less than 40%, the linear expansion coefficientincreased with the mixed quantity of fly ash,when the percent was 30, the linearexpansion coefficient rise 30.6% than the benchmark concrete after one day.Mixing fly ash reduced the autogenous shrinkage of concrete, and increase dryingshrinkage. When the percent of fly ash was 50%, the autogenous shrinkage of was94.2% lower than benchmark, but dry shrinkage was 97.9% higher after 90 days at 20℃. High temperature will accelerate early shrinkage of concrete, autogenous shrinkageand drying shrinkage increased by 13.3% and 20% respectively on the 7th day withdegrees Celsius temperature from 20 go up to 35 When the percent of fly ash was 30.Maintenance condition is an important factor in the cracking condition.Under thesame environment; fly ash would delay the through cracks. By using optical fiber Bragggrating measuring deformation of the concrete under flat restraint conditions showedthat: For the concrete exposured,the shrinkage of inter is 41.5% lower than the surface,and the edge is 29.8% lower than the center on 7th day; For the concrete under seal, thedeformation relatively is lower. Using Optical fiber Bragg can accurately monitoring thestrain of mass concrete, and accurately caught the cracking time and crack width.