Study On Efficiency Of Fly Ash And Its Application In Steam-Curing Concrete

Aim at the key technology problems of the pre-stressed concrete sleepers, this paper studies the pozzolan effect of fly ash and the effect on the properties of concrete. The effect of the original alkalinity, the addition of chemical activators and cure regime on the pozzolan effect of fly ash is focused on investigating. The influence of fly ash on the interface adhesion strength, the mechanical properties and durability of concrete is explained. On based of study on the optimization of mix parameters, the mechanical properties, drying shrinkage, creep and durability of concrete, this steam-cured fly ash concrete is applied, the remarkable technical and economic benefits, social and environmental protection effects have brought.The main achievements and contribution of the thesis are as follows:1.The rule of the fly ash on the pH of system with different original alkalinity is systematically studied, pH=13.15 is the critical value of active mineral dissolving from fly ash, the original alkalinity can advance pozzolan effect of fly ash. When pH≥9.0, the active mineral of fly ash can react with the alkalinity. The addition of chemic activator can influent the pH of system, so influent the starting time of the pozzolan effect of fly ash.2.By using the strength index of the pozzolan effect and the pozzolan effect index, the pozzolan effect of fly ash is analyzed. The early hydration degree of fly ash is low regardless of with or without chemical activators, the main effect of fly ash is micro-aggregate and dense-filling. The test results of non-evaporation water and content of Ca(OH)2 and the analyse of XRD and SEM can confirm this viewpoint.3.The influence of fly ash on the interface between the past and aggregate is systematically studied. The content of fly ash has remarkable influence on this interface, the adhesion strength of interface can increase with the increase of fly ash, has little effect by the fineness of fly ash. When the W/B and the age is same, ground fly ash and air classified fly ash have the same influence on the improving-strength of the interface. By the analyse of the effect of the interface, the improving-strength of the interface and the influence coefficient of the interface, fly ash has a clear effect of improving-strength on the interface between the paste and aggregate.4.The effect of fly ash reducing water and increasing strength, prolonging the setting time and restraining the slump loss, is studied. On based of the study on the prepare technology, the method of increasing the pozzolan effect and combining with other mineral addition, the steam-curing adaptability of low-calcium fly ash concrete is improved. The papers study the influence of curing regime on the fly ash concrete, and put forward the reasonable curing regime.6.The mechanical properties and durability of steam-curing fly ash concrete is studied. Fly ash has less influence on the drying shrinkage of fly ash concrete, the model of ACI209 can forecast the drying shrinkage after 7d. Curing regime, content of fly ash, W/B, sand ratio, the kind of coarse aggregate has influence of drying shrinkage. The creep of steam-cured fly ash concrete using railway sleeper is studied for the first in China. Because Fly ash has micro-aggregate and dense-filling effect, the diameter of pore is small, the density of concrete is improved, and the creep of concrete is remarkable decreased. The steam-curing fly ash concrete has excellent durability.7.30% Grade I fly ash or 20% Grade II fly ash replaced eaual quality cement is used to produce the railway sleeper for the first in China. The addition of fly ash into steam-curing concrete has remarkable technical and economic benefits, social and environmental protection effects.