Experimental Study On The Tensile Creep At Early Ages Of Low Calcium Fly Ash Based Geopolymer Concrete

Geopolymer concrete is a new type of environmentally-friendly building material based on industrial waste materials such as fly ash and blast furnace slag.It has the characteristics of high early strength,rapid strength development,and good corrosion resistance.The application of geopolymer concrete can not only reduce the carbon emission threat brought by the traditional cement industry,but also provide a new method for the reuse of industrial waste.But at the same time,similar to ordinary concrete,geopolymer concrete is also a kind of multiphase and inhomogeneous brittle material with small tensile strength and ultimate tensile strain.In the early age of the construction and use of geopolymer concrete structures,it is easy to produce cracks caused by restrained shrinkage,which will damage the safety,reliability and durability of the structure,and restrict the popularization and development of such kind of new building material.In order to solve this problem,based on the low calcium fly ash based geopolymer concrete(FAGPC),a series of experimental and analytical studies on the tensile creep characteristics at early age,which is of great significance to alleviate the restraint stress,were carried out in this thesis.The law of its early age tensile creep and its advantages in practical engineering were comprehensively evaluated.The main work carried out in this thesis and the main conclusions are as follows:(1)The mix design of FAGPC was carried out,and the development law of its basic mechanical properties at early age was studied.The results show that the compressive strength,splitting tensile strength and compressive elastic modulus of the FAGPC at the age of 2 days can reach 95.4%,72.6% and 81.9% of these properties at the age of 28 days after 24-hour sealing curing at room temperature and then 24-hour sealing curing at high temperature.In the room temperature curing stage after high temperature curing,the increase of its basic mechanical properties is small and reach a state of excellent at the age of 28 days.(2)The test of early age tensile creep of FAGPC was carried out to study the effect of different initial loading ages on the tensile creep characteristics.According to the test results,a mainstream concrete creep model was modified.The results show that the law of tensile creep of FAGPC is similar to that of ordinary concrete.The smaller the initial loading age is,the larger the tensile creep coefficient is and the faster the average creep growth rate is.But FAGPC has smaller shrinkage and greater tensile creep at early age.The modified concrete creep model has good applicability and accuracy to the test results of early age tensile creep of FAGPC in this thesis.(3)The aging coefficient for early age tensile creep of FAGPC was calculated and applied to the calculation of early age restraint stress of reinforced concrete structure.The results show that it is reasonable to take 0.8 as the value of aging coefficient,and more accurate results of restraint stress calculation of FAGPC structures can be obtained according to this value.Compared to the ordinary concrete,FAGPC has more advantages in alleviating the cracking risk of concrete structure.Therefore,because of its excellent basic mechanical properties at early age and its characteristics of environmentally-friendly,the application of FAGPC in practical engineering is of great significance.