Early-age Concrete Creep Test And Simulation:Considering Temperature And Relative Humidity Effects

Creep,as the inherent property of concrete,significantly affects the security and durability of most structure.On one hand,it can be beneficial because it reduces undesirable tensile stresses to some degree and optimize the distribution of stresses in statically indeterminate structure.On the other hand,excessive deformations caused by creep can be detrimental,for ins tance,destabilization and collapse lean of concrete elements;loss of prestress in bridges and increase of deflections.Creep and shrinkage always happen at the same time,both heavily dependent upon internal humidity(moisture inside the concrete).They are also affected by other factors such as ambient humidity,ambient temperature and the size and shape of structure component.When the internal humidity is relatively low,creep develops slowly.In the process of self-desiccation,however,creep develops at a faster pace.Given that such correlation is particularly evident in the early age,studies on how temperature and humidity affects early age creep prove to be very meaningful.This paper involves a series of experiments on compressive,tensile and flexural creep of early-age concrete.Loading ages,ambient temperature and humidity parameters are also factored into the testing.Basic creep at normal temperature and under sealed conditions is the control group and sealed concrete specimen at elevated temperature to study effects of varying temperature.Creep at normal temperature and in an unsealed condition is also tested to account for the effects from different humidity,including creep in high relative humidity and low relative humidity environment.Microprestress-solidification(MPS)theory is a widely accepted and applied creep model that considering how varying temperature and humidity influences creep and shrinkage.It was only validated by compressive creep in mature age.This paper improved and tested the model to better simulate early-age tensile creep.Moreover,according to MPS theory,microprestress is more sensitive to humidity change than temperature variations.Thus,previous simulation only adopted temperature parameters for creep at elev ated temperature.This paper will analyze the feasibility of adding humidity parameters.By using the improved MPS model,this paper enables prediction of early-age stress development in constraint condition(considering temperature effect).First,a series of experiments of the fully restrained concrete specimen under different controlled temperature process was conducted(by Pane),then computer programs was work out to verify the application of this model.In the last part,this paper compares the sealed basic creep and unsealed total creep with compression,tension and flexural strain and concludes similarities and differences between the three kinds of creep.It then attempts to find out some reasons behind the variances.