EXPERIMENTAL AND STATISTICAL INVESTIGATION OF HEAVY CONCRETE CREEP CHARACTERISTICS WITH ITS AGING CONSIDERED

The results for experimental and statistical investigation of nonlinear creep deformation of heavy concrete with its aging considered are presented. Based on the obtained experimental data resulting from the two year testing of twins prism-shaped samples, we established a linear correlation between the secant modulus of deformation η ττ η τ ε σ ,t,,t, /Å' = and the initial constant relative stress levels ητ = σ τ / fcd at any given time (t - τ) of their interaction, where σ τ is a starting long-acting constant aging stress; εη,t,τ is full relative concrete deformation that considered its creepiness at a random time t loaded at τ with constant compressive load (t - τ). Considering these aspects we discovered the dependence ( τ ñò ,ñò ,t ÅÅ > ) in identifying the heavy concrete creep characteristics with its aging considered. It reflects the actual work of concrete under the influence of long-acting constant compressive load more accurately when compared with its definition without aging considered. The values of full φ0,t,τ and limited φR,t,τ creep characteristics at any given time (t - τ) in the proposed dependence equals the stress level at ητ = 0 and ητ = 1 received bybeing approximated in the time period following the hyperbolic dependence. The statistical parameters of creep characteristics α 1 and n1 with the approximated initial φ0,t,τ do not depend on the kind of concrete and can be adopted α 1 = 0,0044 и n1 = 0,5. The experiments by R. A. Miller and K. S. Karategin conducted with heavy concrete and processed with the proposed dependencies, proved that despite their different compositions the duration of the compressive load and the time of loading of expression to determine φ0,t,τ and φe,t,τ are the same. The main variable parameters are limiting values of φ0,∞,τ and φR,∞,τ that indicate the acceptability of the proposed dependencies for all kinds of heavy concrete. The solution of the problem of approximating φ0,t,τ and φe,t,τ using exponents give better results but are more time-consuming. Hyperbolic dependencies to express φ*η,t,τ are recommended for practical applications. α 2 and n2 parameters with approximated limited value φR,t,τ of creep properties depend on the type of concrete. We recommend α 2 = 0,01 и n2 = 0,1 for heavy concrete. This dependence allowed us to identify theoretical values of the creep characteristics with aging considered for heavy concrete at every level where there is permanent compressive stress at any time of its action. At the same time 20% security of the theoretical values received from the proposed dependence is 97%.