Experimental Research On Mechanical Properties Of Early Age Concrete Materials And Structures

The performance index of early age concrete is one of the important basis for determining the quality of concrete in advance.Early age concrete strength is not only the key factor of the construction safety and the restriction factor of the engineering progress,but also directly affects the performance and durability of concrete in service.The research on the field of reinforced concrete in early age is mostly limited to the field of materials research,and the mechanical properties have not been studied systematically.Therefore,the research on the mechanical properties and the changing laws of concrete materials and structures at early age has important theoretical significance and engineering application value.The main research work and the innovations of this paper are as follows:(1)The test of concrete block cube compressive strength,axial compressive strength,splitting crack strength,static elastic modulus,uniaxial compression curve,whose age are 0.5 days,1 day,3 days,7 days,14 days,28 days and 90 days.The observation of similarities and differences of the test specimen phenomenon in each age,the analysis of test data,the summary of development law of early age mechanical performance index with ages,and the reasonable uniaxial compression constitutive relationship model on an experimental basis.(2)The tests of C40 steel reinforced concrete beam,whose age are 1 day,3 days,7 days,and 28 days,the in-depth analysis of typical failure modes for different age test pieces in grading loads.The study on load,age and other factors to the load-carrying capacity,deformation properties and the influence of pre loaded on the late bearing capacity.This paper proposes flexural bearing capacity calculation formula of early age reinforced concrete beam.This paper simulates the stress and deformation maps of steel and concrete whose age are 3 days,7 days,and 28 days,in using ABAQUS software,and extends finite element analysis in accordance with the variation of ratios with reinforcement and shear-span.(3)The eccentric loading tests of C40 reinforced concrete columns whose age are 1 days,3 days,7 days,28 days,5 days and 90 days are completed.In the course of the experiment,component of deflection,axial deformation,rotational deformation and strain of the beam cross-section are measured,leading to column crack distribution diagram under monotonic loading.Normal section cracking load calculation formula of early age reinforced concrete columns under eccentric compression are Proposed.According to the modified flat section assuming method,the paper presents an calculation method of early age eccentric compression bearing force.The calculated values of this formula are in good agreement with the experimental data.Based on experiments,the ultimate load that this paper simulated by the finite element software ABAQUS agrees well with test load for 3 days,7 days,28 days,and in accordance with the ratio of reinforcement,eccentricity finite element analysis has been extended.(4)By early age C40 concrete performance tests this paper studies influence of density and crack resistance about materials,concrete mix concrete,etc.,and through the early age of concrete carbonation depth,freedom of contract,limit expansion,tablet constraints testing,analysis and verify that the selected materials and the ratio on the durability of concrete,established the high durability technology control indicators of early age concrete.Through systematic experimental study,this paper proposes the development law of C40 early age concrete compressive strength,splitting tensile strength,elastic modulus and the uniaxial compression curve variation with the age,deducing the reasonable compression constitutive relationship model;The load characteristics and damage mechanism of RC members subjected to different age are analyzed,and the calculating formula of the bearing capacity of the reinforced concrete members is presented;According to the performance characteristics of early age,this paper studies on raw material selection,concrete mix ratio on concrete high durability,propose technical indicators controlling of the compactness and concrete crack resistance.