Investigation On Early Strength Field Evaluation Of Negative Temperature Concrete

The early age strength of concrete in winter construction is an important indicator to determine the time of demoulding,the subsequent maintenance plan,whether the concrete is damaged by freezing,and the degree of influence on the late strength development after the concrete is frozen.The mechanical properties of early-age concrete have a restrictive effect on the construction progress and structural safety during the construction period.At present,there are few literatures on the mechanical properties of the early-age concrete at the negative temperature and the lack of negative temperature conditions.Systematic research and reliable technical means for rapid monitoring and evaluation.In this paper,according to ASTMC900 and ASTMC803,the pre-embedded pull-out test and penetration test of concrete under normal temperature and negative temperature conditions are completed respectively.In winter,the concrete at the construction site is under negative temperature conditions,and local heating must be performed to raise the temperature of the detection zone to positive temperature.Based on MATLAB,a three-dimensional stochastic model of concrete with random distribution of aggregate,water and mortar was established.The finite element transient analysis was used to obtain the temperature rise curve of concrete with different negative temperature conditions and different proportions of concrete rising to positive temperature.The reliability was verified by infrared heating test.The main research contents of this thesis are as follows:(1)Based on the ASTMC900 specification,the pull-out force of the C20~C50 four-strength concrete standard test block was obtained by the pre-embedded extraction method,and the correlation between the compressive strength and the pull-out force was analyzed,and the corresponding functional relationship was obtained.(2)Based on the ASTMC803 specification,the penetration test of the C20~C50 four-strength concrete test block was carried out by the penetration method,and the correlation between compressive strength and penetration depth was analyzed to obtain the corresponding functional relationship.(3)The pre-embedded extraction method and the penetration method were used to test the concrete frozen at-20 °C.The pull-out force and the penetration depth and the compressive strength in the frozen state showed a large dispersion,which was not applicable in the icing state.The strength was measured by the pre-embedded extraction method and the penetration method,and the relationship between the drawing force and the penetration depth after the melting and the compressive strength was similar to that when the ice was not frozen.(4)Based on the Monte Carlo method,the internal water of concrete is simplified into spherical particles similar to aggregate particles.The random aggregate model is established and the temperature rise curve of negative temperature concrete under external heating source is simulated.The experimental verification proves that the random aggregate model is proved.The applicability provides a method for calculating the heating time of the concrete at the construction site.