Research On Mix Proportion Design And Performance Of Pumice Mixed Aggregate Concrete

Mixed aggregate concrete is a transitional concrete developed on the basis of ordinary concrete and light aggregate concrete.Compared with light aggregate concrete,mixed aggregate concrete has the advantages of higher strength and elastic modulus,smaller shrinkage deformation and creep.Compared with ordinary concrete,the density is reduced and the degree of hydration is increased.At present,the mix proportion design of mixed aggregate concrete mainly considers the single performance index such as strength or durability.The output of pumice aggregate in China is very rich,and there are few studies on concrete mix proportion in practical engineering.In order to meet the comprehensive performance of pumice aggregate concrete mix proportion design in the actual project to better promote the popularity and application of pumice aggregate concrete in China.In this experiment,pumice aggregate was used instead of ordinary gravel to prepare pumice aggregate concrete.Based on the orthogonal test method,a lot of work has been done on the design and experimental study of the mix proportion of pumice aggregate concrete.(1)The orthogonal test method was adopted to design the mix proportion of pumice mixed aggregate concrete,and the orthogonal design table of four factors and five levels was selected,respectively taking into account the five change levels of the four factors of water-cement ratio,light aggregate substitution rate,sand rate and aggregate gradation.The influence of various factors on the working performance,mechanical properties,frost resistance and apparent mass of pumice aggregate concrete was discussed and analyzed.The order of impact on slump is as follows: water-cement ratio > sand rate > light aggregate substitution rate > aggregate grading;The order of influence of 28 d cube compressive strength and axial compressive strength is as follows: replacement rate of light aggregate > water-binder ratio > sand rate > aggregate grading;The order influencing factors of frost resistance and apparent mass are as follows: the replacement rate of light aggregate > water glue ratio > aggregate graded > sand rate.(2)The pore characteristics of pumice mixed aggregate concrete were studied and analyzed by nuclear magnetic resonance technology.As the water-cement ratio and the replacement rate of light aggregate increase with the increase of parameters,the proportion of harmful holes in pumice mixed aggregate concrete tends to increase.When the fractal dimension of aggregate gradation is 2.5,the proportion of harmful holes is the least.With the increase of sand rate,the proportion of harmful pores showed a decreasing trend,reaching a minimum of 59.68% at 50%.(3)The objective weight assignment-gray relational degree analysis method was used to design the optimal mix proportion of pumice aggregate concrete with multi-indexperformance.Meet the slump of 70 mm,56 mpa 28 d cube compressive strength,axial compressive strength of 50 mpa,freeze-thaw cycle 100 times strength loss rate of 25%,the apparent density of 1950 kg/m3,porosity more than 0.175% of the performance index request,based on objective weight given-grey correlation analytic method under the various factors parameters of water/cement ratio is 0.40,lightweight aggregate replacing rate was 50%,the aggregate grading fractal dimension is 2.5,sand at a rate of 40%.