Experimental Study On Meso-structure And Frost Resistance Of CMA Concrete

Livestock and poultry manure is the most reusable biomass resource in agricultural waste,and burning it as fuel is one of the main utilization ways.In Tibetan areas of northwest China,drying cow dung as fuel is a necessity of life,and a large amount of cow dung ash（CMA）will be produced after burning.In recent years,studies have found that CMA has pure quality and stable composition,which can replace part of cement and be used to make green concrete.At present,the research on CMA concrete focuses on various macroscopic properties.This paper mainly conducts mechanical compression test,freeze-thaw cycle test and mesopore structure analysis of concrete with different water-binder ratio（0.51,0.44,0.38）and different CMA content（0,5%,10%,15%）,exploring the influence of water-binder ratio and CMA content on concrete,and provide technical support for the best preparation method of CMA concrete.（1）Using CMA after burning at 650°C to prepare concrete,and analyze effect of water-binder ratio and CMA content on compressive strength of concrete.The results showed that there was a negative correlation between water-to-binder ratio and compressive strength.Concrete strength increased with decreasing water-binder ratio.As the amount of CMA increased,the compressive strength of concrete decreased,and the compressive strength of concrete mixed with CMA is lower than that of reference group concrete（without CMA）.When the CMA content did not exceed 10%,CMA had little effect on the compressive strength of the concrete.（2）Analyze the influence of water-binder ratio and CMA content on the microscopic pore structure of concrete by using nuclear magnetic resonance instrument,and discuss the law of T₂spectrum distribution,porosity,pore size distribution,etc.The test results showed that with the increase of CMA content,the most probable pore diameter inside the concrete decreased,the proportion of pores smaller than 1.0μm increased,and the proportion of mesopores and macropores larger than 1.0μm decreased,the total number of pores increased,and the number of small and medium pores increased.With increasing and gradual refinement,the porosity of CMA concrete is smaller than that of the reference group concrete.The smaller the water-binder ratio,the denser the pore structure,the less the number of pores,and the smaller the porosity.（3）Through the freeze-thaw cycle test,it explored the influence of water-binder ratio and CMA content on the durability of concrete freeze-thaw.A comprehensive analysis of concrete appearance damage,quality loss,relative dynamic elastic modulus,and compressive strength after freezing and thawing are carried out.The test results showed that with the increase of CMA content,the appearance damage and quality damage intensify,but the relative dynamic elastic modulus and compressive strength of concrete show that with the increase of CMA content,there is a trend of first decreasing and then increasing.Concrete with a CMA content of 5%performed best,a CMA content of 10%was similar to that of the benchmark group concrete,and a CMA content of 15%performed the worst.（4）The degradation of concrete pore structure after freeze-thaw was studied by NMR.The test results showed that the freezing and thawing effect changed the pore structure characteristics of the concrete.The pore structure of concrete was inferior to CMA concrete,and the smaller the water-binder ratio,the less affected by freezing and thawing and the less damage.The law of pore size and concrete freeze-thaw damage is that,after the freeze-thaw cycle,when the pores smaller than 0.1μm decreased and the pores larger than1.0μm increased,the freeze-thaw damage of concrete increasesd,and when the pores smaller than 0.1μm increased and the pores between 1.0μm and 10μm decreased,freeze-thaw damage to concrete was aggravated.