Study On The Durability Of Non-Spontaneous Combustion Gangue Concrete Under Freeze-thaw And Sulfate Attack

With the accumulation of coal mining,coal gangue produced along with coal mining not only occupies land resources,but also causes environmental pollution.The recycling of coal gangue has become a research topic.Adding coal gangue as aggregate to concrete can achieve social and economic benefits of environmental protection.In this paper,non-spontaneous combustion gangue is used as concrete aggregate to replace stone and sand,study on compressive strength and durability of non-spontaneous combustion gangue concrete to provide scientific basis for the utilization of non-spontaneous combustion gangue concrete.The main research contents and conclusions of this paper are as follows.The experimental study was carried out to select the water-to-binder ratio of 0.4,0.45 and0.5 and the replacement ratio of fly ash to 0%,5%,10%,15%,and 20%under non-spontaneous combustion gangue concrete at the age of maintenance 3d,7d and 28d compressive strength value and variation law.The test results show that:for the early strength of 3d and 7d,the compressive strength of fly ash replacement rate increases from 0%to 20%,the compressive strength increases first and then decreases.The 10%replacement rate of fly ash can improve the early strength of concrete.However,the effect of fly ash on compressive strength at 28d is not significant,group W0.4F10 was 2%higher than group W0.4F0 and 7.8%higher than the W0.4F20 group.With the same replacement rate of fly ash,the compressive strength of the28-day gradually decreases with the increase of the water to glue ratio.The optimum mix ratio obtained by the mechanical property test is that:water-to-binder ratio is 0.4,and the fly ash replacement rate is 10%.The mix ratio is used as the base mix ratio,and the fly ash replacement rate is 0%,10%,and 20%.The water-to-binder ratio is 0.4,0.45and 0.5,and the Na₂SO₄ concentration is 0%,2.5%,5%and 10%.Durability test study under three environments:single freeze-thaw,single sulfate attack and freeze-thaw sulfate attack coupling,.With quality loss rate,relative dynamic elastic modulus and compressive strength loss rate as evaluation criteria,comprehensive reflection,it comprehensively reflects the influence of different influencing factors on the durability of non-spontaneous combustion gangue concrete.The anti-freezing ability decreases with the increase of the water to glue ratio.The compressive strength loss rate decreases first and then increases with the increase of the fly ash replacement rate,when the fly ash replacement rate is 10%,the resistance the compressive strength loss rate is the smallest,but the mass loss rate and the relative dynamic elastic modulus at this time are not optimal results.The damage of the freeze-thaw cycle is more serious than that of sulfate attack,and the damage is the most serious under the coupling effect.The number of freeze-thaw cycles of single freeze-thaw is 50-75 times and only 25⁵0 times under coupling effect.At the same time,combined with scanning electron microscopy and microscopic analysis of energy spectrum analysis,the microscopic conditions of non-spontaneous combustion gangue concrete under different environments was studied.From the test results,we can know:The freeze-thaw cycle will cause micro-cracks in the gangue aggregate,and under the action of sulfate attack,Na₂SO₄ crystals and acicular ettringite crystals will be formed inside the concrete.These expansive crystals destroy the cementation between the cement colloid and the coal gangue aggregate.From the energy spectrum analysis,as we can see that after the single sulfate attack and the freeze-thaw sulfate attack coupling,there is a large amount of Na element in the concrete,and the erosion of the coal gangue concrete by Na₂SO₄ is obvious.The binary surface model of each evaluation index with cycle number,water to glue ratio and fly ash replacement rate was created by using the software fitting function of Origin software.A multivariate regression model between each evaluation index and influencing factors under the coupling of freeze-thaw sulfate erosion was established.The fitting accuracy of each fitted model was evaluated by residual analysis.According to the regression model,the prediction model of durability life of non-spontaneous combustion gangue concrete is derived,which provides a reference for practical engineering application.There are 76 figures,35 tables and 91 references in the dissertation.