Study On Mix Proportion Optimization Design And Performance Of Spontaneous Combustion Gangue Aggregate Concrete

On one hand,with the rapid development of national infrastructure and urbanization construction,the supply of sandstone aggregates for concrete as basic building materials is in short supply.On the other hand,while enjoying coal as energy,human beings are suffering from air,water and soil pollution caused by coal gangue.At present,the stock of coal gangue in China is up to 6 billion tons,of which the over fire spontaneous combustion gangue accounts for about20%.As a kind of sub lightweight aggregate,spontaneous combustion gangue has a place in the family of sub lightweight aggregate with the characteristics of large reserves,easy mining and low price.However,the basic research of coal gangue aggregate concrete is weak,and the lack of relevant theoretical guidance has become the main obstacle to the large-scale application of coal gangue.Therefore,it is of great significance to carry out the research on the mix design of spontaneous combustion gangue aggregate concrete,whether for scientific research or the promotion of spontaneous combustion gangue concrete.In this paper,a concrete mix design method based on the physical and chemical properties of spontaneous combustion gangue is proposed.The relationship between raw material composition,preparation and performance of spontaneous combustion gangue aggregate concrete is studied.Combined with the engineering practice,through the bending performance test of spontaneous combustion gangue coarse aggregate concrete composite floor,the reliability of concrete design method and the feasibility of engineering application of spontaneous combustion gangue aggregate concrete are tested.The main work is as follows:（1）The Bolomey strength formula of spontaneous combustion gangue aggregate concrete is modified by using the regress function of MATLAB software based on a large number of previous test data of the research group.And the selection range of unit water consumption and sand ratio which accord with the characteristics of spontaneous combustion gangue aggregate is given.On the basis of fully considering the water absorption characteristics of spontaneous combustion gangue aggregate,the mix design method of spontaneous combustion gangue aggregate concrete based on pure water-cement ratio is proposed.（2）By improving the feeding sequence of concrete mixtures of spontaneous combustion gangue aggregate and pre-wetting the coarse and fine aggregates of spontaneous combustion gangue,the initial slump of concrete mixtures of spontaneous combustion gangue aggregate and the time-dependent loss of slump of mixtures are effectively improved.By introducing the parameters of slurry volume（_eV）and dry mortar volume(V_es),the relationship between them and bleeding and separation of spontaneous combustion gangue aggregate concrete mixture is quantitatively analyzed,which provides reference for quality control of field mixtures.（3）Based on the description of the mechanical failure process and the analysis of the test results,the mechanical failure characteristics and strength growth law of spontaneous combustion gangue aggregate concrete with different combination forms and strength grades are revealed.The strength of spontaneous combustion gangue aggregate concrete is negatively correlated with the bone-cement ratio.Reducing the bone-cement ratio can improve the strength of concrete.For concrete with the same aggregate combination,the slope of the rising section of stress-strain curve increases with the increase of concrete strength grade.For concrete of the same strength grade,the slope of the rising and decreasing section of stress-strain curve decreases with the increase of the content of spontaneous combustion gangue aggregate.According to Guo’s model,the stress-strain curve model of spontaneous combustion gangue aggregate concrete is established.The model accuracy is more than 0.9,which verifies the reliability of the model.（4）Using the mix design method established in this paper,a semi spontaneous combustion gangue coarse aggregate concrete and semi ordinary concrete unidirectional composite slab（SSCS）and an all ordinary concrete unidirectional composite slab（NNCS）are prepared combined with engineering practice,and three points bending static loading test was carried out.The results show that:The two slabs show similar deformation characteristics,and both of them have the good integrity,high rigidity and bearing capacity,which shows that the concrete design method is reliable and it is feasible to use spontaneous combustion gangue coarse aggregate concrete as structural floor.