| The utilization of industrial solid waste is an important part of sustainable development strategy in China.Due to the special properties of many industrial waste residues,it can be used as a concrete admixture,which not only can improve the performance of the concrete,but also can reuse the waste and reduce pollution and energy consumption.At present,the research on admixtures at home and abroad is limited to fly ash,slag,etc.,and the resources are scarce and the price is high,so it is urgent to develop new high-quality admixtures to alleviate the pressure of expensive and scarce admixtures.At the same time,the output of industrial solid waste is huge in China,and it continues to pollute the atmosphere and the ecological environment.Based on the above reasons,this article will focus on the development of local solid waste to prepare high-quality concrete admixtures to achieve the concept of developing green building materials.The main research object of this paper is a kind of pozzolanic material piled up in Youyang county,Chongqing,which has been spontaneously combusted for ten years.It will be compounded with limestone material to prepare a new pozzolanic composite admixture.In this paper,the physical properties and chemical composition of the pozzolanic material are first tested to determine its feasibility as an admixture,and then the raw material sorting method and compound ratio are determined for the preparation of the composite admixture.After preparation,the microstructure and hydration products of the new composite admixture cement hardened paste were analyzed by means of SEM-EDS,and then the effect of the composite admixture on the properties of the concrete was detected and analyzed.The main conclusions of the research are shown as below:（1）The basic physical and chemical properties,pozzolanic properties,and radionuclides of the pozzolanic material all meet the requirements of the current relevant standards.The material has pozzolanic property and can be used as a pozzolanic admixture.（2）The core of the sorting method is to sort out the materials with sufficient spontaneous combustion and high pozzolanic in the mine as far as possible,and the research results show that the closer to the lower and deeper of the mine,the more fully it combusted.The simulation of the mine spontaneous combustion Schematic diagram is drawn to provide a basis for sorting;in addition,through the mortar activity index experiment,the ratio of pozzolanic material and limestone material is determined to be7:3 as the optimal ratio.Finally,the compound admixture is prepared according to the sorting method and the optimal ratio.（3）Through SEM-EDS,it can be observed that the pozzolanic material will have secondary hydration in the cement hardened paste,which consumes the Ca（OH）2crystals that are unfavorable for strength generated by the cement hydration,and generates more C-S-H gel.The gel is wrapped on the surface of the limestone particles,which improves the degree of condensation and density of the test block.At the age of90d,the Ca/Si and Ca/（Si+Al）in the hardened paste are effectively reduced and the Al/Si value is increased,resulting in a low Ca/Si ratio hydration product with more excellent performance.（4）When the content of pozzolanic composite admixture is within 25%,the working performance is better,which can effectively reduce the loss of concrete over time.At the same time,the post-strength of concrete can be greatly improved.And the pozzolanic composite admixture can play a greater contribution in the concrete with higher strength grade.（5）The pozzolanic composite admixture can effectively reduce the shrinkage rate of concrete.For concrete with higher strength grade,the anti-shrinkage effect is better.At the same time,the pozzolanic admixture can also effectively improve the resistance of chloride ion penetration in concrete.The concrete mixed with the pozzolanic composite admixture has a higher level of resistance to chloride ion penetration than that of the reference concrete. |
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