Experimental Study And Application Of Coal Gangue-carbide Slag Geopolymer Cementing Material To Solidify Soft Soil

Cement and lime are the traditional binders for the stabilization of soft soil.However,there is a significant environmental effect for the manufacturing of cement and lime in terms of high consumption of energy and excessive emission of CO₂.Besides,due to the high output and low utilization,the accumulation of coal gangue and calcium carbide residue not only occupies lots of lands and consumes high treatment cost,but also seriously threaten to the environment and ecology.Based on the above problems,firstly the hypothesis that calcium carbide residue is conducive to coal gangue to prepare high strength geopolymer cementitious material in low concentration alkali excitation solution is proposed.Secondly,the rationality of the hypothesis is proved through the study of its strength characteristics and microstructural mechanism.Finally,it is applied to the stabilization of soft soil,which could provide the scientific basis for new materials to replace cement or lime for stabilizing soft soil,and also provide experimental and theoretical reference for the recycling and utilization of coal gangue and calcium carbide residue.The main works and research results are summarized as follows:(1)On the strength characteristics of coal gangue-calcium carbide residue geopolymer cementitious material:Based on the compressive strength experiment,the hypothesis has been proved that the calcium carbide residue could improve the compressive strength of coal gangue-calcium carbide residue geopolymer cementitious materials.Furthermore,this research studies the effect of various factors on the strength of the geopolymer cementitious materials development,including content of calcium carbide residue mass ratio,alkali excitation solution(Na OH:Na₂Si O₃),liquid-solid ratio(L/(CCR+CG)),and curing time.The experimental results show that there is an optimal value of calcium carbide residue content.For example,compare with the pure coal gangue geopolymer cementitious materials,the coal gangue and calcium carbide residue geopolymer cementitious materials with 20%calcium carbide residue content could achieve the highest strength of 44.4 MPa,about 327.6%higher than that of pure coal gangue geopolymer cementitious materials.The experimental results suggest that the optimal ratio is that the calcium carbide residue content is 20%,the ratio of Na OH:Na₂Si O₃and L/(CG+CCR)is 50:50 and 0.5 respectively,through comprehensive analysis combing with economic cost and construction operability.(2)On the microstructural mechanism of geopolymer cementitious materials:Based on the microstructural experiment results including X-ray diffraction(XRD),Fourier transform infrared spectroscopy(FTIR),thermogravimetric analysis(TGA),mercury intrusion method(MIP),and field emission scanning electron microscopy(SEM),the microstructural mechanism was demonstrated.It can be founded that the calcium carbide residue plays an important effect in the process of component supplemented,stimulating the internal mechanism and the intensity of the microstructural mechanism of strength development.The results illustrate that the microstructural mechanisms affecting the strength development of geopolymer cementitious materials,including mineral composition,phase transformation,thermal stability,pore distribution and microstructure,are related to the content of calcium carbide residue and curing time.Moreover,the calcium carbide residue can effectively promote the polymerization reaction rate and make the reaction products(such as N-A-S-H and C-A-S-H)increase rapidly,which is the essential reason for the significant increase of the compressive strength of geopolymer cementitious materials.(3)On the mechanical characteristics of soft soil stabilized by geopolymer cementitious materials:Based on the analysis of strength development and microstructural mechanisms,a series of consolidation undrained experiments were conducted to research the mechanical characteristics of stabilized soft soil using an optimal ratio of geopolymer cementitious materials.The results show that the mechanical characteristics of stabilization soft soil are affected significantly by the amount of geopolymer cementitious material,confining pressure,initial moisture content,mixing and stirring method as well as curing time.Moreover,the shear failure plane is the macroscopic symbol of brittle failure and strain softening of the soft soil stabilized by geopolymer cementitious material,which is related to the amount of geopolymer cementitious material and the initial moisture content.Besides,the geopolymer cementitious materials can effectively improve the shear strength of soft soil,and the relationship between them is approximately exponential.When the addition amount equal to 15%,the ultimate strength of stabilized soft soil begins to exceed 1 MPa,which is eligible for the requirement of the engineering project.