Experimental Study On Performance Control Of Calcium-based Geopolymer

Calcium-based geopolymer is a kind of water-hardening cementitious material,which is made of natural inorganic minerals or industrial waste residues containing silica-aluminate as the main raw materials.It is activated by alkali activator after the introduction of calcium component.Calcium-based geopolymer has excellent properties such as high strength,corrosion resistance and high temperature resistance due to the three-dimensional polycondensation network structure of silicon-oxygen tetrahedron and aluminium-oxygen tetrahedron.Therefore,it has broad application prospects.Centering on the subject of the experimental study on performance control of calcium-based geopolymer,the influence of different active factors on the mechanical properties of calcium-based geopolymer was systematically analyzed by adjusting the mix ratio of raw materials,alkali content and sodium silicate modulus.The change rule of compressive strength and the reasons of performance deterioration after calcination of calcium-based geopolymer were explored.What's more,the effects of different active factors on the acid corrosion resistance and sulfate corrosion resistance of calcium-based geopolymer were analyzed.The main results of this paper are as follows:?1?The effects of different active factors on the mechanical properties of calcium-based geopolymer are as follows:alkali content>mix proportion of raw materials>sodium silicate modulus.Calcium-based geopolymer has high early strength,and the compressive strength can reach 44.9 MPa after 3 days maintenance.Appropriate alkali content and raw material mix proportion are conducive to the formation of a relatively dense structure and improve properties.The compressive strength of the optimum mix ratio is 70.1 MPa after 28 days maintenance.?2?The thermal stability of calcium-based geopolymer is less affected by different active factors.After calcination,the linear shrinkage and mass loss of calcium-based geopolymer are larger.The change trend of compressive strength is similar,which decreases gradually with the increase of temperature,and the strength decreases greatly at600?.Microstructural analysis shows that flocculation gel gradually decomposes after calcination,and micro cracks and pores appeare.Nepheline phase is formed by solid-state reaction after calcination at 700?,and the structure of calcium-based geopolymer is destroyed with a large number of pores at 800?.The highest heat-resistant temperature of calcium-based geopolymer is about 600?.?3?Calcium-based geopolymer has nice chemical corrosion resistance,and different active factors have great influence on its chemical corrosion resistance.After soaking in10%sulphuric acid solution for 120 days,the surface of calcium-based geopolymer appears peeling and falling off,and the highest compressive strength is 57.4 MPa.Micro-cracks,holes and rod-like gypsum can be observed by SEM.The corrosion of sulfuric acid on calcium-based geopolymer is the combined effect of the expansive destruction of SO₄^2-and the corrosion damage of H⁺.After soaking in sodium sulfate solution,the appearance of calcium-based geopolymer remaines unchanged except for the generation of white stains.The compressive strength showes a trend of decreasing first and then increasing.The compressive strength of calcium-based geopolymer increases greatly in the later period of soaking because of the activation of Na₂SO₄ on calcium-based geopolymer and the constant hydration of the samples.The highest strength is 75.2 MPa after 120 days of soaking in 10%sodium sulfate solution.