| This paper systematically studies the effects of C/S ratio,siliceous and calcareous materials on the physical properties,mineral composition and microstructure of autoclaved ceramsite and pottery sand using quartz tailings and fly ash as the raw materials,and explores the feasibility of preparing high strength concrete and prestressed pipe pile concrete using ceramsite as coarse aggregates under the condition of low cement content.The freeze-thaw resistance,mechanical properties and the strengthening effect of ceramic sand in cement mortar were also systematically studied.Considering that quartz tailings have good plasticity,pottery sand is prepared by hydrothermal synthesis autoclave curing process with quartz tailing as a silica material.Through orthogonal experiment,it is found that the C/S ratio is the main factor affecting the strength of pottery sand and its cement mortar,and the lead-zinc tailing content is the secondary factor.The results show that the optimum C/S ratio is 0.55,the lead-zinc tailings content is 25%.When pottery sand is applied to cement mortar,the mixing water consumption can be reduced by about 20%,the density of cement mortar can be reduced by 11.6%,and the strength can be increased by about 16.6%.By tracking the diffusion trace of red ink and testing the micro-hardness,it is found that the pottery sand has an internal curing effect on the cement matrix.At3d,the red ink has diffused to mm level in the cement matrix,and the micro-hardness of the diffusion area of red ink is 55MPa,which is higher than that of the cement matrixOn the basis of the preparation of pottery sand,the mechanism of the influence of C/S ratio on the mechanical properties of quartz tailings ceramsite is further studied by XRD,SEM and insoluble matter.The results show that the effect of micro-aggregate is sufficient when the C/S ratio is 0.3,but the cylinder compressive strength of ceramsite can not reach the best value because of the lack of filling effect of hydration products.In the range of C/S ratio of 0.7～0.8,the strength of ceramsite is not the optimal value due to the weakening of micro-aggregate effect,although the hydration products have enough filling effect.In the section of C/S ratio0.4～0.6,the filling effect of hydration products increases with the addition of micro-aggregate effect,leading to cylinder pressure strength of ceramsite increase by 14.3～33.8%.Especially,when the C/S ratio is 0.4,the maximum cylinder pressure strength of ceramsite reaches20.6MPa.The effect of replacing fly ash with quartz tailing on the physical properties of autoclaved ceramsite was studied.The results showed that the effect of quartz tailing replacing fly ash on the micro-aggregate of quartz is enhanced,and the cylinder pressure strength of ceramsite is increased obviously by 6.85～7.44%;The replacement of fly ash by quartz tailing can improve the water absorption of ceramsite by 0.14～4.42%in 1h and 0.77～7.23%in 24h.By changing the type and quantity of siliceous materials,the ceramsite with high water absorption and high strength can be obtained.After adjustment,the maximum cylinder compressive strength and water absorption are 30.1MPa and 12.96%,respectively.In addition,after the soundness test,the surface of ceramsite prepared with quartz tailing and fly ash still maintains integrity.The effects of calcium materials on the physical properties,mineral composition and microstructure of fly ash ceramsite were studied.The results show that the density of ceramsite increases,the water absorption decreases,and the cylinder compressive strength increases obviously with the increase of cement content and reaches the maximum when the cement content is 35%.The results show that with the increase of the content of quicklime,the water consumption of ceramsite granulation increases,the water absorption of ceramsite is significantly improved,and the density decreases.When the content of quicklime is 25%,the cylinder compressive strength of ceramsite reaches the maximum.The hydration products of fly ash ceramsite prepared by different kinds of calcareous materials are tobermorite,hydrographite and CSH（B）,but the hydration products of fly ash ceramsite with different content of the same kind of calcareous materials change obviously,and increase with the increase of the content of calcareous materials.When the content of calcium material is low,the content of Ca2+is less,the content of hydration products is less,and most of them are low calcium silicon than calcium silicate hydrate,the filling effect is weak,the local structure of ceramsite is loose,and the cylinder compressive strength is low;When the content of calcium material is high,Ca2+is rich,ceramsite will produce hydrated calcium silicate with high alkalinity and low strength.Meanwhile,the content of quartz and mullite will be reduced,the micro-aggregate effect will be weakened,and the cylinder compressive strength of ceramsite will be reduced.Therefore,only when the amount of calcium source is appropriate,the compressive strength of ceramsite can reach the maximum.By changing the type and quantity of calcium materials,the strength and water absorption of ceramsite can be controlled.The results of the physical and mechanical properties of ceramsite concrete show that the ceramsite concrete had a lower slump by 12.5%,a lower density by 19.5%and an equivalent strength as compared to crushed stone concrete.The strength of ceramsite concrete is 84～92%of 28d strength at 7d.When the cement content is 191.2～304.8kg/m3,the high-strength prestressed pipe pile concrete can be obtained by secondary maintenance method.When the cement content is 300kg/m3,LC60 high strength concrete can be produced by water curing.The180d drying shrinkage was 676～698 micro-strain.The research on the shell of ceramsite shows that the pozzolanic activity index of the shell is 71.05%,which can continue to react with the cement matrix.The large-scale production of ceramsite with an annual output of 200000m3 has been successfully realized by using hydrothermal synthesis autoclaved curing process of quartz tailing to prepare ceramsite and pottery sand.The annual consumption of quartz tailing is160000 tons,and the lightweight high-strength cloud concrete stone with an apparent density of 1854kg/m3 and cylinder compressive strength of 10.4MPa has been obtained;The strength of concrete can be improved by 4.5～7.5%when cloud concretevstone is used in concrete with25～50%equal volume instead of crushed stone;After 300 freeze-thaw cycles,the mass loss of concrete is only 0.79～1.87%,and the relative dynamic elastic modulus is 85.20～90.28%.The application of cloud concrete stone concrete in the actual engineering floor laying and floor structure is very successful,and the high added value utilization of quartz tailing is realized.The results have demonstration and guiding significance for the recycling of tailings. |
