Study On Mechanical Properties Of Multi-component Solid Waste Cementitious System And Its Solidified Saline Soil Under Sulfate Environment

Xinjiang is one of the regions with the most extensive distribution of saline soil in China.Due to the continental monsoon climate in northwest China,engineering hazards such as salt-frost heave,subsidence and churning are easy to occur under the condition of dissolution,weathering and freeze-thawing.With the in-depth implementation of the "One Belt,One Road" strategy,infrastructure construction in Xinjiang is gradually strengthened,and the bad engineering characteristics of saline soil have increasingly obvious problems such as erosion and salinization of all kinds of buildings in Xinjiang.At the same time,the accumulation of a large amount of industrial solid waste brings serious harm to the environment.The use of solid waste cementitious materials such as calcium carbide slag,slag and fly ash to replace high-energy consumption cement for curing sulphate soil can not only promote the large-scale disposal of bulk industrial waste,but also actively respond to the development strategy of energy conservation and emission reductionIn this paper,carbide slag,slag and fly ash were used as raw materials to prepare the multicementitious system,and the experimental study on the mechanical properties of carbide slag-slag,carbide slag-fly ash and carbide slag-slag-fly ash multi-cementitious system under sulfate environment was carried out,and the PPR-based prediction model of the mechanical strength of the multi-solid waste cementitious system under sulfate environment was established.On this foundation,orthogonal test method was used to test the unconfined compressive strength of cured saline soils with all-solid waste multi-cementitious system,and the mechanism of each influencing factor on the mechanical properties of cured saline soils with all-solid waste composite cementitious materials was explored,the influence ofdifferent curing temperatures on the mechanical properties of cured saline soils with multi-cementitious waste cementitious materials was analyzed anddiscussed.The main research conclusions are as follows:(1)The test results of the compressive strength of the multi-component cementification system show that the compressive strength of the composite cementification system of calcium carbide slag-slag,calcium carbide slag-fly ash,calcium carbide slag-slag-fly ash presents a change rule of first increasing and then decreasing with the increase of calcium carbide slag content and sulfate content.The increase of calcium carbide slag content increases the p H value of the pore solution.The hydration reaction degree of slag and fly ash is accelerated,resulting in the increase of hydration products and the increase of the compaction degree of hydration consolidated body.When the calcium carbide slag is in excess,excess Ca(OH)2 adheres to the surface of hydration products,reducing the compaction degree of the consolidated body and reducing the compressive strength of the sample.The addition of sulfate can promote the formation of rod-like ettringite in the cementitious system,fill the pores,improve the compactness of the consolidated body,and enhance the compressive strength of the sample.However,when the sulfate content in the environment exceeds 8%,a large number of Na2SO4 and Ca SO4 crystals appear in the sample,which will cause erosion and damage to the consolidated body of the cementification system and reduce the compressive strength of the cementification system(2)Based on the projection pursuit regression(PPR)modeling method,a prediction model for the 28 d compressive strength of the pure paste of calcined slag-slag-fly ash composite cementitious system was established considering three factors: the amount of calcined slag admixture,the proportion of slag to volcanic ash material,and the sulfate content.The influencing factors are sorted according to the weight value: slag ratio,sulfate content,carbide slag content,the weight values are: 1,0.322,0.149.The calculated results of the prediction model are in good agreement with the measured results,with an average relative error of 7.61% and a passing rate of 76%,which can prove that the PPR modeling prediction has good stability and reliability.(3)The effects of carbide slag mixture,sulfate content,volcanic ash material mixture and the proportion of slag in volcanic ash material on cured saline soils were analyzed by orthogonal tests.It is concluded that the amount of volcanic ash material mixture and slag mixture are the most important factors affecting the unconfined compressive strength of cured saline soils in ternary solid waste cementitious system,and the amount of calcium carbide slag mixture has the second highestdegree of influence,which is mainly related to the early volcanic ash reactivity of slag.SEM,TG-DTA thermogravimetric analysis showed that the content of hydration products of calcium alumina and hydrated calcium silicate in cured saline soils gradually increased with the increase of slag mixture.(4)The solidified soil samples were cured at 20 °C,25 °C and 30 °C.The unconfined compressive strength test results of the solidified soil samples at 7d,14 d,28d and 56 d showed that the curing temperature of 30 °C and 25 °C was more conducive to improving the hydration reaction of the composite cementitious system and quickly generating a large number of hydration products,so the early compressive strength was higher.At 20 °C,the solidified soil can grow steadily in a long curing age.It shows that 20 °C is more conducive to the later strength growth of solidified saline soil.