A method for treating soft foundation using converter slag and injection desulfurization slag

Abstract

The present invention discloses a method for treating a wet and soft foundation using converter slag and sprayed desulfurization slag, comprising the following steps: S1.1, mixing converter slag with sprayed desulfurization slag; S1.2, filling the obtained mixture as a replacement material for a cushion layer of a wet and soft foundation. The above method for treating a wet and soft foundation using converter slag and sprayed desulfurization slag uses converter slag as coarse aggregate and sprayed desulfurization slag as a cementitious material, and is applied in wet and soft foundation construction as a replacement material for a cushion layer, and eliminates the harm of f‑CaO volume expansion and converts it into a favorable factor for utilization.

Description

Technical Field

[0001] The invention relates to the technical field of road engineering construction, and in particular to a method for treating a wet and soft foundation by utilizing converter slag and spraying desulfurization slag. Background Art

[0002] Wet and soft foundation is a special foundation often seen in road projects. It mainly refers to soil foundations with excessive natural water content, high compressibility, collapsibility, low bearing capacity, and easy sliding or consolidation settlement under load, such as soft soil, swamps, peat, etc. Among them, the clayey soft foundation in the northwest region is typically characterized by liquefaction of the basic loess after contact with water, agglomeration and hardening when dry, and low strength. For wet and soft foundations, the commonly used construction method is to replace gravel, but this method is more suitable for foundations with thinner soft soil layers, and the treated foundation cannot achieve the effect of compaction. Under the long-term continuous action of vehicle loads, it will cause damage to the road, and the treatment effect is not very ideal. The use of sand piles and geotextiles to treat this type of roadbed has high construction difficulty and construction cost.

[0003] Converter slag is a byproduct of the steelmaking process, with the characteristics of high alkalinity. The main component content of slag is more than 50%, which is consistent with the composition of silicate cement clinker. However, the formation temperature of slag is between 1500-1750℃, which is much higher than the calcination temperature of cement, so slag is called overburned silicate cement clinker. At present, slag has been used in road construction for decades, mainly in the base layer, water-stabilizing layer and asphalt concrete surface layer of roads, and there are a lot of literature introductions on the engineering practice of using slag to treat wet and soft foundations. Slag contains a certain amount of f-CaO and f-MgO (i.e. free calcium oxide and free magnesium oxide). Due to the high formation temperature, the grains are coarse, the hydration reaction is slow, and the hydration reaction is accompanied by volume expansion. Therefore, f-CaO and f-MgO are dangerous factors to be controlled in the process of slag resource utilization. The expansion problems of f-CaO and f-MgO are controlled as harmful factors. It is necessary to adopt slag treatment processes to degrade the functions of f-CaO and f-MgO in slag.

[0004] The molten iron spraying passivated magnesium desulfurization technology is to spray passivated lime and passivated magnesium into the molten iron to fully mix the three for desulfurization. The resulting sprayed desulfurization slag has a high MgO content, which limits its resource utilization in the building materials and cement industries. Currently, there are limited ways to utilize the sprayed desulfurization slag, and there is no research or related practical precedent in road engineering. Summary of the invention

[0005] In view of the deficiencies in the prior art, the present invention proposes a method for treating a soft foundation using converter slag and injection desulfurization slag, and uses the converter slag and injection desulfurization slag as replacement materials for the soft foundation cushion layer.

[0006] In order to achieve the above object, the present invention is implemented through the following technical scheme: a method for treating a wet and soft foundation using converter slag and injection desulfurization slag, comprising the following steps:

[0007] S1.1, mixing converter slag with injection desulfurization slag;

[0008] S1.2, the obtained mixture is used as a replacement material for the soft foundation cushion layer.

[0009] Furthermore, step S1.1 is specifically as follows:

[0010] The converter slag with a particle size greater than 10 mm is sorted, and the portion of the converter slag with a particle size greater than 37.5 mm is greater than 60%, and the sorted converter slag is mixed with injection desulfurization slag, wherein the mass ratio of the converter slag to the injection desulfurization slag is 80%:20%.

[0011] Furthermore, step S1.2 is specifically as follows:

[0012] S1.2.1, excavate a foundation trench on the original ground, and backfill the foundation trench with a layer of cushion material mixed with multiple layers of converter slag and injection desulfurization slag;

[0013] S1.2.2, unload the cushion material into the foundation trench, spread and level it;

[0014] S1.2.3, rolling of cushion materials;

[0015] S1.2.4, rolling again after watering and curing;

[0016] S1.2.5, after completing the first layer of filling, repeat steps S1.2.2 to S1.2.4 to complete multiple layers of filling.

[0017] Furthermore, step S1.2.2 is specifically as follows:

[0018] The cushion materials are unloaded into the foundation trench in the order of first the low places and both sides, and then the high places and the center. The loose laying thickness of each layer of cushion materials is 30mm, and then spread and leveled by a bulldozer.

[0019] Furthermore, steps S1.2.3 and S1.2.4 are specifically as follows:

[0020] Use a vibratory roller to roll the material first on both sides and then in the center, and then roll it again in the above manner after watering and curing. The first layer of cushion material shall be cured for 7 days after watering, and the second layer of cushion material shall be cured for 30 to 60 days after watering.

[0021] Furthermore, the method for preparing the sprayed desulfurized slag comprises the following steps:

[0022] S2.1, injecting passivating lime and passivating magnesium into the molten iron;

[0023] S2.2, passivating lime and passivating magnesium react with molten iron to form a blast desulfurization slag including sulfide, tricalcium silicate, dicalcium silicate, calcium oxide, magnesium oxide, calcium-magnesium solid solution, magnesia-iron spinel and continuous solid solution RO phase.

[0024] Furthermore, the temperature range of the molten iron is 1250-1450°C.

[0025] The above method of treating soft foundation using converter slag and injection desulfurization slag has the following beneficial effects: converter slag is used as coarse aggregate and injection desulfurization slag is used as cementitious material. The slags are interlocked to form a stable structure, and the f-CaO in the slag and the CaO in the injection desulfurization slag can fill the gaps between the slag particles. By combining the two materials, it can be applied to the construction of soft foundation and used as a replacement material for the cushion layer of the soft foundation, and the harm of f-CaO volume expansion is eliminated and converted into a favorable factor for utilization. DETAILED DESCRIPTION

[0026] The following embodiments of the technical solution of the present invention are described in detail. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and are therefore only used as examples, and cannot be used to limit the protection scope of the present invention.

[0027] The present invention provides a method for treating a wet and soft foundation by using converter slag and injection desulfurization slag. The converter slag and injection desulfurization slag are used as coarse aggregate and cementitious material respectively, which are applied to the construction of the wet and soft foundation as replacement materials for the cushion layer of the wet and soft foundation.

[0028] Specifically, the steps include:

[0029] S1.1, sorting converter slag. The structure of slag particles is a complex polyhedron. During sorting, slag with a particle size greater than 10 mm is selected as coarse aggregate, of which the particle size greater than 37.5 mm accounts for more than 60%. Slag particles of different particle sizes are interlocked with each other to form a stable structure. The expansion of f-CaO in the slag can fill the gaps between the slag particles. The sorted converter slag is mixed with the injection desulfurization slag, where the mass ratio of converter slag to injection desulfurization slag is 80%:20%.

[0030] S1.2, the obtained mixture is used as a replacement material for the soft foundation cushion layer for filling, and the specific steps are as follows:

[0031] S1.2.1, dig a foundation trench with an average depth of 0.6m on the original ground and a width of 1m outside the slope foot of the roadbed, and backfill the foundation trench with a cushion material of multiple layers of converter slag and injection desulfurization slag.

[0032] S1.2.2, fill the cushion material in layers and compact it in layers. The loose thickness of each layer is 300mm. The cushion material is unloaded and filled in the order of low places and both sides first, and high places and the middle later. After filling, it is spread and leveled by a bulldozer.

[0033] S1.2.3, Use a heavy vibratory roller to roll the ground first on the two sides and then in the center until the settlement observation value meets the requirements.

[0034] S1.2.4. After watering and curing, use a roller to roll the concrete to eliminate the deflection caused by local voids. After the first layer is paved, watering and curing shall be carried out for 7 days. After the second layer is paved, watering and curing shall be carried out for 30 to 60 days. The subsequent curing time is 7 days.

[0035] S1.2.5, after the filling is completed, the subsequent multi-layer filling repeats the steps of S1.4 and S1.5.

[0036] In the above construction method, converter slag and injection desulfurization slag are mixed as cushion materials for wet soft foundation, wherein the injection desulfurization slag is used as a cementitious material. The preparation method of the injection desulfurization slag includes the following steps:

[0037] S2.1, injecting passivating lime and passivating magnesium into the molten iron;

[0038] S2.2, passivating lime and passivating magnesium react with molten iron to form a blast desulfurization slag including sulfide, tricalcium silicate, dicalcium silicate, calcium oxide, magnesium oxide, calcium-magnesium solid solution, magnesia-iron spinel and continuous solid solution RO phase.

[0039] In the above-mentioned step S2.1, passivated lime and passivated magnesium are sprayed into molten iron in the temperature range of 1250-1450°C, which is consistent with the temperature range for the formation of silicate cement clinker, so that the silicate in the sprayed desulfurization slag has the same properties as silicate cement clinker and can replace silicate cement clinker as a cementitious material.

[0040] In the above-mentioned step S2.2, the passivating lime is sprayed into the molten iron and dissociated into alkali metal cations and oxygen ions. The sulfur atoms in the molten iron obtain the electrons provided by the oxygen ions to form sulfur ions. The alkali metal cations and sulfur ions are combined to form sulfides. The oxygen ions react with the silicon, manganese and iron elements in the molten iron, and finally form a continuous solid solution of tricalcium silicate, dicalcium silicate, magnesium iron spinel, iron oxide and manganese oxide with the lime. Passivating magnesium reacts with the molten iron to form magnesium oxide, so the final spraying desulfurization slag includes sulfides, unreacted calcium oxide, magnesium oxide, tricalcium silicate, dicalcium silicate, a small amount of magnesium iron spinel and a continuous solid solution RO phase.

[0041] The sulfides of the sprayed desulfurization slag include calcium sulfide, which can slowly react to form calcium sulfate during the hydration reaction and play a retarding role.

[0042] The hydration reaction rate of the unreacted calcium oxide in the injected desulfurization slag is between that of slaked lime and f-CaO, which is about 6 to 72 hours. This reaction rate is helpful for the secondary coupling reconstruction of the cushion material.

[0043] Compared with the magnesium oxide in magnesia cement, the magnesium oxide in the sprayed desulfurization slag has a higher formation temperature, so the grains are coarser and the hydration reaction activity is slower. It is easy to dissociate magnesium ions and can react with silicon dioxide (SiO2) and aluminum oxide (Al2O3) in the soft foundation to absorb water and solidify the foundation, making full use of the magnesium oxide in the desulfurization slag.

[0044] After the sprayed desulfurized slag is slowly cooled to ambient temperature, both tricalcium silicate and dicalcium silicate will undergo phase change reaction to form β-2CaO·SiO2 with a particle size between 75 and 150 meshes, which can fill the gaps between the slag particles and has a good filling effect.

[0045] After absorbing water and deliquescing, the magnesium oxide and calcium oxide in the sprayed desulfurization slag can partially react with the carbonate in the wet and soft foundation to enhance the strength of the cushion layer. 2+ and Mg 2+ Ions can react with silicon dioxide (SiO2) and aluminum oxide (Al2O3) in the soft foundation to gradually generate stable crystalline compounds insoluble in water, such as calcium silicate hydrate and magnesium silicate hydrate, forming a dense cross-network structure. Its good gelling properties help to solidify the soft foundation.

[0046] The above-mentioned method of treating a wet and soft foundation using converter slag and injection desulfurization slag uses a mixture of converter slag and injection sulfide slag as a cushioning material. While the coarse aggregate slag particles are interlocked to form a stable structure, the f-CaO in the slag and the calcium oxide hydration reactants in the injection desulfurization slag can fill the gaps between the slag particles. Taking advantage of the fact that the injection desulfurization slag contains more dicalcium silicate, magnesium oxide and calcium oxide, the hydration reaction under the wet and soft foundation environment can form water silicates and magnesium salts, which fill and gel the gaps in the slag, thereby eliminating the harm of volume expansion caused by the f-CaO hydration reaction. The slow hydration reaction of f-CaO is fully utilized to convert the harmful factors of the slag into favorable factors. As a replacement material for the cushioning layer of a wet and soft foundation, it diffuses and regulates the road surface load, diffuses stress and consolidates and drains the underlying soil layer, thereby improving the bearing capacity of the foundation and reducing the settlement deformation of the roadbed.

[0047] Moreover, steel slag is a porous material, and its structure contains a large number of penetrating pores and non-penetrating pores. The permeability coefficient of converter steel slag is about 10-4~10-3cm / s, which is 100~1000 times greater than that of soft soil. It can shorten the dissipation time of excess pore water pressure and accelerate the consolidation of soft soil. While using the void structure to drain water, the hydration reaction is carried out in the sprayed sulfide slag. The hydration products formed can close most of the penetrating pores, which provides a guarantee for the cushion material to prevent water penetration in the soft foundation, and also prevents road damage such as frost heave and mud swell. At the same time, as overburned silicate cement, after the cushion material encounters frost heave and crack damage, the steel slag in the process of steel slag crack formation can continue to react with the permeate phase, achieving a self-repairing effect.

[0048] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some or all of the technical features thereof may be replaced by equivalents. Such modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present invention, and should all be included in the scope of the claims and specification of the present invention.

Claims

1. A method for treating soft soil using converter slag and injection desulfurization slag, characterized in that: The following steps are involved: S1.1, mixing converter slag with injection desulfurization slag; S1.2, the obtained mixture is used as a replacement material for the soft foundation cushion layer for filling; The method for preparing the sprayed desulfurized slag comprises the following steps: S2.1, injecting passivating lime and passivating magnesium into the molten iron; S2.2, passivating lime and passivating magnesium react with molten iron to form a blast desulfurization slag including sulfide, tricalcium silicate, dicalcium silicate, calcium oxide, magnesium oxide, calcium-magnesium solid solution, magnesia-iron spinel and continuous solid solution RO phase; Step S1.1 is specifically as follows: The converter slag with a particle size greater than 10 mm is sorted, and the portion of the converter slag with a particle size greater than 37.5 mm is greater than 60%. The sorted converter slag is mixed with injection desulfurization slag, wherein the mass ratio of the converter slag to the injection desulfurization slag is 80%:20%.

2. The method for treating soft soil using converter slag and injection desulfurization slag according to claim 1, characterized in that: Step S1.2 is specifically as follows: S1.2.1, excavate a foundation trench on the original ground, and backfill the foundation trench with a layer of cushion material mixed with multiple layers of converter slag and injection desulfurization slag; S1.2.2, unload the cushion material into the foundation trench, spread and level it; S1.2.3, rolling of cushion materials; S1.2.4, rolling again after watering and curing; S1.2.5, after completing the first layer of filling, repeat steps S1.2.2 to S1.2.4 to complete multiple layers of filling.

3. The method for treating soft soil using converter slag and injection desulfurization slag according to claim 2, characterized in that: Step S1.2.2 is specifically: The cushion materials are unloaded into the foundation trench in the order of first the low places and both sides, and then the high places and the center. The loose laying thickness of each layer of cushion materials is 30mm, and then spread and leveled by a bulldozer.

4. The method for treating soft soil using converter slag and injection desulfurization slag according to claim 2, characterized in that: Steps S1.2.3 and S1.2.4 are specifically: Use a vibratory roller to roll the material first on both sides and then in the center, and then roll it again in the above manner after watering and curing. The first layer of cushion material is cured for 7 days after watering, and the second layer of cushion material is cured for 30 to 60 days after watering.

5. The method for treating soft soil using converter slag and injection desulfurization slag according to claim 1, characterized in that: The temperature range of the molten iron is 1250-1450°C.