Process for constructing a non-cushion road using refining slag and converter slag

Abstract

This invention relates to the field of road engineering, specifically to a process for constructing a road without a subbase using refined slag and converter slag. The process involves crushing converter slag as the skeleton aggregate and mixing it with refined slag as the fine aggregate. Pasteurella multocida inoculum solution and a cementing solution containing soluble calcium salts and urea are alternately sprayed into the mixture in stages and mixed. After paving, compaction, and curing, the mixture is covered and left to stand. Microbial metabolism generates calcium carbonate crystals in situ at the contact points between steel slag particles, forming a microscopic cementing network. This process, through in-situ mineralization and physical coating, blocks the contact between free calcium oxide and moisture inside the converter slag, eliminating local expansion stress caused by delayed hydration of free calcium oxide in the subbase structure, preventing the expansion and fracture of microcracks within the base layer, and cementing the steel slag mixture into a monolithic load-bearing slab.

Description

Technical Field

[0001] This invention relates to the field of road engineering, and specifically to a process for constructing a road without a subbase using refined slag and converter slag. Background Technology

[0002] The current conventional process for constructing highway base courses using converter slag and refining slag typically involves crushing converter slag as the skeleton aggregate and crushing refining slag as the fine aggregate, then mixing them in a predetermined ratio. To create a monolithic slab structure to replace the traditional graded crushed stone subbase, existing practices involve adding cement or lime as an inorganic binder for stabilization. During construction, the steel slag mixture with binder is mixed with water, transported to the site, and spread. Static and vibratory compaction is performed using a road roller, and finally, geotextile is covered and water is sprayed for moisture retention and curing. The base course develops its load-bearing strength through the hydration reaction of the binder.

[0003] Based on the existing processes described above, free calcium oxide remains inside the converter slag during the smelting process. This component undergoes a hydration reaction upon contact with water, accompanied by volume expansion. The cement or lime added in the existing processes can only provide hydration bonding and cannot consume or block the free calcium oxide inside the converter slag. During the service life of the road after construction, when external moisture seeps into the base layer, the free calcium oxide in the converter slag continues to undergo delayed hydration. The resulting local expansion stress cannot be buffered and released in the structure without a subbase, leading to microcracks inside the base layer. Further propagation of these microcracks can cause fractures in the road base layer and cracking in the surface layer. Summary of the Invention

[0004] In view of the shortcomings of existing technologies for constructing roads without a subbase using converter slag and refining slag, when cement or lime is used as an inorganic binder, it is impossible to prevent the delayed hydration and expansion of free calcium oxide in converter slag, which easily leads to cracking of the subbase of the road without a subbase, as well as insufficient structural stability and service life. This invention provides a process for constructing roads without a subbase using refining slag and converter slag.

[0005] To address the aforementioned technical problems, this invention provides a process for constructing a road without a subbase using refining slag and converter slag, comprising the following technical features: crushing converter slag as skeleton aggregate and refining slag as fine aggregate; mixing the skeleton aggregate and the fine aggregate according to a set ratio to obtain a mixture; preparing a Bacillus pasteurellium inoculum and a cementing liquid containing soluble calcium salts and urea; alternately spraying the Bacillus pasteurellium inoculum and the cementing liquid into the mixture in stages for mixing to obtain a mixed material; spreading the mixed material on the roadbed and compacting it using a road roller; covering and allowing the compacted mixed material to cure; the Bacillus pasteurellium inoculum is prepared by inoculating Bacillus pasteurellium into a liquid culture medium for amplification culture, collecting the Bacillus pasteurellium cells by centrifugation, and resuspending the cells in sterile physiological saline.

[0006] This solution is based on microbial induced calcium carbonate precipitation (MICP) technology. Bacillus pasteurellii metabolizes and decomposes urea through its own urease catalysis, producing carbonate and ammonium ions. The carbonate ions react with soluble calcium ions in the cementitious solution on the surface of steel slag aggregate particles and at particle contact points, generating calcium carbonate crystals in situ. These crystals form a continuous three-dimensional cementing network between the aggregates, replacing traditional cement and lime inorganic binders to give the mixture overall load-bearing strength. On the other hand, they can physically coat the surface of converter slag particles, blocking the contact path between free calcium oxide inside the particles and external moisture, eliminating the hidden danger of delayed hydration expansion at the source. The staged and alternating spraying method can ensure that the bacteria are uniformly adsorbed and colonized in the pores of the mixture, avoiding premature mineralization reaction caused by premature mixing of bacterial solution and cementitious solution, ensuring that calcium carbonate crystals preferentially grow in situ at aggregate contact points, greatly improving cementing efficiency and structural integrity.

[0007] Furthermore, in the above technical solution, the converter slag is crushed into coarse aggregate with a particle size between 10 mm and 30 mm as the skeleton aggregate, and the refining slag is crushed into fine aggregate with a particle size less than 5 mm as the fine aggregate; the mass ratio of the skeleton aggregate to the fine aggregate is (65-75):(25-35); the mixture also incorporates converter slag medium aggregate with a particle size between 5 mm and 10 mm, and the coarse aggregate, the medium aggregate, and the fine aggregate form a continuous gradation structure.

[0008] In practice, the continuously graded aggregate structure can significantly reduce the porosity of the mixture, improve the structural density after compaction, and reduce the channels for external moisture to penetrate. At the same time, it can increase the effective contact area between aggregates, provide more attachment sites for the formation of calcium carbonate cementing network, and further improve the cementing strength and overall structural stability.

[0009] Furthermore, in the above technical solution, when preparing the *Bacillus pasteurellii* bacterial suspension, the liquid culture medium used contains yeast extract, ammonium chloride, and glycerol, and the initial pH value of the liquid culture medium is adjusted to 8.5 to 9.0; the temperature of the amplification culture is maintained at 30 to 35 degrees Celsius, and the centrifugation treatment is performed in the late logarithmic growth phase; during resuspension, the optical density OD600 value of the bacterial cells in sterile physiological saline is adjusted to 1.2 to 1.5.

[0010] In practice, Bacillus pasteurellii is an alkaliphilic aerobic microorganism. The alkaline culture medium environment of pH 8.5-9.0 is compatible with the highly alkaline environment of converter slag and refining slag system, which can avoid the sudden drop in metabolic activity caused by the sudden change in pH after the bacteria enter the mixture. The urease activity of the bacteria is at its peak in the late logarithmic growth phase, which can ensure the efficiency of urea decomposition and mineralization reaction. The bacterial solution with an OD600 value of 1.2-1.5 can provide a sufficient quantity of bacteria with stable activity, avoiding the problems of insufficient cementation due to too low bacterial concentration or bacterial aggregation and uneven distribution in the system due to too high concentration.

[0011] Furthermore, in the above technical solution, the soluble calcium salt in the cementing solution is calcium chloride, and the molar concentration of calcium chloride and the molar concentration of urea in the cementing solution are both 0.5 mol / L to 1.0 mol / L; a trace element solution is also added to the cementing solution, the trace element solution containing nickel ions and cobalt ions, the final concentration of nickel ions in the cementing solution is 10 μmol / L to 20 μmol / L, and the final concentration of cobalt ions in the cementing solution is 5 μmol / L to 15 μmol / L.

[0012] In practice, calcium chloride provides soluble calcium ions required for the mineralization reaction. It reacts with carbonate ions produced by urea decomposition in an equimolar ratio to generate calcium carbonate. The equimolar concentration ratio avoids the waste of raw materials caused by excessive calcium source or urea, while preventing excessive free ions from affecting the metabolic activity of the bacteria. Nickel ions and cobalt ions are key coenzyme factors for the synthesis of urease in Bacillus pasteurellii. Trace addition can significantly increase the expression level and catalytic activity of urease, ensuring the stable and efficient mineralization reaction under the high-alkalinity steel slag system.

[0013] Furthermore, in the above technical solution, the specific method of alternately spraying the Pasteurella multocida bacterial solution and the cementing liquid into the mixture in stages for mixing is as follows: in the first stage, half of the total amount of Pasteurella multocida bacterial solution is sprayed into the mixture and stirred and left to stand for a first preset time; in the second stage, half of the total amount of cementing liquid is sprayed into the mixture and stirred and left to stand for a second preset time; in the third stage, the remaining Pasteurella multocida bacterial solution and the cementing liquid are alternately sprayed until the spraying is completed.

[0014] In practice, the first stage involves spraying half of the bacterial solution, which allows Bacillus pasteurellii to fully adsorb and colonize the aggregate surface within the pores of the mixture, preventing the bacteria from failing to adhere effectively after the subsequent cementing solution enters. The second stage involves spraying half of the cementing solution, which provides the colonized bacteria with initial nutrient substrates, initiating urease metabolism and mineralization reactions, and forming initial calcium carbonate crystal nuclei on the aggregate surface. The third stage involves alternately spraying the remaining bacterial solution and cementing solution, which ensures that the mineralization reaction proceeds continuously and evenly, guaranteeing the continuous growth of calcium carbonate crystals at the aggregate contact points, forming a continuous and dense cementing network, and avoiding the problems of uneven reaction and weak local cementation caused by a single large-scale spray.

[0015] Furthermore, in the above technical solution, the first preset time is 2 to 4 hours, the second preset time is 4 to 6 hours; the interval between each alternating spray in the third stage is 1 to 2 hours; in the first stage, the second stage and the third stage, the mixture after spraying the liquid is mixed at low speed using a horizontal twin-shaft mixer, the speed of the low-speed mixing is set to 30 to 50 rpm, and the mixing time for each cycle is set to 3 to 5 minutes.

[0016] In practice, a first settling time of 2-4 hours ensures that the bacteria complete stable adsorption on the aggregate surface, preventing the bacteria from falling off during mixing; a second settling time of 4-6 hours ensures that the bacteria fully activate urease metabolism and form stable calcium carbonate crystal nuclei; a spraying interval of 1-2 hours allows the substrate sprayed in the previous spray to fully react, preventing the accumulation of unreacted substrate that could cause sudden changes in local pH and affect the activity of the bacteria; and a low-speed mixing of 30-50 r / min ensures that the bacterial solution, cementing solution and mixture are mixed evenly, while avoiding high-speed mixing that could damage the aggregate gradation structure and the formed calcium carbonate crystal nuclei, thus ensuring the integrity of the cementing system.

[0017] Furthermore, in the above technical solution, the compaction of the mixture by the roller includes three stages: initial compaction, intermediate compaction, and final compaction. The initial compaction is carried out in static compaction mode twice, the intermediate compaction is carried out in low-frequency high-amplitude vibration mode four times, and the final compaction is carried out in static compaction mode twice to eliminate wheel tracks. The travel speed of the initial compaction is controlled at 1.5 km / h to 2.0 km / h, and the travel speed of the intermediate compaction is controlled at 2.0 km / h to 3.0 km / h.

[0018] In practice, initial static compaction can stabilize the paved mixture and prevent shoving and arching during subsequent vibratory compaction; secondary low-frequency high-amplitude vibratory compaction can effectively stimulate the interlocking of aggregates, significantly improve the density of the mixture, reduce the gaps between aggregates, and make the calcium carbonate cement network more uniformly stressed; final static compaction can eliminate roller tracks and ensure the smoothness of the base surface; and the speed control of staged compaction can avoid insufficient compaction due to excessively fast compaction or aggregate breakage and gradation damage due to excessively slow compaction, thus ensuring the compaction effect and long-term structural stability.

[0019] Furthermore, in the above technical solution, when covering and allowing the rolled mixture to cure, a polyethylene film is used to completely seal the top and sides of the mixture; the ambient temperature for curing is maintained at 25 degrees Celsius to 35 degrees Celsius, and the total curing time is 7 to 10 days; during the first 3 days of curing, the binder is added to the polyethylene film every 12 hours, and the volume of the binder added each time is 10% to 15% of the total pore volume of the mixture.

[0020] In practice, the fully enclosed polyethylene film covering can lock in the moisture inside the mixture, preventing moisture evaporation from reducing the metabolic activity of the bacteria, while also blocking the infiltration of external rainwater to prevent the unstable cementing system from being washed away; 25-35℃ is the optimal growth and metabolic temperature for Bacillus pasteurellii, which can ensure the continuous and efficient mineralization reaction during the curing period; the first 3 days of curing are the critical period for the rapid growth of calcium carbonate crystals, and replenishing the cementing solution every 12 hours can continuously provide substrate for the mineralization reaction, while allowing the cementing solution to penetrate into the pores inside the base layer, filling weak areas, and further improving the density of the cementing network and the water stability of the base layer.

[0021] Furthermore, in the above technical solution, before crushing the converter slag as skeleton aggregate, the converter slag undergoes hydration pretreatment: the converter slag is soaked in hot water at a temperature of 60°C to 80°C, maintaining a liquid-to-solid ratio greater than 3, and soaked continuously for 24 to 48 hours. After removal, it is dried at 105°C to constant weight. Before the refining slag is used as fine aggregate, it is ground into micro powder with a specific surface area of ​​400 m² / kg to 500 m² / kg using a ball mill, and the micro powder is mixed synchronously with the skeleton aggregate and the fine aggregate.

[0022] In practice, soaking in hot water at 60-80℃ can accelerate the premature hydration of free calcium oxide in converter slag, dissolving most of the free calcium oxide that can lead to delayed expansion, thus reducing the risk of expansion from the source; a liquid-to-solid ratio greater than 3 can ensure that the converter slag is completely submerged, allowing the hydration reaction of free calcium oxide to proceed fully; grinding to 400-500m³ 2The refined slag powder per kg has high pozzolanic activity and can undergo a secondary hydration reaction with the calcium hydroxide produced by the hydration reaction, further consuming the alkaline free components in the system. At the same time, the powder can fill the tiny pores between the aggregates, improve the density of the system, and work synergistically with the calcium carbonate cementing network to enhance the impermeability and structural strength of the base layer.

[0023] Furthermore, in the above technical solution, the cementing solution also contains rhamnolipin biosurfactant, the mass fraction of which is 0.05% to 0.1%; when alternately spraying the remaining Bacillus pasteurellium bacterial solution and the cementing solution in the third stage, the Bacillus pasteurellium bacterial solution is pre-mixed with the rhamnolipin biosurfactant before spraying, the mass fraction of which is 0.02% to 0.05% in the mixed Bacillus pasteurellium bacterial solution.

[0024] In practice, rhamnolipin biosurfactants can significantly reduce the surface tension of the bacterial solution and the cementing solution, improve the permeability and dispersion uniformity of the liquid in the pores of steel slag aggregate, prevent the liquid from agglomerating on the aggregate surface and failing to penetrate into the internal pores, and ensure that the bacteria and substrates are evenly distributed throughout the entire mixture system. At the same time, rhamnolipin can enhance the adsorption capacity of bacteria on the aggregate surface, improve the colonization efficiency of bacteria, and make the in-situ generated calcium carbonate crystals more evenly and densely distributed, further improving the integrity of the cementing network and the structural strength of the base layer. The low concentration of addition can avoid the negative impact of surfactants on the metabolic activity of bacteria, while ensuring the modification effect.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This process involves alternately spraying a suspension of Bacillus pasteurellium and a cementing solution containing calcium chloride and urea into a steel slag mixture in stages. After compaction, the mixture is sealed and periodically replenished with liquid for curing. This utilizes microbial metabolism to generate calcium carbonate crystals in situ at the contact points between steel slag particles, forming a cementing network. Combined with the hot water soaking pretreatment of converter slag and the simultaneous mixing of refined slag powder, this mineralized network not only builds cementing strength but also physically encapsulates and blocks the contact path between free calcium oxide inside the converter slag and external moisture. This eliminates the delayed hydration conditions of free calcium oxide and avoids fractures caused by stress concentration within the subbase of highways without a subbase.

[0026] 2. By setting a continuous gradation of coarse, medium, and fine aggregates, combined with low-speed mixing and specific rolling modes of initial, secondary, and final compaction, the structural density of the mixture after the introduction of liquid was ensured. The alkaline environment of the culture medium and the addition of trace amounts of nickel and cobalt ions maintained the metabolic activity of microorganisms in the highly alkaline environment of steel slag. The introduction of rhamnolipid biosurfactants reduced the surface tension of the liquid, promoting the uniform distribution of the bacterial solution and cementing solution within the pores of the steel slag, allowing the in-situ generated calcium carbonate crystals to grow more densely and coherently between particles, thus improving the structural strength and water stability of the base layer. Detailed Implementation

[0027] The present invention will be further described in detail below with reference to embodiments. Those skilled in the art can reproduce the technical solution of the present invention and achieve its claimed technical effects based on the content disclosed in this specification. It should be noted that the following embodiments are only used to explain the present invention and are not intended to limit the scope of protection of the present invention. Any non-substantial improvements and adjustments made based on the core concept of the present invention should fall within the scope of protection of the present invention.

[0028] Example 1: Converter slag was pretreated with hot water at 60-80℃ with a liquid-to-solid ratio of 3.5 and soaked at a constant temperature for 36 hours. The material was then dried at 105℃ to constant weight. The pretreated converter slag was crushed and graded, with particles of 10-30mm used as coarse aggregate and particles of 5-10mm used as medium aggregate. The refined slag was ground in a ball mill to a specific surface area of ​​450m². 2 / kg of fine powder with a particle size <5mm is used as fine aggregate. A continuously graded mixture is prepared by mixing coarse aggregate: medium aggregate: fine aggregate in a mass ratio of 70:10:20.

[0029] A liquid culture medium containing yeast extract, ammonium chloride, and glycerol was prepared. The initial pH of the system was adjusted to 8.8. *Bacillus pasteurellii* was inoculated and cultured at a constant temperature of 32°C. Once the bacteria reached the late logarithmic growth phase, the bacterial pellet was collected by centrifugation and resuspended in sterile physiological saline. The OD of the bacterial solution was adjusted. 600 =1.35, to obtain Pasteurella multocida bacterial solution.

[0030] The cementing solution was prepared with calcium chloride and urea both at a molar concentration of 0.75 mol / L. Trace elements of nickel ion and cobalt ion were added at a final concentration of 15 μmol / L and 10 μmol / L, respectively. At the same time, rhamnolipin biosurfactant with a mass fraction of 0.075% was added. Rhamnolipin was pre-mixed with Bacillus pasteurellis bacterial solution to adjust the mass fraction of rhamnolipin in the mixture to 0.035%.

[0031] The construction process follows a step-by-step alternating spraying procedure: In the first stage, spray 50% of the total bacterial solution, mix at a low speed of 40 r / min for 4 minutes using a horizontal twin-shaft mixer, and let stand for 3 hours; in the second stage, spray 50% of the total cementitious liquid, operate at the same speed and mixing time, and let stand for 5 hours; in the third stage, alternately spray the remaining bacterial solution and cementitious liquid, with a single spray interval of 1.5 hours, and maintain the low-speed mixing parameters throughout the process to obtain a uniform mixture.

[0032] The mixture was spread on the roadbed surface and compacted in stages: initial static compaction twice at a speed of 1.8 km / h; secondary compaction four times with low-frequency high-amplitude vibratory compaction at a speed of 2.5 km / h; and final static compaction twice to eliminate wheel tracks. After compaction, the top and sides of the mixture were fully enclosed with polyethylene film, and the curing temperature was controlled at 30℃ for a total curing time of 8 days. For the first 3 days of curing, binder was added every 12 hours, with the added volume being 12% of the total pore volume of the mixture, thus completing the construction of the road without a subbase.

[0033] Example 2: The mass ratio of skeleton aggregate to fine aggregate is 65:35, and the coarse, medium and fine aggregates work together to form a continuous gradation. The molar concentrations of calcium chloride and urea in the cementitious solution are 0.5 mol / L, the concentration of nickel ions is 10 μmol / L, the concentration of cobalt ions is 5 μmol / L, and the amount of rhamnolipin added is 0.05% in the cementitious solution and 0.02% in the bacterial solution mixture. All other process parameters and operating steps are consistent with those in Example 1.

[0034] Example 3: The mass ratio of skeleton aggregate to fine aggregate was 75:25. The molar concentrations of calcium chloride and urea in the cementing solution were 1.0 mol / L, the concentrations of nickel ions were 20 μmol / L, the concentrations of cobalt ions were 15 μmol / L, and the amount of rhamnolipin added was 0.1% in the cementing solution and 0.05% in the bacterial solution mixture. The other conditions were the same as in Example 1.

[0035] Example 4: Converter slag hot water pretreatment temperature 60℃, soaking time 24h, refined slag powder specific surface area 400m² 2 / kg, and the other raw material ratios, bacterial solution preparation, spraying and mixing, and rolling and curing parameters are the same as in Example 1.

[0036] Example 5: Converter slag hot water pretreatment temperature 80℃, soaking time 48h, refined slag powder specific surface area 500m² 2 / kg, with other conditions the same as in Example 1.

[0037] Example 6: Amplification culture of Bacillus pasteurellii at 30°C, initial pH of the culture medium = 8.5, OD of the bacterial culture 600 =1.2, first settling time 2h, second settling time 4h, alternating spraying interval 1h, mixing speed 30r / min, single mixing time 3min, the rest of the process is the same as in Example 1.

[0038] Example 7: Amplification culture of Bacillus pasteurellii at 35°C, initial pH of the culture medium = 9.0, OD of the bacterial culture 600 =1.5, first settling time 4h, second settling time 6h, alternating spraying interval 2h, mixing speed 50r / min, single mixing time 5min, other conditions are the same as in Example 1.

[0039] Example 8: The initial compaction speed was 1.5 km / h, the secondary compaction speed was 2.0 km / h, the curing temperature was 25℃, the total curing time was 7 days, the single liquid replenishment accounted for 10% of the pore volume, and the other raw material ratios, bacterial solution and cementing solution preparation processes were the same as in Example 1.

[0040] Example 9: Initial compaction speed 2.0 km / h, secondary compaction speed 3.0 km / h, curing temperature 35℃, total curing time 10 days, single liquid replenishment 15% of pore volume, other conditions the same as in Example 1.

[0041] Example 10: Keep all raw material ratios unchanged from Example 1, only adjust the horizontal twin-shaft mixer speed to 35 r / min and the mixing time to 3.5 min. The other spraying sequence, compaction parameters and curing regime remain unchanged.

[0042] Example 11: Keep the raw material ratio of Example 1 unchanged, only adjust the liquid replenishment interval in the early stage of curing to 10 hours, and the rest of the construction steps, rolling process and ambient temperature are the same as in Example 1.

[0043] Example 12: Keep the formula of Example 1 unchanged, only adjust the number of compaction vibration passes to 3, keep the initial and final compaction parameters unchanged, and keep the rest of the construction process exactly the same.

[0044] Comparative Example 1: Without adding Bacillus pasteurellium culture solution, only calcium chloride-urea cementitious solution was sprayed, omitting the microbial induced mineralization step. All parameters for aggregate gradation, compaction, and film sealing curing were consistent with those of Example 1.

[0045] Comparative Example 2: Using the traditional process described in the background technology, cement was used as an inorganic stabilized binder to mix steel slag aggregate. No bacterial solution or cementing solution was prepared, and no microbial mineralization reaction was carried out. Conventional paving, static compaction, and geotextile watering were performed. The amount of other aggregates and the paving dimensions of the subgrade were the same as in Example 1.

[0046] Comparative Example 3: The cementitious solution had a nickel ion concentration of 5 μmol / L and a cobalt ion concentration of 3 μmol / L, both below the limits defined in the claims. The bacterial solution OD... 600 =1.0, exceeding the lower limit of process parameters, the remaining raw material ratios and construction steps are the same as in Example 1.

[0047] Comparative Example 4: The high-temperature hot water hydration pretreatment step of converter slag is omitted. The raw converter slag is directly crushed to prepare the skeleton aggregate. The refining slag ultrafine grinding treatment is not carried out. The remaining bacterial solution preparation, alternating spraying, and rolling curing processes are the same as those in Example 1.

[0048] Effect testing and data analysis: Table 1 Performance test results of each embodiment and comparative example

[0049] Results analysis: Example 1, as the optimal solution, demonstrates a thorough microbial urease-catalyzed mineralization reaction, resulting in a dense and continuous calcium carbonate cementing network, high aggregate density through continuous gradation, and pre-disintegration and physical sealing of free calcium oxide by minerals. Therefore, it exhibits the highest compressive strength, extremely low volume expansion, excellent water permeability, and no long-term cracking risk, achieving optimal overall mechanical and durability properties. Examples 2-12 all involve adjusting the proportions and process parameters within the parameter range of the claims, maintaining excellent levels of all indicators. This proves that the present invention has a wide formulation range, strong process tolerance, and a robust and reliable overall technical solution.

[0050] Comparative Example 1 lacks the core microorganism Bacillus pasteurellii, which cannot form a microbially induced in-situ cemented structure of calcium carbonate. Relying solely on chemical crystallization, it cannot form a stable road network skeleton, resulting in a significant decrease in base layer strength. It cannot prevent the hydration and expansion of free calcium oxide, leading to severe expansion and deformation, serious water seepage, and a high risk of structural cracking.

[0051] Comparative Example 2 uses the traditional cement-lime stabilization process, which cannot consume the free calcium oxide in the converter slag, resulting in a significant delayed hydration expansion effect, a substantial increase in volume expansion rate, and extremely poor water stability. After long-term service, it is prone to base layer cracking and surface layer damage, and its overall performance is far lower than that of the microbial cementing process of this invention.

[0052] Comparative Example 3: When trace elements were below the specified threshold, the urease activity of Bacillus pasteurellii decreased significantly, the mineralization and crystallization efficiency was insufficient, the cementation structure was loose and porous, the compressive strength was low, the expansion stress could not be effectively suppressed, and the risk of water seepage and cracking increased significantly. This proves that the specified concentration of nickel and cobalt ions is a necessary condition for maintaining efficient microbial metabolism.

[0053] Comparative Example 4 omits the converter slag hydration pretreatment and refining slag ultrafine grinding processes, resulting in a large amount of primary free calcium oxide remaining inside the aggregate, continuously delaying hydration expansion. This leads to a significant increase in the overall expansion and deformation of the base course, ineffective filling of pores, insufficient structural density, and a significant deterioration in durability. In summary, this invention, through the synergistic effects of in-situ microbial mineralization cementation, aggregate gradation optimization, raw material pretreatment, and staged reaction curing, significantly inhibits the expansion disease caused by free calcium oxide from steel slag, greatly improves the strength and water stability of the base course of highways without a subbase, and achieves remarkable technical effects that cannot be expected by existing technologies. It possesses outstanding substantive features and significant technological progress.

Claims

1. A process for constructing a road without a subbase using refining slag and converter slag, the process comprising the following steps: The converter slag is crushed and used as the skeleton aggregate, and the refining slag is used as the fine aggregate. The skeleton aggregate and the fine aggregate are graded and mixed according to a set ratio to obtain a mixture. Prepare a Pasteurella multocida bacterial solution and a cementing solution containing soluble calcium salts and urea. Spray the Pasteurella multocida bacterial solution and the cementing solution alternately into the mixture in stages and mix them to obtain a mixed material. The mixture is spread on the roadbed and compacted using a road roller. The compacted mixture is then covered and left to cure. The Pasteurella multocida bacterial suspension is prepared by inoculating Pasteurella multocida into a liquid culture medium for amplification culture, collecting the Pasteurella multocida cells by centrifugation, and resuspending the bacterial cells in sterile physiological saline.

2. The process according to claim 1, characterized in that, The converter slag is crushed into coarse aggregate with a particle size between 10 mm and 30 mm as the skeleton aggregate, and the refining slag is crushed into fine aggregate with a particle size of less than 5 mm as the fine aggregate. The mass ratio of the skeleton aggregate to the fine aggregate is (65-75):(25-35); The mixture also incorporates converter slag aggregate with a particle size between 5 mm and 10 mm, and the coarse aggregate, the medium aggregate, and the fine aggregate form a continuous gradation structure.

3. The process according to claim 1, characterized in that, In preparing the Pasteurella bacterial culture, the liquid culture medium used contains yeast extract, ammonium chloride and glycerol, and the initial pH of the liquid culture medium is adjusted to 8.5 to 9.0; The amplification culture was maintained at a temperature of 30 to 35 degrees Celsius, and the centrifugation was performed in the late logarithmic growth phase. During resuspension, the optical density OD600 value of the bacterial cells in the sterile physiological saline was adjusted to 1.2 to 1.

5.

4. The process according to claim 1, characterized in that, The soluble calcium salt in the cementing solution is calcium chloride, and the molar concentration of calcium chloride and the molar concentration of urea in the cementing solution are both 0.5 mol / L to 1.0 mol / L. The cementing solution also contains a trace element solution, which includes nickel ions and cobalt ions. The final concentration of nickel ions in the cementing solution is 10 μmol / L to 20 μmol / L, and the final concentration of cobalt ions in the cementing solution is 5 μmol / L to 15 μmol / L.

5. The process according to claim 1, characterized in that, The specific method for alternately spraying the Bacillus pasteurellium bacterial solution and the cementing solution into the mixture in stages for mixing is as follows: In the first stage, half of the total amount of Bacillus pasteurellium bacterial solution is sprayed onto the mixture and stirred and left to stand for a first preset time. In the second stage, half of the total amount of cementing liquid is sprayed onto the mixture and stirred and left to stand for a second preset time. In the third stage, the remaining Bacillus pasteurellium bacterial solution and cementing liquid are sprayed alternately until the spraying is completed.

6. The process according to claim 5, characterized in that, The first preset time is 2 to 4 hours, and the second preset time is 4 to 6 hours; The interval between each alternating spray in the third stage is 1 to 2 hours; In the first stage, the second stage, and the third stage, the mixture after spraying the liquid is mixed at low speed using a horizontal twin-shaft mixer. The speed of the low-speed mixing is set to 30 to 50 rpm, and the mixing time for each cycle is set to 3 to 5 minutes.

7. The process according to claim 1, characterized in that, The compaction of the mixture using the roller includes three stages: initial compaction, intermediate compaction, and final compaction. The initial compaction is carried out by two passes of static compaction, the secondary compaction is carried out by four passes of low-frequency high-amplitude vibration, and the final compaction is carried out by two passes of static compaction to eliminate wheel tracks. The initial pressure travel speed is controlled between 1.5 km / h and 2.0 km / h, and the secondary pressure travel speed is controlled between 2.0 km / h and 3.0 km / h.

8. The process according to claim 1, characterized in that, When covering and allowing the mixture to cure after compaction, a polyethylene film is used to completely seal the top and sides of the mixture. The ambient temperature for static curing is maintained between 25 and 35 degrees Celsius, and the total duration of static curing is between 7 and 10 days. During the first 3 days of static curing, the adhesive liquid is added to the interior of the polyethylene film every 12 hours, and the volume of the adhesive liquid added each time is 10% to 15% of the total pore volume of the mixture.

9. The process according to claim 1, characterized in that, Before crushing the converter slag as aggregate, the converter slag undergoes hydration pretreatment: The converter slag is soaked in hot water at a temperature of 60°C to 80°C, maintaining a liquid-to-solid ratio greater than 3, for 24 to 48 hours. After being removed, it is dried at 105°C to constant weight. Before being used as fine aggregate, the refining slag is ground into micro powder with a specific surface area of ​​400 m² / kg to 500 m² / kg using a ball mill, and the micro powder is then mixed synchronously with the skeleton aggregate and the fine aggregate.

10. The process according to claim 4, characterized in that, The cementing solution also contains rhamnolipin biosurfactant, the mass fraction of which is 0.05% to 0.1%. During the third stage of alternating spraying of the remaining Bacillus pasteurellium bacterial solution and the cementing solution, the Bacillus pasteurellium bacterial solution is pre-mixed with the rhamnolipin biosurfactant before spraying, wherein the mass fraction of the rhamnolipin biosurfactant in the mixed Bacillus pasteurellium bacterial solution is 0.02% to 0.05%.

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