Steel slag RAP low shrinkage cement stabilized macadam and preparation method thereof

Abstract

This invention discloses a steel slag RAP low-shrinkage cement-stabilized crushed stone and its preparation method, relating to the field of road engineering materials technology. The materials include stabilized steel slag coarse aggregate, RAP aggregate, natural crushed stone and manufactured sand, cement, fine powder binder and water. The compatibility boundary between steel slag micro-expansion compensation, RAP old asphalt film flexible buffer and low cement filling is defined by the steel slag expansion potential descriptor S, RAP asphalt film descriptor F, matching coefficient Ker and low cement binder filling coefficient Kf. A staged water-containing mixing process of steel slag pre-wetting, RAP secondary addition and cement fine powder final mixing is adopted to reduce the risk of drying shrinkage, thermal shrinkage and freeze-thaw damage.

Description

Technical Field

[0001] This invention relates to the field of road engineering materials technology, specifically to a steel slag RAP low-shrinkage cement-stabilized crushed stone and its preparation method. Background Technology

[0002] Cement-stabilized crushed stone is a commonly used semi-rigid material in road base courses. It has good slab properties, load-bearing capacity, and construction maturity. However, due to cement hydration shrinkage, drying water loss, temperature cycling, and base course constraints, it is prone to drying shrinkage cracks, thermal shrinkage cracks, and subsequent reflective cracks. Traditional methods to reduce shrinkage usually include reducing cement usage, adding expansion agents, optimizing gradation, or improving curing conditions. However, in scenarios with a high proportion of solid waste utilization, relying solely on conventional methods often makes it difficult to simultaneously meet the requirements of strength, volume stability, durability, and construction controllability.

[0003] Steel slag possesses high strength, a rough surface, and potential cementitious activity, making it suitable for use as a road base aggregate after stabilization treatment. Residual f-CaO and f-MgO components in steel slag may undergo volume changes in an aqueous environment, posing stability risks if uncontrolled. However, by controlling particle size, dosage, and moisture content, these changes can be transformed into micro-expansion compensation for shrinkage in cement-stabilized materials. RAP (milled asphalt pavement aggregate) contains old aggregate and old asphalt film. The old asphalt film exhibits hydrophobicity, flexibility, and interfacial buffering properties, reducing moisture migration rates and alleviating localized shrinkage stress. However, excessive RAP dosage or inappropriate particle size selection can weaken the rigid framework and early strength of cement-stabilized materials.

[0004] Existing technologies include crack-resistant cement-stabilized crushed stone, steel slag shrinkage-compensating cement-stabilized crushed stone, RAP recycled water-stabilized base course, steel slag-RAP asphalt mixture, and steel slag-based cementitious materials, such as CN113943128A, CN109437745A, CN114905623A, CN116623487A, CN109241661B, and CN114804763B. These technologies improve material properties from the perspectives of admixture crack resistance, steel slag micro-expansion compensation, recycled aggregate utilization, mixing process control, and steel slag-based cementitious systems.

[0005] However, the aforementioned technologies typically revolve around single material substitution, single admixture crack resistance, or empirical mixing processes, lacking a unified calculation boundary for the coupling relationship between the potential expansion of steel slag, the flexible buffering of RAP old asphalt film, low cement fine powder filling, and the construction moisture content sequence.

[0006] Taking the application of RAP in cement-stabilized materials as an example, existing research shows that there is a significant contradiction between the effects of RAP dosage on drying shrinkage and durability. Jiang et al.'s study on cold-recycled mixtures of RAP and old cement-stabilized base materials showed that when the RAP dosage increased from 20% to 40%, the 90-day drying shrinkage strain decreased from 125 με to 93 με, indicating that the flexible buffering effect of RAP can reduce shrinkage. However, at the same time, the 28-day unconfined compressive strength first increased and then decreased (3.9 MPa for 20% RAP, 5.4 MPa for 30% RAP, and 4.5 MPa for 40% RAP), and the strength loss after 10 freeze-thaw cycles increased from 20.5% to 42.2%. Therefore, relying solely on RAP cannot simultaneously achieve shrinkage control, strength retention, and durability.

[0007] Similarly, the shrinkage compensation effect of steel slag in cement-stabilized materials also has boundary conditions: increasing the steel slag content can significantly reduce drying shrinkage strain, but excessively high content will increase temperature shrinkage sensitivity. In existing technologies, the potential expansion of steel slag is often regarded as a risk factor, and the old bitumen film of RAP is mostly treated as an inert filler phase. The synergistic compensation relationship between the two lacks quantitative description.

[0008] Furthermore, the application of steel slag in cement-stabilized materials also presents a duality. Studies by Wang et al. have shown that increasing the steel slag content can significantly reduce drying shrinkage strain, but excessive steel slag content increases temperature shrinkage sensitivity; under a diurnal temperature range of 20℃, the cumulative drying shrinkage strain is approximately 300–600 × 10⁻⁶. -6 The equivalent thermostatic strain is approximately 150–350 × 10⁻⁶. -6 This indicates that relying solely on the micro-expansion compensation of steel slag is insufficient to simultaneously control both drying shrinkage and thermal shrinkage, necessitating the introduction of other functional components (such as the flexible buffer of RAP old asphalt film) for synergistic regulation.

[0009] Therefore, when steel slag and RAP are used together in cement-stabilized crushed stone base courses, the key is not simply to increase the solid waste substitution rate, but to establish a detectable, calculable, and feedback-adjustable matching relationship between the expansion potential of steel slag, the softening capacity of RAP asphalt film, low cementitious filling, and staged water-content mixing. Summary of the Invention

[0010] The purpose of this invention is to provide a low-shrinkage cement-stabilized crushed stone with steel slag and RAP and its preparation method, aiming to solve the problems of expansion risk, strength fluctuation, drying shrinkage and thermal shrinkage cracking and construction segregation that easily occur when steel slag and RAP are simply used to replace natural aggregates in cement-stabilized crushed stone.

[0011] To achieve the above objectives, the technical solution of the present invention is as follows:

[0012] A steel slag RAP low-shrinkage cement-stabilized crushed stone comprises steel slag coarse aggregate, RAP aggregate, natural aggregate, cement, fine powder binder and water;

[0013] The steel slag coarse aggregate has a steel slag expansion potential descriptor S, which is calculated according to formula (1):

[0014] (1)

[0015] Among them, Es n P autn Ca n Mg n , respectively, are the normalized values ​​of 0 to 1 for the water immersion expansion rate, autoclaving pulverization rate, f-CaO content, and f-MgO content of steel slag, where w1, w2, w3, and w4 are weighting coefficients and ;

[0016] The RAP aggregate has a RAP bitumen film descriptor F, which is calculated according to formula (2):

[0017] (2)

[0018] Among them, Ar n Bc n T n P n These are the normalized values ​​of 0 to 1 for the asphalt content, surface coverage, old asphalt film thickness, and penetration of RAP, respectively, where v1, v2, v3, and v4 are weighting coefficients. ;

[0019] The compatibility parameters Ker and K of the steel slag RAP low-shrinkage cement-stabilized crushed stone are as follows: f Satisfying: Ker = S×Q s / (Q r ×F+0.1), K f = (F p +G) / C, where Q s Q is a correction term for steel slag content. r F is a correction term for RAP doping. p G represents the mass fraction of mineral powder, fly ash, slag powder, limestone powder, or other fine powder binders; G represents the converted amount of active fine steel slag; and C represents the amount of cement used.

[0020] Furthermore, Ker should be controlled between 0.65 and 1.25. f The concentration should be controlled between 0.35 and 1.20.

[0021] Furthermore, the particle size of the steel slag coarse aggregate is 4.75mm to 31.5mm, and the particle size of the RAP aggregate is 0.075mm to 9.5mm.

[0022] Furthermore, the steel slag coarse aggregate has a water immersion expansion rate of 0.62%, a pressure steam pulverization rate of 1.8%, an f-CaO content of 1.8%, an f-MgO content of 3.6%, a crushing value of 14.8%, and a water absorption rate of 1.9%.

[0023] Furthermore, the RAP aggregate has an asphalt content of 4.8%, an old asphalt film thickness of 8μm to 12μm, a surface coating rate of 78%, and a recycled old asphalt penetration of 32 (0.1mm).

[0024] Furthermore, the fine powder binder includes one or more of mineral powder, fly ash, slag powder, and limestone powder, and the activity coefficient α of the steel slag powder is 0.76.

[0025] Furthermore, by mass fraction, steel slag coarse aggregate comprises 26–39 parts, RAP aggregate comprises 16–28 parts, natural aggregate comprises 41–42 parts, cement comprises 3.2–3.6 parts, fine powder binder comprises 1.0–3.4 parts, steel slag micro powder or fine steel slag aggregate comprises 0.34–0.58 parts, and water comprises 5.5%–6.2% of the total dry mass.

[0026] A method for preparing steel slag RAP low-shrinkage cement-stabilized crushed stone includes the following steps:

[0027] S1. Add steel slag coarse aggregate and natural coarse aggregate to the mixing equipment, add water of 30% to 50% of the total water volume, pre-wet and mix for 30 to 120 seconds, and let stand for 2 to 10 minutes.

[0028] S2. Add RAP aggregate, natural fine aggregate and remaining water and mix for 30-90 seconds.

[0029] S3. Add cement and fine powder binder and mix for 60-180 seconds, controlling the total moisture content within the range of ±0.5% to 1.0% of the optimum moisture content.

[0030] Furthermore, in step S1, the pre-wetted mixture is left to stand so that the water absorption on the surface of the steel slag tends to stabilize; in step S3, the cement and fine powder binder are pre-dry mixed for 30 seconds before being added.

[0031] Furthermore, prior to step S1, a compatibility verification step is included: when Ker is less than 0.65, the proportion of steel slag coarse aggregate is increased or the proportion of RAP aggregate is decreased, and Ker is recalculated; when Ker is greater than 1.25, the proportion of steel slag coarse aggregate is decreased or the proportion of RAP aggregate is increased .... f When the value is less than 0.35, increase the amount of fine powder binder or steel slag powder and recheck K. f When K fWhen the value is greater than 1.20, reduce the amount of fine powder binder or steel slag powder and optimize the particle size of 0.075mm to 2.36mm and the total moisture content.

[0032] Compared with the prior art, the beneficial effects of the present invention are:

[0033] This invention transforms the potential expansion of steel slag from a risk factor into a controlled micro-expansion compensation factor, thereby reducing the risk of shrinkage and cracking of cement-stabilized crushed stone.

[0034] This invention quantitatively describes RAP (reclaimed asphalt film) as a flexible buffer and hydrophobic interface, thereby improving the functional utilization value of RAP in semi-rigid base courses.

[0035] This invention establishes a compatibility boundary between the expansion potential of steel slag and the softening ability of RAP asphalt film through Ker, avoiding performance fluctuations caused by simple blending.

[0036] This invention controls the fine powder binder filling of the low-cement system through Kf, which balances reducing cement usage and maintaining early strength.

[0037] This invention, through Ker / Kf matching and staged mixing, achieves lower drying shrinkage and thermal shrinkage strain at 90d and 180d ages. The strength loss rate and mass loss rate after 5 and 10 freeze-thaw cycles are lower than those of ordinary cement-stabilized crushed stone, steel slag RAP group without Ker / Kf matching, and one-time mixing group. Compared with steel slag cement-stabilized crushed stone reported in the literature, this invention reduces drying shrinkage without a significant increase in thermal shrinkage sensitivity, indicating an effective synergy between the steel slag expansion potential and the buffering capacity of the RAP asphalt film.

[0038] This invention improves construction stability by reducing the conflict between water absorption by steel slag, hydrophobicity of RAP, and encapsulation by cement slurry through phased water inclusion and mixing sequence.

[0039] This invention enables the high-value synergistic utilization of steel slag and RAP, reduces the consumption of natural aggregates and cement, and has low-carbon and solid waste resource utilization value. Attached Figure Description

[0040] Figure 1 This is a schematic diagram of the expansion potential-asphalt film matching and Ker / Kf control closed loop of the present invention.

[0041] Figure 2 This is a schematic diagram of the system composition of the steel slag RAP low-shrinkage cement stabilized crushed stone of the present invention.

[0042] Figure 3 This is a flowchart of the method for preparing steel slag RAP low-shrinkage cement-stabilized crushed stone according to the present invention.

[0043] Figure 4 This is a schematic diagram of the Ker and Kf ratio adjustment rules of the present invention. Detailed Implementation

[0044] Normalization method description

[0045] In this application, the normalization of each indicator is performed according to the following formula:

[0046] X n = (X 实测 -X min ) / (X max -X min )

[0047] In the formula, X n The normalized value; X 实测 X represents the measured value of the corresponding indicator. min and X max These are the lower and upper normalization limits of the indicator, respectively.

[0048] The normalized upper and lower limits are the engineering calibration boundaries used in this application for calculating the mix proportions of steel slag and RAP, and are not equivalent to the raw material quality acceptance limits. Raw materials should still meet the relevant specifications and stability requirements for road base materials.

[0049] When X 实测 ≤ X min At that time, X n =0; when X 实测 ≥X max At that time, X n =1.

[0050] Table 1. Normalized Upper and Lower Limits of Steel Slag and RAP Indicators

[0051] index symbol unit <![CDATA[X min ]]> <![CDATA[X max ]]> Water swelling rate <![CDATA[Es n ]]> % 0.20 0.80 Pressure pulverization rate <![CDATA[P autn ]]> % 0.50 2.50 f-CaO content <![CDATA[Ca n ]]> % 0.50 2.50 f-MgO content <![CDATA[Mg n ]]> % 1.00 4.00 Asphalt content <![CDATA[Ar n ]]> % 3.00 5.50 Surface coating rate <![CDATA[Bc n ]]> % 50.00 85.00 Old asphalt film thickness <![CDATA[T n ]]> μm 6.00 12.00 Penetration <![CDATA[P n ]]> 0.1mm 20.0 40.0

[0052] When the thickness of the old asphalt film is measured in intervals, the arithmetic mean of the intervals is used in the calculation. For example, when the thickness of the old asphalt film is 8–12 μm, T = 10 μm is taken.

[0053] The expansion potential descriptor S of steel slag is calculated using the following formula:

[0054]

[0055] The RAP bitumen film descriptor F is calculated using the following formula:

[0056]

[0057] In the formula, , , , , , , and These are the normalized values ​​of the corresponding indicators.

[0058] Table 2 Weighting coefficient values

[0059] Weight symbol Recommended range The value in this embodiment Water swelling rate weight <![CDATA[w1]]> 0.35～0.45 0.40 Pressure pulverization rate weight <![CDATA[w2]]> 0.15～0.25 0.20 f-CaO weights <![CDATA[w3]]> 0.20～0.30 0.25 f-MgO weights <![CDATA[w4]]> 0.10～0.20 0.15 Asphalt content weight <![CDATA[v1]]> 0.20～0.30 0.25 Package rate weight <![CDATA[v2]]> 0.30～0.40 0.35 Film thickness weight <![CDATA[v3]]> 0.20～0.30 0.25 Penetration weight <![CDATA[v4]]> 0.10～0.20 0.15

[0060] in:

[0061]

[0062]

[0063] The aforementioned weights are used for the relative evaluation of different steel slag and RAP combination schemes within the same project batch. Immersion swelling rate and f-CaO content have a more direct impact on the volume stability of steel slag, and therefore are assigned higher weights; RAP surface coating rate can more directly reflect the continuity and buffering capacity of the old asphalt film, and therefore is assigned a higher weight in the RAP asphalt film descriptor.

[0064] make:

[0065]

[0066] In the formula, This refers to the mass fraction of steel slag coarse aggregate. RAP aggregate mass fraction; The mass fractions of natural crushed stone and manufactured sand; This refers to the mass ratio of steel slag coarse aggregate to the total dry aggregate.

[0067] Steel slag dosage correction item Calculate using the following segmented formula:

[0068]

[0069] In the formula, This is used to correct the amplifying or weakening effect of changes in steel slag content on the expansion potential of steel slag. When the proportion of steel slag increases, Increase; when Once it reaches 1.25, it will not be increased further to avoid over-extrapolation of the empirical model.

[0070] RAP Dosage Correction Item Calculation

[0071] make:

[0072]

[0073] In the formula, RAP aggregate represents the mass ratio of RAP aggregate to the total dry aggregate.

[0074] RAP Dosage Correction Item Calculate using the following segmented formula:

[0075]

[0076] In the formula, This is a correction term for the effective utilization of RAP asphalt membrane. The RAP asphalt membrane descriptor F already reflects the quality, wrapping rate, membrane thickness, and flexibility level of the old asphalt membrane; This is further used to correct the effect of RAP doping variations on the effective buffering effect. When the RAP doping is too high, the rigid framework may be weakened, local agglomeration may occur, and the interfacial bonding may be insufficient, thus the effective buffering contribution per unit mass of RAP will gradually decrease.

[0077] The matching coefficient Ker between the expansion potential of steel slag and the buffering capacity of RAP asphalt film is calculated by the following formula:

[0078]

[0079] In the formula, 0.1 is a correction constant to avoid the denominator being zero.

[0080] steel slag powder activity coefficient Measurement:

[0081] steel slag powder activity coefficient The 28-day activity index was used for conversion. The steel slag powder was taken from the undersize material of steel slag after aging and stabilization treatment, magnetic separation, crushing and screening, and the particle size was preferably less than 0.075 mm.

[0082] A comparative test was conducted using a reference mortar and a steel slag micronized mortar. The reference mortar used cement as the binder; the steel slag micronized mortar used steel slag micronized powder to replace 30% of the cement by mass. The water-cement ratio, mortar-cement ratio, molding method, and curing conditions were kept consistent between the two mortar groups.

[0083] 28-day activity index of steel slag powder Calculate using the following formula:

[0084]

[0085] In the formula, The 28-day compressive strength of the mortar specimens incorporating steel slag micron powder; The 28-day compressive strength of the reference mortar specimen.

[0086] steel slag powder activity coefficient Determine by the following formula:

[0087]

[0088] The equivalent quantity G of active fine steel slag is calculated using the following formula:

[0089]

[0090] In the formula, This refers to the actual mass fraction of steel slag powder or active fine steel slag. The value represents the activity coefficient of steel slag powder.

[0091] Examples 1-5 of this application use steel slag powder from the same batch, with the same pretreatment process and the same particle size range. Therefore, the 28-day activity index and activity coefficient of the steel slag powder are... Maintain consistency. Different embodiments adjust the actual mass fraction of steel slag active fines. This changes the equivalent amount G of active fines in steel slag.

[0092] The steel slag powder used in Examples 1-5 is the undersize powder obtained by magnetic separation, crushing and screening of the same batch of aged and stabilized converter steel slag. The particle size range is <0.075 mm, the measured 28-day activity index (I28) is 76, and (α) is 0.76.

[0093] To further explain the calculation process of the equivalent amount G of active fine steel slag, the following is added:

[0094] Table 4. Calculation of the equivalent amount G of steel slag active fines in the examples.

[0095] Example Actual mass fractions of active fine steel slag ( ) ( ) Conversion quantity ( ) Example 1 0.50 0.76 0.38 Example 2 0.50 0.76 0.38 Example 3 0.50 0.76 0.38 Example 4 0.34 0.76 0.26 Example 5 0.58 0.76 0.44

[0096] The above-mentioned conversion quantities are used to calculate the low cement binder filling coefficient:

[0097]

[0098] In the formula, G represents the mass fractions of fly ash, mineral powder, slag powder, limestone powder, or other fine powder binders; G represents the converted amount of active fine steel slag; and C represents the amount of cement used.

[0099] A steel slag RAP low-shrinkage cement-stabilized crushed stone comprises steel slag coarse aggregate, RAP aggregate, natural aggregate, cement, fine powder binder, and water. The steel slag coarse aggregate provides structural support and controlled micro-expansion compensation; the RAP aggregate provides filling, flexible buffering of the old asphalt film, and hydrophobic moisture regulation; and the cement and fine powder binder provide low-cement-binding filling. These materials do not simply replace natural aggregate, but rather achieve this through the application of S, F, Ker, and K... f This forms a compatibility relationship that is calculable, verifiable, and adjustable with feedback.

[0100] The steel slag expansion potential descriptor S is used to characterize the potential micro-expansion compensation capacity of steel slag in aquatic environments and cement-stabilized systems. It can be obtained by normalized weighting of immersion expansion rate, autoclaving pulverization rate, f-CaO content, and f-MgO content. The RAP bitumen film descriptor F is used to characterize the flexible buffering, wrapping, and hydrophobic moisture regulation capacity of RAP old bitumen film. It can be obtained by normalized weighting of bitumen content, wrapping rate, film thickness, and penetration or flexibility index.

[0101] Steel slag coarse aggregate has a steel slag expansion potential descriptor S, where S is defined as S = w1·Es. n +w2·Paut n +w3·Ca n +w4·Mg n Calculate; where Es n Paut n Ca n and Mg n The values ​​are normalized from 0 to 1 for the immersion expansion rate of steel slag, autoclaving pulverization rate, f-CaO content, and f-MgO content, respectively. w1, w2, w3, and w4 are all weights from 0 to 1, and the sum of the weights is 1.

[0102] RAP fine aggregate or RAP composite aggregate has a RAP bituminous film descriptor F, where F is defined as F = v1·Ar n +v2·Bc n +v3·T n +v4·P n Calculate; where Ar n Bc n T n and P n These are the normalized values ​​of 0 to 1 for RAP asphalt content, surface coverage, old asphalt film thickness, and penetration or flexibility index, respectively. v1, v2, v3, and v4 are all weighted from 0 to 1, and the sum of the weights is 1.

[0103] Ker reflects the relative matching state between the expansion potential of steel slag and the buffering capacity of the old RAP asphalt film. A Ker that is too low indicates insufficient micro-expansion compensation or excessive RAP softening, while a Ker that is too high indicates that the expansion risk of steel slag exceeds the buffering capacity of RAP; f K reflects the combined effect of fine powder binder filler on strength, shrinkage, and water demand in low-cement systems. f If it is too low, increase F p Or G-reinforced fine powder cementitious filler, K f If it is too high, reduce F. p Alternatively, G can be optimized to use 0.075 mm to 2.36 mm particle sizes to reduce water demand and shrinkage risk.

[0104] A method for preparing steel slag RAP low-shrinkage cement-stabilized crushed stone includes:

[0105] Step 1: Steel slag testing and grading.

[0106] Steel slag was aged, magnetically separated, crushed, screened, and subjected to stability testing. Testing indicators included water immersion swelling rate, autoclaving pulverization rate, f-CaO content, f-MgO content, crushing value, water absorption rate, and particle size distribution. Steel slag that did not meet the stability requirements for road base courses was discarded. For steel slag that met the requirements, the expansion potential descriptor S was calculated, and it was preferentially configured in the framework phase with a thickness of 4.75 mm or more.

[0107] Step 2: RAP detection and grading.

[0108] RAP is crushed, sieved, and tested for moisture content. The RAP asphalt content, old asphalt film thickness, surface coverage, softening point, penetration, or image-recognized coverage degree are measured, and the RAP asphalt film descriptor F is calculated. RAP is preferentially used for 0.075 mm to 9.5 mm filler and buffer phases.

[0109] Step 3: Ker calculation and steel slag-RAP ratio adjustment.

[0110] Based on the steel slag expansion potential descriptor S and the steel slag content correction term Q s RAP doping correction term Q r Calculate Ker using the RAP bitumen membrane descriptor F: Ker = S × Q s / (Q r ×F+0.1). When Ker is between 0.65 and 1.25, the micro-expansion compensation of steel slag is relatively matched with the flexible buffer of RAP asphalt film; when Ker is less than 0.65, the expansion compensation is insufficient, and the proportion of stable steel slag skeleton can be increased or the proportion of high asphalt film RAP can be reduced and Ker can be recalculated; when Ker is greater than 1.25, the expansion risk is too high, and the amount of steel slag should be reduced, the buffering proportion of RAP asphalt film should be increased, or steel slag with lower expansion potential should be selected and Ker should be recalculated.

[0111] Step 4: K f Calculation and adjustment of low cementitious filler.

[0112] K is calculated based on cement dosage, fine powder content, and active fine aggregates from steel slag. f :K f =(F p +G) / C. Where F p G represents the mass fraction of mineral powder, fly ash, slag powder, limestone powder, or other fine powder binders; G is the product of the mass fraction of steel slag micro powder or fine steel slag and the activity coefficient α, where α ranges from 0 to 1; and C is the cement dosage. f The optimal range is 0.35–1.20. K f When it is below 0.35, increase F. p Or G and recheck the cement usage C; Kf When it is above 1.20, decrease F. p Or G, and optimize the 0.075 mm to 2.36 mm particle size and total moisture content.

[0113] Step 5: Moisten and mix in stages.

[0114] First, add steel slag coarse aggregate and natural coarse aggregate to the mixing equipment, and add 30%–50% of the total water for pre-wetting and mixing for 30–120 seconds. If necessary, let it stand for 2–10 minutes to allow the water absorption on the steel slag surface to stabilize. Then, add RAP, natural fine aggregate, and the remaining water for secondary mixing for 30–90 seconds. Finally, add cement, mineral powder, fly ash, slag powder, limestone powder, or steel slag powder for final mixing for 60–180 seconds, controlling the total moisture content within the optimum moisture content (OMC) ± 0.5%–1.0%. This sequence can reduce the disturbance of the optimum moisture content caused by the instantaneous water absorption of steel slag and also prevent the old RAP asphalt film from being completely coated by cement slurry too early.

[0115] Step 6: Molding, compaction, curing and verification.

[0116] The mixture is shaped, compacted, and cured, and its unconfined compressive strength, splitting tensile strength, drying shrinkage strain, thermal shrinkage strain, water immersion swelling rate, water stability, freeze-thaw stability, and water permeability or erosion resistance are tested. If the indicators do not meet the requirements, the mix proportions are adjusted according to the deviation direction of Ker and Kf.

[0117] Example 1: Determination of low shrinkage ratio.

[0118] Aged steel slag meeting stability requirements was selected as coarse aggregate (4.75 mm or larger), and screened RAP was selected as filler aggregate (0.075 mm to 9.5 mm). The water immersion expansion rate, autoclaving pulverization rate, f-CaO content, f-MgO content of the steel slag, as well as the RAP asphalt content, encapsulation rate, old asphalt film thickness, and penetration were measured to obtain S and F. Multiple mix proportions were generated according to the target base course strength grade, and Ker and Kf were calculated. If a mix proportion had a Ker of 1.40, it indicated that the expansion potential of the steel slag was relatively high compared to the buffering capacity of the RAP, and the proportion of steel slag should be reduced or low-expansion steel slag should be selected. If Ker was 0.50, it indicated insufficient micro-expansion compensation or excessive RAP softening, and the proportion of stable steel slag skeleton should be increased or the proportion of high-film RAP should be reduced. Finally, the scheme with Ker between 0.65 and 1.25 and Kf between 0.35 and 1.20 was selected for performance verification.

[0119] In a specific mix proportion, steel slag coarse aggregate is 32 parts, RAP aggregate is 22 parts, natural crushed stone and manufactured sand total 42 parts, cement is 3.5 parts, fly ash and mineral powder total 2.0 parts, and water is controlled at OMC 5.8%. After testing and normalization, taking S=0.70, F=0.72, Qs=1.10, Qr=1.02, Ker=0.70×1.10 / (1.02×0.72+0.1)≈0.92; taking Fp=2.0, G=0.38, C=3.5, Kf=(2.0+0.38) / 3.5≈0.68. This mix proportion was used for performance verification in Example 1.

[0120] Table 5 Comparison of Example 1 and Comparative Example Data 1

[0121] Group Ker Kf 180d drying shrinkage strain / με <![CDATA[Average temperature shrinkage coefficient / 10 -6 ·°C -1 > Thermal shrinkage strain / με, ΔT=30℃ Strength loss after 5 freeze-thaw cycles / % 5 times quality loss / % Example 1 0.92 0.68 292 8.3 249 8.5 1.6 Comparative Example 1 — — 368 8.9 267 12.5 2.2 Comparative Example 2 1.42 0.30 360 10.4 312 16.8 2.8 Comparative Example 3 0.92 0.68 335 9.2 276 12.0 2.3

[0122] Example 1, due to its Ker / Kf matching, the buffering effect of the old RAP asphalt film, and staged mixing, exhibited lower drying shrinkage strain than the ordinary water-stabilized and unmatched steel slag RAP groups. Comparative Example 2, with its higher Ker and lower Kf, showed a mismatch between the steel slag expansion potential and the RAP buffering capacity, resulting in greater thermal shrinkage and freeze-thaw losses. Comparative Example 3, although having a satisfactory Ker / Kf, suffered from insufficient interfacial coating and moisture content control due to one-time mixing, thus exhibiting weaker drying shrinkage and freeze-thaw performance than Example 1. Steel slag can reduce drying shrinkage but may increase temperature sensitivity; the RAP dosage affects drying shrinkage, thermal shrinkage, and freeze-thaw performance—trends consistent with published literature conclusions.

[0123] Staged mixing: In this embodiment, the proportions of each component per cubic meter of mixture are as follows: 640 kg / m³ of aged and stabilized steel slag coarse aggregate, 440 kg / m³ of RAP aggregate, 840 kg / m³ of natural crushed stone and manufactured sand, 70 kg / m³ of cement, 20 kg / m³ of fly ash, 20 kg / m³ of mineral powder, and 118 kg / m³ of water. The steel slag coarse aggregate, RAP aggregate, natural crushed stone and manufactured sand, cement, fly ash, mineral powder, and water are all prepared separately.

[0124] The cement used was PO 42.5 ordinary Portland cement; the steel slag coarse aggregate consisted of aged, magnetically separated, crushed, and screened steel slag with a particle size of 4.75 mm to 31.5 mm, a water immersion swelling rate of 0.62%, a autoclaving pulverization rate of 1.8%, an f-CaO content of 1.8%, an f-MgO content of 3.6%, a crushing value of 14.8%, a water absorption rate of 1.9%, and an apparent density of 3.20 g / cm³. 3The RAP aggregate consists of crushed and screened RAP with a particle size of 0.075 mm to 9.5 mm, an old asphalt content of 4.8%, an old asphalt film surface coating rate of 78%, an old asphalt film thickness of 8 μm to 12 μm, a recycled old asphalt penetration of 32 (0.1 mm), and a moisture content of 1.2%. The natural crushed stone and manufactured sand are limestone crushed stone and manufactured sand, with a crushing value of 16.5%, a water absorption rate of 0.7%, and a mud content of 0.4%. The fly ash is Class II fly ash, the mineral powder is S95 grade mineral powder, and the water is tap water.

[0125] Based on the steel slag test data, the steel slag expansion potential descriptor S=0.70, and based on the RAP test data, the RAP bitumen film descriptor F=0.72; the steel slag content correction term Qs=1.10, and the RAP content correction term Qr=1.02, then Ker=S×Qs / (Qr×F+0.1)=0.70×1.10 / (1.02×0.72+0.1)=0.92. Taking the total fly ash and mineral powder Fp=2.0 parts by mass, the converted amount of steel slag active fines G=0.38 parts by mass, and the cement content C=3.5 parts by mass, then Kf=(Fp+G) / C=(2.0+0.38) / 3.5=0.68. Both Ker and Kf are within the preferred range defined in this application.

[0126] First, steel slag coarse aggregate and natural coarse aggregate are added to a forced mixer, along with water equal to 45% of the total volume, approximately 53 kg / m³. 3 The first pre-wetting mixing was carried out for 90 seconds. After pre-wetting mixing, the mixture was allowed to stand for 5 minutes to stabilize the water film on the surface of the steel slag coarse aggregate and the natural coarse aggregate, and to make the water absorption state of the steel slag basically balanced, thus obtaining pre-wetted coarse aggregate mixture A.

[0127] The mixture consists of RAP aggregate, natural fine aggregate, and the remaining 55% water, approximately 65 kg / m³. 3 Add the pre-wetted coarse aggregate mixture A and mix for the second time for 60 seconds to form a uniformly dispersed filling and buffer structure with the RAP old asphalt film, steel slag skeleton and natural fine aggregate, to obtain wetted aggregate mixture B.

[0128] Cement, fly ash, and mineral powder were pre-dry mixed for 30 seconds to obtain cemented fine powder mixture C; then cemented fine powder mixture C was added to wet aggregate mixture B for final mixing, with a final mixing time of 120 seconds, and the moisture content of the discharged mixture was controlled to be the optimum moisture content of 5.8% ± 0.3%, to obtain steel slag RAP low-shrinkage cement-stabilized crushed stone mixture.

[0129] The resulting mixture was molded using heavy compaction or vibratory compaction methods, with the compaction degree of the specimens controlled at 98%. Unconfined compressive strength specimens were φ150 mm × 150 mm cylindrical specimens; splitting tensile strength specimens were φ150 mm × 150 mm cylindrical specimens; and drying shrinkage specimens were 100 mm × 100 mm × 400 mm beam-type specimens. After molding, the specimens were cured in a standard curing room at 20±2℃ and a relative humidity of not less than 95% until the specified age. The 7-day unconfined compressive strength specimens were cured for 6 days and then immersed in water for 24 hours before testing. The 28-day splitting tensile strength, drying shrinkage strain, thermal shrinkage strain, water immersion expansion rate, and freeze-thaw stability specimens were tested according to the "Test Procedure for Inorganic Binder Stabilized Materials in Highway Engineering" JTG 3441—2024.

[0130] To determine the reasonable control boundaries of Ker and Kf, single-factor gradient tests of Ker and Kf were conducted under the same steel slag, RAP, natural aggregate and cement system.

[0131] In the Ker gradient test, Kf was kept relatively stable at 0.65–0.70. Only the steel slag expansion potential descriptor S, the RAP bitumen film descriptor F, and the steel slag / RAP content were adjusted to make Ker approximately 0.50, 0.65, 0.80, 0.95, 1.10, 1.25, and 1.30, respectively.

[0132] In the Kf gradient test, Ker was kept relatively stable at 0.90–0.95. Only cement C, fine powder Fp, and steel slag active fine material G were adjusted so that Kf was approximately 0.30, 0.35, 0.50, 0.68, 0.90, 1.20, and 1.30, respectively.

[0133] The criteria for determining the control boundaries of Ker and Kf are: 7-day strength meets the requirements of the base layer; 28-day splitting strength is not less than 95% of that of the ordinary water-stabilized control group; drying shrinkage strain is more than 10% lower than that of the control group; water immersion expansion rate does not exceed 0.30% to 0.35%; and strength loss after 10 freeze-thaw cycles does not exceed 25%.

[0134] Experimental results show that when Ker < 0.65, the softening and hydrophobic buffering effects of RAP are relatively too strong, the controlled micro-expansion compensation of steel slag is insufficient, and the early strength and splitting strength of the material decrease; when Ker > 1.25, the expansion potential of steel slag exceeds the buffering capacity of the old RAP asphalt film, and the immersion expansion rate and freeze-thaw loss increase significantly. Therefore, the control range of Ker is determined to be 0.65–1.25.

[0135] When Kf < 0.35, the fine powder cementitious filling in the low-cement system is insufficient, resulting in high porosity and freeze-thaw losses. When Kf > 1.20, there is an excess of fine powder and active powder, leading to increased water demand, drying shrinkage strain, and temperature shrinkage sensitivity. Therefore, the control range for Kf is determined to be 0.35–1.20.

[0136] Example 2: Ker lower endpoint 0.65

[0137] Table 6 Data from Example 2

[0138] project numerical values Steel slag coarse aggregate 26 copies RAP aggregate 28 copies Natural crushed stone and manufactured sand 42 copies cement 3.5 copies fly ash + mineral powder 2.0 copies OMC 5.9% S 0.62 F 0.82 Qs 0.92 Qr 0.95 Ker 0.62×0.92 / (0.95×0.82+0.1)=0.65 Kf 0.68

[0139] This group is at the lower end of Ker. The test results show that the strength just meets the requirements of the base course, the drying shrinkage is lower than that of ordinary water-stabilized base course, but the tensile reserve is not as good as the preferred range of Ker=0.90~1.00.

[0140] Example 3: Ker upper endpoint 1.25

[0141] Table 7 Data from Example 3

[0142] project numerical values Steel slag coarse aggregate 39 copies RAP aggregate 16 copies Natural crushed stone and manufactured sand 41 copies cement 3.5 copies fly ash + mineral powder 2.0 copies OMC 5.8% S 0.78 F 0.60 Qs 1.18 Qr 1.06 Ker 0.78×1.18 / (1.06×0.60+0.1)=1.25 Kf 0.68

[0143] This group is at the upper end of Ker. The strength still meets the requirements, but the water immersion swelling rate and freeze-thaw loss are close to the control limit; further increasing to Ker=1.30 will significantly increase the swelling and freeze-thaw loss, so it is no longer recommended.

[0144] Keeping Kf≈0.68, the main focus of the investigation is on the steel slag / RAP matching relationship.

[0145] Table 8. Performance variation of Ker from 0.50 to 1.30

[0146] Group Ker 7d unconfined compressive strength / MPa 28d splitting strength / MPa 90d drying shrinkage strain / με Water swelling rate / % Strength loss after 10 freeze-thaw cycles / % Weight loss after 10 freeze-thaw cycles / % K0.50 0.50 3.7 0.55 292 0.07 27.5 5.8 K0.65 0.65 4.2 0.64 268 0.12 21.8 4.5 K0.80 0.80 4.5 0.68 255 0.15 17.6 3.8 K0.95 0.95 4.7 0.72 246 0.18 14.5 3.1 K1.10 1.10 4.8 0.71 252 0.23 15.8 3.5 K1.25 1.25 4.5 0.67 265 0.31 22.6 4.9 K1.30 1.30 4.2 0.61 285 0.39 29.8 6.7

[0147] As can be seen from the table:

[0148] When Ker is below 0.65, the main problems are insufficient strength and tensile reserve; when Ker is above 1.25, the main problems are increased expansion rate and freeze-thaw loss.

[0149] Therefore, 0.65 to 1.25 can be considered a reasonable control range.

[0150] Example 4: Kf lower endpoint 0.35

[0151] Table 9 Data from Example 4

[0152] project numerical values Steel slag coarse aggregate 32 copies RAP aggregate 22 copies Natural crushed stone and manufactured sand 42 copies Cement C 3.6 copies Fine powder Fp 1.00 copies Conversion of active fine steel slag to G 0.26 copies Ker 0.92 Kf (1.00+0.26) / 3.6=0.35

[0153] The fine powder binder in this group is at the minimum acceptable boundary. The strength is still acceptable, but the pore filling is insufficient, and the freeze-thaw strength loss and mass loss are relatively high.

[0154] Example 5: Upper endpoint of Kf 1.20

[0155] Table 10 Data from Example 5

[0156] project numerical values Steel slag coarse aggregate 32 copies RAP aggregate 22 copies Natural crushed stone and manufactured sand 42 copies Cement C 3.2 copies Fine powder Fp 3.40 copies Conversion of active fine steel slag to G 0.44 copies Ker 0.92 Kf (3.40+0.44) / 3.2=1.20

[0157] This group represents the upper end of Kf. The fine powder binder provides sufficient filling and the strength meets requirements, but the drying shrinkage strain and optimum moisture content begin to increase. Further increasing Kf to 1.30 results in a significant increase in shrinkage deformation, therefore this method is not recommended.

[0158] Keep Ker≈0.92, and mainly adjust the proportions of cement, fine powder and steel slag active fine materials.

[0159] Table 11 Performance variation of Kf from 0.30 to 1.30

[0160] Group Kf 7d unconfined compressive strength / MPa 28d splitting strength / MPa 90d drying shrinkage strain / με Permeability coefficient / m·s⁻¹ Strength loss after 10 freeze-thaw cycles / % Weight loss after 10 freeze-thaw cycles / % F0.30 0.30 3.8 0.57 285 <![CDATA[1.8×10 -6 ]]> 28.6 6.2 F0.35 0.35 4.1 0.62 270 <![CDATA[1.2×10 -6 ]]> 22.4 4.8 F0.50 0.50 4.4 0.66 258 <![CDATA[9.5×10 -7 ]]> 17.5 3.9 F0.68 0.68 4.6 0.70 250 <![CDATA[7.8×10 -7 ]]> 14.8 3.2 F0.90 0.90 4.7 0.72 256 <![CDATA[8.2×10 -7 ]]> 15.6 3.4 F1.20 1.20 4.5 0.68 278 <![CDATA[1.1×10 -6 ]]> 19.2 4.3 F1.30 1.30 4.2 0.62 318 <![CDATA[1.5×10 -6 ]]> 25.7 5.9

[0161] As can be seen from the table:

[0162] When Kf is below 0.35, the main problem is insufficient cementitious filling in the low-cement system, resulting in decreased strength, water permeability, and freeze-thaw stability; when Kf is above 1.20, the main problem is excessive fine powder leading to increased water demand and increased drying shrinkage strain.

[0163] Therefore, Kf = 0.35 to 1.20 is a reasonable control range, and Kf = 0.60 to 0.90 can be considered a better range.

[0164] To determine the control boundaries of Ker and Kf, the applicant conducted gradient tests using the same batch of steel slag, RAP, natural aggregate, and cement materials. However, due to differences in materials and processes, S and F fluctuated to some extent. In the Ker gradient test, Kf was kept approximately 0.68, and the steel slag content, RAP content, steel slag expansion potential descriptor S, and RAP bitumen film descriptor F were adjusted to make Ker values ​​of 0.50, 0.65, 0.80, 0.95, 1.10, 1.25, and 1.30, respectively. The experimental results show that when Ker=0.50, the 7-day unconfined compressive strength is only 3.7 MPa, the 28-day splitting strength is 0.55 MPa, and the strength loss after 10 freeze-thaw cycles reaches 27.5%. When Ker=0.65, the 7-day strength increases to 4.2 MPa, the 28-day splitting strength is 0.64 MPa, and the strength loss after 10 freeze-thaw cycles decreases to 21.8%, reaching an acceptable level. When Ker is increased to 1.25, the material strength still meets the requirements, but the water immersion swelling rate reaches 0.31%, and the strength loss after 10 freeze-thaw cycles is 22.6%, close to the upper limit of control. When Ker is further increased to 1.30, the water immersion swelling rate rises to 0.39%, and the strength loss after 10 freeze-thaw cycles rises to 29.8%, which is not advisable. Therefore, the control range of Ker is determined to be 0.65–1.25.

[0165] In the Kf gradient test, Ker≈0.92 was maintained, and the cement dosage C, fine powder binder Fp, and the equivalent amount of steel slag active fine aggregate G were adjusted to make Kf 0.30, 0.35, 0.50, 0.68, 0.90, 1.20, and 1.30, respectively. The test results show that when Kf=0.30, the 7-day strength is 3.8 MPa, and the permeability coefficient is 1.8×10⁻⁶. -6 The strength loss after 10 freeze-thaw cycles was 28.6% at a speed of m / s, indicating insufficient cementation. At Kf=0.35, both strength and freeze-thaw stability reached acceptable levels. At Kf=1.20, the 90-day drying shrinkage strain was 278 με, still within the acceptable range. At Kf=1.30, the 90-day drying shrinkage strain increased to 318 με, and the freeze-thaw strength loss increased to 25.7%, indicating that excessive fine powder led to increased water demand and shrinkage risk. Therefore, the Kf control range was determined to be 0.35–1.20.

[0166] Comparative Example 1: Ordinary Cement Stabilized Crushed Stone Base Material

[0167] Comparative Example 1 uses ordinary cement-stabilized crushed stone base course material, without adding steel slag coarse aggregate and RAP aggregate, and without calculating Ker and Kf. The proportions of each component, calculated per cubic meter of mixture, are: natural crushed stone 1160 kg / m³ 3 760 kg / m³ of manufactured sand 3 Cement 70 kg / m 3 20 kg / m³ of fly ash3 Mineral powder 20 kg / m 3 Water 112 kg / m 3 The overall gradation of natural crushed stone and manufactured sand is basically consistent with the aggregate gradation range in Example 1, so as to ensure that Comparative Example 1 and Example 1 have similar skeleton gradation conditions.

[0168] The cement, fly ash, mineral powder, and water are the same as in Example 1; the natural crushed stone is limestone crushed stone with a maximum particle size of no more than 31.5 mm, a crushing value of 16.5%, a water absorption rate of 0.7%, and a mud content of 0.4%; the fineness modulus of the manufactured sand is 2.6, and the mud content is less than 1.0%.

[0169] In preparation, natural crushed stone and manufactured sand were first added to a forced mixer, along with 50% of the total water volume, and mixed for 60 seconds. Then, cement, fly ash, mineral powder, and the remaining water were added, and mixing continued for 120 seconds to obtain a common cement-stabilized crushed stone mixture. Subsequently, it was molded and tested according to the same compaction work, compaction degree, specimen size, curing conditions, and testing methods as in Example 1. This comparative example was used to evaluate the shrinkage and freeze-thaw performance of common cement-stabilized crushed stone without steel slag micro-expansion compensation and RAP old asphalt film buffering.

[0170] Comparative Example 2: Steel slag RAP material but without Ker / Kf matching

[0171] Comparative Example 2 uses steel slag RAP cement-stabilized crushed stone material, but the matching and adjustment of steel slag, RAP, cement, and fine powder binder are not performed according to the control ranges of Ker and Kf. The proportions of each component are calculated per cubic meter of mixture as follows: 800 kg / m³ of steel slag coarse aggregate. 3 RAP aggregate 280 kg / m 3 840 kg / m³ of natural crushed stone and manufactured sand 3 Cement 70 kg / m 3 fly ash 7 kg / m³ 3 7 kg / m³ of mineral powder 3 Water 118 kg / m 3 .

[0172] The sources of steel slag coarse aggregate, RAP aggregate, natural crushed stone and manufactured sand, cement, fly ash, mineral powder, and water are the same as in Example 1. Based on the raw material testing data, the steel slag expansion potential descriptor S=0.82, the RAP bitumen film descriptor F=0.58, the steel slag content correction term Qs=1.192, and the RAP content correction term Qr=1.073. Therefore, Ker=0.82×1.192 / (1.073×0.58+0.1)=1.35, exceeding the preferred control upper limit of 1.25 in this application. Taking the total fly ash and mineral powder Fp=0.70 parts by mass, the converted amount of active fine aggregate G=0.35 parts by mass, and the cement content C=3.5 parts by mass, then Kf=(0.70+0.35) / 3.5=0.30, which is lower than the preferred control lower limit of 0.35 in this application.

[0173] The preparation process still uses the same staged mixing method as in Example 1: First, steel slag coarse aggregate and natural coarse aggregate are added to a forced mixer, along with 45% of the total water volume, and pre-wetted and mixed for 90 seconds, then allowed to stand for 5 minutes; then, RAP aggregate, natural fine aggregate, and the remaining 55% of the water are added, and mixing continues for 60 seconds; finally, cement, fly ash, and mineral powder are added, and final mixing is performed for 120 seconds, controlling the output moisture content to be 5.8% ± 0.3%. Subsequently, it is compacted, cured, and tested using the same methods as in Example 1. This comparative example is used to demonstrate that when only steel slag and RAP are added without Ker / Kf matching, problems such as excessively high steel slag expansion potential, insufficient RAP buffering, and insufficient low-cement fine powder cementitious filling may occur.

[0174] Comparative Example 3: One-time mixing of steel slag RAP material

[0175] Comparative Example 3 used the exact same raw materials and proportions as Example 1, namely 640 kg / m³ of steel slag coarse aggregate. 3 RAP aggregate 440 kg / m 3 840 kg / m³ of natural crushed stone and manufactured sand 3 Cement 70 kg / m 3 20 kg / m³ of fly ash 3 Mineral powder 20 kg / m 3 Water 118 kg / m 3 Its Ker=0.92 and Kf=0.68 are the same as those in Example 1.

[0176] Unlike Example 1, Comparative Example 3 does not employ a staged mixing process involving pre-wetting of steel slag coarse aggregate, secondary addition of RAP, and final mixing of cement fine powder. Instead, it uses a one-time mixing process. Specifically, steel slag coarse aggregate, RAP aggregate, natural crushed stone, manufactured sand, cement, fly ash, mineral powder, and all mixing water are added to a forced mixer at once and continuously mixed for 180 seconds to obtain a steel slag RAP cement-stabilized crushed stone mixture.

[0177] After discharge, the material was molded and tested according to the same compaction work, compaction degree, specimen size, curing conditions, and testing methods as in Example 1. This comparative example is used to demonstrate that even if Ker and Kf are within the preferred range, if a staged moisture content and staged mixing process are not adopted, inconsistencies may still occur between the instantaneous water absorption of steel slag, the hydrophobicity of the old RAP asphalt film, and the cement paste coating, leading to a decrease in mixture homogeneity, interfacial bonding, shrinkage control, and freeze-thaw stability.

[0178] Specimens were prepared and tested according to Example 1 and Comparative Examples 1-3 as described above, and the results are shown in the table below.

[0179] Table 12 Comparison of Example 1 and Comparative Example Data 2

[0180] Group Ker Kf 7d unconfined compressive strength / MPa 28d splitting strength / MPa 90d drying shrinkage strain / με Water swelling rate / % Strength loss after 10 freeze-thaw cycles / % Weight loss after 10 freeze-thaw cycles / % Example 1 0.92 0.68 4.6 0.70 250 0.18 14.8 3.2 Comparative Example 1 — — 4.8 0.68 310 0.05 21.0 4.9 Comparative Example 2 1.44 0.30 4.1 0.59 295 0.42 28.5 6.5 Comparative Example 3 0.92 0.68 4.2 0.62 280 0.22 20.5 5.2

[0181] The results in the table show that Example 1 meets the requirements of the base material in terms of 7-day unconfined compressive strength, while its 90-day drying shrinkage strain is lower than that of Comparative Example 1, which uses ordinary cement-stabilized crushed stone. Compared with Comparative Example 2, which does not use Ker / Kf matching, Example 1 has significantly reduced water immersion swelling rate and freeze-thaw loss. Compared with Comparative Example 3, which is mixed in one go, Example 1 has higher 7-day strength, 28-day splitting strength, and lower drying shrinkage strain and freeze-thaw loss under the same Ker and Kf conditions. This indicates that this application can simultaneously improve the shrinkage performance, volume stability, and durability of steel slag RAP cement-stabilized crushed stone through Ker / Kf matching and staged mixing.

[0182] First, add steel slag coarse aggregate and natural coarse aggregate to the mixing equipment, and add 30%–50% of the total water for pre-wetting and mixing for 30–120 seconds. If necessary, let it stand for 2–10 minutes to allow the water absorption on the steel slag surface to stabilize. Then, add RAP, natural fine aggregate, and the remaining water for secondary mixing for 30–90 seconds. Finally, add cement, mineral powder, or steel slag powder for final mixing for 60–180 seconds, controlling the total moisture content within the optimum moisture content (OMC) ± 0.5%–1.0%. This sequence can reduce the disturbance of the optimum moisture content caused by the instantaneous water absorption of steel slag and also prevent the old RAP asphalt film from being completely coated by cement slurry too early.

[0183] The above-mentioned phased water content and mixing steps are consistent with steps 5 and Example 1; when one or more of fly ash, mineral powder, slag powder, limestone powder or steel slag powder are used as fine powder binders, they should be added in the final mixing stage, and the discharge moisture content and the uniformity of the mixture should be used as construction control indicators.

[0184] Performance verification.

[0185] Under the same compaction work, moisture content control, and curing conditions, the exemplary verification results are shown in Table 13. The conclusions are: In Example 1, Ker and Kf are both within the control range, the strength meets the requirements, and shrinkage is controlled; Comparative Example 1 is a benchmark group for ordinary cement-stabilized crushed stone, and Ker and Kf calculations are not applicable. It is used to evaluate the shrinkage and freeze-thaw performance without steel slag micro-expansion compensation and RAP old asphalt film buffering; Comparative Example 2 has a higher Ker and a lower Kf, increasing both expansion and cementation filling risks; Comparative Example 3 has the same mixing parameters but an unfavorable mixing sequence, and insufficient interface and moisture content control.

[0186] Table 13 Preferred Performance Control

[0187] index Preferred control requirements Technical role 7-day unconfined compressive strength Meets the base course design requirements of the corresponding road grade Ensure the early load-bearing capacity of low-cement systems 28-day splitting strength Not less than 95% of the control group of ordinary cement-stabilized crushed stone, preferably not less than the control group. Ensure that the RAP retains its tensile strength reserve after softening. Drying strain Compared to ordinary cement-stabilized crushed stone, it reduces costs by more than 10%, with an optimal reduction of 15% to 35%. This demonstrates the low shrinkage effect of controlled micro-expansion of steel slag and the flexible buffering effect of RAP. Water swelling rate Meets the stability requirements of road base materials To avoid volume instability caused by unstabilized steel slag Natural aggregate replacement rate 30%～70% Improve the synergistic resource utilization rate of steel slag and RAP Cement reduction rate Reduced by 5% to 20% compared to conventional methods. Reduced carbon emissions and driving forces of drying and thermo-shrinkage

[0188] During implementation, the following parameters were recorded: steel slag aging time, water immersion swelling rate, f-CaO, f-MgO, crushing value, water absorption rate, and particle size distribution; RAP asphalt content, old asphalt film thickness or wrapping rate, penetration, softening point, moisture content, and sieve composition; and Ker, Kf, optimum moisture content, maximum dry density, and compaction curves for each mix proportion. The 7-day and 28-day unconfined compressive strength, 28-day splitting tensile strength, drying shrinkage strain, thermal shrinkage strain, water immersion swelling rate, freeze-thaw stability, water stability, erosion resistance, as well as the crack rate, deflection, and core integrity of the field test section were used as closed-loop feedback indicators.

[0189] Based on the above-described preferred embodiments of the present invention, and through the foregoing description, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification.

Claims

1. A steel slag RAP low-shrinkage cement-stabilized crushed stone, characterized in that, It includes steel slag coarse aggregate, RAP aggregate, natural aggregate, cement, fine powder binder and water; The steel slag coarse aggregate has a steel slag expansion potential descriptor S, which is calculated according to formula (1): (1) Among them, Es n P autn Ca n Mg n , respectively, are the normalized values ​​of 0 to 1 for the water immersion expansion rate, autoclaving pulverization rate, f-CaO content, and f-MgO content of steel slag, where w1, w2, w3, and w4 are weighting coefficients and ; The RAP aggregate has a RAP bitumen film descriptor F, which is calculated according to formula (2): (2) Among them, Ar n Bc n T n P n These are the normalized values ​​of 0 to 1 for the asphalt content, surface coverage, old asphalt film thickness, and penetration of RAP, respectively, where v1, v2, v3, and v4 are weighting coefficients. ; The compatibility parameters Ker and K of the steel slag RAP low-shrinkage cement-stabilized crushed stone are as follows: f Satisfying: Ker = S×Q s / (Q r ×F+0.1), K f = (F p +G) / C, where Q s Q is a correction term for steel slag content. r F is a correction term for RAP doping. p G represents the mass fraction of mineral powder, fly ash, slag powder, limestone powder, or other fine powder binders; G represents the converted amount of active fine steel slag; and C represents the amount of cement used. Furthermore, Ker should be controlled between 0.65 and 1.

25. f The concentration should be controlled between 0.35 and 1.

20.

2. The steel slag RAP low-shrinkage cement-stabilized crushed stone according to claim 1, characterized in that, The coarse steel slag aggregate has a particle size of 4.75 mm to 31.5 mm, and the RAP aggregate has a particle size of 0.075 mm to 9.5 mm.

3. The steel slag RAP low-shrinkage cement-stabilized crushed stone according to claim 1, characterized in that, The steel slag coarse aggregate has a water immersion expansion rate of 0.62%, a pressure steam pulverization rate of 1.8%, an f-CaO content of 1.8%, an f-MgO content of 3.6%, a crushing value of 14.8%, and a water absorption rate of 1.9%.

4. The steel slag RAP low-shrinkage cement-stabilized crushed stone according to claim 1, characterized in that, The RAP aggregate has an asphalt content of 4.8%, an old asphalt film thickness of 8μm to 12μm, a surface coating rate of 78%, and a recycled old asphalt penetration of 32 (0.1mm).

5. The steel slag RAP low-shrinkage cement-stabilized crushed stone according to claim 1, characterized in that, The fine powder binder includes one or more of mineral powder, fly ash, slag powder, and limestone powder, and the activity coefficient α of the steel slag powder is 0.

76.

6. The steel slag RAP low-shrinkage cement-stabilized crushed stone according to claim 1, characterized in that, By mass percentage, steel slag coarse aggregate is 26–39 parts, RAP aggregate is 16–28 parts, natural aggregate is 41–42 parts, cement is 3.2–3.6 parts, fine powder binder is 1.0–3.4 parts, steel slag micro powder or fine steel slag aggregate is 0.34–0.58 parts, and water accounts for 5.5%–6.2% of the total dry mass.

7. A method for preparing steel slag RAP low-shrinkage cement-stabilized crushed stone as described in any one of claims 1 to 6, characterized in that, Includes the following steps: S1. Add steel slag coarse aggregate and natural coarse aggregate to the mixing equipment, add water of 30% to 50% of the total water volume, pre-wet and mix for 30 to 120 seconds, and let stand for 2 to 10 minutes. S2. Add RAP aggregate, natural fine aggregate and remaining water and mix for 30-90 seconds. S3. Add cement and fine powder binder and mix for 60-180 seconds, controlling the total moisture content within the range of ±0.5% to 1.0% of the optimum moisture content.

8. The preparation method according to claim 7, characterized in that, In step S1, the pre-wetted mixture is left to stand so that the surface of the steel slag can absorb water and become stable; in step S3, the cement and fine powder binder are pre-dry mixed for 30 seconds before being added.

9. The preparation method according to claim 7, characterized in that, Before step S1, a compatibility verification step is also included: when Ker is less than 0.65, the proportion of steel slag coarse aggregate is increased or the proportion of RAP aggregate is decreased and Ker is recalculated; when Ker is greater than 1.25, the proportion of steel slag coarse aggregate is decreased or the proportion of RAP aggregate is increased and Ker is recalculated; when Ker is less than 0.65, the proportion of steel slag coarse aggregate is increased or the proportion of RAP aggregate is decreased and Ker is recalculated; when Ker is greater than 1.25, the proportion of steel slag coarse aggregate is decreased or the proportion of RAP aggregate is increased and Ker is recalculated. f When the value is less than 0.35, increase the amount of fine powder binder or steel slag powder and recheck K. f When K f When the value is greater than 1.20, reduce the amount of fine powder binder or steel slag powder and optimize the particle size of 0.075mm to 2.36mm and the total moisture content.

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