Introduction

Production, refining, storage, and transportation of petroleum generally produce oil-contaminated soil (labeled as OCS)1,2. OCS usually comprises of water, oil, and solids such as soil or sand1,3,4. Treatment of OCS is of great concern due to its hazardous nature to the ecological environment and human health1,2,3,4,5. Various methods have been suggested by the researchers to deal with it which include chemical cleaning2,6,7,8,9, solvent extraction10,11,12,13,14, centrifugation15,16, flotation and electrical flotation17,18,19,20, pyrolysis21,22,23, freeze/thawing24, sonication25,26, supercritical treatment27,28, microwave radiation29,30,31, bio-treatment technology32, and a combination of different processes33,34,35,36. Although these methods are effective in removal of oil from soil particles, the de-oiling sludge obtained from these methods are difficult to manage with no clear methods to dispose it. The solidification/stabilization (S/S) method can utilize de-oiling sludge as a road construction material to reduce its environmental burden. Lin et al.37 used Portland cement to solidify OCS, and found that the S/S method was effective for immobilization of heavy metals without affecting the stability of hydrocarbons. Jebeli et al.38 studied the S/S efficiency of total petroleum hydrocarbons contaminated soil in the waste of a used oil treatment plant by employing quick lime and modified clay. They investigated the mobility and leaching of petroleum hydrocarbons, effect of modified clay on the hydration process of quick lime, along with possible reuse of the waste, as well as estimation of the cost of S/S based on the optimum mixture.

In the S/S method, solidifying agents are used to immobilize the contaminants in the sludge via chemical or mechanical action during the solidifying process37,38,39,40,41,42,43,44,45. Ordinary Portland cement and magnesium oxychloride cement (MOC) are commonly used as curing agents37,38,39,40,41,42,43,44,45. The engineering and mechanical properties, such as fast curing, air hardening, and resistance to abrasion and fire are better for MOC compared to ordinary Portland cement41,42,43,45,46,47. Recently, urban river sludge and residual sludge from sewage disposal plants were solidified using MOC consisted of MgO and MgCl2 and the effects of several factors on unconfined compressive strength like MOC dosage, molar ratio of MgO to MgCl2, mass ratio of liquid to solid, and curing time were studied41,42,48. However, MOC has not been reported so far for OCS. Herein, we tried to find out the evolution law of unconfined compressive strength (RC) and water resistance of solidified oil-contaminated soil products (marked as MS) during the solidification of OCS by MOC for evaluating the possibility of reusing the contaminated soil in civil construction such as road brick.

In this study, we employed MOC to solidify OCS and analyzed the RC and water resistance of the obtained MS. In order to obtain the appropriate solidifying parameters, effects of several factors such as liquid-to-solid mass ratio (RW/S), OCS dosage (DS), and oil content (Wo) in OCS on RC were investigated. Furthermore, optimization of RC was also carried out by employing Na2SiO3 aqueous solution (Dn) of appropriate concentration and fly ash dosage (Df). To investigate the influences of Wo, Dn, and Df on water resistance, water resistance tests of several representative samples were carried out for 14 days in water solution having different pH values at 25.0 ℃. The water resistance in acidic, neutral, and basic aqueous solutions was evaluated based on the coefficient (Kf) of water resistance. To analyze the intrinsic mechanisms, microstructure and crystal composition of the MS were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD).

Experiments

Materials

OCS used in this study was polluted by crude oil from Jilin oil field of China. Composition of the OCS was 10.49 wt% oil (Wo), 12.32 wt% water (a), and 77.19 wt% soil (WS) analyzed by the mass–loss method2,10. The TOC value (TOCS) of the dried OCS as shown in Table 1 was measured using a Multi N/C3100 instrument (Analytik Jena AG, Germany). To determine the specific surface area and particle size of calcined OCS, a N2 adsorption − desorption method Quadrasorb SI-MP system (Quantachrome Instruments, USA) and a Zetasizer Nano S90 Mastersizer (Malvern Instruments Co., Ltd., UK) were used. The obtained values of specific surface area and particle size were 16.61 m2·g− 1 and 497.9 nm respectively. The de-oiling sludge with an oil content of 6.11 wt% (marked as OCS2) obtained though deoiling OCS1 by chemical detergent and almost oil-free soil (marked as OCS3) were used for the solidification test. The composition of the OCS samples is shown in Table 1.

Table 1 Composition of oil-contaminated soil.
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Analytical grade MgO and MgCl2 were purchased from Bidepharm Medical Technology Co. Ltd. (Shanghai, China). Analytical grade Na2SiO3 (modulus of 2.43) was purchased from Shanghai Rhawn Chemical Technology Co. Ltd. (Shanghai, China). Industrial-grade fly ash which mainly contained SiO2, Al2O3, Fe2O3, and CaO was purchased from Henan Gongyi Longze Water Purification Material Co. Ltd. (Gongyi, China)40,41. Analytical grade NaOH and HCl were purchased from Tianjin Damao Chemical Technology Co. Ltd. (Tianjin, China). The deionized water used in this study was obtained from a Hitech-Kflow water purification system (Hitech Co., Ltd., Beijing, China).

Solidification test of oil-contaminated soil

Homogeneous MOC fluid was obtained by adding a given amount of MgO to the MgCl2 aqueous solution, which was followed by thoroughly mixing. The molar ratio of MgO to MgCl2 was maintained as 5.0 for this MOC fluid 5.0 because this ratio provided a higher RC41. The liquid-to-solid ratio (RW/S), based on the calculation using Eq. (1), was varied in the range of 0.4–0.9. This is due to the fact that when RW/S was < 0.4, the mixing resistance was large which results in unevenly mixed mud, and when RW/S>0.9, the high fluidity of the mixing mud caused water loss from the mold crack, affecting the hydration reaction. Subsequently, OCS was added to the MOC fluid at a designed DS (calculated using Eq. (2)) varying in the range of 30.0–70.0% to maximize the rate of utilization of OCS. A given amount of fly ash was further added into the MOC-OCS slurry for optimization the compressive strength. As our previous report40,41, increasing the amount of fly ash, does not enhance the RC in a linear manner. 5% fly ash was observed to be more appropriate dosage. Thus, Df was varied in the range of 5.0-15.0%. Meanwhile, deionized water was replaced with Na2SiO3 aqueous solution with Dn of 1.0-5.0%. As is known, larger the Dn, higher is the value of RC, but in this work it was hard to stir the MOC-OCS slurry evenly when Dn was more than 5.0%. The values of Dn and Df were calculated using Eqs. (3) and (4), respectively. The mixture was prepared using a YD90S–8/4 cement mortar mixer (Wuxi Construction Engineering Test Equipment Co., Ltd., Wuxi, China). Ratios of the material are listed in Table 2.

Table 2 Material composition of MS.
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$$R_{{W/S}} = \frac{{m_{S} \times a + m_{w} }}{{m_{S} \times (1 - a) + m_{{MOC}} + m_{f} }}$$
(1)
$$D_{S} = \frac{{m_{S} }}{{m_{{TS}} }}$$
(2)
$$D_{n} = \frac{{m_{n} }}{{m_{S} \times a + m_{w} + m_{n} }} \times 100\%$$
(3)
$$D_{f} = \frac{{m_{f} }}{{m_{{MOC}} }} \times 100\%$$
(4)

Here ms, mw, mf, and mn correspond to the mass (g) of oil-contaminated soil, adscititious water, fly ash, and Na2SiO3, respectively; mMOC is the total mass (g) of MgO and MgCl2; and mTS is the total mass (g) of solids including oil-contaminated soil, fly ash, and MOC.

After shaking on a shaking table for 10 min to remove air bubbles, all the obtained mixture slurries were injected into a cubic plexiglass mold (40 mm × 40 mm× 40 mm), and cured at room temperature for 24–72 h. After the formation of solidified blocks, the cubic plexiglass mold was removed and the demolded solidified blocks were sealed with plastic cling film and then placed under natural maintenance conditions at approximately 25 ℃ for 3–28 days40,41. A YAW–1000A electro–hydraulic servo pressure testing machine controlled by a computer (Jinan Dong Fang Test Instrument Co., Ltd., Jinan, China) was used to measure the uniaxial pressure of a specimen for 3–28 days at a speed of 2400 ± 200 N/s until it was destroyed. The maximum load was FC, and Eq. (5) was used to calculate RC.

$$R_{C} = F_{C} /A$$
(5)

Here FC is the maximum load (newton) at failure, A is the pressure area (mm2), and RC is the uniaxial pressure (MPa) of the specimen.

Water resistance test of solidified blocks

After 28-day curing, the MS8, MS10, MS14, and MS15 samples were immersed in water having different pH values (2.0–11.0) for 7–14 days. The pH value of the water was monitored every 24 h using a pHS-3 C meter (INESA Scientific Instrument Co., Ltd., Shanghai, China) and HCl or NaOH was added to maintain the pH. Subsequently, the unconfined compression strength of the MS was denoted as RAC. Water resistance was evaluated by using the coefficient (Kf) of water resistance which was calculated as the ratio of RAC to RC using Eq. (6). Higher the value of Kf, better the water resistance.

$${K_{\text{f}}}=\frac{{{R_{{\text{AC}}}}}}{{{R_C}}}$$
(6)

All the above-described tests were conducted in triplicate, and average of three measurements was taken as the final RC or RAC values.

Characterization

After the measurement of RC, fragmented MS8, MS10, MS11, MS14 and MS15 samples were dried in an oven at 105 ℃ for 16 h and then crushed to powder using a DM500 multifunctional pulverizer (Nanjing Dongmai Technology Instrument Co., Ltd., Nanjing, China). The powdered sample was lapped again using agate mortar and then characterized by SEM using a JSM-7610 F Plus (Jeol, Japan) to observe the morphology of solidified sludge samples and XRD using a D8 Advance diffractometer (Germany Bruker Co., Ltd., Delaware, USA) with Cu Kα radiation (λ = 1.54184 Å) operating at 40 kV and 40 mA to analyze the crystal structure.

Besides, for carrying out the leaching experiments of organics, all the four types of dried MS samples were added (10.00 g each) into 100.0 mL deionized water in a glass bottle with a lid. The bottle was vibrated at a speed of 100 times/min for 8.0 h after placing in a horizontal shaking bath. The lixivium obtained after static settlement for 16.0 h was analyzed for the TOC value (TOCL) using a Multi N/C3100 instrument (Analytik Jena AG, Germany). Hypothesis, organics in 10.00 g dried MS from OCS migrated mostly to 100.0 mL deionized water used in leaching experiment.

Results and discussion

Unconfined compressive strength analysis of MS

The effect of R W/S on R C of MS

Figure 1 shows the images of MS produced at different RW/S for 50.0% DS. During the course of this study, no frosting phenomenon was observed, nor any water droplets appeared on the surface of specimens. Volume of the MS was not influenced by the RW/S.

Fig. 1
figure 1

Image of MS produced at different RW/S when DS was 50.0%.

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Fig. 2
figure 2

Relative curves of RC vs. curing time for MS produced using OCS with Wo of 10.49 wt% at different RW/S and DS = 50.0%.

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The relative curves of RC vs. curing time for MS using OCS with Wo of 10.49 wt% are presented in Fig. 2 for at different RW/S and DS = 50.0%. Increasing RW/S from 0.4 to 0.9 resulted in decreasing RC, which is consistent with the literature report41. The maximum RC of 21.30 MPa obtained at RW/S = 0.4 was close to the maximum RC (20.90 MPa) of MOC solidified surplus sludge obtained at RW/S = 0.90 and DS = 50.0%41. It is because some unstable phase 5 could be converted to Mg(OH)2 or soluble ions when the water dosage is exceeded, and thus resulting in reduction of strength. Besides, for a given RW/S, increasing curing time resulted in an increase of RC which almost reached an equilibrium value after 21 days of curation.

The effects of D S and W o on R C of MS

Figure 3 shows the images of MS with different DS produced at a fixed RW/S = 0.4. In this study, also, even after 28 days curing no frosting phenomenon was observed and no water droplets appeared on specimens’ surfaces. Furthermore, no shrinkage or volume expansion was observed, with no cracks on the surface which was smooth.

Fig. 3
figure 3

The images of MS with different DS prepared at RW/S=0.4.

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Fig. 4
figure 4

(a) Effect of DS on RC of MS5-MS9 prepared using OCS1 at RW/S = 0.4; (b) effect of Wo on RC of MS8, MS10, and MS11 prepared using OCS1, OCS2, and OCS3 at DS = 40.0% and RW/S = 0.4.

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Figure 4a shows the effect of DS on RC of MS5-MS9 prepared using OCS1 (Wo = 10.49 wt%) at RW/S = 0.4. Increasing the DS from 30.0 to 70.0% resulted in an initial increase of RC followed by a decrease, which is consistent with earlier reports38,41,47,49. The maximum RC of 24.20 MPa which is higher than that of MOC solidified surplus sludge was obtained at DS = 40.0%41. Increasing the petroleum sludge dosage from 0 to 40% reduced the the RC of 28-day curing for ordinary Portland cement solidified petroleum sludge from 22 MPa to 0 MPa47. The minimum RC of MS6 with DS = 70.0% was even higher than the highest RC (3.08 MPa) of Portland cement and modified bentonite solidified cresol-contaminated soil50.

The possible reason is that a small quantity of OCS used in the solidification process enhanced the strength of MS by playing the role of a sand aggregate. However, an excessive amount of OCS would reduce the MOC percentage in the MS, thus resulting in a reduction in strength due to the decreased output of crystal phase 5. Figure 4b shows the effect of Wo on RC of MS8, MS10, and MS11 prepared using OCS1, OCS2, and OCS3, respectively, at DS = 40.0% and RW/S = 0.4. The results demonstrate that with increasing Wo, the value of RC decreased. Similar result indicating the positive correlation between solidification effect of organic contaminated soil with the consumption of organic matter has been reported: higher the consumption, better is the solidification effect51. Compared to MS8, the maximum RC of MS11 (free oil) was improved by approximately 35% to reach a value of 33.10 MPa. The possible reason could be the formation of an oil film on the water surface, which impedes the hydration reaction of MOC and thus affects the formation of phase 5.

Fig. 5
figure 5

SEM images of MS8, MS10, and MS11 samples.

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Fig. 6
figure 6

XRD spectra of MS samples.

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To understand the microscopic mechanisms, SEM images and XRD spectra of MS8, MS10, and MS11 samples were obtained which are in Figs. 5 and 6, respectively, and indicate the formation of phase 5. SEM images indicated a rod-like structure seemingly grew in length as Wo decreased. As reported earlier41,42,48, needle-like crystal phase 3 and rod-like crystal phase 5 generated during the MOC hydration process are responsible for the strength of MS. This indicates that the microscopic structure of MS is affected by oil and was also supported by the XRD spectra. The XRD spectra shown in Fig. 6 indicates the presence of diffraction peaks corresponding to phase 5. Moreover, compared to MS8, the intensities of the peaks at 2θ = 11.6° and 2θ = 46.0° corresponding to phase 5 in the XRD spectra of MS10 and MS11 increased as Wo decreased. Meanwhile, as DS decreased, the intensity of the peak at 2θ = 46.0° corresponding to phase 5 for MS6, MS8 and MS9 increased, indicating increased yield of phase 5 due to the increase in MOC dosage.

The effects of D n and D f on R C of MS

Figure 7 shows the images of MS prepared under different Dn and Df at RW/S = 0.4 and DS = 40.0% using OCS2. After being cured for 28 days, no frosting phenomenon was observed, no water droplets appeared on the surfaces, there was neither shrinkage nor expansion in volume, and the surface was smooth without any crack.

Fig. 7
figure 7

The images of MS12-MS17 in sequence produced under different Dn and Df.

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Fig. 8
figure 8

Effects of Dn (a) and Df (b) on RC of MS12-MS14 and MS15-MS17 at RW/S = 0.4 and DS = 40.0%. MS10 without fly ash and Na2SiO3 used as blank sample prepared under same RW/S and DS.

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Increasing Dn from 0.0 to 5.0% resulted in an increase in RC of MS10, MS12, MS13 and MS14 as shown in Fig. 8a and all the obtained RC values were higher than that of MS10 (28.50 MPa). This indicates RC can be improved via addition of Na2SiO3. With an approximate increase of 30% compared to MS10, the maximum RC of 37.10 MPa was obtained at Dn = 5.0%. This result is again consistent with that of the previous reports40,41. Some SiO2 produced during the MOC hydration process due to the alkaline solution of Na2SiO3 filled the pores of MS structure. Compared to MS8, the diffraction peaks of SiO2 at 2θ = 42.8° and 2θ = 60.0° in the XRD spectrum (PDF#46-1045) of MS14 were strengthened which indicated an increase in SiO2 yield. Besides, Mg3(Si2 − xO5)(OH)4−4x formed due to the reaction of Mg2 + with silicate ion and OH− was observed in the XRD spectrum of MS14 with a diffraction peak at 2θ = 12.0° (PDF#10–0381), which is very similar to the peak of phase 5 at 2θ = 11.6° shown in Fig. 6, thus, seemingly strengthening the diffraction peak of phase5 in Fig. 6. Compared to MS10 (see Fig. 1S), the SEM image of MS14 shown in Fig. 9 displays a relatively dense structure composed of a large number of rod-like structures of phase 5 and some particles. These are the possible reasons for the improvement in RC after the addition of Na2SiO3 to MS.

Fig. 9
figure 9

SEM images of MS14 and MS15 samples.

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Figure 8b shows the effect Df on RC of MS15, MS16 and MS17 at RW/S = 0.4 and DS = 40.0%. It was found that increasing Df from 0.0 to 5.0% resulted in an increase in RC of 28-day curing and then further increase in Df from 5.0 to 15.0% led to a decrease in the value of 28-day curing RC. Compared to MS10, the maximum RC increased by ~ 14% to reach 32.60 MPa at Df=5.0%. And the maximum RC is higher than that of MOC–residual sludge solidified blocks (28.40 MPa), silidified oily sludge using ordinary Portland cement, fly ash, silica fume and phosphogypsum (5.89 Mpa), and modified clay and lime solidified petroleum hydrocarbon contaminated soil (< 1 Mpa)38,41,49. Increasing the Df to 15.0% resulted in decrease of RC of 28-day curing to 29.40 MPa, which was close to that of MS10. This is caused by the decrease of MOC dosage with increasing Df41,52,53. Fly ash is rich in SiO2 and Al2O3. During the hydration of MOC, Mg(OH)2 can react with SiO2 and Al2O3 to produce magnesium-aluminum silicate hydrate, which fills the pores of the MS structure with fine fly ash, resulting in improved compactness and strength of the MS41,52. The magnesium-aluminum silicate hydrate was observed in the XRD spectrum of MS15 at 2θ ≈ 12.6° as shown in Fig. 6, enhancing the peak of phase 5 at 2θ = 11.6°. Beyond this, the cross-linked structure of MS15 was formed as observed in the SEM image shown in Fig. 9, and the structure was more compact compared to that of MS10 (see Fig. 1S). These may be the reasons responsible for the improvement in RC after the addition of fly ash.

Water resistance analysis

Figure 10 shows the relationships of RAC (a) and Kf (b) versus pH values for MS8, MS10, MS14 and MS15 samples when immersed for 7–14 days in water with different pH values. Except for that of MS14, all other samples showed the best water resistance was achieved at pH = 9.0. Compared to the immersion time of 14 days, RAC and Kf were higher after 7 days of immersion, suggesting that the water resistance decreased as the immersion time increased. Similar trends have been reported earlier41,42,48. For the samples MS8, MS10, and MS15, increasing the pH value increased from 2.5 to 9.0 resulted in gradual increase in RAC and Kf, followed by a decrease when the pH value was further increased from 9.0 to 11.0. For MS14, the values of RAC and Kf increased gradually with an increase of pH from 2.5 to 7.0, with the values being near identical at pH = 7.0 and pH = 9.0. Further increase in pH from 9.0 to 11.0 resulted in the corresponding values to decrease. The water resistance of MS8 and MS10 in a water environment with the pH ranging of 6.3 to 11.0 was greater than that in an acidic water environment. The maximum Kf values of MS8 and MS10 after being immersed in water for 14 days at pH = 9.0 were 81.40% and 89.47%, respectively, with the maximum RAC values being 19.70 MPa and 25.50 MPa, respectively. This result indicates that reducing the Wo resulted in enhanced water resistance. On a comparative scale, the maximum Kf and the maximum RAC of MS10 are higher than those of MOC solidified urban river sludge (the maximum Kf was about 70% and the RAC was about 2 MPa) as well as blast furnace slag-modified MOC solidified waste sludge (the maximum Kf was about 85% and the RAC was about 1.72 MPa) after immersion in water for 14 days42,48. Three possible reasons behind strength deterioration after water immersion can be: (1) reinforced repulsive force among solid particles in water, (2) damaged chemical interface binding and (3) dissolution of phase 548.

After 14 days immersion in water having pH = 9.0, the maximum Kf values of MS14 and MS15 were 67.65% and 84.66%, while the maximum RAC values were 25.10 MPa and 27.60 MPa respectively. The maximum Kf values of MS14 and MS15 were lower compared with MS10, but the maximum RAC values of MS14 and MS10 were similar while the maximum RAC of MS15 had higher value compared to both. In neutral solution of water, the RAC of MS15 was 28.80 MPa and 26.90 MPa after 7 days and 14 days immersion, respectively (see Fig. 2Sa), which were the highest among the four samples. Furthermore, after 7 days immersion, Kf values were all higher than 80% except MS14, and only MS10 and MS 15 had Kf values more than 80% when immersed for 14 days (see Fig. 2Sb).

The above results indicate that water resistance is hardly improved by the addition of Na2SiO3 or fly ash, rather sometimes reduced by it. Compared to the MOC solidified residual sludge41, in neutral (pH = 7.0) or alkaline (pH = 9.0) water, the water resistance of MS is relatively lower, though is relatively higher in acidic water.

Fig. 10
figure 10

The relationships of RAC and Kf vs. pH values of MS8, MS10, MS14, and MS15 samples immersing in different water with different pH values for 7–14 days.

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Leaching tests of organics in MS

In order to understand the stability of organics in MS, leaching experiments of MS8, MS10, MS14, and MS15 were carried out at 25 ℃. The results can be seen in Table 3. As seen from the Table, the TOCL of MS8 was 16.365 mg∙L− 1, while the TOCL values of MS10, MS14 and MS15 were 4.643 mg∙L− 1, 3.946 mg∙L− 1 and 4.703 mg∙L− 1, respectively. Compared to the value of TOC0, MOC can be seen to prevent the entry of more than 90% of oil into the lixivium. It is evident that addition of Na2SiO3 can prevent the escape of organic matter from MS, while addition of fly ash has no obvious effect on the migration of organics in MS. Therefore, the immobilization of organics in MS may take place mainly through (i) solidifying mechanism of MOC hydration and (ii) attraction of Na2SiO3 aqueous solution via adhesion. As reported, for cement-solidified oily sludge, the minimum of TOCL was about 17.5 mg∙L− 1 for a low mass ratio (1:3) of oily sludge (the hydrocarbons content was 0.4−2.1%) to cement with a better RC of about 40 MPa37. Jebeli et al.38 used modified clay and lime to solidify the contaminated soil having a concentration of 211,895 mg∙kg− 1 for total petroleum hydrocarbon (TPH), and found 0.13 mg∙L− 1 (ratio of liquid to solid is 20:1) to be the maximum leached concentration of TPH. Considering the different solid to liquid ratios used during leaching tests, this leached concentration of TPH is lower than half of TOCL (liquid to solid = 10:1) shown in Table 3, but the corresponding value of RC (< 1 MPa) is much lower than that of obtained for MS (24.20 MPa-37.10 MPa)38.

Table 3 TOC values of organics in leaching experiment test at 25 ℃.
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Conclusions

In this process of solidifying the OCS by MOC, RW/S, DS, and Wo had significant effect on the RC of the produced MS. The optimal curing appropriates of RW/S, Wo, and DS values were found to be 0.4, free oil, and 40.0%, respectively, with the obtained RC value being 33.10 MPa under this condition. Replacing water with a Na2SiO3 aqueous solution resulted in an increase of RC of the 28-day curing with consequent increase of Dn from 0.0 to 5.0%. Increasing Df from 0.0 to 15.0%, resulted in an initial increase of RC followed by subsequent decrease. The optimal values of Dn and Df were 5.0% for both and addition of Na2SiO3 or fly ash enhanced the value of RC. The water resistances of MS8, MS10, MS14 and MS15 were better in the pH range of 7.0–9.0 compared to the pH range of 2.5-6.0. Maximum water resistance was obtained after soaking in water with pH of 9.0 for 7–14 days. And among the four samples, the water resistance of MS14 was the lowest which indicated that addition of Na2SiO3 impaired RC. However, adding fly ash hardly affected water resistance. We observed the water resistance only for 14 days and was found to decrease over time. Longer immersion time of 30–60 days or higher working temperature of 30–40 ℃ may result in obvious decrease. This work provides theoretical data and guidance for the treatment or reuse of OCS. In the future, long-term resistance for freeze-thaw cycles, long-term water resistance, corrosion to rebar and consumption of organics in solidified blocks, leaching of contaminants, and so on should be looked into for widening the applicability of this process.