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Article

Study on the Durability of High-Content Oil Shale Concrete

by
Yunyi Wang
1,
Cong Zeng
1,*,
Yingshuang Wang
2,
Mingyi Tang
3 and
Mengqiu Gao
3
1
School of Civil Engineering and Architecture, Northeast Electric Power University, Jilin City 132012, China
2
Power China Jilin Electric Power Engineering Co., Ltd., Changchun 130022, China
3
Northeast Electric Power Design Institute Co., Ltd., China Power Engineering Consulting Group, Changchun 130021, China
*
Author to whom correspondence should be addressed.
Buildings 2024, 14(8), 2547; https://doi.org/10.3390/buildings14082547
Submission received: 21 June 2024 / Revised: 2 August 2024 / Accepted: 14 August 2024 / Published: 19 August 2024
(This article belongs to the Special Issue Sustainable and Low-Carbon Building Materials and Structures)
Browse Figures
Versions Notes

Abstract

:
This study evaluated the potential and environmental benefits of using oil shale residue as a replacement for fine aggregate in concrete through a series of experiments. Initially, the crushing value test confirmed the oil shale residue’s value at 16.7%, meeting the load-bearing standards for fine aggregates, thus proving its viability as a complete substitute. Further, the oil shale residue was treated with a 60 mg/L concentration of Tween 80 and other surfactants for oil removal. The treated concrete specimens demonstrated excellent compressive performance and a dense internal structure. Building on this, the mechanical properties of the oil shale residue concrete were explored across different replacement ratios (from 40% to 100%), revealing an increase in compressive strength with higher replacement ratios. In the durability tests, compared to the JZ group, the oil shale residue concrete modified with desulfurization gypsum exhibited a 0.03% reduction in mass loss rate and a 10.13% reduction in relative moving elasticity modulus loss rate, particularly noticeable after 175 freeze–thaw cycles where specimens B1 to B4 exhibited no significant damage, highlighting its remarkable durability. Overall analysis indicated that using oil-removed oil shale residue as a substitute for fine aggregate in concrete, combined with desulfurization gypsum modification, not only enhances concrete performance but also significantly reduces the consumption of natural aggregates and environmental pollution, promoting resource utilization and sustainable development.

1. Introduction

As modernization steadily progresses and the economy rapidly grows, the societal demand for energy also increasingly intensifies, exacerbating the energy supply dilemma [1,2]. The development of unconventional oil and gas resources, such as oil shale, has alleviated the supply pressure of limited non-renewable resources, such as oil and natural gas, offering significant social and economic benefits. Improper disposal of residual oil shale ash post-refinement poses severe environmental hazards [3]. The primary methods for handling oil shale residue involve natural piling and landfilling (Wangqing County, Jilin Province, see Figure 1), both of which not only consume extensive land resources but also pollute groundwater and farmland, severely impacting soil quality and health [4]. Globally, the extensive daily consumption and use of concrete for infrastructure and other purposes could be offset by maximizing the incorporation of oil shale residue into concrete. This approach could effectively address the challenges of disposing of oil shale residue, facilitating its resource utilization, and generating considerable economic and social benefits, thus promoting sustainable and green development in the oil shale industry [5,6,7,8].
The development and utilization pathways of oil shale residue are primarily manifested in its application as a construction material. In the field of construction materials, it is mainly used for the production of cement or concrete, the manufacturing of blocks, and as a component of road materials. Mohammad et al. [9] conducted a series of experimental studies on the substitution of cement with oil shale residue and reported that, when the substitution rate of oil shale residue reached 10%, the compressive strength of the concrete peaked. Moreover, the compressive strength of the concrete did not decrease significantly when the substitution rate was maintained below 30%. Arina et al. [10] substituted a portion of cement with oil shale waste to prepare soft soil subbases using a specific mix ratio of waste and cement. The experimental results indicated that stabilized soft soil subbases fabricated by waste and cement possess good bearing capacities and meet the demands of road construction. Thus, they reduce construction costs and address the challenges associated with oil shale waste disposal. Liu et al. [11] used oil shale slag as an auxiliary cementitious material and reported that, when the oil shale slag was calcined at 600 °C and substituted for cement at a replacement rate of 10%, the compressive strength of the composite material increased by 8% (after curing for 3 days) and 11% (after curing for 28 days). Wei et al. [12] studied the feasibility of using fly ash, oil shale ash, and modified powdery clay as subbase materials. Their research revealed that a mixture ratio of oil shale ash–fly ash–modified powdery clay of 40:20:40 yielded the highest California bearing ratio. Additionally, the modified soil leachate did not pollute surface water or groundwater, which indicates that the use of oil shale ash in subbase materials is viable.
The chemical composition of desulfurization gypsum is CaSO4·2H2O. It is widely applied in construction materials. Shihua [13], in a study on the application of a desulfurized gypsum slag powder in concrete, demonstrated that an appropriate amount of desulfurized gypsum could enhance the early activity, compressive strength, and durability of the slag powder. Xin et al. [14] analyzed the feasibility of substituting cement with desulfurization gypsum and reported that concrete modified with desulfurization gypsum achieved a compressive strength of 44 MPa and flexural strength of 9.5 MPa. Its application in concrete construction could also reduce the number of processes.
This study systematically processed oil shale residue through crushing and de-oiling to explore its potential as a substitute for fine aggregate in concrete. Experimental results demonstrated that the treated oil shale residue could fully replace fine aggregate. Further, the study examined the effects of modifying 100% oil shale residue concrete with desulfurization gypsum, conducting freeze–thaw cycle tests and sulfate erosion tests to assess the enhancement of concrete durability by the gypsum. Additionally, the microstructural changes in the concrete were observed using a scanning electron microscope (SEM).

2. Experimental Design

2.1. Oil Shale Residue Particle-Crushing Value Test

Oil shale residue is processed through crushing and screening before undergoing a crushing value test aimed at determining the feasibility of substituting fine aggregate in concrete with oil shale residue and verifying whether the particle hardness of the oil shale residue meets the standard requirements. The fine aggregate crushing value is measured as the ability of crushed oil shale residue to bear load, determined by a prescribed method [15]. After the crushing value test, the ratio of the mass of aggregates smaller than a specified size to the mass of fine aggregates before crushing is expressed as a percentage. The crushing value test serves as an indicator of the mechanical properties of oil shale residue.

2.1.1. Materials Tests

The oil shale residue used in this experiment was provided by the Longteng Group in Wangqing County, Jilin Province. The contents of the various components are shown in Table 1.

2.1.2. Oil Shale Residue Crushing Value Test Method

The fine aggregate crushing value is an indirect method of assessing its strength, conducted according to the ‘Test Methods of Aggregate for Highway Engineering’ (JTG E42-2005) standard [16].
Steps for the fine aggregate crushing value test using the measurement device are as follows:
(1) Place the mold containing the sample onto the press. Ensure that the press head is leveled and centered on the pressure plate.
(2) Start the press and apply the load uniformly at a rate of 500 N/s, pressurizing up to 25 kN. Maintain the pressure for 5 s, and then unload at the same rate. See Figure 2 for the loading device.
(3) Remove the mold from the press, extract the sample, and sieve it through the lower-limit sieve of the particle size group (e.g., sieve the 4.75 mm~2.36 mm size group through a 2.36 mm standard sieve). Weigh the retained mass (m1) and the passed mass (m2) of the sample, accurate to 1 g. Refer to Figure 3 for the sieving and weighing process.
(4) Calculate the crushing value indices for each group according to Formula (1), accurate to 1%.
Y i = m 1 m 1 + m 2 × 100 %
In the formula, Yi represents the crushing value index (%) of the fine aggregate of the i particle size; m1 is the mass of the sieve residue (g); m2 is the mass of the material that passes through the sieve (g).

2.1.3. Analysis of Crushing Value Test Results for Oil Shale Residue

Conduct tests on the compressive strength of crushed oil shale residue; results are shown in Table 2.
Referencing the ‘Test Methods of Aggregate for Highway Engineering’ (JTG E42-2005) [16], the crushing value index for each particle size group is represented by the average of three test results, accurate to 1%. The highest single particle size crushing value index is taken as the crushing index for the fine aggregate. Thus, the crushing value index for oil shale residue is 16.7%. The standard for the crushing value index of manufactured sand refers to ‘Sand for construction’ (GB/T 14684-2022) [17], as shown in Table 3.
After undergoing the bearing capacity test, the crushing value index of the crushed fine aggregate of oil shale residue was found to be 16.7%, which is below the specified standard requirements and meets the compressive strength requirements for fine aggregates. The test results demonstrate that after crushing and screening, oil shale residue can replace fine aggregate in the preparation of high-content oil shale residue concrete.

2.2. Oil Shale Residue De-Oiling Experiment

2.2.1. Particle De-Oiling Agent

During the de-oiling cleaning process, oil-containing solid waste comes into contact with a biosurfactant agent. The oil phase and the solid phase interact with the surfactant, which reduces the wetting contact angle between the oil phase and solid particles, decreasing the wetting angle between hydrocarbons and mineral particles. This reduction in interfacial tension allows the oil phase to separate from the solid particles and then dissolve in the de-oiling agent solution [18]. This experiment used sophorolipid, Tween 80 biosurfactant, and water for de-oiling cleaning. Surfactants have dual characteristics; they are both lipophilic and hydrophilic. Surfactants also tend to concentrate on the solution surface to cause adsorption, thereby reducing the interfacial tension between the oil phase and the solid phase. As the concentration of the surfactant in the solution continuously increases, its adsorption at the interface also increases, thereby reducing surface tension.

2.2.2. Particle De-Oiling Test

De-oiling treatments on oil shale residues (2.36 mm–4.75 mm) were conducted using sophorolipid, Tween 80, and water. In the experiments, the concentrations of sophorolipid and Tween 80 were varied at 20 mg/L, 40 mg/L, and 60 mg/L. During the experiment, the temperature of the reagent solution was maintained at 40 °C, and each sample set was left to sit for 30 min, with a ratio of oil shale residue to de-oiling solution maintained at 1:5. The specific steps were as follows: Initially, crushed oil shale residue was poured into a plastic container. Then, pre-mixed de-oiling reagent was added to the container to ensure the oil shale residue was completely submerged. After the oil shale residue had been left in the container for half an hour, it was turned over to enhance the contact between the oil shale surface and the de-oiling agent, thereby effectively removing any residual oil from the surface. De-oiling, cleaning, and airing are shown in Figure 4.

2.3. Oil Shale Residue De-Oiling Specimen Preparation and Performance Test

2.3.1. Properties of Other Materials Used

(1) Cement
The cement used in this experiment was P·O42.5 ordinary Portland cement produced by a company in Jilin City; the chloride ion concentration is 0.01%; the specific surface area was 395 m²/kg; the cement’s consistency water requirement is 27%; the water retention rate was 87%; the initial setting time was 169 min; and the final setting time was 252 min. The performance indices are shown in Table 4.
(2) Fine aggregate
We utilized an ordinary river sand (Jilin) with a medium sand gradation (2.35–4.75 mm 15.6%, 1.18 mm 32.3%, 300–600 μm, 43.4%, 150 μm, 8.7%). The properties of the fine aggregates must satisfy the requirements of GB/T 14684-2022 [17].
(3) Coarse aggregate
We employed crushed stone from a quarry in Jilin with particle sizes of 5–10 and 10–20 mm. The crushed stone complied with the basic requirements for construction pebbles and crushed stone specified in ‘Pebble and crushed stone for construction’ GB/T 14685-2022 [19].
(4) Water-reducing agents
A polycarboxylate-based water-reducing agent was used. The polycarboxylate water reducer dosage was 1.1 kg/m3, achieving a water reduction rate of up to 30% at 1.95 kg/m3.
(5) Water
The water used in this experiment was tap water from the laboratory.
(6) Gypsum
The gypsum used in this experiment was a desulfurization gypsum (CaSO4·2H2O) (Jilin).

2.3.2. Preparation of Oil Shale Residue Concrete Specimens

To explore the effects of using de-oiled oil shale residue to replace fine aggregate and the impact of adding desulfurization gypsum modification on oil shale residue concrete. De-oiled oil shale particles were used to replace 40% of the fine aggregate, and standard blocks sized 150 mm × 150 mm × 150 mm were prepared, numbered A1 to A8. Additionally, a set of untreated oil shale waste concrete blocks was made as a control group, numbered JZ. Moreover, completely replacing the fine aggregate with oil shale residue, standard blocks of the same size were made, and the gypsum content was set to decrease, starting from 0.5%, with blocks sequentially numbered from B1 to B5. Specific mix proportions are detailed in Table 5.
Begin by measuring the coarse aggregate, fine aggregate, cement, oil shale residue, water, gypsum, and water-reducing agent according to the mix design for oil shale residue concrete [20]. Once all materials and tools are prepared, add an appropriate amount of water to the compulsory concrete mixer for pre-wetting to minimize moisture loss during mixing. Start the mixer, and after it runs smoothly, sequentially add coarse aggregate, fine aggregate, and oil shale residue, mixing for 2 to 3 min to ensure thorough mixing. Next, add cement and continue mixing for another 2 to 3 min. Subsequently, pour in half of the water and water-reducing agent mixture, mix for 1 to 2 min, then add the remaining water and water-reducing agent mixture until the mix is uniform. Pour the mixed concrete into standard cubic molds and perform two rounds of vibration on a vibrating table as follows: vibrate once after filling half, then fill the mold completely and vibrate again until the concrete surface is smooth and free of air bubbles. Finally, smooth the surface of the specimen and mark it. Cure under natural conditions for 28 days before conducting various tests.

2.4. Experimental Methods

2.4.1. Compressive Strength

The test method follows the ‘Standard for Test Method of Physical and Mechanical Properties’(GB/T 50081-2019) [21]. The soundness tests are conducted using a 200-ton microcomputer-controlled hydraulic press in the experimental structure hall. After curing the specimens under standard conditions for 28 days, pressure is applied in the vertical direction of casting. The load rate is set at 0.5 MPa/s, and the failure load is recorded. Results are averaged from three specimens per group.

2.4.2. Freeze–Thaw Cycle

Concrete specimens measuring 100 mm × 100 mm × 400 mm, cured for 28 days, are tested in a freeze–thaw cycle box. After every 25 cycles, the lateral fundamental frequency of the specimens is tested, and both mass loss and relative dynamic modulus are calculated to evaluate the freeze resistance of the concrete [22]. The test concludes when the concrete mass loss exceeds 5% or when the relative dynamic modulus falls below 80% of its initial value. The maximum number of freeze–thaw cycles and results are recorded, averaging three specimens per group.

2.4.3. Sulfate Attack Test

The sulfate attack test is conducted after the standard curing period of 28 days, using a wet–dry cycling method [23]. First, specimens are immersed in a 5% NaSO4 solution for 16 h, followed by drying at 80 °C for 6 h in a forced-air drying oven, then cooled for 2 h. This cycle, lasting 24 h, is repeated. After 30, 60, 90, 120, and 150 cycles, the apparent damage, mass loss, and compressive strength of the specimens are recorded. Results are averaged from three specimens per group.

3. Test Results Analysis

3.1. Compressive Strength Results

3.1.1. Analysis of Compressive Strength Results after Oil Removal

The results of the uniaxial compressive strength test, as shown in Figure 5, indicate that replacing fine aggregate with oil shale residue is feasible. Group A1, serving as the control group, used oil shale waste slag without any oil removal treatment, and its strength was essentially the same as that of Group A2, which used water for oil removal. From the perspective of concrete block strength, the effectiveness of using water to remove oil from oil shale residue is not satisfactory. Groups A3, A4, and A5, which treated the oil shale residue with Tween 80 surfactant, showed increasing concrete block strength with higher concentrations of the oil removal agent, demonstrating that Tween 80 is effective for removing oil from oil shale residue. Groups A6, A7, and A8, treated with sophorolipid biosurfactant, showed less strength improvement compared to Groups A3–A5 as the concentration increased, but still a slight improvement over the control group.
In summary, the analysis of concrete block strength shows that treating oil shale residue with appropriate oil removal agents can enhance the strength of the resulting concrete, although the impact on the strength of ordinary concrete is minimal. Therefore, using 60 mg/L of Tween 80 surfactant to remove oil from oil shale residue can enhance the strength of the resulting oil shale residue concrete.

3.1.2. Analysis of Compressive Strength with Varying Oil Shale Residue Replacement Rates

The Figure 6 presents the compressive strength of concrete specimens with various replacement levels of oil shale residue. As the substitution rate of oil shale residue increases, the 28-day strength of the specimens shows little change. When the replacement rate reaches 55%, there is a slight reduction in strength, though not significant. At replacement rates of 70%, 85%, and 100%, the strength of the specimens slightly improves. This demonstrates that using oil shale residue to replace fine aggregate in concrete production is feasible. The oil shale residue exhibits some reactivity, partly participating in the hydration reaction, leading to an increase in concrete strength over time. The strength meets the regulatory requirements, and it is possible to use 100% oil shale slag to replace fine aggregate in concrete, facilitating the large-scale disposal of oil shale residue waste and achieving true waste utilization.

3.2. Durability Analysis of Modified Oil Shale Residue Concrete

The analysis and comparison of the compressive strength of oil shale residue concrete reveal that as the content of oil shale slag increases, the concrete meets the basic compressive strength requirements [24]. Thus, it is concluded that the complete replacement of fine aggregate with oil shale residue is feasible. To further enhance its performance, desulfurization gypsum is introduced to modify the concrete made entirely from oil shale residue as a replacement for fine aggregate. This study analyzes potential improvements in freeze–thaw resistance and resistance to sulfate attack.

3.2.1. Freeze–Thaw Cycle Test

Freeze–thaw cycle tests were conducted on specimens B1 through B5. The freeze–thaw cycles of specimen B1 are shown in Figure 7.
As shown in Figure 8, the relative dynamic modulus decreases with the reduction in the content of modified gypsum, indicating a positive correlation. This suggests that the freeze–thaw resistance of concrete diminishes as the content of desulfurized gypsum decreases. After 50 freeze–thaw cycles, the reductions in relative dynamic modulus for B1, B2, B3, B4, and B5 compared to the JZ group were 1.23%, 1.23%, 1.44%, 2.05%, and 2.46%, respectively. After 100 cycles, these reductions were 0.64%, 1.07%, 1.61%, 2.36%, and 3.10%. After 150 cycles, they were 2.42%, 4.74%, 7.38%, 8.37%, and 10.13%. As the number of freeze–thaw cycles increased, the impact of oil shale slag content on the relative dynamic modulus of concrete became more pronounced [25]. When the freeze–thaw cycles reached 175, samples with 100% oil shale slag content were completely damaged, thus subsequent data were not recorded.
As indicated in Figure 9, with the increase in the number of freeze–thaw cycles, the mass loss rates of concrete specimens containing different amounts of gypsum and oil shale residue exhibited an upward trend. This is attributed to the repeated freeze–thaw cycles causing internal cracking and surface spalling in the concrete, leading to a reduction in mass. During the first 50 cycles, the increase in mass loss rate of the concrete specimens is relatively slow. However, after exceeding 100 cycles, the rate of increase in mass loss accelerates. After 50 freeze–thaw cycles, the mass loss rates for groups B1, B2, B3, B4, and B5 are only 0.17%, 0.18%, 0.22%, 0.23%, and 0.25%, respectively. After 150 cycles, these rates increase to 1.47%, 1.49%, 1.51%, 1.53%, and 1.53%. These observations suggest that the damage to the surface and interior of oil shale residue concrete specimens becomes more severe in the later stages of the cycles, decreasing the bonding strength between aggregates and cementitious materials and leading to aggregate detachment and increased mass loss. Under the same number of cycles, the mass loss rates of the groups are in the order of B5 > B4 > B3 > B2 > B1, indicating that the mass loss rate increases as the desulfurization gypsum content decreases.
Although replacing fine aggregates with oil shale residue serves as a filler, its early pozzolanic activity is low, and this disadvantage becomes more apparent with greater inclusion rates. Additionally, the porous structure of the oil shale residue is well-developed; adding gypsum improves the flowability of the concrete and facilitates the formation of ettringite. After molding, the inert oil shale residue and the pores of the slag not involved in secondary hydration reactions encapsulate substantial amounts of free water. Upon freezing and thawing in a testing chamber, this free water expands as it freezes, creating microcracks and damaging the specimens. This damage is irreversible. Li found the resistance of low-volume fly ash and high-volume-based concrete mixtures to the combined effects of freeze–thaw cycles and sulfate attack increased along with the coarse recycled concrete aggregate content as replacement of coarse natural aggregates [26]. The resistance was more affected by FA content than by the replacement of coarse natural aggregates with coarse recycled concrete aggregates [27]. The adverse conditions in the freezing chamber also mean that internal secondary pozzolanic reactions in the concrete, which begin after 28 days, rarely occur after initial damage. Thus, with increasing freeze–thaw cycles, more microcracks and their propagation led to progressively deteriorating performance of the concrete.

3.2.2. Sulfate Resistance Test

(1) Mass Loss Rate
Figure 10 illustrates the mass change process of modified oil shale residue concrete subjected to different numbers of wet–dry cycles in a 5% Na2SO4 solution. This process is divided into stages of mass increase and mass decrease.
Phase One: During the 0 to 60 wet–dry cycles, the mass of the modified oil shale residue concrete gradually increased. Initially, the Na2SO4 solution reacted with the surface cement mortar, forming Na2SO4 crystals upon drying, which slightly increased the mass. As Na2SO4 further penetrated and reacted with the cement hydration products to form ettringite (AFt) [28], the expansive crystals led to microcrack formation. As the cracks were filled with AFt, their propagation increased. The addition of desulfurization gypsum slowed down the penetration of Na2SO4 and the formation of AFt, resulting in a more gradual mass increase.
Phase Two: After 60 to 180 wet–dry cycles, there was a rapid decline in concrete mass, with surface spalling and chipping, and partial exposure of aggregates. The addition of desulfurization gypsum helped the oil shale residue particles and cement to work together, reducing aggregate loss [29]. Compared to the control group without gypsum, the mass loss was less, and it further decreased with an increase in gypsum content.
Overall, compared to concrete without desulfurization gypsum, the gypsum-added oil shale residue concrete exhibited significantly lower mass loss rates and enhanced resistance to sulfate attack under sulfate wet–dry cycling conditions [30]. This is mainly because the synergistic action of gypsum and cement could fill the internal pores of the concrete to some extent, effectively obstructing the penetration of sulfate solution and enhancing the concrete’s resistance to sulfate attack.
(2) Relative Dynamic Modulus of Elasticity
Under the influence of wet–dry cycles in a 5% Na2SO4 solution, the relative dynamic modulus of elasticity of the modified oil shale residue concrete initially increased and then decreased. Initially, Na2SO4 reacted with cement hydration products to form voluminous ettringite, which filled the pores without generating expansive pressure, thus densifying the internal structure, and gradually increasing the relative dynamic modulus. As the sulfate continued to penetrate, the increase in expansive materials led to the formation and expansion of internal cracks, accelerating chemical reactions and the proliferation of cracks, which deteriorated the internal structure of the concrete, ultimately resulting in a significant decrease in the relative dynamic modulus [31].
As shown in Figure 11, prior to 60 wet–dry sulfate cycles, the relative dynamic modulus of elasticity of the oil shale residue concrete increased rapidly, with the group without gypsum showing a slightly higher rate of increase compared to the gypsum-added group. This is because the addition of gypsum enhanced the compactness of the concrete, slowing down the penetration of the sulfate solution and the rate of internal hydration reactions [32]. After exceeding 60 cycles, the relative dynamic modulus began to decline rapidly, with the rate of decrease being higher in the group without gypsum. Specific data indicate that the relative dynamic modulus for Group B5 increased to 118.5% at 60 cycles but dropped to 81.5% after 180 cycles. With increasing gypsum content, the dynamic modulus curve of the oil shale residue concrete exhibited a gradual and then rapid change, indicating that its resistance to sulfate attack initially improved and then weakened with the increase in gypsum content, but overall, it still performed better than Group B5.

3.3. Microstructural Characteristics

Microscopic morphological analysis was conducted on the 28-day specimens of Group B1, observing the hydration products of concrete where 100% of the fine aggregates were replaced by modified oil shale residue. The microstructural morphology of Group B1 is shown in Figure 12 below.
Scanning electron microscope (SEM) observations revealed that the concrete specimens had formed numerous C-S-H gels and crystals with a relatively dense internal structure. No significant voids or cracks were observed. The images indicate that at a 20,000× magnification under the SEM, the presence of abundant flocculent C-S-H gel interweaving into a continuous network is more evident, containing a small amount of Ca(OH)2 crystals. Oil shale residue particles were evenly distributed within, providing structural support. Most of the C-S-H gel and Ca(OH)2 had undergone secondary hydration reactions, forming a large amount of calcium magnesium carbonate (CaMg(CO3)2) crystals, resulting in a denser and more stable internal structure of the concrete.
Microstructural analysis was conducted on the 28-day specimens of Group B5, observing the hydration products of concrete where 100% of the fine aggregates were replaced. The microstructural morphology of Group B5 is shown in Figure 13.
As shown in SEM image 13, the internal structure was relatively dense, with no significant voids, cracks, or other defects observable. As illustrated in Figure 13b, a large amount of C-S-H flocculent gels were intertwined, forming a cohesive and dense network structure. The majority of C-S-H gels, along with a small amount of Ca(OH)2, had undergone a secondary hydration reaction, transforming into a substantial quantity of crystalline forms, such as magnesium calcium carbonate (CaMg(CO3)2). The formation of these crystals contributed to the enhancement of the material’s microstructural stability.
The reasons for the aforementioned observations are as follows: (1) The modified surface of the oil shale residue has a composition similar to that of the cement paste, which leads to fewer pores and cracks in the interfacial transition zone during curing. This reduces the infiltration of sulfate ions, resulting in a lower concentration of internal sulfate ions. This indicates that modified oil shale residue concrete can effectively resist the intrusion of sulfate ions, thereby enhancing the specimen’s resistance to corrosion. (2) The modified oil shale concrete exhibits larger pores and cracks in the interfacial transition zone compared to ordinary oil shale residue concrete, making it easier for sulfate ions to infiltrate through these pores and cracks, and similarly, calcium ions can also pass through these spaces more easily. At this location, metal cations react with sulfate ions to form corrosive products, causing the corroded layer to gradually become friable and spall off, which macroscopically manifests as an increase in mass loss rate and a reduction in both the relative dynamic modulus of elasticity and compressive strength. This correlates with the patterns observed in macroscopic mechanical performance tests.

4. Conclusions

(1) After undergoing the crushing value test, the oil shale residue demonstrated a crushing value of 16.7%, meeting the highest standard requirements for fine aggregate compressive capabilities, thereby confirming that oil shale residue can replace fine aggregates in the preparation of oil shale residue concrete.
(2) Oil removal treatments were performed on oil shale residue using water, Tween 80, and sophorolipid, with the effectiveness of these reagents reflected in the compressive strength of the concrete blocks. The compressive strength of all specimens met the standard requirements, exhibiting a dense internal structure with no significant voids or cracks. The experiment proved that a concentration of 60 mg/L of Tween 80 surfactant achieved the best oil removal results.
(3) Concrete was prepared using 40%, 55%, 70%, 85%, and 100% replacement of fine aggregates with de-oiled oil shale residue, and their compressive strength was tested. It was found that the compressive strength slightly increased with the rising replacement level of fine aggregates, suggesting that 100% replacement is viable when using large amounts of oil shale residue.
(4) Different contents of desulfurization gypsum were added to oil shale slag concrete with 100% replacement of fine aggregates. Freeze–thaw cycle and sulfate attack tests showed that the mass loss rates for specimens from groups B1 to B5 were all below 5%, and the relative dynamic modulus loss rate was maintained below 20%. After 175 freeze–thaw cycles, only the B5 specimen showed damage, while B1 to B4 specimens remained unaffected, indicating that the addition of desulfurization gypsum significantly improved the frost resistance of oil shale residue concrete. In sulfate attack tests, specimens with desulfurization gypsum showed better stability in terms of mass loss and dynamic modulus loss compared to the gypsum-free B5 group.
(5) In summary, using a Tween 80 solution with a concentration of 60 mg/L to remove oil from the oil shale residue, a concrete mix with the following proportions was prepared: 390 kg/m3 of cement, 657.5 kg/m3 of oil shale residue, 1170 kg/m3 of coarse aggregate, 1.95 kg/m3 of water-reducing agent, and 187.2 kg/m3 of water, achieving 100% replacement of fine aggregate. It was found that incorporating 2% desulfurization gypsum significantly improved the durability of the modified concrete. This approach not only conserves natural aggregate resources but also substantially utilizes oil shale residue, effectively mitigating environmental pollution caused by oil shale residue accumulation. This utilization of oil shale residue promotes resource recovery and generates considerable economic and social benefits, supporting sustainable and green development.

Author Contributions

Software, M.G.; Formal analysis, M.T.; Data curation, Y.W. (Yingshuang Wang); Writing—original draft, Y.W. (Yunyi Wang); Writing—review & editing, C.Z. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Data Availability Statement

Data are contained within the article.

Conflicts of Interest

Author Yingshuang Wang was employed by the company Power China Jilin Electric Power Engineering Co., Ltd. Authors Mingyi Tang and Mengqiu Gao were employed by the company Northeast Electric Power Design Institute Co., Ltd. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

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Buildings 14 02547 g001
Figure 1. Oil shale residue stockpile site.
Figure 1. Oil shale residue stockpile site.
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Figure 2. Crushing value test.
Figure 2. Crushing value test.
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Figure 3. Aggregate crushing value test.
Figure 3. Aggregate crushing value test.
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Figure 4. Oil removal experiment of oil shale residue particles.
Figure 4. Oil removal experiment of oil shale residue particles.
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Figure 5. Compressive strength of different groups.
Figure 5. Compressive strength of different groups.
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Figure 6. Compressive strength of different fine aggregate replacement rate.
Figure 6. Compressive strength of different fine aggregate replacement rate.
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Figure 7. Freeze–thaw results for 100% oil shale residue replacement of fine aggregate.
Figure 7. Freeze–thaw results for 100% oil shale residue replacement of fine aggregate.
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Figure 8. Relative dynamic modulus of elasticity.
Figure 8. Relative dynamic modulus of elasticity.
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Figure 9. Number of cycles.
Figure 9. Number of cycles.
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Figure 10. Mass loss rates for different gypsum contents.
Figure 10. Mass loss rates for different gypsum contents.
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Figure 11. Relative dynamic modulus of elasticity for different gypsum contents.
Figure 11. Relative dynamic modulus of elasticity for different gypsum contents.
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Figure 12. B1 SEM images at 5000× and 20,000× magnifications.
Figure 12. B1 SEM images at 5000× and 20,000× magnifications.
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Figure 13. B5 SEM images at 5000× and 20,000× magnifications.
Figure 13. B5 SEM images at 5000× and 20,000× magnifications.
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Table 1. Main chemical composition of oil shale residue.
Table 1. Main chemical composition of oil shale residue.
Chemical componentsSiO2Al2O3Fe2O3CaOK2O + MgO + Na2O + TiOSO3
Content/%55.8418.594.7810.78.21.89
Table 2. Crushing value of oil shale residue.
Table 2. Crushing value of oil shale residue.
Condition of the Stone MaterialCrushing Value of Oil Shale Waste Slag %Average Crushing Value
Natural state16.715.816.116.2
Table 3. Table of crushing index parameters.
Table 3. Table of crushing index parameters.
ProjectIndex
IIIIII
Single-Stage Maximum Crushing Index % ≤202530
Table 4. Mechanical performance indicators of ordinary Portland cement.
Table 4. Mechanical performance indicators of ordinary Portland cement.
Density/g·cm−33-Day Flexural Strength28-Day Flexural Strength3-Day Compressive Strength28-Day Compressive Strength
3.183.58.616.254.5
Table 5. Mix proportions of oil shale residue concrete and additional materials.
Table 5. Mix proportions of oil shale residue concrete and additional materials.
NumberCement
(kg/m3)		Fine Aggregate
(kg/m3)		Oil Shale Residue
(kg/m3)		Coarse Aggregate 5–10 mm
(kg/m3)		Coarse Aggregate 10–20 mm
(kg/m3)		Water-Reducing Agents (kg/m3)Water
(kg/m3)		De-Oiling AgentConcentration
(mg/L)		Gypsum
(kg/m3)
JZ390657.50467.5702.51.95187.2///
A1390394.5263467.5702.51.95187.2///
A2390394.5263467.5702.51.95187.2Water//
A3390394.5263467.5702.51.95187.2Tween 8020/
A4390394.5263467.5702.51.95187.2Tween 8040/
A5390394.5263467.5702.51.95187.2Tween 8060/
A6390394.5263467.5702.51.95187.2Sophorolipid20/
A7390394.5263467.5702.51.95187.2Sophorolipid40/
A8390394.5263467.5702.51.95187.2Sophorolipid60/
B13900657.5467.5702.51.95187.2Tween 806048.0
B23900657.5467.5702.51.95187.2Tween 806036.0
B33900657.5467.5702.51.95187.2Tween 806024.0
B43900657.5467.5702.51.95187.2Tween 806012.0
B53900657.5467.5702.51.95187.2Tween 80600
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Wang, Y.; Zeng, C.; Wang, Y.; Tang, M.; Gao, M. Study on the Durability of High-Content Oil Shale Concrete. Buildings 2024, 14, 2547. https://doi.org/10.3390/buildings14082547

AMA Style

Wang Y, Zeng C, Wang Y, Tang M, Gao M. Study on the Durability of High-Content Oil Shale Concrete. Buildings. 2024; 14(8):2547. https://doi.org/10.3390/buildings14082547

Chicago/Turabian Style

Wang, Yunyi, Cong Zeng, Yingshuang Wang, Mingyi Tang, and Mengqiu Gao. 2024. "Study on the Durability of High-Content Oil Shale Concrete" Buildings 14, no. 8: 2547. https://doi.org/10.3390/buildings14082547

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