1. Introduction
Urbanization has surged with the rapid expansion of China’s economy, leading to the rapid proliferation of demolition and reconstruction projects targeting numerous dilapidated structures, aged buildings, and obsolete infrastructure. This surge has, in turn, substantially increased the generation of construction waste. As of 2020, construction waste emissions have surpassed 5 billion tons, creating significant environmental challenges [1]. Concurrently, there has been exponential growth in the scale of infrastructural development. Gravel and other materials are commonly employed in cement-stabilized macadam bases in highway engineering construction. At the same time, due to the large amount of CO2 produced in the production of cement, the use of a large amount of cement in the project has also caused irreversible damage to the ecological environment. However, the current scenario is marked by the soaring prices of natural resources, exacerbating the conflict between environmental conservation and the sustainable advancement of engineering projects. Consequently, it is necessary to explore alternatives to mitigate this issue.
Currently, there is an emphasis on utilizing construction waste in the production of cement-stabilized macadam base materials [2,3]. Recycled aggregates are prepared to re-place natural aggregates in the formulation of road cement-stabilized macadam bases via crushing and screening processes [4,5,6,7]. This transformation of construction waste into a valuable resource significantly enhances its utilization efficiency, curtails engineering costs, alleviates the strain on natural building material extraction, and mitigates environmental degradation [8].
A large number of scholars have fully studied the composition and physical properties of recycled aggregate from construction waste and reached a series of similar conclusions. Shah et al. [9] investigated the physical properties of recycled aggregates of concrete waste and revealed their excellent particle size distribution, durability, and shape. Kolay and Akentuna [10] and Bestgen et al. [11] conducted comparative analyses on the properties of recycled aggregates versus natural aggregates, establishing the similarity in their physical and mechanical characteristics. Hansen et al. [12] assessed the performance of recycled aggregates using primary concrete crushing tests with varying water–cement ratios. Their findings indicated a relationship between the water absorption rate and particle size, while the water–cement ratio showed no significant correlation with the water absorption rate. Hasaba et al. [13] observed that the water absorption of recycled aggregates of waste concrete ranging from 4.75 mm to 26.5 mm in particle size was approximately 7%. However, for recycled aggregates with particle sizes below 4.75 mm, the water absorption was approximately 11%, consistent with Hansen’s results.
On the basis of previous studies, many researchers began to explore the preparation of stabilized materials from recycled aggregate and compared and analyzed some possible influencing factors. Jeselay H. C. Reis et al. [14], Ding et al. [15], and Esfahani [16] examined the influence of the recycled aggregate content on the strength characteristics of road base materials, noting a significant impact on their mechanical properties, but does not give an appropriate particle content index. Luo et al. [17] conducted unconfined compressive strength tests on construction waste materials, analyzing the effects of cement dosage and age on compressive strength. Yang et al. [18] studied the influence of the recycled aggregate content and different admixtures instead of natural aggregates on the crack resistance of recycled aggregate base materials. The researchers paved a test road to verify the material’s feasibility. Nhieu et al. [19] studied the influences of the cement content, natural latex content, and other factors on the performance of a cement-stabilized recycled concrete aggregate as a pavement base material, analyzing the material’s basic performance from a microscopic perspective. Due to the complex composition and other characteristics of recycled aggregate, the research results have limitations, and the main research object is not 100% content. Increasing the content of recycled aggregate plays a decisive role in the large-scale consumption of construction waste.
There is a lack of research on the 100% replacement of natural aggregates with construction waste recycled aggregates. Meng [20] investigated the feasibility of utilizing a 100% construction waste recycled aggregate in cement-stabilized materials. However, the analysis did not consider the various factors influencing the materials’ mechanical properties. Rey et al. [21] used a construction waste recycled fine aggregate (mainly comprising a 0~8 mm recycled concrete aggregate) to prepare cement-stabilized base materials. The mechanical properties and durability were studied, and the effects of the particle size and aggregate source were analyzed. Therefore, focusing on construction waste with multiple components, this study developed a technology for the 100% replacement of natural aggregates with construction waste recycled aggregates to prepare road base materials and analyzed the influences of various factors, such as the curing age and cement content, on the materials’ strength via relevant experiments. This study first evaluated the feasibility of preparing a cement-stabilized macadam base with selected raw materials via experiments. Subsequently, compaction tests were conducted to ascertain the maximum dry density and optimum moisture content with different mix proportions. Finally, unconfined compressive strength tests were employed to investigate the mechanical characteristics of recycled aggregate road base materials. This study analyzed and discussed the influences of differing dosages of cementitious materials (5% and 6%) and various ages (1 d, 3 d, 7 d, 14 d, and 28 d) on the strength of the recycled aggregate base materials. Furthermore, the influence of the curing agent content on the early strength of recycled aggregate base materials was analyzed by adding a curing agent to develop early-strength materials. At the same time, 144 standard specimens were prepared for the frost resistance test, and the frost resistance of the material was analyzed. This study provides a new and reliable method for the large-scale consumption of construction waste and has positive significance for promoting the sustainable development of infrastructural construction. After the large-scale promotion and application of this research, it can absorb construction waste on a large scale, protect the ecological environment, and 100% replace natural materials can relieve the mining pressure of natural materials and promote the sustainable development of the industry.
This study solved the problem of a 100% content of construction waste recycled aggregates in municipal road base materials. However, the cement content is high. Despite solving the environmental problem of construction waste, the excessive use of cement also causes environmental problems. The problem of reducing the cement content will be further studied to promote sustainable infrastructural development.
2. Research Scheme and Test Method
2.1. Testing Material
The recycled aggregate from construction waste employed in this study originated from Qingdao construction solid waste. The solid waste mainly comprised waste concrete, bricks, and a small number of ceramic tiles. It was categorized into three specifications based on particle size: a recycled fine aggregate with a particle size range of 0~5 mm, and two specifications of recycled coarse aggregate with particle size ranges of 5~10 mm and 10~25 mm, respectively, as depicted in Figure 1. The recycled aggregate of construction waste was equipped with a perfect aggregate production line, ensuring its storage stability, local availability, and material applicability. Shanshui brand 42.5 R ordinary Portland cement was utilized. A powdered inorganic curing agent produced by a manufacturer in Shandong was used. The initial setting time was 215 min, the final setting time was 295 min, the compressive strength was 43.5 MPa, and the flexural strength was 9.6 MPa. The curing agent was based on Portland cement and other active materials as the main components and mixed with various activators, water retention agents, and polymer materials.
2.2. Research Program
In this study, a recycled road base material was designed utilizing construction waste mixed recycled aggregate with cement as the stabilizing agent. The aggregate consisted entirely of recycled construction waste aggregate. According to the requirements of mechanical properties and durability specifications, the design idea of gradually reducing the number of cementitious materials, and the local construction conditions, 5% and 6% cement contents were selected. Based on the local construction experience in Qingdao and the characteristics of the curing agent, a curing agent with a dosage of 2‰ is selected. This study’s experimental group design was based on the characteristics of recycled aggregates and practical engineering experience. The performance indices of the raw materials were analyzed via various tests. Subsequently, compaction tests were conducted to determine the maximum dry density and optimum moisture content across the different mix ratios. Finally, the specimens were prepared according to the compaction test data, and the mechanical properties of the recycled aggregate road base material were studied with the unconfined compressive strength test. The influences of different dosages of cementitious materials (5% and 6%) and various ages (1 d, 3 d, 7 d, 14 d, and 28 d) on the early strength of the recycled aggregate base were analyzed and discussed, alongside the impact of increasing the curing agent dosage on the early strength of the recycled aggregate base material. At the same time, 144 standard specimens were prepared for the frost resistance test, and the frost resistance of the material was analyzed.
Four groups of samples, namely, A1, A2, B1, and B2, were designed. The cement–recycled aggregate mix ratios of the cement-stabilized recycled aggregate were set as 5:100 and 6:100. Additionally, a test group incorporating a curing agent was included, with the dosage set at 2‰ of the total mass of the cementitious material and recycled aggregate. The specific sample mixes are detailed in Table 1. In the compaction test, two groups were set up in the A1 and B1 test groups, five tests were set up for each group of dry density measurements, and ten test boxes were set up for each water content group. In the unconfined compressive strength test, 13 specimens were prepared for each of the 1 d, 3 d, 7 d, 14 d, and 28 d test conditions. The A2 and B2 groups with the curing agent were prepared with the same amount. A total of 260 specimens were set up in the unconfined compressive strength test. The study also conducted frost resistance tests, preparing 18 standard specimens for each group and standard curing for 28 days, of which 9 were freeze-thaw specimens and 9 were non-freeze–thaw comparison specimens. A total of 144 specimens were tested for frost resistance.
2.3. Test Method
The performance of the raw materials was assessed according to the test methods outlined in the ‘Highway Engineering Aggregate Test Procedure’ (JTG E42-2005) [22], ‘High-way Pavement Base Construction Technical Rules’ (JTG/TF20) [23], and ‘General Portland Cement’ (GB175-2007) [24] to evaluate their suitability for road base applications. The compaction tests for the A1 and B1 test groups were conducted using the heavy compaction method outlined in the test procedure for inorganic binder-stabilized materials for high-way engineering (JTG E51-2009) [25]. The specimens for the unconfined compressive strength test were prepared using a pressure testing machine, as shown in Figure 2a. Building on this, the unconfined compressive strength test method for inorganic binder-stabilized materials outlined in the ‘Highway Engineering Inorganic Binder-Stabilized Material Test Procedure’ (JTG_E51-2009) [25] was employed to ascertain the unconfined compressive strength of the inorganic mixtures with varying mix ratios (cement–recycled aggregate = 5:100 and 6:100) and different curing ages (1 d, 3 d, 7 d, 14 d, and 28 d), as displayed in Figure 2b. Based on actual engineering experience and construction methods, compare the construction costs of recycled aggregate and natural aggregate, and analyze the economic benefits. At the same time, the research carried out the frost resistance test according to the test specification to understand the material performance more comprehensively.
3. Raw Material Analysis
3.1. Recycled Aggregate
To detect and evaluate the physical properties of the recycled aggregates from construction waste, samples were extracted from several representative recycled aggregates following construction waste disposal. Upon observation of the aggregates’ appearance characteristics, the recycled coarse aggregate, unlike the natural coarse aggregate, exhibited a substantial accumulation of aged cement mortar on its surface. The particles possessed more edges and corners, presenting a rough surface, and were interspersed with a higher proportion of brick particles. This discrepancy is fundamental to distinguishing recycled aggregates from natural aggregates.
As per the testing methodology specified in the ‘Highway Engineering Aggregate Test Procedures’ (JTG E42-2005), three specifications of recycled aggregate were sieved, and two groups of recycled aggregate for each specification were analyzed, to investigate the gradation of directly crushed recycled coarse aggregates. The average passing percentage across the three specifications is depicted in Figure 3. This figure demonstrates that the gradation composition of the recycled aggregate was suboptimal, with relatively concentrated particle sizes and approximately 90% of the 5~10 mm aggregate concentrated at approximately 5 mm.
There is currently no standardized basis for the grading criteria of recycled aggregate base subbase particles. A comprehensive approach was adopted, drawing on the grading requirements for cement-stabilized graded aggregates outlined in the ‘Technical Rules for Construction of Highway Pavement Base’ (JTG/TF20) and the principle of multiscale sol-id particle close packing. This approach fully integrated the characteristics of the recycled aggregate, including a complex composition, numerous microcracks, a high crushing index, and elevated water absorption.
The three specifications of recycled aggregate were intermixed to adjust the gradation, aiming to achieve a synthetic gradation closely aligned with the median gradation stipulated by the specifications. Based on the screening outcomes and specification mandates, the proportion of the synthetic graded crushed stone aggregate (0~5 mm:5~10 mm:10~25 mm = 24:26:50) was determined. The refined distribution of the recycled aggregate percentages is illustrated in Figure 4.
According to the test method outlined in the ‘Highway Engineering Aggregate Test Regulations’ (JTG E42-2005), various properties including the crushing index, water absorption, water content, needlelike particle content, apparent density, bulk density, and mud content of the recycled aggregates were examined and compared against the technical criteria specified in the ‘Highway Pavement Base Construction Technical Rules’ (JTG/TF20-2015). The results are presented in Table 2 and Table 3. The tables demonstrate that the physical properties of the recycled aggregate without cementitious binding materials meet the technical requirements of the ‘Technical Specification for Construction of High-way Pavement Base’ (JTG/TF20-2015) for base aggregates. This indicates its potential suitability as a substitute for natural aggregates in road base applications.
3.2. Cement
The cement samples’ principal chemical compositions and mechanical and physical properties were evaluated following the procedures outlined in ‘General Portland Cement’ (GB175-2007). The cement’s setting time and the cement mortar’s strength were determined per GB/T1346 and GB/T17671, respectively. The outcomes are detailed in Table 4 and Table 5. The tables show that the measured parameters align with the specifications outlined in ‘General Portland Cement’ (GB175-2007).
Compared with the technical specifications, the crushing value, water absorption, and other indicators of recycled aggregate meet the specifications. The properties of raw materials meet the specification requirements, and it is feasible to prepare road base stabilization materials.
4. Test Result Analysis
4.1. Moisture–Density Test
Two tests are set for each mix proportion, and the results are taken as the average of the two tests.
(1) Cement–synthetic recycled graded aggregate = 5:100
Based on the proportion of aggregate synthesis, the aggregate mass of a single specimen was determined to be 5500 g (0~5 mm: 1320 g; 5~10 mm: 1430 g; and 10~25 mm: 2750 g), while the cement mass was 275.0 g. Compaction tests were conducted with water contents ranging from 8% to 12%. The average values of the optimum water content and maximum dry density from the two tests were computed. The optimum water content was 10.55%, with a corresponding maximum dry density of 1.981 g/cm3. The compaction curve depicted in Figure 5 exhibits an approximately parabolic trend.
(2) Cement–synthetic recycled graded aggregate = 6:100
According to the aggregate synthesis ratio, the aggregate mass of a single specimen was 5500 g (0~5 mm: 1320 g; 5~10 mm: 1430 g; and 10~25 mm: 2750 g), while the cement mass was 330.0 g. Compaction tests were conducted with water content ranging from 9.5% to 12.5%. The average values of the optimum water content and maximum dry density from the two tests were computed, resulting in an optimum water content of 10.82%. The maximum dry density was 2.006 g/cm3. The compaction curve depicted in Figure 6 exhibits an approximately parabolic trend.
4.2. Unconfined Compressive Strength Test
The test groups A1, A2, B1, and B2 were evaluated following the test method for the unconfined compressive strength of inorganic binder-stabilized materials outlined in the ‘Test Specification for Inorganic Binder Stabilized Materials for Highway Engineering’ (JTG_E51-2009 T0805). The failure modes of the 260 test specimens were approximately the same. Figure 7 depicts the two specimens with obvious failure modes. The surfaces of the specimens significantly fell off, after which the specimens had an ‘upper and lower symmetrical triangle’ shape. The middle parts also significantly fell off. The specimens contained oblique longitudinal cracks. A main crack ran throughout the whole of each specimen at approximately 70–80 degrees, which was key to the specimens’ failure. The knocked-out specimens contained many microcracks, which caused the specimens to fall off again, and they could not bear the due pressure. The average values of all the results measured in each test condition of each group are shown in Table 6.
Figure 8 illustrates the strength comparison between the recycled aggregate bases at various ages with consistent curing agent quantities and varying cement amounts. The cement-stabilized recycled aggregate base demonstrated commendable mechanical properties. With a cement content of 5%, the 7-day unconfined compressive strength met the technical specifications for heavy and extremely heavy traffic on highways, as outlined in the ‘Highway Pavement Base Construction Technical Rules’ (JTG/TF20-2015). Upon increasing the cement content to 6%, the 1-day strength of group B1 without a curing agent approached 5 MPa. The 1-day strength of group B2 with a curing agent reached as high as 6.55 MPa. Increasing the cement content from 5% to 6% significantly enhanced the unconfined compressive strength of the cement-stabilized recycled aggregate base.
Using the 7-day age as an example, the strength of Group B1 surpassed that of Group A1 by 69.5%, while the strength of Group B2 exceeded that of Group A2 by 67.8%. Comparing Figure 8a and Figure 8b, the increase in the unconfined compressive strength with age was more pronounced without a curing agent, whereas it remained relatively consistent over time with a curing agent. On the premise of meeting the technical performance and maintaining the ecological environment, 5% cement content is the best choice for the preparation of the material.
Figure 9 presents the strength comparison between the recycled aggregate bases at different ages with varying quantities of the curing agent and consistent cement amounts. Adding the curing agent effectively enhanced the early strength of the recycled aggregate base, with significant increases observed at 1 day and 3 days and marginal increases after 7 days. This phenomenon arises from the curing agent’s ability to expedite cement hydration and react with cement to generate C-S-H and promote ettringite formation, thereby enhancing the base structure’s compactness. Consequently, the later strength primarily relies on the cement, resulting in a minor increase in strength with the same cement quantity.
Comparing Figure 9a with Figure 9b, adding the curing agent substantially boosted the early strength of the cement-stabilized recycled aggregate base with a cement content of 6%, with 42.3% and 12.1% strength increases at 1 day and 3 days, respectively. Conversely, the increase was relatively minor with a cement content of 5%. This discrepancy primarily stemmed from the curing agent’s ability to promote a more comprehensive reaction of the cementitious system with a sufficient cement quantity. When 5% cement content is selected, the curing agent can not be added because the early strength improvement is relatively small. When 6% cement content is selected, whether to add a curing agent can be considered according to the actual demand. Even if no curing agent is added, the material can also be used as the base stabilization material of municipal roads. When the curing agent is added, the early performance of the material is far from meeting the technical requirements. In municipal road construction, 100% recycled aggregate can alleviate the shortage of natural materials and the ecological deterioration caused by quarrying.
Figure 10 shows the test results of frost resistance. It can be seen from Figure 10a that the mass loss rate of the base course specimens with two kinds of cement content after freezing and thawing is less than 5%. The original strength of the specimen with 6% cement content is higher, so the mass loss rate is lower than 5% cement content. The freeze-thaw mass loss rate of the test group with the curing agent was slightly lower than that of the test group without the curing agent, indicating that the curing agent can improve the compactness and cohesion of the recycled aggregate base. It can be seen from Figure 10b that the residual compressive strength ratio of recycled aggregate base specimens after freeze-thaw is greater than 70%. When the cement content is 6%, the residual compressive strength of the specimen after five freeze-thaw cycles at the age of 28 days is 81%, which is higher than that of the 5% cement content. There is a direct linear relationship between the residual compressive strength and the original strength. The test group with high initial strength has high strength after freeze-thaw. The addition of the curing agent improves the frost resistance of recycled aggregate base. The materials with two kinds of cement content showed good frost resistance.
Qingdao municipal road engineering mainly uses a semirigid base, and the thickness of the structural layer is large, which has a large demand for aggregate. The use of construction waste recycling materials to prepare various materials for municipal road engineering has the characteristics of a large amount of construction waste, strong operability, and stable product performance. Taking the construction of a two-way 8-lane urban expressway as an example, the road project is estimated based on the design thickness of the Cement-Stabilized Graded Crushed Stone Subbase of 20 cm and the design thickness of the base course of 20 cm. It can absorb about 30,000 tons of recycled aggregate per kilometer, saving 27,000 tons of natural coarse aggregate and 3000 tons of natural fine aggregate of the same quality. According to the price data of natural sand and stone in China in June 2023, the average price of natural coarse aggregate (granite 10–25 mm) is 95 yuan/ton, the average price of natural coarse aggregate (granite 5–10 mm) is 95 yuan/ton, and the average price of natural fine aggregate (0–5 mm) is 115 yuan/ton. The total amount of natural sand and stone used in the project is about 2.91 million yuan. However, at present, the comprehensive estimated unit price of such recycled aggregate is 60 yuan/ton, and the total amount of recycled sand and stone used in the project is about 1.8 million yuan, reducing the cost of raw materials by 38.1% year-on-year, with significant economic benefits.
5. Conclusions
A construction-waste-recycled aggregate can replace only part of a natural aggregate. To address this problem, the mechanical properties of cement-stabilized macadam base materials prepared via the 100% replacement of a natural aggregate with a construction-waste-recycled aggregate were examined in this study. Physical and chemical tests on the raw materials were carried out to evaluate the feasibility of various raw materials for preparing a cement-stabilized macadam base. A compaction test was carried out to determine the maximum dry density and optimum moisture content in different mix ratios. Finally, an unconfined compressive strength test was carried out by preparing a test piece to study the mechanical characteristics of the recycled aggregate road base material. The influences of different dosages of cementitious materials and different ages on the strength of the recycled aggregate base were analyzed and discussed, alongside the improvement in the early strength of the base material with the curing agent. At the same time, the standard specimens were prepared for the frost resistance test. The conclusions are as follows:
The physical and chemical properties of the raw materials meet the requirements of relevant specifications and are feasible for preparing road cement-stabilized macadam base materials.
The material exhibits good mechanical properties. With a cement content of 5%, the 7-day unconfined compressive strength meets the technical requirements for heavy and extremely heavy traffic on highways. With a cement content of 6%, the 1-day strength approaches the technical requirements. The higher the cement content, the better the mechanical properties.
Incorporating a curing agent effectively enhanced the early strength of the recycled aggregate base. The unconfined compressive strength significantly increased with the increase in the cement content. This phenomenon is attributed to the more comprehensive reaction of the cementitious system facilitated by a sufficient cement content.
The material has good frost resistance, with a mass loss rate of less than 5% after freeze-thaw, and a residual compressive strength ratio of over 70%.
This study achieved the 100% replacement of a natural aggregate with a recycled aggregate of construction waste to prepare road base materials, meeting the requirements of relevant specifications. Nevertheless, the cement content is high, which increases the environmental problems caused by cement despite solving the problem of environmental pollution from construction waste. Future research should focus on reducing cement content, reducing dependence on cement materials, and reducing the large amount of CO2 generated from cement production. In this study, it can be seen that curing agents can improve the mechanical properties and frost resistance of materials. Therefore, new types of curing agents can be explored to achieve the preparation of base stabilization materials with low cement content. Under the premise of lower cement content, using a large amount of recycled aggregate to prepare stable materials, large-scale consumption of construction waste, breaking the technological bottleneck of industry development, and promoting green and sustainable development of the industry. While consuming construction waste on a large scale, attention should also be paid to the necessity of low cement content.
Conceptualization, Y.Y.; methodology, X.H.; software, K.W.; validation, Z.L., M.Z. and Y.Y.; formal analysis, X.H.; investigation, Y.Y.; resources, X.H.; data curation, M.Z.; writing—original draft preparation, K.M.; writing—review and editing, M.Z.; visualization, K.W.; supervision, K.M.; project administration, K.M.; funding acquisition, K.M. All authors have read and agreed to the published version of the manuscript.
The original contributions presented in the study are included in the article, further inquiries can be directed to the corresponding author.
Authors Yingjie Yuan and Kai Wang were employed by the company Qingdao Greensail Recycled Building Materials Co., Ltd. Authors Xianhu Hu and Zhi Liu were employed by the company Shandong Academy of Building Sciences 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.
Footnotes
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Enlarge this image.Figure 1. Construction waste recycled aggregates: (a) 0~5 mm recycled fine aggregate; (b) 5~10 mm recycled coarse aggregate; and (c) 10~25 mm recycled coarse aggregate.
Enlarge this image.Figure 2. Representative photos of test: (a) specimen compaction; (b) unconfined compressive strength test.
Enlarge this image.Figure 5. Compaction curve (cement content 5%): (a) the first group; (b) the second group.
Enlarge this image.Figure 6. Compaction curve (cement content 6%): (a) the first group; (b) the second group.
Enlarge this image.Figure 7. Crushing of representative test pieces (on the left is the A1 group test piece, and on the right is the B1 group test piece).
Enlarge this image.Figure 8. The influence of the cement content on the strength of the recycled aggregate base: (a) A1—B1 test group; (b) A2—B2 test group.
Enlarge this image.Figure 9. The influence of curing agent on the strength of recycled aggregate base: (a) A1–A2 test group; (b) B1–B2 test group.
Enlarge this image.Figure 10. Frost resistance test results: (a) mass loss rate of the specimen after freezing and thawing; (b) Residual compressive strength ratio of the specimen after freezing and thawing.
Sample mix ratios.
| Numbering | 42.5 R Ordinary Portland Cement (%) | Curing Agent (‰) | Recycled Aggregate (%) | |||
|---|---|---|---|---|---|---|
| 0~5 mm | 5~10 mm | 10~25 mm | ||||
| A | A1 | 5 | 0 | 24 | 26 | 50 |
| A2 | 5 | 2 | 24 | 26 | 50 | |
| B | B1 | 6 | 0 | 24 | 26 | 50 |
| B2 | 6 | 2 | 24 | 26 | 50 | |
Test results for physical properties of recycled coarse aggregates.
| Index | Technical Requirement | 5~10 mm Recycled Coarse Aggregate | 10~25 mm Recycled Coarse Aggregate | Test Method |
|---|---|---|---|---|
| Measurement Results | ||||
| Apparent density (kg/m3) | —— | 2519 | 2505 | T0304 |
| Bulk density (kg/m3) | —— | 1230 | 1220 | T0309 |
| Crush value (%) | ≤22 | —— | 20.9 | T0316 |
| Water absorption (%) | —— | 8.8 | 4.0 | T0307 |
| Water content (%) | —— | 1.9 | 0.79 | T0305 |
| Sil content (%) | ≤1.2 | 0.2 | 0.2 | T0310 |
| Fat elongated particle content (%) | ≤18 | 2.6 | 16 | T0312 |
Test results of physical properties of recycled fine aggregate.
| Index | Technical Requirement | 0~5 mm Recycled Fine Aggregate | Test Method |
|---|---|---|---|
| Measurement Results | |||
| Apparent density (kg/m3) | —— | 2431 | T0328 |
| Bulk density (kg/m3) | —— | 1424 | T0331 |
| Crush value (%) | ≤30 | 23.0 | T0350 |
| Water absorption (%) | —— | 8.9 | T0330 |
| Water content (%) | —— | 4.3 | T0332 |
| Sil content (%) | ≤3.0 | 2.8 | T0333 |
Chemical composition of cement.
| SiO2 | Al2O3 | Fe2O3 | CaO | MgO | SO3 | R2O | Ignition Loss |
|---|---|---|---|---|---|---|---|
| 22.13 | 5.80 | 3.93 | 61.22 | 1.86 | 2.62 | 0.67 | 1.52 |
Physical and mechanical properties of cement.
| Specific Surface Area (m2/kg) | Density | Setting Time (min) | Break-Off Strength (MPa) | Compressive Strength (MPa) | |||
|---|---|---|---|---|---|---|---|
| Initial Set | Final Set | 3 d | 28 d | 3 d | 28 d | ||
| 348 | 3.11 | 269 | 366 | 6.2 | 8.1 | 34.4 | 53.5 |
Unconfined compressive strengths of cement-stabilized recycled graded aggregates (MPa).
| Test Group Number | A1 | A2 | B1 | B2 | |
|---|---|---|---|---|---|
| Instar | |||||
| 1 d | 2.69 | 3.07 | 4.60 | 6.55 | |
| 3 d | 3.55 | 3.86 | 6.84 | 7.67 | |
| 7 d | 5.13 | 5.22 | 8.70 | 8.76 | |
| 14 d | 6.03 | 6.05 | 9.22 | 9.35 | |
| 28 d | 6.31 | 6.44 | 9.87 | 10.02 | |
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1 College of Transportation, Shandong University of Science and Technology, Qingdao 266590, China;
2 Shandong Academy of Building Sciences Co., Ltd., Qingdao 266000, China;
3 Qingdao Greensail Recycled Building Materials Co., Ltd., Qingdao 266043, China;
4 College of Transportation, Shandong University of Science and Technology, Qingdao 266590, China;