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Article

Experimental Study on Preparation and Characteristics of Concrete Modified by Construction Waste

by
Jing Zhang
1,2,*,
Xuejun Zhu
3,
Mingyuan Zhou
2 and
Xianwen Huang
4,*
1
Department of Architecture and Engineering, Yancheng Polytechnic College, Yancheng 224005, China
2
School of Civil Engineering, Jiangsu University of Science and Technology, Zhenjiang 212003, China
3
School of Civil Engineering, Nantong University, Nantong 226019, China
4
School of Civil Engineering, Suzhou University of Science and Technology, Suzhou 215009, China
*
Authors to whom correspondence should be addressed.
Appl. Sci. 2024, 14(5), 1974; https://doi.org/10.3390/app14051974
Submission received: 2 February 2024 / Revised: 18 February 2024 / Accepted: 21 February 2024 / Published: 28 February 2024
(This article belongs to the Special Issue Advances in Tunnelling and Underground Space Technology)
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Abstract

:
With the advancement of urbanization construction, the proportion of construction waste to the total urban waste continues to increase, especially waste concrete. The treatment and reuse of waste concrete is a major trend that poses enormous pressure on environmental protection. This article focuses on the problems in the preparation of recycled aggregates from waste concrete, which has important practical value. This article presents a new type of recycled concrete prepared through surface modification of recycled coarse aggregate and design experiments to change the replacement rate of coarse aggregate. The physical properties of recycled coarse aggregate, workability of fresh concrete, and mechanical properties of recycled concrete are analyzed. The research results indicate the following: (1) Through surface modification, recycled concrete can improve the workability of fresh concrete at a fixed water cement ratio, which can meet the requirements of mixing, transportation, and pouring of fresh concrete. (2) By modifying the surface of recycled aggregates, the strong water absorption performance of recycled aggregates caused by old mortar and surface defects has been reduced. And the modification effect of recycled aggregate improves the hydration process of recycled concrete, making the surface structure dense and further enhancing the strength of recycled concrete. (3) The compressive strength of recycled concrete specifications from construction waste shows a decreasing trend with the increase in coat aggregate replacement rate. The final ratio is as follows: modular dose of 12%, modification time of 90 min, and 20% recycled aggregate content.

1. Introduction

Nowadays, many buildings are built with concrete, and concrete has a lifespan limit. Therefore, the resource utilization of concrete waste is an important way to achieve sustainable development. Not only can it avoid environmental pollution caused by waste stacking, but it can also solve the problem of shortage of construction sand, gravel, and coarse aggregates [1,2,3]. However, so far, the overall situation of construction waste treatment around the world has been disappointing, especially in the recycling of new buildings. Recycled concrete refers to the use of waste concrete as raw material, which is screened and crushed to produce coarse aggregates suitable for preparing fresh concrete, replacing natural aggregates in concrete. The preparation of recycled concrete is a good way to reuse waste concrete [4,5,6,7,8].Making recycled aggregates from dismantled construction waste for the preparation of recycled concrete not only solves the pollution problem of construction waste, but also saves natural aggregates, and protects resources and the environment, which is of great significance for achieving sustainable development [9,10,11,12].The implementation of “Recycled coarse aggregates for concrete” (GB/T 25177-2010) [13] and “Recycled fine aggregates for concrete and mortar” (GB/T25176-2010) [14] standardizes the preparation of recycled concrete aggregates [15,16,17].Many scholars have conducted extensive research on the mechanical properties and other aspects of recycled concrete [18,19,20,21,22,23,24,25].The production of recycled concrete using waste concrete coarse aggregate as variables of substitution rate and water cement ratio shows that the higher the substitution rate, the more unfavorable the mechanical and working properties of recycled concrete. The higher the strength of the original waste concrete, the better the mechanical properties of recycled concrete. However, it was not taken into account that recycled coarse aggregates have a rough and porous surface and complex properties compared to natural coarse aggregates, which increases the water absorption rate of recycled aggregates. Bai Weifeng et al. [26] conducted uniaxial compression dynamic mechanical performance tests using recycled coarse aggregates from waste concrete instead of natural coarse aggregates, indicating that recycled concrete has good deformation characteristics, this study demonstrates the possibility of using recycled coarse aggregate to prepare concrete. Wang Chenggang et al. [27] applied recycled coarse aggregate from waste concrete to steel-concrete components, indicating that steel pipes have a good restraining effect on recycled concrete, as well as good bearing capacity and ductility. Robalo et al. [28] research has observed that due to the cement hydration reaction, waste concrete has a high porosity and water absorption. Abudushalamu [29] have shown that the microstructure of cement-based recycled materials is much more complex than that of ordinary concrete. They believe that the interface transition zone containing a large number of micro pores and cracks seriously affects the ultimate strength of cement-based recycled materials. The authors attribute this to the increased consumption of water by pores and cracks, which reduces the amount of water involved in hydration reactions. Xiao Jianzhuang [30] research found that the main reason affecting the performance of recycled aggregates is the presence of a certain amount of old hardened mortar in the recycled aggregates. The various properties of old hardened mortar are weaker than those of stone, which leads to weaker comprehensive performance of recycled aggregates compared to natural aggregates. Due to the old hardened mortar in recycled aggregates, more interface transition zones are introduced, and the distribution of interface transition zones between recycled aggregates varies due to the different content of hardened mortar, resulting in more complex structures and affecting the mechanical properties of cement-based recycled materials. Research by Adamson et al. [31] has shown that there is a difference in strength between recycled concrete aggregates and natural aggregates, and the average strength of concrete prepared with recycled aggregates is slightly higher than that of natural aggregates. Therefore, the preparation of recycled aggregates from waste concrete is feasible. Ahmad S I [32] also indicates that the strength of recycled aggregate concrete is directly proportional to the improvement in the quality of recycled aggregate. Peng Gaifei et al. [33] pointed out that compared to using recycled aggregates to prepare cement-based recycled materials, the mechanical properties of concrete prepared with natural aggregates are significantly lower in the latter. And it is believed that the main reason for this phenomenon is the stone damage caused by the preparation process of recycled aggregates and the hardened mortar attached to the surface. Purushothaman R et al. [33,34,35,36] found that there is a significant difference in the water absorption and strength properties of recycled aggregates compared to natural aggregates, mainly manifested in the high water absorption rate, high crushing value, and low apparent density of recycled aggregates. The water absorption rate of recycled aggregate is about four times higher than that of natural coarse aggregate, and the crushing index is also 23.85% higher than that of natural coarse aggregate. Çakır Ö et al. [37,38,39] studied recycled coarse aggregate concrete and found that the physical and mechanical indicators of recycled coarse aggregate recycled concrete were lower than those of ordinary concrete. However, it is feasible to prepare concrete with lower strength, If high-strength concrete is prepared, it needs to be achieved through the addition ratio and modification effect of recycled aggregates. In summary, existing research has mainly focused on the study of recycled concrete with a single recycled aggregate. Compared to natural aggregates, due to the adhesion of waste mortar on the surface of recycled aggregates and the distribution of numerous micro cracks on the surface and inside, the water absorption rate of recycled aggregates increases and the strength decreases, becoming a key factor limiting the promotion and application of recycled aggregates. In order to more stably control the quality of recycled aggregates and improve their applicability, it is necessary to carry out low-cost surface modification treatment on recycled aggregates.
At present, most urban buildings in China are in the form of concrete structures, and the construction waste generated is mainly waste concrete. The recycling and utilization of waste concrete is very important. There are some studies on the preparation of recycled low strength concrete from waste concrete, but there is relatively little research on the surface modification of recycled coarse aggregates from waste concrete, and there is a lack of relevant mix design. Due to the high content of mortar on the surface of recycled fine aggregate, the crushed recycled fine aggregate has more cracks and pores than the recycled coarse aggregate, and the higher water absorption rate is more unfavorable for the preparation of recycled rubber sand. Therefore, conducting mix proportion research on waste concrete is of great significance. In order to design the mix ratio of different types of recycled coarse aggregate concrete, recycled coarse aggregate of waste concrete is used to replace natural aggregate. Through the surface modification of recycled coarse aggregate, the action time of the modifier and the replacement rate of recycled coarse aggregate, the influences of different mix ratios on the performance, failure form, and mechanical properties of the newly mixed recycled concrete are explored. It provides reference for the research on the mix ratio of recycled high-strength concrete. In order to design the mix ratio of different types of recycled coarse aggregate concrete, recycled coarse aggregate of waste concrete is used to replace natural aggregate. Through the surface modification of recycled coarse aggregate, the action time of the modifier and the replacement rate of recycled coarse aggregate, the influences of different mix ratios on the performance, failure form and mechanical properties of the newly mixed recycled concrete are explored. It provides a reference for the research on the mix ratio of recycled high-strength concrete.
Research Significance: This article takes waste concrete as raw material and introduces a method of chemical reagent activation. The aim of the study is to explore the effects of modifier dosage, action time, and recycled aggregate dosage on the characteristics, microstructure, and performance of cement mortar samples, in order to fully utilize waste concrete resources. Therefore, if construction waste is recycled and reused as a resource, and recycled aggregates and admixtures are applied to concrete and building mortar, it can not only achieve sustainable development and minimize environmental pollution, resource and energy consumption, CO2 emissions, and other problems caused by construction waste, but can also be applied as renewable resources in building materials products, green environmental protection, energy conservation, and improved resource utilization, It is in line with the economic development strategy and the development trend of the building materials industry, and can generate huge economic benefits.

2. Materials and Methods

2.1. Raw Materials

Cement: P·O52.5 grade ordinary cement produced by Zhangjiakou Xuanhua Jinyu Cement was used, and all its indicators meet the specification requirements. The basic performance indicators are shown in Table 1. Cement clinker particle size distribution curve is shown in Figure 1.
Recycled aggregate surface modifier: KH-560 methacryloxy functional group silane; its general formula is RSiX3, a light yellow transparent liquid with a refractive index of (nD25) 1.4260–1.4280 and a specific gravity of (dD25) 1.065–1.072. The regenerated aggregate was put into the modifier solution for impregnation and modification. After impregnation, the regenerated aggregate was taken out and placed in an environment of 20 ± 5 °C, drained for 1 d, and then dried at 105 ± 5 °C to constant weight. Then, the related performance of the regenerated aggregate was tested.
Polycarboxylic acid superplasticizer: water reduction rate of 30%, solid content of 30%.
Silica fume: The silica fume produced by Beijing Lihong Chuangye International Co., Ltd. (Beijing, China) has an average particle size of 0.045 μm, and its properties are shown in Table 2.
The waste concrete is obtained from the project site, the steel bar is removed, the crusher is broken and screened, and a suitable particle size of recycled aggregate is selected. The production process of waste concrete recycled aggregate is shown in Figure 2.
The porosity of concrete is divided into total porosity and effective porosity. Total porosity is the percentage of the volume of all voids in concrete to its total volume. It is the main factor affecting the strength of concrete. The relationship between the porosity of concrete and the particle size of crushed stones is shown in Figure 3a. If the cement dosage is kept constant, as the size of coarse aggregate increases, its specific surface area becomes smaller, and there is less water demand, which allows a decrease in the water cement ratio. This is beneficial for improving concrete strength and reducing costs. However, the probability of internal defects occurring in large particle aggregates is relatively high, while small particle aggregates are relatively dense, and due to their generally low water cement ratio, the reduction in water cement ratio caused by the above factors is not significant. However, it can increase the bonding area with cement and improve the strength of concrete. At the same time, if the coarse aggregate particle size is too large, it will reduce the interfacial bonding performance between mortar and coarse aggregate, and seriously affect the impermeability and crack resistance of concrete. The relationship between compressive strength and particle size of concrete is shown in Figure 3b. Therefore, the particle size of recycled waste concrete aggregate selected in this test is 15–20 mm.

2.2. Test Method

Compressive strength test: According to the standard test methods for mechanical properties of ordinary concrete (GB/T 50081-2002) [40], the compressive strength test should use a 100 mm × 100 mm × 100 mm cube specimen. In this experiment, a loading rate of 1.3 MPa/s was selected. Based on the test results, 15% of the upper and lower limits of the middle value was taken as the available data, and the average value was finally selected as the failure load. The pressure machine used in this experiment is the NYL-3000 digital hydraulic universal pressure testing machine (Midland Industries, Kansas City, MO, USA). Strength calculation formula:
R p = P L × B
The variables in the formula are defined as follows: R p —compressive strength, unit is MPa; P —maximum failure load, unit is N; L —length of compressed surface, unit is mm; B —width of compressed surface, unit is mm.
The sample preparation process is as follows: (1) First, weigh the materials required for the experiment. (2) Put the weighed cementitious materials (cement, recycled aggregates, silica fume, etc.) into the mixer in sequence and mix them dry for 1 min to ensure that the cementitious materials are evenly mixed. (3) Mix the weighed water and modifier evenly in the container, slowly pour them into the mixer, and stir for 3 min. (4) Then, the measured sand and stone is poured into the mixer, stirring for 6 min, according to the test, the mixing time can be extended appropriately. Then, the evenly stirred mixture is loaded into the mold, and finally the test mold is filled and vibrated tightly. After the vibration is completed, use a spatula to scrape off the excess mixture on the edge of the test mold, and smooth it, and place it indoors, and cover the surface with plastic film to prevent water evaporation. The sample preparation process is shown in Figure 4.
Collapse test: Conduct concrete expansion test according to the Standard Test Method for Performance of Ordinary Concrete Mixtures (GBT50080-2016) [41]. The final result of the experiment is taken as the average of the two maximum diameters that are perpendicular to each other. The slump test is shown in Figure 5.
SEM Testing: The KYKY-EM6200 scanning electron microscope (KYKY Technology Co. Ltd., Beijing, China) was used for electron microscopy scanning testing. Cut the test blocks during the axial compressive strength testing process into cubes not exceeding 10 mm, and then dry them in an oven at a temperature of 80 °C for 24 h to ensure complete evaporation of moisture. Before conducting electron microscopy scanning, steps such as gold spraying and vacuum pumping are required. The experimental instrument is shown in Figure 6.
Sample curing: According to the relevant provisions of the national standard “Test Methods for Physical and Mechanical Properties of Concrete” (GB/T 50081-2019) [42], the compressive strength test block size for ultra-high performance concrete mix proportion selection is 100 mm × 100 mm × 100 mm, the specimen is left to stand at room temperature for 24 h before demolding, and the specimen is placed in a standard curing box for curing. The temperature is maintained at 20 + 2 °C and the humidity is above 90%. After 28 days, the specimen is taken out for mechanical performance testing. The constant temperature curing box is shown in Figure 7.

2.3. Orthogonal Experimental Design

The orthogonal design is a mathematical method of arranging multi-factor tests to determine the primary and secondary factors and find the optimal mix ratio of recycled concrete [43,44]. In this experiment, the water–binder ratio of concrete was 0.29, and the particle size of recycled concrete was 15–20 mm. In this experiment, modifier content was selected as factor A, and the three levels of factor A were 8%, 10%, and 12%, respectively. The action time of the modifier was factor B, and the three levels of factor B were 30 min, 60 min, and 90 min, respectively. The content of recycled aggregate is factor C, and the three levels of factor C are 20%, 40%, and 60%, respectively. The test indexes are water absorption of reclaimed aggregate, slump of newly mixed concrete, and 28 d compressive strength of reclaimed concrete sample. Orthogonal tests were conducted according to the test factors and the number of levels. The factors and levels are shown in Table 3.

3. Results

The orthogonal experimental plan and experimental results are shown in Table 4. The factors A, B, and C are modifying agent, modification time, and recycled aggregate content. We can see from Table 4 that after modifying the coarse aggregate, the water absorption rate ranges from 3.6% to 12.1%. The slump is 142–169 mm, and the compressive strength range is 52–68 Mpa.

3.1. The Effect of Modification Time on Water Absorption Rate

The effects of the concentration of modifier, modification time, and the amount of recycled aggregate on the water absorption performance are shown in Figure 8. As shown in Figure 7, with the increase in modifier dosage, the water absorption rate of recycled aggregate shows a significant downward trend. This is because as the concentration of modification solution increases, more hydration product wrapping layers are generated on the surface of recycled aggregate, blocking the pores and cracks on the surface of recycled aggregate, making the surface of recycled aggregate more dense and improving the apparent density of recycled aggregate; with the extension of modified impregnation treatment time, the water absorption rate of recycled aggregates decreases, and the overall performance is worse than the dosage of modifiers; with the increase in recycled aggregate content, the water absorption rate of recycled aggregate shows a significant and rapid increase trend, increasing from 3.4% to 10.73%, mainly due to the increase in recycled aggregate content, which increases the contact area with water. In summary, the factors affecting the water absorption rate of recycled aggregates in descending order are as follows: recycled aggregate content > modifier concentration > modification time. According to the analysis of experimental results, the combination with lower water precipitation rate of recycled aggregate is A3B3C1.

3.2. Slump Analysis

The concentration of modifier, modification time, and the change in slump of recycled aggregate content are shown in Figure 9. Analyzing the data in Figure 9, it can be seen that the modification time and dosage of the modifier have an increasing trend on the slump of the concrete mixture, but the effect is relatively small; the dosage of recycled aggregate has a significant impact on the slump of concrete mixtures, showing a decreasing trend overall. When the dosage of recycled concrete increases from 20% to 60%, the slump of concrete mixtures decreases from 167.3 mm to 144 mm, a decrease of 13.93%. Based on the above analysis, the dosage of modifier and modification time have a relatively small impact on the slump of concrete, while the dosage of recycled aggregate has the greatest impact on the slump. The main reason is that the increase in recycled aggregate will absorb more water, making the fresh concrete more viscous and reducing the fluidity of the concrete. This is because the apparent density of recycled fine aggregate is low, the water absorption rate is high, the cohesion is greatly reduced, and the flowability of recycled concrete mixtures is reduced. The cohesiveness of recycled concrete deteriorates with the increase in the content of broken brick aggregates. According to the analysis of experimental results, the ideal slump combination for recycled concrete is A3B3C1.

3.3. The Influence of Admixture Dosage on Concrete Strength

The changes in the axial compressive strength of concrete under various factor levels of modifier concentration, modification time, and recycled aggregate are shown in Figure 10. As shown in Figure 10, with the increase in modifier dosage, the overall compressive strength of recycled concrete shows an increasing trend. The modifier dosage increases from 8% to 12%, and the axial compressive strength of concrete increases by 12.81%; with the increase in modifier dosage, the axial compressive strength of concrete also shows an increasing trend. When the modification time is increased from 30 min to 90 min, the axial compressive strength of concrete increases by 6.33 MPa, an increase of 11.24%; the axial compressive strength of concrete decreases with the increase in recycled aggregate content, increasing from 20% to 60%. The axial compressive strength of concrete decreases by 2.67 MPa, a decrease of 4.15%. The main reason is that the surface of recycled aggregate is wrapped in cement slurry, which promotes the hydrophilicity of recycled aggregate and reduces the elastic modulus between recycled aggregate and cement slurry. Due to the high strength of the interface between cement slurry and coarse aggregate and the mortar itself, the fracture often runs through the middle of coarse aggregate. Excessive recycled aggregate does not promote the compressive strength of concrete. Therefore, the dosage of recycled aggregates plays a very important role in the strength of high-strength concrete. According to the analysis of the experimental results, the 28 d axial compressive strength of recycled concrete is relatively combined as A3B3C1.
In summary, based on the comprehensive analysis of fluidity, water precipitation rate, and concrete axial compressive strength, the optimal proportion of recycled concrete A3B3C1 is determined, which is a modifier content of 12%, a modification time of 90 min, and a waste content of 20%.

4. Analysis of Modification Mechanism

The microstructure of the interface transition zone between recycled aggregate and cement slurry is shown in Figure 11. The macroscopic properties of materials are closely related to their microstructure, which can reflect their macroscopic properties. The interface transition zone has a significant impact on the performance of cement-based materials. Therefore, the microstructure of different interface transition zones is analyzed [45,46,47,48,49]. When conducting concrete compressive strength experiments, four representative samples that comply with electron microscopy scanning were selected at the fracture surface. After plasma sputtering and gold spraying treatment, the microstructure differences in each sample were scanned and analyzed under a scanning electron microscope to further analyze their mechanism of action on recycled aggregate concrete. The SEM images of the transition zone between recycled aggregates and cement-based slurries show the distribution of materials. The aggregates and cement-based slurries are bonded to each other, surrounded by sheet-like calcium hydroxide (CH) and needle-shaped ettringite (AFt). The bonding strength at the interface connection is low, and when the sample is subjected to load, it is easy to break in areas with poor bonding. After modification with modifiers, the water consumption at the interface of recycled aggregate will be further reduced, resulting in more complete hydration reaction between cementitious slurry and the bonding surface of recycled aggregate, greatly enhancing the overall strength of concrete materials.
Due to the adhesion of waste mortar on the surface, the surface of recycled aggregate is loose and porous, and a large number of micro cracks are distributed on the surface and inside, resulting in high water absorption and a low strength of recycled aggregate. The workability and strength of the prepared recycled concrete deteriorate. Based on the characteristics of recycled aggregates, surface modification methods can be considered from two aspects. One is surface chemical modification. Using modifiers to form a coating layer on the surface of the aggregate, covering the surface including pores and microcracks, making the inorganic aggregate surface organic while making it more compact, exhibiting good hydrophobicity and reducing its water absorption rate. The second is surface physical encapsulation modification, which does not change the surface hydrophilicity of inorganic aggregates. The modifier undergoes a hydration reaction with the waste mortar adhered to the surface of recycled aggregates, and the generated hydration products physically fill the pores and microcracks on the surface of recycled aggregates, making the surface more compact and reducing their water absorption rate. On the other hand, defects such as loose and porous surface waste mortar layer and micro cracks are cemented, strengthening the weak interface transition zone between waste mortar and aggregate, resulting in an increase in the strength of recycled aggregate and a decrease in crushing index.
Silane coupling agent is a special type of silicon-based compound, with a structural formula usually represented as Y (CH2) nSiX3. The molecular structure contains two functional groups: X and Y groups. As a hydrolyzable functional group, X mainly affects the hydrolysis rate and efficiency of silane, with commonly used groups being methoxy and ethoxy, improving affinity between inorganic substances through chemical reactions or adsorption on their surfaces. The Y group is an active functional group, such as methyl, vinyl, and epoxy groups. Due to its affinity reaction with polymer molecules, it usually has a significant impact on the properties of composite materials when interacting with them. Silane coupling agents have dual functional groups that are both organic and inorganic friendly, which can connect two types of interfaces with significant differences in chemical structure and performance. They act like molecular bridges, and the interface transition zone is the weak part of concrete. Before the load is applied to the concrete, microcracks will occur during the hardening process of the cement slurry due to shrinkage reactions; after loading, fracture patterns located in the interface transition zone between aggregates and cement mortar can usually be observed. The reason for this is that the bonding strength between cement slurry and aggregates is mainly generated by van der Waals forces between molecules, and during the mixing process of concrete, the adsorption capacity of aggregates for water is stronger than the bonding force in plastic mortar. Therefore, a layer of water film is formed on the surface of aggregates, resulting in the “edge wall effect”. Usually, when the fine aggregate particle shape is needle-like, it will lead to local bleeding, and the generated bubbles will be blocked and then accumulate on the lower surface of the aggregate. Due to the above reasons, the local water cement ratio of the interface layer between cement slurry and coarse aggregate is greater than the design value, which will cause a large amount of ettringite and calcium hydroxide crystals, resulting in a looser skeleton structure and larger porosity of the interface layer compared to cement slurry or mortar matrix, The formed interface transition zone is also prone to damage, and the properties of the transition layer determine the performance of concrete materials, which helps to improve the structure of its interface transition zone. Therefore, the research on improving the quality of the interface layer between cement slurry and aggregate has taken into account the urgent needs of current and future concrete performance, and is of both theoretical and practical significance.

5. Conclusions

This article uses orthogonal experiments to conduct modification experiments on recycled concrete and develops recycled concrete materials. The following conclusions are drawn:
  • The water absorption rate of recycled aggregate shows a decreasing trend with the dosage of modifier and modification time, which is also reflected in the slump test of fresh concrete, indicating that the modification of recycled aggregate is effective.
  • Targeting the 28 d strength of recycled concrete, the optimal factor level combination is A3B3C1, with a water cement ratio of 0.29, a modifier dosage of 12%, a modification time of 90 min, and a recycled aggregate dosage of 20%.
  • In the interface transition zone between modified recycled fine aggregate and cement stone, only small size tabular CH crystals can be seen, and the hydration products C-S-H gel, ettringite, etc. are interspersed with each other, with a dense structure and no obvious pores.

6. Discussion

Some scholars are committed to researching the reuse of waste concrete, and they have also achieved some good results. However, research on the modification of recycled aggregates for waste concrete is relatively rare. The construction industry still needs to conduct sufficient experimental research on the preparation of recycled aggregates from waste concrete, such as recycled concrete and recycled rubber sand. It is of practical significance to study the performance of recycled aggregates from construction waste, especially the surface modification of recycled aggregates. Based on previous research, this article proposes to modify recycled aggregates and design orthogonal experiments to obtain optimal proportions of recycled concrete, providing a reference for the reuse of waste concrete in the future.

Author Contributions

J.Z. and M.Z. performed data curation, formal analysis, investigation, methodology, validation, and writing of the original manuscript; X.Z. and X.H. contributed to data curation, conceptualization, investigation, supervision, and editing of the manuscript. All authors have read and agreed to the published version of the manuscript.

Funding

This project was supported by Natural Science Research Project of Colleges and Universities of Jiangsu Province (22KJD560007). A Project Supported by Scientific Research Fund of Yancheng Polytechnic College (ygy1911). Industry-university-research cooperation project: 2024HX-009.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Data are contained within the article.

Conflicts of Interest

The authors declare no conflicts of interest.

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Applsci 14 01974 g001
Figure 1. Cement clinker particle size distribution curve.
Figure 1. Cement clinker particle size distribution curve.
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Figure 2. Waste concrete recycled aggregate preparation process.
Figure 2. Waste concrete recycled aggregate preparation process.
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Figure 3. Relation of porosity and strength with particle size.
Figure 3. Relation of porosity and strength with particle size.
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Figure 4. Process of making concrete samples.
Figure 4. Process of making concrete samples.
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Figure 5. Slump test.
Figure 5. Slump test.
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Figure 6. SEM testing instrument (ZESIS, Jena, Germany).
Figure 6. SEM testing instrument (ZESIS, Jena, Germany).
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Figure 7. YH-40B standard constant temperature curing box (Zijin Mining Group Co., Ltd., Longyan, China).
Figure 7. YH-40B standard constant temperature curing box (Zijin Mining Group Co., Ltd., Longyan, China).
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Figure 8. The influence of various factor levels on water absorption rate.
Figure 8. The influence of various factor levels on water absorption rate.
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Figure 9. Slump test results.
Figure 9. Slump test results.
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Figure 10. Concrete strength at various factor levels.
Figure 10. Concrete strength at various factor levels.
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Figure 11. Microstructure of the interface transition zone between recycled aggregate and cement slurry. (a) The test number 1; (b) The test number 3; (c) The test number 6; (d) The test number 9.
Figure 11. Microstructure of the interface transition zone between recycled aggregate and cement slurry. (a) The test number 1; (b) The test number 3; (c) The test number 6; (d) The test number 9.
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Table 1. Physical performance indicators of cement.
Table 1. Physical performance indicators of cement.
SSA (m2/kg)LossSetting Time (min)Bending Strength (MPa)Compressive Strength (MPa)
Initial SettingFinal Set3 d28 d3 d28 d
3351.55%902404.58.121.657.5
Table 2. Physical parameters of silica fume.
Table 2. Physical parameters of silica fume.
NameSiO2 (%)SSA (m2/kg)Loss (%)Cl− (%)Moisture (%)Water Proportion (%)
silica fume8621,0003.50.21.85110
Table 3. Orthogonal test protocol L9 (33).
Table 3. Orthogonal test protocol L9 (33).
GroupA/Modifying Agent (%)B/Modification Time (min)C/Recycled Aggregate Content (%)
11 (8)1 (30)1 (20)
21 (8)2 (60)2 (40)
31 (8)3 (90)3 (60)
42 (10)1 (30)2 (40)
52 (10)2 (60)3 (60)
62 (10)3 (90)1 (20)
73 (12)1 (30)3 (60)
83 (12)2 (60)1 (20)
93 (12)3 (90)2 (40)
Table 4. Results of orthogonal experiments.
Table 4. Results of orthogonal experiments.
GroupABCTest Results
Water Absorption (%)Slump (mm)28 d Strength (MPa)
11 (8)1 (30)1 (20)4.216252
21 (8)2 (60)2 (40)6.715358
31 (8)3 (90)3 (60)12.114661
42 (10)1 (30)2 (40)7.615256
52 (10)2 (60)3 (60)10.714263
62 (10)3 (90)1 (20)3.917159
73 (12)1 (30)3 (60)9.414461
83 (12)2 (60)1 (20)2.116964
93 (12)3 (90)2 (40)3.615868
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Zhang, J.; Zhu, X.; Zhou, M.; Huang, X. Experimental Study on Preparation and Characteristics of Concrete Modified by Construction Waste. Appl. Sci. 2024, 14, 1974. https://doi.org/10.3390/app14051974

AMA Style

Zhang J, Zhu X, Zhou M, Huang X. Experimental Study on Preparation and Characteristics of Concrete Modified by Construction Waste. Applied Sciences. 2024; 14(5):1974. https://doi.org/10.3390/app14051974

Chicago/Turabian Style

Zhang, Jing, Xuejun Zhu, Mingyuan Zhou, and Xianwen Huang. 2024. "Experimental Study on Preparation and Characteristics of Concrete Modified by Construction Waste" Applied Sciences 14, no. 5: 1974. https://doi.org/10.3390/app14051974

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