1. Introduction
The purpose of asphalt pavement construction control is to ensure that the road has good quality. In the domestic context (China), control is currently achieved mainly in accordance with the Technical Specification for Highway Asphalt Pavement Construction (JTG F40-2004) [
1] (hereinafter referred to as the construction specification) to guide and control the quality of asphalt pavement construction. The specification gives the degree of influence of each inspection item on the quality of the pavement, and the constructors are not aware of the influence of each inspection item on the control index, making the construction somewhat blind [
2]. Wang et al. showed through indoor tests and field investigations that non-uniformity (gradation segregation, temperature segregation and compaction segregation) has a large impact on the road performance of asphalt mixtures [
3], while non-uniformity in asphalt pavements is mainly caused during the construction process. Therefore, to ensure the performance of asphalt pavements, the occurrence of non-uniformity in the asphalt mixture needs to be controlled during construction [
4].
Abroad, in the 1950s, AASHTO recorded a large amount of asphalt pavement test data, which laid the foundation for later control techniques, as well as developing quality control specifications for raw materials and introducing the concept of statistics into quality control [
5]. In the 1970s, the US applied statistical methods to pavement construction, used statistical methods to analyze variability in indicators, first proposed a QC/QA (quality control/quality assurance) system and established a complete quality control system for asphalt pavements in the 1980s. Since the 1990s, with the promotion of SHRP results, QC/QA systems have been widely used and have achieved better results in practical applications. In addition, there are more studies abroad on the influencing factors of pavement performance. The Mechanistic Empirical Pavement Design Guideline (MEPDG) method [
6] in the USA predicts a rutting model for asphalt pavements that considers the mechanical response of the pavement structure and the performance of the asphalt mixture. The US NCHRP 9-22 report [
7] analyzed the effects of factors including construction-related factors on fatigue cracking, rutting and low temperature cracking. More research has been carried out on prediction models such as cracking and rutting [
8,
9], e.g., rutting prediction models can be categorized as empirical, theoretical and mechanistic-empirical models [
10,
11]. Mirzahosseini et al. [
12] predicted the Flow Number of asphalt mixes based on machine learning methods using parameters such as asphalt dosage, coarse aggregate ratio, filler ratio, mineral gap ratio and void ratio.
The construction of asphalt pavements is a complex process in which materials, processes, personnel and equipment all have an impact on the quality of the asphalt pavement, and when coupled with adverse conditions such as environmental conditions, traffic load and tire tension, it will cause irreversible deformation of asphalt pavement, which will affect the service life of asphalt pavement [
13,
14,
15]. There are many discussions on the control of asphalt pavement construction process, but most of them can be summarized into the following categories: first, analyze the construction control indicators, select or improve the construction indicators in the specification, and control the construction process of asphalt pavement through statistical control charts; secondly, analyze the variability of construction control indicators, get the variation range of indicators through experiment or simulation verification, and then dynamically control the pavement construction process through statistical control principle; thirdly, through the analysis of statistical control, select or recommend more convenient or appropriate quality control chart, and then carry out dynamic control of asphalt pavement construction process. However, other influencing factors in the construction are often not considered comprehensively, the control of the construction process is not comprehensive enough, and there are some phenomena such as insufficient attention to the control of the overall performance of asphalt pavement. Numerous factors need to be considered when evaluating asphalt pavement construction control, and as these indicators are either quantitative or qualitative, new evaluation models need to be applied to objectively describe and address construction control issues.
Around asphalt pavement, many scholars have carried out relevant research. Ahmed et al. [
16] investigated the effect of using four local industrial waste/by-product materials (marble, granite, steel slag and hydrated lime powder) as mineral fillers on asphalt mixture characteristics, and the testing results show that the asphalt mixture containing marble as a filler yields the highest stability. Tarbay et al. [
17] present the use of waste materials (marble and granite) and by-product material (steel slag) as alternative to the conventional mineral filler, and show that mixtures containing waste marble yielded the highest stability. Moreover, marble is able to improve the moisture damage resistance in terms of tensile strength ratio and loss of stability.
As for the evaluation method, commonly used evaluation methods include the fuzzy comprehensive evaluation method [
18], the analytic hierarchy process (AHP), and the superiority assessment method based on the toposable set theory. For example, Zhang et al. [
19] proposed a decision framework based on fuzzy comprehensive evaluation (FCE) and analytic hierarchy process (AHP) for selecting the best mineral filler from four mineral fillers for pavement structures in selected areas. The proposed methodology combines qualitative and quantitative factors, thus increasing the credibility of the material suitability assessment. Han et al. [
20] proposed a new construction quality evaluation framework, which was a combination of the building information model (BIM) and geographic information system (GIS). The framework performed the real-time and full-process quality evaluation of asphalt pavement construction. Taking the Phnom Penh-West Halluk highway construction project as a case study, the results show that the framework provides a good information environment for construction quality evaluation. Xiong et al. [
21] proved through experiments that gap-graded mix performed better in rutting resistance than dense-graded specimens. Modification with high viscosity agents could significantly inhibit rutting propagation, offering an important improvement the construction quality of asphalt pavement.
The indicator system of the fuzzy evaluation method is a static attribute. The indicator values are selected as a set of real numbers, and the measured data are interval point values of fuzziness [
19,
22]. Toposable sets [
23] are an extension of classical and fuzzy sets and are able to describe the degree of variability, quantitative processes and qualitative processes of things. Literature research shows that the evaluation index system of fuzzy comprehensive evaluation is a static attribute, the judgment matrix lacks elasticity, the weight determination is subjective, and the selection of index values is a real number set. Practice shows [
24] that the conventional indexes of asphalt might meet the specification requirements without necessarily ensuring the asphalt is in a good state. Based on this, on the premise of meeting the requirements of the specification, this paper uses each index to classify each respective requirement. For the convenience of data analysis, each index is normalized and dimensionless [
25]. Combined with expert survey data, the extension interval number judgment matrix [
26] is constructed, and the extension interval values are used instead of specific point values to construct the extension judgment matrix. This not only considers the subjectivity of expert judgment, but also combines the weight solution with the consistency test of judgment matrix, which simplifies the calculation and overcomes the shortcomings of rough calculation process and strong subjectivity of traditional analysis methods. Finally, the weight of each index is calculated by extension set theory analysis. By constructing an extension set for a comprehensive evaluation model of asphalt pavement construction control, the evaluation grade of construction control is calculated by the extension method, enabling to evaluate the asphalt pavement construction control. Combined with specific examples, the model calculation and verification are carried out, and the verification results are more scientific and reasonable. Various factors in the construction are comprehensively considered, which provides reference for the control process of asphalt pavement construction and ensures the construction quality of asphalt pavement.
4. Case Study
4.1. Calculation of Weights
According to the indicator system constructed in the previous section and the principle of comparison by the 1–9 scale method, experts were invited to make a two-by-two comparison of the relative importance between elements, and the judgment matrix
A of each attribute of the criterion layer to the target layer was established as shown in
Table 3.
Then the matrices
and
are:
The eigenvectors
and
are calculated as
The coefficients and are calculated from Equations (1) and (2). Clearly , which meets the requirements.
Calculated from Equation (3): , , , and . In turn, the weights were calculated.
Following the calculation of the weights above, the matrices
and
are constructed in turn, and
and
are calculated to obtain:
, and the weights are then calculated. The calculation results are shown in
Table 8.
From the above analysis, it can be seen that there are many factors affecting the construction of asphalt pavement, and the weights of each factor are different. According to the analysis results of each evaluation index in
Table 8, paving factors have the greatest influence on the construction and quality of asphalt pavement, among which paving temperature and paving speed play a vital role. Therefore, in order to ensure the construction quality of asphalt pavement meets the requirements, the first thing is to strengthen the control of paving factors in the construction process of asphalt pavement, and strictly grasp the temperature and speed in the paving process of asphalt pavement according to the corresponding specifications and the actual construction environment on site.
4.2. Determination of Assessment Levels
According to the construction characteristics of the pavement and relevant information, the construction control evaluation of asphalt pavement is divided into five grades: excellent (I), good (II), medium (III), lower (IV) and poor (V), as shown in
Table 9. The grading of the indicators is determined by reference to the relevant range of provisions in the specification [
1]. For example, the range of crushing values is 0–26%, and it has been pointed out in the literature that coarse aggregates with crushing values greater than 25% are susceptible to crushing during the rolling of the mix [
27], which proves that the choice of crushing value range is significant. For the mixing temperature indicator, the asphalt heating temperature and the mix discharge temperature are used for consideration, with the median temperature range of the specification being the optimum temperature value, and the relative temperature deviation determines the range for each level. If the temperature range specified in the specification is
, and the measured heating temperature is
, the two ratios
of the asphalt heating temperature and the mix discharge temperature are calculated according to Equation (18), and the larger of these is taken as the basis for evaluating the mixing temperature index. For the paving temperature and rolling temperature indicators, respectively, then the respective minimum temperature requirements are the lower limit; the upper and lower limit of the mixture discharge temperature are the upper limit of paving and rolling; the average of the interval is graded into five levels, and the higher the temperature indicates a better state; such that for the determination of the temperature limit range of
, the actual measured heating temperature of
, and the ratio
calculated according to Formula (19) are the basis for evaluation. For the oil to stone ratio and thickness indicators, the grades are divided by deviation. Practical experience shows that asphalt content deviating from the optimum oil to stone ratio by more than 0.3% significantly affects the performance of the mix, so 0.3% can be used as a grading range for the oil to stone ratio. Here the permissible deviation of −5% of the total thickness design value of the highway is taken as the grading range of thickness, and the deviation is treated as 0 when positive. Other grades of pavement can be divided according to the corresponding grade for similar division methods. For the qualitative indicators, a rating between 0~100 was used for the grading based on consideration of the norms and the actual situation. The ranking of each indicator is shown in
Table 10.
As the data between the evaluation levels of each evaluation index is not comparable, in order to facilitate the analysis of the data, the indexes are dimensionless and normalized in this paper. If the nature of the effect of the index on construction control is positive, treat it according to Equation (20); if the nature of the effect of the index on construction control is reversed, treat it according to Equation (21).
The intervals of the processed index levels and the measured values are shown in
Table 11.
4.3. Constructed Asphalt Pavement Construction Control of Matter-Element
From Equations (1) and (2), the classical and nodal domains of asphalt pavement construction control can be obtained as follows:
4.4. Calculation of the Correlation of Evaluation Indexes
The degree of correlation is calculated by Equation (4) and the results are shown in
Table 12.
4.5. Evaluation of Asphalt Pavement Construction Control
From Equation (8),
is calculated as:
Similarly, it can be calculated that:
In summary, the correlation of the asphalt pavement construction control level calculated from Equation (9) is
According to , the construction control level of this asphalt pavement is level II, and the eigenvalue of the level variable is obtained from Equation (11) as , which integrates the construction control bias of this asphalt pavement to level III.
According to the evaluation results, the construction control level of the paving and rolling factors is Level II and the evaluation conclusion is “Good”, but the evaluation result of the thickness and rolling speed of the subsystem is “Low”. For thickness control of the paver parameter settings, the screed and auger arrangement should be checked for reasonableness and the height of the mix around the fabric should be cofirmed. For the control of the rolling speed, the selection and training of the roller operator should be improved. The level of construction control for the material and mixing factors is level III, with an evaluation conclusion of “Medium”. The analysis shows that the evaluation conclusion for the material factor is “Poor” for the sludge content indicator and “Low” for the mixing factor for the gradation factor. There is a lot of room for improvement and upgrading. During the construction control process, the detection and control of mud content and gradation should be strengthened, especially the mud content index, which needs special attention in order to improve the construction control of asphalt pavement and ensure its construction quality.
5. Discussion
Firstly, from the perspective of research methods, the evaluation index system of analytic hierarchy process (AHP) and fuzzy comprehensive evaluation adopted in the literature [
18,
19,
20,
21] is a static attribute, the judgment matrix is inflexible, the weight determination is subjective, and the selection of index value is a set of real numbers. By contrast, the method adopted in this paper selects a set of real numbers, and the measured data is the interval point value of fuzziness, which can describe the variability of things, the quantitative change process and the degree of the qualitative change process. In addition, this paper considers using the extension interval value instead of the specific point value to construct the extension judgment matrix, which not only considers the subjectivity of expert judgment, but also combines the weight solution with the consistency test of the judgment matrix, thereby simplifying the calculation and overcoming the shortcomings of the rough calculation process and strong subjectivity of the traditional analysis method. Second, asphalt pavements construction is a complex process, and material, technology, personnel, and equipment all have influence on the quality of the asphalt; in addition, the environmental conditions, traffic load and the tension of tires and other adverse conditions, including the action of will, can cause irreversible deformation of asphalt pavement, affecting the service life of the asphalt road surface. Therefore, in the asphalt pavement construction control evaluation, many factors need to be considered, including quantitative and qualitative indicators, and there is a need to apply a new evaluation system to describe and deal with the construction control problem. However, literature [
6,
7,
8,
9,
10,
11,
12] considers relatively single factors, which is insufficient to comprehensively and objectively analyze the construction quality of asphalt pavement.