Guidance for Increasing the Use of Recycled Concrete Pavement Materials

Recycling concrete pavements has been a common practice in the US for decades, and recently, public agencies have been more closely examining recycling opportunities. Reasons supporting recycling include the diminishing quantity of good natural materials, economics, improved project execution, minimizing traffic disruption, and supporting sustainability goals. Many states, however, have specifications or policies that restrict concrete pavement recycling. The contracting industry may overlook opportunities to use recycled concrete aggregates (RCAs) due to a lack of familiarity with technical requirements or uncertainty of performance. The National Concrete Pavement Technology Center (CP Tech Center) recently completed a comprehensive set of technical resources for the Federal Highway Administration to assist practitioners with sound approaches to project selection, scoping and construction requirements to support increased use of recycled concrete pavement materials. This paper describes the results of a 2016 survey of agency and industry RCA usage, presents an overview of the technical resources prepared as part of this initiative, and presents recommendations for supporting broader application of recycling concrete pavement materials.

ANALYSIS ON OPTIMIZATION DECISION OF PAVEMENT MAINTENANCE MODE BASED ON ANALYTIC HIERARCHY PROCESS

With the rapid development of China's transportation and the improvement of people's living standards, China's highways have entered the peak maintenance period. According to the old road conditions and financial conditions, how to choose the appropriate maintenance technology to meet the technical and economic requirements of highway maintenance and construction projects has become a difficult problem faced by highway maintenance management departments. Therefore, based on the principle of index selection, this study comprehensively considered the impact of various factors on maintenance decision-making, determined four evaluation indexes, and systematically studied the compre-hensive decision-making system of asphalt pavement recycling maintenance. Based on the subjective-objective linkage and probability statistics method, the eigenvalue of the applicability of recycling mode was transformed to the same scale of 0 to 100, and the fuzzy scoring interval of the four bids was proposed. The calculation method of pavement quality recovery index (PQRI) and the analysis basis of economic benefits were clarified. Finally, the weight of each index was calculated by analytic hierarchy process, and the multi-index comprehensive decision-making method of pavement maintenance is constructed and used to theoretically verify and guide the actual road section. Results demonstrate that the proposed PQRI can realize the operability of quantifying the later operation of pavement. The weight of each index from big to small is PQRI > economic benefit > applicability of recycling mode. The recycled pavement quality recovery indices and applicability of the four recycling modes have small differences, and the proposed four bids interval makes the decision-making evaluation process more simple and explicit. The decision evaluation results of actual road section verify the rationality and practicability of the decision method. The conclusions are important for the maintenance and management of asphalt pavement recycling technology. Keywords: road engineering, recycling maintenance, intelligent decision-making, fuzzy evaluation

Development of Roughness Prediction Models for Life Cycle Assessment Studies of Recycled Pavement Projects

The few existing life cycle assessment studies considering pavement recycling techniques usually omit the stages of maintenance and rehabilitation (M&R) and use. The reason for this omission is the lack of information about how the pavement’s performance evolves over time and absence of methods to determine the M&R frequency and service life for completed projects. As a result, the deterioration of pavement recycling projects in the long term is not clearly understood. Few projects have available data, the majority of which are on low volume primary and secondary roads. This paper describes an approach to develop a family of roughness models for recycling projects in Colorado using functional data analysis, and individual models for selected projects in Virginia to support ongoing life cycle assessment (LCA) studies. In the case of Colorado, full depth reclamation (FDR) projects will most likely deteriorate following an average group rate of 1.4 in./mi/year, with an initial international roughness index (IRI) between 52 and 70 in./mi. For the individual roughness models developed for Virginia projects, the initial IRI values and the rate of change for the treatments analyzed were found to range between 49 and 107 in./mi and between 0.7 and 5.2 in./mi/year, respectively, depending on the recycling method and type of stabilization treatment. The results of an LCA case study show that, in addition to recycling, Virginia Department of Transportation can achieve statewide emission reduction goals if focus is placed on achieving smoother roads while measures are taken to keep the annual rates of deterioration low.

Study of highway asphalt pavement recycling maintenance scheme decision system and decision method

With modern economic and social development, the technical and economic requirements of highway maintenance and construction projects have become increasingly complicated. Meticulous and in-depth investigation and demonstration guided by scientific theories and methods are of considerable importance to highway maintenance scheme decision. As basis for the selection of highway asphalt pavement recycling maintenance scheme, the factors influencing the decision are analytically demonstrated and an evaluation system is proposed, including three major decision indexes: applicability of recycling mode, recycled pavement quality recovery index, and economic benefit. According to the principles of data statistics and analysis, this study proposes a calculation method for the recycled pavement quality recovery index, analyzes the economic benefits of decision schemes using economic models such as recycling ratio and cost, and puts forward an optimal evaluation method of engineering cost and its fuzzy score intervals. Index weights are calculated through the analytic hierarchy process, and the comprehensive decision evaluation system and comprehensive evaluation method are established. Subsequently, the decision-making method is analyzed on the basis of the decision system by combining the related data. Results show maximum weight of the pavement quality recovery index and minor differences among four recycling schemes in the quality recovery index and applicability. The decision-making results are simplified with clear hierarchical feature because of the fuzzy score intervals of each index. Findings can provide a reference for the asphalt pavement recycling scheme decision.

The Definition of the Parameters of Innovative Transport and Technological Equipment for the In-Road Pavement Recycling, Using the Method of The Analysis of Fourth Coordinate of The Process

The features of the workflow of innovative transport and technological machines with non-waste technology, multi-purpose machines, recyclers and others similar are described in the article. The calculation methodology for determining the optimal parameters of machines and modes of operation, based on method of the analysis of fourth coordinate (duration) of the operating cycle, is presented. Dependences for determination of the power drive units of recycler are given. The procedure allows optimizing the parameters of the individual equipment units and of the entire recycler machine is described.

Study of the Incorporation of Ladle Furnace Slag in the Manufacture of Cold In-Place Recycling with Bitumen Emulsion

Cold in-place recycling with bitumen emulsion is a good environmental option for road conservation. The technique produces lower CO2 emissions because the product is manufactured and spread in the same location as the previous infrastructure, and its mixing with bitumen emulsion occurs at room temperature. Adding materials with cementitious characteristics gives the final mixture greater resistance and durability, and incorporating an industrial by-product such as ladle furnace slag (of which cementitious characteristics have been corroborated by various authors) enables the creation of sustainable, resistant pavement. This paper describes the incorporation of ladle furnace slag in reclaimed asphalt pavements (RAP) to execute in-place asphalt pavement recycling with bitumen emulsion. Various test groups of samples with increasing percentages of emulsion were created to study both the density of the mixtures obtained, and their dry and post-immersion compressive strength. To determine these characteristics, the physical and chemical properties of the ladle furnace slag and the reclaimed asphalt pavements were analyzed, as well as compatibility with the bitumen emulsion. The aforementioned tests define an optimal combination of RAP (90%), ladle furnace slag (10%), water (2.6%), and emulsion (3.3%), which demonstrated maximum values for compressive strength of the dry and post-immersion bituminous mixture. These tests therefore demonstrate the suitability of ladle furnace slag for cold in-place recycling with bitumen emulsion.