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Concrete Pavement Technology Update

August 2008

CPTP Update—New Products and Recent Activities

Products and Reports

Several CPTP reports and related products have been completed recently. These include:

  • Cost-Effectiveness of Sealing Transverse Contraction Joints in Concrete Pavements (CPTP Task 9). This report reviews the history of transverse joint construction and sealing in concrete pavements, summarizes the results of a field survey program in which distress and deflection data were collected from 117 test sections, and presents the findings of a detailed analysis of that data.
  • Inertial Profile Data for PCC Pavement Performance Evaluation (CPTP Task 63). The ProVal software program (which allows users to view and analyze pavement profiles in many different ways) was employed to help minimize the harmful effects of thermal curling and moisture warping in concrete pavement slabs. Work conducted under this CPTP task contributed to the development of ProVal 2.0.
  • Computer-Based Guidelines for Job-Specific Optimization of Paving Concrete (CPTP Task 64). A beta-version software program called COMPASS has been developed to assist engineers in determining the ideal paving mixture for a particular project (see COMPASS article).

ETG Plans Next Steps

The CPTP Engineering Expert Task Group met on November 6, 2007, in conjunction with a CPTP-sponsored international conference. The group heard updates on CPTP and related projects and discussed priorities for CPTP activities during the coming months. The following action items were identified:

  • Conduct an aggressive marketing effort to promote the CPTP Best Practices workshops.
  • Develop a TechBrief on joint sealing following approval of final report.
  • Emphasize the need for more concrete pavement training at all levels.
  • Update and emphasize the CPTP Product Catalog.
  • Consider a TechBrief on COMPASS after the final report is available.
  • Organize a conference in spring 2009 focused on effective strategies for concrete pavement maintenance and rehabilitation.

In addition, Bill Farnbach summarized activities at Caltrans related to concrete pavement with a focus on “green” concrete, environmental impact, and long-life pavements.

COMPASS—Concrete Mixture Performance Analysis System Software

With the emphasis on accelerated construction and long-lasting pavements coupled with a wider variety of materials options, concrete mixture optimization has become more challenging than ever. Mixture design requires the consideration of a wide array of aggregate sources, cement sources and types, chemical admixtures, supplementary cementitious materials, and recycled materials. The designer must also consider the interaction of ingredients within the mixture and how a given environment may affect the construction and the long-term performance of the pavement. “What was needed was a mixture optimization tool that could simplify the approach to the mix design and proportioning process based on job-specific conditions,” said Peter Kopac of the Federal Highway Administration’s (FHWA) Office of Infrastructure Research and Development. To meet that need, FHWA developed the new COMPASS software.

The Windows-based system consists of two main parts, a knowledge base (expert system) and four computer modules. The optimization process is illustrated below.

The knowledge base is a compilation of information on concrete properties, testing methods, material characteristics, and material compatibilities with one another and with the environment. The information is interactively accessed, filtered, and logically presented to the user.

Optimization Process Employing a Knowledge Base and Computerization

The mixture optimization process is sketched, beginning with the contents of its knowledge base (multiple rock sources, multiple sands, multiple cements, fly-ashes, GGBFS 8, fume, natural pozzolans, and chemical admixtures); next, a subset of materials is selected (e.g., two rock sources, one sand, two cements, one Class F fly-ash, one GGBFS, and two chemical admixtures); optimization techniques then yield a list of the optimum rock, sand, cement, Class F fly-ash, and chemical admixture and their optimum proportions.

Four computer modules accept user-defined, job-specific inputs and perform the analysis:

  1. Mix Expert
  2. Gradation
  3. Proportioning
  4. Optimization

Each module has the ability to be used independently, or the user can perform a comprehensive analysis across modules 1 to 4 building upon each consecutive module’s analysis. The flow for the comprehensive analysis is as follows:

  1. Identify the performance criteria relative to site-specific conditions (Module 1–Performance Criteria).
  2. Select materials that best suit the conditions (Module 1–Materials Selection).
  3. Determine optimal aggregate gradations for maximum packing density and workability (Module 2–Gradation).
  4. Determine preliminary mixture proportions (Module 3–Proportioning).
  5. Optimize the concrete mixture proportions based on job-specific criteria (Module 4–Optimization).

The inputs to the first module are cross-referenced with the information in the knowledge base to help guide the user in selecting the performance criteria and materials to meet those criteria. This information is used to optimize the paving mixture for the environment at the pavement project. Modules 2 to 4 include analytical subroutines to optimize materials proportions based on job-specific criteria. Yet, to simplify and reduce training requirements, a number of input options are fixed.

The COMPASS system has undergone extensive peer review and field application testing, and the draft final report and a user’s manual have been completed and are undergoing FHWA review.

Article prepared by Ken McGhee, CPTP Implementation Team (kvmcghee3@aol.com).

 

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Updated: 04/07/2011
 

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