BACKGROUND: AASHTO T 277/ASTM C 1202, Electrical Indication of Concrete Ability to Resist Chloride Ion Penetration, has been widely accepted for assessing the durability of concrete. The test provides an indication of the concrete’s ability to resist chloride ion penetration, but it has many shortcomings: it is slow and time consuming, destructive, and prone to errors caused by sample heating, and it fails to adequately capture features associated with supplementary cementitious materials (SCMs). Electrical resistivity measurements (AASHTO T 358, Standard Method of Test for Surface Resistivity Indication of Concrete’s Ability to Resist Chloride Ion Penetration and ASTM C 1760, Standard Test Method for Bulk Electrical Conductivity of Hardened Concrete) have the potential of providing performance-based evaluation of concrete. Although the data from these methods are easy to obtain, they may not relate to concrete water permeability. It is suggested that a formation factor that incorporates the ratio of the resistivity (ñ) of the bulk concrete to the resistivity (ñ0) of the pore solution or other approaches could be used to provide a better assessment of fluid transport properties. There is a need to consider using such approaches for rating concrete permeability based on resistivity measurements and providing an expedited means for assessing concrete water permeability to facilitate the evaluation of concrete durability.
OBJECTIVE: The objective of this research is to develop a recommended procedure for rating concrete water permeability based on electrical resistivity measurements.
Accomplishment of the project objective will require at least the following tasks.
Phase I: (1) Review literature, ongoing research findings, and current practices relevant to concrete electrical resistivity and water permeability measurements and their relationship. This information may be assembled from published and unpublished reports, contacts with academia, transportation agencies, industry organizations, and other sources. (2) Identify and evaluate concrete mixture and test parameters that influence electrical resistivity measurements (e.g., aggregate sources including lightweight aggregates, cementitious materials, chemical admixtures, water to cementitious materials ratios, age of concrete, and curing regimen) and the methods currently used in the United States and other countries for measuring concrete electrical resistivity. Discuss the merits and deficiencies of these methods, and recommend potential methods and/or modifications thereof for use in the experimental investigation in Phase II. (3) Identify and evaluate concrete mixture and test parameters that influence concrete water permeability (e.g., aggregate sources including lightweight aggregates, cementitious materials, chemical admixtures, water to cementitious materials ratios, age of concrete, and curing regimen) and the methods currently used in the United States and other countries for measuring concrete water permeability. Discuss the merits and deficiencies of these methods and recommend potential methods and/or modifications thereof for use in the experimental investigation in Phase II. (4) Based on the information obtained in Tasks 1, 2, and 3, update the research plan that will be executed in Phase II for (a) refining test method(s) for measuring electrical resistivity, (b) developing and demonstrating test method(s) for measuring water permeability, (c) evaluating the effects of a range of the concrete mixture parameters identified in Tasks 2 and 3 on concrete resistivity and water permeability measurements, and (d) relating concrete water permeability to electrical resistivity measurements using approaches such as formation factor. The proposed concrete mixtures should cover the range of CaO/(Al2O3+SiO2) ratios obtained for mixtures made with 100% portland cement to those made with commonly used SCM types and proportions. (5) Prepare an interim report that documents the research performed in Phase I, and includes the updated research plan for Phase II. Following review of the interim report by the panel, the research team will meet with the project panel. Work on Phase II of the project will not begin until the interim report and the Phase II research plan are approved by the NCHRP. The decision on proceeding with Phase II will be based on the contractor’s documented justification of the updated research plan.
Note: The research plan prepared in in Task 4 must provide details on the work anticipated in Phase II. The work proposed for Task 6 must be divided into subtasks, and the work proposed in each subtask must be described in detail (e.g., details of the proposed experimental investigation: test methods including descriptions of non-standard test methods, concrete mixtures, number of specimens, test conditions, etc.).
Phase II: (6) Execute the plan approved in Task 5. Based on the results of this work, recommend (a) a test method for measuring concrete electrical resistivity, (b) a test method for measuring concrete water permeability, and (c) procedure for rating concrete water permeability based on electrical resistivity measurements (including a recommended rating of concrete permeability as very low, low, moderate, and high based on resistivity values). For recommended test methods that are not currently part of AASHTO or ASTM standard test methods, protocols should be developed and presented in AASHTO format. The recommendations for rating concrete permeability based on resistivity measurements should be prepared in the form of a recommended practice in AASHTO format. (7) Prepare and submit a final deliverable that documents the entire research effort. The recommended test protocol(s) and practice shall be prepared as stand-alone documents appropriate for incorporation into the AASHTO Standard Specifications for Transportation Materials and Methods of Sampling and Testing.
STATUS: Research in progress.