James E Bruinsma

REVIEW OF STUDIES CONCERNING EFFECTS OF UNBOUND CRUSHED CONCRETE BASES ON PCC PAVEMENT DRAINAGE

Recycled concrete aggregate (RCA) products are sometimes used as replacements for virgin aggregate products in concrete pavement structures. Recent concerns have centered on the deposit of RCA-associated fines and precipitate suspected of reducing the drainage capacity of RCA base layers and associated drainage systems. Environmental concerns have focused on the relatively high pH of the effluent produced by untreated RCA base layers. Several studies have examined these concerns and others; the results of some of these studies have not been published or publicized. The most relevant of these studies are summarized herein. These research efforts demonstrate that calcium-based compounds are present in most recycled concrete aggregates in quantities sufficient to be leached and precipitated in the presence of carbon dioxide. Precipitate potential appears to be related to the amount of freshly exposed cement paste surface. Thus, selective grading or blending with natural aggregates can reduce, but not eliminate, precipitate problems. It was also noted that insoluble, noncarbonate residue makes up a major portion of the materials found in and around pavement drainage systems. Washing the RCA products before using them in foundation layers appears to reduce the potential for accumulation of dust and other fines in the drainage system, but probably has little effect on precipitate potential. Field studies have shown that precipitate and insoluble materials can significantly reduce the permittivity of typical drainage fabrics but that attention to drainage design details can minimize the effects of these materials on pavement drainage.

CHEMICAL APPROACH TO FORMATION OF CALCITE PRECIPITATE FROM RECYCLED CONCRETE AGGREGATE BASE LAYERS

The use of recycled portland cement concrete aggregate in pavement base layers has been associated with the reduction of filter fabric permittivity and the accumulation of calcite precipitate and other materials in pavement subdrainage systems. A mechanism of portlandite dissolution within base-layer pore waters, followed by exposure to atmospheric carbon dioxide via subdrainage systems, and subsequent calcite precipitation is explored using chemical thermodynamic techniques. Ion activities and pH levels are estimated for the equilibrium states of rainwater entering the pavement, base-layer pore water isolated from the atmosphere, and subdrainage water exposed to the atmosphere. Results derived agree with field and laboratory observations of pH levels.

Accelerated Practices for Construction of Airfield Concrete Pavement: Lessons Learned from Planning Phase

Information and experiences about accelerated or fast-track portland cement concrete (PCC) paving projects from the airport pavement industry are presented. The focus is on steps that can be taken during the planning phase to accelerate airfield PCC paving projects; the presentation is based on detailed case studies that were developed under an Innovative Pavement Research Foundation project. These case studies were developed from an extensive list of accelerated projects compiled from sources within the airfield paving industry, including contractors, designers, owners, and industry representatives. The key to applying accelerated paving techniques for rigid pavements lies in understanding the available strategies and in knowing when and how these strategies should be applied. A range of materials is available for accelerating pavement opening times, which is most often thought of as accelerated paving. However, beyond the simple selection of appropriate materials, many other strategies can accelerate an airfield PCC paving or repair project, including thorough planning and coordination of project activities, considering procurement and contract factors, and application of appropriate phasing and scheduling techniques during the project planning phase. Strategies addressing design, construction, and ancillary issues are included in the Accelerated Practices for Airfield Concrete Pavement Construction final documents.

Quality Assurance For Airport Pavement Construction: Planning For Success

This paper describes how, in the past, on a typical airport construction project, the contractor was responsible for construction and the owner agency was responsible for measuring the quality of that construction. Today, on many airport construction projects the contractor is responsible for his own quality control (QC) and the owner tracks quality through a quality assurance (QA) program. This redistribution of responsibilities and resources has led to an uncertainty regarding the different roles and requirements for both contractors and owners on these projects. On a quality control/quality assurance (QC/QA) project, the contractor is now responsible for daily testing to ensure that the delivered product meets the project specifications and the construction process is in control while the owner is responsible for acceptance testing only. As part of the QA plan, the owner is also required to provide random testing at specified frequencies to ensure that the contractors testing procedures are being conducted within accepted standards. On some projects, the contractor may even be responsible for the acceptance testing. While QC/QA projects are fairly widespread, a thorough understanding of the implications of such projects, especially regarding roles and responsibilities, is not. This paper examines the experiences from several recent projects and presents observations and recommendations that can be used by airport owners, engineers, and contractors, to improve both the QC/QA process and the quality of airfield pavement construction.