Subgrades and Subbases for Concrete Pavements

Analysis of the Federal Highway Administration’s (FHWA’s) Long-Term Pavement Performance (LTPP) data reveals that a pavement’s foundation (base or subbase and subgrade) is one of the most critical design factors in achieving excellent performance for any type of pavement.* For concrete pavements, the design and construction require ments of a roadbed or foundation structure may vary con siderably, de - pending upon subgrade soil type, environmental conditions, and the amount of anticipated heavy traffic. In any case, the primary objective for building a roadbed or foundation for concrete pavement is to obtain a condition of uniform support for the pavement that will prevail throughout its service life. Drainage considerations are also important in the proper design and construction of a roadbed or foundation for concrete pavement. It is important not to build a supporting layer system that holds water underneath the pavement slabs. This has been a common mistake in the design of concrete pavement structures, which has led to poor field performance of some concrete pavement sections. It is equally important not to over design the permeability of a subbase layer. Overzealous engineering of a permeable subbase will most likely lead to a foundation that does not provide the requisite stability for longterm pavement performance. Where stability has been sacrificed for drainage, concrete pavements have performed poorly and have experienced unacceptable numbers of faulted joints and cracked slabs within a relatively short period. Free-draining and daylighted subbases are the reasonable alternatives to rapidly draining permeable subbases with an edge drainage system that often lack stability for long-term perfor mance or cause other performance problems. In northern or cold climates, the influence of frost and freezing of the roadbed is an important consideration. Certain subgrade soils are particularly susceptible to frost action, which raises the foundation and concrete pavement layer(s) vertically during freezing periods (commonly referred to as heaving or frost heaving). Generally, frost heave is limited to areas of freezing climates with silty soils. If the heaving is uniform along a pavement section it is not detri mental, but if heaving is localized, it upsets the unifor mity of support provided to the surface pavement. Removing or treating these materials will be necessary to ensure that the pavement performs as expected. For nearly every pavement design there are many different subbases to choose from (i.e., unstabilized recycled concrete aggregate, cement-treated, lean concrete, etc.), as well as the decision of a natural or a treated subgrade. In some cases, as for most clays and some silty soils, it may be most economical and advanta geous to treat the subgrade soil and then to provide a unstabilized (granular) subbase as a construction platform. In the case of a road for a relatively low level of traffic it is likely that a natural subgrade may suffice, as long as it is evaluated to be acceptable as a roadbed. The optimal subbase and subgrade design or selection must balance both cost and performance consid erations. The same combination of subbase and subgrade treatment used for heavily-trafficked highways is likely not necessary for a low-volume roadway, even in the same area and subject to the same climate. Finally, it is likely that as this document is printed and distributed, some new and emerging technologies are advancing within the grading and paving industries. This guide captures the fundamental parameters, recommendations, and considerations for subgrades and subbases for concrete pavement. Emerging technologies, such as intelligent compac - tion and GPS-guided grading/placing equipment, are likely to become more commonplace in the future. These improvements to existing methods are not a replacement for the necessary consideration of the fundamentals. By the same token, we encourage agencies and contractors to advance their construction methods and improve the quality of their work using advanced technology.

Guide to Improving the Effectiveness of Cement-Based Stabilization/Solidification

Provides information on additives and field techniques that can improve the effectiveness of cement-based stabilization/solidification treatment of wastes. This 47-page guide includes discussions commonly occurring hazardous constituents in wastes and suggests additives and field techniques that can be used to successfully stabilize these constituents.

Portland cement-bases stabilization/solidification (S/S), has been used to successfully treat a wide variety of wastes. Some situations (because of the waste itself, the disposal scenario, and/or the regulatory requirements) require the use of additives or physical/chemical techniques to improve the effectiveness of cement-based S/S. The problems encountered in S/S can be broadly classified into solidification problems, i.e., adequately immobilizing the hazardous constituents of the waste. The Guide lists additives and techniques that can be applied to specific solidification problems such as problems in development of set, compressive strength, and free liquids. Also included are lists of additives and techniques that can be applied to immobilization of specific hazardous constituents such as lead, cadmium, and chromium, as well as classes of constituents such as volatile organics, organo-metallics and soluble salts. The Guide lists a variety of generic additives for specific desired stabilization/solidification effects, including those that can be used to control the pH of wastes; to reduce, oxidize, and co-precipitate constituents; and to accelerate or retard set.Contents1. Introduction2. Problems in Solidification and Physical Property Development - Setting Problems - Compressive Strength Development Problems - Permeability Development Problems - Durability Problems3. Problems in Target Constituent Stabilization - Chemical Properties - Metals - Organics - Organo-Metallics - Soluble Salts4. Additives Used in Cement-Based Solidification/Stabilization - Metal Stabilization - Immobilization of Organic Constituents -Processing and Anti-Inhibition Aids5. Physical/Chemical Techniques Used in Cement-Based Solidification/Stabilization - Anti-Inhibition Aids - Physical Property Development - Processing Aids - Mixing Techniques

‪USACE Geotechnical Investigations‬

‪USACE Retaining and Flood Walls‬

‪USACE Design of Sheet Pile Cellular Structures‬

Subsurface Drainage Manual for Pavements in Minnesota

A guide for evaluation of highway subsurface drainage needs and design of subsurface drainage systems for highways has been developed for application to Minnesota highways. The guide provides background information on the benefits of subsurface drainage, methods for evaluating the need for subsurface drainage at a given location, selection of the type of drainage system to use, design of the drainage system, guidelines on how to construct/install the subsurface drainage systems for roads, and guidance on the value of maintenance and how to maintain such drainage systems.

Solidification and Stabilization of Wastes Using Portland Cement

Solidification and stabilization (S/S) technology is currently being used to treat a wide variety of wastes. Although considerable information is available on S/S technology, much of it addresses research work or case studies on specific waste sites. This material usually contains very little on the characteristics of the binding agent used to treat the wastes. In addition, chemical reactions that occur during waste treatment are generally presented for those who are highly technically oriented. As a result, there is still a lack of familiarity with S/S technology among many consulting engineers, material suppliers, government officials, waste site owners, and the general public. This publication is intended to explain what portland cement is and how it can be used to solidify and stabilize various wastes. The Portland Cement Association contracted Construction Technology Laboratories, Inc., (CTL) to prepare a state-of-the-art report on waste stabilization using portland cement. This engineering bulletin was developed from that report.