Since 1892–when the very first concrete pavement was placed in America–concrete pavement technology has been changing, continually evolving to meet current and future needs. These advances happen on many different fronts and are the result of contributions by people and organizations (industry, the public sector, and academia), all working to provide the best choices to meet construction, rehabilitation, and restoration/preservation.
Take a look at just a few of the underlying concrete pavement technologies that have emerged since that first concrete pavement was placed more than a century ago. For quick reference, be sure to check out how these technologies fit with various construction strategies and different applications.
Concrete Pavement—In its most basic form, a concrete pavement is an extruded slab of concrete made from cement, aggregate, sand, and water. As concrete technology has advanced, blended cements or the addition of secondary cementitious materials have been used to enhance concrete properties. To handle heavy loads, reinforcing materials—including steel and plastic fibers—have been used to increase both durability and strength. Chemical admixtures, which can increase production efficiencies and/or impart desirable performance features, have also used increasingly. Aggregates are no longer just rock, but may be natural stone, man-made materials, or recycled concrete materials. These are just a few ways concrete pavements have changed over the years. The descriptions below show other technologies that make concrete pavements so versatile and useful for just above every construction strategy and application. Strategies | Applications
Jointed Concrete Pavements (Doweled or Undoweled)—By far, the most commonly used concrete pavements for highways, airports, and many streets and roads, are jointed concrete pavements, which are designed and constructed with controlled cracking in mind. By their very nature, concrete pavements will crack, so the idea is to sawcut the green pavement to form joints, which are actually controlled cracks. Jointed pavements have enough joints to control the location of all expected natural cracks. With joints designed and constructed into the pavement,, cracks occur at joints and not elsewhere in the slabs.
The most common type of jointed pavements are jointed plain concrete pavements (JPCP’s), which do not contain any steel reinforcement, but may include dowel bars or other devices that transfer the weight of vehicles across the slabs. These load transfer devices are placed at transverse joints, while tiebars (or deformed steel bars) are placed at longitudinal joints.
By contrast, lesser-used jointed reinforced concrete pavements (JRCP’s) contain steel mesh reinforcement (sometimes called distributed steel). In JRCP, designers intentionally increase the joint spacing and include reinforcing steel to hold together mid-panel cracks. Strategies | Applications
Continuously Reinforced Concrete Pavements—Continuously reinforced concrete pavements (CRCP’s) do not require any transverse contraction joints, but instead, are constructed with reinforcing steel to hold cracks together tightly. Transverse cracks are expected in the slab, usually at intervals of 1.5 ft to 6 ft (0.5 to 1.8 m), so the reinforcing steel is placed prior to the placement of concrete. Determining an appropriate spacing between the cracks is part of the design process for this type of pavement. CRCP often cost more than jointed concrete pavements, but typically have design lives of 30 to 40 years. Some state highway agencies use CRCP in urban traffic corridors where heavy traffic over the service life of the pavement can be amount to tens of millions of equivalent load repetitions. Strategies | Applications
Concrete Overlays—There are six basic types of concrete overlays, but they fall into two broad categories. Here’s a brief description of the two categories and how they are used for pavement preservation and rehabilitation. Strategies | Applications
- Bonded Concrete Overlays for Pavement Preservation
Bonded concrete pavement overlays may be used as part of a pavement preservation strategy. Bonded concrete overlays are thin (typically 2 in. to 6 in. thick), and may be placed directly on an underlying asphalt, concrete, or composite pavement that is still structurally sound. Bonded concrete overlay and the underlying structural pavement create a monolithic pavement. These overlays can be used to extend pavement life—typically by 15 to 25 years—and improve the surface characteristics. Advantages of concrete overlays include reduced costs compared to reconstruction; improved durability over asphalt solutions; and reduced maintenance and repairs.
- Unbonded Concrete Overlays for Pavement Rehabilitation
Typically, unbonded concrete overlays may be used to rehabilitate existing asphalt, concrete, or composite pavements. They are typically 4 in. to 11 in. thick and are placed on a stable base to serve as a new full-depth pavement section. These overlays can be used to extend pavement life, typically by 15 to 30+ years. Advantages of concrete overlays include reduced costs compared to reconstruction; improved durability over asphalt solutions; and reduced maintenance and repairs.
Precast Pavements—Precast pavements are typically used for constructing or repairing a concrete pavement surface where casting and curing of panels are done in advance. Precast pavements are a highly durable finished pavement, not just a temporary fix. They are a repair option for jointed concrete pavements (JCP) and may be a reconstruction option for either jointed plain concrete pavements or asphalt pavements. Rapid placement of the hardened panels can then be conducted within short traffic closure windows. They have high load-carrying capacity, are relatively fast to construct, and may be placed during short (overnight or weekend) closures, thereby reducing lane closures and user delays. Strategies | Applications
Next Generation Concrete Surface—In response to noise issues on urban highways and the public’s demand for quieter urban roadways, ACPA led a large-scale initiative involving industry and academia, which developed and tested a unique surface texture that can be used for either new or existing concrete pavements.
NGCS sections are proving to be as quiet as or quieter than any alternative, including the newest generations of asphalt pavements. Concrete pavements with NGCS are not only quiet when they are first built, they remain quiet during their service lives. Strategies | Applications
Roller-Compacted Concrete—Roller-compacted concrete (RCC) is a stiff, zero slump, strong concrete mixture that is typically placed with high-density paving equipment. RCC is increasingly being used as monolithic surface pavement, but also may be used as a support layer. Roller-compacted concrete pavements can be used for low-speed or industrial applications, and are finding increasing acceptance for low volume roads, industrial pavements, military applications. They can typically be constructed quickly, may be constructed with no forms or finishing; and do not require steel reinforcement. They also offer the benefits of early opening to traffic and high load-carrying capacity. Strategies | Applications
Concrete Pavement Restoration—Concrete pavement restoration (CPR) is a term that applies to restoring a concrete pavement’s ride quality and/or surface texture. CPR can preserve and extend the service life of older concrete pavements when sections become uneven or when the pavement loses some of its surface features. CPR typically involves data collection; a distress survey; data evaluation; la testing; and final evaluation.
A key element of a CPR plan involves diamond grinding away a small amount of the surface to remove bumps and minor damage, leaving a like-new pavement that is smooth, quiet, durable, and safe.
Diamond grinding is almost always a cost-effective alternative to overlays, particularly on heavily traveled routes where asphalt resurfacing may last only five to seven years. Diamond grinding can extend highway pavement life by another 16 or 17 years, according to research by the California Department of Transportation.
Full-Depth Reclamation–Full-depth reclamation (FDR) is a technique in which hot-mixed asphalt (HMA) material from the existing pavement is removed, combined with portland cement, and used to create a new and improved base. The FDR base is then topped with a new concrete surface or HMA wearing course to provide a strong, uniform base or subbase. FDR also can be completed quickly; reduces or eliminates the need for virgin aggregates; and improves the structural capacity of the stabilized base over unstabilized base material. Strategies | Applications
Cement-treated base (CTB) is a mixture of aggregate material and/or granular soils combined with engineered amounts of portland cement and water that hardens after compaction and curing to stabilize a variety of soils, which in turn, creates a stronger, stiffer, and more durable paving material. Cement-treated base is used as concrete pavement subbase or flexible pavement base material. CTB provides a strong, uniform base/subbase for current and future loading conditions using in-place or locally available marginal soils and granular material. It also allows the use of marginal aggregates—including recycled materials—thereby reducing the need for high quality, virgin aggregates. Strategies | Applications
Recycled Concrete Aggregates
Recycled concrete aggregates (RCA) are aggregates produced from the recycling of existing concrete. Existing concrete is removed, processed into appropriate aggregate sizes, and reused in various pavement applications. This sustainable solution reduces construction costs; reduces the dependency on high quality, virgin aggregates; reduces disposal costs; and allows the use of pavements affected by alkali silica reactivity or D-cracking. Strategies | Applications
No discussion about technological advancements in concrete pavements would be complete without mentioning that the technologies noted above all come from improvements in the materials; equipment and instruments; and the practices and processes used today.
- Cementitious Materials…Manufacturing advances make better cement and make cement better for all concerned. Breakthroughs include blended cements, speciality cements, and believe it or not, even “smog-eating” cement.
- Value-added products…Plastic fibers can make concrete pavement stronger. Industrial by-products can make it last longer. Chemical admixtures can make it cure faster.
- Reinforcements and Load Transfer Products…Steel reinforcement products, dowel baskets, and dowel bars made from a wide variety of materials; and other products help distribute the weight of vehicles across the pavement, contributing to longer life and few (if any) repairs.
- Equipment and Instruments…Since 1948, the “slipform” paver has been increasing speed and quality in the extrusion of concrete pavement. More recently, 3-D or stringless machines can make the finished pavement ride smoother; real time time testing instruments help contractors make adjustments that avoid bumps and improve quality; and other
- Practices and Processes…Okay, these are not products, but no discussion about technological advances would be complete without life-cycle and life-cycle cost analysis; traffic management; close tolerance paving; fast-track paving; and other processes and practices that have helped improve concrete pavement quality, cost-competitiveness, smoothness, durability, and other positive attributes.
To learn even more about concrete pavement technology, please visit our Wikipave™ encyclopedic resource at http://wikipave.org.
To see examples, case histories, and other application info, please visit our Count on Concrete resource center at http://countonconcrete.org