The Rehabilitation Solution for Alabama’s Concrete Pavements In this presentation, the concept of using rubblization of concrete pavements with a Hot Mix Asphalt overlay is shown as an effective alternative for pavement rehabilitation. www.AsphaltAlliance.com

Overview Effective rehabilitation for PCC Break PCC into small segments Overlay with Hot Mix Asphalt User-friendly Rubblize and pave in off-peak hours High production rates Strong and Durable Final Product The way this works in short is that an old, deteriorated concrete pavement is fractured into small particles which are compacted together and overlaid with HMA. Because of the high production rates possible with this process and because HMA surfaces can be subjected to traffic soon after construction, rubblization is an ideal rehabilitation solution when considering the inconvenience of traffic delays to motorists. The construction can take place during off-peak hours and traffic can use the roadway during rush hour. The final product is a smooth, long-lasting HMA surface which will not show the joints, cracks or other problems of the underlying concrete.

What is rubblization? Fracturing: Eliminates slab action Destroys bond between concrete and steel Rubblized base responds as a tightly keyed, interlocked high-density, unbound layer Layer cannot crack; already fractured Rubblization eliminates slab action by 1) destroying the geometry of the slab and 2) seating the concrete firmly against the underlying subbase or soil. It also breaks the bond between the concrete and any steel present in the slab, eliminating detrimental effects caused by corrosion of the steel and further reducing the ability of the concrete to act as a mass. The rubblized concrete responds as a tightly packed, high-density granular material. The rough, hard particles provide an internal friction to resist rutting while the lack of tension prevents cracking.

Why Rubblize? Fracturing PCC to segments less than 9” precludes reflection of: Joints Cracks Faults Production rates up to 1 lane-mile/day Fracturing the surface of the concrete to a relatively small size means that features and problems in the old concrete surface such as joints, cracks and faults cannot reappear in the HMA overlay. This prolongs the life of the overlay and helps to ensure a smooth pavement. Production rates with rubblization are up to 1 lane-mile per day, much faster than other types of PCC rehabilitation. This means lower construction costs and less inconvenience to road users, giving substance to the slogan “Get In, Get Out, Stay Out.”

Purposes for Overlaying PCC Pavements Improve ride quality Correct surface defects improve surface drainage increase surface friction Delay/prevent structural deterioration Strengthen pavement structure (rehabilitation) Concrete rubblization followed by an HMA overlay improves ride quality by removing bumps caused by faulting in joints and cracks. It corrects surface defects in the roadway providing improved surface drainage. The elimination of joints and faults keeps water from ponding as readily. Surface friction is improved by reducing hydroplaning potential. Deterioration of the structure is slowed by preventing the intrusion of surface water into the old concrete. This is especially important when durability cracking is present in the old PCC. By eliminating the water, the action of freeze-thaw cycles is greatly diminished. Because a substantial structural overlay is placed on the rubblized concrete, the pavement is strengthened for future traffic.

Pavement Rehabilitation Design Factors Pavement type Condition of existing pavement Drainage Distress Response to load Foundation strength/stiffness Subbase Subgrade Future traffic loading Additional corrections (safety, capacity, etc) As with any pavement design, rubblization requires good site investigation, planning and design in order to be successful. The type of concrete pavement and its thickness will dictate the effort necessary to fracture the slab. For instance, a thin, plain jointed concrete pavement will require less fracture energy than a thick continuously reinforced concrete pavement. The adequacy of drainage, types of surface distress and structural integrity of the existing pavement need to be considered in the rubblization and overlay thickness design. The subgrade type and its stiffness and strength are important considerations. If the PCC slabs are lying directly on a fine-grained soil that is close to saturation, the rubblization process may cause the material to liquify. It is important to carry out a good site investigation to identify possible problems. The HMA overlay thickness must be such that future traffic demands are met. Attention must be also be given to other project aspects such as correcting alignments or adding capacity. It is important that details such as maintaining drainage flow are considered in the planning and design stages.

Reflection Cracking Reflection crack By far, the biggest problem in HMA overlays of PCC pavement Caused by movement at PCC joints and cracks Load-induced movement HMA PCC The most common form of distress in HMA overlays of PCC is reflection cracking. This is a result of the concrete slabs contracting and expanding with temperature changes, which cause the joints and cracks to open and close. This opening and closing causes a crack to form in the HMA directly over the opening in the concrete. Also, if the concrete slabs are not firmly seated on the underlying material, traffic loads going over the joints will cause the joints to move up and down vertically. This movement will cause shearing in the asphalt over the joint and create a reflection crack. Slabs Contract Joint Opens Slabs Expand Joint Closes

Larger Pieces = Larger Movement = Cracking HMA PCC The more concrete there is to expand and contract as the temperature changes, the greater the movement of the slab, and the greater the opening of joints and cracks. (Presenter: Hit enter to show progress of movement and widening of PCC joint and reflection crack.)

Smaller Pieces = Smaller Movement = No Cracking HMA PCC Rubblization reduces the size of concrete pieces so that the expansion and contraction causes a minimum of movement. The space between the fractured pieces moves less so that the cracks are not reflected through the surface. And, because the process seats the pieces of concrete, reflection cracking through shearing at the joints does not occur.

Benefits Time savings Economic Savings Choose work hours High production rates Economic Savings Reduce user delay costs Reduce construction costs In addition to better HMA overlay performance, rubblization offers savings in terms of flexibility for construction time. So, if paving during rush hour is prohibitive due to traffic volume, construction can be moved to off-peak hours. And, because production rates of up to 1 mile/day can be achieved, the road can be rehabilitated quickly. Rubblization with an HMA overlay means economic savings to both users and agencies. Because of the speed of construction, users may avoid costly delays. Construction costs are reduced due to the speed of construction, the ability to leave the old PCC in place, and the lower cost of HMA placement.

Environmentally friendly Benefits (continued) Environmentally friendly Reduce landfill Reduce fuel consumption/air pollution Smoothness Eliminate reflection cracking/faulting Rubblization leaves the PCC material in place so landfill space is conserved and haul trucks do not contribute to air pollution and fuel consumption. The problems in the existing PCC associated with cracking and faulting will not appear in the new HMA surface, ensuring a smooth ride.

Construction Procedure Install/replace existing edge drainage system as required Remove existing overlay (if present) Remove existing HMA patches, replace with aggregate base as required Fracture the concrete pavement Roll Place HMA overlay (multiple lifts) The construction process is straight forward. First concerns about subsurface drainage should be addressed by placing edge drains in the pavement if they are needed. If there is an existing HMA overlay, it should be milled off. Any HMA patches in the concrete should be removed and replaced with aggregate base material as needed. The point is to give uniformity to the pavement support and ensure proper drainage. The concrete is fractured using either a multiple head breaker or a resonant breaker. The rubblized material is then compacted using a combination of rollers to ensure that the concrete pieces are seated and locked together. And, finally, the required thickness of an HMA overlay is placed over the top.

The Resonant Pavement Breaker (RPB) uses a low-amplitude 2000-pound force applied at a frequency of 44 cycles per second to fracture the concrete pavement.

The multi-head breaker (MHB) has a number of hammers mounted laterally in pairs. Half of the hammers are located in a forward row and the rest are diagonally arranged in a rear row so that breakage occurs continuously from side to side. The MHB is capable of rubblizing a 13-foot lane in one pass.

Rolling Once the rubblization is complete, a 10-ton steel wheel vibratory roller is used to pack the loose rubble together initially. This is usually followed by one or two passes of a pneumatic roller. Finally, the material is rolled for one or two more passes by a vibratory roller just before the first lift of HMA.

Particle Size PCC fractured into 9 in.-minus pieces Most pieces are 1- 4 in. diameter Aggregate interlock maintained beneath surface Rolling knits together surface particles Most specifications allow for a maximum particle size of 6 to 9 inches in the top part of the concrete slab. The majority of the concrete particles are in the range of 1 to 4 inches. Aggregate interlock is maintained in the concrete because the subsurface particles are only fractured, not reoriented. The rolling after rubblization helps to knit the surface particles together and seat the bottom of the concrete firmly against the underlying material.

When to Rubblize Patching > 10%. Severe D-cracking. Severe ASR or ACR cracking. Dowel bar locking Severe joint deterioration Persistent faulting. Some general guidelines on when to rubblize concrete pavement include: When patching is needed in more than 10% of the slab, When severe durability (D) cracking is present, Alkali-silica reaction (ASR) or alkali-carbonate reaction (ACR) cracking is present, When dowel bars have locked up due to corrosion, When faulting reappears shortly after retexturing the concrete surface. All these distresses are indications that major systemic problems exist in the concrete pavement, and that a rehabilitation consisting of rubblization with an HMA overlay is viable.

Precaution Weak soils may make construction difficult. Option 1 Adjust breaking pattern (12 - 18”) in soft areas. Use normal seating rolling. Resume smaller pattern after weak area. It is not unusual to run into occasional soft spots of soil. In these conditions, rubblization may weaken the soils and cause the rubblized particles to punch through the underlying material. When this happens, there are a couple of options which should be immediately considered. The first option is to reduce the effort in fracturing the slab. This can be done by adjusting the breaking pattern to produce larger pieces. If the softening seems to stop, then use a normal rolling pattern to seat the concrete and resume the original pattern after the soft area.

Precaution Option 2 Cease rubblization Define weak area Remove/replace problem material Resume normal operations when past weak area Perform a good soils evaluation prior to construction The next option is to cease rubblization. This should be done if adjusting the breaking pattern does not work. The area of soft soil should be defined to mark the limits. The concrete should be removed along with the problem soil in the local area. Normal rubblization operations can proceed after the soft area. These types of problems may be reduced significantly if a good soils investigation is performed ahead of construction. Past project records, soils maps and non-destructive testing may provide vital clues to identifying problem areas.

How Effective is Rubblization? Witczak and Rada, 1992 "Rubblization . . . is the preferred rehabilitation method for all types of PCC pavements." Thompson, 1999 Rubblization is a "viable and cost-effective rehabilitation option." Rubblization is an established technology. Matt Witczak and Gonzalo Rada, in their 1992 TRB paper (Transportation Research Record No. 1374), state that, “Rubblization . . . is the preferred rehabilitation method for all types of PCC pavements.” In 1999, Marshall Thompson won the prestigious K.B. Woods Award at TRB for his paper on rubblization for pavement rehabilitation (Transportation Research Record No. 1684). In this article he states that rubblization is a “viable and cost-effective rehabilitation option.”

How Effective is Rubblization? 26 States have specifications for Rubblization Arkansas 100 miles of rubblization in 2001 300 miles over a 3-year period Currently, over half the state highway agencies in this country have specifications for concrete rubblization. Arkansas is embarking on a major rehabilitation effort in which over 100 miles of concrete pavement will be rubblized next year and about 300 miles will be rubblized in a 3-year period. Researchers and agencies have found rubblization to be a viable rehabilitation option for severely distressed PCC.

Projects I-440, Raleigh Beltway, North Carolina $21.5 million contract 3 1/2 mile project AADT = 100,000+ Awards 1993 Sheldon G. Hayes Award - NAPA 1993 Pinnacle Award - AGC 1995 NQI Achievement Many high quality rubblization projects have been constructed and are performing well. One of these, I-440 in North Carolina won the prestigious NAPA Shelton G. Hayes Award in 1993. It also won the state AGC award and the very first NQI Achievement award. This freeway had a traffic level of over 100,000 vehicles per day and it was a 3.5 mile long project.

I-440, Raleigh Beltway, North Carolina This photo shows I-440 after construction. It is still in excellent condition today, eight years later.

I-65, Alabama Rubblize existing concrete pavement Widen overall roadway Place Permeable Asphalt Treated Base under new lanes Overlay with Superpave FHWA Showcase October 1997 The concrete pavement on I-65 in Alabama was rubblized in 1997. In this project, the objective was to rehabilitate the existing pavement and widen the roadway. A permeable asphalt treated base was constructed adjacent to the rubblized concrete pavement to ensure drainage. The entire roadway was overlaid with a Superpave mixture. The FHWA showcased the project in Birmingham in October.

Projects As of July 1999 20 + projects no projects 1-4 projects The popularity of rubblization as a rehabilitation technique for concrete pavements is shown on this map. Michigan, Wisconsin and New York have all had more than 20 projects each, while Illinois, Indiana and Alabama have each had 10 or more projects. Another 25 states have rubblized concrete pavements on between one and ten projects each. no projects 5 + projects 1-4 projects 10 + projects 20 + projects

Rubblizing Performance All Data PCR =70 @ 22.4 years The expected life of an HMA overlay on rubblized PCC is shown in this graph. The PCR or pavement condition rating is based upon visual observations of pavement surface distress. Rehabilitation should be performed when the PCR falls below 70. The Asphalt Institute’s rubblization database includes projects that range from 1 to 12 years old, and based upon the average performance of these sections, an HMA overlay of rubblized concrete can be expected to last for over 20 years before another rehabilitation is needed.

Alternatives: Comparisons Rubblize PCC, overlay with 10“ HMA Remove PCC, replace with 12” Fast Track PCC Leveling course, 10” Fast Track PCC In a comparison of typical alternatives for PCC rehabilitation or reconstruction, we can examine the relative costs of: 1) an HMA overlay of rubblized PCC 2) removal of an existing PCC pavement, replace with 12” of rapid curing PCC and 3) an HMA leveling course or bond breaker, followed by a 10” PCC surface of rapid curing concrete.

Comparisons Typical costs for these treatments show that the HMA overlay, at $17 to $23 per square yard, is far cheaper than the other two alternatives. The unbonded PCC overlay comes in at $26 to $36 per square yard and the remove and replace with concrete costs between $34 and $46 per square yard.

References There are a number of excellent references on rubblization, two of which are available from NAPA and the Asphalt Institute.

Conclusions Rubblization is effective. Prevents reflective cracking. Rubblization can be done rapidly, minimizing delays. Researchers and agencies have concluded that rubblization is technically sound. To wrap up our discussion, rubblization with an HMA overlay is an effective concrete pavement rehabilitation technique. Because the concrete pieces are reduced to a small size, reflection cracking is eliminated. The process is fast with production rates on the order of one mile per day. This allows contractors to work in non-peak traffic hours and to reduce the overall time of construction in order to minimize traffic disruption. Researchers and agencies alike have come to the conclusion that rubblization is a viable technology that can be effectively employed to provide long-lasting HMA surfaces.