In 2011, a steel recycling company asked Nycon to provide a solution for a longer lasting, more durable concrete for the company’s heavy-duty roads and scrap pads. The plant’s scrap pads are the most abused areas where scrap steel is received in dump trailers or rail cars. Once received, the scrap is off-loaded and pushed into stockpiles, waiting to be loaded into hoppers and transported to the steel processing plant. The plant scrap pads are required to endure tremendous abuse including supporting 300 ton scrap melt hoppers, 100 ton Lift- King wheel loads, and impact from falling scrap steel as well as abrasion from scraping, pushing and loading equipment. Due to the around-the-clock abuse, the plant’s usual concrete mix and scrap pad designs were not holding up well. The scrap pads failed quickly after being placed into service with cracks, depressions, gouges and scraping wear so intense that failures included abrasion-exposed rebar which would puncture tires and require constant maintenance.
Typically, the scrap pads would only survive about eighteen (18) months before requiring complete rehabilitation. Clearly, the company’s scrap pad areas needed a super heavy-duty slab made from a new concrete mix capable of enduring the tremendous abuse. Moreover, since the facility operates 24/7, a new concrete mix needed to be made, cast-in-place and be ready for the heavy traffic and abuse within one week. The steel recycling company wanted the extreme, heavy-duty concrete to have improved impact and abrasion resistance as well as increased life to avoid disruption to the plant operations and improve their return on investment.
The solution developed by Nycon was TUFF-MIX™. The new, super heavy-duty slab design requirement was 18” (45cm) thick to endure the plant’s 300-ton 4-point load scrap melt hoppers and the 100-ton wheel load Lift-King equipment.
The TUFF-MIX™ design included one layer of steel reinforcing bars placed 4 inches (10cm) up from the bottom of the slab as well as dowelled construction joints. The Nycon design did not require any steel reinforcing bars on the top section of the slab. The TUFF-MIX™ mix design is a high performance, low water/cement ratio concrete made with a blend of two Nycon-PVA fibers that requires standard QC placement techniques, control joints and proper cast-in-place curing.
The project design for making the TUFF-MIX™ included developing a low water/cement ratio, high strength mix including production of a trial batch at the ready-mix producer’s plant. The trial TUFF-MIX™ made with the Nycon-PVA blend was sampled and attained 3,000 psi (21 MPa) in 3-days, 5,000 psi (35 MPa) in 7-days and 9,000 psi (62 MPa) in 28-days. The TUFF-MIX™ trial batch was also cast-in-place into a small area to allow finishing crew an opportunity to work with the new mix design.
Once the trial TUFF-MIX™ slab was placed into service and load-tested, the steel recycling plant asked the concrete contractor and ready-mix supplier to proceed with construction of the 40,000 SF TUFF-MIX™ scrap pad. The plan included a staged construction schedule for the contractor to 1) demolish one-third of the old concrete slab, 2) excavate the base and sub-grade to the proper depth, 3) place a well compacted crusher-run base, 4) build forms and install the fine aggregate slip layer, 5) install the steel rebar 4” (10 cm) up from bottom-of-slab and 6) insert the dowel bars to prepare for the first of the three-sections pours.
The super heavy-duty TUFF-MIX™ was batched at a concrete plant into 10 CY transit-mix trucks with pre-water and admixtures which then rotated at full mixing speed for four (4) minutes prior to adding the two Nycon-PVA fibers. The concrete plant used a portable belt conveyor to charge the transit mix trucks with the dose of the two Nycon- PVA fibers while the trucks were rotated at slow mixing speed to assure fiber dispersion.
The transit mix trucks were then dosed with the final trim water and rotated at full mixing speed for four (4) more minutes to complete the mixing cycle. The TUFF-MIX™ was sampled and tested by QC at the plant prior to departure for the scrap pad construction site. The mix was routinely tested to confirm the slump range of 5” to 7” (12cm to 17cm), an air content of 2% to 4% and a unit weight of 155 lb/cf.
Upon completion and proper curing of each of the three sections, the recycling plant moved all operations onto the newly constructed TUFF-MIX™ scrap pad. The new TUFF-MIX™ slab offered operations the opportunity to improve efficiency by providing a well constructed super-heavy-duty area for loading the 300 ton 4-point load melt hoppers and for the full hoppers to be easily and quickly captured and transported by the Lift-King tractors.
During production and placement of the new TUFF-MIX™ slab, extra test cylinders, beams and panels were cast for comparison testing. The samples were sent to an independent testing laboratory for curing and testing. Tests were performed on the cylinders, beams and panels to compare a normal performance 4 ksi (28 MPa) concrete mix to the TUFF-MIX™ mix made with and without the blend of Nycon-PVA fibers. The testing was performed to confirm the dramatic resistance to failure provided by TUFF-MIX™, as well as the significant improvement to toughness, impact and abrasion resistance.
Nycon-PVA fibers are the only fiber that develops a molecular bond to concrete, which is activated when the PVA fiber comes into contact with the elevated pH alkalinity of the concrete paste. The Nycon-PVA fiber unique molecular bond to the cement paste provides the dramatic improvement to the concrete without any loss of compressive strength. After two years of constant use, the new TUFF-MIX™ at the steel recycling plant has no cracks, displacement, gouges or deformation compared to previous slabs which began to fail within two to three weeks.
The independent testing laboratory performed tests on the samples made at the plant and project site. All the samples were tested immediately upon completion of the 3, 7 and 28-days of curing.
Patterson remains focused on expanding our offering through acquisitions and partnerships which include Nycon Corporation for reinforcement fibers and Kraft Curing Systems, Inc., the global leading manufacturer of concrete curing systems. It is through these partnerships that Patterson remains the largest single source supplier in North America to precast and prestress producers. For more information on Nycon reinforcing fibers, visit www.nycon.com or call toll free: 1-800-456-9266