|Three-edge bearing test determines fiber-reinforced specimen’s supporting strength, D-Load, and corresponding ASTM C76-defined Class.|
|Transducers measure vertical and horizontal deflections of pipe under loading.|
American Concrete Pipe Association (ACPA) and BASF Corp. (Admixture Systems) officials joined University of Texas at Arlington Structural and Applied Mechanics Professor Seyedali (Ali) Abolmaali for a World of Concrete 2016 presentation on how a new ASTM Committee C13 on Concrete Pipe standard positions dry cast structures more competitively against less robust drainage alternatives.
The committee published ASTM C1818-15 Standard Specification for Rigid Synthetic Fiber Reinforced Concrete Culvert, Storm Drain, and Sewer Pipe in December. The standard is the result of the most extensive research study to date on fibrous mixes for product meeting C13’s benchmark, ASTM C76 Standard Specification for Reinforced Concrete Culvert, Storm Drain, and Sewer Pipe. Overseeing the five-year study was Dr. Abolmaali, whose structural mechanics insights have landed him leading roles in National Transportation Safety Board investigations—most notably those probing the 2007 Interstate 35W bridge collapse in Minneapolis (steel plate fatigue) and 2006 failure of Boston Central Artery/Tunnel suspended precast ceiling anchors (epoxy creep).
With ACPA and BASF assistance, he and fellow researchers tested pipe specimens a) 15- to 48-in. in diameter and of ASTM C76 Class I-V strength levels; b) fabricated on packerhead or vibration and compaction machinery; and, c) designed with conventional steel cage reinforcement or BASF’s MasterFiber MAC Matrix synthetic macrofiber dosed at 6 to 18 lbs./cubic yard. Association member producers Forterra Building Products and Northern Concrete Pipe, respectively, supplied the small and medium bore pipe from Texas and Michigan plants for short- to long-term D-Load testing under lab or in-ground conditions. Dr. Abolmaali and the team were especially mindful of the creep performance of macrofiber specimens under long-term, sustained loading. Low rates of deformation over a period of 10,000 hours demonstrated how fibrous concrete pipe can perform to levels consistent with public agency and private construction owner expectations for drainage systems.
BASF approached ACPA on dry cast pipe research after observing performance of the 2.1-in. polypropylene MasterFiber MAC Matrix as secondary reinforcement in slabs on grade, composite metal deck slabs, shotcrete, underground construction, septic tanks, vaults and other precast concrete elements. Results from testing at the UT-Arlington lab, plus Forterra and Northern Concrete plants, drove development of ASTM C1818. The standard establishes a serviceability factor of 0.90 or higher for synthetic macrofibers specified in lieu of traditional steel reinforcement. That threshold reflects fibers’ capacity to help fiber-reinforced concrete pipes maintain at least 90 percent of their initial vertical internal diameter through 10,000 hours of loading—a measure of reinforcing capacity, toughness and low creep performance.
MasterFiber MAC Matrix is the first macrofiber to meet ASTM C1818. In addition to supporting research underpinning the standard, BASF has created an analysis tool to calculate MasterFiber MAC Matrix economy against the use of conventional steel reinforcement. The calculator factors material, cage machinery and maintenance, plus cage fabrication and handling costs.
“Fibers like MasterFiber MAC Matrix allow the concrete pipe to be lighter, safer, and easier to install than concrete pipe made with traditional steel reinforcement,” says BASF Industry Manager Kenneth Kruse. “The use of fibers can also improve long-term durability, and provide operational benefits to a producer when compared to casting pipe using traditional steel cages. In turn, this makes concrete pipe more competitive with product made from plastic and other materials.”