Design of Concrete Slabs with Optimized Geometry

Paper by COVARRUBIAS JR ROESLER COVARRUBIAS from ISCR 11th 2010 Seville Spain

A new methodology has been developed to design the concrete slab thickness by optimizing the slab size given the geometry of the truck axles, the design is based on an unbonded system with either granular, HMA, Stabilized or Concrete Base. The key principle of the design method is to configure the slab size so that not more than one set of wheels are on any given slab thereby minimizing the critical top tensile stress. Full-scale test sections have been constructed and tested under accelerated pavement loading with concrete thickness of nominally 10, 15, and 20 cm on both an aggregate and asphalt base layer. The testing demonstrated that these thinner concrete slabs with reduced slab dimensions could sustain a significant number of ESALs before cracking. Concrete slabs on granular bases with 20 cm slab thickness showed no fatigue cracking at an average of 35 million ESALs. Slabs with 15 cm thickness showed cracks initiating at 12 million ESALs on average while 8 cm slabs withstood 75,000 ESALs before cracking commenced. The testing also demonstrated fiber reinforced concrete slabs can sustain more traffic before cracking relative to plain concrete as well as provide a longer service life. Mechanistic-based software, called OptiPave, has been developed to geometrically optimize the design of concrete slabs for any set of climate, traffic, layer, and material inputs. Critical tensile stresses have been calculated using finite element analysis for a variety of mechanical and thermal loading conditions and load positions. Slab cracking is determined based on the concrete fatigue and performance models utilized for the 2007 Interim AASHTO Guide and calibrated with the full-scale test sections. The new methodology designs slabs that are on average 7 cm thinner for higher trafficked roadways relative to traditionally designed AASHTO (1993) pavements. The design method also is able to efficiently design lower volume concrete roads that are not comprehensively covered with existing pavement design methods.

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