Design of concrete pavement with optimized slab geometry

Abstract

A new technology has been developed to design concrete pavements, which reduces slabs’ thickness and optimizes their sizes, because of trucks axles’ geometry. The design is supported by a gravel base treated with concrete or asphalt. It assumes there is no adherence between the base (existing pavement) and the concrete slab. The core principle of this design method consists of designing a slab size, so that no more than one wheel set stays on a given slab, thus minimizing the critical tensile stress on the surface. Test segments have been built on a large scale and they have been tested under accelerated loads, with concrete thickness of 8, 15 and 20 cm, all of them having a gravel base and non-adhered asphaltic layers. Tests demonstrated that a reduced-size slab, of low thickness, might bear a considerable amount of equivalent axles before cracking takes place. Concrete slabs on gravel bases with 20 cm thickness did not suffer from cracking, in spite of being tested under more than 50 millions of equivalent axles. Slabs of 15 cm thickness suffered from cracking when tested under an average of 12 millions equivalent axles, while slabs of 8 cm thickness endured 75,000 equivalent axles before the first cracking took place. Besides the executed tests demonstrated that fiber concrete slabs may endure until 20 times more traffic before cracking and they are able to provide a longer life span after cracking. Based on this fact, a mechanical-empirical software design has been developed and named OptiPave, which optimizes slab geometrical design and concrete slabs thickness by considering the particular conditions on a given project, such as weather conditions, traffic volume, layer and materials. Critical tensile stresses have been calculated by employing the finite elements analysis for different conditions of mechanical and thermal loads at different positions. Slabs’ cracking is determined by calculating concrete fatigue damage and models employed by the design guide AASHTO, 2007, and by means of calibration test sections on large scale. The new methodology designs concrete slabs for high traffic volume ways, which in average are 7 cm thinner than traditional pavement design developed by AASHTO (1993). This design method is also able to effectively design concrete pavements for lower traffic volume roads, which are not considered by the existing pavement design methods, thus providing an alternative to asphalt solutions.