Shunzhi Qian

Dynamic Life-Cycle Modeling of Pavement Overlay Systems: Capturing the Impacts of Users, Construction, and Roadway Deterioration

Pavement systems provide critical infrastructure services to society but also pose significant impacts related to large material consumption, energy inputs, and capital investment. A life-cycle model was developed to estimate environmental impacts resulting from material production and distribution, overlay construction and preservation, construction-related traffic congestion, overlay usage, and end of life management. To improve sustainability in pavement design, a promising alternative material, engineered cementitious composites (ECC) was explored. Compared to conventional concrete and hot-mixed asphalt overlay systems, the ECC overlay system reduces life-cycle energy consumption by 15 and 72%, greenhouse gas emissions by 32 and 37%, and costs by 40 and 47%, respectively. Material, construction-related traffic congestion, and pavement surface roughness effects were identified as the greatest contributors to environmental impacts throughout the overlay life cycle. The sensitivity analysis indicated that traffic growth has much greater impact on the life-cycle energy consumption and environmental impacts of overlay systems compared to fuel economy improvements.

Influence of Concrete Material Ductility on Shear Response of Stud Connections

The authors investigate the use of material ductility to overcome brittle concrete fracture failure in steel/concrete interaction zones. An experimental study was performed on the influence of concrete material ductility on the shear response of stud connections. Using a unique strain-hardening fiber-reinforced engineered cementitious composite (ECC), a series of pushout specimens were tested. Results show that, in addition to improved structural integrity, the stud connections with ECC exhibit a higher ultimate strength and slip capacity and a more ductile failure mode when compared with connections of other concrete materials. The large enhancement of ductility suggests that using an ECC material could be effective in redistributing loads among the shear studs and in improving composite action between concrete bridge decks and steel girders.

Introduction of Transition Zone Design for Bridge Deck Link Slabs Using Ductile Concrete

This paper presents an innovative approach to designing the transition zones between concrete deck slab segments and an adjacent highly deformable link slab on a steel girder composite bridge deck. (A link slab provides a special class of jointless bridge for which only the bridge deck is made continuous rather than both the deck and girders). The transition zones represent a fraction of the ends of the link slab introduced to divert stress from the potentially weak link slab/deck slab interface. The link slab studied herein is built with an engineered cementitious composite (ECC), an ultra ductile concrete, adopted in a recent demonstration project in Southeast Michigan. Conventional design of concrete link slabs leaves the old/new concrete interface as the weakest part of the bridge deck system. Due to the presence of a link slab debond zone (part of the link slab is debonded from bridge girder to provide hinge flexibility), this interface also experiences high stress concentrations. In addition, the effectiveness of the link slab design depends on the integrity of the interface so that imposed rotation and tensile deformation will be accommodated within the highly deformable ECC link slab. The basis of the suggested approach is to isolate the concrete/ECC interface away from the structural interface between the debond zone and composite zone to prevent interfacial cracking. The shear studs and lap-spliced reinforcement located within transition zones facilitate load transfer between the concrete deck and the ECC link slab. These modifications are expected to cause a shift of the stress concentration from the concrete/ECC interface to the bulk part of the ECC link slab. In support of this new design concept, experimental tests are carried out on the behavior of the ECC link slab-bridge deck-girder connection. Detailing of the transition zone, that is, spacing of shear stud and development length/lap splice length requirement is then laid out in a design procedure based on results of shear stud/ ECC pushout and reinforcement pullout tests.

Influence of Concrete Material Ductility on Headed Anchor Pullout Performance

There has not been full resolution of anchor/concrete connection fracture failure problems associated with the inherent brittleness of concrete, despite the wide use of steel anchors in the construction industry. There is systematic investigation of material ductilitys influence on anchor pullout performance in this paper by replacing normal concrete with engineered cementitious composites (ECCs), a relatively new ductile concrete material. ECC strain hardens to several percent tensile strain capacity, which is also known as tensile ductility, or a materials maximum sustainable tensile strain before fracture failure-induced load drop. That when compared with connections with regular concrete materials, anchor/ECC connections exhibit higher energy absorption, higher displacement capacity, higher ultimate strength, and more ductile failure mode, is shown in experimental results. In concrete materials, distributed inelastic damage made of microcracking over a volume of material near the anchor heads replaces the typically observed cone-shaped brittle fracture. Improved steel anchor connection load response results through ECC material uses significant effectiveness in load redistribution among anchors in a group is suggested through this significant enhancement of ductility.

Influence of fly ash type on mechanical properties and self-healing behavior of Engineered Cementitious Composite (ECC)

This paper aims to clarify the influence of different types of fly ash on the mechanical properties and self-healing behavior of Engineered Cementitious Composite (ECC). Five types of fly ash with different chemical and physical properties were used in ECC mixtures. The fly ash to cement ratio was fixed at 3.0. The compressive and uniaxial tensile tests were conducted to evaluate the influence of fly ash type on mechanical properties. The permeability test was used to assess self-healing behavior of ECCs with different types of fly ash. The microtopography and chemical characteristics of the self-healing products in the crack were observed and examined by scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDS). The fly ash with relatively higher calcium content and smaller particle size was found conducive to a higher compressive strength. The lower combined Al2O3 and CaO content of this fly ash, however, was found to enhance the tensile strain capacity. Furthermore, high calcium fly ash accelerates the self-healing process of ECC for the same pre-damaged level. The self-healing product was a mixed CaCO3/C-S-H system with the CaCO3 as the main ingredient.