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Roller compacted concrete and stepped spillways
Published in H.-E. Minor, W.H. Hager, Hydraulics of Stepped Spillways, 2020
Eric J. Ditchey, David B. Campbell
A variation to the use of normal form work to achieve concurrent placement of facing concrete and RCC is the use of slipform equipment. Slipform machines, developed for the paving industry, move along the axis of concrete placement and both form and vibrate the facing concrete (Dolen 1988). This approach was first used at the Upper Stillwater Dam in Utah, U.S.A. (Photo 8). With a conventional, formed and cast concrete there is considerable flexibility in step height and geometry. Most designers have found greater comfort in mechanically attaching the conventional concrete to the RCC using reinforcing steel or steel tie rods. The method of RCC placement results in what are called lift joints, continuous horizontal joints from abutment to abutment and from upstream to downstream every 0.3 m. If the upstream primary water barrier is not highly effective, these lift joints provide permeable paths to transmit seepage to the downstream face. Most designers have incorporated internal drainage systems to attempt to collect and conduct this inevitable seepage away from the dam before it reaches the downstream face. When a downstream facing system such as cast-in-place concrete is used, an internal drainage system becomes extremely important to prevent the build up of seepage forces behind the facing system.
Precast segmental bridge construction in seismic zones
Published in Fabio Biondini, Dan M. Frangopol, Bridge Maintenance, Safety, Management, Resilience and Sustainability, 2012
Fabio Biondini, Dan M. Frangopol
ABSTRACT: Slip-form construction is a construction method for tall structures, such as buildings, bridges, towers, offshore platforms and dams, in which concrete is poured into a continuously moving form. These forms serve as supporting walls strong enough to bear the concrete weight poured over top of it. Slipform has been used for the construction of tall piers of long span bridges not only to reduce the construction period but also to ensure the safety The slip-form method, however, sometimes has showed several problems, such as vertical errors under construction or deflections of forms, from irregular loads by construction materials, workers or its weight, or unsettled friction or bond between concrete and forms. These include, but not limited to, problems in mechanical and hydraulic operations due to greater weight of steel form, problems in ensuring that the slip-form remains plumb i.e. the horizontal deviations do not exceed specified limits and certain other handling problems arising due to the weight of the form itself. This paper presents a case of construction errors that aroused during vertical slip-forming in the construction of bridge pier using steel as the slip-form. Moreover, it also includes field inspection, shape survey, structural assessment through the structural analysis and the measures taken against these errors.
Construction of Concrete Pavements
Published in Rajib B. Mallick, Tahar El-Korchi, Pavement Engineering, 2017
Rajib B. Mallick, Tahar El-Korchi
The paving machine rides on treads (or pad line) over the area to be paved. The paver is guided using previously set stringlines and paver sensing wands (or new laser-and GPS-guided sensors). Fresh concrete is deposited in front of the paving machine, which then spreads, shapes, consolidates, screeds, and float-finishes the concrete in one continuous operation. Great coordination between concrete production, delivery, and placement is needed to maintain adequate forward progress of the slipform paver, which is required for producing smooth pavements. Slipform paving is an extrusion process that uses very low slump concrete, and allows for high-production paving on the order of 1 mile (1.6 km) per day.
Placement of ultra-high performance concrete for inclined-surface pavement
Published in Road Materials and Pavement Design, 2021
Tae Yong Shin, Jae Hong Kim, Kyung-Taek Koh, Gum-Sung Ryu, Kejin Wang
To overcome issues related to intense vibration, high slump concrete, or highly flowable concrete (slump >175 mm), has gradually come into use in slipform paving over the last decade. Self-consolidating concrete (SCC) has been applied for bridge decks, with careful consideration to obtain a cross slope of 2.0% (Ouchi et al., 2003). Semi-flowable self-consolidating concrete has been employed for paving and has demonstrated a high potential for use in pavements with slopes without sacrificing ease of casting and placement (Kejin et al., 2005; Lomboy et al., 2012, 2014; Pekmezci et al., 2007). Recently, ultra-high performance concrete (UHPC) has also been introduced for concrete bridge decks. UHPC is a dense, self-consolidating, fiber-reinforced concrete mixture made with well-packed, various sized powder and granular materials, sufficient high-range water-reducing admixture (HRWRA), and networking steel fibers. UHPC often possesses high strength (over 150 MPa at 28d), a low permeability (Richard & Cheyrezy, 1995, 1994; Rossi, 2001; Yoo & Yoon, 2016), high ductility and toughness, and strain hardening behaviour (Bonneau et al., 1997; Graybeal & Davis, 2008; Jungwirth & Muttoni, 2004; Kang et al., 2018, Kang, Choi et al., 2016, Kang, Lee et al., 2016). It is increasingly used for bridge decks or bridge deck overlays to substantially improve the strength-to-weight ratio and longevity of concrete structures. Nevertheless, it is challenging to cast UHPC on an inclined surface or to use UHPC to form a slope, because its inherent self-leveling ability prevents it from holding its shape. Theoretically, this challenge can be addressed if the flow properties (such as yield stress, viscosity, and thixotropy) of UHPC are properly modified (Banfill et al., 2000; Estellé et al., 2008; Feys et al., 2013; Kim et al., 2016; Yim et al., 2013); however, this subject has not been studied because applications of UHPC for slope casting are still limited.