# Ultra-High-Performance Concrete (UHPC) Piles and Splicing Options
## 1 Introduction  
Conventional piles such as precast-prestressed concrete, steel, timber, and composite piles are options commonly available for pile foundations. Concrete and steel piling are used more frequently [1]. Concrete piles with conventional steel can be cast in place, but precast prestressed concrete piles (PPCPs) and steel piles are typically fabricated in plants and driven at the site. There are some limitations associated with these pile types. Steel piles are susceptible to corrosion and are undesirable in marine environments, splicing is often not encouraged for timber piles, and the presence of corrosive soil or water accelerates corrosion in concrete piles in coastal areas [2]. Concrete piles made using UHPC are recently proposed to overcome some challenges associated with other conventional pile options.  
UHPC material is made of Portland cement, fine aggregate, silica fume, fibers (typically steel), high water-reducing admixture, and water to form a cementitious mixture [2, 3, 4]. There are a variety of proprietary (prebagged and commercially available) and non-proprietary (open-recipe mix from locally available constituent materials) UHPC mixtures that have been developed and used for different applications in bridge construction [2, 3, 4, 5, 6, 7, 8, 9]. In general, the mechanical properties of UHPC include compressive strength ranging from 117 MPa to 152 MPa and sustained post-cracking tensile strength greater than 4.96 MPa. UHPC has a very low water-binder ratio, a high packing density, low porosity that resulted in increased resistance to harmful medium erosion, decreased permeability, enhanced wear-resistance, and a discontinuous pore structure that reduces liquid ingress [10, 11, 12]. Theseproperties give UHPC pile comparative advantages over other pile options, especially in corrosive or marine environments. It should be noted that although the production cost of UHPC pile is initially high, the extraordinarily high durability of UHPC is expected to cut the maintenance expenses considerably, resulting in a decrease in the bridge's total lifecycle cost [13].  
Pile-splicing refers to any method used to join pile segments in the field during driving to continue the operation. The method can be performed for preplanned (prepared from the precast plant) or unplanned (prepared on the field during installation) situations. Splices are typically designed to resist compression, tension, bending, and shear normally equivalent to that of the pile at the point of the joint [14]. There are quite a number of pile splices which generally rely on the principles and concepts of welding, bolting, and dowelling, as well as some new methods that have recently been proposed. Effective splicing of the piles can reduce or eliminate many problems associated with the installation of long piles relating to time and preparation. Also, proper splicing methods eliminate the need to predict precise pile lengths and allow for the extensions of piles when necessary [15].  
Just as with other types of piles, splicing becomes desirable and, in some cases, necessary also for UHPC piles. Splicing may be needed for several reasons: (1) ease of handling, transporting, and driving of shorter pile segments; (2) possible concrete cracking reduction during transportation; (3) facilitating pile extension in the field during unplanned situations; (4) reduction in transportation time and costs; (5) when there is limited headroom for driving; and (6) ease of storage at the precast plant and on the field during construction [16; 17]. For conventional prestressed precast concrete and steel piles, a variety of pile-splicing systems have been developed that can be utilized in the splicing of UHPC piles. This paper aims to investigate the applicable splicing systems for connecting UHPC piles. Accordingly, various driven piles are briefly discussed, and all the available information on splicing systems are compiled and analyzed to help form an effective approach when considering the development of new alternatives.