The use of UHPC in accelerated bridge construction

超高性能混凝土(UHPC)是一种新型建筑材料，具有强度增长快、强度比混凝土高4倍、耐久性好等特点。在过去的十年中，超高性能混凝土在桥梁建设中的使用有所增加。2006至2019年间，美国和加拿大建造了300多座采用超高性能混凝土组件的桥梁。超高性能混凝土最常用于现场浇筑施工缝，或用作桥面铺装层。快速建造桥面可最大限度地缩短关键交通基础设施无法使用的时间，而超高性能混凝土有能力实现这一点。高质量的桥面面板可以预制，但现场浇注高质量的接缝仍然是一个挑战。接缝质量差对桥面整体耐久性不利。粘结强度在预制梁与现浇节点之间的剪力传递过程中起着重要的作用。本文的研究重点是确定超高性能混凝土与预制混凝土和现浇超高性能混凝土的粘结强度。这项研究的目标是量化重要的粘结参数，并修改现有的控制桥面超高性能混凝土节点剪力传递的设计公式。几项关于超高性能混凝土与预制混凝土之间在静载下的粘结性能的研究，包括申请人的研究组完成的两项研究，发现界面粘结强度随着基材粗糙度的增加而增加。然而，目前的结果是定性的，而不是定量的。本研究计划将使用多种方法来评估表面粗糙度，以便在现场浇注接头中使用超高性能混凝土时，建立测量表面粗糙度的质量控制和施工规程。摩擦系数和内聚力/粘附力将作为表面粗糙度和超高性能混凝土龄期的函数来确定。这将导致超高性能混凝土连接的优化设计。本研究将探讨超高混凝土与混凝土、超高混凝土与现浇超高混凝土界面的剪切摩擦机理。在静载和循环荷载作用下，建立了剪切摩擦机理与配筋率、粗糙度和超高性能混凝土龄期的函数关系。本研究项目将研究超高性能混凝土界面粘结的疲劳行为，这是一个尚未得到有效研究的课题。这项研究计划的结果将为工程师提供关键粘结参数的设计值，如粘聚力和摩擦力，并为节点配筋的优化提供指导。它还将开发评估施工现场关键参数的方法，从而实现更可控的结果和更好的长期联合性能。这项研究计划将培训七名HQP了解这种尖端建筑材料的行为、应用和设计。由于超高性能混凝土的设计标准目前正在制定中，我将带着我的HQP作为观察员参加ACI和CSA委员会举行的讨论。

Ultra-high performance concrete (UHPC) is a new construction material exhibiting rapid strength gains, strengths four times higher than concrete, and excellent durability. Over the last decade, the use of UHPC in bridge construction has increased. Between 2006 and 2019, over 300 bridges with UHPC components were built in the United States and Canada. Most frequent use of UHPC is in field-cast construction joints, or as bridge overlays. Rapid bridge deck construction minimizes the time that critical transportation infrastructure is out of service, and UHPC is capable of enabling this. High quality deck panels can be prefabricated, but field-casting high quality joints remains a challenge. Poor quality joints are detrimental to overall bridge deck durability. Bond strength plays a significant role in the shear transfer between precast bridge girders and field-cast connections. The proposed research focuses on determining the bond strength of UHPC with precast concrete, and cast-in-place UHPC. The goal of this research program is to quantify important bond parameters and to modify existing design equations governing shear transfer in bridge deck UHPC joints. Several studies on bond performance between UHPC and precast concrete under static load, including two completed by the applicant's research group, found increase in interface bond strength with the degree of substrate roughness. The results however are qualitative rather than quantitative at this time. This research program will use several methods to assess surface roughness in order to establish quality control and construction protocols for measurement of roughness when UHPC is used in field-cast joints. Coefficient of friction and cohesion/adhesion will be determined, as function of surface roughness and UHPC age. This will lead to optimization of the design of UHPC connections. This research program will investigate the shear friction mechanism for both UHPC-concrete, and UHPC- cast in place UHPC interface. Design equations will be developed for shear friction mechanism as function of reinforcement ratio, roughness and UHPC age under static and cyclic loads. This research program will investigate fatigue behavior of UHPC interface bond, a topic that has yet to be effectively studied. The results of this research program will provide engineers with design values of critical bond parameters, such as cohesion and friction, and guidelines for optimization of joint reinforcement. It will also develop methods for evaluating critical parameters on the construction site leading to more controlled outcomes and better long-term joint performance. This research program will train seven HQP in understanding this leading edge construction material behaviour, application, and design. Because design standards for use of UHPC are currently under development, I will bring my HQP as observers to the discussions that are held in the ACI and CSA committees.