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，具有快速的强度增加，强度是混凝土的四倍，并且具有优异的耐久性。在过去的十年中，UHPC在桥梁建设中的使用有所增加。在2006年至2019年期间，美国和加拿大建造了300多座带有UHPC组件的桥梁。UHPC最常用于现场浇筑施工缝，或作为桥梁覆盖层。快速桥面施工可以最大限度地减少关键交通基础设施的停机时间，而UHPC能够实现这一点。高质量的甲板板可以预制，但现场铸造高质量的接头仍然是一个挑战。接缝质量差，会影响桥面整体耐久性。粘结强度对预制梁与现浇节点之间的剪切传递起着重要作用。本文的研究重点是确定UHPC与预制混凝土和现浇UHPC的粘结强度。本研究计划的目标是量化重要的粘结参数，并修改现有的控制桥面UHPC接缝剪切传递的设计方程。几项关于静载下UHPC与预制混凝土粘结性能的研究，包括申请人课课组完成的两项研究，发现界面粘结强度随着基材粗糙度程度的增加而增加。然而，目前的结果是定性的而不是定量的。该研究计划将使用几种方法来评估表面粗糙度，以便在UHPC用于现场铸造接头时建立测量粗糙度的质量控制和施工协议。摩擦系数和黏聚力/附着力将被确定，作为表面粗糙度和UHPC年龄的函数。这将导致UHPC连接的优化设计。本研究计划将探讨超高强度混凝土-混凝土及超高强度混凝土-现浇超高强度混凝土界面的剪切摩擦机制。在静荷载和循环荷载作用下，将建立剪力摩擦机制的设计方程，该方程是配筋率、粗糙度和UHPC龄期的函数。本研究项目将研究UHPC界面粘结的疲劳行为，这是一个尚未得到有效研究的课题。该研究项目的结果将为工程师提供关键粘结参数的设计值，如黏聚力和摩擦，并为节点加固优化提供指导。它还将开发评估施工现场关键参数的方法，从而更好地控制结果和更好的长期联合性能。这项研究计划将训练7名HQP了解这种前沿建筑材料的行为、应用和设计。由于使用UHPC的设计标准目前正在制定中，我将带着我的HQP作为观察员参加在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.