Lessons Learned from Field and Laboratory Testing of a DBR Project

Where faulting takes place due to the absence of dowel bars and inadequate subbase support in jointed concrete pavement (JCP), dowel bar retrofit (DBR) is used to improve load transfer efficiency (LTE) and to prevent further faulting of slabs at transverse joints. Even though DBR generally improves LTEs and overall performance of JCPs, not all DBR projects have been successful. Faulting reoccurred within 2?years after DBR treatment on US59 in Texas. An investigation from the cores taken in the project revealed excessive voids under a dowel bar due to poor consolidation of the grouting material. A laboratory investigation was performed to determine the most critical factors for adequate consolidation of grouting materials in DBR. Typical rapid-setting grout materials widely used in DBR were selected and full-scale specimens were made for evaluations. Four testing variables for consolidation performance were investigated: time of placement after mixing, vibration time, slot width, and maximum aggregate size. Maximum aggregate size and slot width were not critical factors for consolidation performance of grout. The most significant factor was vibration time. Twenty s of vibration is recommended. Placement time was also an important factor, with grout materials placed after initial set performing poorly. Delayed placement of grout materials without vibration led to the most voids under the dowel bars.     

大城市城区改造的一次探索：北京“国宾花园”设计

通过北京“国宾花园”的设计,论述了大城市繁华地段改造规划设计的特点,并就如何达到改造资金的平衡,变建筑的单栋设计为整体设计进行了探讨。