Browsing College of Engineering and Mines (CEM) by Author "Ahn, Il-Sang"
Examination of the Variability in Grout Test ResultsAhn, Il-Sang; Friend, Trenton (2019-08-31)Keyway grouting is an operation that connects decked bulb-tee girders into one system. The quality of grout should be well maintained through reliable material test procedures. Due to the issues of discrepancy and variability, there have been several cases in which grout materials did not satisfy the compressive strength standard specified in the DOT&PF Standard Specifications for Highway Construction. This research examined the causes of such issues. Six factors – grout material, mix consistency, workmanship, initial curing/storing, curing method, and test equipment – were identified as the causes of strength variation. Their effects on strength variation were investigated by testing compressive strength of cube and cylinder specimens made from 5 grout materials that were used or considered to be used in DOT&PF projects. Grout material characteristics such as grout material and mix consistency have significant effect on strength variation. Workability and consolidation can be different from one material to another. Consequently, they affect compressive strength and its variation. Workmanship and test equipment were evaluated in this research to have moderate effect on strength variation. Especially, strength variation can increase when the workmanship factor combines with the grout material characteristics factor.
Pre-Stress Loss Due to Creep in Precast Concrete Decked Bulb-Tee Girders Under Cold Climate ConditionsVandermeer, Drew; Ahn, Il-Sang (2019-07-31)Accurate estimation of pre-stress losses is one of the important issues for the design of precast, pre-stressed concrete bridge girders. While this subject has been long studied by many researchers, studies on pre-stress losses in cold climates are minimal. In the present research, long-term pre-stress loss due to concrete creep was studied based on concrete creep test. Two concrete creep test frames were fabricated and placed indoors and outdoors. Concrete strains were measured by Demountable Mechanical Strain Gauge (DEMEC) from two 612 high-strength concrete cylinders in each frame. The concrete strains were collected for 11 months (7/26/2017 – 6/21/2018) after loading, and outdoor ambient temperature dropped below 0C between 100 and 250 days. Between 50 and 100 days, two curves from the two frames are similar in their patterns and values. After 100 days, the total strain from the indoor frame slowly increased reaching 1,600 and 1,700 after 250 days. However, the total strain from the outdoor frame varied between 1,000 and 1,500 and the averaged total strain was 1,300 after 250 days. In cold temperature, the occurrence of concrete creep and shrinkage was suppressed.