L. K. Crouch
"This material was prepared with the support of the US Department of Energy, Federal Energy Technology Center through it's Cooperative Agreement No. DE-FC26-998FT40028 with West Virginia University Research Corporation. However, any opinions, findings, conclusions, or recommendations expressed herein are those of the author(s) and do not necessarily reflect the views of WVU or DOE."
Twenty-three different EFF mixtures were placed in trenches simulating utility cuts during March through May of 2001. All EFF mixtures were tested for flow, unit weight, gravimetric air content, suitability for load application, and compressive strength development over time. The trenches were excavated in March 2003.
Nine EFF mixtures were used to access the impact of Portland cement content and ASTM C 618 Class F fly
ash content. Portland cement contents of 30, 45, and 60 lbs/CY and ASTM C 618 Class F fly ash contents of 300, 370, and 440 lbs/CY were used to evaluate the impact of component proportions. PC-F Ash EFF mixtures with cementitious materials contents between 415 and 500 lbs/CY were found to have a high probability of having an ASTM D 6103 flow greater than 8-inches and passing the ASTM D 6024 ball drop test in less than 24 hours. In addition, the PC content of PC-Class F fly ash EFF mixtures appears to be more important to early compressive strength development. Further, strong relationships exist between component material proportions and 28-day and maximum compressive strengths and excavation difficulty.
Six EFF mixtures were used to access the impact of Portland cement content and high-unburned carbon fly ash content. Portland cement contents of 45 and 60 lbs/CY and high-unburned carbon fly ash contents of 370, 440, 510 lbs/CY were used to evaluate the impact of component proportions. The use of high carbon ash typically extended the time required to pass the ball drop test and often generated some erratic strength results. Therefore, the research team was hesitant to recommend the use of mixtures containing high carbon ash without further research.
The influence of aggregate type on EFF mixtures was evaluated by using five different aggregate types in the EFF mixture recommended by TRMCA (45 lbs/CY Portland cement and 370 lbs/CY ASTM C 618 Class F fly ash). Unfortunately, the previously mentioned strong relationships between component material proportions and 28-day and maximum compressive strengths and excavation difficulty appear to be aggregate dependent. In addition, very uniform fine aggregates were found to be likely to produce EFF mixtures that bleed excessively and are prone to segregation and flow problems. Further, limestone screenings produced the highest 28-day and maximum compressive strengths and river sand produced the lowest 28-day and maximum compressive strengths in PC-F Ash EFF mixtures.
Four comparison EFF mixtures were also used in the study (1 TDOT and 3 air-entrained EFF mixtures). There appears to be an excellent relationship between compressive strength of air-entrained EFF mixtures and excavation difficulty. Further, air-entrained EFF mixtures are easier to excavate at the same compressive strength than non-air-entrained PC-Class F fly ash EFF mixtures. Finally, the Excavation Index (EI) combines the effects of compressive strength and density to predict excavatability. EFF mixtures with EI less than 10.0 are excavatable with a Case 580E backhoe.
After reviewing the results of the recent TDOT / TRMCA / KRMCA EFF study, KRMCA asked "What about C-ash?" They pointed out that a large number of Kentucky producers use C-ash. The situation was similar in Tennessee. The research team at TTU thought this was a valid concern and formulated a C-ash study plan. TRMCA and KRMCA agreed to support the study.
The study began in June 2003 and will continue about 15 months. The table shows EFF mixture proportions used in the study.
|PC lbs/CY||300 lbs/CY C-Ash||370 lbs/CY C-Ash||440 lbs/CY C-Ash||510 lbs/CY C-Ash||580 lbs/CY C-Ash|
|60||C14||C15||C16 TTU Cap|
Mixtures shaded in blue have corresponding F-Ash comparison mixtures
Mixtures shaded in green are new mixtures
Results will be available in fall 2004.
Approximately 2400 cubic yards of 4500-psi PCC containing Type 1 PC and Class C fly ash were placed for a portion of the seismic retrofit of Pier A of I-40 Bridge over the Mississippi River in Memphis Tennessee on Thursday 1/08/04. Figure 1 shows a portion of the temperature data collected at the site.
TDOT and TTU are interested in looking at alternative PCC mixtures which will produce the desired hardened (4500-psi @ 28-days) and plastic properties yet generate less heat (thus reducing temperature induced cracking potential). The following mixtures have been suggested:
Results available in fall 2004.