Controlling Air Content in Concrete That is Being Pumped: A Synthesis Study : Final Report

18 Pages·1998·0.38 MB·English

by  Scholer, Charles F. (Charles Frey)

Joint
Transportation
Research
Program
JTRP
FHWA/IN/JTRP-98/1
1
Final Report
Controlling Air Content in Concrete That is Being
Pumped, A Synthesis Study
Charles F. Scholer
Jay Grossman
August 1998
Indiana
Department
of Transportation
Purdue
University

1
Final Report
FHW
A/IN/JTRP-98/1
A
Controlling Air Content in Concrete That is Being Pumped, Synthesis Study
by
Charles F. Scholer
Professor ofCivil Engineering
Purdue University
West Lafayette, Indiana
and
Jay Grossman
Graduate Research Assistant
School ofCivil Engineering
Purdue University
West Lafayette, Indiana
Joint Transportation Research Program
ProjectNo: C-36-61N
File No: 5-14-14
Prepared in Cooperation with the
IndianaDepartment ofTransportation and
the U.S. Department ofTransportation
Federal Highway Administration
The contents ofthis report reflect the views of the authors who are responsible for the
facts and the accuracy of the data presented herein. The contents do not necessarily
reflect the official views or policies of the Federal Highway Administration and the
Indiana Department of Transportation. This report does not constitute a standard,
specification or regulation.
Purdue University
West Lafayette IN 47907
August 1998
Digitized by the Internet Archive
in 2011 with funding from
LYRASIS members and Sloan Foundation; Indiana Department of Transportation
http://www.archive.org/details/controllingaircoOOscho
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Contents
1 Introduction 1
2 Changes in Air Content at Delivery 1
3 Air Losses in the Pump Line 2
3.1 High Pressure Dissolution ofAir Voids 2
3.2 Bursting ofVoids by Vacuum 3
3.3 Impact Force 4
3.4 Controlling Air Loss 4
4 Testing for Air Content 6
5 Conclusion 7
6 Implementation 7
7 Recommended Further Activity 8

1 Introduction
Changes in the intentionally entrained air content offresh concrete can occur at a number
ofplaces in the pumping process. These locations include as the concrete is initially
being loaded into the pump hopper, as it passes through the pump line, and when it exits
the line. This synthesis reviews the findings ofrecent research studies which deal with
air content change in pumped concrete and summarizes methods ofreducing entrained air
loss caused by handling.
2 Changes in Air Content at Delivery
Some change ofair content in concrete being delivered to the site and loaded into the
pump has been noted. Yazdani (1996) reportsthat, "a small amount ofair appears to mix
with the concrete when the concrete first enters the pump due to the pressure present in
the pump line." He further notes that:
The concrete and the pump should be protected from adverse weather. If
pumping has to occur during rain, a method should be implemented to
keep excess water from building up in the pump's hopper. This water can
increase the concrete air content because the excess water which does not
hydrate eventually evaporates and causes airvoids.
These air voids are not intentionally entrained, are not in a bubble form, and therefore do
not contribute to freeze/thaw durability. Other changes in the air content may take place
ifthe delivering trucks must wait a long time to unload. Continuous mixing ofconcrete
containing micro-silica or fly ash may shift the void size finer, which an air meter might
interpret as a loss ofair content (Hover 1989).