Title: Configuration and Sampling Investigation of Pumped Concrete in a Controlled Environment
Principal Investigator's Name(s): Dr. Khaled Ksaibati, P.E.
Project Sponsor: Wyoming Department of Transportation
Background:
There are several factors that affect the strength, durability and longevity of portland cement concrete. The amount of entrained air within the concrete mix is one of these factors of great importance. These air bubbles allow the trapped water within the hardened concrete to move as it freezes. When the water is not allowed to expand due to freezing, it will cause the concrete to break. This breakage is called scaling. Scaling causes the surface to become rough and accelerates the degradation of the concrete.
Too much air within the hardened concrete result in lack of binding between cement particles and thus creates weak concrete. Too little air causes the expansion of freezing water to break and degrade the concrete. In either case, the concrete section must be replaced prior to reaching its normal life expectancy.
The Wyoming Department of Transportation (WYDOT) has implemented specification for the air content in concrete pavements and bridges. This specification allows for a range of air contents from 4.5% to 7.5%. The new Quality Control and Quality Assurance (QC/QA) specification for air entrainment in concrete has been written to eliminate the premature failures of concrete due to improper air content.
Air content can be affected by several factors. One factor that has potentially significant effects is the method used to place the concrete. In bridges, a typical placement method involves the use of a concrete pump to facilitate pouring concrete where it is needed. Pumping can significantly affect the air void content in concrete.
Objective of the Control Project:
The main purpose of the on-going research study is to determine the air change in hydraulic concrete across a pump. So far, the data analysis has shown that a combination of factors affects air change in concrete due to pumping. It is important that these factors be evaluated in a controlled environment. Therefore, a control project is proposed to provide more benefits and comprehensive answers from this study. The proposed control project will allow sampling concrete with specific pump configurations, instead of depending on the site limitations to dictate when tests will be taken.