Governing Factors and Prediction of Pumpability of Flowable Concrete
The pumping of concrete relies heavily on the experience of the pumping
professionals and takes into account limited characteristics of the fresh concrete, mainly its slump (or
slump flow determined by the DIN flow table). However, such flow property does not reflect the
plastic viscosity of the concrete that can significantly affect pumping mobility and stability.
Most of the guidelines that have been developed for pumping of conventional vibrated concrete (CVC)
involve the use of concrete with moderate slump consistency where pumping is mainly affected by the
rheological properties of the lubricating layer formed near pipe walls. In the case of CVC, the
majority of the concrete moves at the same velocity due to the formation of a plug flow at the
central portion of the pipeline.
Unlike CVC, flowable concrete and especially self-consolidating concrete (SCC) undergo extensive
shearing during pumping, which can significantly affect their rheological properties and air-void
distribution. This can lead to loss of filling ability, passing ability, static and dynamic
stability, and eventually strength and durability. With the increasing use of flowable concrete and
SCC, it is important to take into account the rheological properties (yield stress and plastic
viscosity) of the concrete mixture and lubricating layer in predicting pumping pressure
and determine the effect of pumping on key concrete properties.
Objective: The project will validate recent scientific contributions made to incorporate various
principals of physics to understand concrete rheology and its influence on workability and
stability, and complex computational fluid dynamics of heterogeneous materials that can take place
during pumping. The main objectives of the research are to:
1. Develop a simple test method to evaluate rheological properties of the lubricating layer.
2. Select a reliable rheometer to assess rheological properties of flowable concrete and SCC.
3. Develop proper experimental protocols to assess rheological properties and account for
measurement artifacts, including particle migration, segregation, plug flow, and wall slip.
4. Evaluate the anticipated changes in workability (filling ability, passing ability, and
stability) and rheological properties of flowable concrete and SCC during pumping as well as
changes in temperature, air content, strength, transport properties, and air-void system.
5. Develop and validate prediction models to determine pressure loss of SCC of various strength
classes in long-distance horizontal and vertical pumping. The model should take into consideration
the effect of flow rate, equivalent pumping length, pipeline geometry, initial rheological
properties of the concrete, lubrication layer, and their changes during
pumping, as well as changes in concrete temperature and air volume.
The increasing use of flowable concrete for the construction and rehabilitation of
transportation infrastructure necessitates better understanding of factors affecting the pumping of
such concrete and the evaluation of changes in concrete properties during pumping. The present
research will seek to develop proper strategies enabling the prediction of pressure loss during pumping of flowable concrete based on the rheological properties of the concrete and those of the
lubricating layer are required to ensure safe pumping operations and adequate concrete flow
properties and durability.
The proposed research is expected to include the following tasks:
1. Perform a critical review of leading models and approaches to evaluate form pressure.
2. Develop simple test methods to evaluate tribology of lubricating layer.
3. Evaluate different concrete rheometers that can be used on site for pumping.
4. Carry out full-scale field validation of the results using SCC and highly flowable concrete
mixtures of different mix designs - short loop circuit and/or vertical pumping.
5. Develop a model to predict pump pressure.
6. Establish recommendations and guidelines.
Related Words - Portland cement concrete, workability, rheology, tribology, pumpability, pressure loss, high-performance concrete, self-consolidating concrete, safety.
|Sponsoring Committee:||AFN40, Concrete Materials and Placement Techniques
|Research Period:||24 - 36 months|
|RNS Developer:||Kamal H. Khayat|
|Index Terms:||Pumped concrete, Rheological properties, Lubrication, |
Bridges and other structures