Research Activities: 2012

Optimization of Rheological Properties of Self-Consolidating Concrete by
Means of Numerical Simulations, to Avoid Formwork Filling Problems in Presence of
Reinforcement Bars
 
 Status Complete                        View Final Report: PDF
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Sequential Number R344
 
Identification Number 00042528
   
Matching Research Agency

Missouri University of Science & Technology
 
Principal Investigator

Dimitri Feys
Assistant Professor
Missouri University of Science and Technology
Rolla, MO 65409
(573) 341-6947
feysd@mst.edu
 
Student Involvement

One graduate student
 

Project Objective		 The main objective of this project is to perform numerical single-fluid simulations to identify critical rheological parameters of Self-Consolidating Concrete for which formwork filling problems occur. As a function of the variables studied, namely the formwork width, the rebar diameter, the concrete cover (distance between rebar and formwork), the distance between rebars (group effect) and the discharge rate, this project allows to establish a set of guidelines for the rheological properties of concrete to avoid the presence of dead zones or zones with very high shear rates. In this way, the occurrence of construction defects can be reduced.
 

Project Abstract		 Self-Consolidating Concrete is a relatively new type of concrete which does not require any energy for consolidation. Consequently, the hardened properties of the cast structural element are largely influenced by the flow pattern of SCC in the formwork. Several examples are available in
literature showing the existence of dead-zones, dynamic segregation induced by high shear rates, filling of formworks as a function of the concrete yield stress, lower mechanical properties due to multi-layer casting, etc. All these examples were predicted by means of numerical, single fluid simulations, in which the concrete is assumed to be a fluid without particles. However, numerical simulations that take into consideration the influence of reinforcement bars on local patterns in
SCC flow have not been reported extensively. Preliminary simulations have shown that a vertical bar creates additional zones with very low and very high shear rates, compared to the flow in non-reinforced elements.
In this project, the influence of reinforcement on the flow of SCC in a vertical wall is studied.
Different structural parameters, such as the formwork width, reinforcement bar diameter, concrete cover (distance between rebar and wall) and the distance between the rebars (to investigate group effects) will be considered in the investigation, in combination with the flow rate. The objective of the project is to identify, for each situation, minimum and maximum limits for the rheological properties (yield stress and plastic viscosity) to obtain a good formwork filling. In other words, the rheological properties will be varied for each formwork and reinforcement condition to identify any dead zones, in which the concrete is at rest, or any zones
with very high shear rates, which might cause segregation of the concrete. In the dead zone, entrapped air bubbles are less likely to evacuate, reducing the mechanical properties of the concrete and potentially the bond between the concrete and the rebars. Coarse aggregates might
migrate away from the zone with high shear rate, increasing the concentration of coarse aggregates in other zones, potentially leading to blocking further downstream the formwork.
 

Relationship to other Research/Projects

This project will be useful for future applications considering concrete flow and its interactions with hardened concrete properties, such as strength, durability and the properties of the concrete cover. Numerical simulations allow the avoidance of large experimental program and only
necessitate the validation of the critical parameters.
Studies on numerical simulation of concrete flow are also directly applicable to simulation of other slurry flows with similar flow behaviors (such as yield-stress). Therefore, this project has a potential to contribute to new projects related to processing of slurry flows, such as nuclear waste,
ceramic processing, and biomass processing for biofuel production.
   

Transportation-Related Keywords

 Self-Consolidating Concrete, flow, formwork filling, numerical simulations, rheology, reinforcement
   

Technology Transfer Activities

With the obtained results, one joint journal and three joint conference papers and presentations are anticipated, including a presentation and/or poster at the annual NUTC Conference. The project will also be described in a presentation for NUTC Webinars and in an article for the NUTC Newsletter.

A half-day inter-department workshop will be organized to favor the exchange of information with other students and faculty doing research on concrete mix design and properties, numerical modeling of the flow of complex suspensions, sediment flow, rheology, …
   

Project Deliverables

 At the end of this project, the research team anticipates to have established guidelines for SCC rheological properties guaranteeing no major formwork filling problems, based on single-fluid numerical modeling. These guidelines will be valid for a variety of parameters, such as
formwork width, rebar diameter, concrete cover, rebar spacing, and the flow rate in the formwork.
Furthermore, this collaboration should enable the researchers to set up future collaborations in the form of joint projects on numerical simulations of concrete flow.
   

Anticipated Benefits

As a direct benefit for the transportation construction industry, guidelines for rheological parameters of SCC, dependent on the formwork and reinforcement design will be established.
This allows identifying specific formwork filling problems, such as dead zones, leading to air entrapment and loss of bond with the rebars, and high-shear zones, which might indicate dynamic segregation, on its turn reducing concrete uniformity and increase the risk of blocking further downstream. As a result, the construction defects due to improper formwork filling are reduced, decreasing the costs for premature repair, rehabilitation and replacement of the infrastructure.
As additional benefits, this project is the start of collaboration between the Civil and Chemical Engineering department in the evolving domain of concrete flow simulations. This collaboration can lead to further in-depth studies of more complex flow problems, including the presence of
aggregates, thixotropy and structural breakdown. The further development of knowledge in the domain of concrete flow simulations is necessary to increase success rate for future joint project applications. Pursuing joint projects will lead to a fundamental understanding of concrete flow and will eliminate construction defects, as rheological properties (workability) should be an additional requirement for concrete mix designs, in the long term.

Milestones
Project Start Date: 05/15/2013
Project End Date:

01/30/2014