RE-CAST UTC Project Information

Project Title

Formwork Pressure Measurements and Prediction of High Performance Concrete with Adapted Rheology

Universities

University of Illinois at Urbana-Champaign

Principal Investigator

David Lange
University of Illinois at Urbana-Champaign

PI Contact Information

dlange@illinios.edu;  217-333-4816

Funding Source(s) and Amounts Provided (by each agency or organization)

University of Illinois at Urbana-Champaign $60,082
RE-CAST $60,082

Total Project Cost

$120,163

Matching Agency ID or Contract Number

University of Illinois at Urbana Champaign: internal
RE-CAST: 00042134-02-2

RE-CAST Grant Award Number

DTRT13-G-UTC45

Start and End Dates

Start Date: June 1, 2016
End Date: June 30, 2017

Brief Description of Research Project

The research objectives of this Re-CAST study are to:

1. Improve methods for measuring and modeling formwork pressure of HPCAR,

and improve methods by appropriate laboratory experiments and

analysis.

2. Study fresh and hardened properties, and the transition from one to the

other. The transition from liquid to solid is not merely a function of

hydration, but of rheological behavior. HPC-AR must exhibit “robustness”

and “stability” in real-world application. Develop better understanding of

gelation and microstructure development to develop predictive models for

material properties.

3. Develop improved mixture design methodology to produce HPC-AR with

reliable, stable, robust performance while having desired flow and hardened

properties.

4. Conduct field tests of placement of HPC-AR in tall forms. Measure formwork

pressure, fresh properties, robustness, and assess all aspects of

constructability.

Describe Implementation of Research Outcomes

A field test program supported in part by this project was conducted at the St. Mary’s Cement site in Toronto, ON, Canada. The extensive study was a collaboration of several universities and industry sponsors. The focus of the study was to measure lateral pressure by casting eight tall columns 6.00 m (20 ft) in height, and examining how the measured lateral pressure envelopes varied with rates of concrete placement of 3, 5, and 10 m/h (10, 16, and 32 ft/h). Variables included reinforcement density and levels of concrete thixotropy.

The full details of the field test program are documented in a published article by N.J. Gardner et. al. [2]. The factors affecting SCC are further discussed by the same team in a document by K.H. Khayat et. al. [3]. A prior study in Stockholm served as an essential precursor to the Toronto field test program [5].

The Toronto field test program included analysis of formwork pressure using six prediction methods. While the models differed in terms of input data and formulation, it was shown that all six equations could be successful and effective for prediction of formwork pressure.

Impacts/Benefits of Implementation

 The project produced new insight into testing SCC, analyzing formwork pressure, and validating analytical models used for formwork pressure. A method for achieving the accurate yield stress values using the ICAR rheometer was developed. The accuracy of the pressure data obtained using pressure sensors was also evaluated. Based on the results obtained, the accuracy of the Lange and Tejeda model in predicting the formwork pressure of self consolidating concrete was studied. The results showed that within first few hours of the pressure decay, the reversible changes in concrete dominate the pressure decay and slight variation in the mix proportions, mixing procedure alter the pressure decay significantly indicating the sensitivity of SCC mixes.
The formwork dimensions also affect the pressure decay indicating the importance of including the formwork dimension parameter while developing the models for prediction of formwork pressure.
Recommendations were made for reducing the variation in the mix properties, the importance of focusing on the particle to particle interaction within concrete for understanding its thixotropic properties that seem to be the primary cause of the pressure decay in the initial hours after casting before the hydration process becomes dominant. From the mix design point of view, using the oven dried aggregates (with fines sieved off) and aggregate with low absorption capacity is recommended as it offers better control over the mix in terms of available water in the concrete mix for workability and hydration thereby controlling the variation formwork pressure.
The formwork dimensions (height, diameter, and height to diameter ratio) have a significant on the pressure decay so its effect should be considered when developing the models for the
estimation of formwork pressure. Reversible effects dominate the pressure decay for the first few hours so to understand the pressure decay completely the fresh properties of concrete and cement paste with emphasis on the thixotropy and its behavior under constrained and creep load conditions need to be studied. A small variation in the material proportions affect the pressure decay, yield stress data significantly making the prediction of the field lateral pressure exerted by a concrete mix based on the results obtained in the laboratory studies.

Web Links

Project website: https://recast.mst.edu/projects/formworkpressure/

Final Report: PDF

Supplemental report: http://hdl.handle.net/2142/97509