Material List

(Please see attachments for additional material details).

• Gypsum Cement
• Small Beam Forms
• Rebar Tie Wire
• Small Gage Threaded Rod
• Small Beam Testing Apparatus

Introduction

What if you could introduce a new material that allows students to rapidly prototype concrete beam designs? This card showcases how connecting gypsum cement in a civil engineering application can uncover unexpected insights for students - allowing different elements of the 3Cs to be applied in beam construction. This may especially be helpful for institutions that do not have the equipment of time for traditional approaches.

Most undergraduate civil engineering programs include an introductory course in reinforced concrete design.  The course typically focuses on fundamental behavior of primary members: beams, columns, and other basic elements.  Students learn both aspects of analysis and design.  It can be difficult, however, for students to truly understand how these elements perform in reality through basic classroom discussion and/or watching videos.

Some institutions have the capability to perform beam construction and testing. This experience is often out of reach of many institutions for a variety of reasons.  The material, formwork, and laboratory equipment necessary to test these beams can be cost prohibitive for most undergraduate programs.  Beam construction also takes a significant amount of time.  Just casting a beam often requires at least 28 days of curing time, let alone the time required to tie rebar cages and construct formwork.  Even for classes the get to test beams, there is often only enough time to test a single set (i.e. no prototyping or learning from failure). Also, students need to begin construction well before they have covered enough content to understand the design of what they are building.

This card presents a method to facilitate hands-on, rapid construction and testing of reinforced concrete beams. Students are able to construct and test small-scale beams in less than 24 hours.

Design Challenge

Students are asked to design and construct a reinforced concrete beam for the following load condition: 

To earn the maximum number of points, students are tying to optimize the following equation which awards points for quality of their prediction and the strength to weight ration compared to other teams in the class:

where,

P_mea - Peak measured load
P_pre - Predicted max capacity
W_mea - Measured beam weight
P_min - Smallest measured capacity of all teams
W_max - Largest measured beam weight of all teams
P_max - Largest measured capacity of all teams
W_min - Smallest measured beam weight of all teams.

The beam must span 24" and can be no larger than 2" x 2" in cross- section.  Students are supplied with 8-32 all thread bar and 16 Gauge Tie Wire for stirrups.  Students are provided with a beam mold matching the maximum dimensions.  Students also receive 3/4" insulation foam so they can create block-outs to create unique shapes.

Gypsum Cement

Rather the traditional Portland Cement Concrete, this module makes use of Gypsum Cement.  The benefit of this material is that is achieves full strength within 24 hours.  Depending on the mix, you can achieve compressive strengths up to 10,000 psi.  The material behavior is also quite similar to regular reinforced concrete.  The mix suggested in this module is just water and gypsum cement, however, you can experiment with adding small aggregate and sand for different material properties.

Module Variations or Enhancements

This module can be adapted or enhanced to add several different learning opportunities:

• DEMONSTRATION - Use two beams: 1 with no reinforcement and one with reinforcement to introduce the basic concept of reinforced concrete.  The instructor applies load to the unreinforced beam in stages asking students to make observations.  Students are also asked prompting questions...Can unreinforced beam carry load?  Do you see any cracks?  How much load is on the beam.  The unreinforced beam will break suddenly without warning, and hopefully a nice loud noise that gets a jump out of students.  Then there is a time for reflection on how the design could be improved.  The instructor the places the reinforced beam on the supports.  However, the beam is "accidentally" placed upside down.  The instructor waits for students to identify the mistake.  Then the faculty member gets to emphasize the the reinforcement goes on the tension side of the beam, not the bottom of the beam.  The instructor can then show the significant capacity increase by adding reinforcement and the added warning prior to failure.
• PROTOTYPING - Students are given this challenge early in the quarter, and asked to optimize their design over the term.  Students would be provided with a chance to improve their design and learn through failure.  This would also work well with allow students a chance to experiment with their mix design including different aggregates, sands, or other material variations.
• REPORT WRITING - Students can be asked to write a report that includes structural drawings, calculations for capacity, and a short report.