Muhammad Ali Center Case Study
The Muhammad Ali Center (“Ali Center”) is a multicultural center with an award-winning museum dedicated to the life and legacy of Muhammad Ali. The Ali Center museum captures the inspiration derived from the story of Muhammad Ali’s incredible life and the Six Core Principles that fueled his journey. The Ali Center is also an educational center, a hosting space for many special events and a cultural landmark in Louisville, Kentucky. The Ali Center organization decided to renovate the lobby to update and modernize the space, while also reflecting Muhammad Ali’s cultural significance. Part of this modernization included demolishing the existing patterned stained concrete floor topping, filling the recess left after removing the concrete topping, and installing a four-color patterned epoxy terrazzo floor.
This project presented various challenges throughout the installation, including a radiant tube heating system that reached excessive temperatures, moisture permeating through the curtain wall, and a post-tension slab without control joints. The radiant tube heating system reached a temperature of 117° Fahrenheit. The temperature of the heating system did not increase gradually but rather reached it almost immediately. Epoxy terrazzo cannot withstand temperatures above 90° Fahrenheit and is liable to crack due to thermal expansion if exposed to excessive temperatures. 
The leak near the curtain wall kept the concrete slab moist which would likely cause the new terrazzo flooring to delaminate if it was not corrected. Several areas were visibly damp due to moisture seeping in through the curtain wall, and this area tested at 100% relative humidity. Eliminating the source of the moisture was imperative before the epoxy terrazzo flooring system could be poured. 
The substrate consisted of a post-tension slab that did not require contraction -joints in the concrete slab. This slab was over an unheated garage and the lobby had a two-story curtain wall that created significant thermal expansion and contraction due to sunlight hitting the floor and the radiant heat system warming the floor. This thermal expansion and contraction could potentially cause the epoxy terrazzo topping to crack. 
Terrazzo Trade Standards
Radiant heating systems must gradually increase in temperature and cannot exceed 90° Fahrenheit when installed beneath an epoxy terrazzo topping. The recommended temperature range for terrazzo is between 60° and 90° Fahrenheit. The coefficient of expansion for epoxy is greater than that of concrete , so large temperature shifts could cause delamination and cracking. This particular heating system specified at least ¾” space between the radiant tube heating and concrete topping however the radiant tubes in many places were near the top of the concrete slab. The original stained concrete topping placed on top of the concrete slab was demolished and replaced with Custom Tech-level 150 self-leveling underlayment. An epoxy terrazzo topping requires the substrate to have a tensile strength of at least 300 psi in order to prevent the epoxy from “pulling” the substrate , and Tech-level 150 provides a tensile strength of 333 psi. , and Tech-level 150 provides a tensile strength of 333 psi.
The relative humidity must be between 75% and 80% before terrazzo can be poured. Any sources of moisture must be mitigated, or the terrazzo could delaminate. Proper moisture testing requires the ASTM-F-2170 deep probe test between the radiant heating tubes at two inches in depth. 
Some post-tension slabs are engineered to eliminate contraction joints. This particular slab did not have any contraction joints, so control joints in the terrazzo were necessary to prevent the terrazzo topping from cracking due to thermal expansion. According to NTMA standards, control joints are required in areas of potential stress or where radiant heat could cause thermal expansion, such as between columns and curtainwall. 
Engineers were tasked with modifying the radiant tube heating system to gradually increase in temperature and to not exceed 90° Fahrenheit. The radiant heating system was turned off entirely during the epoxy terrazzo installation and remained off until modifications were completed. The original topping slab was demolished, and Tech-level 150 was poured to fill the recess left after the topping slab was removed and to provide an additional barrier between the radiant heating tubes and the epoxy terrazzo flooring. It also provided the tensile strength necessary in the substrate.
To prevent further moisture migration, the owner of the center hired a contractor to remove two feet of the sand-set paving along the perimeter of the exterior plaza adjacent to the lobby curtain wall. The exterior side of the foundation for the curtain wall was water-proofed and flashed under the curtain wall. These measures sufficiently mitigated the moisture penetration through the curtain wall, and the relative humidity tested at acceptable levels. Key Resin’s moisture vapor barrier was applied to the affected area.
Because the post-tension slab did not have contraction joints in it, control joints were added to the terrazzo floor at various points, including between columns and at certain wall junctions. Divider strips were also placed in a grid to aid in mitigating the potential for cracking due to the thermal expansion from the exposure to sunlight through the curtain wall. These joints allow for the terrazzo to expand and contract with any thermal changes.
This job had several challenges throughout the terrazzo installation, including moisture infiltration, thermal expansion from sunlight and radiant heat over an unheated garage space and the lack of contraction joints on a post-tension slab. These issues were successfully mitigated by applying the industry standards established by the National Terrazzo and Mosaic Association.
 Email from architect after reviewing radiant heat system specifications
 NTMA Email 7/24/14
 Statement from Technical Services at Custom Building Products