Fort Worth Botanical Gardens – Case Study
A well-known Texas public attraction was extending its parking facilities when the contractor uncovered industrial waste that, while not particularly noxious, was going to be an expensive waste disposal issue.
During construction of the parking lot at the Fort Worth Botanical gardens, the contractor found dozens of 55 gallon drums filled with waste (mill slag). The cost to re-mediate this was prohibitive and out of all proportion to the waste material involved as it was not particularly hazardous.
The EPA has very strict guidelines on waste disposal and re-mediation, but also allows for some relatively low cost, in-situ solutions that include ‘encapsulation’ of hazardous material such as asbestos, provided there is no water movement involved. These drums were in a relatively stable condition with minimal exposure to wet conditions.
Encapsulation was deemed to be the cost-effective and practical solution that would , for the foreseeable future, guarantee the long term integrity of the site, preventing any leakage of any low level toxic residues.
The decision was made to smother the area with shotcrete (a highly-durable, spray-able concrete) and then coat (encapsulate) the shotcrete with a weatherproof, non-toxic shield of Castagra Ecodur 201-50S to not only reinforce the concrete but create a sealed barrier against water movement. Water has a tremendous ability to transport toxic substances through ground and into highly vulnerable water tables.
The contractors built a caste-in-place concrete wall in front of the Shotcrete/Castagra wall and then back fill dirt between the two layers to make it look pretty. Out of sight/out of mind has never been more apparent.
The combination of shotcrete and Ecodur 201-50S provides a double shield of protection. The shotcrete is a very strong physical barrier to any potential compression loads, and the Ecodur, which retains a certain degree of flexibility throughout an extensive temperature ranges, providing an additional physical barrier as well as an insulating one to further protect the shotcrete below.
It is also completely non-toxic and does not emit any vapors as it was made without the use of solvents. Ecodur has a near 20-year antecedent history of protecting marine vessels in tough salt-laden environments without degradation. It is also highly resistant to acids and ultra violet radiation. In dry conditions, without physical abrasion, its longevity can be calculated in the order of decades.
The cost-effectiveness of the application is very high. On the environmental side of the equation, the solution has satisfied the regulatory requirements and eliminated the potential to create any further disposal issues revolving around the transportation of waste and its disposal.
The combination of shotcrete and Ecodur will see wider use in encapsulation scenarios as appreciation grows for inert, non-toxic protective solutions, that, when used together, radically extend re-mediation solutions into what are near permanent solutions for all practical purposes.