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2016SpringShotcreteEMag

The Need for Shotcrete Provisions for State DOTs Many State Departments of Transportation (DOTs) have tried shotcrete in the past and had a negative experience. That negative experience has led them to dismiss shotcrete as a viable repair method for highway applications. I’ve read multiple state shotcrete specifications. Unfortunately, the majority of them are outdated and don’t contain language that prevents improper shotcrete techniques or materials. There have been many advances in the shotcrete industry over the past years, and many state specifications simply haven’t kept up with those changes. These specifications clearly need to be updated to keep up with the times. By Dennis Bittner Shotcrete repairs, like all repairs, should be accompanied by a strong state provision. If a company is hired to repair a bridge deck using a rapid-set material, each state has a provision (a method of repair that must be followed). Generally, these provisions tell the contractor exactly how to perform that work. Layout of the repair, demolition, reinforcement guidelines, material requirements, and finishing techniques are included in the provision. Frequently, shotcrete provisions give much less direction to the contractor—sometimes providing no direction as to the placement of the material. Let’s discuss common objections and misconceptions about the shotcrete process held by many DOTs. I’ll also cover the importance of key items to include in a state provision, and how they can help guarantee a successful project. One objection to shotcrete is a concern over quality of work. There are several elements to a well-written provision that help ensure the level of proficiency of the applicator. First, ACI Certified Nozzlemen should be required. This certification must be understood. It guarantees the nozzleman meets a basic level of shotcrete proficiency and experience. Beyond the certification requirement, language requiring an experience level possessed by the nozzleman, supervisor, crew, and the contractor commensurate to the project are advisable. Prequalification test panels should be shot and tested. The material and equipment to be used on the job should be used to produce those panels. Also, the panels should be in the same orientation as the work to be performed— vertical and overhead as applicable. All of these points should be included in a provision. Another common objection to shotcrete is the belief that shotcrete is not structural. Oftentimes, shotcrete is referred to as a mortar. Obviously, there is a misconception about the strength of the material. Shotcrete is not a product; it is a process— a method of placing concrete. The material used in the shotcrete process is by definition and composition concrete. Shotcrete commonly reaches 28-day strengths between 6000 and 10,000 psi (41 and 69 MPa). These strengths are in excess of commonly used concretes on highway structures, which typically don’t exceed 4000 psi (28 MPa). Shotcrete is the industry standard in the (a) (b) Fig. 1(a) and (b): Two large, round bridge piers being repaired and returned to their original contour using shotcrete 18 Shotcrete • Spring 2016


2016SpringShotcreteEMag
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