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2016FallShotcreteEMag

Fact: Concrete usually has a significant amount of unhydrated cement that will hydrate over time. Continuing exposure to moisture and ongoing hydration increases strength, reduces permeability, and thus improves long-term durability. Concrete over 100 years old will still be strengthening. The contractor was wrong in stating concrete loses strength. Also, 2500 psi (17 MPa) is a very low compressive strength and indicates the use of improper materials, equipment, or poor nozzling techniques. ASA maintains that all shotcrete should have a minimum compressive strength of 4000 psi (28 MPa) at 28 days. Inquiry: I am a structural engineer and we have recently begun work with a shoring contractor. We have been designing soil nails, micropiles, soldier piles, and so on with temporary and permanent shotcrete facings. The contractor has requested that some of our future designs use chain link mesh in lieu of welded wire mesh, particularly in temporary situations with walls under 10 ft (3 m). I understand that chain link is a cost-effective alternative and, according to the contractor, handles the shotcrete great. Is it acceptable reinforcing for shotcrete? Misconception: Chain link fencing material is adequate for reinforcing shotcrete in underground applications. Fact: Some mines have used chain link mesh in shotcrete in severely deforming ground and claim that it is better in holding the ground than mesh after large deformations, in which the shotcrete sustains major cracking with deformations. Other than for such unusual applications, we do not recommend the use of chain link mesh in shotcrete. It cannot be fixed “tight” and as such is susceptible to vibration and movement during shooting, resulting in shotcrete sloughing and formation of voids in the shotcrete. Also, the mesh interconnections are conducive to the formation of voids during shooting. Additionally, there doesn’t appear to be any consistent material standards on the strength, flexibility, or brittleness of the steel (or other materials) used in the fencing material, so a designer has no way to establish the tensile or flexural strength of the concrete sections. In brief, don’t use chain link mesh if you want to produce quality, durable shotcrete. Inquiry: I’ve heard that dry-mix shotcrete is not acceptable for exposure to freezing-and- Over 30 years of experience, nationwide service.... American Concrete Restorations, Inc. Amerconcrete@aol.com www.americanconcreterestorations.com Phone: 630-887-0670 Fax: 630-887-0440 Restoring America using the Shotcrete Solution Interstate 80 - Joliet, IL 14 Shotcrete • Fall 2016


2016FallShotcreteEMag
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