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Fig. 4: Improper sealing at pipe-shotcrete transition, leaving unsealed Fig. 5: Hydration issue areas. Applying a sealant to the entire dig out area that is not compatible due to variation in plaster with cementitious materials thickness at dig outs The following considerations, as to the type of the surface of a monolithic shotcrete structure; material and method of installation, are suggested however, these will be sealed shut with the appli- for sealing or plugging penetrations: cation of the cementitious interior finish coating. 1. The use of non-shrinking or low-shrinkage Structural movement cracks may not. Continued cementitious plugging material; movement of the structure can reopen existing 2. Non-sanded cementitious materials should be cracks or create new cracks. used only as a thin slurry coating within the dig out, as per manufacturer’s recommendations, and should not be used as a method of filling the entire dig out; Jonathan E. Dongell is Dir- 3. The inclusion of a polymeric fortifier, proven ector of Research & Develop- stable underwater, with the cementitious plugging ment, Pebble Technologies, material, as per manufacturer’s recommendations; Scottsdale, AZ. Dongell has 4. The use of sealants that are not compatible with worked in concrete construc- cementitious materials should be confined to tion and with cementitious sealing only the immediate area at the interface materials spanning over 30 of the penetration and the shotcrete and should years. His roles have included not be used to seal or coat the interior of the Technician, Superintendent, Manager, Contractor, dig out, piping, or other fixtures; and President. He is Past President, Whitestone 5. The removal of any loose material or debris Cement Company, Scottsdale, AZ (1998-2005), and thorough washing around penetrations to and Universal White Cement Co, Inc., Glendale, ensure a good adhesion bond or “keying” of AZ (1992-1998). He is a member and past Chair the interior finish coating with the shotcrete; of ACI Committee 524, Plastering, and is a 6. Plugging or filling dig outs flush with the member of ACI Committees 201, Durability of overall shotcrete surface, as opposed to using Concrete; 225, Hydraulic Cements; 232, Fly Ash finish coating material while plastering, may in Concrete; 308, Curing Concrete; 350, Envi- help to prevent differential hydration dis- ronmental Engineering Concrete Structures; and coloration caused by the interior finish 555, Concrete with Recycled Materials. Dongell coating’s increased thickness at dig outs; and also currently serves on the Concrete Research 7. Plugging material should be allowed to thor- Council (CRC). He is a member of several ASA oughly dry or cure, as per the manufacturer’s Committees, including the ASA Pool & Recre- recommendations, prior to applying the in - ational Shotcrete Committee. He is a member of terior finish coating. several ASTM International committees and subcommittees. Dongell is the author of several Sealing of Other Cracks books, including The Durability of Cementitious The use of a good shotcrete mixture design and Materials in a Water Contact Environment. He is limiting of the water-cement ratio can reduce the an inventor and holds three patents on cementi- amount and size of shrinkage cracks that develop tious materials. He is a designated expert witness in shotcrete. Proper engineering, shotcrete mate- in the fields of cement, concrete, stucco/plaster, rials, and trade practices should ensure that the and water chemistry. He was the recipient of hardened structure will have no structural cracks. the ACI Delmar L. Bloem Distinguished Service Plastic and autogenous cracks may be visible on Award in 2007. Shotcrete • Summer 2015 11


2015SummerShotcreteEMag
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