A spall within a concrete surface is defined as “a fragment, usually in the shape of a flake, detached from a larger mass by a blow, by the action of weather, by pressure, or by expansion within the larger mass; a small spall involves a roughly circular depression not greater than 20 mm in depth and 150 mm in any dimension; a large spall, may be roughly circular or oval or in some cases elongated, is more than 20 mm in depth and 150 mm in greatest dimension.” Spalling or spalled concrete is frequently encountered when coating or lining a concrete substrate. Before any lining or coating can be applied it is very important to properly clean, prepare and repair the concrete.
Prior to beginning repairs, the concrete must be evaluated to determine the level of repair required. First, a detailed visual inspection should be completed of the cleaned concrete substrate. In addition, it should be determined if there is any physical damage, chemical damage or attack, contamination, concrete defects, curing issues and moisture concerns. The structural integrity of the concrete should also be considered and any needed reinforcing steel repair should be completed.
Once the preliminary work has been done and you’re ready to repair and resurface the concrete, as with all proper coating applications, selecting the correct means and degree of surface preparation is key. One must take into account the relevant industry consensus surface preparation standards and the contents of the material manufacturer’s product data sheet to determine the correct level of cleanliness and the needed profile. For typical concrete applications, you’ll need to reference both SSPC-SP13/NACE 6 Surface Preparation of Concrete and ICRI 310.2R Selecting and Specifying Concrete Surface Preparation for Sealers, Coatings, Polymer Overlays and Concrete Repair. The SSPC/NACE document outlines the required degree of cleanliness, while the ICRI document governs the level of profile and provides acceptable means and methods to achieve a range of results. ICRI CSP (Concrete Surface Profile) coupons also provide a much needed visual representation of the required surface profile that compliments the standard’s technical instructions and definitions.
Product selection is also critical to the success of your repairs. There are many factors to consider when selecting your repair material, including project specific service conditions and exposures, required thicknesses, curing schedules, and its ability to accept subsequently applied coating and lining materials. Each repair product exhibits unique benefits and limitations, so it is important to understand the differences and which materials are applicable to which types of projects.
Tnemec’s Series 217 MortarCrete is a time tested cementitious repair mortar with superior performance properties that has been used widely for decades in a myriad of exposures. Series 217 is a calcium sulfoaluminate (CSA) cement, a generic chemistry which typically lends itself to higher early compressive strengths, and often achieves near target 28-day strength in as little as 24 hours. Rapid setting and high early strength gain is critical in situations where a repaired structure must be returned to service in a very short amount of time.
High early strength gain is also a contributing factor to CSA cement’s low-shrinkage or non-shrink capabilities.This is largely due to the fact that while CSA cement requires a greater water to cement ratio in its mix designs than traditional Portland cement, the CSA exhausts the bulk of the water in the hydration process, thereby significantly reducing the amount of bleed water that must escape during curing.
CSA cements are also more environmentally friendly than Portland cements. CSA clinker is softer than Portland clinker, consuming less energy at the mill to grind and significantly lower kiln temperatures. Portland cement typically requires kiln temperatures of 1500°C (2700°F), whereas CSA cements require only 1250°C (2250°F).
CSA’s, including Tnemec Series 217 MortarCrete cure very quickly, gain high early strength, can be used to build a wide range of application thicknesses (1/4 inch to 4 inches) in a single lift, are substantially more chemical resistant then other types cementitious repair mortars, and allow for coating and lining applications much sooner (12 hours at 75 degrees).
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