What is concrete “bruising,” how is it evaluated, and how can it be minimized?
Bruising refers to damage in a surface layer of remaining substrate concrete that is weakened by fine interconnected
cracks caused by the use of high-impact, mechanical methods for concrete removal and surface preparation. The bruised (or fractured) layer left by such surface preparation methods typically extends to a depth of 1/8 to 3/8 in. (3 to 10 mm) or more below the remaining substrate surface and, if not removed, generally results in lower repair bond strengths. Bruising, which can be detected through pulloff testing and petrographic examination, can be effectively minimized by selecting the most appropriate method and equipment for the given application.
How important is the modulus of elasticity as a property of surface repair materials?
Modulus of elasticity is an important physical property of surface repair materials. For structural repairs, the modulus of elasticity of the repair materials should be similar to that of the substrate concrete, whereas in the case of nonstructural repairs, a lower modulus of elasticity may be beneficial.
When a structural evaluation to determine capacity is to be performed, knowledge of member sizes, reinforcing details, and material properties is required. In cases where this information is not readily available through drawing document records, it needs to be obtained through in-place measurements and sampling.
Rehabilitation projects often involve the need to increase the load-carrying capacity of members within existing concrete structures that are deficient due to increased load demand associated with change of use, deficiencies in the original design or construction, or deterioration. Such strengthening often includes increasing shear capacity.
What is the proper procedure for determining the in-place density of fresh roller-compacted concrete (RCC) according to ASTM C1040/C1040M, “Standard Test Methods for In-Place Density of Unhardened and Hardened Concrete, Including Roller Compacted Concrete, By Nuclear Methods?”
This guide describes techniques for imparting aesthetic finishes to concrete flatwork, of which many can be combined for unique effects. The owner and architect/engineer will acquire detailed, practical guidance for achieving aesthetic effects using proven techniques. Recommendations are made for the production of cast-in-place decorative concrete flatwork, decorative stains, and overlays. In addition to attention to the specified materials, mixture designs, concrete placement, curing, protection, sealing, and other treatments, this guide also considers the effects of these treatments on the overall aesthetics of the project.
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