Technical Manual: Conduits through Embankment Dams (FEMA 484)

Conduits through Embankment DamsSulfate attack (ACI, 2000): Either a chemical reaction, physical reaction, or bothbetween sulfates usually in soil or ground water and concrete or mortar; the chemicalreaction is primarily with calcium aluminate hydrates in the cement-paste matrix,often causing deterioration.Surface air voids (ACI, 2000): Small regular or irregular cavities, usually notexceeding about 0.5 inch in diameter, resulting from entrapment of air bubbles in thesurface of formed concrete during placement and consolidation. Commonlyreferred to as bugholes.Surface hardness: The surface hardness of concrete can be measured to provide arelative indication of the strength of in-situ concrete. Surface hardness can bemeasured by rebound hammer (also called Schmidt Hammer or Swiss Hammer,ASTM C 805) or by the penetration resistance test (also called Windsor Probe,ASTM C 803). Surface hardness is affected by the condition of the surface,composition of concrete, type of coarse aggregate, and degree of carbonation of theconcrete surface. To improve accuracy of the inferred strength, the test methodsmust be calibrated with laboratory strength tests performed on samples of theconcrete.Tailings: The fine-grained waste materials from an ore-processing operation.Tailings dam: See Dam, tailings.Tailwater (ASCE, 2000): The elevation of the free water surface (if any) on thedownstream side of an embankment dam.Terminal structure: A structure located at the downstream end of the conduit.Terminal structures often include gates or valves and may include some type ofstructure to dissipate the energy of rapidly flowing water and to protect the riverbedfrom erosionTether: A cable that attaches two things together.Thermocouple (ACI, 2000): Two conductors of different metals joined together atboth ends, producing a loop in which an electric current will flow when there is adifference in temperature between two junctions.Thermoplastic (ASTM F 412, 2001): A plastic that can be repeatedly softened byheating and hardened by cooling through a temperature range characteristic of theplastic, and that in the softened state can be shaped by flow into articles by moldingor extrusion.418