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75 Alkaliâsilica reactivity (ASR): Some aggregates are siliceous, which is acidic, leading to potential reactions with concrete pore fluid, which is alkaline. The reactions produce a gel that expands in the presence of water, leading to concrete cracking. Bending wave method: Pile integrity test method that involves striking the surface of a foundation element and measuring the reflected bending wave at the surface. Can be used in some applications to identify foundation depth as well as limited structural integrity information. Condition assessment: Investigation of an existing foundation to evaluate its structural integrity. Corrosion: An electrochemical process wherein air, water, and negatively charged ions oxidize steel, resulting in its degradation. Corrosion of steel reinforcement is a primary concern regarding concrete durability. Cross-borehole tomography: Borehole geophysical method used to generate images of the sub surface between boreholes based on travel times of seismic waves traveling between the boreholes. Deck: Portion of the bridge that carries traffic. Deterioration: Loss of structural integrity over time. Electrical methods: Geophysical methods that identify materials based on variations in their electri cal properties. Examples include electrical resistivity (ER) and induced polarization (IP). Electrical resistivity (ER): See âelectrical methods.â Electrochemical chloride extraction: Method for prolonging service life of reinforced concrete by removing chloride ions from the concrete to halt or prevent corrosion of reinforcing steel. Foundation reuse: For the purposes of this Synthesis, foundation reuse refers to any agency action that changes the design load of the existing foundation. Examples of foundation reuse included in the Synthesis definition include bridge superstructure replacement, bridge widening, bridge repur posing, and retrofitting for seismic or other purposes. Reuse may include using the existing founda tion asÂis or it may include modifications such as the addition of piles or widening a footing. For the purposes of this Synthesis, bridge deck replacement is not considered foundation reuse. Other definitions of foundation reuse beyond the one used in this Synthesis are possible (e.g., Jalinoos et al. 2016). Freeze-thaw durability: FreezeÂthaw durability refers to concreteâs ability to withstand cycles of freezing and thawing without cracking or scaling. Cracking occurs when water in concrete pore space expands upon freezing. Geophysical methods: According to FHWAâs Application of Geophysical Methods to Highway Related Problems (Wightman et al. 2004), geophysics is âthe science of applying the principles of physics to investigation related to the structure and properties of the earth . . . essentially the mea surement of contrasts in the physical properties of materials beneath the surface of the earth and an attempt to deduce the nature and distribution of the materials responsible for these observations.â Ground penetrating radar (GPR): Electromagnetic geophysical method that detects dielectric contrasts to locate interfaces between geologic strata, the groundwater surface, or buried structures. GPR is limited to identifying shallow foundation dimensions, and the reliability of such measure ments may be low. Glossary
76 Induced polarization (IP): See âelectrical methods.â Parallel seismic: Borehole geophysical method involving striking an existing foundation and record ing seismic waves in an adjacent borehole. Results are generally more reliable than those from pile integrity and surfaceÂbased methods. Preventive maintenance: Planned strategy of costÂeffective treatments that preserves the system, retards future deterioration, and maintains or improves the functional condition (FHWA 2011). Primary details (with respect to an existing foundation): Basic information regarding an existing foundation system, including the type of foundation, foundation material, dimensions of the foundation elements, location of the foundation elements, and depth of foundation. Rehabilitation: Major work required to restore the structural integrity of a bridge (FHWA 2011). Replacement: Total replacement of a structurally deficient or functionally obsolete bridge with a new facility constructed in the same general traffic corridor. Scour: Erosion of earthen material surrounding bridge foundations as a result of the flow of water. Scour countermeasure: Methods of improving a bridgeâs resistance to scour including hydraulic measures (e.g., placement of riprap), structural measures (e.g., underpinning), biotechnical measures, and monitoring. Seismic surface methods: A series of geophysical methods performed using sensors and sources installed at the ground surface including reflection, refraction, surface waves, and tomography. Surface wave methods include spectral analysis of surface waves (SASW) and multiÂchannel analysis of surface wave (MASW). The methods generally involve interpreting features such as soil layer boundaries based on stiffness contrasts that impact seismic wave velocities. Sonic echo (SE)/impulse response (IR): Pile integrity test method that involves striking the surface of a foundation element and measuring the reflected compression wave at the surface. In some applications, this can identify foundation depth and limited structural integrity information. Substructure: Portion of the bridge that transfers superstructure loads to the ground though abutments or piers and ultimately foundation systems. Sulfate attack: Chemical reactions between cement paste and sulfate ions. The reactions produce chemicals that swell in the presence of water, potentially resulting in cracking. Superstructure: Portion of the bridge that supports the deck and connects substructure elements. Ultraseismic: Pile integrity test method that involves striking the surface of a foundation element and measuring the four reflected wave modes at the surface. This can be used in some applications to identify foundation depth as well as limited structural integrity information. The ultraseismic method is considered somewhat more reliable than bending wave or sonic echo (SE)/impulse response (IR) methods. Unknown foundation: NBI designation for bridges over waterways for which bridge plans are miss ing, resulting in significant risk of scour. FHWAâs Foundation Characterization Program expanded the term to consider all bridges, especially within the context of changes in service loads, geoÂhazards, and reuse of foundations.