Determining the condition of a concrete structure using...

Details Determining the condition of a concrete structure using... Determining the condition of a concrete structure using...

1999-12-08

2002-08-06

Gregory, Bernarr E. (Department: 3662)

Communications: directive radio wave systems and devices (e.g.,

Transmission through media other than air or free space

C342S027000, C342S175000, C342S195000

Reexamination Certificate

active

06429802

ABSTRACT:

FIELD OF INVENTION
This invention relates to determining the condition of an inhomogeneous structure. More particularly, this invention relates to a system and method for accurately locating deteriorated portions of a reinforced concrete structure such as, for example, a bridge deck, using electromagnetic signals.
BACKGROUND OF INVENTION
A bridge deck is the portion of a bridge upon which traffic travels. The life expectancy of a bridge deck (the period of time during which the structural integrity of the bridge deck is sufficient to safely support the traffic load for which it was intended) is typically one-half of the expected life span of the entire bridge. Consequently, during the life span of a typical bridge, its deck surface is replaced at least once.
Bridge decks are typically made of reinforced concrete. As referred to herein, concrete is a mixture of fine and coarse aggregates such as, for example, crushed stone or gravel, firmly bound into a monolithic mass by a cementing agent such as, for example, Portland cement. Reinforced concrete as referred to herein is concrete in which metal rods or bars, preferably made of steel, are incorporated into the concrete in such a manner as to reinforce or strengthen the more or less brittle nature of concrete. Such rods or bars carry the tension to which a concrete structure may be subjected, thus reinforcing the concrete, and are referred to herein as reinforcing bars or rebars. As used herein, a substantially concrete structure is a structure where the primary constituent is concrete. Such a substantially concrete structure may contain reinforcing bars to improve tensile strength, a waterproofing membrane to protect the structure from moisture, an asphalt layer or overlay, other added elements to improve durability or performance, and possible inadvertently added elements.
The short life expectancy of a typical bridge deck relative to the entire bridge structure is due in part to the intense loading cycles from vehicular traffic to which the bridge deck is subjected. Further, a bridge deck may be subjected to extreme climates such as, for example, snow, ice, and thermal freeze-thaw cycles. Further, such extreme climates, and human intervention to permit the flow of traffic on the bridge amidst these harsh conditions, may result in the ingress of road salt. These factors may lead to the eventual deterioration of portions of the bridge deck, making travel on the bridge unsafe. Thus, for safety reasons, the inspection and analysis of the condition of a bridge deck is a continual process, with inspections becoming increasingly important as the bridge deck grows older.
As used herein, deterioration refers to any physical change in a concrete or other comparable structure resulting in a loss of structural integrity of the concrete structure. Many forms of deterioration result from moisture present in the concrete, which may be caused by freeze-thaw cycles, intense loading cycles, the ingress of road salt, and severe weather, as discussed above. In a reinforced concrete bridge deck (or reinforced deck), such moisture may cause one or more rebars to corrode. Signs of deterioration visible from the exterior of a concrete bridge deck include concrete cracking, staining, disintegration, and delamination. Cracking may occur, for example, where the concrete becomes too dry and brittle. Staining may occur where the deterioration of a portion of concrete causes a discoloring of the portion of concrete. Disintegration may occur where the deterioration of a portion of the concrete results in the loss of structural integrity of the portion, either removing the portion of the concrete entirely from the concrete structure or reducing the portion to individual particles. Delamination is the peeling away of a layer of concrete from the remainder of a concrete structure such as, for example, when a layer of concrete pulls away from a layer of rebar.
As discussed above, concrete structures, including concrete bridge decks, typically are reinforced with rebars to provide tensile strength to the concrete structure. Although deterioration results from moisture, chemical activity and the corrosion of rebars, such deterioration may not lead to any externally visible signs of deterioration, and this potentially dangerous situation may go unnoticed.
One known method of determining the structural integrity of a concrete bridge deck is to visually inspect portions of the surface of the concrete structure to determine the presence of any externally visible signs of deterioration, such as those discussed above. The internal condition of the portion is then inferred from the visual inspection. Although visual inspection may detect some of the areas of deterioration present within a reinforced concrete bridge deck, visual inspection often does not detect internal deterioration such as, for example, the corrosion of rebars, that do not manifest themselves on the exterior of the bridge deck.
Other known methods such as, for example, the “chain drag” and “hammer sounding” technique involve listening to sounds reflected from portions of a bridge to determine the structural integrity the portion. Using the chain drag technique, a chain is dragged across sections of the surface of a bridge deck. For the hammer sounding technique, sound is generated by banging a hammer at different sections of the surface of the bridge deck. In either technique, by listening to the reflection of the resulting sound from the bridge deck and/or the transmission of sound through the deck, the presence of deterioration may be determined. Typically, the presence of deterioration is assumed detected if the sound is more “hollow” than that from a bridge deck in good condition. Both of these sound methods are prone to inaccuracy as it is difficult to determine from reflected sound a detailed, localized picture of the structural integrity of a concrete structure.
Yet another sound technique is the “impact echo” technique. For this technique, an acoustic source transmits acoustic waves into the bridge deck. The resulting reflected sound waves are collected by a receiver that is tightly coupled to the surface of the bridge. The technique is useful for locating delaminations and cracks in concrete. The impact echo technique is limited in usefulness due to the recording time per measurement (0.5 seconds or greater), its diminished capabilities when used on asphalt-overlaid concrete and because it cannot locate corroded rebars.
Many concrete bridge decks are covered with a layer of material such as, for example asphalt. When a layer of asphalt is present, the hammer sounding, chain dragging, and visual inspection techniques are ineffective. The asphalt absorbs the sound waves or interferes with the resolution of the sound waves, and visual insection is ineffective because the surface of the bridge deck can not be seen through the layer of asphalt. Consequently, to use one of these techniques at all, the layer of asphalt must be peeled away, which adds more cost and time to the bridge inspection process and makes it inherently destructive.
The above-described techniques may be referred to as non-invasive techniques because they do not require invading or penetrating the concrete structure to determine its structural integrity. An alternative to these non-invasive techniques would be to actually penetrate the concrete structure at various points to determine the structural integrity of the concrete structure at those points. Such invasive techniques, however, are time consuming, costly, and damaging to the structural integrity of the bridge deck.
Thus, the need exists for a reliable, fast, cost-effective and non-invasive technique to locate deteriorated areas of concrete structures, particularly reinforced concrete bridge decks covered with asphalt.
SUMMARY OF THE INVENTION
Ground penetrating radar (GPR) is a technique that may be used to image the inside of a structure by collecting the echoes (or reflections) resulting from electromagnetic signals such as, for example, electromagnetic waves of typic

Affiliated with

Also associated with

Rating

Determining the condition of a concrete structure using... does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Determining the condition of a concrete structure using..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Determining the condition of a concrete structure using... will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2951405