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How to Evaluate & Repair Concrete Structures


Quiz Questions

1.A visual inspection of the exposed concrete is the first step in an on-site examination of a structure. The purpose of such an examination is to locate and define areas of distress or deterioration.
It is important that the conditions observed be described in unambiguous terms that can later be understood by others who have not inspected the concrete. Terms typically used during a visual inspection are listed by category in Table 2-1.
True
False
2. Typical construction faults that may be found during a visual inspection include bug holes, evidence of cold joints, exposed reinforcing steel, honeycombing, irregular surfaces caused by improperly aligned forms, and a wide variety of surface blemishes and irregularities. These faults are typically the result of poor workmanship or the failure to follow accepted good practice.
True
False
3. Cracks that occur in concrete may be described in a variety of ways. Some of the more common ways are in terms of surface appearance, depth of cracking, width of cracking, current state of activity, physical state of concrete when cracking occurred, and structural nature of the crack.
True
False
4.Figure 2-3 shows and example of:
Cold joint
Pattern cracking
5.Figure 2-5 shows cracking caused by restrained volume changes.
True
False
6.The cracking figure 2-6 has been caused by:
Alkali-slice reaction
Transportation overload
7.The disintegration of concrete in figure 2-12 has been caused by:
Exposure to aggressive water.
Alkali reaction
8.Figures 2-16, and 2-17 shows:
Light and medium Scaling
Sulfate attack
9.Figures 2-22 and 2-23 show deterioration and loss of joint sealant.
True
False
10.Corrosion of reinforcing steel may open cracks that allow moisture greater access to the interior of the concrete.
True
False
11. The following list could be the causes of Distress and Deterioration of Concrete

Accidental Loadings
Chemical Reactions
Acid attack
Aggressive-water attack
Alkali-carbonate rock reaction
Alkali-silica reaction
Miscellaneous chemical attack
Sulfate attack
Construction Errors
Corrosion of Embedded Metals
Design Errors
Inadequate structural design
Poor design details
Erosion
Abrasion
Cavitations
Freezing and Thawing
Settlement and Movement
Shrinkage
Plastic
Drying
Temperature Changes
Internally generated
Externally generated
Fire
Weathering

True
False
12. Accidental loading such as the impact of a barge against a lock wall or an earthquake can generate stresses higher than the strength of the concrete, resulting in localized or general failure.
True
False
13.Accidental loadings by their very nature cannot be prevented. Minimizing the effects of some occurrences by following proper design procedures (an example is the design for earthquakes) or by proper attention to detailing (wall armor in areas of likely impact) will reduce the impacts of accidental loadings.
True
False
14.Diamond-blade cutting. Diamond-blade cutting (Figure 5-3) is applicable for making cutouts through slabs, walls, and other concrete members where access to only one face is feasible and depth of cut is 600 mm (24 in.) or less. Blade selection is a function of the type (hardness) and percent of coarse aggregate and on the percent of steel reinforcing. The harder the coarse aggregate and the higher the percentage of steel reinforcement in the cut, the slower and more costly the cutting. Diamond-blade cutting is also applicable for making cuts along removal boundaries to reduce feathered edges in support of other methods.
True
False
15.Diamond-wire cutting (Figure 5-4) is applicable for making cutouts through concrete where the depth of cut is greater than can be economically cut with a diamond-blade saw. Cuts can be made through mass concrete and in areas of difficult access. The cutting wire is a continuous loop of multistrand wire cable strung with steel beads containing either embedded or electroplated diamonds. Beads with embedded diamonds last longer but are more expensive than beads with electroplated diamonds (single layer).
True
False
16.Stitch cutting. Method applicable for making cutouts through concrete members where access to only one face is feasible and depth of cut is greater than can be economically cut by diamond-blade saw. Depth of cuts is dependent on the accuracy of drilling equipment in maintaining overlap between holes with depth and on the diameter of boreholes drilled.
True
False
17. One of the most important steps in the repair or rehabilitation of a concrete structure is the preparation of the surface to be repaired. The repair will only be as good as the surface preparation, regardless of the nature or sophistication (expense) of the repair material. For reinforced concrete, repairs must include proper preparation of the reinforcing steel to develop bond with the replacement concrete to ensure desired behavior in the structure.
True
False
18.High-strength concrete is defined as concrete with a 28-day design compressive strength over 41 MPa (6,000 psi) (ACI 116R). This method is similar to an extension of the conventional concrete placement method described in Section 6-4. Chemical admixtures such as water-reducing admixtures (WRA’s) and HRWRA’s are usually required to achieve lower w/c and subsequently higher compressive strengths. Mineral admixtures are also frequently used. The special procedures and materials involved with producing high strength concrete with silica fume are discussed in paragraph 6-30.
True
False
19.Polymers commonly used to repair cracks or joints by injection may be generally categorized as either rigid or flexible systems. Epoxies are the most common rigid systems used for structural repair or "welding" of cracks to form a monolithic structure. Flexible polyurethane systems are most often used for stopping water flow and sealing active cracks. Cracks as narrow as 0.05 mm (0.002 in.) can be bonded
True
False
20.In the design of lock wall repairs, the depth of frost penetration in the area should be considered, particularly in repair of old nonair-entrained concrete. It appears that if the thickness of any repair section is less than the depth of frost penetration, freezethaw deterioration of the existing nonair-entrained concrete should be expected. This deterioration can drastically affect the performance of repair sections without adequate anchoring systems.
True
False
21.Nearly every concrete structure has joints that must be sealed to ensure its integrity and serviceability. This is particularly true for monolith joints in hydraulic structures such as concrete dams and navigation locks. Embedded waterstops are used to prevent water passage through the monolith joints of such structures. Traditionally, waterstops have been subdivided into two classes: rigid and flexible. Most rigid waterstops are metallic: steel, copper, and occasionally lead. A variety of materials are suitable for use as flexible waterstops; however, polyvinyl chloride (PVC) is probably the most widely used
True
False