Deformation Inspection for a Precast Concrete Bridge

Purpose of Test

In order to prevent accidents from falling concrete, a soundness assessment was conducted at an overpass. The superstructure of this bridge is composed of 15 precast T-shape girders. In this case study, CTS-02v4 was used to detect delamination of the girders and slabs.

Figure 1: Measurement Target

Figure 2: Measurement Lines

Measurement Procedure

All girders and slabs were tested during this assessment as shown in the Figure 1. 12 measurement lines were set for each girder and two measurement lines were set for each slab as shown in Figure 2. Measurement points were arranged at a constant pitch (100mm) for each line.

Results of the Test

As the result of the assessment by CTS-02v4, it was confirmed that the grinders had no defects. However, delaminated areas were detected in some area of the slabs between G3 - G4 and G4 – G5 as shown in Figure 3 and Figure 4. Based on the result of this assessment, these defected slabs were repaired with minimal costs as inspection narrowed down the area needing repair.

*Red areas with square show where measurement was not conducted due to obstructions.

Figure 3: Measurement result of slab (BP side)

Figure 4: Measurement result of slab (EP side)

Advantage of CTS-02v4

The hammer sounding test is the most common method for testing delaminated concrete. However, test results of the hammer sounding test are subjective and depend on judgement of an inspector. CTS02-v4 was used in this case since it provides objective and impartial test results and is not dependent on the inspector's skill or experience.

Nitto CTS Vol 2

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Compressive Strength Test on Bridge Slab

Purpose of Test

Many of the more than 171,000 bridges in Japan were constructed over 50 years ago. Bridges, especially those located in an area with heavy snowfall, are exposed to tough condition. In this case study, Concrete Tester (CTS-02v4) was used to assess compressive strength of a bridge slab in Hokkaido, where they have the coldest winters and heaviest snowfall in Japan, with 6 months out of the year hovering around freezing and an average snowfall around 9-10 inches.

Measurement Scene

Measurement Procedure

Some parts of the bridge slab were in danger of collapsing due to frost damage. Measurement points were arranged at constant intervals (200mm x 100mm) to assess current compressive strength distribution of the slab. An inspector strikes 3 times at each point with CTS-02v4, and the average value was used to evaluate the compressive strength at each point.

Figure 1: Measurement Result

Results of the Test

Measurement results are shown as Figure 1. Red lines in the figure shows cracks on the slab. Compressive strength tends to be lower where cracks are clustered together. Although apparent critical damage was not observed, partial repair was conducted to maintain the durability of the slab.

Advantage of CTS-02v4

There are several types of NDT equipment for compressive strength estimation such as the rebound hammer, impact elastic wave method, or ultrasonic wave method. CTS-02v4 was selected for this case because it is easy to use and systematically and efficiently measures compressive strength and deterioration compared to other NDT equipment.

Nitto CTS Vol 1

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A Study on Estimating Concrete Compressive Strength by Mechanical Impedance

We are happy to announce that an article on our study on concrete testers is now available at ForConstructionPros.com, an established resource for construction industries.

“A Study on Estimating Concrete Compressive Strength by Mechanical Impedance” is an in-depth analysis of the theoretical background of reactive mechanical impedance measurement and results of laboratory and field tests on compressive strength estimation of concrete.

Click the link below for the whole article.

https://www.forconstructionpros.com/concrete/equipment-products/concrete-hand-tools/article/21232440/nitto-construction-co-ltd-the-accuracy-of-concrete-compressive-strength-tests-by-the-mechanical-impedance-method