Non-destructive Tests for PCC Pavements
Written on Friday, January 17, 2014 by Jose Sanchez Marquez
The following information was the result of a Project conducted at Concordia University, Montreál, Canada called.
Use of Non-destructive Tests for Quality Assurance in Portland Cement Concretes (PCC) Pavements.
by,Matin Nabavi, Reza Mahsoudi and Jose Sanchez Marquez,submitted for the Master Course Pavement Design CIVI 6451 (Fall 2013). In addition this project was presented in the 1st Annual MSC-CTRF Transportation Conference at Concordia University.
In this post you are going to find the use of two Non-destructive test (NDT’s) Electrical Resistivity and GWT test to determine durability characteristics of new PCC pavement located in the city of Montreal, Canada.
(Note: the all project is not presented here, only some parts of it. However the final conclusion and references are fully shared).
Introduction
Portland cement concrete (PCC) pavement is commonly used because of its capability to support compression and tension stresses, making it the first alternative in scenarios where high traffic and heavy loads are predominant.
A durable concrete is not only one that can resist a number of axle loads for a period of time, but it must also have a series of properties for the particular environment in which it is exposed during its service life (Taylor et al., 2013). Concrete durability is generally defined as ability to resist weathering action, chemical attack, abrasion, or any process of concrete deterioration.
In order to achieve durability the concrete must have good quality material, an effective construction control, and consolidation, finishing and curing must guarantee a durable concrete in order to avoid early deterioration and excessive maintenance efforts.
The Non-destructive tests (NDT) durability tests such as Water Absorption and Electrical Resistivity (Wenner probe) can determine the moisture content and permeability of the PCC pavement at an early stage.
Besides, NDT also determines the layer thickness quality assurance in PCC pavements. This method has lower time and cost compared to traditional methods like coring extraction (Maser et al., 2005). The objective of this study is to identify whether NDT tests can be useful for contractors in general or in specific areas. This is done by proving that this approach is a less time consuming and less expensive alternative for monitoring quality assurance control in the different PCC pavements.
In order to establish the pavement layer thickness, Ground Penetrating Radar (GPR) is by far the most established technology (other than coring) for measuring pavement thickness or Mechanical wave techniques, such as impact-echo (IE), that seems to work more effectively in concrete (Maser et al., 2005). The electrical resistance of a hardened concrete can be measured by the by the Wenner - four electrode probe (electrical resistance). This test can be correlated with permeability (Shahroodi et al., 2010).
Field Test Results
The reason why the place was chosen at Westmount QC H3Z 2A6 was because during the end of summer 2013 (September) a PCC pavement was placement in this intersection.
Greene Avenue and Boulevard de Maisonneuve, Intersection 1299 Greene Ave Westmount QC H3Z 2A6
The testing date was the 11th October 2013 during the morning, for the two tests, Water Absorption and Wenner four probe were conducted and the weather air and pavements conditions were measured at that date:
Air Temperature: 14 °C
Air Humidity: 72 %
Pavement Temperature: 18.7 °C
Pavement Humidity: 82.3%
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The figure bellow shows the intersection location and the street distance between the place and Concordia University.
1. Wenner Four Probe Test
In order to conduct the test was necessary to saturate with tap water for some minutes the concrete surface where the device is going to be place. For the field test a total time of 1 hour saturation was applied into the surface.
According to the following figure develop at Concordia University from a Master thesis research in progress called “Evaluation of Saturation Techniques for In-situ Surface Electrical Resistivity Measurements” by Dr. Michelle Nokken and Jose Sanchez Marquez. A significant decrease in the resistivity value up to 6 hours is observed but then it became stable (same value). At the end, an average difference of -9.5 % is observed between the first measurement (1 hour) and the last one measurement done at 72 hours.
A total of 24 measurements were done on each slab, 8 measurement at different slab zones (1MS, 2MS and 3MS) in order to obtain a final resistivity value. Figure bellow shows the three locations in where the device was located over the slabs.
The final Average Resistivity Value obtain for the two slabs, 13.6 and 13.4 KΩ-cm. Which means that, the resistivity value and the degree of permeability of the concrete placed at the intersection street and tested for this research work is the one expected in this kind of cement. Moreover, it also means that, for the two slabs tested the placement and curing procedure were good enough, due to the values obtained are similar to the ones obtained at laboratory conditions (ideal conditions).
2. Water Absorption – GWT Test
The Water absorption test was conducted the same day of the Wenner Probe test, the 11th October 2013. The following weather information was measured that day;
Slab No. 01 Temperature: 18.7 °C
Slab No. 02 Temperature: 19.1 °C
Pavement Humidity: 82.3%
Once in the field, over the slab the pressure chamber containing a watertight gasket was secured tightly to the surface by two anchored clamping pliers or by means of a suction plate.
Then the chamber was filled with water and the valves closed. The top lid of the chamber was turned until a desired water pressure is achieved. The pressure selected is maintained by means of a micrometer gauge pressing a piston into the chamber (20 MN), substituting the water penetrating into the material. The travel of the piston over time was used for characterizing the permeation of the surface tested.
According to previous researches it was possible to estimate that a high pressure (permeability) and low pressure (absorption) tests could be done for duration of up to 30 minutes. Based on this results it was concluded that test duration of 20 minutes can provide sufficient number of data points in order to calculate related indices (Basheer et al., 1995). The following table shows the pressure range against test time for the two slabs.
As a result the PCC pavement tested showed a good capability to absorb water.
Observations
One of the main factors that are in the service life of new and existing pavement concretes is durability performance and durability is a function of permeability.
In this Paper Term study different types of existing permeability tests were used to evaluate the the durability of the Greene Avenue and Boulevard de Maisonneuve - Intersection, 1299 Greene Ave concret PCC pavement.
The scope of the research included the characterization of fluid transport with two different tests, Wenner Four probe test and water absorption test. Two concrete slabs were tested in this research.
The result of the Electrical Resistivity test indicates that the final resistivity value for Slab No. 01 and Slab No. 2 are 13.4 and 13.6 respectively. If we want to compare these values with 28-Day Surface Resistivity (According to table 1), it shows that the permeability of the mentioned concrete is in the range of moderate permeability class. In addition, for the water absorption according to the results obtained from the test, sorptivity index is around 2.3 for the slab and the humidity and water ratio are 83% and 0.45 respectively, so according to figure 14, Concrete is ranked as a good condition in terms of capability.
Although for this research work we contacted some companies from Montreal and from province of Ontario it was not possible to find and use a GPR or IE device in order to evaluate the thickness at the same place where the other two test were done (intersection Avenue), due to the highly cost of the equipment and also due to their complexity, is necessary to have some hours training before testing in the field. However, we really believed that the use of electrical wave as method to measure pavement thickness is going to be the more efficient, less time and man-hour consuming way to establish thickness.
Conclusions
Conclusions
The results presented in this term paper show the effectiveness of these two methods for determining the permeability and the capability to absorb water. Both identify that, the moderate permeability and good capability to absorb water are the result of a high cement factor, well graded and a low w/c of 0.45. Moreover, a good revibration of the concrete during the placement stage also probably helped to reduce the permeability and eventually when the intersection avenue has to be exposed to deicing salts is going to perform an excellent behave.
Regarding to Non- Destructive Test (NDT) is possible to conclude that, these tests are performed in a manner that does not affect the future usefulness of the object or material. In other words, NDT allows parts and material to be inspected and measured without damaging them. Additionally, NDT provides an excellent balance between quality control and cost-effectiveness. Generally speaking, NDT applies to industrial inspections.
Comparing traditional approaches like core extraction that is a Destructive test and requires more time and resources (money) in comparison with NDT tests.
One disadvantage that we found is that special weather conditions are required in order to do the Water Absorption and Wenner four Probe tests, the temperature should not be below 5°C, what it means that during the winter season is not recommended use these test on outside concrete expose to this weather conditions.
References
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Basheer, M., Goncalves, A. F., Torrent, R. (2006). Chapter 4. Non-destructive methods to measure water transport. Non-Destructive Evaluation of the Penetrability and Thickness of the Concrete Cover RILEM TC 189-NEC: State-of-the-Art Report.
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Morris, W.; Moreno E.I.; and Sagues, A.A., (1996) “Practical Evaluation of Resistivity of Concrete in Test Cylinders using a Wenner Array Probe,” Cement and Concrete Research, Vol.26, p.1779-1787.
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Proceq test concrete Manual. Available on internet: http://www.proceq.com/fileadmin/documents/proceq/products/Concrete/Resipod/English/resipod_SF_E_2013.06.19_low.pdf
Shahroodi, Ahmad. (2010) “Development of Test Methods for Assessment of Concrete Durability for Use in Performance-Based Specifications” M.A.Sc., Thesis submitted to University of Toronto.
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Testing of Pavements and Back calculation of Moduli, 3, 1999 (American Society for Testing and Materials: West Conshohocken, PA)
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Posted in
concrete or asphalt,
Non-destructive test,
PCC pavements,
Quality Assurance
