Information about the Triaxial Test

Triaxial testing aims to determine the deformation behaviour and shear strength of soil. It can be utilised for many different applications, but it mainly serves to learn about bank stability and for calculating deformations on sheet piles. For this test, a cylindrical soil sample is placed between a top plate and rigid bottom while confined with a rubber membrane. A vertical load is placed on the soil sample before horizontal pressure is applied on all sides by applying pressure to the water, which surrounds the sample.

Throughout the triaxial test, water pressure must be constantly maintained at a certain level. The sample should gradually compress until shearing occurs, and this can be achieved as you increase the vertical force at a constant velocity. The triaxial test should reveal two shear strength parameters: the angle of internal friction and the cohesion. A test may be used to learn the rigidity parameters of the sample, too.

A basic triaxial test is a laboratory testing technique for various soil types under undrained or drained conditions. Preparations for the specimen are dependent on the type of soil that needs to be tested. Cohesive soil samples are usually directly prepared from a saturated compacted sample, either remoulded or undisturbed. For cohesion less soil, the sample is prepared using a mould, which maintains its required shape.

There are three major kinds of triaxial tests that can be performed depending on the combination of drainage and loading conditions, and these are CD (consolidated – drained), UU (unconsolidated – undrained), and CU (consolidated – undrained). In consolidated tests, the triaxial test is initiated by applying the confining pressure in the pressure chamber to drain the sample. This first step of the test pertains to the sample’s consolidation. Deviatoric load is applied through a vertical axis, and deviatoric stress reveals the difference between vertical stress and confining stress.

Information about Concrete Resistivity Meter

Concrete resistivity meters measures surface resistivity, which is an extremely useful piece of data that helps determine the state of a concrete structure. Surface resistivity is directly linked to the rate of concrete corrosion as recent studies show a correlation between chloride diffusion rate and concrete resistivity.

A typical concrete resistivity meter features a 4-point Wenner probe used for measurement of values in a non-destructive test. Made out of robust materials, resistivity meters are designed to work even in the most demanding environments.

Resistivity is a key controlling factor once corrosion starts. It controls the rate of ion flow between cathodic and anodic sites on concrete reinforcements. Measuring concrete resistivity helps evaluate whether a structure where corrosion is present, is going to deteriorate quickly or if the likely corrosion rate is slow enough to be addressed in a conservative manner. Combined with half-cell potential measurements, concrete resistivity is a useful test when locating hot spots for the likelihood of corrosion.

A surface resistivity test is also a much quicker and a more convenient test for estimating the permeability of concrete. The traditional testing method, which is the lab-based rapid chloride penetration, is very laborious and time-consuming, requiring a total of 4 days of preparation and actual testing, whereas concrete resistivity meters can produce results in as little as 10 minutes from standard cured cylinder samples. This versatile method is highly useful in the following applications:

• Indication of corrosion rate
• Estimation of corrosion likelihood
• Correlation of chloride permeability
• Determination of zonal requirements, particularly for cathodic protection systems
• On site assessment of curing efficiency
• Indication of variations in cement to water ratios within concrete structures
• Identification of wet and dry areas in concrete structures
• Correlation to rock’s water permeability; and
• Indentification of areas susceptible to chloride penetration within structures.