A Retrospective view of EMM-ARM: Application to quality control in soil-improvement and complementary developments

Abstract

The EMM-ARM (Elasticity Modulus Measurement through Ambient Response Method) is a technique that allows the continuous measurement of the E-modulus of a given material under test, since the instant in which it is cast into the testing mould. The technique has been initially developed in 2008-2009 and it is particularly useful to monitor the hardening process of cement-based materials or any similar materials that can be cast into a mould and endure significant stiffness changes since early ages. EMM-ARM is based on the identification of the resonant frequency of the testing mould, which evolves along time due to the hardening process of the tested material, and then the E-modulus of the tested material can be inferred with basis on the dynamic equations of motion of the testing system. Even though the method has been originally devised to test concrete, it has quickly been extended to other materials such as mortar, cement paste, stabilised soils and even epoxy resins. In the particular case of stabilised soils, the method has been successfully applied to both cement-based stabilization and lime-based stabilization. This paper intends to provide a wide perspective of the several evolutions that EMM-ARM has endured throughout its applications to stabilised soils, namely in regard to: (i) mould geometry and material; (ii) sampling procedures for in-situ application; (iii) excitation and modal identification techniques; (iv) systematic application to several mix formulations and comparative evaluation of hardening kinetics. Indeed, one of the foremost applications of EMM-ARM in the context of soil stabilization is the capability to provide real-time data about the stiffness of the material, allowing the users to take early decisions in regard to the expectable stiffness that a recently improved soil will predictably attain. This readily available information can have strong economic impacts in the case of rejection of a given stabilised layer.