Simple Method of Dynamic Young’s Modulus Determination in Lime and Cement Mortars

This study demonstrates the feasibility of using a simple method to measure the resonant fundamental frequency for determining the MOE (dynamic Young’s modulus) of lime and cement mortars. The procedure follows the instructions stated in the UNE-EN ISO 12680-1 standard for refractory products although in this study the instructions are applied to standardized RILEM 4x4x16 cm test samples made of lime and cement mortars. The simplicity of the procedure as well as its correlation to other measured variables, suggest that it can be widely applied in studies about the evolution of the physical characteristics in lime mortars, such as mechanical strength, static Young’s modulus, carbonation depth, etc. 1.-Introduction With respect to the mortars used for restoration, it is especially important to know its modulus of elasticity. Usually some of the cement mortars overstiffen the building causing changes in its structural performance. Since those restoration mortars are formulated from air limes (with or without puzzolana) and hydraulic limes, it is interesting to know the procedure of the carbonating process, the mechanical resistance gain, the stiffness, etc. One of the basic parameters in the resistance of the materials and therefore in the area of the buildings materials is the Young’s modulus, which indicates the deformation capability of a given material in its linear elastic span depending on the strain to which is subjected. The common method used in laboratory settings is the static testing by which mechanical properties of mortar lime are determined. Bearing in mind the assumption of homogeneity of the investigated media, elastic properties are characterized by a constant-static modulus that determines the relation between the stress and the strain applied. Another group of techniques involves the application of non-destructive acoustic waves that have been successfully used in other materials such as wood, natural stones and refractory products. The method enabling the determination of the dynamic modulus is relatively simple, inexpensive and suitable also for field application. This non-destructive testing minimizes the possibility of rupture of the material or test specimens which represents a saving on the one hand and on the other provides new results for testing in the estimation of the material parameters. For some of the specific materials, such as natural stone [1] and refractory products [2], the application of analysis methods of its fundamental natural frequency or resonant frequency in order to determine its MOE (dynamic Young’s modulus) has been standardized although this standardization has not been made in the case of the mortars. 2.-Objective The aim of our work is to obtain some preliminary results for evaluating the possibility of applying the non-destructive test based on the resonant frequency analysis of mortars samples RILEM 4x4x16 made from very simple and economic elements. With the aim to refine the determination of the mortars modulus of elasticity, some standards could be determined by the investigation. Some of the tests we can use to calculate the relative reliability of those standards are: MOE (dynamic elasticity modulus of elasticity) determination test by impulse excitation of vibration and the subsequent analysis of the resonant basic frequency. MOE determination test from the velocity at which ultrasonic impulses propagates through the sample. Static flexural test to obtain the linear spam of the stretch-deformation graph. Flexural and compressive fracture test. 3.-Mortars to test Since the main objective of this work is to study the validation and reliability of the non-destructive testing methods, the mention of this point will be brief and only to illustrate results more clearly. The natural frequency analysis test will be applied on standard specimens according to RILEM 4x4x16 cm. The mortars are of 8 different types depending on the conglomerates and sand dosage, but the study is centred on two types of conglomerates (hydraulic lime NHL-3,5 and air lime CL-90 and Portland cement CEM I-42,5) and two types of aggregate granulometric curves of calcareous origin (Table 1).