PSI - Issue 17

Ana Isabel Marques et al. / Procedia Structural Integrity 17 (2019) 1002–1009 Ana Isabel Marques / Structural Integrity Procedia 00 (2019) 000–000

1003

2

1. Introduction

Wall coating mortars should have the ability to deform, without failure, when subjected to external loading actions (Veiga, 2000; Veiga et al., 2019). When the mortar cannot cope with these deformations, internal stresses arise in the coating, which can lead to cracking. Coating mortar cracking is one of the most frequent and damaging anomalies in building facades that compromises their intended purposes. To minimize this issue, knowledge of the coating mortar’s modulus of elasticity ( E ) is essential during the design process of building facades, in order to achieve proper compatibility between the mortar and the substrate in terms of material deformability. Although the importance of E in the characterization of mortars is well known, scientific publications on the subject are still scarce regarding which is the best evaluation method to determine it. The lack of consensus regarding which method is more appropriate to use makes for inconsistent mortar characterization results. There are two major approaches to experimentally determine the E for mortars: static experimental methodologies and dynamic experimental methodologies (Tamin, 1986). The results obtained from static methodologies are significantly different and more reliable than those obtained with dynamic methodologies (Mehta and Monteiro, 2001), but since there is no consensus on a consistent and viable static test methodology for mortars, civil engineers are led to use dynamic E methodologies (Farinha et al., 2015; Damas et al., 2018). As part of a larger study, this paper briefly describes an improved experimental methodology to determine the static E for coating mortars. Specimens made from four cement based compositions were tested. The proposed experimental methodology is based on standard cyclic compression tests for concrete specimens, complemented with several specific improvements that result in an experimental method designed to test coating mortars. In order to validate this methodology, the obtained results are compared with two, well-established, dynamic experimental methodologies: the Resonance Frequency methodology and the Direct Ultrasonic methodology. The goal was to develop an experimental methodology to determine static E to be applied in coating mortar related studies. This paper also includes a preliminary study on ratios between static and dynamic E values for cement compositions. The experimental campaign consisted on several tests with four cement based mortar compositions. These four mortar compositions vary in binder-aggregate ratio and aggregate type, as presented in Table 1. Table 1. Description of the cement mortar compositions used in the experimental campaign. Mortar Composition Binder-aggregate ratio Type of aggregate Ci_1:2 1:2 Well graded siliceous river sand Ci_1:3 1:3 Well graded siliceous river sand Ci_1:4R 1:4 Well graded siliceous river sand Ci_1:4A 1:4 Pit siliceous-clayish sand Workability and bulk density determination tests of the fresh mortar were carried out for all compositions according to the standard EN 1015-3 (2006), as presented in Table 2. 2. Experimental campaign 2.1. Mortar compositions

Table 2. Fresh mortar properties. Mortar Composition

Consistency [mm]

Water/powder ratio [%]

Bulk density of the fresh mortar [kg/m 3 ]

Ci_1:2 Ci_1:3

13.6 16.2 17.9 18.1

2030 1980 2050 2070

160 159 163 164

Ci_1:4R Ci_1:4A