# Effect of Metallic Waste Addition on the Physical and Mechanical Properties of Cement-Based Mortars
## 3 Results and Discussion
### Influence of Metallic Waste on the Elastic Modulus of the Test Specimens  
Figure 9 shows the average results of the static elastic modulus obtained from compressive tests (\(E_{c}\)) and the dynamic elastic modulus obtained from ultrasonic tests (\(E_{u}\)) of specimens with different amounts of fibres and shavings. From this Figure, it can be observed that: (i) the compressive elastic modulus proportionally increased with the increase of the amount of metallic waste added to the mortar, while (ii) the dynamic elastic modulus obtained from ultrasonic tests proportionally decreased with the increase of metallic waste. Additionally, comparing average values of the modulus obtained with the two different methods in Figure 9, it can be observed that the modulus measured by ultrasounds was higher than that measured by standard mechanical tests. This increase of magnitude in the modulus results can be associated with an increase in the test frequency, but it may also be due to the different testing methods [36]. Theoretically, the static compressive test considers the whole mechanical behaviour of materials, i.e., a stress-strain curve with a non-linear component. Nevertheless, the non-destructive  
Figure 8: Normal probability-probability plots for the maximum force values registered under the (**a**) flexural and (**b**) compressive tests. Figure 9: Average results of the elastic modulus obtained from compressive and ultrasonic tests of cement-mortar specimens reinforced with (**a**) steel shavings; and (**b**) steel wool fibres. method using ultrasonic tests evaluates the mechanical behaviour of materials just in the linear zone of the stress-strain curve, since it is a short time and high frequency test [32]. Furthermore, Figure 9 shows that regardless of the type of metallic waste and the curing time, the elastic modulus obtained by ultrasonic tests decreased with the increase of the amount of metallic waste added to the mortar specimens, reaching values in the order of magnitude of elastic modulus obtained from compressive tests. This can be due to the influence of metallic waste on the physical properties of the studied mortars. In order to prove that hypothesis, Figure 10 presents the average results of bulk density and porosity of all the evaluated specimens. It can be observed that when the amount of metallic waste added to the mortar matrix increased, bulk density of the specimens decreased, consequently increasing their porosity, see Figure 10a,b, respectively. In this study, the obtained result was independent of the waste type and the curing age. Thus, specimens with higher contents of metallic waste (higher porosity) presented higher ultrasonic pulse times and consequently lower values of the dynamic modulus, see Figure 9.  
Additionally, although previous works [32] proved that both elastic modulus types are physically related, we were not able to determine the static elastic modulus from the compressive test (\(E_{c}\)), knowing the dynamic elastic modulus from ultrasonic tests (\(E_{u}\)). With the aim of demonstrating this, Figure 11 shows the relationship between the elastic modulus obtained from compressive and ultrasonic tests, measured on the same test specimen for all the specimens tested. Figure 11: Relationship between the dimensionless compressive and ultrasonic elastic modulus. Figure 10: Average results of (**a**) bulk density and (**b**) porosity of the cement-mortar specimens with different waste content and curing times (s: shavings; f: steel wool fibres). To facilitate their comparison, the moduli in Figure 11 have been normalised (0-1) dividing each value of modulus by the maximum value of each data series. By analysing Figure 11, it can be proven that there is no relationship between static and dynamic elastic modulus obtained from the mortar specimens reinforced with metallic fibres and shavings.