SIXTEEN PROPERTIES OF Eucalyptus tereticornis WOOD FOR STRUCTURAL USES DEZESSEIS PROPRIEDADES DA MADEIRA DE Eucalyptus tereticornis PARA USOS ESTRUTURAIS

Forest Red Gum eucalypt provides a versatile wood and is converted into different purposes. However, such wood is somewhat limited in structural ends, which highlights the need to exploit this gap through diffusion of mechanical properties of such timber. This study aimed to evaluate the effect of moisture content reduction, from 30 to 12%, in physical and mechanical properties of Eucalyptus tereticornis, using Brazilian and American documents, to reinforce the structural potential wood and assisting engineers and architects in decision-making for its best building application. We evaluated two physical and fourteen mechanical properties of Eucalyptus tereticornis at two different moisture contents, following the prescriptions of Brazilian (ABNT NBR 7190: 1997) and North American (ASTM D-143-14: 2014) standards. Thus, 1091 repeats were carried out for all properties. By a moisture reduction, the bulk density and eleven strength properties statistically showed changes such as modulus of rupture (static bending, parallel and perpendicular compressions), modulus of elasticity (perpendicular compression and static bending), shear stress, tangential cleavage, and parallel and perpendicular hardnesses. Then, the Eucalyptus tereticornis timber could be better usable if is further applied for structural construction uses.

Hard and heavy, Eucalyptus tereticornis timber has dark red colored heartwood (WALLIS, 1970;FAO/UN, 1981) with moderately fine texture and interlocked grain (Figure 1b). Its sapwood is pale, yellowish, and susceptible to attack by Lyctus (BOLAND et al., 2006), whose heat modification reduces such borer attacks (POONIA; TRIPATHI, 2016). This timber is durable and has been used for poles, sills, paving blocks, flooring, and bearings in windmills (WALLIS, 1970). Also, tereticornis wood is weather-resistant and could present 25-year soil-exposure durability as suggested by the Australian Standard (AS 5604:2005). Due to extensive studies for pulp and paper and the lack of timber characterization for structural purposes, this study aimed to evaluate the effect of moisture content reduction, from 30 to 12%, in sixteen physical and mechanical properties, using Brazilian and American documents, to reinforce the structural potential of Eucalyptus tereticornis wood.

MATERIAL AND METHODS
Thirteen Eucalyptus tereticornis trees were harvested in five cities at São Paulo state, Brazil, whose timber was obtained from log conversion into sawn wood (beams). Table 1 indicated this information as well as the age of each harvested tree and its respective diameter at breast height.
Two physical properties were the bulk and volumetric mass densities, which were tested using the standard prescriptions from the Brazilian ABNT NBR 7190:1997 document. By means of American ASTM D-143-14:2014 and Brazilian ABNT NBR 7190:1997 documents, the following mechanical properties were studied at 30% moisture condition: modulus of rupture in static bending, parallel and perpendicular compressions to grain, parallel and perpendicular tensiles to grain; modulus of elasticity in static bending, perpendicular and parallel compressions to grain, parallel tensile to grain; and, shear stress, tangential cleavage, tangential toughness, parallel and perpendicular hardnesses. Eucalyptus tereticornis wood samples were produced and standardized in shape and dimensions with respect to prescriptions from these respective standard documents, and submitted in a predrying stage to regularize their moisture content in a stable green point at 30%. Half of samples were dried at 12%. All samples were tested in both moisture contents (30 and 12%), together with a universal testing machine. This research inquired the influence of these two moisture contents for two physical and fourteen mechanical properties, comparing their progresses by means of testing of Eucalyptus tereticornis wood, such as were followed by Lahr et al. (2017) and Nogueira et al. (2018a,b,c). In total, 1091 repeats were performed.
Due to the consideration of sampling independence, randomization of sampling process, and the normality admission, the t-test was utilized to verify statistical differences among results at both moisture conditions of 30 and 12%, similarly to those analyses from Lahr et al. (2017) and Nogueira et al. (2018a,b,c). For this, statistical hypotheses of interest were established, where in the first condition (H0: µ1 = µ2) there is no statistical differences, and in the second one (H1: µ1 ≠ µ2) these means do differ. This test considered distinct and unknown variances, and the decision was based on the P-value associated to a significance level of 5%. Lastly, the hypothesis of average equality is rejected if the P-value associated is less than 5%.

RESULTS
This research was based on physical and mechanical properties evaluation of Eucalyptus tereticornis species because of lack of information about this timber characterization for construction. In short, this gap has not been filled, because recent studies only have evaluated its timber properties essentially for decay resistance, weather resistance, and/or natural durability such as revealed Carvalho et al. (2016), Delucis et al. (2016a;2016b), Lazarotto et al. (2016). Then, this present research is necessary for better utilization of this species in timber industry.
Tables 2, 3, 4 and 5 respectively refer to results for properties of densities, modulus of rupture, modulus of elasticity and other mechanical properties for Eucalyptus tereticornis wood species. Information described in each table involves moisture content (MC), number of repeats (n), and standard deviation (sd). The average of each studied property was described as MD for densities, MR for modulus of rupture, ME for modulus of elasticity, and MO for other properties.
In the analyzed condition of moisture reduction from 30% to the standard point at 12% (ABNT NBR 7190: 1997), bulk density notably decreased 18.92% (0.21 g/cm 3 ), as well as volumetric mass density was 0.70 g/cm 3 , being stable as expected for this property (Table 2).

DISCUSSION
Through this observed moisture content reduction from 30% to 12%, only bulk density has decreased its value, and volumetric mass density remained stable such as was fully expected for this test (Table 2).
In analysis of these results by t-test, we observed that, for bulk density, there was a rejection of the null hypothesis of mean equality (Table 2), i.e., moisture content indicated a significant difference in the averages when moisture content of the Eucalyptus tereticornis was reduced from 30 to 12% (P-value<0.05).
In relation to mechanical testing, all five modulus of rupture properties rejected the null hypothesis of mean equality (Table 3) by t-test, i.e., moisture content had significant difference in these averages when the moisture content was reduced from 30 to 12% (P-value<0.05). For modulus of elasticity, parallel tensile and compression did not reject the null hypotheses of mean equality (Table  4), considering that static bending and perpendicular compression tests had visible average differences with moisture reduction (P-value<0.05). However, shear stress, tangential cleavage, perpendicular and parallel hardnesses properties rejected the null hypothesis of mean equality (Table 5), i.e., the moisture content indicated a significant difference in the averages when the moisture content is reduced (P-value<0.05). Only tangential toughness did not reject the null hypothesis, which revealed the nonsignificant average difference from cited reduction. NOGUEIRA, M. C. J. A. et al. Comparing these results to ones found to Eucalyptus umbra (NOGUEIRA et al., 2018a), Eucalyptus camaldulensis (NOGUEIRA et al., 2018b), Eucalyptus maidenii (NOGUEIRA et al., 2018c), and Eucalyptus urophylla (LAHR et al., 2017), the Eucalyptus tereticornis timber is efficient from the structural point of view (Tables 3 to 5), being interesting for heavy and light buildings and rural uses due to result similarities. In addition, this study reinforced that tereticornis species could be useful in these purposes, testifying Gutiérrez (1976) and Boland et al. (2006) similar affirmations from their eucalypt "encyclopedic studies", despite their non-specification of any numerical value for Eucalyptus tereticornis mechanical properties.

CONCLUSIONS
Bulk density presented a visible decrease with the moisture content reduction from 30 to 12%, while volumetric mass density remained obviously stable in accordance to the expected; All mechanical properties increased significantly their values when the moisture content was reduced. However, statistically, eleven strength properties showed changes in this analysis: modulus of rupture in static bending, and parallel and perpendicular compressions, modulus of elasticity in perpendicular compression and in static bending, shear stress, tangential cleavage, parallel and perpendicular hardnesses.
Most of mechanical properties showed significant increases with the moisture reduction and, similarly to other studied eucalypt wood species, Eucalyptus tereticornis could also be better usable if is further applied for structural solid elements and parts for construction.