A comprehensive analysis of the genetic diversity and environmental adaptability in worldwide Merino and Merino-derived sheep breeds

BACKGROUND: To enhance and extend the knowledge about the global historical and phylogenetic relationships between Merino and Merino-derived breeds, 19 populations were genotyped with the OvineSNP50 BeadChip specifically for this study, while an additional 23 populations from the publicly available genotypes were retrieved. Three complementary statistical tests, Rsb (extended haplotype homozygosity between-populations), XP-EHH (cross-population extended haplotype homozygosity), and runs of homozygosity (ROH) islands were applied to identify genomic variants with potential impact on the adaptability of Merino genetic type in two contrasting climate zones. RESULTS: The results indicate that a large part of the Merino's genetic relatedness and admixture patterns are explained by their genetic background and/or geographic origin, followed by local admixture. Multi-dimensional scaling, Neighbor-Net, Admixture, and TREEMIX analyses consistently provided evidence of the role of Australian, Rambouillet and German strains in the extensive gene introgression into the other Merino and Merino-derived breeds. The close relationship between Iberian Merinos and other South-western European breeds is consistent with the Iberian origin of the Merino genetic type, with traces from previous contributions of other Mediterranean stocks. Using Rsb and XP-EHH approaches, signatures of selection were detected spanning four genomic regions located on Ovis aries chromosomes (OAR) 1, 6 and 16, whereas two genomic regions on OAR6, that partially overlapped with the previous ones, were highlighted by ROH islands. Overall, the three approaches identified 106 candidate genes putatively under selection. Among them, genes related to immune response were identified via the gene interaction network. In addition, several candidate genes were found, such as LEKR1, LCORL, GHR, RBPJ, BMPR1B, PPARGC1A, and PRKAA1, related to morphological, growth and reproductive traits, adaptive thermogenesis, and hypoxia responses. CONCLUSIONS: To the best of our knowledge, this is the first comprehensive dataset that includes most of the Merino and Merino-derived sheep breeds raised in different regions of the world. The results provide an in-depth picture of the genetic makeup of the current Merino and Merino-derived breeds, highlighting the possible selection pressures associated with the combined effect of anthropic and environmental factors. The study underlines the importance of Merino genetic types as invaluable resources of possible adaptive diversity in the context of the occurring climate changes

Laboratory mechanical characterisation of cold recycled mixtures produced with different RAP sources

Cold Recycled Mixtures (CRM) are composed of high amounts of Reclaimed Asphalt Pavement (RAP) together with bitumen emulsion. As additional binder, some ordinary cement is normally employed. Since RAP aggregates represents almost the entire solid structure, it is important to fully characterise Cement-Bitumen Treated Materials (CBTM) produced with different RAP materials. This work focuses the characterisation at small strain level, investigating the stiffness modulus at three testing temperatures; at the failure point, measuring the Indirect Tensile Strength; and studying the fracture behaviour, in Semi-Circular Bending Test configuration. From the results, it is possible to confirm the influence of different RAP materials, also characterised by different aggregates Nominal Maximum Size. As a consequence, a reliable RAP classification can allow a better prediction of the final CBTM mechanical properties

Influence of low production temperatures on compactability and mechanical properties of cold recycled mixtures

In cold regions, the production of Cement-Bitumen Treated Materials (CBTM) represents an issue in terms of annual time available for production. The objective of this research is to study the influence of different combinations of production temperatures for mixing, compacting and curing (developed in two steps) on the mechanical properties of CBTM produced with two sources of bitumen emulsion. Workability, compactability, indirect strength and other additional tests were involved in the analysis. Findings highlighted the critical effect of transportation and compaction temperatures on CBTM workability. Moreover, the emulsion source significantly affects the mixture strength when produced at low temperatures

Visco-Elasto-Plastic Characterization in the Small Strain Domain of Cement Bitumen-Treated Materials Produced at Low Temperatures

In the framework of recycling techniques employed in maintenance and rehabilitation projects for the road industry, cement bitumen-treated materials (CBTMs) provide good performance as well as economic and environmental benefits. Because these materials are produced with bitumen emulsion at atmospheric temperature, the environmental factors during production are extremely important to guarantee the quality of the final product. This paper focuses on the stiffness of CBTMs produced and conditioned at low temperatures, and cured in two different conditions (sealed and unsealed). The mixtures were evaluated in terms of rheological properties using complex modulus (E*) tests performed 1 year after production. Results were modeled with an adapted version of the Di Benedetto-Neifar (DBN) model for plastic dissipation for small cycles (PDSC), accordingly called DBNPDSC. Results showed that the curing conditions, as well as the low production temperatures, significantly changed the rheological properties of the material. In fact, mixing or compacting the mixtures at 5°C compared with 25°C resulted in a loss in stiffness of around 30% in the small strain domain. This model is a good tool to describe, in the small strain domain, such material behavior, which shows plastic nonviscous phenomena

Visco-Elasto-Plastic Characterization in the Small Strain Domain of Cement Bitumen-Treated Materials Produced at Low Temperatures

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Use of fine aggregate matrix to analyze the rheological behavior of cold recycled materials

Nowadays, one of the main challenges to a wider application of cold recycling techniques is the lack of reliable information on the mechanical behavior of cold recycled materials (CRM). In this context, measurement and modelling of the complex modulus of CRM mixtures may give an important contribution to the design and analysis of pavements including cold recycled layers. In this study, we analyzed the rheological behavior of CRM mixtures produced using bitumen emulsion and cement through the study of their fine aggregate matrix (FAM). Starting from a fixed CRM mixture composition, we compared different FAM mortars, focusing on the effect of water and air content. Then, we selected a composition as representative of the FAM in the mixture and investigated the evolution of both materials during a fixed curing period. Next, we measured the complex modulus of the CRM mixture and FAM at two curing stages and applied a rheological model to simulate and compare their behavior. Results showed that the properties of CRM mixtures are comparable to those of FAM mortars produced using all the binding agents (bitumen emulsion and cement) and a fraction of the voids contained in the mixture. Despite the huge difference in volumetric compositions, the FAM mortar controlled the curing and the thermo-rheological behavior of the CRM mixture, while the coarse reclaimed asphalt aggregate fraction and the voids mainly affected the asymptotic properties (equilibrium and glassy moduli) and the non-viscous dissipation component

Thermo-rheological modelling of cement-bitumen treated materials in the small strain domain

Cold recycled materials (CRM) have been introduced as structural materials in road pavement structures thanks to their significant economical and environmental benefits. Among them, cement-bitumen treated materials (CBTM) are often employed because of both contributions given by bitumen (in form of emulsion) and cement. The first confers a bituminous behaviour, whereas the second ensures good short-term performance otherwise penalized by the presence of water. Water plays a fundamental role in providing workability of the mixture at the atmospheric production temperatures. Due to such peculiarities, CBTM mixtures require attention when rheological modelling is performed in the small strain domain. This paper provides an overview on the most common rheological model applied to bituminous mixtures (2S2P1D) and the main issues related to the application to CBTM mixtures are highlighted. Afterwards, another model is proposed from the literature, the DBN model, and applied to three mixtures. The mixtures were prepared to assess the effect of the bitumen emulsion used, as well as the type of curing conditions. Results showed that the DBN model seems to be an excellent tool for not only CBTM rheological modelling in the small strain domain and it is recommended for applications in wider experimental programs

Effect of RAP Source on Compactability and Behavior of Cold-Recycled Mixtures in the Small Strain Domain

Cold recycled materials (CRMs) are products of modern recycling techniques that are used in maintenance and rehabilitation of pavement structures with significant economical and environmental benefits. CRM mixes are produced at ambient temperature using bitumen emulsion or foamed bitumen as a binding agent, and the aggregate phase is composed mainly of reclaimed asphalt pavement (RAP). This paper investigated the compactability of two RAP sources and their effects on the behavior of CRM mixtures tested in the small strain domain. The compactability was studied using experimental results and the compressible packing model (CPM). Complex modulus tests of CRM mixtures were conducted, and the results were modeled using the Di Benedetto-Neifar (DBN) model. Findings showed that in CRM mixtures with the same gradation and formulation, one RAP source required almost half of the compaction energy of the other source to reach the design air voids content. The rheological analysis results highlighted the impact of the RAP source on the behavior of the CRM mixes in the small strain domain

A new approach to determine absorption water of reclaimed asphalt pavement aggregate (RAP) for the production of cold recycled mixtures (CRM)

Absorption ability of aggregates is one of the most important material characteristics in the perspective of a bituminous mixture mix design. In particular, this aspect gains more importance in the framework of cold recycled mixtures (CRM). Since such materials are produced at ambient temperature, the workability is ensured by the employment of bitumen emulsion and water. As a consequence, the water absorption of the aggregate phase needs to be clearly stated, in order to know the amount of effective water which will affect workability and mechanical properties of the mixtures. The determination of absorption water is clearly described in international standards (ASTM and European Standard). Nevertheless, both practices leave some aspects unclear, leading to misleading results if applied to the same material. In this paper, a new approach to determine the water absorption of reclaimed asphalt pavement (RAP) used to produce CRM is proposed. Results showed that both standards used in this work gave different absorption water values, making difficult to assess which one is reliable. The new approach highlighted the possibility to evaluate in a more precise and scientific way the absorption water of RAP aggregate, studying the volumetric changes at different water content under compaction

Effect of gradation on volumetric and mechanical properties of cold recycled mixtures (CRM)

In recent times, recycling using cold bituminous mixtures has become one of the most interesting techniques in pavement engineering from sustainability aspect. This study focuses on the clarification of the steps concerned with the cold mixture mix design to determine the initial aggregate gradation of the mixture. The study has been developed involving procedures followed in Canada and Italy. In both the cases, three different gradations, normally employed in the production of traditional bituminous mixtures, were compared. The effect conferred by the gradation type has been studied in terms of workability, compactability and mechanical properties. Results show that in both the procedures the gradation influenced the workability and the compaction behaviour of the mixtures studied. At the same time, in terms of mechanical properties, the gradation influenced the strength of the final mixture in only one of the procedures applied