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- Hydric behavior of earth materials and the effects of their stabilization with cement or lime: Study on repair mortars for historical rammed earth structuresPublication . Gomes, Maria; Diaz Gonçalves, Teresa; Faria, PaulinaEarthen building materials bear interesting environmental advantages and are the most appropriate to conserve historical earth constructions. To improve mechanical properties, these materials are often stabilized with cement or lime, but the impact of the stabilizers on the water transport properties, which are also critical, has been very rarely evaluated. The researchers have tested four earth-based repair mortars applied on three distinct and representative rammed earth surfaces. Three mortars are based on earth collected from rammed earth buildings in south of Portugal and the fourth mortar is based on a commercial clayish earth. The main objective of the work was over the commercial earth mortar, applied stabilized and not stabilized on the three rammed earth surfaces to repair, to assess the influence of the stabilizers. The other three earth mortars (not stabilized) were applied on each type of rammed earth, representing the repair only made with local materials. The four unstabilized earth materials depicted nonlinear dependence on t1/2 during capillary suction. This behavior was probably caused by clay swelling. Stabilization with any of the four tested binders enabled the linear dependence of t1/2 expected from Washburn's equation, probably because the swelling did not take place in this case. However, the stabilizers also significantly increased the capillary suction and the capillary porosity of the materials. This means that, in addition to increasing the carbon footprint, stabilizers, like cement and lime, have functional disadvantages that discourage their use in repair mortars for raw earth construction.
- Earth-based mortars for repair and protection of rammed earth walls. Stabilization with mineral binders and fibersPublication . Gomes, Maria; Faria, Paulina; Diaz Gonçalves, TeresaThe use of earth as a building material offers many advantages in terms of sustainability: it is a natural material, most probably non-toxic and ecological, with low energy intensity, low carbon emissions and recyclable. Earth-based mortars are re-gaining its place as building materials for plastering, rendering and repair of earthen walls, not only in the sustainable context but also in terms of efficiency. However, the scientific knowledge about these mortars is still scarce. In particular, the opinions regarding the effects of adding fibers or mineral binders as stabilizers, to improve the performance of the mortar, are contradictory. The study presented in this article is intended to advance the knowledge about the effects of adding low amounts of hemp fibers, hydrated air lime, hydraulic lime, natural cement and Portland cement on the mechanical (flexural and compressive strength, dynamic modulus of elasticity), physical (shrinkage, thermal conductivity, porosity) and hydric (water absorption under low pressure, capillary water absorption, drying) characteristics of mortars formulated with different earth materials. Results show that the addition of the fibers decreases the thermal conductivity of the mortars, which is remarkably good for the mortars made from clayey soil, and slowers the drying of the mortars. They also show that adding the mineral binders will negatively affect the hydric behaviour of the mortars: the water absorption coefficient increases and the drying become slower as the percentage of binder increases. In addition, the use of these binders has no significant effect on the flexural and compressive strength of the mortar.
- Rammed earth walls repair by earth-based mortars: The adequacy to assess effectivenessPublication . Gomes, Maria; Faria, Paulina; Diaz Gonçalves, TeresaRepairs in rammed earth walls are often necessary mainly because of degradation occurring during the life time of a building with continuous environmental exposure. The defects that arise in the walls are generally associated with loss of its thickness, on the surface or in greater depth. They must be repaired with a mortar technically efficient and compatible with the rammed earth, to ensure protection and, as possible, long-term durability. The present study describes and discusses the adequacy of earth-based mortars to repair unstabilized rammed earth walls and the behaviour of the systems rammed walls-earth repair mortars when subjected to accelerated aging tests by wetting-drying cycles. Even under aggressive capillarity tests, the results observed corroborate that unstabilized earth repair mortars behave better in comparison to similar mortars with additions of low amounts of different inorganic binders.