Effect of salts and absorption cycles in the capillary coefficient of building materials with different joints

Abstract

in buildings, may be explained by the capillary water migration from the the soil through the porous network of the materials in the building elements. In old buildings, mostly constucted in mansory, the effects of rising damp assume a greater expression, due to the porous materials tipically used such as ceramic bricks, mortars and stones [1], [2].The presence of dissolved salts in the water, which up rises through the porous network of building elements, constitutes an annoying factor for its degradation [8], [9]. The salts follow the water during its rise in liquid phase, however the same doesn't occur when the water evaporates. The salts remain in the pores of the building materials, eventually crystallizing after the solution has reached its super-saturation state. The salt crystallization can occur on the surface of the materials, developing efflorescence that disturb the aesthetical appearance of the building, or inside the porous network, dealing great pressures in the pore walls that can fragment them when exceeds its mechanical resistance [10], [11]. The hygrothermal variations of the surronding environment may promote cycles of crystallization/dissolution and develop breaking tensions in the pores for each cycle.The elements and components in the constructive systems, specially the masonry, hinge their functional efficiency on the combination of different materials and characteristics, which adds to the complexity of the moisture transfer analysis. This heterogeneity require knowledge about the individual characteristics of the materials as well as the continuity conditions of the interface that separates the different materials, bidding the crucial importance of the study of the joints influence in the transport phenomenon [12], [13], [14].This paper intends to report the experimental work carried out with brick specimens, aiming to evaluate the effect of salt solutions in the capillary absorption of monolithic and multilayer brick specimens in comparison with water. Sodium sulphate and potassium chloride were the chosen salts to perform the experiments. The first is one of the salts that impose more degradation to buildings, the second was chosen for being very commonly found in building materials, especially the ion chloride. Materials and methodsThe test specimens used were nine red brick monolithic samples with the dimensions 5 × 5 × 10 cm 3 (three for each Rising damp can reduce building's aesthetical value, comfort and health mark, when combined with the existence of soluble salts in the building components and in the ground water can even lead to material decomposition and compromise its structural performance. This research work intended to study the effect of different absorption cycles of two saturated solutions of sodium sulphate and potassium chloride in the capillary absorption curves obtained through the partial immersion of red brick samples without and with different joints. The results revealed significant differences in the capillary coefficients obtained when samples were tested wit...

A critique on characterising interface resistances with maximum moisture flows

“…In February 2018, this journal published the article "Interface influence on moisture transport in buildings" [1], wherein an enquiry into the impact of material interfaces on moisture absorption in building materials is documented. This article continues previous research of this group on this topic [2][3][4][5][6], which was originally initiated with the seminal paper of de Freitas et al in 1996. In all of these studies, the interface impacts are characterised with maximum moisture flows over the interface, contrary to the much more widely employed characterisation with interface resistances though [7][8][9][10][11][12][13][14]. The investigation in [1] targets three types of material interfaces: 'air space' (two brick samples separated by an air space), 'perfect contact' (two brick samples in direct contact) and 'hydraulic contact' (bonded brick-mortar samples).…”

“…Other publications on the theme of material interfaces [7][8][9][10][11][12][13][14] have consistently opted to describe their impact with an interface resistance, the flow through which hence is controlled by the difference in capillary pressure over that interface. The critiqued publication [1], as well as its related articles [2][3][4][5][6], chooses for another approach, by characterising the interface impact via the more direct post-interface flow. This is a peculiar decision, since this strongly restricts the generalisa- Initially, one can best understand this by thinking about the thermal analogon.…”

“…and 'air layer' configurations only, where often large interface resistances can be expected. The approach was though abstractly expanded to 'hydraulic contact' configurations in [4,5] and really applied for 'hydraulic contact' configurations in [1,6], without verifying however whether the premise of location-independent and time-constant post-interface flows still applies for their typically smaller interface resistances. The flow values in Table 1 actually disclose that the location-independent assumption has been abandoned, as distinct values are reported for interfaces at different heights.…”

“…Using such declining post-interface flow as indicator for the genuine presence of an interface resistance is hence Postprint: Janssen H. 2020. A critique on characterising interface resistances with maximum moisture flows, Construction and Building Materials, 243:118301. doi: 10.1016/j.conbuildmat.2020.118301 7 not as dependable as assumed in [1][2][3][4][5][6]. The graphs on the left in Figure 4 portray the impact of a dominant interface resistance: the post-interface flow is significantly reduced, it is relatively lo- The impact of a far less important interface resistance is illustrated with the graphs on the right in Figure 4: the postinterface flow is still strongly reduced -which should be largely attributed to the lower sorptivity of the top material though -but it is highly dependent on the interface location and it substantially decreases over time.…”

A Critique on “Measurement of the Hygric Resistance of Concrete Blocks with Perfect Contact Interface: Influence of the Contact Area”

“…He can only note that the roughly similar values presented in the article's Table 4 together with their mentioned coefficients of variation of "approximately 15%" instil a notion of acceptable homogeneity, contradicted, however, by the widespread found in Fig. (4). 4).…”