Gypsum efflorescence on clay brick masonry: Field survey and literature study

Abstract

h i g h l i g h t s 28 Belgian cases of persistent masonry efflorescence were investigated. Gypsum is the major persistent efflorescence component. The formation mechanism is related to moisture transport and not to air pollution. Both brick and mortar can be the source of gypsum efflorescence. Many aspects remain hypothetical, rising important research questions. a b s t r a c tBelgian masonry facades are being increasingly affected by unsightly persistent efflorescence. This results in disappointed customers and consequently creates a threat for the brick industry. Our paper presents a field survey and literature review on the topic. An investigation of Belgian cases reveals gypsum abundance in the deposit. The specific characteristics and literature review indicate masonry as the source and moisture transfer as the transport mechanism. However, there is currently no sound explanation for the crystallisation of gypsum on the surface and its only recent occurrence. One hypothesis points at mortar additives, which may affect the transport and crystallisation of gypsum.

The mathematical model and numerical calculation method of efflorescence

“…Efflorescence refers to the phenomenon which cement hydration product Ca(OH) 2 in the pore solution and the external environment of the molar concentration gradient driven continues to lose and cause of C─S─H gel and ettringite continuous decalcified dissolution, resulting in calcium ion concentration in the pore solution declining, pH continued to decrease, and the hydration products gradually lose gelation when cement‐based materials in soft water or other media environment. For buildings, it is not conducive to the sound insulation performance, fire performance and decoration engineering quality control . The results showed that the Ca(OH) 2 of hydration product had the following relationship with C─S─H. Ca(OH) 2 and C─S─H remained relatively stable when the concentration of calcium ion in the pore solution is high; when the pore solution c (Ca 2+ ) < 20 mmol/L, Ca(OH) 2 begins to dissolve; when the pore solution c (Ca 2+ ) < 4 mmol/L, C‐S‐H begins to decalcification dissolve; when the pore solution c (Ca 2+ ) < 2 mmol/L, the chemical loss of concrete reaches the maximum, and the residue of this stage is the silica gel with no binding properties. …”

“…For buildings, it is not conducive to the sound insulation performance, fire performance and decoration engineering quality control. 8,9 The results showed that the Ca(OH) 2 of hydration product had the following relationship with C─S─H.…”

Selection of Method of Chemical Analysis in Measuring the Salinity of Mineral Materials

“…Moreover, salt solubility is not a measure of aggressiveness of a given solution although it is true that salts with the highest solubility are more dangerous [10]. The main and direct cause of salt aggressiveness towards the mineral material is not the salt solution itself but first of all crystallisation of salt from this solution [8,[11][12][13][14][15].…”

“…A wider approach to the assessment of salinity of mineral materials is proposed in "A guide to salt damp in historic and older buildings" [2], according to which the determination of salt content in materials should be based on a full chemical analysis of cations and anions using, e.g., ion chromatography for the cations and coupled plasma atomic emission spectrometry for the anions. Additionally, full identification of the type and amount of salt facilitates the selection of methods for desalination of walls, which in consequence allows for an effective process of their drying and carrying out conservation work [9,11,[16][17][18][19]. Depending on the type and content of salt, the process of degradation of functional properties takes place with different intensity [8].…”

Mitigation of efflorescence of wallboard by means of bio-mineralization

“…Mostly, whitish deposits of water soluble salts are alkali sulfate or sodium chloride, which generally appear soon after erection of the facade. In addition, the appearance of white efflorescence depends on environmental circumstances, material parameters of bricks, mortar and concrete blocks, and may additionally be influenced by treatments of the façade (Brocken and Nijland, 2004; Chwast et al, 2015). According to the existing researches, a physicochemical model was developed to explain the key features and the formation of efflorescence (Kresse, 1982, 1987; Vickers and Moukwa, 1996; Dow and Glasser, 2003).…”