Water extraction out of mortar during brick laying : a NMR study

The water extraction out of mortar during brick laying was studied using nuclear magnetic resonance. The experiments show that using a fired-clay brick, the water is extracted out of the mortar within 3 minutes, whereas in the case of a sand-lime brick this takes about 10 minutes. Prewetting a fired-clay brick hardly affects the water extraction, whereas prewetting a sand-lime brick slows down the water extraction, although the effect is small. The extraction process is slowed down only if the bricks are almost fully saturated. These effects are explained with the help of computer simulations. The final moisture content of the mortar is shown to depend on the suction of the brick and thereby on the equilibrium moisture content of the brick. By adding a water retention agent to the mortar, the extraction process seems to slow down, although the final moisture content of the mortar is not changed. The water extraction experiments suggest that the suction of the mortar which is formed depends on the water extraction rate and thereby on the type of brick that is used in the extraction experiment. Petrographic analyses indicate that the extent of bonding between the brick and the mortar is different for fired-clay brick and sand-lime brick

Determinants of ventilation behavior in naturally ventilated dwellings: Identification and quantification of relationships

Background: Ventilation in dwellings is essential for well-being and health. However, insight in determinants of ventilation behavior is still limited. Aim: Identifying determinants of ventilation behavior and quantifying relationships. Secondly, identifying households characteristics associated with low ventilation activity. Methods: In a cross sectional study, ordinal and binary logistic regression analyses were performed, in a large population based survey, to identify determinants of window and vent opening behavior in the main living areas during the heating season in naturally ventilated dwellings. Relationships were quantified. Results: Window opening behavior was associated (although not always consistently between models) positively with household size, negatively with disposable income (living- and bedroom), and with ethnicity (association different in direction between room types). Furthermore, window opening behavior was positively associated with ‘respondent or partner does not have a paid income’ (living room only), presence of females and age of the oldest occupant (bedroom only). In addition, significant associations were found between dwelling characteristics and window opening behavior, including the presence of vents (strong negative association, both room types), type of dwelling (association different in direction between room types), and the overall heat transfer coefficient by transmission. A smaller number of household and dwelling characteristics was found associated with vent opening behavior. Conclusion: Window and vent opening behavior was associated with a range of both household and dwelling characteristics. More research is needed to confirm associations