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Water extraction out of mortar during brick laying. An NMR study

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Author: Brocken, H.J.P.
Type:article
Date:1996
Source:International Symposium on NMR Spectroscopy in Cement-Based Materials, Bergamo, Italië, 10-11 June
Identifier: 329024
Keywords: Architecture and Building · Water extraction · Moisture diffusivity · Brick masonry · Mortar

Abstract

The water extraction out of mortar during brick laying was studied by nuclear magnetic resonance. The water extraction is an important parameter that determines, e.g., the stiffness of the mortar due to compaction of the cement particles and the bond strength of the cured-mortar interfaces but allo the hygric properties of the mortar joints. Because of the large amount of paramagnetic ions present in both mortar and brick, the hydrogen nuclei have short transverse relaxation times and a broad resonance linewidth. Therefore a specially designed NMR apparatus had to be used. With this instrument the moisture profiles in the brick and the mortar can be measured with an accuracy of I % and a spatial resolution of 1 mm. Using a multiple-slice technique a profile over 20 mm can be measured within 90 seconds. Water extraction experiments were performed using fired-clay brick and sand-lime brick. These experiments show that most of the water extraction occurs within the first 3 to 10 minutes. Prewetting the fired-clay bricks had hardly any effect on the water extraction rate, in contrast to sand-lime brick. However, prewetting the brick can influence the final equilibrium moisture content of the mortar and thereby the final hydration conditions.