The use of nuclear magnetic resonance (N M R) in cement and concrete research has been reviewed and the potential oj the technique Jor Juture research has been elucidated. The most important nuclei Jor cement and concrete research are IH, l3C, 27AI and 29Si, and representative examples are given Jor each oj them. N M R can be utilized to study the degree oj hydration, the reactivity of pozzolanic materials, clinker composition, interaction oJorganic admixtures with cement minerals, the different states oj-water in concrete, etc.

The pozzolanic activity of condensed silica fume replacing 15% of di- and tricalcium silicates at a w/(c + s) ratio of O·70 has been studied by solid-state 29Si magic angle spinning nuclear magnetic resonance. The hydration characteristics of the two cement minerals have been studied by the same technique in mixtures with and without silica fume. The water in the mixtures was pre-mixed with alkalis to partly simulate the initial solution formed when water is mixed with cement, since alkalis are believed to strongly affect the conversion rate of silica fume. The combination of NMR data with information from thermogravimetry (TG) has been utilized to balance the total chemical reaction for each mixture, and thereby the empirical formula of the CSH gel as well. The consumption rate of silica fume is found to be faster than the hydration of the minerals after three to seven days. Furthermore, the average chain length of the linear polysilicate anions in the CSH gel is longer in mixes with silica fume than without. The latter is accompanied with a lower CIS ratio in the gel. The C/S ratio of the gelfrom the pure cement minerals tends to increase with age. Silica fume accelerates the hydration of the cement minerals at early age, but retards the hydration at a later stage under the current conditions.

Carbonation in hardened pastes of fly ash cements, stored in a CO2 atmosphere and exposed to different relative humidities, has been investigated in order to study its effects upon different properties of cement pastes. Thermogravimetry (TG), x-ray diffractometry, SEM, and mercury porosimetry (MIP) have been used to characterize the carbonation phenomenon. The results indicate that different relative humidities in the storage chambers lead to carbonation of different solid phases in the hydrated pastes. This effect is discussed in terms of TG- and x-ray analysis. Changes in pore size distribution due to carbonation have been analyzed by MIP and SEM.

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