ARE ALKALIS INCORPORATED INTO THE STRUCTU RE OF ALKALI-REACTION GEL PRODUCTS IN CONCRETE

Using two distinct series of experiments, the behaviour of the alkalis (Na, Li) in solutions equilibrated with a synthetic gel (CaO/SiO2 = 0 .5), analogous to the gels produced by the alkali-reactions in concret es, was studied. In the first series of experiments, a fixed volume (1 0 ml) of a 0.01 M LiCl solution is introduced, after precipitation of the gel, into n identical gel (Ca-Si)/solution (Na) systems in equilib rium, then n. 20 mi of distilled water (n = 0, 1, 2, 3). Once a new eq uilibrium has been established, the amounts of Na and Li in solution a re determined in each one of the n systems. In the second series of ex periments, Li is introduced in the same amounts, before precipitation of the gel, into the n systems, the remainder of the experimental proc ess being unchanged. The results obtained corroborate that Na and Li, comply with the process of simple dilution, as a function of n. It com es out from this study that Na and Li, take no part in the gel structu re and are present in a free state in the ambient solutions. We can as sume that this is probably the case for the alkali-reaction gels in co ncretes.