Cement Paste Pore Solution Research Articles

The chemistry of the pore fluid of silica fume-blended cement systems

The behaviour of silica fume in cement systems, particularly, the pozzolanic reaction was investigated by monitoring the chemistry of the pore solution of silica fume-blended cement pastes. This was supported by heat of hydration studies on similar mixes. Silica fume accelerated cement hydration during the early hours. The increased rate of hydration is believed to be due to enhanced precipitation of hydration products on the submicroscopic silica fume particles which possibly served as nucleation sites for crystallization during the early hours when it existed as chemically inert filler. The study also revealed evidence of pozzolanic reaction within three days after the formulations of the mixes, irrespective of the water-to-binder ratio used. This evidence is apparent in blends made with portland as well as blastfurnace slag cements. In both cases, OH −, Ca 2+, K +, and Na + were chemisorbed from the cement solution.

Alkali-silica reaction: The relation between pore solution characteristics and expansion test results

The use of condensed silica fume (CSF) causes a reduction of Na +, K + and OH − ion concentration of the pore solution of cement paste and concrete samples. Expansion tests also showed that CSF reduces expansion caused by alkali-silica reactive rock in mortar bars and concrete prisms. The reduction of expansion seems to be proportional to the amount of CSF used. For a given amount of CSF, however, the reduction of expansion of the concrete prisms appears to be greater than the observed reduction of Na +, K + and OH − ions in pore solution would predict.

Influence of sodium chloride on alkali-silica reaction

Synopsis The possible effect of sodium chloride in increasing the alkalinity of concrete and exacerbating alkali-aggregate reaction has been investigated by experiments involving the addition of sodium chloride and synthetic seawater to cement pastes, mortars and concretes. Measurements of the composition of the pore solution of cement pastes and expansion of mortars and concretes made with reactive aggregates are reported. It was found that small additions of both sodium chloride and synthetic seawater elevated the hydroxyI ion concentration of the cement pastes to a level similar to that produced by a Portland cement with an equivalent alkali level. Similarly the sodium chloride and synthetic seawater had an effect on the expansion of mortars and concretes which was in line with the effect produced by an equivalent amount of alkali in the cement.

Pore solution expression as a method to determine the influence of mineral additives on chloride binding

A collaborative project on cement paste pore solution analysis has been carried out by Institutes in Sweden, Denmark and Austria to determine: (i) the reproducibility of the pore solution expression method; (ii) the effect of added chlorides on the OH − concentration of OPC pastes from the three countries and (iii) the influence of flyash, slag and silica fume additions on the degree of chloride binding by the cement.