Bound water Portland cement pastes

Figure 23.2 Content of bound water in cement pastes made with different cements and exposed to different temperatures. OPC, ordinary Portland cement BFSC, blast furnace slag cement with 50% of granulated blast furnace slag PFA, fly ash cement with 25% of pulverised fly ash Trass=trass cement with 25% of trass SF=Portland cement with 10% of added sihca fume.

Fig. 4.62 The bound water content in Portland cement pastes measured at difTerent time and curing temperature (according to [194]). Cement composition C3S—58%, CjS—22%, C,A—8%, C,AF—5.4%, gypsum—3.4%, w/c = 0.25...

At equal starting water/cement ratios and degrees of hydration the porosity of pastes made from sulfobelite cements is distinctly lower than that of ordinary Portland cement pastes. This is due to the higher amount of water bound within the crystalline lattice of the solid phases formed in the hydration of the former cement, especially in that of the AFt phase. 

The way in which organic compounds are bound within the hardened Portland cement paste, and their effect on hydration and the stmcture of the Itydrates formed, may vary greatly. Compounds that are insoluble in water usually have no effect, whereas those that are at least partially soluble may or may not slow down the rate of hydration, alter the stmcture of the hydrated paste, and decrease its strength. Compounds that exhibit an adverse effect on Portland cement hydration include various phenols, chlorophenols, and ethylene glycol, whereas metlianol or ethanol have almost no effect (Gmtzek, 1992). 

Koster, H., and Odler, 1. (1986) Investigation on the stracture of fully hydrated Portland cement and tricalcium siUcate pastes. 1. Bound water, chemical shrinkage and density of hydrates. Cement and Concrete Research 16,207-214. 

The total mass of solids does not stay constant during cement hydration free water is bound into hydration products (Figure 4.16) and the initial porosity is filled. Rietveld results normalised on a total solids base for dried samples will need to be corrected. Therefore, the final step in the data analysis is to recalculate the QPA to a common basis. This base of comparison may be the initial paste (free water + anhydrous binder) content, the initial binder (SCM + portland cement) or the initial portland cement or clinker content. The recalculation depends on whether free water is removed to stop the hydration reactions. If the sample is assumed to be undried and... 

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