Pore size distributions composite cement pastes

The most important characteristic of cement is its pore structure and aqueous phase hence, the microstructure of the hardened cement paste via the pore system. It is highly alkaline (pH >13) due to rapid and almost quantitative dissolution of Na and K salts from the cement clinker. The porosity of the paste comprises interconnected and isolated pores, the pore sizes of which are important to the strength and dimensional stability of cement products. Different types of cement are used to meet different performance criteria. Properties can be estimated from compositions and fineness (i.e., particle size and size distribution). In the past, additives... 

Fig. 9.6 Pore size distributions for pastes of Portland and composite cements (vv/s = 0.45. curing temperature 21 C), determined using mercury intrusion porosi-metry. CID. CIY Portland cement pastes cured for 1 day and 1 year. S2D. SIY Portland-blastfurnace slag cement (70% slag) pastes, cured for 2 days and I year. F.3D, FI Y pfa cement pastes (13% CaO in fly ash) cured for 3 days and 1 year.. After Feldman (F34).

Fig. 9.6 compares curves obtained on first intrusion for pastes of Portland and composite cements. At early ages, pfa or slag cement pastes are more porous than comparable Portland cement pastes because of the relatively slow reactions of the mineral additions, but the pore size distribution curves indicated by MIP are essentially similar in shape. For mature pastes, the apparent distributions for the composite cements indicate that there is a greater proportion of fine porosity. For the pfa cement paste, the mercury porosity obtained at maximum pressure are greater than that of the Portland cement paste. Day and Marsh (D32) agreed with Feldman that discontinuity... 

Uchikawa et al. (U18) studied pastes of Portland and composite cements by N2 sorption. In all cases, the pore size distributions peaked at 2 nm. Partial replacement of cement by slag increased the height of the peak, and partial replacement by pfa decreased it. 

The factors that influence the mechanical behavior of concrete are shape of particles, size and distribution of particles, concentration, their orientation, topology, composition of the disperse and continuous phases, and that between the continuous and disperse phase and the pore structure. The important role played by cement paste is already described. 

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