Slag-cement pastes

Table 9.4 Calculated mass balance and compositions by weight and by volume for a 14-month-old slag cement paste Percentages on the ignited weight for material equilibrated at 11% RH... 

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... 

Under some circumstances, the Mg enters sparingly soluble phases other than brucite. Roy et al. (R70) observed the formation of a hydro-talcite-type phase in a slag cement paste that had been treated with MgS04 solution. Its formation was possibly favoured by the enhanced availability of A1(0H)4 provided by the slag. Cole (C70) reported the formation of a hydrated magnesium silicate in a deteriorated concrete seawall. 

In Table 6.4 the effective chloride ions diffusion coefficients in the pastes from various cements, determined by Page et al., are presented [191,211]. The NaCl molar solution in saturated Ca(OH)2 solution, as well as the saturated Ca(OH)2 solution were applied in two chambers of measuring stand. As can be concluded from these data, the chloride ions diffusion coefficient is ten times lower in slag cement paste and three times lower at 30 % fly ash addition. As it can be concluded, the resistance of slag and pozzolanic cements to the attack of aggressive water solutions is significantly higher. This relates undoubtedly to the much lower capillary porosity of these cement pastes. 

Fig. 6.54 Shrinkage of the samples from alkali activated slag cement paste without Portland eement elinker, with Na SiO addition in concentrated MgClj solution. (After [246])...

Fig. 6.56 Pores size distribution in the alkali activated slag cement paste after 2 years of curing in the magnesium chloride solution of high concentration. (According to [245])...

Fig. 7.13 Phase composition of supersulphated slag cement paste after 3 days of hydration at w/c=0.5 (after [87])...

The microstmcture of Portland-slag cement pastes is not too different from that of plain Portland cement. The main difference consists in a reduced amount of free Ca(OH) 2- Just as with clinker grains, layers of reaction products formed in situ are also present at the boimdaries of the slag grains, in addition to the hydrated material formed within the space originally filled with water. 

At comparable consistencies of the starting mix, alkali-activated slag cement pastes exhibit lower porosity than comparable Portland cement pastes, owing to the lower initial water/solid ratio. The proportion of pores with r<10 nm is usually higher in hardened AAS pastes (Shi et al, 1992) however, the actual pore size distribution also depends on the activator used. In a comparative study, mixes produced with sodimn silicate exhibited the finest and those made with NaOH the coarsest pore stmcture (Shi, 1996, 1997). The specific surface area of AAS cement pastes is higher (by about 35-55%) than that of comparable ordinary Portland cement pastes (Tailing and Brandstetr, 1993). 

Richardson, LG. (1997) The stincture of C-S-H in hardened slag cement pastes, in... 

As to the phase transformations, in blast furnace slag cement pastes increasing amounts of melilite [a sohd solution of gehlenite (C2AS) and akermanite (C2MS2)] are formed as the amount of slag in the original cement increases, at the expense of yff-dicalcium silicate, which is formed in Portland cement pastes under similar conditions. In pastes made from cements that contain distinct amoimts of fly ash, yff-dicalcium silicate is also the main final decomposition product. In parallel, quartz, which is a common constituent of fly... 

The prineiple hydration produets of slag cements are essentially similar to those found in pordand eement pastes. The microstructure of slag cement pastes is also similar to that of portland cement pastes. X-ray microanalysis has, however, shown that the C/S ratio of C-S-H product in hydrated slag cement is lower than that found in portland cement paste. 

Tenoutasse, N., and Dieryck, V., Effect of Cement-Plasticizer Interactions on the Rheological Properties of Slag Cement Paste, 6 CANMET/ACI Int. Conf. on Fly Ash, Silica Fume, Slag and Natural Pozzolans in Conor., Bangkok, Thailand, supplementary papers, pp. 293-306 (1998)... 

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