Fly ash addition

Both cements (Table 7) compile with the requirements of the Yugoslav standard JUS B.C1.011, concerning chemical composition. Portland fly ash cement PPC has the expected higher insoluble residue and the loss on ignition regarding Portland cement OPC because of the fly ash addition. Other constituents were not significantly changed with the fly ash addition. 

Fly ash addition was obviously (Table 8) increasing the demand for the water for the standard consistence and prolonging the setting time, but has no influence on the other cement characteristics. All characteristics were in the compliance with the Yugoslav standard JUS B.C1.011. 

Portland fly ash cement samples, which was expected because it is known that the fly ash addition increases the resistance to acid media. It could be said that the lead in the concentration of 10,000 mg H was successfully stabilized in the Portland cement and Portland fly ash cement matrix [43]. 

The deactivated catalyst was analyzed by energy dispersive X-ray analysis. At the entrance of the channels of the honeycomb catalyst enhanced amounts of Si02, AI2O3, Fc203, CaO, and K2O were found over a length of 2 cm [130]. The composition resembles that of fly ash. Additionally, sulfur was found. 

Effect of calcium carbonate and cement/fly ash additives on chemical stabilization of fine-grained sediment from Hamburg harbour (Calmano et al., 1986)... 

C-S-H in cement pastes reveals the C/S ratio in the range from 1.75 to 1.85 and these value do not alter neither with time nor with w/c, as it has been establish by Rayment and Lachowski [51] in numerous experiments. In the pastes of cement with slag or fly ash addition this C/S ratio is much lower. 

For the pore size distribntion determirration the sample must be dried, arrd as it has been merrtioned, the properties of cemerrt paste rrricrostmcture strongly depend on the conditiorrs of drying. Marsh [59] studied the pore size distribution for the samples dried at terrrperatirre of 105 °C and the samples in which water was replaced by propane. The samples cirred one day and those with the fly ash addition after different time of cirring reveal the sirbstantial differences (Fig. 5.28). However, the results for Portland cement pastes matured for longer time are relatively similar [59]. 

The similar reduction of water permeability was found in the case of a paste from cement with silica fume, rice hush ash and slags [138, 141], Also concretes produced of cement with 35 % fly ash addition show 2-5 times lower permeability, as compared to concrete from cement with no mineral additions [139]. 

Fig. 5.66 Effect of slag and fly ash addition on the pore structure in the pastes after different time of curing at constant w/c=0.45 (according to [139]). SJ, S2 maximum pores...

Application of limestone sand results in a substantial decrease of expansion [165, 180]. According to Kurdowski and Duszak [181], expansion does not occur practically at 3 0 % of hmestone addition. However, as it has been shown by Kelham [182], the expansion is only seriously delayed and can start after about 1,000 days. Finally, it is identical as in a concrete with quartz sand. However, 30% of fly ash addition ehminate expansion [175,181]. 

The granulated blastfurnace slag and siliceous fly ash addition will have a similar effect on the ability of chloride ions binding in cement pastes, because they will also decrease the C/S ratio in C-S-H gel. Uchikawa and Okamura [210] report the following C/S ratio 1.7 for Portland cement, 1.6 in case of 40% slag addition and 1.2 at 40% of sihceous fly ash addition. Simultaneously, these additions will cause the aluminates content decrease in favor of calcium silicate hydrates. 

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. 

There are traditional prejudices against the use of slag cement or Portland cement with fly ash addition in reiirforced concretes, however, they have not been proved experimentally [311, 352], On the contrary, a quite different behaviour of these materials was reported presumably this can be the consequence of reduced permeability of concrete and the resulting lower diffusion (see Table 6.9). However, apphcation of higher content and higher class cement has a positive influence on the dnrabihty of reinforcement. 

Concretes from cements with fly ash addition exhibit a higher sensitivity to the moisture deficiency at early age. They should be carefully cured protected against the moisture loss, because of the shrinkage cracks risk. 

Fig. 7.21 Relative strength of cement pastes with 30 % fly ash addition (according to [137])...

The increased resistance to the aggressive environment is an advantageous feature of these materials. It is linked with Ca(OH)2 content lowering in the paste, but primarily to the reduction of larger pores share, that means the permeability decrease. The ion exchange ability decreases and this counteracts the corrosion reactions progress. Obviously, these properties are developing with the fly ash content increase, and in the case of sulphate attack— with CjA content decrease in cement clinker. The apparent diffusion coefficient of Na and Q decrease with siUceous fly ash addition is shown in Fig. 7.23 [139]. 

Fly ash addition is diminishing also the risk of reaction of alkalis from cement with aggregate, which was discussed in Sect. 6.4. The fly ash addition, which allows the reduction of OH ions concentration in the liquid phase of the paste to 0.3 mol/1 is protecting concrete against destraction [140]. This corresponds to about 40% of fly ash addition to cement with average alkalis content (Na2O =0.92%) or about 30% in the case of cement with lower alkalis content (Na2O =0.68%). 

The three component cements with fly ash addition, apart from granulated blastfurnace slag CEM II/B-(S-V), have the advantageous properties first of all fairly good strength development. 

A part of cement in concrete production can be replaced by siliceous fly ash. The quantity of fly ash addition is then determined according to PN-EN 206-1 Standard, which is introducing k coefficient and the maximum fly ash/cement ratio cannot be higher than 0.33. The water/binder ratio can be calculated using this... 

The authors [142] are reporting that the same advantage can be achieved in concrete production using cement with fly ash addition, with simultaneous warranty of its quality and optimum properties, which are under constant control. These authors are reminding also that the new ASTM C 1157 Standard edited in 1998, does not restrict the type and percentage of mineral addition, under the condition that cement complies with other standard requirements [142],... 

The fly ash or natural pozzolana addition is influencing simultaneously on the chnker phases hydration. Quite similarly as slag also fly ash addition is iiKreasing the ahte hydration rate, particularly in the post-induction period [18]. Presumably it is hnked with the chemisorption of Ca ions on the fly ash grain and subsequent crystalhzation of C-S-H on these grains. For example if in comparable condition the C3S hydration degree after 1 day is 35%, then in the mixture with 30% fly ash, of specific surface 370 m /kg, is increased to 45%. 

Ali, M.M., and Mullick, A.K. (1998) Volume stabilization of highMgO cement effect of curing conditions and fly ash addition. Cement and Concrete Research 28,1585-1594. 

At low fly ash additions— that is, below 15%—the extent of carbonation in mature fly ash concrete tends to be equal to or lower than that in similar concrete mixes with no ash, in spite of the lower calcium hydroxide content of the formed hydrated cement paste (Buttler et al., 1983 Hobbs, 1988 Goni et al, 1997). This is due mainly to the reduced permeability of the paste to CO2. However, at higher fly ash contents the resistance to carbonation is significantly reduced (Goni et al, 1997). 

Portland fly-ash cement It contains upto 30% fly ash. The fly ash is pozzolanic, so that ultimate strength is maintained. Because fly ash addition allows a lower concrete water content, early strength can also be maintained. Where good quality cheap fly ash is available, this can be an economic alternative to ordinary Portland cement. 

Glinicki, M. A., Zielinski, M. (2008) The influence of CFBC fly ash addition on phase composition of air-entrained concrete, Bulletin of the Polish Academy of... 

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