Portland cement with mineral additions,

The other fine powder components, added to control the workability of concrete mixture are fly ash, limestone flour and ground granulated blastfurnace slag. The content of these mineral additions can be substantially high when cement type CEM 1 is used they substitute up to 50% cement, particularly that of class 42.5. One can conclude that the Portland cements with mineral additions can be also applied. The effect of limestone flour on the properties of concrete mixture was studied, among the others, by Gizeszczyk [32],... 

Fig. 5.60 Relation between the total porosity (determined with helium method) and permeability of water saturated pastes (according to [133]) empty circles—Portland cement pastes, black circles—pastes from cements with mineral additions, cured at 20-80 C, one year measurements...

The concretes produced from cements with natural pozzolana addition are particularly resistant to the chemical corrosion, but the resistance to physical factors is only slightly changed. However, they should be cured for a longer time in humid condition than the concrete produced from Portland cement without mineral additions. They are useful in these conditions where a low heat of hardening and high resistance to chemical corrosion is required [5]. 

Portland cement clinker potential phase composition is presented in Table 4. It could be seen that the C3A content in the clinker was 9.46% which is important for the cement hydration rate and cement sulfate resistance. Common Portland cement is not resistant to the sulfate influence because of the significant C3A content, whose hydrates react with sulfate ions resulting in expansive compounds. Portland cement with the higher resistance to sulfates must have low C3A content. Moderate to high content of mineral alite - C3S (54.72%) is usual for the Serbian cement plants and enables the addition of higher quantities of mineral admixtures without influencing the quality of final cement. 

Nowadays blended cements are normally used, which are obtained by intergrinding or blending Portland cement with particular mineral substances. Among these, those with the addition of pozzolanic materials or ground granulated blast furnace slag are of particular interest with regard to durabihty of reinforced concrete. 

Slag cements 32.5N should not be used when eonereting proeeed at low tem-peratirres, particularly below 5 °C, beeaitse of very slow strength development, as compared to Portland eement concrete. This is related also to the Portland cement class 32.5 with mineral additions (Table 7.2) [83]. 

Mineral additions may be broadly categorized as pozzolanic materials or latent hydraulic cements. Neither type reacts significantly with water at ordinary temperatures in the absence of other substances. Pozzolanic materials are high in Si02 and often also in AI2O3, and low in CaO they are sufficiently reactive that mixtures of them with water and CaO produce C-S-H at ordinary temperatures and thereby act as hydraulic cements. If they contain AI2O3, calcium aluminate or aluminate silicate hydrates are also formed. Because they are low in CaO, this component must be supplied in stoichiometric quantity. In a composite cement, it is provided by the Portland cement through decreased formation of CH and decreased Ca/Si... 

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... 

Partial replacement of Portland cement by a mineral addition can greatly decrease the permeability to water provided the age is such that sulhcienl reaction of the addition has occurred. For a paste with w/s 0.47 and 30% replacement of cement by pfa, cured at 20°C for 1 year, Marsh et al. (M87) found a permeability of 10 m s the corresponding paste of pure... 

Bamforth [23] suggested the recommendations given in Table 12.6 that show how the use of normal Portland cement does not produce concrete adequate for a service Hfe of 75 y in a chloride-containing environment, unless class C50/60 concrete and concrete covers of 100 mm are used. Cements with a high percentage of mineral additions allow the use of more reasonable concrete cover thicknesses and lower classes of strength. 

Wood is not abrasive to equipment like inorganic fillers/fibers, but certain desired properties can only be obtained with additions of mineral fillers such as talc (for lubricity and strength), calcium carbonate, calcium oxide, alumina, wollastonite (for scratch and wear resistance), or even Portland cement, as a reactive filler supplying strength and fire retardancy. 

Additionally the strength of cement with air entraining agent, but without mineral addition is as for J(SM). Clinker can be replaced by Portland or slag cement. 

Mineral additions reduce the maximum pore radius and effective diffusion coefficient (Fig. 6.49) [221]. The rate of chloride ions diffusion in the paste increases in the following order slag cement < cement with siliceous fly ash < Portland... 

The increasing costs of fuel, as well as, quite recently, the restrictions of CO2 emission, increased the use of mineral additions and accelerated, the studies aimed with the searching of binders having the properties corresponding to Portland cement, but produced with lower energy consumption. The investigations tent to the following materials ... 

The term composite cement or blended cement is used to denote inorganic binders that contain a mineral addition in combination with Portland chnker and usually also with calcium sulfate. 

Composite cements may be produced by grinding the mineral addition (or additions) together with Portland clinker and calcium sulfate, or by blending them with Portland cement produced separately. 

Fig. 17.1 Flow diagram for the manufacture of Portland cement by the wet process. The limestone is crushed, mixed with wet clay, and ground to a fine slurry in a mill. This raw material is stored and corrected for composition by blending before being fired in a rotary kiln where the process of water evaporation, mineral dehydration, limestone dissociation, and chemical reaction proceeds. Clinker formation forms finally at 1,450 °C and is cooled and ground with additives before storage... 

Portland cement can be produced by burning a homogenized mix of materials containing clay and lime. When partly melting at 1400-1500 °C, a number of calcium silicates and calcium aluminates, the so-called clinker minerals, are formed. The burnt product - the cement clinkers - are then ground with addition of a few per cent of gypsum, which results in the commercial product Portland cement. 

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