Partial Replacement of Cement

Canpolat et al. [33] have suggested the usage of zeolite, coal bottom ash and fly ash as replacement materials for production of the cement. It has been opined that the inclusion of zeolites, up to 15 %, results in an increase in the compressive strength of the cement, at early ages, whereas a decrease in compressive strength is observed when zeolites are used in combination with the fly ash. However, the setting time is found to decrease due to the replacement of clinker by the zeolite. This has been attributed to presence of adsorbed water (the excess water remained unused after the hydration process in the cement) on the zeolite surface. 

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Partial replacement of cement with fly ash improves the workability but reduces the strength up to 28 days. At 90 days the strengths attained are very similar to 100% Portland cement mixes. 

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. 

Fig. 11.6 Effects of partial replacement of cement by finely ground silica on the compressive strengths of mixes cured normally and in the autoclave. After Mcnzcl (MHO).

All mixtures that contained different fiber volume fractions percentages and silica fume, rice husk ash and glass as partial replacement of cement were fabricated and tested in order to assess fresh and hardened properties of FRSFEC. Materials, specimen fabrication, curing... 

The water sorptivity of ordinary concrete containing 1 wt% CaCOs nanoparticles was approximately 17% and 30% lower at 28 and 90 days, respectively, than the ordinary concrete. In addition, the use of 1 wt% CaCOa nanoparticles in HVFA concrete was found to be significantly effective in reducing the water sorptivity when combined with 39% FA as a partial replacement of cement in concrete. This is an indication that the 1% CaCOa nanoparticle addition in an HVFA system forms a finer pore stmcture than HVFA paste alone. 

Polymer-modified cementitious floor toppings are now widely used instead of separately laid granolithic toppings. The polymers used are normally supplied as milky white dispersions in water and are used to gauge a carefully selected sand/aggregate/cement mix as a whole or partial replacement of the gauging mortar. They must always be mixed in a forced-action mixer. 

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... 

Fig. 3. Photomicrographs of (A) microcrystalline non-ferroan dolomite at the very top of a sandbody with partial replacement of detrital silicate grains, and (B) grain-rimming quartz cement (Q) and pore-filling ferroan dolomite (DOL) enclosing the quartz cement. Remnant porosity (0) is minor and occupies pore centres. Scale bars 200 pm.

Polymer-modified or polymer cement mortar (PCM) and concrete (PCC) are a category of concrete-polymer composites which are made by partially replacing the cement hydrate binders of conventional cement mortar or concrete with polymers, i.e., polymeric admixtures or cement modifiers, thereby strengthening the binders with the polymers. Polymer-modified or polymer cement paste, which is prepared widiout any aggregate, is sometimes used. 

Portland cement (see section 0.00) is hardly suitable for use in acid environments. No significant differences have been found between the performances of ordinary and high-iron, I0W-C3A Portland cements, but cements with a higher C3S content, which liberate more calcium hydroxide in the course of hydration, seem to be more susceptible to acids (Matthew, 1992). Partial replacement of the clinker by pulverized fly ash does not... 

The replacement of cement clinker by GGBS may vary from 10% up to 70% or even more for pure slag cements, and different kinds of blended cements are available. The use of GGBS as a partial replacement of Portland cement has a significant ecological effect. The deposits of industrial waste are transformed into a constituent of concrete. The emissions of dusts and gases into the atmosphere from cement production are limited and the need of natural raw materials is proportionally reduced (Bijen 1996). 

Metakaolin (calcined clay) is an ultra fine pozzolana, produced from the mineral kaolin at temperature between 700°C and 900"C in that temperature kaolinite loses water. This thermal activation is also referred to as calcining. The obtained product is highly pozzolanic and in recent years there has been an increasing interest in the utilisation of metakaolin used as partial replacement of Portland cement (up to 30%), often as an alternative to the use of SF. 

Partial replacement of Portland cement by natural or artificial pozzolans reduces the heat of hydration and also the unit price of concrete it slows down the process of hardening and the early strength is lower. Nevertheless, the majority of the volume of structural concrete used in technically advanced regions of the world are based on rational compositions of Portland cement and so called secondary binding materials fly ash, ground granulated blastfurnace slag, metakaolin, SF, and others. 

The influence of fly ash, ground blast-furnace slag and other micro-fillers on the properties of high performance concrete is positive. As for ordinary concretes, these mix components densify the structure, and because of their pozzolanic properties they take part in hydration processes. Partial replacement of Portland cement by fly ash and ground slag enables a decrease in the cost of materials, improves the workability and reduces the heat of hydration. In practice, the majority of concrete structures are made with binary or ternary blended cements, which means that more than one additional binder is used with Portland cement. 

Partial replacement of Portland cement with mineral admixtures enables appreciable savings in energy and cost to be made. 

Fly ash may be used as a replacement of cement or fine aggregate or as an additional component at the concrete mixing plant. Fly ash has been used up to 60% replacement of cement. Addition of fly ash reduces the water requirement for a particular consistency or flow. Low calcium fly ash acts largely as a fine aggregate initially, but with time will react to pozzolanic compounds. High calcium fly ash participates in the early cementing reactions. Partial replacement of fly ash results in the reduction in temperature rise in fresh concrete due to the reduction in the heat of hydration. 

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