Portland-pozzolan cement

Portland-Pozzolanic cement contains a material (in our case fly ash) that reacts with the calcium hydroxide produced by Portland cement to form calcium aluminosilicates to give a cement with improved properties. 

Portland pozzolan cement It includes fly ash cement, since fly ash is a pozzolan, but also includes cements made from other natural or artificial pozzolans. In coimtries where volcanic ashes are available (e g. Italy, Chile, Mexico and the Philippines), these cements are often the most common form in use. 

Calcium chloride increases compressive strength of cement pastes especially at earlier times. The most significant effect on compressive strength occurs with portland blast furnace cement and marginally with portland-pozzolan cement. The compressive strength of cement pastes in the presence of 2% CaCl2 improves by about 50,41,11,9, and 8% overthe reference at 6 hours, 1, 3, 7, and 28 days, respectively.P" ]... 

Zeolitic tuff is also utilised in the cement industry as pozzolanic addition (see Sub-sec. 5.2.2.) to portland cement. This application recalls the use of pozzolana, since the beginning of the 1900s, to obtain blended cements, able to fix the lime formed by the hydration of the calcium silicate components of the portland clinker. The utilisation of zeolitic tuff, as substitute of pozzolana, to obtain pozzolanic cements is based on both economic and technical considerations. On one hand, manufacturing blended cements allows a 40% fuel savings, without reducing the quality of the produced binder (it is to bear in mind that the mixture lime-pozzolana is itself a cement), on the other, it involves some advantages, e.g., the... 

When it is required to seal the steel casing of gas and oil wells to the walls of the borehole and to seal porous formations, a grout mixture is used. Both Portland and pozzolanic cements are used as setting agents. The latter consists of slaked lime and a pozzolan. The setting time of the pozzolanic cement is shortened by the addition of an accelerator (e.g. soda ash which is immediately causticised by the lime) and by the relatively high temperatures at depth [32.27]. 

The setting reactions for Portland cement are similar to those for the ancient pozzolanic cement. The first reaction is the hydration of C3A. This reaction is rapid, occurring within the first 4 hours, and causes the cement to set ... 

Excel files for plotting subternary diagrams of hydrated portland-pozzolan-limestone cements... 

EXCEL FILES FOR PLOTTING SUBTERNARY DIAGRAMS OF HYDRATED PORTLAND-POZZOLAN-LIMESTONE CEMENTS... 

Solidification of the upper layers can be accomplished by blending pozzolanic additives, modified clay, or stabilization reagents into moist soil and compacting the mass. Pozzolanic additives include such fixatives as portland cement, quick lime,... 

The HAZCON solidification process is an ex situ technology for the immobilization of metals and inorganic hazardous wastes in wet or dry soil and sludges. The technology is a cement-based process in which the contaminated material is mixed with pozzolanic materials such as Portland cement, a patented additive called Chloranan, and water. The process is capable of treating solids, sludges, semisolids, or liquids. The mixture hardens into a cohesive mass that immobilizes heavy metals. 

Pozzolanic S/S systems use portland cement and pozzolan materials (e.g., fly ash) to produce a strucmrally stronger waste/concrete composite. The waste is contained in the concrete matrix by microencapsulation (physical entrapment). It is a chemical treatment that uses commercially available soluble silicate solutions and various cementious materials such as cement, lime, poz-zolans, and fly ash. By addition of these reagents and rigorous mixing, the waste is fixed or stabilized. Contaminant mobility is reduced through the binding of contaminants within a solid matrix, which reduces permeability and the amount of surface area available for the release of toxic components. 

ASTM 1994. ASTM C618 Standard Specification for Fly Ash and Raw or Calcined Natural Pozzolan for Use as a Mineral Admixture in Portland Cement Concrete. ASTM International. World Wide Web Address http// www.astm.org. 

Ash from pulverized coal combustion is a strategic material that has many critical applications from a source of aggregate to the most important source of pozzolan for addition to Portland cement concrete. Environmental control measures on the emissions of coal combustion have resulted in a loss of quality for these materials. In response we have seen the advent of beneficiation processes applying both proven and new technologies to produce high-quality consistent products from these materials. Currently we estimate that about one-fifth of all ash products marketed are processed through some form of beneficiation method. We expect that the demand for quality and consistency will continue and the relative amount of process ash products will increase in the future. 

We have demonstrated that supercritical C02 can be used to accelerate the natural carbonation reactions in unmodified Portland cements, and that this treatment enhances the physical properties of the cement. Further, it has been proven that the use of supercritical C02 allows the replacement of Portland cement powder with inexpensive, lower-grade pozzolans, such as fly ashes. 

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... 

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