Portland-Pozzolanic cement

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. 

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. 

In cements containing pozzolanic additions, the Ume needed to react with pozzolana is provided by the hydration of Portland cement. The hardened cement paste (compared to that obtained with ordinary Portland cement) has a lower lime content and higher content of C-S-H. The amount of pozzolanic addition to Portland cement generally ranges from 20 to 40 % of the total cement content it should be adjusted to the amount of lime produced in the hydration of Portland cement. Any excess of the pozzolanic addition wiU not react and thus will behave as an inert addition. 

Gutierrez et al. [50] investigated the effect of replacing part of Portland cement by pozzolans as silica fume, fly ash and metakaolin on the mechanical properties of cement mortar reinforced with synthetic and natural fibers. The mechanical behavior and durability of composite materials was improved by replacing 15 wt% of cement with metakaolin or silica fume however, because of its low pozzolanic power, fly ash had no effect on the durability of these materials. Khorami and Ganjian [62] increased flexural strength in 20% of cementitious materials reinforced with straw fibers and eucalyptus, by replacing 5 wt% of Portland cement with silica fume. 

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. 

By replacing the cement Portland with groimd glass type II the expansion rate of the specimens decrease aroimd 15%. According to last researches materials with pozzolanic characteristics can suppress the alkali-silica reaction (ASR) and decrease the expansion... 

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" ]... 

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. 

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... 

Chemical tests of pozzolanicity have proved of limited use for evaluation, because the 28-day strength depends much more on the w/s ratio than on this property, and there appears to be no effective substitute for direct testing of the relevant properties on mortars or, preferably, on concretes. The degree of pozzolanic activity is, however, important for the development of strength and decrease in permeability at later ages. For equal 28-day strengths, the strengths at 91 days or more normally exceed those of otherwise similar concretes made with pure Portland cements. 

Uchikawa (UI7) reviewed the hydration chemistry of pfa and other composite cements. Pfa cements differ from pure Portland cements notably in (i) the hydration rates of the clinker phases, (ii) CH contents, which are lowered both by the dilution of the clinker by pfa and by the pozzolanic reaction, (iii) the compositions of the clinker hydration products and (iv) formation of hydration products from the pfa. The two last aspects cannot be wholly separated. 

Of the pfa characteristics that influence reactivity, the glass content appears to be much the most important, but specific surface area, glass composition and the effect of stress in the glass caused by the crystalline inclusions may also be relevant (U17). Of external factors, the RH, temperature (C43) and alkali content of the cement are probably the most important. Sulphate ion may also enhance reactivity by promoting the removal of AF from the glass (U17). The rates of the pozzolanic reaction and of strength development are more sensitive to temperature than are those of hydration and strength development for pure Portland cements (e.g. Ref. H52). 

Traetieberg (T47) showed that microsilica used as an addition with cement has considerable pozzolanic activity, mainly in the period 7-14 days after mixing, and that the reaction product formed with CH probably had a Ca/Si ratio of about 1.1. Several subsequent studies have shown that the pozzolanic reaction is detectable within hours and also that the early reaction of the alite is accelerated (H37,H54,H55). Huang and Feldman (H54,H55) studied the hydration reactions in some detail. In pastes with 10% or 30% replacement and w/s ratios of 0.25 or 0.45, the CH content passed through maxima usually within the first day before beginning to decrease in those with 30% replacement, it had reached zero by 14 days. Table 9.9 gives some of the results obtained for CH content and non-evaporable water in these pastes. As with pfa cements, and for the same reason, the non-evaporable water contents of mature pastes are considerably lower than those of comparable pastes of pure Portland cements. 

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