Cement-based pozzolan

Major categories of industrial waste solidiflcation/stabilization systems are cement-based processes, pozzolanic processes (not including cement), thermoplastic techniques, organic polymer techniques, surface encapsulation techniques, and self-cementing techniques (for high calcium sulfate sludges). Vitrification (discussed previously) can also be considered a solidification process. 

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. 

Abstract Solidification/stabilization treatment processes immobilize hazardous constituents in the waste by changing these constituents into immobile (insoluble) forms, binding them in an immobile matrix, and/or binding them in a matrix which minimizes the material surface exposed to weathering and leaching. Solidification/stabilization treatment processes can include aluminum silicate and cement-based fixation, pozzolanic-based fixation, or vitrification. 

Before concluding this subject, mention is made here of two more novel approaches for using SBE. Pollard et al. (143) have reported that SBE can be used to prepare a pseudo-graphitic char suitable as a low-cost replacement for activated carbon in the stabilization/solidification of industrial wastes. In their process, they char 2 1 blends of SBE and ZnCl2 at 450°C/1 hour and then activate the material at 600°C/1 hour. The resultant hybrid material is as effective as activated carbon for fixing toxic organics and, because of its aluminosilicate framework, exhibits additional pozzolanic activity in the cement-based stabilization/solidification reactions in which these materials are used. Very recently (144), Bohling reported on... 

Polymer encapsulation is an ex situ S/S technique involving the application of thermoplastic resins such as bitumen, polyethylene and other polyelfins, paraffins, waxes, and sulfur-based cements, as opposed to cements and pozzolans. Polymer encapsulation has been used primarily to immobilize low-level radioactive wastes and those waste types that are difficult to immobilize in cement, such as Cl- and SO4-based salts. Bitumen (asphalt) is the least expensive and (hence) used most often. Thermoplastic encapsulation heats and mixes the contaminated soil with the resin at 130 to 230°C in an extrusion machine. Organic pollutants and water boil off during the extrusion and are collected for treatment or disposal. The final product, a stiff yet plastic resin, is then discharged into a drum or other container and land-filled (U.S. EPA, 1997). 

The distinct types of CSM used for the construction of base/sub-base layer are as follows (a) cement-treated aggregate (CTA) or cement-treated base (CTB), (b) lean concrete (LC), (c) soil cement (base course), (d) lime-cement-fly ash base or pozzolanic-stabilised mixture, (e) lime-stabilised soil (LSS) and (f) open-graded cement stabilised. 

In hardened cement-based composites the transportation of liquids and gases through pore and microcrack systems plays a very important role in many processes, such as hydration of Portland cement, pozzolane effects of microfillers, carbonation, corrosion of cement paste and reinforcement due to reaction with external agents, shrinkage and creep, etc. These processes are partly described in respective Sections 4.1, 4.3, 6.5 and 11.5. Only basic information is reiterated below concerning the flow of liquids and gases through concretes and mortars. 

The plaster is removed and masonry is cleaned from any loose material. The (metallic or nonme-tallic) grid of reinforcement is placed on the faces of masonry and fixed on it (using anchors). In order to achieve better bond of the reinforced plaster, it is advisable to remove the mortar from the joints as deep as possible and fill them during the application of the plaster. In case of metallic reinforcement (steel grid), the plaster is usually a cement-based one. In case of nonmetaUic reinforcement (e.g., fiber-reinforced wires or bars), the plaster can be a hydraulic lime + pozzolan mortar. 

Petroleum. Apart from its use ia petrochemicals manufacture, there are a number of small, scattered uses of lime ia petroleum (qv) production. These are ia making red lime (drilling) muds, calcium-based lubricating grease, neutralization of organic sulfur compounds and waste acid effluents, water treatment ia water flooding (secondary oil recovery), and use of lime and pozzolans for cementing very deep oil wells. 

Petrifix A process for solidifying aqueous wastes, converting them to a solid form suitable for landfill. Cementitious additives are used, based on the compositions used by the Romans for making Pozzolanic cements. Developed by Pec-Engineering, Paris, France. In 1979 it had been used in France and Germany. 

For special high strength applications, ie, up to 69 MPa (10,000 psi), special formulations of Pordand cement concretes have been developed. These are based on the use of chemical and mineral admixtures. The typical mineral admixtures are fumed silica and other pozzolanics. The chemical admixtures are generally chemicals termed superplasticizers that allow very low water to cement ratios, ie, between 0.4 and 0.25, and reduce the amount of water needed to provide plasticity or flow to the concrete. Public works applications take just under 32% of the total Pordand cement market streets and highways represent 68% of this usage, and water and waste account for 23%. 

Lime/fly ash pozzolanic processes combine the properties of lime and fly ash to produce low-strength cementation. Kiln dust processes involve the addition of kiln dust to eliminate free liquids and usually form a low-strength solid. Lime-based processes for solidification use reactions of lime with water and pozzolanic (siliceous) materials, such as fly ash or dust from cement kilns, to form concrete, called a pozzolanic concrete. Wastes of desulfurization of gases and other inorganic wastes can be immobilized by this method. 

The nature of mortar has changed considerably over time. The primitive clay based mortars gave way to the lime-sand formulation of the Romans with additions of plaster, crushed brick, and/or volcanic earth (pozzolan). The rediscovery of natural cements occurred in the eighteenth century and finally Portland cement was developed. Mortars in use changed accordingly to include the new products. In each case the type, size and amount of charge added in the mix has a large influence on properties such as the bulk density and porosity of the final product. 

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... 

This describes the specific curing behavior of fly ash, cement dusts, and certain steel works byproducts, is based on the reaction of silicate and aluminous materials with quick lime. Here too, as with the above-mentioned additives, a higher pH causes the precipitation of metal hydroxides and carbonates. The British SEALOSAFE-Process uses fly-ash plus Portland cement, or alkali silicate glass and Fe/Al hydroxides to solidify a broad spectrum of wastes. In the POZ-O-TEC-Process, the wastes from flue gas scrubbers are solidified together with grate ash and fly-ash. The pozzolanic processes have the advantage of excellent longterm stability however, the products solidify rather slowly and are susceptible to acids. 

Stabilized base Aggregate Cementitious materials - Pozzolan - Pozzolan activator Self-cementing material... 

The most commonly used activators or chemical binders in pozzolan-stabUized base (PSB) mixtures are lime and Portland cement, although cement kUn dusts and lime kUn dusts have also been used with varying degrees of success... 

FGD scrubber material Stabilized base - Stabilized or fixated FGD scrubber material has been used successfully for road base construction, at a number of different sites in Florida, Pennsylvania, Ohio, and Texas - Stabilization or fixation of FGD scrubber material can be accomphshed by the addition of quicklime and pozzolanic fly ash, Portland cement, or selfcementing fly ash - The FGD scrubber sludge is dewatered before the addition of stabilization or fixation reagents - Additional fixation reagents may need to be added for stabilized base construction in order to meet compressive strength or durability requirements 66-80... 

It is known from the past that hydrates leach from concrete. Taylor [21] has proposed various measures against leaching by using Pozzolanic materials, alumina cement, dense concrete, carbonated concrete, autoclave curing, and so on. Even ancient concrete used 5000 years ago in China [22] did not use steel the cement close to today s low-heat Portland cement had carbonated, and had helped to maintain the long-term soundness of the material. Based on such information, the leaching resistance of carbonated concrete and Pozzolan material was evaluated. The dissolution equilibrium relationships... 

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