Lime Silico-Phosphate Cement

Quick setting silico-phosphate cements have been considered for use as pavement patching material. These are cement compositions which have a sufficiently high and rapidly developed early strength to support normal highway loads within one hour after application. 

Concrete nominally contains 1 part phosphate solution, 1 part magnesia and 4 parts dolomite. Setting usually occurs in less than 30 minutes and up to 50 MPa compressive strength is developed within 4 hours. Factors affecting strength development are the particle size of the wollastonite, the P2O5 content of the liquid, and the liquid/powder ratio. 

X-ray diffraction analysis of this cement system gives only those peaks attributable to wollastonite. It is suggested that an acid-crystal surface interaction occurs, reducing the apparent wollastonite surface area and freeing the bonding constituents for matrix development. Microprobe analysis shows that the matrix binding wollastonite grains contains phosphorus, calcium, silicon, and some aluminum and zinc. 

Typical strength development data of air cured silico-phosphate cement indicate that this system develops about 30% of its 28 day compressive strength in 2 hours. The tensile bond strength, compared with conventional concrete substrates, is very poor.I ] 

A minor amount of blast-furnace fines can be added to the wollas-tonite-sand mixture to decrease the set time ofthe cement. A corresponding reduction of compressive strength also results. The use of 20% blastfurnace fines has resulted in satisfactory properties. 

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Porcelain dental cements were developed by Steenbock [6] who produced silico-phosphate dental material using 50 wt% concentrated phosphoric acid solution and an aluminosilicate glass. Wilson et al. [7] showed that various brands of commercial cements consist of powdered alumina-lime-silica glass mixed with phosphoric acid, which form a hard and translucent product. The phosphoric acid used in these cements is partially neutralized by aluminum oxide. 

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