Portland cement is one of the most widely used materials in the construction industry. Although unmodified concrete and cement mortar systems (i.e., those not containing a polymer latex modifier) have adequate properties for many construction applications, there remain many areas in which such properties, particularly strength properties, are not acceptable.
Latex-modified portland cement systems have been developed that radically change the physical properties of unmodified concrete and cement mortar. Of such latex-modified cement systems, the addition of vinylidene chloride polymer latexes to portland cement have provided compositions having exceptionally high strength. British Pat. No. 967,587 is directed to such latex-modified portland cement systems and serves to illustrate the unique characteristics of such compositions as contrasted with other latex-modified cement systems.
Prior known vinylidene chloride polymer latexes have often been found, however, to be colloidally unstable in portland cement compositions (primarily due to high pH and high calcium ion concentrations in such cement compositions) and thus were characterized by a substantial bleeding of the latex modifier from the cement with resultant losses in desired properties of the cement systems.
U.S. Pat. No. 3,250,736 discloses a means for greatly reducing bleeding of vinylidene chloride polymer latex from cement compositions by addition, during the manufacture of the latex, of a comonomeric surfactant, e.g., 2-sulfoethyl methacrylate. Utilization of surfactants of this type is successful in providing latex-modified cement compositions having excellent resistance to bleeding and which, after placement and curing, produce good dry bond strengths, compressive strengths, tensile strengths, flexural stengths, and chemical and solvent resistance.
Such latex-based cement additives, however, have been found to be deficient with regard to obtaining optimum mechanical and shear stability, freeze/thaw stability and workability, i.e., the rheological characteristic generally known as a "bingham" body. Further, prior known modified cement compositions fail to provide desired adhesion to cementitious substrates, e.g., to concrete surfaces such as pavements and bridge decks, cement blocks, bricks and the like to which they are conventionally applied.
USPTO Backgrounds
USPTO Backgrounds