Portland Cement at www.japanese-home-gardens.com

The resulting cement, produced from the formerly discarded grappiers, was of much higher quality than that obtained from the unsintered material. This fact was firmly established by the English cement manufacturer L. C. Johnson in 1845, and the term "portland cement" has since been applied solely to the cement made from the sintered material. This period marks the real beginning of the portland cement industry.

(5) Portland cement concrete. This is made by mix-ng Portland cement, sand, stone or gravel, and water. Portland cement is produced by mixing together argil-aceous and calcareous materials (such as clay or shale md limestone), heating them to a high temperature, and ;rinding the resulting clinker to a fine powder. (6) Miscellaneous materials. These are blast furnace ilag, seashells, coral rock, caliche (in natural deposits), ind the residue of the spontaneous combustion of waste 'rom lignite coal mines. They are useful in road sur-acing because they do not soften when it rains or break eadily under wheel loads.

Types of Portland Cement. Five types of port-land cement are included in the standard specifications of the American Society for Testing Materials and the Federal Specifications Board. The properties of each depend in great part on the relative proportions of the compounds described in the preceding section. Typical compositions of the five standard types of portland cement are given in the Table on page 158.