Planetary boundary layer. The planetary boundary layer (PBL) is also known as the atmospheric boundary layer (ABL). It is the lowest part of the atmosphere and its behavior is directly influenced by its contact with the ground. It responds to surface forcings in a timescale of an hour or less.
Portland cement is the most common type of cement in general use around the world, used as a basic ingredient of concrete, mortar, stucco, and most non-speciality grout. It was developed from other types of hydraulic lime in England in the mid 19th century and usually originates from limestone.
Some basic definitions used in cement and concrete. A few useful basic definitions follow, since the meanings of the words 'cement' and 'concrete' are rather blurred in general use. Portland Cement: Material made by heating a mixture of limestone and clay in a kiln at about 1450 C, then grinding to a fine powder with a small addition of gypsum.