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.
Portland cement is a type of hydraulic cement, which means that when water is added through a process called hydration, it starts the chemical reaction that causes the cement to harden and set, holding the aggregates together in a rocklike mixtureâconcrete.ortland cement is not a brand name. Instead, itâs a generic term for the most prevalent type of cementâjust like stainless is a type of steel, not a trademarked name. A Briton, Joseph Aspdin, developed the building material in the eighteenth century.