Hydraulic cements are materials that set and harden after being combined with water, as a result of chemical reactions with the mixing water, and that, after hardening, retain strength and stability even under water. The key requirement for this strength and stability is that the hydrates formed on immediate reaction with water be essentially insoluble in water.
Most construction cements today are hydraulic, and most of these are based on Portland cement, which is made primarily from limestone, certain clay minerals, and gypsum in a high temperature process that drives off carbon dioxide and chemically combines the primary ingredients into new compounds.
Non-hydraulic cements include such materials as non-hydraulic lime and gypsum plasters, which must be kept dry in order to gain strength, and oxychloride cements, which have liquid components. Lime mortars, for example, “set” only by drying out, and only gain strength very slowly by absorption of carbon dioxide from the atmosphere to re-form calcium carbonate through carbonatation.
The most important use of cement is the production of mortar and concrete – the bonding of natural or artificial aggregates to form a strong building material, which is durable in the face of normal environmental effects.
Mortar is a binding agent used in the construction of clay brick, concrete masonry, and natural stone masonry walls and, to a lesser extent, landscape pavements. Modern mortars are improved versions of the lime and sand mixtures historically used in building masonry walls. Masonry mortar is composed of one or more cementitious materials, such as masonry cement or Portland cement and lime, clean sand, and sufficient water to produce a plastic, workable mixture.
Mortars are closely related to concrete, but generally do not contain coarse aggregate. Mortars function with the same calcium silicate-based chemistry as concrete and grouts, bonding with masonry units into a contiguous, weatherproof surface in the process. Masonry cement or Portland cement-lime mortars are usually formulated to address job-specific requirements including setting time, rate of hardening, and extended workability.
Concrete Masonry Units (CMU, Cinder Block, Concrete Block)
A concrete masonry unit or foundation block is a large rectangular block used in construction. Concrete blocks are made from cast concrete, i.e. Portland cement and aggregate, usually sand and fine gravel for high-density blocks. Lower density blocks may use industrial wastes as an aggregate. Those that use cinders (fly ash or bottom ash) are called cinder blocks in the United States, and are called breeze blocks (breeze is a synonym of ash) in the United Kingdom (U.K.). Clinker blocks use clinker as aggregate. Clinker is a general name given to waste from industrial processes, such as coke, coal, slag, charcoal, grit, and other waste materials. Concrete blocks that do not contain cinders are often mistakenly called cinder or breeze blocks in everyday speech. Lightweight blocks can also be produced using aerated concrete.
Concrete blocks are usually produced with hollow cores or centers to reduce weight or improve insulation. The use of block work allows structures to be built in the traditional masonry style with layers (or courses) of overlapping blocks. Blocks come in various sizes. In the United States, the most common size is 8 in × 8 in × 16 in (20 cm × 20 cm × 41 cm); the actual size is usually about 3/8 in (1 cm) smaller to allow for mortar joints. In the UK, blocks are usually 44 cm × 21.5 cm × 10 cm excluding mortar joints (approximately 17.3 in × 8.5 in × 3.9 in).
Concrete block (when reinforced with concrete columns and tie beams) is a very common building material for the load-bearing walls of buildings, in what is termed CBS construction for Concrete Block Structure. Suburban Homes, in the U.S. typically employ a concrete foundation and slab with a concrete block wall on the perimeter.
Terra Cotta Block and Stone
Terra Cotta block and stone were predominately used in the 19th Century, and early in the 20th Century as material for wall construction. In the late 20th and now in the 21st Century, these products are used as fascia for above grade outside wall facing of brick, stone, etc., providing a decorative, durable surface, which is not load bearing.