Concrete Blocks: History and Raw Materials

A ______ block is primarily used as a building material in the construction of walls.

The term ______ refers to the fact that the blocks are formed and hardened before they are brought to the job site.

Most ______ blocks have one or more hollow cavities, and their sides may be cast smooth or with a design.

In use, ______ blocks are stacked one at a time and held together with fresh concrete mortar to form the desired length and height of the wall.

The first hollow ______ block was designed in 1890 by Harmon S.Palmer in the United States.

The concrete commonly used to make ______ blocks is a mixture of powdered portland cement, water, sand, and gravel.

Concrete masonry units are manufactured in three classes, based on their ______: lightweight units, medium-weight units, and normal-weight units.

By 1905, an estimated 1,500 companies were manufacturing ______ blocks in the United States.

Concrete blocks were initially patented by Harmon S.Palmer in the year ______.

Steam is then gradually introduced to raise the temperature at a controlled rate of not more than 60°F per ______.

There are three basic forms of concrete block, ______, cellular and hollow, and within each type a variety of products are available.

The nominal dimension is greater than its specified (or ______) dimension by the thickness of the mortar joint, usually 10 mm.

The properties of concrete blocks depend to a varying degree on the type and proportions of the ______ materials, the manufacturing process, and the mode and duration of curing employed.

The density of concrete blocks is largely a function of the ______ density, size and grading, degree of compaction or aeration and the block form.

Concrete masonry units can be classified as ______ bearing (ASTM C90) and non–______ bearing (ASTM C129).

The compressive strength of concrete blocks is dependent mainly on their ______ composition, degree of compaction and to a lesser extent on the aggregate type and curing normally used.

In general, for a given set of materials the strength of a concrete block will increase with its ______.

The typical range for dry ______ is 500-2100 kg/m3.

Well-graded ______, gravel, and crushed stone are used to manufacture normal-weight units.

Lightweight aggregates such as pumice, scoria, cinders, expanded clay, and expanded ______ are used to manufacture lightweight units.

The sand and gravel are stored outside in piles and are transferred into storage bins in the plant by a ______ belt as they are needed.

The portland cement is stored outside in large vertical ______ to protect it from moisture.

The dry materials then flow into a stationary ______ where they are blended together for several minutes.

The compacted blocks are pushed down and out of the ______ onto a flat steel pallet.

The pallets of blocks are conveyed to an automated ______ or loader which places them in a curing rack.

The kiln is an enclosed room with the capacity to hold several racks of blocks at a time. There are two basic types of ______ kilns.

In this type, the blocks are held in the kiln for one to three hours at room temperature to allow them to harden ______.

The compressive strength of individual concrete masonry units is determined by capping the unit and applying load in the direction of the ______ of the unit until failure.

The amount of water absorption of concrete masonry units is controlled by ______ standards to reduce the effect of weathering and to limit the amount of shrinkage due to moisture loss after construction.

The absorption of concrete masonry units is determined by immersing the unit in water for ______ hours.

The magnitude of dimensional changes, to a varying degree, is largely influenced by the ______ materials (mainly the aggregate), mix proportions and the process of block-manufacturing adopted.

Drying shrinkage of concrete blocks can be reduced significantly by ensuring that the units are properly ______ and by preventing them from becoming excessively wet on site prior to their use.

In general, concrete blocks are adequately durable for most normal ______.

Fair faced blocks with strength in excess of ______ Mpa should be used in extreme conditions of pollution (chemical attack) and weather (frost attack).

Open-texture blocks are more susceptible to ______ attack than other blocks owing to the freedom with which water can move within the block on freezing.

Strength Requirements of Load Bearing and ______ are specified in ASTM C90.

Efflorescence in concrete blocks normally consists of ______ carbonates formed as a result of a reaction between the corresponding free hydroxides brought to the surface and atmospheric carbon dioxide.

Concrete blocks have good ______ properties, but their actual fire-endurance is controlled by numerous factors.

The thermal conductivity of a concrete block is largely dependent on its ______ density as can be seen from the relationship.

Autoclaved aerated concrete and lightweight concrete blocks have relatively low ______ conductivities.

The thermal conductivity of a concrete block is further affected by its ______ content, increasing as the moisture content increases.

Most concrete blocks of 100 mm thickness can provide an adequate resistance to fire for up to 2 hours if ______ or up to 4 hours if non-load-bearing.

As a general rule, concrete blocks of a certain thickness can provide an adequate resistance to fire for up to 2 hours if ______ or up to 4 hours if non-______.

The thermal conductivity of a concrete block is also affected by the type of ______ used in its manufacturing process.

Efflorescence of the type found in clay bricks is rarely a problem with ______ blocks.