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Questions and Answers
A ______ block is primarily used as a building material in the construction of walls.
A ______ block is primarily used as a building material in the construction of walls.
concrete
The term ______ refers to the fact that the blocks are formed and hardened before they are brought to the job site.
The term ______ refers to the fact that the blocks are formed and hardened before they are brought to the job site.
precast
Most ______ blocks have one or more hollow cavities, and their sides may be cast smooth or with a design.
Most ______ blocks have one or more hollow cavities, and their sides may be cast smooth or with a design.
concrete
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.
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.
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The first hollow ______ block was designed in 1890 by Harmon S.Palmer in the United States.
The first hollow ______ block was designed in 1890 by Harmon S.Palmer in the United States.
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The concrete commonly used to make ______ blocks is a mixture of powdered portland cement, water, sand, and gravel.
The concrete commonly used to make ______ blocks is a mixture of powdered portland cement, water, sand, and gravel.
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Concrete masonry units are manufactured in three classes, based on their ______: lightweight units, medium-weight units, and normal-weight units.
Concrete masonry units are manufactured in three classes, based on their ______: lightweight units, medium-weight units, and normal-weight units.
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By 1905, an estimated 1,500 companies were manufacturing ______ blocks in the United States.
By 1905, an estimated 1,500 companies were manufacturing ______ blocks in the United States.
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Concrete blocks were initially patented by Harmon S.Palmer in the year ______.
Concrete blocks were initially patented by Harmon S.Palmer in the year ______.
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Steam is then gradually introduced to raise the temperature at a controlled rate of not more than 60°F per ______.
Steam is then gradually introduced to raise the temperature at a controlled rate of not more than 60°F per ______.
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There are three basic forms of concrete block, ______, cellular and hollow, and within each type a variety of products are available.
There are three basic forms of concrete block, ______, cellular and hollow, and within each type a variety of products are available.
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The nominal dimension is greater than its specified (or ______) dimension by the thickness of the mortar joint, usually 10 mm.
The nominal dimension is greater than its specified (or ______) dimension by the thickness of the mortar joint, usually 10 mm.
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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 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.
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The density of concrete blocks is largely a function of the ______ density, size and grading, degree of compaction or aeration and the block form.
The density of concrete blocks is largely a function of the ______ density, size and grading, degree of compaction or aeration and the block form.
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Concrete masonry units can be classified as ______ bearing (ASTM C90) and non–______ bearing (ASTM C129).
Concrete masonry units can be classified as ______ bearing (ASTM C90) and non–______ bearing (ASTM C129).
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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.
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.
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In general, for a given set of materials the strength of a concrete block will increase with its ______.
In general, for a given set of materials the strength of a concrete block will increase with its ______.
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The typical range for dry ______ is 500-2100 kg/m3.
The typical range for dry ______ is 500-2100 kg/m3.
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Well-graded ______, gravel, and crushed stone are used to manufacture normal-weight units.
Well-graded ______, gravel, and crushed stone are used to manufacture normal-weight units.
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Lightweight aggregates such as pumice, scoria, cinders, expanded clay, and expanded ______ are used to manufacture lightweight units.
Lightweight aggregates such as pumice, scoria, cinders, expanded clay, and expanded ______ are used to manufacture lightweight units.
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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 sand and gravel are stored outside in piles and are transferred into storage bins in the plant by a ______ belt as they are needed.
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The portland cement is stored outside in large vertical ______ to protect it from moisture.
The portland cement is stored outside in large vertical ______ to protect it from moisture.
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The dry materials then flow into a stationary ______ where they are blended together for several minutes.
The dry materials then flow into a stationary ______ where they are blended together for several minutes.
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The compacted blocks are pushed down and out of the ______ onto a flat steel pallet.
The compacted blocks are pushed down and out of the ______ onto a flat steel pallet.
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The pallets of blocks are conveyed to an automated ______ or loader which places them in a curing rack.
The pallets of blocks are conveyed to an automated ______ or loader which places them in a curing rack.
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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.
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.
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In this type, the blocks are held in the kiln for one to three hours at room temperature to allow them to harden ______.
In this type, the blocks are held in the kiln for one to three hours at room temperature to allow them to harden ______.
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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 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.
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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 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.
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The absorption of concrete masonry units is determined by immersing the unit in water for ______ hours.
The absorption of concrete masonry units is determined by immersing the unit in water for ______ hours.
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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.
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.
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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.
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.
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In general, concrete blocks are adequately durable for most normal ______.
In general, concrete blocks are adequately durable for most normal ______.
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Fair faced blocks with strength in excess of ______ Mpa should be used in extreme conditions of pollution (chemical attack) and weather (frost attack).
Fair faced blocks with strength in excess of ______ Mpa should be used in extreme conditions of pollution (chemical attack) and weather (frost attack).
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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.
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.
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Strength Requirements of Load Bearing and ______ are specified in ASTM C90.
Strength Requirements of Load Bearing and ______ are specified in ASTM C90.
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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.
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.
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Concrete blocks have good ______ properties, but their actual fire-endurance is controlled by numerous factors.
Concrete blocks have good ______ properties, but their actual fire-endurance is controlled by numerous factors.
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The thermal conductivity of a concrete block is largely dependent on its ______ density as can be seen from the relationship.
The thermal conductivity of a concrete block is largely dependent on its ______ density as can be seen from the relationship.
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Autoclaved aerated concrete and lightweight concrete blocks have relatively low ______ conductivities.
Autoclaved aerated concrete and lightweight concrete blocks have relatively low ______ conductivities.
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The thermal conductivity of a concrete block is further affected by its ______ content, increasing as the moisture content increases.
The thermal conductivity of a concrete block is further affected by its ______ content, increasing as the moisture content increases.
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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.
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.
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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-______.
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-______.
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The thermal conductivity of a concrete block is also affected by the type of ______ used in its manufacturing process.
The thermal conductivity of a concrete block is also affected by the type of ______ used in its manufacturing process.
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Efflorescence of the type found in clay bricks is rarely a problem with ______ blocks.
Efflorescence of the type found in clay bricks is rarely a problem with ______ blocks.
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Study Notes
Blocks
- A concrete block is a building material used in wall construction, also known as a concrete masonry unit.
- The first hollow concrete block was designed by Harmon S. Palmer in the United States in 1890.
- By 1905, around 1,500 companies were manufacturing concrete blocks in the United States.
Raw Materials
- Concrete blocks are made from a mixture of powdered portland cement, water, sand, and gravel.
- The mixture produces a light gray block with a fine surface texture and high compressive strength.
- Concrete masonry units are manufactured in three classes: lightweight, medium-weight, and normal-weight units, based on their density.
Manufacturing Process
- The process involves mixing, molding, and curing.
- Mixing involves blending dry materials (sand, gravel, and cement) with water and admixture chemicals.
- Molding involves compacting the mixed concrete into blocks, which are then pushed out of molds onto a flat steel pallet.
- Curing involves conveying the blocks to an automated stacker or loader, which places them in a curing rack.
Form and Size
- There are three basic forms of concrete blocks: solid, cellular, and hollow.
- Concrete masonry units are specified by their nominal dimensions, which are greater than their actual dimensions by the thickness of the mortar joint.
- Different types of concrete blocks include solid, cellular, hollow, common, facing, normal, insulating, lintel, quoin, cavity closure, and multipurpose blocks.
Properties
- The properties of concrete blocks depend on the type and proportions of constituent materials, manufacturing process, mode and duration of curing, and form and size of the block.
- Density ranges from 500-2100 kg/m3, depending on aggregate density, size, and grading, degree of compaction, and block form.
- Compressive strength is the basic requirement of concrete blocks, and is dependent on mix composition, degree of compaction, and aggregate type.
- Water absorption is controlled by ASTM standards to reduce weathering effects and limit shrinkage due to moisture loss.
- Dimensional changes occur due to variations in ambient moisture and temperature conditions, influenced by constituent materials, mix proportions, and manufacturing process.
- Durability is generally adequate for most normal applications, but may be affected by extreme conditions of pollution and weather.
- Efflorescence is rarely a problem with concrete blocks, but may occur as a result of a reaction between free hydroxides and atmospheric carbon dioxide.
- Fire resistance is good, with most concrete blocks providing adequate resistance to fire for up to 2 hours if load-bearing or up to 4 hours if non-load-bearing.
- Thermal conductivity is largely dependent on block density, with autoclaved aerated concrete and lightweight concrete blocks having relatively low thermal conductivities.
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Description
Learn about the history of concrete blocks, from their invention to their widespread use, and understand the raw materials used to make them.
