Concrete blocks are made from a mixture of Portland cement,gravel,sand and water.The product is a light grey colored block with a finely textured surface and high compressive strength. Weight of the block depends on its size of course but the commonest variety weighs in at around 38 to 43 lbs.
The concrete mix used to make concrete blocks has less water and sand than concrete used for general construction purposes. This makes for a dry quite stiff mixture which retains its shape when emptied from the mold.
Cinder blocks are made by using coal cinders or volcanic cinders instead of gravel and sand in the concrete mix. The product is a dark grey colored block with a coarse to medium surface texture. compressive strength is less than that of standard blocks. Insulation qualities of the block are higher and sound deadening properties are improved with this type of block. A common cinder block weighs aboput 26 to 33 lbs.
Lightweight concrete blocks are maded by using expanded clay,slate or shale instead of sand and gravel. Expanded clay,shale and slate are made by crushing the raw material to small size then heating to 2000 degrees Fahreheit(1093 degrees centigrade).The heat causes organic material in the basic materials to vaporise and puff up the clay. a lightweight block of this type is used only in non load bearing walls and partitions and commonly weighs 22 to 28 lbs.
The concrete mix may also have chemicals added to hasten drying time,improve compressive strength or workability of the materials. colored pigments are sometimes added to produce colored blocks.The surface of the block is sometimes glazed for decoration or to prevent chemical dissolution.
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