Sandcrete

Sandcrete is a building material.

It is made of portland cement and sand in a ratio of circa 1:8, so it is similar but weaker than mortar, for which the ratio is circa 1:5.

Sandcrete is usually used as hollow rectangular blocks, often 45 cm wide, 15 cm thick, and 30 cm high, and yellow/whitish in colour, with hollows that run from top to bottom and occupy circa 1/3 of the volume of the block.

Sandcrete blocks are joined together with mortar.

Picture

I don't own a picture of sandcrete blocks, but you can find some pictures of finished and half-finished buildings made with them [http://ghanadistricts.com/districts/?r=10&_=43&inc=projects here] .

trength and usage

The final compressive strength of sandcrete can be as high as 4.6 N/mm2, which is much less than concrete's 40 N/mm2, so sandcrete is not suited for load-bearing columns, and is mainly used for walls, but is also used for foundations if no suitable alternative is available.

As material for walls, it's strength is less than that of fired clay bricks, but sandcrete is considerably cheaper.

Sandcrete is the main building material for walls of single-storey buildings (such as houses and schools) in countries such as Ghana and Nigeria.

Measured strengths of commercially available sandcrete blocks in Nigeria was found to be between 0.5 and 1 N/mm2, which is well below the 3.5 N/mm2 that is legally required there.

This may be due to the need of the manufactureres to make the price low, and since the main cost-factor is the portland cement, they reduce that, which results in a block that starts behaving more like loose sand.

There is current research in using organic ash to replace portland cement, which is better than simply using less portland cement.

Adding coarse aggregate

Addition of coarse aggregates (stones) has been tried, since it is a cheap way to increase compressive strength, but since the cement content of sandcrete is small, so is the amount of water that is added to the sand/cement mix to cure it, and adding more solid materials makes the mix much less fluid, so it becomes too difficult to cast into blocks.

External links

* [http://lejpt.academicdirect.org/A08/58_70.htm "Study of blocks made of sandcrete/rice-husk-ash mixtures"]
* [http://www.crystal-netbook.info/e126290/e128109/e128188 "Foundation materials"]
* [http://cat.inist.fr/?aModele=afficheN&cpsidt=13776632 "Adding coarse aggregate"] (non-free material)