The common and ordinary type of concrete hollow blocks are those with four core. However , there are other types specially designed for architectural and structural purposes. One of which is the concrete blocks with two hollow core or cells.

The purpose of manufacturing these types of blocks is to create a wider cell to accommodate concrete and steel reinforcement. The estimating method is similar with the ordinary blocks using the constant value of 12.5 pieces per square meter and 25 pieces for half block although this half block is usually determined by direct counting.

It will be noticed that the thickness of the block is only used in estimating the cement mortar for block laying and as filler of the hollow core. It is the side portion which is being used in estimating the number or quantity more particularly the Area method.

With the introduction of these special types of hollow blocks, housing projects are being constructed eliminating the use of reinforced concrete posts because the wall is designed as a continuous inter-locking support of the roof framing. Corner block and Stretcher blocks are used on corners provided with reinforcement instead of concrete post. With this method, cost of forms is felt as a big savings.

If the cement mortar is solely used in block laying and as filler of the hollow core, cost will be substantially high because of the higher content of the cement in proportion with sand. However, cost could be reduced materially if the hollow core filler is a mixture of mortar and gravel. Experience proved that the masonry worker could hardly observed the used of concrete as filler because it is more convenient for them to use only mortar rather than concrete. Hence, estimating cement mortar as filler is a safe estimate.

http://www.philippine-builder.com/home/construction-basics/272-special-types-of-concrete-hollow-blocks.html

Rice hull ash used in hollow blocks 

By Helen Flores (The Philippine Star) Updated October 23, 2008 12:00 AM Comments (0) 

Amid the rising cost of construction materials, the Department of Science and Technology (DOST) is

promoting the use of rice hull ash as ingredient for making hollow blocks.

The DOST’s Forest Products Research and Development Institute (FPRDI) recently developed rice hull

ash cement (RHAC) hollow block — a combination of refined rice hull ash, cement and sand.

Rice hulls or rice husks are the hard protecting coverings of palay grains.

“These blocks are as durable as the concrete hollow blocks yet much cheaper,” the FPRDI said in a

statement.

“The rice hull contains high-temperature forms of silica, which in amorphous state (burned between 700 to

750 degrees Celsius) is pozzolanic or possesses binding property,” it said.

“But at very high temperatures (beyond 750 degrees Celsius), the amorphous silica turns crystalline, thus

losing its binding property,” it added.

The FPRDI said pozzolana is either a natural or an artificial material usually with high silica content and often

with alumina and others, but generally with lesser chemical components than cement.

“It is not cementitious by itself, but when finely ground and mixed with lime sets and hardens at ordinary

temperature in the presence of water, as in cement,” the FPRDI said.

Since natural pozzolanas are usually of volcanic origin and occur in only a few regions of the world, artificial

pozzolanas such as rice hull ash cement serve as cement substitutes, it said.

The FPRDI said RHAC blocks can be mass-produced for low-cost housing projects, while at the same time

ease the disposal of rice hull waste.

“The raw materials are readily available and inexpensive, while the processing equipment can be made

locally. Ash from incinerated rice hull can replace considerably commercial cement used in construction,” it

said.

Earlier, a researcher from San Fernando, La Union discovered the potential of rice husk ash as

supplementary material in cement paste and concrete.

Marshal Calica of the Saint Louis College said rice husk ash can be used as “admixtures”

in cement   paste  and concrete because it contains silica, a compound that serves as cement “binder.”

He said replacing 10 percent of cement with rice husk ash does not mean sacrificing the strength of

concrete.

Calica said people could save P20 for every P200 worth of commercial cement bag.

http://www.philstar.com/Article.aspx?articleId=409297

Rice hulls (or rice husks) are the hard protecting coverings of grains of rice. In addition to protecting rice

during the growing season, rice hulls can be put to use as building material, fertilizer, insulation material,

or fuel.

Contents

 [hide]

1 Production

2 Use

o 2.1 Chemistry

o 2.2 Pet food fiber

o 2.3 Building material

o 2.4 Pillow stuffing

o 2.5 Fertilizer

o 2.6 SiC production

o 2.7 Fuel

o 2.8 Brewing

o 2.9 Juice extraction

o 2.10 Rice husk ash

3 See also

4 External links

5 References

[edit]Production

Rice hulls are the coating for the seeds, or grains, of the rice plant. To protect the seed during the growing

season, the hull is made of hard materials, including opaline silica and lignin. The hull is mostly

indigestible to humans.

One practice, started in the seventeenth century, to separate the rice from hulls, it to put the whole rice

into a pan and throw it into the air while the wind blows. The hulls are blown away while the rice fell back

into the pan. This happens because the hull isn't nearly as dense as the rice. These steps are known as

winnowing. During the milling process, the hulls are removed from the grain to createbrown rice, the

brown rice is then milled further to remove the bran layer to become white rice.

[edit]Use

A number of rice-producing countries, (e.g. Thailand), are currently conducting research on industrial

uses of rice hulls. Some of the current and potential applications are listed below.

[edit]Chemistry

Rice hulk can be used to produce mesoporous molecular sieves (e.g., MCM),[1][2] which are applied

as catalysts for various chemical reactions, as a support for drug delivery system and

as adsorbentin waste water treatment.

[edit]Pet food fiber

Rice hulls are the outermost covering of the rice and come as organic rice hulls and natural rice hulls.

Rice hulls are an inexpensive byproduct of human food processing, serving as a source of fiber that is

considered a filler ingredient in cheap pet foods.[3]

[edit]Building material

Rice hulls are a class A insulating material because they are difficult to burn and less likely to allow

moisture to propagate mold or fungi. It has been found out that when burned, rice hull produces

significant amounts of silica. For these reasons it provides excellent thermal insulation.

[edit]Pillow stuffing

Rice hulls are used as pillow stuffing. The pillows are loosely stuffed and considered therapeutic as they

retain the shape of the head.

[edit]Fertilizer

Rice hulls are organic material and can be composted. However, their high lignin content can make this a

slow process. Sometimes earthworms are used to accelerate the process.

Usingvermicomposting techniques, the hulls can be converted to fertilizer in about four months.

[edit]SiC production

Rice hulls are a low-cost material from which silicon carbide "whiskers" can be manufactured. The SiC

whiskers are then used to reinforce ceramic cutting tools, increasing their strength tenfold.[4]

[edit]Fuel

With proper techniques, rice hulls can be burned and used to power steam engines. Some rice mills

originally dispose of the hulls in this way

[edit]Brewing

Rice hulls can be used in brewing beer to increase the lautering ability of a mash.

[edit]Juice extraction

Rice hulls are used as a "press aid" to improve extraction efficiency of apple pressing.[5]

[edit]Rice husk ash

The ash produced after the husks have been burned, (abbreviated to RHA), is high in silica. A number of

possible uses are being investigated for this. These uses include

aggregates and fillers for concrete and board production

economical substitute for microsilica / silica fumes

absorbents for oils and chemicals

soil ameliorants

as a source of silicon

as insulation powder in steel mills

as repellents in the form of "vinegar-tar"

as a release agent in the ceramics industry

as an insulation material for homes and refrigerants

IN Kerala, India- Rice husks (Umikari- in malayalam)was universally used for over centuries in

cleaning teeth - before toothpaste replaced it.