Rice hull ash used in hollow blocks

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.