An answer to your question can be deduced from the following synthesis references:

1- Malhotra and Mehta (2004) reported that ground RHA with fine  particle size than OPC improves concrete properties.including higher substitution amounts in lower water absorption values and the addition of RHA caused an increment in the

compressive strength.

2- Adewuyi and Ola (2005) have carried out research on the binary blends of OPC with different pozzolanic material in making cement composites. Supplementary cementious materials have been proven to be effective in meeting most of the requirements of durable concrete.

3- Habeeb and Fayyadh (2009) have investigated the influence of RHA average particle size on properties of concrete and found out that at early ages the strength was comparable, while at the age of 28 days.the finer RHA exhibited higher strength than the sample with coarser RHA.

4- Lee et al (2005) in their study concluded that some of the waste products like Rice husk which possess pozzoalanic properties and used in the blended cements include fly ash.silica fume, volcanic ash.corn cob ash hence providing good strength properties to concrete.

5- Gunduz and Ugur (2004) in their study concluded that the greatest advantages of light weight concrete are its low density, allowing for construction on the ground with only moderate bearing capacity, the use of less reinforcement, the

ability to construct taller structures.greater economy in lifting and use of more thermally efficient material. The unit weight of rice husk concrete can be lowered by either using porous materials, there fore lightweight aggregates instead of ordinary

ones,introducing air into mortar or removing the fine fraction of aggregate and then by partially compacting the concrete. In all cases.the main goal is to introduce voids into aggregates and mortar or between mortar or aggregate.

6- Khedari et al (2001) have studied the characteristic properties of  various light weight aggregates like pumice,coal slag.flying ash,rice husk,straw,saw dust.cork granules, wheat husk.coconut fiber and coconut shell used in partial replacement for concrete production. The organic waste used in light weight concrete is

mainly of plant origin. They concluded that by using plant waste that is abundantly found in rural areas, it may be possible to construct cheaper and good quality agricultural constructions. Sari and Pasamehmetoglu (2004) have concluded that rice husk as an organic waste.is a significant problem in rice cultivating

areas because it is not used profitably and is generally burned after harvest, which causes environmental problems. Generally concrete with a unit weight of less than 2000 kg/m3 is classified in the light concrete class. According to ACI (American Concrete Institute) Committee, light weight concrete is divided into three categories on the basis of its strength and density.

The following attached papers may be helpful 

The following attached papers may be helpful 2

please refer the following link.

http://krishisanskriti.org/journal11/Paper%206.pdf

http://eaas-journal.org/survey/userfiles/files/v5i402%20Civil%20Engineering(1).pdf