Investigation of Rice Husk Ash (RHA) as a Supplement in Cement for Building Applications
Emmanuel B Ettah1, Jerome G Egbe2*, Emmanuel S Ubi2 and Ekei E Okon2
1Physics department, Cross River University of Technology, Nigeria
2Civil Engineering department, Cross River University of Technology, Nigeria
Submission: June 09, 2018;Published: July 20, 2018
*Corresponding Author: Jerome Egbe, Civil Engineering department, Cross River University of Technology, Calabar, Nigeria,
How to cite this article: Emmanuel B E, Jerome G E, Emmanuel S U, Ekei E O. Investigation of Rice Husk Ash (RHA) as a Supplement in Cement for
Building Applicationsl. Civil Eng Res J. 2018; 6(2): 555681. DOI:10.19080/CERJ.2018.06.555681
An investigation of Rice husk ash Pozzolan as a supplement in cement for building applications was carried out. A controlled burning of rice husk ash (RHA) at 5000C produced amorphous Silica (SiO2). The rice husk ash (RHA) was substituted for cement in proportions of 0%, 5%, 10%, 20% and 30% of concrete. The concrete was cured for 7 days, 14 days, 21 days and 28 days respectively. It was observed that 20% replacement of Rice husk ash (RHA) provides the optimum strength. Comparison of mixtures with particle sizes of 600 microns, 425 microns, 300 microns, 212 microns, 150 microns and 75 microns, showed that 75 microns provide the optimum strength. X-ray fluorescence (XRF) analysis was performed to determine the content of various chemical oxides in RHA, which indicated that Mg 0.9%, Si 81.8%, P 5.48%, K 3.19%, Ca 1.80%, Mn 0.417%, Fe 0.782%, Zn 0.140% and Ru 0.270%. X-ray diffraction (XRD) analysis to determine low crystallinity of the samples showed the peak value at 26.66 known to be the quartz primary.
The utilization of pozzolanic materials in cement and concrete manufacturing has increased significantly. RHA is an agro waste product and it indicates a high amount of silica which is a very good value for workability. Rice husks are the natural sheaths that form on rice grains during their growth; these are removed during the milling of rice, although these seem to have no commercial interest. However, it can be made useful through a variety of thermochemical conversion processes .
In the majority of rice producing Countries, most of the husks produced from the processing of rice are either burnt or dumped as a waste. Rice husk is unusually high in ash compared to other biomass fuels; it has close to 20% of ash as a by-product . Ash is 92-95% silica, highly porous and lightweight, with an external surface area. So with large ash content and silica content in the ash, it becomes economical to extract silica from ash which takes care of ash disposal . The ideal temperature for producing RHA is between 6000 to 7000 S. Patil and B. Patil . Rice husk ash (RHA) is a term describing all types of ash produced from burning rice husks which vary considerably according to burning techniques. According to . The silica in the ash undergoes structural transformations depending on conditions such as time and temperature of combustion. At 5000C to 7000C amorphous ash is formed and at a temperature greater than this, crystalline ash is formed . These types of silica have different properties and it is important to produce ash of the correct specification for the particular end use. Despite the importance of rice husk ash, few academic studies have been carried out in Nigeria to find the elemental content of the ash using Neutron Activation Analysis Technique X-ray diffraction analysis to determine the atomic and molecular structure of the compounds in the ash. The applicability of the X-ray fluorescence to determine the concentration of the chemical elements and the thermal conductivity test is to determine the insulating properties of the material.
Pozzolans are materials containing reactive silica and alumina which on their own have little or no binding property but when mixed with lime in the presence of water, will set and harden like cement.
Furthermore, pozzolans are important addictive aggregates in the production of alternative cementing materials to ordinary Portland Cement (OPC). Alternative blocks of cement provide an excellent technical option to OPC at a much lower cost and
have the potential to make a significant contribution towards
the provision of low-cost building materials and consequently,
According to he discussed that; Pozzolans can be used in
combination with lime and OPC, he further stresses that the
Pozzolans will greatly improve the properties of lime-based
mortars, concretes and renders suitably for use in a wide or range
of building applications. Alternatively, they can be blended with
OPC to improve the durability of concrete and its workability, and
considerably reduce its cost, According to Cook and Vienna.
However, Ghassan and Hilmi, focused on the study of rice husk
ash and its uses as a cement replacement material and investigated
the properties of rice husk ash (RHA) produced by using a Ferrocement
furnace. The XRD analysis has been extensively been used
in conducting and verifying the presence of amorphous silica in
the ash. Furthermore, the average particle size and percentage on
concrete workability, fresh density, superplasticizer (SP) content
and the compressive strength were also studied. The concluded
that RHA concrete gave an excellent improvement in strength
for 10% replacement (30.8% increment compared to the control
mix), and up to 20% of cement could be valuable replaced with
RHA without adversely affecting the strength.
Kartini et al, , rice husk ash pozzolanic material for
sustainability]. An intensive study on RHA was conducted to
determine its suitably from the various grade of concrete (Grade
30, 40, 50) studied. In their conclusion it was revealed that up to
30% replacement of OPC with RHA has the potential to be used
as partial cement replacement (PCR), having good compressive
strength performance and durability, thus have the potential of
using RHA as PCR material and this can contribute to sustainable
Sudisht et al, discuss the effect of rice husk ash on cement
mortar and concrete. They find out that workability compressive
strength and durability are three basic properties of concrete.
They concluded that reduction in water absorption, from results
obtained from six test concrete and three tests on mortar sample,
was observed that up to 10% RHA with concrete and mortar
enhances all properties and it is observed that 12.5% of Rice
Husk Ash by mass of cement as the optimum are to be added in
the concrete production M20 particularly when the husk is burnt
under field condition to utilize the easily available and low-cost
resources for betterment of concrete structure with respect to
economy, durability and strength.
Patnaikuni, et al. coined out studies on the determination of
compressive strength of different grades of rice husk ash-an Ecofriendly
concrete and has evolved as an innovative technology,
capable of achieving the status of being an outstanding
advancement in the sphere of concrete technology. The
investigated that the utilization of rice husk ash (RHA) will reduce
the dumping of rice husk as well as reduce the construction cost.
Investigation for the determination of residual compressive
strength of M30 and 40 grades of RHA concretes exposed at
different temperature were carried out almost all specimens
of M30 and 40 grades of RHA concrete and normal concrete
exhibited zero strength at a temperature of 10000C. It shows that
concrete cannot withstand a temperature of 10000C and above.
The concluded that compressive strength of RHA concrete was
higher at a temperature below 5000C and decreases above 5000C.
Omotola carried out an investigation on instrumental analysis
of rice husk ash. He finally showed that rice husk ash (RHA) is one
of the most silica raw materials containing about 90-98% silica
after complete combustion among the family of other agro-wastes.
Ash samples from rice husks of five origins were prepared at two
different temperatures, 5000C and 1000OC respectively and the
ash content evaluated at each temperature. X-Ray Diffraction
(XRD), X-Ray Fluorescence (XFR), Instrumental Neutron Activation
Analysis (INAA) alongside with a simple chemical process were
the techniques adopted for the characterization of each ash
sample heated to 10000C in terms of silica content. While XRD
analysis indicates the compounds present in each sample, XRF
and INAA analysis indicate only trace (impurity) elements present
in each ash sample. He concluded that XRF and INAA showed that
RHA had a very low impurity concentration indicating that rice
husk which is an agricultural waste is a potential source of silica,
and the result was confirmed by the XRD analysis where almost all
the compounds presents where silicates and the simple chemical
process employed confirmed the very high silica presence of
between 93-96%, and the XRF result shows a high purity level of
94-98.9% while the INAA shows a purity level of 88.4%.
Omotola & Onojah, in their research work they reported
that the potentiality of rice husk is a good source of high
technological materials. That every year approximately 600
million tons of paddy are produced globally. These give around
120 million tons of rice husk (RH) and 21 million tons of rice husk
ash (RHA) annually. There are four major uses of rice husk ash:
in steel, cement, refractory bricks and semiconductor industry.
Besides these, it can be utilized in many civil construction works.
The concluded that the use of rice husk for electricity generation
in an efficient manner is likely to transform this agricultural waste
into a valuable fuel for industries and thus help in boosting the
farm economy and rural development and at the same time, waste
disposal of rice husk is addressed while generation of employment
will become possible.
The materials used in this work were rice husk, burning
furnace, hammer mill, sieve machine, mortal and weight balance.
Ground granulated blast furnace slag and RHH were used in
this research as components. The (America society for testing
and materials (ASIM) Type I) was used to compare the different
properties including physical, chemical binding, flow and
compressive strength were collected from local stations in Obubra, Ogoja, and Bekwara Local Government Areas in Cross River State,
known to be major rice producers in Cross River State Nigeria, the
Ikom-Abi river sand which passed through a 4.75mm sieve and
had a specific gravity of about 2.89 was used as fine aggregate
x-ray fluorescene (XRF) was done for the chemical composition
using a Bruker brand XRF machine. The Abrasion machine was
used grinding of the RHA; the detailsof the furnace were reported
by Zain etal.
Where, W/R is the water / RHA cement ratio, W/C is the water
/ cement ratio which gives the strength as that of W/R ratio. The
value of e can be obtained by routines laboratory tests.
The equation 2.2 can be applied to all pozzolanic materials
and it can be used to relate the strength of RHA concrete to that
of OPC concrete having the same W/C ratio and values of e can be
obtained from the plotted RHA and OPC concrete, Nelson S .
By rearranging these equations, we have general form
Where, wc is the free water content, ST and Sc are the weights
of water required to provide the standard consistence of the
RHA cement and OPC respectively. The f is the proposed design
parameter that can be obtained by routine laboratory tests [9-13].
The amount of free water for lubrication of aggregate is given below:
Where, LAT = free water content for lubrication of aggregate,
LCr = free water content for lubrication of RHA
WT = free water content of the RHA concrete
ST = weight of water required to achieve standard
consistence of RHA cement (Table 1).
The husks were properly burned for the voltaic hydrocarbon
to escape, the husk was poured into crucibles which were placed
in the muffle furssnace for combustion to a temperature of 500°C.
The ash obtained at this temperature was allowed to cool in the
muffle furnace for some hours and with the use of forceps and
content of the crucibles were transferred into a pan [14,15].
The paste and mortar were prepared according to ASTM
C305-06 specification. The compaction of the mold was achieved
manually. Finally, samples were immersed into a curing tank at
room temperature until the desired testing ages of 7, 14, 21 and
28 days were achieved.
The RHA was ground into a fine powder, hammer mill was
used for this purpose, and was sieve with different sieve sizes,
with the help of a sieving machine of the aperture of 600 microns,
425 microns, 300 microns, 212 microns, 150 microns and 75
microns, and this becomes our pozzolans, 0%, 5%, 10%, 20%, and
30% ratio of the pozzolanic were mixed with part of cement and
laterite, were cast and cured for 7 days, 14 days, 21 days and 28
days, and tested with the help of a compression testing machine to
know the optimum strength .
The rice husk ash (RHA) heated at temperature of 500oC were
analyzed with x-ray fluorescence (XRF) analysis, indicating the
compounds present in the sample: Mg, Si, P, K, Ca, Ti, Cr, Mn, Fe, Ni,
Cu, Zn, Rb, Sr, Y, Zr, Ba and Eu. From the test carried out, it revealed
that Si contains the highest percentage of silica with 81.8% with
the x-ray diffraction (XRD) analysis also showing the presence of
SiO2 as an amorphous silica. The peak value at 26.66 known to
be quartz primary is weak thus a low level of crystallization. See
Table 2 for the chemical properties of the materials.
The result of the different mixed ratio of portees at 75 microns,
150 microns, 212 microns, 300 microns, 425 microns and 600
microns, cast and cured for 7 days, 14 days, 21 days and 28 days.
It was tested with the help of a compression test machine shown
in Table 3 below .
A graph of strength at various portee size of 75 micron, 150
micron, 212 micron, 300 micron, 425 micron and 600 micron
against number of days of 7 days, 14 days, 21 days and 28 days.
Indicating that 75 micron has the optimal strenght  (Figure 1).
The result of the different mixed ratio of pozzolan at 0%,
5%, 10%, 20%, and 30%. Cast and cured for 7 days, 14 days, 21
days and 28 days and also tested with help of a compression test
machine is shown in Table 4 below.
A graph of strength at various pozzolan of 0%, 5%, 10%, 20%,
and 30%. Against a number of days of 7 days, 14 days, 21 days and
28 days. Indicating that pozzolan at 20% has the optimal strength
[19-22] (Figure 2).
The ashes heated at 5000C were milky white in colour
indicating that there is no un-burnt carbon present. The ashes
were sieve with different sieve sizes with the help of a sieving
machine. Sieve analysis was carried out, and a graph was plotted
indicating that the particles size were coarse grains. The result of
the ratio mixed for 5%, 10%, 20%, and 30% Pozzolan indicated
that 20% ratio has the optimum strength while the result of 600
microns, 425 microns, 300 microns, 212 microns, 150 microns
and 75 microns indicated that the 75 micron has the optimum
strength. Correctly proportioned Pozzolanic cement concrete is
suitable for most forms of general construction but, as with all
concretes, proper attention must be paid to the curing process.
The extended setting time and slow early strength development of
pozzolanic cement require extended curing times [22-25].
For a given water/cement ratio, pozzolanic cement will
produce a significantly lower 28 days compressive strength than
Portland cement. Therefore, the free water/cement ratio required
for given concrete strength must be reduced. Effectively, this
means that the cement content for given water content should be
increased. Typically around 30% more cement would be required
for 16/20 concrete when compared with Portland cement. The
XRF analysis indicated 20 elements, which are as follows; Mg, Si, P,
Ca, Ti, V, Cr, Mn, Fe, Ni, Zn, Rb, Sr, Y, Zr, Ru, Ba, and Eu. In all showed
that Si with 81.8% contains the highest percentage of silica. The
main impurities include P(5.48%), Ka (3.19%) and Ca (1.80%).
The result of XRD analysis showed a low peak intensity for the
quartz primary. Therefore, rice husk as an agricultural waste can
be converted into valuable product which has so many industrial
and domestic applications.
Pozzolan produced from rice husk ash (RHA) is coarse grains
material. The concrete Mixed and cured for different days showed
that 20% Pozzolan and 75 micron has the optimum strength.
Strength the experimental result revealed that salaamed RHA
could be used as substitutes of cement provided that these
materials are processed properly with the maintenance of high
fineness and with the use of a chemical activator. The physical
and chemical test result of the selected Pozzolanic material from
Obubra, Ogoja and Bekwara contain a high amount of silica and
sufficient amount of the major oxides; however, they perform
credibly as an alternative binder in the presence of chemical
Pozzolan produced from rice husk ash (RHA) is recommended
to develop low-cost building material in order that more of the
lower - income sector of developing countries may obtain
adequate housing, and to develop lime- Pozzolan cement (LPC)
AND LPC- based building material for construction of low-cost
housing for the poor.