Foamed Concrete using Red Gypsum and Palm Oil Fuel Ash: A Sustainable Building Material

. Concrete is the most commonly used building material. Even then, it has a drawback that it hasheavy density. Hence, researches are progressing everywhere to develop a new building material, which has low density, less water absorption as well as economical. And here lies the importance of foamed concrete. Foamed concrete is a type of lightweight concrete in which stable foam is used as the main ingredient. Stable foam is produced from standard foaming agent using a foam generator. The peculiarity of foamed concrete is that no coarse aggregate is used in it. An attempt is made in this research to use palm oil fuel ash as a partial replacement for cement and red gypsum as a partial replacement for manufactured sand. Both of these materials are waste materials and are abundantly available. The concrete made up of this will be more sustainable as well as economical. By adjusting the addition of stable foam, foamed concrete of various densities can be developed. Foamed concrete blocks made up of these materials can be used for load bearing as well as non-load bearing masonry works. It has been observed that the addition of Palm Oil Fuel Ash and Red Earth has improved the properties of foamed concrete.


Introduction
Foamed concrete is a special type of concrete in which coarse aggregate is completely avoided.Here, stable foam is used as one of the ingredients, which makes the concrete as light as possible.Foamed concrete consists of cement, fine aggregate, water and stable foam.This type of concrete can be easily pumped and they are self-compacting.The application of this type of concrete apart from ordinary concrete is increasing day by day.The use of foamed concrete blocks for the construction of partition walls will reduce the total load coming over the structure, which will totally reduce the size of the structural elements considerably leading to an economical construction.The present study is to make the concrete more economical.Hence, it has been decided to replace cement partially with Palm Oil Fuel Ash (POFA) and to replace fine aggregate partially with red gypsum.POFA can be used as a partial replacement of cement in concrete due its high pozzolanic properties.The use of these industrial waste materials make the concrete more economical as well as environment friendly.Light weight foamed concrete is usually prepared by mixing stable foam, with cement mortar slurry.Stable foam is produced from a suitable foaming agent with the help of a foam generator.Foaming agents are of two types, protein based and synthetic based.Here, synthetic based foaming agent was used for the study.The quantity of foam determines the characteristics of foamed concrete i.e.; lightness, strength and insulation property.Here, the research aims to investigate the effects of red gypsum and palm oil fuel ash as replacement of cement and fine aggregate respectively.The production of light weight foamed concrete incorporated with red gypsum and POFA could benefit towards achieving a sustainable building material.So POFA and red gypsum become a good substitute for cement and fine aggregate

Need for the Research
With the recent upsurge in environmental concerns, Carbon dioxide emission is a very important factor for describing durability and sustainability of any building material.Building sector is one of the largest energy-consuming sectors in the world.In many cases, production processes of the building materials are not sustainable.Apart from this, heavy weight hollow/solid concrete blocks, which are used as infills in almost all the multistoried framed structures cause increase in dead load on various structural elements leading to large cross sectional areas to beams, columns etc, This will lead to uneconomical cross sections of structural elements.Considering all these facts into account, an attempt is taken in this research to minimize the use of cement by replacing it with POFA and manufactured sand with red gypsum.The lightweight building blocks made out of this can be very well used as an alternate building material for the construction of partition walls in framed structures.The density of such building blocks varies from 300-1800kg/m 3 .The density is controlled by varying the addition of stable foam in the concrete mix.Minimum percentage of foam to be added is 20%.Hence, the total load coming over the structure can be reduced considerably thereby the sizes of structural elements can be reduced leading to more economical structures.Kearsley and Wainwright (2002) have conducted studies on fly ash based foamed concrete and have reported that high fly ash content resulted in a reduction in compressive strength at early ages.Further, it has been revealed that strength has been improved after one year, even the replacement was up to 75% of the weight of cement.Nambiar and Ramamurthy (2006) have conducted studies on foamed concrete using fly ash.It has been reported that the strength to density ratio was higher at lower densities with the addition of Class F fly ash as a substitute for fine aggregate.It is to be noted that Pulverized River sand finer than 300 microns was used for their study.The filler cement ratio selected for the study was 1:1, which means that the cement content was high.Nambiar and Ramamurthy ( 2007) have conducted studies on sorption characteristics of foam concrete and was found that the sorption values were lower than the corresponding base mix and the values got reduced with an increase in foam volume.The study has been conducted by replacing fine aggregate with fly ash.It has been inferred that the reduction in water absorption and sorptivity with foam volume was attributed to the reduction in paste content in foamed concrete.Further, it has been identified that the increased paste volume due to reduced foam content will contribute to the sorption of fly ash mixes.Raman et al. (2011) have conducted studies on concrete with rice husk ash and fly ash and have come out with better results.It has been observed that fly ash is an excellent substitute for cement while making concrete.Jose et al. ( 2020) have conducted studies on foamed concrete using cement replaced with ground granulated blast furnace slag (GGBFS).It has been observed that 30% of cement can be substituted with GGBFS for better compressive strength, Jose et al. ( 2021) have observed that fly ash can be excellently used as a substitute for cement by around 40% for achieving better compressive strength.In another study, conducted by Jose et al. (2021), it has been revealed that 70% of manufactured sand can be very well substituted with quarry fines without any compromise to compressive strength.

Materials
Red gypsum is a by-product obtained during the extraction of titanium dioxide from ilmenite.It was collected from M/s Travancore Titanium Products Ltd. near Kochuveli, Trivandrum, Kerala and Palm Oil Fuel Ash is the residue from palm oil production and was collected from M/s Oil Palm India Ltd. at Anchal, Kollam.Kerala.Synthetic type foaming agent obtained from Tamil Nadu was used as foaming agent.53 grade ordinary Portland cement was used for the production of foamed concrete.

Properties of Materials
Preliminary tests were carried out to determine the properties of materials and are presented in the following sub heads.

Cement
The cement used was 53 grade ordinary Portland cement and its properties are presented in Table 1.

Fine Aggregates
In the literature, it can be seen that river sand was used as the fine aggregate.Since the extraction of river sand is strictly banned by the Government, manufactured sand was used as fine aggregate instead of that.For the production of foamed concrete, fine aggregates finer than 300 microns are used.If large sized particles were used, it causes the collapse of air bubbles leading to formation of large bubbles causing formation of voids inside the concrete.This will cause decrease in density as well as compressive strength.The test results of manufactured sand are presented in Table 2.

Red Gypsum
The chemical composition and test results of Red Gypsum are presented in Tables 3 and 4 respectively.

Palm Oil Fuel Ash
The chemical composition of POFA is presented in Table 5.

Experimental Investigation
The of the research is to produce a sustainable and economical foamed concrete block.As it contains waste materials produced as byproducts such as red gypsum and POFA partially replacing fine aggregate and cement respectively, the environmental pollution and other environmental hazards regarding the disposal of these waste materials can be reduced.Use of cement can be minimized thereby reducing environmental problems caused during manufacture of cement.Hence, a sustainable and eco-friendly building block can be produced economically.The mix proportions are presented in Table 6.

Compressive Strength
Compressive strength of cube specimen with various percentages of POFA and RG were tested using compression testing machine and the results are presented Table 7. Fig. 1 gives an idea about the variation of compressive strength with the addition of POFA and RG.

Dry Density
The dry density test results obtained for foamed concrete specimen with various percentages of red gypsum and Palm Oil Fuel Ash were carried out and results are presented in Table 4.3.

Conclusions
The conclusions drawn from this research are listed below.
• The maximum compressive strength obtained for foamed concrete using red gypsum and palm oil fuel ash as partial replacement for fine aggregate and cement respectively is 9.1N/mm 2 • Water absorption of foamed concrete decreases with percentage replacement of POFA and Red Gypsum.
• Maximum value of water absorption was 3.82% for 30% replacement for both cement and fine aggregate.
• Maximum dry density is found at 10% replacement of POFA and RG which is 1700kg/m 3 • Since considerable amount of industrial waste was used in the study, it is found to be cost effective, eco-friendly and thus a sustainable material can be produced.

Fig. 3 .
Fig. 3. Variation of dry density with variation in POFA and RG

Table 1 .
Test results on properties of cement

Table 2 .
Test results on Manufactured sand

Table 3 .
Chemical composition of red gypsum

Table 4 .
Test results on properties of red gypsum

Table 5 .
Chemical composition of POFA

Table 6 .
Mix proportion of concrete