*Proceeding Paper* **Utilizing Corn Cob Ash and Bauxite as One-Part Geopolymer: A Sustainable Approach for Construction Materials †**

**Raheel Arif \*, Ammar Iqtidar and Safeer Ullah Khattak**

**\*** Correspondence: raheelarif021@gmail.com

† Presented at the 5th Conference on Sustainability in Civil Engineering (CSCE), Online, 3 August 2023.

**Abstract:** This research focused on creating sustainable geopolymer mortar using waste materials such as corn cob ash (CCA) and bauxite. The CCA was obtained by burning corn cobs in an open environment and then further treated at 600 ◦C to remove carbon impurities. The resulting ash was ground to improve reactivity and used as a binder. Sodium silicate was used as an activator for geopolymerization. The geopolymer was prepared by combining the binder with fine aggregate, ground bauxite, and CCA in different proportions. The curing process involved heating the samples at 70 ◦C for 24 h followed by ambient temperature curing. Compression testing was conducted at 7, 14, and 28 days to assess the strength and durability of the geopolymer mortar. Testing was performed according to ASTM standards.

**Keywords:** geopolymer; corn cob ash; bauxite; construction; materials

#### **1. Introduction**

Concrete is the most used building material all around the world. Concrete is a composite material composed of fine and coarse aggregate bonded together with cement. Many researchers have tried to reduce the harmful environmental effects of cement by replacing it with supplementary cementations materials such as rice rusk ash, fly ash, ground granulated blast furnace slag, and corn cob ash (CCA) [1]. Pakistan produced almost 7.9 million tons of corn from 2021–2022 and this production is increasing every year at a rate of 4.97% [2]. One possible way of utilizing CCA is its use as secondary cementitious material (SCM). Studies have shown that CCA possesses all the properties which would make it suitable to be used as an SCM [3]. Bauxite is a naturally occurring rock which is rich in alumina. It is found in abundance in the Kotli AJK region. The purpose of using bauxite with CCA in this research is that it will not cause any sudden depletion of natural resources as no other industry utilizes it and it is considered waste. It is easily mineable as it is soft rock and contains 45–50% Al2O3, not more than 20% Fe2O3, and 3–5% Silica [4].

This research will be limited to only the synthesis of one-part geopolymer mortar (GM). Different mass ratios of CCA and bauxite will be used to find the optimum combination of CCA and bauxite that can be adopted for preparation of a high-strength geopolymer. The research aims to contribute to sustainable construction practices and explore the potential of agricultural waste materials in geopolymer technology.

#### **2. Research Methodology**

The research was conducted as per the following procedures and details:

#### *2.1. Materials Preparation*

Corn cob was burnt in an open environment before burning in a controlled environment at 600 ◦C for 2 h. The obtained ash was crushed in a jar mill and then passed through sieve No. 200. Bauxite was jar milled and passed through sieve No. 200.

**Citation:** Arif, R.; Iqtidar, A.; Khattak, S.U. Utilizing Corn Cob Ash and Bauxite as One-Part Geopolymer: A Sustainable Approach for Construction Materials. *Eng. Proc.* **2023**, *44*, 18. https://doi.org/ 10.3390/engproc2023044018

Academic Editors: Majid Ali, Muhammad Ashraf Javid, Shaheed Ullah and Iqbal Ahmad

Published: 29 August 2023

**Copyright:** © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

Department of Civil Engineering, COMSATS University Islamabad, Abbottabad Campus, Abbottabad 22020, Pakistan; ammariqtidar@gmail.com (A.I.); safeer@cuiatd.edu.pk (S.U.K.)

#### *2.2. Mortar Preparation*

Mix design for GM is shown in Table 1 below:

#### **Table 1.** Mix design for GM.


Cubes were cast for different tests according to mix design.

#### *2.3. Curing*

Curing was conducted at the high temperature of 70 ◦C in an oven for 7, 14, and 28 days.

#### *2.4. Tests*

Sieve analysis was conducted on fine aggregates (ASTM C136-05) [5]. Temperatures of mortar mixes were checked (ASTM C1064) [6]. Initial setting time of GM was noted through Vicat needle apparatus in accordance with ASTM Standard C191 [7]. Slump test was conducted on all the cubes of GM (ASTM C143) [8]. Compressive strength test was performed to check the compressive strength of GM in a universal testing machine (UTM) (ASTM C109) [9]. Cubes were observed for appearance of cracks.

#### **3. Results**

#### *3.1. Sieve Analysis of Fine Aggregates*

The sand was obtained from Lawrencepur quarry. Sieve analysis was conducted to determine the fineness modulus of the sand. Equation (1) was used to find the fineness modulus. Fineness modulus helps in determining the particle size of sand. It affects the mechanical properties of the GM. The sieves were arranged in the following way according to their openings per linear inch: 4, 8, 16, 30, 50, 100, Pan.

The fineness modulus is given by:

$$\text{Finness Modulus} = \frac{\Sigma \text{ Percent cumulative retained on sieve upto 160 micro meter}}{100} \quad (1)$$

The fineness modulus was calculated as 2.54, which was within limits. Fineness modulus for fine aggregate should be within the range 2.3 to 3.2.

#### *3.2. Temperature of the Mortar*

Temperature plays a crucial role in the hydration and curing process of construction materials. In this research, the temperature range of 15.6 ◦C to 26.7 ◦C suggests that the curing conditions were controlled within an acceptable range, promoting proper hydration and curing of the GM.

#### *3.3. Setting Time of the Mortar*

Initial setting times for different mortar mixes are presented in Table 2 below:

**Table 2.** Initial setting times of different mortars.


#### *3.4. Compressive Strength*

Compressive strength for all the GM mixes were checked by testing them with the universal testing machine. A total of three cubes were tested for determination of strength for one day. The average of three cubes was taken as the strength of that day. Beside GM cubes, OPC mortar cubes were also tested for the sake of comparison. Compressive strengths of different mix designs are shown in Table 3. After compressive tests, it was found that the compressive strength of C20B80 cubes was the highest of all. It was 62 percent more than that of OPC at 28 days of curing. It can be seen in Table 3 below that the compressive strengths of all the GM cubes were greater than those of OPC mortar cubes.


#### **Table 3.** Compressive strengths of different mix designs.

#### *3.5. Cracks*

It can be seen in Figure 1 that no cracks were observed in GM cubes. The absence of cracks in the GM cubes is a positive outcome, indicating that the mortar exhibited good structural integrity and resistance to cracking under the tested conditions. It suggests that the mixture proportions, including the binder-to-sand ratio and the incorporation of waste materials like corn cob ash and bauxite, were appropriate and resulted in a cohesive and robust mortar. Furthermore, the absence of cracks in the GM cubes may also be attributed to the curing conditions employed during the testing. The curing process, including the temperature and duration, likely played a significant role in allowing the mortar to develop its strength and preventing the formation of cracks.

**Figure 1.** Geopolymer cubes.

#### **4. Conclusions**

The following conclusions can be drawn from the conducted study:


**Author Contributions:** Experimental methodology, research, R.A.; writing, editing and figures, A.I.; research, supervision, and writing—review, S.U.K. All authors have read and contributed to revising the paper. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** Not applicable.

**Acknowledgments:** The authors express their gratitude to Muhammad Faisal Javed for his supervision and visualization of research.

**Conflicts of Interest:** The authors declare no conflict of interest.

#### **References**


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