Mechanical and durability properties of blended cement mortar by incorporating palm oil fuel ash and bentonite / Md Kamrul Hasan

Faculty of Civil Engineering Technology

Thesis (Master of Science) -- Universiti Malaysia Pahang Al Sultan - 2025

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Due to the quickening industrialization and urbanization processes, Portland cement, a key concrete component, is one of the most widely used building material globally. The cement sector contributes significantly to world carbon dioxide (𝐶𝑂􀬶) emissions, producing at a rate of 1 tonne 𝐶𝑂􀬶 per tonne of cement production, corresponding to 5-7% of total global emissions. Therefore, supplementary cementitious materials (SCMs) such as fly ash (FA), blast furnace slag, and silica fume (SF) are frequently used in cement-based materials (CBMs) as partial cement replacements to mitigate and minimize the environmental impact of cement production. However, these materials are the industry's by-products, and their supply is anticipated to reduce soon. Thus, researchers increasingly focus on using natural and agricultural waste products in cement replacement. In this research, palm oil fuel ash (POFA), an agro-industrial waste by-product from palm oil mills, and bentonite (BT), a naturally occurring substance created through the transformation of volcanic ash and rocks following significant exposure to water, are used as a partial cement substitute ranging from 0% to 20% in 5% increments in blended cement mortar (BCM). Meanwhile, the other mortar components, including water, fine aggregate (FAA), and superplasticizer (SP), remained constant across all mortar mixes. First, characterization and morphological analysis tests were conducted to assess the suitability of using POFA and BT. Subsequently, workability, dry bulk density, compressive strength, flexural strength, and dynamic modulus of elasticity were measured at curing intervals of 7 to 90 days to evaluate the fresh and mechanical properties of BCM. Additionally, water absorption, acid and sulfate resistance, and porosity were measured at the same curing intervals to assess the durability properties of BCM. Finally, response surface methodology (RSM) was used to validate the mechanical properties of BCM with varying combinations of POFA and BT at different curing ages. The results showed that adding 0-10% BT and 10-20% POFA to the mortar specimens achieved a successful pozzolanic activity index (PAI) greater than 75%. The highest flow diameter value of 223.5 mm was observed when 20% POFA replaced the cement. Additionally, incorporating BT into the mortar mix resulted in the lowest dry bulk density. The highest compressive strength of 49.52 MPa was reached at 90 days, along with flexural strength and dynamic elastic modulus values of 6.39 MPa and 36.48 GPa, respectively. In terms of durability, adding 20% POFA resulted in the lowest water absorption and porosity. The acid and sulfate resistance tests also revealed that 20% POFA led to the lowest mass loss, strength loss, and expansion compared to the addition of BT after 60 and 90 days of curing. This is because, POFA's high silica content reacts with calcium hydroxide (𝐶𝑎(𝑂𝐻)􀬶) to form additional calcium silicate hydrate (C-S-H) gel, which strengthens and densifies the concrete. In contrast, BT acts mainly as a filler with low pozzolanic reactivity and may cause microcracks due to its swelling and waterretentive nature, reducing its effectiveness. However, a mix containing 5% BT and 15% POFA demonstrated better performance than the control mix in terms of fresh properties, mechanical strength, and durability after 60 and 90 days of curing. Besides, ANOVA analysis indicated that curing age had a greater effect on compressive and flexural strengths, while the combined effect of POFA and BT addition was more influential on the dynamic modulus of elasticity than curing age. Overall, the findings suggest that by understanding the mechanisms of POFA and BT in cement mortar, it is possible to develop durable, cost-effective, and environmentally friendly green concrete for the betterment of the construction industry.