Experimental and ANN-based prediction of the mechanical properties of fly ash geopolymer concrete

Effect of Alkali Activators on Mechanical and Durability Properties of Fly Ash based Geopolymer Concrete

The production of ordinary Portland cement (OPC) is one of the major sources of carbon dioxide emissions in the construction industry, creating a need for more sustainable building materials. Fly ash-based geopolymer concrete (GPC) has emerged as a promising alternative because it can reduce environmental impact while providing good engineering performance. This study examines how different proportions of sodium hydroxide (NaOH) and sodium silicate (Na₂SiO₃) affect the strength and durability of GPC compared with conventional OPC concrete. Initial trials using NaOH:Na₂SiO₃ ratios of 1:0.5 and 0.5:1 were conducted to identify a suitable curing condition. The main investigation was then carried out using geopolymer mixes with activator ratios of 1:1 and 0.5:1, all oven-cured at 80°C, with OPC concrete used as the control mix. Compressive, split tensile, flexural, shear, and pull-out strengths were evaluated using Indian Standard methods, while durability was assessed through water penetration and X-ray diffraction (XRD) tests. The results showed that heat curing significantly improved early-age strength, especially for the 0.5:1 mix. Although OPC concrete achieved slightly higher 28-day strength, the geopolymer mixes showed comparable mechanical performance, lower water penetration, and clear evidence of successful geopolymerization.

Sustainable self-compacting concrete incorporating fly ash and rice husk ash: experimental, statistical, and environmental assessment

Experimental Investigation of the Influence of Fly Ash Fineness on the Mechanical Properties of M50 Grade Geopolymer Concrete

The manufacture of Ordinary Portland Cement (OPC) is a significant source of global carbon dioxide emissions, creating a strong need within the construction sector for more sustainable binder alternatives. Fly ash-based geopolymer concrete (FAGC) has developed as a potential sustainable alternative to conventional cement concrete by completely replacing OPC with Class F fly ash activated using sodium hydroxide (NaOH) and sodium silicate (Na₂SiO₃). Although many investigations have studied the effects of alkali-activator type, molarity, and proportion on geopolymer concrete, relatively limited attention has been given to the influence of fly ash fineness, expressed through particle size and specific surface area, on highstrength M50 geopolymer concrete. The present investigation compares two fineness levels from the same fly ash source—an asreceived coarse fraction and a processed/ground fine fraction—to determine their effect on the mechanical behaviour of M50 geopolymer concrete while maintaining the alkali-activator composition and other mix parameters unchanged. Specimens are evaluated for compressive, split-tensile, flexural, shear, and pull-out strength in accordance with the applicable Indian Standard (IS) codes to identify the fly ash fineness that provides the most favourable overall mechanical performance. The findings are intended to contribute to the development of sustainable high-strength geopolymer concrete and promote its potential use as a structural substitute for conventional M50 grade cement concrete

Performance and Durability Assessment of Sustainable Green Concrete Incorporating Fly Ash and Rice Husk Ash

The global demand for concrete has escalated rapidly due to the swift expansion of residential and commercial infrastructure. This phenomenon has consequently intensified cement manufacturing and aggravated anthropogenic carbon dioxide (CO2) emissions. To tackle these environmental issues and restrict fluid-induced microcracking in concrete elements, this experimental work evaluates the engineering properties of modified M20 concrete utilizing agro-industrial byproducts as alternative cementitious binders. In this study, Ordinary Portland Cement (OPC) was partially substituted with Class F fly ash at replacement levels of 30%, 35%, and 40%, alongside rice husk ash (RHA) at 5% and 10% by weight, establishing six distinct replacement categories. A total of seventy-seven cube specimens (150 mm × 150 mm × 150 mm) were fabricated to investigate workability, water absorption, compressive strength development, and water permeability resistance. The laboratory outcomes demonstrate that high cement substitution rates significantly alter the internal pore network, thereby governing both the strength gain and long-term durability behavior. Slump values across all formulated design mixes exceeded 100 mm, classifying the fresh concrete as collapsed slumps with high fluid consistency. Although the unblended control mixture displayed the highest 28-day compressive strength (19.53 N/mm²) and superior fluid penetration resistance (80.44 mm depth), the ternary blend containing 5% RHA and 40% fly ash was identified as the optimal eco-friendly formulation. This specific matrix yielded a 28-day compressive strength of 17.79 N/mm² and recorded the highest resistance to water penetration among all modified cohorts (141.00 mm). Even though the high volume of fly ash prevented the blended mixes from satisfying the empirical threshold of standard M20 concrete, the formulated green concrete exhibits promising technical viability for structural applications under the M15 classification. Ultimately, this research validates viable pathways for recycling natural waste products to minimize infrastructure deterioration and promote circular economy strategies within the construction sector.

Experimental Investigation on Mechanical and Durability Properties of M60 Grade High-Performance Fly Ash-Based Geopolymer Concrete

Ordinary Portland cement (OPC) production is energy intensive and emits significant amount of carbon dioxide, thus the need for sustainable alternatives in the construction industry. This study experimentally examines the mechanical properties and durability of the high-performance geopolymer concrete (HPGPC) with 100% Class F fly ash as the sole binder. Sodium hydroxide and sodium silicate solutions were used for activation of the geopolymer binder and the geopolymer specimens were oven cured at 80°C for 48 h. OPC concrete was prepared with conventional M60 grade mix proportion and water cured as a control sample for comparison. The mechanical properties evaluated were compressive strength at 7, 14, 28, 56 and 90 days and split tensile strength at 7, 14 and 28 days. Durability was tested by rapid chloride permeability test (RCPT), 5% sulphuric acid attack test and water permeability. The geopolymer concrete at 28 days showed a compressive strength of 68.58 MPa which is equal to the conventional concrete of 69.18 MPa, and a split tensile strength of 4.83 MPa was also achieved, which is equal to the conventional concrete of 5.08 MPa. The geopolymer concrete also had excellent durability, with a charge passed of 319 coulombs compared with 578 coulombs for conventional concrete. The geopolymer concrete exhibited lower weight and strength loss under acid exposure of 2.02% and 14.4%, respectively, after 90 days of exposure, while the OPC concrete exhibited weight and strength loss of 6.19% and 26.8%, respectively, after 90 days of exposure. Also, the penetration depth of water has decreased from 14.5 mm to 11.2 mm. The outcome shows that the mechanical properties of this 100% fly ash based HPGPC are also approximately equal to OPC-based test sample and the durability is better, suggesting that this material has potential as a sustainable material for high-performance structural applications.

Geopolymer Concrete Using Bottom Ash as Fine Aggregate

The present study explores performance of geopolymer concrete (GPC) using GGBFS as a Entire replacementfor OPC and bottom ash incorporated as a substitute for natural fine aggregate. Bottom ash was incorporated at replacement levels ranging from 0% to 50%, while NaOH and (Na₂SiO₃) served as alkaline activators. The workability of fresh concrete was evaluated using slump cone and compaction factor tests, whereas compressive strength and split tensile strength were determined after 7 and 28 days of ambient curing. The results showed that the mechanical properties improved with increasing bottom ash content up to an optimum level and decreased thereafter due to the porous nature of bottom ash. The mix containing 30% bottom ash (M-GPCB30) exhibited the best overall performance in terms of strength and durability. The findings demonstrate the potential of bottom ash as a partial alternative to river sand in GPC, enhancing sustainability in the construction industry by the utilization of industrial by-products and reducing environmental impacts.