NOVEL SUPERPLASTICIZER IN REALIZING SELF-COMPACTING GEOPOLYMER CONCRETE AND METHOD OF PRODUCING THE SAME

Abstract

This invention discloses a novel, cement-less, ambient cured self-compacting geopolymer concrete production method with a superior cost-effective superplasticizer, realized through agricultural waste like rice husk, even unprocessed, justifying its field applicability, proceeding towards a sustainable concrete creation. The derivation of the alternate superplasticizer involves the dissolution of unprocessed rice husk in an aqueous sodium hydroxide solution followed by boiling and filtration. This alternate superplasticizer is then utilized to develop an SCGC system suitable for structural applications, incorporating ground granulated blast furnace slag collected from TATA Steel Limited, sodium-based alkaline activators, and natural aggregates. The developed rice husk-derived superplasticizer-based workable SCGC demonstrates superior compressive strength when cured under room temperature conditions than other SCGCs with commercially available superplasticizers. Additionally, it provides an enhanced durability characteristic. Furthermore, the developed SCGC is not only eco-friendly but also economical compared to conventional cement-based/geopolymer concrete. Figure. 1.

Specification

Description:FIELD OF INVENTION
[0001] The present invention pertains to the creation of an innovative superplasticizer derived from agricultural waste and an alkaline solution aimed at producing a novel self-compacting geopolymer concrete utilizing industrial waste materials.
BACKGROUND OF INVENTION
[0002] Concrete is the most extensively used construction material worldwide. Its popularity stems from substantive load-bearing capacity, durability, versatility, low maintenance requirements, availability, and affordability. Ordinary Portland Cement (OPC) is a key component of conventional concrete. Unfortunately, cement production needs a huge amount of energy and releases a massive greenhouse gas into the atmosphere. One ton of OPC manufacture consumes around 80 kWh of energy and emits 0.94 tons of CO2 to the environment (Priya et al. 2024). India produced 370 million metric tons of cement in 2022, around 9% of the total global cement yield (cycles and Text 2023), posing a crippling environmental situation. Additionally, the enormous industrial waste generation leads to severe environmental issues, such as air, water, and soil pollution, affecting adversely the ecosystems and human health (Krishnan et al. 2021). In this context, geopolymer concrete (GPC) has emerged as a sustainable alternative through industrial waste incorporation as a binding material, eliminating the need for cement. Despite these environmental advantages, GPC faces challenges owing to its large viscosity, hindering its global employment. To address this issue, self-compacting geopolymer concrete (SCGC) has been developed, amalgamating the benefits of GPC with the self-compacting characteristics, needed for the placement.
[0003] SCGC primarily consists of binders derived from industrial or agricultural waste, alkaline activators, aggregates, superplasticizers, and additional water. The SCGC self-compacting characteristics are primarily influenced by the superplasticizer dosage and additional water content, with the superplasticizer dosage being the sensitive one. It has been observed that even slight variations in the superplasticizer dosage can significantly affect the flow characteristics and mechanical behavior of SCGC. Thus, the selection and dosage of superplasticizers play a critical role in SCGC production. However, the cost and environmental impact of commercially available superplasticizers remain significant barriers to their widespread adoption.
[0004] The performance of SCGC relies on the process of geopolymerization, involving a reaction between binder or aluminosilicate precursors, such as fly ash or slag, and alkaline activators to form a network of aluminosilicate polymers. In this process, the aluminosilicate precursors dissolve in the highly alkaline solution (e.g., sodium hydroxide or potassium hydroxide), breaking down into silicate (SiO₄⁴⁻) and aluminate (AlO₄⁴⁻) monomers. These monomers then undergo polycondensation, forming a three-dimensional network of aluminosilicate gels, which serve as the primary binding mechanism in geopolymer concrete. Among various aluminosilicate precursors, ground granulated blast furnace slag (GGBFS) has shown the potential to achieve the required strength at ambient temperature curing conditions.
[0005] Superplasticizers, also known as high-range water reducers, adsorb onto the surface of aluminosilicate particles, reducing inter-particle attraction and improving the dispersion of these particles. This enhanced dispersion facilitates the reaction between the precursor and the alkaline activator, resulting in more efficient geopolymerization. Currently, superplasticizers of three generations are commercially available. The first generation, lignosulfonates (Ligno-based), introduced in the 1960s, offers a 5-12% water reduction with improved workability. The second generation, naphthalene sulfonate (Naptha-based), and melamine sulfonate, introduced in the 1970s and 1980s, provided up to 25% water reduction with significant workability enhancement. The third generation, polycarboxylate ethers (PCE-based), introduced in the 1990s, enables up to 30% water reduction. These plasticizers are widely used in construction based on specific project requirements, but their cost and environmental impact continue to pose challenges.
[0006] Meanwhile, rice, a staple food in Southeast India, including Odisha, generates a large amount of rice husk (RH) during its milling. Globally, rice production exceeds 750 million tons annually, resulting in around 150 million tons of husk. India ranks as the second-largest rice producer globally, contributing 24% of total production, with China leading at 28.5%. Rice husk constitutes roughly 20% of the rice's weight and is primarily composed of cellulose (25-33%), hemicellulose (18-21%), lignin (25-31%), and silica (15-20%). Due to its high silica and lignin content, rice husk has limited nutritional value, making it unsuitable as a ruminant feed. The substantial volume of rice husk generated poses serious disposal issues, particularly in Asian countries where open burning is common. This practice contributes to air pollution, soil degradation, and greenhouse gas emissions (Kordi et al. 2024; Shukla et al. 2022). These environmental concerns highlight the need for sustainable solutions, including exploring rice husk's potential applications in construction industries.
[0007] To promote sustainability in construction, researchers have explored methods for utilizing rice husk ash (RHA) in material production concerning SCGC. Rakesh and Rao (2023) proposed a method (IN202341064052) for producing alkali-activated materials using rice husk ash as a precursor or source material. Similarly, Das and Patro (2023) (IN202331066940) developed an alternative alkali activator by combining sodium hydroxide solution and rice husk ash.
[0008] Patents employing RHA as a precursor and alkali activator solution though available, similar research using locally available unprocessed RH as a source of superplasticizer is not available. In this context, the current invention introduces an easy and innovative method for producing an RH-based superplasticizer with the help of an alkaline solution. This involves dissolving RH in an aqueous sodium hydroxide (NaOH) solution intended for the development of a thriving GGBFS-based SCGC. Moreover, the proposed method adopts an ambient temperature curing process for hardened SCGC production, simplifying the overall process, minimizing manpower requirements for curing, and improving field applicability and cost-effectiveness.
OBJECT OF INVENTION
[0009] The main objective of the present invention is to develop a cost-effective and environmentally friendly superplasticizer made from Indian rice husk (RH) for producing SCGC.
[0010] Another objective of the present invention is to study the employed RH- derived superplasticizer impact on the fresh (workability) and hardened concrete characteristics (compressive strength, and durability) of the GGBFS-based self-compacting geopolymer system concerning the commercially available superplasticizer-based SCGC. Also, the microstructural analysis of the crushed SCGC specimen was accomplished to understand the behavior of the hardened concrete characteristics.
[0011] Yet another objective of the present invention is to promote the utilization of RH-based superplasticizers as an alternative to commercially available superplasticizers, thereby directly or indirectly benefiting the construction, rice, and chemical industries.
SUMMARY OF THE INVENTION
[0012] This invention presents a method and composition for producing SCGC, suitable for structural applications employing a self-invented superplasticizer. SCGC thus yielded, utilizes an alternative superplasticizer derived from rice husk (RH), produced by dissolving the RH in an aqueous sodium hydroxide solution. The efficacy of this superplasticizer is demonstrated by utilizing GGBFS as source materials. The resulting SCGC system exhibited acceptable workability, commendable compressive strength, and greater durability characteristics, justifying its suitability in structural applications. The RH-derived superplasticizer-based SCGC presents a dense and compact microstructure concerning the other commercial superplasticizer-based SCGCs, justifying its superiority in strength and durability.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
[0013] The resulting SCGC exhibits commendable outcomes concerning fresh and hardened concrete characteristics, making it suitable for structural applications. The superior results are further justified through its dense and compact microstructure. The following drawings accompany this specification:
[0014] Figure 1: Illustrates a graph showing the preparation of a rice husk-derived superplasticizer solution in producing SCGC specimens.
[0015] Figure 2: Presents a comparison of workability results [(a) Filling ability; (b) Passing ability; (c) Segregation resistance] in SCGC produced through different superplasticizers.
[0016] Figure 3: Presents a comparison of strength development in GGBFS-based SCGC utilizing rice husk-derived and commercially available superplasticizers.
[0017] Figure 4: Shows the durability performances [(a) water absorption; (b) chloride ingression] of SCGC developed through different superplasticizers
[0018] Figure 5: Illustrates the scanning electron microscopy (SEM) results analysis of crushed SCGC samples prepared through Ligno-based and RH-based superplasticizers
DETAILED DESCRIPTION OF THE INVENTION
[0019] The present invention claims a novel method and superplasticizer material composition for producing self-compacting geopolymer concrete suitable for structural applications, using ground granulated blast furnace slag (GGBFS) activated with sodium-based activators with the utilization of rice-husk (RH) derived superplasticizers. The superiority of the innovative RH-based composite has been established concerning different commercial superplasticizer-based composites through fresh and hardened concrete characteristics.
[0020] In an embodiment the superplasticizer composition for producing self-compacting geopolymer concrete comprises: 30% to 35% by mass of sodium hydroxide (NaOH); 5% to 10% by mass of agricultural waste, such as rice husk; and 55% to 60% by mass of water.
[0021] In another embodiment, the superplasticizer composition has the following desirable properties: a specific gravity of 1.38; and a pH value of 7.03.
[0022] In yet another embodiment, the superplasticizer composition is prepared by a method comprising the following steps: dissolving 560 g of NaOH pellets in one liter of water to produce a 14M aqueous sodium hydroxide (NaOH) solution; adding 100 g of rice husk to the aqueous sodium hydroxide solution after 24 hours; stirring the mixed solution for 10-15 minutes; boiling the mixed solution for one hour at 80°C - 100°C; cooling the mixed solution at room temperature for one hour; filtering the solution and storing it in an airtight bottle.
[0023] In yet another embodiment, the self-compacting geopolymer concrete (SCGC), comprising: a self-compacting geopolymer concrete (SCGC) mix solution; a natural river sand as fine aggregate at 1030 kg/m³; and natural coarse aggregate at 650 kg/m³ - 670 kg/m³.
[0024] In yet another embodiment, self-compacting geopolymer concrete (SCGC) mix solution, comprising: an alkali activator solution (AAS); a superplasticizer; and additional water.
[0025] In yet another embodiment, self-compacting geopolymer concrete (SCGC) mix solution has composition mix ratios of 1:2.15:1.36, 1:2.15:1.37, 1:2.15:1.36, and 1:2.15:1.39 to produce four distinct SCGC mix solutions.
[0026] In yet another embodiment, the alkali activator solution (AAS) comprising: a ground granulated blast furnace slag (GGBFS) as the primary binder; a 14M aqueous sodium hydroxide (NaOH) solution and sodium silicate as the activator in a 0.4 ratio.
[0027] In yet another embodiment, self-compacting geopolymer concrete (SCGC) mix solution is designed for M25-grade concrete to produce self-compacting geopolymer concrete (SCGC).
[0028] In yet another embodiment, the self-compacting geopolymer concrete (SCGC) is prepared by a method comprising the following steps: preparing the superplasticizer according to a specified proportion; preparing the self-compacting geopolymer concrete (SCGC) mix solution according to a specified proportion; mixing an alkali activator solution (AAS) with fine aggregate and coarse aggregate in a saturated surface dry condition, then adding the required superplasticizer and additional water; uniformly mixing the resulting mixture for 3-5 minutes using a drum mixer until a homogeneous and plastic mix is obtained; pouring the homogeneous mixture into cubical molds, demoulding the specimens after 48 hours of casting, and allowing ambient curing for 28 days.
[0029] In yet another embodiment, the durability assessment indicates that the SCGC with rice husk-based superplasticizer is comparatively stronger and more durable than commercially available superplasticizer-based geopolymer concretes.
[0030] The GGBFS utilized in this invention was sourced from TATA Steel Limited, Odisha, and its chemical composition was determined using X-ray fluorescence (XRF) analysis, as shown in Table 1. The GGBFS was light in color, with a specific gravity of 2.8. When sieved, 2% of the material, by weight, was retained on a 90 µm sieve. The activator employed in the SCGC mix was a combination of 14 molar sodium hydroxide (NaOH) and sodium silicate solutions such that a ratio of 2.5 is maintained between sodium silicate and sodium hydroxide solution.
Table 1: Chemical composition of GGBS
Material GGBS
SiO2 35.805
Al2O3 16.66
CaO 37.523
Fe2O3 0.82
MgO 6.9
Na2O 0.337
K2O 0.462
TiO2 0.98
ZrO2 0.067
SrO 0.065

[0031] This study introduces an innovative approach to establishing SCGC by utilizing locally available Zone II natural river sand as fine aggregate and 20mm down coarse aggregates, with specific gravities of 2.67 and 2.65, respectively. These inert aggregates contributed to the novel SCGC mix. The water absorption of the fine and coarse aggregates were 1.1% and 2.34%, respectively, with fineness modulus of 2.12 and 6.57. Clean tap water was used as additional water in the mix.
[0032] Three commercially available superplasticizers were sourced from Sika India Pvt Ltd. to compare the SCGC performance with these superplasticizers concerning the SCGC with a rice husk-derived superplasticizer. The commercial superplasticizers were SikaViscoflow 4005 NS (PCE-based), Sikament 2004 NS (Naptha-based), and Sika Plastiment-114 (Ligno-based), with specific gravities of 1.11, 1.18, and 1.12, respectively.
[0033] A novel superplasticizer was prepared by dissolving RH in an aqueous sodium hydroxide (NaOH) solution. The rice husk was collected from a local mill, Annapurna Rice Mill, in Remed Chowk, Sambalpur, Odisha. To prepare the superplasticizer, 560g of NaOH pellets were dissolved in one liter of water to create a 14M solution. Then, 100g of rice husk was added to this solution after 24 hours, stirred for 10-15 minutes, and boiled for one hour at 100°C. The resulting dark brown solution was cooled for two hours, filtered, and stored in an airtight bottle with a specific gravity of 1.38 and a pH of 7.03. The preparation procedure is given in Figure 1.
[0034] SCGC mixes were designed for M25-grade concrete. Ground granulated blast furnace slag (GGBFS) was used as the primary binder, with a combination of sodium hydroxide (14M) and sodium silicate as the activator in a 0.4 ratio. The mix design utilized an alkali activator solution (AAS)/binder ratio of 0.45, with 7% superplasticizer and 21% additional water. Four mixes were prepared: one with rice husk-derived superplasticizer (Mix-4) and three with commercially available Sika superplasticizers [PCE (Mix-1), Naptha (Mix-2), and Ligno-based (Mix-3)].
[0035] The SCGC mixing process was performed in a drum mixer, with 2-3 minutes of dry mixing for aggregates and GGBFS, followed by the slow addition of the activator solution. The superplasticizer, mixed with additional water, was then gradually added, and the wet mixing continued for 3-5 minutes to achieve a uniform mix. The resulting SCGC was subjected to workability tests, poured into molds, and left to cure at 25°C (ambient temperature) to gain strength.
[0036] The workability of the fresh SCGC mixes was assessed using a slump flow test and V-funnel test for filling ability, while the L-box and V-funnel (T5 minutes) tests evaluated passing ability and segregation resistance, respectively. Figure 2 represents the graphical variations of workability outcomes. The results, interpreted according to EFNARC guidelines, indicated that all mixes met the required workability criteria. Table 2 provides the workability permissible limits as per EFNARC guidelines. SCGC mixes prepared with Naptha and Ligno-based superplasticizers exhibited higher workability compared to PCE-based mixes. The rice husk-derived superplasticizer demonstrated acceptable workability (a little lower than the commercial superplasticizers), falling within the required range for self-compacting concrete. Additionally, all mixes passed the passing ability test and are not segregated, indicating all four SCGC mixes are workable and suitable for structural applications.
Table 2: EFNARC (2002) Guidelines
Test Slump Flow (mm) V-Funnel (sec) V-Funnel at 5minutes (sec) L-Box (H1/H2)
Acceptance Range 650-800 6-12 0-3 sec More than V-Funnel 0.8-1

[0037] Figure 3 illustrates the compressive strength of the SCGC mixes and each result is the average of three cubical specimens of 100 mm side. The rice husk-derived superplasticizer achieved a 28-day compressive strength of 37.5 MPa, outperforming the SCGC mixes prepared with PCE (34.2 MPa), Naptha (34.4 MPa), and Ligno-based (32.15 MPa) superplasticizers. All mixes surpassed the target strength for M25 concrete (31.6 MPa), though the Ligno-based mix was close to the threshold value. At 7 and 90 days, similar trends were observed, with the rice husk-based SCGC mix displaying superior early-age strength (20.5 MPa at 7 days) and continued strength gains at later ages too. The PCE and Naptha-based mixes exhibited comparable 28-day strength, but the rice husk-derived mix consistently manifested the highest compressive strength.
[0038] Figure 4 presents the durability assessment of the SCGC mixes, specifically in terms of water absorption and chloride ion penetration resistance. After 28 days of curing, the rice husk-derived mix demonstrated the lowest water absorption (6.52%), indicating superior resistance to water ingress. It may be due to a better geopolymer matrix that results in the filling of microvoids, which are the primary pathways for water ingress. Chloride ion penetrability, evaluated through the rapid chloride penetration test (RCPT), revealed that all SCGC mixes were classified as having "low" penetrability according to ASTM C1202: 2019 standards. However, the rice husk-derived mix exhibited the least chloride ion ingression (1122 C), outperforming the PCE (1248 C), Naptha (1239 C), and Ligno-based (1756 C) mixes. Such significant durability enhancement can be attributed to the formation of a dense and homogeneous aluminosilicate gel.
[0039] The microstructural analysis, shown in Figure 5, used scanning electron microscopy (SEM) to examine the internal structure of the hardened SCGC mixes. Figure 5 includes the SEM images of Ligno and rice husk-based SCGC mixes for a comparable analysis. The SEM images revealed that the Ligno-based mix contained a significant amount of unreacted GGBS particles, indicating incomplete geopolymerization and resulting in lower strength. In contrast, the rice husk-derived SCGC mix exhibited a dense microstructure with well-formed C-S-H (calcium silicate hydrate) gel, minimal unreacted particles, and fewer voids, justifying its enhanced mechanical strength and durability. The alkaline medium preparation of rice husk-derived superplasticizer improves the degree of geopolymerization in the geopolymer matrix.
[0040] This present SCGC system eliminates the need for ordinary Portland cement (OPC) and costly commercially available superplasticizers, unlike traditional cement-based and conventional geopolymer concrete. As a result, it leads to a significant reduction in cost and embodied carbon footprint compared to both these systems. Moreover, it utilizes various waste materials, including blast furnace slag and rice husk. This presents a compelling opportunity for various industries to utilize their waste byproducts leading toward a sustainable construction practice, minimizing production costs, and promoting an improved circular economy. , Claims:I / We Claim
1. A superplasticizer composition for producing self-compacting geopolymer concrete comprises:
from 30% to 35% by mass of sodium hydroxide (NaOH);
from 5% to 10% by mass of agricultural waste, such as rice husk; and
from 55% to 60% by mass of water.
2. The superplasticizer composition as claimed in claim 1, wherein the composition has the following desirable properties:
(a) a specific gravity of 1.38; and
(b) a pH value of 7.03.
3. The superplasticizer composition as claimed in claim 1, wherein the composition is prepared by a method comprising the following steps:
dissolving 560 g of NaOH pellets in one liter of water to produce a 14M aqueous sodium hydroxide (NaOH) solution;
adding 100 g of rice husk to the aqueous sodium hydroxide solution after 24 hours;
stirring the mixed solution for 10-15 minutes;
boiling the mixed solution for one hour at 80°C - 100°C;
cooling the mixed solution at room temperature for one hour;
filtering the solution and storing it in an airtight bottle.
4. A self-compacting geopolymer concrete (SCGC), comprising:
a self-compacting geopolymer concrete (SCGC) mix solution;
a natural river sand as fine aggregate at 1030 kg/m³; and
a natural coarse aggregate at 650 kg/m³ - 670 kg/m³;
wherein, the self-compacting geopolymer concrete (SCGC) mix solution, comprising:
an alkali activator solution (AAS);
a superplasticizer; and
an additional water.
5. The SCGC mix solution as claimed in claim 4, wherein the SCGC mix solution has composition mix ratios of 1:2.15:1.36, 1:2.15:1.37, 1:2.15:1.36, and 1:2.15:1.39 to produce four distinct SCGC mix solutions.
6. The SCGC mix solution as claimed in claim 4, wherein the alkali activator solution (AAS) comprising:
a ground granulated blast furnace slag (GGBFS) as the primary binder;
a 14M aqueous sodium hydroxide (NaOH) solution and sodium silicate as the activator in a 0.4 ratio.
7. The SCGC mix solution as claimed in claim 4, wherein the mix solution is designed for M25-grade concrete to produce self-compacting geopolymer concrete (SCGC).
8. The self-compacting geopolymer concrete (SCGC) as claimed in claim 4, wherein the SCGC is prepared by a method comprising the following steps:
preparing the superplasticizer according to a specified proportion;
preparing the self-compacting geopolymer concrete (SCGC) mix solution according to a specified proportion;
mixing an alkali activator solution (AAS) with fine aggregate and coarse aggregate in a saturated surface dry condition, then adding the required superplasticizer and additional water;
uniformly mixing the resulting mixture for 3-5 minutes using a drum mixer until a homogeneous and plastic mix is obtained;
pouring the homogeneous mixture into cubical molds, demoulding the specimens after 48 hours of casting, and allowing ambient curing for 28 days.
9. The self-compacting geopolymer concrete (SCGC) as claimed in claim 4, wherein the durability assessment indicates that the SCGC with rice husk-based superplasticizer is comparatively stronger and more durable than commercially available superplasticizer-based geopolymer concretes.

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