What is Geopolymer?
Geopolymer is a novel cementitious material developed as an alternative to ordinary Portland cement. It is formed through alkali activation of materials rich in silicon (Si) and aluminum (Al) such as fly ash, metakaolin, slag and others. When such aluminosilicate materials are reacted with highly alkaline solutions like sodium hydroxide or potassium hydroxide, they undergo a polycondensation process forming 3D framework structures similar to natural zeolites. Depending on the reaction conditions and the precursor materials used, this geopolymeric binder can exhibit properties similar or superior to OPC in terms of strength, durability and sustainability.
History of Geopolymer Development
The concept of geopolymer was first discovered in the late 1970s by French scientist Joseph Davidovits while he was researching alternatives to dwindling oil resources. He coined the term 'geopolymer' to describe the product formed from alkali activation of aluminosilicate materials. However, initial research focused more on synthesizing zeolitic materials for adsorbents and catalysts. It was not until the 1980s that geopolymers started gaining traction as cementitious binders that can replace Portland cement. Pioneering works by Davidovits, Glukhovsky, Fernandez-Jimenez, and Palomo among others established the alkali activation process and characterization of geopolymeric binders. Over the decades, significant advances have been made in understanding geopolymer chemistry, curing conditions, structural development, and application of geopolymers. Today geopolymer concrete is commercially available in certain parts of the world.
Production of Geopolymer Concrete
The primary raw materials required for Geopolymer concrete production are fly ash or slag, soluble alkali activators like sodium silicate and sodium hydroxide solutions. Fly ash is a by-product from coal-fired power plants while slag is obtained from blast furnaces during steel manufacturing. These aluminosilicate materials hold the key to geopolymerization as they provide the building blocks i.e. silicon, aluminum in correct proportions. The activators undergo hydrolysis releasing silicate and aluminate species which then polycondense with aluminosilicate precursors forming 3D interconnected geopolymeric network.
Mix design proportions for geopolymer concrete are determined based on the chemical composition and reactivity of source materials. Typically the mix contains 400-500 kg of fly ash or slag, 100-200 kg of alkaline liquid per 1 m3 of concrete. Sodium silicate to sodium hydroxide ratio in the activator solution is maintained around 2.5. Other ingredients like fine aggregates, coarse aggregates, admixtures are added similar to conventional concrete. Geopolymer concrete exhibits workability for a period of 30-60 minutes and sets within 24 hours at ambient or slightly elevated temperatures. Curing is a crucial step where wet curing or steam curing for 48-72 hours leads to higher strength development.
Properties and Performance of Geopolymer Concrete
Compared to ordinary Portland cement concrete, geopolymer concrete offers several advantages due to the nature of geopolymeric binder:
Higher early and ultimate compressive strengths up to 100 MPa within a day are achievable. Strength gain is comparatively faster in the first 7 days.
Improved fire resistance and thermal stability as the bound gel phase retains integrity at high temperatures up to 800°C.
Excellent acid, sulfate, and alkali resistance owing to the insoluble geopolymeric network structure. This makes it suitable for aggressive environments.
Durable in marine, offshore and structures exposed to chlorides as it does not depend on calcium silicate hydration products like C-S-H gel.
Up to 80% reduction in CO2 emissions during production compared to OPC concrete. This gives it a lower carbon footprint.
Utilizes industrial by-products like fly ash, slag making effective use of waste materials and promoting sustainability and circular economy.
Workability and fresh concrete properties can be varied based on activator type and content to suit different placement and compaction requirements.
Surface hardness and abrasion resistance exceeding that of OPC concrete, suitable for high traffic floors and pavements.
Applications of Geopolymer Concrete
With the techno-commercial benefits provided, geopolymer concrete is finding acceptance in infrastructure and construction applications where durability, sustainability and strength are paramount. Some key application areas are:
Precast concrete industry for manufacturing quality precast elements with faster production cycles.
Marine structures like jetties, bridges and offshore platforms to counter corrosion from seawater.
Sewage and water treatment plants requiring highly chemical resistant structures.
Waste containment and immobilization due to its ability to encapsulate hazardous and radioactive wastes.
Industrial floors in chemical plants, refineries facing aggressive environments.
Roads and pavements for improved skid resistance and longer service life.
Refractories and kiln linings in the steel and ceramics industries for superior fire resistance.
With further research focusing on optimizing mix designs, improving processing methods and standardization, geopolymer concrete has the potential to significantly reduce the carbon footprint of the global construction industry. A greener and more sustainable future of construction seems within reach with advancements in alkali activated materials.
For more insights, read- https://www.newsstatix.com/geopolymers-trends-size-and-share-analysis/
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