Effect of Bentonite Replacement and Polypropylene Fiber Reinforcement on Physico-Mechanical and Durability Performance of One-Part Slag-Based Geopolymer Foam Concretes

Öz

The main challenge in Geopolymer Foam Concrete (GFC) applications is balancing low density with mechanical durability. Although fibers and mineral additives are often used to enhance performance, a key question remains: how does their combined use affect the delicate rheological balance of 'one-part' systems, and does their interaction cause unexpected foam instability? To address this, the physical, mechanical, and durability properties of a one-part (powdered sodium metasilicate) slag-based GFC were studied by replacing 0–20% of the bentonite with polypropylene fiber (PPF) reinforcement at 0–1% by volume. The main objective was to produce a lightweight and insulating material. However, the most critical finding of the study was the unexpected negative synergistic interaction (foam collapse) of bentonite and PPF on the fresh mortar rheology. The combined effect of bentonite's high water absorption capacity and the physical network formed by the fibers in the mortar increased the viscosity and yield stress of the mixture above a critical threshold. These findings strongly suggest that the increased viscosity caused the stable foam bubbles to break down mechanically during mixing, resulting in 'foam collapse'. This unexpected phenomenon divided the materials into two completely different classes than the targeted ones: (1) Stable GFCs (e.g., 0BP5); materials with low density (641 kg/m³), high porosity (61.2%) and good thermal insulators (0.172 W/m.K), but mechanically weak (2.32 MPa) and low freeze-thaw (F-T) strength. (2) Dense foamed mortars (e.g. 20BP5); materials that reach a high density of up to 1779 kg/m³, have low porosity (11.9%), become thermally conductive (0.543 W/m.K), but surprisingly have exceptionally high compressive strength reaching 20.56 MPa and excellent F-T strength (mass loss 1.84%). High-temperature tests also confirmed that at 250°C, all samples underwent additional curing (strength increase), and that at 750°C, bentonite contributed to thermal stability. The results show that rheological control is the main factor influencing the balance between insulation and mechanical durability in GFC production.

Anahtar Kelimeler

• Bentonite
• Polypropylene fiber
• Freeze-thaw effect
• Geopolymer foam concrete
• Sorptivity

Bentonit İkamesi ve Polipropilen Lif Takviyesinin Tek Bileşenli Cüruf Esaslı Geopolimer Köpük Betonların Fiziko-Mekanik ve Dayanıklılık Performansı Üzerindeki Etkisi

Öz

Geopolimer Köpük Beton (GFC) uygulamalarındaki en büyük zorluk, düşük yoğunluk ile mekanik dayanıklılığı dengelemektir. Performansı artırmak için sıklıkla lifler ve mineral katkı maddeleri kullanılsa da, önemli bir soru hala cevapsız kalmaktadır: bunların birleşik kullanımı, 'tek bileşenli' sistemlerin hassas reolojik dengesini nasıl etkiler ve etkileşimleri beklenmedik köpük kararsızlığına neden olur mu? Bu soruyu ele almak için, tek bileşenli (toz sodyum metasilikat) cüruf esaslı bir GFC'nin fiziksel, mekanik ve dayanıklılık özellikleri, bentonitin %0-20'sinin hacimce %0-1 oranında polipropilen lif (PPF) takviyesi ile değiştirilmesiyle incelenmiştir. Ana amaç, hafif ve yalıtkan bir malzeme üretmektir. Bununla birlikte, çalışmanın en kritik bulgusu, bentonit ve PPF'nin taze harç reolojisi üzerindeki beklenmedik negatif sinerjik etkileşimi (köpük çökmesi) olmuştur. Bentonitin yüksek su emme kapasitesi ve harçtaki lifler tarafından oluşturulan fiziksel ağın birleşik etkisi, karışımın viskozitesini ve akma gerilimini kritik bir eşiğin üzerine çıkarmıştır. Bu bulgular, artan viskozitenin, karıştırma sırasında kararlı köpük kabarcıklarının mekanik olarak parçalanmasına ve 'köpük çökmesine' neden olduğunu güçlü bir şekilde göstermektedir. Bu beklenmedik olgu, malzemeleri hedeflenenlerden tamamen farklı iki sınıfa ayırmıştır: (1) Kararlı GFC'ler (ör. 0BP5); düşük yoğunluğa (641 kg/m³), yüksek gözenekliliğe (%61,2) ve iyi ısı yalıtımına (0,172 W/m.K) sahip, ancak mekanik olarak zayıf (2,32 MPa) ve düşük donma-çözülme (F-T) dayanımına sahip malzemeler. (2) Yoğun köpüklü harçlar (ör. 20BP5); 1779 kg/m³'e kadar yüksek yoğunluğa ulaşan, düşük gözenekliliğe (%11,9) sahip, ısı iletkenliği yüksek (0,543 W/m.K) ancak şaşırtıcı bir şekilde 20,56 MPa'ya ulaşan olağanüstü yüksek basınç dayanımına ve mükemmel F-T dayanımına (kütle kaybı %1,84) sahip malzemeler. Yüksek sıcaklık testleri ayrıca, 250°C'de tüm numunelerin ek kürleme (dayanım artışı) geçirdiğini ve 750°C'de bentonitin termal kararlılığa katkıda bulunduğunu doğruladı. Sonuçlar, reolojik kontrolün, GFC üretiminde yalıtım ve mekanik dayanıklılık arasındaki dengeyi etkileyen ana faktör olduğunu göstermektedir.

Anahtar Kelimeler

• Bentonit
• Polipropilen lif
• Donma-çözülme etkisi
• Geopolimer köpük beton
• Kapilarite

Kaynakça

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