Effect of Grinding Treatment of Fly Ash on Compressive Strength of Hardened Geopolymers using Warm Press Method

Abstract

Abstract. In this study, starting mixed wet powders were uniaxially compressed at 200 MPa for 40 min and simultaneously heated at 200 °C to form hardened bodies. Three different starting slurries composed of 100 g of fly ash powders with particles of different sizes after grinding treatment, 15 g of reagent-grade sodium, and 33.3 g of fresh water were considered. In this time, the uniaxial pressure was fixed at 200 MPa. This method is called the warm press method because the heating temperature is not as high as that in the conventional hot press sintering method used for ceramics. When ground fly ash with a diameter of 6.8 μm was used, the average compressive strength of the hardened bodies reached approximately 120 MPa. As the heating temperature and duration were increased at the fixed uniaxial pressure of 200 MPa, the compressive strength of the geopolymers increased. When ground fly ash with a diameter of 6.8 μm was used and the heating temperature and duration were 280 °C and 60 min, respectively, the compressive strength of the geopolymers reached approximately 150 MPa.

Cold sintering of ceramics and glasses: A review

“…A mixture of fly ash, NaOH solution and sodium water glass was heated to 130°C/2 h under 200 MPa pressure. The formed components had 71% relative density and high compressive strength values reaching 149 MPa [59,259]. It is known that dense calcium hydroxide body (slaked lime plaster) is hard to obtain by conventional sintering approaches.…”

Strength and Durability Properties of High-Volume Fly Ash (HVFA) Binders: A Systematic Review

“…Mass gain within the first 28 days is attributed to the absorption of sulphuric acid in the pores within the HVFA binder. Hashimoto et al, 2017 [96] reported that HVFA pastes are highly resistant to the sulfuric acid solution at temperatures between 60 • C and 220 • C. Exposure of HVFA to sulfuric acid exceeding 4 days results in the formation of natroalunite crystals, which adds to the dense matrix of the binder and increases the compressive strength [79]. Similarly, Hashimoto et al (2017) [96] concluded that 5% Na 2 SO 4 has no deteriorating effect on HVFA binders whereas MgSO 4 has an acute decalcification effect yielding gypsum as a product.…”

“…Hashimoto et al, 2017 [96] reported that HVFA pastes are highly resistant to the sulfuric acid solution at temperatures between 60 • C and 220 • C. Exposure of HVFA to sulfuric acid exceeding 4 days results in the formation of natroalunite crystals, which adds to the dense matrix of the binder and increases the compressive strength [79]. Similarly, Hashimoto et al (2017) [96] concluded that 5% Na 2 SO 4 has no deteriorating effect on HVFA binders whereas MgSO 4 has an acute decalcification effect yielding gypsum as a product. HVFA binders are satisfactorily resistant to chloride attacks with short exposures characterised by no major change in compressive strength [55].…”