Using Carbonated BOF Slag Aggregates in Alkali-Activated Concretes

Abstract

This experimental study aimed to develop alkali-activated concretes containing carbonated basic oxygen furnace (BOF) slag aggregates. In the first stage, the impacts of replacing normal aggregates with carbonated BOF slag aggregates in different alkali-activated concretes were determined by assessing mechanical properties (compressive and flexural strengths), morphology, thermogravimetric analyses (TGA), differential thermogravimetry (DTG) and the crystalline phases using X-ray diffraction analysis. Second, the developed plain alkali-activated concrete was reinforced by different fibre types and dosages to limit the negative impacts of the drying shrinkage and to improve strength. Therefore, the effects of using different fibre contents (1% and 1.5% in Vol.) and types (Polyvinyl alcohol [PVA], Polypropylene [PP], basalt, cellulose and indented short-length steel) on hardened state properties were evaluated. These evaluations were expressed in terms of the compressive and flexural strengths, ultrasonic pulse velocity, mass changes, drying shrinkage and efflorescence. Then, the impacts of aggressive conditions on the hardened properties of fibre-reinforced alkali-activated concretes were evaluated under carbonation, high temperature and freeze/thaw tests. The results showed that using carbonated BOF slag aggregates led to obtain higher strength than using normal aggregates in alkali activated concretes. Moreover, the maximum enhancement due to reinforcing the mixtures was recorded in alkali-activated concretes with steel fibres.

Durability of the Reinforced One-Part Alkali-Activated Slag Mortars with Different Fibers

“…After reaching 600 °C, both plain and reinforced AASs indicated 60% strength loss. Mastali et al reinforced AASs with different fibers (PVA, polypropylene, cellulose, steel, and basalt) and assessed their resistance to a high temperature (600 °C) for 4 h [32]. Similar to the findings of the present study, the minimum compressive and flexural strength loss (around 75% and 70%, respectively) were reported for the AASs reinforced with steel fibers.…”

“…Similar to the findings of the present study, the minimum compressive and flexural strength loss (around 75% and 70%, respectively) were reported for the AASs reinforced with steel fibers. The maximum strength loss was found for AASs reinforced with PVA fibers, while basalt fibers resulted lower strength loss than other nonmetallic fibers [32]. This confirms that nonmetallic fibers have different impacts on strength loss at high temperatures, depending on the properties of the matrix and bond at the fiber/matrix ITZ.…”

“…The carbonation test was performed with three prismatic beams (40 × 40 × 160 mm 3 ) from each mixture, which were exposed to 23 °C, 60% relative humidity, and 5% CO 2 gas for 7 days [32]. Then, the impacts of carbonation were evaluated on flexural and compressive strength.…”

“…The maximum increase (20%) and decrease (30%) in flexural strength were reported for St0.5PVA0.5 and Bs0.5PVA0.5, respectively. Mastali et al showed that exposing AASs reinforced with PVA and polypropylene fibers to carbonation reduced compressive and flexural strength, while other fiber types (cellulose, basalt, and steel) increased these types of strength [32].…”

“…To the best of the author's knowledge, although a few studies have reported the durability performance of fiberreinforced AASs [32,33], no extensive experimental study has been conducted on the effects of using different fibers as reinforcement on OAASs' mechanical and durability properties. It is worth stating that there are some investigations regarding development of ultra-high fiber reinforced concrete using reinforcement of one-part alkali activated materials with Polyethylene (PE) and PVA fibers [34][35][36].…”