Yazar "Acik, Volkan" seçeneğine göre listele

Listeleniyor 1 - 2 / 2
  • Küçük Resim Yok
    Öğe
    Hybrid portland cement-slag-based geopolymer mortar: Strength, microstructural and environmental assessment
    (Elsevier, 2025) Kina, Ceren; Tanyildizi, Harun; Acik, Volkan
    The aim of the current work is to investigate the strength, microstructure, environmental and economic effects of hybrid ordinary portland cement (PC) and ground granulated blast-furnace slag (GGBS) based geopolymer mortar as an alternative to ordinary cement mortar. Eleven mixtures were prepared for this. In this regard, PC was blended with GGBS content of 0-90 wt% in these mixtures. The designed mortar samples were cured at ambient temperature (20 +/- 2 degrees C) to be more applicable in the construction industry, unlike most geopolymer productions and ordinary PC mortar samples were also produced to be comparable to the designed hybrid PC/ GGBS-based geopolymer mortars. The compressive strength (fc) development, ultrasonic pulse velocity (UPV), and dynamic modulus of elasticity (Edyn) values of these ten-hybrid PC/GGBS-based geopolymer mortars were compared with the designed ordinary PC mortar. The results indicated that the incorporation of 20 % PC with 80 % GGBS in the alkali-activated system had the best 28-day compressive strength value with 74.26 MPa, which was 91.07 % higher than that of the designed ordinary PC mortar. The techniques of scanning electron microscopy (SEM)-EDS, Fourier transform-infrared spectroscopy (FT-IR), and thermogravimetric analysis (TGA) were used to identify the microstructural changes caused by the use of ambient temperature cured hybrid 20 % cement-80 % GGBS based alkali-activated mortar. The relatively higher ratios of Ca/Al and Ca/Si compared to ordinary PC mortar proved the more excellent binding property of the C-A-S-H gel, and a denser microstructure was observed in the SEM results. The superior strength development of the hybrid 20 %cement-80 %GGBS alkaliactivated mortar was confirmed by the formation of highly cross-linked C-S-H and C-A-S-H gels due to the higher degree of polymerization and hydration. Additionally, the designed hybrid 20% cement-80 % GGBS geopolymer mortar presented significant environmental and economic benefits compared to those of ordinary PC mortar, with 32.6 % and 23.5 % lower CO2 emission and cost intensity values, respectively.
  • Küçük Resim Yok
    Öğe
    Macro-micro-nano and mechanical characteristics of cement clinker-gypsum-slag-based hybrid geopolymer mortars: A novel approach for reducing the cost and carbon footprint
    (Elsevier, 2025) Tanyildizi, Harun; Kina, Ceren; Acik, Volkan
    This study introduced a new binder system that includes gypsum, clinker, and blast furnace slag (BFS) within an alkali-activated system to reduce carbon dioxide (CO2) emissions in cement production. The key innovation lies in separately using clinker and gypsum, eliminating the grinding process and combining them with alkali-activated BFS at varying replacement ratios. In this context, ten ambient temperature-cured (20 +/- 2 degrees C) alkali-activated mortars, blended with clinker, gypsum, and slag, were designed, along with one water-cured control mortar containing only clinker and gypsum. Their flow diameters, as well as the initial and final setting times, were evaluated to assess their fresh properties. The optimal replacement ratio of clinker and gypsum with BFS was determined by assessing the 3-and 28-day compressive strengths, bulk density, and dynamic modulus of elasticity. The results showed that the alkali-activated mortars having 20 wt % clinker + gypsum combined with 80 wt% BFS exhibited the highest 28-day strength of 69.26 MPa. The microstructural characteristics of these samples were identified through scanning electron microscopy/energy dispersive X-ray (SEM/EDX), Fourier Transform Infrared (FT-IR), and Thermogravimetric (TG) analysis. The molar ratios of Ca/Si and Na/Al in alkali-activated BFS mortar blended with 20 wt% clinker + gypsum indicated the predominance of calcium aluminosilicate hydrate (C-A-S-H) and a denser microstructure with an 11 % pore fraction. Nano-indentation tests revealed that the calcium/sodium aluminosilicate hydrate ((C, N)-A-S-H) volume fraction was 35 %. In contrast, no phases related to geopolymerization were observed in the alkali-activated clinker + gypsum mortar, which showed noticeable deep cracks and a 15 % pore fraction. The high-density calcium silicate hydrate (C-S-H) volume was 45 % for pure clinker + gypsum-based mortar and 30 % for the alkali-activated version. Furthermore, replacing 20 wt% clinker + gypsum achieved a CO2 capture of 32.16 % and a cost saving of 20.0 %. Consequently, using clinker + gypsum-without grinding process-into alkali-activated BFS in suitable proportions offered a promising alternative for improving eco-efficiency and sustainability.