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    Bacteria-Based Crack Healing of Nanosilica and Carbon Nanotube Modified Engineered Cementitious Composites
    (Asce-Amer Soc Civil Engineers, 2024) Tanyildizi, Harun; Bulut, Metehan; Ziada, Mahmoud
    This study investigated bacteria-based crack healing of nanosilica and carbon nanotube modified engineered cementitious composites (ECC). Nanosilica (NS) and carbon nanotubes (CNT) were used in ratios of 0%, 0.25%, 0.50%, and 0.75% of the cementitious materials by mass. NS and CNT modified ECC samples were produced and cured in plastic bags at 23 degrees C +/- 2 degrees C for 28 days. After 28 days, the microcracks were formed in the ECC specimens. Then, the healing procedure by a bacterial solution containing Sporosarcina pasteurii was applied to these samples. After this procedure, the splitting tensile strength, ultrasonic pulse velocity water permeability, and rapid chloride permeability were performed on the samples. Also, energy-dispersive X-ray (EDX), scanning electron microscopy (SEM), X-ray diffraction analysis (XRD), and Fourier Transform Infrared Spectroscopy (FTIR) analyses were used to examine the morphology of healing products. This study found that 0.75 NS-ECC had a higher healing ability than all samples, and the splitting tensile strength recovery rate of this sample was 131.46%.
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    Comparative analysis of long-term and high temperature performances of OPC based high strength mortar and silica fume based high strength geopolymer mortars
    (Elsevier Science Inc, 2024) Saridemir, Mustafa; Celikten, Serhat; Bulut, Metehan; Deniz, Suvat
    The effects of Class C fly ash (FA) contents on the performance of silica fume (SF) based high strength geopolymer mortars (HSGM) subjected to high temperatures up to 1000 degrees C are investigated. The percentages of FA substitution by SF are 10%, 15%, 20% and 25% by weight. The alkali activators used consist of sodium silicate (SS) and sodium hydroxide (SH) and are used in mixtures with SH/SS ratios of 0.3, 0.4, 0.5 and 0.6. In order to compare SF based HSGMs, ordinary Portland cement (OPC) based high strength mortar (HSM) as a control mortar is also produced with the same dosage and water content. The results at environmental temperature show that higher mechanical properties are obtained from SF based HSGMs compared to OPC based HSM. The optimum replacements of Class C FA and SH/SS ratios are 15 % and 0.3 or 0.4 in terms of mechanical properties. At 28 days, SF based HSGMs with flexural strength (ffs) of 15 MPa and compressive strength (fc) of 100 MPa can be produced without thermal curing. High reductions in the mechanical properties are seen on the OPC based HSM and SF based HSGMs subjected to high temperatures. In addition, SF based HSGMs with fc values above 25 MPa can also be obtained after exposure to 1000 degrees C. Alterations in the microstructure of OPC based HSM and SF based HSGMs under the influence of high temperatures are also examined with XRD, FTIR, SM, and FESEM/EDX analyses. Particularly, a spongy structure with volumetric expansion is seen with the formation of the glassy phase in the matrix of SF based HSGMs subjected to a temperature of 1000 degrees C.
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    Effects of different curing conditions on the long-term properties of alkali activated GBP plus GBFS mortars exposed to high temperatures
    (Elsevier Sci Ltd, 2022) Saridemir, Mustafa; Bulut, Metehan; Akca, Ugurcan
    This study investigates the effects of Na concentration, steam curing and oven curing conditions on the long-term mechanical and microstructural properties of alkali activated ground basaltic pumice (GBP) and ground blast furnace slag (GBFS) mortars subjected to ambient and high temperatures. The alkali activated mortars are produced with 50% GBP + 50% GBFS as binding material. To bind these materials, liquid Na2SiO3 and solid Na (OH) as activator are used at different Na concentrations. The alkali activated GBP + GBFS mortars subjected to ambient and high temperatures are tested for unit weight, ultrasonic pulse velocity, flexural strength and compressive strength. Additionally, XRD, SEM and EDAX analyses are performed on the alkali activated GBP + GBFS mortars subjected to ambient and high temperatures. The results have shown that the higher strength values can be obtained from alkali activated GBP + GBFS mortars compared to the control mortars. Moreover, the results have shown that the strength values gradually decrease as the temperature exposed to the control mortars increases, but the strength values of alkali activated GBP + GBFS mortars up to 450 degrees C temperature gradually increase, and decrease gradually at later high temperatures.
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    Effects of fly ash, activator ratio and steel fiber on freeze-thaw cycle, sulfuric acid, thermal conductivity and impact resistance of silica fume based AAHSMs
    (Elsevier Sci Ltd, 2024) Saridemir, Mustafa; Bulut, Metehan
    This study is focused on the effects of Class C fly ash (FA), NaOH/Na2SiO3 (SH/SS) ratio and steel fiber (STF) on the freeze-thaw (F-T) cycle, sulfuric acid, thermal conductivity and impact resistance of silica fume (SF) based alkali activated high strength mortars (AAHSMs). In the AAHSM mixtures, FA in different proportions (10%, 15%, 20% and 25%) is used instead of SF by weight. All the mixtures are prepared with water-to-binder rate of 0.32. F-T cycle results exhibit that the flexural strength (ffs) fs ) and compressive strength (fc) c ) values of SF based AAHSMs without and with STF are less affected than those of ordinary Portland cement (OPC) based high strength mortars (OPCHSMs) without and with STF. After 300 F-T cycles, the f fs and fc c values of SF based AAHSMs without and with STF are still over 14 MPa and 95 MPa, respectively. After exposure to 20% sulfuric acid solution for 90 and 180 days, the SF based AAHSMs without and with STF exhibit super performance (i.e., fc c values between 78.95 MPa and 96.81 MPa), while the surfaces of OPCHSMs without and with STF are disintegrated. Additionally, the effects of F-T cycle and sulfuric acid solution on SF based AAHSM and OPCHSM are examined with the microstructure analyses. Thermal conductivity results show that the SF based AAHSMs without and with STF perform better than the OPCHSMs without and with STF. The thermal conductivity results of OPCHSMs without and with STF vary between 0.630 W/m.K and 0.697 W/m.K, while the thermal conductivity results of SF based AAHSMs without and with STF range from 0.507 W/m.K and 0.623 W/m.K. Thermal conductivity results are adversely influenced by increasing STF content in the SF based AAHSMs and OPCHSMs. Impact resistance results show that the SF based AAHSMs without and with STF perform better than the OPCHSMs without and with STF. Moreover, the impact resistance values increase, as the amount of STF used in the SF based AAHSMs and OPCHSMs increases.
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    Effects of ground basaltic pumice and high temperatures on the properties of HSMs
    (Elsevier, 2021) Saridemir, Mustafa; Bulut, Metehan
    The mechanical and microstructural properties of high strength mortars (HSMs) containing ground basaltic pumice (GBP) subjected to 25, 300, 600, 900 and 1050 degrees C temperatures are investigated in this article. The mortars containing GBP employing the replacement ratio up to 25% GBP by weight of ordinary Portland cement (OPC) as well as a control mortar manufactured with OPC are produced. Two different cures, which are steam curing and pochette curing, are applied to the fresh mortars produced. The unit weight (rho), ultrasonic pulse velocity (U-pv), flexural strength (f(s)) and compressive strength (f(c)) of mortars containing GBP are investigated at the short/long terms and high temperatures. The microstructural properties of mortars containing GBP at high temperatures are also investigated by X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDAX) analyses. The results have shown that GBP can be successfully used instead of OPC in the mortar mixtures. Especially, the steam curing application has improved the mechanical properties of mortars containing GBP better than those of pochette curing.
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    Long-term properties of steel fiber reinforced silica fume based AAMs at ambient and high temperatures
    (Elsevier Sci Ltd, 2024) Saridemir, Mustafa; Bulut, Metehan; Deniz, Suvat; Deneme, Ibrahim Ozguer
    In this study, the influences of Class C fly ash (FA), steel fiber (STF) and high temperature are researched on the mechanical and microstructural properties of STF reinforced silica fume (SF) based alkali activated mortars (AAMs) cured at the ambient (25 degrees C) temperature. The STF reinforced SF based AAMs are produced with 10%, 15%, 20% and 25% Class C FA by weight in place of SF, 0.5%, 1% and 1.5% STF by volume, liquid sodium silicate (Na2SiO3) and solid sodium hydroxide (NaOH). The apparent density (rho(a)), ultrasonic pulse velocity (U-pv), flexural strength (f(fs)) and compressive strength (f(c)) results of the STF reinforced control mortars (CMs) and SF based AAMs subjected to the ambient and elevated temperatures are investigated. The microstructural investigations are conducted with X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM)/energy dispersive X-ray (EDAX). Moreover, color changes, pores and interfacial transition zones (ITZs) in samples exposed to the ambient and high temperatures are examined by a stereoscopic microscope (SM). The results have shown that the high strengths can be obtained from STF reinforced SF based AAMs at ambient temperature (25 degrees C) and the optimum Class C FA and STF contents are 15% and 1%. Additionally, when STF reinforced SF based AAMs are exposed to high temperatures (especially 750 degrees C and 1000 degrees C), a serious decrease in the mechanical properties is observed due to the formation of a porous and spongy structure in the matrix and the STFs completely oxidizing and losing their properties.
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    Self-Healing Performance of Nanosilica-Modified Engineered Cementitious Composites Exposed to High Temperatures
    (Asce-Amer Soc Civil Engineers, 2024) Tanyildizi, Harun; Bulut, Metehan
    This study investigated the self-healing performance of nanosilica-modified engineered cementitious composites (ECCs) exposed to high temperatures. Nanosilica (NS) was used in 0%, 0.25%, 0.50%, and 0.75% proportions of cementitious materials by mass in the mixtures. NS-modified ECC cylindrical samples (o100x200 mm) were produced and cured at 23 degrees C +/- 2 degrees C for 28 days. Then, these samples were exposed to 20 degrees C +/- 2 degrees C, 100 degrees C, 200 degrees C, 300 degrees C, 400 degrees C, 500 degrees C, 600 degrees C, 700 degrees C, and 800 degrees C temperatures. After the samples were cooled at room temperature, microcracks were formed in the ECC samples, but the samples exposed to higher than 400 degrees C were dispersed when the crack was formed. The wetting-drying cycles were applied for the self-healing of cracked samples. Lastly, the splitting tensile strength, ultrasonic pulse velocity, and chloride ion permeability of the NS-modified ECC samples were determined. Scanning electron microscopy (SEM), and energy-dispersive X-ray (EDX), X-ray diffraction analysis (XRD), and Fourier transform infrared spectroscopy (FTIR) analyses were also performed to examine the microstructure of NS-modified ECC samples. This study found that all samples were self-healed within 15 days, and the highest splitting tensile strength recovery rate was obtained from 0.75 NS-modified ECC samples with 107.44%.
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    The effect of carbon nanotube on self-healing properties of engineered cementitious composites subjected to high temperatures
    (Ernst & Sohn, 2024) Tanyildizi, Harun; Bulut, Metehan
    This study aims to examine the effect of carbon nanotubes (CNT) on the self-healing performance of engineered cementitious composites (ECC) subjected to high temperatures. In ECC samples, CNT was used at 0%, 0.25%, 0.50%, and 0.75% by weight instead of cementitious materials. The cylindrical specimens containing CNT (o100 x 200 mm) were manufactured. The produced specimens were subjected to temperatures of 23 +/- 2, 100, 200, 300, 400, 500, 600, 700, and 800 degrees C after being cured at 23 +/- 2 degrees C for 28 days, and then, they left to cool at 23 +/- 2 degrees C for 1 day. Then, these specimens were preloaded at 70% of the ultimate splitting tensile strength to produce microcracks. Lastly, wetting-drying cycles were performed on ECCs for self-healing. The ultrasonic pulse velocity (UPV), splitting tensile strength (fst), and rapid chloride permeability (RCPT) tests were applied to evaluate the self-healing performance of specimens. Moreover, microstructural analyses such as scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDX), and X-ray diffraction (XRD) were accomplished to identify the healing products formed in self-healed cracks. According to the results of this study, the highest recovery rate of fst with 103.46% was attained from the ECC specimen containing 0.25% CNT exposed to 200 degrees C.