Impact of cation type and fly ash on deterioration process of high belite cement pastes exposed to sulfate attack

2021 ◽  
Vol 286 ◽  
pp. 122961
Author(s):  
Chunmeng Jiang ◽  
Linhua Jiang ◽  
Shuangxi Li ◽  
Xinjun Tang ◽  
Lei Zhang
Keyword(s):  
Fly Ash ◽  
Sulfate Attack ◽  
Cement Pastes ◽  
Deterioration Process ◽  
Cation Type ◽  
Belite Cement

scholarly journals Physical and Chemo/Mechanical behaviors of fly ash and silica fume belite cement pastes- Part I

NanoNEXT ◽  
2021 ◽  
pp. 1-15
Author(s):  
Darweesh H.H.M
Keyword(s):  
Fly Ash ◽  
Silica Fume ◽  
Total Porosity ◽  
Ultrasonic Pulse Velocity ◽  
Ultrasonic Pulse ◽  
Pulse Velocity ◽  
Heat Of Hydration ◽  
Hardened Cement ◽  
Cement Pastes ◽  
Belite Cement

Physical, chemical and mechanical properties of high belite cement (HBC) blended with high pulverized fly ash (HPFA) with stable ratio of silica fume (SF) in comparison with Portland cement (OPC) were investigated. Results showed that the water of consistency and setting times (Initial and final) tended to increase with the increase of HPFA content. The bulk density and compressive strength were also improved and enhanced with the increase of HPFS content at all hydration times, but only up to 15 % HPFA, and then decreased with further increase.  However, the total porosity slightly decreased, but started to increase with further increase of >15 % HPFA. The free lime content of the pure OPC and HBC gradually were increased as the hydration times progressed up to 90 days, while those of blended cements increased only up to 7 days and then decreased onward. The results were confirmed by measuring the heat of hydration and ultrasonic pulse velocity for the optimum cement pastes comparing with those of both OPC and HBC. The heat of hydration of the optimum cement pastes was decreased at all hydration times and become lower than those of OPC and HBC. The ultrasonic pulse velocity test (USPV) proved that the uniformity and quality of the matrix of the hardened cement pastes are good with no cracks.

Belite Cement Prepared from High Carbon-Content Fly Ash

2016 ◽  
Vol 866 ◽  
pp. 20-24
Author(s):  
Yuan Yuan Wan ◽  
Yong Hao Fang
Keyword(s):  
Fly Ash ◽  
Carbon Content ◽  
Hydrothermal Reaction ◽  
Sulfate Attack ◽  
High Carbon ◽  
Steam Curing ◽  
High Carbon Content ◽  
Rapid Setting ◽  
High Sulfate ◽  
Belite Cement

Stockpiled high carbon-content fly ash and lime was used to prepare belite cement by hydrothermal reaction followed by low temperature calcination. Sodium hydroxide was added as an activator to accelerating the reaction. 0-1.5 wt% Na2O equivalent NaOH was added as a aqueous solution into the mixture of 20 wt%-35 wt% CaO and 65 wt%-80 wt% fly ash. The mixture was formed into granules and steam-curing the at 97°C for 12 h, followed by heating at 800°C for 1 h. The results show that adding 1.0 wt% Na2O to the mixture of fly ash and CaO can efficiently promote the hydrothermal reaction. Belite cement with practicable strength and characterized by rapid setting and high sulfate attack resistance was synthesized.

scholarly journals Sulfate Attacks on Uncarbonated Fly Ash + Cement Pastes Partially Immersed in Na2SO4 Solution

Materials ◽  
2020 ◽  
Vol 13 (21) ◽  
pp. 4920
Author(s):  
Zanqun Liu ◽  
Min Pei ◽  
Yuelin Li ◽  
Qiang Yuan
Keyword(s):  
Fly Ash ◽  
Cement Paste ◽  
Exposure Period ◽  
Sulfate Attack ◽  
X Ray Diffraction ◽  
Cement Pastes ◽  
Evaporation Zone ◽  
Chemical Attack ◽  
Physical Attack ◽  
Deterioration Mechanism

In this study, the sulfate attack on uncarbonated cement paste partially exposed to Na2SO4 solution was experimentally investigated and compared with that on carbonated specimens with the same exposure regime and uncarbonated specimens without exposure. N2 was used to protect specimens from carbonation throughout the sulfate exposure period. The effects of the water-to-cement (w/c) ratio and the fly ash as cement replacement on the sulfate attack were evaluated. Portland cement paste specimens with different w/c ratios of 0.35, 0.45, and 0.55 or fly ash replacement rates of 10%, 20%, and 30% were prepared. These specimens were partially immersed in 5% Na2SO4 solution for 50 d and 100 d exposure periods. The micro-analysis was conducted to evaluate the effect of the partial sulfate attack on the uncarbonated cement paste using X-ray diffraction (XRD) and thermo-gravimetric (TG) techniques. The results confirmed that, for uncarbonated cement paste, the chemical attack rather than the physical attack is the deterioration mechanism and is responsible for more severe damage in the evaporation zone (dry part) compared with the immersed zone (immersed part). When the effect of carbonation is well excluded, there is an optimal w/c ratio of 0.45 for minimizing the sulfate attack, while incorporating fly ash tends to reduce the sulfate attack resistance.

scholarly journals Durability and chemical resistance of nanoparticles fly ash and silica fume belite cement pastes against sulfate and chloride aggressive media- Part II

NanoNEXT ◽  
2021 ◽  
Vol 2 (4) ◽  
pp. 1-13
Author(s):  
Darweesh H.H.M
Keyword(s):  
Compressive Strength ◽  
Fly Ash ◽  
Silica Fume ◽  
Chemical Resistance ◽  
Sulfate Solution ◽  
Chloride Ions ◽  
Cement Pastes ◽  
Total Chloride ◽  
Total Sulfate ◽  
Belite Cement

The durability (chemical resistence) of the Portland cement (OPC), belite cement (BC) and the optimum belite cement (B4), which their physical and chemo/mechanical properties were perviously investigated in Part I, against 4 % MgSO4 and 4% MgCl2 solutions up to 12 months in terms of compressive strength, total sulfate and total chloride was evaluated and studied. Results showed that the optimum belite cement (B4) containing 15 % High pulverized fly ash (HPFA) and 5 % Silica fume (SF) could be resisted up to 6 months, while that of BC could be withstood only up to 5 months, and the OPC could not resist more than three months of immersion in 4% MgSO4 solution. The compressive strength values exhibited by the samples immesed in sulfate solution at 3, 5 and 6 months of immersion were 83.81, 76.38 and 91.13 MPa, respectively. The same trend was displayed when the same samples were exposed to 4% MgCl2 solution. The compressive strength values exhibited by the same samples exposed to chloride solution at 3, 5 and 6 months of immersion were 84.49, 82.23 and 93.32 MPa, respectively. The total sulfate and chloride contents were enhanced with immesion time up to 12 months, but their values were the minimum with B4 and the maximum with OPC, while with BC were the medium. The optimum cement batch (B4) achieved the highest resistance where it recorded the lowest values for sulfate and chloride ions, but the OPC exhibited the lowest resistance where it recorded the highest values of sulfate and chloride contents at all immersion ages till 12 months.

scholarly journals Properties and Mechanism of Hydration of Fly Ash Belite Cement Prepared from Low-Quality Fly Ash

2020 ◽  
Vol 10 (20) ◽  
pp. 7026
Author(s):  
Yongfan Gong ◽  
Cong Liu ◽  
Yanli Chen
Keyword(s):  
Fly Ash ◽  
Low Temperature ◽  
Portland Cement ◽  
Hydration Reaction ◽  
Low Grade ◽  
Early Hydration ◽  
Cement Pastes ◽  
Technological Support ◽  
20 Nm ◽  
Belite Cement

Fly ash belite cement (FABC) is predominantly composed of α′L-C2S and C12A7. It is prepared from low-grade fly ashes by hydrothermal synthesis and low-temperature calcination methods. The formation, evolution process, and microstructure of FABC hydration productions were studied in this work, and the ultimate aim is to give a theoretical foundation and technological support for the application of the new cementitious material made of low-quality fly ash. The results showed that the optimal amount of gypsum was about 7% of cement by weight. The 3-day and 28-day compressive strength of cement pastes with 7% gypsum was 13.6 and 60.2 MPa, respectively. Meanwhile, the 28-day flexural and compressive strengths of mortars with 7% gypsum were 4.6 and 25.9 MPa, respectively. The early hydration heat release rate of this low-temperature calcined cement was higher compared with that of high-temperature calcined cement as Portland cement. FABC hydration pastes contained mostly C-S-H, ettringite (AFt), unreacted mullite, and quartz. It was significantly different from Portland cement in that no calcium hydroxide [Ca(OH)2] was observed in the hydration products of different ages because all Ca(OH)2 formed in the hydration reaction could react completely to generate AFt. The ratio of harmful pores (d ≥ 50 nm) reached 55.04% after 3-day hydration. However, it decreased to 6.71%, which was lower than that of Portland cement pastes (35.72%) after 28-day hydration. In the later hydration period from 3 to 28 days, the strength developed rapidly, and a compact microstructure appeared in the hardened paste due to the presence of pores less than 20 nm in diameter.

Impact of calcium leaching on mechanical and physical behaviors of high belite cement pastes

2021 ◽  
Vol 286 ◽  
pp. 122983
Author(s):  
Chunmeng Jiang ◽  
Linhua Jiang ◽  
Xinjun Tang ◽  
Jingwei Gong ◽  
Hongqiang Chu
Keyword(s):  
Cement Pastes ◽  
Calcium Leaching ◽  
Belite Cement

scholarly journals New Approach for the Determination of Radiological Parameters on Hardened Cement Pastes with Coal Fly Ash

Materials ◽  
2021 ◽  
Vol 14 (3) ◽  
pp. 475
Author(s):  
Ana María Moreno de los Reyes ◽  
José Antonio Suárez-Navarro ◽  
Maria del Mar Alonso ◽  
Catalina Gascó ◽  
Isabel Sobrados ◽  
...  
Keyword(s):  
Fly Ash ◽  
Activity Concentration ◽  
Gamma Ray ◽  
Coal Fly Ash ◽  
Cementitious Materials ◽  
New Method ◽  
Supplementary Cementitious Materials ◽  
Hardened Cement ◽  
Cement Pastes ◽  
Activity Concentrations

Supplementary cementitious materials (SCMs) in industrial waste and by-products are routinely used to mitigate the adverse environmental effects of, and lower the energy consumption associated with, ordinary Portland cement (OPC) manufacture. Many such SCMs, such as type F coal fly ash (FA), are naturally occurring radioactive materials (NORMs). 226Ra, 232Th and 40K radionuclide activity concentration, information needed to determine what is known as the gamma-ray activity concentration index (ACI), is normally collected from ground cement samples. The present study aims to validate a new method for calculating the ACI from measurements made on unground 5 cm cubic specimens. Mechanical, mineralogical and radiological characterisation of 28-day OPC + FA pastes (bearing up to 30 wt % FA) were characterised to determine their mechanical, mineralogical and radiological properties. The activity concentrations found for 226Ra, 212Pb, 232Th and 40K in hardened, intact 5 cm cubic specimens were also statistically equal to the theoretically calculated values and to the same materials when ground to a powder. These findings consequently validated the new method. The possibility of determining the activity concentrations needed to establish the ACI for cement-based materials on unground samples introduces a new field of radiological research on actual cement, mortar and concrete materials.

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