scholarly journals Rheology of Cement Pastes with Siliceous Fly Ash and the CSH Nano-Admixture

Materials ◽  
2021 ◽  
Vol 14 (13) ◽  
pp. 3640
Author(s):  
Bartosz Szostak ◽  
Grzegorz Ludwik Golewski
Keyword(s):  
Fly Ash ◽  
Modern Technology ◽  
Heat Of Hydration ◽  
Hydration Heat ◽  
Cement Composites ◽  
Standard Samples ◽  
Cement Pastes ◽  
Positive Effects ◽  
Calcium Silicates ◽  
Positive Effect

The use of fly ash in cement composites adversely affects its mechanical properties during the first days of mixture curing. Modern technology, in the form of an admixture containing the hydrated calcium silicates, allows to accelerate the hardening and binding process of concrete. In this paper, studies on the influence of the admixture on properties of concretes with the ordinary Portland cements (OPC) containing the addition of siliceous fly ash (FA) have been carried out. As part of the experimental research, the authors conducted a series of studies for cement pastes modified with the addition of FA and the CSH nano-admixture (NA). In order to compare the mixtures, the following tests of cement pastes were carried out: the compressive and flexural strength, heat of hydration, SEM and rheological shrinkage. The mechanical parameters were tested after 4, 8, 12 and 24 h. The hydration heat test and microstructure analysis were carried out during the first 24 h of the concrete curing. All tests were carried out on the standard samples. On the basis of the heat of hydration test, much higher hydration heat was found in mixtures modified with the NA. During the shrinkage test, a positive effect of the NA was observed—the shrinkage during the first 28 days of mixture curing was lower than in the reference samples. The application of the CSH nano-admixture to cement pastes with the addition of FA has brought positive effects. Apart from a significant increase in strength in the first 24 h of mixture curing, a reduction in the rheological shrinkage was observed. The admixture can be successfully used in the ash concretes, in which a higher early strength is required.

Synergistic Effect of High Temperature Fly Ash with Fluidized Bed Combustion Fly Ash in Cement Composites

2016 ◽  
Vol 722 ◽  
pp. 113-118
Author(s):  
Martin Ťažký ◽  
Rudolf Hela
Keyword(s):  
High Temperature ◽  
Fly Ash ◽  
Fluidized Bed ◽  
Fossil Fuels ◽  
Cement Composite ◽  
Pozzolanic Reaction ◽  
Cement Composites ◽  
Fluidized Bed Combustion ◽  
Cement Pastes ◽  
Free Cao

Using high temperature fly ash for his pozzolan properties to cement composite production is known a few years ago. New ways combustion of fossil fuels also creates a new type of fly ash, named fluidized bed combustion fly ash. However, this fly ash has same pozzolan properties as has high temperature fly ash, this type is not using for production of cement composites. Fluidized bed combustion fly ash has highly variable chemical composition but usually it has a higher amount of free CaO together with sulphates. This higher amounts of free CaO after mixing of fluidized bed combustion fly ash with water to some extent becomes an activator for the beginning of the pozzolanic reaction, during which is consumed the extinguished CaO. If there is also present high temperature fly ash in cement composite, it could be accelerated his pozzolanic reaction in the same manner using a fluidized bed combustion fly ash. In this experiment was tested a synergy effect in the use of fluidized bed combustion fly ash with high temperature fly ash as an additive. The experiment was carried out on cement pastes that have been studied in particular the progress of hydration processes, pointing to a possible acceleration of pozzolanic reactions of both types of fly ash.

Experimental Study on the Impact of Admixture for Concrete Heat of Hydration and Early-Age Contractile Properties

2012 ◽  
Vol 253-255 ◽  
pp. 385-389 ◽  
Author(s):  
Jian Cheng Sun ◽  
Bo Jun Wang ◽  
Wen Zhong Zhao
Keyword(s):  
Experimental Study ◽  
Fly Ash ◽  
Concrete Structure ◽  
Autogenous Shrinkage ◽  
Heat Of Hydration ◽  
Reducing Agent ◽  
Hydration Heat ◽  
Early Age ◽  
Mix Proportion ◽  
Structure Crack

During the technology development of modem concrete, concrete structure crack (especially early-age crack) becomes more and more serious and has been one of main research directions of civil engineering. This paper aims at the seriousness of concrete structure crack and presents one of main cause is that concrete early-age (especially autogenous shrinkage) become large through the experimental study. autogenous shrinkage are mainly belongs to temperature cracks and desiccation cracks. Analyses the affection of ash and water reducing agent on the hydration heat, under the optimum proportion experiment which aims at reducing he hydration heat of cement. The best program are obtained that double mix with 20% fly ash and 1.5% water reducing agent .Design mortar’s early anti-crack experiment, and study crack-resistance and other mechanical properties based on different ages & different mix proportion. From the experiment, analyses early cracking under the influence of admixtures. The mix proportion of 20% fly ash, 10% slag and 1.2% water reducing agent can minimize the creation of cracks.

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.

scholarly journals Undissolved Ilmenite Mud from TiO2 Production—Waste or a Valuable Addition to Portland Cement Composites?

Materials ◽  
2020 ◽  
Vol 13 (16) ◽  
pp. 3555 ◽  
Author(s):  
Filip Chyliński ◽  
Jan Bobrowicz ◽  
Paweł Łukowski
Keyword(s):  
Fly Ash ◽  
Portland Cement ◽  
Silica Fume ◽  
High Reactivity ◽  
Heat Of Hydration ◽  
Pozzolanic Activity ◽  
Cement Composites ◽  
Level Of Activity ◽  
Natural Pozzolana ◽  
Thermal Analysis Techniques

This paper presents a method of utilising ilmenite MUD created during the production of titanium dioxide (TiO2) according to the sulphate method as an additive for Portland cement composites. After the production process, undissolved MUD was additionally rinsed with water and filtrated in the factory to make it more useful (R-MUD) for implementation and also to turn back some of the by-products of the production of TiO2. R-MUD is less hazardous waste than MUD. It has a lower concentration of sulphuric acid and some heavy metals. The rinsing process raised the concentration of SiO2, which is a valuable part of R-MUD because of its potential pozzolanic activity. This means that the R-MUD might be a reactive substitute of part of Portland cement in building composites. The article presents the results of research on the pozzolanic activity of R-MUD and other materials with proved pozzolanic activity, such as silica fume, fly ash and natural pozzolana (trass). Tests were performed using thermal analysis techniques. The tests showed that the pozzolanic activity or R-MUD after three days is at the same level as silica fume and after 28 days it is twice as high as the activity of fly ash. Beyond the 180th day of curing, R-MUD had the same level of activity as fly ash. The summary is supplemented by calorimetric tests, which confirm the high reactivity of R-MUD compared to other commonly used concrete additives, already in the initial hydration period. In summary, heat of hydration after 72 h of Portland cement with R-MUD is at the same level as the heat of hydration of Portland cement with silica fume and also pure Portland cement grout. The results confirm that the process of formation of micro-silica contained in R-MUD react with calcium hydroxide to form the C-S-H phase, which is responsible for the microstructure of cement composites.

Heat of hydration of cement pastes containing high-volume fly ash and silica fume

2019 ◽  
Vol 138 (3) ◽  
pp. 2065-2075 ◽  
Author(s):  
Watcharapong Wongkeo ◽  
Pailyn Thongsanitgarn ◽  
Chi-Sun Poon ◽  
Arnon Chaipanich
Keyword(s):  
Fly Ash ◽  
Silica Fume ◽  
High Volume ◽  
Heat Of Hydration ◽  
Cement Pastes ◽  
High Volume Fly Ash

scholarly journals Concept of Evaluation of Mineral Additives’ Effect on Cement Pastes’ Durability and Environmental Suitability

Materials ◽  
2021 ◽  
Vol 14 (6) ◽  
pp. 1448
Author(s):  
Robert Figmig ◽  
Adriana Estokova ◽  
Miloslav Luptak
Keyword(s):  
Natural Zeolite ◽  
Holistic Approach ◽  
Cement Composites ◽  
Cement Pastes ◽  
Supplementary Cementitious Material ◽  
Environmental Suitability ◽  
Evaluation Approach ◽  
Mineral Additive ◽  
Mineral Additives ◽  
Positive Effect

This experimental study focuses on the assessment of mineral additives and their incorporation into cement composites (CC). The assessment was based on a holistic approach to the performance of the durability properties of CC. Environmental suitability was also taken into consideration. In the experiments, cement pastes with w/c ratios of 0.3, 0.4, and 0.5, respectively, were prepared. Natural zeolite (NZ) and densified silica fume (SF) at doses of 7.5 and 15.0 wt.% of cement were used as the investigated (replacement) materials. Their effects (including development over time) on density, strength (flexural and compressive), porosity by water absorption, permeability by rapid chloride penetration (RCP) test, phase content by thermal analysis, and hydration progression, were observed. The results were then used to propose an evaluation approach. Natural zeolite was used for its known pozzolanic activity and classification as a supplementary cementitious material (SCM). In contrast SF acted as a filler in cement pastes, and thus did not have a direct positive effect on durability. The concept of comprehensive analysis for unknown additive classification is proposed to expressly differentiate between SCM, inert, and improving mineral additive. This concept could be applied to the assessment of mineral additives with regards to the durability and suitability of cement composites.

scholarly journals Biopolymer-Based Hybrids as Effective Admixtures for Cement Composites

Polymers ◽  
2020 ◽  
Vol 12 (5) ◽  
pp. 1180
Author(s):  
Agnieszka Ślosarczyk ◽  
Izabela Klapiszewska ◽  
Patryk Jędrzejczak ◽  
Łukasz Klapiszewski ◽  
Teofil Jesionowski
Keyword(s):  
Hybrid Materials ◽  
Weight Ratio ◽  
High Energy ◽  
Cement Composites ◽  
Cement Pastes ◽  
Colorimetric Data ◽  
Physical Interactions ◽  
Ratio Of Components ◽  
Positive Effect ◽  
Satisfactory Plasticity

In the framework of this publication, silica-lignin hybrid materials were designed, obtained, characterized and then used as admixtures for cement composites. High-energy mechanical grinding of individual components was used to produce the systems that allowed ensuring adequate homogeneity of the final products. As a result of the analysis of Fourier transform infrared spectroscopy, it has been confirmed that weak physical interactions occur between the components. This allowed classifying the resulting systems as I class hybrid materials. In addition, the efficiency of obtaining final products was also inferred on the basis of obtained porous structure parameters and colorimetric data. The achieved bio-admixture with different weight ratios of silica and lignin was added to cement pastes in the amount ranging from 0.5 to 1 wt.%. The study showed that increasing the ratio of lignin in the admixture from 0.15 to 1 wt.% had a positive effect on the rheological properties of the pastes, while the mechanical properties of the composite were deteriorated. In turn, a higher amount of silica in the admixture acted in reverse. The most favorable results were obtained for a silica-lignin bio-admixture with a weight ratio of components equal to 5:1 wt./wt. A significant increase in compressive strength was gained at satisfactory plasticity of the paste.

scholarly journals Comparison of the influence of participation in screen golf on self-esteem, loneliness, depression, social isolation, and life satisfaction between people with and without disabilities in Republic of Korea

2021 ◽  
Vol 89 (1) ◽  
pp. 11-21
Author(s):  
Chul-Ho Bum ◽  
Mary A. Hums ◽  
Amy Picklesimer ◽  
Chulhwan Choi
Keyword(s):  
Life Satisfaction ◽  
Sport Participation ◽  
Leisure Activities ◽  
People With Disabilities ◽  
Leisure Activity ◽  
Self Esteem ◽  
Modern Technology ◽  
Validity And Reliability ◽  
Positive Effects ◽  
Positive Effect

AbstractScreen golf is a product of the combination of modern technology and leisure. This new form of sport can provide people with disabilities opportunities for positive life experiences through sport participation. This study aimed to investigate differences in the effect of screen golf participation on psychosocial factors (self-esteem, isolation, depression, loneliness, and life satisfaction) in people with and without disabilities. With 293 survey respondents in this study, the Multivariate Analysis of Variances (MANOVA) was performed twice to measure differences between groups after ensuring the validity and reliability of the instrument. Participation in screen golf demonstrated a positive effect for all factors for people with disabilities. Results also showed a more positive effect on self-esteem and life satisfaction for people without disabilities with screen golf experience than for those without any screen golf experience. This study demonstrated that screen golf, as a physical leisure activity, was helpful to all study participants, with greater positive effects observed for participants with disabilities. This finding suggests that ubiquitous leisure activities such as screen golf made possible by advancements in modern technologies offer desirable benefits to many. This study is highly meaningful since it demonstrated how technologies could be helpful to people with disabilities who historically have has less access to leisure activities than able-bodied people.

Impact of Digitalization on Service Work in Knowledge-Intensive Business Services: An Empirical Study in Tax Consultancies

2019 ◽  
Vol 3 (4) ◽  
pp. 209-222
Author(s):  
Philipp K. Görs ◽  
Henning Hummert ◽  
Anne Traum ◽  
Friedemann W. Nerdinger
Keyword(s):  
Work Engagement ◽  
Service Work ◽  
Psychological Consequences ◽  
Business Services ◽  
Knowledge Intensive Business Services ◽  
Positive Effects ◽  
Knowledge Intensive ◽  
The Impact ◽  
Positive Effect ◽  
Special Case

Digitalization is a megatrend, but there is relatively little knowledge about its consequences for service work in general and specifically in knowledge-intensive business services (KIBS). We studied the impact of digitalization on psychological consequences for employees in tax consultancies as a special case of KIBS. We compare two tax consulting jobs with very different job demands, those of tax consultants (TCs) and assistant tax consultants (ATCs). The results show that the extent of digitalization at the workplace level for ATCs correlates significantly positively with their job satisfaction. For TCs, the same variable correlates positively with their work engagement. These positive effects of digitalization are mediated in the case of ATCs by the impact on important job characteristics. In the case of TCs, which already have very good working conditions, the impact is mediated by the positive effect on self-efficacy. Theoretical and practical consequences of these results are discussed.

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