scholarly journals Synthesis of Pectiniform Polyurethane-Modified Polycarboxylate and Its Preliminary Application in Ultrahigh-Performance Concrete

2020 ◽  
Vol 2020 ◽  
pp. 1-16
Author(s):  
Shuncheng Xiang ◽  
Yingli Gao
Keyword(s):  
Silica Fume ◽  
Negative Impact ◽  
Raw Materials ◽  
Synthesis Method ◽  
Autogenous Shrinkage ◽  
Drying Shrinkage ◽  
Isophorone Diisocyanate ◽  
Initiation System ◽  
Dry Shrinkage ◽  
Preliminary Application

In this paper, modified polyurethane prepolymer was synthesized by the segmental synthesis method using isophorone diisocyanate (IPDI), hydroxyl-terminated silicone, and polyether glycol dimethylolpropionic acid as raw materials. After that, pectiniform polycarboxylate, of which side chains were in roughly the same polymerization degree and main chains were in different lengths, was synthesized at normal temperature in the complex initiation system of H2O2, APS, sodium bisulfite, and Vc. Then, compared with commercial Sika polycarboxylate, their applications in ultrahigh-performance concrete (HUPC), including flowability, strength, drying shrinkage, and autogenous shrinkage, were investigated. The results showed that, due to the molecular structure of polyorganosiloxane, the synthesized polycarboxylate could be better dispersed. Dosage of silica fume could effectively improve the compressive strength of UHPC, while slag had a certain negative impact on its strength. Incorporation of slag and silica fume could effectively reduce the dry shrinkage of UHPC.

scholarly journals Synthesis of Modified Polycarboxylate and Its Application in Ultra-High Performance Concrete

2021 ◽  
Vol 8 ◽  
Author(s):  
Shuncheng Xiang ◽  
Yansheng Tan ◽  
Yingli Gao
Keyword(s):  
Silica Fume ◽  
High Performance ◽  
Chain Transfer ◽  
High Performance Concrete ◽  
Raw Materials ◽  
Synthesis Method ◽  
Drying Shrinkage ◽  
Polymerization Reaction ◽  
Ultra High Performance Concrete ◽  
Initiation System

Modified polyurethane prepolymer was prepared using the segmental synthesis method. Then, pectiniform polycarboxylate was synthesized at normal temperature in the complex initiation system of H2O2, APS, sodium bisulfite, Vc, and Rongalit according to the free radical polymerization reaction mechanism, using TPEG, AA, and PEG as raw materials and TGA as the chain transfer agent. Compared with commercial Sika polycarboxylate, its flowability, strength, drying shrinkage, and auto-shrinkage were studied. The experimental results show that the synthesized polycarboxylate could be better dispersed. Adding silica fume can enhance the compressive strength of ultra-high performance concrete (UHPC), while slag may decline its strength. By incorporating slag and silica fume, the drying shrinkage of UHPC was reduced, but its auto-shrinkage was increased.

scholarly journals Investigation on the Properties of Sustainable Reactive Powder Concrete by Utilization of Coir Pith Aggregates and Pyrogenic Silica

2021 ◽  
Author(s):  
Oorkalan A ◽  
Chithra S
Keyword(s):  
Silica Fume ◽  
Low Cost ◽  
Autogenous Shrinkage ◽  
Drying Shrinkage ◽  
Particle Packing ◽  
Reactive Powder Concrete ◽  
Fine Aggregate ◽  
Coir Pith ◽  
Pyrogenic Silica ◽  
Reactive Powder

Abstract The present study investigates the properties of RPC developed using low cost eco-friendly materials such as pyrogenic silica (PS) and coir pith (CP) fine aggregates. This study investigates the effects of PS as silica fume replacement which is the main constituent for the production of reactive powder concrete which contained coir pith as a fine aggregate replacement instead of quartz sand up to 25%. The use of silica fume increases the particle packing density of RPC but increases the shrinkage phenomenon in RPC due to the minimum w/b ratio adopted. Therefore, in this research PS is used as a partial substitute for SF up to 30% and its effect on the mechanical and durability properties of coir pith containing RPC is studied. The test results showed that the mechanical strength values decreased with an increase in the addition of CP aggregate beyond 5% whereas the decrement in compressive strength was partially reduced when PS is used as silica fume replacement up to a maximum of 30%. The chloride penetration resistance was also improved with increasing PS substitution in RPC containing CP aggregates. The autogenous shrinkage and drying shrinkage were also significantly reduced due to the internal curing ability of the CP aggregates in combination with PS. The development of dense CSH gels from hydration is also evident from low CaO/ SiO2 ratio obtained from the EDS analysis. Hence the combination of PS with CP aggregates can reduce the shrinkage characteristics of RPC thereby providing eco-friendly sustainable concrete at low cost.

Dry Shrinkage and Compressive Strength of Blended Cement Pastes with Fly Ash and Silica Fume

2012 ◽  
Vol 535-537 ◽  
pp. 1735-1738 ◽  
Author(s):  
Yan Li ◽  
Dao Sheng Sun ◽  
Xiu Sheng Wu ◽  
Ai Guo Wang ◽  
Wei Xu ◽  
...  
Keyword(s):  
Compressive Strength ◽  
Fly Ash ◽  
Silica Fume ◽  
Cement Paste ◽  
Blended Cement ◽  
Drying Shrinkage ◽  
Cementitious Material ◽  
Strength Increase ◽  
Cement Pastes ◽  
Dry Shrinkage

This paper reports the drying shrinkage and compressive strength results of cement pastes with fly ash and silica fume. In this study, Portland cement (PC) was used as the basic cementitious material. Fly ash (FA) and silica fume (SF) were used as cement replacement materials at levels of 0%, 5%, 10%, and 15% , 40%, 35%, 25%, and 15% by weight of the total cementitious material, respectively. The water/cement (PC + FA + SF) ratios (w/c) was 0.28 by weight. The samples produced from fresh pastes were demoulded after a day; then they were cured at 20 ±1°C with 50 ± 3% relative humidity (RH) until the samples were used for drying shrinkage and compressive strength measurement at various ages. The results show that drying shrinkage and compressive strength increase with increasing SF content, and the optimum composition of blended cement pastes is the cement paste with 30% fly ash and 10% silica fume, which possesses lower drying shrinkage values than that of plain cement paste and higher early age strength than that of blended cement pastes with fly ash. Furthermore, a linear relationship is established between compressive strength and drying shrinkage. By comparing the development of compressive strength and the drying shrinkage deformations, it appears possible to predict the drying shrinkage according to the acquired compressive strength.

Shrinkage Properties of Cement-Silica Fume Blended Pastes in Early Age

2017 ◽  
Vol 726 ◽  
pp. 521-526
Author(s):  
Di Zou ◽  
Lian Zhen Xiao ◽  
Wen Chong Shi
Keyword(s):  
Silica Fume ◽  
Rapid Growth ◽  
High Performance ◽  
High Performance Concrete ◽  
Autogenous Shrinkage ◽  
Drying Shrinkage ◽  
Early Age ◽  
Shrinkage Ratio ◽  
Study Results ◽  
Expansion Period

The cement-silica fume blended pastes were prepared with different silica fume (SF) dosages of 0%, 5%, 10%, and 15% at different water-binder ratios (W/B) of 0.4 and 0.5. The autogenous shrinkage (AS) and the drying shrinkage (DS) of the paste samples in the hydration period of 7d (168 hours) were measured by a new measurement technique to explore the influence of W/B and silica fume incorporation on the shrinkage in early age. The study results can provide reference for high performance concrete mix design.It is found that ether the AS or the DS of the paste samples shows a similar pattern, and the AS development with hydration time appeared a temporary expansion period after a rapid growth, especially in the samples at a higher W/B or with a lower SF content. However, the DS development did not occur obvious expansion period.Three development trends were obtained for the factors of W/B and SF content. 1) the AS and DS of the pastes mainly occurred in early ages. The lower W/B, the shorter the rapid growth periods, and the higher the shrinkage ratio of 1d to 7d. For the pastes with W/B of 0.4, the AS grew rapidly in 1d and the DS grew rapidly in the first 10h, and the AS value in 1d reached to 63.6% of 7d, and the DS value reached to 62.1% of 7d in the paste with SF of 10%. For the pastes with W/B of 0.5, the rapid growth periods of the AS and DS respectively extended to 30~33h and 12h, and the AS value in 1d reached to 60.0% of 7d, and the DS value reached to 57.2% of 7d in the paste with SF of 10%. 2) The lower W/B, the higher the shrinkage ratio of the AS to the DS. When the SF dosage is 10%, the ratio of the AS value to the DS value of 7d is 21.66%~21.15% for W/B of 0.4, and only 6.06%~5.78% for the W/B of 0.5. 3) the higher SF content results in the higher AS in cement-SF blended pastes. For the pastes with W/B of 0.4, the ratio of the AS to the DS increased from 6.98% to 30.16% with the increase of content of SF from 5% to 15% in 1d, from 15.1% to 28.19% in 3d, from 16.78% to 26.16% in 7d.

scholarly journals Silica Fume and Nanosilica Effects on Mechanical and Shrinkage Properties of Foam Concrete for Structural Application

2020 ◽  
Vol 2020 ◽  
pp. 1-10 ◽  
Author(s):  
Jianqing Gong ◽  
Lilin Zhu ◽  
Jiusu Li ◽  
Da Shi
Keyword(s):  
Electron Microscopy ◽  
Flexural Strength ◽  
Silica Fume ◽  
Autogenous Shrinkage ◽  
Foam Concrete ◽  
Ultrasonic Detection ◽  
Structural Application ◽  
Opposite Trend ◽  
Dry Shrinkage ◽  
Scanning Electron

Adding the appropriate amount of silica fume (SF) or nanosilica (NS) can improve the strength and reduce the shrinkage of foam concrete (FC), thereby widening its application. This paper reports on a study of FC mechanical and shrinkage properties when varying SF and NS proportions were used to replace cement. Scanning electron microscopy (SEM) and nonmetallic ultrasonic detection were employed to investigate the mechanism of strength changes. The result showed that when the SF and NS content was 15% and 4%, in the 28 days, the compressive strength of FC peaked at 32.8 MPa and 35.8 MPa, and the flexural strength maximized at 7.9 MPa and 9.1 MPa, respectively. The autogenous shrinkage reached the minimum value, separately, i.e., 741.2 × 10−6 and 797.1 × 10−6. The dry shrinkage value was the highest (862.5 × 10−6 and 1387.5 × 10−6). The results indicated that the compressive and flexural strength of FC first increased and then decreased as SF and NS content increased. Autogenous shrinkage first decreased and then increased with the increase of SF or NS content. An opposite trend of dry shrinkage could be observed. FC made with NS had higher shrinkage than it did with SF. The results also indicated that there was a correlation between microstructure and sound velocity in the presence of SF or NS.

Organic chemical devulcanization of rubber vulcanizates in supercritical carbon dioxide and associated less eco-unfriendly approaches: A review

2021 ◽  
pp. 0734242X2110085
Author(s):  
Jabulani I Gumede ◽  
Buyiswa G Hlangothi ◽  
Chris D Woolard ◽  
Shanganyane P Hlangothi
Keyword(s):  
Carbon Dioxide ◽  
Supercritical Carbon Dioxide ◽  
Negative Impact ◽  
Raw Materials ◽  
Chemical Components ◽  
Organic Chemical ◽  
Attractive Alternative ◽  
Special Focus ◽  
Waste Tyres ◽  
Supercritical Carbon

There is a growing need to recover raw materials from waste due to increasing environmental concerns and the widely adopted transition to circular economy. For waste tyres, it is necessary to continuously develop methods and processes that can devulcanize rubber vulcanizates into rubber products with qualities and properties that can closely match those of the virgin rubber. Currently, the most common, due to its efficiency and perceived eco-friendliness in recovering raw rubber from waste rubbers, such as tyres, is devulcanization in supercritical carbon dioxide (scCO2) using commercial and typical devulcanizing agents. The scCO2 has been generally accepted as an attractive alternative to the traditional liquid-based devulcanization media because of the resultant devulcanized rubber has relatively better quality than other processes. For instance, when scCO2 is employed to recover rubber from waste tyres (e.g. truck tyres) and the recovered rubber is blended with virgin natural rubber (NR) in various compositions, the curing and mechanical properties of the blends closely match those of virgin NR. The atmospheric toxicity and cost of the commonly used devulcanization materials like chemical agents, oils and solvents have enabled a shift towards utilization of greener (mainly organic) and readily available devulcanization chemical components. This literature review paper discusses the approaches, which have less negative impact on the environment, in chemical devulcanization of rubber vulcanizates. A special focus has been on thermo-chemical devulcanization of waste tyres in scCO2 using common organic devulcanizing agents.

scholarly journals Production of Microfibrillated Cellulose from Fast-Growing Poplar and Olive Tree Pruning by Physical Pretreatment

2021 ◽  
Vol 11 (14) ◽  
pp. 6445
Author(s):  
David Ibarra ◽  
Raquel Martín-Sampedro ◽  
Bernd Wicklein ◽  
Úrsula Fillat ◽  
María E. Eugenio
Keyword(s):  
Negative Impact ◽  
Raw Materials ◽  
Olive Tree ◽  
Barrier Properties ◽  
Microfibrillated Cellulose ◽  
Mechanical Resistance ◽  
Fast Growing ◽  
Wide Range ◽  
Pfi Refining ◽  
Tree Pruning

Motivated by the negative impact of fossil fuel consumption on the environment, the need arises to produce materials and energy from renewable sources. Cellulose, the main biopolymer on Earth, plays a key role in this context, serving as a platform for the development of biofuels, chemicals and novel materials. Among the latter, micro- and nanocellulose have been receiving increasing attention in the last few years. Their many attractive properties, i.e., thermal stability, high mechanical resistance, barrier properties, lightweight, optical transparency and ease of chemical modification, allow their use in a wide range of applications, such as paper or polymer reinforcement, packaging, construction, membranes, bioplastics, bioengineering, optics and electronics. In view of the increasing demand for traditional wood pulp (e.g., obtained from eucalypt, birch, pine, spruce) for micro/nanocellulose production, dedicated crops and agricultural residues can be interesting as raw materials for this purpose. This work aims at achieving microfibrillated cellulose production from fast-growing poplar and olive tree pruning using physical pretreatment (PFI refining) before the microfibrillation stage. Both raw materials yielded microfibrillated cellulose with similar properties to that obtained from a commercial industrial eucalypt pulp, producing films with high mechanical properties and low wettability. According to these properties, different applications for cellulose microfibers suspensions and films are discussed.

scholarly journals New Circular Challenges in the Development of Take-Away Food Packaging in the COVID-19 Period

Energies ◽  
2021 ◽  
Vol 14 (15) ◽  
pp. 4705
Author(s):  
Ewa Kochańska ◽  
Rafał M. Łukasik ◽  
Maciej Dzikuć
Keyword(s):  
Social Transformation ◽  
Food Packaging ◽  
New Technologies ◽  
Negative Impact ◽  
Raw Materials ◽  
Distribution Channels ◽  
Low Carbon ◽  
Industrial Transformation ◽  
Specific Distribution ◽  
Food Market

The COVID-19 pandemic has set new challenges for the HoReCa industry. Lockdowns have coincided with and strongly impacted the industrial transformation processes that have been taking place for a decade. Among the most important HoReCa transition processes are those related to the rapid growth of the delivery-food market and ordering meals via internet platforms. The new delivery-food market requires not only the development of specific distribution channels, but also the introduction of appropriate, very specific food packaging. Food packaging and its functionality are defined by the administrative requirements and standards applicable to materials that have contact with food and principally through the prism of the ecological disaster caused by enormous amounts of plastic waste, mainly attributed to the food packaging. To meet environmental and administrative requirements, new technologies to produce food packaging materials are emerging, ensuring product functionality, low environmental impact, biodegradability, and potential for composting of the final product. However, predominantly, the obtained product should keep the nutritional value of food and protect it against changes in color or shape. Current social transformation has a significant impact on the food packaging sector, on one hand creating a new lifestyle for society all over the world, and on the other, a growing awareness of the negative impact of humans on the environment and increasing responsibility for the planet. The COVID-19 pandemic has highlighted the need to develop a circular economy based on the paradigm of shortening distribution channels, using local raw materials, limiting the consumption of raw materials, energy, water, and above all, minimizing waste production throughout the life cycle of products, all of which are in line with the idea of low-carbon development.

scholarly journals Recent Advances in Fabrication of Non-Isocyanate Polyurethane-Based Composite Materials

Materials ◽  
2021 ◽  
Vol 14 (13) ◽  
pp. 3497
Author(s):  
Piotr Stachak ◽  
Izabela Łukaszewska ◽  
Edyta Hebda ◽  
Krzysztof Pielichowski
Keyword(s):  
Raw Materials ◽  
Synthesis Method ◽  
Polymeric Materials ◽  
Original Research ◽  
Significant Group ◽  
Oh Groups ◽  
New Class ◽  
Hazardous Chemical ◽  
Wide Range

Polyurethanes (PUs) are a significant group of polymeric materials that, due to their outstanding mechanical, chemical, and physical properties, are used in a wide range of applications. Conventionally, PUs are obtained in polyaddition reactions between diisocyanates and polyols. Due to the toxicity of isocyanate raw materials and their synthesis method utilizing phosgene, new cleaner synthetic routes for polyurethanes without using isocyanates have attracted increasing attention in recent years. Among different attempts to replace the conventional process, polyaddition of cyclic carbonates (CCs) and polyfunctional amines seems to be the most promising way to obtain non-isocyanate polyurethanes (NIPUs) or, more precisely, polyhydroxyurethanes (PHUs), while primary and secondary –OH groups are being formed alongside urethane linkages. Such an approach eliminates hazardous chemical compounds from the synthesis and leads to the fabrication of polymeric materials with unique and tunable properties. The main advantages include better chemical, mechanical, and thermal resistance, and the process itself is invulnerable to moisture, which is an essential technological feature. NIPUs can be modified via copolymerization or used as matrices to fabricate polymer composites with different additives, similar to their conventional counterparts. Hence, non-isocyanate polyurethanes are a new class of environmentally friendly polymeric materials. Many papers on the matter above have been published, including both original research and extensive reviews. However, they do not provide collected information on NIPU composites fabrication and processing. Hence, this review describes the latest progress in non-isocyanate polyurethane synthesis, modification, and finally processing. While focusing primarily on the carbonate/amine route, methods of obtaining NIPU are described, and their properties are presented. Ways of incorporating various compounds into NIPU matrices are characterized by the role of PHU materials in copolymeric materials or as an additive. Finally, diverse processing methods of non-isocyanate polyurethanes are presented, including electrospinning or 3D printing.

scholarly journals Effect of Fly Ash on Compressive Strength, Drying Shrinkage, and Carbonation Depth of Mortar with Ferronickel-Slag Powder

2021 ◽  
Vol 11 (3) ◽  
pp. 1037
Author(s):  
Se-Jin Choi ◽  
Ji-Hwan Kim ◽  
Sung-Ho Bae ◽  
Tae-Gue Oh
Keyword(s):  
Compressive Strength ◽  
Fly Ash ◽  
Construction Industry ◽  
Bituminous Coal ◽  
Raw Materials ◽  
Drying Shrinkage ◽  
The Other ◽  
Test Results ◽  
Slag Powder ◽  
Ferronickel Slag

In recent years, efforts to reduce greenhouse gas emissions have continued worldwide. In the construction industry, a large amount of CO2 is generated during the production of Portland cement, and various studies are being conducted to reduce the amount of cement and enable the use of cement substitutes. Ferronickel slag is a by-product generated by melting materials such as nickel ore and bituminous coal, which are used as raw materials to produce ferronickel at high temperatures. In this study, we investigated the fluidity, microhydration heat, compressive strength, drying shrinkage, and carbonation characteristics of a ternary cement mortar including ferronickel-slag powder and fly ash. According to the test results, the microhydration heat of the FA20FN00 sample was slightly higher than that of the FA00FN20 sample. The 28-day compressive strength of the FA20FN00 mix was approximately 39.6 MPa, which was higher than that of the other samples, whereas the compressive strength of the FA05FN15 mix including 15% of ferronickel-slag powder was approximately 11.6% lower than that of the FA20FN00 mix. The drying shrinkage of the FA20FN00 sample without ferronickel-slag powder was the highest after 56 days, whereas the FA00FN20 sample without fly ash showed the lowest shrinkage compared to the other mixes.

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