30 research outputs found
Environmentally friendly immobilization of radioactive wastes in an alkali activated cement matrix
The paper presents data on efficiency of immobilization of low level radioactive wastes of nuclear power stations using the alkali activated cements as a binding agent in comparison with Portland cement. Much higher efficiency of the alkali activated cements is attributed to abilities of the alkali activated cement matrix, on the contrary to the Portland cement one, to bind radioactive nuclides not only physically and adsorptionally, but chemically. As a result of specific features of the alkali activated cement hardening processes the conditions occur, under which the zeolite-like phases (analogues to natural zeolites) with the crystalline lattices in which Cs and Cr can be disposed, to form, for example, Na-Sr-analcime – wairakite, Na-Cs-analcime – pollucite, gismondine (with the higher adsorption capacity) occur. Compositions of the alkali activated cements and those of the final products using real nitrate- and borate-containing wastes of various composition were chosen experimentally at the nuclear power stations after preliminary work with the waste imitators at the laboratory. Properties of the final products, these were: leachability, biological resistance, freeze/thaw resistance, water resistance, strength, were tested and the results are discussed. A conclusion was made that all above properties of the final products in which the alkali activated cements were used were at least by 10–20 % higher than those of similar products made using Portland cement, and in leachability (leach rate) exceeded by 5–10 times.
The paper also includes description of solidification processes used at the nuclear power plants with using of alkali activated cements
The Influence of Interfacial Transition Zone on Strength of Alkali-Activated Concrete
A process of structure formation taking place in the interfacial transition zone (ITZ) “cement stone-aggregate” was studied on a variety of concretes made with artificial and real aggregates. The study of these processes in the case of artificial aggregate prepared from a mixture of clay loam and alkali-activated slag cement showed that not only active SiO2 and Na2O but also other substances of both cement and aggregate are involved in the formation of the ITZ. This results in the formation of alkaline and alkaline-alkali-earth aluminosilicate hydrates which strengthen the ITZ and improve strength and durability of the concrete. Thus, the alkali-silica reaction (ASR) transforms from a destructive one (negative effect) into a constructive one (positive effect). The study on the ITZ in the alkali-activated cement concretes made with real alkali-susceptible aggregates selected from crushed basalt rock, glassy waste product from basalt fiber production, crushed perlite rock, and expanded perlite suggested to make a conclusion on the possibility to prevent the destructive processes in the ITZ through the addition of the metakaolin additive into the cement composition in quantities of 5–10% by mass. These conclusions were supported by the long-term testing of strength of these concretes, by measuring the deformations “shrinkage-expansion” as well as the results of study on hardness of the ITZ
Alkaline Fly-Ash Cements and concretes, influence of care on early stage of hardening
There are a lot of not well investigated processes in alkaline fly-ash cement technology. Among them the role o f fly-ash type and type o f alkaline component in structure formation processes in different stages, new phases formation and connected with this properties of cements and concretes, including corrosion resistant, durability and other. It was necessarry to investigave influence of concrete care curing, humidity temperature on properties of fly ash-alkaline concrete, on their early stage strength, stability and possibility to self-destruction.Also, it is important to now about strength development o f different types o f alkaline fly-ash
cements and concretes on their base in time and special properties o f such material, especially
m case of investigation possibility to uncover fresh concrete surface
Genesis of Structure and Properties of the Zeolite-Like Cement Matrices of the System Na(K)-Al<sub>2</sub>O<sub>3</sub>-SiO<sub>2</sub>-H<sub>2</sub>O within a Temperature Range of 20–1200°C
The chapter deals with a genesis of structure and properties of the zeolite-like cement matrices of the Na(K)-Al2O3-SiO2-H2O system within a temperature range of 20–1200°С. Due to the fact that zeolite-like structures and their characteristics vary within wide ranges, materials with high-performance properties can be obtained through regulation of the structure formation processes. This can be provided by a proper choice of type of an aluminosilicate component, cation of an alkaline component and additives, including Ca-containing ones, and curing conditions. When the cement matrix formation process is appropriately directed, the zeolite-like products (hydrosodalite, analcime, chabasite, faujasite etc.) dominate in the microstructure that is formed. The ability of some zeolites to recrystallize with temperature increase into stable feldspar-like aluminosilicates without destroying the basic skeleton opens a pathway that is worth to explore in the production of materials similar to low temperature ceramics, intumescent coatings, high temperature and corrosion resistant structures, etc. The examples are given on how to use the above cement matrices for making some of the above listed materials
The effect of hydrodynamic cavitation on performance of the alkaline aluminosilicate coatings for metal structures
Load-bearing metal structures working in atmospheric conditions are exposed to corrosion. Known-in-the art paint-and-lacquer protective coatings can provide protection of metal for rather short period of time (5…10 years). These structures can be effectively protected by more advanced coatings of new generation, namely: alkaline aluminosilicate binder-based coatings of barrier type. These binders differ from the known-in-the-art binding materials by formation in their hydration products of zeolite-like minerals and feldspathoids. The paper discusses principles laid down in formulating the binder composition in the (хК, уNa)2OAl2O3nSiO2mH2O system, target synthesis of hydration products of the binder matrix under influence of dynamic of the binder matrix in cavitation, optimal parameter order to synthesis of cavitation treatment aimed at nanostructuring of zeolite-like and hydromica phases after solidification. These coatings exhibit high corrosion resistance, high adhesion to metal substrate and durability results of restoration works that had been carried out in December 2010 of the Big Bell Tower of the Kiev Petchersk Lavra in order to protect corroded metal surfaces by applying the aluminosilicate binder-based coatings, the major constituent (binder) of which was represented by (0.72Na2O+0.28K2O)1.5Al2O3(4.56)SiO217.5H2O are discussed in details. In 2016, after 6 years of service in high humidity conditions and other aggressive exposures, the coated metal structures were examined and no sign of corrosion of metal substrate and damage of the applied coating was found
High-Performance Alkali-Activated Cement Concretes for Marine Engineering Applications
The contribution covers results of studies on the alkali-activated cement concretes intended for marine engineering applications. Such properties as strength, wear, corrosion, freeze-thaw, weather resistance and many others have been studied, and the results are reported and discussed in detail. The obtained results suggested to draw a conclusion on high potential of the alkali-activated cement concretes for marine engineering applications, since in their performance properties these concretes are highly advantageous over other concretes used as marine concretes and big savings can be expected in the future due to the longer span of service life. The results are supported by long-term observations in real conditions. The above advantages are attributed to more perfect micro- and macrostructure of the alkali-activated cement stone. The authors have summarized their own experience and results collected by PhD and DSc students under their supervision dedicated to assessment of durability of these concretes, in particular, for marine engineering applications. In order to bring these advanced materials into practice of construction worldwide, two rilem (International Union of Laboratories and Experts in Construction Materials, Systems and Structures) committees have been founded: “Alkali-activated Materials” (2010–2013) and “Durability Testing of Alkali Activated Materials” (2013–ongoing)
Порівняльні дослідження впливу метакаоліна і каоліна на властивосі і структуру шлаколужного цементу і бетону
The influence of the metakaolin and kaolin additives on the formation and properties of the alkali-activated slag cements and concretes was studied.The influence of the metakaolin and kaolin additives on macro- and microstructure formation of the cements and concretes was studied.A conclusion was drawn that the processes of microstructure formation of the cement stone with the additive flow in a similar sequence but with different intensity. A conclusion was drawn that the addition of the kaolin instead of metakaolin affected as follows: 2.5–10 % by mass reduced the value of NCP by 9.5–8.7 %, respectively; 2.5–5 % by mass did not affect setting times, but with increase up to 10 % by mass the initial setting time was shorter (from 48 min to 40 min); 2.5–5 % by mass did not affect compressive strength at all stages of hardening, but with increase up to 10 % by mass reduced strength characteristics of the cement-sand specimens (from 57.0 MPa to 49.0 MPa).In case of the addition of 5 % kaolin by mass, an optimal macrostructure of the concrete is formed in which the quantities of the ''conditionally'' closed pores are by 17.7 % higher compared to those of the concretes with the same quantities of the metakaolin. This resulted in the higher freeze/thaw resistance of the concrete (from F400 up to F500). Based on the comparison of properties and structure of the cement and concrete containing the kaolin and metakaolin additives, a possibility to substitute metakaolin by kaolin as a correcting additive was established.Исследовано влияние добавок метакаолина и каолина на формирование микро- макроструктуры и свойств щелочеактивированных шлаковых цементов и бетонов. Проведено сравнительное исследование влияния этих добавок. Установлено, что введение 2,5–5,0 % добавки каолина оказывает более эффективное влияние на процессы структурообразования и свойства, чем добавка метакаолина. Кроме того, замена добавки метакаолина каолином упрощает технологический процесс производства и существенно снижает стоимость цемента и бетонаВстановлено вплив добавок метакаоліна і каоліна на формування мікро- макроструктури й властивостей лугоактивованих шлакових цементів і бетонів. Проведено порівняльне дослідження впливу цих добавок. Встановлено, що введення 2,5–5,0 % добавки каоліну має більш ефективний вплив на процеси структуроутворення і властивості, ніж добавка метакаоліну. Окрім того, заміна добавки метакаоліну каоліном спрощує технологічний процес виробництва й суттєво знижує вартість цементу и бетон
Disperse reinforcing of alkaline aluminosilicate binders for protection materials of structures
The review of the literature and the analysis of the problem of durability and reduction of cracking of binders and materials for the protection of building structures have been carried out, an effective method of improving their cracking resistance during the entire lifetime has been proposed. The influence of reinforcement of the matrix of alkaline aluminosilicate binders on their technological and physical-mechanical properties was investigated. According to the study of influence reinforcing components on the properties of binders, it should be noted that the highest the conditional coefficient of crack resistance is characterized by the contents containing in its composition as a reinforcing component of the basalt scales. The microstructure of the connecting substance and the contact zone “compound substance - the reinforcing component” has been analyzed, the type and the optimum amount of the reinforcing component have been established to provide the technological and operational properties of the materials for the protection of building structures
Розробка складу лужного портландцементу з використанням мінеральних добавок техногенного походження
This paper reports results of the development of cement compositions and production technology for common cement systems "portland cement clinker – mineral additives – alkaline activator – water-reducing admixture", which contain more than 60 % by weight of mineral additives. The additives have been selected from the group: granulated blast furnace slag, ash from thermal power plants (fly ash and disposed ash) and red mud (waste of alumina production). The relevance of the work relates to the need to improve a number of indicators that limit the widespread application of traditional cements, highly filled with waste (slag portland cement), in particular, early strength and setting terms.We have devised basic principles of the structural arrangement of cement compositions, as well as show the technology of their production. It was established that in terms of the requirements based on acting Ukrainian and European standards, in particular EN 197-1, the designed cements are not inferior to the EN cements, CEM I, CEM II, CEM III, in their characteristics, but even outperform them for strength. The developed cement compositions, which contain the portland clinker in the amount not exceeding 40 % by weight, meet the requirements of the EN standard for the classes of compressive strength (at the age of 28 days) 32,5N − 32,5R; 42,5R − 52,5R.We have investigated the influence of alkaline components on the structure formation processes of artificial stone in the alkaline activated cement at different levels. It was established that an increase in the alkalinity of a cement environment predetermines a decrease in the basicity of the phase composition of neo formations of cement at the micro level, as well as contributes to increasing the total porosity of an artificial stone, which, at the same time, tends to closing and decreases over time.Статья охватывает результаты разработки цементных составов и технологии производства для распространенных цементных систем «портландцементный клинкер – минеральные добавки – щелочной активатор – водоредуцирующая добавка», которые содержат более 60 % от массы минеральных добавок. Добавки были выбраны из группы: доменный гранулированный шлак, золы тепловых электростанций (зола уноса и отвальная зола) и красный шлам (отход глиноземного производства). Актуальность работы связана с необходимостью улучшения целого ряда показателей, которые ограничивают широкое использование традиционных высоконаполненных отходами цементов (шлакопортландцемента), в частности, ранней прочности и сроков схватывания.Разработаны основные принципы конструкционного построения цементных составов, а также показана технология их производства. Установлено, что с точки зрения требований существующих украинских и европейских стандартов, в частности EN 197−1, разработанные цементы не только не уступают EN цементам: CEM I, CEM II, CEM III по характеристикам, но и превосходят в прочности. Разработанные цементные составы, которые содержат портландцементный клинкер не более 40 % по массе соответствуют требованиям стандарта EN согласно классам прочности на сжатие (в возрасте 28 суток) 32,5N − 32,5R; 42,5R − 52,5R.Исследовано влияние щелочных компонентов на процессы структурообразования искусственного камня щелочного цемента на разных уровнях. Установлено, что повышение щелочности среды цемента обуславливает снижение основности фазового состава новообразований цемента на микроуровне, а также способствует повышению общей пористости искусственного камня, которая, в то же время, имеет тенденцию к заращиванию и уменьшению во времениРобота охоплює результати розробки складів цементу і технології виробництва для поширених цементних систем «портландцементний клінкер – мінеральні добавки – лужний активатор – водоредикуюча добавка», що містять більше 60 % за масою мінеральних добавок. Добавки обрано з групи: доменний гранульований шлак, золи теплових електростанцій (зола виносу та відвальні золи) та червоний шлам (відходи глиноземного виробництва). Актуальність роботи пов’язана із необхідністю покращення цілої низки показників, що обмежують широке застосування традиційних високонаповнених відходами цементів (шлакопортландцементу, зокрема ранньої міцності та строків тужавлення).Розроблено основні принципи конструкційної побудови цементних складів та показана технологія виробництва. Встановлено, що з точки зору вимог існуючих українських та європейських стандартів, а саме EN 197−1, розроблені цементи не тільки не поступаються цементам EN: CEM I, CEM II, CEM III за властивостями, але й перевершують за міцністю. Розроблені склади цементів, що містять портландцементний клінкер, не більше ніж 40 % за масою відповідають вимогам стандарту EN згідно класам за міцністю на стиск (у віці 28 діб) 32,5N – 32,5R; 42,5R-52,5R. В деяких випадках вміст супутніх продукті промисловості у складі цементу може сягати 95 % за масою.Досліджено вплив лужних компонентів на процеси структуроутворення штучного каменю лужного цементу на різних рівнях. Встановлено, що підвищення лужності середовища цементу обумовлює зниження основності фазового складу новоутворень цементу на макрорівні. Використання лужного активатора сприяє збільшенню загальної пористості штучного каменю, яка здатна знижуватись протягом часу експлуатаці