36 research outputs found

    Comparative Study of Superabsorbent Polymers and Pre‐soaked Pumice as Internal Curing Agents in Rice Husk Ash Based High‐Performance Concrete

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    Utilisation of superabsorbent polymers (SAP) and pre‐soaked lightweight aggregates (LWA) as internal curing (IC) agents for the mitigation of autogenous shrinkage and micro‐cracking of high strength/highperformance concrete (HSC/HPC) have been well researched and documented in literature. Rice husk ash (RHA) on the other hand has been adjudged to be of good pozzolanic activity and a possible alternative to silica fume (SF) in low water/binder (W/B) concrete production. An experimental comparative study was conducted in the current work to assess the effectiveness of the two known ICagents on rice husk ash (RHA) based HPC. HPC mixtures of fc,cube28=60 MPa minimum target strength produced and internally cured with 0.3% content of SAP by weight of binder (bwob) and varied content of pre‐soaked pumice (5 to 10% in steps of 2.5%) by weight of coarse aggregate (bwocg) were cast using 100 mm cubes samples. Thereafter, the samples were cured for 7, 14, 28 and 56 days by water immersion before subjecting them to compressive strength test. The results showed 0.2% bwob SAP HPC (SHPC1) to be the best performed internally cured HPC at the early ages with similar long‐term strength values as 5 and 7.5% bwocg saturated pumiced HPC (PHPC1&2). The study thereby recommends SAP content of 0.2% bwob and saturated pumice content up to 7.5% bwocg for use as ICagent in HPC

    НЕОПРЕДЕЛЕННОСТЬ РЕЗУЛЬТАТОВ КОНТРОЛЯ РАДОНА В ПОМЕЩЕНИЯХ. ЧАСТЬ 1. ПРОБЛЕМА ОЦЕНКИ СОДЕРЖАНИЯ РАДОНА И СОВРЕМЕННЫЙ ПРИНЦИП КОНТРОЛЯ

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    Radon control in buildings is being performed for decades in different countries of the world, including Russia. However, there is a lack of unified standard for the assessment of the uncertainty of the results of the control, considering the protocol and duration of the measurements. It is obvious that the uncertainty of the control increases with the reduction of the duration of the measurements. The lack of data on confidence interval for the average annual radon concentration in housings does not allow correct and precise comparison with the regulatory level, both for the commissioned and operated buildings. Additionally, it complicates a development of the effective method, mass control strategy and identification of buildings with high radon concertations. A reliable method of control, considering time variations of radon and duration of exposure, was developed in Russia several years ago, but it is not well-known and not applied on practice. This paper is focused on a novel principle of radon control, based on simple criteria, widely used in metrology and complying to the modern standards. This principle introduces a new parameter – the radon time variation coefficient KV(t), which reflects main constituent of the uncertainty of the average annual radon concentration depending on the protocol and duration of the measurements. A novel algorithm for the estimation of KV(t) is proposed, developed on the base of the results of continuous annual radon monitoring in representative experimental housings. Additionally, the structure of the correcting coefficient is presented, considering an impact of the temperature on the radon behavior. The use of the corrective coefficient allows lowering the KV(t)value, but its application is limited.Контроль радона в зданиях проводится уже многие десятилетия в разных странах мира, включая Россию. Однако до сих пор отсутствует единый стандарт, позволяющий оценивать значение неопределенности результата контроля с учетом режима и продолжительности измерений. Очевидно, что с уменьшением продолжительности измерений увеличивается неопределенность контроля. Отсутствие данных о доверительном интервале величины среднегодового содержания радона в помещении не позволяет выполнять корректное и надежное сравнение с нормативным уровнем как на стадии приемки зданий в эксплуатацию, так и в эксплуатируемых зданиях. Это также существенно затрудняет развитие эффективного метода, стратегии массового контроля и выявление зданий с высоким содержанием радона. В России несколько лет назад был разработан надежный метод контроля, учитывающий временные вариации радона и продолжительность измерений, однако он до сих пор малоизвестен и не имеет практического применения. В статье приводится принцип контроля радона, основанный на простых критериях, широко используемых в метрологии и отвечающих требованиям современных стандартов. Этот принцип вводит новый параметр – коэффициент временных вариаций радона KV(t), который выражает основную составляющую неопределенности среднегодового уровня радона в зависимости от режима и продолжительности измерений. Предложен оригинальный алгоритм определения значений KV(t), разработанный на основе результатов непрерывных годовых мониторингов радона в представительных экспериментальных помещениях. Кроме того, показана структура поправочного коэффициента, учитывающего влияние температуры на поведение радона. Использование поправочного коэффициента позволяет снизить величину KV(t), однако его применение ограничено

    Metakaolin

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    peer reviewedMetakaolin (MK) is known to be a highly pozzolanic material that can be used in concrete. MK is usually produced by heating kaolin-containing clays, within the temperature range of about 600–900 ℃. This chapter summarizes the utilization of metakaolin in relevant worldwide standards, mainly in Europe and North America. The health, safety and environmental sustainability concerns on using metakaolin as a supplementary cementitious material are also addressed in this chapter. It is reported that MK incorporation has benefits on both early-age and long-term properties. On the other hand, this chapter also reports that the results of heat of hydration and rate of reaction in metakaolin-blended concrete are controversial and need further investigation. Overall, the optimum level of cement replacement by MK is around 10–20%, which provides concrete the maximum strength. Metakaolin appears to have an excellent potential as a supplementary cementitious material in structures made of high-performance concrete, because it controls deleterious expansion due to alkali-silica reaction in concrete (depending on the nature of the aggregate), and reduces the ingress of chloride by improving the microstructure and chloride binding behavior. © RILEM 2018

    Стандартизация контроля радона в зданиях на основе рационального критерия оценки соответствия

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    Significant temporal variations in radon are observed in any buildings, including unoccupied buildings with limited ventilation. This fact causes serious difficulties in radiation monitoring to assess the compliance of premises with the requirements of the normative, which limits the annual average level of radon in buildings. Therefore, neither at the national nor at the international level has yet been solved the problem of standardizing the indoor radon measurement if the test duration is less than a year. An analysis of approaches to radon measurement, including an assessment of the effectiveness of regulation, shows very significant differences between practices established in different countries. For example, in Russia, rapid (no more than 20 min) measurements are mainly used and mitigation measures to protect existing buildings from radon are practically not carried out. In European countries, mainly long-term (at least two months) measurements are used, while mitigation measures are still relatively rare, with the exception of the UK and Sweden. In the USA, short-term (2–7 days) measurements are widely used, which are not only carried out, but also paid for by residents themselves, including mitigation measures. However, despite the established approaches to indoor radon monitoring in Russia and the USA, there is a persistent distrust among specialists in the results of shortterm and, especially, rapid measurements. In this regard, a compromise approach is proposed to standardize radon measurements based on a rational criterion by applying fundamental ISO/IEC concepts such as “measurement uncertainty” and “conformity assessment”. The rational criterion for conformity assessment allows using measurements of different durations, providing a given reliability when making a decision. It also proposes a rationale for optimizing indoor radon monitoring through the participation of not only professional inspectors, but also the population itself due to the possibility of introducing simple methods and inexpensive radon devices within the rational criterion.Влюбыхзданиях, включаянезаселенныесограниченнойвентиляцией, наблюдаютсязначительные временные вариации радона. Этот факт обусловливает серьезные затруднения в проведении радиационного контроля для оценки соответствия помещений требованиям норматива, который ограничивает среднее за год содержание радона в зданиях. Поэтому ни на национальном, ни на международном уровне до сих пор не решена проблема стандартизации контроля радона в зданиях, если продолжительность теста меньше 1 года. Анализ подходов к контролю радона, включая оценку эффективности регулирования, показывает весьма существенные отличия между практиками, сложившимися в разных странах. Например, в России в основном применяются мгновенные (не более 20 мин) измерения, а мероприятия по защите существующих зданий от радона практически не проводятся. В европейских странах, как правило, применяются долгосрочные (не менее 2 месяцев) измерения, а мероприятия по защите зданий от радона проводятся все еще относительно редко, за исключением Великобритании и Швеции. В США массово применяются краткосрочные (2–7 дней) измерения, которые не только проводят, но и оплачивают сами жители, включая мероприятия по защите зданий от радона. Однако, несмотря на сложившиеся подходы к контролю радона в зданиях в России и США, существует устойчивое недоверие среди специалистов к результатам краткосрочных и тем более мгновенных измерений. В этой связи предлагается компромиссный подход для стандартизации контроля радона на основе рационального критерия за счет применения таких фундаментальных концепций ISO/IEC, как «Неопределенность измерения» и «Оценка соответствия». Рациональный критерий оценки соответствия позволяет использовать измерения разной длительности, обеспечивая заданную надежность при принятии решения. Также предлагается обоснование оптимизации контроля радона в зданиях через участие не только специалистов, но и самого населения благодаря возможности внедрения простых методов и недорогих средств измерений радона в рамках рационального критерия

    UNCERTAINTY OF THE RESULTS OF THE RADON CONTROL IN HOUSINGS. PART 1. THE PROBLEM OF ASSESSMENT OF THE RADON CONCENTRATION AND MODERN CONTROL PRINCIPLES

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    Radon control in buildings is being performed for decades in different countries of the world, including Russia. However, there is a lack of unified standard for the assessment of the uncertainty of the results of the control, considering the protocol and duration of the measurements. It is obvious that the uncertainty of the control increases with the reduction of the duration of the measurements. The lack of data on confidence interval for the average annual radon concentration in housings does not allow correct and precise comparison with the regulatory level, both for the commissioned and operated buildings. Additionally, it complicates a development of the effective method, mass control strategy and identification of buildings with high radon concertations. A reliable method of control, considering time variations of radon and duration of exposure, was developed in Russia several years ago, but it is not well-known and not applied on practice. This paper is focused on a novel principle of radon control, based on simple criteria, widely used in metrology and complying to the modern standards. This principle introduces a new parameter – the radon time variation coefficient KV(t), which reflects main constituent of the uncertainty of the average annual radon concentration depending on the protocol and duration of the measurements. A novel algorithm for the estimation of KV(t) is proposed, developed on the base of the results of continuous annual radon monitoring in representative experimental housings. Additionally, the structure of the correcting coefficient is presented, considering an impact of the temperature on the radon behavior. The use of the corrective coefficient allows lowering the KV(t)value, but its application is limited

    Metakaolin

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    International audienceMetakaolin (MK) is known to be a highly pozzolanic material that can be used in concrete. MK is usually produced by heating kaolin-containing clays, within the temperature range of about 600–900 ℃. This chapter summarizes the utilization of metakaolin in relevant worldwide standards, mainly in Europe and North America. The health, safety and environmental sustainability concerns on using metakaolin as a supplementary cementitious material are also addressed in this chapter. It is reported that MK incorporation has benefits on both early-age and long-term properties. On the other hand, this chapter also reports that the results of heat of hydration and rate of reaction in metakaolin-blended concrete are controversial and need further investigation. Overall, the optimum level of cement replacement by MK is around 10–20%, which provides concrete the maximum strength. Metakaolin appears to have an excellent potential as a supplementary cementitious material in structures made of high-performance concrete, because it controls deleterious expansion due to alkali-silica reaction in concrete (depending on the nature of the aggregate), and reduces the ingress of chloride by improving the microstructure and chloride binding behavior. © RILEM 2018

    UNCERTAINTY OF THE RESULTS OF THE RADON CONTROL IN HOUSINGS. PART 2. EXPERIMENTAL ASSESSMENT OF THE TEMPORAL VARIATIONS OF RADON

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    The first part of the paper was devoted to a detailed investigation of the problems of radon control in buildings as well as to the description of the accurate principle of radon control on housings, which is based on the new parameter – temporal variation coefficient KV(t). This coefficient equalizes the main component of the uncertainty of the average annual level of radon depending on the protocol and duration of measurements. Additionally, a novel algorithm for the estimation of KV(t) is proposed, developed on the base of the results of continuous annual radon monitoring in representative experimental housings. This part of the paper is focused on the results of the annual continuous monitoring of volume activities of radon and its daughter products in ten experimental housings in 2006–2013. These housings were located in seven buildings mainly in the Moscow region. All the experimental buildings have the detailed description. The use of original algorithm of the processing of the results of annual monitoring allowed estimating particular and table values of KV(t) co-efficient, depending on the protocol and duration of the measurements. The values of the coefficient are lower up to a factor of two if the temperature is considered. However, the possibility of such consideration is significantly limited by the number of factors. Additionally, an importance of considering a geological factor is discussed. Evaluation of the representativeness of the data obtained and the method for verification and elaboration of the table values of KV(t) are provided as well. Based on the results obtained, there is a possibility for the development of the approaches in the field of sanitary-epidemiologic surveillance in the field of practical realization of the strategy of mass radon control and effective identification of buildings with increased radon levels
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