BESTÅR – Durable concrete with recycled aggregate In this project the properties of different types of recycled aggregate were investigated: recycled excavated masses, recycled construction and demolition waste (CDW), and reclaimed crushed concrete from concrete production. The content of different minerals, rocks, manmade materials, and chemical substances has been analysed, as well as the freeze-thaw resistance and alkali-silica reactivity. In addition to the testing of aggregate properties, concrete with recycled CDW was tested with respect to compressive strength, freeze-thaw resistance, carbonation resistance, and the risk for deleterious alkali silica reactions. The high water absorption of recycled CDW and reclaimed crushed concrete means that these materials can not be regarded as freeze-thaw resistant. As expected, the freeze-thaw resistance testing in salt water resulted in about five times as extensive scaling for concrete where 30% of the coarse aggregate fraction consisted of recycled CDW, as anticipated with concrete with only natural aggregates of typical igneous and metamorphic rocks. The content of potentially alkali-silica reactive particles was low in all batches (<8 %) and all batches were classified as innocuous aggregate when tested with RILEM AAR-2 and NT Build 295. When concrete with 30 % of the coarse aggregate consisting of recycled CDW and with two different binder compositions was tested, neither exceeded the maximum accepted expansion value. However, the results indicated that when the effective alkali content of the concrete is calculated, the alkali content of aggregate of recycled CDW or crushed reclaimed concrete must be included. The replacement of up to 30 % of the coarse aggregate by recycled CDW did not affect the concrete strength development, and the carbonation resistance even increased. Due to the higher water absorption of recycled CDW, it should be ascertained that all accessible pores in the aggregate are filled with water during mixing of the concrete, to avoid negative effects on the water-to-cement ratio and misleading measured air content.

In 2013 the European Commission has published its latest basic safety standards for protection against the dangers arising from exposure to ionising radiation (Council Directive 2013/59/Euratom). The council directive regulates radiation exposure from building materials through the presence of radioactivity (226Ra, 232Th and 40K) in these materials. Pivotal to successful regulation is the availability of a harmonised test method for the determination of the radionuclide concentrations as these nuclides form the basis for dose assessment and compliance. In 2017 a Technical Specification (CEN, 2017) on the determination of the activity concentrations of 226Ra, 232Th and 40K in construction products was published by the European Committee for Standardization (CEN). The purpose of this work is to give an outline of the proposed method, with the protocols for sampling, measurement and data processing as well as a summary of the robustness testing and the expert comments that have been received following the final consultation. 

One of the major issues with radiation from the natural isotopes 40K, 226Ra (238U) and 232Th and their decay products is the forthcoming legislation from the European Commission in relation to its Basic Safety Directive (2014). The European legislation is mandatory and could not be overthrown by national legislation. Hence, even though the BSS is still a directive it is foreseen as becoming a regulation in due time.

The reference value of the natural isotopes, from a radiation point of view, set for building materials is 1 mSv per year (EC, 2014). Earlier recommendations (The Radiation Protection Authorities in Denmark, Finland, Iceland, Norway and Sweden, 2000) within the Nordic countries set an upper limit at 2 mSv per year of radiation from building materials.

The main objective within the frame of the thesis was to investigate gamma radiation in relation to Swedish aggregates and their use as final construction products and the applicability and use of a model (EC, 1999) for building materials to calculate the effective dose within a pre-defined room. Part of the thesis also investigates different methodologies that can be used to assess the radiation in a construction material made up of several constituents (building materials) and aims to show that for some purposes as for the construction industries (precast concrete), that a hand-held spectrometer can be used with good accuracy, even though the object is limited in thickness and size. Secondly, the author proposes a simplified way of assessing the radiation in a construction material by use of correlation coefficient of a specified recipe by use of a hand-held spectrometer. Moreover, an understanding of the different building materials´ contribution to the finalized construction product, e.g. concrete is demonstrated, and how to achieve a good control of the radiation levels in the concrete building.

The reference level for effective dose due to gamma radiation from building materials and construction products used for dwellings is set to 1 mSv per year (EC, 1996, 1999), (CE, 2014). Given the specific conditions presented by the EC in report 112 (1999) considering building and construction materials, an I-index of 1 may generate an effective dose of 1 mSv per year. This paper presents a comparison of the activity concentrations of 4 0K, 226Ra and 232Th of aggregates and when these aggregates constitute a part of concrete. The activity concentration assessment tool for building and construction materials, the I-index, introduced by the EC in 1996, is used in the comparison. A comparison of the I-indices values are also made with a recently presented dose model by Hoffman (2014), where density variations of the construction material and thickness of the construction walls within the building are considered. There was a ~16-19% lower activity index in concretes than in the corresponding aggregates. The model by Hoffman further implies that the differences between the I-indices of aggregates and the concretes' final effective doses are even larger. The difference is due, mainly to a dilution effect of the added cement with low levels of natural radioisotopes, but also to a different and slightly higher subtracted background value (terrestrial value) used in the modeled calculation of the revised I-index by Hoffman (2014). Only very minimal contributions to the annual dose could be related to the water and additives used, due to their very low content of radionuclides reported.

The recommended levels of ionizing radiation from construction materials in effective dose is set to a maximum of 1 mSv/year, EC (1996, 1999, 2013), ICRP (2007), IAEA (2011). By using a theoretical model proposed by the European Union (1999), this is equivalent to I-index 1. By using of concrete slabs with dimensions of 1.5 m × 1.5 m × 0.15 m, an empirical approach is suggested for the calculation of the I-index of naturally occurring ionizing radiation from construction materials. Measurements of 40K, 226Ra, 232Th and the total gamma radiation were conducted and the I-index values were calculated for each concrete mix. A good linear relationship could be established between measurements performed by the Swedish Cement and Research Institute (CBI) and the laboratory results acquired from the Radiation and Nuclear Safety Authority of Finland (STUK) and Centre de Recherches Pétrographique et Géochimiques/ Le Centre National de la Recherche Scientifique (CRPG/CNRS). The results indicate that 60 % of the investigated construction materials are in agreement with the stipulated levels set out by the EC (1999, 2013). The cause for the higher levels of ionizing radiation is often elevated concentrations of all the radioactive elements measured. Regarding the concrete samples yielding values of I-index > 1, 232Th makes the largest contribution.