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the conscious waste handling is getting more important worldwide. in the past fifteen years several detailed decrees and regulations were issued, dealing with this topic. the independent category of industrial waste of the construction industry is about 15-years old as well. in our research, the opportunities in recycling autoclaved aerated concrete (AAc) waste were investigated. AAc is a rather young building material, compared to the ancient ones, e.g. concrete, wood, or natural stone. the first factory, producing this material, was founded in 1929, in sweden, and the first one in Hungary in 1963 (at kazincbarcika). the following question has been raised: What is going to happen with the large amount of AAc building elements (mainly in family houses) when they reach their design lifetime, and are to be demolished, creating AAc waste? in our research, different ways for recycling this material were investigated. our theories were confirmed by laboratory tests. our ultimate task was to develop some new, useful concrete products, made from AAc waste. in the past 3 years, two research phases were finalized, both for different purposes of use. in the first phase, load bearing and insulating lightweight concrete mixtures with crushed AAc aggregate have been made. in the second phase, the mixtures were designed for vertical covering applications. Laboratory tests were made according to european and Hungarian standards. keywords: Autoclaved aerated concrete (AAc), cellular concrete, building industrial waste, recycling, lightweight aggregate concrete (LWAc) olivér Fenyvesi, Phd civil engineer (msc), monument protection engineer, PhD, Assistant Professor at Bme Dept. of construction materials and technologies. main fields of interest: early age shrinkage cracking of normal and lightweight concretes, application of recycled waste materials for concrete (normal and lightweight aggregates), protection of building heritage, construction diagnostics, corrosion of reinforced concrete and steel structures. secretary of the szte concrete Division, member of fib Hungarian Group. bence JanKus 5 th-year architecture student in the Budapest university of technology and economics, Faculty of Architecture. main fields of interest: Lightweight aggregate concretes, recycling building industrial waste as concrete aggregate, especially AAc.

An analytic-empirical model was developed to describe the heat transfer process in raw straw bulks based on laboratory experiments for calculating the thermal performance of straw-based walls and thermal insulations. During the tests, two different types of straw were investigated. The first was barley, which we used to compose our model and identify the influencing model parameters, and the second was wheat straw, which was used only for validation. Both straws were tested in their raw, natural bulks without any modification except drying. We tested the thermal conductivity of the materials in a bulk density range between 80 and 180 kg/m3 as well as the stem density, material density, cellulose content, and porosity. The proposed model considers the raw straw stems as natural composites that contain different solids and gas phases that are connected in parallel to each other. We identified and separated the following thermal conductivity factors: solid conduction, gas conduction in stem bulks with conduction factors for pore gas, void gas, and gaps among stems, as well as radiation. These factors are affected by the type of straw and their bulk density. Therefore, we introduced empirical flatness and reverse flatness factors to our model, describing the relationship between heat conduction in stems and voids to bulk density using the geometric parameters of undisturbed and compressed stems. After the validation, our model achieved good agreement with the measured thermal conductivities. As an additional outcome of our research, the optimal bulk densities of two different straw types were found to be similar at 120 kg/m3.

This paper aims to raise awareness regarding the obstacles limiting alkali-activated binders’ (AABs) application as a sustainable solution in the construction industry. Such an evaluation is essential in this industry, which has been introducing a wide range of alternatives to cement binders yet achieved limited utilisation. It has been recognised that technical, environmental, and economic performance should be investigated for the broader adoption of alternative construction materials. Based on this approach, a state-of-the-art review was conducted to identify the key factors to consider when developing AABs. It was identified that AABs’ adverse performance compared to conventional cement-based materials mainly depends on the choice of which precursors and alkali activators to employ and the regionalised practices adopted (i.e., transportation, energy sources, and data on raw materials). In light of the available literature, increasing attention to incorporating alternative alkali activators and precursors by utilising agricultural and industrial by-products and/or waste seems to be a viable option for optimising the balance between AABs’ technical, environmental, and economic performance. With regard to improving the circularity practices in this sector, employing construction and demolition waste as raw materials has been acknowledged as a feasible strategy.

.1/B-09/1/KMR-2010-0002). Olivér FenyvesiDepartment of Construction Materials and Engineering Geology, BME, H-1521, Budapest, Hungary e-mail: fenyvesioliver@yahoo.com 1 Introduction 1.1 Early age shrinkage in concrete In concrete, mortar and cement paste shrinkage takes place from the very beginning of the life of the material. This is caused by water movement in the porous and rigid body. During the hydration of cement, while the cement paste is plastic, it undergoes a volumetric contraction (autogenous shrinkage) whose magnitude is of the order of one per cent of the absolute volume of dry cement. However, the extent of hydration prior to setting is small, and once a certain stiffness of the system has developed, the contraction induced by the loss of water by hydration is greatly restrained [38]. Withdrawal of water from concrete, mortar or cement paste stored in unsaturated air causes drying shrinkage. A part of this drying shrinkage is irreversible and should be distinguished from the reversible moisture movement caused by alternating storage under wet and dry condition [24,38].Influencing factors of early age shrinkage in mix design: