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Freezing and thawing cycles, with or without de-icing agents, are the principal causes of concrete structure degradation during the winter. This paper explores the effects of aggregate type on the level of degradation of self-compacting concrete (SCC) due to freeze-thaw (f/t) action. Natural river (NRA) and/or natural crushed (NCA) aggregate, as well as the recycled aggregate of known (RCA-N) and unknown provenance (RCA-A), were employed to produce six different SCC mixtures. The temperature, density, air content, and consistency were determined for fresh concrete, while compressive strength, water absorption by gradual immersion and vacuuming, and frost resistance with and without de-icing salts were tested for hardened concrete. Even though all tested concretes have met the criteria for frost resistance with and without the de-icing salts, it was found that the type of aggregate has a noticeable influence on it. The type of natural aggregate has little effect on SCC frost resistance, but it does influence its behavior when frost and salt are present at the same time. In f/t conditions, RCA-N can be used the same way as natural aggregate, while RCA-A causes the biggest frost resistance reduction. However, both RCAs are not recommended for application in conditions of simultaneous frost and salt impacts.

Traditionally, residential buildings in Vojvodina have masonry walls. Various types of mortar of mineral origin are most often used for joining masonry elements and finishing. The total amount of mortar for the construction of one building is not negligible. The estimated annual consumption of mortar in Vojvodina is about 198 thousand tons i.e. 27 thousand tons of cement and about 31.5 thousand tons of hydrated lime. It can easily be seen conventional mortars based on cement and lime are unacceptable in the light of environmental protection and sustainable development in the contemporary construction industry. Therefore, there is a need for research and development of new, alternative types of binders, based on locally available renewable and/or waste materials. The ceramic masonry elements and tiles industry generates ceramic waste during the production process. This waste, in powder form, could potentially be used as supplementary cementitious material (SCM). Biomass ash, generated by the combustion of harvest residues, as a renewable energy source, is another alternative to cement in modern building composites. This paper emphasizes the physical, chemical, and pozzolanic characteristics of the available agro-waste ashes and ceramic waste powder, originating from Vojvodina. The results indicate relatively high pozzolanicity of all tested ceramic powders and biomass ash based on cob corn, owing to their high fineness and reactive silica content. Furthermore, a catalogue of collected waste materials, illustrating basic data on the raw materials, processing method, landfilling, available quantities, and their tested properties is given.

The paper gives an overview of the repair solution of the RC structure of the bridge over the Lepenica River in Kragujevac with a detailed description of the adopted solution for the repair/strengthening of the main RC girders. All necessary parameters (degree of environment aggressiveness, classes of exposure, the thickness of the concrete cover, principles and methods of repair, etc.) for the proper selection of products (materials) and the techniques of repair, were defined according to the Regulations on technical standards for concrete structures exposed to aggressive environments, EN 206, EC 1992-1-1 and standard EN 1504.

The analysis of available experimental results of high-volume fly ash concrete mechanical properties showed that extensive amount of research had been done so far. However, a comprehensive analysis of basic high-volume fly ash concrete mechanical properties was not found in the literature. Having that in mind, the database of 440 high-volume fly ash concrete and 151 cement concrete mixtures collected from literature was made. The application of European Code EN 1992-1-1 prediction models for cement concrete mechanical properties, as well as existing proposals for high-volume fly ash concrete properties, were statistically evaluated on the results from the database. The analysis showed that the prediction models defined in EN 1992-1-1 for compressive strength, tensile strength and for modulus of elasticity can be used for high-volume fly ash concrete, in the given form or with modifications proposed in literature, with similar accuracy and variation of results as for cement concrete. Own model for fly ash efficiency prediction was developed.

Biomass ashes originating from wood and harvest residues combustion may be considered as one of the prospective environmentally friendly candidates for supplementary cementitious materials (SCM) production. In the region of Vojvodina province, biomass waste is becoming increasingly important as ''green'' fuel, thus allowing the reduction of the environmental impact of waste disposal, lowering the expensive fossil fuels application and its subsequent greenhouse gasses emission. In the light of the above, the present paper surveys the experimental studies of harvest residues ash (HRA) as a pozzolanic additive for engineering applications. Thus far conducted research on the HRA possible application in cementitious systems, worldwide and in the studied region, has been summarized and the benefits of such approaches outlined. Finally, locally available types of wheat straw, soya straw, sunflower husk, silo waste, oil rapeseed - based ashes were collected, characterized both physically and chemically, evaluated and presented through catalogue. The reactivity results, depending on the amorphous silica content and the achieved level of fineness, are very promising in terms of the potential reuse of these ashes in cementing systems.

The durability of concrete infrastructure is related to the properties of the applied concrete and the effects of the aggressive external environment on it. When concrete is directly exposed to soft water, the leaching of calcium ions from hardened cement or cement-based pastes occurs, causing reduction in strength and further deterioration of the concrete structure. This paper presents the experimental results of soft water attack effects on phase composition and compressive strength of blended cement pastes, when cement is replaced with 0, 10, 20 and 30% of natural zeolite. In order to simulate soft water attack in laboratory conditions, paste specimens were exposed to leaching in deionised water up to 180 days. The evaluation of the changes in phase composition (ettringite, portlandite, calcium silicate hydrate gel) due to calcium ion leaching was made based on X-ray diffraction analysis, Fourier-transform infrared spectroscopy and paste compressive strength tests. The presence of portlandite and ettringite after 180 days of exposure to deionised water indicates that leaching did not influence the stability of the hydration products in blended cement pastes. Moreover, blended cement paste with 10% of natural zeolite had a higher compressive strength than the reference one.

This paper aims at reviewing the basic properties of fresh-state extrusion-based three-dimensional (3D) printed concrete in order to explain the specific properties of this construction technology. The review was conducted using the bottom-up approach. The most recent literature in the field of extrusion-based concrete printing was used as a starting point, while additional papers were included through screening the references of relevant papers. Based on the inclusion criteria, review and experimental papers containing data on fresh-state 3D printed concrete properties were included, as well as materials used for 3D printing, since their properties directly affect the fresh-state properties of concrete mixture. Papers concerning data only on hardened properties were excluded. Reviewed properties are: technological properties (pump ability and flow ability) and printability properties(extrudability, print quality and buildability).

This paper presents the numerical modelling of the experimental determination of the compressive strength and the static modulus of elasticity of the lightweight concrete using the finite element method (FEM). In the theoretical review, a concrete damage plasticity (CDP) model of the concrete behaviour is described. Numerical modelling and nonlinear static (incremental-iterative) analyses were performed for two different configurations using the Abaqus © software. The first configuration of the model considers the experimental determination of the concrete compressive strength of the concrete cube, and the second one the determination of the static modulus of elasticity on the concrete cylinder. Steel plates in the three-dimensional FEM models located on the upper and lower sides of the specimens, which serve as the support or for the load application, thus capturing the contact conditions of concrete specimens with testing equipment more realistically, have also been taken into account.

This paper presents the results of the study examining the effect of natural zeolite from Igroš, Serbia, on the hydration and compressive strength of Portland cement based pastes, in which a part of cement has been replaced by natural zeolite. The experimental part comprises three stages. In the first stage, the chemical composition of natural zeolite and the textural properties of both natural zeolite and Portland cement have been examined. In the second stage, Portland cement based pastes incorporating 0%, 10%, 20% and 30% per weight of natural zeolite have been prepared and cured for 28 and 60 days. Finally, mineralogical properties and compressive strength of pastes have been examined. The products of hydration and relative changes of portlandite consumption throughout hydration process (28 and 60 days) have been studied by the means of X-ray diffraction and Fourier transform infrared spectroscopy. Additionally, mercury intrusion porosimetry has been used to characterise pore structure.

The paper points out the problems of damage that can occur during the preparation and exploitation of a cement screed. There were described the types and properties and presented test results obtained on the samples of cement composites prepared with the addition of fibre reinforcement and shrinkage-reducing admixture. Testing procedure included the following properties: density, compressive strength, ultrasound, coefficient of construction advantages and shrinking, and above all the impact of compaction procedure on the quality of cement screed. The testing results of experimental research show that the use of polypropylene fibres and shrinkage-reducing admixture contributes to the improvement of mechanical and deformation properties of cement screeds and that installation which includes some method of vibration is crucial for screed quality. The above statements are also recommendations in the execution of cement screed in practice.

Construction product means any product or kit which is produced and placed on the market for incorporation in a permanent manner in construction works, or parts thereof, and the performance of which has an effect on the performance of the construction works with respect to the basic requirements for construction works. Safety in case of fire and Energy economy and heat retention represent two among seven basic requirements which building has to meet according to contemporary technical rules on planning and construction. Performances of external walls building materials (particularly reaction to fire) could significantly affect to fire spread on the façade and other building parts. Therefore, façade shaping and materialization in building renewal process, has to meet the fire safety requirement, as well as the energy requirement. Brief survey of fire protection regulations development in Serbia is presented in the paper. Preventive measures for fire risk reduction in building façade energy renewal are proposed according to contemporary fire safety requirements.