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Abstract: The present study aims to develop environmentally friendly concrete by using industrial waste materials, namely ground granulated blast furnace slag (GGBS) and rice husk ash (RHA), to produce green concrete. Geopolymer concrete (GPC) has emerged as an alternative to eliminate the use of cement. The main objective of this study is to design and evaluate geopolymer concrete of M40, M50, and M60 grades. Mixes were prepared by replacing GGBS with RHA at 0%, 10%, 20%, and 30% replacement levels for each grade. The resistance of these mixes against 5% sulphuric acid exposure was also examined. Experiments were conducted to determine compressive strength under different parameters, including NaOH concentration, proportions of RHA and GGBS, and curing duration. Additional tests assessed the effect of acid exposure on strength and weight loss. The cost-effectiveness of GPC production was also compared with that of ordinary Portland cement (OPC). The results revealed that, for all three grades, replacement of GGBS with more than 10% RHA led to a decrease in compressive strength. Furthermore, the production cost of GPC was found to be more economical compared to OPC. Both weight loss and strength loss increased progressively with longer acid exposure. Strength reduction for M40, M50, and M60 grade concretes reached 75.4%, 76.1%, and 79.9%, respectively, when 10% of GGBS was replaced with RHA.
Keywords: geopolymer concrete, rice husk ash, ground granulated blast furnace slag, sulphuric acid, cost analysis
Published in DiRROS: 23.06.2026; Views: 136; Downloads: 134
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Abstract: This research proposes an alternative low-cement multicomponent binder for extrusion-based 3D concrete printing to reduce CO2 emissions associated with high Portland cement content. Due to the extremely low Portland cement content (100 kg/m3), the proposed mixture presents several limitations, making it unsuitable for 3D printing without additional activation. To overcome these limitations, chemical and physico-chemical activation methods were applied to promote rapid early-age structuration, partly associated with accelerated ettringite formation, thereby improving compliance with the printing process requirements. The results demonstrate that both activation methods positively affect Portland cement hydration and improve printing-related properties. The research focuses primarily on the hardened properties of 3D-printed concrete, showing that activation reduces macroscopic porosity and increases density and compressive strength. The applied activation methods also increase overall shrinkage compared to the nonactivated low-cement mixture. However, the absolute shrinkage remains approximately 25–30 % lower than that of a conventional reference mortar with a high Portland cement content. The suitability of the components used in the multicomponent binder was evaluated through pozzolanic activity testing. In contrast, the effects of chemical and physico-chemical activation on binder phase composition were investigated by X-ray diffraction, and the hardened properties of concrete were assessed using X-ray computed tomography, mercury intrusion porosimetry, shrinkage measurements, density, and compressive strength testing. The results demonstrate that chemical and physico-chemical activation enables the effective use of low-cement multicomponent binders in extrusion-based 3D concrete printing, providing a more sustainable alternative to conventional high-cement mixtures.
Keywords: 3D-tiskanje betona, večkomponentno vezivo z nizko vsebnostjo cementa, kemična aktivacija, fizikalno-kemična aktivacija, krčenje, 3D concrete printing, low-cement multicomponent binder, chemical activation, physico-chemical activation, shrinkage
Published in DiRROS: 15.05.2026; Views: 218; Downloads: 285
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Abstract: Performance-based structural fire design relies on models that capture material and structural behaviour during heating and cooling. Such models require experimental data, but experiments are often time- and resource- intensive. Optimal Experimental Design (OED) can reduce the number of tests needed by minimizing the variance of parameter estimates. This study demonstrates the use of OED, using D-optimality as the optimization criterion, for an experimental setup that measures the thermal elongation of concrete specimens. In these tests, cylindrical concrete specimens are slowly heated to a predefined maximum temperature while their elongation is being measured. The goal of the experimental campaign is to calibrate a model for the free thermal strain of concrete during cooling. The OED determines the optimal exposure that is expected to result in the lowest variance around the mean values of the parameter estimates. The results of the OED are compared with a baseline experimental design without optimization, showing that the advantages of OED become increasingly evident as the number of experimental runs grows and intuitive reasoning becomes less reliable. In addition, the approach is validated considering real experimental data.
Keywords: optimal experimental design, concrete, thermal strain, cooling
Published in DiRROS: 08.04.2026; Views: 227; Downloads: 62
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Abstract: With the rise of performance-based structural fire design, understanding the behaviour of materials during both the heating and cooling phases of a fire has become essential. Traditionally, research has focused on the heating phase, resulting in limited data on material properties during cooling, in particular for the free thermal strain of concrete. This gap is critical, as free thermal strain significantly influences load redistribution in reinforced concrete structures. Two experimental campaigns were conducted to expand the available data: one using the UGent HIFREP (‘High Intensity Fast-Response Electric Radiant Panel’) and the other employing an electric furnace. The first test campaign provided an extensive dataset on the residual thermal strain, whereas the time- consuming furnace tests provided data for the entire fire event (heating and cooling). These datasets were used to update an existing model through Bayesian inference, coherently integrating the new information. The outcome is a comprehensive probabilistic model that accurately captures the free thermal strain behaviour of concrete throughout both heating and cooling, allowing for a full reliability-based evaluation of concrete structures in fire.
Keywords: concrete, cooling, free thermal strain, fire safety, structural fire engineering, experiments, bayesian inference
Published in DiRROS: 10.03.2026; Views: 368; Downloads: 74
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Abstract: Due to bridges’ critical role in transportation networks, the assessment and maintenance of existing bridges have become a priority. Prestressed concrete bridges constitute a significant portion of Europe’s transportation network, yet many no longer meet today’s technical requirements. This is primarily due to two factors: (i) the unforeseen increase in heavy goods traffic, and (ii) insufficient experience with early reinforced and prestressed concrete construction methods, coupled with inadequate regulations, which resulted in design weaknesses and structural deficiencies. One critical failure mechanism, identified when recalculating existing bridges based on updated guidelines, is insufficient shear load-bearing capacity, which has prompted the premature demolition of numerous bridges. A thorough understanding and rigorous monitoring of shear behavior is essential since neglecting this problem could lead to notable consequences, especially for aging infrastructure. In this paper, a distributed fiber optic sensor (DFOS) based monitoring system, inspired by shear detection concepts, is tested. A decommissioned prestressed concrete bridge girder was equipped with a DFOS grid, allowing for detailed monitoring of crack width, location, and shape. Preliminary test results confirm the successful installation and early detection of cracks, highlighting the system’s potential to identify microcrack formation, monitor crack growth, and support maintenance strategies.
Keywords: structural health monitoring, distributed fiber optic sensors, microcracking, crack growths, load testing, prestressed concrete
Published in DiRROS: 27.01.2026; Views: 477; Downloads: 273
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