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This study presents a new approach towards the production of sol-gel silica-coated Bi2O3/Gd2O3 cement additives towards the improvement of early mechanical performance and radiation attenuation. Two types of silica coatings, which varied in synthesis method and morphology, were used to coat Bi2O3/Gd2O3 structures and evaluated as a cement filler in Portland cement pastes. Isothermal calorimetry studies and early strength evaluations confirmed that both proposed coating types can overcome retarded cement hydration process, attributed to Bi2O3 presence, resulting in improved one day compressive strength by 300% and 251% (depending on coating method) when compared to paste containing pristine Bi2O3 and Gd2O3 particles. Moreover, depending on the type of chosen coating type, various rheological performances of cement pastes can be achieved. Thanks to the proposed combination of materials, both gamma-rays and slow neutron attenuation in cement pastes can be simultaneously improved. The introduction of silica coating resulted in an increment of the gamma-ray and neutron shielding thanks to the increased probability of radiation interaction. Along with the positive early age effects of the synthesized structures, the 28 day mechanical performance of cement pastes was not suppressed, and was found to be comparable to that of the control specimen. As an outcome, silica-coated structures can be successfully used in radiation-shielding cement-based composites, e.g. with demanding early age performances. [ABSTRACT FROM AUTHOR]

Incorporating metal oxide nanoparticles into cement-based composites delays the hydration process and strength gain of cementitious composites. This study presents an approach toward improving the performance of bismuth oxide (Bi2O3) and gadolinium oxide (Gd2O3) particles in cementitious systems by synthesizing core–shell structures via a sol-gel process. Two types of silica coatings on cementitious pastes with 5% and 10% substitution levels were proposed. The rheology, hydration, and mechanical properties of the pastes were analyzed to determine the relationship between the coating type and nanoparticle concentration. The results indicate that despite the significant disparities in the performance of the resulting material, both methods are appropriate for cement technology applications. Bi2O3's silica coatings accelerate the hydration process, leading to early strength development in the cement paste. However, due to the coarse particle size of Gd2O3, silica coatings exhibited negligible effects on the early age characteristics of cement pastes. [ABSTRACT FROM AUTHOR]

There are several calculation models for estimation of shrinkage in concrete. The most popular ones are: ACI-209R-92 method, Bažant-Baweja model (B3), Gardner’a-Lockman’a model (GL 2000), CEB-FIP (CEB MC90-99), Spanish model (EHE), EuroCode method (EC-2) from 2004 and Tazawa–Miyazawa model (JSCE). Majority of aforementioned models do not include the deformation caused by the autogenous shrinkage. The methods assume the total deformation as a result of drying shrinkage action. Additionally, a non-standard method was proposed by Jonasson and Hedlund. However it only is used to determine the autogenous shrinkage of High-Performance Concretes (HPC). Tazawa-Miyazawa model and Jonasson-Hedlund method are based on the proportions and material properties such as water/cement ratio, water/binder ratio, type of the cement, or start of setting time. In contrary, the CEB MC90-99 and EC-2 models correlate the autogenous shrinkage with the overall compressive strength of concrete. The article presents the analysis of various calculation models in comparison to actual measurements. The autogenous shrinkage was measured in four cement composites starting at casting up till 28 days of curing.

The article presents the selection process of a static system and optimization for steel bridge span. The issue was addressed as an entry to a BRICO 2017 contests in designing steel bridges. The proposed solutions were checked in terms of their bearing capacity, technological assembly and economics. General guidelines for geometry selection were described. The designed construction was produced and tested under load to determine the deflection in both vertical and horizontal plane. Furthermore, the article details the joints and technological issues met during the design process. Theoretical calculations and actual measurements on a real life model were compared. The process of structural design of civil engineering structures is a complicated, time consuming multilayered issue. The key to a good design lies in a compromise between esthetics, functionality, capacity exhaustion and technical possibilities.