Search

Even though concrete is considered to be durable, the environment to which the concrete is exposed plays an important role in its durability. The durability of concrete is challenged due to its porous nature, which is especially important in harsh exposure conditions such as marine environment. The reinforced concrete elements of marine structures such as bridges, wharves, docks, etc. are subjected to various types of exposures such as wetting and drying action [WDA], fully submerged condition, and in contact with chlorides. To refine the pore structure of concrete and to improve the durability characteristics of such structures, it is essential to use high performance concrete [HPC]. In this study, metakaolin [MK] is used as partial replacement of cement to produce HPC. The use of metakaolin is found to be very effective in reducing the porosity of concrete. As the porosity of concrete decreases, the corrosion rate can be reduced considerably. The durability characteristics of metakaolin-incorporated HPC is studied for 365 days to investigate the changes in its pore structure in long term. The iCOR® NDT method is used to find the corrosion performance and concrete resistivity of high performance metakaolin concrete under a simulated wetting and drying action [WDA] of seawater over several periods. The deterioration effect caused by the simulated WDA of seawater is also studied by considering the bond strength of specimens subjected to normal and corrosive exposure conditions.

Publikacja finansowana w ramach programu Ministra Nauki i Szkolnictwa Wyzszego pod nazwą „Dialog” w latach 2018–2020 na potrzeby projektu Centrum Europejskiego Natolin Elektroniczna platforma transferu wiedzy i zasobow źrodlowych. Wizje roli Polski w Europie Środkowo-Wschodniej w koncepcjach geopolitycznych, gospodarczych i cywilizacyjno-kulturowych w XX w.

In the years 1921–1939 one of the largest military garrisons operated in Grodno. Its strength and importance was evidenced by the presence of regular troops as well as the authorities and military institutions that had their headquarters in this city. Many famous officers who actively participated in the life of the city were associated with the Grodno garrison. The history of the garrison is full of events such as daily service, matters of training and discipline, education and upbringing of soldiers. It is also a sport and the participation of garrison officers in various events that go beyond their daily duties. Its character and significance changed after the withdrawal of regular military units to fight the Germans, just before the outbreak of World War II. The garrison ceased to exist in September 1939 and did not revive after 1945. The aforementioned extensive subject exceeds the framework of the presented text, therefore only some of the threads are presented. They are only a small fragment of the garrison’s history, the history of which is not widely known. Despite the rich source base gathered in the Central Military Archives in Warsaw, in the National Historical Archives of Belarus in Grodno and information contained in the pre-war press, the Grodno garrison’s monograph has not yet been created.

Tensile stresses resulting from a combination of thermal volumetric changes, due to the heat of hydration and ambient conditions, autogenous deformations and boundary restraints, often induce a significant intrinsic load on massive concrete structures. Whenever such stresses attain the concrete tensile strength, cracking occurs, which may in turn impair the serviceability and durability of the structure. This study is an output of Working Group 7 of RILEM Technical Committee 254-CMS: Thermal cracking in massive concrete structures and is presenting case studies of early-age thermal cracking in massive concrete structures where internal restraining conditions often prevail, such as thick blocks, armour units, footings, dams and spillways, and large-sized columns. It covers the analysis of causes of this type of cracking together with the lessons learned from the collected evidence along with best mitigation practices (often resulting from forensic investigations by means of computer-based simulations). Based on the evidence retrieved from the analysed case studies, the concept of massivity used to indicate potential thermal crack proneness in massive concrete structures is significantly improved to account for binder type and content as well as casting and fresh concrete temperature, in addition to the geometrical characteristics of the element under investigation. The use of such an indicator may lead to a more robust pre-design assessment of the likelihood for thermal cracking occurrence in massive concrete elements, advising designers and contractors dealing with such structures whether more complex analyses should be performed already at the design stage.

Winter is not the best time for miltary operations. It is necessary when political situation or international agreements are contained. In 1919 and 1920 Polish Army has served in Lithuania and Latvia in winter time. In Lithuania the soldiers have practiced patrol and garrison duty on polish-lithuanian border. In the same time other polish units have taken part in military operation in Latvia. There were the common features of these mission: winter, snow, low temperatures. In these circumstances the duty was much difficult. What else, the soldiers have fallen ill like cold and frost-bites.

This paper is an effect of coordinated efforts of Working Group 7 of RILEM TC 254-CMS: Thermal cracking in massive concrete structures. The paper deals with a negative effect of restrained hardening-induced strains in reinforced concrete wall-on-slab structures which is cracks formed at the stage of construction of the walls. The aim of the paper was to collect real-life examples of wall-on-slab structures in which hardening-induced cracking was reported, and make a comparative study of these cases to observe patterns and trends on the cracking behaviour of such elements. The study covered a set of almost 20 cases with detailed material and technological data as well as observed cracking patterns. Characteristics of these structures which determine the capacity of crack development were indicated. In addition, for chosen cases the expected crack width was calculated and compared with the measured value. The calculations were performed with the use of current standardised guidance (EN 1992-3 and CIRIA C766) using an approach available at the design stage. This investigation showed that the method of CIRIA C766, being less conservative, consistently predicts smaller crack widths for a fixed set of assumptions compared to EN 1992-3, and both methods showed important discrepancies between the predicted and measured values of crack widths. Changes in calculation methods were proposed to improve the predictability of crack width calculations in wall-on-slab structures under restrained hardening-induced strains., This study is an output of the Working Group 7 of the RILEM TC 254-CMS: Thermal cracking in massive concrete structures. The authors would like to acknowledge members of TC 254-CMS who provided examples and data used in this paper, as well as remarks and insightful comments to this work: Anders Hosthagen (LTU, Sewden), Farid Benboudjema (ENS-Cachan/Paris-Saclay, France), Matthieu Briffaut (3SR Lab, France), Laurent Charpin and Benoit Masson (EFD R&D, France), Vit Smilauer (CTU Prague, Czech Republic), Yunus Ballim (University of the Witwatersrand, South Africa) and Rui Faria (University of Porto, Portugal). The authors would like to acknowledge networking support by the COST Action TU1404 (www.tu1404.eu).Funding provided by the Portuguese Foundation for Science and Technology (FCT) to the Research Project IntegraCrete (PTDC/ECMEST/1056/2014-POCI-01-0145-FEDER-016841) is gratefully acknowledged. This work was partially supported by UID/ECI/04029/2019 -ISISE funded by national funds through the FCT/MCTES (PIDDAC). In particular case of the leading author, funding of the research by the Polish Ministry of Science and Higher Education within the grant BK-298/RB6/2020 is acknowledged. The contents of this paper reflect the views of the authors, who are responsible for the validity and accuracy of presented data, and do not necessarily reflect the views of their affiliated organisations.

Nowadays foam concrete is commonly used as replacement of compacted soil to fill excavations, underground channels. There are also attempts to structural use of this material; among the examples are precast walls and slab foundations. The high degree of thermal insulation makes foam concrete a perfect material for use in the passive houses design. Unfortunately, foam concrete cannot be reinforced as easily as traditional concrete. Because of low resistance to concentrated stresses it is difficult to ensure sufficient bond of reinforcement. The idea of solid foam concrete slab presented in the paper incorporates bi-directional composite reinforcing mesh placed in tensile zone of the slab where transverse fibers are ensuring anchorage for fibers in main direction. This method of reinforcement, apart from the increase of bearing capacity, should reduce the risk of uncontrolled failure due to cracking. The paper describes the results of preliminary laboratory tests of nine slabs made of foam concrete reinforced with meshes made of carbon fibers. The results obtained at the initial stage show great potential of this method of reinforcement. There was a significant increase in capacity and less brittle failure mode.

Cellular concretes cannot be reinforced as easily as traditional ones. Generally porous materials do not ensure sufficient bond of reinforcement; additionally, due to limited amount of aggregate, interlock between aggregate particles and reinforcement ribs is not satisfactory. The idea of reinforcement presented in the paper incorporates bi-directional composite reinforcing grids placed in tensile zone of the cellular concrete slab where transverse fibres are ensuring anchorage for fibres located in the main direction of stresses. The concept is based on geotechnical applications where grids are commonly used as soil stabilization, but the grids adopted in this solution are much stronger thanks to introduction of high strength fibres as composite reinforcement.

Modelling of early-age behaviour of cement-based materials is still a challenging task. The challenge is implied by the extent of the knowledge on the subject which results in a variety of different models used for simulation of cement-based materials. That is why a numerical benchmark program has been launched within the COST Action TU1404 aiming at improvement and harmonisation of computational prediction of early-age behaviour of cement-based materials as well as its behaviour on structural level. This paper presents the result of the proof-of-concept stage of the benchmark. The goal of this stage of benchmark was to compare the performance of currently used models for simulation of early-age behaviour of concrete. The participants were requested to simulate thermo-chemomechanical behaviour of simple concrete elements covering adiabatic and real evolution of temperature, shrinkage, stiffness and stresses accounting for early-age creep. The tasks were formulated based on the experimental measurements. This stage of benchmark allowed to evaluate the influence of different phenomena occurring in early-age concrete on the behaviour of early-age concrete structures, define the discrepancies between experimental results and numerical simulations, as well as to indicate the weak points in the models., COST Action TU1404, Competitivity Factors Operational Programme– COMPETE, Polish Ministry of Science and Higher Education (BK-237/RB-6/2018)., info:eu-repo/semantics/publishedVersion