The article is focused on the medium-term negative effect of groundwater on the underground grout elements. This is the physical-mechanical effect of groundwater, which is known as erosion. We ...conduct a laboratory verification of the erosional resistance of grout mixtures. A new test apparatus was designed and developed, since there is no standardized method for testing at present. An erosion stability test of grout mixtures and the technical solutions of the apparatus for the test's implementation are described. This apparatus was subsequently used for the experimental evaluation of the erosional stability of silicate grout mixtures. Grout mixtures with activated and non-activated bentonite are tested. The stabilizing effect of cellulose relative to erosion stability has been also investigated. The specimens of grout mixtures are exposed to flowing water stress for a certain period of time. The erosional stabilities of the grout mixtures are assessed on the basis of weight loss (WL) as a percentage of initial specimen weight. The lower the grout mixture weight loss, the higher its erosional stability and vice versa.
This paper focuses on the experimental determination of the shrinkage process in Self-Compacting High-Performance Concrete (SCC HPC) exposed to dry air and autogenous conditions. Special molds with ...dimensions of 100 mm × 60 mm × 1000 mm and 50 mm × 50 mm × 300 mm equipped with one movable head are used for the measurement. The main aim of this study is to compare the shrinkage curves of SCC HPC, which were obtained by using different measurement devices and for specimens of different sizes. In addition, two different times
are considered for the data evaluation to investigate the influence of this factor on the absolute value of shrinkage. In the first case,
is the time of the start of measurement, in the second case,
is the setting time. The early-shrinkage (48 h) is continuously measured using inductive sensors leant against the movable head and with strain gauges embedded inside the test specimen. To monitor the long term shrinkage, the specimens are equipped with special markers, embedded into the specimens' upper surface or ends. These markers serve as measurement bases for the measurement using mechanical strain gauges. The test specimens are demolded after 48 h and the long term shrinkage is monitored using the embedded strain gauges (inside the specimens) and mechanical strain gauges that are placed, in regular intervals, onto the markers embedded into the specimens' surface or ends. The results show that both types of measurement equipment give a similar result in the case of early age measurement, especially for the specimens cured under autogenous conditions. However, the early age and especially long term measurement are influenced by the position of the measurement sensors, particularly in the case of specimens cured under dry air conditions. It was proven that the time
have a fundamental influence on the final values of the shrinkage of investigated SCC HPC and have a significant impact on the conclusions on the size effect.
This paper presents experimental and analytical work of which the main objective was to support the introduction of a new technology for the production of sewer pipes. In this technology, the pipes ...produced consist of two differently produced parts. The direct part uses conventional vibro press compacted concrete. In the curved part, on the other hand, self-compacting concrete technology is used. The cooperating company, Prefa Brno a.s., defined possible negative effects on concrete of sewer pipes. The task of the research team and now the author’s team was to propose a procedure for the development of suitable self-compacting concrete variants and subsequently the design of a methodology to verify their durability in aqueous environments containing sulfates. To increase the efficiency of the development, the model mortar method was used in the experimental work. That is, instead of the original concrete, a model mortar derived from it was tested. The principle and procedure of derivation of model mortars are described in the paper. In total, eight variants of model mortars were tested, and at least three of them fulfilled the requirements. An optional but beneficial part of the carried out work was the derivation and practical application of the time-anchored-triangles-of-cracking graphical method developed during the research. This method is used to quickly compare the degree of attack of different silicate composites tested in a common bath inducing type III corrosion.
This paper focuses on the calculation of residual stresses due to shrinkage with a tensile creep effect. Whereas the shrinkage of concrete causes stresses in the material, the tensile creep ...counteracts the shrinkage as a stress relaxation mechanism. The main objective of this paper is to evaluate the ageing coefficient c (referred to as Trost-Bazant Coefficient) reflecting the load history. The coefficient is used for the residual stress analysis by means of a simplified method called Age-adjusted Effective Modulus Method. The tensile creep effect was evaluated according to the rheological model provided by Eurocode 2. Although the Eurocode predicts the creep for the structural members subjected to compressive stresses, this study proves that it can be used for the tensile creep prediction as well. We tested three types of concrete: reference concrete, high-performance concrete with reduced shrinkage magnitude by means of special admixtures, and fibre concrete with the content of polypropylene fibres. From the obtained results, it can be stated, that the ageing coefficient can be considered to be the value of 0.45 for any shrinkage development. It was also proved, that the tensile creep value essentially affects the magnitude of residual stresses, even in the “early age” concrete. The correctness of the calculated residual stresses was verified by means of a Ring-test.
The paper deals with an experimental determination of resistance of concrete to the corrosive effects of demineralised water with aggressive carbon dioxide. Three types of concrete were used for the ...experiment, one designated for reference, another one contained a crystallising admixture, and the third type contained admixtures and was designed to be very resistant. The actual tests were, however, not conducted directly on these concretes but on model mortars derived from those concretes. The paper provides reasons why the tests specimens were produced from the model mortars and not from the given concretes. The conclusion of this paper presents not only the results of the described experiment but also comparisons with the results of previously conducted and published tests.
This paper briefly discusses the basic theoretical findings about sulphate-induced corrosion of concrete and also the possibilities how to determine the degree of concrete resistance to such ...corrosion in the most effective way. The described experiment involves a twofold comparative test – monitoring of selected parameters of two model mortars stored in both the corrosive and the reference environments (water bath). During the test, these model mortars represent commonly used concrete for the manufacture of concrete sewer pipes. The article also explains why and how the mortars were designed and tested instead of concrete. The conclusion of the paper presents the results and their evaluation.
The paper compares the sulphate ion attack resistance in several mixtures of high-performance concrete. The corrosion tests were not performed with the actual concretes, but with model mortars ...derived from them. The resistance was compared by means of a comparative, specifically double-comparative, methodology. The paper devotes much attention to describing this method, deriving the model mortars, and choosing the correct specimens and parameters to be observed. All important test results, which confirm the effectiveness of the method, are listed. The resistance of each mortar was identified with sufficient accuracy.
This paper suggests an interpretation of the concrete resistance to cracking caused by shrinkage. Cement hydration leads to many chemical processes which cause volume changes and changes of the other ...physico-mechanical properties of concrete. It is necessary to know the development of residual stresses and corresponding capacity of concrete to establishing of the resistance to shrinkage cracking. Intersection of stress and capacity is a time point which determines that resistance. All necessary concrete properties was established experimentally. The three types of micro-concretes were monitored. On the basis of acquired results it can be stated that the optimal composition of micro-concrete was found because no shrinkage cracks should occur during its life-time.
The paper discusses an experimental technique of comparing different concretes in terms of their resistance to leaching corrosion. Specifically, the experiment compared the resistance of three ...different high-performance concretes exposed to deionised water with aggressive carbon dioxide. To control the duration of the laboratory tests, they were not performed on these particular concretes, but rather on model mortars derived from them; the mortars proved perfectly sufficient to give the desired information. The paper also describes how these mortars were created on the basis of known or assumed concrete formulae. The actual corrosion test was designed as a double-comparative experiment. The paper lists all the basic test results, which confirm the effectiveness of the comparative method – the experiment was successful in drawing clear comparison between the concrete variants.
The main objective of this paper is connected with the search of an optimal anchorage length of reinforcement in lightweight and ultra-lightweight concretes. Experimentally obtained values of the ...bond stress between lightweight concrete and reinforcing bars are presented. The density classes of lightweight concrete were D1,0, D1,2 and D1,4. The results are compared with equal ones of normal density concrete. The tests with ordinary reinforcement and with non-metallic hybrid reinforcement C-GFPR (30% portion of carbon fibres) were conducted.
PDF
