Papers by Keyword: Modified Concrete

Abstract: It was defined that structural elements of a building made from electrically conductive concrete may reduce their performance characteristics due to the corrosion environment. The main reasons for that process are supplement corrosion factors such as a wide range of temperature, humidity as well as chemical agents in the environment. In this article results of different properties (mechanical, electrical) of electrically conductive concrete are discussed including their alterations due to sulphate attack. Also, microstructure as well as physical and chemical properties of modified concrete have been considered after being exposed to sulphate attack (Na₂SO₄) for 112 days. That component has been used for modeling the sulphate attack environment. Compressive strength, rate of the corrosion process, the volume of absorbed SO₄^2– ions from a water-based solution of Na₂SO₄ was defined in order to analyze the effect of sulphate attack. Scanning electron microscopic investigation, energy dispersive spectroscopy, differential thermal analyses were applied for observing morphology and properties changes of modified samples. To assess the influence of sulphate attack on mineral composite materials the approach was suggested and this method might be useful to foresee the durability of concrete while exposing it to the high corrosion environment. In addition to that, a possible method of protection for electrically conductive concrete from sulphate attack was also considered in the article.

Abstract: A filled two-component polymer cold curingsystem (FTCPS) is discussed in the article. To assess its corrosion resistance and durability, the indexes of reagent resistance were determined in accordance with the sorption method. What is optimal, since this value depends on the parameters of mass transfer, the intensity of the reaction, the size of the product, the duration of exposure to aggressive media and other factors. As aggressive media were taken: water, 5% hydrochloric acid solution, 25% aqueous ammonia solution, 10% sodium hydroxide solution, saturated sodium chloride solution. The exposure time was 360 days. Reagent resistance evaluation of the developed FTCPScompositionswas carried out on the basis of guidelines for determining the anticorrosive properties of protective coatings of concrete and laboratory test methods. Changes in the mass of the samples and their reagent resistance as a result of exposure to chemical reagents simulating an aggressive environment during operation were evaluated. The change in the index of reagent resistance in laboratory conditions did not go beyond the value of 0.80, which makes it possible to ensure reliable protection and operation of polymer-coated products under conditions of exposure to these aggressive environments.

Abstract: The applicability of a proposed model similar to a well-known Hirsch's model for predicting the E-modulus of concrete and the creep coefficient of concrete depending on the composition of the concrete, the properties of the components of concrete mix and the possible effect of the superplasticizer on the deformation properties of cement stone both under short-term and long-term loading is proved. Value ​​of the E-modulus of self-compacting concrete can be reduced to 20% with respect to the ordinary concrete of equal compressive strength, which is confirmed by the model calculation data and some experimental data. For concretes with mineral additives, the influence of mineral additives on the E-modulus was not established. Both an increase and decrease in the E-modulus is possible. The effect depends on the type of additive. The creep coefficient of self-compacting concrete, obtained by calculation according to the model, due to the increased content of cement stone and the possible influence of superplasticizer on the creep of cement stone, can be from 1.3 to 1.8 of the coefficient of creep of ordinary concrete. This result agrees well with some experimental data. The creep coefficient of concrete with mineral additives (silica fume, white ash and metakaolin), obtained by calculation according to the model, can be from 0.5 to 0.6 of the coefficient of creep of ordinary concrete. This result agrees well with some experimental data.

Abstract: The speed of concrete curing and design concrete strength depend on the environmental conditions of construction site. Dry and hot climate conditions intensify the process of water evaporation from concrete and cause the concrete shrinkage and the loss of the potential concrete strength. The research work is devoted to study the layer changes of the concrete strength; determination of the minimum period of care for concrete; assessment of negative impact of dry and hot climate conditions on modified concretes, prepared on the composite binders with various chemical additives. The results and methodology, as well as the information about concrete composition and the boundary conditions of the experiments are given in the research work. The obtained research results show that chemical additives and composite binders with low water consumption contribute to get the design strength in spite of the environmental conditions. They also allow concluding that the minimum period of care for concrete should be determined by not the time of its curing, but the critical strength, which it gets to the moment of ending of caring. This concrete strength is able to resist various destructive processes.

Abstract: In this article the effect of plasticizing and siliceous additives on the fluidity of the concrete mix and strength of concrete is investigated. Additives: superplasticizer S-3, fused microsilica FMS-85, hyperplasticizer PENTAFLOW AC 2, and a mixture of hyperplasticizer and microsilica CM 02-10 (10% MS and 0.2% HP)​​. In this paper presented results of tests of samples aged 3, 7 and 28 days.

Abstract: Modern concrete technology requires the use of a large scale of different types of additives that modify the concrete’s properties of features. Often, complicated technical conditions impose the usage of concretes with certain properties. One such example is a mixture transported by gravitational methods using rain gutters. In this situation, it is required to have a concrete mixture that has a high degree of fluidity and does not undergo segregation, sedimentation or other modification of uniformity while in transit. When placing the additional requirement that the concrete must have a high water resistance; bentonites may be particularly useful. This paper presents the results of mechanical and physical properties of concrete with different concentrations of ground sodium bentonite. The particle size being from 30 to 60 nm was added as a dry ingredient together with the aggregate at 1, 2, 3 and 4% by weight of the cement. The ground sodium bentonite demonstrated significant changes in the characteristics of the fresh and hardened concrete, such as: consistency, strength and the amount of capillary pressure.

Abstract: For revealing the behaviors of modified concrete materials against eroding from composite solution, accelerated deterioration tests of Portland concrete, polypropylene fiber concrete, fly ash concrete and concrete mixed with polypropylene fiber and fly ash were made under continuous immersion in two types of composite corrosion solutions, which were sulfate composite solution and magnesium composite solution. The compressive strength, splitting tensile strength and elastic modulus of modified concrete subjected to corrosion were detected. The results show that capacity of corrosion resistance of concrete is enhanced remarkably by modifying approach of mixing fly ash and polypropylene fiber into concrete. The deteriorated splitting tensile strength of modified concrete is able to be increased by 30%-60% compared with ordinary concrete. The research results are benefit to engineering design and application.