Papers by Keyword: Frost Resistance

Abstract: Concrete mixtures with water-to-cement ratios (w/c) of 0.50, 0.40, and 0.30 were prepared. In the last mixture, 10% and 20% of aggregates were substituted with water-saturated expanded clay. This resulted in the creation of self-cured concrete mixtures. The mechanical properties and frost resistance of these mixtures were discussed concerning the results obtained for concrete without aggregate substitution. It was observed that self-curing can enhance the frost resistance of HPC, even though LWA reduces both flexural and compressive strength.

Abstract: With the rapid development of ferrous metallurgy, the production of iron tailings as waste after beneficiation is increasing. Due to the shortage of natural stone in road construction, iron tailings can be used as an alternative material to natural stone in semi-rigid bases. In order to study the feasibility of application of cement stabilized iron tailings (CSIT) in semi-rigid base, unconfined compressive strength (UCS), indirect tensile strength (ITS) and cyclic freeze-thaw tests were carried out on cement stabilized iron tailings (CSIT). The gradation composition and cement content were selected as influencing factors. The results show that under the condition of the same cement content, the UCS and ITS of CSIT are proportional to the particle size in the mixture. In CSIT with the same gradation, the mechanical properties increase with the increase of cement content; CSM-40(B) has a higher UCS and CSM-40(C) has a higher ITS, the frost resistance coefficient of CSIT increases with the increase of cement content and the tendency of frost resistance coefficient decreases with the increase of cement content. The frost resistanceofCSM-40 (B) is better than that of CSM-40 (C) for the same cement content. Therefore, for the use of iron tailings in CSM, a suitable gradation composition and cement content should be selected.

Abstract: Cement asphalt mortar (CA mortar) is one of the key materials of slab ballastless track structure, and its performance directly affects the overall quality of ballastless track. The design of CA mortar mix proportion is studied by orthogonal exerimental method, and the reasonable dosage of cement, emulsified asphalt, sand and other materials is determined. The change of gas content of CA mortar is analyzed by adding air entraining agent and adjusting stirring process. The working properties, mechanical properties and freezing resistance of CA mortar are tested. The results show that the reasonable dosage of cement, emulsified asphalt and sand in CA mortar are 280~325kg/m³, 420~555kg/m³ and 360~690kg/m³, respectively. The dosage of cement has the most obvious influence on the 28d compressive strength of CA mortar, followed by emulsified asphalt. With the increase of air entraining agent content, stirring speed and stirring time, the air content in mortar will increase. Through the test of mortar's working performance, mechanical properties and frost resistance, it is shown that the appropriate amount of air entraining agent and mixing process can improve the frost resistance of CA mortar.

Abstract: This article deals with defects in solid fired bricks caused by repeated freezing and defrosting. Defects can be divided into surface (visible) such as cracks or chips of the test element. The second type of defects are those in the internal structure (invisible on the surface). The defects in the internal structure can be the easiest detected by non-destructive methods such as the resonant pulse method or the ultrasonic pulse method. This article deals with the possibility of detecting defects in the internal structure of solid fired bricks and their relation to surface defects. The test elements were repeatedly frozen and defrosted, and after a certain number of cycles, changes in the internal structure were monitored by the resonance method and by the ultrasonic method. The variable for monitoring the failure of the internal structure is the relative dynamic modulus of elasticity (RDM).

Abstract: This article is focused on changes in the properties of colored concrete due to frost. In contrast to conventional concrete structures, fair-faced concrete is exposed to external conditions and is therefore also prone to degradation of its surface. The durability of the surface layers is mainly reflected in the color saturation and resistance to mechanical damage. Therefore, the paper focuses on measuring the change in color and strength characteristics after 75 cycles of frost resistance. The measurement was performed on concrete samples colored with yellow, red and green powdered metal oxide-based pigments. Based on the results, we can concluded the frost resistance of colored concrete depends primarily on the type of pigment used.

Abstract: In this study, the utilization of two types of spongilites in various addition in cement mortars has been investigated with the purpose of exploring a new application of this natural pozzolans as cement mortar additives. The influence of the addition of spongilites on the physico-mechanical properties, frost-resistance, and microstructure of cement mortars as a function of time was studied. The results revealed that the rising proportion of spongilites in cement mortars causes increase in water retention of mortars, reduction of their bulk density, increase in porosity of mortars due to the growing predominance of capillary pores maintaining sufficient mortars strengths, and slightly increase in the frost-resistance of mortars. After initial tests, partial replacement of cement in fine-grained cement mortars with hitherto unexploited spongilites seems to be very promising. Based on the achieved results, a 20% cement replacement can be recommended as optimal.

Abstract: When erecting monolithic reinforced concrete structures, the structure of concrete can differ significantly from the laboratory standard due to the complexity of providing favorable conditions for hardening, and therefore the compressive strength and especially the frost resistance of concrete may not meet the design requirements, which can negatively affect the reinforced concrete structure durability and require amplification, especially in earthquake-prone areas [1, 2]. Increasing the durability of reinforced concrete structures is possible by creating a rational stress field, for example, by prestressing, incl. variable along the length of the structure [3,4], but this technique is difficult to implement for monolithic reinforced concrete structures. It is possible to use effective materials or methods of manufacturing structures [5, 6]. But this is also mainly problematic for use in the construction of monolithic reinforced concrete structures. Generally accepted methods of calculating the reinforced concrete structures durability subjected to cyclic freezing-thawing during operation, incl. in a water-saturated state, do not exist. At the design stage, ensuring the durability of such reinforced concrete structures is mainly reduced to the reasonable assignment of requirements for concrete quality indicators, depending on the operating conditions, which is the focus of BC 28.13330.2017 (EN 206) and GOST 31384-2017 from the premise of ensuring durability of at least 50 years. In the above-mentioned norms of the Russian Federation, in fact, two approaches are presented to ensure the durability of reinforced concrete structures during cyclic freezing-thawing, incl. in a water-saturated state, namely: designing a concrete structure capable of working under such conditions by standardizing the values of cement consumption, W/C ratio, class of concrete in terms of compressive strength, amount of entrained air, or rationing of concrete grades in terms of frost resistance F₁ (first base method GOST 10060-2012 provides for freezing in air, saturation and thawing in water) or F₂ (second base method GOST 10060-2012 provides for freezing in air, saturation and thawing in 5% sodium chloride solution). The purpose of this work is to compare various approaches to ensuring the durability of reinforced concrete structures operated during cyclic freezing-thawing and to analyze the provision of durability with standardized indicators when designing the structure of concrete.

Abstract: Magnesia binders provide strength to the stone, but have one drawback-low resistance and salt resistance. Increasing water and salinity tolerance, mechanical strength of the hardening magnesia binders can be achieved by introducing the system of micro-aggregates. The quality criteria that determine the activity of the micro filler are: high chemical resistance to water, aggressive media, high mechanical strength. Among the effective microfillers composite magnesia binders include diopside, wollastonite. It is shown that the introduction of 60-80 wt%. wollastonite or diopside with a specific surface of 2000-3500 cm²/g provides significant improvement in strength and water resistance that allows you to lengthen the lifespan and maintain the required quality of products based on composite of magnesia binders.

Abstract: The paper deals with a comparison and interpretation of results of frost resistance tests of concrete specimens taken from a structure and test specimens produced in a laboratory using plastic moulds. A concrete block had to be produced for the experiment to simulate a real structure. The concrete used for the production of this block was also used in a laboratory to produce the test specimens. Core samples were drilled out from the concrete block and were subsequently used to make sets of core specimens. The test specimens, which differed in size, shape and the production method in particular, were subjected to frost resistance tests. The output of the paper is both a comparison of the results obtained on individual types of test specimens and a recommendation on how to approach the determination of frost resistance of concrete in a structure.

Abstract: Energy saving is one of today’s biggest challenges. Since the construction industry is very energy intensive, there is a question of drastic reduction of energy consumption in all types of buildings. There are different approaches to this issue, but ultimately there is a need to create materials that have high thermal resistance.