No abstract

There has been a tendency to design ever slender building construction using high strength concrete in recent years. Application of HSC is also growing in tunnel construction. One of the most important challenges is to control explosive spalling of concrete and the method recommended by Eurocode 2 (EN 1992-1-2:2008/NA:2010P) is addition of polypropylene fibres to the mix. The purpose of the research described in this paper was to evaluate the changes of mechanical properties of HSC exposed to the effect of high temperature.The tests were carried out on three types of high strength concrete: air-entrained concrete, polypropylene fibre-reinforced concrete and reference concrete having constant water/cement ratio. The properties of hardened concrete including compressive strength, tensile splitting strength, flexural strength and E-modulus were studied. The latter tests were carried out on both on concrete cured at 20 °C and concrete subjected to high-temperature conditions at 300 °C, 450 °C and 600 °C. The results enabled us to evaluate the effect of high-temperature conditions on the properties of high-performance concrete and compare the effectiveness of the two methods designed to improve the high-temperature performance of the concrete: addition of polypropylene fibres and entrainment of air.Keywords: high strength concrete, mechanical properties of HSC, high temperature, effect of high temperature.

No abstract

The paper presents an analysis of the possibilities of using glass waste from recycled lighting materials as aggregates for cement concrete. The research material was obtained from a company that utilizes electrical waste. Glass from pre-sorted elements was transported to the laboratory and crushed in a drum crusher. In this way, the aggregate obtained was subjected to the basic tests that are carried out for aggregates traditionally used in construction. The specific density of aggregate, bulk density, absorbability, crushing index, grain shape, texture type and aggregate flatness index were examined. In the next stage of research work, concrete mixtures were made in which crushed aggregate from crushed fluorescent lamps was used as a substitute for gravel aggregate. Mixtures containing 10%, 30%, 50% and 100% aggregate were made. A mixture containing only sand and gravel aggregate was made as a comparative mixture. Basic tests of both fresh concrete mix and hardened concrete were carried out for all concrete made. The consistency of the fresh concrete mix, the air content in the concrete mix, the density of hardened concrete, absorbability, water permeability under pressure and the basic compressive and tensile (flexular) strength tests were performed. The test results showed that the greater the addition of recycled glass aggregate, the less advantageous are the features of the concrete obtained with its participation. Microscopic analyses carried out in order to explain this phenomenon indicated an unfavorable influence of the grain shape of the aggregate thus obtained. Despite this fact, recycling of lighting waste in concrete composites is recommended as a pro-ecology measure; however, attention was paid to the benefits of using only 30% by mass of said waste in relation to the weight of the traditional aggregate used. Composite with such a quantity of waste retained the characteristics of cement concrete, which qualified its use for construction concrete.

In the recent years a tendency for design of increasingly slender structures with the use of high performance concrete has been observed. Moreover, the use of high performance concrete in tunnel structures, subject to high loads with possibility of extreme loads occurrence such as fire, has an increasing significance.Presented studies aimed at improving high performance concrete properties in high temperature conditions (close to fire conditions) by aeration process, and determining high temperature impact on the concretes features related to their durability.In this paper it has been proven that it is possible to obtain high performance concretes resistant to high temperatures, and additionally that modification of the concrete mix with aerating additive does not result in deterioration of concrete properties when subject to water impact in various form.