Key Engineering Materials Vol. 677

Abstract: Self-consolidating-concrete (SCC) has gained wide acceptance in the construction industry given its ability to reduce construction duration and cost. All ready-mix concrete commonly used in hot weather countries, such as United Arab Emirates (UAE), is subjected to continuous agitation during hauling to construction sites. Prolonged mixing, especially at high temperatures can lead to loss of workability and increased difficulties for concrete placement and consolidation. This may result in lower mechanical and durability properties. In this paper, the mechanical and durability properties of self-consolidating concrete (SCC) under hot weather conditions were investigated. Mixing and testing were conducted outdoor at the construction material lab of Abu Dhabi University during last summer of 2014. The test results showed that the mixing time and hot weather adversely affected the fresh properties. The SCC mixtures were continuously mixed for 2 hours under a temperature ranged from 25 to 40 °C, to simulate concrete in a transit truck during transportation to a construction site under hot weather. Polycarboxylate-based high-range water-reducing admixture (PC) and fly ash were incorporated in the investigated SCC mixtures. The results showed that both the compressive strength and durability of SCC were highly affected by fly ash dosage and temperature.Keywords: Hot weather; hauling time, self-consolidating concrete.

Abstract: The paper reviews the so far known information about the properties of biological shielding concrete used in the containment vessel of nuclear power plants (NPP) and its behaviour when exposed to radiation. The damage of concrete caused by neutron and gamma radiation as well as by the accompanying generation of heat is described. However, there is not enough data for the proper evaluation of the negative impacts and further research is needed.

Abstract: By drills realization in order to obtain petroleum and natural gas, the isolation of the individual layers along the height of drilling activity is the most important factor for judging the serviceability and follow-existence of the finished work. The special cements for drilling are used as plugging material suited according to API Spec. 10A (American Petroleum Institute).Recently, in the institute we have dealt with the impact of the time factor on the pressure characteristics and stress-strain diagrams of samples from the drilling mud additives [1], due to the time factor for composites containing drilled and subsequently in practice applied aggregates [2] and also the characteristics of a drilling cement made for lower and laboratory increased temperatures [3]. In the article we deal with a similar topic. Results for tension and pressure characteristics gathered in time up to 120 hours were used to generate the stress-strain diagrams, static and dynamic modules in compression. Heat background of tests answers the real terms of drilling activities up to 1200 m. In conclusion, we will compare the results with available foreign results.

Abstract: The aim of this study was to describe mechanical properties decline and macroscopic changes after cyclic thermal load of refractory slabs. Investigated elements were made from refractory cement composite containing natural basalt aggregate, fine ceramic powder, aluminous cement with high volume of Al₂O₃, different dosage of basalt fibres, water and plasticizer. Slabs with dimension 300 x 200 x 38 mm were exposed to elevated temperature 600 °C for three hours (temperature gradient 10 °C/min) and cooled to laboratory condition. This loading cycle was repeated six times. Tensile characteristics were investigated by bending test with clear span of supports 200 mm. Maximum force and displacement increased with increasing amount of basalt fibres. Maximum flexural strength of slabs corresponded to material characteristics measured on specimens 40 x 40 x 160 mm. Slabs with 1% of basalt fibres achieved flexural strength 4.8 MPa (after six loading cycles). The highest weight decline took place after the first loading cycle. Successful design of original fibre-cement composite has been approved by cyclic loading of larger dimension specimens.

Abstract: Development of new composite materials is the worldwide extremely progressive branch of engineering activity. Composite materials are applied in many industries. The principle of composite materials is a combination of different materials providing an entirely new material with specific properties. Fiber-reinforced composites rank to the most frequently used composites because of their suitable mechanical properties. There were studied mechanical properties of fibre reinforced cementitious composites (FRCC) exposed to high temperatures of 600 °C and 1000 °C in the paper. For the production of refractory FRCC were used aluminous cement Secar®71 with 70 % of Al₂O_3. Various composites differed in the used type of fibers - basalt, carbon and ceramic fibres were applied in doses of 2 % by volume. For the experimental program were prepared prismatic specimens with the total dimensions of 40 × 40 × 160 mm³ and cured for 28 days in humid environment. Residual bulk density, flexural and compressive strength were investigated in the performed experimental program. The results showed the positive effect of the fibers used in refractory composition and the dependence on the length of the used fibers.

Abstract: Concrete exposed to high temperature considerably changes its properties down to total destruction. The paper describes renovation of concrete floor damaged by a fire of a factory building. Individual steps of determination of damage of concrete floor structures caused by high temperatures are described. Structure of damaged floor was technically analyzed, redevelopment was designed and renovation works were carried out.

Abstract: This paper summarizes different types of degradation of concrete in the energy industry. There is described the most of important kinds of degradation and what effects they can cause. In conclusion, this article is formulated several points to prevent the degradation of building materials.

Abstract: The paper discusses durability of glass and carbon fibers which are exposed to alkali environment of concrete. Mainly glass fibers are affected by the high alkali environment with pH of concrete exceeding 12.0. The degradation of fibers is reflected by decreasing of its tension strength, while the rate of decreasing is depended on exposition time and temperature. The paper briefly presents results of a large experimental investigation which should specify an influence of alkali ions concentration in a solution on reduction of the mechanical properties of fibers. Reference samples were immersed in a bath with distilled water and the others were stored at ambient air only.

Abstract: This paper describes an experimental investigation of the effect of early age prestressing on the ultimate geometry and the load bearing capacity of precast concrete elements. The experimental is performed with a small-scale T-beam which are prestress at three different ages. The experimental results obtained after seven days after prestressing are compared with calculated estimations on the shrinkage and creep according to B3 model.