Key Engineering Materials Vol. 677

Abstract: The paper introduces development of new type of high-performance Portland cement based composite applicable for number of practical utilization. The fundaments of performed research was to design mixture with controlled process of hydration, easy production, suitable time of setting, good workability and rapid evolution of mechanical properties as well as satisfactory long-term stability of hardened composite. Selected mixture were evaluated by means of mechanical properties and volume changes determination.

Abstract: Engineered cementitious composites (ECC) are characterized with increased ductility and strain hardening due to its internal structure design. ECC is especially useful for applications where common steel reinforced concrete is not applicable and the structural members undergo large strains or dynamic action. Such conditions are often combined with environmental effects where structures are partly or fully immersed in water possibly containing some harmful substances such as chloride or sulfuric ions. To maintain sufficient durability of the composite it is necessary to decrease its water absorbability. One of the very efficient ways to do this is to use external or internal hydrophobization of the composite as shown in this paper.

Abstract: In the article the possibility of lightweight cement concrete manufacturing has been presented with use of binder in which part of cement was replaced with siliceous fly ash Class F. It was used lightweight aggregate Pollytag and Keramzyt. Total amount of binder was 400 kg/m³ with w/b=0.5. Mechanical properties has been tested as well as properties affecting durability of concrete. Replacing part of cement with fly ash improved concrete resistance on chloride ion migration, reduced compressive and tensile strength of concrete and increased carbonation depth.

Abstract: Environmental impacts and sustainable development are two words, which are mentioned every day. The responsibility of our generation is growing up. People consider about the new ways of using materials. Some of them were waste in the recent past. In present time people think about the possibilities how the waste could be reduced, recycled, reused or recovered. In this paper are presented the chemical and physical properties of different coal ash. In the research were tested the XRD analyse, the quantity of Free CaO, the granulometry, volume stability, loose bulk density and shake down loose bulk density.

Abstract: Using of fly ash in concrete screed is becoming a common practice. This situation entails both environmentally and economically positive effect. The problem may occur with the durability and life of such materials. Therefore, it is important to correctly grasp these materials and final properties sufficiently verify. One of these properties is frost resistance. This paper presents the results of measurements on the frost resistance of concrete screed with the substitution fly ash 0-50% by weight of clinker. Specimens were subjected to destructive and non-destructive test of frost resistance after 28 days of ripening and the results were evaluated.

Abstract: This paper describes rheological characteristics of concrete mixtures based on alkali-activated fly ash. There are shown relationships between workability of fly-ash fresh concrete mixtures and water–fly-ash ratio in fresh alkali-activated concrete. In addition, there is described relationship between workability in fresh mixture on compressive strength of alkali-activated concrete.

Abstract: The water vapour transport and the liquid water transport of high performance concrete (HPC) with the content of natural pozzolana are the described in this paper. Studied properties are presented by means of water vapour diffusion coefficient, water vapour diffusion resistance factor and absorption coefficient respectively. The natural pozzolana (NP), namely natural zeolite, is used as supplementary cementitious material which affects the durability properties of the end product. The obtained results revealed the effectiveness of NP in the terms of both studied properties when used in small amounts, i.e. at about 20% of cement weight. On the other hand substitutions higher than 40% result in worsening of the resistance of the concrete to water and water vapour ingress and its movement trough the material.

Abstract: Durability and high strength of concrete are closely associated with low porosity and generally denser material structure. This is achieved using the addition, which include also silica fume. This article deal with an effective dosage of silica fume in high performance concrete, in a proportion of 0-25 % by the weight of cement. Compressive strength, rheological behaviour and economic benefits were the main questions in this work. The expected increase in compressive strength showed itself in lower doses of silica fume, while higher doses did not produce a further increase in strength. In the case of rheological behaviour, we can confirm lower bleeding and segregation, but also faster drying of the surface layer. From the economic point of view, a small doses of silica fume are better, because then we have observed the highest increase in strength.

Abstract: The article compares the basic physical, mechanical and both liquid water and water vapour transport properties of self-compacting concrete containing different pozzolanic admixtures. Limestone, fly ash and metakaolin were used. A concrete mixture without any pozzolana was also manufactured as a reference. The best values of studied properties were recorded for the metakaolin concrete.

Abstract: The paper deals with the use of concrete with crystalline admixture for special remedial structure which is exposed to intensive ground moisture and high level of air humidity. Additional protection of ground part of older buildings against subsurface water and ground moisture is one of the most important measures to ensure their long-time durability and satisfactory user properties. One of the most used remediation method are the air ducts which principle is to enable air flow along the moist structure surface to allow the sufficient evaporation of moisture from the structure. This group of methods includes also the ventilated underground tunnel along the perimeter walls. Presently the ventilated tunnels are designed as masonry structure whose durability in contact with the ground moisture is limited. The paper introduces a new technical solution of this method based on the special shaped concrete blocks whose durability is ensured by using of concrete with crystalline admixture. The waterproofing effect of the crystalline admixture is declared by the results of laboratory tests (in comparison with efficiency of crystalline coating).