Key Engineering Materials Vol. 677

Abstract: The paper touches on the issue of plastic shrinkage of concrete and cement mortars. In this connection, the volume changes were monitored batch of studied depending on the intensity of surface evaporation. Volume changes were measured on a prototype contactless gauge. The article outlines the possibility of suppressing plastic shrinkage by adding a polymer fibre reinforcement possibly coated fibres.

Abstract: The comparison of really measured compressive strength static modulus of elasticity with table values stated in Eurocode 2 is essential part of the paper. Since the standard draws from modulus of elasticity - concrete strength class, the set compressive strengths will be classified in concrete particular classes. Experimental part was based on several concrete design compositions differing in particular input raw-materials. Monitored values were set with concretes in different ages with final value 180 days. The experiment tries to demonstrate the impossibility of static modulus of elasticity derivation from table values which do not match the present-date produced concretes.

Abstract: This article is focused on cement based composites. Two cements differing in mineralogical composition are utilised as main binder in composites mixtures. Results of measured physical parameters of studied materials are presented. For the sake of comparison, a reference material with Portland cement was also prepared. Basic physical properties (measured by water vacuum saturation method and by helium pycnometry), characterizations of pore system (determined by mercury porosimetry) and mechanical properties are the matter of this study. Composites show various open porosity; the results of open porosity of materials containing special cements show higher values, in comparison with composite based on Portland cement. This fact of course influences other material characteristics - mainly mechanical properties.

Abstract: Portland cement got his name derived from the appearance of concrete that resembles sandstone located near city of Portland in England. In 1824, John Aspdin was granted a patent for the production of Portland cement.In the past, energy and economic demands on production of cement were lower than they are today. Production was characterized by a slower burning mode and coarser grinding. Product produced this way were reaching lower compressive strength.Currently there are several companies producing Portland cement. Main ones in Czech Republic are Holcim, Heidelbergcement group and Lafarge Cement a.s. Their production methods are very similar. The differences are mostly in the possibility of using local raw materials with different chemical composition and the technical equipment of factories. In the production, the main emphasis is on reducing energy and financial cost.One way to save energy and money is to use mechanical-chemical activation when grinding Portland clinker.

Abstract: This paper deals with numerical analysis of unreinforced compressed masonry column. The experimental program is part of a research project NAKI [1]. Three material models usually used for simulation rock, soil, concrete and other quasi-brittle materials were assumed for numerical modelling of masonry column and mutually compared. The material characteristics were identified based on literature research since the needed mechanical properties were not available. The determination of own material characteristics and comparison numerical simulation with experimental test can be outlined as a future goals. For all simulations the commercial software package ABAQUS was used and the obtained numerical results are discussed.

Abstract: Development of extremely thin concrete structures and demand for extremely thin elements are the reason of using composite non-traditional materials as reinforcement. Steel reinforcement is not very chemically resistant and it limits the thickness because of the required concrete cover as protection. This is the reason why textile reinforced concrete (TRC) going to be very famous and modern material. TRC in combination with fine grain high performance concrete (HPC) allows a significant saving of concrete. Due to its non-corrosive properties of composite technical textiles it is possible to design very subtle structures and elements. TRC and HPC in general are developed at the Faculty of Civil Engineering and the Klokner Institute, CTU in Prague. This present paper investigates the cohesion influence of textile reinforcement on four point bending test. All small experimental panels were reinforced with the same 3D technical textile from AR-glass roving with different type of cover layer. Different conditions of interaction between technical textiles and HPC were ensured by modified surface using silica sand and silica flour.

Abstract: Several different types of aggregates were used for production of tested samples, namely: the standard sand of a fraction 0-4 mm, quartz sand of a fraction 0-0.4 mm, finely ground recycled limestone powder of a fraction 0-0.07 mm, finely ground recycled concrete of a fraction 0-0.13 mm (ground by Lavaris Company), and finally crushed bricks of a fraction 2-5 mm. The Portland cement CEM I 42.5 R produced in Radotín was used as a binder. Testing was carried out on prismatic samples of dimensions 40 × 40 × 160 mm. Compressive strength and static Young ́s modulus were measured for individual samples and these differed by the type of a microfiller and its amount.

Abstract: Main target of this study is a comparison of material properties of plasters, which were obtained with use non-destructive methods and destructive methods and find out relation between them. These parameters were investigated on plasters. In this research the destructive methods were focused in obtain three parameters: the compressive strength, the tensile strength and the modulus of elasticity. For non-destructive testing was used pulse velocity method. Testing was carried out on specifically fabricated test specimens. With this study were obtained relations of the parameters for each type plasters measured with the non-destructive methods and with the destructive techniques. Obtained data were compared and then evaluated. These relations are very important and necessary for possibility to eliminate destructive methods in future.

Abstract: The United Arab Emirates (UAE) is one of the largest consumers of concrete in the region due to the enormous number of mega reinforced concrete projects constructed in the country. The harsh weather of the UAE, where temperature may reach to above 45 °C and the humidity at coastal areas up to 100%, requires special attention to the design of the concrete mixes used in these projects to make sure that they meet the strength requirement and satisfy the sustainability condition. To insure the sustainability of the projects constructed in the UAE a local sustainability rating system called “Estidama” was developed by Abu Dhabi Urban Planning Council. The Estidama sustainability rating system is equivalent to the LEED, but tailored to the special culture and climate of the UAE and the region. This system is mainly implemented in the UAE’s capital city Abu Dhabi and gaining more publicity in the region. The main objective of this paper is to evaluate collected concrete mixes implemented in some major projects in the UAE’s based on Estidama’s requirements, and to come up with an optimization process to choose the most sustainable concrete that satisfies the mechanical properties requirements, durability requirements and has the least embodied CO₂ emission. This research will concentrate on concrete mixes commonly used in the UAE with emphasises on those incorporating slag as a partial replacement of cement in concrete.

Abstract: Literature often concludes that the drop in mechanical properties of recycled concrete, compared to concrete made with natural aggregates, is unfavourable for concrete durability in aggressive environments. The agricultural industry is one of these environments where concrete floorboards and walls are confronted with weak organic acids. A research program was undertaken to determine the resistance of concrete, made with coarse recycled concrete aggregates (0-75%), against these acids. In this research two different qualities of recycled aggregates were used: while the first originated from road demolition and contained porphyry as main aggregate, the latter originated from mixed demolition and contained mostly limestone. One reference concrete mixture and six different recycled mixtures were made. These seven concretes were exposed to three different acids: acetic, tartaric and citric acid. Beside the acidic resistance tests, workability, density (fresh and hardened) and water absorption (both by capillarity and submersion) were also determined for each mixture. The results show that the increase of acid soluble material increases the resistance of concrete against erosion due to weak acids.