Papers by Keyword: Concrete

Abstract: Research in the field of recycled aggregate reuse in load-bearing structures is essential, as is the increase in awareness of the impact of construction on the environment. Using secondary raw materials also reduces landfilling and rock mining, and, from a practical point of view, this practice provides new materials for concrete. In this paper, the effect of using recycled aggregate concrete (RAC) on the basic properties of standard concrete is studied. Three types of concrete were studied: natural aggregate concrete (NAC) and two mixtures with 50 % and 75% replacement of natural coarse aggregates by recycled concrete aggregate. Results showed that using recycled aggregates reduces the mechanical properties of hardened concrete. The different properties of hardened concrete with a rate of recycled aggregate also impact the design process of the load-bearing structures of the buildings. The standard regulations in Slovakia allow using recycled concrete aggregate for up to 55% of all aggregates, but many designers do not trust this material. However, we cannot avoid using secondary raw materials in designing new structures in the future. The knowledge of recycled aggregate concrete presented in this paper provides directions for research and the concrete industry to focus on sustainable concrete products systematically.

Abstract: Creep and shrinkage of concrete are important parameters for verification of ultimate and serviceability limit states. The prediction models which can be found in design codes, are applicable for ordinary concrete types. Unusual concrete types, like e.g., white concrete can be used, but their properties should be investigated by experimental testing. The paper is focused on measurement of shrinkage and creep of white and grey concrete of the same strength class. The experiments showed that both, creep and shrinkage of white concrete are higher than those of ordinary grey concrete. The measured shrinkage strains were compared with predicted shrinkage strains using various prediction models.

Abstract: The paper presents the rules for determining the minimum reinforcement in reinforced concrete structures that have been recommended in recent years and currently. It has been analyzed whether the reinforcement in structural members designed in different periods of time on the basis of various standard regulations regarding minimum reinforcement meets the conditions for protecting the structure against brittle failure. The necessary reinforcement has been determined using the method derived on the basis of nonlinear fracture mechanics of concrete. In the performed analysis the scale effect has been taken into account as well.

Abstract: The Sweating Slab Syndrome (SSS) was first mentioned in 2005 [3] and has further been discussed in [1], [2], [5], [6]. The condition is typically marked by the build-up of moisture in so-called big-box warehouse buildings on the top surface of concrete slab-on-ground construction which, when severe, can interfere with the routine operations of the facility, e.g. forklift traffic. The buildings are typically located in southern to southeastern regions of the United States and have non-climate controlled indoor environments. After drying, residues remain on the surface of the slab-on-ground, which have been identified as carbonation products of alkaline salts. Speculations as to the cause of this syndrome have included dew-point condensation, high vapor permeability of the slab, the troweling finishing process, bond breaker influence, unreacted silicates from integral or spray applied admixtures, and the absence of vapor retarder sheets under the slab. None of the speculated causes have been given supporting data or studied in detail, however. To determine the cause of the SSS, Wiss, Janney, Elstner, Associates, Inc. (WJE) applied a standard scientific methodology in 2019 consisting of three parts. The first part of this methodology was to collect data through observation, instrumentation, numerical simulation, and laboratory analysis. Second, a set of hypotheses was generated based on the data collection and logic. Finally, collected data was paired with one or multiple hypotheses in a logical way to disprove or support their validity. Results will be shown.

Abstract: The design of concrete structures with embedded non-metallic composite reinforcement (FRP) is becoming more widespread. The behavior of statically determinate concrete structures reinforced by this durable material is already widely understood and known. Usage of glass and carbon fiber reinforcement is also included in the new generation of Eurocodes for concrete structures. However, in common practice, we also encounter statically indeterminate structures such as continuous beams or slabs. In the case of traditional steel reinforcement of continuous beams, it is possible to assume a certain redistribution of bending moments and to use the principle of linear elastic analysis with limited redistribution in design. According to ACI 440.1R-15 and the new generation of Eurocode a moment redistribution of internal forces on continuous beams or other statically indeterminate structures reinforced with FRP reinforcement should not be considered, given the lower material stiffness and linear elastic behavior up to failure. However, in reality, a redistribution of internal forces can occur. Based on a limited number of studies and experiments that have been carried out in this area globally, there is a premise that some degree of redistribution of bending moment may occur in FRP reinforced indeterminate structures. The objective of this work is to support this assumption through an analytical study of the behavior of a concrete cross-section reinforced with FRP bars, demonstrating its potential for internal force redistribution. The aim of this paper is to present the results of an analytical study capturing the behavior of a concrete cross-section reinforced with FRP, the determination of the deformation characteristics of such a section, and the possible application of the results to a two-span concrete beam. The main emphasis is placed on the stress-strain diagram of concrete and its influence on deformation characteristics, mainly moment-curvature relationship.

Abstract: In today's contemporary world, concrete is a top choice, but curing issues persist due to water scarcity. Civil engineering offers alternatives like polyethylene and self-curing concrete, but they are costly. Over the past two decades, wastewater recycling for purposes like concrete curing has gained attention after treatment. The aim of this literature review is to thoroughly assess the viability of using treated wastewater, particularly sewage water, for the curing process. It focuses on articles from reputable journals published over the last decade. The review begins by examining concrete curing and its techniques and insufficiency cause. Subsequently, it delves into the philosophy of wastewater treatment need, source and the treatment process itself. Consequently, waste water treatment is suggested as an affordable and eco-friendly solution for concrete curing. Lastly, the feasibility of adopting treated waste water in developing nations is scrutinized, with an emphasis on its real-world applicability following comprehensive analysis of its overall performance. Membrane filtration technique is preferred for treatment of waste water due to its reasonable results.

Abstract: This research project focuses on the experimental investigation of using zeolite as a partial replacement for cement in M25 grade concrete. Zeolite, a naturally occurring mineral with pozzolanic properties, has gained attention as a sustainable alternative to cement in concrete production. The study aims to assess the effects of incorporating zeolite on the properties of M25 concrete, such as compressive strength, durability, and workability. Through a series of laboratory tests and analysis, the project intends to evaluate the feasibility and effectiveness of utilizing zeolite in reducing cement content while maintaining the required performance standards of M25 concrete. The findings of this research could contribute to promoting eco-friendly practices in the construction industry by reducing the environmental impact of cement production.

Abstract: In this experiment cement was exchanged with varying amounts of rice husk ash and silica powder sf such as 10%,15% and 20% to examine the features of the resulting concrete according to research M30 grade demonstrates great compressive and split tensile strength and performs best in 15% transfer the effects of substituting 15% of cement with RHA and SF on the overall properties of concrete are demonstrated in detail which contributes to a better understanding and development of building practices.

Abstract: The main perspective of this paper is enhancing the physico-mechanical and protective characteristics of concrete. This was achieved by incorporation Layered double hydroxide (LDH) in mix design of concrete with different doses. The concrete specimens were prepared with LDH percentages (0.5, 1.0, 1.5, and 2) % by the cement weight. After the characterization of LDH, the prepared concrete specimens were investigated as follows: the workability and density of the fresh concrete, effect of the addition of LDH on the compressive strength of hardened concrete were determined. The protective performance of concrete was evaluated by determining water absorption, contact angle, and chloride permeability. The obtained results detected that the physico-mechanical and protective performance of concrete are enhanced gradually by the addition of LDH up to 1.5% as follows; concrete slump decreased from 110 mm for control sample (concrete without LDH addition) to 47mm for M3 sample (concrete with 1.5% LDH) by 57% decrease percent. Density of concrete with 1.5% LDH increased by 5% as compared with control sample. Compressive strength increased by 25% for concrete with 1.5% LDH as compared with controls one. On the same time experimental results demonstrated that both water absorption and chloride permeability were decreased by 20% & 43% respectively, meanwhile contact angle increased by 24% for the same comparative samples. After this percent (1.5%), LDH is agglomerate and therefore unable to disperse uniformly so the optimum calculated percent of LDH for enhancing concrete performance is 1.5%.

Abstract: This article is devoted to the modeling of the stress-strain diagram of compressed concrete under the action of dynamic loads of various intensities. The main attention is paid to the influence of the strain rate of concrete on the determining parameters of this diagram. The degree of dependence of the dynamic increase factor (DIF) and the level of critical deformability of compressed concrete both on the rate of its deformation and on the level of elastic-plasticity (class) has been established. The analytical relationship between the main static and dynamic characteristics of the deformation diagrams of compressed concrete is established using the hypothesis of invariance and independence from the load mode of the specific potential energy of the ultimate deformation (destruction) of the material.