Papers by Keyword: Workability

Abstract: The use of different supplementary cementitious materials (SCMs) has attracted the interest of researchers for years. These materials have their advantages and dis-advantages. The optimal use of these SCMs in concrete may call for blending them together in concrete instead of using them individually. The blend may increase their quality as one disadvantages may be catered for by another one advantages. The present study focusses on investigating the effect of proportional combination of these SCMs on strength development. Three different South African SCMs (Ground granulated blast-furnace slag, Silica fume and Fly ash) were blended at different proportions and used as replacement of cement in concrete. Compressive strength test based on SANS 5860:2006 standard were adopted. The compressive test was performed on 16 different mixes at 7, 14, 28, 90 and 120 days curing periods. The water/cement ratio for all the mix was maintained at 0.5. The compressive strength results are desirable for each curing age at the 30% replacement of cement in which each SCM contributes 10% to the mix, greater strength value at curing age beyond 120 days compared to control sample was envisaged for this sample.

Abstract: Concrete use is fundamental to most infrastructural development plan of humanity today. This underscores the need to understand the strength characteristics of concrete made with crushed glass aggregate as partial replacement for fine aggregate and mixed with magnetic field treated water (MFTW). This study investigates the mechanical properties of concrete mixes prepared and cast into cubes of varying constituents such as concrete mixed with normal water, concrete mixed with MFTW, concrete with varying degree of crushed glass as replacement of fine aggregate from 15 to 45% with or without MFTW. The cubes were thereafter crushed after 7, 14, 28 and 56 days of curing to determine their compressive and tensile strengths. From the results obtained, it was observed that the optimum percentage partial replacement of sand with crushed glass aggregate is 15% to attain a suitable using MFTW in the mixing of the concrete. At this percentage replacement, it was observed that both the compressive and tensile strengths of the concrete mixed with MFTW improved by 25-30% relative to the conventional concrete. The study therefore recommend the use of MFTW in place of normal water in concrete production and use especially when partially replacing fine aggregate with crushed glass aggregate.

Abstract: The by-products of energy industry are nowadays often affected by new limits governing the production of harmful gases discharged into the air. These stricter and stricter criteria are often met by electricity producers by changing the combustion process in thermal power plants itself. Nowadays, the SNCR (selective non-catalytic reduction) application is quite common in the combustion process in order to help reduce the nitrogen oxide emission. This article deals with the primary measures of thermal power plants, which in particular consist of a modified treatment of raw materials (coal) entering the combustion process. These primary measures then often cause the formation of fly ash with unsuitable fineness for the use in concrete according to EN 450. The paper presents the comparison of the physico-mechanical parameters of several fly ashes with a different fineness values. The primary task is to assess the impact of non-suitable granulometry in terms of EN 450 on the other physico-mechanical parameters of fly ashes sampled within the same thermal power plant. Several fly ashes produced in the Czech Republic and surrounding countries were evaluated in this way.

Abstract: Work is focused on study of workability changing of heat resistant nickel-based Ni-15Co-10Cr alloy produced by selective laser sintering from metal powder. Experimental research of HRC hardness changing was provided on plate samples 2х10х30 mm after sintering and typical heat treatment for this alloy. Heat treatment was: annealing at temperature of 1,000oС during 1.5 hours, and then at the temperature of 1,180oC for 2.5 h – 3 h. After that samples were treated in a furnace for 50 – 60 minutes at the temperature of 1,050oС. Then they were cooled-off to the temperature of 1,000oС during 50 – 60 minutes. After that they were further quenched at ambient temperature. After quenching the samples were subjected to ageing at the temperature of 850oC during 3, 6, 9, 12 and 15 hours. The bending and measurement of triangle height was proposed for work ability assessment of samples. Increased hardness was found with duration of ageing. Work ability grew up with duration of ageing but where was a gap of workability for 9 hours ageing. Calibration of sintered parts and samples are recommended to perform after quenching and ageing at 850oC no longer 6 hours.

Abstract: This study focuses on the study of the mechanical behavior of non-metallic hybrid Basalt-PVA fiber reinforced concrete. Total five mixes were investigated with one control plain concrete and four with fiber volume fraction of 0.3%, 0.6%, 0.9% and 1.2%. Basalt and PVA were used in same quantity. Fiber decreased workability, therefore superplasticizer was used to maintain workability constant. The increase in superplasticizer and fiber content decreased compression, split tensile and flexure strengths because of formation of big size pores. Whereas fiber enhanced the post peak load zone in the load-deflection curve. Fiber improved the bridging action by increasing energy absorption. Fiber vanished the brittle behavior of high strength concrete and increased first crack toughness, flexure toughness and also maximum deflection. 0.3% volume fraction of fiber was found to be optimum with the negligible decrease in compression, split tensile and flexure strength while caused the considerable increase in first crack toughness, flexure toughness, and maximum deflection.

Abstract: Use of waste materials in concrete is now a global trend for efficient waste management so as to achieve a sustainable green environment and with the added advantages of preserving the natural resources as well as producing a better performing concrete. This study examined the properties of concrete containing ground waste glass powder (GP) as partial replacement for cement. The waste glass was finely grounded into powder and the morphology imagery of the powder materials was carried out using scanning electron microscopy (SEM). Moreover, the chemical composition of the glass powdered material was determined using X-ray fluorescence (XRF). Laboratory tests were carried out to determine the strength activity index, workability, split tensile and compressive strength properties of the concrete with 0%, 15%, 18%, 21%, 24%, 27% and 30% partial replacement of cement with the ground waste glass powder. The results showed that the oxides composition of the glass powder meets the requirements for pozzolanic material, while the SEM morphology shows materials of amorphous flaky solid masses, and based on the 28-day strength activity index, concrete containing 21% cement replacement shows a higher strength index above therecommended 75%. It was also observed that workability of the concrete reduced with increase in percentage glass content while significant improvement of the compressive strength of the concrete was achieved at 21% cement replacement, after which a decrease in strength with increasing percentage glass content was observed. The revealed results were confirmed by the microstructural examination using SEM showing a denser concrete at 21% cement replacement but increase porosityas the glass content increases. However, a decrease in split tensile strength was observed with increasing glass content. The results clearly showed that it is possible to produce moderate strength sustainable concrete for structural application using 20% glass powder as cement replacement.

Abstract: This study deals mainly with the mix proportions using granite and unwashed gravel as coarse aggregate for self-compacting concrete (SCC) and its workability, by considering the water absorption of unwashed gravel aggregate. Mix proportions for SCC were designed with constant cement and fine aggregate while coarse aggregates content of granite-unwashed gravel combination were varied in the proportion 100%, 90%/10%, 80%/20%, 70%/30%, 60%/40%, 50% /50%, represented by SCC1, SCC2, SCC3, SCC4, SCC5 and SCC6. 100% granite (SCC1) serves as the control. The workability of the samples was quantitatively evaluated by slump flow, T₅₀₀, L-box, V- funnel and sieve segregation tests. Based on the experimental results, a detailed analysis was conducted. It was found that granite and unwashed gravel with SCC1, SCC2 and SCC3 according to EFNARC (2002) standard have good deformability, fluidity and filling ability, which all passed consistency test. SCC1, SCC2 and SCC3 have good passing ability while all mixes were in the limit prescribed by EFNARC (2002). It can be concluded that the mix design for varying granite-unwashed gravel combination for SCC presented in this study satisfy various requirements for workability hence, this can be adopted for practical concrete structures.

Abstract: The modification of matrix is an important method to improve the mechanical properties of strain hardening cementitious composite (SHCC). The influence of the properties of the matrix water binder ratio (W/B) and fresh state rheology on SHCC tensile behaviors are useful for the SHCC design. The W/B influences only on tensile strength, but not the stain capacity, if the fresh state workability remains uniform. On the other hand, the workability has a significant influence on SHCC strain capacity through its influence on the fiber distribution. Consequently, it is important to cast SHCC carefully and make sure the even fiber distribution to insure the bridging function and mechanical properties of SHCC.

Abstract: The results of experimental studies of the different machinability group materials’ characteristics, including tool steel DIN C125W, heat-resistant steel (C - 0.1%, Si - 0.6%, Cu - 0.3%, W - 0.1%, Mn - 0.4%, Ni - 23%, P - 0.01%, Cr - 12%, S - 0.01%, V - 0.01, Mo - 1.5%, Ti - 3%, V - 0.001%, Al - 0.6), nickel-based superalloy (Fe - 4%, C - 0.1%, Si - 0.6%, Mn - 0.5%, S - 0.01%, P - 0.01%, Cr - 15%, Ce - 0.01%, Mo - 4%, W - 6%, V - 0.3%, Ti - 2%, Al - 2%, B - 0.01%), the changes in the minimum surface wear, maximum cutting path, and cutting temperature in the processing of these materials, as well as the experimental data analysis showed that the extreme values of changes in the materials’ physical and mechanical properties under the temperature impact can be defined as the minimum surface wear temperature and maximum cutting path temperature, that is, the conditions corresponding to the maximum workability of the materials. It is possible to use the materials physical and mechanical property dependence on temperature for defining the maximum material workability temperature when processing it by cutting. The article suggests a method to define the maximum material workability temperature.

Abstract: This article deals with the ways of mixing method for concrete with extremely low water-cement ratio (w/c) typical for ultra-high performance concretes. For this purpose, the mixture with w/c ratio of 0.2 and amount 6% superplasticizers of cement weight was used. In total 6 various mixing methods was tested, which differed in application of superplasticizers, mixing order or mixing length. Workability, electricity consumption during mixing and compressive and flexural strength after 28 days were examined. The performed experiments showed that workability can be increased by, for example, separate doses of superplasticizers and water or other mixing methods. Strength of concrete was identical for all produced mixtures, even though the total mixing time was shortened in two cases.