The various approaches, established for concrete mix design, are not universal because design mixes are explicit to local climate, available materials, and type of exposure. The new-generation mix design method should be developed based on the performance criteria. The concrete strength obtained from the designed concrete mix
and optimum cement content should not be considered as the only parameter for the
suitability of the concrete mix. This study was carried to compare the proportioning
of concrete mixes obtained by following procedures of Indian Standard (IS), American Concrete Institute (ACI) and British Standard (BS) of concrete mix design without
the use of admixtures to validate for use in a moderate climate like Kashmir, India.
The concrete mixes have been prepared with the necessary 28 days resistance in
compression as “15 MPa, 20 MPa, 25 MPa, 30 MPa and 35 MPa”. The assessment of
water-cement (w/c) ratio; cement, water, fine aggregate (FA) and coarse aggregate
(CA) proportion was carried. The w/c ratio among all formulated mixes is significantly high in the BS method and low for IS method. The BS method uses less quantity
and IS method uses the maximum quantity of cement. In addition, the ratio of total
aggregate content (TAC) and the aggregate-cement ratio is higher in BS design
method as compared to IS and ACI design methods. The aggregate content in ACI mix
design appears to be consistent and it added to the relative high compressive
strength. The specimens cast following BS guidelines failed to attain the target mean
strength (TMS) due to a higher volume of aggregate content, high w/c proportion,
less quantity of cement in the mix. The specimens cast by ACI and IS mix design upon
compression testing showed higher results than the calculated TMS. The cost analysis per cubic meter of concrete revealed that IS and ACI mix proportioning are expensive than BS method. The IS procedure results in dense concrete followed by ACI procedure. It is expected that with a comprehensive investigation on selected design parameters concentrating more on local challenges, the present study will floor the way
for the development and adoption of performance-based design mix selection for moderate climate.
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The effects of the types of fibers on mechanical properties of normal and high
strength concrete under high temperature, up to 700 °C, was investigated. Three different- type fiber; "Steel Fiber (SF), Glass Fiber (GF) and Polypropylene Fiber (PPF)"
are added into the concretes in five different ratios (0, 0.50, 1.00, 1.50 and 2.0%)of
the volume under the following temperatures; 22, 100, 400 and 700°C. The results
indicate that all the different types of fibers researched contribute to both the compressive and flexural strengths of concrete under high temperature, however, it is
also found that this contribution decreases with an increase in temperature. The flexural strengths and compressive strengths for NSC and HSC mixes at 28 days under
high temperature decreases as the temperature increases especially up to 400°C.
Also, the best compressive and flexural strengths performance under high temperature was also those of SF. The compressive strength of the concrete incorporating SF
was reduced under high temperature only, while the mixes containing PPF and GF
were reduced under high temperature or with fiber addition. The optimum fiber addition ratios of the mixes containing PPF and GF are between 0.5-1.0 percent by volume. And for SF, it is 1.5% by the volume
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The effect of high temperature on self-compacting concrete, which contains different
amounts of fly ash, has been investigated. By considering the effect of concrete age
and increased temperatures, the optimum fly ash-cement ratio for the optimum concrete strength is determined using experimental studies. Self-compacting concrete
specimens are produced, with fly ash/cement ratios of 0%, 20% and 40%. Specimens
were cured for 28, 56 and 90 days. After curing was completed, the specimens were
subjected to temperatures of 20°C, 100°C, 400°C, 700°C and 900°C for three hours.
After the cooling process, tests were performed to determine the unit weight, ultrasonic pulse velocity and compressive strength of the specimens. According to the experiment results, an increase in fly ash ratio causes a decrease in the compressive
strength of self-compacting concrete. However, it positively contributes to self-compaction and strength loss at high temperatures. The utilization of fly ash in concrete
significantly contributes to the environment and the economy. For this reason, the
addition of 20% fly ash to concrete is considered to be effective.
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Concrete is known as one of the fundamental materials in construction with its high
amount of use. Lightweight concrete (LWC) can be a good alternative in reducing the
environmental effect of concrete by decreasing the self-weight and dimensions of the
structure. In order to reduce self-weight of concrete artificial aggregates, some of
which are produced from waste materials, are utilized, and it also contributes to develop a sustainable material Artificial neural networks have been the focus of many
scholars for long time with the purpose of analyzing and predicting the lightweight
concrete compressive and flexural strengths. The artificial neural network is more
powerful method in terms of providing explanation and prediction in engineering
studies. It is proved that the error rate of ANN is smaller than regression method.
Furthermore, ANN has superior performance over nonlinear regression model. In
this paper, an ANN based system is proposed in order to provide a better understanding of basalt fiber reinforced lightweight concrete. In the regression analysis predicted vs. experimental flexural strength, R-sqr is determined to be 86%. The most
important strength contributing factors were analyzed within the scope of this study.
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Self-compacting concrete (SCC) has great potentials as it offers several environmen-tal, economic and technical benefits. Moreover, the use of fibers extends its possibil-ities since fibers arrest cracks and retard their propagation. Incorporation of Quarry Dust (QD) in SCC help to reduce environmental hazards during the production of QD. This study evaluated the fresh and hardened properties of steel fiber self-compacting concrete (SFSCC) incorporating QD. The optimum fiber and QD contents with no ad-verse effects on fresh and hardened properties were determined. A comparative study on behavior of SCC and SFSCC mixtures in terms of workability, compressive strength, compressive strength development ratio, tensile, flexural and energy ab-sorption capacity was carried out. Test results showed that compressive strength in-creased with increase in QD contents at fixed fiber content by mass of Portland ce-ment (PC) and then decreased. Strength development ratio (C28/C7) for SCC was 1.13, while it was 1.06, 1.08, 1.10 and 1.01 after reinforcing with 0.10, 0.20 and 0.30 contents of fiber. The compressive, tensile, flexural and energy absorption capacity or Toughness of SFSCC increased with the inclusion of the aforementioned contents of steel fiber up to 0.20 % volume of total binder at constant QD content and then decreased when compared with control SCC values. From these results, optimum value for the variables studied was obtained from mix QD20 + 0.2fr. Hence, steel fiber and QD could be successfully used in SCC production not minding the slight draw back on workability of SCC caused by inclusion of steel fiber, but with a modified dos-age of super-plasticizer (SP), fresh and hardened properties, in accordance with spec-ifications in relevant code(s) can be achieved.
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Researchers and decision makers are continuously looking out to determine the po-tential and effectiveness of fly-ash as a partial replacement of cement in concrete. The current study is carried out to check the optimum or nearly optimum quantity of fly-ash with which cement should be replaced to get most of the properties of concrete enhanced and to give the idea about the quantities of fly-ash that can be used in a better way and better cause so that a proper management scheme of its usage and disposal can be implied. Further, a comparison is given between normal concrete and fly-ash concrete to show the properties which can be enhanced by proper utilization of fly-ash as a partial replacement of cement. After carrying out the lab experiments, it has been seen that the replacement of fly-ash in concrete has resulted in general increase in compressive strength, flexural strength and splitting tensile strength up to 15% replacement and after then the strength is decreased considerably than that of normal concrete. Addition of fly-ash in concrete has resulted in decrease in the water absorption of concrete and hence decreases in permeability of concrete. There is a progressive increase in workability with increase in percentage of fly-ash in con-crete. The current study has led to a conclusion that in order to achieve best results in use of fly-ash concrete, the fly-ash used for replacing cement in concrete should have the required properties as specified by the standards and proper techniques of processing fly-ash as well as mixing of fly-ash with cement must be employed.
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Polymer materials are used in different engineering applicationsbecause of their ex-cellent engineering properties. Theuse of thesematerials in different engineering fields has increased in recent years. It is predicted that polymermaterials will be one ofthemost remarkable and popular engineering materials in the near future becauseof their unique properties. This paper focuses on Methyl Ethyl Ketone Peroxide (MEKP), which is oneof the main catalysts and investigate its effect on the mechani-cal properties of Polymer Concrete (PC).The main aimsof the study are to under-stand the mechanical properties of the polymer concreteincluding different amount of MEKP and to investigate the influence of MEKP on the mechanicalcharacteriza-tions of the PCs. For this purpose, five different samples containing 0.15%(Mixture-1), 0.25% (Mixture-2), 0.35% (Mixture-3), 0.45% (Mixture-4) and 0.55% (Mixture-5) MEKP ofthe total weight were prepared and some experimental studieswere per-formed on the prepared mixtures.The obtained strength values were discussed and evaluated effect of MEKP on mechanical properties ofPCs.
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Early distress in RCC (Reinforced Cement Concrete) structures in the recent times poses a major problem for the construction industry. It is found that in most of cases, distresses in reinforced concrete structures are caused by corrosion of rebar embed-ded in the concrete. The HYSD (High Yield Strength Deformed) rebars which are used to offer excellent strength properties is detrimental to durability due to action of ribs as stress concentrators. Nowadays, concept of PSWC rebars (plain surface with wave type configuration rebars, formerly known as C-bars/mild steel rebar with curvy profile) is emerging to have a compromise between strength and durability. This in-vestigation assesses the flexural behaviour of RCC elements reinforced with PSWC rebars. The flexural performance of RC beams of size 1000mm x 150mm x 150mm reinforced with PSWC rebars at 4mm and 6mm deformation level was studied by conducting test as per IS 516-1959 under four point loading. The performance of PSWC bar reinforced elements are compared with beams reinforced with mild steel rebars, HYSD rebars with spiral and diamond rib configuration to assess the viability of PSWC rebars to replace conventional reinforcement. The test results are validated by numerical analysis with the help of ANSYS software. Totally 15 beams are sub-jected to flexure test and the performance evaluators are first crack load, deflection at first crack load, ultimate load carrying capacity, deflection at ultimate load, load-deflection behaviour, load-strain behaviour and failure pattern. It is found that PSWC rebars as reinforcement in concrete beams enhanced the ductile behaviour of beams as compared to conventional HYSD and mild steel rebar beams. The energy absorbing capacity has increased significantly for beams reinforced with PSWC rebars when compared with conventional HYSD and mild steel rebar beams. The load-deflection behaviour and failure mode of PSWC rebars reinforced concrete beams were found to be similar to that of high yield strength rebars irrespective of deformation level. The analytical investigation from ANSYS software gave good agreement with the ex-perimental results. It is concluded that PSWC bar has the potential to replace conven-tional HYSD rebar. Further study needs to be done to optimize the profile level and stirrup locations; and usage with high concrete grade for effective exploitation.
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Tuba BAHTLİ, Nesibe Sevde OZBAY
Tuba BAHTLİ, Nesibe Sevde OZBAY
In this study, the effects of finely-milled bronze and waste tire on the mechanical properties of concrete have been investigated. Approximately 2.5% and 5% by weight for each additive (bronze sawdust and waste tire) were added to dry concrete. The open porosity, density, compressive strength values of cured concrete have been determined. In addition, the Schmidt rebound hammer (SRH) and the ultrasonic pulse velocity (UPV) tests, which are non-destructive test methods, were applied. The microstructure and fracture surfaces of these materials were characterized by scan-ning electron microscopy (SEM). It was observed that the density of pure concrete was 2.35 g/cm3 while the density was 2.19 g/cm3 for a C+5%B+5%T material. Simi-larly, pure concrete had an almost three times better compressive strength and a two times better SRH value than those of the C+5%B+5%T material. The density and me-chanical properties of concrete materials containing bronze and waste tire decreased due to micro crack formations, weak bonding and deep cracks forming especially be-tween the concrete and additives.
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The locations of structural members can be provided according to architectural pro-jects in the design of reinforced concrete (RC) structures. The design of dimensions isthe subject of civil engineering, and these designs are done according to the expe-rience of the designer by considering the regulation suggestions, but these dimen-sions and the required reinforcement plan may not be optimum. For that reason, the dimensions and detailed reinforcement design of RC structures can be found by using optimization methods. To reach optimum results, metaheuristic algorithms can be used. In this study, several metaheuristic algorithms such as harmony search, bat al-gorithm and teaching learning-based optimization are used in the design of several RC beams for cost minimization. The optimum results are presented for different strength of concrete. The results show that using high strength material for high flex-ural moment capacity has lower cost than low stretch concrete since doubly rein-forced design is not an optimum choice. The results prove that a definite metaheuris-tic algorithm cannot be proposed for the best optimum design of an engineering problem. According to the investigation of compressive strength of concrete, it can be said that a low strength material are optimum for low flexural moment, while a high strength material may be the optimum one by the increase of the flexural mo-ment as expected.
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