A major advantage of high-strength concrete (HSC) is the reduction in size of members in a reinforced concrete building. The present research examines the application of HSC as a jacketing material to increase the shear strength of columns. Self-compacting concrete of two different strengths (high and normal) was used to jacket twelve shear-critical beam-column specimens. The details of specimen preparation, tests and results are discussed in this paper. It was observed that the use of HSC is suitable for increasing the shear capacity of columns with thin jackets, with improvement in dowel action of the added longitudinal bars and diagonal crushing strength of the concrete. There was no undesirable increase in stiffness as compared to the specimens jacketed with normal-strength concrete.
The purpose of this paper is to discuss some of the challenges encountered during the design of two reinforced concrete drilled shafts situated in poor soils and subject to very large reactions. These difficulties include conforming to limitations on deflections, shaft top projections, effects of frost depths, evaluation of skin friction contribution to axial resistance and rebar arrangement. Two recent designs, where permanent steel casings are used to encompass the drilled shafts, are presented. Suggestions for the future include performing geotechnical investigation well in advance to avoid later-stage problems and to include skin friction while estimating axial or vertical load resistance.
Ordinary Concrete and High Strength Concrete (HSC) could be distinguished with respect to its compressive strength (CS). CS of concrete can be found out by conducting direct compression test on concrete cube or cylinder specimens; whereas, the tensile and shear strength (SS) of concrete may be determined in an indirect way. The present paper reviews the previous studies done on the CS, SS of Steel fiber HSC and their results. It is inferred that many authors have proposed their equations based on research work performed to predict the SS of concrete. The results of proposed equations incorporated in ACI have low coefficient of determination (R2) value and higher Average Absolute Error (AAE) value which shows large variation in its results than other proposed models. Thus, it formulates more erroneous depiction of SS for high strength steel fiber reinforced concrete beams having shear span to effective depth ratio (‘a/d’) more than 3. Thus, more rational and analytical models need to be developed for predicting the SS of HSC structures.
Geopolymer concrete is one of the most emerging alternate construction materials to conventional cement concrete. Fly ash is the source materials rich in silica and alumina, which reacts with alkali solution to produce alumina silicate gel that binds the fine as well as coarse aggregates to produce a good mode of concrete. Most of the authors reported geopolymer concrete tests in hot curing method rather than ambient curing due to its less strength. In this paper, the behaviour of fly ash based geopolymer concrete on mechanical and durability properties with various percentages of lime and silica fume have been studied experimentally in ambient curing. Two series of experiments have been conducted to optimize the addition of lime of 5%, 7.5%, 10% and secondly with the optimized lime percentage silica fume has been added of 1%, 2%, 3% & 4% partially by replacing fly ash with different concentration of molarity of NaOH (6M, 8M, 10M & 12M) with alkali solutions of sodium hydroxide and sodium silicate ratio 1:2 at average room temperature 32oC inside the laboratory. In the first series, addition of lime at 7.5% has shown good results and similarly in second series with addition of lime at 7.5% and silica fume at 3% of 12 M results were found to have great improvement with respect to normal cement concrete (NCC) specimen of M-30 grade on strength and durability parameters. The lime and silica fume contents have shown similar behaviour in durability tests.
Concrete is one of the mainly extensively used construction material. Due to growing environmental awareness and increasing interest in the use of high-strength fly ash concrete. Knowledge of material properties at high temperature is critical for evaluating the fire response of structures. This paper presents the experimental investigations on the effect of temperature on compressive strength of high strength high volume fly ash concrete of M60 grade at an age of 7, 28, 56 and 91 days. Cement is replaced with 30, 40 and 50% of fly ash at temperatures ranging from 27 to 500°C, with the aim of sustainability development; compressive strength and percentage loss of weight is also assessed. Experimental results of tests indicate that there is significant increase in compressive strength at low temperatures and degradation at high temperatures.
The cost of maintenance of irrigation infrastructure including water gates has absorbed substantial budget of APBN Directorate of Water Resources of PUPR Ministry, it is necessary to design water gate which is cheaper, easy to maintain and durable. One of them is to make a water gate from concrete panel with reinforcement from bamboo petung. After conducting laboratory study by making concrete panel with size 40 cm x 60 cm with water gate thickness of 3 cm and 3.5 cm, then variation of concrete quality used include K175, K. 225, K.300 and K.300 so obtained concrete panels with 8 different variations. From a series of experiments that have been done, the concrete structure in the form of panels with bamboo reinforcement can be used and able to withstand the hydrostatic load of water so it can be used as a plate on the water gate. The most optimal construction on effective thickness 3 cm with K.175 quality and bamboo reinforcement with a distance of 5 cm with the ability to hold eban up to 1080 kg.
Fire remains one of the serious potential risks to most buildings and structures. The extensive use of concrete as a structural material has led to the demand to fully understand the effect of fire on concrete. Although concrete is generally believed to be an excellent fireproofing material, many recent studies have shown extensive damage or even catastrophic failure at high temperatures. This paper presents the results of experimental investigation carried out to evaluate the strength performance of concrete by replacing cement by fly ash in various percentages when subjected to elevated temperature with gradual and sudden cooling. The replacement of 0%, 5%, 10%, 15%, 20%, 25% and 30%, of cement with fly ash is considered and the concrete is exposed to elevated temperature of 200°C, 400°C, 600°C, 800°C and 1000°C for 4 hours. The various strength parameters studied are compressive strength, tensile strength, flexural strength and impact strength as per the relevant IS standards. It is observed that all the strength properties of fly ash concrete when subjected to sustained elevated temperature with sudden cooling have drastically reduced as compared to that of gradual cooling. The gradual cooling has less deteriorating effect on the strength properties of fly ash concrete when subjected to sustained elevated temperature.
The Indian Concrete Journal, Vol. 94, No. 4, April 2020.
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