Concrete Age Research Articles

Evolution Mechanism of Wind Vibration Coefficient and Stability Performance during the Whole Construction Process for Super Large Cooling Towers

Wind-induced damage during the construction process and the evolution of damage over time are important reasons for the wind-induced destruction of large cooling towers. In fact, wind vibration coefficient and stability performance will evolve with the construction height and material properties over time. However, the existing studies generally ignore the impact of wind load and structural performance during the construction period. In this study, we built the 3D physical model separately for all eight construction stages a super large cooling tower which is being currently constructed and stands 210 m. The dynamic characteristics of the cooling tower were analyzed in each stage. First, the flow field information and 3D time history of aerodynamic forces were obtained for the whole construction process using large eddy simulation (LES). Full transient dynamic finite element analysis was used to calculate the dynamic responses of the tower under the real-time changes of wind loads during the whole construction process. Five calculation methods were used to trace the evolution of wind vibration coefficient during the whole construction process of the super large cooling tower. Then the formula for wind vibration coefficient changing with the construction height was fitted. The differential values of wind vibration coefficient during the whole construction process of the cooling tower were discussed by taking the meridional axial force as the objective function. On this basis, the influence and working mechanism of wind vibration coefficient, concrete age, construction load, geometric nonlinearity, internal suction force on buckling stability, and ultimate bearing capacity of the cooling towers were investigated. This research provides an enhanced understanding on the evolution of wind-induced stability performance in super large cooling towers and a methodology to prevent wind-induced damage during the construction process.

Strength Prediction Model for Accelerated Cured Fly-Ash Based Concrete

The most important property of concrete is its compressive strength, which is carried out after 28-days proper curing of concrete. This test is affected by other factors like the condition of curing, water to cement ratio, method of transportation, handling of the concrete, extent of vibrations and quality of the ingredients of mix proportion. This research study is an attempt to develop a simple Mathematical equation also known as mathematical model, by using linear regression analysis to estimate the 28-day fc’ (Compressive Strength) of concrete from the test results carried out atearly age. This simple linear equation develops a relationship of 28.5 hours accelerated cured compressive strength with normal cured compressive strength after 28-days. These results show that most of the predicted values of compressive strength, calculated via equations, lies within permissible range difference for compressive strength achieved by experimental method, which is clear indication of credibility of the equations obtained for compressive strength at different age of concrete. The results showed that compressive strength of concrete increases with the increase in content of FA (Fly Ash) upto 30% replacement, and the compressive strength of the concrete starts decreasing beyond 30% FA substitution. This argument is totally in line with all the literature carried out for this research.

AN INNOVATION OF HIGH PERFORMANCE CONCRETE BY REPLACING CEMENT WITH NICKEL SLAG POWDER

ABSTRACT
 Nickel slag is a solid waste produced from the nickel smelting process. At present, In Indonesia, the total capacity of domestic nickel smelting reaches 5 million tons/year with the assumption of NPI or FeNi production with a Ni level of 10%, requiring the input of Ni ore raw materials around 40 million tons/year in which around 30 million tons will become waste/slag. Currently, the area of Southeast Sulawesi has a potential of huge nickel resources of 97.4 billion tons, which spread over 480 thousand hectares of land. This has led to a continuous increase in the demand of concrete towards infrastructural development in Indonesia. Therefore, the aim of this research is to reuse nickel slag powder in the context of environmentaly friendly by analyzing the tensile strength using nickel slag powder (NSP) as a cement substitution material for the manufacture of high-performance concrete. Specimens were made with water-cement ratio of 0.31 and compared with 100% OPC Type 1 cement (as reference). Furthermore, the NSP substitution of cement were 5%, 10%, 15%, 20%, 25% and 30% with a concrete age of 3, 7, 14 and 28 days. Analysis of physical characteristics of nickel slag powder and cement were carried out by using the Le Chatelier method, while the mechanical characteristics comprised ease of work in the field (workability) and split tensile strength. The manufactured concrete was made by using Sika Viscocrete 8015 superplasticizer admixture with split tensile strength test results for NSP substitution at 28 days ≥ 5% of the value of compressive strength.
 
 Keywords: High-performance concrete, Nickel slag powder, Split tensile strength,

Simulacija starenja betona brana na primjeru numeričke analize brane HE Jablanica

Simulacija starenja betona brana na primjeru numeričke analize brane HE Jablanica

Mechanical properties of polypropylene plastic waste usage and high-density polyethylene in concrete

Using plastic waste as a construction material was one of the techniques used to overcome the inconsistencies associated with environmental pollution created by indiscriminate dumping of plastic waste. It was refined into aggregates that were utilized as a fractional replacement for coarse aggregates in concrete mixtures. The sole objective of this research work is to analyze the use of plastic waste in concrete. Two types of aggregates extracted from plastic waste namely: Polypropylene (PP) and High-Density Polyethylene (HDPE) were used in carrying out this study. The percentages of PP used were 5%, 10%, 15%, while 15%, 20%, 25% were used for HDPE. Similarly, the slump value, compressive strength, and tensile strength were tested for 28 days and at a concrete age of 3.7. The results obtained proved that a percentage increase in plastic aggregate would invariably reduce the value of slump, compressive strength, and tensile strength. The optimum percentage of PP and HDPE used were 10% and 15% respectively. This research contributed to providing an alternative to overcoming plastic waste.

Compressive strength prediction of lightweight foamed concrete with various densities

A research has been undertaken to study the compressive strength of foamed concrete with various concrete density. This paper reports experimental investigation on lightweight foamed concrete of 300, 600, 800 and 1000 kg/m3 densities and correlates compressive strength and density for further strength prediction. A total of 72 foamed concrete cubes with various densities and water cement ratio were prepared and tested for compressive strength at the concrete age of 7 and 28 days. Inverted slump and flow table spread value were obtained based on the test method stated in ASTM C1611. The foams were produced by using foam generator by mixing them with cement mortar (Ordinary Portland Cement, OPC and dry sand of size 850μm). The experimental results showed the highest compressive strength was recorded as 2 MPa for the density of 1000kg/m3 and water cement ratio of 0.6. The results revealed that consistency of the foamed concrete is in the range of 0.97 to 1.03, whereas stability index is in the range of 0.98 to 1.19 which showed the bubbles in the foamed concrete were stable during casting and curing process. A prediction model with exponential equations were proposed for foamed concrete compression strength with different water-cement ratio and it can be preliminary used to predict the foamed concrete strength.

Experimental investigation of mechanical properties and physical characteristics of concrete under standard fire exposure

Purpose This paper aims to explain the influence of Standard Fire as per ISO 834 on the strength and microstructure properties of concrete specimens with different strength grade. Design/methodology/approach The strength grades of concrete considered for the experimental investigation were Fck20, Fck30, Fck40 and Fck50. The specimens were heated up to 1, 2, 3 and 4 h as per standard fire curve. Effect of elevated temperature on compressive and flexural behavior of specimens with various strength grades was examined. Effects of age of concrete, weight loss, surface characteristics and thermal crack pattern were also investigated. Findings Experimental investigation shows that strength grade, duration of exposure and age of concrete are the key parameters affecting the residual strength of concrete. For the beams exposed to 3 and 4 h of heating, the residual flexural strength was found to be so insignificant that the specimens were not able to even sustain their own weight. The loss in compressive and flexural strength of Fck50 concrete specimens heated up to 1 h were found to be 26.41 and 86.03 per cent of the original unheated concrete, respectively. The weight loss was found to be more for higher grade concrete specimens, and it was about 8.38 per cent for Fck50 concrete. Regression analysis was carried out to establish the empirical relation between residual strength and grade of concrete. Scanning electron microscopy and thermogravimetric analysis were carried out to examine the damage level of fire-affected concrete specimens. Originality/value Empirical relationship was developed to determine the residual strength of concrete exposed to elevate temperature, and this will be useful for design applications. This database may be useful for identifying member strength of reinforced beams subjected to various durations of heating so that suitable repair technique can be adopted from the available database. It will be useful to identify the proper grade of concrete with regard to fire endurance, in the case of concrete under compression or flexure.

Evaluation of water absorption and chloride ion penetration of rice straw ash and microsilica admixed pavement quality concrete

The effects of rice straw ash (RSA) and microsilica (MS) on durability properties (water absorption and chloride ion penetration) of M40 grade Pavement Quality Concrete (PQC) were studied. Ten concrete samples were prepared by partially substituting cement with RSA and MS in various proportions. A significant reduction was observed in the water absorption and chloride ion penetration in concrete samples with an increase in the curing age as well as with an increase in the proportion of MS and RSA. The maximum reduction in water absorption and chloride ion penetration was observed in R2M3 (10% RSA and 7.5% MS) as compared to control concrete (R0). The analytical relationships were developed between the above-mentioned parameters and curing age of concrete. A linear equation was established between the initial and secondary rate of water absorption of concrete and also between the chloride ion penetration of concrete at 10–20 mm and 25–35 mm depth. Both these equations were applicable to all the concrete samples of this study. Predictive charts were generated between the above-mentioned parameters and days of curing in water.

Experimental study on electrical conductivity of carbon nanofiber reinforced concrete

To study the effect of carbon nanofibers (CNFs) on the electrical conductivity of concrete, we used the four-electrode method to measure the resistance and resistivity of carbon nanofiber reinforced concrete (CNFRC) under different ages, different fiber content and different test voltages. The results show that the incorporation of CNFs into concrete can improve the electrical conductivity of concrete. The electrical resistance and electrical resistivity of CNFRC increase with the increase of concrete age, but the growth rate decreases gradually. The resistance and electrical resistivity of CNFRC decrease with the increase of carbon nanofiber content and the optimum dosage range is 0.1%-0.3%. The resistance and electrical resistivity of CNFRC decrease with the increase of test voltage, and when the test voltage is 1V~5V, the resistance and electrical resistivity decrease significantly.

Effect of Nano Iron Oxide on Strength and Durability Characteristics of High Volume Fly Ash Concrete for Pavement Construction

Cement is the principal component of cement concrete used for construction of rigid pavements and is produced by an energy intensive process. Large scale production and its subsequent utilization detrimentally contributes towards global warming. In order to cater for sustainable development, there is a need to utilize waste materials having cementitious properties as a partial substitute for cement. Fly ash is one of such waste which is being extensively used for the production of cement concrete. Concrete produced by utilizing fly ash more than fifty percent of cement is termed as high volume fly ash concrete (HVFAC). Although HVFAC facilitates utilization of large volume of fly ash, it however has the disadvantage of delayed gain in strength which limits its usage as pavement quality concrete (PQC). Contemporary literatures show the usage of various types of nanomaterials to overcome this disadvantage. The present study was carried out to investigate the influence of nano iron oxide on strength and durability properties of HVFAC. The HVFAC used in the study was prepared by replacement of fifty five percent ordinary Portland cement with F-type fly ash obtained from thermal power plant. Nano iron oxide was utilized in different percentages to improve the strength and durability characteristics of HVFAC. The strength properties of the concrete was evaluated by flexural, compressive and split tensile strength tests, whereas the durability characteristics were evaluated by density, permeability, sorptivity, ultrasonic pulse velocity and rapid chloride penetration tests. The tests were carried out at 28, 56 and 90 days age of concrete. The test result showed that HVFAC modified with 0.75% nano iron oxide by weight gave the optimal strength and durability results which were comparable with that of normal cement concrete used for construction of rigid pavements.

Effect of pozzolanic materials on mechanical properties and aging of glass fiber reinforced concrete

Glass fibers have shown to improve the mechanical properties of concrete as tensile strength and flexural strength. However, it has been shown that these fibers tend to corrode with concrete aging to affect glass fiber reinforced concrete (GFRC) properties in an adverse manner. To prevent glass fiber corrosion in concrete environment, different percentages of pozzolanic materials were used in this study. It was found that the glass fibers inclusion would lead to partial reduction in concrete compressive strength. Modulus of rupture and toughness index were observed to improve greatly as a result of reinforcing concrete with glass fibers. Moreover, inclusion of nanosilica and metakaolin was found to prevent declines in concrete toughness and modulus of rupture with aging. Investigation of the pozzolanic contribution to modulus of rupture in GFRC revealed that the specific strength of cement declined within 7–90 days. This is while the specific strength of pozzolanic effect increased with time.

Case investigation on application of steel fibers in roller compacted concrete pavement in Thailand

This case study aims to investigate the improvement in mechanical behavior of roller compacted concrete pavement (RCCP) mixed with steel fibers. Hooked end type steel fibers were used at 0.5 and 1.0% by volume fractions. The modified Proctor test was adopted in the mix proportional process to determine the optimum moisture content for each type of RCCP. The Vebe consistency test was used to determine their consistencies under surcharge load. The experimental series consisted of compression and flexural performance tests to investigate the development of compressive strength, strain energy density, flexural strength, flexural toughness, and residual strength at different concrete ages. Tests were carried out at 3, 7, 14, and 28 days. Results showed that the water requirement and density of fiber reinforced roller compacted concrete pavement (FRRCCP) were slightly higher than those of RCCP. The compressive strength was found to decrease by 1–2% with an increase in fiber content. However, flexural strength, toughness, and residual strength improved significantly with the addition of steel fibers. All mechanical properties were found to increase with age.

INVESTIGATION ON ALKALI ACTIVATED FLY ASH BASED GEOPOLYMER CONCRETE

Cement industry plays major role for emission of greenhouse gasses. So, there is need for manufacturing of environmental friendly concrete. Geopolymer concrete helps in reduce global warming as well as fly ash disposal problem. This paper presents study the effect of types of curing, temperature, curing time and rest period. These parameters were studies like one variable parameter and other three are fixed parameter. One by one these parameter were finalize. The types of curing analyze with temperature optimization, rest period and curing time of geopolymer concrete. The type of curing like oven, accelerated, membrane, steam, wet and natural sun light (room temperature). The temperature differs like 600C, 900C, 1200C and 1500C. Once the temperature for type of curing is lock then proceed to curing time i.e. 6, 12, 18 and 24 hours. At the end temperature, type of curing and curing time finalize then optimize the rest period or testing age of concrete. The rest period differ like 1, 3, 7, 14, 21, 28, 56 days. In this study these variable are to be analyze with the help of compressive strength of geopolymer concrete.

Bond properties of deformed steel bars in concrete during construction under reversed cyclic loading

To investigate the bond properties of deformed steel bars in concrete during construction under reversed cyclic loading, concentric pull-out tests under reversed cyclic loading were performed on specimens with six concrete ages and three concrete strength grades. The effects of concrete age and strength grade on the following bond response indicators were examined: maximum bond stress, slip corresponding to the maximum bond stress, residual bond stress, cumulative energy dissipation, unloading stiffness, and frictional bond stress factor. The results indicated that for specimens with the same concrete strength grade, with an increase in the concrete age, the maximum bond stress, residual bond stress, unloading stiffness, frictional bond stress factor, and energy-dissipation capacity increased, whereas the slip at the maximum bond stress decreased. Moreover, with regard to specimens with the same concrete age, with increasing concrete strength grade, the maximum bond stress, residual bond stress, unloading stiffness, frictional bond stress, and energy-dissipation capacity increased, whereas the slip corresponding to the maximum bond stress decreased. According to the analysis of the bond properties of the specimens with different concrete ages and strength grades, empirical bond stress–slip models of a deformed steel bars in concrete during construction under reversed cyclic loading were proposed. A good agreement was observed by comparing the proposed models with the experimental results in this study and the existing models in the literature.

Fractional-order model of the compressive strength of hydraulic concrete in a real temperature and humidity environment

Concrete is a kind of composite material that is in a plastic flow state in its initial stage, gradually hardening with the cement hydration reaction and then finally reaching a relatively stable condition. In addition, the compressive strength of concrete is related to not only the curing age but also the curing temperature and humidity. The Kelvin model with a software element is used to describe the growth rule of the compressive strength of concrete. The equivalent age theory is used to consider the coupling effect of the temperature and humidity, and then a fractional-order model of the compressive strength of hydraulic concrete considering this coupling effect is proposed. Next, tests of the compressive strength of concrete under three different curing conditions for different concrete ages are performed, and a fractional-order model of the compressive strength is implemented using the test data. The analysis results show that the fitting effect of the fractional-order model can reach a high level of accuracy with only a few model parameters, and with a better fit than the combinatorial exponential model or combinatorial modified logarithmic model.

Effect of Tension at Early Age on Bearing Capacity of PC Continuous Girder Bridge

In order to study the influence of prestressed steel bundles on the bearing capacity of bridges in the early age of concrete, a new 5×20 m prefabricated continuous box girder bridge is used as the engineering background, and MIDAS/CIVIL simulation is used. When the age of precast box girder concrete is 3d (working condition 1), 5d (working condition 2), 7d (working condition 3), the steel bundle is tensioned. The ultimate state check and prestress loss analysis of the mid-span middle beam after tensioning at different ages are analyzed. The results show that the positive section bending capacity of working condition 1 and working condition 2 decreased by 13.15% and 6.51% respectively and the earlier the tensile age, the greater the prestress loss value of the steel bundle. Combined with the simulation analysis, the load test is carried out on the bridge (the actual construction is tensioning at 5d): the strain check coefficient is between 0.599 and 0.753, and the deflection check coefficient is between 0.596 and 0.705. The results show that when the concrete age is 5d, the steel bundle is tensioned, and its bearing capacity can still meet Highway Class I requirements

Studi Kuat Tekan Beton Speedcrete Dengan Zat Additive Naphthalene Berdasarkan Variasi Umur

This research aims to determine the maximum compressive strength value of concrete speedcrete using naphthalene additive additive at each test age and compare with normal concrete 28 days. This research used cylindrical test object with diameter 15 cm and height 30 cm. Speedcrete concrete does not undergo the treatment process while the normal concrete test object through the treatment process. Testing compressive strength of concrete speedcrete using Crushing Test Machine tool. In this research the compressive strength was produced by using superplasticizer type naphthalene and compared with normal concrete without using additive. The target quality plan is fc '35 MPa with the use of additive dose of 1.7% of the weight of cement. The results of this research showed an increase in the value of compressive strength of concrete speedcrete with aadditive materials added naphthalene increased with increasing age of concrete. The results showed that the compressive strength of concrete speedcrete with naphthalene additive materials of 12 hours, 18 hours, 28 hours and 48 hours was 0.5 MPa, 17,81 MPa, 31,14 MPa and 45,77 MPa. Normal strength concrete strength with the addition of 20% water age 28 days that is equal to 54.76 MPa.

Leaching of ANC and Chromium from Concrete: Effect of Aging Simulated by Sample Carbonation

Chemicals leached from concrete are an important way that urban stormwater can influence water quality. In this study, we evaluated the weathering properties of sidewalk samples and tested how carbonation (exposure to elevated levels of gaseous CO2) can be used to simulate natural aging of concrete. The experiments focused on acid neutralizing capacity (ANC), which is known to be released by concrete in large amounts, and Cr(VI), because of its established carcinogenicity and prevalence in concrete. Chemical weathering of crushed sidewalk samples was measured with upflow recirculating columns carrying simulated acid rain. The weathering rate of ANC from four different samples was found to decrease after 1 week of exposure to a 5% carbon dioxide atmosphere and to remain constant thereafter through 8 weeks of carbonation treatment. In contrast, weathering of chromium (VI) increased after exposure to a 5% carbon dioxide atmosphere for 1 week, though it also remained stable from then through 8 weeks of carbonation. Almost all ions approached steady state after 2.5 h in the recirculation columns irrespective of carbonation time. The main contributor of ANC was Ca2+ ion, though this was partly balanced by an unexpectedly high amount of SO42−. A notable exception to the temporal leaching pattern was largely un-ionized Si, which continued to increase in concentration for at least 3 days of recirculation. Si levels were also higher than is generally observed for aluminosilicate weathering in small watersheds, a novel finding.

Redistribution of corrosion products on steel bar/concrete interfaces in repaired concrete under influenced of aggressive ions

The important cases contribute to deterioration of reinforced concrete structure were due to corrosion attack to the reinforcing steel bar. Instead of penetration of aggressive ions for example chlorides, sulphates, acids and others; the selection of materials used for repair should be concern as well. Due to this factor, the understanding on the electrochemical behavior of reinforcing steel bar using different materials for repairing for deteriorated concrete structures will be considered. To understand this phenomenon, the ready-cast specimens mixed with chloride as prepared earlier will be demolished at 301 days of concrete age. Surprisingly, potential measurement of reinforcing steel bars was reoriented to a lower corrosion risk at 301 days of concrete age. The chemical and microstructural factors related to corrosion products were quantitatively identified and correlated it using electrochemical measurements results. For corroding reinforcing steel bar by fully and partially influenced of chloride ions, the corrosion products were mainly contained wuestite, magnetite and lepidocrocite confirmed by XRD patterns. Depending on morphology and multi-elemental content, it shows that chloride ion is approaching the reinforcing steel bar that lead to greater corrosion rate in Reference specimen compared to repaired ones. However, the existence of Ca(OH) in the vicinity between concrete/reinforcing steel bar helps to prevent further corrosion attacks

Development of Strain-Induced Stresses in Early Age Concrete Composed of Recycled Gravel or Sand

Development of Strain-Induced Stresses in Early Age Concrete Composed of Recycled Gravel or Sand