Search results for: early age concrete strength

Authors: Zhifeng Xu, Zhongfan Chen

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A series of tests on cold-formed steel foamed concrete (CSFC) composite walls subjected to axial load were proposed. The primary purpose of the experiments was to study the mechanical behavior and identify the failure modes of CSFC composite walls. Two main factors were considered in this study: 1) specimen with pouring foamed concrete or without and 2) different foamed concrete density ranks (corresponding to different foamed concrete strength). The interior space between two pieces of straw board of the specimen W-2 and W-3 were poured foamed concrete, and the specimen W-1 does not have foamed concrete core. The foamed concrete density rank of the specimen W-2 was A05 grade, and that of the specimen W-3 was A07 grade. Results showed that the failure mode of CSFC composite wall without foamed concrete was distortional buckling of cold-formed steel (CFS) column, and that poured foamed concrete includes the local crushing of foamed concrete and local buckling of CFS column, but the former prior to the later. Compared with CSFC composite wall without foamed concrete, the ultimate bearing capacity of spec imens poured A05 grade and A07 grade foamed concrete increased 1.6 times and 2.2 times respectively, and specimen poured foamed concrete had a low vertical deformation. According to these results, the simplified calculation formula for the CSFC wall subjected to axial load was proposed, and the calculated results from this formula are in very good agreement with the test results.

Keywords: cold-formed steel, composite wall, foamed concrete, axial behavior test

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Authors: Ki-Seok Kwon, Heung-Youl Kim

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This research evaluated fire resistances of high-strengthened reinforced concrete (RC) column, spiral wire rope which applied with 60, and 100MPa. The fire resistance test of RC column with loading condition was conducted following the ISO 834 (3 hours). This experiment set mixing of fiber (PP fiber, Steel fiber) and types of horizontal reinforcement as a variable of reinforcement method. The fire resistance test measured the main steel bar’s max and mean temperatures also the shrinkage and shrinking ratio of columns(500 X 500 X 3,000mm) with loadings. As a result, the specimen of 60MPa attained three hours fire resistance with only spiral wire rope. Also, the specimen of 100MPa must be reinforced with fibers and spiral wire rope to attain three hours fire resistance.

Keywords: reinforced concrete column, high strength concrete, wire rope, fire resistance test

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Authors: Vitalijs Lusis, Videvuds-Arijs Lapsa, Olga Kononova, Andrejs Krasnikovs

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Steel fibres use in a concrete, such way obtaining Steel Fibre Reinforced Concrete (SFRC), is an important technological direction in building industry. Steel fibers are substituting the steel bars in conventional concrete in another situation is possible to combine them in the concrete structures. Traditionally fibers are homogeneously dispersed in a concrete. At the same time in many situations fiber concrete with homogeneously dispersed fibers is not optimal (majority of added fibers are not participating in a load bearing process). It is obvious, that is possible to create constructions with oriented fibers distribution in them, in different ways. Present research is devoted to one of them. Acknowledgment: This work has been supported by the European Social Fund within the project «Support for the implementation of doctoral studies at Riga Technical University» and project No. 2013/0025/1DP/1.1.1.2.0/13/APIA/VIAA/019 “New “Smart” Nanocomposite Materials for Roads, Bridges, Buildings and Transport Vehicle”.

Keywords: fiber reinforced concrete, 4-point bending, steel fiber, SFRC

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Authors: Jeon Chi-Ho, Lee Jae-Bin, Shim Chang-Su

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National bridge inventory in Korea shows that the number of old prestressed concrete (PSC) bridgeover 30 years of service life is rapidly increasing. Recently tendon corrosion is one of the most critical issues in the maintenance of PSC bridges. In this paper, mechanical properties of corroded strands, which were removed from old bridges, were evaluated using tensile test. In the result, the equations to express the mechanical behavior of corroded strand were derived and compared to existing equation. For the decision of tendon replacement, it is necessary to evaluate the effect of corrosion level on strength and ductility of the structure. Considerations on analysis of PSC girders were introduced, and decision making on tendon replacement was also proposed.

Keywords: prestressed concrete bridge, tendon, corrosion, strength, ductility

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Authors: D. G. Rejon-Parra, B. Escobar-Morales, Romeli Barbosa, J. C. Cruz

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In the southeast of Yucatan Peninsula, sedimentary limestone has different degrees of compaction. Due to its recent geological formation (Quaternary) and weathering effects causing an affordable aggregate for local manufacturers of concrete. It is characterized as lightweight aggregates (average density of 2,50), susceptible to abrasion and varying porosities (water content exceeding 7,50 % of its mass, in saturated condition). In this study, local aggregates with two moisture conditions (saturated and dry), have been examined in order to compare them for optimizing the performance of concrete. It is possible that these aggregates favour a phenomenon of mass transport (self-curing by porous aggregate); influencing the water reactions to form crystalline and gel hydration products. Based on the ACI methodology, a concrete mixture of 250 kg/cm2 was designed, with portland blended cement 30R. The bond between the mortar and the coarse aggregate was characterized as physicochemical based on trials which were carefully observed during time span of 28 days. The BET technique was used to analyse the micro porosity and surface areas of contact of the different crystalline phases of the limestone. Its chemical composition and crystal structures were verified with scanning electron microscopy SEM-EDS. On the third day, the samples with saturated aggregate reached 237 kg/cm2 of resistence, nearly the design strength; while samples with dry aggregate, exceeded the design strength, with a capacity of 308 kg/cm2. Aggregates in dry conditions demand a high quantity of water in the initial mixture, causing high resistance at the early stages. In saturated conditions, the development of resistance is progressive but constant.

Keywords: concrete, internal curing, limestone aggregate, porosity

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Authors: Igor Shardakov, Anton Bykov, Alexey Shestakov, Irina Glot

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This article focuses on the cycle of experimental studies of the formation of cracks and debondings in the concrete reinforced with carbon fiber. This research was carried out in Perm National Research Polytechnic University. A series of CFRP-strengthened RC beams was tested to investigate the influence of preload and crack repairing factors on CFRP debonding. IRT was applied to detect the early stage of IC debonding during the laboratory bending tests. It was found that for the beams strengthened under load after crack injecting, СFRP debonding strain is 4-65% lower than for the preliminary strengthened beams. The beams strengthened under the load had a relative area of debonding of 2 times higher than preliminary strengthened beams. The СFRP debonding strain is weakly dependent on the strength of the concrete substrate. For beams with a transverse wrapping anchorage in support sections FRP debonding is not a failure mode.

Keywords: IC debonding, infrared thermography, non-destructive testing methods, quality control, strengthening

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Authors: Ahmet Kurklu, Abdussamed Sarp, Gokmen Arikan, Akin Eren, Arif Ulu, Ferit Cakir

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Our natural resources are diminishing day by day with the needs of the growing world population. There is a danger that these resources will be depleted if they are not used in a controlled manner. As a result of the rapid increase in the consumption of limited natural resources, one of the issues where studies have gained importance is recycling. Many countries have carried out various research and development activities on recycling and reuse to prevent wastage of resources. For sustainable and healthy living, the limited amount of raw material resources in nature should be consumed consciously, and the necessary awareness should be given for recycling activities. One of the sectors where the consumption of raw materials is high is the construction sector. With the changing consumption habits of the evolving technology in the construction sector, the need to use special concrete along with the normal concrete has arisen. With the increasing need for specialty concretes, polymer concrete, which was discovered in the early 1900s, has evolved to the present day. Polymer concretes are special concretes with high strength, water impermeability, resistance to chemical action, and low surface roughness. Thanks to these properties, they find wide applications in many fields such as swimming pools, drainage systems, repair works. In the study, the effect of using recycled aggregates instead of natural aggregates in the production of polymer concrete on the performance of polymer concrete is investigated. In the experiments conducted for this purpose, the use of natural aggregate is reduced at certain rates, and instead, recycled aggregate is added at the same rate. The recycled aggregate to be used in the study is obtained from the polymer concrete drainage channel production facility of Mert Casting Co., Istanbul, Turkey. In order to clearly observe the effect of recycled materials on the product in the study, the other components (resin, hardener, accelerator, and additive) are kept constant in the concrete mix. In the study, fresh and hardened concrete tests are to be carried out on the mixes to be prepared.

Keywords: concrete, mechanical properties, polymer concrete, recycle aggregate

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Authors: Syfur Rahman, Mohammad J. Khattak

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Every year a huge quantity of recycling concrete aggregate (RCA) is generated in the United States of America. Utilization of RCA can solve the storage problem, prevent environmental pollution, and reduce the construction cost. However, due to the overall low strength and durability characteristics of RCA, its usages are limited to a certain area like a landfill, low strength base material, replacement of a few percentages of virgin aggregates in Portland cement concrete, etc. This study focuses on the improvement of the strength and durability characteristics of RCA by introducing the concept of roller-compacted geopolymer concrete. In this research, developed roller-compacted geopolymer concrete (RCGPC) and roller-compacted cement concrete (RCC) mixtures containing 100% recycled concrete aggregate were evaluated and compared. Several selected RCGPC mixtures were investigated to find out the effect of mixture variables, including sodium hydroxide (NaOH) molar concentration, sodium silicate (Na₂SiO₃), to sodium hydroxide (NaOH) ratio on the strength, stiffness and durability characteristics of the developed RCGPC. Sodium hydroxide (NaOH) and sodium silicate (Na₂SiO₃) were mixed in different ratios to synthesize the alkali activator. American Concrete Pavement Association (ACPA) recommended RCC gradation was used with a maximum nominal aggregate size of 19 mm with a 4% fine particle passing 0.075 mm sieve. The mixtures were made using NaOH molar concentration of 8M and 10M along with, Na₂SiO₃ to NaOH ratio of 0 and 1 by mass and 15% class F fly ash. Optimum alkali content and moisture content were determined for each RCGPC and RCC mixtures, respectively, using modified proctor test. Compressive strength, semi-circular bending beam strength, and dynamic modulus test were conducted to evaluate the mechanistic characteristics of both mixtures. To determine the optimum curing conditions for RCGPC, effects of different curing temperature and curing duration on compressive strength were also studied. Sulphate attack and freeze-thaw tests were also carried out to assess the durability properties of the developed mixtures. X-ray diffraction (XRD) was used for morphology and microstructure analysis. From the optimum moisture content results, it was found that RCGPC has high alkali content, which was mainly due to the high absorption capacity of RCA. It was found that the mixtures with Na₂SiO₃ to NaOH ratio of 1 yielded about 60% higher compressive strength than the ratio of 0. Further, the mixtures using 10M NaOH concentrations and alkali ratio of 1 produced about 28 MPa of compressive strength, which was around 33% higher than 8M NaOH mixtures. Similar results were obtained for elastic and dynamic modulus of the mixtures. On the other hand, the semi-circular bending beam strength remained the same for both 8 and 10 molar NaOH geopolymer mixtures. Formation of new geopolymeric compounds and chemical bonds in the newly formed novel RCGPC mixtures were also discovered using XRD analysis. The results of mechanical and durability testing further revealed that RCGPC performed similarly to that of RCC mixtures. Based on the results of mechanical and durability testing, the developed RCGPC mixtures using 100% recycled concrete could be used as a cost-effective solution for the construction of pavement structures.

Keywords: roller compacted concrete, geopolymer concrete, recycled concrete aggregate, concrete pavement, fly ash

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Authors: Fatih Hattatoglu, Abdulrezzak Bakiş

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In this study, fiberless reactive powder concrete (RPC) was produced with high pressure and flexural strength. C30/37 concrete was chosen as the control sample. In this study, 9 different cure types were applied to fiberless RPC. the most suitable combined cure type was selected according to the pressure and flexure strength. Pressure and flexural strength tests were applied to these samples after curing. As a result of the study, the combined cure type with the highest pressure resistance was obtained. The highest pressure resistance was achieved with consecutive standard water cure at 20 °C for 7 days – hot water cure at 90 °C for 2 days - drying oven cure at 180 °C for 2 days. As a result of the study, the highest pressure resistance of fiberless RPC was found as 123 MPa with water cure at 20 °C for 7 days - hot water cure at 90 °C for 2 days - drying oven cure at 180 °C for 2 days; and the highest flexural resistance was found as 8.37 MPa for the same combined cure type.

Keywords: combined cure, flexural test, reactive powder concrete (RPC), rigid pavement, pressure test

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Authors: Amrit Pal Singh Arora

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The paper reports the results of a study undertaken to study the effects of addition of steel fibres of different aspect ratios on the permeability and strength characteristics of steel fiber reinforced fly ash concrete (SFRC). Corrugated steel fibres having a diameter of 0.6 mm and lengths of 12.5 mm, 30 mm and 50 mm were used in this study. Cube samples of 100 mm x 100 mm x 100 mm were cast from mixes replacing 0%, 10%, 20% and 30% cement content by fly ash with and without fibres and tested for the determination of coefficient of water permeability, compressive and split tensile strengths after 7 and 28 days of curing. Plain concrete samples were also cast and tested for reference purposes. Permeability was observed to decrease significantly for all concrete mixes with the addition of steel fibers as compared to plain concrete. The replacement of cement content by fly ash results in an increase in the coefficient of water permeability. With the addition of fly ash to the plain mix the7 day compressive and split tensile strengths decreased, however both the compressive and split tensile strengths increased with increase in curing age.

Keywords: curing age, fiber shape, fly ash, Darcy’s law, Ppermeability

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Authors: Conceição, J. F. M., Rebelo H., Corneliu C., Pereira L.

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This research analyses the response of two distinct types of concrete blocks, each possessing an approximate unconfined compressive strength of 30MPa, when exposed to high-velocity impacts produced by an Explosively Formed Penetrator (EFP) traveling at an initial velocity of 1200 m/s. Given the scarcity of studies exploring high-velocity impacts on concrete, the primary aim of this research is to scrutinize how concrete behaves under high-speed impacts, ultimately contributing valuable insights to the development of protective structures. To achieve this objective, a comprehensive numerical analysis was carried out in LS-DYNA to delve into the fracture mechanisms inherent in concrete under such extreme conditions. Subsequently, the obtained numerical outcomes were compared and validated through eight experimental field tests. The methodology employed involved a robust combination of numerical simulations and real-world experiments, ensuring a comprehensive understanding of concrete behavior in scenarios involving rapid, high-energy impacts.

Keywords: high-velocity, impact, numerical analysis, experimental tests, concrete

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Authors: Binyamien Rasoul

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Portland cement is one of the most widely used construction materials in the world today; however, manufacture of ordinary Portland cement (OPC) emission significant amount of CO2 resulting environmental impact. On the other hand, rice husk ash (RHA), which is produce as by product material is generally considered to be an environmental issue as a waste material. This material (RHA) consists of non-crystalline silicon dioxide with high specific surface area and high pozzolanic reactivity. These RHA properties can demonstrate a significant influence in improving the mechanical and durability properties of mortar and concrete. Furthermore, rice husk ash can provide a cost effective and give concrete more sustainability. In this paper, chemical composition, reactive silica and fineness effect was assessed by examining five different types of RHA. Mortars and concrete specimens were molded with 5% to 50% of ash, replacing the Portland cement, and measured their compressive and tensile strength behavior. Beyond it, another two parameters had been considered: the durability of concrete blended RHA, and effect of temperature on the transformed of amorphous structure to crystalline form. To obtain the rice husk ash properties, these different types were subjected to X-Ray fluorescence to determine the chemical composition, while pozzolanic activity obtained by using X-Ray diffraction test. On the other hand, finesses and specific surface area were obtained by used Malvern Mastersizer 2000 test. The measured parameters properties of fresh mortar and concrete obtained by used flow table and slump test. While, for hardened mortar and concrete the compressive and tensile strength determined pulse the chloride ions penetration for concrete using NT Build 492 (Nord Test) – non-steady state migration test (RMT Test). The obtained test results indicated that RHA can be used as a cement replacement material in concrete with considerable proportion up to 50% percentages without compromising concrete strength. The use of RHA in the concrete as blending materials improved the different characteristics of the concrete product. The paper concludes that to exhibits a good compressive strength of OPC mortar or concrete with increase RHA replacement ratio rice husk ash should be consist of high silica content with high pozzolanic activity. Furthermore, with high amount of carbon content (12%) could be improve the strength of concrete when the silica structure is totally amorphous. As well RHA with high amount of crystalline form (25%) can be used as cement replacement when the silica content over 90%. The workability and strength of concrete increased by used of superplasticizer and it depends on the silica structure and carbon content. This study therefore is an investigation of the effect of partially replacing Ordinary Portland cement (OPC) with Rice hush Ash (RHA) on the mechanical properties and durability of concrete. This paper gives satisfactory results to use RHA in sustainable construction in order to reduce the carbon footprint associated with cement industry.

Keywords: OPC, ordinary Portland cement, RHA rice husk ash, W/B water to binder ratio, CO2, carbon dioxide

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Authors: Hatem Hamdy Ghieth

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In the recent time many fires happened in many skeleton buildings. The fire may be continues for a long time. This fire may cause a collapse of the building. This collapse may be happened due to the time of exposure to fire as well as the rate of the loading to the carrying elements. In this research a laboratory study for reinforced concrete columns under effect of fire with temperature reaches (650 ْ C) on the behavior of columns which loaded with axial load and with exposing to fire temperature only from all sides of columns. the main parameters of this study are level of load applying to the column, and the temperature applied to the fire, this temperatures was 500oC and 650oc. Nine concrete columns with dimensions 20x20x100 cms were casted one of these columns was tested to determine the ultimate load while the least were fired according to the experimental schedule.

Keywords: columns, fire duration, concrete strength, level of loading

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Authors: Talebi Aliasghar, Ebrahimpour Komeleh Hooman, Maghsoudi Ali Akbar

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In reinforced concrete (RC) structures, beam-column connection region has a considerable effect on the behavior of structures. Using fiber reinforcement polymer (FRP) for the strengthening of connections in RC structures can be one of the solutions to retrofitting this zone which result in the enhanced behavior of structure. In this paper, these changes in behavior by using FRP for high strength concrete beam-column connection have been studied by finite element modeling. The concrete damage plasticity (CDP) model has been used to analyze the RC. The results illustrated a considerable development in load-bearing capacity but also a noticeable reduction in ductility. The study also assesses these qualities for several modes of strengthening and suggests the most effective mode of strengthening. Using FRP in flexural zone and FRP with 45-degree oriented fibers in shear zone of joint showed the most significant change in behavior.

Keywords: HSC, beam-column connection, Fiber Reinforcement Polymer, FRP, Finite Element Modeling, FEM

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Authors: Jagannath Prasad Tegar, Zeeshan Ahmad

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The Ordinary Portland Cement (OPC) is a major constituent of concrete, which is being used extensively since last half century. The production of cement is impacting not only environment alone, but depleting natural materials. During the past 3 decades, the scholars have carried out studies and researches to explore the supplementary cementatious materials such as Ground granulated Blast furnace slag (GGBFS), silica fumes (SF), metakaolin or fly ash (FA). This has contributed towards improved cementatious materials which are being used in construction, but not the way it is supposed to be. The alkali activated slag concrete is another innovation which has constituents of cementatious materials like Ground Granuled Blast Furnace Slag (GGBFS), Fly Ash (FA), Silica Fumes (SF) or Metakaolin. Alkaline activators like Sodium Silicate (Na₂SiO₃) and Sodium Hydroxide (NaOH) is utilized. In view of evaluating properties of alkali activated slag concrete blended with polypropylene shredding and accelerator, research study is being carried out. This research study is proposed to evaluate the effect of polypropylene shredding and accelerating admixture on mechanical properties of alkali-activated slag concrete. The mechanical properties include the compressive strength, splitting tensile strength and workability. The outcomes of this research are matched with the hypothesis and it is found that 27% of cement can be replaced with the ground granulated blast furnace slag (GGBFS) and for split tensile strength 20% replacement is achieved. Overall it is found that 20% of cement can be replaced with ground granulated blast furnace slag. The tests conducted in the laboratory for evaluating properties such as compressive strength test, split tensile strength test, and slump cone test. On the aspect of cost, it is substantially benefitted.

Keywords: ordinary Portland cement, activated slag concrete, ground granule blast furnace slag, fly ash, silica fumes

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Authors: Atef Ahmad Bleibel

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Most codes of practice, like ACI 318-14, require the use of strut-and-tie modeling to analyze and design reinforced concrete deep beams. Though, investigations that conducted on deep beams do not include ring deep beams of influential parameters. This work presents an analytical parametric study using strut-and-tie modeling stated by ACI 318-14 to predict load capacity of 20 reinforced concrete ring deep beam specimens with different parameters. The parameters that were under consideration in the current work are ring diameter (Dc), number of supports (NS), width of ring beam (bw), concrete compressive strength (f'c) and width of bearing plate (Bp). It is found that the load capacity decreases by about 14-36% when ring diameter increases by about 25-75%. It is also found that load capacity increases by about 62-189% when number of supports increases by about 33-100%, while the load capacity increases by about 25-75% when the beam ring width increases by about 25-75%. Finally, it is found that load capacity increases by about 24-76% when compressive strength increases by about 24-76%, while the load capacity increases by about 5-16% when Bp increases by about 25-75%.

Keywords: load parameters, reinforced concrete, ring deep beam, strut and tie

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Authors: Brahim Safi, Mohammed Saidi, A. Benmounah, Jozef Mitterpach

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The aim of this work is to study the rheological and physico-mechanical properties of a self-compacting concrete elaborated with sea shells as an addition cementitious (total replacement of limestone fillers) and sand (partial and total substitution fine aggregate). Also, this present study is registered in the context of sustainable development by using this waste type which caused environmental problems. After preparation the crushed shells (obtaining fine aggregate) and finely crushed shells (obtaining end powder), concretes were manufactured using these two products. Rheological characterization tests (fluidity, filling capacity and segregation) and physico-mechanical properties (density and strength) were carried on these concretes. The results obtained show that it can be used as fin addition (by total replacement of limestone) or also used as sand by total substitution of natural sand.

Keywords: seashells, limestone, sand, self-compacting concrete, fluidity, compressive strength, flexural strength

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Authors: P. Parthiban, J. Karthikeyan

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This paper deals with the performance of semi-light weight concrete, prepared by using wood ash pellets as coarse aggregates which were improved by partial replacement of cement with alccofine. Alccofine is a mineral admixture which contains high glass content obtained through the process of controlled granulation. This is finer than cement which carries its own pozzolanic property. Therefore, cement could be replaced by alccofine as 0%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, and 70% to enhance the strength and durability properties of concrete. High range water reducing admixtures (HRWA) were used in these mixes which were dosed up to 1.5% weight of the total cementitious content (alccofine & cement). It also develops the weaker transition zone into more impermeable layer. Specimens were subjected in both the accelerated curing method as well as conventional curing method. Experimental results were compared and reported, in that the maximum compressive strength of 32.6 MPa was achieved on 28^th day with 30% replacement level in a density of 2200 kg/m³ to a conventional curing, while in the accelerated curing, maximum compressive strength was achieved at 40% replacement level. Rapid chloride penetration test (RCPT) output results for the conventional curing method at 0% and 70% give 3296.7 and 545.6 coulombs.

Keywords: Alccofine, compressive strength, RCPT, wood ash pellets

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Authors: Moosa Mazloom, Hojjat Hatami

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The aim of this article is to access the optimal mix design of self-compacting light weight concrete. The effects of magnetic water, superplasticizer based on polycarboxylic-ether, and silica fume on characteristics of this type of concrete are studied. The workability of fresh concrete and the compressive strength of hardened concrete are considered here. For this purpose, nine mix designs were studied. The percentages of superplasticizer were 0.5, 1, and 2% of the weight of cement, and the percentages of silica fume were 0, 6, and 10% of the weight of cement. The water to cementitious ratios were 0.28, 0.32, and 0.36. The workability of concrete samples was analyzed by the devices such as slump flow, V-funnel, L box, U box, and Urimet with J ring. Then, the compressive strengths of the mixes at the ages of 3, 7, 28, and 90 days were obtained. The results show that by using magnetic water, the compressive strengths are improved at all the ages. In the concrete samples with ordinary water, more superplasticizer dosages were needed. Moreover, the combination of superplasticizer and magnetic water had positive effects on the mixes containing silica fume and they could flow easily.

Keywords: magnetic water, self-compacting light weight concrete, silica fume, superplasticizer

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Authors: Akram Salah Eddine Belaidi, Said Kenai, El-Hadj Kadri, Benchaâ Benabed, Hamza Soualhi

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Self-compacting concrete (SCC) was developed in the middle of the 1980’s in Japan. SCC flows alone under its dead weight and consolidates itself without any entry of additional compaction energy and without segregation. As an integral part of a SCC, self-compacting mortars (SCM) may serve as a basis for the mix design of concrete since the measurement of the rheological properties of SCCs. This paper discusses the effect of using natural pozzolana (PZ) and marble powder (MP) in two alternative systems ratios PZ/MP = 1 and 1/3 of the performance of the SCC. A total of 11 SCC’s were prepared having a constant water-binder (w/b) ratio of 0.40 and total cementitious materials content of 475 kg/m3. Then, the fresh properties of the mortars were tested for mini-slump flow diameter and mini-V-funnel flow time for SCMs and Slumps flow test, L-Box height ratio, V-Funnel flow time and sieve stability for SCC. Moreover, the development in the compressive strength was determined at 3, 7, 28, 56, and 90 days. Test results have shown that using of ternary blends improved the fresh properties of the mixtures. The compressive strength of SCC at 90 days with 30% of PZ and MP was similar to those of ordinary concrete use in situ.

Keywords: self-compacting mortar, self-compacting concrete, natural pozzolana, marble powder, rheology, compressive strength

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Authors: Kazeem K. Adewole, Ismail A. Yahya

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In the published literature, Palm Kernel Shell (PKS), an agricultural waste has largely been used as a large aggregate in PKS concrete production. In this paper, the development of Crushed Palm Kernel Shell Fine Aggregate Concrete (CPKSFAC) with crushed PKS (CPKS) as the fine aggregate and granite as the coarse aggregate is presented. 100mm x 100mm x 100mm 1:11/2:3 and 1:2:4 CPKSFAC and River Sand Fine Aggregate Concrete (RSFAC) cubes were molded, cured for 28 days and subjected to a compressive strength test. The average wet densities of the 1:11/2:3 and 1:2:4 CPKSFAC cubes are 2240kg/m3 and 2335kg/m3 respectively. The average wet densities of the 1:11/2:3 and 1:2:4 RSFAC cubes are 2606kg/m3 and 2553kg/m3 respectively. The average compressive strengths of the 1:11/2:3 and 1:2:4 CPKSFAC cubes are 15.40MPa and 14.30MPa respectively. This study demonstrates that CPKSFA is suitable for the production of non-structural C8/10 and C12/15 concrete specified in BS EN 206-1:2000.

Keywords: crushed palm kernel shell, fine aggregate, lightweight concrete, non-structural concrete

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Authors: Said Boukais, Ali Kezmane, Kahil Amar, Mohand Hamizi, Hannachi Neceur Eddine

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This paper presents an analytical study on the behavior of rectangular reinforced concrete walls with an aspect ratio between one and tow. Several experiments on such walls have been selected to be studied. Database from various experiments were collected and nominal wall strengths have been calculated using formulas, such as those of the ACI (American), NZS (New Zealand), Mexican (NTCC), and Wood equation for shear and strain compatibility analysis for flexure. Subsequently, nominal ultimate wall strengths from the formulas were compared with the ultimate wall strengths from the database. These formulas vary substantially in functional form and do not account for all variables that affect the response of walls. There is substantial scatter in the predicted values of ultimate strength. New semi empirical equation are developed using data from tests of 46 walls with the objective of improving the prediction of ultimate strength of walls with the most possible accuracy and for all failure modes.

Keywords: prediction, ultimate strength, reinforced concrete walls, walls, rectangular walls

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Authors: Qaiser uz Zaman Khan

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This research article provides a comprehensive study of combining steel fiber and polypropylene fibers in concrete at different mix ratios. This blending of various fibers has led to the development of hybrid fiber-reinforced concrete (HFRC), which offers notable improvements in mechanical properties and increased resistance to cracking. Steel fibers are known for their high tensile strength and excellent crack control abilities, while polypropylene fibers offer increased toughness and impact resistance. The synergistic use of these two fiber types in concrete has yielded promising outcomes, effectively enhancing its overall performance. This article explores the key aspects of hybridization, including fiber types, proportions, mixing methods, and the resulting properties of the concrete. Additionally, challenges, potential applications, and future research directions in the field are discussed.

Keywords: FRC, fiber-reinforced concrete, split tensile testing, HFRC, mechanical properties, steel fibers, reinforced concrete, polypropylene fibers

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Authors: Mehdi Habibagahi, Shami Nejadi, Ata Aminfar

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A significant degradation factor that impacts the durability of concrete structures is the alkali-silica reaction. Engineers are frequently charged with the challenges of conducting a thorough safety assessment of concrete structures that have been impacted by ASR. The alkali-silica reaction has a major influence on the structural capacities of structures. In most cases, the reduction in compressive strength, tensile strength, and modulus of elasticity is expressed as a function of free expansion and crack widths. Predicting the effect of ASR on flexural strength is also relevant. In this paper, a nonlinear three-dimensional (3D) finite-element model was proposed to describe the flexural strength degradation induced byASR.Initial strains, initial stresses, initial cracks, and deterioration of material characteristics were all considered ASR factors in this model. The effects of ASR on structural performance were evaluated by focusing on initial flexural stiffness, force–deformation curve, and load-carrying capacity. Degradation of concrete mechanical properties was correlated with ASR growth using material test data conducted at Tech Lab, UTS, and implemented into the FEM for various expansions. The finite element study revealed a better understanding of the ASR-affected RC beam's failure mechanism and capacity reduction as a function of ASR expansion. Furthermore, in this study, decreasing of the residual mechanical properties due to ASRisreviewed, using as input data for the FEM model. Finally, analysis techniques and a comparison of the analysis and the experiment results are discussed. Verification is also provided through analyses of reinforced concrete beams with behavior governed by either flexural or shear mechanisms.

Keywords: alkali-silica reaction, analysis, assessment, finite element, nonlinear analysis, reinforced concrete

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Authors: Mohammed Zaki, Hayder Rasheed

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This paper evaluates the flexural response of sand-lightweight Perlite concrete using full-scale reinforced concrete T beams strengthened and anchored with carbon fiber reinforced polymer (CFRP) materials. Four specimens were prepared with the same geometry, steel reinforcements, concrete properties, and span lengths. The anchored beams had a similar number of CFRP sheets but were secured utilizing different arrangements of CFRP fiber anchors. That will allow for effective and easily making comparisons to examine the flexural strengthening behavior of sand-lightweight Perlite concrete beams with anchors. The experimental outcomes were also compared with the numerical study and the comparisons were discussed. The test results showed an improvement in flexural behavior due to the use of CFRP sheets and anchors. Interestingly, the anchored beams recorded similar ultimate strength regardless of the number of CFRP fiber anchors used due to the failure by excessive wide cracks in the concrete.

Keywords: perlite concrete, CFRP fiber anchors, lightweight concrete, full-scale T-beams

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Authors: Ahsan R. Khokhar, Fizza Hassan

Abstract:

Alkali-Silica Reaction (ASR) has been recognized as a potential cause of concrete degradation in the world since the 1940s. In Pakistan, mega hydropower structures like dams, weirs constructed from aggregates extracted from a local riverbed exhibited different levels of alkali-silica reactivity over an extended service period. The concrete expansion potential due to such aggregates has been categorized as slow-reactive. Apart from hydropower structures, ASR existence has been identified in the concrete structural elements of a Textile Mill building which used aggregates extracted from the nearby riverbed. The original structure of the Textile Mill was erected in the 80s with the addition of a textile ‘sizing and wrapping’ hall constructed in the 90s. In the years to follow, intensive spalling was observed in the structural members of the subject hall; enough to threat to the overall stability of the building. Limitations such as incomplete building data posed hurdles during the detailed structural investigation. The paper lists observations made while assessing the extent of damage and its effect on the building hall structure. Core testing and Petrographic tests were carried out as per the ASTM standards for strength degradation analysis followed by the identifying its root cause. Results confirmed significant structural strength reduction because of ASR which necessitated the formulation of an immediate re-strengthening solution. The paper also discusses the possible tracks of rehabilitative measures which are being adapted to stabilize the structure and seize further concrete expansion.

Keywords: Alkali-Silica Reaction (ASR), concrete strength degradation, damage assessment, damage evaluation

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Authors: L. Chiriatti, H. Hafid, H. R. Mercado-Mendoza, K. L. Apedo, C. Fond, F. Feugeas

Abstract:

Substituting natural aggregate with recycled aggregate coming from concrete demolition represents a promising alternative to face the issues of both the depletion of natural resources and the congestion of waste storage facilities. However, the crushing process of concrete demolition waste, currently in use to produce recycled concrete aggregate, does not allow the complete separation of natural aggregate from a variable amount of adhered mortar. Given the physicochemical characteristics of the latter, the introduction of recycled concrete aggregate into a concrete mix modifies, to a certain extent, both fresh and hardened concrete properties. As a consequence, the behavior of recycled reinforced concrete members could likely be influenced by the specificities of recycled concrete aggregates. Beyond the mechanical properties of concrete, and as a result of the composite character of reinforced concrete, the bond characteristics at the rebar/concrete interface have to be taken into account in an attempt to describe accurately the mechanical response of recycled reinforced concrete members. Hence, a comparative experimental campaign, including 16 pull-out tests, was carried out. Four concrete mixes with different recycled concrete aggregate content were tested. The main mechanical properties (compressive strength, tensile strength, Young’s modulus) of each concrete mix were measured through standard procedures. A single 14-mm-diameter ribbed rebar, representative of the diameters commonly used in the domain of civil engineering, was embedded into a 200-mm-side concrete cube. The resulting concrete cover is intended to ensure a pull-out type failure (i.e. exceedance of the rebar/concrete interface shear strength). A pull-out test carried out on the 100% recycled concrete specimen was enriched with exploratory acoustic emission measurements. Acoustic event location was performed by means of eight piezoelectric transducers distributed over the whole surface of the specimen. The resulting map was compared to existing data related to natural aggregate concrete. Damage distribution around the reinforcement and main features of the characteristic bond stress/free-end slip curve appeared to be similar to previous results obtained through comparable studies carried out on natural aggregate concrete. This seems to show that the usual bond mechanism sequence (‘chemical adhesion’, mechanical interlocking and friction) remains unchanged despite the addition of recycled concrete aggregate. However, the results also suggest that bond efficiency seems somewhat improved through the use of recycled concrete aggregate. This observation appears to be counter-intuitive with regard to the diminution of the main concrete mechanical properties with the recycled concrete aggregate content. As a consequence, the impact of recycled concrete aggregate content on bond characteristics seemingly represents an important factor which should be taken into account and likely to be further explored in order to determine flexural parameters such as deflection or crack distribution.

Keywords: acoustic emission monitoring, high-bond steel rebar, pull-out test, recycled aggregate concrete

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Authors: Soner Guler, Demet Yavuz, Fuat Korkut

Abstract:

Synthetic fibers are commonly used in many civil engineering applications because of its some superior characteristics such as non-corrosive and cheapness. This study presents the results of experimental study on compressive strength of synthetic fiber reinforced concretes. Two types of polyamide (PA) synthetic fiber with the length of 12 and 54 mm are used for this study. The fiber volume ratio is kept as 0.25%, 0.75%, and 0.75% in all mixes. The plain concrete compressive strength is 36.2 MPa. The test results clearly show that the increase in compressive strength for synthetic fiber reinforced concretes is significant. The greatest increase in compressive strength is 23% for PA synthetic fiber reinforced concretes with 0.75% fiber volume.

Keywords: synthetic fibers, polyamide fibers, fiber volume, compressive strength

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Authors: Jason Ting Jing Cheng, Lee Foo Wei, Yew Ming Kun, Mo Kim Hung, Yip Chun Chieh

Abstract:

This research delves into the structural characteristics of distinct construction material, rubberized lightweight foam concrete (RLFC) wall panels, which have been developed as a sustainable alternative for the construction industry. These panels are engineered with a RLFC core, possessing a density of 1150 kg/m3, which is specifically formulated to bear structural loads. The core is enveloped with high-strength fiber cement boards, selected for their superior load-bearing capabilities, and enhanced flexural strength when compared to conventional concrete. A thin bed adhesive, known as TPS, is employed to create a robust bond between the RLFC core and the fiber cement cladding. This study underscores the potential of RLFC wall panels as a viable and eco-friendly option for modern building construction, offering a combination of structural efficiency and environmental benefits.

Keywords: structural performance, rubberized concrete wall panel, fiber cement board, insulation performance

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Authors: Guneet Saini, Uthej Vattipalli

Abstract:

In a world with increased demand for sustainable construction, waste product of one industry could be a boon to the other in reducing the carbon footprint. Usage of industrial waste such as fly ash and ground granulated blast furnace slag have become the epicenter of curbing the use of cement, one of the major contributors of greenhouse gases. In this paper, empirical studies have been done to develop alkali activated self-compacting geopolymer concrete (GPC) using ground granulated blast furnace slag (GGBS), incorporated with 2% nano-silica by weight, through evaluation of its fresh and hardening properties. Experimental investigation on 6 mix designs of varying molarity of 10M, 12M and 16M of the alkaline solution and a binder content of 450 kg/m³ and 500 kg/m³ has been done and juxtaposed with GPC mix design composed of 16M alkaline solution concentration and 500 kg/m³ binder content without nano-silica. The sodium silicate to sodium hydroxide ratio (SS/SH), alkaline activator liquid to binder ratio (AAL/B) and water to binder ratio (W/B), which significantly affect the performance and mechanical properties of GPC, were fixed at 2.5, 0.45 and 0.4 respectively. To catalyze the early stage geopolymerisation, oven curing is done maintaining the temperature at 60˚C. This paper also elucidates the test results for fresh self-compacting concrete (SCC) done as per EFNARC guidelines. The mechanical properties tests conducted were: compressive strength test after 7 days, 28 days, 56 days and 90 days; flexure test; split tensile strength test after 28 days, 56 days and 90 days; X-ray diffraction test to analyze the mechanical performance and sorptivity test for testing of permeability. The study revealed that the sample of 16M concentration of alkaline solution with 500 Kg/m³ binder content containing 2% nano silica produced the highest compressive, flexural and split tensile strength of 81.33 MPa, 7.875 MPa, and 6.398 MPa respectively, at the end of 90 days.

Keywords: alkaline activator liquid, geopolymer concrete, ground granulated blast furnace slag, nano silica, self compacting

Procedia PDF Downloads 123