55 research outputs found
Role of recycled crushed clay bricks as fine aggregates in enhancing the performance of ferrocement-strengthened RC beams
Get PDFFerrocement is a highly effective composite material for enhancing damaged-reinforced concrete (RC) structural elements thanks to its excellent fracture resistance, tensile and flexural strength, crack resistance and durability. This material is applied in thin layers of cement mortar reinforced with steel wire mesh. The resulting structures are strong, lightweight, and cost-effective while allowing for incorporating recycled materials, promoting sustainability and environmental friendliness. Inspired by the outstanding performances of this technique, this study investigated 20 RC beams strengthened using ferrocement. Ferrocement mortar was fabricated with five various substitute rates (0–100 %, with 25 % incremental) of natural sand (NS) by recycled crushed clay brick (RCCB) and two water to cement ratios (w/c) of 0.30 and 0.50. Compressive, tensile, and flexural strength, and porosity of the mortar, were also investigated. In addition, a data-based model was developed and validated with experimental results. A significant enhancement in flexural resistance was recorded for the strengthened beam with up to 50 % RCCB than the unstrengthened beam-USB (15 % and 6 % for w/c of 0.30 and 0.50, respectively, higher than USB), which is aligned with the substantially higher mechanical strength and lower porosity of mortar. It was registered that the damaged beams strengthened with 50 % RCCB were able to nearly reach the stiffness of the USBs and deliver higher deflection (81 % and 31 % for a w/c of 0.30 and 0.50, respectively, higher than 100 % USB) with ductile failure induced by multiple flexural and diagonal cracks. The proposed data-based modelling achieved excellent results, accurately predicting the beams' load deflection and the mortar mixes' strengths and porosity
Impact of Induction Furnace Steel Slag as Replacement for Fired Clay Brick Aggregate on Flexural and Durability Performances of RC Beams
No full textThis research investigates the flexural and durability performances of reinforced concrete (RC) beams made with induction furnace steel slag aggregate (IFSSA) as a replacement for fired clay brick aggregate (FCBA). To achieve this, 27 RC beams (length: 750 mm, width: 125 mm, height: 200 mm) were made with FCBA replaced by IFSSA at nine replacement levels of 0%, 10%, 20%, 30%, 40%, 50%, 60%, 80%, and 100% (by volume). Flexural tests of RC beams were conducted by a four-point loading test, where the deflection behavior of the beams was monitored through three linear variable displacement transducers (LVDT). The compressive strength and durability properties (i.e., porosity, resistance to chloride ion penetration, and capillary water absorption) were assessed using the same batch of concrete mix used to cast RC beams. The experimental results have shown that the flexural load of RC beams made with IFSSA was significantly higher than the control beam (100% FCBA). The increment of the flexural load was proportional to the content of IFSSA, with an increase of 27% for the beam made with 80% IFSSA than the control beam. The compressive strength of concrete increased by 56% and 61% for the concrete made with 80% and 100% IFSSA, respectively, than the control concrete, which is in good agreement with the flexural load of RC beams. Furthermore, the porosity, resistance to chloride ion penetration, and capillary water absorption were inversely proportional to the increase in the content of IFSSA. For instance, porosity, chloride penetration, and water absorption decreased by 43%, 54%, and 68%, respectively, when IFSSA entirely replaced FCBA. This decreasing percentage of durability properties is in agreement with the flexural load of RC beams. A good linear relationship of porosity with chloride penetration resistance and capillary water absorption was observed
Long-term strength and durability performance of eco-friendly concrete with supplementary cementitious materials
No full textResearch has shown that adding supplementary cementitious materials (SCMs), such as fly ash (FA) and slag (SL), to concrete improves its mechanical and durability properties up to certain limits. However, the long-term performance of concrete made with FA and SL is not fully known. This study investigates the impact of FA and SL on the long-term (up to 900 days) performance of concrete. The concrete specimens were made with six replacement percentages (0, 10, 20, 30, 45 and 60 by weight) of ordinary Portland cement (OPC). The short-term fresh and hardened properties of all concrete mixes were assessed after 14, 28, 60, and 90 days of water curing. After 120, 365, 730, and 900 days of water curing, the long-term performance was investigated for 100% OPC (control), 30% FA, and 30% SL concretes. At 28 days, no significant difference in strength development was observed for the concrete mixes containing up to 30% FA and 30% SL than the control concrete (100% OPC). In contrast, a remarkable enhancement in strength development was registered for all mixes containing up to 30% FA and 30% SL at 60 and 90 days of tests. Likewise, 30% FA and 30% SL showed the lowest porosity and water absorption than the control. The mechanical strength of concrete prepared with 30% FA and 30% SL gradually rises over time (from 14 to 900 days) compared to the control concrete. With increasing concrete age, a reduction in porosity and capillary water absorption was seen (up to 900 days)
Strength recovery of thermally damaged high-performance concrete subjected to post-fire carbonation curing
No full textThis study investigates the efficacy of post-fire curing using carbonation with a 20% carbon dioxide concentration and a relative humidity cycle set between 40% and 90% for restoring the mechanical properties of thermally damaged high-performance concrete (HPC) specimens containing 0%–40% silica fume. The HPC specimens were exposed to temperatures of 600, 800, and 1000 °C for 1 h, and the compressive strength recovery was measured. The microstructure, porosity, pore size distribution, and chemical composition of the HPC specimens were analyzed to explore the strength recovery mechanism. After exposure to elevated temperatures, the average compressive strength of samples without silica fume decreased by 49.2 MPa. Subsequent carbonation recuring resulted in a significant recovery of 73.9 MPa in the average compressive strength. This recovery surpassed the original strength for the samples heated to 600 and 800 °C, attributable to the filling and coalescing effects of calcium carbonate polymorphs formed through the carbonation of residual cement particles and β-C2S. The samples containing 20% silica fume exhibited the second highest average strength recovery of 34.1 MPa. However, the strength recovery for the samples with 40% silica fume exposed to 800 and 1000 °C was negligible, as the microcracks exceeding 1 μm in width had barely been restored by the carbonation of the low-calcium calcium silicates with low reactivity. Overall, this study presents an exciting future prospect for the labor and cost-effective restoration of thermally damaged concrete structures through the use of carbonation curing
Mechanical strength, shrinkage, and porosity of mortar reinforced with areca nut husk fibers
No full textCement-based materials perform well in compression but poorly in tension due to their brittleness. They also exhibit shrinkage cracking over time, which can be mitigated by incorporating fibers. Areca nut husk fiber (AHF) is agricultural waste, which is eco-friendly, light in weight, renewable, offers higher corrosion protection, and is a sustainable construction material. A novel application of AHF in a cement-based material has been undertaken. The effect of incorporating AHF (0%, 0.25%, 0.50%, 0.75%, and 1.0% by volume of mortar) on the properties of mortar was investigated. Workability, mechanical strength (compressive, tensile, and flexural), shrinkage, and porosity tests were performed. The results were compared to those obtained with jute and coir fiber mortars, as no data on mortar/concrete containing AHF have been reported. The mechanical strength of the mortar was increased at an AHF content of 0.5%. Beyond this level, the strength declined but was not lower than that of the control mix (0% AHF). Furthermore, significant shrinkage mitigation was observed with an increase in the AHF percentage. The porosity of the mortar increased with an increase in the content of AHF. This study reveals that 0.5% AHF can be used in mortar, given its excellent performance among all mixes
Eco-friendly concrete with chemically treated end-of-life tires: mechanical strength, shrinkage, and flexural performance of RC beams
No full texthe disposal of waste end-of-life vehicle tires has become a major environmental issue around the globe, as it is not completely biodegradable and can be a massive threat to the environment. Several researchers have attempted to use tires as aggregate with and without chemical treatment. However, to the best of the authors' knowledge, no research has investigated the performance of clay brick aggregate (CBA) concrete by replacing the CBA with bleached powder-treated waste rubber tire aggregate (WRTA) at different treatment times. Within this context, this study examines the mechanical strength, shrinkage, and flexural performance of reinforced concrete (RC) beams made with seven replacement percentages (0, 5, 10, 15, 20, 30, and 50 % by volume) of CBA by WRTA treated with H2O, NaOH, and bleaching powder (BP) for 2 h and 72 h. The experimental outcomes reveal that as the percentage of untreated WRTA increases, the slump, dry density, and mechanical strength decrease. Furthermore, concrete shrinkage increases with the increasing content of untreated WRTA in the mix. Likewise, the flexural load of RC beams declines with an increased percentage of untreated WRTA. It has been observed that the concrete made with WRTA treated with NaOH and BP has significantly higher mechanical strength, a flexural load carrying capacity of RC beams, and lower shrinkage compared to the untreated WRTA. The improvement in all properties was more remarkable for the treatment with BP than NaOH and treatment of 72 h than 2 h. The findings reveal that 15 % WRTA treated with BP solution for 72 h can be used as a CBA replacement whose design strength is not significantly high ( fcat28days ≈ 20 MPa)
Impact of overburnt distorted brick aggregate on the performance of concrete at ambient temperature and after exposure to elevated temperatures
No full texthis study examines the mechanical and durability properties of five concrete mixes made with different replacement percentages (0 %, 25 %, 50 %, 75 %, and 100 % by volume of regular brick aggregates-RBA) of RBA by overburnt distorted brick aggregate (ODBA) before and following exposure to elevated temperatures (250, 400, and 600 °C). The compressive, splitting tensile strength and the flexural load of the beams increased by 17 %, 23 %, and 18 %, respectively, at 28 days, when 75 % RBA was replaced with ODBA. The porosity decreased for the concrete containing up to 75 % ODBA. Conversely, the compressive strength decreased as the temperature increased, which agrees with the increased porosity with the increasing temperature
Effets du chargement en compression et du type de ciment sur le risque d'écaillage du béton au feu.
No full textLa recherche présentée dans cette thèse vise à examiner le mécanisme d’écaillage des bétons exposés au feu et comprendre l’influence du chargement mécanique appliqué en compression durant le chauffage. Des cubes (200 x 200 x 200 mm3) et des dalles (800 x 800 x 100 mm3) de béton fabriqués avec des ciments CEM II et CEM III (B40-II et B40-III: fc28days ≈ 40 MPa) ont été exposés à un feu ISO 834-1 sous différents niveaux de chargement uniaxial (cubes) et biaxial (dalles). En outre, l'effet du chargement mécanique (pression de confinement et charge uniaxiale) sur la perméabilité résiduelle au gaz a été étudié. Afin de mieux analyser les résultats expérimentaux et comprendre les mécanismes à l’origine de l'écaillage, des calculs numériques ont été réalisés en utilisant un modèle thermo-mécanique du code aux éléments finis CAST3M. Les résultats expérimentaux ont clairement montré que les éprouvettes chargées (uniaxial et biaxial) présentent un risque d’écaillage plus important que les éprouvettes non chargées. L’écaillage augmente avec le niveau de contrainte appliquée. Une partie des essais mais pas tous, ont montré que le B40-II (3% de laitier) présente un écaillage plus important que celui du béton B40-III (43% de laitiers).À partir de cette étude sur deux bétons ordinaires, il peut être mis en évidence qu'un certain niveau de contrainte de compression externe (uniaxiale ou biaxiale) est nécessaire pour induire l'écaillage du béton ordinaire. Les pressions des pores se combine avec les contraintes thermiques dûes aux gradients thermiques. Les contraintes de compression appliquées empêchent la création de certaines fissures générées par l'incompatibilité des déformations thermiques de la pâte de ciment et des granulats et des gradients thermiques. Pour l'échantillon non chargé, la création de fissures augmente la perméabilité et empêche naturellement le développement des pressions de pores.Pendant un feu réel, les membres structurels en béton sont toujours chargés ou retenus. La présence d'un chargement compressif pendant le chauffage augmente considérablement le stress de compression (diminue le stress de traction) et la grandeur de la pression des pores, ce qui augmente le risque d'écaillage. Ensuite, le stress compressif appliqué est un facteur clé très important que la conception de la résistance au feu des structures en béton devrait prendre en compte lors de l'écaillage. Par conséquent, il est recommandé que les essais d'écaillage ne soient pas effectués uniquement sur des échantillons non chargés.The research presented in this thesis seeks to examine and understand the mechanism of fire spalling role played by the external compressive loading during heating. Concrete cube (200 x 200 x 200 mm3) and slab (800 x 800 x 100 mm3) specimens made with CEM II and CEM III cements (B40-II and B40-III: fc28days ≈ 40 MPa) were exposed to ISO 834-1 fire curve under different levels of external uniaxial (for cube) and biaxial (for slab) compressive stress. Additionally, the effect of external compressive loading (confining pressure and uniaxial load) on the residual gas permeability of concretes have been investigated. In order to better analyse the experimental results and to provide more insight into the mechanism behind the fire spalling behaviour of concrete, numerical computations were carried out by using the existing thermo-mechanical model implemented in a finite element code CAST3M. The experimental results have clearly shown that the loaded specimens (uniaxial and biaxial) are more prone to spalling than unloaded specimens, with increasing amounts of spalling for higher values of applied compressive stress. Part of the tests, but not all have shown that B40-II (3% of slag) exhibited higher spalling than the B40-III (43% of slag).From this study on two ordinary concretes, it highlights that a certain level of external compressive stress (uniaxial or biaxial) was necessary to induce spalling. A possibility is that the applied compressive stress prevents the creation of cracks naturally due to thermal mismatch between cement paste and aggregates and thermal gradients. For unloaded specimen, the creation of cracks increases the permeability and naturally prevents the pore pressure to exceed a value that favours spalling.During a real fire, concrete structural members are always loaded or restrained. The presence of compressive loading during heating significantly increases the compressive stress (decreases the tensile stress) and the magnitude of pore pressure, which increase the risk of fire spalling. Then, the applied compressive stress is a very important key factor that the fire resistance design of concrete structures should take into account when considering spalling. Hence, it is recommended that the fire spalling test should not be carried out only on unloaded specimens, especially for the ordinary concrete
Fire spalling behaviour of concrete: Role of mechanical loading (uniaxial and biaxial) and cement type
No full textFire poses one of the most severe environmental conditions that can act on concrete structures as an external load and can induce severe damages (cracks, spalling) or even lead to collapse. Fire spalling of concrete is a complex phenomenon, which might occur due to pressure build-up in the pores, thermal and load-induced stresses. In this context, ordinary concrete specimens (B40-II and B40-III: fc28days ≈ 40 MPa) were exposed to standard fire curve (ISO 834-1), while a constant uniaxial or biaxial compressive load was applied. Six different levels of uniaxial compressive stress on cubes and four different levels of biaxial compressive stress on slabs have been investigated. The test results showed that loaded specimens are more susceptible to spalling than unloaded specimens, with increasing amount of spalling for higher values of applied load. It has been found that biaxially loaded specimens are more prone to spalling than uniaxially loaded specimens. B40-II concrete (3% of slag) exhibited higher spalling than the B40-III concrete (43% of slag)
Strengthening of RC beams by ferrocement made with unconventional concrete
Get PDFSome countries in South Asia has very limited availability of natural stones due to geological features, therefore, most of the concrete buildings of the past are made with burnt clay brick aggregates whose strength is rather low those are more vulnerable to collapse due to any extreme loads. However, ferrocement strengthening has several advantages such as good mechanical performance, cost-effectiveness, locally availability of the materials, and simplicity, this latter making available workmanship able to implement such technique (aspect which is very important in developing countries such as Bangladesh). Hence, the paper deals with the efficacy of ferrocement technique in improving the performance of reinforced concrete beams made in low-strength concrete (beam width 230 mm, height 230 mm, and length 2135 mm). The beams are made with unconventional concrete whose strength is about 12.5-13.0 MPa. The flexural tests are performed experimentally and numerically via the finite element software ABAQUS by considering the following loading configurations: (i) 2 point loads placed at L/3, (ii) 2 point loads are to the support, (iii) 2 point loads close to the mid-span, and (iv) 1 load next to the support and 1 load on the mid-span. The experimental results have shown that unsymmetrical loading decreases the overall load carrying capacity and increases the deformability due to the localization of the damage. The ferrocement beams reinforced by steel wire mesh exhibits high ultimate load carrying capacity and more ductile behavior. The outcome of this research can be used for future modeling and for the development of appropriate design guidelines on the strengthening of concrete structures dealing with different loading conditions
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