Comportamiento a la flexión de vigas de hormigón geopolímeras a base de escoria reforzadas con fibras de acero

Este estudio incluye nueve vigas de hormigón armado ensayadas. Está diseñado para fallar en flexión bajo carga de dos puntos. Todas las vigas se clasifican según el tipo de hormigón y el porcentaje de PVA en tres grupos. El primer grupo que incluye cuatro vigas de hormigón armado con geopolímero con un porcentaje de PVA fue del 0,2 %; el segundo grupo incluía cuatro vigas de hormigón armado con geopolímero con un porcentaje de PVA de 0,75 % y el tercer grupo incluía una viga de hormigón armado normal. Los resultados mostraron que al comparar la viga de hormigón geopolímero con la viga de hormigón normal, se observó que la resistencia última es equivalente a muchas veces la del hormigón normal. El mejor porcentaje para mejorar la carga última para la viga NO.6 (GSSB10), donde el porcentaje de aumento fue del 132%, esta viga está reforzada con barras de acero de 2ɸ12 mm en la parte superior y 2ɸ16 mm en la parte inferior. En cuanto a las otras vigas, el aumento porcentual en la carga última fue para la viga NO.1 (46%), viga NO.2 (99%), viga NO.3 (13%), viga NO.4 (60%), viga NO.5 (58%), viga NO.7 (32%) y viga NO.8 (66%). La deflexión máxima en todas las muestras fue alta en comparación con el hormigón normal, donde la deflexión máxima alcanzó los 30 mm, mientras que en el hormigón normal fue de 9,65 mm

EFFECT OF POLYPROPYLENE FIBER ON PROPERTIES OF GEOPOLYMER CONCRETE BASED METAKOLIN

Climate changes and global warming are an international issue around the world and caused by the accumulation of greenhouse gases, and one of these reasons Portland cement industry which releases high amounts of CO2, which causes 65% of the global warming effect. So the essential component for sustainable development in the construction industry is the improvement of alternatives for cement. One of the promising materials in the field of concrete industry is the geopolymer concrete, which attracted spotlight over the past decade with its comparable performance with Portland cement. This paper presents a systematic review of different research works done in the region of geopolymer concrete based metakoalin reinforced with polypropylene fiber and under ambient temperature. The mechanical behavior was enhanced significantly through experimental results. The compressive strength was improved 14.75% with 1% of polypropylene fiber while the increment of splitting tensile strength was 12.3 %, 15.76 % respectively. The flexural strength of specimens was also improved when compared with the non-fiber geopolymer concrete. The highest increment obtained with 1.5% of fiber volume content was 27.3%. Modulus of elasticity was also improved with increment to 13.1%, when compared with the non-fiber geopolymer concrete, also from experiment adding of fibers lead to a decrease in the density of GPC. The compressive performance and flexural performance of fiber-reinforced geopolymer concrete were also better than specimens without fiber

Improvement of poor subgrade soils using cement kiln dust

Construction of pavements layers on subgrade with excellent to good properties reduces the thickness of the layers and consequently reduces the initial and maintenance cost of highways and vice versa. However, construction of pavements on poor subgrade is unavoidable due to several constrains. Improvement of subgrade properties using traditional additives such as lime and Portland cement adds supplementary costs. Therefore, using by-products in this domain involves technical, economic, and environmental advantages. Cement kiln dust (CKD) is generated in huge quantities as a by-product material in Portland cement plants. Therefore, it can be considered as an excellent alternative in this domain. In Iraq, Portland cement plants generate about 350000 tons of CKD annually which is available for free. Therefore, Iraq can be adopted as a case study. This paper covers using CKD to improve the properties of poor subgrade soils based on series of California Bearing Ration (CBR) tests on sets of untreated samples and samples treated with different doses of CKD in combination with different curing periods to investigate their effects on soil properties. The results exhibited that adding 20% of CKD with curing for 14 days increases the CBR value from 3.4% for untreated soil to 48% for treated soil; it, also, decreases the swelling ratio. To determine the effects of using this dose under the mentioned curing period on the designed thicknesses of pavements layers, a case study was adopted. The case study results exhibited that treatment of the subgrade soil by 20% of CKD with curing for 14 days reduces the cost of the pavements by $25.875 per square meter

The Effect of Opening Size and Location on the Performance of Reinforced Concrete T-Beams under Pure Torque

IN modern buildings, transverse openings are often used in order to pass the pipes of health services, electrical cables or air conditioning ducts and other prepuce. The presence of these openings leads to a weakening of the beam so it must work to investigate the behavior of these beams in order to know how the presence of openings affects beam resistance. In this research, the behavior of reinforced concrete T-beams with circular openings exposed to pure torsional moment is studied. The experimental program involves testing of five beams with same dimensions and reinforcements. One of them is solid beam and used as reference for comparison with other beams with an opening and the other four T- beams containing circular openings of deferent dimension(100 and 150) and location(Lc/2 and Lc/3). Practical results show that the T-beam with circular openings of diameter (100mm) with different locations (Lc/2 and Lc/3), where Lc is the clear span of the beam, have an ultimate torsional capacity lower than that for solid beam by about (23% and 30%) respectively. The increase of the openings size causes a significant decrease in torsional capacity, where the beams with circular openings of diameter (150mm) with different locations (Lc/2 and Lc/3) have an ultimate torsional capacity lower than that for solid beam by about (56 % and 61%) respectively. Practical results show also that the presence of circular openings with diameter of 47% and 71% from the total depth increases the angle of twist significantly as compared with reference beam for the same applied torque level

Workability and Compressive Strength Properties of (Fly Ash-Metakaolin) based Flowable Geopolymer Mortar

RPC (Reactive Powder Concrete) is a high-strength concrete with outstanding technical qualities. One of the most crucial critical criteria in RPC development is the cement content. Cement production is seen as an environmentally unsustainable process. As a result, it is necessary to substitute cement in RPC manufacturing with an environmentally acceptable binder. Geopolymer seems to be a novel binder that can completely replace cement. The properties of constituents and their percentages in the mix significantly affect the behavior of geopolymer concrete or mortar. This research aims to produce Geopolymer RPC (GRPC) and verify the impact of the ratios of fly ash/pozzolanic materials (FA/P), sand/pozzolanic materials(S/P), finer sand/fine aggregate (S2/S1), and alkaline solution/pozzolanic materials (A/P) on its mechanical and durability properties. The results of the current works demonstrate that increase in alkaline solution to binder ratio increase the compressive strength of the mortars from 62.28 to 70.01 MPa at 62.50% to 100% alkaline/binder ratio, respectively. As well as, vfor the same alkaline/binder ratio the workability subsequently improves from 15 to 17.3mm

Clay calcination technology: state-of-the-art review by the RILEM TC 282-CCL

The use of calcined clays as supplementary cementitious materials provides the opportunity to significantly reduce the cement industry's carbon burden; however, use at a global scale requires a deep understanding of the extraction and processing of the clays to be used, which will uncover routes to optimise their reactivity. This will enable increased usage of calcined clays as cement replacements, further improving the sustainability of concretes produced with them. Existing technologies can be adopted to produce calcined clays at an industrial scale in many regions around the world. This paper, produced by RILEM TC 282-CCL on calcined clays as supplementary cementitious materials (working group 2), focuses on the production of calcined clays, presents an overview of clay mining, and assesses the current state of the art in clay calcination technology, covering the most relevant aspects from the clay deposit to the factory gate. The energetics and associated carbon footprint of the calcination process are also discussed, and an outlook on clay calcination is presented, discussing the technological advancements required to fulfil future global demand for this material in sustainable infrastructure development.LM