Mechanical Properties of RC Beams with Polypropylene Fibers under High Temperature

The objective of this study is to examine the impact of polypropylene fibers on fire resistance of steel reinforced concrete beams. In order to achieve this, concrete mixtures are prepared by using different contents of polypropylene; 0, 0.45 and 0.67 kg/m3. Simply supported beams are heated in an electric furnace to a temperature of 400 for exposure up to 4.5 hours and tested under a static point load on a universal loading frame. Based on the results of this study, it is concluded that the ultimate residual strengths of RC beams containing polypropylene fibers are higher than those without polypropylene fibers. Furthermore, the researchers find out that RC beams which are prepared using 0.67 kg/m3 of polypropylene fibers can significantly promote the residual ultimate strengths during heating

الخواص الميكانيكية للكمرات الخرسانية فائقة الأداء ذات الألياف المعدنية

The objective of this study is to examine the mechanical properties of Ultra High Performance Concrete using steel fibers. Specimens are prepared for compressive strength, splitting tensile strength and flexural strength. For the compression test four silica fume contents and three volumes of steel fibers are used in preparing the mixes. Moreover, for the splitting tensile strength and flexural strength tests, one silica fume content, two aspect ratios and two volumes of steel fibers are used. Based on the results of this study, it is concluded that the addition of steel fibers results in a slight increase in compressive strength. On the other hand, the addition of steel fibers has a positive impact on splitting tensile strength and flexural strength of concrete.هدف هذه الدراسة هو فحص الخواص الميكانيكية للخرسانة فائقة الأداء بإستخدام ألياف من الحديد الصلب، فقد تم إعداد عينات لفحوصات مقاومة الضغط ومقاومة الخرسانة في الشد. وبالنسبة لإختبار مقاومة الضغط فقد تم إستخدام أربع نسب من السليكافيوم وثلاث نسب من ألياف الحديد الصلب في إعداد الخلطات الخرسانية، وبالإضافة إلى ذلك فقد تم إستخدام نسبة واحدة من السليكافيوم ونسبتين من ألياف الحديد الصلب ونسبتي إستطالة مختلفتين لهذه الألياف. وبناء على نتائج هذه الدراسة فقد تم التوصل إلى أن إضافة ألياف الحديد الصلب تؤدي إلى زيادة طفيفة في مقاومة الخرسانة للضغط بينما تؤدي إلى زيادة جوهرية في مقاومة الخرسانة في الشد

Pull-out behavior of post installed rebar connections using chemical adhesives and cement based binders

This study investigated the effectiveness of several types of adhesives used in post-installed rebar connections as a bonding agent between steel reinforcement bars and old concrete under pull-out test. The cylindrical samples (96 + 24 Nos) of 15 dia. × 30 cm with anchors rebar of varying diameter (8, 10, 12 mm) with different embedded length (10, 15 and 20 × rebar diameter). The control (24 Nos) was the cast in-place rebar concrete specimens while other samples (96 Nos) were post rebar-installed concrete specimen of varied bonding agents-chemical adhesives (Sikadure-31CF and EPICHOR 1786) or cement-based binders (mortar, ultra-high performance self-compacting concrete (UHPSCC). The findings showed that the use of the adhesives and UHPCC pull-out load values were in close proximity while they all outperformed mortar bonded specimens. The pull-out load (bond strength) increases with

Permeability and chloride penetration of concrete subjected to Gaza seawater exposures

Permeability and chloride penetration of concrete subjected to Gaza seawater exposure

Investigating the Effect of Sulfate Attack on Compressive Strength of Recycled Aggregate Concrete

This research aimed at studying the effect of sulfate attack on the compressive concrete strength with various percentages of recycled aggregate replacements (0%, 30%, 60% and 100%). Water cement ratio (0.42) are used, MgSO4 solution was used with two concentration (6% and 9 %) to represent the effect of sulfate attack on the concrete compressive strength. The experimental tests focused on physical properties of recycled aggregate; density, unit weight, sieve analysis, Los Angles test and specific gravity. Tests have also been performed on 108 concrete cubes samples at 7 days, 14 days and 28 days for compressive strength. The results of  compressive strength at 28 days using (0%, 30%, 60% and 100%) recycled aggregate are (330, 280, 266 and 244) Kg/cm2 respectively, with reduction in compressive strength was (15.2%, 19.4% and 26%)  for replacement ratio (30%, 60% and 100%) respectively. MgSO4 solution has an effect on compressive strength after 90 days of immersion in 6% and 9% concentrated of MgSO4 solution. The results of this study show that the reduction in compressive strength using recycled aggregate is more sensitive against the sulfate attack compared with natural aggregate

Repairing and Strengthening of Damaged RC Columns Using Thin Concrete Jacketing

This research aims to investigate the efficiency of repairing damaged concrete columns using thin concrete jacketing. The experimental program included casting of nine reference 300 mm long reinforced concrete column specimens: three specimens had a cross-sectional dimension of 100 mm × 100 mm, three specimens had a cross-sectional dimension of 150 mm × 150 mm, and three specimens had a cross-sectional dimension of 170 mm × 170 mm. A total of 36 identical column cores were cast with similar cross sections of 100 mm × 100 mm and a height of 300 mm. These cores were damaged by loading them with approximately 90% of their actual ultimate axial load capacities. Then, the columns were repaired and strengthened by applying two jacketing materials, which were 25 and 35 mm thick, on all four sides. Group 1 consisted of 18 column cores jacketed by normal strength concrete with a maximum aggregate size of 4.75 mm and steel reinforcement, whereas Group 2 consisted of 18 column cores jacketed using ultrahigh-performance fibre-reinforced self-compacting concrete with steel reinforcement. The experimental program showed that the Group 1 specimens had ultimate load capacities more than twice those of the unjacketed reference columns and the same axial capacity as the monolithically cast reference columns. The Group 2 specimens showed a significant increase in ultimate load capacity, which was approximately 3 times that of the unjacketed reference column and 1.86 times that of the monolithically cast reference columns. Moreover, using the shear studs was found to be the most effective …This research aims to investigate the efficiency of repairing damaged concrete columns using thin concrete jacketing. The experimental program included casting of nine reference 300 mm long reinforced concrete column specimens: three specimens had a cross-sectional dimension of 100 mm × 100 mm, three specimens had a cross-sectional dimension of 150 mm × 150 mm, and three specimens had a cross-sectional dimension of 170 mm × 170 mm. A total of 36 identical column cores were cast with similar cross sections of 100 mm × 100 mm and a height of 300 mm. These cores were damaged by loading them with approximately 90% of their actual ultimate axial load capacities. Then, the columns were repaired and strengthened by applying two jacketing materials, which were 25 and 35 mm thick, on all four sides. Group 1 consisted of 18 column cores jacketed by normal strength concrete with a maximum aggregate size of 4.75 mm and steel reinforcement, whereas Group 2 consisted of 18 column cores jacketed using ultrahigh-performance fibre-reinforced self-compacting concrete with steel reinforcement. The experimental program showed that the Group 1 specimens had ultimate load capacities more than twice those of the unjacketed reference columns and the same axial capacity as the monolithically cast reference columns. The Group 2 specimens showed a significant increase in ultimate load capacity, which was approximately 3 times that of the unjacketed reference column and 1.86 times that of the monolithically cast reference columns. Moreover, using the shear studs was found to be the most effective

Effects of hospital facilities on patient outcomes after cancer surgery: an international, prospective, observational study

Background Early death after cancer surgery is higher in low-income and middle-income countries (LMICs) compared with in high-income countries, yet the impact of facility characteristics on early postoperative outcomes is unknown. The aim of this study was to examine the association between hospital infrastructure, resource availability, and processes on early outcomes after cancer surgery worldwide.Methods A multimethods analysis was performed as part of the GlobalSurg 3 study-a multicentre, international, prospective cohort study of patients who had surgery for breast, colorectal, or gastric cancer. The primary outcomes were 30-day mortality and 30-day major complication rates. Potentially beneficial hospital facilities were identified by variable selection to select those associated with 30-day mortality. Adjusted outcomes were determined using generalised estimating equations to account for patient characteristics and country-income group, with population stratification by hospital.Findings Between April 1, 2018, and April 23, 2019, facility-level data were collected for 9685 patients across 238 hospitals in 66 countries (91 hospitals in 20 high-income countries; 57 hospitals in 19 upper-middle-income countries; and 90 hospitals in 27 low-income to lower-middle-income countries). The availability of five hospital facilities was inversely associated with mortality: ultrasound, CT scanner, critical care unit, opioid analgesia, and oncologist. After adjustment for case-mix and country income group, hospitals with three or fewer of these facilities (62 hospitals, 1294 patients) had higher mortality compared with those with four or five (adjusted odds ratio [OR] 3.85 [95% CI 2.58-5.75]; p<0.0001), with excess mortality predominantly explained by a limited capacity to rescue following the development of major complications (63.0% vs 82.7%; OR 0.35 [0.23-0.53]; p<0.0001). Across LMICs, improvements in hospital facilities would prevent one to three deaths for every 100 patients undergoing surgery for cancer.Interpretation Hospitals with higher levels of infrastructure and resources have better outcomes after cancer surgery, independent of country income. Without urgent strengthening of hospital infrastructure and resources, the reductions in cancer-associated mortality associated with improved access will not be realised

Effect of polypropylene fibers on concrete fire resistance / Polipropireno pluoštoį taka betono atsparumui ugniai

The objective of this study is to investigate the impact of polypropylene fibers on fire resistance of concrete. In order to achieve this, concrete mixtures are prepared by using different percentages of polypropylene; 0%, 0.5% and 1%, by volume. The samples are heated to 200, 400 and 600 °C, for exposures up to 6 hours, and tested for compressive strength. Based on the results of the study, it is concluded that the relative compressive strengths of concretes containing PP fibers were higher than those of concretes without PP fibers. Furthermore, it can be concluded that concrete mixes which are prepared using 0.5% PP fibers, by volume, can significantly promote the residual compressive strength during the heating. Santrauka Tyrimo tikslas – išnagrinėti polipropireno pluošto įtaką betono atsparumui ugniai. Buvo gaminami betono mišiniai su 0%, 0,5% ir 1% polipropireno dalimis. Bandiniai buvo kaitinami iki 200, 400 ir 600 °C, laikomi šiose temperatūrose 6 valandas ir bandomi nustatant gniuždomajį stiprį. Remiantis bandymų rezultatais daroma išvada, kad betono su polipropireno pluoštu stipris buvo didesnis už betono be šio priedo stiprį. Kita straipsnio išvada ta, kad betono mišiniai, kurių 0,5% tūrio sudaro polipropireno pluoštas, leidžia labai padidinti liekamajį gniuždomajį įkaitinto betono stiprį. Reikšminiai žodžiai: polipropirenas, pluoštas, atsparumas ugniai, patogumas kloti, poveiki

Effects of silica fume, ultrafine and mixing sequences on properties of ultra high performance concrete

The aim of this study is to investigate the effects of changing silica fume content, amount of crushed quartz powder as ultra fine aggregate and the sequence of mixing procedure on the main properties of Ultra High Performance Concrete (UHPC), with particular emphasis on 28 days compressive strength, density and slump. Several concrete mixes involving different contents of Silica fume and crushed quartz powder are prepared and tested for this purpose. Based on the results of this study, it is concluded that the optimum silica fume content necessary for producing UHPC is about 15% of cement mass. At this percentage, compressive strength is about 60% more than the strength for the zero content of silica fume. Added to this, the results show that adding 40% of the quantity of superplastisizer to the UHPC mixture at the first stage of the mixing with all dry materials has a positive effect on the 28 days compressive strength, while enhancing the workability. Moreover, as the ultrafine content increases, the compressive strength increases with the highest compressive achieved using ultrafine to cement ratio of 0.50

EFFECT OF GAZA SEAWATER ON CONCRETE STRENGTH FOR DIFFERENT EXPOSURES

EFFECT OF GAZA SEAWATER ON CONCRETE STRENGTH FOR DIFFERENT EXPOSURE