Wyniki 1-3 spośród 3 dla zapytania: authorDesc:"Hakim S. Abdelgader"

Concrete repair using two-stage concrete method DOI:10.15199/33.2015.08.17


  Wciągu ostatnich dziesięcioleci technologia betonowania rozwinęła się w różnych kierunkach, m.in. ulepszając metody przygotowania i układania betonu w celu osiągnięcia wysokiej jakości przy utrzymaniu niskich kosztów.Metoda dwuetapowego betonowania polega na umieszczeniu grubego kruszywawformie, a następniewprowadzeniu zaprawy cementowej tak, abywypełnić puste przestrzenie między cząstkami kruszywa. Ze względów ekonomicznych i technicznych beton otrzymany tą metodą jest stosowany przede wszystkimdo budowy i naprawy konstrukcjimasywnych, zwłaszcza fundamentów, konstrukcji podwodnych, a takżewewszystkich rodzajach konstrukcji z gęsto rozmieszczonym zbrojeniem. W artykule przedstawiono wybrane realizacje, w których wykorzystano taki betonwpracach remontowych, a takżewytyczne iwzory opisujące jego parametry mechaniczne: moduł sprężystości, wytrzymałość na rozciąganie i skurcz. Na podstawie badań stwierdzono, że moduł sprężystości orazwytrzymałość na rozciąganie betonu otrzymanego metodą dwuetapowego betonowania są równe lub większe niż betonu zwykłego o tej samej wytrzymałości na ściskanie. Słowa kluczowe: beton otrzymany metodą dwuetapowego betonowania,moduł sprężystości,wytrzymałość betonu na ściskanie i rozciąganie, skurcz.Concrete is one of the most important materials for construction. Scientific studies and research programmes were focused on the development of technologies to improve distinct concrete parameters, improve economical cost at production stage or at long term(durability).Apossible direction to improve the concrete technology is the concept of two-stage concrete (pre-placed aggregate concrete) or TSC. The TSC gets its name from the method used for concrete placement. Following this technique, first a formwork is constructed and the stone aggregate fraction is densely placed. The stone aggregate iswashed and screened prior to placement in order to remove all fines. Grout is then injected through the forms [...]

Mechanical properties of no-fines concrete DOI:10.15199/33.2016.08.40


  The paper presents a laboratory study to determine the relationship between compressive strength of no-fines concrete (NFC) and its tensile strength measured both by double-punch test and modulus of rupture test methods. The compressive strength was carried on 100 x 100 x 100 mm cubes. The specimens for tensile strength tests were 150 x 150mmcylinders, and 100 x 100 x 500 mm beams. Crushed limestone was used as coarse aggregate with max size of 19 mm. Sixteen concrete mixes were prepared with water-to-cement ratios: 0.40; 0.42; 0.44; and 0.46 cement-to-aggregate ratios (C/A) 1 : 5, 1 : 7, 1 : 9, and 1 : 11. The total of 48 cubes, 48 cylinders, and 48 beams were prepared. Compressive and tensile strength tests were carried on the concrete specimens according to relevant standards ASTMC39/ C39M. 2016 andASTM-C78/C78M. 2015 and the average of three results was recorded each time. It was found that tensile strength measured by modulus of rupture test gave higher results than that measured by double-punch test. The tensile strength from the double-punch test was about 20% of the compressive strength and from the modulus of rupture was about 30% of the compressive strength according to test results obtained in this study. Keywords: no-fines concrete, laboratory study, compressive and tensile strength.No-fine concrete (NFC) is composed of cement paste and coars[...]

Effect of coarse grain aggregate on strength parameters of two-stage concrete DOI:10.15199/33.2019.03.01


  The Two-Stage concrete (TSC) is made by placing the gravel into the mold and then filling the empty spaces between them by the mortar of sand and cement. Usually, emptying spaces between gravel are performed in two ways: weighing and injecting. In the weighting method, the mortar is poured on top of the mold filled with grit and, with the help of a compacting or vibrating, mortar fills the empty spaces. This method can be used in concrete with a maximum height of 300 mm. In the injection method, by placing the injection tubes inside the mold, the mortar is injected into themold by the pump and the injection tubes are gradually increased [1]. TSC differs from conventional concrete (CC) in several aspects. First, all ingredients of conventional concrete are mixed together and then placed in the formwork, while in TSC the grout ingredients are mixed separately and then injected into the pre-placed aggregatemass as mentioned earlier. Second, TSC has a higher coarse aggregate content than that of conventional concrete. TSC can be considered as a skeleton of coarse aggregate particles resting on each other, leaving only internal voids to be filled with grout. Conversely, in normal concrete the aggregates are rather dispersed. Therefore, TSC has a specific stress distributionmechanismat which the stresses are transferred through contact areas between coarse aggregate particles. Coarse aggregate forms about 60% of the total volume of TSC,while coarse aggregate forms about 40% of the total volume of conventional concrete [2, 8]. Abdelgader [3], through some experiments, presented an algorithm for designing TSC. Additionally, he determined the optimalwater-cement and sand-cement ratios formanufacturingTSC, and concluded that a water-cement ratio of 0.47 and a cement-sand ratio of 1 produce the highest mortar quality [3]. Compared to conventional concrete, TSC is superior in economic and geomechanical aspects and is [...]

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