Increasing amount of construction waste and, concrete remnants, in particular pose a serious problem. Concrete waste exist in large amounts, do not decay and need long time for disintegration. Therefore, in this work old demolished concrete is crashed and recycled to produce recycled concrete aggregate which can be reused in new concrete production. The effect of using recycled aggregate on concrete compressive strength has been experimentally investigated; silica fume admixture also is used to improve recycled concrete aggregate compressive strength. The main parameters in this study are recycled aggregate and silica fume admixture. The percent of recycled aggregate ranged from (0-100) %. While the silica fume ranged from (0-10) %. The experimental results show that the average concrete compressive strength decreases from 30.85 MPa to 17.58 MPa when the recycled aggregate percentage increased from 0% to 100%. While, when silica fume is used the concrete compressive strength increase again to 29.2 MPa for samples with 100% of recycled aggregate.
Ultra-High Performance Fibre Reinforced Concrete (UHPFRC) is a superior type of concrete. It has ultra-high strength, ductility and durability. Despite the large number of researches that have been performed to study it, no perfect approach has been determined yet to identify the proportion of materials involved in its composition, nor ideal curing methods after casting with the possibility of performing effectively. Also, there is no uniform technique for pouring concrete to ensure that fibres are spread properly. This paper focuses on the review of techniques carried out to choose the quality and quantity of materials used for UHPFRC with the analysis and comparison of the researchers’ findings to identify optimal proportions, pouring and treatment regimens to attain the best results of mechanical properties of UHPFRC. The optimum packing density resulting from high cement content, using silica fume, fine aggregate, low w/cm ratio and high dosage of HRWRA are the key factors to reach ultra-high strength. Incorporation of short steel fibres leads to improving ductility, tensile strength and enhance strain hardening of UHPFRC. Heat treatment or steam curing stimulates the reaction between SiO2 in cementitious materials and Ca(OH)2 produced on cement hydration which results in rising strength.
This paper presents experimental and numerical investigations to reveal effecting of incorporating basalt fibers into a concrete matrix on the structural behavior and loading capacity of axially loaded short columns. Six volume fractions of chopped basalt fibers are added to the same concrete mixture to prepare six identically reinforced columns. The results illustrate that the bonding forces between microfilaments and matrix increase to provide good internal confinement for concrete ingredients, which enhances compressive strength and column loading capacity. The 0.3 % basalt fiber awarded the best compressive strength, while 0.15 % and 0.3 % awarded the best load capacity to the column. The Addition of basalt fibers delays cracking to increase the cracking load by about 50 % more than no fiber column, which indicates that it needs more energy to overcome the bonding strength between filaments and matrix. At the ultimate state, the loading capacity increases by 15 % and 17 % for 0.15 % and 0.3 % of basalt fibers and by 10 % and 12 % for 0.45% and 0.6% of basalt fiber. The 0.75 % decreased compressive strength by about 6 % but raised the column's ultimate load by 18 %. Therefore, basalt fiber benefits the cracking load more than the maximum load. The finite element showed approaching the peak load in numerical and experimental results. The longitudinal rebars and ties do not yield at the ultimate state. Increasing the reinforcement ratio raises loading capacity while lowering the yield stress of bars minimizes the maximum load.
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