مرتضی مهروند

One Of the effective parameters in the final strength and durability of self-compacting concrete is post-fabrication curing. External Curing with water Supply and moisture retaining coating are commonly used despite the limitation of these methods. Internal curing is one of the main issues in the implementation of reinforced concrete and bulk concrete structures with much less restrictions, especially in high performance concrete. The aim of this study was to investigate the effect of internal curing of self-compacting concrete using superabsorbent polymers on mechanical properties and durability of concrete. These polymers absorb some water and gradually release it during the hydration process. Using this method, the curing process is performed more efficiently, not only on the surface but also in the depth of concrete elements. Two types of superabsorbent polymer powders based on sodium and potassium with two different amounts have been used in this research. Concrete samples at 7 and 28 days of age were subjected to compressive strength, electrical resistance, water permeability, thaw-freeze cycle and microstructure tests including SEM, XRD and XRF. Compressive strength of samples with internal curing increased by 11.4% compared to control samples. In terms of durability parameters, the samples with internal curing show a reduction of more than 100% in water permeability and 16.7% improvement in electrical resistance. The result of microstructural experiments showed an improvement in evolution of the hydration process by at least 2.4% and at most 8.3% due to internal curing.

The use of fiber reinforced polymers, FRP, is one of the methods for strengthening and retrofitting concrete structures. In this research, the strengthening of reinforced self-compacting concrete beams against shear, torsion and bending has been investigated using GFRP. For reinforcing the beams against shear, bending and torsion, the strips of GFRP were used in the forms of U-shape, straight on the bottom surface and screwed around the beams respectively. In this study, the experimental results were compared with the results of the numerical models and their accuracies were confirmed. Then reinforcement sheets were applied in one and two layers on concrete beam models. By studying the numerical results obtained from Abaqus software, it was observed that with the increase of cracks in the concrete beams, their stiffness decreased and then the stresses were tolerated by the adhesive layers and the GFRP sheets, which has led to an increase in the bearing capacity of the beams. The results of numerical finite elements modeling show that by reinforcing the concrete beams with one layer of GFRP, the load bearing capacities of the beams improved in shear and torsion about 32% and 47% respectively. Moreover, if two layers of reinforcement sheets were used, the shear and torsion capacities of the beams increased about 45% and 61% respectively. The bending capacities of the concrete beams strengthened with one and two layers of GFRP increased up to 32% and 48% respectively.

This paper expresses the effects of silica fume, super plasticizer and GFRP on the torsional strength of self-compacting concrete (SCC) beams. SCC and control concrete mix designs in this study are based on 20 different mixes with the water-cement ratios of 0.35 and 0.45. For Torsion tests, beams with the dimensions of 40 × 10 × 10 cm were casted. To determine the compressive strength and Pundit tests, Cubic specimens with the dimensions of 10 × 10 × 10 cm and standard cylindrical specimens with the dimensions of 15 × 30 cm height were made and cured for 28 days before testing. The obtained experimental results show that the effect of silica fume in w/c=0.45 was more than the other on torsional capacity was. The torsional strength of concrete beams with GFRP was increased about 43%. The error of estimating the compressive strength of concrete by pundit test was 2%. In addition, the existing equations for estimating the torsional strength of ordinary concrete can be used for Self Compacting concrete.