One of the important issues in the production of Concrete is environmental variability that affects the Concrete and elements constructed from this material. Due to the importance of different characteristics of Concrete in short- and long-term conditions, this article aims to investigate the influence of initial temperature conditions of self-compacting Concrete on its long-term characteristics and determine the initial optimal temperature of Concrete. For these purposes, several experiments under three temperature conditions of 5, 20, and 40 degree-of-Celsius were conducted to evaluate the rheology and mechanical properties of fresh Concrete in the range of 7 and 28 days. In these experiments, alternative mineral admixtures of cement such as micro-silica, fly ash, and zeolite were used to build the Concrete specimens. Results demonstrate that the mechanical properties of the specimens increase with increasing initial temperature in the short term, while such properties significantly decrease in the long term compared to the specimens constructed under lower initial temperature. Moreover, the fluidity of self-compacting Concrete increases with increasing initial temperature.

The purpose of this study is to investigate strategies to improve the skid resistance of Roller-Compacted Concrete. Since the main weakness of Roller-Compacted Concrete is the lack of pavement macrotexture, in this study, three types of macro textures, 1-Seeding (in three aggregate sizes), stamping (in two sizes), and grooving (one-way and two-way) were considered. In this research, eight mixing designs were selected to make rollercompacted Concrete samples. The skid resistance of treated samples for 28 days before and after abrasion was evaluated by a British pendulum test. The results showed that Concrete surface abrasion reduces the skid resistance of Concrete samples by about 10%. The results also showed that changing different mixing designs did not have a significant effect on skid resistance. While the skid resistance is completely dependent on the type of macrotexture so that the grooved macrotexture shows the highest and the seeding shows the lowest skid resistance before and after abrasion.

Plastic hinge properties play a crucial role in predicting the nonlinear response of structural elements. The plastic hinge region of reinforced Concrete normal beams has been previously studied experimentally and analytically. The main objective of this research is to evaluate the behavior of the plastic hinge region of reinforced Concrete deep beams and its comparison with normal beams through finite element simulation. To do so, ten beams contain six deep beams, and four normal beams, under concentrated and uniformly distributed loading, are investigated. Lengths in the plastic hinge region involving curvature localization, rebar yielding, and Concrete crushing zones are studied. The results indicate that the curvature localization zone is not suitable for the prediction of plastic hinge length in reinforced Concrete deep beams. Based on the results it can be stated that in simply supported normal beams the Concrete crushing zone is focused on the middle span, but in simply supported deep beams by creating a compression strut between loading place and support, the Concrete crushing zone spreads along the compression trajectory. The rebar yielding zone of simply supported beams increases as the loading type is changed from the concentrated load at the middle to the uniformly distributed load.

In this study, the Concrete-steel bond strength of Concrete filled cylindrical steel tubes has been experimentally investigated. 22 short, high strength and normal Concrete filled circular steel tubes were tested. Push-out test was carried out as the common method to evaluate the bond carrying capacity. Four different Concrete mixes were used in preparing the specimens. The steel tubes were welded type with the nominal inside diameters of 3, 4, 6 and 8 inches. According to the test results bond strength increases with reduction of the w/c ratio of Concrete mixes. The high strength to normal Concrete bond strength ratio increases with the diameter of steel tubes. The bond strength decreases for higher diameters in both normal and high strength Concrete specimens.

One of the efforts to produce more environmentally friendly Concrete is to reduce the use of OPC by replacing the cement in Concrete with geopolymers. In geopolymer Concrete no cement is used, instead fly ash and alkaline solutions such as sodium hydroxide (Na OH) and sodium silicate (Na2O, SiO2) and potassium hydroxide (KOH) are used to make the binder necessary to manufacture the Concrete. One tone of fly ash can be utilized for manufacturing about 2.5 cubic meter of high quality Geopolymer Concrete. Test experiments proved as fly ash based Geopolymer Concrete has excellent Compressive strength, suffers very low drying shrinkage, low creep, excellent resistant to sulphate attack and good acid resistance. Trial mixes were done and noted the properties of the Concrete both in fresh state and in hardened conditions. The workability of the Concrete in terms of slump and compacting factor are observed to be excellent. The geopolymer Concrete in fresh state observed to be highly viscous and good in workable. Collapsed slump was observed with compaction factor of 0.95. Cube compressive strength of the geopolymer Concrete cubes verified at the age the Concrete 28 days from the date of their casting. Based on the test results of the trial mixes, this experimental study is carried out for 5 different mix proportions of fly ash to alkaline chemical ratios of Concrete specimen. Test specimen of standard sizes of cubes (30 nos), cylinders (30 nos), and prisms (15 nos) were cast and tested for workability in terms of slump and compacting factors in fresh state and for mechanical properties such as Compressive Strength, Splitting Tensile Strength, Flexural Strength, and Modulus of Elasticity of Concrete in hardened state. The test experiment proved that a Concrete of compressive strength of 30 MPa could be achieved in geopolymer Concrete by adopting alkaline solution to fly ash ratio of 0.50 at 16 molarity of Na OH.

In this paper a new method for nonlinear analysis of three dimensional reinforced Concrete frames (3D-RCF) under cyclic and monotonic loading is proposed. Each reinforced Concrete frame is divided into two types of joint and beam-column elements. The effect of bond-slip has been considered in the formulation of beam-column element. The effect of biaxial flexure and axial load on the cross section is assumed for nonlinear behavior while the effect of tensional behavior of beam-column element is assumed linear. The pull-out effect of reinforcing bar is considered in the formulation of joint elements. Formulation and relevant equations are displacement based upon which a computer program is developed. The reliability of the method has been assessed through the comparison of numerical and an experimental result by achieving of excellent agreement. Also the effect of bond-slip and bar pull-out occurring at joint on the response of RC frames is evaluated by utilizing various analyses.

A new method for seismic retrofitting Concrete structures is proposed using an X-shaped precast prestressed Concrete brace. This PPC brace is made of four precast Concrete parts and middle section that are assembled and added to the existing frame. This method has the following benefits: there is no need to work with wet Concrete in site or anchor and bolt to the existing frame, which may lead to a fast and economic retrofitting method. The X-shaped Concrete brace was made in half size and its efficiency is confirmed. That X-shaped precast prestressed Concrete brace was simulated and evaluated by computerized analysis using ABAQUS FEA modeling by authors of this paper earlier, and the proposed brace showed proper results in reducing lateral drifts and that method is considered as a proper method for seismic retrofitting. Here we are suggesting a different setup for the brace, which may lead to faster and more economic strengthening of RC structures. The new setup is omitting the middle section and suggests the brace to be used as a single diagonal. A model of this proposed method is simulated in ABAQUS FEA and the results show it is proper in reducing lateral displacements.