Advanced Materials Research Vols. 261-263

Abstract: In this paper, the influence of recycled aggregates volume fraction (Fra) on chloride induced permeability of recycled aggregates concrete (RAC) was investigated. Finite element analyses of single modeled RAC with regular aggregate arrangements were performed. The recycled aggregate fraction (Fra ) was varied between 0.38 and 0.63. The finite element method (FEM) were based on a mass diffusion approach in which RAC were simplified as three-phase cylindrical inclusions with 1 mm thickness. The analysis results were interpreted by change of permeability. The results show that the chloride concentration on the corresponding boundary vary wavely in a wide range from from 0.00196603 (mg/mm3) to 0.00238315 (mg/mm3) and increase entirely with the increasing Fra due to the influence of old adhered mortar. The effective chloride diffusivities of RAC and the value of chloride amount increase linearly with the increasing Fra.

Abstract: The Steel-polypropylene fiber reinforced concrete take full advantage of steel fiber’s macro-scale crack resistance function on the concrete as well as the polypropylene fiber’s micro-scale crack resistance and toughening effect on the concrete matrix. In this paper, the three kinds of concrete specimens including plain high-strength concrete, steel fiber reinforced concrete and steel-polypropylene fiber concrete are selected for a flexural toughness experimental study, their compressive strength and deformation performance are analyzed, and their toughness index are investigated with ASTM-C1018 and PCS(post-crack strength) method. The results show that steel-polypropylene fiber reinforced concrete has better strength and toughness property as well as deformation performance.

Abstract: The shock Hugoniot relationship of concrete was studied based on concrete test subjected to the high-velocity impacting loading by one stage gas gun. The P-U(pressure-partical speed) shock Hugoniot relationship curve of concrete was gained from the D-U(shocking wave speed-partical speed) curve of concrete, and the equation of volume pressure P and volume strain v was put forward according to the example analysis. Moreover, based on the polynomial Grьneisen equation, the parameters of high-pressure equation of state of concrete were got by fitting the test date, and the theoretical values from the equation matched well with the experimental ones.

Abstract: The numerical simulation method has been used to projectile penetrating concrete for many years. However, most previous research work has concentrated on the cuboids concrete model. Very few studies have been conducted to investigate the penetration process of complex concrete model. In this paper, numerical simulations of laboratory tests are conducted to show the penetration process of wedge concrete model. A double scalar damage model based on the concept of continuum damage mechanics is applied to modeling the failure of concrete. In the numerical model of wedge concrete, the wedges with different angles are modeled.

Abstract: An analytical model for compressive stress-strain curve of polypropylene fiber reinforced concrete (PPFRC) was proposed. The polypropylene fiber used was 60-mm long twisted fiber with aspect ratio of 120. The fiber was added in three volume fractions 0.2%, 0.4% and 0.6%. Tow concrete mixtures with varying water-cement ratio were used. The accuracy of the proposed model was evaluated by comparing the area under stress-strain curves for experimental and analytical model. The results showed good agreement between the experimental and analytical curves. In addition; empirical equations were proposed to quantify the effect of polypropylene fiber on compressive strength, strain at peak stress, and toughness of concrete in terms of fiber volume fraction.

Abstract: Difference between creep behaviors of concrete made from stone chips and crushed clay bricks, i.e. brick chips as coarse aggregate are examined by means of creep testing on their representative samples. Two different grades of concrete 17.2 and 27.5 N/mm² are prepared from brick chips and stone chips using appropriate mix design and are tested for creep for up to 50 days. Stone chips and brick chips aggregates used are selected in a way so that their gradation and fineness modulus remains as close as possible. Results from creep testing shows that concrete made from brick chips as coarse aggregate having same strength as that of concrete made from stone chips shows higher creep strain. As concrete strength increases, the difference in creep strain becomes more pronounced. Also, at initial loading condition, concrete made from brick chips shows higher rate of creep strain than that of concrete made from stone chips.

Abstract: Based on damage mechanics and thermo, the mechanical degradation of concrete material under the coupled action of stress and freeze-thaw cycles was analyzed in this paper. The tensile stress in concrete during freeze-thaw cycles was obtained considering freezing-induced pore pressure variation with the change of temperature. A revised fatigue fracture model is proposed for the reliability analysis of concrete durability, which can evaluate damage status and the remaining service life of concrete structure after freeze-thaw cycles with different loading levels. The present model can serve as references for design and safety assessment for concrete structures in cold regions.

Abstract: In order to systematically study dynamic mechanics character of reactive powder concrete (RPC), impact compression experiments and impact flattened Brazilian disc specimens of RPC have been investigated with modified split Hopkinson pressure bar (SHPB) experimental facility using brass pulse shaper, curves about stress versus strain and other parameters at strain rates of 20.3/s~137.0/s were obtained from impact compression. The dynamic tensile strength and tensile failure strain at strain rates of 3.4/s~26.2/s were obtained from impact flattened Brazilian. For comparison, the quasi-static compress and split tension of RPC were obtained with an MTS 810 materials test system and CSS-88500 electron universal material testing machine.The experimental result show that dynamic compression strength , elastic modulus and failure strain,dynamic tensile strength and failure strain significantly increase comparing to quasi-static experiment, RPC have the character of impact harding and ductility enhancement. RPC exhibit excellent failure patterns at high strain rate. Whether impact compression or impact splitting under strain rate including this paper ’s experiments, the relationship between the DIFC or DIFT and the logarithm of strain rateis linear.

Abstract: Based on experiments of uniaxial compression and flexural experiments, the basic mechanical properties (compressive strength and flexural strength) of reactive powder concrete (RPC) were investigated, the effect of the steel fiber content on mechanical properties of RPC was studied in this work. The resu1ts indicate that the axial compressive strength of RPC had no obvious change with the change of steel fiber content. When the steel fiber content varied from 1.0% to 2.0%, the flexural strength of RPC had no obvious change.When the steel fiber content varied from 2.0% to 5.0%, the flexural strength of RPC increased dramaticlly with the increase of steel fibers content. According to experiment curves, an equation for the compressive stress-strain curve of RPC was deduced with different stee1 fiber content.

Abstract: Aim & Goff model was used to predict the packing density of cementitious material including cement, ultra-pulverized fly ash and silica fume. The mix proportions of reactive powder concrete (RPC) with different packing density and calcium-silicon ratio of cementitious material were designed, and a strength test was carried out. The study results reveal that the flexural strength and compressive strength of RPC are related to the packing density and calcium-silicon ratio of cementitious material. For the mix proportion of RPC with the calcium-silicon ratio of 1.179, calcium hydroxide reacts with silicon dioxide fully, and the superfluous ultra-pulverized fly ash and silica fume fill the voids of RPC. The packing density of its cementitious material is the largest, and its strength approaches summit.