Applied Mechanics and Materials Vols. 438-439

Abstract: The skeleton of concrete is determined by aggregate gradation. This paper studies the permeability and mechanical properties of pervious concrete affected by the aggregate gradation. Eight levels of aggregate gradation were selected, which included the single grain grading, double size grain grading and continuous grading. It is found that by series of tests, compared to the pervious concrete with the single grain grading and double size grain grading, the pervious concrete with continuous grading has low porosity, small permeability coefficient, high cubic compressive strength and similar splitting tensile strength and the flexural strength.

Abstract: To establish an appropriate random aggregate model at meso-level is the basis for successfully simulating the meso-mechanical behaviors of concrete. This paper proposes a new simple method to generate random aggregates of concrete by PFC2d. And the distribution of aggregate in the two-dimensional concrete specimen cross-section is determined by Walraven formula. The results show that the numerical aggregate distribution matches well with the theoretical grading curve.

Abstract: Concrete multi-step mixing technology means the construction technology of multi-step material mixing and multi-step stirring. Based on the tests about impermeability, frost resistance and anti-carbonization in the same material and the same proportioning using the method of aggregate enveloped with cement of multi-step mixing technology, it demonstrated that the method of aggregate enveloped with cement can obviously improve the performance of concrete on impermeability, frost resistance and carbonization resistance.

Abstract: As the effects of climatic change become more evident and extreme, there is significant pressure being mounted onto port authorities and infrastructure stakeholders to ensure that their assets are resilient to the effects of a more aggressive and corrosive climate. Typically, the reinforcing steel within concrete which provides its flexural strength is protected from corrosion by both the alkalinity of the cement and the distance of cover from the chloride laden environment. However, studies are suggesting that as the hydrological cycle around the equator begins to accelerate, the salinity of the oceans at these lower latitudes (namely from 25°S to 25°N) will increase. As demonstrated through Ficks 2^nd Law of diffusion, there will then be an effect on the build-up of surface chlorides and thus, chloride ingress through the cement matrix to initiate corrosion. Through an extensive literature review of climatic forecasts, and both laboratory and in-field trials, this paper will numerically demonstrate the relationship between salinity concentration and surface chloride levels at varying temperatures. The results illustrate a strong positive relationship between the two parameters suggesting faster corrosion initiation, and more frequent operational downtime for stakeholders into the future. To fill this gap in knowledge, the surface chloride equations presented should be considered when design, maintenance, and retrofitting options are being considered for stakeholders within the affected locations.

Abstract: Applying grey relational analysis method, this paper calculated the relational grades between the mix proportion parameters and the compressive strength, the slump of green high-performance concrete (GHPC) respectively. Besides, the sequence results of influencing degree of the factors affecting the compressive strength and workability were obtained. The results indicate that the compressive strength and slump of GHPC are affected by various mix proportion factors with different sensitivity, and the sensitivity could be well analyzed by the grey relational analysis. Among the four selected parameters of mix proportion such as water to binder ratio, cement dosage, fly ash dosage and sand ratio, the water to binder ratio and the cement dosage greatly influence on the compressive strength of GHPC, the water to binder ratio and the sand ratio greatly influence on the workability of GHPC.

Abstract: Support vector machine (SVM) is a statistical learning theory based on a structural risk minimization principle that minimizes both error and weight terms. A SVM model is presented to predict compressive strength of concrete at 28 days in this paper. A total of 20 data sets were used to train, whereas the remaining 10 data sets were used to test the created model. Radial basis function based on support vector machines was used to model the compressive strength and results were compared with a generalized regression neural network approach. The results of this study showed that the SVM approach has the potential to be a practical tool for predicting compressive strength of concrete at 28 days.

Abstract: The effect of different water absorption and texture of fine aggregate on properties of dam concrete is significant. This paper studies the properties of dam concrete made by the same and different kinds of fine aggregates. The results showed that concrete made by fine aggregate with high water absorption have higher degree of hydration, larger workability, lower ultimate tensile strength, compared to concrete made by limestone sand. Concrete made by basalt sand have lower strength, higher dry shrinkage, lower autogenously volume deformation.

Abstract: By changing the grading of pebble and water cement ratio, the influence of pebble grading on the compressive strength and flexural strength of concrete is studied at the same pebble content. Test results show that the compression strength and bending strength of concrete decrease with the increasing of the maximal size of coarse aggregate, while the maximal size (D_max) of pebble aggregate achieves 10mm, 20mm, 40mm and 60mm. And concrete strength decreases significantly when D_max is 60mm. Meanwhile, the influence of aggregate gradation is obviously with the increase of age time.

Abstract: Based on the statistical damage theory and the experimental phenomena, the statistical damage constitutive model for concrete under biaxial tension is proposed. The two meso-scale damage modes, rupture and yield are considered, and the whole damage evolution process is driven by the principal tensile damage strain. The results show that the proposed statistical damage model can accurately predict the constitutive behavior in the uniform damage phase for concrete under biaxial tension. The damage mechanism is discussed in the view point of biaxial strength and deformation properties.

Abstract: Different confined concrete models and their influences on column lateral load-deformation relations are compared and studied in this paper. The analytical results show that models have remarkable discrepancies on the descending branch of constitutive curves, and these discrepancies are weakened in predicting of column lateral load-defromation curves due to eccentric compression of confined concrete.