Applied Mechanics and Materials Vols. 584-586

Abstract: The influence of the chemical structures of styrene/butyl acrylate/hydroxyl propyl methacrylate emulsion on some properties of ordinary Portland cement concretes has been investigated as concrete curing agent. The structural parameters that are varied included the fractions of HPMA and the polymer structure of the shell-core. The result of the study showed that the hydroxyl monomer HPMA played an important role on the improvement of water retention and the optimal proportion is about 5 wt% of the polymer. In addition, the shell-core structure of the emulsion with HPMA located in shell polymer can further enhance the water-retention rate. Besides, the emulsion with hydroxyl groups could smooth the surface of the concrete, inhibit the carbonation and had positive influence on the compressive strength.

Abstract: This paper tested the pore structure, capillary water absorption and impermeability of cement mortars modified with three polymers respectively, establishing the relationship between the pore structure and waterproof performance. The results show that with the polymer dosage growing, especially as the polymer/cement ratio (m_p/m_c) increases from 0% to 5%, the reduction in the capillary water absorption and the penetration depth of water into mortar is significant. In the m_p/m_c range of 0%~20% the open porosity presents a gradual decrease trend. The capillary water absorption and the penetration depth of water into mortar show linear growth and exponential growth respectively with the open porosity increasing.

Abstract: This paper focuses on the assessment of the shear strength prediction established in the brazilian concrete code, NBR6118/2007[1], for reinforced concrete beams without web reinforcement. The values obtained by using the brazilian code equation are compared with a significant number of available experimental data and with those predicted by the expressions of other national and international codes, such as CEB-FIP MC90[2] and ACI-318/11[3]. The brazilian concrete code regarding shear capacity of reinforced concrete elements are explicitly assumed to be valid only for concrete strengths up to 50 MPa. It is shown that the code equation may be unconservative in a large number of cases. This discrepancy increases with increasing concrete strength, decreasing longitudinal reinforcement ratio and increasing beam depth.

Abstract: A multidimensional constitutive model for shape memory alloys (SMA) is developed in the paper, which is based on the thermodynamics theories of free energy and dissipation energy. This model can well describe both the shape memory effect (SME) and super elasticity effect (SE) of the thin-walled SMA cylinder under an axial tensional force and torsion.

Abstract: As the potential of using natural log is explored in the temporary structure, especially in template as the shores, it is important to gain further understanding of the microstructure and properties of cells such as undersize tree of Northeast larch that under macro buckling load. The research described in this paper focuses, for the first time, after the initial preparation by microtoming, on investigating the microstructure of log by analyzing of the ESEM images, and a model for deformation and failure mechanism of the cell had been proposed, then, the properties of cells were calculated through image software. Results show that the cells including early wood and late wood under without extra load are regularly arrayed, the deformation of the wall was induced by asymmetric out of plane twisting and splitting due to buckling of the logs, failure of the early wood cell is easily than late wood that following the large deformation occurs at plasticity, and two properties including late wood percentage and cell wall percentage has a direct proportion with the strength of log. The presented results indicate that it is improve to understand and analyze the failure process of cell when the log under concrete compression loading, and the reason that log as sustainable material is due to the unbroken cell clusters recover themselves as quickly as possible during at a certain enough time.

Abstract: New progress of research and applications of CFRP at home and abroad are introduced in this paper. The circular concrete-filled tubular CFRP-steel stub column under axial loads is studied based on the unified strength theory in the paper. The effect of intermediate principal stress on the ultimate strength for the concrete-filled tubular CFRP-steel stub column have been investigated. The ultimate load calculation formula for the concrete-filled tubular CFRP-steel stub column is derived in this paper, and can be simplified for cases without CFRP. Compared with the solution obtained in this paper and the experimental results, the good agreement can be found. The effects of the intermediate shear stress, the cross-section deformation ratio and also the inner friction angle of the concrete are all considered in the theory analysis. The analysis result further tests the applicability of the unified strength theory in the field of concrete-filled CFRP-steel tube. It has an important theory value for engineering application.

Abstract: This study investigates carbonation properties of concrete mixed with alkaline potential water (APW). A miniature electrolyzer made up of diaphragm electrolytic cells was made to produce APW. Results show that APW concrete gains greatly in carbonation property - carbonation depth deepened by 21% in the 28day fast carbonation test. A new mold is developed to make concrete samples with spherical concaves which promised a smooth test surface to the sample, realizing the lossless test of concrete carbonation. A long term carbonation test (90 days) of concrete mixed with ARPW is carried out. Applying grey system theory, the time dependence rule, which decides the dynastic model of carbonation formula is studied, offering a more scientific basis for estimating the structural durability of concrete.

Abstract: The Hong Run petrochemical oil depot is located in a saline area in the north of Weifang, where the contents of chloride and sulfate in this area are very high. Due to the rigorous environmental conditions, concrete with 50 years durability and C40 strength grade was prepared. A kind of corrosion resistance concrete with high performance superfine mineral powder and high performance pumping agent was developed to adapt to the conditions in saline areas. The chloride-penetration resistance ability was investigated by the test of chloride ion rapid electric transport (ASTM C1202). The concrete compressive strength and mortar expansion rate under continuous immersion in four different corrosion solutions was studied. The results showed that the chloride-penetration grade is very low. The compressive strength is high and the mortar expansion rate lower than 0.1%.

Abstract: The understanding of stress relaxation and tensile creep behavior is extremely important in accurate stress analysis and crack prediction of early-age concrete. The free shrinkage deformations of concrete with different strength grade were examined. The early-age tensile elastic modulus of concrete was investigated through temperature-stress testing machine. The tensile creep and shrinkage stress were obtained through the modified restrained ring test. The results indicate that the development of free shrinkage coordinates well with the inner strain of steel ring. Tensile creep decreases as water-binder ratio increases. Creep counteracts tensile stress of concrete by 28%~40% , decreases the possibility of cracking of concrete at early ages.

Abstract: The present study investigated experimentally effects of temperature on drying shrinkage of concrete in different water cement ratio and containing mineral admixture. Concrete was exposed to a controlled environment of 20±1oC, 35±1oC, 50±1oC, and 60% ± 5 RH, respectively. The drying shrinkage of concretes with water cement ratio of 0.3, 0.4 and 0.5 were evaluated. The resuluts showed that with the increase of temperature from 20 oC to 50 oC, the influence of water cement ratio on drying shrinkage of concrete was gradually weakened. The shrinkage strain of concretes with replacement of cement by 20% of ground granulated blast-furnace slag (GGBS), 10% of silica fume (SF), and 20% of fly ash (FA) were measured, respectively. Test results showed that GGBS had a little impact on drying shrinkage of concrete; Silica fume could increase the drying shrinkage of concrete significantly in the early and later ages, especially when concrete was subjected to high temperature; Fly ash reduced drying shrinkage in early ages and increased drying shrinkage of concrete in the later ages.