Advanced Materials Research Vols. 753-755

Abstract: The reasons of the chalking on concrete pavement were discussed according to the project case. The effects of water to cementitious material ratios (W/C ratios), mineral powder contents and construction curing conditions on the concrete chalking were investigated. The technical measures were proposed to prevent or reduce chalking at the concrete surface. The results indicate that the major compositions of chalking material are mineral powder, quartz and part of hydration products of cement. The bleeding of concrete, which mainly caused by lower cement amount, higher surface water to cementitious material ratio and excessive vibration during the construction, is the main cause of concrete chalking. The concrete chalking can be prevented or reduced under the conditions of lower W/C ratios (<0.45), longer wet curing ages (at least 14 d) and good supervisions of construction.

Abstract: The corrosion behavior of rebar HRB335 in simulated concrete pore solution (3.5 wt.% NaCl solution) and the tensile mechanical properties before and after corrosion were investigated. The results showed that, with corrosion time increasing from 30 days to 90 days, the corrosion rate increases. With the increase of corrosion time (corrosion rate), the yield strength and tensile strength decrease, but the elongation decreases at first and then increases.

Abstract: Cement hydration products carbonation is not only blamed for the carbonation-induced hardened cement paste or concrete cracking, also attributed to the pore water PH-value decrease, which causes the reinforcement corrosion under the existence of water and oxygen due to removal of oxide film passivating rebar surface, in hardened cement paste and concrete. Based on chemical thermodynamics, this paper presents the susceptibility of different cement hydration products to carbonation through calculating their Standard Gibbs Free Energy respectively, Gibbs free energy under temperature variation and the minimum equilibrium pressure of carbon dioxide triggering the carbonation process. The calculated results show that, under standard state (25°C, 100kpa), the minimum equilibrium pressure of carbon dioxide triggering carbonation process is significantly variable for different types of cement hydration products. For example, mono-sulfate sulfoferrite hydrates (3CaOFe₂O₃CaSO₄12H₂O) is the most susceptible to carbonation, followed by mono-sulfate aluminate hydrates (3CaOAl₂O₃CaSO₄12H₂O), while multi-sulfate sulfoaluminate hydrates (3CaOAl₂O₃3CaSO₄32H₂O) is the least vulnerable to carbonation, followed by silicate hydrates (5CaO6SiO₂5.5H₂O). The findings in this paper are significant in understanding thermodynamic mechanism of cement hydrates carbonation and seeking the solution to prevent cement hydrates from carbonation-induced deterioration.

Abstract: Self-compacting rock-fill concrete with natural and recycled aggregate can be applied in large structural components’production. According to the deep analysis of material's mechanical properties test data, the author makes a study on the strength mechanism of the concrete material. The results show that the concrete material essentially is concrete, and the concrete strength of large-sized natural aggregate and recycled aggregate are basically the same. However, due to the varieties in material production process and material shape as well as the influence of the mechanical properties and aggregate size, the strength mechanism of them is different. Effective control on mechanical properties of self-compacting rock-fill concrete and aggregate's appearances and shapes is helpful to the strength design of the self-compacting rock-fill concrete with large aggregate.

Abstract: Performance Based Design (PBD) is being developed as a more reasonable and flexible design method for a next generation of design method. To implement PBD, this paper presents a systematic approach (Bayesian method) for developing concrete material mixture design to satisfaction criterion level relationship. Satisfaction curves describe the probability of concrete reaching or exceeding different criterion level at specified levels of concrete material.

Abstract: The sustainable development is a new requirement put forward to urban planners in the current ecological environment. This paper describes the great significance of sustainable urban planning and also gives some measures to achieve the principles of sustainability in urban planning and construction.

Abstract: This paper discussed the experimental results of exploiting brick materials with iron tailing materials in Tanshang area. Through preparation of iron tailing bricks, the technical flow and production proportion was obtained. The results show that a burning-and steam curing-free brick product with a compressive strength of 28.30 MPa and Flexural strength of 5.63 MPa as the following: iron tailing; fly ash; sand; CaO; gypsum; cement. And long-term properties of a burning-and steam curing-free brick is also studied by experiments in this paper. Put forward a new technique of making materials with iron tailing. At the same time, the micro mechanism of iron tailing brick was also studied with X-Ray Diffractometer (XRD) and Scanning Electron Microscope (SEM).

Abstract: Portland cement, crushed stone, sand and superplasticizer were used to obtain a high strength concrete with a low water to binder ratio. Three steel fibers such as waste steel wire, corrugated steel fiber and arch steel fiber were added into the high strength concrete. The effects of the three fibers on the slump and the strengths such as compressive strength, tensile strength and bending strength were researched. The reduction of the slump and the increasing of the strength of the concrete with the arch steel fiber were the most significant due to the highest length-diameter ratio.

Abstract: This paper experimentally presents the effects of different bolted connection types on the seismic performance of column-tree steel moment connections used in moment resisting frames. Two full scale test specimens were fabricated and tested: one specimen with slip critical bolted beam splices and the other one with bearing type bolted beam splices. The bearing type splice specimen was expected an improved deformation capacity by means of bolt slippage. The experimental results showed that the slip critical splice specimen successfully developed ductile behavior without brittle fracture until 5% story drift ratio, however for the bearing type splice specimen, the beam bottom flange fractured at 4.0% story drift ratio due to stress concentration around the weld access hole area. However the energy dissipation capacity of the bearing type splice specimen was better than that of the slip critical splice specimen until 4.0% story drift ratio.

Abstract: The objective of this research was to investigate the influence of WMA additives on the properties of WMA binders through a series of laboratory testing such as viscosity, penetration, ductility, and softening points on the binders. The experimental design included the use of three WMA additives of Sasobit, Rediset, and Evotherm at a recommended content of 2, 2 and 0.6% respectively, two base binder sources, and one modified binder sources. The properties of WMA binders were compared to those of original asphalts without the additives as controls. Results from this study showed that: (1) Three WMA additives of Sasobit, Evotherm and Rediset increased the dynamic viscosity (60°C) of asphalt binders; (2) The additives of Evotherm and Rediset reduced the kinematic viscosity (130°C) of tested WMA asphalt binders. Adding 2 % Sasobit did not affect the kinematic viscosity; (3) Adding 2 % Sasobit reduced the penetration of WMA asphalt binder obviously. The most reduced rate of penetration is 22.7 % for SK base asphalt binder; (4) The WMA additives increased the softening point of WMA asphalt binders, except for the case with 0.6 % Evotherm. The effect of adding 2% Sasobit on the softening point of asphalt binders is the most significant, while the effect of adding 0.6 % Evotherm is the least; (5) adding 0.6 % Evotherm increased the ductility of warm asphalt binders by 28.6 %, while adding 2 % Sasobit reduced the ductility of warm asphalt binders obviously.