Index of Factors Influencing the Shear Strength of Asphalt Mixtures

Asphalt mixtures with high shear strength have great capability to resist perpetual deformation under high temperatures. We used a single penetration test to analyze the material design indexes for high performance asphalt mixtures. The test results show that the performance of the asphalt binder and the performance of the coarse aggregate, especially the fine aggregate, greatly affect the shear strength of asphalt mixtures. We also suggest that the coarse aggregate with a high aggregate particle index, fine aggregate with high angularity, and asphalt with high viscosity can increase sharply the shear strength of an asphalt mixture. Furthermore, the degree of compaction of an asphalt mixture should be controlled to guarantee excellent long term performance of asphalt pavement.     

Effects of Silane Coupling Agent on Road Performances of Composite Asphalt Mixtures

Aiming at the influence of mastics to aggregate adhesion on the performances of asphalt mixtures, three modeling techniques were adopted to prepare composite asphalt mixtures specimens. The influences of silane coupling agent on their road performances were studied and coupling mechanism was analyzed with Infrared Spectroscopy (IR) and Scanning Electron Microscope (SEM). The results indicated that the road performances at 7 day and 28 day curing age increased in the beginning and then decreased with the increase of silane coupling agent dosages. The road performances, such as freeze thaw splitting strength ratio, Marshall stability and compression modulus would be enhanced 10%~30% at 0.6% in asphalt emulsion mass. There was Si O Si chemical bond on interface between mastics and modified granite aggregate by Si O chemical bond of silane coupling agent. Surface of cement asphalt emulsion mastics was rough and its structure was dense. The cement asphalt emulsion mastics can be adhered to granite aggregate surface and mastics to aggregate interface structure is improved with silane coupling agent addition.     

Improvement of Alkaline Fillers on Anti-stripping Properties of Asphalt Concrete

Anti stripping is an important objective of asphalt concrete engineering.Effects of acidic and alkaline fillers on anti stripping of asphalt concrete, and the possibilities of solid powder wastes added into asphalt concrete as the filler, have been explored. The result shows that additions of alkaline filler such as limestone and EF material into asphalt concrete as the filler, compared to acidic fillers such as siliceous mineral filler and fly ash, can effectively enhance the Marshell stability, resilient modulus and split tensile strength for this mixture. Meanwhile, the anti-stripping ability of asphalt concrete would be greatly improved.     

Research on BRA Asphalt Mixture Pavement Performance Based on Containing BRA Rock

AH-70 road asphalt as the basis, Buton rock asphalt mixture pavement performance was studied by using six different Buton rock asphalt adding quality and six different AC20 aggregate gradation. The results show that Buton rock asphalt raw materials including the rock mineral significantly affects aggregate gradation and the pavement performance; reasonable choice OAC can significantly improve the road performance, and the road performance in the condition of 0.7%~1.3% optimum OAC is close to that of the SBS modified asphalt mixture, but Buton rock asphalt improving the water stability is limited; Buton rock asphalt optimum dosage is 23.7%, and Buton rock asphalt OAC and OAC of Buton rock asphalt raw material is almost the same.     

Characteristics of Asphalt Rubber Mortar and Aggregate Gradation Optimization Based on High Temperature Condition

To improve the performance of asphalt rubber mixture under high temperature, an optimal proposal was put forward which selected asphalt rubber mortar and aggregate gradation as the main objects. According to experimental tests, the anti rutting factors and phase angles of asphalt mortar was studied with different rations of filler bitumen. And then, with the characteristics of asphalt rubber, the optimal gradation was presented by means of the adjustment of aggregate gradation which chose dynamic stability and relative deformation as value indexes. The results shew that asphalt rubber mixtures would show an optimal high temperature performance if the following measures can be taken: (1) making an adjustment of ratio of filler bitumen to about 1.2; (2) replacing mineral powder with cement; (3) making an adjustment of aggregate gradation and lower the proportion of mineral powder based on SMA.     

Influence of Fine Recycled Aggregate on Physical and Mechanical Properties of Concrete

Based on a series of recycle process, waste concrete can be made into fine recycled aggregate which can be used completely or partly to compound concrete as a substitute for natural sand. But the special properties of fine recycled aggregate make the performance of concrete with fine recycled aggregate different from normal concrete. Characteristics of fine recycled aggregate and its influence on physical and mechanical properties of concrete are studied. On this basis, the influence of fine recycled aggregate on gas permeation properties, chloride permeability, and carbonation resistance of concrete are also studied. It is found that fine recycled aggregate produces a lot of defects in crushing preparation. And the compressive strength, the chloride permeability and the carbonation resistance of the concrete with fine recycled aggregate as substitution show difference from that of normal concrete.     

Application of Grey Clustering Method for Quality Grade Estimate of Recycled Concrete Coarse Aggregate

A comprehensive estimate scheme employed multiple parameters is proposed for quality grade of recycled concrete coarse aggregate based on grey clustering theory. In the scheme, seven parameters are selected as comprehensive evaluation indices according to Recycled Coarse Aggregate for Concrete of China. The parameters are apparent density, porosity, sturdiness, crushing index, micro-mist content, silt content and water absorption respectively. Secondly, weighted similarity method is adopted to determine the objective weight, and divide the quality grade into four grey ranks according to characteristics of grade assignment interval of the indices. Then, whitening weight function is employed to make an estimate model, by which the quality grade estimate result of recycled concrete coarse aggregate can be achieved through compute of grey clustering coefficients. Finally, a case study is adopted to verify the practicability of the proposed scheme.     

Properties of Steel Fiber Asphalt Concrete and Its Application

To prevent asphalt pavement from cracking under low temperatures and prolong its fatigue life, we tested the properties of a new type of steel fiber asphalt pavement. The tests evaluated Marshall stability, dynamic ruts, and cleavage strength under both low and normal temperature conditions. We also analyzed the anti-corrosion property of steel fiber and the factors affecting the properties of the steel fiber asphalt mixture. The steel fiber asphalt pavement was installed on a highway in Chongqing, P. R. China to investigate the construction art of the steel fiber asphalt mixture and examine its effect in field use. The test results and concrete use in the field show that the cleavage strength and flexibility of steel fiber asphalt concrete increase due to the action of steel fiber. We conclude that the anti-cracking capacity of asphalt pavement under low temperature conditions can be improved by steel fiber. The construction art of steel fiber asphalt pavement is the same as common asphalt pavement without the necessity of anti-corrosion processing for steel fiber. The research results are useful for pavement material selection in low temperature regions and heavy traffic road pavement designs.     

Study on flammability and flame-retardant mechanism of modified asphalt for tunnel pavement synergisticly flame retarded by BFR-Ti and ZB

Tunnel fire resistant asphalt can be prepared by mixing SBS modified asphalt and BFR-Ti/ZB. The combustion performances of the SBS modified asphalt/BFR-Ti/ZB and the synergism mechanism of the BFR-Ti and ZB are studied systematically through different methods, such as oxygen index (LOI) method, density of smoke, cone calorimetry, thermogravimetric analysis, etc. The result indicates that compared with SBS modifiedasphalt/BFR-Ti, BFR-Ti/ZB has synergistic effect which can make smoke density, heat release rate(HRR), mass loss rate(MLR) and effective heat of combustion(EHC) of SBS modified asphalt/BFR-Ti/ZB systems significantly decrease while the oxygen index of the SBS modified asphalt/BFR-Ti/ZB and the practice carbon content increase. SBS modified asphalt/BFR-Ti system has significant endothermic-antiflaming mechanism and condensed phase flame-retardance character. SBS modified-asphalt / BFR-Ti/ZB is based on the condensed phase flame-retardance mechanism while with synergistic flame-retardance and endothermic-antiflaming mechanism.     

Study on Influence of Fiber to Stability of Asphalt Concrete Pavement

The effect of fiber in asphalt mixtures has attracted general concern. For study of this problem, four kinds of fibers are chosen in this test. Asphalt and modified asphalt are adopted in asphalt mixtures AC-16I. The road performance influenced by additional fiber was analyzed impersonally,i, e. the stability of asphalt concrete under high temperature condition, anti-crack ability under low temperature condition, the water resistance and fatigue performance. It was shown through the research that the optimum asphalt content, air void rate, clearance rate of the mineral powder, saturation degree, and the flow value were increased and the density was decreased after adding the fiber. The road performance, such as the stability of asphalt concrete under high temperature condition, anti-crack ability under low temperature condition, water resistance and fatigue performance, was obviously improved,and the high temperature stability and fatigue performance improved most evidently. The fiber asphalt mixture performance reached and even exceeded the modified asphalt mixture performance. The modified asphalt performance after adding fiber would be improved more greatly.     

Rut resistance Properties of a Large stone Flexible Base under Heavy Loads

The rut resistance properties of large stone flexible bases are studied, taking into consideration heavy loads and using computer simulation and numerous indoor tests. In computer simulations of large stone flexible bases, a calculation method was formulated for predicting asphalt pavement rut under dynamic loads. The method was based on the coupling of vehicle dynamic loads and pavement surface unevenness. The results of indoor testing and three dimensional numeric calculation under dynamic loads are confirmed by tracking observation results of a test road. We conclude that the rut resistance properties of large stone flexible base asphalt pavement built using low grade asphalt and low crush value high performance aggregate with reasonable gradation is no worse than that of the semirigid base asphalt pavement, and that ruts mainly are caused by the lateral shear.     

Experiments on the asphalt fume suppression agents and properties of asphalt concrete with fume suppression agent

Through lots of screening tests, two fume suppression agents, i.e. SBS and nanometer CaCO3, which can reduce the asphalt fume without affecting the properties of asphalt, are screened from seven additives. The best ratio of two agents for suppressing fume is presented by contrast tests of fume suppression effect, and the fume can be reduced about 30%. The properties of asphalt concrete with fume suppression agents and the mechanism of SBS and nanometer CaCO3 reducing the asphalt fume are investigated. The research findings are useful for reducing the asphalt fume in bad ventilation condition of channel pavement and urban road pavement construction.     

Asphalt pavement structure design of expressway on soft soil foundation

Non homogenous settlement will occur while the expressway is constructed on soft ground. The differential settlement can cause the bigger additional stress inside the asphalt pavement structure accelerating bituminous pavement destruction. Therefore,we must choose reasonable pavement structure when constructing road on soft base in order to reduce the influence on surface layer structure from the differential settlement. Based on ABAQUS finite element method and through analysis, this article draws the conclusion that establishing unbound graded aggregate sandwich structure under the asphalt pavement structure can effectively reduce the horizontal additional stress of the stress controled layer and better prevent crack reflection which is beneficial for constructing the asphalt pavement structure on the soft ground.     

Properties of Concrete Made from Composite Fine Aggregate

In this paper,the workabiltiy,strength.Shrinkage and creep of concrete made from composite fine aggregate (CFC) were studied. Resuits show that the properties of CFC is familiar to those of concrete made from natural middle-size of fine aggregate when the mixture proportion is the same.The composite fine aggregate composed of man-made limestone sand and natural super-fine sand could be used for producing flowing corcrete.     

Rubber Powder Modified Frost Resistance of Recycled Aggregate Concrete

Utilizing relative dynamic elastic modulus and weight loss of concrete as evaluation indices, the frost resistance of concrete with 0.45 water-cement ratio and different recycled aggregate replacement proportions was studied in the water and 3.5% sodium chloride solution. The mass proportions of recycled aggregate are 25%, 50% and 75%, respectively. Furthermore, the frost resistance of the modified concrete with 5% and 10% rubber powder volume fractions replacing fine aggregates was studied. The results show that: the frost resistance of concrete decreases with the increase of recycled aggregate, when the recycled aggregate mass fractions are 25% and 50%, its influence on the frost resistance of concrete is little, and mixing rubber powders can effectively improve the frost resistance of concrete; when the recycled aggregate mass fraction reaches 75%, its effect on the frost resistance of concrete is significant, and mixing rubber powders has certain improvement effect, but compared with the benchmark group of concrete the maximum freeze-thaw cycles decreases more than 30%. In water frozen test, the weight loss is small and the relative dynamic elastic modulus loss is quite obvious. The frost resistance is better when adding 5% volume fraction of rubber powders. In salt frozen test, the main characteristic is the weight loss exceeds the requirements. The frost resistance is better when adding 10% volume fraction of rubber powders. The improvement effect of rubber powder to the frost resistance of concrete in salt solution is much better than that in water.     

Meso-scale numerical investigation on the crack process of concrete cover induced by rebar non-uniform corrosion

Concrete cover cracking induced by corrosion of steel reinforcement is a major influencing factor for durability and serviceability of reinforced concrete structures. In order to investigate the cracking process of concrete cover induced by rebar corrosion, the heterogeneity of concrete meso-structure and non-uniformity of rebar corrosion are accounted for. The undamaged concrete is assumed to be a three-phase composite material composed of aggregate, mortar matrix and the interfacial transition zone (ITZ). And a concrete random aggregate structure is established for the study on the mechanical behavior of the non-uniform radial corrosion expansion. In the present simulations, non-uniform radial displacement is adopted to simulate the non-uniform corrosion of the rebar; the plasticity damaged model is used to describe the mechanical behavior of the mortar matrix and the ITZ, and the aggregate is assumed to be elastic. The cracking of concrete cover due to the non-uniform corrosion of the middle located rebar is numerically simulated. The comparison of the analysis and the test result on failure pattern of cover concrete shows fairly good agreement. And then the failure patterns under uniform corrosion and non-uniform corrosion obtained from the macro-scale homogeneous model and the meso-scale heterogeneous model are compared. Furthermore, the influences of concrete cover thickness and rebar diameter on the failure pattern of concrete cover, the expansive pressure and the corrosion rate of the rebar when cover concrete cracks are investigated.     

Preliminary Discussion on Mixing Design of Porous Concrete

Porous concrete is an eco-concrete with high porosity and high strength,whose application was restricted to some extent,because there is lack of appropriate and unitive mixing design method.According to the features of porous concrete,proportion design idea of porous concrete whose major design parameter was porosity and strength was satisfied by changing variety of cementing material and aggregate size.The design method of porous concrete was that the raw materials were selected according to design requirement at first,secondly,aggregate dosage per unit volume of porous concrete was calculated,thirdly,dosage of cementing material was calculated by apparent density of aggregate and porosity of design requirement,finally,cement dosage of the unit physical volume and water dosage were calculated by water cement ratio deter mined by requirement of forming process.The test result indicated that this mixing design method of porous concrete was reliable and feasible.     

上海市青浦区生态用地建设评价指标体系研究

生态用地是生态环境的载体,其在生态环境保护和农业的可持续发展中具有重要的意义。采用频度分析法筛选指标,应用AHP-Delphi法确定各指标的权重,并根据上海市青浦区2020年的规划目标确定了一些基准值,在此基础上建立了上海市青浦区生态用地的综合评价指标体系,并对研究区生态用地建设的现状进行了综合的分析与评价,结果表明：该区评价等级处于Ⅲ级,具有很大的建设优化潜力,与实际调查情况相符。文中的分析指标体系具有极强的针对性和可靠性等特点。     

The Effect of Water-Cement Ratio on the Plastic Shrinkage Cracking of Lightweight Aggregate Concrete

In this paper, the characteristic of the plastic shrinkage cracking of the lightweight aggregate concrete (LWAC) was studied under the condition of prescribed quantity of cement and aggregate and was compared with that of the normal aggregate concrete (NC) with the same proportion of materials for the LWAC. The results suggested that the water evaporation quantity in the concrete became larger with the increase of w/c, and water evaporation velocity reached maximum value around two hours. When the water-cement ratio was low, the area of the plastic shrinkage cracking of LWAC was large and when w/c was 0.40, the area reached the maximum value and then became smaller with the increase of w/c.     

Information fusion for tactile sensor array signals

According to the solubility parameters of aged asphalt system, the effect of the recycling agent components on the compatibility of aged asphalt was studied by using the molecular dynamics method. And the mechanism between the recycling agent and the aged asphalt is investigated based on the interaction energies analysis. The results show that the aromatic is helpful to improve the compatibility of aged asphalt, and the more the aromatic is, the better the recycling effect would be. However, the effect of saturate is negative. These results are consistent with the experimental data. With the increase in dosage, the interaction energy between aromatic and aged asphalt increases significantly because of their bigger electrostatic interaction energy and smaller Van der Waals forces. However, the interaction energy between the saturate and aged asphalt shows no obvious change in which the electrostatic and van der Waals interaction energy is almost the same. The main factor for aged asphalt recycling is electrostatic interaction energy between molecules.