公路工程水泥混凝土原材料的试验检测及质量控制分析

混凝土是现代工程建设常用的一种施工材料,它有着抗压、抗寒以及耐腐蚀的优点。水泥混凝土对公路工程施工质量的影响是很大的,所以采取措施来提升混凝土的施工质量是非常有必要的。而要想了解哪些因素会对混凝土质量产生影响,其作用如何,就需要检测它的原材料,确保材料的各项指标也是符合相关比奥运与要求的,以此来保证混凝土的施工质量。

Combined effect of steel fibres and steel rebars on impact resistance of high performance concrete

The impact properties of normal concrete (NC) and reinforced concrete (RC) specimens,steel fibre reinforced concrete (SFRC) specimens and RC+SFRC specimens with different steel fibre dosages were investigated with the drop-weight impact test recommended by ACI Committee 544.The results indicate that the number of blows to final failure is greatly increased by addition of steel fibres.Moreover,the combination of steel fibres and steel rebars demonstrates a significant positive composite effect on the impact resistance,which results in the improvement in impact toughness of concrete specimens.In the view of variation of impact test results,the two-parameter Weibull distribution was adopted to analyze the experimental data.It is proved that the probabilistic distributions of the blows to first crack and to final failure of six types of samples approximately follow two-parameter Weibull distribution.

Air-void parameters measurement of fresh concrete and hardened concrete

Air content, spacing factor and specific surface of fresh concrete and hardened concrete with different air contents, slumps and mineral admixtures (fly ash, slag, fly ash + slag, fly ash + slag + silica fume composite) were studied by the air-void analyzer (AVA) method and the microscopical method. The correlations between the test results obtained from different methods were analyzed. The results show that, there is a close correlation of air content and spacing factor between the fresh concrete and the hardened concrete, but the specific surface correlation is weak. The air content of concrete measured by the AVA method is smaller than that of the pressure method and the microscopical method, because AVA device captures only the air voids with the size smaller than 3 mm. Spacing factor of the fresh concrete measured by the AVA method is greater than that of the hardened concrete measured by the microscopical method, while the specific surface is smaller. When the criterion of 4%-7% air content measured by the pressure method and microscopical method is acceptable for concrete freezing-thawing (F-T) durability in cold weather, the air content measured by the AVA method should be 2.4%-4.6%. For the concrete F-T durability, when the criterion of the spacing factor measured by the microscopical method is 300 μm, the spacing factor measured by the AVA method should be 360 μm.

Effect of Recycled Coarse Aggregate on Concrete Compressive Strength

The effect of recycled coarse aggregate on concrete compressive strength was investigated based on the concrete skeleton theory. For this purpose, 30 mix proportions of concrete with target cube compressive strength ranging from 20 to 60 MPa were cast with normal coarse aggregate and recycled coarse aggregate from different strength parent concretes. Results of 28-d test show that the strength of different types of recycled aggregate affects the concrete strength obviously. The coarse aggregate added to mortar matrix plays a skeleton role and improves its compressive strength. The skeleton effect of coarse aggregate increases with the increasing strength of coarse aggregate, and normal coarse aggregate plays the highest, whereas the lowest concrete strength occurs when using the weak recycled coarse aggregate. There is a linear relationship between the concrete strength and the corresponding mortar matrix strength. Coarse aggregate skeleton formula is established, and values from experimental tests match the derived expressions.

Degradation of bond between steel bar and freeze-thaw concrete after electrochemical chloride extraction

The effect of electrochemical chloride extraction （ECE） on bond strength between steel bar and freeze-thaw concrete contaminated by chloride was experimentally investigated for beam specimens with dimensions of 100 mm × 100 mm × 400 ram. During the experiment, 3% NaC1 （vs mass of cement, mass fraction） was mixed into concrete to simulate chloride contamination, and the specimens experienced 0, 25, 50, 75 freeze-thaw cycles before ECE. In the process of ECE, different current densities and durations were adopted. It is indicated that the bond strength between reinforcement and concrete decreases with the increase of freeze-thaw cycles; the more the current and the electric quantity of ECE are, the more the loss of bond strength is; and the largest loss is up to 58.7%. So, it is important to choose proper parameters of ECE for the reinforced concrete structures contaminated by chloride and subjected to freeze-thaw cycles.

Numerical Simulation of Response of SRC Columns Subjected to Blast Loading

The dynamic characteristics and failure modes of steel reinforced concrete (SRC) columns subjected to blast loading are complicated because of the transient stress wave in the SRC columns and the interaction between steel and concrete. This paper presents a numerical simulation of the response of SRC columns subjected to blast loading using hydrocode LS-DYNA. In the numerical model, a sophisticate concrete material model (the Concrete Damage Model) is employed with consideration of the strain rate effect and the damage accumulation. An erosion technique is adopted to model the spalling process of concrete. The possible failure modes of SRC columns are evaluated. It is observed that the failure of SRC columns subjected to blast load can generally be classified into three modes, namely, a direct failure in concrete body due to the stress wave, a transverse shear failure near the support sections due to the high shear force, and a flexural failure pertaining to large local and global deformation of the reinforcing steel.

Mechanical properties of pervious cement concrete

Compressive and flexural strength,fracture energy,as well as fatigue property of pervious cement concrete with either supplementary cementitious materials (SCMs) or polymer intensified,were analyzed.Test results show that the strength development of SCM-modified pervious concrete (SPC) differs from that of polymer-intensified pervious concrete (PPC),and porosity has little effect on their strength growth.PPC has higher flexural strength and remarkably higher flexural-to-compressive strength ratio than SPC at the same porosity level.Results from fracture test of pervious concrete mixes with porosity around 19.5% show that the fracture energy increases with increasing the dosage of polymer,reflecting the ductile damage features rather than brittleness.PPC displays far longer fatigue life than SPC for any given failure probability and at any stress level.It is proved that two-parameter Weibull probability function describes the flexural fatigue of pervious concrete.

Performance of Cross-Shaped Concrete Columns Confined by Stirrups

The stress-strain curves of confined concrete were obtained based on tests of seven cross-shaped columns confined by stirrups under axial load. The experiment results showed that the strength and deformation of confined concrete can be enhanced effectively by stirrups for cross-shaped columns. Compared with the non-confined concrete, when the stirrup characteristic value is in the range of 0.046-0.230, the confined concrete compressive strengths has an increase of 8%-43%, and the strain corresponding to the peak stress of confined concrete has an increase of 25%-195%. According to the test results, the effects of stirrup characteristic and stirrup spacing on the compressive strength and strain of confined concrete were analysed. It is shown that the compressive strength of confined concrete has a linear relationship with the product of stirrup characteristic value and stirrup effective restraint coefficient, and the strain corresponding to the peak stress of confined concrete has a nonlinear relationship with the product of stirrup characteristic value and stirrup effective restraint coefficient. The stress-strain curve equation of confined concrete was proposed for cross-shaped columns, and the calculated curves are in good agreement with the experimental curves.

Experimental research on ultimate bearing capacity of grouted-round-steel-tube N-joint

As an important structural member in self-supporting concrete floor during construction,encased steel truss-concrete composite beam has brilliant prospect in outer-jacketing structures for adding stories or mega frame structures.Compared with encased angle truss,encased round steel tube truss can facilitate layout of itself in column and facilitate layout and anchorage of prestressed reinforcement placed horizontally.N-joint is wildly used in encased steel truss.For cave-in failure easily occurs in hollow steel-tube joint,the idea that the chord is grouted to increase cave-in bearing capacity of hollow tube is proposed.Test results of 8 grouted-round-steel-tube N-joints from the beginning of loading to failure are reported.Mechanical property and failure mode of this kind of truss joint are analyzed,and the formulas of ultimate bearing capacity of the joint corresponding to different failure modes are established.All these can provide basic data for spreading encased steel truss-concrete composite beam.

Improved methods for decreasing stresses of concrete slab of large-span through tied-arch composite bridge

Mechanical behavior of concrete slab of large-span through tied-arch composite bridge was investigated by finite element analysis (FEA). Improved methods to decrease concrete stresses were discussed based on comparisons of different deck schemes, construction sequences and measures, and ratios of reinforcement. The results show that the mechanical behavior of concrete slab gets worse with the increase of composite regions between steel beams and concrete slab. The deck scheme with the minimum composite region is recommended on condition that both strength and stiffness of the bridge meet design demands under service loads. Adopting in-situ-place construction method, concrete is suggested to be cast after removing the full-supported frameworks under the bridge. Thus, the axial tensile force of concrete slab caused by the first stage dead load is eliminated. Preloading the bridge before concrete casting and removing the load after the concrete reaching its design strength, the stresses of concrete slab caused by the second stage dead load and live load are further reduced or even eliminated. At last, with a high ratio of reinforcement more than 3%, the concrete stresses decrease obviously.

Adsorption properties of CFBC ash-cement pastes as compared with PCC fly ash-cement pastes

Circulating fluidized bed combustion （CFBC） ash can be potentially used as supplementary cementitious materials for concrete production due to its desirable pozzolanic activity. The adsorption properties of CFBC ash-cement pastes were studied, and ordinary pulverized coal combustion （PCC） fly ash-cement pastes were used as control. The water-adsorption and superplasticizer （SP）-adsorption properties of the pastes were evaluated by water demand and UV-visible absorption spectroscopy respectively. The results show that CFBC ash-cement system has greater compressive strength as compared with PCC fly ash-cement system at a given curing age, although the water demand of the former is significantly higher than that of the latter. CFBC ash-cement pastes possess higher adsorption ability of aliphatic SP than PCC fly ash-cement pastes and the adsorption amount increases with an increase in ash replacement ratio. CFBC ash- cement pastes exhibit lower workability with higher slump loss. It is concluded that CFBC ash can be potentially used as supplementary cementitious material in concrete production, but the mix design of CFBC ash concrete needs to be appropriately adjusted. It is suggested that CFBC ash is used for the production of the concrete needing low flowability.

Uplift behavior and load transfer mechanism of prestressed high-strength concrete piles

Prestressed high-strength-concrete (PHC) tube-shaped pile is one of the recently used foundations for soft soil. The research on uplift resistance of PHC pile is helpful to the design of pile foundations. A field-scale test program was conducted to study the uplift behavior and load transfer mechanism of PHC piles in soft soil. The pullout load tests were divided into two groups with different diameters, and there were three piles in each group. A detailed discussion of the axial load transfer and pile skin resistance distribution was also included. It is found from the tests that the uplift capacity increases with increasing the diameter of pile. When the diameter of piles increases from 500 to 600 mm, the uplift load is increased by 51.2%. According to the load-displacement (Q-S) curves, all the piles do not reach the ultimate state at the maximum load. The experimental results show that the piles still have uplift bearing capacity.

Research on the influence of the fly ash on the concrete carbonation

The influence of fly ash on the fresh properties, mechanical properties and carbonation properties were studied in this paper. The performance of a kind of curing agent which was applied to the hardened concrete surface was evaluated. Incorporating large volume of fly ash will risk the concrete carbonation. The curing agent could prevent the concrete carbonation, and the mechanism was explained.

Analysis and behaviour of FRP-confined short concrete columns subjected to eccentric loading

Fibre-reinforced polymer (FRP) composites were widely utilized in civil engineering structures as the retrofit of reinforced concrete (RC) columns. To design FRP jackets safely and economically, the behaviour of such columns should be predicted first. This paper is concerned with the analysis and behaviour of FRP-confined RC circular and rectangular short col- umns subjected to eccentric loading. A simple design-oriented stress-strain model for FRP-confined concrete in a section analysis was first proposed. The accuracy was then proved by two test data. Following that, a parametric study including amount of FRP confinement, FRP strain capacity, unconfined concrete strength and shape of column section is provided. Some conclusions were obtained at the end of the paper. The work here will provide a comprehensive understanding of the behaviour of FRP-confined concrete columns. The simplicity of the model also enables a simple equivalent stress block to be developed for direct use in practical design.

Chloride ion penetration into concrete under hydraulic pressure

The lining concrete of subsea tunnel services under combined hydraulic pressure, mechanical and environmental loads. The chloride ion and water penetrations into concrete under hydraulic pressure were investigated. The experimental results indicate that the water penetration depth, chloride ion transportation depth, and the concentration of chloride ion ingression into concrete increase with raised hydraulic pressure and hold press period. But the chloride ion transportation velocity is only 53% of that of water when concrete specimens are under hydraulic pressure. The chloride transportation coefficient of concrete decreases with hold press period as power function. And that would increase 500% 600% in chloride transportation coefficient when the hydraulic pressure increases from 0 to 1.2 MPa. The hydraulic pressure also decreases the bound chloride ion of concrete to about zero. Besides, the low water-cementitions materials and suitable content of mineral admixture(including fly ash and slag) improve the resistance capacity of chloride penetration, and binding capacity of concrete under hydraulic pressure.

Proposition of a New Type of Jointless System For Existing Concrete Bridges

Since 1990s, the use of deicing salts （i.e., chlorides） has dramatically increased in areas with heavy snowfall in Japan. As a result, the water mixed with salts has accelerated the damage of the reinforced concrete （hereafter, RC） structures. Recently conducted inspection results of RC bridges have reported that many of the damages or deteriorations are observed at the girder ends and abutments This is caused from the water leakage due to the aged expansion joints. In general, the cost for repairing the damaged RC structures is much higher than that for renewing the expansion joints. Therefore, to prevent these damages, we developed a new highly durable jointless system, named RC plug joint, for existing RC bridges with a bridge length less than 40 meters. The RC plug joint connects the abutment＇s backwall to the superstructure＇s deck using reinforcing steel bars and fiber reinforced concrete. The newly developed RC plug joint system can prevent water leakage and allow for a smooth ride of vehicles at the joint. This paper will explore and discuss the development of the RC plug joint, analysis of conducted investigations, and future installation methods.

Evaluation method of cracking resistance of lightweight aggregate concrete

The cracking behavior of lightweight aggregate concrete(LWAC) was investigated by mechanical analysis, SEM and cracking-resistant test where a shrinkage-restrained ring with a clapboard was used. The relationship between the ceramsite type and the cracking resistance of LWAC was built up and compared with that of normal-weight coarse aggregate concrete(NWAC). A new method was proposed to evaluate the cracking resistance of concrete, where the concepts of cracking coefficient ζt(t) and the evaluation index Acr(t) were proposed, and the development of micro-cracks and damage accumulation were recognized. For the concrete with an ascending cracking coefficient curve, the larger Acr(t) is, the lower cracking resistance of concrete is. For the concrete with a descending cracking coefficient curve, the larger Acr(t) is, the stronger the cracking resistance of concrete is. The evaluation results show that in the case of that all the three types of coarse aggregates in concrete are pre-soaked for 24 h, NWAC has the lowest cracking resistance, followed by the LWAC with lower water absorption capacity ceramsite and the LWAC with higher water absorption capacity ceramsite has the strongest cracking resistance. The proposed method has obvious advantages over the cracking age method, because it can evaluate the cracking behavior of concrete even if the concrete has not an observable crack.

Effects of Vibration Technology and Polyvinyl Acetate Emulsion on Microstructure and Properties of Expanded Polystyrene Lightweight Concrete

To prevent expanded polystyrene （EPS） beads from rising up to the surface in the molding process of EPS lightweight concrete, vibration with pressure was applied and the polyvinyl acetate （PVA） emulsion was adopted to improve its mechanical properties. The mechanical properties, thermal properties and durability of EPS lightweight concrete were tested. The microstruetures of EPS lightweight concrete were observed by scanning electron microscope （SEM）. Vibration with pressure reduces the number of small cracks. The 180 d compressive strength and flexural strength increase obviously as a large amount of PVA was added. The mixed amount of PVA has no obvious influence on the thermal performance when it is not more than 10% of the cement. Vibration with pressure and surface modification of EPS beads by PVA improve the combination of EPS beads with cement stone and the mechanical properties of EPS lightweight concrete.

A Survey of Steel Arch Bridges in China

A review of the current status and progress of steel arch bridges in China is presented in this paper. The existing steel arch bridges in China were analyzed in terms of steel material, span, structure type, main arch rib form and construction method. The comparison with CFST arch bridges and RC arch bridges is also conducted. It is shown that steel arch bridge has gain rapid development in China since 2000, characterized by long main spans. As for the span, most of the steel arch bridges have a span less than 250 m, while when the span exceeds 350 m, steel arch bridges are strongly competitive against CFST or RC arch bridges. Over 80% of the bridges are through and half-through bridge types, and the arch ribs are hingeless structures. The rise-to-span ratios of the arches are mainly between 1：4 and 1： 5. Most of the arches use solid box ribs, and a small portion of arches use truss ribs in which box sections are mostly adopted for the truss members. The cantilever method and scaffolding method are the two main construction methods used, but some other construction methods have also been developed.

Experimental investigation of axially loaded steel fiber reinforced high strength concrete-filled steel tube columns

An experimental study on the compressive behavior of steel fiber reinforced concrete-filled steel tube columns is presented. Specimens were tested to investigate the effects of the concrete strength, the thickness of steel tube and the steel fiber volume fraction on the ultimate strength and the ductility. The experimental results indicate that the addition of steel fibers in concrete can significantly improve the ductility and the energy dissipation capacity of the concrete-filled steel tube columns and delay the local buckling of the steel tube, but has no obvious effect on the failure mode. It has also been found that the addition of steel fibers is a more effective method than using thicker steel tube in enhancing the ductility, and more advantageous in the case of higher strength concrete. An analytical model to estimate the load capacity is proposed for steel tube columns filled with both plain concrete and steel fiber reinforced concrete. The predicted results are in good agreement with the experimental ones obtained in this work and literatures.