泥水平衡盾构新型不分散泥水材料试验研究

鉴于目前大多采用的分散泥水体系有废弃泥浆排放量大、浆液指标控制难、新浆材料用量大等不足,在室内试验与现场试验的基础上,开发了新型配方的不分散泥水材料.新配置的泥水材料具有不分散性、触变性、抑制性、携带性等特点,各个配方在工程相关的要求上表现良好,泥浆回收率可达90%以上;新型材料泥浆对携带细小颗粒作用明显,试验数据证明理论上的泥水网状结构是存在的;经过循环后,泥水黏度值基本不变.

大型泥水盾构泥水材料体系及其调控技术

结合上海人民路越江双线隧道工程实际,探讨了不同泥水材料体系对掘进土层适应性问题,同时自主开发出提高粘度和砂性土层适应性更强的新型高效泥水材料。详细介绍了针对不同土层属性相适应泥水材料体系调控方法:两线隧道浆液调配法、补充工程废浆(黏土粉)法、黏土粉新浆匹配法。

泥水盾构穿越高渗透性地层泥浆配制研究

本文从泥水盾构基本原理、泥浆的作用出发,系统地阐述了适合泥水盾构掘进用泥浆的基本性质及测定方法,泥浆材料的种类与选取原则、制配情况。该研究对类似工程中泥浆配制有重要的指导意义。

Enhanced photocatalytic performance of cementitious material with TiO_2@Ag modified fly ash micro-aggregates

A TiO2 photocatalyst is coated on the surface of a zeolite fly ash bead（ZFAB） to improve its dispersability and exposure degree in a cement system.The application of Ag particles in TiO2/ZFAB modified cementitious materials is to further enhance the photocatalytic performance.Various Ag@TiO2/ZFAB modified cementitious specimens with different Ag dosages are prepared and the characteristics and photocatalytic performance of the prepared samples are investigated.It is observed that the multi-level pore structure of ZFAB can improve the exposure degree of TiO2 in a cement system and is also useful to enhance the photocatalytic efficiency.With an increment of the amounts of Ag particles in the TiO2/ZFAB modified cementitious samples,the photocatalytic activities increased first and then decreased.The optimal Ag@TiO2/ZFAB modified cementitious sample reveals the maximum reaction rate constant for degrading benzene（9.91×10^-3 min^-1）,which is approximately 3 and 10 times higher than those of TiO2/ZFAB and TiO2 modified samples,respectively.This suggests that suitable Ag particles coupled with a ZFAB carrier could effectively enhance the photocatalytic effects and use of TiO2 in a cement system.Thus,ZFAB as a carrier could provide a potential method for a high efficiency engineering application of TiO2 in the construction field.

Experimental and numerical study on flexural behaviors of steel reinforced engineered cementitious composite beams

To investigate the flexural behaviors of steel reinforced engineered cementitious composite （ECC） beams, the behaviors of the steel reinforced ECC beam and the conventional steel reinforced concrete beam subjected to flexural load are experimentally compared. The experimental results show that the flexural strength and ductility of the steel reinforced ECC beam are 24.8% and 187.67% times larger than those of the steel reinforced concrete beam, and the substitution of concrete with ECC can significantly delay the propagation of cracks. Additionally, a simplified constitutive model of the ECC material is used to simulate the flexural behaviors of beams by the finite element analysis （FEA）. The results show a good agreement between the simulation and test results. The crack width of the steel reinforced ECC beam can be limited to 0.4 mm under the service load conditions. The application of ductile ECC can significantly increase the flexural performance in terms of flexural strength, deformation capacity and ductility of the beams.

Development of engineered cementitious composites with local ingredients

In order to reduce the cost of high performance polyvinyl alcohol（PVA） fiber reinforced cementitious material（called engineered cementitious composites,ECC）,a ductile ECC material is developed using domestic PVA fibers along with other local ingredients,such as fly ash,cement and sand.In addition to the economic analysis of ECC,the four-point bending test and the optical microscope are employed to investigate the deflection capacity of ECC,its crack width and the occurrence of the self-healing phenomenon.The experimental results suggest that ECC made with domestic ingredients exhibits larger deformability and the average crack width is controlled around 60 μm.Furthermore,the self-healing behavior is observed in cracks of the specimens after cycles of wet and dry curing.The economic analysis shows that the cost of ECC can be greatly reduced via employing domestic PVA fibers.It is,therefore,feasible to produce low cost ECC material employing domestic PVA fibers,while simultaneously retaining high material ductility.

Fracture suppression at steel/concrete connection zones by ECC

In order to avoid brittle fracture failure, a ductile engineered cementitious composite （ECC） was attempted in steel/concrete connection zones to replace normal concrete. The influence of the ECC material ductility on connection failure modes and structural performance was investigated via the pushout test of stud/ECC connection, the pullout test of two-dimensional anchor bolt/ECC connection and the finite element modeling （FEM）. The experimental results suggest that the micromechanically designed ECC with a tensile ductility 300 times that of normal concrete switches the brittle fracture failure mode to a ductile one in steel connection zones. This modification in material behavior leads to higher load carrying capacity and structural ductility, which is also confirmed in FEM investigation. The enhancement in structural response through material ductility engineering is expected to be applicable to a wide range of engineering structures where steel and concrete come into contact.

Fracture Properties of Cement Composites Reinforced with Steel Polypropylene Hybrid Fibres

Polypropylene fibres and three sizes of steel fibres reinforced concrete are discussed. The total fibres content ranges from 0 4%-0 95% by volume of concrete. A four point bending test is adopted on the notched prisms with the size of 100?mm×100?mm×500?mm to investigate the effect of hybrid fibres on crack arresting. The research results show that there is a positive synergy effect between large steel fibres and polypropylene fibres on the load bearing capacity in the small displacement range. But this synergy effect disappears in the large displacement range. The large and strong steel fibre is better than soft polypropylene fibre and small steel fibre in the aspect of energy absorption capacity in the large displacement range. The static usage limitation for the hybrid fibres concrete with “wide peak' or “multi peaks' load CMOD pattern should be carefully selected. The ultimate load bearing capacity and the crack width or CMOD at this load level should be jointly considered.

Flexural behaviors of steel reinforced ECC/concrete composite beams

An engineered cementitious composite （ECC） is introduced to partially substitute concrete in the tension zone of a reinforced concrete beam to form an ECC/reinforced concrete （RC） composite beam, which can increase the ductility and crack resisting ability of the beam. Based on the assumption of the plane remaining plane and the simplified constitutive models of materials, the stress and strain distributions along the depth of the composite beam in different loading stages are comprehensively investigated to obtain calculation methods of the load-carrying capacities for different stages. Also, a simplified formula for the ultimate load carrying capacity is proposed according to the Chinese code for the design of concrete structures. The relationship between the moment and curvature for the composite beam is also proposed together with a simplified calculation method for ductility of the ECC/RC composite beam. Finally, the calculation method is demonstrated with the test results of a composite beam. Comparison results show that the calculation results have good consistency with the test results, proving that the proposed calculation methods are reliable with a certain theoretical significance and reference value.

Flexural behaviors of double-reinforced ECC beams

In order to investigate the flexural behaviors of engineered cementitious composites （ECC）, theoretical and experimental researches are done on flexural doublereinforced ECC beams. Based on the assumption of the plane section remaining plane in bending and simplified constitutive models of materials, the calculation methods of load carrying capacities for different critical stages are obtained. Then, these calculation methods are demonstrated by comparing the test results with the calculation results. Finally, based on the proposed theoretical formulae, the effects of the compression strength, compression strain and tension strength of ECC, and the reinforcement ratio on the flexural behaviors of double-reinforced ECC beams are analyzed. The calculated and measured results are in good agreement, which indicates that the theoretical model can be used to predict the momentcurvature response of steel reinforced ECC beams. And the results of parametric studies show that the increase in the compression strength of ECC can greatly improve the flexural performance of beams; the increase in the ultimate compression strain can significantly improve the ultimate curvature and ductility, but has little effect on the load bearing capacity of beams. little effect on the flexural The tensile strength of ECC has behaviors of ECC beams. The increase in the steel reinforcement ratio can lead to significant improvement of the load bearing capacity and the stiffness of beams, but a degradation of the ductility of beams. The theoretical model and parameter analysis results in this paper are instructive for the design of steel reinforced ECC beams.

Mechanical behaviors of steel reinforced ECC / concrete composite columns under combined vertical and horizontal loading

In order to improve the load capacity, seismic performance and performance-cost ratio of the columns, the concrete at the base of reinforced concrete （RC） columns is substituted with engineered cementitious composites （ECC） to form ECC/RC composite columns. Based on the existing material properties, the mechanical behaviors of the ECC columns, ECC/RC composite columns and RC columns were numerically studied under combined vertical and horizontal loading with the software of ATENA. Then, the failure mechanism of ECC columns and ECC/RC composite columns were comprehensively studied and compared with that of the RC columns. Then, the effects of the height of the ECC, the axial compression ratio, and the transverse reinforcement ratio on the mechanical behaviors of the composite or the ECC column are studied. The calculation results show that the ultimate load capacity, ductility and crack resistance of the ECC or ECC/RC composite columns are superior to those of the RC columns. The ECC/RC composite column with a height of the ECC layer of 1.2h （ h is the height of the cross section） can achieve similar mechanical properties of a full ECC column. With high shear strength, ECC can undertake the shear force and significantly reduce the amount of stirrups, avoiding construction issues and promoting its engineering application.

Influence of different curing regimes on the microstructure and macro performance of UHPFRCC

This study investigates the influence of different curing regimes on the microstructure and macro properties of ultra-high performance fiber reinforced cementitious composite （UHPFRCC）, and aims to discover whether it is possible to produce qualified UHPFRCC using different curing regimes. A control mix of UHPFRCC is prepared. The mechanical performance and the short-term durability of the UHPFRCC matrix under three curing regimes are studied. In addition, the microstructures of the UHPFRCC matrix with different curing conditions are analyzed by combining scanning electron microscopy （SEM） and mercury intrusion porosimetry （MIP）. The results explore how different UHPFRCC curing regimes affect its microstructure and how the microstructure affects its macro behavior. Heat and steam curing for 3 d is succeeded to produce the UHPFRCC with nearly the same mechanical properties and durability as those of the 90 d standard curing. However, the heat cured UHPFRCC does not show great resistance to chloride-ion penetration.

A new clay-cement composite grouting material for tunnelling in underwater karst area

A new clay-cement composite grouting material (CCGM) for tunnelling in underwater karst area was developed through the excellent synergistic interactions among cement, clay, meta-aluminate and lignin. The probable formation mechanism of the material was proposed based on a series of experimental tests. The results show that with an optimal mass ratio (2:1:1:0.024) for water, cement, clay and additives, the obtained CCGM displayed an excellent grouting performance for karst in an underwater condition. Compared with neat cement grouts and clay-cement grouts, CCGM has faster gel time, lower bleeding rate and bulk shrinkage rate, greater initial viscosity, and a strong resistance to water dispersion. A successful engineering application indicates that CCGM not only fulfils a better grouting performance for karst in underwater conditions but also reduces the engineering cost and environmental pollution.

Effect of graphene on mechanical properties of cement mortars

Functionalized graphene nano-sheets(FGN) of 0.01%-0.05%(mass fraction) were added to produce FGN-cement composites in the form of mortars. Flow properties, mechanical properties and microstructure of the cementitious material were then investigated. The results indicate that the addition of FGN decreases the fluidity slightly and improves mechanical properties of cement-based composites significantly. The highest strength is obtained with FGN content of 0.02% where the flexural strength and compressive strength at 28 days are 12.917 MPa and 52.42 MPa, respectively. Besides, scanning electron micrographs show that FGN can regulate formation of massive compact cross-linking structures and thermo gravimetric analysis indicates that FGN can accelerate the hydration reaction to increase the function of the composite effectively.

Effects of superabsorbent polymer particles on flexural properties and self-healing behavior of ECC

In order to improve the self-healing behavior and the recovery of mechanical properties of engineered cementitious composites(ECC),the approach of incorporating superabsorbent polymer(SAP)in mixtures is investigated.The rapid water penetration test and four-point bending test were conducted to evaluate the effects of self-healing on the water permeability and mechanical properties of pre-damaged ECC.The self-healing process and self-healing products were observed by the environment scanning electron microscope(ESEM)and energy dispersive X-ray spectroscopy(EDS).The experimental results show that all ECC mixtures exhibit excellent flexural capacity,meanwhile maintaining a crack width below 50μm.The incorporation of SAP particles in ECC can apparently improve the mechanical recovery of ECC mixtures after 10 healing curing cycles,such as flexural deformation and flexural stiffness.The flexural stiffness of ECC containing 4%SAP particles after self-healing can be recovered to 80%.The self-healing test results show that when the water permeability of ECC mixtures incorporating SAP particles is close to zero,only three healing cycles are needed.When ECC incorpora ting more SAP particles,the accelerated self-healing process can be finished in the first three cycles,and self-healing product is mixed Ca(OH)2/CaCO 3 with CaCO 3 being a major component in the later stage.It is,therefore,feasible to produce ECC materials incorporating SAP particles,while simultaneously maintaining higher material ductility and self-healing behavior.

Hydration mechanism of low quality fly ash in cement-based materials

The hydration mechanism of low quality fly ash in cement-based materials was investigated. The hydration heat of the composite cementitious materials was determined by isothermal calorimetry, and the hydration products, quantity, pore structure and morphology were measured by X-ray diffraction(XRD), thermalgravity-differential thermal analysis(TG-DTA), mercury intrusion porosimetry(MIP) and scanning electron microscopy(SEM), respectively. The results indicate that grinding could not only improve the physical properties of the low quality fly ash on particle effect, but also improve hydration properties of the cementitious system from various aspects compared with raw low quality fly ash(RLFA). At the early stage of hydration, the low quanlity fly ash acts as almost inert material; but then at the later stage, high chemical activity, especially for ground low quality fly ash(GLFA), could be observed. It can accelerate the formation of hydration products containing more chemical bonded water, resulting in higher degree of cement hydration, thus denser microstructure and more reasonable pore size distribution, but the hydration heat in total is reduced. It can also delay the induction period, but the accelerating period is shortened and there is little influence on the second exothermic peak.

Real-time in situ visualization of internal relative humidity in fluorescence embedded cement-based materials

The transmission and distribution of moisture in cement-based materials are of great significance to the properties and durability of materials. Traditional macro-humidity monitoring equipment in civil engineering cannot capture the microscale humidity inside cement-based materials in situ. In this paper, a method of using rhodamine 6G fluorescence to characterize the change in relative humidity in cement-based materials is proposed. Two kinds of moulding processes are designed, which are premixed and smeared after moulding, and the optimal preparation concentration is explored. The results showed that rhodamine 6G can reflect the relative humidity of cement-based materials in situ by its fluorescence intensity and had little effect on the hydration heat release and hydration products of cement-based materials;the fluorescence intensity was much higher when the internal relative humidity was 63% and 75%. The research results lead the application of polymer materials in the field of traditional building materials, help to explore the performance evolution law of cement-based materials in micro scale, and have important significance for the evolution from single discipline to interdisciplinary.

Mechanical properties of polyvinyl alcohol-basalt hybrid fiber engineered cementitious composites with impact of elevated temperatures

In the present study,the mechanical properties of polyvinyl alcohol(PVA)-basalt hybrid fiber reinforced engineered cementitious composites(ECC)after exposure to elevated temperatures were experimentally investigated.Five temperatures of 20,50,100,200 and 400℃ were set to evaluate the residual compressive,tensile and flexural behaviors of hybrid and mono fiber ECC.It was shown that partial replacement of PVA fibers with basalt fibers endowed ECC with improved residual compressive toughness,compared to brittle failure of mono fiber ECC heated to 400℃.The tension tests indicated that the presence of basalt fibers benefited the tensile strength up to 200℃,and delayed the sharp reduction of strength to 400℃.Under flexural load,the peak deflections corresponding to flexural strengths of hybrid fiber ECC were found to be less vulnerable ranging from 20 to 100℃.Further,the scanning electron microscopy(SEM)results uncovered that the rupture of basalt fiber at moderate temperature and its pullout mechanism at high temperature was responsible for the mechanical evolution of hybrid fiber ECC.This work develops a better understanding of elevated temperature and basalt fiber impact on the residual mechanical properties and further provides guideline for tailoring ECC for improved fire resistance.

Strength characteristics of modified polypropylene fiber and cement-reinforced loess

The reinforcement and stabilization of loess soil are duscussed by using fibers as the reinforcement and cement as the stabilization materials.To study the strength characteristics of loess soil reinforced by modified polypropylene(MPP) fiber and cement,samples were prepared with six different fiber contents,three different cement contents,three different curing periods and three kinds of fiber length.The samples were tested under submergence and non-submergence conditions for the unconfined compressive strength(UCS),the splitting tensile strength and the compressive resilient modulus.The results indicated that combined reinforcement by PP fiber and cement could significantly improve the early strength of loess to 3.65–5.99 MPa in three days.With an increase in cement content,the specimens exhibited brittle fracture.However,the addition of fibers gradually modified the mode of fracture from brittle to ductile to plastic.The optimal dosage of fiber to reinforce loess was in the range of 0.3%–0.45% and the optimum fiber length was 12 mm,for which the unconfined compressive strength and tensile strength reached their maxima.Based on the analysis of failure properties,cement-reinforced loess specimens were susceptible to brittle damage under pressure,and the effect of modified polypropylene fiber as the connecting "bridge" could help the specimens achieve a satisfactory level of ductility when under pressure.

Seismic behaviors of steel reinforced ECC/RC composite columns under low-cyclic loading

To improve the seismic performance of columns, engineered cementitious composite （ECC） is introduced to partially substitute concrete at the base of the columns to form ECC,/reinforced concrete （ RC） composite columns. The mechanical behaviors of the ECC/RC composite columns are numerically studied under low-cyclic loading with the finite element analysis softwareof MSC. MARC. It is found that the ECC/RC composite columns can significantly enhance the load capacity, the ductility ad energy dissipation of columns. Then, the effects of the height of the ECC, the axial compression ratio and the longitudinal reinforcement ratio on the seismic behaviors of the composite columns are parametrically studied. The results show that the ECC/RC composite column with a height of the ECC layer of 0. Sh（h is the height to the cross-section） can achieve similar seismic performance of a full ECC column. The peak load of the composite column increases significantly while the ductility decreases with the increase of the axial compression ratio. Increasing the longitudinal reinforcement ratio within a certain range can improve the ductility and energy dissipation capacity and almost has no effect on load capacity. The aalysis results ae instructive and valuable for reference in designing ECC structures.