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Based on the structural characteristics of pervious concrete, an improved mix design method for pervious concrete was developed based on permeability, compressive strength and slurry layer thickness relationships. The results of validation experiments showed that when the slurry layer thickness of the pervious concrete is about 0.35–0.55 mm, the effective porosity is about 22–36%, the permeability coefficient is about 4.88–8.90 mm/s and the compressive strength is about 5.9–18.5 MPa. With an increase in the slurry layer thickness of the pervious concrete, the compressive strength increased, but the effective porosity and permeability coefficient decreased, and vice versa. The results of this study proved that pervious concrete can be formulated to satisfy permeability and compressive strength requirements by using the improved mix design method.

The self-compacting concrete (SCC) filling layer is a key structural component of the China railway track system type III ballastless track structure. The quality of the filling layer directly affects the durability, comfort and safety of the track system. Based on job site practice in the construction of the Zhengzhou–Fuyang high-speed railway, the distribution characteristics of the dynamic elastic modulus and homogenisation index of the SCC used as the filling layer with different workability parameters (slump flow, T500 and filling time) were obtained by sampling the SCC core from the filling layer. Image analysis software was employed to analyse the size and distribution characteristics of the surface defects statistically. The filling layer quality was evaluated according to the homogenisation index and the surface defect ratio. The results showed that the dynamic elastic modulus of the SCC in the filling layer tended to decrease from the intermediate filling hole to the four outlets. The order of influence of workability parameters on the filling layer quality was found to be T500, slump flow and filling time.

Phase change materials (PCMs) are widely used in solar energy utilization, industrial waste heat recovery and building temperature regulation. However, there have been few studies on the application of PCMs in the field of biomedicine. In recent years, some scholars have carried out research in the biomedicine field using the characteristics of PCMs. It was observed that the excellent properties of PCMs enhance the quality of a variety of biomedical applications with many advantages over existing applications, which provide new methods for the treatment of disease. PCMs have broad application prospects in the field of biomedicine. Therefore, a timely review of relevant research progress is of great significance for the continuous development of new methods. Innovatively, from the unique perspective of the biomedical field, this paper systematically reviews the application and related research progress of PCMs from four aspects: cold chains for vaccines and medicines, drug delivery systems, thermotherapy/cold compress therapy and medical dressings. In addition, we summarize and discuss the general principles of the design and construction of PCMs in the biomedical field. Finally, existing problems, solutions and future research directions are also put forward in order to provide a basis for guidance and promote the future applications of phase change materials in the biomedicine field.

Direct electric curing (EC) is a new green curing method for cement-based materials that improves the early mechanical properties via the uniform high temperature produced by Joule heating. To understand the effects of EC and steam curing (SC) on the mechanical properties and microstructure of cement-based materials, the mortar was cured at different temperature-controlled curing regimes (40°C, 60°C and 80°C). Meanwhile, mechanical properties, hydrate phase and pore structure of specimens were investigated. The energy consumption of two curing methods was compared and analyzed. The results show that the EC specimens have better and more stable growth of mechanical strength. The pore structure of EC specimen is also better than that of SC specimen at different maintenance ages. However, the hydration degree and products of samples cured by EC are similar to that SC samples. The energy consumption of EC is lower than SC. This study provides an important technical support for the EC in the production of energy-saving and high early-strength concrete precast components.

Particle-packing theory has been widely applied in the field of composite particle materials, and packing density (Φ) is an important parameter to evaluate the compactness of particle packi...

As one of the core components, high quality self-compacting concrete filling layer is of great importance to the long-term safe service of CRTS III type slab ballastless track. The present paper designed a freeze and flexural-loading coupling action testing system to investigate the mechanical characteristics of self-compacting concrete applied in filling layer (FLSCC), aiming at understanding the service behavior of filling layer under severe environment condition. The effects of temperature, cycle number and stress level on mechanical properties including flexural strength, dynamic elastic modulus and damping ratio of FLSCC were discussed. Results show that the freeze and cyclic load coupling action aggravates the deterioration of concrete compared to single cyclic load condition. FLSCC exhibits better resistance to freeze and cyclic load action than other three investigated concretes in term of flexural strength, dynamic elastic modulus and damping ratio. The flexural strength of FLSCC decreases with increasing cycle number stress level at low temperature (−20 °C) and the damage variable of FLSCC increases exponentially with cycle number. The outstanding resistance of FLSCC to freeze and cyclic load coupling action results from the excellent microstructure which can maintain its good deformation capacity and delay the damage propagation.

The hot-dry environment in high geothermal tunnels negatively affects the development of properties of cementitious materials. In order to improve the mechanical properties of cementitious materials in such environments, a proper curing system was developed, the material compositions were taken into account, and the related mechanism was analyzed by microscopic tests. The results showed that the mechanical properties and microstructure of cementitious materials can be improved effectively by adopting film curing and an adequate dosage of fly ash in a hot-dry environment. Compared with standard curing, a hot-dry environment accelerates the evaporation of water in fresh cementitious materials and the early hydration rate of cementitious materials, resulting in lots of unhydrated cement particles and an uneven distribution of hydration products, seriously decreasing the properties of the cementitious materials. Film curing keeps the water from evaporating and ensures enough water is available for hydration at an early age. The addition of FA reduces the amount of cement clinker and decreases hydration reaction rate in high temperature environments at an early stage, avoiding the unevenness of hydration products. High temperatures stimulate the pozzolanic activity of fly ash and promote the degree of secondary hydration reaction, producing more hydration products, as well as contributing to the improvement of the mechanical properties and microstructure of cementitious materials. In this study, in a hot-dry environment, the mechanical properties of mortar with 25% fly ash and 2–3 d film curing are better than those of other experimental groups, including those of standard curing.

Self-compacting concrete (SCC) is widely used in the China Rail Track System (CRTS) III slab ballastless track filling-layer structure for high-speed railways (HSRs). In cold regions, the t...

In order to study the synergistic effects of organic and inorganic thickening agents on the rheological properties of cement paste, the rheological parameters, thixotropy cement-paste containing limestone powder (LP), re-dispersible polymer powder (RPP), and hydroxypropyl methylcellulose ether (HPMC) were investigated using the Anton Paar MCR 102 rheometer at different resting times. The early-age hydration process, hydration products, and microstructure were also analyzed with scanning electron microscopy (SEM) and thermogravimetry analyses (TGA). The results showed that the addition of LP, RPP, and HPMC affected the rheological properties of cement paste, but the thickening mechanism between organic and inorganic thickening agents was different. The small amount of LP increased the plastic viscosity but decreased the yield stress of cement paste due to its dense filling effect. Adding 1% of RPP improved the thixotropic property of cement paste by 50%; prolonging the standing time could improve the thixotropic performance by as much as two times. Only 0.035% HPMC added to the cement paste increased the plastic viscosity by 20%, while the yield stress increased nearly twice. The more HPMC added, the more significant effect it showed. Cement paste compounds with LP, RPP, and HPMC balanced the yield stress and plastic viscosity and improved the thixotropy. The C-L6-R1.0-H0.035 paste presented as a pseudoplastic, its rheological indexes were close to one, and it was hardly affected by the resting time. The composite superposition effect of organic and inorganic thickening agents reduced the impact of resting time for all pastes. As the organic thickening component inhibited the hydration more than the LP promoted the hydration of the cement paste, indicating that the C-L6-R1.0-H0.035 paste remained in the particle fusion stage after curing for three days, as shown by the SEM images.

To understand the effects of direct electric curing condition on the mechanical strength and microstructure of cement paste, a series of experiments were carried out to investigate the effects of alternative current voltages and frequency on compressive strength of samples. And the corresponding microstructure of samples were also analyzed by several measurements including X-ray diffraction, thermogravimetric analysis, scanning electron microscopy and mercury intrusion porometer. The results show that alternative current electric voltage and frequency can greatly influence the early compressive strength of a cement paste. And a suitable electric curing condition can make hardened cement paste keep a steady growth of compressive strength and excellent microstructure. The Joule heat of direct electric curing on cement paste is the main reason that accelerates the hydration and improve the early strength development of sample. This study will provide an important technical support for exploring low carbon rapid electric curing method to produce green high early strength cement concrete prefabricated element.

In CRTSIII ballastless track structure, the bonding interface between self-compacting concrete (SCC) filling layer and steam-cured concrete track slab not only affected the interaction between filling layer and track slab, but also affected the effect and bond stiffness of connecting reinforcement, which was one of the key links of the whole track structure. Quality control of rheological properties of SCC mixture was proving to be critical for the success of the bond between steam-cured concrete and SCC layer concrete. In this research, the fractal dimension was calculated to characterize the bonding interface characteristics with different plastic viscosities. Moreover, the effect of plastic viscosity on mechanical properties was studied between SCC layer and steam-cured concrete. The bonding interface zone between SCC layer and steam-cured concrete was defined by microhardness and BSE tests. The experimental results indicated that the fractal dimension can better characterize the characteristics of bond surface and had a negative correlation with splitting tensile strength. Mechanical properties and bonding interface structure between steam-cured concrete and SCC layer improved with increasing the plastic viscosity of SCC mixture, especially when the viscosity was greater than 100 pa.s. The bonding interface zone model was established to explain the mechanism of the bond between steam-cured concrete and SCC layer.

Based on the relations between slump flow (SF), coarse aggregate average diameter (dav,i) and volume of coarse aggregate (Vg,i) used in self-compacting concrete (SCC), it was found that the preferable SF was that coarse aggregate could flow into a compact single layer status when SF testing was taken. Therefore, an improved mix design method of SCC was proposed according to relations among SF, dav,i and Vg,i. In the same Vg,i condition, large dav,i is suitable for small SF, but small dav,i should match large SF. When nominal size of coarse aggregate was 5–20 mm, proper SF for SCC should be 570 mm–720 mm. Results from the validated experiment show that properties of SCC including workability and compressive strength can satisfy the requirements. This improved mix design method helps to further develop SCC and cuts cost in real engineering projects.

Cement pastes subjected to initial steam-curing cycle have a poor later strength and durability. This adverse effect is originated from the steam-curing process. In order to investigate the microstructure changes of cement paste during steam-curing process, the XCTs with different spatial resolutions were combined used to detect the pore structure and the hydration development of cement pastes subjected to different curing regimes. The hydration heterogeneity and spatial distribution of pore network of cement pastes at various steam-curing ages were obtained on both mesoscale and microscale. The results indicate that the XCT is competent for figuring out the hydration development and of which the steam-cured cement paste is much higher than the standard-cured one at early age but has slight difference at later age. Besides, the steam-cured cement paste has a higher porosity and pore connectivity in the studied scales than the standard-cured one with the same hydration volume. Moreover, the pore structure of steam-cured cement paste has a less fractal characteristic, resulting in a microstructural damage and thus a lower fracture toughness and higher brittleness under elevated temperature steam-curing condition.

Rheological behaviors are the essential workability characteristics of fresh concrete. Generally speaking, paste volume in self-compacting concrete (SCC) are no less than 340 L/m3. Therefore, rheology of paste could be mainly responsible for rheology of SCC. Mineral admixtures are important for modern concrete, taking great influence on concrete rheology. In this paper, an experiment was designed to investigate the shear thickening behaviors of cement paste replaced by fly ash (FA), slag (SL) and limestone powder (LP), respectively. Results show that plastic viscosity of paste discussed in this paper prominently decrease first and then increase with the shear rate increasing. Therefore, there exist critical shear rate (γcrit), critical shear stress (τcrit) and minimum plastic viscosity (ηmin) in rheological curves at the beginning of shear thickening taking place. The addition of FA, SL and LP into cement paste not only decrease the γcrit, τcrit and ηmin, resulting in cement paste easy to exhibit shear thickening, but also increase the rheological index (n), leading to shear thickening intensity augmenting. γcrit of cement paste with addition 30% SL drops to10 s−1, displaying shear thickening response taking place easily compared to cement paste with the same FA and LP contents. Rheological index (n) of cement paste with SL is also larger than cement paste with FA and LP at the same mineral admixtures contents. The shear thickening intensity sequence of cement paste under the effects of mineral admixtures are SL, FA and LP, respectively.

Sealed-space-filling self-compacting concrete (SSFSCC) is used in China Rail Track System (CRTS) III ballastless slab track of high-speed rail, which has been originally developed in China recently. In this track system, SSFSCC needs to be grouted into a flat, narrow, and sealed space (90 mm × 2500 mm × 5600 mm) which is enclosed by above prefabricated slab and bottom base plate. Good bonding between SSFSCC filling layer and above prefabricated slab has to be secured since these two layers are required to work as a composite plate. SSFSCC presents some special characteristics in comparison with normal SCC. This paper elaborated the property requirements of SSFSCC and the structural characteristics of SSFSCC layer of CRTS III ballastless slab track of high-speed rail. The compositions and mix proportioning of SSFSCC as well as construction technology were briefly introduced. The challenges of the application of this special SCC were also addressed.

The influences of four nanoparticles of nanosilica (SiO2), nano-calcium carbonate (CaCO3), nano-aluminium oxide (Al2O3) and nano-iron oxide (Fe2O3) on workability, hydration, pore structure and mechanical strength of reactive powder concrete (RPC) are investigated by macro/microscopic methods. The aim of this study is to provide an essential basis for exploiting new-generation cementitious materials with ultra-high strength and super-long service life by employing modern nano-modification technology. The results indicate that addition of low-dosage nanoparticles to RPC shows a remarkable influence on the mechanical strength, hydration and pore structure compared to the ordinary cement system with a relatively high water/cement ratio. The compactness and mechanical strength of RPC can be greatly improved by incorporating nanoparticles. The promotive ratio of flexural and compressive strength of RPC is up to 30%. The elevated temperature further promotes the effect of nanoparticles on the strength of RPC. The seeding effect of nanoparticles on hydration of cement and the nano-size filling role are strengthened in the RPC system.

Effective foundation reinforcement treatment is essential for modern large and complex infrastructure, while it is significant for developing new green high-performance materials for foundation reinforcement. This study investigates a new green concrete by using high volume fly-ash and coal gangue aggregates, which is expected to apply for foundation treatment of modern infrastructure with high loading-bear ability. In this experiment, 12 mix proportions of fly ash coal gangue mixture (the material name, abbreviated FGM) were designed, and its mechanical properties and durability performance were investigated. The mechanical properties of FGM include compressive strength, dynamic elastic modulus, dynamic shear modulus, Poisson&rsquo, s ratio, and the stress&ndash, strain behaviors. The durability performance was evaluated by the parameters of acid resistance, which simulated an acid circumstance. After that, the environmental effects about carbon emission of this material were also investigated. Results show that the FGM with 84.6% wastes utilizing rate is a cost-effective material for foundation reinforcing treatment. Its compressive strength at 28 days and 60 days can reach more than 8 MPa and 10 MPa, respectively. After being immersed in the acid environment for 140 days, the mass loss (%) of the material could be under 3.5%. The greenness shows that the e-CO2 indices of FGM are lower than 20 kg/MPa&middot, m3, and the e-energy indices are at below 150 MJ/MPa&middot, m3. FGM has the advantages of acid resistance, waste recycling, and lower carbon emissions than the previous methods for foundation improvement.

© 2017 American Society of Civil Engineers. The filling layer of a China rail track system III (CRTS III) type ballastless track structure of a high-speed railway is a complicated structure typically constructed from self-compacting concrete (SCC). Excellent properties of SCC are of great importance to ensure the quality of construction technology and long-term service performance of the filling layer. In this study, preparation methodologies and properties of SCC applied as a filling layer are systematically investigated by series of experiments. The results indicate that high-performance SCC with high stability in a fresh state and low deformation in a hardened state was successfully achieved by optimizing aggregates and binder components. Use of viscosity-enhancing compounds can not only effectively improve the workability of fresh SCC, but also significantly enhance mechanical properties and decrease drying shrinkage and creep of hardened concrete.

The dynamic mechanical property of concrete is one of the key parameters, which greatly influences durability of infrastructures subjected to continuous heavy loading, such as girder and track slab of high-speed railway foundation structure. This paper reports serials of experiments designed to investigate the deterioration of dynamic mechanical properties of different concretes under fatigue loading condition. Four parameters including relative dynamic elastic modulus (RDEM), relative dynamic shear modulus (RDSM), relative compressive strength (RCS) and water absorption (WA) of concrete were evaluated to assess the dynamic properties and microstructures of concretes. Results show that the fatigue stress levels and fatigue cycle durations significantly influence the dynamic mechanical properties of concrete including dynamic elastic modulus and dynamic shear modulus. Addition of proper mineral admixture can improve the dynamic mechanical characteristics of concrete and increase its resistance against the fatigue loading effect. Keeping the amount of mineral admixture in concrete constant, its dynamic mechanical property with fly ash is lower than that with fly ash and silica fume. The water absorption in concrete, which is an indirect parameter reflecting capillary porosity, increases evidently after bearing fatigue-loading. There is a close correlation between the deterioration of dynamic mechanical property and the increasing of water absorption of concrete. This indicates that the damage of microstructure of concrete subjected to fatigue loading is the indispensable reason for the decay of its dynamic mechanical performance.

Steam-cured concrete is widely used to manufacture prefabricated units of high-speed railway foundation structure such as girder and track slab. The dynamic mechanical property of steam-cured concrete is one of the key properties affecting service performance of high-speed railway foundation structure. In the present paper, serial macro/micro-experiments were carried out to investigate the dynamic elastic modulus, shear modulus, damping ratio, and microstructure of steam-cured concrete. The relationships between compositions, curing regime, microstructure, and dynamic properties of steam-cured concrete as well as the corresponding mechanisms were discussed. The results indicate that steam-cured concrete in early age has a larger dynamic elastic modulus and shear modulus as well as a smaller damping ratio compared with standard-cured concrete. On the contrary, at a later age a slightly smaller dynamic elastic modulus and a larger damping ratio of steam-cured concrete are observed. Addition of mineral admixture results in a bit lower dynamic elastic modulus and damping ratio of concrete than that of the control specimen without mineral admixtures. The achievements can provide some fundamental suggestions for materials parameters selection during structural design of steam-cured concrete precast element.

Rheological curves of cement&ndash, fly ash (C&ndash, FA) paste incorporating nanomaterials including nano-SiO2 (NS), nano-CaCO3 (NC) and nano-Al2O3 (NA) at different resting times (hydration time of 5 min, 60 min, and 120 min) were tested with a rheometer. The rheological behaviors were described by the Herschel&ndash, Bulkley (H&ndash, B) model, and the influences of these nanomaterials on rheological properties of C&ndash, FA paste were compared. Results show that the types, content of nanomaterials and resting time have great influences on the rheological properties of C&ndash, FA paste. Incorporating NS and NA increases yield stress and plastic viscosity, and decreases the rheological index of C&ndash, FA paste. When the content of NS and NA were 2 wt%, the rheological index of C&ndash, FA paste was less than 1, indicating rheological behavior changes from shear thickening to shear thinning. Meanwhile, with rising resting time, yield stress and plastic viscosity increased significantly, but the rheological index decreased evidently, showing paste takes on shear thinning due to the rise of resting time. However, incorporating 3 wt% NC and the rising of resting time did not change the rheological properties of C&ndash, FA paste. These differences are mainly that the specific surface area (SSA) of NS (150 m2/g) and NA (120 m2/g) are much larger than that of NC (40 m2/g). The huge SSA of NS and NA consume lots of free water and these tiny particles accelerate the hydration process during resting time.

Invading track of chloride ions and chloride ion distribution rule in cement-based materials were investigated by partially soaking in 3.5% (mass fraction) NaCl solution and fully immerging in 3.5% and 5.0% (mass fraction) NaCl solution, respectively, and relevant invading mechanisms were discussed. Results indicate that under full immerging condition, the invading track of chloride ions in cement mortar is similar to beeline that is vertical to chloride ion invading direction, and chloride ion content decreases rapidly with the increase of chloride ion invading depth. Under partial soaking condition, the invading track of chloride ion in cement mortar is similar to the shape of concave parabola, and chloride ion content decreases slowly along the lengthway direction of cement mortar samples in the distance of 20–80 mm from the bottom. Lots of chloride ions accumulate in cement mortar surface layer under the effect of capillary rise and evaporation and then invade cement mortar by diffusion effect. Under partial soaking condition, cement mortar is distinguished by four areas, i.e., immerging area, wet area, crystallization area and dry area.