•SCA reduces hydrophilicity to enhance BF water damage resistance and compatibility with asphalt.•SCA makes BF surface become rough to enhance chemical bonding and mechanical occlusion effect.•Better ...adhesion and force-transmitting between BF and asphalt helps to gain stronger interaction.•SCA heightens low and high temperature mechanical performances of fiber-reinforced asphalt.
The main goal of our work was to study mechanism of interfacial adhesion between basalt fiber and asphalt. Solution of silane coupling agent (2.5 wt%, KH-550) was used to modify fiber surface. Modified fibers were then used for fiber-reinforced asphalt fabrication with different fiber concentrations (0.5, 1.0 and 1.5 wt%). Samples were analyzed by DMA, DSR, EDS, ESEM, ACAM and FTIR. Treatment with KH-550 resulted in fibers with rough surface and weak hydrophilicity. It also increased surface area of fibers, improved their compatibility with asphalt and enhanced their chemical bonding with asphalt, all of which resulted in overall increase of mechanical performance of asphalt. Our research provides foundation for fiber surface modification for applications in road pavement engineering.
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.
Ultra-high performance concrete (UHPC) is one of the most promising materials to reduce the detrimental effects of building materials on the environment because UHPC requires fewer materials and ...post-maintenance in comparison with normal concrete. However, the high cost and CO2 emission of UHPC are the major factors influencing its large-scale application in China. This study presents a series of comprehensive methods, including the optimization design of the binder system, utilization of nano-particles and chemical activators as well as heat curing, to prepare UHPC with relatively lower environmental impact. The workability, compressive strength, flexural strength, hydration heat and environmental impact of UHPC were investigated. The results indicate that each of the above methods has a significant effect on the strength and carbon emission of UHPC. UHPC with cement content lower than 200 kg/m3 can be prepared by optimizing its binder system and curing conditions, and its embodied CO2 index is lower than 3 kg/MPa·m3, while the embodied CO2 index of conventional UHPC ranges from 5.5 to 7 kg/MPa·m3. The designed UHPC has a low hydration release heat which may decrease the cracking risk caused by hydration temperature rise. For improving the mechanical strength and the eco-friendliness of UHPC, chemical activating method and heat curing have a synergistic effect.
•The low carbon emission UHPC has been successfully prepared in this study.•The effect of compositions and curing regime on environmental impact of UHPC were studied.•The effect of nano-silica and chemical activators on environmental impact of UHPC were studied.•The environmental impact of the optimized and normal UHPC is compared.
The introduction of metakaolin into magnesium phosphate cement (MPC) can improve the compressive strength, volume stability, water resistance and freeze-thaw resistance significantly. Two possible ...reasons were proposed in this study. Firstly, metakaolin decreases the total porosity of MPC and improves the pore structure which is directly related to the mechanical properties. Secondly, part of metakaolin can dissolve in MPC and take part in hydration, even though no new hydration products can be observed in XRD patterns. This study not only gives a compressive evaluation on the application of metakaolin in magnesium phosphate cement, but also explains the possible reason for the improvement of the properties of magnesium phosphate cement.
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•Strength and durability of MPC incorporating metakaolin were systematically studied.•Possible mechanism of metakaolin influencing MPC was proposed by multi-analysis.•The more homogeneous microstructure in metakaolin modified MPC can explain the property improvement.
Metakaolin has been generally used as a filler in Portland cement-based materials, and it was proved to be able to enhance the performance of magnesium phosphate cement composites. In this research, metakaolin was introduced into MPC, and compressive strength, tensile bonding strength, porosity and durability of MPC were measured. The microstructure of MPC before and after water immersion was evaluated. The experimental results indicate that the presence of metakaolin can lead to higher plastic viscosity of fresh MPC mortar, 28-day compressive strength, higher tensile bonding strength, better freeze-thaw resistance, better water resistance, lower drying shrinkage and better optimized microstructure. Physical effects of metakaolin including filling effect and inducing effect play the leading role in MPC. Metakaolin particles can fill in the pores or cracks, resulting in the decrease in porosity. In addition, metakaolin particles can provide lots of sites for crystallization of hydration products, inducing in the generation of more homogeneous microstructure. Finally, the dissolution and chemical reaction of metakaolin particles were confirmed by BSE analysis.
One-part geopolymers prepared by powder activators, similar to Portland cement in cast-in-situ application, are promising building materials due to the relatively slighter embodied environmental ...impact. There are three types of commercial sodium metasilicate powders in the China market, and they are Na2SiO3-anhydrous/NS0, Na2SiO3·5H2O/NS5 and Na2SiO3·9H2O/NS9, respectively. This study employed ultra-fine fly ash sinking beads (FASB) and ground granulated blast furnace slag (GGBS) as precursor materials to analyze the influences of NS0, NS5 and NS9 on the properties, microstructure and environmental impact of one-part geopolymer by measuring and characterizing compressive strength, porosity, reaction heat release, geopolymerization products and carbon dioxide equivalent (CO2-e) emission. The experimental results indicate that NS0 has the most rapid and effective activated effect in both single GGBS and GGBS-FASB composites. The strength of geopolymer activated with NS0 is the highest, followed by that with NS9, and followed by that with NS5. The products are mainly gelatinous phases, and the gels in NS0 and NS9 activated geopolymers are better geopolymerized than those in NS5 activated geopolymer, which is proved to be responsible for the difference in macro-performance. The evaluations of the cost and CO2-e emission per MPa of one-part geopolymer demonstrate that NS0 and NS9 are much cheaper and cleaner than NS5 for preparing one-part geopolymer. The embodied CO2 indexes of NS0 and NS9 activated single GGBS are only about 26.5% and 34.0% of that of ordinary Portland cement. This study not only partially explains the reasons for the different properties of one-part geopolymer activated by different types of sodium metasilicate, but also provides a guidance for preparing one-part geopolymer with reasonable cost and slight environmental impact.
•Properties of one-part geopolymer activated by three Na2SiO3·nH2O powders were studied.•Influence of the type of Na2SiO3·nH2O on hydration products and microstructure was analyzed.•Advantages of one-part geopolymer in environmental impact and economic efficiency were confirmed.
Filling layer self-compacting concrete (FLSCC) is a key material in newly-built China Rail Track System (CRTS), which is commonly subjected to cyclic dynamic load from high-speed train and various ...ambient temperature during service. In this paper, a series of indoor simulating experiments was conducted to investigate the impact resistance of FLSCC suffering from cyclic flexural load and different temperature conditions with a Φ75 mm split Hopkinson pressure bar (SHPB). The dynamic increase factors were introduced to evaluate the strain rate effect on various mechanical properties of FLSCC and the corresponding mechanisms were explained. Results show that the dynamic increase factor of compressive strength (
DIF
c
) and peak strain (
DIF
ε
) of FLSCC increase linearly with logarithm of strain rate, while specific energy absorption increases exponentially with strain rate. The impact resistance of FLSCC is greatly influenced by cyclic flexural load and low temperature. The strain rate sensitivity of compressive strength of FLSCC at minus temperature (−20°C) is weaker than that at normal temperature (20°C) and after freeze-cyclic load coupling action the sensitivity decreases further. Similar tendencies were also observed in peak strain and specific energy absorption.
In order to solve the problems of the sudden loss of fluidity and low expansion rate of CAM I (cement asphalt mortar type I) in a construction site with high environmental temperature, this paper ...studies the effect of temperature on the fluidity, expansion ratio and pH value of CAM I. The mechanism of action was analyzed by IR (infrared spectrometry), SEM (scanning electron microscopy) and other test methods. The results showed that a high temperature accelerates aluminate formation in cement paste. Aluminate adsorbs emulsifiers leading to demulsification of emulsified asphalt, and wrapped on the surface of cement particles, this causes CAM I to lose its fluidity rapidly. The aluminum powder gasification reaction is inhibited, resulting in an abnormal change in the expansion ratio. Based on findings, the application of an appropriate amount of superplasticizers can effectively improve the workability and expansion characteristics of CAM I at a high temperature.
Understanding the dynamic behavior of Lightweight Aggregate Self-Compacting Concrete (LWASCC) is of importance to the safety of concrete structures serving in dynamic loading conditions. In this ...study, the fundamental dynamic properties of LWASCC with three types of LWA were investigated by the impact resonance method. Results show that the dynamic elastic and shear modulus generally decrease with the increase of LWA volume fraction, whereas three types of LWA exert limited influence on dynamic Poisson’s ratio. The dynamic elastic and shear modulus show good linear dependence upon compressive strength. The inclusion of three types of LWA significantly increases the damping ratio, indicating significantly enhanced damping capacity of LWASCC under dynamic loading conditions. The damping ratio of LWASCC is improved by 2.0%, 4.4%, and 2.9% when adding 1% (by volume) expanded clay, rubber, and expanded polystyrene, respectively. The compressive strength and dynamic performances of LWASCC are highly influenced by the intrinsic properties (elastic modulus, damping capacity, wettability, etc.) and geometrical characteristics (size, surface roughness, etc.) of LWA, as well as the LWA-matrix bonding capacity.
One-part geopolymer similar to conventional Portland cement by just adding water is a clean cementitious material. Several commonly used activators include powdered sodium metasilicate and sodium ...hydroxide whose productive processes consume huge energy and emit a lot of greenhouse gases. In this study, sodium sulfate was introduced into one-part geopolymer in order to replace partial Na2SiO3-anhydrous, and its effects and mechanisms were studied by property measurements and microscopic characterization. Results indicate that the strength reduces with increasing the replacement level of sodium sulfate. Sodium sulfate reduces the initial rate of heat release and prolongs the induction period to some extent. At the initial stage of hydration process, a portion of sodium sulfate exists in the form of phase with crystal water, which lead to the initial volume expansion. And then, sodium sulfate takes part in hydration which is detected by XRD analysis, even though no new hydration products can be detected in geopolymer. Sodium sulfate decreases the drying shrinkage remarkably due to the early-term volume expansion generated by the phase change of sodium sulfate. The subsequent drying shrinkage leads to a certain internal stress which can explain more micro-cracks appearing in geopolymer with sodium sulfate observed in SEM photos. Not only that, the presence of sodium sulfate increases the total porosity, especially the proportion of harmful pores in one-part geopolymer. Two indexes synthesizing compressive strength and total CO2-e emission were employed to evaluate the cost and environmental implication. Sodium sulfate was proved to be a more suitable activator to prepare cleaner one-part geopolymer because the potential CO2 emission drops at least 20% after adding sodium sulfate. Even though, the more effective activator system which can decrease the use of Na2SiO3-anhydrous and drying shrinkage further and the corresponding mechanisms should be studied in deeper insight. The method to induce producing the more homogeneous microstructure in low-alkalinity one-part geopolymeric cement is also a novel research field.
The influence of sodium sulfate on one-part geopolymer prepared by granulated blast furnace slag, GGBS and fly ash sinking beads, FASB was studied. The presence of sodium sulfate indeed delays the geopolymerization process and decreases the compressive strength, especially at early curing stage. Sodium sulfate can take part in geopolymerization, and reaction products are amorphous minerals. The reaction products in geopolymer activated by both sodium sulfate and Na2SiO3-anhydrous have more Al phase and higher Ca/Si ratio. And more micro-cracks can be observed after adding sodium sulfate, which corresponds to the higher porosity and the change in volume stability. These can explain the mechanisms of sodium sulfate influencing the properties of one-part geopolymer. Sodium sulfate can decrease the cost of one-part geopolymer without sacrificing the environmental friendliness and mechanical properties of one-part geopolymers. Display omitted
•The presence of sodium sulfate affects the hydration kinetics, strength and volume stability of one-part geopolymer.•Sodium sulfate makes the products have more Al phase and higher Ca/Si ratio, and no new products can be detected.•The coarse microstructure can explain the change in porosity, strength and volume stability to some extent.•Sodium sulfate makes one-part geopolymer much cleaner without sacrificing the performance.
•The width of ITZ of steam-cured concrete was analyzed by microhardness.•A novel analysis method was used to obtain the microhardness distribution.•The change in ITZ observed by microhardness ...indicates the heat damage in steam-cured concrete.
In order to understand the influencing mechanisms of curing temperature on the performances of steam cured concrete further, the microhardness characteristics of the interfacial transition zone between cement paste and coarse aggregate under different curing temperatures were studied through microhardness measurements, backscattered electronic microscopy (BSEM) and mathematical statistical analysis. The experimental results indicate that the microhardness of the hardened cement paste presents a significant statistical distribution characteristic. That is to say, there are two microhardness characteristic values which reflect the hydrated products and unhydrated cement particles, respectively. The curing temperature has a significant effect on the microhardness of interfacial transition zone. In other words, the microhardness decreases, and the thickness range of interfacial transition zone increases with increasing the curing temperature. The relationship of the microhardness value of the interfacial transition zone to the distance from the aggregate surface conforms to the Peal function.
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