•Premature deterioration mechanism of steam-cured concrete track slab was investigated.•Steam-cured heat damage (SCHD) makes track slab concrete surface layer loose, porous and more micro ...cracks.•3.Long-time dynamic load and moist environment acting on track slab enlarges micro cracks and results in water penetration into concrete easily.•Ingression of water into concrete causes the formation of alkali-silica gel and delayed ettringite.
Deterioration mechanisms of some premature damaged steam-cured concrete track slabs (CTS) in Chinese railway less than 4 years were investigated. Field investigation, raw materials test and suspicious products analysis were carried out. Results show that steam-cured heat damage (SCHD) of concrete takes place in steam-cured process. Expansion products are ettringite in hydrated products and alkali-silica gels between the interface of hydrated products and coarse aggregate. SCHD makes CTS surface layer loose, porous and more micro-cracks. Long-term fatigue load from high-speed train acting on CTS enlarges concrete microcracks, leading to water penetrating into concrete easily in moist and rainy environment. In the process of water ingression, alkali-silica reaction (ASR) and delayed ettringite formation (DEF) take place, hence resulting in CTS cracking and premature deterioration.
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's ratio, and the stress-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-CO
indices of FGM are lower than 20 kg/MPa·m
, and the e-energy indices are at below 150 MJ/MPa·m
. FGM has the advantages of acid resistance, waste recycling, and lower carbon emissions than the previous methods for foundation improvement.
In this work, ceramsite was utilized to fabricate the sound-absorbing boards, in which two types of structure were considered, specifically, single-layer board with homogenous structure and ...double-layer board with gradient structure. The physical, mechanical and acoustic properties of these prepared ceramsite sound absorbing boards were studied, including the bulk density, compressive strength, flexural strength, softening coefficient, sound absorption coefficient and sound reduction index. The results show that the double-layer board with appropriate mixture design exhibited almost identical bulk density and mechanical strength to the single-layer board. All ceramsite sound absorbing boards had compressive and flexural strengths of more than 3 MPa and 1 MPa, respectively, and also demonstrated good water resistance. In terms of sound absorption and sound insulation properties, the overall performance of the double-layer board with reasonable gradient structure was better than that of the single-layer board. In addition, the physical structure models of ceramsite sound absorbing boards were established to illustrate the variation of mechanical properties and disclose the mechanism of sound absorption and insulation in the material.
In the tunnels of the Cheng-Kun Railway in China, concrete failure can usually be observed from the effect of sulfates. A field investigation was conducted to analyze the concrete damage mechanism by ...means of XRD, IC, AAS and EPMA. The results showed that (1) large amounts of Na2SO4 were generated on the surface layer of the concrete lining, causing concrete detachment layer by layer; (2) the concrete lining in contact with air had been neutralized to more than 50mm in depth, and the cement hydration products had been converted into CaCO3; (3) ettringite and gypsum, the products of chemical sulfate attack, were also detected in the neutralized concrete lining. This analysis of a field case concluded that Na2SO4 crystallization caused the detachment of the surface layer of the concrete lining, and the chemical sulfate attack occurred in the inner part of the concrete lining.
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.
Heat treatment is widely used to accelerate the strength-gaining rate of concrete. In general, the ultimate strengths of the heated-treated concrete are lower than those of the standard cured ...specimens. When ultrafine fly ash (UFA) is included in concrete, the pozzolanic reaction is accelerated through the heat treatment. Sometimes, various chemical activators were used to activate the reactivity of fly ash. In the current study, UFA and slag were used as a replacement for cement, steam curing and chemical activators were used to accelerate hydration of cement and fly ash, and then compared with moist curing. This paper presents the influence of steam curing on the compressive strength of concrete containing UFA with or without slag. The experimental results indicated that the concrete containing UFA has low early strength after 13-h steam curing and that the difference between the 28-day compressive strength of concrete through 13-h steam curing and that of moist-cured concrete is large, but the concrete with UFA and CaSO
4 or Ca(OH)
2 has a high early strength, thus, the reactivity of fly ash must be accelerated. Concrete containing UFA and ground slag was prepared, whose compressive strengths were improved.
•The environmental impacts of SCCs with different mixing proportions were investigated.•The relationships between environmental impact and compressive strength of SCC were analyzed.•Some suggestions ...for designing more sustainable and greener SCC were proposed.
The present paper focuses on understanding the relationship between the mixing proportion parameters of self-compacting concrete (SCC) and its environmental impact and thus developing more greener SCC. Three simple indices combining the embodied environmental impacts with engineering properties (such as strength) of SCC are proposed. And 16 SCC mixtures with different compositions are designed to quantitatively evaluate the corresponding environmental impacts of SCC by use of the proposed index. Results indicate the ecological impact index of SCC closely depends on the mixing proportions. The addition of high volume mineral admixtures not only can effectively reduce the e-CO2 and e-resource indices but also decrease the e-energy index. Selecting a reasonable aggregate volume can help decrease the environmental impact of SCC. Employing recycled limestone sand to replace river sand will increase the e-CO2 index and e-energy index of SCC, although it can reduce the e-resource index. Regardless of the mixing proportion parameters, the e-CO2, e-energy and e-resource index of SCC both decrease with the increasing compressive strength for SCCs with a compressive strength ranging from 30 to 60MPa.
•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.
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