Abstracts:The use of asphalt mixtures in railway tracks provides a positive contribution to the bearing capacity, stability, durability and more importantly damping properties of the railway structure particularly for the new generation of low-vibration-railway track systems. However, one of the main concerns in the use of asphalt mixtures in railways is their fatigue cracking caused by the repeated traffic loading. The present study focused on the fatigue damage behavior of asphalt mixtures in the railways through using the viscoelastic continuum damage theory. Three experiments of creep compliance, constant crosshead rate and cyclic fatigue tests were carried out on some asphalt mixtures with different air void contents and aging conditions. Based on the results obtained, the crumb rubber modification of railways asphalt mixtures at low stress levels increases the fatigue life of asphalt up to 7.2 times while this increase is at the most 3.6 for the highway asphalt mixture. Furthermore, reducing the air void content from 4% to 2% for the crumb rubber modified asphalt mixture increases the fatigue life by 9.4 times at high stress levels and 18.2 times at low stress levels, which is a great improvement. It was shown that the lowest fatigue life is obtained in the aged crumb rubber modified mixture (i.e., 20 percent of unmodified asphalt mixture).

Abstracts:In order to promote the regular use of steel fibre reinforced concrete (SFRC), a rational framework of material models identifying the key material parameters must be established. When considering the design of a structural member manufactured with SFRC, the defining property is its post cracking, or residual, tensile strength. In principle, a direct tension test is the ideal test that should be used in gathering the softening, or residual, parameters of SFRC experimentally. However, there are many parameters which may influence the results of the uniaxial tension test, and the choice of boundary conditions for the test is one of the most relevant ones. Three boundary or end conditions are possible: fixed-fixed, fixed-rotating, and rotating-rotating. In this paper, results of uniaxial tensile tests on twelve identical SFRC “dogbone” specimens tested with the end conditions listed above are presented. Each condition exhibits behaviour not present in the theoretically ideal tensile softening curve. Investigating this is the focus of the present study. It is concluded that the fixed-rotating end conditions serves as a compromise to the issues associated with the other test setups and seems to be more suited for uniaxial tension testing of softening SFRC.

Abstracts:Concrete strength (CS) is one of the most important performance parameters that are crucial in the design of concrete structure. The reliable prediction of strength can reduce the cost and time in design and avoid the waste of materials caused by a large number of mixture trials. In this study, a novel predictive model is put forward to predict the CS of high performance concrete (HPC) using support vector machine (SVM) approach, which has benefits of nonlinear mapping, high robustness and great generalisation capacity. In the proposed model, the input variables include the contents of water, cement, blast furnace slag, fly ash, super plasticiser, coarse and fine aggregates and curing age, which produces the CS of HPC as the output. In order to improve the model performance, a type of enhanced cat swarm optimisation (ECSO) is adopted to optimise the key parameters of SVM. Finally, the model is trained and evaluated using a total of 1761 data records, which are collected from existing literatures. The results indicate that the proposed SVM-based model exhibits better recognition ability and higher prediction accuracy than other commonly used models, and it can be considered as an effective method to predict the CS property of HPC in infrastructure practice.

Abstracts:Uncertainties significantly influence the durability-related experiments and field studies, which can hardly be addressed by deterministic approaches. This work aims at developing a stochastic numerical framework to disentangle the influence of material uncertainty on the case of leaching. To ensure the robustness of the numerical framework, a realistic stochastic reactive-transportation model is developed, which consists of a novel sampling algorithm and a comprehensive deterministic model. By using the proposed sampling algorithm, a more effective and efficient sampling process can be achieved without compromising the randomness of the uncertain properties. Besides, realistic mechanisms of leaching are considered by the deterministic model, including the simultaneous processes of ionic transportation, chemical reactions and material degradation. By performing the stochastic leaching analyses, numerical results suggest the overwhelming influence of the physical uncertainty on long-term leaching, while the impact of chemical uncertainty is more evident in terms of short-term leaching. It is also revealed that the root-time relation as determined from short-term experiments is inappropriate for long-term predictions. Thus, a modified relation is developed based on the stochastic leaching analysis, which generates accurate predictions for both the short-term and long-term leaching.

Abstracts:Ca/Al-Layered Double Hydroxide (Ca/Al-LDH), was a kind of important anionic clays with broad applications owing to its properties of exchangeable anion and adjustable particle size. In this study, Ca/Al-LDH had been successfully prepared by co-precipitation method, and it was found that the particle size, crystallinity and morphology of Ca/Al-LDH could be tuned via changing ethanol/water ratio of solution. More interestingly, with the increase of the Ca/Al-LDH’s dosage, the different crystal structure of Ca/Al-LDH had promoting effect on the development of the early strength of the cement slurries, however, the change trend of the strength growth rate of various kinds of cement slurries were quite different. Meanwhile, experimental results disclosed that the crystallinity and particle size of Ca/Al-LDH determined its interaction with cement hydration particles. That was likely to lead to a change in tricalcium silicate (C3S) and tricalcium aluminate (C3A) hydration process of accelerating or retarding under the different Ca/Al-LDH content, thus enabling the early strength development of slurry to exhibit different trends. And this finding could provide further interpretation for the effect of hydrotalcite-like materials on cement hydration process and offer a theoretical exploration for its practical application in the future.

Abstracts:This research aimed to study the minimum requirements of shear reinforcement for ultra high performance fiber reinforced concrete deep beams. The experimental results showed that increasing the provided vertical web reinforcement ratio has slight effect on the diagonal cracking strength and the ultimate shear strength. The maximum spacing between the vertical web reinforcement required by ACI 318-2014 for reinforced concrete beams (d/5) is not suitable for ultra-high performance fiber reinforced concrete deep beams, while for the EC-2 (2b) and that required by the Egyptian code ECP-203-2017 (200 mm) is applicable. The recommendations of AFGC-2013 and KCI-2012 are safe and conservative more than that required by ACI 318-2014.

Abstracts:In the present study, intermediate temperature cracking performance of different types of asphalt binders containing warm mix asphalt (WMA) additives was evaluated using three test methods namely, Superpave fatigue parameter, linear amplitude sweep (LAS) and double edge notch test (DENT). The Superpave fatigue, LAS, and DENT tests are based on dissipated energy, viscoelastic continuum damage (VECD) and work of fracture approaches, respectively, and thus each of the tests may result into different performance ranking of asphalt binders. The outcome of the Superpave fatigue, LAS and DENT tests are G^∗sinδ, number of cycles to fatigue failure (Nf), and critical tip opening displacement (CTOD) based on which cracking potential of asphalt binder can be assessed. An asphalt binder having a low Superpave parameter, high Nf and high CTOD values are expected to have better intermediate temperatures cracking performance. The present study selected three control binders namely virgin (AC), styrene-butadienestyrene (SBS) and crumb rubber modified (CRM) binders were modified using three WMA additives namely Fischer-tropsch (FT) wax based, chemical surfactant (CS) based and water based (WB). Control binders were modified with 2%, 6% and 2% (by weight of asphalt binder) of FT, WB and CS, respectively, using a mixer. The results showed that, based on G^∗sinδ and CTOD parameters, CS modification reduced stiffness (reduced G^∗sinδ) and improved ductile performance (increased CTOD) of control binders. However, WB and FT modification increased stiffness and degraded the ductile performance of control binders, except for SBS with 6%WB binder which showed higher CTOD than control SBS binder. On the other hand, considering performance based on Nf parameter, WMA additive modification improved fatigue life of control binders, except for SBS with 2%CS binder which showed lower Nf as compared to control SBS binder. Control binders with and without WMA additives were ranked based on G^∗sinδ, Nf and CTOD parameters. AC and CRM binder with and without WMA additives followed similar performance ranking based on G^∗sinδ and CTOD parameters. It is difficult to conclude over the best suitability of intermediate temperature performance parameter as mentioned tests involve different loading conditions and analysis approaches. Hence, further investigation on asphalt mixes is necessary to identify the best suited intermediate temperature performance parameter of asphalt binders, and its possible correlation with mix performance.

Abstracts:To shorten a steel building recovery time after an earthquake, a dual and damaged-controlled system is proposed, in which the seismic energy is absorbed by a highly ductile buckling restrained brace (BRB) and the gravity load is resisted by high-strength column. Because the seismic energy is mainly dissipated by the BRB, to accurately simulate the BRB hysteretic behavior is essential. Thus, kinematic hardening and two surface theories are adopted and coded as an ABAQUS user-defined material (UMAT). Particle swarm optimization (PSO) is used to find the optimal design equivalent to a corresponding traditional structure. The performance of the optimal frame is verified by nonlinear time history and fragility analysis. Based on the found optimum, a practical design guideline is recommended. The performance of high-strength steel and a high-ductility structural system such as the inter-story drift, maximum roof acceleration, property of BRB hysteresis, strength ratio between the main frame and BRB and cumulative fatigue damage are investigated. In addition, the economic feasibility of using high-strength steel in the structural system is compared to that using traditional steel materials.

Abstracts:The strength development of termite mound cement paste and concrete was investigated using the termite clay mound material to replace cement by mass in the proportions of 0%–25%, and evaluating its effects on the termite mound clay paste and concrete. The setting times of the material showed, it behaved like an accelerator. The compressive strength decreased as the percentage replacement increased, and 5%–20% of the material can be used to produce good quality concrete. The statistical evaluation further confirmed the suitability of the material for concrete production.

Abstracts:Sulfate attack is one of the reasons which cause deterioration and damages of concrete structures throughout the world. Thus, sulfate attack resistance is an important durability and serviceability concern for materials used in construction. Various geopolymer mortars and OPC mortars were manufactured to evaluate magnesium sulfate resistance. This paper studied the effect of curing temperature, sodium hydroxide solution molarity, alkaline solution to binder ratio and binder type on magnesium sulfate resistance of geopolymer mortar and make a comparison between OPC mortar and various geopolymer mortars. Specimens were immersed in 10% magnesium sulfate solution up to 48 weeks. The evaluated properties in this study were water absorption and voids ratio, visual inspection, microstructure of specimens, weight change, compressive strength, flexural strength and expansion strain. Results indicated that increasing curing temperature, sodium hydroxide solution molarity and decreasing alkaline solution to binder ratio enhanced magnesium sulfate resistance of geopolymer mortar. Mixes containing 50% fly ash, 35% ground granulated slag (GGBS) and 15% silica fume achieved the best performance in magnesium sulfate solution. Generally, various geopolymer mortars achieved better performance in magnesium sulfate solution compared to OPC mortars.