Assessment of in-situ alkali-silica reaction (ASR) development of glass aggregate concrete prepared with dry-mix and conventional wet-mix methods by X-ray computed micro-tomography

A recent study showed that concrete products prepared with the dry-mix method have better alkali-silica reaction (ASR) resistance than that prepared by the wet-mix method. But the mechanism of ASR in dry-mix glass concrete remains unclear. Meanwhile, the techniques such as Scanning Electron Microscopy (SEM) and Mercury Intrusion Porosimetry (MIP) cannot reflect the in-situ evolution of the microstructure with the progress of the ASR. In this study, two common casting methods, the wet-mix and dry-mix methods, were adopted to prepare the glass concrete. The non-destructive X-ray computed micro-tomography (X-ray μCT) technique was applied to observe the pore geometries of both the wet-mix and dry-mix glass concrete, to determine their porosities using 3D volumes and to investigate the generation of cracks during ASR development. This study firstly observed the irregular pore geometry of the glass concretes by quantitatively comparing the pore geometries using the sphericity developed by Wadell for both dry-mix and wet-mix glass concrete. The test results of the porosity measured by 3D volume showed that the porosity of the dry-mix glass concrete decreased after the ASR test. However, no obvious change was observed in the porosity of the wet-mix glass concrete. This change may be attributed to the large pores in the dry-mix glass concrete which can accommodate the ASR gel. Through the in-situ observation using 3D X-ray μCT, no new cracks were generated in the dry-mix glass concrete during the progressive development of ASR. On the contrary, new cracks which were filled with ASR gel were densely distributed in the wet-mix glass concrete, which led to failure of the concrete matrix. This is because the expansive ASR gel formed could not be accommodated by the limited pore space in the wet-mix glass concrete, and the swelling pressure of ASR gel induced new cracks in the wet-mix glass concrete.     

Development of a universal accelerated test for alkali-silica and alkali-carbonate reactivity of concrete aggregates

A universal accelerated test for both alkali-silica and alkali-carbonate reactivity was proposed based on extensive comparative studies on existed Accelerated Mortar Bar Test (AMBT), (e.g., ASTM C1260, CSA A23. 2–25A, RILEM TC191-ARP-AAR02) and Chinese accelerated procedures. A single size fraction of 2.5–5.0 mm aggregate particles is used in the test instead of five-graded requirements in the AMBT, and 0.15–0.80 mm fine particles for ASR, 5–10 mm particles for ACR in existed Chinese accelerated tests. Three short-fat bars, 40 × 40 × 160 mm, made at fixed cement-aggregate ratio of 1:1, and water-cement ratio of 0.33 are used and the length change of the bars is monitored till 28 days in 1 M NaOH solution at 80°C after being soaked in 80°C water for 24 h. Over 40 kinds of aggregates from various origins, which include both ASR and ACR aggregates and show a broad range of reactivity levels in the concrete prism test (CPT), were used to evaluate the reliability of the new test in this study. Experimental results indicate that, for ASR aggregates, the new test gives a better indication than the AMBT does of both the reactive/nonreactive characteristic and reactive levels of almost all tested aggregates based on an acceptance criteria of 0.093% at 14 days, although some very highly reactive aggregates show low expansions relative to the CPT. The “abnormal” low expansion of some highly reactive aggregate in the test is mainly due to the rapid formation and loss of fair amount of low viscosity ASR product into the soaking alkali solution. The results on some typical ACR aggregates usually undetected by the AMBT show that the new test gives the same outcome as using 5–10 mm particles in the Chinese Accelerated Concrete Microbar Test for ACR aggregates and is in agreement with the CPT, which suggests that it has good potentials to be used for ACR aggregate when an expansion criteria of 0.1% after 28 days is used.     

Impact behaviour of preloaded glass/polyester woven plates

In this work, the effect of a biaxial preload in the behaviour of glass/polyester woven-laminate plates subjected to high-velocity transversal impact was studied. For this, an analytic model based on energy considerations that include the presence of an in-plane preload was used. The results of the analytic model for the biaxial preload state were compared with those found for a non-preload plate, the difference between them being minimal for the pre-stressed level reached in the tests (31% of the static UTS). Therefore, numerical simulations were made in order to study the effect of the preload in greater detail; furthermore, experimental tests were conducted, validating the analytic and numerical model. In general, the two methods revealed minimal differences between the values of the ballistic limit and those of the residual velocity.     

Initial conditions for simulating glass fiber orientation in the filling of center-gated disks

This work is concerned with the effect that initial conditions play in simulating long (>1 mm) glass fiber (LGF) orientation in the filling of a center-gated disk (CGD). For the CGD, most orientation simulations begin at the gate and make assumptions about the initial fiber orientation entering the mold. This paper reports on a method for simulating LGF orientation in a CGD by simulating the sprue, gate, and mold (S–G–M) as a single domain. The velocity field solution is determined using a finite element method including the advancing front. To predict LGF orientation, rigid and flexible fiber models are employed using parameters obtained from rheology. It is observed that predicting LGF orientation in systems with either model is highly sensitive to the choice of initial conditions. Furthermore, the flexible fiber model is observed to be more successful at predicting LGF orientation based on agreement with experimental results.     

Dielectric behaviour of glasses and glass ceramics in the system BaO-PbO-TiO2-B2O3-SiO2

Glasses with varying molar ratios of PbO/BaO in the system BaO-PbO-TiO₂-B₂O₃-SiO₂ were prepared keeping (BaO + PbO)/TiO₂ ratio equal to one. The glasses were ceramized by two-stage heat treatment. X-ray diffraction indicates that PbTiO₃ crystallizes in lead-rich glasses while BaTiO₃ precipitates in barium-rich compositions. Solid solution (Ba, Pb)TiO₃ does not seem to crystallize over the entire range of compositions. Simultaneous presence of PbO and BaO in the initial glass composition reduces the yield of ferroelectric phase. Dielectric properties have been interpreted in terms of microstructural features.     

Anisotropic behaviour of the glass transition temperature in thin films of Langmuir-Blodgett deposited side chain polymers

Langmuir-Blodgett (LB) films of side chain polyamic acids were formed, deposited onto optical waveguides and imidized via heating to the corresponding polyimides on the optical waveguides. The LB film formation of the side chain polyamic acids, the imidization reaction and the glass transition behaviour of the polyimide thin films were investigated. Polarisation dependent waveguide mode spectroscopy was applied therefore. It was found that the glass transition temperature (Tg) of bulk and LB thin film samples of these polymers are identical and only depend on the spacer length between the side chain and backbone, not on film thickness. Our investigation shows that in the case of the ultrathin film geometry, the glass transition temperature exhibits an anisotropic behaviour. We find the classical kink in the temperature scan (a change in slope of the free volume vs. temperature plot) due to the thermal expansion change at Tg, in p-polarisation only, which is perpendicular to the main chain orientation. In the s-polarisation measurements (parallel to the main chains) no kink was found, only an offset in the vicinity of Tg. We attribute the anisotropic thermal behaviour to a transition, the freezing of segmental motion, in the side chains only.     

Effect of fiber surface texture on the mechanical properties of glass fiber reinforced epoxy composite

The effect of fiber sizing and surface texture on the strength and energy absorbing capacity of fiber reinforced composites has been evaluated at two length scales using the macromechanical quasi-static punch shear test and the micromechanical microdroplet test methods. E-Glass/SC-79 epoxy composite laminates with four different fiber sizing formulations with various degrees of chemical bonding and surface texture have been investigated. The failure modes during perforation and different energy dissipating damage mechanisms were identified and quantified. The punch shear strength and the total energy absorption per unit volume of composite with hybrid sizing have increased by 48% and 100% over the incompatible sizing. These results showed linear correlations with the interphase properties reported earlier by the authors (Gao et al., 2011) and provided a methodology for developing new sizing by tailoring chemical bonding and the fiber surface texture at the fiber–matrix interphase for improving both strength and energy absorption of composites.     

Feasible use of large volumes of GGBS in 100% recycled glass architectural mortar

The use of 100% recycled glass as aggregates in architectural mortar is regarded as an environmentally friendly, cost-effective and attractive feature for construction applications due to the natural characteristics of glass (e.g. aesthetic pleasing, impermeability, chemical resistance properties). However, the need to use large quantities of white cement for architectural products may increase the overall cost of production. Therefore, the possibility of using a near-white coloured ground granulated blast furnace slag (GGBS) to replace white cement for architectural mortar production is an attractive option. This paper reports a study which is an extension of our previous work aiming to investigate the feasibility of using large volumes of GGBS (ranging from 15% to 75% white cement replacements) to produce self-compacting-based architectural mortars. To improve the appearance (whiteness) of the mortar, a small quantity of titanium dioxide (TiO₂) was added to the selected mixes for comparison purposes. Fresh and hardened properties of the mortar including mini-slump flow, density, water absorption, flexural strength, equivalent compressive strength, drying shrinkage, alkali silica reaction (ASR) and acid attack resistance were investigated. The overall performance showed that it is feasible to use GGBS for the production of architectural mortar and 60% replacement of white cement by GGBS was determined to be optimal. The replacement significantly increased the flexural strength, and reduced the drying shrinkage and risk of ASR expansion, as well as improved the ability to resist acid attack of the mortar produced.     

A continuum damage model for glass/epoxy laminates in tension

The present work is concerned with the study of the damage behaviour of a composite material based on glass fibre reinforced polymer (GFRP). The main goal is to predict the rupture force using model equations that combine enough mathematical simplicity to allow their usage in engineering problems with the capability of describing a complex nonlinear mechanical behaviour. A model for tensile developed within the framework of Continuum Damage Mechanics that accounts for the effect of the load rate and temperature of the system is proposed and analyzed. The predicted values of tensile stress for different values of the load rate and temperature are compared with experimental data, showing a good agreement.     

Characterization of the dynamic failure behaviour of a glass-fiber/vinyl-ester at different temperatures by means of instrumented Charpy impact testing

Instrumented Charpy impact testing is used to investigate the strength and failure properties of a glass-fiber/vinyl-ester composite. The test technique, originally developed for testing of steel specimens, is presented in its basic aspects; reported are the conventional procedures for determining load, displacement and energy absorption that a specimen experiences, over the entire phase of loading and subsequent failure of the specimen. Techniques are described for generating data of sufficient accuracy when applying the test to composites. In particular, the necessity of utilizing measurement chains of sufficiently high frequency response and striker tups of sufficiently high sensitivity is emphasized. Tests are performed with glass-fiber/vinyl-ester specimens, provided with notches oriented in two different directions with respect to the plies of woven glass fiber rovings. Two different types of failure result: fiber breakage ahead of the notch due to tensile stresses, and delaminations of the interface planes between the plies of woven glass fiber rovings due to shear stresses. Specifically, energies absorbed by the specimen over the entire failure process and values of maximum load occurring during the impact process are measured over a large range of temperatures. The data are correlated with the observed failure phenomena. The high level of information obtained in characterizing the failure behaviour by means of a test which requires limited technical effort proves the instrumented Charpy impact test to be a simple but effective tool for quantifying the quality of a composite in practical applications, as e.g. in surveillance programs for controlling processes such as manufacturing or aging of the material.     

Neural network approach for estimating the residual tensile strength after drilling in uni-directional glass fiber reinforced plastic laminates

The drilling of fiber reinforced plastics (FRP) often results in damage around the drilled hole. The drilling induced damage often serves to impair the long-term performance of the composite products with drilled holes. The present research investigation focuses on developing a predictive model for the residual tensile strength of uni-directional glass fiber reinforced plastic (UD-GFRP) laminates with drilled hole which has not been developed worldwide till now. Artificial neural network (ANN) predictive approach has been used. The drill point geometry, the feed rate and the spindle speed have been used as the input variables and the residual tensile strength as the output. The results of the predictive model are in close agreement with the training and the testing data.     

Optimum mixing ratio of epoxy for glass fiber reinforced composites with high thermal stability

The optimum condition of glass fiber/epoxy composites was investigated according to mixing ratio of two epoxy matrices. Novolac type epoxy and isocyanate modified epoxy were used as composites matrix. Based on chemical composition of mixing matrix, optimum mixing ratio of epoxy resins was obtained through FT-IR instrument. In order to investigate thermal stability and interface of epoxy resin, glass transition temperature was observed by DSC instrument, and static contact angle was measured by reflecting microscope. Change of IR peak and T_g was conformed according to different epoxy mixing ratios. After fabrication of glass fiber/epoxy composites, tensile, compression, and flexural properties were tested by UTM by room and high temperature. The composites exhibited best mechanical properties when epoxy mixing ratio was 1:1.     

Use of pre-wetted lightweight fine expanded shale aggregates as internal nutrient reservoirs for microorganisms in bio-mineralized mortar

Interest in developing bio-based self-healing cement-based materials has gained broader attention in the concrete community. One of challenges in developing bio-based self-healing cement-based materials is that cell death or insufficient metabolic activity might occur when the cells are inoculated to the cement paste. This paper investigates the use of internal nutrient reservoirs via pre-wetted lightweight fine expanded shale aggregates to improve cell viability in mortar. Incorporation of internal nutrient reservoirs resulted in an increase in the vegetative cells remaining without any substantial loss in strength. These results pave the way to develop a self-healing and self-curing concrete with an extended service life.     

Controlled oxidative synthesis of Bi nanoparticles and emission centers in bismuth glass nanocomposites for photonic application

Here we demonstrate an oxidative process to control metallic bismuth (Bi⁰) nanoparticles (NPs) creation in bismuth glass nanocomposites by using K₂S₂O₈ as oxidant and enhanced transparency of bismuth glasses. Formation of Bi⁰ NPs has been monitored by their distinct surface plasmon resonance (SPR) band at 460 nm in the UV-visible absorption spectra. It is further confirmed by the transmission electron microscopy (TEM) images which disclose the formation of spherical Bi⁰ NPs whereas the selected area electron diffraction (SAED) pattern reveals their crystalline rhombohedral phase. These glasses are found to exhibit visible and near infrared (NIR) luminescence bands at 630 and 843 nm respectively on excitation at 460 nm of the SPR band. It is realized that the luminescence center of bismuth species is an uncertain issue, however, it is reasonable to consider that the emission band at 630 nm is due to the combination of ²D_5/2 → ⁴S_3/2 of Bi⁰ and ²P_3/2 (1) → ²P_1/2 of Bi²⁺ transitions, and that of NIR emission band at 843 nm is attributed to the ²D_3/2 → ⁴S_3/2 of Bi⁰ transition.     

Comparison of methods to determine CTOD for SENB specimens in different strain hardening steels

Methods for determining crack tip opening displacement (CTOD) given in national and international standards are compared for steels with a range of strain hardening characteristics. Crack tip opening displacement measurements were made from single‐edge notched bend notches using a silicone rubber casting method. The finite element model produced good agreements with predictions of these CTOD measurements. The versatility of the finite element model enabled CTOD from the original crack tip and the 45° intercept method to be compared. The 45° CTOD generally underestimates the original crack tip CTOD, and is less useful for conditions with stable crack extension. Apart from the high strain hardening material, CTOD calculated using BS 7448‐1, WES 1108 (JWES), and ASTM E1820 was slightly lower than the values determined from silicone measurements and modelling, which is conservative. ASTM E1820 gave the largest underestimation of CTOD, whilst BS 7448‐1 may be unsuitable for higher strain hardening steels, where the standard predicts higher CTOD than measured from the replica. JWES gives the most consistent estimation of CTOD for steels with a wide range of strain hardening values.     

Sol-gel coatings in the ZrO2-SiO2 system for protection of historical works of glass

Different kinds of protective treatments based on sol-gel coatings have been designed and prepared. Final application of these coatings would be used for protection and preventive conservation of a wide variety of historical glasses from several times and provenance. Historical glasses show a superficial deterioration depending on the exhibition conditions submitted by the ancient objects since their origin.The coatings effectiveness was confirmed by means of accelerated ageing tests under simulated atmospheric polluted conditions by using SO₂ as a pollutant and different kind of glasses as reference substrates.Coatings with compositions 100SiO₂ and 10ZrO₂·90SiO₂ (mol%) proved to be highly protective when they were densified up to 250 and 400 °C for 1 h. Those coatings densified at lower temperature (for instance, 60 °C for 3 days) appeared partially cracked and detached after the ageing tests. For compositions 50ZrO₂·50SiO₂ and 100ZrO₂ the major problem was concerned to the high surface reflectance provided by the zirconium oxide, which modifies very much the appearance of the substrate glasses.     

Investigation of combined stress state failure criterion for glass fiber/epoxy interface by the cruciform specimen method

The interfacial failure criterion under combined stress state in a glass fiber/epoxy composite is investigated by the cruciform specimen method. Experiments were conducted by using specimens with a fiber whose angle from the loading direction is varied in order to make various stress state of normal and shear at the interface. Finite element analysis is performed to calculate the interfacial stress distribution. By combining the experimental measurement of the specimen stress at the interfacial debonding initiation and the finite element stress analysis, it is possible to obtain the interfacial stress state at interfacial failure. A method to determine the interfacial failure criterion and the interfacial failure initiation location simultaneously is proposed in the present study. We conclude the value of the interfacial shear strength is higher than that of the interfacial normal strength for the material system used in the present study.     

Elastic behaviour and failure mechanism in epoxy syntactic foams: The effect of glass microballoon volume fractions

A representative elementary volume (REV) in epoxy syntactic foams was generated to incorporate randomly distributed glass microballoons that followed a log-normal size distribution. Finite element modelling of the REV foam was developed and experimentally validated to investigate the elastic behaviour and failure mechanism in the foams with different microballoon volume fractions (V). The localised stresses concentrate in various zones within the foam, and can cause the vertical splitting fracture of microballoons and the micro-crack formation in the matrix. Dependent on the microballoon volume fraction, micro-cracks can propagate to join adjacent micro-cracks and voids left by fractured microballoons, and finally develop into a macro-crack either in the preferred longitudinal (for low V) or diagonal (for high V) directions. This is consistent with the macroscopic observations of the fracture process in the foam specimens. It was also found that elastic characteristics of the foam vary with microballoon volume fractions.     

Implementation of a constitutive micromechanical model for damage analysis in glass mat reinforced composite structures

A micromechanical model based on a probabilistic approach is implemented in the finite element code CASTEM 2000 to develop numerical simulations that efficiently predict the overall damaged behaviour of random oriented fibre composites. The proposed damage constitutive model is based upon the generalised Mori and Tanaka scheme and Eshelby's equivalence theory. Damage mechanisms occurring at each composite constituent (fibres, matrix and interface) are associated to Weibull probabilistic functions to model their onset and progressive growth at the microscopic scale level. It is obvious that the damaged behaviour of the composite material depends widely on the microscopic material parameters (fibre length, fibre volume fraction, fibre orientation, …). On one hand, the micromechanical model uses homogenisation techniques which enabled us to link these microscopic parameters to the material behaviour and to evaluate explicitly their influences. On the other hand, the implementation of the derived behaviour law into a finite element code enabled us to reflect on the effect of these microscopic parameters on the overall response of a simple composite structure presenting heterogeneous stress fields. In fact, the damage evolution in each constituent (local scale) and the related stiffness reduction are estimated at any material point (integration point) or node of the considered structure subject to a specific loading. Numerical simulations of a composite plate with a hole under in-plane tension were performed to validate the implementation of the behaviour law. Numerical results have been compared to experimental curves and damage evolutions monitored by acoustic emission techniques. Simulations agree well with experimental results in terms of damage onset and growth.     

Mechanisms of Yb sensitization to Tm for blue upconversion luminescence in fluorophosphate glass

The sensitization mechanisms of Yb³⁺ to Tm³⁺ for the blue upconversion luminescence in fluorophosphate glass were studied. Two different mechanisms exist in the sensitization. One is the sequential sensitization that Tm³⁺ is excited from ³H₆ to ¹G₄ through absorbing three photons transferred from Yb³⁺ one by one. Another is the cooperative sensitization that two Yb³⁺ ions form a couple cluster firstly, and then the couple cluster Yb³⁺ ions transfer their energy to Tm³⁺ and excite it to ¹G₄. With the increment of the concentration of Yb³⁺ ions, the sequential sensitization becomes weak and the cooperative sensitization becomes intense, and the transformation trend of sensitization mechanism with the increment of Yb³⁺ concentration can be clarified by the introduction of Tb³⁺ ions in the glass.