Monitoring the cementitious materials subjected to sulfate attack with optical fiber excitation Raman spectroscopy

Formation of ettringite and gypsum from sulfate attack together with carbonation and chloride ingress have been considered as the most serious deterioration mechanisms of concrete structures. Although electrical resistance sensors and fiber optic chemical sensors could be used to monitor the latter two mechanisms on site, currently there is no system for monitoring the deterioration mechanisms of sulfate attack. In this paper, a preliminary study was carried out to investigate the feasibility of monitoring sulfate attack with optical fiber excitation Raman spectroscopy through characterizing the ettringite and gypsum formed in deteriorated cementitious materials under an optical fiber excitation + objective collection configuration. Bench-mounted Raman spectroscopy analysis was also conducted to validate the spectrum obtained from the fiber-objective configuration. The results showed that the expected Raman bands of ettringite and gypsum in the sulfate-attacked cement paste can be clearly identified by the optical fiber excitation Raman spectrometer and are in good agreement with those identified from bench-mounted Raman spectrometer. Therefore, based on these preliminary results, it is considered that there is a good potential for developing an optical fiber-based Raman system to monitor the deterioration mechanisms of concrete subjected to sulfate attack in the future

Application of Raman spectroscopy for tracing the status of silica fume in cementitious materials

Silica fume (SF) is an important component for manufacturing high performance concrete (HPC), owing to its superb pozzolanic reactivity and physical filling effects. However, application of SF in concrete may cause potential hazards issues. Although using SF in slurry form can somehow reduce the potential biotoxicity, the long-term stability and status of the SF particles within cementitious materials is still uncertain. In the current study, attempts were made to use Raman spectroscopy as an innovative alternative technique for tracing and identifying the status of SF both in its original SF slurry and in a 6-month-old hydrated cement paste. Light-optical microscope was also used to examine the morphology of the SF particles in the aforementioned samples. The results showed that under Raman spectroscopy, the various components of the SF in slurry, such as amorphous silica, silicon crystal, and carbon, were clearly recognised. In addition, the SF agglomerates formed in the slurry were also detected. On the other hand, the chemical composition, status, and morphology of both SF and SF agglomerates in the 6-month-old paste were also identified. The study reported in this paper indicates that Raman spectroscopy could be a potential technique for tracing the status of SF, so that the potential safety hazards of SF can be monitored

A Raman spectroscopy based optical fibre system for detecting carbonation profile of cementitious materials

Sensors demonstrate huge potential in civil engineering for monitoring the health condition and performance of concrete structures. Amongst various chemical deterioration mechanisms causing inadequate durability of concrete structures, carbonation is one of the most severe mechanisms. It occurs from the chemical reactions between intruded CO2 and calcium-bearing phases, hence is accompanied by the formation of calcium carbonate (CaCO3) and the decrease of the alkalinity of concrete pore solution, causing corrosion of rebar in concrete. Thus, detecting carbonation process, especially, determining the carbonation profile (i.e. the content of carbonation products formed against the depth into concrete structure), is of great importance to the diagnosis of the health condition of concrete structures and the prediction of service life. Unfortunately, existing sensors for health monitoring systems suffer from various limitations. Optical fibre Raman technology offers a unique opportunity for developing a novel chemical sensor system capable of monitoring the service-condition of concrete in situ. In the current work, a bespoke ‘coaxial’ optical fibre sensing platform based on Raman spectroscopy was successfully established with a 514.5 nm laser. All the optics were tailored for efficiently exciting and receiving signals from cementitious materials, and their diameters were restricted within 0.5 in. in order to explore the feasibility of developing an embeddable miniature sensor system in the future. This sensing system was then employed to detect the carbonation mechanism of a plain Portland cement (PC) paste. The calcium carbonate polymorphs as well as the carbonation profile in the PC paste was successfully recognised and established with the results being verified favourably by bench-mounted Raman, X-ray Diffraction (XRD) and Thermogravimetry (TG) analyses. Our results demonstrate a good potential for developing a novel Raman spectroscopy based optical fibre sensor system for monitoring the health condition and the performance of concrete structures in future

Tracing the status of silica fume in cementitious materials with Raman microscope

Silica fume (SF) is an essential material for formulating high performance concrete (HPC). However, its small particle size could cause safety-hazards. Although replacing SF powder with slurry can somehow avoid the potential bio-toxicity, its long-term stability within cementitious materials is unknown. In this study, Raman microscope which combines Raman spectroscopy with light-optical microscope was successfully applied to characterise the composition and morphology of SF in original slurry and hydrated SF-Portland cement (PC) pastes. The unhydrated SF-agglomerates were clearly detected in the original SF slurry and the 22-hour and 6-month hydrated SF-PC pastes

Comparative study on microstructure and surface properties of keratin- and lignocellulosic-based activated carbons

© 2015 Elsevier B.V. All rights reserved. The paper probed the preparation of activated carbon by potassium silicate (K2SiO3) activation from keratin waste (cowhair waste, CW) and lignocellulosic materials (Cyperus alternifolius, CA) and the comparisons of physicochemical properties of the resulting carbons. These impregnation conditions were as follows: one impregnated at room temperature for 12 h then dipped at high temperature for 30 min; the other was only impregnated at room temperature for 12 h, producing four activated carbons CWAC-1, CWAC-2, CAAC-1, and CAAC-2. The influence of activation time, K2SiO3/precursor weight ratio, and the pre-process on properties of activated carbons was discussed. The CWAC-1 produced at 700°C with the K2SiO3/precursor weight ratio of 2:1 possessed the Brunauer-Emmet-Teller (BET) surface area of 1965 m2/g and total pore volume of 1.345 cm3/g, while CAAC-1 prepared at the same conditions attained the BET surface area of 1710 m2/g and total pore volume of 0.949 cm3/g. The surface area and total pore volume of CAAC increased with the impregnation ratio. Moreover, CWAC-1, CWAC-2, CAAC-1, and CAAC-2 exhibited high portion of micropores, illustrating the role of K2SiO3. The analysis with a Fourier transform infrared spectrometer indicates that CWAC has more functional groups than CAAC, as well as CWAC-1 and CWAC-2 which possess similar functional groups

Establishing the Carbonation Profile with Raman Spectroscopy: Effects of Fly Ash and Ground Granulated Blast Furnace Slag

Establishing the carbonation profile is of great significance to the prediction of the service life of reinforced concrete structures. In our previous work, Raman spectroscopy was shown to be an efficient tool for characterizing calcium carbonate (CaCO3) polymorphs and their profile in plain Portland cement (PC) matrices. However, as supplementary cementitious materials (SCMs), particularly fly ash (FA) and ground granulated blast furnace slag (GGBS), are widely used in concrete, establishing the carbonation profile without considering the possible effects of these SCMs could be of little significance to the real world. This paper, thus, investigated the effects of FA and GGBS on the working capacity and reliability of Raman spectroscopy for establishing the carbonation profile in PC blends containing SCMs. The thermogravimetry (TG) analysis was also conducted to verify the results from Raman spectroscopy. The results show that Raman spectroscopy demonstrated a good capacity for differentiating the variation of CaCO3 contents in FA or GGBS blends. However, the incorporation of FA and GGBS into the PC system caused some adverse effects on the quantification of CaCO3 by Raman spectroscopy, which could be attributed to the darker color and weak scatter nature of FA and the high content of glassy phases in GGBS

Recent changes of water discharge and sediment load in the Yellow River basin, China

The Yellow River basin contributes approximately 6% of the sediment load from all river systems globally, and the annual runoff directly supports 12% of the Chinese population. As a result, describing and understanding recent variations of water discharge and sediment load under global change scenarios are of considerable importance. The present study considers the annual hydrologic series of the water discharge and sediment load of the Yellow River basin obtained from 15 gauging stations (10 mainstream, 5 tributaries). The Mann-Kendall test method was adopted to detect both gradual and abrupt change of hydrological series since the 1950s. With the exception of the area draining to the Upper Tangnaihai station, results indicate that both water discharge and sediment load have decreased significantly (p<0.05). The declining trend is greater with distance downstream, and drainage area has a significant positive effect on the rate of decline. It is suggested that the abrupt change of the water discharge from the late 1980s to the early 1990s arose from human extraction, and that the abrupt change in sediment load was linked to disturbance from reservoir construction.Geography, PhysicalGeosciences, MultidisciplinarySCI(E)43ARTICLE4541-5613

Earliest Triassic microbialites in the South China Block and other areas; controls on their growth and distribution

Earliest Triassic microbialites (ETMs) and inorganic carbonate crystal fans formed after the end-Permian mass extinction (ca. 251.4 Ma) within the basal Triassic Hindeodus parvus conodont zone. ETMs are distinguished from rarer, and more regional, subsequent Triassic microbialites. Large differences in ETMs between northern and southern areas of the South China block suggest geographic provinces, and ETMs are most abundant throughout the equatorial Tethys Ocean with further geographic variation. ETMs occur in shallow-marine shelves in a superanoxic stratified ocean and form the only widespread Phanerozoic microbialites with structures similar to those of the Cambro-Ordovician, and briefly after the latest Ordovician, Late Silurian and Late Devonian extinctions. ETMs disappeared long before the mid-Triassic biotic recovery, but it is not clear why, if they are interpreted as disaster taxa. In general, ETM occurrence suggests that microbially mediated calcification occurred where upwelled carbonate-rich anoxic waters mixed with warm aerated surface waters, forming regional dysoxia, so that extreme carbonate supersaturation and dysoxic conditions were both required for their growth. Long-term oceanic and atmospheric changes may have contributed to a trigger for ETM formation. In equatorial western Pangea, the earliest microbialites are late Early Triassic, but it is possible that ETMs could exist in western Pangea, if well-preserved earliest Triassic facies are discovered in future work

The cost of promiscuity: sexual transmission of Nosema microsporidian parasites in polyandrous honey bees

Multiple mating (and insemination) by females with different males, polyandry, is widespread across animals, due to material and/or genetic benefits for females. It reaches particularly high levels in some social insects, in which queens can produce significantly fitter colonies by being polyandrous. It is therefore a paradox that two thirds of eusocial hymenopteran insects appear to be exclusively monandrous, in spite of the fitness benefits that polyandry could provide. One possible cost of polyandry could be sexually transmitted parasites, but evidence for these in social insects is extremely limited. Here we show that two different species of Nosema microsporidian parasites can transmit sexually in the honey bee Apis mellifera. Honey bee males that are infected by the parasite have Nosema spores in their semen, and queens artificially inseminated with either Nosema spores or the semen of Nosema-infected males became infected by the parasite. The emergent and more virulent N. ceranae achieved much higher rates of infection following insemination than did N. apis. The results provide the first quantitative evidence of a sexually transmitted disease (STD) in social insects, indicating that STDs may represent a potential cost of polyandry in social insects

A two-wheeled machine with a handling mechanism in two different directions

Despite the fact that there are various configurations of self-balanced two-wheeled machines (TWMs), the workspace of such systems is restricted by their current configurations and designs. In this work, the dynamic analysis of a novel configuration of TWMs is introduced that enables handling a payload attached to the intermediate body (IB) in two mutually perpendicular directions. This configuration will enlarge the workspace of the vehicle and increase its flexibility in material handling, objects assembly and similar industrial and service robot applications. The proposed configuration gains advantages of the design of serial arms while occupying a minimum space which is unique feature of TWMs. The proposed machine has five degrees of freedoms (DOFs) that can be useful for industrial applications such as pick and place, material handling and packaging. This machine will provide an advantage over other TWMs in terms of the wider workspace and the increased flexibility in service and industrial applications. Furthermore, the proposed design will add additional challenge of controlling the system to compensate for the change of the location of the COM due to performing tasks of handling in multiple directions