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A novel effective while low-cost capacitive transducer (CT), which can precisely measure rebar size and reinforcement position in both x-axis and y-axis under concrete cover using capacitance signals, is originally developed. In this paper, numerical simulations and experiments have been carried out to verify the effectiveness of the developed capacitive sensor. In the numerical simulations, electrostatic field distribution has been built and FEM method is adopted to compute the theoretical capacitance outputs during the rebar position testing, in which two kinds of capacitance measuring methods are compared. The same-face electrodes capacitance sensing method is proved to have better performance of rebar position prediction in both x-axis and y-axis directions than the face-to-face electrodes capacitance sensing method. To verify the effectiveness of the developed capacitive sensor in the real onsite scenario, experiments have also been conducted for the rebar position testing in the reinforced concrete. Both simulations and experimental results have shown that the developed CT with innovative capacitance measuring method has great accuracy in predicting the rebar size and position, which is the foundation of the future reinforcement corrosion detection.

Flexural fatigue behavior of ferrocement elements is evaluated in this paper. Ferrocement elements were developed by incorporating fly ash cenosphere (FAC) as lightweight filler material in various amounts, PVA fibers as discontinuous reinforcement in the matrix, and galvanized iron welded wire mesh as primary reinforcement. Both single and double layer reinforced ferrocement elements were cast. The developed composites were tested for static flexural strength as well as flexural fatigue strength under three-point flexural loading. The fatigue lives, thus, determined at various stress levels and stress ratios were used develop S-N relationships, and equations have been proposed to predict the flexural fatigue strength of ferrocement. The results suggest that the probabilistic distribution of fatigue life of ferrocement can be modeled by two-parameter Weibull distribution. Thus, the Weibull distribution is further employed to incorporate the failure probabilities into the fatigue life of ferrocement. The fatigue lives corresponding to different failure probabilities have been calculated and the data so obtained have been used to generate Pf-S-N diagrams. The obtained results were also compared with the three - parameter Weibull distribution, modeled by ProFatigue, for probabilistic assessment of experimental fatigue data sets. It is found that FAC is useful in producing structural lightweight ferrocement elements with enhanced ductility and improved flexural fatigue characteristics. Further, two - parameter Weibull model is more accurate, in predicting failure fatigue lives of double layer reinforced ferrocement structural elements, as compared to ProFatigue modeling employing three - parameter Weibull model. For single layer reinforced elements, both models can be used with fair confidence level. © 2019 by the fib. All rights reserved.

Flexural fatigue behavior of ferrocement elements is evaluated in this paper. Ferrocement elements were developed by incorporating fly ash cenosphere (FAC) as lightweight filler material in various amounts, PVA fibers as discontinuous reinforcement in the matrix, and galvanized iron welded wire mesh as primary reinforcement. Both single and double layer reinforced ferrocement elements were cast. The developed composites were tested for static flexural strength as well as flexural fatigue strength under three-point flexural loading. The fatigue lives, thus, determined at various stress levels and stress ratios were used develop S-N relationships, and equations have been proposed to predict the flexural fatigue strength of ferrocement. The results suggest that the probabilistic distribution of fatigue life of ferrocement can be modeled by two-parameter Weibull distribution. Thus, the Weibull distribution is further employed to incorporate the failure probabilities into the fatigue life of ferrocement. The fatigue lives corresponding to different failure probabilities have been calculated and the data so obtained have been used to generate Pf-S-N diagrams. The obtained results were also compared with the three - parameter Weibull distribution, modeled by ProFatigue, for probabilistic assessment of experimental fatigue data sets. It is found that FAC is useful in producing structural lightweight ferrocement elements with enhanced ductility and improved flexural fatigue characteristics. Further, two - parameter Weibull model is more accurate, in predicting failure fatigue lives of double layer reinforced ferrocement structural elements, as compared to ProFatigue modeling employing three - parameter Weibull model. For single layer reinforced elements, both models can be used with fair confidence level. © 2019 by the fib. All rights reserved.

Fresh water makes up a very small fraction of total available water in earth. One major challenge for marine infrastructure is the shortage of fresh water for making concrete. To save fresh water, sea water can be used for mixing in concrete. This study focuses on the mechanism and microstructure characteristics of seawater based cementitious system. Firstly, the early age properties and mechanism of seawater cement paste samples was investigated. The seawater samples showed faster setting time and increased hydration rate. Rate of increase of hydration increases the dispersion of particles from cement increasing the hydration product formation. Molecular dynamics simulation was performed on C(N)ASH gel to, study the interactions of sodium and calcium atom in gel system. Secondly, the properties of seawater cement paste samples are investigated. Different samples made with different percent of salt and pozzolans are tested for compressive strength properties, thermal loss, X-ray diffractogram crystals and microstructures & morphology. 29 Si and 27Al NMR test was conducted on seawater cement paste samples to know the structure and atomic co-ordination of the seawater system. The study revealed that seawater cementitious system has no peaks of Q4 and Q3 and Al is present in tetrahedral and octahedral co-ordination. Thirdly, the durability of pozzolans seawater system was investigated by storing the samples in corrosive solutions for 6 months. Based on the observations, seawater samples made with slag and fly ash binders showed superior performance in corrosive solution. The LC2 sample suffered the maximum weight loss of 13.5% in sulphate solution. The properties of seawater samples improved when pozzolans were added to the system. Lastly, studies were performed on geopolymer seawater cementitious system. The performance of geopolymer in seawater was comparatively better. But the samples were affected by excessive carbonation

In this study, the effect of nano silica (NS) on the properties of cement pastes incorporated with of fly ash cenospheres (FACs) has been investigated. A fixed amount of 1 % NS was added to cement pastes containing various proportions of FAC. It was found that NS was beneficial in improving the mechanical strength of the FAC modified cement pastes. At the 7 – day age, the strength increase for NS modified pastes was about 17 % as compared to pastes without NS. However, the strength enhancement effect decreased with increasing age and FAC content. The dense microstructure of the NS modified pastes compensated for the higher porosity associated with FAC incorporation, leading to the reduced total porosity. With NS, there was better bonding of the FAC particles in the matrix, due to the enhanced interface. The reduced Ca(OH)2 content and partially consumed FAC spherical shells at the early age showed that NS increased the pozzolanic activity of FAC in the cement pastes. © 2017 Elsevier Ltd

The remarkable properties of graphene oxide (GO) make it as an ideal candidate for developing high performance cementitious composites. In this study, it is the first time to investigate the early-age physical adsorption and chemical interactions between the GO and cement hydrates, which have a great influence on the hydration development, microstructures and drying shrinkage of the GO modified cement paste. The experimental results indicated that the addition of GO led to the decreased fluidity of cement paste, resulting from the rapid interaction between the GO and divalent metal cations released from cement hydrates, characterized by Ultraviolet-visible spectroscopy and X-ray photoelectron spectroscopy. It was found that 0.08 wt% GO improved the cement hydration rate/heat by accelerating the cement dissolution, providing nucleation site and regulating the microstructure of cement hydrates. The GO covered cement hydrates at the hydration of 10 min was characterized by scanning electron microscopy. Moreover, the addition of GO restricted the 28-day drying shrinkage of cement paste due to the more compacted microstructures and self-curing effect at the early age. In conclusion, the research finding gives a thorough understanding on early-age interaction mechanism when the GO is immediately mixed with cement particles, and provides a valuable guidance to the sustainable design of GO modified cementitious materials for construction use.

This paper presents an experimental assessment on the suitability of fly ash cenosphere (FAC), a waste residue from coal fired power plants, for use in lightweight ferrocement construction. Ferrocement is a special type of thin walled reinforced concrete constructed of hydraulic cement mortar and closely spaced layers of steel wire mesh. In this study, the mortar mix was prepared by replacing the sand (a typical ingredient of ferrocement matrix) with FAC at 40 %, 50 % and 60 % FAC weight fractions in mortar. Single and double layers of galvanized iron welded wire mesh were used as the main reinforcement while small volume fraction (0.50 %) of PVA fibers was also added as a discontinuous reinforcement resulting in a hybrid composite. The mortar mixes were tested for mechanical strength including compressive strength, elastic modulus and Poisson’s ratio whereas the ferrocement composites were evaluated for flexural performance. The ferrocement composite properties were compared with high strength quartz sand mortar matrix as well. FAC was found to be excellent in producing structural lightweight ferrocement composites (density 1332.09–1457.89 kg/m3) with excellent mechanical properties. The PVA fibers helped improve the inherent brittleness of FAC composites. Thus, lightweight ferrocement elements with higher specific strength (18.39–26.65 kPa/kgm−3), flexural strength (14.47–28.13 MPa), and tensile strength (5.69–11.06 MPa) can be produced, with utilizing FAC waste residue. The use of such composites in construction can promote sustainable development by minimizing waste. © 2017 Elsevier Ltd

Thermal insulating composites help to reduce the total power consumption in a building by creating a barrier between external and internal environment. Such composites can be used in the roofing tiles or wall panels for exterior surfaces. This study purposes to develop lightweight cement-based composites for thermal insulating applications. Waste materials like silica fume (an industrial by-product) and fly ash cenosphere (FAC) (hollow micro-spherical shells obtained as a waste residue from coal fired power plants) were used as partial replacement of cement and lightweight filler, respectively. Moreover, aerogel, a nano-porous material made of silica, was also used in different dosages for improved thermal insulating behavior, while poly vinyl alcohol (PVA) fibers were added for enhanced toughness. The raw materials including binders and fillers were characterized by X-Ray Diffraction (XRD), X-Ray Fluorescence spectroscopy (XRF), and Brunauer–Emmett–Teller (BET) analysis techniques in which various physical and chemical properties of the raw materials were evaluated like specific surface area, chemical composition (oxide form), and pore size distribution (if any). Ultra-lightweight cementitious composites were developed by varying the amounts of FAC and aerogel with 28-day unit weight ranging from 1551.28 kg/m3 to 1027.85 kg/m3. Excellent mechanical and thermal insulating properties of the resulting composites were obtained ranging from 53.62 MPa to 8.66 MPa compressive strength, 9.77 MPa to 3.98 MPa flexural strength, and 0.3025 W/m-K to 0.2009 W/m-K as thermal conductivity coefficient (QTM-500). The composites were also tested for peak temperature difference between outer and inner surfaces when subjected to heating (in a specially designed experimental set-up) by a 275W infrared lamp. The temperature difference up to 16.78 oC was achieved, which indicated outstanding properties of the developed composites to act as a thermal barrier for building envelopes. Micros

The effects of glass cenosphere particles on the properties of fiber-reinforced cement-based composites are explored in this study. Lightweight glass cenospheres were used as fillers in the cementitious composites and incorporated in various proportions. The developed composites were evaluated for mechanical strength parameters including compressive strength, flexural strength, tensile strengths, and elastic modulus. Microstructural investigations were also carried out. The results showed that utilizing glass cenospheres up to 30% (by cement weight) leads to adequate mechanical strength where the corresponding specific strength of 28 kPa/kg m−3 could be achieved. Microstructural analyses further revealed that increased porosity due to glass cenospheres incorporation is primarily responsible for strength loss with increasing weight fraction.