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Ferrocement is a construction material that (in comparison to traditional reinforced concrete) provides superior crack control, impact resistance, and toughness. However, while extensive literature exists on the deterioration mechanisms and maintenance of reinforced concrete structures, little attention has been given to the durability of ferrocement. In this study, the adoption of ethyl silicate, a newly developed nanomaterial, is investigated to improve durability of ferrocement. Such nanomaterials are expected to penetrate the cementitious matrix without changing the appearance of the surface. Once penetrated, pozzolanic behavior is displayed forming calcium silicate hydrate and consequently increasing durability and mechanical performance. Particular attention is given to the carbonation-induced corrosion of reinforcement, which should be considered a major concern in ferrocement due to the initially small diameter of the mesh wires and the thin mortar cover. Despite its importance, there is a limited amount of literature on carbonation- induced corrosion of ferrocement structural elements. [ABSTRACT FROM AUTHOR]

In this paper, the hydration process of Portland cement at early age was characterised by Fourier transform infrared spectroscopy (FTIR); the results showed that FTIR is a simple and rapid research method in operation, which can reflect the basic variation in the primary cement hydration products. As the hydration reaction proceeded, the peak value corresponding to silicon–oxygen (Si–O) vibrations in the FTIR spectrum shifted from low wavenumbers to high wavenumbers, which not only reflected the polymerisation process of silicon–oxygen tetrahedrons in the calcium–silicate–hydrate gel, but also the hydration reaction speed of cement paste at this stage. This was confirmed by experiment on samples with added superplasticiser. The shifting characteristics of the absorption peaks in the range 800–1025 cm−1 for samples at the ages of 8–12 h were comprehensively investigated in this study. The research results showed that the shifting speed of the characteristic peak for the blank sample was exactly the same as that for the sample reinforced with carbon nanotubes (CNTs). Therefore, the addition of CNT materials into Portland cement did not influence the hydration reaction at the early age. This conclusion was verified by the thermometry test for hydration temperature. [ABSTRACT FROM AUTHOR]

In this paper, the cement paste and the mortar were tested using the PF-QNM technique. It is shown that the PF-QNM technique is very powerful to characterize the mechanical properties of micro- and nanostructures in the cement-based materials. It does not have strict requirements for test environment and it does not damage the surface of the material. High-resolution images can be obtained very easily, and they can be analyzed statistically. The test results show that PF-QNM analysis can test not only the mechanical properties of the cement paste, but also investigate the interfacial regions in the cement-based material, including the variation in the mechanical properties of interface regions and the extension of the interfacial regions. During the test, care must be taken to choose the size of test area; indeed, a test area too small is not representative but too large leads to lack of stability. The recommended side is a square with a length of in the range 10–30 μm. [ABSTRACT FROM AUTHOR]

The addition of carbon nanofibers (CNF) has the potential to have a major impact in the concrete materials industry due to the high modulus and specific surface area of CNF. Past research has focused on characterization of the mechanical and flexural strength behavior of CNF-modified cement-based materials. In this study, the influence of CNF on the autogenous shrinkage and shrinkage cracking of cement mortar is investigated. It is found that CNF is not only able to mitigate the autogenous shrinkage of cement paste and mortar but is also effective in restraining shrinkage cracking. By comparing the fiber count in both paste and mortar, the effect in mortar is more pronounced than in paste, which suggests a modification of the interface area between the aggregate and the paste area. Targeting the large autogenous shrinkage of high-performance concrete at early age, CNF combines the beneficial effects of the traditional microfiber reinforcement and shrinkage-reducing admixture. [ABSTRACT FROM AUTHOR]

The modification effects of nanoSiO2 on properties of the interface region between cement grain and C-S-H gel in cement-based composites are investigated by means of the nanoscratch technique. The nanoscratch test involves driving a Berkovich diamond tip across the interface boundary perpendicularly and recording the lateral force while the normal load applied to the indenter is kept constant. The coefficient of friction (COF), defined as the ratio of lateral force to normal load, indicates an interfacial width close to 200 nm, which is irrelevant to the addition of nanoSiO2. However, the COF value within the interface region decreases significantly if nanoSiO2 is incorporated. The decreased friction between the indenter and the interface is mainly attributed to the reduction of adhesion friction, because the addition of nanoSiO2 has a densification effect on the interface. This study further confirms that nanoSiO2 addition is beneficial for the formation of a denser layer surrounding the unhydrated cement particles in early hydration ages. [ABSTRACT FROM AUTHOR]

Cement asphalt emulsion (CA) mortar is a key material in the nonballast slab track. Its properties are largely dependent on the compatibility between asphalt emulsion and cement. The mixing stability of asphalt emulsion with cement is investigated by analyzing the viscosity of CA paste. Viscosity and the critical particle volume fraction of CA paste are proposed as indexes in evaluating the mixing stability of asphalt emulsion with cement, and factors influencing the mixing stability of asphalt emulsion are studied. Mixing stability is dependent on mixing method, superplasticizer, and emulsion type. The premixing cement method, superplasticizer, and good asphalt emulsion can increase the critical particle volume fraction of CA paste, which is helpful in achieving a low water–to–cement mass ratio (W/C). Anionic emulsion has much better mixing stability with cement than does cationic emulsion. The critical particle volume fraction of CA pastes with anionic emulsion increases stably with the mass ratio of asphalt emulsion to cement (AE/C), but the critical particle volume fraction of CA pastes with cationic emulsion increases little with AE/C. This work proposes a method for choosing an asphalt emulsion with good mixing stability, and provides methods to improve the mixing stability of asphalt emulsion with cement. [ABSTRACT FROM AUTHOR]

Cement asphalt emulsion paste (CA paste) is known to be a low-yield stress suspension suitable for many applications in which high flowability is desired. The factors that lead to the low yield stress of CA paste are still unknown, however. The effect of the components in CA paste on the rheology of fresh CA paste is studied to reveal the primary factors that lead to the low yield stress. The effect of emulsifier and superplasticizer on cement paste, the effect of asphalt emulsion, and viscosity modifying agents on CA paste are studied. Results indicate that emulsifier can reduce the yield stress and apparent viscosity of cement paste, but the effect of emulsifier is small compared to the effect of the superplasticizer. The low yield stress of CA pastes is primarily because of the combined effect of superplasticizer and asphalt emulsion. Both CA paste without superplasticizer and cement paste have high yield stress. Viscosity modifying agents can significantly increase yield stress of CA paste without changing minimum apparent viscosity, which is an efficient way to change the rheological behavior of CA paste with low yield stress. [ABSTRACT FROM AUTHOR]

To investigate the stress distribution in recycled aggregate concrete (RAC) under uniaxial compression, modeled recycled aggregate concrete (MRAC) was studied by numerical simulation. The mechanical properties of interfacial transition zones (ITZs) of RAC were measured by the nanoindentation technique. A two-dimensional numerical study of the stress distribution characteristics of MRAC under the uniaxial compression is presented. The simulation was verified by experimental results. A parametric analysis is then conducted to study the sensitivity of each phase's mechanical properties and the amounts of old cement mortar in the MRAC. Simulation results demonstrate that a concentration of tensile stress and shear stress appears around new and old ITZ regions. It is found that when the elastic modulus of natural aggregates increases, the magnitude of tensile stress concentration becomes higher, whereas as the elastic modulus of ITZs increases, the magnitude of stress concentration decreases. It is also shown that the higher relative elastic modulus of new cement mortar compared with that of the old cement mortar significantly reduces the stress concentrations at the regions between recycled coarse aggregate particles. The amount of old cement mortar affects the stress distribution in the new ITZ much more obviously than that in the old ITZ. [ABSTRACT FROM AUTHOR]