Tensile Strength Of Cement Paste Research Articles

Evaluating tensile strength of cement paste using multiscale modeling and in-situ splitting tests with micro-CT

This study investigated a strategy to simulate splitting tests to evaluate the tensile strength of cement paste within a multiscale framework, and validated the approach with in-situ micro-CT measurements. Phase-field fracture model was used to simulate the splitting test using virtual microstructures reconstructed from the macroscale micro-CT measurements. Among the modeling parameters, the range of the diffusive crack width, which is an internal parameter for phase-field fracture model, was further investigated. The cracks propagated through the weaker solid phase, and the predicted strengths and standard deviations were comparable to those obtained from the experiments. It was found that the diffusive crack width should be smaller than the characteristic length of the weaker phase to predict the crack pattern accurately. These findings confirm the effectiveness of the proposed multiscale modeling approach in predicting the tensile strength of cement paste.

Multi-scale analysis framework for predicting tensile strength of cement paste by combining experiments and simulations

The experimental method that accurately assesses the responses of cementitious materials with complex microstructures requires significant time and effort. To address this issue, a multi-scale analysis approach that synergistically combines experiments and simulations can be adopted. In this study, a framework was designed to evaluate the macroscale (upper-scale) tensile strength of cement paste using microscale (lower-scale) characteristics and properties. The upper- and lower-scale microstructures of the cement paste are obtained through this approach using high-resolution synchrotron X-ray micro-CT. Solid-phase properties at the lower-scale are determined using a nanoindentation experiment and lower-scale micro-CT characteristics. The upper-scale solid phase properties are correlated by comparing the distributions of the linear attenuation coefficients or the grayscale values of the micro-CT images from the two scales. To evaluate the proposed method, splitting tensile test simulations of the cement pastes were conducted with upper-scale solid-phase input material parameters. The simulated results were comparable to the experimental ones. It was concluded that the proposed multi-scale approach combining experiments and simulations can reduce the time and effort required to evaluate the mechanical responses of cement paste. It thus contributes to advancing material innovations.

Combined experimental and numerical study on micro-cube indentation splitting test of cement paste

The aim of this paper is to investigate the fracture performance of cement paste at micro scale by both experimental and numerical methods. Micro cubic specimens with length of 100 µm were fabricated by precision cutting, grinding and micro-dicing, and tested by splitting with a wedge tip mounted on a nano-indenter. A nominal splitting tensile strength was derived from the maximum load of the recorded load-displacement diagram to represent the global fracture performance of the fractured micro-cube. To achieve this, an analogy was made between the micro-cube indentation splitting test and the standard Brazilian splitting test. To cope with the inherent heterogeneity of this material at micro scale, for cement paste with each water/cement (w/c) ratio (0.3, 0.4 and 0.5), more than hundred micro-cube specimens were fabricated, tested and analysed using Weibull statistics. The analysis shows that the splitting tensile strength of cement paste on the micro scale is much higher than on the macroscopic scale but lower than tensile strength of distinct hydrated cement phases measured on micro or nano scale. Furthermore, higher and less scattered values of splitting tensile strength were observed for the specimens with lower w/c ratio. In parallel with the experiments, a micro-structure informed lattice fracture model was adopted to simulate the fracture process of the micro-cube under indentation splitting. The simulated results were compared with the experimental one and have a good consistency in terms of the load-displacement curve and fracture pattern. With the method presented in this paper the framework for validation of the modelling results at micro scale is created.

Thermal, mechanical, and surface properties of poly(vinyl alcohol) (PVA) polymer modified cementitious composites for sustainable development

ABSTRACTThis study aimed to investigate the effect of poly(vinyl alcohol) (PVA) polymer on the thermal, mechanical, and surface properties on cementitious composites for sustainable development. Thermal properties of the PVA‐modified cement paste, including thermal insulation and energy absorption ability, were first studied and correlated with the porosity and microstructures. The experimental results indicated that the thermal conductivity of cement paste can be greatly reduced by 42.9% with 2.0 wt % addition of PVA due to the more porous structure. However, at the same time, more thermal energy can be captured and concentrated at the surface of cement paste with the increasing amount of PVA, causing an increased thermal load and a negative effect on thermal insulating efficiency of cement paste. The contradictory effect of PVA on thermal properties of cement paste should be balanced before it is used as a foaming modifier to fabricate cementitious composites with thermal insulation. In addition, the contact angle measurement revealed that PVA can be used as an effective additive to improve the hydrophobicity of cement‐based materials. Only 3.0% PVA can turn the surface nature from hydrophilicity to hydrophobicity for cement paste, which benefited to the development of self‐cleaning cementitious composites. Finally, the mechanical properties of the PVA‐modified cement paste, especially for the tensile strength that has been rarely reported, were investigated and correlated with its thermal and surface properties. Due to the compensative effects of irregular packing, formation of PVA films and microcracks, tensile strength of cement paste can be improved by 23.5% with a small scarifying of the compressive strength by adding 2.0% of PVA. In conclusion, the PVA‐modified cement‐based materials with lower thermal conductivity, hydrophobic surface nature and enhanced mechanical properties have a great potential to satisfy the high requirements in developing sustainable infrastructure. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46177.

Effects of graphene oxide aggregates on hydration degree, sorptivity, and tensile splitting strength of cement paste

It has recently been found the graphene oxide (GO) aggregates form in cement paste due to the chemical cross-linking of calcium cations. Therefore, the effects of GO addition on the properties of cement based materials should be dependent on the properties of GO aggregates rather than GO nanosheets. In this study, GO aggregates were first characterized by particle size measurement. Then, the effects of GO aggregates on the degree of hydration, sorptivity, and tensile strength of cement paste were investigated. The aspect ratio of GO aggregates is much larger than that of the original GO nanosheets. Compared to plain cement paste, the increase of non-evaporable water content of the cement paste was found to be very limited, around 1.17% and 3.90% for cement pastes containing 0.02% and 0.04% by weight GO, respectively. The sorptivity of cement paste, especially the secondary sorptivity, was notably reduced for GO incorporated cement paste. The tensile strength was significantly improved by GO aggregates. Incorporation of 0.04% by weight GO increased the tensile strength by 67% compared to that of plain cement paste.

The influence of sulfonated asphalt on the mechanical properties and microstructure of oil well cement paste

In this work, sulfonated asphalt was chosen as an admixture, and the influence of the quantity (1%, 2%, 3%, 4% of the weight of the cement) of sulfonated asphalt on the mechanical properties of hardened cement slurry was studied. Moreover, the micro-morphology and porous structure characteristics were examined using the SEM and nitrogen adsorption-desorption method, respectively. Studies showed that the addition of asphalt had great potential to improve the tensile strength and toughness of cement paste. The tensile strength of cement paste with 3% sulfonated asphalt increased by 45% at 7days and 17% at 28days in comparison with that of specimens without sulfonated asphalt. In addition, 2–3% sulfonated asphalt levels were advantageous for improving the toughness of oil well cement paste. Asphalt particles caused crack bending and deflection as well as toughened oil well cement paste. The addition of 3% asphalt had a positive good effect on the pore size distribution in cement paste. The addition of asphalt decreased the compressive and flexural strength of cement paste at the same curing age. The content of 4% asphalt increased the pore size and caused deterioration of the mechanical properties of cement paste. It is necessary to balance the mechanical properties of cement paste and the amount of asphalt in the range 2–3% to be beneficial for this application.

Mechanical Properties and Mechanism of Graphite Oxide Reinforced Oil Well Cement

The effect of graphite oxide (GO) on the mechanical properties of oil well cement was experimentally studied, in view of the zonal isolation failure due to the brittleness. The microstructure of cement stone was observed by SEM, and the mechanism of graphite oxide reinforced cement stone was also investigated. The result illustrates that the mechanical properties of cement was improved significantly due to the addition of GO. When the GO dosage was 0.05%, the compressive strength, flexural toughness, and splitting tensile strength of cement paste at 7 day age were increased by 61.32%, 15.46% and 145.34% respectively. GO had no bad effect on the application properties of cement slurry, and the stability of the slurry was favorable. Besides, GO could reduce the fluid loss of cement slurry. When GO reinforced cement stone undergoes damage under complex stress, if damage occurs within graphite oxide layer, chemical bonds of GO layers must have been broken, and the force between the layers of GO must be overcome when interlaminar peeling happens, which will lead large amounts of energy consumption as well. The mechanical properties of the cement stone were enhanced by the above two aspects. The research results can provide a theoretical reference for solving the brittle fracture of oil well cement stone.

Nano–micro modelling of mechanical properties of cement paste based on molecular dynamics

The elastic properties and tensile strength of cement paste were investigated from a theoretical viewpoint. By means of molecular dynamics (MD) simulations, the Mori–Tanaka homogenisation method and Griffith fracture theory, a comprehensive methodology was developed to explore the mechanical properties of cement paste from nanoscale to microscale. A series of nanostructures representing the main constituents of cement paste was constructed and analysed in the light of MD simulations, in which microporomechanics analysis was conducted to consider the influence of gel porosity. The outcomes were then upscaled for the elastic constants of cement paste using the Mori–Tanaka homogenisation method. Finally, the tensile strength of cement paste was obtained according to Griffith fracture theory. The calculation results were in good agreement with the experimental data, which shows that the multiscale coupling method based on MD is capable of capturing the mechanical properties of cement paste from the atomic scale, thus providing a new perspective on the multiscale study of cement-based materials.

Relationship between fracture area and tensile strength of cement paste with supplementary cementitious materials

Fly ash (FA), silica fume (SF), and blast furnace slag (BFS) were used as the supplementary cementitious materials (SCMs) in cement paste. The axial tensile strength, ultimate strain and the area of fracture surface of cement paste with SCMs were experimentally investigated in this study, and the relationship between tensile strength and fracture area of specimens were analyzed. The test results show that the tensile strength of the specimens decreases with the increasing addition of SCM. Except for SF, there is a negative correlation between the tensile strengths of specimens and W/B ratio. The increasing dosage of BFS, FA, and SF improves the ultimate strain. The fracture area of cement paste decreases with an increase in water-binder (W/B) ratio. The total fracture area is relatively large, as the tensile strength value is relatively low.

Relationship between Autogenous Shrinkage and Tensile Strength of Cement Paste with SCM

Fly ash (FA), silica fume (SF), and ground blast furnace slag (GBFS) were used as the supplementary cementitious materials (SCMs) in cement paste. The autogenous shrinkage (AS) and the shrinkage cracks of cement paste with SCMs were experimentally investigated in this study, and the relationship of AS, tensile strength, and crack area of cement paste were analyzed. The test results show that FA decreases the AS of cement paste and SF increases the AS. Both the AS and the crack area of cement paste decrease with the increase of the water-binder (W/B) ratio. When W/B ratios of different cement pastes are kept the same, the tensile strength of cement paste is not influenced by the AS if the specimens can shrink freely. Equations are established to describe the relationship among AS, tensile strength, and crack area of the cement paste with SCMs.

Molecular Dynamics to Understand the Mechanical Behavior of Cement Paste

The tensile strength of cement paste is one of the most important mechanical properties that influence shrinkage cracks in cementitious materials. Cement pastes that exhibit low tensile strength tend to exhibit greater shrinkage crack potential and reduced durability. Increasing the tensile strength in cement paste can minimize the shrinkage cracking potential. It is believed that the strength and cohesion of cement paste are controlled by the formation of calcium silicate hydrate (C-S-H) gel. To enhance macroscopic mechanical properties (tensile strength), it is necessary to understand the structure and behavior of C-S-H gel at the atomic level. Previously, molecular statics was used to determine minimal potential energy and the mechanical properties of crystalline C-S-H structures. From this study, a plausible atomic structure of C-S-H gel is proposed. This research effort builds on the aforementioned work by using molecular dynamics to derive tensile and compressive strengths of C-S-H structures from uniaxial stress–strain data. The results from the molecular dynamics simulations showed that the maximum strengths (i.e., compressive and tensile) for the proposed C-S-H structures are three orders of magnitude higher than the strength at the macrolevel. However, the tensile strength of the proposed C-S-H gel is 23% of the compressive strength. This research also concludes that electrostatic forces and bond forces in the silicate chains are the main contributors to cement strength at the atomic level and that breakage in silicate chains leads to low tensile strength in C-S-H gel.

Silane-treated carbon fiber for reinforcing cement

The tensile strength of cement paste was increased by 56% and the modulus and ductility were increased by 39% by using silane-treated carbon fibers and silane-treated silica fume, relative to the values for cement paste with as-received carbon fibers and as-received silica fume. Silane treatment of fibers and silica fume contributed about equally to the strengthening. Silane treatment of fibers and silica fume also decreased the air void content and the drying shrinkage. The strengthening, air void content reduction and drying shrinkage reduction were less when the fiber treatment involved either potassium dichromate or ozone. Silane’s effectiveness is due to its hydrophilic nature.

Carbon fiber reinforced cement improved by using silane-treated carbon fibers

The tensile strength of cement paste was increased by 56% and the modulus and ductility were increased by 39% by using silane-treated carbon fibers and silane-treated silica fume, relative to the values for cement paste with as-received carbon fibers and as-received silica fume. Silane treatment of fibers and silica fume contributed about equally to the strengthening. Silane treatment of fibers and silica fume also decreased the air void content. The strengthening and air void content reduction were less when the fiber treatment involved potassium dichromate instead of silane and even less when the treatment involved ozone. Silane’s effectiveness is due to its hydrophilic nature.

Discussion: A new approach to the determination of the tensile strength of cement paste by centrifugal force

Discussion: A new approach to the determination of the tensile strength of cement paste by centrifugal force

A new approach to the determination of the tensile strength of cement paste by centrifugal force

Summary A method of determining the tensile strength of a small cement paste specimen at ages varying between one and twenty-eight days has been achieved by subjecting the specimens to high centrifugal forces in an air-driven centrifuge.