Flexural Strength Of Cement Paste Research Articles

Thermal performance and mechanical properties of phase change cement paste with Nano-SiO2 grafted straw-paraffin

In paraffin-based phase change concrete, rice straw can be used as the carrier for paraffin, however, the compatibility between rice straw and cement matrix is poor. In this study, Nano-SiO2 was grafted on straw-paraffin to improve the interfacial compatibility, and its influences on thermal performance and mechanical properties of phase change cement paste were investigated. Firstly, the phase change potential heat and tensile property of Nano-SiO2 grafted straw-paraffin were tested. Then, the thermal performance and mechanical properties of cement paste with Nano-SiO2 grafted straw-paraffin were tested. The results indicate that: (1) The melting temperature of Nano-SiO2 grafted straw-paraffin (PRS-1%) is 51.15℃, 0.39% lower than paraffin-straw without Nano-SiO2(PR), the enthalpy value is 85.64 J/g, 8.74% higher than PR. (2) The tensile strength of PRS-1% is 38.63 MPa, which is 18.63% higher than PR. After 100 phase change cycles, its tensile strength is 23.98% higher than PR. (3) The Nano-SiO2 grafting can reduce the volume of pores and cracks at straw-paste interface, decrease the content of Ca(OH)2 and increase the content of C-S-H gel at the interface. (4) Compared with cement paste with PR, the compressive strength and flexural strength of cement paste with PRS-1% increase by 21.05% and 16.55%, respectively. (5) The Nano-SiO2 grafting (1%) can increase the specific heat capacity and thermal conductivity of straw-paraffin based phase change cement paste by 2.24% and 9.64%, respectively.

Hybrid effect of GNPs, GOs, and CNTs on the flexural and compressive strengths of cement paste

This paper presents the individual and synergic effects of Graphene Nanoplatelets (GNPs), Graphene Oxides (GOs) and Carbon Nanotubes (CNTs) on the flexural and compressive strengths of cement paste. Mixes containing several nanoparticle types and weight fractions were prepared with Polycarboxylate ether (PCE) surfactant and tested after 90 days of curing. After that, the microstructure of the failed samples was studied using a Scanning Electron Microscope (SEM). Response Surface Methodologies (RSM) techniques were then employed to determine the strength functions' response to the nanofilaments' types and weight fractions. Finally, a cost analysis was done to evaluate the mixes' performance in-terms of strength and cost. Test results showed that the flexural strength of cement paste could be enhanced by 57.33% when using 0.04 wt % GOs. The results also showed that mixes containing 0.08 wt % GOs and 0.12 wt % CNTs improved the flexural strength by 47.03 and 44.38%, respectively when compared with the control cement paste mix. In-terms of compressive strength, mixes containing 0.04 wt % GNPs attained the highest compressive strength improvement of 15.7% when compared with the control mix. In hybrid mixes containing more than one nanoparticle type, the best synergistic action was generated between 50% CNTs and 50% GOs at a total dosage of 0.04% wt, where the compressive strength increased by 20.2%. The microstructural analysis showed good dispersion qualities and nanoparticles embedment within cement hydration products. On the other hand, RSM analysis showed that the maximum compressive and flexural strength functions' responses are obtained at the lowest nanofilaments’ weight fraction of 0.04 wt %. The desirability analysis confirmed that the compressive and flexural strengths of cement paste could be improved by 7 and 53%, respectively, using the predicted formulas. Finally, the cost analysis showed that GO-modified cement pastes are considerably more expensive than other mixes, yielding the lowest economic index.

Dispersion of single wall carbon nanotube using air entraining agent and its application to portland cement paste

There is a growing interest in research on application of carbon nanotube (CNT) for development of high-performance cementitious composites. However, most of the research works on cementitious composites were focused on utilization of multi-walled carbon nanotube (MWCNT) which is cheaper and more readily available in the market. Since single-walled carbon nanotube (SWCNT) has superior mechanical properties to MWCNT, it is necessary to investigate the effect of SWCNT on properties of cement paste. In this study, SWCNT was dispersed in water using commercial air entraining agent (AEA). Sodium deoxycholate (DOC) was also used as a dispersing agent for comparison purposes. Cement paste samples containing SWCNT solutions were prepared, and rheological behavior, mechanical strengths and microstructural observation were investigated. According to the results, the addition of SWCNT solutions decreased plastic viscosity, but increased yield stress of cement paste. It was also found that addition of SWCNT increased both compressive and flexural strength of cement paste regardless of the type of dispersing agent used. Although cement paste with SWCNT dispersed by AEA showed less mechanical strength than that dispersed by DOC, it is still possible to be used as a dispersing agent for SWCNT because of its higher mechanical strength than plain cement paste as well as better economic efficiency and readiness of AEA toward construction business.

Cellulose nanofibrils with and without nanosilica for the performance enhancement of Portland cement systems

This article presents a comprehensive investigation on the effects of pure cellulose nanofibrils (CNF) and nanosilica containing CNF on the performance of ordinary portland cement (OPC) paste. The effects of CNFs on cement paste rheology, hydration, microscopic phase formation, compressive strength, and fracture parameters were monitored. Sol-gel method was used to synthesis nanosilica particles within CNF slurry. The effects of CNF on cement hydration was found to be dependent on the water to cement ratio (w/c). Specifically, CNFs accelerated the early age cement hydration at 0.35 w/c, but this acceleration effect was not prominent for 0.45 w/c. Such w/c dependent effect was attributed to the negatively charged hydroxyl and carboxyl surface sites of CNFs which can bind alkali ions or cement particles. The concentration of alkali ions in cement pore solution depends on the w/c and hence, resulting the w/c dependent effects of CNF. The colloidal stability of CNF was found to improve due to the addition of nanosilica particles. Addition of CNF was found to increase the flexural strength of cement paste up to 75%. The effects of CNF addition on the compressive strength of cement paste matrix was negligible.

Effect of Carbon Nanotube and Styrene-Acrylic Emulsion Additives on Microstructure and Mechanical Characteristics of Cement Paste

Carbon nanotubes (CNTs) are considered as one of the ideal modifiers of cement materials, since CNTs can improve the mechanical properties of cement paste effectively. However, the interfacial interaction between CNTs and the cement matrix is weak. Moreover, it is difficult to disperse CNTs within cement paste. To overcome these shortages, in this study, CNTs were firstly dispersed into a styrene-acrylic emulsion (SAE). Then the homo-dispersion CNT/SAE emulsion was incorporated into cement paste. The effect of the CNT/SAE hybrid-system on the mechanical properties and microstructure of cement paste was studied. For purposes of comparison, the properties of cement paste mono incorporating CNTs or SAE are also investigated. The results show that CNT/SAE network films could be observed in cement paste by using a field emission scanning electron microscope (FESEM). These network films could bridge the cracks and refine the pores of a cement matrix. Infrared analysis and Raman spectroscopy show that the CNT/SAE hybrid modifier has stronger interfacial adhesion and better load transfer ability over the mono adding of CNTs and SAE emulsion. As a result, the hybrid addition of CNT/SAE significantly improved the flexural strength of cement paste. Especially, the addition of 0.1% CNTs and 15% SAE by mass of cement improved the 28-day flexural strength of cement paste by 21% and 25% as compared to the mono addition of CNTs or SAE, respectively.

Effects of anti-clay agents on fresh and hardened properties of concrete containing clay

In this paper, four kinds of agents (2000 polyethylene glycol (pg2000), aminosalicylicacid (ASA), saodium alginate (SA), sodium metasilicate anhydrous (SMA)) were investigated as potential anti-clay agents combined with polycarboxylate water reducer (PCE), and the fluidity, compress strength, and flexural strength of cement paste, mortar, and concrete containing aforementioned anti-clay agents were tested. It found that among the tested potential anti-clay agents, PG2000 have performed well. The fluidity of the concrete with PG2000 increased 16mm compared to the control sample. In order to understand the mechanisms underlying this improvement, X-ray Diffraction(XRD) of cement paste was carried. The results show PG2000 has the highest interlayer spacing(d=2.865142nm) compare with control sample(d=2.828410nm) (not added PG2000), which make it more effective on the fluidity of concrete.

Mechanical property and toughening mechanism of water reducing agents modified graphene nanoplatelets reinforced cement composites

The unique attractive properties that make graphene nanoplatelets (GNPs) effective nano-reinforcer for cement composites. Dispersion of GNPs with dispersant is a conventional method. In order to avoid the introduction of dispersant left in cement-based materials, water reducing agent was directly used to disperse GNPs. This article investigated GNPs were dispersed using different water reduced agents, the mechanical properties and toughening mechanism of modified GNPs reinforced cement composites. In this research, GNPs were dispersed well in aqueous solution using polycarboxylate superplasticizer (PS), naphthalene superplasticizer (NS) and melamine superplasticizer (MS) as dispersants with ultrasonication. Results showed that water reducers can improve the influence of GNPs on cement-based materials and a GNPs dosage of 0.06 wt% could make the GNPs/cement composites as flowable as the plain sample. The flexural strength of cement paste increased up to 16%, 13% and 20% with 0.06 wt% PS, NS and MS modified GNPs at 28d, it increased the compressive strength of the GNPs/cement composites by 8%, 5% and 11.2%. The ratio of compressive-bend strength of decline rates of PS and NS modified GNPs/cement composites were 7.4% and 8.2% at 0.06 wt% GNPs at 28d, while the ratio of compressive-bend strength of decline rates of MS modified GNPs/cement composites were 10.9% with 0.09 wt% GNPs at 28d. It found that GNPs could accelerate hydration process of cement composite, leading to more hydration products, finer CH crystals, longer mean chain length of CSH gel and lower porosity, and thus the propagation of cracks of the cement composites was inhibited.

Influence of high temperature on strength, ultrasonic velocity and mass loss of calcium carbonate whisker reinforced cement paste

Calcium carbonate whisker (CW) can reinforce the flexural strength of cement paste and limit the development of micro-cracks at ambient temperature (25 ± 2 °C), but the effect of CW on mechanical properties of cement paste after exposure to high temperatures is still unknown. Therefore, mechanical properties, i.e. flexural strength, compressive strength and splitting tensile strength were measured using CW reinforced cement specimens before and after they were exposed to high temperatures. In addition, performance of CW reinforced cement paste after exposure to high temperatures was studied by ultrasonic test and mass loss test. At last, microstructural analysis (differential thermogravimetric analysis and scanning electron microscopy) were employed to study the deterioration mechanism of temperature and reinforcement mechanism of CW. These experimental results suggested that CW played a significant role in hindering the development of cracks before 600 °C. When temperatures increased up to 200 °C, the flexural strength decreased. However, the compressive strength and splitting tensile increased. When temperatures varied from 200 °C to 400 °C, the three strengths reacted differently to the elevated temperatures. Subsequently, the residual strength rapidly decreased up to 1000 °C. After that, the three strengths increased slightly. The residual strength, ultrasonic velocity and mass loss were related to the temperatures and CW content and quantitative measurement of these factors was also discussed.

Dispersion of graphene oxide agglomerates in cement paste and its effects on electrical resistivity and flexural strength

Actual dispersion of graphene oxide (GO) in cement paste was investigated by using both X-ray computed tomography and X-ray photoelectron spectroscopy. It was found that GO nanosheets are mainly agglomerated, as an individual phase, with platelet-like morphology and little GO being absorbed onto surfaces of cement particles and hydration products. By performing an electrical resistivity test, GO agglomerates are found to be more electrically insulative than cement paste. Therefore, it is not possible to develop self-sensing cement composites by incorporating GO directly without resolving its dispersion issue. However, GO agglomerates enhance the flexural strength of cement paste because of their special morphology and intrinsic strength. Results showed that the flexural strength of cement paste was increased by 83% with incorporation of 0.04% GO by weight of cement.

Fitting Function for Flexural Strength of Cement Paste

There are many analytical expressions for compressive strength as functions of porosity of cement-based materials but only a few such expressions exist for flexural strength of these materials. In the present paper a new functional candidate for fitting the data of flexural strength of hydrated Portland cement paste has been tested. The functional candidate has been initially derived for porous polymeric materials on the basis of the percolation theory. The parameters of this function have been optimized for the cement paste by using the Levenberg-Marquardt iterative fitting procedure. The optimized function has been capable of accurate reproducing all the measured flexural data. This fact has been confirmed by a high value of the correlation coefficient and rather low values of statistical uncertainties. It has been shown that this modified fitting function is well applicable to the pastes of ordinary Portland cements and probably to other cementitious materials, too.

Application of Alkaline-resistant Glass Fiber in Road Concrete: Corrosivity and Applicability

The main technical requirements of road concrete are high flexural strength and fatigue durability because shear failure is the major failure mode for road concrete. Adding glass fiber into concrete could greatly increase flexural strength and wearing resistance of concrete. However, glass fiber has the great potential of corrosion in the alkaline environment formed during the cement hydration, which will directly affect the long-term performance and strength stability. Systematic researches have been launched on the corrosion mechanism, surface treatment and anti-corrosion methods of fiber, however, few works have been made in the application and design method of alkaline-resistant glass fiber in road concrete. In this paper, the corrosion mechanism and property of alkaline-resistant glass fiber in cement paste were analyzed firstly, and the corrosion inhibition of active admixture on alkaline-resistant glass fiber was discussed. The practicability and applicability of alkaline-resistant glass fiber in road concrete were illustrated though the discussion of changing trend of flexural strength of cement paste mixed with different proportion of fly ash based on the experimental results, and the appropriate amount of activated additive of fly ash was also confirmed. The results suggested a prosperous application prospect for the application of alkaline-resistant glass fiber concrete with fly ash in road projects.

Enhanced mechanical properties of cement paste by hybrid graphene oxide/carbon nanotubes

The prominent mechanical properties of carbon nanotubes (CNTs) make them to be potential candidates for enhancing cementitious material. However, CNTs are hard to be dispersed uniformly due to the Van der Waals’ force between them. Many methods have been attempted by researchers to improve the dispersion of CNTs. This research investigated the use of graphene oxide (GO) as a dispersant for CNTs to overcome the obstacles. UV–vis spectroscopy and scanning electron microscopy (SEM) results revealed that CNTs were highly dispersed by GO rather than by surfactants. More importantly, the excellent reinforcing capabilities of the hybrid GO/CNTs were demonstrated by the enhanced fracture resistance properties of the cementitious matrix. The hybrid GO/CNTs (0.02wt%GO and 0.04wt%CNTs by weight of cement) with poly-carboxylate superplasticizer had a great contribution to improving the compressive and flexural strength of cement paste by 23.9% and 16.7%, respectively, which was higher than cement paste reinforced by CNTs or GO. Scanning electron microscopy images showed that the hybrid GO/CNTs were well dispersed in the cement hydration products. Furthermore, mercury intrusion porosimetry (MIP) results indicated that the addition of the GO/CNTs promoted the refinement of pores in 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.

Investigation of the Mechanical Properties and Microstructure of Graphene Nanoplatelet-Cement Composite.

In this work, graphene nanoplatelets (GNPs) were dispersed uniformly in aqueous solution using methylcellulose (MC) as a dispersing agent via ultrasonic processing. Homogenous GNP suspensions were incorporated into the cement matrix to investigate the effect of GNPs on the mechanical behavior of cement paste. The optimum concentration ratio of GNPs to MC was confirmed as 1:7 by ultraviolet visible spectroscopy (UV-Vis), and the optical microscope and transmission electron microscopy (TEM) images displayed remarkable dispersing performance. The GNP–cement composite exhibited better mechanical properties with the help of surface-modified GNPs. The flexural strength of cement paste increased up to 15%–24% with 0.05 wt % GNPs (by weight of cement). Meanwhile, the compressive strength of the GNP–cement composite increased up to 3%–8%. The X-ray diffraction (XRD) and thermal analysis (TG/DTG) demonstrated that the GNPs could accelerate the degree of hydration and increase the amount of hydration products, especially at an early age. Meanwhile, the lower porosity and finer pore size distribution of GNP–cement composite were detected by mercury intrusion porosimetry (MIP). In addition, scanning electron microscope (SEM) analysis showed the introduction of GNPs could impede the development of cracks and preserve the completeness of the matrix through the plicate morphology and tortuous behavior of GNPs.

Influence of kaolinite clay on the chloride diffusion property of cement-based materials

To constitute blended cement concrete with high chloride diffusion resistivity, the effects of kaolinite clay on the mechanical properties and chloride diffusivity of cement paste, mortar and concrete were investigated. Ordinary Portland cement was partially replaced by kaolinite clay at 0%, 1%, 3%, 5%, 7% and 9% by weight of cement. All blended cement-based samples were prepared using a w/c ratio of 0.5. The microstructure, workability, early-age and long-term flexural strength of pastes were tested. The chloride diffusivity of mortars was measured. And the compressive strength and chloride diffusivity of concrete were measured. Mercury Intrusion Porosimetry (MIP) was employed to evaluate porosity characteristics. Scanning Electron Microscopy (SEM) and Energy Dispersive Spectra (EDS) were applied to investigate the micro morphology and chemical element distribution inside the cement matrix, and the rapid chloride migration (RCM) method was applied to test chloride diffusivity. The MIP test results show that the addition of clay improves the micro-pore structure in the cement paste and limits the introduction of chloride ions. SEM imaging suggests that the kaolinite clay is acting as both filler and accelerator of cement hydration. It is found that the addition of clay alters the water requirement of normal consistency and the setting time of cement, whereas it has little influence on the soundness. Compared to the control, the flexural strength of cement paste with 1% kaolinite clay increased by 30.41%, 39.04%, 36.27% and 38.32% at 1, 3, 7 and 90days, respectively. The 28-day flexural strength only increased slightly. It is observed that the cement mortar with clay has lower chloride diffusion coefficient values compared to the plain mortar, the 28-day diffusion coefficient of chloride ion (DCl-) of cement mortar is decreased by 53.03% with 5% clay. The increase in compressive strength of the cement concrete with clay is 12%, 13.5%, and 28.4% compared to the control at 1%, 3% and 5% addition, respectively. The chloride diffusion coefficient of cement concrete decreases exponentially with the clay addition. The reduction of chloride diffusion coefficient of cement concrete is 8.68% and 18.87% at 1% and 5% clay, respectively. The 28-day compressive strength increases linearly with the chloride diffusion coefficient of the concrete.

Properties and interaction of cement with polymer in the hardened cement pastes added absorbent polymer

Ordinary Portland cement mixed with various amounts of absorbent polymer in the form of sodium acrylate ((–CH–)nCOONa) have been studied. As the content of absorbent polymer increased, heat evolution of samples decreased up to 1.15 wt % of absorbent polymer addition and conversely increased over 1.75 wt %. Flexural strength of cement paste with absorbent polymer was improved more than 20%. As the content of absorbent polymer increased, the porosity values decreased and mean pore diameter shifted to small pore diameter region. Flexural strength of ordinary Portland cement paste had a linear correlation with non-evaporable water content but, that of cement paste with absorbent polymer deviated from a linear correlation with non-evaporable water content. The chemical difference between cement pastes with and without absorbent polymer was found by the inductively coupled plasma-atomic emission spectroscopy and the infrared spectroscopy. For the infrared spectra of absorbent polymer, bands at 1416 and 1560 cm− 1 were assigned to C–O single bond and C=O double bond respectively, namely, unidentate complex. As the curing time increased, the absorption bands near 1416 cm− 1 shifted to longer wave number and the absorption bands near 1560 cm− 1 to shorter wave number and finally bidentate complex was formed. Absorbent polymer released sodium ions to pore solution under the basic condition of pH 12.5–13.5 and became polyacrylic acid. Then some of these polyacrylic acid were crosslinked with others by calcium ions leached from cement grains. Calcium ion was regarded as a central charge connecting the negative parts in carbon-oxygen polarization of absorbent polymer' functional groups.

Effect of water and other dielectrics on subcritical crack growth in portland cement paste

In studying the effect of water and a series of aliphatic alcohols on subcritical crack growth in cement paste, log crack velocity-stress intensity factor curves were obtained by means of a double-torsion technique. The relative position of the curves was found to be dependent on the dielectric constant of the test media. Flexural strength of cement paste saturated in organic fluids is also dependent on the dielectric constant. Stress corrosion processes involving chemical attack of SiO bonds in cement paste appear to be operative.