Synthesis of Calcium Nitrate Self-Healing Microcapsules Using Aerosol OT Hexane Solution for Cementitious Materials

Calcium nitrate synthesis of in urea-formaldehyde shell has recently been used to produce self-healing microcapsules for construction applications. The original synthesis was based on water-in-oil emulsion with sulfonic acid as fundamental ingredient of the oil (continuous) phase. It has been modified herein by changing the composition of the continuous (oil) phase by mixing anionic surfactant, Aerosol OT (AOT) with hexane to prepare the solution while keeping the aqueous phase unchanged. The submicron refined calcium nitrate microcapsules. In order to characterize the microcapsules encapsulated using the aforementioned, procedure, a Scanning Electron Microscopy (SEM) was utilized. The obtained microcapsules had satisfactory diameter and shell thickness. To assess the effect of the prepared microcapsules on the compressive and flexural strengths, mortar mixes containing 75% microcapsules (by weight of cement), as an introductory dosage, were made. It has been demonstrated that incorporating the self-healing microcapsules prepared using the procedure suggested in this study did not cause significant reductions in the mortar samples' strengths. Hence, the encapsulation methodology presented here may be utilized to investigate their self-healing efficiency in cementitious materials

Carbon nanotube effect on the ductility, flexural strength, and permeability of concrete

Recently, remarkable types of carbon nanofilaments called carbon nanotubes (CNTs) have raised the interest of many concrete and cementitious composite researchers due to their significant mechanical, electrical, thermal, kinetic, and chemical properties. These nanofilaments are considered promising applicants to use in producing high-performance cement-based composite materials. In this research, the effect of CNT use on the flexural strength, strain capacity, permeability, and microstructure of concrete was investigated. Concrete batches of 0, 0.03, 0.08, 0.15, and 0.25 wt.% CNTs were prepared using a mixing method that consisted of a 30-minute solution sonication and a 60-minute batch mixing. On the 28th day, the mechanical properties were determined. The results indicated that concrete prepared using high CNT contents of 0.15 and 0.25 wt.% increased the flexural strength by more than 100% in comparison with 0% CNT concrete. Furthermore, the results showed that CNTs would increase the ductility of concrete beams by about 150%. The permeability test results showed the benefits of CNT inclusion in reducing the permeability of concrete. The permeability coefficient (kT) decreased by at least 45% when CNTs were added to concrete. A qualitative microstructural analysis illustrated the uniform dispersion of CNT filaments within the concrete hydration products in all batches.Scopu

A Comparison between Natural Pozzolana and Fly Ash Replacements on the Mechanical Properties of Concrete

This study investigates the effect of Natural Pozzolana (NP) and Fly Ash (FA) substitutes on concrete's mechanical and microstructural properties. Mixes containing 10 - 50 % cement substitute ratios were prepared and tested for flexure and compressive strength after 28 days of curing. Then, qualitative microstructural analysis was performed using Scanning Electron Microscope (SEM). In terms of compressive strength, the mixes containing only 10 % replacement ratios of both NP and FA showed an improvement of 10 % compared to the plain control mix. On the other hand, all mixes containing FA could attain at least a 25 % development in their flexural strength compared to the control mix. The microstructural analysis illustrated that adding FA and NP enhances cement hydration by improving the formation of dense hydration products such as calcium silicate hydrate (C-S-H) and calcium hydroxide (C-H), which are mainly responsible for the performance of the improved mechanical properties of concrete

Aerosol OT Quantity Impacts on Calcium Nitrate Self-Healing Microcapsule Properties Used for Sustainable Construction Applications

This paper is a continuation of a previously published paper on this issue that studied the microencapsulation of calcium nitrate in urea-formaldehyde shell using Aerosol OT (AOT) in hexane solution. The aim of this paper is to determine the quantity of AOT that optimizes microcapsule distribution, diameter, and shell thickness. Different quantities of AOT, namely 0.25 g, 0.50 g, 1.5 g, and 2.5 g were dissolved in 180 g of hexane solution to prepare the continuous phase. A Scanning Electron Microscopy (SEM) was used to characterize the distribution and the diameters of the prepared microcapsules. A Transmission Electron Microscopy (TEM) was used to investigate the microcapsule shell thicknesses. The SEM images have shown that using 0.25 g of AOT may be insufficient to totally polymerize the whole quantity of the core materials into fully independent capsules. On the other hand, using 0.50 g of AOT has shown a uniform distribution and almost complete polymerization of the core material components into distinct microcapsules. Higher quantities of AOT (i.e., 1.50 g and 2.5 g) have resulted in agglomerated microcapsules and nonuniform distributions. The results have also demonstrated that the quantity of AOT does not have a significant impact on the microcapsule diameter. Microcapsule average shell thicknesses were found to decrease by increasing AOT amount up to 0.50 g and to increase again due to the agglomeration witnessed for increased AOT quantity. Accordingly, 0.50 g of AOT was recommended for the preparation of calcium nitrate microcapsules in future research work

Optimum carbon nanotubes' content for improving flexural and compressive strength of cement paste

This study investigated the effect of multi-walled carbon nanotubes’ (MWCNTs) weight fraction on the setting time and mechanical properties of cementitious composites. Different cement mixes containing CNT-to-cement weight fractions of 0.03, 0.08, 0.15, 0.25, 0.35 and 0.5 wt% were prepared in addition to the control mix. The initial and final setting times of the fresh pastes were measured on the cast day and the flexural and compressive strengths of the hardened samples were determined after 28 days of moist curing. The fractured surfaces of the samples were then examined using a scanning electron microscope (SEM). The results showed that the 0.25 wt% CNTs is the optimum weight fraction in terms of achieving maximum strength at a reasonable cost. Batches with lower CNTs’ contents than 0.25 wt% demonstrated lower flexural and compressive strengths, whereas batches with higher CNTs’ contents than 0.25 wt% produced similar or slightly higher strengths. Analysis of variance (ANOVA) confirmed that increasing CNTs’ concentration above 0.25 wt% will not have a significant effect on the compressive and flexural strengths. Investigations of the microstructure, which was carried out using SEM, showed good dispersions of the nanofilaments within the cement matrix. Spots of agglomerations were noticed in batches containing 0.25, 0.35 and 0.5 wt%. SEM images have also indicated that CNTs were embedded within the cement hydration products. The study findings were useful for determining the CNTs’ content required to achieve both optimum dispersion and maximum strength enhancement of cementitious composites.Scopu

Using Aerosol OT in Hexane Solution to Synthesize Calcium Nitrate Self-Healing Refined Microcapsules for Construction Applications

The micro-encapsulation procedure of calcium nitrate in urea-formaldehyde shell is well known. The most recent developed method for the synthesis of the calcium nitrate self-healing micro-capsules was based on the in-situ polymerization using water-in-oil emulsion. Although the microcapsules’ yield was significantly improved using this approach, incorporating the micro-capsules into concrete mixes has been found to reduce strength. One potential strength reduction cause might be the presence of sulfonic acid as a component in the continuous (oil) phase. As the anionic surfactant, Aerosol OT (AOT) has been widely used to prepare water-in-oil emulsions and to form aggregates in non-polar solvents; submicron calcium nitrate refined microcapsules were synthesized using AOT in hexane solution. While the aqueous phase in the original encapsulation procedure has not been altered, the continuous organic phase was prepared by dissolving AOT in hexane. The prepared microcapsules were characterized using Scanning Electron Microscopy (SEM). The preliminary assessment of the effect of incorporating of the refined microcapsules into cementitious materials has been carried out by preparing mortar mixes using 75% capsules’ concentration (by weight of cement). The reported yield values, average shell thickness, and average diameter of the prepared microcapsules were found satisfactory. Moreover, the mortar samples containing calcium nitrate refined microcapsules that were prepared using the proposed method did not experience significant reduction in their mechanical properties. Hence, such encapsulation procedure may be adopted for further investigation of the self-healing efficiency in cementitious materials of the microcapsules prepared using the proposed procedure. Future work shall be directed towards this end

The Effect of Fiber Geometry and Interfacial Properties on the Elastic Properties of Cementitious Nanocomposite Material

This paper investigates the elastic (Young’s) modulus of carbon Nanotube- (CNT-) reinforced cement paste using 3D and axisymmetric models using Abaqus software. The behavior of the CNT and the cement matrix was assumed to be fully elastic while the cohesive surface framework was used to model the interface. To investigate the effect of fiber waviness on the value of the elastic modulus, 3D models were developed assuming different distributions of fibers. The results obtained using the 3D model were compared to those obtained using the simplified three-phase axisymmetric model which consists of one single CNT aligned in the center of composite unit cell, an interface, and cement matrix. A parametric study was then carried out using the axisymmetric model to study the role of the interface in the composite elastic modulus without accounting for the presence of the interfacial transition zone (ITZ or interphase). The results showed that the CNTs waviness significantly reduced their reinforcing capability in the cement paste. On the other hand, the results obtained using the axisymmetric model were found to be in good agreement with those obtained using the 3D model. Moreover, the results of the parametric study showed that the interface properties significantly affect the composite elastic modulus and alter its behavior

Effect of calcium nitrate healing microcapsules on concrete strength and air permeability

This study investigates the compressive and flexural strengths, flexural modulus and air permeability of concrete samples containing 0·75% by cement weight of modified calcium nitrate self-healing microcapsules. The compressive and flexural strengths of concrete mixes with microcapsules were determined before healing and compared with those of the control mix. Moreover, another set of samples were loaded up to 60% of their ultimate load and placed in a water bath to accelerate their healing. The samples\u27 air permeability was measured before loading, after applying 60% of the ultimate load, and after 3 and 7 d of healing. The stress-strain curves were plotted to determine the flexural modulus. The results show that there is a significant statistical difference in the compressive strengths of mixes with and without microcapsules. However, the mix flexural strength did not show a significant statistical effect. Scanning electron micrograph images of the fracture surfaces of samples with microcapsules showed a good healing efficiency of calcium nitrate microcapsules. It was also found that the addition of microcapsules considerably decreased the samples\u27 air permeability. Although the flexural moduli of samples containing microcapsules were found to be less than those of samples without microcapsules before healing, modulus recovery was reported after 7 d of self-healing

Performance of modified self-healing concrete with calcium nitrate microencapsulation

This study investigates the strength reduction associated with incorporating calcium nitrate microcapsules in concrete. It also proposes modifications to the calcium nitrate micro encapsulation procedure to minimize the concrete strength reduction. These modifications consist of altering the continuous phase composition and keeping that of the aqueous phase the same. Amounts of 1%-10% of low Hydrophilic-Lipophilic Balance (HLB) emulsifier and 0.1%-1.0% of oil-soluble sulfonic acid catalyst (by weight of water in the aqueous phase) were dissolved in an organic solvent to prepare the continuous phase. The average diameter and shell thickness of the produced microcapsules were characterized using Scanning Electron Microscopy (SEM). Mortar mixes were prepared for various calcium nitrate concentrations of microcapsules that were encapsulated using the modified procedure. The compressive and flexural strengths and the elastic modulus of the mortar mixes were determined. The results show that the use of the modified encapsulation procedure resulted in a statically insignificant reduction of both compressive and flexural strengths compared to the original encapsulation method. The SEM micrographs of the fracture surface of the samples containing microcapsules showed that the strength reduction may be due to the agglomeration of the un-hydrated particles on the surface (shell) of the microcapsules. The compressive and flexural strengths of samples prepared using the proposed encapsulation procedure were enhanced compared to those prepared using previous encapsulation techniques.This work was made possible by a National Priority Research Program award [NPRP 6-280-2-117] from the Qatar National Research Fund (a member of The Qatar Foundation). The statements made herein are solely the responsibility of the authors.Scopu