PROGRESS REPORT GCCETR 11-12 PROJECT

Project Title: Improving the self-healing properties of concrete materials by using composite action with fiber reinforced polymers PI: Michele Barbato Department of Civil and Environmental Engineering Louisiana State University and A&M College 3418H Patrick F. Taylor Hall Ph: 225-578-8719 E-mail: mbarbato@lsu.edu Co-PI: Marwa Hassan Department of Construction Management Louisiana State University and A&M College 3130A Patrick F. Taylor Hall Ph: 225-578-9189 E-mail: marwa@lsu.edu This document is a progress report for the research project “Improving the self-healing properties of concrete materials by using composite action with fiber reinforced polymers.” Please find below: (1) the research accomplishments to date, (2) the research tasks to be completed and their expected completion date. Accomplishments to date: The research accomplishments achieved to date are: • Successful production of microcapsules of dicyclopentadiene (DCPD) and sodium silicate in the laboratory. • Successful control of size, morphology and shell thickness of the microcapsules of DCPD and sodium silicate. • Experimental validation of the self-healing process of concrete due to the addition of DCPD and sodium silicate microcapsules. • Identification of appropriate analytical models for prediction of strength, stiffness, and ductility of concrete confined with fiber reinforced polymers (FRP). • Extension of the previously identified material constitutive models to cyclic loading conditions. • Implementation of the aforementioned material constitutive models into a general purpose code for nonlinear finite element analysis. • Preparation of one paper that has been accepted for presentation at the 2013 TRB Annual Meeting (see attached copy of the submitted paper). • Submission of a proposal to NSF (Division: CMMI, Program: Structural Materials and Mechanics, Title: “COLLABORATIVE RESEARCH: A NEW GENERATION OF

INFRASTRUCTURE ELEMENTS MIMICKING SELF-HEALING MECHANISMS OF LIVING ORGANISMS”). This proposal is based on the preliminary results obtained in this current research project (see attached copy of the summary of the proposal, which is currently under review). • Preparation of the self-healing concrete specimens, both with and without FRP confinement. • Repair of the MTS machine to allow the testing of self-healing concrete specimens confined with FRP. Research tasks to be completed and their expected completion date: The research tasks to be completed are: • Experimental compressive test of self-healing concrete confined with FRP. • Complete the final report. The PI and co-PI expect to complete both research tasks before the end of February 2013. Reason for delay: The experimental compressive test requires the use of the large MTS machine of the CEE Department. However, this machine was not in working condition due to a problem with the adaptor of the load cell. Repairing the machine proved to be much more complex than originally expected and required the design of new components for the machine. This issue has been resolved recently, and the machine was successfully tested on November 29th, 2012. Benefits gained to the project from the granting of this extension: The investigators will complete all research tasks proposed for the funded project and will include the results obtained in the final report. These results will also be included in a second journal paper. It is noteworthy that, from the point of view of self-healing material production and property control, the PI and Co-PI have already completed a significant amount of research and obtained important research results, which are even beyond what originally proposed in the project.

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Evaluation of Microencapsulation of Dicyclopentadiene (DCPD) and Sodium Silicate for Self-Healing Concrete

LCDR James Gilford III1, CEC, USN, Marwa M. Hassan2, Tyson Rupnow3, Michele Barbato4, Ayman Okeil5, and Somayeh Asadi6

ABSTRACT

Considerable interests have been given in recent years to utilize self-healing materials in

concrete. The concept of microcapsule healing is based on a healing agent being encapsulated

and embedded in the concrete. The objective of this study was to evaluate the effects of

preparation parameters, namely, temperature, agitation rate, and pH on the shell thickness and

size (diameter) of the microcapsules. Two healing agents were evaluated in this study,

dicyclopentadiene (DCPD) and sodium silicate. Based on the results of the experimental

program, it was determined that as the pH was reduced, the shell thickness increased for sodium

silicate. Unlike DCPD, sodium silicate shell thickness was almost twice the amount of DCPD.

The more uniform and coherent microcapsules were produced at a temperature of 55°C. For the

DCPD microcapsules and at 49°C, the solution remained an emulsion and no encapsulation took

place. The increase in agitation rate resulted in a decrease in the average diameter of the

microcapsules for DCPD. This is due to the large microcapsules being broken up into smaller

ones when high shear is applied. On the other hand, the diameter of the microcapsules remained

1 Graduate Research Assistant, Department of Construction Management and Industrial Engineering, Louisiana State University,3218 Patrick F. Taylor,Baton Rouge, LA 70803, e-mail: jgilfo1@tigers.lsu.edu. 2 Assistant Professor, Department of Construction Management and Industrial Engineering, Louisiana State University, 3218 Patrick F. Taylor, Baton Rouge, LA 70803, e-mail: marwa@lsu.edu. 3 Concrete Research Engineer, Louisiana Transportation Research Center, 4101 Gourrier Ave., Baton Rouge, LA 70808, e-mail: tyson.rupnow@la.gov 4 Department of Civil and Environmental Engineering, Louisiana State University, 3418H Patrick F. Taylor, Baton Rouge, LA 70803, e-mail: mbarbato@lsu.edu 5 Department of Civil and Environmental Engineering, Louisiana State University, 3418H Patrick F. Taylor, Baton Rouge, LA 70803, e-mail: aokeil@lsu.edu 6 Assistant Professor, Department of Civil and Architectural Engineering, Texas A&M University-Kingsville, MSC 194. 700 University Blvd, Kingsville, TX 78363, email: somayeh.asadi@tamuk.edu

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constant for sodium silicate microencapsulation as the agitation rate increased. Testing of

concrete specimens modified with the two healing agents showed that DCDDbased

microcapsules were effective in enhancing the modulus of elasticity of un-cracked concrete and

increasing its modulus of elasticity after healing. For sodium silicate, an optimum pH value

should be identified in order to produce microcapsules that enhance the modulus of elasticity of

concrete before and after healing.

Keywords: Self-healing concrete, Microcapsulation, Sodium silicate, dicyclopentadiene

INTRODUCTION

The aging transportation infrastructure system in the US represents a serious challenge to

complete maintenance and repair needs using only limited available resources. It is envisioned

that a long term solution of this problem can only be achieved through new and creative

transformative approaches that can significantly reduce the costs associated with inspection,

maintenance, and repair of infrastructure elements. One solution for this problem involves the

use of a new paradigm known as “self-healing concrete.” Self-healing concrete can be defined

as the ability for concrete to autonomously heal cracks that may become imbedded throughout its

structure. By incorporating self-healing properties into concrete mixes, the process will not only

change concrete quality design and control methods, but the goal is to positively impact concrete

construction processes as a whole.

Considerable interests have been given in recent years to utilize self-healing materials in

concrete (Sharp and Clemena 2004)). This has led to the introduction of a new class of smart

materials that have the ability to heal after damage. Self-healing applications in concrete have

led to the introduction of bacteria-based self-healing concrete and microcapsule-based self-

healing concrete. The concept of bacteria-based self-healing concrete is based on applying a

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mineral-producing bacteria, which is found able to seal surface cracks (Jonkers 2011). The

concept of microcapsule healing is based on a healing agent such as sodium silicate being

encapsulated and embedded in the concrete (Pelletier et al. 2011) (3). When the crack

propagates until it reaches the microcapsule, the capsule breaks and the healing agent is released

into the crack to repair it. This becomes a proactive approach rather than reactive

countermeasure for cracks that develop within concrete structures.

In spite of these promising benefits and before self-healing microcapsules can be applied

effectively to concrete infrastructure elements, specific microencapsulation preparation

parameters need to be studied to control and optimize microcapsule properties. Therefore, the

objective of this study is twofold. First, an experimental program was designed and performed

to study the effects of preparation parameters, namely, temperature, agitation rate, and pH on the

shell thickness, size, and morphology of the microcapsules. Second, the effect of

microencapsulated self-healing materials on the concrete was evaluated in the laboratory.

BACKGROUND

Since their introduction in the 1950s, microencapsulation has been evaluated in numerous

construction materials including mortar, lime, cement, marble, sealant, and paints (Boh and

Sumiga 2008)). It has also been patented and tested in the food, chemical, textile, and the

pharmaceutical industries. The most common mechanism to trigger microcapsule healing is

through external pressure, which ruptures the microcapsule and releases the healing agent from

the core. Therefore, the microcapsule must be sufficiently stiff to remain intact during

processing but then it must break during damage of the concrete (Pelletier et al. 2011). In

addition, the microcapsule shell provides a protective barrier between the catalyst and the healing

agent to prevent polymerization during the preparation of the composite.

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There are three main methods for preparation of microcapsule (Boh and Sumiga 2008): (1) The

mechanical method, which mechanically applies the microcapsule around the healing agent; (2)

The coacervation method, which applies the microcapsule wall around the core and then

solidifies around the healing agent; (3) The polymerization method, which was used in this

study, consists of applying the healing agent as an emulsion and then solidifies to form the

microcapsule wall. The polymerization method is categorized as either in-situ polymerization in

which the healing agent is added to the liquid phase of an emulsion or as interfacial

polymerization in which the healing agent is dissolved into the liquid phase. In this study, in-situ

polymerization was selected for preparation of the microcapsules.

As shown in Figure 1, two main design parameters are of interest during microcapsule

preparation, shell thickness and size of the microcapsule, i.e., diameter. Microcapsule walls that

are too thin would fail during the manufacturing process (Tseng et al. 2005). In contrast, capsule

shells that are too thick will not allow breaking or fracturing of the shell as the crack penetrates

through the microcapsules plane. A well-developed process of microencapsulation using the

urea-formaldehyde method was developed by Brown et al. (2003). The in-situ encapsulation

method for water-immiscible liquids, by the reaction of urea with formaldehyde at acid pH,

which was outlined by (Dietrich et al. 1989), was the foundation of this preparation method.

Two healing agents were evaluated in this study, dicyclopentadiene (DCPD) and sodium silicate.

Dicyclopentadiene (C10H12) is a white crystalline solid/clear liquid solution (depending on its

potency) with an energy density of approximately 10,975 Wh/l. Its main use within industry and

private practice is for resins/unsaturated polyester resins (Li et al. 2005). This chemical can be

used as a monomer in polymerization reactions, such as ring-opening metathesis polymerization

or olefin polymerization. Sodium silicate (Na2O3Si), which is also known as liquid glass, is a

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sodium metasilicate compound. This solid or aqueous solution is used in concrete applications

to reduce its porosity. When added, a chemical reaction occurs with the excess of CaOH2, which

is already present in concrete (Greenwood et al. 1997). When Na2O3Si reacts with CaOH2, the

concrete permanently binds with the silicates at the surface. This makes the product a great

sealer as well as a great water repellent. Although theoretically possible, micro-encapsulation of

sodium silicate using the urea-formaldehyde method has never been successfully accomplished

before. White and his team were able to streamline the microcapsulation of DCPD by

controlling its diameter as well as its morphology (Kessler et al. 2003) ).

The microcapsule self-healing method has the ability to independently resolve issues such as

internal cracking and micro-cracking. When cracks occur, an imminent path towards structural

failure is initiated. By filling these voids and cracks with self-healing materials, concrete

structures will have a longer life cycle along with a less likelihood of destruction from unwanted

moisture and corrosion wear (Brown et al. 2003). Although DCPD is an exceptional healing

agent alone, in order for the agent to achieve maximum effectiveness, an appropriate interaction

is required to polymerize the healing agent within the damaged area. A process called ring

opening metathesis polymerization (ROMP) is used to polymerize the healing agent. This

process provides the following advantages for self-healing microcapsules (White et al. 2001):

1. A more durable long lasting shelf life;

2. A low monomer viscosity and volatility;

3. Increased rapid polymerization during ambient conditions; and

4. Low shrinkage rate during polymerization.

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ROMP utilizes a Grubbs catalyst (transition metal catalyst), which incorporates a high metathesis

method. The use of this catalyst allows multiple chemical groups to be utilized within the

chemical process (such as oxygen and water). When DCPD encounters the Grubbs catalyst,

polymerization occurs (Brown et al. 2005, Brown et al. 2005) . Sodium silicate, however, does

not require a matrix and can be used as an individual healing component. The first reaction

consists of sodium silicate reacting with calcium hydroxide, which is a product of cement

hydration (Nonat 2004). The second reaction occurs between sodium hydroxide and silica.

What is essential in both processes is the mending agent that resides in an aqueous environment

within the microcapsule itself (Nonat 2004) . Water enables the hydration of the damaged

cement and also allows, further bonding of the mending agent. The products of both reactions

will fill the crack, and subsequently permits recovery of strength. Both processes support the

presence of the aqueous mending agent, which again provides further integrity of the concrete by

creating a bond, healing the crack (Brown et al. 2005).

EXPERIMENTAL PROGRAM

Test Materials

The chemicals utilized in the preparation of the microcapsules based on in-situ polymerization

are presented in Table 1.

DCPD Microencapsulation Procedure

The adopted procedure was performed by using in situ polymerization, in an oil-in-water

emulsion. For better presentation, the main steps of this procedure are shown in Figure 2 and are

as follows

1. Place 200 ml of DI water in a 1000 ml beaker;

2. Dissolve 50 ml of 2.5 wt.% EMA copolymer using a magnetic stirrer and ultra sound water

bath to develop an aqueous solution;

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3. Agitate using a IKA RW 20 digital mixer, with a driving 55 mm low shear three-bladed

mixing propeller placed just above the bottom of the beaker;

4. Under agitation, add 5.00 g urea, 0.50 g resorcinol and 0.50 g ammonium chloride in the

solution;

5. Set the pH by using sodium hydroxide (NaOH) and hydrochloric acid (HCl) drop-wise with a

disposable pipet;

6. Add two to three drops of 1-octanol to reduce surface bubbles;

7. Allow the solution to stabilize for approximately 6 – 8 minutes at the appropriate pH and rpm

agitation rate, before 100 ml of DCDP is added at a slow stream rate;

8. Allow the solution to stabilize for 13 – 15 minutes before 12.7 g of 37 wt% aqueous solution

of formaldehyde was added to the emulsion;

9. Wrap and cover the solution with aluminum foil, and slowly heat to the set temperature;

10. Turn off the hot plate after 4 hours of continuous agitation;

11. Once cooled to ambient temperature, the suspension of microcapsules was separated under

vacuum filtration;

12. Rinse microcapsules with DI water three times with 500 ml of DI water, and then allow to air

dry for 48 - 72 h.

Sodium Silicate Microencapsulation Procedure

This procedure was accomplished by using in situ polymerization, in an oil-in-water emulsion.

For better presentation, the main steps of this procedure are shown in Figure 3 and are as

follows:

1. Place 200 ml of DI water in a 1000 ml beaker;

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2. Dissolve 50 ml of 2.5 wt.% EMA copolymer using a magnetic stirrer and ultra sound water

bath to develop an aqueous solution;

3. Agitate using a IKA RW 20 digital mixer, with a driving 55 mm low shear three-bladed

mixing propeller placed just above the bottom of the beaker;

4. Under agitation, add 5.00 g urea, 0.50 g resorcinol and 0.50 g ammonium chloride;

5. Set the pH by using sodium hydroxide (NaOH) and hydrochloric acid (HCl) drop-wise with a

disposable pipet;

6. Add two to three drops of 1-octanol to reduce surface bubbles;

7. Allow the solution to stabilize for approximately 6 – 8 minutes at the appropriate pH and rpm

agitation rate;

8. Mix 170 ml of DI water with 60 ml of an aqueous sodium silicate and add to the solution;

9. Agitate the solution for approximately 5 min. While under agitation, HCL was slowly added

to the solution to form a gel/aqueous solution;

10. Add 100 ml of the gel/aqueous solution to the emulsion while maintaining a pH of 3.0 – 3.5;

11. Allow the solution to stabilize for 13 – 15 minutes before 12.7 g of 37 wt% aqueous solution

of formaldehyde was added to the emulsion;

12. Wrap and cover the solution with aluminum foil, and slowly heat to the set temperature;

13. Turn off the hot plate after 4 hours of continuous agitation;

14. Once cooled to ambient temperature, the suspension of microcapsules was separated under

vacuum filtration;

15. Rinse microcapsules with DI water three times with 500 ml of DI water, and then allow to air

dry for 48 - 72 h.

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Test Factorial

An experimental program was developed to evaluate the effects of preparation parameters,

namely, temperature, agitation rate, and pH on the shell thickness and size of the microcapsules.

Table 2 presents the experimental factorial developed in this study. Two healing agents were

evaluated, DCPD and sodium silicate. During synthesis, the agitation rate, temperature, and pH

were varied. The constant level of temperature, pH, and agitation for the DCDP was 55°C, 3.7,

and 550 rpm respectively and the constant level of temperature, pH, and agitation for the sodium

silicate was 55°C, 3.0, and 550 rpm. The agitation rate was varied at 6 levels for the DCPD

synthesis and at 4 levels for the sodium silicate synthesis; while the temperature and pH were

kept constant. Similarly, to test the effect of the temperature, three levels were used while the

pH and agitation rate were kept constant. Three pH levels were used while the temperature and

agitation rate were kept constant. This resulted in a total of 10 synthesis methods tested using

DCDP and 8 synthesis methods tested using sodium silicate.

RESULTS AND ANALYSIS

Microcapsule Parametric Analysis

Numerous factors can affect morphology, diameter, and shell thickness of the prepared

microcapsules. The evaluated factors were pH, temperature, and agitation rate. Morphology,

diameter, and shell thickness calculations were conducted based on image analysis of scanning

electron microscopy (SEM) images. Sputtering technique was used to prepare microcapsules for

SEM. SEM was conducted using a Quanta 3D FEG scanning electron microscope. The highest

yield strength for DCPD was 79.0% at an agitation rate of 350 rpm, temperature of 55°C, and a

pH of 3.7. The highest yield strength for sodium silicate was 94.9% at an agitation rate of 350

rpm, a temperature of 55°C, and a pH of 3.2.

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Effects of pH on Morphology and Shell Thickness

Figure 4 (a and b) presents the effects of pH on the shell thickness for sodium silicate and DCDP

microcapsules, respectively. The goal for the shell wall thickness is to be between 140 – 200

nm. As shown in this Figure 4(a), the increase in pH values resulted in an increase in the shell

thickness for sodium silicate. As the pH is lowered, the shell wall became nonexistent as no

microencapsulation took place. Results in Figure 4(b) show that the increase in pH values

resulted in a decrease in the shell thickness for DCPD.

Figure 5 (a to d) presents SEM images of the microcapsules prepared with DCPD and sodium

silicate at different pH values. As shown in this figure, the microcapsules prepared with DCPD

were spherical and more uniform than the microcapsules prepared with sodium silicate. In

addition, the size of the microcapsules was reduced as the pH value was increased. The outer

surface of the microcapsule had a rough permeable layer, whereas the inside was smooth and

free of cavities.

Effects of Temperature

Figure 6 (a and b) presents the effects of temperature on the shell thickness for sodium silicate

and DCPD microcapsules, respectively. For sodium silicate, there were no microcapsules

formed at 53°C. For the DCPD microcapsules and at 49°C, the solution remained an emulsion

and no encapsulation took place.

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Figure 7 (a to d) presents SEM images of the microcapsules for DCPD and sodium silicate

prepared at different temperatures. As shown in this figure, the microcapsules prepared with

DCPD were spherical and more uniform than the microcapsules prepared with sodium silicate.

In addition, the size of the microcapsules was reduced as the temperature was increased.

Effects of Agitation Rate

Figure 8 (a and b) shows the effect of agitation rate on the average diameter of the microcapsules

for DCPD and sodium silicate microcapsules, respectively. As shown in this figure, the increase

in agitation rate results in a decrease in the average diameter of the microcapsules for DCPD.

This is due to the large microcapsules being broken up into smaller ones when high shear is

applied. The optimum size of the microcapsules is dependent on the crack size that is expected

to be filled during the healing mechanism. On the other hand, the diameter of the microcapsules

remained constant for sodium silicate microencapsulation as the agitation rate increased, Figure

8a. This may be attributed to the attempt to stabilize the alkalinity of the sodium silicate solution

for the microencapsulation procedure using Urea-Formaldehyde. SEM images shown in Figure

9 also show a reduction in diameter with the increase in agitation rate.

Laboratory Evaluation of Self-Healing Concrete

The incorporation of the prepared microcapsules in concrete was evaluated in the laboratory.

Concrete specimens were prepared using a standard ready-mix design with a water/cement ration

of 0.5 that would achieve a compressive strength of 4,000 psi (28 MPa). Sodium silicate

microcapsules were added to the mixing water at a content of 0.5, 1.0, 2.5, and 5.0% by weight

of cement. Sodium silicate microcapsules were also prepared at three pH values (3.0, 3.1, and

3.2) in order to vary the shell thickness and were added to the mixing water at a content of 5.0%

by weight of cement. DCPD was used at a content of 0.25% by weight of cement for

microcapsules prepared at a pH of 3.1, 3.4, and 3.7 to vary the shell thickness.

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Cylindrical concrete specimens were demolded after 24 hours and were cured by applying steam

curing for six days. Three replicates were prepared for each testing condition with an average

coefficient of variation of 10% Modulus of Elasticity. Specimens were tested based on a

modified version of ASTM C 469, Standard Test Method for Static Modulus of Elasticity and

Poisson’s Ratio of Concrete in Compression, by applying 70% of the ultimate concrete strength.

The maximum load was increased to 70% instead of 40% as required in ASTM C 469 to induce

damage in the concrete specimens and to observe the effect of the microcapsules on the healing

mechanism. Specimens were loaded and unloaded for three cycles and were then left in the

curing room for 48 hours to heal. After the healing period, specimens were then retested using

the same test protocol. The initial tangent modulus, which is defined as the slope of the tangent

from the origin, was calculated before and after healing.

Figure 10(a) presents the effects of DCDD and sodium silicate microcapsules on the modulus of

elasticity before and after healing. The pH was 3.1 at different sodium silicate content (i.e. 0.5%,

1%, 2.5%, and 5%). As shown in this figure, sodium silicate caused a small decrease in the

modulus of elasticity as compared to the control mixture. However, the modulus of elasticity

after healing increased for all sodium silicate content except 0.5%, which may be due that this

content was insufficient to enhance the healing capacity of the prepared concrete. Figure 10(b)

presents the effects of sodium silicate microcapsules prepared at three pH values and at a content

of 5.0%. A new sample with 5% sodium silicate content was used in figure 10(b). As shown in

this figure and by varying the pH value, one may produce microcapsules with an optimum shell

thickness that would enhance the modulus of elasticity of concrete before and after healing. For

the results presented in Figure 10(b), a pH value of 3.1 at a sodium silicate content of 5.0% was

found to be optimum.

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For DCPD, the original modulus of elasticity increased at a pH of 3.1 as compared to the control

mix but a small decrease in the modulus of elasticity was noted at a pH of 3.4 and 3.7, Figure

10(a). After healing, the modulus of elasticity increased for all DCPD-modified concrete

specimens. The microcapsules prepared at a pH value of 3.1 were the most effective as the

modulus of elasticity decreased with the increase in pH value. Results presented in Figure 4(b)

showed that the increase in pH values resulted in decrease in the shell thickness for DCPD-based

microcapsules.

Specimens that cracked during testing were used for visual observation of crack healing. Figure

11 presents a visual inspection of a cracked specimen before and after 1-week healing for the

concrete prepared with 0.25% DCPD (pH = 3.4) and 5.0% Sodium Silicate (pH = 3.1). These

pictures were taken at the same environmental condition the only difference between them is the

healing age. As shown in this figure, part of the surface crack healed when it reached the

microcapsule, which was released into the crack to repair it. From these results, it also appears

that DCPD-based microcapsules were effective in healing the cracks in the concrete specimens.

CONCLUSIONS

The objective of this study was to evaluate the effects of preparation parameters, namely,

temperature, agitation rate, and pH on the shell thickness and size (diameter) of the

microcapsules. Two healing agents were evaluated in this study, DCPD and sodium silicate.

Sodium silicate, however, was not consistent with the normal parameter matrix, due to its

alkaline nature. Based on the results of the experimental program, the following conclusions

may be drawn:

• As the pH was reduced, the shell thickness increased in case of the DCPD microcapsules.

Unlike DCPD, sodium silicate shell thickness was almost twice the amount of DCPD. This

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was due to sodium silicate being transformed into a gel like solution prior to micro-

encapsulation. This gel solution made the compound much easier to encapsulate, as well as

build a much stronger shell wall.

• The more uniform and coherent microcapsules were produced at a temperature of 55°C. For

the DCPD microcapsules and at 49°C, the solution remained an emulsion and no

encapsulation took place.

• The increase in agitation rate results in a decrease in the average diameter of the

microcapsules for DCPD. This is due to the large microcapsules being broken up into

smaller ones when shear is increased. On the other hand, the diameter of the microcapsules

remained constant for sodium silicate microencapsulation as the agitation rate increased.

• DCPD-based microcapsules were effective in enhancing the modulus of elasticity of un-

cracked concrete and increasing its modulus of elasticity after healing. For sodium silicate,

an optimum pH value should be identified in order to produce microcapsules that enhance the

modulus of elasticity of concrete before and after healing. From the results presented in this

study, a pH value of 3.1 at a sodium silicate content of 5.0% was found to be optimum.

ACKNOWLEDGEMENTS

This work was funded through a grant from the Gulf Coast Research Center for Evacuation and

Transportation Resiliency. The authors would like to acknowledge the support of Louisiana

Transportation Research Center (LTRC) for granting access to their laboratory.

REFERENCES

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2. Jonkers, H.M., Bacteria-Based Self-Healing Concrete, HERON Publications, Vol. 56, No. 1,

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List of Tables and Figures

Table 1. Required Chemicals for Interfacial Polymerization Synthesis

Table 2. Experimental Test Factorial

Fig.1 Schematic of the Components of a Microcapsule

Fig.2 DCPD Microencapsulation Process.

Fig.3 Sodium Silicate Microencapsulation Process

Fig. 4 Effect of pH Values on the Shell Thickness for (a) Sodium Silicate and (b) DCPD

Microcapsules

Fig.5 Effect of pH Values on the Morphology of Microcapsules for (a) and (b) DCPD and (c)

and (d) Sodium Silicate

Fig. 6 Effect of Temperature on the Shell Thickness for (a) Sodium Silicate and (b) DCPD

Microcapsules

Fig.7 Effect of Temperature on the Morphology of Microcapsules for (a) and (b) DCPD and (c)

and (d) Sodium Silicate

Fig.8 Effect of Agitation Rate on the Diameter of the (a) Sodium Silicate and (b) DCPD

Microcapsules

Fig.9 Effect of Agitation Rate on the Morphology of Microcapsules for (a) and (b) DCPD and

(c) and (d) Sodium Silicate

Fig. 10 Effect of Microcapsules on Modulus of Elasticity before and after Healing for (a) SS and

DCPD Microcapsules and (b) for SS Microcapsules Prepared at Different pH

Fig.11 Effects of (a and b) DCPD and (c and d) Sodium Silicate (1%) on Crack Healing after 1-

Week Recovery

18

Table. 1 Required Chemicals for Interfacial Polymerization Synthesis

Chemical Function Manufacturer Urea Creates endothermic reaction in water The Science Company Ammonium Chloride Assists with curing Process The Science Company

Resorcinol (Technical Grade Flake) Reacts with formaldehyde and is a chemical intermediate for the synthesis process

NDSPEC Chemical Corporation

ZeMac E60 Copolymer Improves mechanical properties Vertellus Specialties, Inc. ZeMac E400 Copolymer Improves mechanical properties Vertellus Specialties, Inc. Octanol Prevents surface bubbles Oltchim Hydrochloric Acid Lowers pH The Science Company Sodium Silicate Reacts with Ca(OH)2 The Science Company Sodium Hydroxide Increases pH The Science Company

Formaldehyde Reacts with urea during synthesis process

The Science Company

Grubbs Catalyst Reacts with DCPD and polymerizes Materia, Inc. DETA (diethylenetriamine) Mix with EPON 828

Used in synthesis of catalysts, epoxy curing agent, and corrosion inhibitors

Huntsmann

DCPD Selected Resin to Heal Concrete Crack

Texmark- 87% & 89% Purity Cymetech- 99% Purity

19

Table 2. Experimental Test Factorial

Variables DCPD Sodium Silicate Agitation Rate 250,350,450,550,800,

and 1000 250,350,450, and 550

Temperature 49,52, and 55 51,53, and 55 pH value 3.1, 3.4, and 3.7 3, 3.1, and 3.2

Fig. 1. Schemmatic of the Componennts of a Micrrocapsule

20

21

DI Water

Add EMA 400 or 60 Co-polymer

Add Formaldehyde

Add DCDP

Add UreaAdd Resorcinol

Add Ammonium Chloride

Allow 4 hours to Cook and 2 hours to cool to room

temperature

Filter and Wash 3 X 500 ml using Vacuum Filtration System

Begin Agitation

Turn on and Set Desired

Temperature

Adjust Agitation/ Adjust pH

Fig. 2. DCPD Microencapsulation Process

22

Fig. 3. Sodium Silicate Microencapsulation Process

DI Water

Add EMA 400 or 60 Co-polymer

Add Formaldehyde

Add Sodium Silicate

Add UreaAdd Resorcinol

Add Ammonium Chloride

Allow 4 hours to Cook and 2 hours to cool to room

temperature

Filter and Wash 3 X 500 ml using Vacuum Filtration System

Begin Agitation

Turn on and Set Desired

Temperature

Adjust pH

Adjust Agitation/ Adjust pH

Fig. 4.

She

ll T

hick

ness

(nm

)S

hell

Thi

ckne

ss (

nm)

Effect of p

0

100

200

300

400

500

600

700

800

900

1000

0

50

100

150

200

250

300

350

400

H Values on

3.01

3.1

n the Shell TMic

(a)

(b) Thickness focrocapsules

3.12

pH

3.4

pH

for (a) Sodiu

3

um Silicate

3.2

3.7

and (b) DC

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Yie

ld S

tren

gth

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Yie

ld S

tren

gth

23

PD

g

Fig. 5. E

599.8 μ

Effect of pH

289.1 μm

μm

218.5

320.6 μm

319.7 μm

(

(b

(c

(d

H Values on

5 μm

3

(a) pH = 3.1

b) pH = 3.7

c) pH = 3.0

d) pH = 3.2

the Morpho(c) and (d

987.1 μm

315.9 μm

313.9 μm

247.4 μm

1 (250 rpm,

(250 rpm, T

(251 rpm, T

(255 rpm, T

ology of Mid) Sodium S

m

m

T = 55°)

T = 55°C)

T = 55°C)

T = 55°C)

icrocapsulesilicate

786.8

315.9 μm

181.3

1

s for (a) and

8 μm

3 μm

133.8 μm

d (b) DCPD

24

and

Fig.6. EEffect of Tem

0

100

200

300

400

500

600

700

800

She

ll T

hick

ness

(nm

)

0

50

100

150

200

250

She

ll T

hick

ness

(nm

)

mperature

51

49

on the ShellMic

Temp

Shell T

Tem

Shell T

(a)

(b) l Thickness crocapsules

53

perature (°C)

Thickness Y

52

mperature (°C

Thickness Y

for (a) Sod

55

)

Yield

55

C)

Yield

dium Silicate

0%

20%

40%

60%

80%

100%

0%10%20%30%40%50%60%70%80%90%100%

e and (b) DC

%

Yie

ldS

tren

gth

%

Yie

ld S

tren

gth

25

CPD

Fig. 7.

599.8 μ

847.5 μ

311.4

530.4 μ

Effect of Te

μm

μm

4 μm

μm

(a

(b

(c)

(d) emperature

a

31

293

5

a) T = 55° (p

b) T = 52° (p

) T = 55°C (

T = 51°C (e on the Morand (c) and

5.9 μm

858

3.9 μm

540.6 μm

pH = 3.7, rp

pH = 3.7, rp

(pH = 3.2, rp

(pH = 3. 2, rrphology of(d) Sodium

.9 μm

pm = 250)

pm = 250)

pm = 255)

rpm = 255)f Microcaps

m Silicate

672.2 μm

701.4 μm

489.6 μm

sules for (a)

and (b) DC

26

CPD

Fi

Di

t(

)

g. 8. Effect

1

10

100

1000D

iam

eter

(µ

m)

1

10

100

1000

Dia

met

er (

µm

)

of Agitation

250 3

1

0

0

0

250

n Rate on thand (b)

349 451

Ag

Dia

350

Agi

Dia

(a)

(b) he DiameterSodium Sili

1 549

gitation Rate

ameter Yeil

451

itation Rate

ameter Yeil

r of the (a) Dicate

800

e (RPM)

ld

552

(RPM)

ld

DCPD Micr

01234567891

1000

0%

20%

40%

60%

80%

100%

2

rocapsules

0%0%

20%0%

40%0%

60%70%0%

90%00%

Yie

ld S

tren

gth

%

Yei

ld S

tren

gth

27

Fig. 9. E

Effect of Ag

599.8 μm

165.7 μm

591.

498.1 μm

(a) Agita

(b) Agita

(d) Agita

(d) Agitati

gitation Ratea

.6 μm

m

ation Rate =

ation Rate =

ation Rate =

ion Rate = 5

e on the Moand (c) and

786.8 μm

609.9 μm

= 250 rpm (p

= 549 rpm (p(c)

= 257 rpm (p(e)

551 rpm (pH

orphology o(d) Sodium

315.9 μm

81.4 μm

pH = 3.7, T

pH = 3.7, T

pH = 3.2, T

H = 3.2, T =

of Microcapm Silicate

265.2 μm

701.4

46

T = 55°C)

T = 55°C)

T = 55°C)

= 55°C)

sules for (a)

672.2 μm

4 μm

67.5 μm

) and (b) DC

28

CPD

29

(a)

0

1000

2000

3000

4000

5000

6000

7000

8000

Control SS 0.5%pH=3.1

SS 1%pH=3.1

SS 2.5%pH=3.1

SS 5%pH=3.1

DCDP0.25%pH=3.1

DCDP0.25%pH=3.4

DCDP0.25%pH=3.7

Mod

ulus

of

Ela

stic

ity

(ksi

)

Sample ID

Before HealingAfter Healing

Fig. 10. (a) SS

(a) BeforFig. 1

2

3

4

5

6M

odul

us o

f E

last

icit

y (k

si)

Effectand DCPD

re healing 11. Eff

0

1000

2000

3000

4000

5000

6000

t of MicrocaMicrocapsu

fects of (a aH

Control

B

apsules on Mules and (b)

nd b) DCPDHealing afte

SS 5% p

Before Healing

(b) Modulus of ) for SS Mic

D and (c ander 1-Week R

pH=3.0 S

Sample ID

g After

Elasticity bcrocapsules

(b) Afterd d) Sodium

Recovery

SS 5% pH=3

D

r Healing

before and aPrepared a

r 1-week of hm Silicate (1

.1 SS 5%

after Healinat Different

healing 1%) on Crac

% pH=3.2

30

ng for pH

ck

A. PROJECT SUMMARY COLLABORATIVE RESEARCH: A NEW GENERATION OF INFRASTRUCTURE

ELEMENTS MIMICKING SELF-HEALING MECHANISMS OF LIVING ORGANISMS The objective of this project is to test the hypothesis that dual-action healing can drastically improve the self-repairing properties of reinforced concrete (RC) structures. The dual-action healing will be obtained by combining concrete prepared with microcapsules self-healing agents with Shape-Memory Alloy (SMA) reinforcement. The new class of RC composite material will mimic biological systems by partially healing moderate crack damage and by recovering from large deformations. The basic hypothesis is that the SMA can mechanically reduce the size of permanent cracks associated with yielding of the reinforcing steel, and the self-healing microcapsules can heal these cracks, thus recovering most of the stiffness and strength loss due to damage. A comprehensive experimental plan will characterize the mechanical and microscopic properties of the new class of RC composite materials using standard and advanced material characterization techniques. Size and morphology of self-healing microcapsules will be characterized using Scanning Electron Microscopy (SEM) coupled with Energy Dispersive X-Ray Spectroscopy (EDX). Self-healing processes in the concrete surface cracks will be characterized over time using SEM coupled with EDX and Atomic Force Microscopy (AFM). Material specimen tests will be used to identify and optimize the properties of the microcapsules and SMA. Laboratory testing will measure the recovery of flexural strength, stiffness and deformation for the new class of RC members after loading damage. Educational activities will enhance the knowledge and understanding of advanced materials’ applications among high school and undergraduate students. To achieve this objective, six undergraduate students from underrepresented groups (from Texas A&M University, Kingsville, a historically Hispanic institution, and from Southern University, a historically Black institution, and two from LSU) will receive summer internships that will expose them to innovative laboratory research activities and encourage them to pursue graduate studies related to advanced construction materials. Additional instruction/outreach activities for undergraduate students, high school students and teachers, and the general public will be performed through collaboration with several well-established and already successful diversity programs at LSU.

Intellectual Merits: This research project will introduce a new class of RC members that mimic living organisms with self-repair and damage restoration capabilities. The proposed project will innovatively combine the benefits of self-healing microcapsules (which have the ability to heal concrete after damage) with SMAs (which have the ability to recover large deformations and steel yielding upon heating and removal of stress). The basic hypothesis is that composite action can improve the self-repair capabilities of RC structures. Experimental and microscopic results will fill the gap in our knowledge by addressing the following issues: (1) Validate that the proposed approach can provide a superior class of RC composite materials; (2) Quantify the recovery in mechanical properties of damaged RC members that are built based on the proposed approach; (3) Determine the optimal properties and ratio with cement of self-healing microcapsules for the proposed application; and (4) Identify the benefits and limitations of the proposed preparation approach and its potential applications in structural and bridge engineering.

Broader impacts: This research proposal innovatively addresses the important societal need to reduce costs associated with inspection, maintenance, and repair of RC structures by introducing a new paradigm of RC elements that are designed to autonomously self-repair up to moderate damage levels. The proposed experimental activities will provide the necessary fundamental knowledge to facilitate the practical implementation of this new class of RC members in Civil Engineering applications. Results from this research could lead to the design/construction of new bridges and upgrade of existing bridges, a more efficient use of taxpayers’ dollars, creation of new jobs in the construction industry, and reduction of the cost associated with traffic restrictions on degraded bridges in the US. This research is characterized by a strong multidisciplinary component and proposes a significant and well-coordinated effort for involvement/education of undergraduate and K-12 students especially from underrepresented groups.

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