2.2 Methods

21 m in the south, 3–4 m near Cayo Centro, and 2 m in the north. A Thalassia testudinum seagrass bed and garden eels, sometimes at high densities, are found in the reef lagoon. The reef lagoon extends for several tens of kilometers west of the bank and is extremely productive [13]. Under its waters the first thing we identify are sponges, fans and sea whips, and isolated colonies of stony corals and a huge diversity of multicolored reef fishes or small fish that are by hundreds hidden under the rocky cavities of where they come out and create a lively silver spot. However, the diversity and abundance of someone groups (e.g., the management program [14] reports 95 species of Cnidaria, 35 sponges, 96 birds, 11 reptilian, 135 algae, and 104 species of mollusk), the main fauna inhabiting this tropical ecosystem is practically unknown (cichlid, crocodiles, etc.). Some of this species have never been described; maybe others are relict species, and others are a complex of subspecies interacting biologically and ecologically between them. Aggregation of the queen conch (Strombus gigas) and spiny lobsters (Panulirus argus) and abundance of large fish are frequent; turtles probably occur too. Cayo Centro is an important breeding site for frigate birds (Fregata magnificens) and olivaceous cormorant (Phalacrocorax

Lagoon Environments Around the World - A Scientific Perspective

olivaceous). The area is fished for queen conch (Strombus gigas) and lobster (Panulirus argus) by fishermen from Xcalac and Chetumal; there are three fishery cooperatives with 60–70 elements each one; the current disturbance for fishing is probably small, because of a forbidden period for the Fishery Secretary decree [14]. There are two lighthouses and many wrecks. The reef is gradually becoming popular with scuba divers who make 4- to 5-day trips from Cancún, Cozumel, and Quintana Roo coasts. The area has frequent climatological disturbance (winds of the

north and south and hurricanes) (Figure 1).

Figure 1.

212

Sampling sites in both oceanic reefs.


**3.3 Loss in biodiversity**

Animal waste and droppings are not treated properly, as farmers often dispose of their waste in rivers, where they pollute the water and impend the biodiversity of the ecosystem. Waste products of poultry emit ammonia and nitrous oxide leading to nitrogen pollution of water and soil [24]. Uneven use of pesticides and fertilizers can also pollute soil, water, and air [25]. The continuous degradation of environment and loss in biodiversity is an alarming sign for global warming [25].


**1. Introduction**

The arrival of the optical fiber allowed for an enormous increase on communication line bandwidth. This naturally led to deploying networks with dispersed topologies, as scarce (even unique) paths linking the diverse sites are enough to fulfill all the requirements regarding data exchanges. Yet dispersed topologies have a problem: the ability of the network to keep all sites connected is affected by the failure of few (even one single) communication links or switch sites. Before the introduction of the optical fiber, topologies were denser; upon failure of few links, there was a probable reduction of throughput, yet keeping all sites connected. With disperse fiber-based designs, the network behaves much more as an "all-ornothing" service; either, it fulfills all requirements of connectivity and bandwidth, or it fails to connect some sites. Therefore, the problem of designing networks with minimal costs and reliability thresholds has since gained relevance.

In view of the above, the networks must continue to be operative even when a component (link or central office) fails. In this context, survivability means that a certain number of pre-established disjoint paths among any pair of central offices must exist. In this case, node-disjoint paths will be required, which show a stronger constraint than the edge-disjunction ones. Assuming that both the links and the nodes have associated certain operation probabilities (elementary reliability), the main objective is to build a minimum-cost sub-network that satisfies the nodeconnectivity requirements. Moreover, its reliability, i.e., the probability that all sites are able to exchange data at a given point in time, ought to surpass a certain lower bound pre-defined by the network engineer. In this way the model takes into account the robustness of the topology to be designed by acknowledging its structure even in probabilistic terms.


*Self-Healing Concrete and Cementitious Materials DOI: http://dx.doi.org/10.5772/intechopen.92349*

**Table 2.** *Autonomic*

 *self-healing:*

*Encapsulation*

 *materials and techniques used ('–' means 'not reported', 'x' means 'not applicable', '*√*' means 'yes' and '/' means 'no'). (upgraded from [53]).*

**Shell material**

> Capsule for self-healing

**202**

 Spherical

 Expanded clay Expanded clay Expanded clay

Diatomaceous

 earth

> Gelatin

Gelatin Gelatin Gelatin

Wax Paraffin

Cement + paraffin

UF UFF

PU Silica gel

Silica Silica

Gelatin + acacia gum

> Cylindrical

Glass Glass Glass

epoxy

Na2FPO3 Bacteria CaC6H10O6

Bacteria Acrylic resin

Epoxy

Tung oil

Ca(OH)2 Retarder agent

Water

SAP Epoxy Epoxy Na2SiO3 MMA/ TEB

Epoxy Na2SiO3

–

5000

–

x

∕

√

x

5–20

300–700

–

800

1000

100

100

∕

Mineral oil+ Na2SiO3

CA CA

800, 1500,

—

 —

75, 75, 100

∕

3000

3000–4000

 5000–7000

—

250

∕ –

—

—

—

—

——

4.15

—

 —

x

√

x

√

40–800

—

x

√

20–70

—

x

—

120

4

x

√

x x

x

x

—

—

—

—

—

—

——

900

—

 —

x

—

x

—

120

—

x

√

50

—

x

√

50

—

x

√

50

—

x

√

125–297

—

x

—

\_

x

x

√

 1000–4000

 1000–4000

4000

x x x

x

√

*Advanced Functional Materials*

x

√

x

√

**Core material**

**Øi (μm)**

 **Øo (μm)**

 **Wall thickness**

**Length**

**Mixed**

**(mm)**

**in**

**(μm)**

**Figure 10.**

*(a) Vascular network in concrete slab panel and (b) vascular network combination with PET in field trial (Reproduced from [56]).*

#### **4.2 Autonomic microcapsule self-healing system**

Microcapsules are developed to avoid challenging issues in tubes-based capsulation systems incorporation in bulk concrete production. In this healing technique, microcapsules preserving reactive healing agents are ruptured by the forces imposed on capsules'shell due to the cracks propagation in the matrix. The released healing agent then reacts with the cementitious matrix crack surface to form healing compounds that bridge the gap and eventually heal the cracks.

Further advancement with sodium silicate encapsulated in gelatin and gum arabic shell materials (**Figure 11**) was found in recent studies [57, 60]. These microcapsules survive mixing with cement and rupture successfully upon crack formation and release sodium silicate solution. Although increasing microcapsules volume fractions in a 24% reduced the mechanical properties, the crack sealing was just under 100%. Besides, the crack depth and sorptivity coefficient were decreased by 70 and 54%, respectively. These microcapsules were also successfully implemented

*(a) Microscopic image of microcapsules (scale bars correspond to 500 μm) and (b) ruptured microcapsules*

The colloidal silica solution capsules up to 16 vol% in PC grout increased the sealing efficiency from 20% for the only PC to 85% in 28 days [62]. However, monodisperse photo-polymerised acrylate shell with hydrophilic mineral core microfluidic droplets are further advancement in the self-healing microcapsule

Although the direct addition of potential minerals to the concrete mix improves autogenous self-healing performance, protecting those minerals in initial mixing may further enhance the healing process. With this in mind, pellets of potential healing mineral agents have been used for improved concrete self-healing.

Sisomphon et al. [47] used expanded lightweight clay aggregates (LWAs) impregnated with a solution of sodium mono fluorophosphate (Na2FPO3, Na-MFP) and coated by cement paste layers. The entire mechanism is schematically presented in **Figure 12a**. Pellets with expansive minerals such as a reactive MgO were spraycoated (10–50 μm) with polyvinyl alcohol (PVA) to produce PVA-coated MgO pellets for self-healing concrete applications (**Figure 12b**). A PVA-coated granulated CSA (calcium sulpho aluminate)-based expansive mineral was used for improving the self-healing performance of cementitious materials [48]. Replacement of CSA pellets was up to 10% by wt. of cement and mortar was prepared with 1:3 cement-to-sand ratio and w/c = 0.5. Cracks in the range of 0.1–0.2 mm were healed completely within 14 days whereas larger crack >0.2 healed within 16 days. Granules of expansive self-healing agent coated with an extra layer of cement compounds were investigated by [64]. The self-healing concept is schematically

in the filed trail of a road improvement scheme by M4L project [61].

*appearing as 'wet' spots on the digital image of the split face (Both reproduced from [60]).*

*Self-Healing Concrete and Cementitious Materials DOI: http://dx.doi.org/10.5772/intechopen.92349*

**4.3 Coated minerals (pellets and granules) for self-healing**

field [63].

**205**

**Figure 11.**

The compatibility of microcapsules with bulk concrete depends on a wide variety of factors. Major influencing factors are the size and volume fraction of microcapsules used, the capsules' mechanical properties and interlock properties between the capsules and the surrounding materials [57]. The shape of the embedded capsule is another major factor that should be considered for compatibility issues. Spherically shaped capsules provide a more controlled and enhanced release of the healing agent upon breakage. It also reduces the stress concentrations around the void left from the empty capsule. However, a tubular capsule can cover a larger internal area of influence on the concrete for the same volume of a healing agent (higher surface area to volume ratio).

Yang et al. have investigated methyl methacrylate (MMA) as a monomer and triethylborane (TEB) as the healing agent and the catalyst [25]. In the investigation, about 50.2 and 66.8% reduction in permeability has been achieved within 3 and 30 days, respectively. Microscopic imaging confirms that some ruptured microcapsules existed and filled the cracks of the sample after 80% ultimate compressive strength at 28 days.

About 2% crystalline sodium silicate in polyurethane-encapsulated microcapsules with a diameter ranging from 40 to 800 μm increased 24% mechanical load recovery compared to 12% in the control samples [58]. However, the compressive strength of the composite reduced by 12% compared to that of the control mix. In the concrete containing microcapsules, sodium silicate reacts with calcium hydroxide of cement and produces a calcium-silica-hydrate (C-S-H) gel that heals the cracks partially. The C-S-H further reacts with dissolved CO2 in water and sodium oxide, which produced calcium carbonate. This is similar to the main hydration phase of cement, which causes strengthening.

Sodium silicate encapsulated in double-walled polyurethane/urea-formaldehyde (PU/UF) was reported in [59]. The addition of 2.5 and 5% microcapsules resulted in about 24 and 35% healing efficiency based on the crack depth measurements.

**Figure 11.**

**4.2 Autonomic microcapsule self-healing system**

area to volume ratio).

**Figure 10.**

*(Reproduced from [56]).*

*Advanced Functional Materials*

strength at 28 days.

**204**

phase of cement, which causes strengthening.

Microcapsules are developed to avoid challenging issues in tubes-based capsulation systems incorporation in bulk concrete production. In this healing technique, microcapsules preserving reactive healing agents are ruptured by the forces imposed on capsules'shell due to the cracks propagation in the matrix. The released healing agent then reacts with the cementitious matrix crack surface to form healing compounds that bridge the gap and eventually heal the cracks.

*(a) Vascular network in concrete slab panel and (b) vascular network combination with PET in field trial*

The compatibility of microcapsules with bulk concrete depends on a wide variety of factors. Major influencing factors are the size and volume fraction of microcapsules used, the capsules' mechanical properties and interlock properties between the capsules and the surrounding materials [57]. The shape of the embedded capsule is another major factor that should be considered for compatibility issues. Spherically shaped capsules provide a more controlled and enhanced release of the healing agent upon breakage. It also reduces the stress concentrations around the void left from the empty capsule. However, a tubular capsule can cover a larger internal area of influence on the concrete for the same volume of a healing agent (higher surface

Yang et al. have investigated methyl methacrylate (MMA) as a monomer and triethylborane (TEB) as the healing agent and the catalyst [25]. In the investigation, about 50.2 and 66.8% reduction in permeability has been achieved within 3 and 30 days, respectively. Microscopic imaging confirms that some ruptured microcapsules existed and filled the cracks of the sample after 80% ultimate compressive

About 2% crystalline sodium silicate in polyurethane-encapsulated microcapsules with a diameter ranging from 40 to 800 μm increased 24% mechanical load recovery compared to 12% in the control samples [58]. However, the compressive strength of the composite reduced by 12% compared to that of the control mix. In the concrete containing microcapsules, sodium silicate reacts with calcium hydroxide of cement and produces a calcium-silica-hydrate (C-S-H) gel that heals the cracks partially. The C-S-H further reacts with dissolved CO2 in water and sodium oxide, which produced calcium carbonate. This is similar to the main hydration

Sodium silicate encapsulated in double-walled polyurethane/urea-formaldehyde (PU/UF) was reported in [59]. The addition of 2.5 and 5% microcapsules resulted in about 24 and 35% healing efficiency based on the crack depth measurements.

*(a) Microscopic image of microcapsules (scale bars correspond to 500 μm) and (b) ruptured microcapsules appearing as 'wet' spots on the digital image of the split face (Both reproduced from [60]).*

Further advancement with sodium silicate encapsulated in gelatin and gum arabic shell materials (**Figure 11**) was found in recent studies [57, 60]. These microcapsules survive mixing with cement and rupture successfully upon crack formation and release sodium silicate solution. Although increasing microcapsules volume fractions in a 24% reduced the mechanical properties, the crack sealing was just under 100%. Besides, the crack depth and sorptivity coefficient were decreased by 70 and 54%, respectively. These microcapsules were also successfully implemented in the filed trail of a road improvement scheme by M4L project [61].

The colloidal silica solution capsules up to 16 vol% in PC grout increased the sealing efficiency from 20% for the only PC to 85% in 28 days [62]. However, monodisperse photo-polymerised acrylate shell with hydrophilic mineral core microfluidic droplets are further advancement in the self-healing microcapsule field [63].


Acknowledgements

This work is partly supported by National Natural Science Foundation of China (Grant No. 41775128, 41405034, 11204319), the External Cooperation Program of the Chinese Academy of Sciences (Grant No. GJHZ1726), the Special Fund for Basic Research on Scientific Instruments of the Chinese Academy of Science (Grant No. YZ201315), and the Chinese Academy of Science President's International Fellowship Initiative (PIFI, 2015VMA007). Finally, the Scientific Research Foundation for the Returned Overseas Chinese Scholars, State Education Ministry, is gratefully acknowledged.