Save the world with Seaweed

Excerpt from the book Seasteading, Chapter 3

Eat Greenhouse Gas

Insert seaweed, otherwise known as macroalgae, into the middle of our eight global problems, and the entire snafu transforms into a global circle of life. Consider how each of the grand challenges can be solved by the common weed of the sea:

Reduce Carbon Pollution. Seaweed builds itself with the C02 in the ocean, which reduces the acidity of the ocean, which pulls CO2 out of the atmosphere.

Clean the Dead Zones. To build itself with CO2, seaweed eats nutrients such as nitrogen, found most abundantly in ocean dead zones poisoned by farmland runoff. Our sewage is seaweed food, and seaweed is sashimi food, and sashimi is people food.

Feed the World. All food, for all life, is based on photosynthesis, performed most spectacularly by powerhouses like seaweed.

Power Civilization. Fossil fuel is the product of ancient photosynthesis, which was performed by ancient algae like seaweed.

End Poverty in Coastal Nations. Seaweed is farmed most commonly by poor people tying it to strands of rope and letting it grow. Infrastructure required: ropes and rowboats. What if we increased the demand by a thousand times?

Get Healthy. Doctors tell us to eat more omega-3 fatty acids, found most abundantly in fish. fish don't synthesize their own omega-35; they get it by eating seaweed. Doctors also tell us to eat low-calorie, low-fat, high-quality fat, high-fiber, nutrient-rich, high amino-acid protein. Where on earth are we supposed to find this perfect food? Oh, yeah. Seaweed.

Save the Environment. Conservationists tell us we’ve depleted the topsoil, wasted the water, poisoned the pests, and destroyed ecosystems with our endless eating and consuming. Where are we supposed to find an abundant food that needs no soil, freshwater, or pesticides? We could try seaweed. Okay, but where can we establish farms that need no farmland and can be expanded to virtually any size; farms that suffer no droughts and don't know the meaning of floods? We could try the sea.

Fine, but how are we supposed to fuel it? The best possible nanotechnology would be self-assembling solar panels that are also edible. Hey, wait a minute. Seaweed again!

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“The next Green Revolution should be blue,” says Ricardo. “The productivity of giant kelp has been compared with that of the most highly productive land crops, like sugar cane. Macroalga cultivation, attached to ropes or even free floating, is possibly the easiest form of sea farming, and it requires the least financial investment. Thus it is more implementable in poorer countries. The sea has all the needed water and space and generally sufficient nutrients for macroalgae to grow. Fertilizing them is already a common practice in Asia in areas of intensive production.

“Instead of getting more water to the farms,” Ricardo continues, “we must simply move the farms to the water. Such sea farming is already a reality in some places. I have been doing it for over fifteen years. Many thousands of hectares of marine areas can be farmed right now, with millions of tons of new food added to the stream. Each ton of seaweed harvested frees one million liters of freshwater from agriculture. It will be soon possible to produce billions of tons."

Every hectare of agriculture that becomes aquaculture means less land devoted to farming, less CO2 released into the atmosphere, more CO2 absorbed from the atmosphere,less water used to produce food, fewer pesticides, cleaner oceans, less need for depleting wild populations offish, and more incentives for increasing populations of farmed fish.

According to Ricardo, algae will allow us to feed the world with the C02 that's already in our atmosphere and the nutrients that are already in the sea. You don't have to choose between saving the environment and feeding the world. You feed the world by saving the environment.

In 1999 economist Peter Drucker predicted, “Aquaculture, not the Internet, represents the most promising investment opportunity of the twenty-first century.” The green economy aspires to protect the environment, but the blue economy aspires to restore theenvironment. The bridge from green to blue is blue-green algae. Algae, the basis oflife, must become the keystone of the blue economy.

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Dr. Fred Lubnow, director of aquatic programs for Princeton Hydro, which builds floating islands in Pennsylvania lakes, says, “A two-hundred-fifty-square foot island can remove about ten pounds of phosphorus. It may not seem like a lot, but every one pound of phosphorus has the potential to create eleven hundred pounds of algae goo," by which he means wet algae biomass.

Here's the crazy part: seaweed and pond scum already volunteer to do this job. Humans just have to cooperate with these two branches of algae, and they will provide a boon of food, feed. fuel, fertilizer, and water, freeing up vast tracts of farmland for the songbirds. Want to restore the oceans, lower greenhouse gases, increase oxygen, feed the world, empower the poor, and fuel civilization cheaply? Algae is already on it. We just need to cooperate with it instead of ignoring it. We can feed the world with our waste if only we let algae convert waste into food. Humans can't overpopulate the Earth faster than algae can be grown. Algae can beat humans and their farm animals in a race to grow living tissue any day of the week.

Ricardo laughs. “It sounds too good to be true, I know. Anyone who works at sea knows nothing is easy at this point. But when we were colonizing the Amazon or the Wild West, it wasn't easy at all. Beginnings are hard.”

By putting seaweed at the center ofour global cycle oflife, we can clean the oceans, reduce greenhouse gases, feed the world, fuel civilization, save fresh water, empower poor coastal people to support themselves, and make an enormous amount of money. So why don't we just do it?

Hilarious History of Seasteading Part I

Wanna laugh and learn about Seasteading at the same time?

Intro on Seasteading: seasteading is basically creating floating cities.

Excerpt from the book Seasteading, Chapter 1

Like a fish to Water

In the summer of 2009, the Seasteading Institute hosted the first annual floating festival of self-governance on the Sacramento Delta and called it Ephemerisle, which has since come to beknown as “Burning Man on the water.” (Burning man is a New Age festival and temporary city in the middle of the Black Rock Desert in the Western United States.) Every year, a few hundred people create a makeshift island by connecting a variety of boats, platforms, inner tubes, and floating art projects. Want to attend? Bring your own land.

The annual event has since blossomed without our help and with no central organizer. This kickvstart method is the essence ofour nonprofit role. The vision was that Ephemerisle could grow in size, duration, and frequency until a man-made island was floating year-round, and as ocean folk learned the tricks of ocean living, eventually Ephemerisle would move to international waters. Upon this dream a small bluetopia was born.

Given that people are people, conflicts emerged. The people who wanted to dance and party clashed with the people who wanted peace and quiet. The people who set up a floating disc jockey clashed with the people who organized a lecture series. The people who brought children clashed with the adults who acted like children. Three years of peace and harmony culminated in the Great Shouting Match of 2011. After exchanging threats of excommunication. partiers. parents, pranksters, and lecturers stared down one another, eyeball to eyeball. Nobody could agree on what the “real Ephemerisle" was all about! What should we do? Hold a vote? Let the majority enforce its will on the minority? Which group should we kick off the island? We had a realityTV show in the making.

Incredibly, the principles of seasteading emerged without anyone commanding it or even remarking upon it until this writing, as far as we know.

In 2012 Ephemerisle split off into three islands. People who wanted peace and quiet formed Titan, an orderly avenue of houseboats requiring life jackets, safety whistles, and a strict buddy system. The party people renamed it Uptightan. The loud twentysomethings who wanted their rave parties built a floating dance floor made of wood and nails. Titan residents named it Tetanus. A group of environmentalist artists known as Los Angelopes, an LA bicycle gang, improvised Blanket Fort Island, constructed mostly from recycled materials such as barrels, pallets, canoes, and anything else that could be lashed together to float. As it tilted and partially sank, it was christened the SS Shit Show. Anyone who glanced at Shit Show risked being mooned by a butt with the words “sell out" painted on it. Perhaps in response, a medical nurse crowdfunded Meditation Platform, a shaded “quiet space in which to recharge without any social pressures."

Once partiers, scholars, artists, and introverts formed their separate jurisdictions, do you think they each sat, sulked, and refused to interact? Not a chance. Separation made all hearts grow fonder. A taxi system of motorboats was organized among the islands. The “seatizens" of Tetanus allowed a freewheeling approach of boats to dock and launch at will, leading to some laugh-inducing fender benders. Horrified. the seatizens of uptightan instituted an immigration policy, enforcing an ordered approach of motorboats, especially those filled with suspect party people. Unfortunately, this policy involved bullhorns, leading to a policing innovation known as “the roving DoucheCam,” where people who lost their tempers were videoed and publicly humiliated on YouTube. What if no taxi was available? A flotilla of pool rafts was anchored to a spot between the three islands, sewing as both a remote getaway and a rest stop for swimmers between the islands.No boss planned any of it, and everybody participated in it. The emergence of these arrangements only increased the fluid rate at which people migrated and visited neighbors as the mood struck them. Want to be among children? Head to the family-friendly island. Want to stay up all night dancing with the under-thirty crowd? Go hang out with those people, if that's your bag. Want to enjoy peace and quiet with the fortysomethings who hold formal lectures about economics and political theory? Head to that island and maybe crash there amid the quiet. Sick and tired of all these rules, man? Blanket Fort, the recycler's paradise, tilts defiantly a short swim away. Patri (one of the pioneers and visionaries of Seasteading) has two kids, loves to dance, loves to lecture and attend lectures, and volunteers to drive motorboats between all three main islands. Joe is a proud seatizen of uptightan, where kids need to respect their elders’ need for naps.So far, conflicts are rare, but when they occur, they are policed by mockery, painful nicknames, and subversive performance art. Want to spite the libertarian consensus that prevails during the lecture series? Name your subisland Revenge of cuba. which is the most recent act of “seacession." Imagine a political science scholar carefully parsing the nuances of Federal Reserve policy, while just offshore, residents ofCuba make a big show of offering free first aid services to anyone who may one day be injured on Tetanus.

Sure, seasteading is supposed to be about breaking away, but what about merging? Stop reading for a moment and guess which islands are the least likely to join forces. How long do you think it took for enemy islands to marry?

By 2014, the rave dancers and Titan residents had become one. The party people admitted they needed the Titan residents to help them organize, and the Titaniers admitted they needed the party people to help them have fun. The orderly avenue ofTitan houseboats formed a neighborhood block, with front doors facing inward and decks facing outward. so boats could approach from any side, meaning they could nix the bullhorns. What do you think was built at the center? A magnificent dance floor free from nails, with a posted schedule for quiet times during lectures. Splitting in a huffin 2012, the Uptightans and Tetanusitians formed one island paradise by 2014. Hugs all around.

Is bluetopia finally at hand? Not exactly. The Cubans continue to give the public middle finger to every island that doesn't offer free health care to all Ephemerislians, flying their flag of socialist spite and spending most of their time on Titan’s dance floor and rnooching from Titan'salphabetically arranged snack tray, which offers vegan, paleo, vegetarian, gluten-free, and dairy-free vittles organized by spreadsheet.

On water, human nature does not change. What changes is the technology by which humans establish rules. Ephemerisle started as an experiment in getting along, and already several new start-up experiments have broken away and learned lessons. We'd venture to guess that every single year, every single Ephemerislian visits every single island, proving that good waters make good neighbors.

The success of the Ephemerisle community so far is evidenced by its rejection by a reality TV production company. In 2015 a seasoned TV production team contacted the Seasteading Institute curious to create a TV documentary. Once scouting Ephemerisle, they became discouraged byhow readily conflicts were quelled on a fluid medium. How to add drama? Get rid ofmobility and choice. They went back to the United Kingdom and elected to set up their own reality TV show on several fixed offshore military forts, to set up the traditional dynamics for land-based conflict. If you want people to fight, condemn them to a crowded space where they can't take their land and go elsewhere.

Ephemerisle began as a do-it~yourself seasteading start-up, and it has evolved in ways no one could have planned. Even the distributed Ephemerisle community is smarter than any centralized governor. The social mechanics of seasteading have emerged already.

Tenochtitlan the first floating city... not really

Tenochtitlan was an island in the middle of a lake that was expanded by pounding stakes into the lake bed and lashing them together with reeds, then pouring earth into these artificial islands. These islands didn't float, thought the lake made sure that water levels stayed fairly constant.

That said, Tenochtitlan gives us many, many ideas on how a sea city could work. It is like a huge checkerboard with canals like streets on a pre-planned city.

Sea level rise might eventually reach 60 meters, so earth work will be very expensive compared to a floating island. Problem is, how to anchor them???

Can seaweed save the world?

Search Youtube: "Can seaweed save the world?" Lots of solutions here

https://www.youtube.com/watch?v=HnEh_UJqJKw

03 Can Seaweed Save the World ABC 2017 1

This was 1 year ago. I wonder what has happened since?

So far I've learned:

Fish ponds create pollution: fish waste in water

Seaweed can take that pollution out of that water (aquaponics concept), and in turn produce... more seaweed

Seaweed can be fed to cows

Seaweed can be baked into biochar (and perhaps take the place of fly ash cement? )

Seaweed can be eaten by Humans (I hope with minimal plastic content )
We can grow seaweed in the Philippines, and it can be an export product of the floating cities
Maybe we can also create floating fish ponds...?

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Idea on farming kelp and selling it as animal feed

"Anyways; kelp field in deep ocean. Southern-California. In federal waters first.

And/or it can be in state waters if it is allowed. With the intention to move out of EEZ. Kelp would be grown from subsurface buoys to surface. It would be possible to moor a boat to the subsurface buoy. Kelp would be processed to something useful and can be sold to people in any country. I think, the simplest way to use kelp is farm animal feed. To harvest kelp, and dry it, bring it to port, and sell it. And Life Aquatic with Steve Zissou."

Geopolymer Concrete, the perfect seasteading material

The forum thread below might be obsolete, see this first: https://www.reddit.com/r/seasteading -------------------------- https://discuss.seasteading.org/t/geopolymer-concrete-the-perfect-seasteading-material/240 This is a long forum thread with lots of ideas I will go through it as I have time What lessons I learn, I will write here on the upper portion

Foam Geopolymer Concrete

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3397519/

This study analyzes the strength of geopolymer after curing in high heat (60 degrees centigrade) for 24 hours as opposed to curing in room temperature.

The samples cured in high heat produced better strength and less water absorption, over all performed much better.

It also mentioned that instead of fly ash, rice husk ash could be used. Other substitute materials include kaolinite, clay, silica fume, or slag

Among the references, we are interested in this one: Narayanan N., Ramamurthy K. Structure and properties of aerated concrete: A review

For purposes of having a backup, the text of the article will be reposted here

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Int J Mol Sci. 2012; 13(6): 7186–7198.

Published online 2012 Jun 12. doi:  10.3390/ijms13067186

PMCID: PMC3397519

PMID: 22837687

Fly Ash-based Geopolymer Lightweight Concrete Using Foaming Agent

Mohd Mustafa Al Bakri Abdullah,1,* Kamarudin Hussin,1Mohamed Bnhussain,2 Khairul Nizar Ismail,3 Zarina Yahya,1 andRafiza Abdul Razak1

Author information ► Article notes ► Copyright and License information ► Disclaimer

This article has been cited by other articles in PMC.

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Abstract

In this paper, we report the results of our investigation on the possibility of producing foam concrete by using a geopolymer system. Class C fly ash was mixed with an alkaline activator solution (a mixture of sodium silicate and NaOH), and foam was added to the geopolymeric mixture to produce lightweight concrete. The NaOH solution was prepared by dilute NaOH pellets with distilled water. The reactives were mixed to produce a homogeneous mixture, which was placed into a 50 mm mold and cured at two different curing temperatures (60 °C and room temperature), for 24 hours. After the curing process, the strengths of the samples were tested on days 1, 7, and 28. The water absorption, porosity, chemical composition, microstructure, XRD and FTIR analyses were studied. The results showed that the sample which was cured at 60 °C (LW2) produced the maximum compressive strength for all tests, (11.03 MPa, 17.59 MPa, and 18.19 MPa) for days 1, 7, and 28, respectively. Also, the water absorption and porosity of LW2 were reduced by 6.78% and 1.22% after 28 days, respectively. The SEM showed that the LW2 sample had a denser matrix than LW1. This was because LW2 was heat cured, which caused the geopolymerization rate to increase, producing a denser matrix. However for LW1, microcracks were present on the surface, which reduced the compressive strength and increased water absorption and porosity.

Keywords: foam concrete, fly ash, geopolymer, alkaline activator, curing temperature

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1. Introduction

Lightweight concrete can be prepared either by injecting air or by omitting the finer sizes of the aggregate or by replacing them with hollow, cellular, or porous aggregate. The density of lightweight concrete usually ranges from 300 to 1800 kg/m3 [1] whereas the density of normal concrete is approximately 2400 kg/m3. Lightweight concrete has been categorized into three groups [2], (1) no-fines concrete; (2) lightweight aggregate concrete; and (3) aerated/foamed concrete. No-fines concrete contains a small amount of aggregate, if any. The coarse aggregate should be a single-size material, with nominal maximum sizes of 10 mm and 20 mm being the most common. The use of blended aggregates (10 and 7 mm; and 20 mm and 14 mm) showed satisfactory performance. However, since this type of concrete is characterized by uniformly distributed voids, it is not suitable for reinforced or pre-stressed concrete used in construction [3]. Lightweight aggregate concrete consists of lightweight aggregate (expanded shale, clay or slate materials that have been fired in a rotary kiln to develop a porous structure) which can be used as a replacement for normal aggregates such as crushed stone or sand [4]. Foamed concrete is produced by using either cement paste or mortar in which large volumes of air are entrapped by using a foaming agent. Such foamed concrete has high flow ability, low weight, and minimal consumption of aggregates, controlled low strength, and excellent thermal-insulation properties [5].

Foamed concrete can be produced either by the pre-foaming method or the mixed-foaming method [1,6]. In the pre-foaming method, a suitable foaming agent is mixed with water, and the foam is combined with paste or mortar. Meanwhile, in the mixed-foaming method, the foaming agent is added to the slurry, and the mixture is whisked into a stable mass that has the required density [1]. The manufacturing of stable mix of foamed concrete depends on many factors, such as the selection of the foaming agent, the method used to prepare the foam to obtain a uniform air-void distribution, selection of materials, strategies for mixture design, and the production of foamed concrete [6]. Various foaming agents have been used to produce foamed concrete, including detergents, resin soap, glue resins, saponin, and hydrolyzed proteins, such as keratin and similar materials [7].

In common foamed concrete, ordinary Portland cement (OPC) and rapid-hardening Portland cement were used [8,9], along with high alumina and calcium sulfoaluminate [10], in order to reduce setting times and improve the early strength. The cost of producing foamed concrete can be reduced by replacing OPC with fly ash [8,10–14] and ground granulated blast-furnace slag [15,16] in quantities of about 30–70% and 10–50%, respectively. With these replacements, the long-term strength of foamed concrete was increased and the heat of hydration was reduced. In addition, the strength of the concrete can be increased by as much as 10% by replacing OPC with silica fume [17–19].

Recently, the potential for replacing the OPC with geopolymer has been explored extensively by researchers. Geopolymer is a term used to describe inorganic polymers based on aluminosilicate, which can be produced by reacting pozzolanic compounds or aluminosilicate source materials with highly alkaline solutions [20]. The aluminosilicate source can be a natural mineral or by-product materials, such as kaolinite, clay, fly ash, silica fume, rice husk ash, or slag. These raw materials must be rich in silicon (Si) and aluminum (Al) in order to produce geopolymer.

Fly ash is suitable for use as a geopolymer source material because it consists mostly of glassy, hollow and spherical particles [21]. Fly ash-based geopolymer cement and concrete have been studied extensively, and they are well known for their properties, which are better than those of normal concrete due to their lower creep [22], lower shrinkage [23], better fire and acid resistance [24], and resistance to sulfate attack [25,26].

However, the manufacturing of fly ash-based geopolymer in terms of lightweight concrete (foamed concrete) has not been explored yet. Hence, the aim of this study was to investigate the properties of fly ash-based foam geopolymer concrete.

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2. Results and Discussion

2.1. X-ray Fluorescence (XRF) Analysis

The comparison of the chemical compositions of the original fly ash and the foamed geopolymer concrete is presented in Table 1. Calcium oxide (CaO) made up 21.6% of the content of the original fly ash, so it must be classified as a class C fly ash (containing more than 20% of CaO) and the ratio of Si:Al was about 3. This fly ash composition is representative of fly ash from the combustion of the sub-bituminous coal that is used in Malaysian power plants [27]. In addition, the content of iron oxide (Fe2O3) was high, which accounted for the darker color of the fly ash [27]. The powder sample of geopolymers LW1 and LW2 showed increases in the content of SiO2. This was due to the reaction between fly ash and the alkaline activator (mixture of sodium silicate and NaOH), which is known as geopolymerization. This process occurs through a mechanism involving the dissolution of the aluminum and silicon species from the surfaces of waste material (fly ash) as well as the surface hydration of undissolved waste particles, followed by the polymerization of active surface groups and soluble species to form a gel and, subsequently, a hardened geopolymer structure [28]. Also, the mass percentages of SiO2 and Al2O3 in LW2 were greater than they were in LW1 due to the heat-induced, rapid geopolymerization process.

Table 1

Composition of fly ash and foam geopolymer concrete as determined by XRF analysis (mass %).

Chemical Composition	Fly Ash	Samples Cured at Room Temperature (LW1)	Samples Cured at 60 °C (LW2)
SiO2	26.4	35.1	37.6
Al2O3	9.3	11.8	12.8
CaO	21.6	19.6	18.7
Fe2O3	30.1	23.3	21.6
MnO	0.3	0.2	0.2
TiO2	3.1	2.3	2.10
K2O	2.6	2.7	2.7
SO3	1.3	0.9	0.8

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2.2. Compressive Strength, Density, Porosity and Water Absorption

Figure 1 shows the compressive strengths at days 1, 7, and 28 for the foamed geopolymer concretes that were cured at room temperature and at 60 °C for the average of 3 samples. For each of the test days, the maximum compressive strength was observed in the samples that had been cured in the oven (LW2). The maximum compressive strength values for the LW2 samples for days 1, 7, and 28 were 11.0 MPa, 17.6 MPa, and 18.2 MPa, respectively. Thus, we concluded that the curing temperature influenced the strength of the geopolymers [29]. The increase in strength of the LW2 samples was nearly complete after seven days, as evidenced by the fact that the strength had increased only slightly on day 28. However, for LW1, the results showed significant differences in strength for day 1, day 7, and day 28. This proved that heat treatment is required to expedite the rate of development of the strength of the geopolymers.

Figure 1

Compressive strengths for two types of foamed geopolymer concrete.

The average density of LW1 is 1650 kg/m3 and for LW2 are 1667 kg/m3 as stated in Table 2. The porosity of the foamed geopolymer concrete is the sum of the entrained air voids and the voids within the paste. The higher compressive strength of LW2 samples was due to their lower porosity and water absorption. The LW1 samples had 15.29% porosity and 2.35% water absorption, whereas the LW2 samples had substantially lower corresponding values of 6.78% and 1.22%, respectively, as shown in Table 2. According to BS 1881: Part 122: 1983, low water absorption is deemed to be anything less than 3%, and both types of samples had water absorption values that were less than 3%. Since LW2 is more dense (higher density than LW1), it produced lower porosity and water absorption as mentioned above.

Table 2

Density, porosity and water absorption of foamed geopolymer concretes.

Sample	Curing	Compressive Strength (Mpa)			Porosity (%)	Water Absorption (%)	Density (kg/m3)
		Day 1	Day 7	Day 28
LW1	Room temp.	3.3	13.5	18.1	15.29	2.35	1650
LW2	60 °C	11.0	17.6	18.2	6.78	1.22	1667

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2.3. X-ray Diffraction (XRD) Analysis

The XRD pattern of fly ash was obtained as shown in Figure 2. The main components of the fly ash were quartz, mullite, anhydrite and f-CaO [24]. Figure 2 also shows the foamed geopolymer concrete, which consisted mostly of amorphous content. When comparing the XRD pattern of the original fly ash with the hardened geopolymer, it can be seen that the crystalline phases that existed in the fly ash originally (quartz and mullite) apparently have not been altered by the activation reactions. The fly ash also was made up of an amorphous phase, as indicated by the broad hump registered between 2θ = 20 °C and 30 °C [30].

Figure 2

XRD pattern of class C fly ash, foamed geopolymer concretes LW1 (room temperature) and LW2 (60 °C).

Additionally, the broad hump between 2θ = 20 °C and 40 °C indicated the characteristic of amorphous gels, including geopolymeric gels and calcium silicate hydrate (C-S-H) gels. This shows that the geopolymeric reaction and the hydrate reaction occurred at the same time [24].

2.4. Fourier Transform Infrared Spectroscopy (FTIR) Analysis

Figure 3 shows the IR bands of the fly ash and the foamed geopolymer concrete, and Table 3 summarizes the IR bands obtained from the FTIR analyses. The IR spectrum of fly ash shows main absorption bands at 1004, 1428, 2358, and 3715 cm−1. The broad component at 1004 cm−1 is due to the Si-O-Si and Al-O-Si asymmetric stretching vibration [31–36] and it becomes sharper and shifts towards lower frequencies (LW1 = 976 cm−1 and LW2 = 969 cm−1) in lightweight geopolymer. This indicates the formation of a new product (the amorphous aluminosilicate gel phase) due to dissolution of fly in alkaline activator [31–36]. In addition, the band at 1428 cm−1 was due to the stretching vibrations of the O-C-O bond indicating the presence of sodium bicarbonate that is suggested to occur due to the atmospheric carbonation of a high alkaline NaOH aqueous phase, which is diffused on the geopolymeric materials surface [31,33,35]. Meanwhile, the broad IR bands at 3715 cm−1 and 2358 cm−1 represent the stretching and deformation vibration of OH and H-O-H groups, respectively, from the weakly-bound water molecules that were adsorbed on the surface or trapped in the large cavities between the rings of the geopolymeric products [24,37].

Figure 3

FTIR analysis of fly ash, LW1 and LW2.

Table 3

Characteristic of IR band for foamed geopolymer concrete.

Bonds	Fly Ash (cm−1)	LW1 (cm−1)	LW2 (cm−1)
Stretching vibration (OH, H-O-H) [24,33,37]	3715–2358	3301–2333	3304–2343
Bending vibration (H-O-H) [30]	-	1652	1653
Stretching vibration (O-C-O) [31,33,35]	1437	-	-
Asymmetric stretching (Si-O-Si & Al-O-Si) [31–36]	1082	970	969

Foamed geopolymer samples (LW1 and LW2) showed broad components at 3301 cm−1, 2333 cm−1, 3304 cm−1 and 2343 cm−1which indicated the stretching vibration of OH and H-O-H, respectively [33]. Moreover, bands at 1652 cm−1 and 1653 cm−1represent the bending vibration of H-O-H [30].

2.5. Microstructure Analysis

The microstructure of the original fly ash based on the SEM observation is shown in Figure 4. The fly ash consists of spherical, vitreous particles of different sizes. These particles are usually hollow, and some spheres may contain other, smaller particles in their interior [38]. The surface texture of fly ash particles appears to be smooth [39] and also some vitreous, unshaped fragments or quartz particles can be seen [32].

Figure 4

Microstructure of fly ash.

Figure 5a–d shows the foamed geopolymer concrete of LW1 and LW2 at different magnifications. The size of the pores in the foamed geopolymer concrete ranged from 4 μm to 37 μm, and the distributions of the pores in both samples were uniform, as shown in Figure 5a,b. As expected, the existence of these pores in the foamed concrete result in its being classified as lightweight concrete. However, at magnifications of 2000× and 5000×, microcracks were observed in the LW1 samples (Figure 5c,e), which contributed to their lower strength by increasing their water absorption and porosity.

Figure 5

(a) Distribution of pores for LW1; (b) Distribution of pores for LW2; (c) LW1 at a magnification of 2000×; (d) LW2 at a magnification of 2000×; (e) LW1 at a magnification of 5000×; (f) LW2 at a magnification of 5000×.

The LW2 samples, which had a denser matrix (Figure 5d,f) than the LW1 samples, produced foamed geopolymer concrete that had greater strength. These stronger samples were heat cured, which facilitated the complete reaction between the fly ash and the alkaline activator to form aluminosilicate gel. Soon after the mixing process, the gel covered the fly ash particles and produced a dense matrix (complete reaction). Nevertheless, there were still some instances of incomplete reaction, as evidenced by the fact that the surface of the fly ash was covered with aluminosilicate gel rather a dense matrix having been formed. This situation was observed on both samples.

Unreacted fly ash was present in both samples. Fly ash with its original spherical shape (Figure 4) was located on the nearby dense matrix. From the SEM analysis, it was determined that the existence of microcracks and the incomplete formation of the dense matrix had caused water absorption and porosity of the LW1 samples to increase, thereby impairing their strength.

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3. Experimental Section

3.1. Materials

Fly ash, sodium silicate, sodium hydroxide (NaOH) and foaming agent (superplasticizer) were used to produce the foam geopolymer concrete. The fly ash was obtained from Manjung Power Station in Lumut, Perak, Malaysia. The chemical composition of the fly ash was determined by X-ray Fluorescence (XRF) as shown in Table 1. The microstructure of the fly ash is shown in Figure 4.

Sodium silicate and the NaOH solution were mixed together to act as the activator. NaOH pellets with 99% purity, made in Taiwan with the brand name of Formosoda-P were used to produce 12 M NaOH solution by adding the NaOH pellets to distilled water. This concentration was based on previous research [40] that indicated that the maximum strength of geopolymer was obtained when 12 M NaOH was used. Meanwhile, a technical grade of sodium silicate was obtained from South Pacific Chemical Industries Sdn. Bhd. (SPCI), Malaysia, with a chemical composition of SiO2 = 30.1%, Na2O = 9.4%, and H2O = 60.5% (SiO2/Na2O = 3.2). The other characteristics were: specific gravity at 20 °C = 1.4 kg/cm3and viscosity = 0.4 Pa s.

3.2. Mix Design and Mixing Process

In order to produce a desirable strength in lightweight concrete, a trial and error process was commonly used [41]. Since no methods have been proposed for producing foamed geopolymer concrete, we decided to use a geopolymer paste-to-foam ratio of 1:2 (by volume). The foam geopolymer concrete was produced by using the pre-foaming method, in which the foam is produced separately and then mixed with the geopolymer paste. The foam was produced by diluting the foaming agent with water based on a foaming agent-to-water ratio of 1:20 by volume. Then, the foam was generated by using a custom-made foam-generating machine: LCM Model 02. The geopolymer paste was produced according to the ratios shown in Table 4.

Table 4

Mix design for foam geopolymer concrete.

Sample	Fly Ash: Activator	Sodium Silicate: NaOH (Activator)	Foam: Geopolymer Paste	Curing Temperature
LW1	2:1	2.5:1	2:1	Room temperature
LW2	2:1	2.5:1	2:1	60°C

The sodium silicate and NaOH were mixed together for three minutes and then mixed with fly ash for another five minutes. After the geopolymer paste was homogeneous, the foam was added and mixed for another five minutes before it was placed in the 50-mm mold. The samples were cured at room temperature (LW1) and 60 °C (LW2). The LW2 samples were cured in the oven for 24 hours and then left at room temperature (open air) until compressive strength testing were conducted. Meanwhile, LW1 was cured at room temperature (open air) until testing day.

3.3. Testing

3.3.1. Compressive Strength

Compressive strength test of all samples were evaluated according to ASTM C 109/C 109 M by using the Shimadzu Universal Testing Machine. A minimum of three samples was tested to evaluate the compressive strength. The samples were tested on days 1, 7, and 28.

3.3.2. The Water Absorption

The water absorption was determined according to ASTM C642 and was calculated by the equation (Equation (1)):

Water absorption = [(Ms - Md)/Md] × 100

(1)

Ms = mass of surface-dried sample (g); Md = mass of oven-dried sample (g).

3.3.3. Porosity

The porosity was determined according to ASTM C642 and was calculated by the equation (Equation 2):

Porosity = [(Mw - Md)/Mw - Ms] × 100

(2)

Mw = mass of specimen after immersion in water (g); Md = mass of specimen after oven dried (g); Ms = mass of specimen suspended in water (g).

3.3.4. X-ray Diffraction (XRD)

The samples were prepared in powder form and analyzed with XRD to determine the pattern of the crystalline phase. XRD analysis was conducted using XRD–6000, Shimadzu X-ray diffractometer with Cu Kα radiation and with auto-search/match software as standard to aid qualitative analysis.

3.3.5. Scanning Electron Microscope (SEM)

The microstructure of the foamed geopolymer concretes with different curing temperatures was determined with a JSM-6460LA model Scanning Electron Microscope (JEOL). The specimens were cut into small pieces before observation.

3.3.6. Fourier Transform Infrared Spectroscopy (FTIR)

Using samples in powder form, infrared bands were recorded for wavelengths between 4000 cm−1 to 650 cm−1 using a Perkin Elmer FTIR Spectrum RX1 Spectrometer. The specimen for testing was prepared using the KBr pellet technique. Potassium Bromide (KBr) and sample powders were put into a mold and compressed by using cold press machine for 2 minutes at a load of 4 tons.

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4. Conclusions

The results of the experimental study led to the following conclusions:

1. The compressive strength of foamed geopolymer concrete LW2 with heat curing (60 °C) produced the maximum compressive strength on days 1, 7, and 28 (11.0, 17.6, and 18.2 MPa), respectively.
2. The compressive strength of the LW2 samples was greater than the compressive strength of the LW1 samples. This was attributed to the fact that the porosity and water absorption of the LW2 samples, at 6.78% and 1.22% respectively, were lower than the porosity and water absorption of the LW1 samples, at 15.29% and 2.35%, respectively.
3. Based on SEM observations, the LW2 samples had a denser matrix than the LW1 samples. This occurred because heat curing increased the rate of geopolymerization and hence, increased the strength. The LW1 samples had microcracks that resulted in increased water absorption and porosity, thus the strength was reduced.

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Acknowledgments

This study was funded by King Abdul Aziz City Science and Technology (KACST). We would like to extend our appreciation to the Center of Excellence Geopolymer and Green Technology in the School of Materials Engineering at the Universiti Malaysia Perlis (UniMAP).

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