RICE HUSKS-DERIVED SILICA AEROGEL AND THE EFFECTS ON THE STRENGTH AND THERMAL PROPERTY OF ORDINARY

PORTLAND CEMENT

INSTITUT PENYELIDIKAN, PEMBANGUNAN DAN PENGKOMERSILAN UNIVERSITITEKNOLOGI MARA 40450 SHAH ALAM, SELANGOR

MALAYSIA

BY

UMI SARAH BT JAIS HAMIDAH MOHD. SAMAN

JANUARY 2006

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B U R E A U OF R E S E A R C H &

Biro Penyelidikan dan Perundingan Universiti Teknologi MARA 40450 Shah Alam, Malaysia Tel: 03-55442094 / 5 / 3 / 2 Fax : 03-55442096 Website: www.uitm.edu.my/brc

UNIVERSITI TEKNOLOGI

25SJMARA

Penolong Naib Canselor (Penyelidikan) 03-55442094/5 aznizl32@salam.itm.edii.my

Koordinator Penyelidikan (Sains dan Teknologi) 03-55442091 dzainonm@salhm.itm.edu.my

Koordinator Penyelidikan (Sains Kemasyarakatan & Kemanusiaan) 03-55442097 rosmimah@salam.itm.edu.my

r Koordinator Perundingan (Kewangan) 03-55442090 shidah@salam.itm. edu. my

Koordinator Perundingan 03-55432100 aro @salam. Urn. edu. my

Penolong Pendaftar 03-55442092 dapeah 794@salam.itm. edu.my

Pegawai Eksekutif 03-55442098 rohani734@salam.itm.edu.my

Pentadbiran 03-55442093

Unit Kewangan Zon 17 03-55442099 03-55443440 453mohdh@salam.itm.edu.my

Surat Kami Tarikh

600 - BRC/ST. 5/3/545 ft Mac 2003

Prof. Madya Dr Umi Sarah Jais Pensyarah Fakulti Sains Gunaan Universiti Teknologi MARA 40450 Shah Alam

Puan

TAJUK PROJEK: RICE HUSK-DERIVED S i0 2 AEROGELS AND THE EFFECTS ON PROPERTIES OF PORTLAND CEMENT

Dengan hormatnya perkara tersebut di atas dirujuk.

Sukacita dimaklumkan bahawa Mesyuarat Jawatankuasa Mengendalikan Penyelidikan ke-65 pada 27 Februari 2003 telah membuat keputusan:

i. Bersetuju meluluskan cadangan penyelidikan yang telah dikemukakan oleh puan dan Dr Hamidah Mohd Saman.

ii. Tempoh projek penyelidikan ini ialah 12 bulan, iaitu mulai 15 Mac 2003 hingga 14 Mac 2004.

iiii. Kos yang diluluskan ialah sebanyak RM 20,000.00 sahaja.

IV.

v.

VI.

Penggunaan geran yang diluluskan hanya akan diproses setelah perjanjian ditandatangani.

Semua pembelian peralatan yang kosnya melebihi RM 500.00 satu item perlu menggunakan Pesanan Jabatan Universiti Teknologi MARA (LO). Pihak puan juga dikehendaki mematuhi peraturan penerimaan peralatan. Panduan penerimaan peralatan baru dan pengurusannya, dilampirkan.

Semua peralatan/kelengkapan penyelidikan yang dibeli adalah menjadi hak milik fakulti. Semua peralatan/kelengkapan hendaklah diserahkan kepada pihak fakulti setelah tamat penyelidikan untuk kegunaan bersama.

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vii. Kertaskerja boleh dibentangkan dalam seminar setelah 75% deraf awal laporan akhir penyelidikan dihantar ke Biro untuk semakan. Walau bagaimanapun, puan perlu membuat permohonan kepada Biro Penyelidikan dan Perundingan.

viii. Pihak puan dikehendaki mengemukakan Laporan Kemajuan Projek Penyelidikan bagi tempoh 6 bulan pertama penyelidikan dijalankan. Laporan Akhir perlu dihantar selewat-lewatnya 3 bulan selepas penyelidikan disiapkan. Format menulis laporan akhir boleh diperolehi di Biro Penyelidikan dan Perundingan atau di fakulti.

Bersama-sama ini disertakan dokumen perjanjian untuk ditandatangani oleh pihak puan. Sila penuhkan perjanjian berkenaan dengan menggunakan pen berdakwat hitam dan kembalikan ke pejabat ini untuk tindakan selanjutnya. Sekian, terimakasih.

"SELAMAT MENJALANKAN PENYELIDIKAN"

Yang benar

PROI R DR AZNIZAIN AHMED Penolong JNaib Canselor (Penyelidikan)

1. Timbalan Naib Canselor (Pembangunan dan Penyelidikan) Universiti Teknologi MARA

2. Dekan Fakulti Sains Gunaan Universiti Teknologi MARA Shah Alam

3. Dekan Fakulti Kejuruteraan Awam Universiti Teknologi MARA Shah Alam

4. Penolong Akauntan Unit Kewangan Zon 17 Biro Penyelidikan dan Perundingan

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Tarikh : 20 Januari 2006 No. Fail Projek : 600-BRC/ST.5/3/545

Penolong Naib Canselor (Penyelidikan) Institut Penyelidikan, Pembangunan dan Pengkomersilan Universiti Teknologi MARA 40450 Shah Alam

Ybhg. Prof.,

LAPORAN AKHIR PENYELD3IKAN "RICE HUSK-DERIVED SI02 AEROGEL AND THE EFFECTS ON THE STRENGTH AND THERMAL PROPERTY OF ORDINARY PORTLAND CEMENT"

Memjuk kepada perkara di atas, bersama-sama ini disertakan 2 (dua) naskah Laporan Akhir Penyelidikan bertajuk "Rice Husk-Derived Sio2 Aerogel And The Effects On The Strength And Thermal Property Of Ordinary Portland Cement"

Sekian, terima kasih.

Yang benar. benar,

PROF. MADVADRUMI SARAH JAIS Ketua Projek Penyelidikan

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PROJECT TEAM MEMBERS

ASSOCIATE PROFESSOR DR UMI SARAH JAIS Project Leader

toU V Tandat&Igan

*->

ASSOCIATE PROFESSOR DR HAMIDAH MOHD. SAMAN

Project Member

kx Tandatangan

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PENGHARGAAN

Setinggi-tinggi penghargaan dan ribuan terima kasih diucapkan kepada semua pihak yang terlibat secara langsung dan tidak langsung bagi membolehkan penyelidikan ini disiapkan dengan sempurna.

Diantaranya:

Prof. Madya Dr. Mohd Kamal Harun (Dekan Fakulti Sains Gunaan)

Prof. Madya Dr. Muhamad Rosli Sulaiman (Fakulti Kejuruteran Kimia)

Staf Bahagian Seramik Teknologi (AMREC, SIRIMBHD, Shah Alam)

dan

Semua pembantu makmal yang telah memberikan kerjasama dan sokongan di dalam menjayakan penyelidikan ini

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TABLE OF CONTENTS

TABLE OF CONTENTS LIST OF TABLES LIST OF FIGURES ABSTRACT

CHAPTER

1 INTRODUCTION 1.1 What are aerogels 1.2 History about the creation and evolution of aerog 1.3 Applications of aerogels 1.4 Research background and the problem

1.4.1 Ordinary Portland cement 1.4.2 Pozzolonic admixture

1.5 Obj ectives of study

2 LITERATURE REVIEW 2.1 Synthesis of silica aerogels

2.1.1 Properties of silica aerogel 2.1.2 The Surface Chemistry of silica aerogel 2.1.3 Drying of silica aerogel 2.1.4 Applications of silica aerogel

2.3.4.1 Thermal insulators 2.3.4.2 Particle detection and counters

2.2 Cement hydration

3 MATERIALS AND METHODS

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3.1 Rice husk sample preparation 17 3.2 Synthesis of rice-husk derived silica aerogel 17 3.3 Characterisation of rice husk-derived silica aerogel 20

3.3.1 Density 20 3.3.2 Porosity 20 3.3.3 Surface area 20 3.3.4 Fourier Transform Infrared Spectroscopy (FTIR) 20 3.3.5 Thermal Gravimetric Analysis (TGA) 20 3.3.6 X-Ray Diffraction (XRD) 21 3.3.7 Scanning Electron Microscopy (SEM) 21 3.3.8 Thermal conductivity 21

RESULTS AND DISCUSSION 22 4.1 Characterisation of rice husk and rice husk-derived aerogel 22

4.1.1 Rice husk 22 4.1.2 Rice husk derived silica aerogel (RH-aerogel) 23

4.1.2.1 Physical properties 23 4.1.3 Hydroxyl content 24 4.1.4 Thermal properties 26

4.2 Effect of RH-aerogel on strength and thermal property of ordinary Portland cement 27

4.2.1 Effect on compressive strength 27 4.2.1.1 Phase evolution during strengthening 30

4.2.1.1.1 XRD 30 4.2.1.1.2 SEM 32

4.2.2 Effect on thermal conductivity. 33

REFERENCES 35 APPENDIX: Paper presented at Regeonal Coference

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List of Tables Page

Table 1.1 Cost involved in commercial production of aerogel 4 Table 1.2 Composition of ordinary Portland cement 5 Table 4.2 Properties of rice-husk aerogel 24 Table 4.3 Thermal conductivities of cement compositions with

7% of different pozzolans as cement replacement 34

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List of Figures

Figure 1.1 Schematic diagram showing thermal insulating 5 property of aerogel-OPC composite

Figure 2.2 Schematic illustration of the different stages 14 of cement hydration

Figure 3.1 Process of obtaining rice husk ash from local rice husk 18 Figure 3.2 Schematic diagram showing the synthesis and 19

characterisation of rice husk=derived aerogel Figure 4.1 Pictures of a) Rice husks and b) Ash obtained after 22

heating rice husk at 1000C for lh Figure 4.2 Pictures of a) Water glass b) Rice husk aerogel 23 Figure 4.3 FTIR spectra of AO Rice husk ash and B) RH-aerogel 25

showing the strong hydroxyl absorption band Figure 4.4 TGA profile of RH-aerogel heated to 1000C at arate of 26

10C/min Figure 4.5a Effect of increasing amounts of RH-ash on strength of 29

OPC composite with varying days of hydration Figure 4.5b Effect of increasing amounts of RH-aerogel on strength 29

of OPC with increasing days of hydration Figure 4.6 XRD profile of A) 7 wt%RH-ash-OPC composite and 31

B) 7 wt% RH-aerogel-OPC composite Figure 4.7 SEM micrographs showing the microstructure of a) OPC 32

and b) RH-ash-OPC composite after 3 days of hydration Figure 4.8 SEM micrographs showing a) CSH fibres in RH-ash- 33

OPC and b) the microstructure of RH-aerogel -OPC after 7 days of hydration

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ABSTRACT

Silica aerogel is a highly porous material and is the lightest material known to date. In this study silica aerogel was synthesised from local rice husk ash using sol-gel process. The effects of adding various quantities ranging from 3 to 7 weight percent of the rice husk-derived silica aerogel on the strength and thermal conductivity of ordinary Portland cement were studied. The strength was measured using ELE compressive strength machine while the thermal conductivity was determined using Lee's disc method. The results indicate that while there was no significant improvement in terms of strength, there was a marked drop in the thermal conductivity of the resultant cement composite. The significant drop in the thermal conductivity indicates that the rice husk-derived silica aerogel is highly potential as a thermally insulating cement replacement material suitable for a hot country like Malaysia.

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CHAPTER 1

INTRODUCTION

1.1 What are aerogels?

Aerogels are the lightest and lowest-density solids known to exist. Aerogels consist

of a fine network of bubbles, with cell walls just a few atoms thick. Inside these cells, typically 50-99.5 %, is simply air, or whatever gas the designer wishes to

include. Due to their high porosity (up to 99%) and nano-structured nature, they

have low density (

or by accident, Kistler found a way to remove the fluid from a wet silica gel, leaving

behind its solid structure.

In the early 1930s, Kistler continued his experiments with aerogels, studying some

of their thermal and catalytic properties. The first commercial aerogels were

produced in 1942 by the Mosanto Corporation, under the trade name Santocel. The

process involved soaking a sodium silicate solution in sulfuric acid, then repeatedly

washing it in alcohol before drying it at high pressure. Mosanto described the

product as "a light, friable, slightly opalescent solid containing as much as 95

percent air volume. It is a very effective heat insulating material." [24] Mosanto

claimed to have produced aerogels with densities of 1.8 pounds per cubic foot (29

kg/m3), but their regular output was between three and five pounds per cubic foot

(48to80kg/m3)[19].

Mosanto marketed Santocel mainly as a flatting agent for paints and varnishes. Its

applications, though not numerous, were as varied as thermal insulation in

household freezers and an ingredient in Napalm. Because of its high manufacturing

cost, however, Mosanto discontinued aerogel production in 1970. Interest in

aerogels, and their very low thermal conductivity, increased in the 1980s as energy

conservation became increasingly important. However, high production costs still

prevent their widespread use [19].

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1.3 Applications of aerogels

According to their physical parameters (density, index of reflection, etc.) aerogels

occupy an intermediate position between solid and gas. For example, the density of

aerogel might be a hundred times less than the density of substances it is synthesized

from and, sometimes, heavier than air. Besides being the best thermal, electrical and

acoustic insulators known, aerogels find application as filters for seawater

desalination, micrometeoroid collectors, and subatomic particle detectors.

In future, aerogels could be used in windows, building insulation, automobile

catalyst converters, and high-efficiency battery electrodes. Also, Stardust spacecraft

will use aerogel to capture particles from comet Wild 2 in 2004 [20].

One of the first developments of aerogels was most strongly promoted by their

utility in detectors of Cerenkov radiation [20]. The speed of light in a given medium

is determined by the medium's index of refraction, and the index of refraction for

aerogels happens to be in a range that can be covered neither by compressed gases

nor by liquids. Aerogels have already been incorporated in several Cerenkov

detectors worldwide. Indeed, this is currently the widest practical application of the

material [20].

NASA used aerogel for thermal insulation on the Mars Exploration Rover, and it

may assist in a proposed fundamental-physics-testing mission and the Mars Scout

Program.

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1.4 Research background and the problem

Although the potential applications for aerogels are wide ranging and virtually

unlimited, they have to be cheaply manufactured in order to have an impact in the

commercial marketplace. As such, researchers have now turned their attention to

achieving these goals. Some groups have sought ways to eliminate the supercritical

drying process and the high capital cost associated with it, while others have sought

to make it more efficient.

The results of the above studies have shown that the cost of starting materials,

alkoxides, have been identified as the major contributor in the high overall cost of aerogel production. The costs of the two most common alkoxides being used

currently as the raw materias are listed in Table 1.1

Table 1.1: Cost involved in the synthesis of aerogel Alkoxide

Tetramethoxyorthosilane (99%)

Tetraehoxyorthosilane (99%)

Cost per liter (RM

1150.00

550.00

Aerogel produced perlitre of alkoxide (g)

100

100

The current study would try to synthesise silica aerogel from local rice husks which

as has been well known to contain silica and indirectly overcome the disposal

problem of an otherwise waste material

In the current study, the potential use of the developed aerogel as insulating material

is explored for walls of buildings in hot countries like Malaysia by adding varying

amounts of the aerogel to Ordinary Portland cement (OPC)

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1.4.1 Ordinary Portland cement

There are several types of cements for special purposes, but this project only concerns ordinary portland cement. OPC consists of five major compounds and a few minor compounds. The composition of a typical portland cement is listed by

weight percentage in Table 1.2.

Figure 1.1: Thermal insulating property of the aerogel-OPC composite

Table 1.2: Composition of ordinary Portland cement

Cement Compound

Tricalcium silicate

Dicalcium silicate

Tricalcium aluminate

Tetracalcium aluminoferrite

Gypsum

Weight Percentage

50%

25% 10%

10%

5%

Chemical Formula

Ca3Si05 or 3Ca0.SiO2

Ca2Si04 or 2CaO.Si02 Ca3Al206 or 3CaO .Al203 Ca4A12Fel0or 4CaO.Al203.Fe203

CaS04.2H20

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1.4.2 Pozzolanic admixture

Pozzolanic admixtures or "pozzolans" contain reactive silica (Si02) and sometimes

also reactive alumina (AI2O3) which in the presence of water react with lime to give

a gel of calcium silicate hydrate (SCH gel).

In the hydration of Portland cement, a considerable amount of calcium hydroxide is

produced. Hence, in mixtures made of pozzolan and Portland cement, a pozzolonic

reaction will take place due to the availability of lime. This availability of lime

facilitates the replacement of Portland cement by pozzolans and explains why such

an admixture can be used to produce pozzolan-based blended cements. The most

common materials are pulverised fly ash (PFA) and rice husk ash (RHA). The very

high surface area, combined with the high silica content, accelerate the pozzolanic

reactions, and thereby accelerate strength development. The very snail silica

particles, however, readily fill the spaces between the much coarser cement grains

and thereby, reduce the spacing between the solids. Hence, on subsequent

hydration, the resulting capillary pores in the silica aerogel containing paste are

much finer than the pores in the neat cement paste. The refinement in the pore

system has important particle implications. It will be seen later that the lower

permeability of silica aerogel containing cement and its associated improved

durability (10)

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1.5 Objectives The objectives of this study are:

1. To synthesis silica aerogel from rice husk ash by sol-gel process

2. To study the effect of the aerogel on the strength and thermal insulating

property of OPC.

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CHAPTER 2

LITERATURE REVIEW

2.1 Synthesis of silica aerogel

Silica aerogel could be derived by sol gel process. The process involved:

i) reacting silica precursor such as silicon aikoxide with sodium hydroxide

to form sodium silicate solution and precipitating it as water glass by

acidifying with acid such as hydrochloric or sulphuric acid,

ii) Drying the gel under supercritical conditions.

I Hj#slysis SiOR + HOH -, : - * SiOH + ROH Equation 2.2

Water | I Ces&nsitlan I I

SiOH + -SiOH ^ - ^ ^ * ^ 0^| + HO] Equation 2.3

-inn + -4 -OR ^ " ^ V -k -HH- l i - + I j ""* I I I Akoto^sis I

R: alkyl (example: CH3, C2H5, etc)

Figure 2.1 Sol gel process

Equation 2.4

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2.1.1 Properties of silica aerogel

Silica aerogel is one of the best candidates for transparent insulating materials [12].

It has very low thermal conductivity and good transparency because of its extremely

large porosity and small pore size [12]. At ambient temperature, the conductivity

value of silica aerogel is less than one half of that of usual insulating materials like

glass wool [12]. But silica aerogel is transparent, and radiative heat transfer

increases with the increase of temperature. The authors expected that the thermal

conductivity of silica aerogel is more affected by the temperature than that of usual

insulating materials.

Silica aerogels contain primary particles of 2-5 nm in diameter [13]. Silica particles

of such a small size have an extraordinarily large surface-to-volume ratio (~2 x 109

m") and a corresponding high specific surface area (-900 m7g) [13]. It is not

surprising, therefore, that the chemistry of the interior surface of an aerogel plays a

dominant role in its chemical and physical behavior. It is this property that makes

aerogels attractive materials for use as catalysts, catalyst substrates, and adsorbents

[13].

2.1.2 The surface chemistry of silica aerogel

The nature of the surface groups of a silica aerogel is strongly dependent on the

conditions used in its preparation. For example, if an aerogel is prepared using the

supercritical alcohol drying process, its surface may consist primarily of alkoxy (-

OR where R in alkyl group) groups. On the other hand, with the carbon dioxide

drying process the surface is almost exclusively covered with hydroxyl (-OH)

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groups. The extent of hydroxyl coverage is ~5 -OH/nm2, a value consistent with

other forms of silica. This value, combined with their high specific surface area,

means that silica aerogels present an extremely large number of accessible hydroxyl

groups. Silica aerogels are therefore a somewhat acidic material. A more striking

effect of the hydroxyl surface is seen in the physical behavior of silica aerogels [13].

As with most hydroxyl surfaces, the surface of silica aerogels can show strong

hydrogen-bonding effects. Because of this, silica aerogels with hydroxyl surface are

extremely hygroscopic. Dry silica aerogels will absorb water directly from moist air,

with mass increases of up to 20%. This absorption has no visible effect on the

aerogel, and is completely reversible. Simply heating the material to 100-120

degrees C will completely dry the material in about an hour (or longer, depending on

thickness).

As the sample cools, water will readsorb quickly (mass increases can be seen almost

immediately) [13]. While the adsorption of water vapor does not harm silica

aerogels, contact with liquid water has disastrous results. The strong attractive forces

that the hydroxyl surface exerts on water vapor also attract liquid water. However,

when liquid water enters a nanometer-scale pore, the surface tension of water exerts

capillary forces strong enough to fracture the solid silica backbone. The net effect is

a complete collapse of the aerogel monolith. The material changes from a

transparent solid with a definite shape to a fine white powder. The powder has the

same mass and total surface area as the original aerogel, but has lost its solid

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integrity. Silica aerogels with fully hydroxylated surfaces are, therefore, classified as

"hydrophilic" [13].

This would appear to pose a significant problem to using silica aerogels in exposed

environments. Fortunately, this problem can be easily circumvented by converting

the surface hydroxyl (-OH) groups to a non-polar (-OR) group. This is effective

when R is one of many possible aliphatic groups, although trimethylsilyl- groups are

the most common.

The derivitization can be performed before (on the wet gel) or after (on the aerogel)

supercritical drying. This completely protects the aerogel from damage by liquid

water by eliminating the attractive forces between water and the silica surface.

In fact, silica aerogels treated in this way can not be wet by water, and will float on

its surface indefinitely. Silica aerogels that have been derivitized in this way are

classified as "hydrophobic" [13].

2.1.3 Drying of silica aerogel

Aerogel properties are greatly influenced by the drying media used in supercritical

drying (SCD). Alcohol [14] and carbon dioxide (CO2) [15] are the two major types of SCD fluid used to prepare silica aerogel. Aerogel is made from an alcohol-based

gel containing silica particles, and in its raw form resembles a cube of DunsenDe

dessert [16]. This gel had to be dried without allowing it to collapse in on it, which

was done by soaking the gel in liquid carbon dioxide and then evaporating the

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alcohol and carbon dioxide at high pressure [16]. This left a structure of silica

particles with air between them. These pores, or spaces between the particles, made

the material both light-weight and a good insulator [16].

2.1.4 Applications of silica aerogel

Research on silica aerogels has focused on its use as a transparent thermal insulator

[17] and in Cherenkov detectors in high-energy physics [18].

2.1.4.1 Thermal insulators

Aerogel materials exhibit the lowest thermal conductivities of any of the solid or

porous materials. This key property of the material leads to many applications

including insulation for architectural purposes [17], piping, heat and cold storage

appliances and devices [17], automotive exhaust pipes, transport vehicles and

vessels. An advantage of silica aerogels for insulation applications is their visible

transparency (which will allow their use in windows and skylights) [17].

2.1.4.2 Particle detectors and counters

Earliest recorded use of aerogels was as particle detectors using the Cherenkov

effect in the early 1980s. High energy physics studies relied on aerogels having

specific refractive indexes for threshold detectors. Solid aerogels, though fragile,

were much easier and safer to apply than high pressure gas alternatives. Aerogel use

for particle detectors and counters continues in space, at accelerators around the

world, and in upper atmosphere balloon borne experiments [18].

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2.2 Cement hydration

Concrete is prepared by mixing cement, water, and aggregate together to make a

workable paste. It is molded or placed as desired, consolidated, and then left to

harden. Concrete does not need to dry out in order to harden as commonly thought.

The concrete (or specifically, the cement in it) needs moisture to hydrate and cure

(harden). When concrete dries, it actually stops getting stronger. Concrete with too

little water may be dry but is not fully reacted. The properties of such a concrete

would be less than that of a wet concrete. The reaction of water with the cement in

concrete is extremely important to its properties and reactions may continue for

many years. This very important reaction will be discussed in detail in this section.

When water is added to cement, each of the compounds undergoes hydration and

contributes to the final concrete product. Only the calcium silicates contribute to

strength. Tricalcium silicate is responsible for most of the early strength (first 7

days). Dicalcium silicate, which reacts more slowly, contributes only to the strength

at later times. Tricalcium silicate will be discussed in the greatest detail.

The equation for the hydration of tricalcium silicate is given by:

Tricalcium silicate + Water>Calcium silicate hydrate+Calcium hydroxide + heat

1 Ca3Si05 + 7 H20 > 3 Ca0.2Si02.4H20 + 3 Ca(OH)2 + 173.6kJ Eqn. 2.5

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