Tests for Light Weight Aggregate Concrete

8/21/2019 Tests for Light Weight Aggregate Concrete

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TESTING PROGRAM OF LIGHTWEIGHT CONCRETE

In order to study the behavior of lightweight concrete, normal concrete testing

was done to determine the material and structural properties of each type of lightweight

concrete and how will these properties differ according to a different type of mixture and

its composition.

Once concrete has hardened it can be subjected to a wide range of tests to prove

its ability to perform as planned or to discover its characteristics. For new concrete this

usually involves casting specimens from fresh concrete and testing them for various

properties as the concrete matures.

3.2 COMPRESSIVE STRENGTH

Compressive strength is the primary physical property of concrete (others are

generally defined from it), and is the one most used in design. It is one of the

fundamental properties used for quality control for lightweight concrete. Compressive

strength may be defined as the measured maximum resistance of a concrete specimen to

axial loading. It is found by measuring the highest compression stress that a test cylinder

or cube will support.

There are three type of test that can be use to determine compressive strength;

cube, cylinder, or prism test. The concrete cube test' is the most familiar test and is used

as the standard method of measuring compressive strength for quality control purposes(Neville, 1994). Please refer appendix 1 for details.

APPENDIX 1

CUBE TESTObjective:-To determine the compressive strength of a lightweight concrete sample.Apparatus:- Standard cube size 100mm^3- Steel rod measured 25x25 mm^2General note:- Compressive strength will be determined at the age of 7 and 28 days.- 3 samples for each age will be prepare

-Average result will be takenProcedure:1. Prepare the mould; apply lubricant oil in a thin layer to the inner surface of themould to prevent any bonding reaction between the mould and the sample(A.M Neville, 1994)2. Overfill each mould with sample in three layers (Standard Method: BS 1881:Part 3: 1970)3. Fill 1/3 of the mould with sample. This would be the first layer4. Compact sample with at least 35 strokes using steel rod. Compaction shouldbe done continuously5. Fill 2/3 of the mould; second layer. Repeat step 4.6. Continue with the third layer and repeat the same compaction step7. After compaction has been completed, smooth off by drawing the flat side of

the trowel (with the leading edge slightly raised) once across the top of eachcube8. Cut the mortar off flush with the top of the mould by drawing the edge of thetrowel (held perpendicular to the mould) with a sawing motion over the mould9. Tag the specimen, giving party number, and specimen identification10. Store cube in moist closet (temperature; 18C - 24C) for 24 hours11. Open mould and preserved cube in water (temperature; 19C - 21C)BS1881; Part 3: 197012. Test cube for 7 days and 28 days accordingly13. Placed cube on the testing machine: cube position should be perpendicularwith its pouring position ( A.M. Neville, 1994)14. Without using any capping material, apply an initial load ( at any convenient


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rate) up to one-half of the expected maximum load (G.E. Troxell, 1956)15. Loading should be increased at a uniform increment; 15 MPa/min (2200Psi/min)BS 1881: Part 4: 1970. Since that certain sample are expected tohave lower compressive strength, some adjustment will be made; loading willbe increased with the increment of 5% of the expected maximumcompressive strength16. When it comes nearer to the expected maximum strength, loading incrementwill be lessen little by little ( A.M. Neville, 1994)

WATER ABSORPTION

These properties are particularly important in concrete, as well as being important

for durability. (J.H Bungey, 1996). It can be used to predict concrete durability to resist

corrosion. Absorption capacity is a measure of the porosity of an aggregates; it is also

used as a correlation factor in determination of free moisture by oven-drying method

(G.E Troxell, 1956).

The absorption capacity is determined by finding the weight of surface-dry

sample after it has been soaked for 24 hr and again finding the weight after the sample

has been dried in an oven; the difference in weight, expressed as a percentage of the dry

sample weight, is the absorption capacity (G.E Troxell, 1956).Absorption capacity can be determine using BS absorption test. The test is

intended as a durability quality control check and the specified age is 28-32 days (S.G

Millard). Test procedure as been describe by BS 1881: Part 122 is as listed in the

appendix 2.

APPENDIX 2

BS Absorption TestObjective:- To determine the absorption capacity of lightweight concrete sampleApparatus:-A balance-An air tight vessel

-A container of water-An ovenGeneral note:- Test will be carried out on 75 mm diameter ( 3mm) specimens- Specified test age is 28-32 days.- 3 samples for each age will be prepare-Average result will be takenProcedure:1. Dry the specimens in an oven at 105C 5C for 72 2 hr.2. Cooled specimen for 24 1/2 hr in an airtight vessel3. Weight the specimen4. Immersed horizontally in the tank of water at 20C 1C with 25 5 mmwater over the top surface

5. Immersed for 30 minutes6. Removed specimen7. Shaken and dried quickly with a cloth to remove free surface water8. Weight the specimen againCalculation:Absorption capacity can be calculate using the formula given below:(Result will be expressed to the nearest 0.1%)Absorption Capacity = Increased In Weight (kg) 100%

Weight of Dry Specimen (kg)


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DENSITY

The density of both fresh and hardened concrete is of interest to the parties

involved for numerous reasons including its effect on durability, strength and resistance

to permeability.

Hardened concrete density is determined either by simple dimensional checks,

followed by weighing and calculation or by weight in air/water buoyancy methods (ELE

International, 1993). To determine the density of lightweight concrete sample, the simple

method is preferred as listed in the appendix 3.

APPENDIX 3

Simple Density Test.Objective:- To determine the density of hardened lightweight concrete sample.Apparatus:- Weighing scale- One cube sampleGeneral Note:- For more economic sample are to be taken from compression test sample;before doing the test- Three sample are going to be used and average result will be taken

Procedures:1. Weight sample using weighing scale2. Get the average weight of those 3 samples3. Calculate the density using the formula given below(Since a standard mould; 100 x 100 x 100 mm is used, volume of eachsample can be determined according to this dimensional)Density = Average Weight Of Samples (kg)

Volume of Sample (m2)

Chemical Shrinkage

Chemical shrinkage, the volume reduction associated with the reaction between cement and water in hydrating

cement paste, was assessed using the method described by Geiker [11], which is similar to that recently employed

by Tazawa et al. [12]. While the latter authors concluded that chemical shrinkage is directly proportional to degree

of hydration, they further stated that chemical shrinkage is not directly related to autogenous or self-desiccation

shrinkage. Conversely, Hua et al. [13,14]have recently established a model which successfully directly relates

autogenous shrinkage to the capillary pressures induced by chemical shrinkage. Thus, measurements of chemical

shrinkage may serve a dual purpose, quantification of hydration rates and indication of system susceptibility to self-

desiccation shrinkage.

To assess chemical shrinkage, a known mass of cement paste (typically 10 g) was placed in the bottom of a small

glass jar, with a diameter of 2.5 cm and a height of about 6 cm. After covering the cement paste with about 1 ml of

water, the remainder of the jar was filled with an hydraulic oil. The jar was then sealed with a rubber stopper

encasing a pipette graduated in 0.01 ml increments. The jar was then placed in a constant temperature water bath ( T

= 25 C ) and the oil level monitored to the nearest 0.0025 ml over time. A control sample using only cement

powder and oil (no water) was used to correct for minor room temperature fluctuations. By normalizing the change

in volume by the mass of cement in the sample, the chemical shrinkage per gram of initial cement (ml/g cement)

could be determined. In all cases, two specimens were run for each w/cratio and cement, with the average result

being reported.

Chemical Shrinkage

Another convenient method for monitoring hydration kinetics is via the measurement of chemical shrinkage [14].

Because the cement hydration products occupy less volume than the starting materials (cement and water), a

hydrating cement paste will imbibe water in direct proportion to its ongoing hydration [14,15]. This is true except

for low w/c ratio pastes (< about 0.4) where the depercolation of the capillary porosity may dramatically reduce the

permeability of the cement paste and limit its imbibition rate below that required to maintain saturation during the
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continuing hydration [9,14]. While no standard ASTM method exists for the measurement of chemical shrinkage, a

draft standard for this test is currently being considered by ASTM C01.31 subcommittee on Volume Change. The

maximum expanded uncertainty [16]in the calculated chemical shrinkage has been previously estimated [9], to be

0.001 mL/(g of cement), assuming a coverage factor of 2 [16].

Knowing the volume stoichiometry of all ongoing hydration reactions, it is straightforward to compute chemical

shrinkage in the VCCTL cement hydration model. Figures7and8provide comparisons of model and experimentalresults for cements 135 and 141, respectively. Excellent agreement is observed between model and experimental

results. The deviation between model and experimental results for cement 135 at later ages (> 40 h) is likely due to

the depercolation of the capillary porosity mentioned above. Chemical shrinkage measurements appear to provide a

rapid and convenient method for assessing early hydration rates and may provide a simple means for evaluating

cement cracking susceptibility [17].

Figure 7:Experimentally measured (circles) and model-predicted chemical shrinkage for CCRL cement 135

(w/c=0.3, hydrated at 25 C).
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Figure 8:Experimentally measured (circles) and model-predicted chemical shrinkage for CCRL cement 141

(w/c=0.4, hydrated at 20 C).

Early-Age CrackingBy Matthew DAmbrosia

1and Nathaniel Mohler

2

Early-age cracking can be a significant problem in concrete. Volume changes in concrete will drive tensile

stress development when they are restrained. Cracks can develop when the tensile stress exceeds thetensile strength, which is generally only 10% of the compressive strength. At early ages, this strength isstill developing while stresses are generated by volume changes. Controlling the variables that affectvolume change can minimize high stresses and cracking.

Mechanisms of Early-Age Volume ChangeThe volume of concrete begins to change shortly after it is cast. Early volume changes, within 24 hours,can influence tensile stress and crack formation in hardened concrete.

Chemical Shrink ageChemical shrinkage occurs due to the reduction in absolute volume of solids and liquids in the hydratingpaste. Chemical shrinkage continues to occur as long as cement hydrates. After initial set, the pasteresists deformation, causing the formation of voids in the microstructure.

Autogenous Shr inkageAutogenous shrinkage is the dimensional change of cement paste, mortar, or concrete caused bychemical shrinkage (Figure 1). When internal relative humidity is reduced below a given threshold (i.e.,extra water is not available), self-desiccation of the paste occurs, resulting in a uniform reduction ofvolume.


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Figure 1Chemical shrinkage and autogenous shrinkage volumechanges of fresh concrete. Not to scale.

CreepCreep is the time-dependent deformation of concrete under sustained load. During early age, concretecreep is generally as much as 3-5 times higher than for mature concrete. Early load application due toconstruction forces or prestressing operations can therefore have a significant impact on totaldeformation. Furthermore, the magnitude of creep in tension is greater than in compression, and earlytensile creep can be relied upon as a stress relaxation mechanism. Creep is influenced by drying or self-dessication at early age, and this synergy is often referred to as the Pickett Effect, after Gerald Pickett, aPCA researcher who discovered the phenomena in the 1940s (Pickett 1947).

Swell ingConcrete, mortar, and cement paste will sometimes swell when sealed or in the presence of externalwater. Swelling is generally caused by pore pressure, but can be accentuated by the formation of someexpansive hydration products. The swelling is not significant, between 50-100 millionths at early ages;therefore, we will not be discussing swelling further.

Thermal Expansio nAs cement hydrates, the reaction provides a significant amount of heat. In large elements, this heat istrapped and can induce significant expansion. When thermal changes are superimposed uponautogenous shrinkage at early age, cracking can occur. In particular, differential thermal stress can occurdue to rapid cooling of massive concrete elements.

Testing of Early-Age Volume Changes

Chemical shrink age testVolume change due to chemical shrinkage can be estimated from the hydrated cement phases and theircrystal densities or it can be determined by physical test. The physical test places a measured amount oflime-saturated water in an open pipet over a known amount of cement paste inside a closed container.The change in water level within the pipet indicates the change in volume due to chemical shrinkage(Figure 2).


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Figure 2Test for chemical shrinkage of cement paste showingflask for cement paste and pipet for absorbed watermeasurement.

ASTM C157 - Modif ied for early age shrinkageThe standard drying shrinkage test for concrete can be modified to capture early age volume change byelimination of the curing period (usually 7-28 days) and beginning measurements as early as possible.Prisms may also be sealed after casting to provide an estimate of autogenous shrinkage. Surfaces shouldbe sealed as quickly as possible to eliminate loss of moisture. It should be emphasized that autogenousshrinkage depends on temperature history (maturity) and will be different in a laboratory prism whencompared to a larger concrete member in service under variable ambient temperatures. As with drying

shrinkage measurements, the test result will not represent the actual shrinkage in the structure.

ASTM C1581 Restrained Ring Shrink ageThe restrained ring shrinkage test consists of a concrete ring specimen 150 mm (6 in.) tall, 13 mm (0.5in.) thick and 330 mm (13 in.) diameter that is cast surrounding an instrumented steel ring (Figure 3). Thesteel ring prevents the concrete from shrinking from the time that the concrete is first cast. Shrinkagestresses continue to grow as the concrete passes from initial set to final set and beyond. Tensile creeprelaxation alleviates stress development and is considered beneficial at early age.The instrumented ringuses strain sensors to monitor the development of stress. If the shrinkage in the concrete is significant,the stresses will eventually cause cracking. The strain sensors provide an indicator of the cracking time,which is used to compare the cracking tendency between different concrete mixtures.

Figure 3Restrained ring shrinkage test setup. (Courtesy of CTLGroup)


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ASTM C512 - Compressiv e CreepThe standard creep test consists of a frame and hydraulic loading system to apply constant stress to150X300 mm (6x12 in.) cylindrical specimens (Figure 4). Deformation is monitored periodically over timeand compard to compansion unloaded specimens to obtain the creep strain of the concrete, which canthen be used to calculate the creep compliance, or specific creep of the material. Tests are typicallystarted at 7 or 28 days of age, but this test can be modified for early age by starting the test as early as24 hours. Sealed tests are used to evaluate basic creep and unsealed tests incorporate the PickettEffect, or drying creep.

Figure 4Standard creep test frames. (Courtesy of CTLGroup)

Mitigating Early-Age Cracking

Optimizat ion of aggregates to reduce tota l cement i t ious contentSince volume changes are more a function of the cement paste, rather than the more volume-stableaggregates, reducing the overall cementitious content is the best way to mitigate early-age volumechanges. Typical concrete mixtures have gap-graded aggregates that leave significant void space forcement paste to fill. By optimizing the aggregate gradation across the entire spectrum, as opposed to thecoarse and fine aggregates individually, the amount of paste required to surround each aggregate particleand fill the void space is minimized (Figure 5); thereby minimizing the effects of early-age volume changeof the paste.

Figure 5A comparison of void space with different aggregate gradations.


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Minimum w /cm rat ioAutogenous shrinkage increases with a decrease in water to cementitious materials ratio (w/cm).Concrete mixtures with a w/cm of 0.30 can experience autogenous shrinkage upwards of half of thenormal drying shrinkage. Using the highest w/cm that still provides adequate strength and durability canreduce the impact of autogenous shrinkage.

Internal curing

Internal curing is a method by which water is encapsulated within a concrete mixture for continuedrelease during the hydration process. Typical internal curing materials include high absorption lightweightaggregate particles and super-absorbent polymers. The self-dessication of the paste draws the water outof these particles to continue the hydration of the cement particles. This is particularly helpful in mitigatingautogenous shrinkage of concrete mixtures with very low w/cm (0.30 or less).

Shr inkage-reducing admixturesShrinkage-reducing admixtures (SRAs) are typically used as mitigation of cracking and curling caused bydrying shrinkage; however, SRAs can be utilized to mitigate autogenous shrinkage as well. The SRA,typically propylene glycol or polyoxyalkylene alkyl ether based, alters the surface tension of the porewater and reduces the stresses developed during desiccation, whether self-induced or by evaporation.

Concret ing proceduresSeveral concreting procedures can be used to minimize early-age volume changes. When autogenous

shrinkage is a concern, the use of moist curing methods will help mitigate self-desiccation near theconcrete surface. The use of a well-developed thermal control plan will mitigate the effects of thermal-based volume changes.

ReferencesKosmatka, Steven H.; Kerkhoff, Beatrix; and Panarese, William C.;Design and Control of ConcreteMixtures,EB001, 14th edition, Portland Cement Association, Skokie, Illinois, USA, 2002, 358 pages.

Pickett, Gerald,The Effect of Change in Moisture Content on the Creep of Concrete Under a SustainedLoad,Research Department Bulletin RX020, Portland Cement Association, 1947.

http://labmanual.blogspot.com/search/label/CE2308
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X-Ray powder diffraction

X-ray Powder Diffraction (XRD)

Barbara L Dutrow, Louisiana State University

,

Christine M. Clark, Eastern Michigan University

What is X-ray Powder Diffraction (XRD)

X-ray powder diffraction (XRD) is a rapid analytical technique primarily used for phase

identification of a crystalline material and can provide information on unit cell dimensions.

The analyzed material is finely ground, homogenized, and average bulk composition is

determined.

Fundamental Principles of X-ray Powder Diffraction (XRD)

Max von Laue, in 1912, discovered that crystalline substances act as three-dimensional

diffraction gratings for X-ray wavelengths similar to the spacing of planes in a crystal lattice.

X-ray diffraction is now a common technique for the study of crystal structures and atomic

spacing.

X-ray diffraction is based on constructive interference of monochromatic X-rays and a

crystalline sample. These X-rays are generated by a cathode ray tube, filtered to produce

monochromatic radiation, collimated to concentrate, and directed toward the sample. The

interaction of the incident rays with the sample produces constructive interference (and a

diffracted ray) when conditions satisfyBragg's Law(n=2dsin ). This law relates the

wavelength of electromagnetic radiation to the diffraction angle and the lattice spacing in a

crystalline sample. These diffracted X-rays are then detected, processed and counted. By

scanning the sample through a range of 2angles, all possible diffraction directions of the

lattice should be attained due to the random orientation of the powdered material.

Conversion of the diffraction peaks to d-spacings allows identification of the mineral because

each mineral has a set of unique d-spacings. Typically, this is achieved by comparison of d-

spacings with standard reference patterns.

All diffraction methods are based ongeneration of X-raysin an X-ray tube. These X-rays are

directed at the sample, and the diffracted rays are collected. A key component of all

diffraction is the angle between the incident and diffracted rays. Powder and single crystal

diffraction vary in instrumentation beyond this.

X-ray Powder Diffraction (XRD) Instrumentation - How Does It Work?

X-ray diffractometers consist of three basic elements: an X-ray tube, a sample holder, and

an X-ray detector.
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Show caption

X-rays are generatedin a cathode ray tube by heating a filament to produce electrons,

accelerating the electrons toward a target by applying a voltage, and bombarding the target

material with electrons. When electrons have sufficient energy to dislodge inner shell

electrons of the target material, characteristic X-ray spectra are produced. These spectra

consist of several components, the most common being Kand K. Kconsists, in part, of

K1and K2. K1has a slightly shorter wavelength and twice the intensity as K2. The specific

wavelengths are characteristic of the target material (Cu, Fe, Mo, Cr). Filtering, by foils or

crystal monochrometers, is required to produce monochromatic X-rays needed for

diffraction. K1and K2are sufficiently close in wavelength such that a weighted average of

the two is used. Copper is the most common target material for single-crystal diffraction,

with CuKradiation = 1.5418. These X-rays are collimated and directed onto the sample.

As the sample and detector are rotated, the intensity of the reflected X-rays is recorded.

When the geometry of the incident X-rays impinging the sample satisfies the Bragg

Equation, constructive interference occurs and a peak in intensity occurs. A detector records

and processes this X-ray signal and converts the signal to a count rate which is then output

to a device such as a printer or computer monitor.

Show caption

The geometry of an X-ray diffractometer is such that the sample rotates in the path of the

collimated X-ray beam at an angle while the X-ray detector is mounted on an arm to

collect the diffracted X-rays and rotates at an angle of 2. The instrument used to maintain

the angle and rotate the sample is termed a goniometer. For typical powder patterns, data

is collected at 2from ~5to 70, angles that are preset in the X-ray scan.

Applications
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X-ray powder diffraction is most widely used for the identification of unknown crystalline

materials (e.g. minerals, inorganic compounds). Determination of unknown solids is critical

to studies in geology, environmental science, material science, engineering and biology.

Other applications include:

characterization of crystalline materialsidentification of fine-grained minerals such as clays and mixed layer clays that are

difficult to determine optically

determination of unit cell dimensions

measurement of sample purity

With specialized techniques, XRD can be used to:

determine crystal structures using Rietveld refinement

determine of modal amounts of minerals (quantitative analysis)

characterize thin films samples by:

o determining lattice mismatch between film and substrate and

to inferring stress and straino determining dislocation density and quality of the film by

rocking curve measurements

o measuring superlattices in multilayered epitaxial structures

o determining the thickness, roughness and density of the film

using glancing incidence X-ray reflectivity measurements

make textural measurements, such as the orientation of grains, in

a polycrystalline sample

Strengths and Limitations of X-ray Powder Diffraction (XRD)?

Strengths

Powerful and rapid (< 20 min) technique for identification of an

unknown mineral

In most cases, it provides an unambiguous mineral determination

Minimal sample preparation is required

XRD units are widely available

Data interpretation is relatively straight forward

Limitations

Homogeneous and single phase material is best for

identification of an unknown

Must have access to a standard reference file of inorganic

compounds (d-spacings, hkls)

Requires tenths of a gram of material which must be

ground into a powder

For mixed materials, detection limit is ~ 2% of sample

For unit cell determinations, indexing of patterns for non-

isometric crystal systems is complicated


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Peak overlay may occur and worsens for high angle

'reflections'

Scanning Electron Microscopy (SEM)

Susan Swapp, University of Wyoming

What is Scanning Electron Microscopy (SEM)

A typical SEM instrument, showing the electron column, sample chamber, EDS detector,

electronics console, and visual display monitors.

The scanning electron microscope (SEM) uses a focused beam of high-energy electrons to

generate a variety of signals at the surface of solid specimens. The signals that derive

fromelectron-sample interactionsreveal information about the sample including external

morphology (texture), chemical composition, and crystalline structure and orientation of

materials making up the sample. In most applications, data are collected over a selected

area of the surface of the sample, and a 2-dimensional image is generated that displays

spatial variations in these properties. Areas ranging from approximately 1 cm to 5 microns

in width can be imaged in a scanning mode using conventional SEM techniques

(magnification ranging from 20X to approximately 30,000X, spatial resolution of 50 to 100

nm). The SEM is also capable of performing analyses of selected point locations on the

sample; this approach is especially useful in qualitatively or semi-quantitatively determining

chemical compositions (usingEDS), crystalline structure, and crystal orientations

(usingEBSD). The design and function of the SEM is very similar to theEPMAand

considerable overlap in capabilities exists between the two instruments.

Fundamental Principles of Scanning Electron Microscopy (SEM)

Accelerated electrons in an SEM carry significant amounts of kinetic energy, and this energyis dissipated as a variety of signals produced byelectron-sample interactionswhen the

incident electrons are decelerated in the solid sample. These signals include secondary

electrons (that produce SEM images), backscattered electrons (BSE), diffracted

backscattered electrons (EBSDthat are used to determine crystal structures and

orientations of minerals), photons (characteristic X-raysthat are used for elemental analysis

and continuum X-rays), visible light (cathodoluminescence--CL), and heat. Secondary

electrons and backscattered electrons are commonly used for imaging samples: secondary

electrons are most valuable for showing morphology and topography on samples and
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backscattered electrons are most valuable for illustrating contrasts in composition in

multiphase samples (i.e. for rapid phase discrimination).X-ray generationis produced by

inelastic collisions of the incident electrons with electrons in discrete ortitals (shells) of

atoms in the sample. As the excited electrons return to lower energy states, they yield X-

rays that are of a fixed wavelength (that is related to the difference in energy levels of

electrons in different shells for a given element). Thus, characteristic X-rays are produced

for each element in a mineral that is "excited" by the electron beam. SEM analysis is

considered to be "non-destructive"; that is, x-rays generated by electron interactions do not

lead to volume loss of the sample, so it is possible to analyze the same materials

repeatedly.

Scanning Electron Microscopy (SEM) Instrumentation - How Does It Work?

Essential components of all SEMs include the following:

Electron Source ("Gun")

Electron Lenses

Sample Stage

Detectors for all signals of interest

Display / Data output devices

Infrastructure Requirements:

o Power Supply

o Vacuum System

o Cooling system

o Vibration-free floor

o Room free of ambient magnetic and electric fields

SEMs always have at least one detector (usually a secondary electron detector), and

most have additional detectors. The specific capabilities of a particular instrument

are critically dependent on which detectors it accommodates.

Applications
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The SEM is routinely used to generate high-resolution images of shapes of objects

(SEI) and to show spatial variations in chemical compositions: 1) acquiringelemental

mapsor spot chemical analyses usingEDS,2)discrimination of phases based on

mean atomic number (commonly related to relative density) usingBSE,and 3)

compositional maps based on differences in trace element "activitors" (typically

transition metal and Rare Earth elements) usingCL.The SEM is also widely used to

identify phases based on qualitative chemical analysis and/or crystalline structure.

Precise measurement of very small features and objects down to 50 nm in size is

also accomplished using the SEM. Backescattered electron images (BSE)can be used

for rapid discrimination of phases in multiphase samples. SEMs equipped with

diffracted backscattered electron detectors (EBSD)can be used to examine

microfabric and crystallographic orientation in many materials.

Strengths and Limitations of Scanning Electron Microscopy (SEM)?

StrengthsThere is arguably no other instrument with the breadth of applications in the study of

solid materials that compares with the SEM. The SEM is critical in all fields that

require characterization of solid materials. While this contribution is most concerned

with geological applications, it is important to note that these applications are a very

small subset of the scientific and industrial applications that exist for this

instrumentation. Most SEM's are comparatively easy to operate, with user-friendly

"intuitive" interfaces. Many applications require minimal sample preparation. For

many applications, data acquisition is rapid (less than 5 minutes/image for SEI, BSE,

spot EDS analyses.) Modern SEMs generate data in digital formats, which are highly

portable.

Limitations

Samples must be solid and they must fit into the microscope chamber. Maximum

size in horizontal dimensions is usually on the order of 10 cm, vertical dimensions

are generally much more limited and rarely exceed 40 mm. For most instruments

samples must be stable in a vacuum on the order of 10-5- 10-6torr. Samples likely

to outgas at low pressures (rocks saturated with hydrocarbons, "wet" samples such

as coal, organic materials or swelling clays, and samples likely to decrepitate at low

pressure) are unsuitable for examination in conventional SEM's. However, "low
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vacuum" and "environmental" SEMs also exist, and many of these types of samples

can be successfully examined in these specialized instruments.EDS detectorson

SEM's cannot detect very light elements (H, He, and Li), and many instruments

cannot detect elements with atomic numbers less than 11 (Na). Most SEMs use a

solid state x-ray detector (EDS), and while these detectors are very fast and easy to

utilize, they have relatively poor energy resolution and sensitivity to elements

present in low abundances when compared to wavelength dispersive x-ray detectors

(WDS)on most electron probe microanalyzers (EPMA). An electrically conductive

coating must be applied to electrically insulating samples for study in conventional

SEM's, unless the instrument is capable of operation in a low vacuum mode.

User's Guide - Sample Collection and Preparation

Sample preparation can be minimal or elaborate for SEM analysis, depending on the

nature of the samples and the data required. Minimal preparation includes

acquisition of a sample that will fit into the SEM chamber and some accommodation

to prevent charge build-up on electrically insulating samples. Most electricallyinsulating samples are coated with a thin layer of conducting material, commonly

carbon, gold, or some other metal or alloy. The choice of material for conductive

coatings depends on the data to be acquired: carbon is most desirable if elemental

analysis is a priority, while metal coatings are most effective for high resolution

electron imaging applications. Alternatively, an electrically insulating sample can be

examined without a conductive coating in an instrument capable of "low vacuum"

operation.

Data Collection, Results and Presentation

Representative SEM images of asbestiform minerals from theUSGS DenverMicrobeam Laboratory

UICC Asbestos Chrysotile 'A' standard
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Tremolite asbestos, Death Valley, California

Anthophyllite asbestos, Georgia
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Winchite-richterite asbestos, Libby, Montana

Literature

The following literature can be used to further explore Scanning Electron Microscopy

(SEM)

Goldstein, J. (2003) Scanning electron microscopy and x-ray

microanalysis. Kluwer Adacemic/Plenum Pulbishers, 689 p. Reimer, L. (1998) Scanning electron microscopy : physics of image

formation and microanalysis. Springer, 527 p.

Egerton, R. F. (2005) Physical principles of electron microscopy : an

introduction to TEM, SEM, and AEM. Springer, 202.

Clarke, A. R. (2002) Microscopy techniques for materials science. CRC

Press (electronic resource)

Nuclear magnetic resonance spectroscopy

Nuclear magnetic resonance spectroscopy, most commonly known as NMR spectroscopy, is a

research technique that exploits themagneticproperties of certainatomic nucleito determine physical and

chemical properties ofatomsor themoleculesin which they are contained. It relies on the phenomenon

ofnuclear magnetic resonanceand can provide detailed information about the structure, dynamics,

reaction state, and chemical environment of molecules.

Most frequently, NMR spectroscopy is used by chemists and biochemists to investigate the properties

oforganic molecules,though it is applicable to any kind of sample that contains nuclei possessing spin.

Suitable samples range from small compounds analyzed with 1-dimensionalprotonorcarbon-13
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NMRspectroscopy to largeproteinsornucleic acidsusing 3 or 4-dimensional techniques. The impact of

NMR spectroscopy on the sciences has been substantial because of the range of information and the

diversity of samples, includingsolutionsandsolids.

Scanning electron microscope

A scanning electron microscope(SEM) is a type ofelectron microscopethat images a sample by

scanning it with a high-energy beam ofelectronsin araster scanpattern. The electrons interact with the

atoms that make up the sample producing signals that contain information about the sample's

surfacetopography,composition, and other properties such aselectrical conductivity.

The types of signals produced by an SEM includesecondary electrons,back-scatteredelectrons

(BSE),characteristic X-rays,light (cathodoluminescence), specimen current and transmitted electrons.

Secondary electron detectors are common in all SEMs, but it is rare that a single machine would havedetectors for all possible signals. The signals result from interactions of the electron beam with atoms at

or near the surface of the sample. In the most common or standard detection mode, secondary electron

imaging or SEI, the SEM can produce very high-resolution images of a sample surface, revealing details

less than 1nmin size. Due to the very narrow electron beam, SEM micrographs have a large depth of

fieldyielding a characteristic three-dimensional appearance useful for understanding the surface structure

of a sample. This is exemplified by the micrograph of pollen shown to the right. A wide range of

magnifications is possible, from about 10 times (about equivalent to that of a powerful hand-lens) to more

than 500,000 times, about 250 times the magnification limit of the bestlight microscopes.Back-scattered

electrons (BSE) are beam electrons that are reflected from the sample byelastic scattering.BSE are

often used in analytical SEM along with the spectra made from the characteristic X-rays. Because the

intensity of the BSE signal is strongly related to the atomic number (Z) of the specimen, BSE images can

provide information about the distribution of different elements in the sample. For the same reason, BSE

imaging can imagecolloidal goldimmuno-labelsof 5 or 10 nm diameter, which would otherwise be

difficult or impossible to detect in secondary electron images in biological specimens. CharacteristicX-

raysare emitted when the electron beam removes aninner shell electronfrom the sample, causing

ahigher energy electronto fill the shell and release energy. These characteristic X-rays are used to

identify the composition and measure the abundance of elements in the sample.

In a typical SEM, an electron beam isthermionicallyemitted from anelectron gunfitted with

atungstenfilamentcathode.Tungsten is normally used in thermionic electron guns because it has the

highest melting point and lowest vapour pressure of all metals, thereby allowing it to be heated for

electron emission, and because of its low cost. Other types of electron emitters includelanthanum

hexaboride(LaB6) cathodes, which can be used in a standard tungsten filament SEM if the vacuum
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system is upgraded andfield emission guns(FEG), which may be of thecold-cathodetype using tungsten

single crystal emitters or the thermally assistedSchottkytype, using emitters ofzirconium oxide.

The electron beam, which typically has anenergyranging from 0.5keVto 40 keV, is focused by one or

two condenser lenses to a spot about 0.4 nm to 5 nm in diameter. The beam passes through pairs of

scanning coils or pairs of deflector plates in the electron column, typically in the final lens, which deflect

the beam in thexand yaxes so that it scans in arasterfashion over a rectangular area of the sample

surface.

When the primary electron beam interacts with the sample, the electrons lose energy by repeated random

scattering and absorption within a teardrop-shaped volume of the specimen known as the interaction

volume, which extends from less than 100 nm to around 5 m into the surface. The size of the interaction

volume depends on the electron's landing energy, the atomic number of the specimen and the specimen's

density. The energy exchange between the electron beam and the sample results in the reflection of high-

energy electrons byelastic scattering,emission of secondary electrons byinelastic scatteringand the

emission ofelectromagnetic radiation,each of which can be detected by specialized detectors. The beam

current absorbed by the specimen can also be detected and used to create images of the distribution of

specimen current.Electronic amplifiersof various types are used to amplify the signals, which are

displayed as variations in brightness on acathode ray tube.The raster scanning of the CRT display is

synchronised with that of the beam on the specimen in the microscope, and the resulting image is

therefore a distribution map of the intensity of the signal being emitted from the scanned area of the

specimen. The image may be captured byphotographyfrom a high-resolution cathode ray tube, but in

modern machines is digitally captured and displayed on acomputer monitorand saved to a

computer'shard disk.

Powder diffraction

Powder diffractionis a scientific technique usingX-ray,neutron, orelectrondiffractionon powder

ormicrocrystallinesamples for structural characterization of materials.[2]

ASTM C330 / C330M - 09 Standard Specification for Lightweight Aggregates for Structural

Concrete

ASTM C332 - 09 Standard Specification for Lightweight Aggregates for Insulating Concrete
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Work Item: ASTM WK34078 - New Specification for Lightweight Aggregate for Internal Curing of Concrete

1. Scope

1.1 This specification covers lightweight aggregate intended to provide internal curing for concrete. It includes test

methods for determining the adsorption and desorption properties of lightweight aggregate. NOTE 1-Internal curing

provides an additional source of curing water to promote hydration and substantially reduce the early-ageautogenous shrinkage and self-desiccation that can be significant contributors to early-age cracking. Appendix X1

provides guidance on the use of lightweight aggregates for internal curing. 1.2 The values stated in either SI units or

inch-pound units are to be regarded separately as standard. The values stated in each system may not be exact

equivalents; therefore, each system shall be used independently of the other. Combining values from the two

systems may result in non-conformance. Some values have only SI units because the inch-pound equivalents are not

used in practice. NOTE 2-Sieve size is identified by its standard designation in Specification E11. The alternative

designation given in parentheses is for information only and does not represent a different standard sieve size. 1.3

The text of this standard references notes and footnotes that provide explanatory material. These notes and footnotes

(excluding those in tables and figures) shall not be considered as requirements of the standard. 1.4 This standard

does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the

user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory

limitations prior to use. This is a proposed specification for lightweight aggregate for internal curing of concrete. It

has been recognized for a long time that wetted lightweight aggregate can provide curing water and mitigate theeffects of self-desiccation in sealed concrete. This has been shown to be very effective for high-performance

concrete mixture with low w/cm. This specification proposes minimum requirements for lightweight aggregates for

internal curing. It introduces the term wetted surface-dry as one of the reference moisture states, which is analogous

to the SSD condition used for normal weight aggregate. The specification includes test methods for measuring

absorption and desorption properties of the aggregate. This specification is needed by the industry to simplify the

incorporation of lightweight aggregate into project specifications.

Keywords

absorption; desorption; internal curing; lightweight aggregate; relative density; wetted surface dry

Tests for Light Weight Aggregate Concrete

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