Glass for Lightweight Aggregate Concrete

Under ‘concrete’ keyword we are now discussing about application, suitability and durability of glass as both fine aggregate, coarse aggregates or as cement replacement. 

Increasing demands of various goods and also due to economic development, with the increment of productions, there is also increasing waste materials. In these circumstances even if there have no interest of economy, for the sake of environment, we are thinking about recycled materials in construction industry.

At first we will have some idea about lightweight aggregate in brief. We have discussed some posts about light weight aggregates, and provided some relevant products available in market. Light weight aggregates may be either natural or artificial materials and characteristics dry density of particles should be less than 125 lb/ft³ (pcf).

Now can glass be used as lightweight aggregate? The answer is bulk density of crushed glass is below 125 lb/ft3, the threshold we provided above. It is 115 lb/ft³ (11250 kg/m³ ). This material is using in concrete construction for decades as light weight aggregate.

The aggregates were used in the form of expanded glass pellet. We are using this concrete for many years, but of low strength and low density too.

Here we are providing a plot that was made considering different light weight aggregates, which provides a relation between compressive strength of concrete with its density.

We have only few data about expanded glass pellet that can be used in concrete for regular or high strength concrete. We have already known about that presence of glass produce susceptibility to produce alkali aggregate reactions. Now-a-days wide verities of expanded glass lightweight aggregates are available in market.

These aggregates will result high compressive strength with particle densities of wide range. The most important property that we like to mention that a special covering over the surface is provided having resistance to alkaline environment present in concrete. They also have low water absorbent property. These lightweight aggregate are produced with

-ground waste glass

-clay

-sodium silicate

This mixture of materials are pelletized heating at 8500.

Concrete produce with such aggregates can yield compressive strength up to 17.3Mpa when cured with steam; this measured after 28 days of curing.

Crushed Glass in Concrete: What is the Effect on Concrete Workability?

Dear reader we have already had few idea about application of glass in concrete production. In the last post, we have discussed about contamination in crushed glass. We know waste glass can be recycled, but this contaminants and foreign materials define whether it can be recycled or be used as other purposes like concrete production. We will discuss about separation of contaminants and foreign materials for glass, in details, in our upcoming posts.

Here our concern is workability of concrete; we are not considering glass to be used in concrete as coarse aggregate. The usual fine aggregate that is very frequently used in concrete industry is sand. This sand can be classified further as fine and coarse sand.

The workability of concrete is significantly impaired when natural sand is replaced with crushed glass in mix proportioning. The detrimental effect on workability is due to several factors as follows:

a. Interlocking nature of glass particles which are angular in shape.

b. Glass particles are coated with water which results surface tension.

c. When water is added suction is developed between large glass particles.

But the workability of fresh concrete remain constant for long period as the glass particles are less absorbent in compare to normal sand concrete. This property is not only always good, as sometimes we have expectation to set concrete rapidly due to different unfavorable site conditions.

Common Contaminants in Glass Powder as Concrete Constituents

We have already learnt about glass powder that can be used in concrete as fine aggregate, coarse aggregate or as replacement of binding agent like cement. The glass powder has some contaminants. Our aim is to learn about contaminants in glass powder.

The screening method for contaminants will be discussed in our upcoming post. Here we will just discuss about contaminants including moisture content, lime content and loss under ignition. Though glass powder and process glass are derived from identical sources, there have some difference between them. Both materials have soluble silica content which is obviously an identical behavior but the difference lies in particle size.

It is established, through different analysis that crushed glasses have contaminants of following forms:

a. Small amount of polymers

b. Small acrylic content found in glass that used as architectural purposes.

c. Polyvinyl butylenes from ELV (End of Life Vehicle) glass. The contaminants can be expressed as PVB.

Notice that first and second types of contaminants are found in small amount, but third one, polyvinyl butylenes covers more than 90 percent of contaminants.

There may have some organic contents in crushed glass which may be paper residue comes from labels provided in bottle and other glass sources. Regarding moisture, there has insignificant amount of moisture (about 0.29%). Free lime contents are 0.26% and 1.22% for glass powder and crushed glass respectively. An about 0.02% loss is found under ignition analysis.

Notice that first and second types of contaminants are found in small amount, but third one, polyvinyl butylenes covers more than 90 percent of contaminants.

Sustainable Concrete: Replacing Aggregate with Waste Glass

The word ‘sustain’ means to maintain a process or system going and sustainability has objective to sustain the life of our planet for foreseeable future. 

The usual constituents of concrete are aggregates (both fine and coarse aggregates), hydraulic cement as cementitious material and water; other constituents are not included (used to make special concrete). The annual global production of concrete reached more than 1 m³ per capita. At the same time around 5 billion tons of by-products from industries and wastes generated after consumption of products in our regular life which can be recycles readily.

Of these our concern is glass products; we will discuss about sources, application and usual contamination in waste glass products in our upcoming posts. Waste glasses sometimes produce problems in disposal specially where population density is high. Usual use of waste glass is disposal as landfill and some fractions are recycled in glass industries with some difficulties. The difficulties in glass recycling will be discussed in upcoming post.

According to Ahmad Shayam and Aimin Xu, 2004-glasses have inert property which facilitates recycling without altering their chemical property and can be used for many times.

Now-a-day, exhausting of natural resources, degradation of environment and global warming are considered in every aspects of development, especially in construction and studies to introduce sustainable construction are funding all over the world. Our concern, as civil engineer, is construction materials, process and applications.

In regard to fine aggregates, now partial replacement of sand and even complete replacement with waste residue are studied and a new concrete named sandless concrete is also studying where all fines are omitted. We will discuss all of these in our next posts.

Demand of concrete as construction material is increasing with time and as fine aggregates if we use river sand following impact on environment and existing structures are observed:

a. Natural resource (sand) is exploited by this process

b. Water table is lowered

c. Structures like bridge piers may be sunk as consequence of extraction of excessive sand etc.

Not only as fine aggregates but also as coarse aggregates, crushed glass was studied; but a reduction in workability of concrete is observed which in turn affect on compressive strength of concrete. The workability reduction will be discussed in our next pos. It is to keep in mind that some deleterious reaction is observed due to siliceous nature of glass like alkali-silica reaction (ASR). 

How to Determine the Clay Minerals in Concrete Aggregates

Procedure for determining clay minerals in concrete is almost same as that of methylene blue capacity for determining quality of bentonite as we are dealing with same clay minerals here. This is smectite.

Bentonite is also clay of same group derived usually from volcanic ash. We have discussed numerous posts about bentonite and drilling fluids, mostly related to drilling of pile.

The test method is named as methylene blue absorption test and described by Pettifer and Hills in 1985. At first we like to introduce methylene blue; it is a dyeing pigment that is soluble in water usually of organic origin. When it is dissolved in water it produces blue color.

When clay of swelling properties (smectite group) remains in aggregates the methylene blue don't produce blue color as it is absorbed by clay minerals. This phenomenon facilitates us to predict presence of clay minerals. The amount of methylene blue required, gives a measure of concentration of search clay minerals.

The sample we like to test should be ground to make powder that will pass standard test 75 µm. Methylene blue is organic dyeing agent, used to determine clay minerals; here for concrete aggregates. We have already introduced this dyestuff.

Of this powdered simple, 1 gm is taken and dispersed in water and then titration is done with Methylene blue. The information we have missed are:

a. Volume of water is 30 ml to disperse sample

b. In titration process each 0.5 ml Methylene blue is added as solution

c. The solution of methylene blue is prepared by dissolving 0.1gm Methylene blue into 200 ml of de-ionized and distilled water.

After each 0.5 ml addition, to disperse evenly, suspension is properly agitated for 1 minute then a drop of suspension is taken using glass rod and kept on filter paper to inspect for any blue color is left by Methylene blue.

For each addition, the color is examined under sunlight, at the end of titration a circular band of pale blue is observed. The amount of Methylene blue is recorded to produce such color and our test is completed.

Now we have to interpret MBV (Methylene blue value) which is express as

MBV=0.1V/M

Where, V= Titrated volume of Methylene blue added to suspension and

            M=Mass of tested portion of powder

Now what does titration means?

Titration means there have no clay particles to absorb Methylene blue and blue color is appeared. This test method is used in France as standard test but has limited experience.

Now some limits about this test-

According to Department of Environment (Northern Ireland)-

For basalt 1 .0 %

      gritstone aggregate 0.7 %

The advantage of this test is it requires simple and usual chemical apparatus. Disadvantage is there should have a rock grinder to make powder of aggregate sample as discussed above.

Glacial Action and Deposition of Loess Soil

The reader we have discussed few topics about loess soil in our previous posts; here you will learn early deposition of loess after Ice Age.

This is about 2.6 million years ago, the ice is began which is also known as glacial age. In this period the most portion of earth was covered with glaciers. After glacial age, the climate began to warm up which leads to melting of hard ice and melted glaciers produced tremendous water to flow down into nearby rivers or valleys.

This process left a huge plain of mud to expose. In course of time, the plain became dry and exposed to action of wind. These sediments were blown with strong winds.

Now how is loess related to glacial action?

When the pulverized inert particles of size of silt produced with glacial action is peaked up by wind and blown from flood plain, loess are formed as a deposition of Aeolian soil.

Now we will know about deposition environment of loess. When adequate humidity in the ambient air was available the grains of a wind transported soil get precipitated. The sources of humidity were either

a. Glacial out wash

b. Or Flowing stream

It is observed in many loess soils that several depositions of loess are staked upon top of other loess deposition. This is due to individual glacial action of several glacier of a region.

These loessial top soils are found in many reasons of the world like

1. Central United States

2. Northwest of United States

3. Central Europe

4. Eastern Europe

5. Eastern China

In our upcoming posts we will discuss about distribution of loess deposition over the world.

Stability of Slope and Cut in Loess Soil

Dear reader we have discussed about properties, sampling and evaluation of collapse potential of loess soil in our previous posts. We have learnt about grain size and shape of loess which is relevant to stability of slope and vertical faces on loess soil.

We have discussed about collapse nature of loess soil earlier in this blog. Now we have to know how long loess remains stable under unfavorable conditions of weather.

The stability in slope and vertical faces on loess are due to cohesion existing in this soil. This interparticle cementation provides stability to this soil so far it is not saturated.

So we should not be surprised at steep slopes or full vertical faces standing freely without any external stabilization. We know the grains are angular in loess which often keep it in banks without slumping for many years.

Perhaps you have heard about loess plateau which covers many provinces of chine like

-Shanxi

-Shaanxi

-Ningxia

-Gansu

-Henan

In these regions cave dwellers makes their ecological friendly solution making caves through loess deposits.

Loess is characterized by vertical cleavage which facilitates excavation for this purpose. Loess is eroded very easily. In several region of the world, the loess ridges are found align against prevailing winds of Ice Age.

How does Density of Loess Soil Indicates Collapse Potential?

Dear reader in previous post we have discussed about a method for determining collapse potential of loess soil. Here we will learn about usual density of loess soil and its application in calculating collapse potential with the help of liquid limit. We are providing range of dry density and liquid limits of loess soil below:

In-situ dry density: (10-16.5) KN/m³

Liquid limit: (25-55) percent

Density of loess soil including other collapsible soil is an important (not only one but one of the most) parameters that can be used to determine collapse potential.

In 1961 Hilf and Holtz recommended that dry density together with liquid limit can be used to determine collapse potential of loess soil. 

Bowels produced a linear equation for convenience of use. This equation is 

where 

W_L=liquid limit expressed as percent

γ_dry=dry density as a function of liquid limit W_L and expressed as KN/m³

Now how to use this equation?

If in situ density of soil is found to be less than the result found from equation (1) (γ_dry), this soil is considered to have susceptibility to collapse. With increase in difference between two densities (one from equation (1) and another from in-situ value), the severity of collapse is also increased.

Though not relevant, we are including optimum moisture content and maximum dry densities of typical loess soil as this post is related to density of loess soil.

Standard compaction (ASTM D698) test, γ_dry= (15.5-17.5) KN/m³

Optimum moisture content= (12-20) percent.

Sampling Difficulties of Collapsible Soil: Loess

Dear reader we have discussed about many aspects of loess so far in this blog; now we will discuss about sampling difficulties of loess soils. We have already learnt about different sampling method, disturbance in soil sampling and measuring disturbance in soil sampling in our previous posts. The equation which produces a measure of collapse potential is as follows:

Where, C_p=estimate of changing in height of undisturbed specimen expressed in percentage 


h_p=change in length of tube sample under consolidation pressure as expected in field. The sample is obviously undisturbed as in ‘C_p’.

h_p׳=change in length of tube sample that is saturated under identical consolidation pressure as in h_p. The initial length (h) for both samples must be same.

This is a simple equation and seems to be very simple to assess C_p but actual difficulty lies in the term ‘undisturbed sample’. Dear reader perhaps we have read about block sampling, discussed in this blog. This is the best way to collect sample of loess soil. But we know that it is very difficult and practically impossible in many situations.

In case of application of thin walled tube sampler, the sample may subject to some degree of compression when sampling process is executed. If we have no way to avoid this sampler, the boreholes must be made dry or without water.

The disturbance may be happened while cutting/trimming sample, placing it into testing arrangement and providing load to required pressure (with minimum side friction or lateral resistance). The depth of saturation zone provides major problems as saturation initiates collapse to such soil.

What is Time Dependent Corrosion in Foundation Elements?

We know steel, concrete and timber are common foundation material. In many cases these materials are subjected to environmental adverse conditions. Corrosion problem in foundation are an important factor in choosing foundation construction material and also in design purposes as well. We have discussed different aspects of foundation corrosion mainly on piling. We use different types of foundation like isolated footing, combined foundation, mat or raft foundation, pile foundation and other deep foundations. Of these piles are often driven or bored in weak soil formation, sometimes through water logged ground or through water in case of marine or other water structures.

We have severe corrosion problem with steel piles and timber piles as well. Concrete piles are more resistant against corrosion when special care is taken.

The corrosion environments that often foundation engineers have to face are:

a. Foundation on pollute ground like older sanitary landfill

b. Areas where dead vegetation found in backwater.

c. Shoreline close to sewer outfall from old industrial plants.

d. Areas where tidal action affects the foundation

Time dependent corrosion is involved where wet and dry cycles results corrosion to foundation elements. Concrete is usually resistant to corrosion, if there have no sulfate in ambient environment. In case of sulfate contamination, sulfate resistant concrete is necessary. Sometimes it is necessary to introduce air-entrainment in concrete to make concrete foundation corrosion resistant.

The salts of sulfate that affect concrete foundation elements are:

a. Magnesium sulfate

b. Sodium sulfate

Sulfate attack is accelerated greatly if it is accompanied by time-dependent corrosion i.e. alternating wetting-drying. Dear reader we will discuss elaborately about sulfate resistant concrete in our upcoming post. But we like to include that sulfate resisting concrete is sometimes disadvantageous when it is suspected to have chloride ions within concrete; for further clarification you have to wait for these posts.

We know that PH=7 is neutral condition, in pile foundation when PH becomes less than 4.0 or above 9.5, metal piles like steel should be replaced by timber. The timber piles should be properly treated.

Monographs 58 & 127 by National Bureau of Standards and Technical Manual-27 by U.S. Army Corps of Engineers are only publications about steel piles to treat against corrosion. They recommended to use steel piles in conditions where they are submerged consistently, that is, not included wetting and drying cycles, this recommendation is also applicable for timber piling.

They were not recommended to use steel piles in marine environment where time dependent corrosion is observed. They have provided limited use of steel piles with proper coating that not subjected to alternate submergence which is almost impossible and so we provided that they did not recommend to use.

In such case, concrete piles are recommended which is properly proportion. So, now-a-days, time dependent corrosion is becoming a key factor for installing steel piles considering previous experiences of corroded foundation. Some useful liks are: 

• Corrosion Environments for Steel Piles

• Corrosion Problem of Steel Piles

• Corrosion induced by chlorides(RCC)

• Development of Fiber Reinforced of Polymer Composite (FRPC) Piles in Foundation Applications

• Factor Affecting the Durability of the Reinforced Concrete in Seawater

Index Properties of Loess Soil

Dear reader we have already learnt about grain size and shape of loess soil. Loess is a collapsible soil. Most of collapsible soils including loess are free from pebbles and gravel. Grain size distribution of loess soils is characterized by a range of (0.01-0.10) mm; though there may have some contamination. The contamination as discussed in previous posts is clay. There have also some sand particles and some contamination by organic leachates.

• The sand particles are usually of less than 0.05 mm. Most of the particles generally pass through no.200 sieve i.e. 0.075mm. 
• The specific gravity of loess soil remains in the range of (2.60-2.80).
• In situ dry densities are observed to be within (10-16.5) KN/m³.

Dear reader we know Atterberg limits of soil is an important parameter depending on which together with other parameter like standard penetration number, we can predict some engineering properties of soil. With these we have a rough idea about engineering properties and in small or unimportant foundation construction work sometimes we depend on prediction.

So we should have idea about atterberg limits of loess. Atterberg limits also known as consistency limits. Consistency limits depend mainly on clay and organic contaminants, if there have any, and the liquid limit falls within (25-55) and plastic limit lies between (15-30) percent.

The in situ porosity of loess is very high and very often it is found greater than 50 percent i.e. a void ratio of greater than 1.0 which leads to higher possibility to collapse when get saturated. The usual value of in-situ void ratio lies between (0.67-1.50).

Loess: An Aeolian Soil Deposit

Dear reader in our last post we have discussed about dune sand as an Aeolian deposit. Here we will discuss about another wind transported soil, loess. We have introduced this soil in our previous post regarding collapsible soil.

The distribution of grain size is as usual uniform more or less like dune sand. But they are distinguished form dune deposit as it consists of silt or particles size identical to silt.

This soil shows cohesion which is mainly a contribution of coating of clay over particles of silt or similar size grains. Thus this soil remains stable unlike dune deposit; but there have a condition. This is soil must be in unsaturated condition more precisely a dry soil.

Some chemical leached with rain water also precipitated in such soil which contributes to cohesion to some extent. These soils have collapsible nature. When it gets saturated, the stability stated above collapsed, as binding strength remains between soil particles is lost.

Being collapse soil, careful interpretation of behavior of loessial deposits is conducted before foundation construction over them. These soils are found in many states of United States as listed below:

a. Iowa

b. Missouri

c. Illinois

d. Nebraska

These deposits are also observed in Mississippi and Tennessee along the river Mississippi

Typical Properties of Dune: An Aeolian Soil Deposit

We have discussed wind transported soil in our previous post. We know that sand blown by wind takes shape like dune. When a dune is formed, wind forces to blow sand over crest of it.

Sand particles as usual roll down along slopes from crest which produces a natural compaction in one side and loose deposit in other side. We are making clear this fact here. In the windward side, a sand deposit of compacted state is found and the opposite scenario are found in leeward side where roll over sand produce loose deposit relative to windward.

Dunes are found in many states of United States. We are listing some regions where dunes are found:

a. Lake Michigan (eastern and southern shores)

b. California (southern coast)

c. Atlantic coast

d. Along coast of Washington and Oregon

e. Rocky and alluvial planes of western USA.

Typical properties of sand of such deposits are as follows:

1. We know that particle size of sand is controlled by wind velocity i.e. it provides a sorting action of having same size particles at particular location. So distribution of particle size is uniform.

2. As discussed above wind velocity is key factor controlling grain size over path from source to particular distance. As wind carries bulky particles lesser distance than small one, the grain size generally decreases with distance.

3. As discussed above the sand in windward is more compacted than leeward. So relative density is all affected. In windward side, the relative density are sometimes found (50-65) % which may be decreased to (0-15) % on leeward side.

Significance of Activity of Soil

In United States, large parts of Africa and India there have severe problems associated with expansive potential of clay soil. The three clay minerals we concern mainly in foundation engineering are:

a. Kaolinite

b. Illite

c. Montmorillonite

If we can identify the mineral structure of clay soils, we can predict their expansion and shrinkage potential. 

Many lighter building in the regions of expansive soil, subjected to severe settlement in the regions stated above of the world; even before they were left for operation.

Montmorillonite is the main mineral element of black cotton soil. The mineral structure of clay is indicative to amount of water and form of their presence in clay minerals. Water can combine separated mineral units to form a sheets stakes over another unit.

Activity of clay soil defines its water retaining capacity and we know that swelling and shrinkage of soil depends on the water within soil. Thus both phenomena of volume change depend on activity of soil. Soils are classified as three types as follows:

a. Inactive soil

b. Normal soil

c. Active soil

Inactive soil

Soil having activity less than 0.75 is considered as inactive soil.

Normal soil

Soil having activity in between 0.75 and 1.25 are taken as normal soil.

Active soil

Soil that has activity greater than 1.25 is considered as active. Identifying clay minerals depending on activity:

Montmorillonite:

Soil having activity greater than 4 have significant amount of montmorillonite.

Kaolinite:

Soil having activity less than 1 has mainly kaolinite

Illite :

Soil having activity in between 1 and 2 have significant amount of illite.

Thus activity furnishes information about effect and type of mineral in clay soil. We conclude following points about activity:

a. Activity remains constant for a soil from specific origin. In such case, plasticity index reduces as quantity of clay fraction reduces and vice versa.

b. In case of highly active clay minerals like montmorillonite, shows great increase in plasticity index under small quantity of clay fraction.

Comparison of Soil with Steel

Soil is very complex in nature and shows distinct behavior other than traditional construction materials. We have discussed about concrete in the last post. Here we will discuss about steel to compare with soil.

Steel is mainly iron alloyed by carbon to change its properties. Other than carbon it may contain

• Manganese

• phosphorous

• sulfur

• Silicon

Sometimes other alloying elements can be added intentionally to have enhanced properties of steel like nickel, titanium, boron, molybdenum, chromium etc.

The carbon and alloying element discussed above render hardening properties to steel. So by adjusting amount of these elements (one or more) and controlling form of presence in steel, the quality of steel can be altered in terms of

• Tensile strength

• Ductility

• Hardness

As an example, with carbon of greater content produce harder steel but having less ductility. The carbon content greater than 2.1 % produce cast iron that is harder and have malleability of null.

So steel is accurately controlled manufactured product whose properties can be tuned with varying alloying element. We have greater control over steel than concrete as discussed in last post.

Before using, we can evaluate its engineering properties accurately in laboratory or from manufacturer information which represent actual condition in which it remains in concrete or other materials. In case soil, we can never accurately simulate the actual in-situ conditions; though modern triaxial test apparatus can simulate many in-situ environments in single arrangement.

We cannot remove unexpected soil from project site as it involve huge soil transportation; in some cases we bound to relocate many structures considering geotechnical and geological conditions. Sometimes compensated foundation is used to suppress unexpected soil from project site when architectural and other requirements seek a number of basements.

Steel is a homogeneous material although its length in contrast to soil which heterogeneous in both horizontal and vertical direction even within few feet.

Steel shows precise modulus of elasticity rather than a soil sample (where shear modulus is important). With modulus of elasticity, compressive and tensile strength, we can easily design a section, but in case of soil we need elaborate testing program to have not accurate but near to actual value. Even under these numerous testing large safety factor is essential in foundation engineering.